Search Results (58)

Figure 1
<p>Overall framework of the 3DVT network model.</p> Full article ">Figure 2
<p>ViT encoder with average pooling projection.</p> Full article ">

Figure 1
<p>Fiber clamping for SMF/TCEDF/SMF splices. (<b>a</b>) This demonstrates how to adhere the fiber to the metric rod with the masking tape and (<b>b</b>) illustrates how splicing is accomplished with the fusion splicer.</p> Full article ">Figure 2
<p>Core-offset splice SMF/TCEDF/SMF design. (<b>a</b>) Illustrates the splicing between fibers, (<b>b</b>) shows the TCEDF cut, (<b>c</b>) U-shape of the MZI filter, (<b>d</b>) exhibits the z-side view of the MZI.</p> Full article ">Figure 3
<p>(<b>a</b>) Interference spectra generated in the optical cavity of each MZI filter, (<b>b</b>) spatial frequency of the transmission spectrum generated by every filter.</p> Full article ">Figure 4
<p>Diagram of the MTEFL ring array: (<b>a</b>) illustrates the configuration scheme, and (<b>b</b>) depicts the process for inducing curvature in the MZI filter to generate wavelength-switchable tunable emission lines.</p> Full article ">Figure 5
<p>MTEFL emission tuning and switching cases generated for single (state-a), quadruple (state-b), triple (state-c), narrow-double (state-d), and double (state-e) lasing signals.</p> Full article ">Figure 6
<p>(State-a) single-emission signal. (<b>a</b>) Tuning lines, (<b>b</b>) emission samples of curvature and SNR, (<b>c</b>) SMSR and SNR of the most significant peaks and their comparison, (<b>d</b>) the polynomial fit between the curvature data and its wavelength shift.</p> Full article ">Figure 7
<p>Switch with quad-emission line. (<b>a</b>) SMSR on each peak, (<b>b</b>) power difference between the peaks and their separation.</p> Full article ">Figure 8
<p>(State-c) double switch of triple-emission signals: (<b>a</b>) SMSR on the first switch, (<b>b</b>) separation and power of peaks, (<b>c</b>) SMSR of the second switch, (<b>d</b>) separation and the power of peaks.</p> Full article ">Figure 8 Cont.
<p>(State-c) double switch of triple-emission signals: (<b>a</b>) SMSR on the first switch, (<b>b</b>) separation and power of peaks, (<b>c</b>) SMSR of the second switch, (<b>d</b>) separation and the power of peaks.</p> Full article ">Figure 9
<p>Narrow-dual-emission signals (state-d). (<b>a</b>) Tuning and the potential difference between peaks and their wavelength comparisons, (<b>b</b>) most significative peaks and power comparison, (<b>c</b>) sensitivity compared to the dispersion of curvature samples.</p> Full article ">Figure 10
<p>Double-emission signal (state-e). (<b>a</b>) Tuning and most significant power peaks, (<b>b</b>) separation comparison, (<b>c</b>) peaks power comparison, (<b>d</b>) sensitivity generated with the curvature/wavelength samples.</p> Full article ">Figure 10 Cont.
<p>Double-emission signal (state-e). (<b>a</b>) Tuning and most significant power peaks, (<b>b</b>) separation comparison, (<b>c</b>) peaks power comparison, (<b>d</b>) sensitivity generated with the curvature/wavelength samples.</p> Full article ">Figure 11
<p>(<b>a</b>) Stability test of the single initial and final emission, (<b>b</b>) power variation, (<b>c</b>) wavelength variation.</p> Full article ">Figure 12
<p>First and last emissions signals of the dual-narrow lasing lines. (<b>a</b>) Stability test, (<b>b</b>) power fluctuation, (<b>c</b>) wavelength stability.</p> Full article ">Figure 13
<p>Stability tests of the dual lasing lines. (<b>a</b>) Stability test on the first emission, (<b>b</b>) power fluctuation, (<b>c</b>) wavelength stability, (<b>a’</b>) stability test on the last emission, (<b>b’</b>) power fluctuation, (<b>c’</b>) wavelength stability.</p> Full article ">Figure 14
<p>(<b>a</b>) Stability tests of the quad-emission line, (<b>b</b>) power variation, (<b>c</b>) wavelength variation.</p> Full article ">Figure 15
<p>Stability tests of the triple emissions. (<b>a</b>) On the first switch, (<b>b</b>) power variation, (<b>c</b>) wavelength variation, (<b>a’</b>) test on the second switch, (<b>b’</b>) power variation, (<b>c’</b>) wavelength variation.</p> Full article ">

Figure 1
<p>Experimental erbium-doped fiber ring laser cavity setup for tunable and multi-wavelength emission.</p> Full article ">Figure 2
<p>(<b>a</b>) MZFI structure formed with a pair of tapered sections fabricated on SMF-28, (<b>b</b>) displacement mechanism to used induce curvature in the MZFI.</p> Full article ">Figure 3
<p>ASE spectrum as the light source from the EDF (black line) and the modified spectrum after passing through the MZFI (red line). The laser oscillation at 1563.07 nm is shown by the blue line.</p> Full article ">Figure 4
<p>(<b>a</b>) The progressive modification of ASE spectrum with increasing curvature applied to the MZFI, (<b>b</b>) an inset in the range of 1541 to 1560 nm demonstrates an FSR of 5 nm.</p> Full article ">Figure 5
<p>The wavelength shifts as a function of curvature (0 m⁻¹ to 2.93 m⁻¹) and the variation of the measured fringe visibility.</p> Full article ">Figure 6
<p>Tunable single laser wavelength between 1563.705 nm to 1558.05 nm for the curvatures from 0 m⁻¹ to 2.79 m⁻¹.</p> Full article ">Figure 7
<p>(<b>a</b>). Switchable dual-wavelength emissions generated at curvatures of 1.53 m⁻¹ with 1559.07 nm and 1563.66 nm, (<b>b</b>) 2.33 m⁻¹ with 1543.21 nm and 1549.287 nm, (<b>c</b>) 2.5 m⁻¹ with 1554.61 nm and 1559.667 nm, (<b>d</b>) 2.75 m⁻¹ with 1556.8 nm and 1561.877 nm.</p> Full article ">Figure 8
<p>(<b>a</b>) Single-wavelength oscillation at 1562.22 nm, (<b>b</b>) dual-wavelength oscillation (1562.22–1562.875 nm), (<b>c</b>) triple-wavelength oscillation (1560.175–1562.22–1562.88 nm).</p> Full article ">Figure 9
<p>(<b>a</b>) Quadruple-wavelength emission (1560.85–1561.51–1562.26–1562.86 nm), (<b>b</b>) quintuple-wavelength emission (1559.59–1560.91–1561.58–1562.93–1563.61 nm), and (<b>c</b>) sextuple-wavelength emission (1560.25–1560.97–1561.63–1562.29–1562.98–1563.64 nm).</p> Full article ">Figure 10
<p>(<b>a</b>) Spectral distribution stability of a single laser oscillation at 1562.22 nm, with high-intensity uniformity across the spectrum, (<b>b</b>) a maximum wavelength shift of 0.01 nm, and (<b>c</b>) output power fluctuations of less than 0.12 dB.</p> Full article ">Figure 11
<p>(<b>a</b>). Stability of the dual-wavelength laser oscillation at 1562.22–1562.785 nm with uniform intensity, (<b>b</b>) a maximum wavelength shift of 0.07 nm, and (<b>c</b>) output power fluctuations of less than 0.25 dB.</p> Full article ">Figure 12
<p>(<b>a</b>) Power stability of the triple-wavelength laser system, (<b>b</b>) maximum wavelength shift of 0.07 nm, and (<b>c</b>) maximum amplitude fluctuation of 0.51dB for the 1562.88 nm line.</p> Full article ">Figure 13
<p>(<b>a</b>) Power stability of the quadruple-wavelength laser system, (<b>b</b>) maximum wavelength shift of 0.22 nm, and (<b>c</b>) maximum amplitude fluctuation of 3 dB for the 1562.83 nm line.</p> Full article ">Figure 14
<p>(<b>a</b>) Power stability of the quintuple-wavelength laser system, (<b>b</b>) maximum wavelength shift of 0.07 nm, and (<b>c</b>) maximum amplitude fluctuation of 1.7 dB for the 1561.58 nm line.</p> Full article ">Figure 15
<p>(<b>a</b>) Power stability of the sextuple-wavelength laser system, (<b>b</b>) negligible wavelength shift, and (<b>c</b>) maximum amplitude fluctuation of 2.71 dB for the 1562.98 nm line.</p> Full article ">

Figure 1
<p>An experimental framework involves a multi-wavelength erbium-doped fiber ring laser with a delayed line interferometer (internal structure enlargement) as the primary component. (TDLI: tunable delay line interferometer; EDFA: erbium-doped fiber amplifier; TBF: tunable bandpass filter; OSA: optical spectral analyzer).</p> Full article ">Figure 2
<p>(<b>a</b>) The spectrum shows multiple FP interferences resulting from the combination of two BS and the primary interference caused by TDLI with different FSRs by virtue of reflections from the end face of the fiber head. The EDFA emits light from port 1 into the TDLI, which is then reflected by port 3 and the BS into port 2 for observation by the OSA. (<b>b</b>) Transmission spectra of two-phase complementary interferences formed by TDLI and spectral characteristics of a multi-wavelength laser capable of output in the <a href="#applsci-14-06933-f001" class="html-fig">Figure 1</a> framework. The EDFA emits light, which passes from ports 3 to 2 and 1, respectively, and then yellow and blue line interferograms can be obtained with the OSA, respectively.</p> Full article ">Figure 3
<p>(<b>a</b>) Dual-wavelength laser with variable spacing and consistent center position of dual wavelengths. (<b>b</b>) Dual-wavelength laser with intertwined wavelength positions. (<b>c</b>,<b>d</b>) Dual-wav-length laser with regular positional tuning and similar wavelength spacing (the subplot is a superimposed drawing of the spectrum that does not correspond to the power scale of the vertical axis).</p> Full article ">Figure 4
<p>(<b>a</b>,<b>b</b>) The same dual-wavelength laser with different interferences and the spectral observation at different times.</p> Full article ">Figure 5
<p>(<b>a</b>) Dual-wavelength laser with the narrowest wavelength spacing. (<b>b</b>) Dual-wavelength laser with several interfering lobes between the lasing wavelengths.</p> Full article ">Figure 6
<p>(<b>a</b>,<b>b</b>) The wavelength position and the power corresponding to the peak of the lasing wavelength per minute are obtained from <a href="#applsci-14-06933-f004" class="html-fig">Figure 4</a>a,b, respectively. (<b>c</b>,<b>d</b>) The wavelength position and the power corresponding to the peak of the lasing wavelength per minute are obtained from <a href="#applsci-14-06933-f005" class="html-fig">Figure 5</a>a,b, respectively. (The yellow lines with circle signs represent the shorter wavelength; the pink lines with square signs represent the longer wavelength; the blue signs correspond to wavelength positions; and the dark signs correspond to power values).</p> Full article ">Figure 7
<p>(<b>a</b>) A record of triple-wavelength lasers with the same wavelength spacing every ten minutes. (<b>b</b>) The wavelength position and the power corresponding to the peak of the lasing wavelength per ten minutes are obtained from (<b>a</b>). (The yellow line is at 1530.1 nm, the bright red line is at 1531.22 nm, and the coffee line is at 1532.34 nm; the dark signs correspond to wavelength positions, and the blue signs correspond to power values).</p> Full article ">

Figure 1
<p>The scheme of multi-wavelength Brillouin Er³⁺-doped fiber laser.</p> Full article ">Figure 2
<p>(<b>a</b>) The output spectra and (<b>b</b>) the number distribution of the Brillouin laser with different 980 nm power.</p> Full article ">Figure 3
<p>First Brillouin wavelength: (<b>a</b>) spectra, (<b>b</b>) OSNR and (<b>c</b>) optical intensity with θ₂ variation.</p> Full article ">Figure 4
<p>The conversion efficiencies for different θ₂.</p> Full article ">Figure 5
<p>(<b>a</b>) The laser bandwidth measurement setup; (<b>b</b>) the measurement of BFL linewidth by the homodyne spectrum method.</p> Full article ">Figure 6
<p>The dual Brillouin wavelengths with EDFA.</p> Full article ">Figure 7
<p>The flatness between two Brillouin wavelengths changing with angle θ₂: (<b>a</b>) the optical spectra; (<b>b</b>) the flatness analysis.</p> Full article ">Figure 8
<p>(<b>a</b>) Fifth-order Brillouin laser spectra with EDFA; (<b>b</b>) peak-values distribution of the 5th-Brillouin laser.</p> Full article ">Figure 9
<p>(<b>a</b>) Five-wavelength Brillouin laser spectra with θ₂ variation; (<b>b</b>) the flatness distribution at different θ₂.</p> Full article ">Figure 10
<p>Stability of 1-wavelength Brillouin laser line in an hour: (<b>a</b>) the optical intensities (<b>b</b>) the central wavelengths.</p> Full article ">Figure 11
<p>Stabilities of 3-wavelength BFL in an hour: (<b>a</b>) the optical intensities (<b>b</b>) the central wavelengths.</p> Full article ">Figure 12
<p>Stabilities of 7-wavelength BFL in an hour: (<b>a</b>) the optical intensities (<b>b</b>) the central wavelengths.</p> Full article ">

Figure 1
<p>Transmission losses’ dependence on the optical fiber length measured for standard single-mode (green curve) and multi-mode fibers (blue curve). The slopes give the dB/km loss parameters, while the intercepts represent the coupling losses from the lasers/patchcords/connectors used. The single-mode fiber is a Corning SMF28-Ultra with a core diameter of 8.2 μm, cladding of 125 μm, and NA ~0.14, which is fed from a pigtailed single-mode 1550 nm laser diode. The multi-mode fiber is a standard graded-index Corning InfiniCor OM1 fiber with a core diameter of 62.5 μm, cladding of 125 μm, and NA ~0.275 coupled from a pigtailed multi-mode 1470 nm laser diode having a 105 μm core and an NA ~0.22. A lens-coupler was used to minimize the coupling losses between the multi-mode laser and the OM1 fiber (OzOptics’ part #AA-300-33-1550-M-SP1) [<a href="#B44-photonics-11-00596" class="html-bibr">44</a>,<a href="#B45-photonics-11-00596" class="html-bibr">45</a>,<a href="#B46-photonics-11-00596" class="html-bibr">46</a>,<a href="#B47-photonics-11-00596" class="html-bibr">47</a>,<a href="#B48-photonics-11-00596" class="html-bibr">48</a>].</p> Full article ">Figure 2
<p>Measured electrical output from Broadcom’s AFBR-POC205A9 multijunction PT10-InGaAs/InP laser power converter for single-mode transmission distances of 1 km (blue crosses) and 5 km (green X) with different optical input powers at 1550 nm. The transmitted optical power on the horizontal axis refers to the output power exiting the output end of the fiber.</p> Full article ">Figure 3
<p>Measured electrical output from Broadcom’s AFBR-POC205A8 multijunction PT10-InGaAs/InP laser power converter for multi-mode transmission distances of 1 km (purple circles at 1550 nm) and 5 km (green circles at 1470 nm) for different optical input powers. The single-mode data of <a href="#photonics-11-00596-f002" class="html-fig">Figure 2</a> are also included for comparison.</p> Full article ">Figure 4
<p>Picture of pigtailed multi-mode 808 nm laser diode in operation at 20 °C, revealing faint light leakage and some slightly brighter spots along the fiber length (<b>top</b>). The picture was taken from a smart-phone camera, which responded to the 808 nm light. Bottom: Another similar 808 nm laser diode in operation (powered with a DC/DC power supply) with room illumination to better view the laser pigtail (<b>bottom left</b>); and corresponding infrared smart-phone view, which highlights the laser light leakage (<b>bottom right</b>). The pigtail at the bottom was set up with a 30 mm diameter loop, which induced additional light leakage.</p> Full article ">Figure 4 Cont.
<p>Picture of pigtailed multi-mode 808 nm laser diode in operation at 20 °C, revealing faint light leakage and some slightly brighter spots along the fiber length (<b>top</b>). The picture was taken from a smart-phone camera, which responded to the 808 nm light. Bottom: Another similar 808 nm laser diode in operation (powered with a DC/DC power supply) with room illumination to better view the laser pigtail (<b>bottom left</b>); and corresponding infrared smart-phone view, which highlights the laser light leakage (<b>bottom right</b>). The pigtail at the bottom was set up with a 30 mm diameter loop, which induced additional light leakage.</p> Full article ">Figure 5
<p>The −40 V dark-current of a silicon photomultiplier (Broadcom’s AFBR-S4xx SiPM) was used to evaluate, with the highest possible sensitivity, the residual light emanating from various multi-mode optical fiber configurations as a function of the ambient temperature. The “common fibers” (blue and purple curves) are step-index fiber types with a 400 μm core and protected with a furcation tubing jacket, as shown in <a href="#photonics-11-00596-f004" class="html-fig">Figure 4</a>. The “polyimide fiber” (green curve) is a bare polyimide fiber (no tubing jacket) from Thorlabs’ FG400LEP multi-mode fiber with a 400 μm core and an NA ~0.22. Compared to the SiPM current in the dark (black curve: “No light”), obtained in complete darkness, the polyimide fiber exhibited no measurable light leakage over the temperature range studied.</p> Full article ">Figure 6
<p>Measured electrical output at 77 K for different optical input powers at 1466 nm transmitted through 10 m of bare polyimide multi-mode fiber, converted using Broadcom’s AFBR-POC205A8 multijunction PT10-InGaAs/InP laser power converter.</p> Full article ">Figure 7
<p>Measured output power as a function of temperature for an AFBR-POC205A9 LPC with 1.5 W of optical input at about 1470 nm. Fiber light leakage can parasitically reduce the measured LPC output power at lower temperatures when fiber types other than bare polyimide fibers are used.</p> Full article ">

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Simplified scheme of the energy levels of Tb³⁺ ions. (<b>b</b>) Emission and absorption cross-sections of ⁷F₅ → ⁷F₆ laser transition.</p> Full article ">Figure 2
<p>(<b>a</b>) Cross-section of chalcogenide multicore fiber with Tb-doped cores arranged in a 5 × 5 square lattice. Modeled electric fields of in-phase (<b>b</b>) and out-of-phase (<b>c</b>) supermodes. Intensity distributions of the laser beam before (<b>d</b>), after one (<b>e</b>), and after two (<b>f</b>) steps of CBC, calculated in the far field after propagating a path of 5 cm.</p> Full article ">Figure 3
<p>(<b>a</b>) Scheme of Tb-doped chalcogenide glass fiber laser. CBC is the system for coherent beam combining by summing out-of-phase supermode with two beamsplitters. Evolution of intracavity powers at pump wavelength (<b>b</b>) and at signal wavelength (<b>c</b>) modeled for <span class="html-italic">P_pump</span> = 30 W, <span class="html-italic">L</span> = 150 cm, and <span class="html-italic">R</span>₂ = 0.19.</p> Full article ">Figure 4
<p>Output laser power vs. fiber cavity length <span class="html-italic">L</span> and reflection coefficient <span class="html-italic">R</span>₂ for <span class="html-italic">P_pump</span> = 30 W. The dashed curve shows the optimal fiber length that maximizes output laser power for certain <span class="html-italic">R</span>₂.</p> Full article ">Figure 5
<p>Output laser power vs. pump power <span class="html-italic">P_pump</span> and reflection coefficient <span class="html-italic">R</span>₂ for <span class="html-italic">L</span> = 150 cm.</p> Full article ">Figure 6
<p>Output laser power vs. pump power, modeled for <span class="html-italic">L</span> = 100 cm (<b>a</b>) and <span class="html-italic">L</span> = 150 cm (<b>b</b>) and varied <span class="html-italic">R</span>₂.</p> Full article ">Figure 7
<p>Output laser power vs. fiber cavity length <span class="html-italic">L</span> and pump power <span class="html-italic">P_pump</span> for <span class="html-italic">R</span>₂ = 0.19. The dashed curve shows the optimal fiber length that maximizes output laser power for certain <span class="html-italic">P_pump</span>.</p> Full article ">Figure 8
<p>Output laser power vs. fiber intracavity length modeled for <span class="html-italic">P_pump</span> = 10 W (<b>a</b>); <span class="html-italic">P_pump</span> = 20 W (<b>b</b>); and <span class="html-italic">P_pump</span> = 30 W (<b>c</b>) for varied <span class="html-italic">R</span>₂.</p> Full article ">Figure 9
<p>Output laser power vs. pump power, modeled for <span class="html-italic">L</span> = 150 cm, <span class="html-italic">R</span>₂ = 0.19, and varied fiber background losses.</p> Full article ">Figure 10
<p>Output laser power vs. fiber intracavity length, modeled for <span class="html-italic">P_pump</span> = 30 W (<b>a</b>); <span class="html-italic">P_pump</span> = 100 W (<b>b</b>), <span class="html-italic">R</span>₂ = 0.19, and varied fiber background losses.</p> Full article ">

Figure 1
<p>Diagrams of energy levels and transitions for some Yb³⁺, Er³⁺, Tm³⁺, and Ho³⁺ ions.</p> Full article ">Figure 2
<p>Energy diagrams of a traditional four-level laser (<b>a</b>) and a radiation-balanced laser (<b>b</b>). <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>λ</mi> </mrow> <mrow> <mi>P</mi> </mrow> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>λ</mi> </mrow> <mrow> <mi>L</mi> </mrow> </msub> <mtext> </mtext> </mrow> </semantics></math>are the pump and laser frequencies, respectively. <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>λ</mi> </mrow> <mrow> <mi>F</mi> </mrow> </msub> </mrow> </semantics></math> is the mean fluorescence frequency. Solid and dushed arrows illustrate photon and phonon transitions, respectively.</p> Full article ">Figure 3
<p>Power evolution of all-fiber laser oscillators operating at ~1000 nm [<a href="#B37-applsci-14-02323" class="html-bibr">37</a>,<a href="#B38-applsci-14-02323" class="html-bibr">38</a>,<a href="#B39-applsci-14-02323" class="html-bibr">39</a>,<a href="#B40-applsci-14-02323" class="html-bibr">40</a>,<a href="#B41-applsci-14-02323" class="html-bibr">41</a>,<a href="#B42-applsci-14-02323" class="html-bibr">42</a>,<a href="#B43-applsci-14-02323" class="html-bibr">43</a>,<a href="#B44-applsci-14-02323" class="html-bibr">44</a>,<a href="#B45-applsci-14-02323" class="html-bibr">45</a>,<a href="#B46-applsci-14-02323" class="html-bibr">46</a>,<a href="#B47-applsci-14-02323" class="html-bibr">47</a>,<a href="#B48-applsci-14-02323" class="html-bibr">48</a>].</p> Full article ">Figure 4
<p>Power evolution of Er³⁺-doped and Er³⁺-Yb³⁺ co-doped fiber lasers operating at ~1.5 μm [<a href="#B50-applsci-14-02323" class="html-bibr">50</a>,<a href="#B51-applsci-14-02323" class="html-bibr">51</a>,<a href="#B52-applsci-14-02323" class="html-bibr">52</a>,<a href="#B53-applsci-14-02323" class="html-bibr">53</a>,<a href="#B54-applsci-14-02323" class="html-bibr">54</a>,<a href="#B55-applsci-14-02323" class="html-bibr">55</a>,<a href="#B56-applsci-14-02323" class="html-bibr">56</a>,<a href="#B57-applsci-14-02323" class="html-bibr">57</a>,<a href="#B58-applsci-14-02323" class="html-bibr">58</a>,<a href="#B59-applsci-14-02323" class="html-bibr">59</a>,<a href="#B60-applsci-14-02323" class="html-bibr">60</a>,<a href="#B61-applsci-14-02323" class="html-bibr">61</a>].</p> Full article ">Figure 5
<p>Power evolution of Tm³⁺-doped and Tm³⁺-Ho³⁺ co-doped fiber lasers operating at ~2 μm [<a href="#B62-applsci-14-02323" class="html-bibr">62</a>,<a href="#B63-applsci-14-02323" class="html-bibr">63</a>,<a href="#B64-applsci-14-02323" class="html-bibr">64</a>,<a href="#B65-applsci-14-02323" class="html-bibr">65</a>,<a href="#B66-applsci-14-02323" class="html-bibr">66</a>,<a href="#B67-applsci-14-02323" class="html-bibr">67</a>,<a href="#B68-applsci-14-02323" class="html-bibr">68</a>,<a href="#B69-applsci-14-02323" class="html-bibr">69</a>,<a href="#B70-applsci-14-02323" class="html-bibr">70</a>,<a href="#B71-applsci-14-02323" class="html-bibr">71</a>].</p> Full article ">Figure 6
<p>Processes that take place in a Raman laser: (<b>a</b>) stimulated Stokes Raman scattering (SSRS), (<b>b</b>) stimulated anti-Stokes Raman scattering (SARS), (<b>c</b>) coherent anti-Stokes Raman scattering (CARS) when it converts a Stokes photon and a pump photon to an anti-Stokes photon and a pump photon, annihilating two phonons, and (<b>d</b>) CARS when it converts an anti-Stokes photon and a pump photon to a Stokes photon and a pump photon, creating two phonons. <math display="inline"><semantics> <mrow> <msub> <mrow> <mtext> </mtext> <mi>ω</mi> </mrow> <mrow> <mi>P</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mrow> <mtext> </mtext> <mi>ω</mi> </mrow> <mrow> <mi>S</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ω</mi> </mrow> <mrow> <mi>a</mi> <mi>S</mi> </mrow> </msub> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>Ω</mi> </mrow> <mrow> <mi>o</mi> <mi>p</mi> </mrow> </msub> </mrow> </semantics></math> are the pump, Stokes, anti-Stokes, and optical phonon frequencies, respectively.</p> Full article ">Figure 7
<p>The energy level diagram of Brillouin scattering. (<b>a</b>) Brillouin Stokes scattering; (<b>b</b>) Brillouin anti-Stokes scattering. <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ω</mi> </mrow> <mrow> <mi>P</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ω</mi> </mrow> <mrow> <mi>S</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ω</mi> </mrow> <mrow> <mi>a</mi> <mi>S</mi> </mrow> </msub> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>Ω</mi> </mrow> <mrow> <mi>a</mi> <mi>p</mi> </mrow> </msub> </mrow> </semantics></math> are the pump, Stokes, anti-Stokes, and acoustic phonon frequencies, respectively.</p> Full article ">Figure 8
<p>Illustration of the cascaded SBS process. It occurs via the interplay of SBS and four-wave mixing.</p> Full article ">

Figure 1
<p>Different types of defects in WAAM, laser AM, and arc welding processes (Reprinted with permission from [<a href="#B40-jmmp-08-00054" class="html-bibr">40</a>]).</p> Full article ">Figure 2
<p>Effect of laser wavelength on the absorption rate of various metals (Reprinted with permission from [<a href="#B26-jmmp-08-00054" class="html-bibr">26</a>]).</p> Full article ">Figure 3
<p>An example of unsuccessful L-PBF-processed copper using laser powers less than 200 W, resulting in highly porous parts (Reprinted with permission from [<a href="#B53-jmmp-08-00054" class="html-bibr">53</a>]).</p> Full article ">Figure 4
<p>Breakage in the optical mirror of the laser source due to laser back reflection during the L-PBF processing of copper (Reprinted with permission from [<a href="#B56-jmmp-08-00054" class="html-bibr">56</a>]).</p> Full article ">Figure 5
<p>The effect of preheating temperature on the density of L-PBF-fabricated copper parts; (<b>a</b>–<b>c</b>) preheating temperature of 200 °C, and (<b>d</b>–<b>f</b>) preheating temperature of 400 °C (Reprinted with permission from [<a href="#B3-jmmp-08-00054" class="html-bibr">3</a>]).</p> Full article ">Figure 6
<p>(<b>a</b>) Effect of laser wavelength on the laser absorptivity of pure copper [<a href="#B55-jmmp-08-00054" class="html-bibr">55</a>], (<b>b</b>) comparison between the optical absorption of pure copper powders, tin-coated powders of R1 (1.36 wt.%) and R2 (0.28 wt.%), and pre-alloyed CuSn0.3 powders (Reprinted with permission from [<a href="#B59-jmmp-08-00054" class="html-bibr">59</a>]).</p> Full article ">Figure 7
<p>(<b>a</b>,<b>b</b>) Optical micrographs, (<b>c</b>,<b>d</b>) SEM images, (<b>e</b>,<b>f</b>) bright-field TEM micrographs, and (<b>g</b>,<b>h</b>) HR-TEM images taken from the L-PBF-fabricated Cu-0.5Cr alloy (Reprinted with permission from [<a href="#B60-jmmp-08-00054" class="html-bibr">60</a>]).</p> Full article ">Figure 8
<p>The top view of L-PBF-fabricated CuCr1 parts using (<b>a</b>) virgin and (<b>b</b>) nitrided powders. The corresponding side views of samples fabricated with (<b>c</b>) virgin and (<b>d</b>) nitrided powders (Reprinted with permission from [<a href="#B64-jmmp-08-00054" class="html-bibr">64</a>]).</p> Full article ">Figure 9
<p>Optical microscopy images showing the porosity level in L-PBF-fabricated CuCr1 samples using (<b>a</b>) carbon-mixed and (<b>b</b>) carburized powders (Reprinted with permission from [<a href="#B65-jmmp-08-00054" class="html-bibr">65</a>]).</p> Full article ">Figure 10
<p>SEM images showing the improvement in the density level of L-PBF-fabricated Cu-0.8Cr alloy manufactured by (<b>a</b>) virgin Cu-0.8Cr powders and (<b>b</b>) Cu-0.8Cr + 0.2 wt.% TiC powders (Reprinted with permission from [<a href="#B66-jmmp-08-00054" class="html-bibr">66</a>]).</p> Full article ">Figure 11
<p>Microstructure of the L-PBF-fabricated Cu-Cr alloys using (<b>a</b>) nitrided CuCr powders (Reprinted with permission from [<a href="#B64-jmmp-08-00054" class="html-bibr">64</a>]), (<b>b</b>) carburized CuCr powders (Reprinted with permission from [<a href="#B65-jmmp-08-00054" class="html-bibr">65</a>]), and (<b>c</b>) carbon-mixed CuCr powders (Reprinted with permission from [<a href="#B63-jmmp-08-00054" class="html-bibr">63</a>]).</p> Full article ">Figure 12
<p>SEM images of the L-PBF Cu-Cr0.5 samples solution-treated at (<b>a</b>) 920 °C, (<b>b</b>) 940 °C, (<b>c</b>) 960 °C, (<b>d</b>) 980 °C, (<b>e</b>) 1000 °C, and (<b>f</b>) 1020 °C (Reprinted with permission from [<a href="#B61-jmmp-08-00054" class="html-bibr">61</a>]).</p> Full article ">Figure 13
<p>TEM images taken from the L-PBF CuCr0.5 sample (<b>a</b>) before and (<b>b</b>) after solution treatment at 1020 °C, confirming the reduction in dislocation density during the heat treatment (Reprinted with permission from [<a href="#B61-jmmp-08-00054" class="html-bibr">61</a>]).</p> Full article ">Figure 14
<p>Microstructure of the L-PBF-fabricated Cu-0.5Cr alloy after (<b>a</b>) direct aging at 480 °C and (<b>b</b>) solutioning at 1020 °C + aging at 480 °C (Reprinted with permission from [<a href="#B61-jmmp-08-00054" class="html-bibr">61</a>]).</p> Full article ">Figure 15
<p>(<b>a</b>) Low-magnification image showing the distribution of Cr in the Cu matrix of a L-PBF processed CuCr20 alloy, and (<b>b</b>) higher magnification of the box shown in image (<b>a</b>). (<b>c</b>,<b>d</b>) Higher magnification images showing the distribution of Cr in the Cu matrix (Reprinted with permission from [<a href="#B67-jmmp-08-00054" class="html-bibr">67</a>]).</p> Full article ">Figure 16
<p>(<b>a</b>) Effect of heat treatment temperature and time on the electrical conductivity of L-PBF-fabricated CuCr20 and CuCr25 alloys (Reprinted with permission from [<a href="#B67-jmmp-08-00054" class="html-bibr">67</a>]) and (<b>b</b>) effect of annealing temperature on the electrical conductivity of L-PBF-fabricated Cu-1.3Cr and Cu-2.5Cr alloys (Reprinted with permission from [<a href="#B62-jmmp-08-00054" class="html-bibr">62</a>]).</p> Full article ">Figure 17
<p>(<b>a</b>) Effect of post-printing aging time and temperature on the Vickers hardness of L-PBF-fabricated CuCr20 and CuCr25 alloys (Reprinted with permission from [<a href="#B67-jmmp-08-00054" class="html-bibr">67</a>]) and (<b>b</b>) effect of annealing temperature on the hardness of L-PBF-fabricated 1.3Cr and 2.5Cr alloys (Reprinted with permission from [<a href="#B62-jmmp-08-00054" class="html-bibr">62</a>]).</p> Full article ">Figure 18
<p>(<b>a</b>) Elongation, (<b>b</b>) yield strength, and (<b>c</b>) tensile strength of traditionally and L-PBF-fabricated Cu-0.5Cr alloy (the applied heat treatment cycles for the L-PBF sample: direct aging at 480 °C, solutioning at 1020 °C, and solutioning at 1020 °C + aging at 480 °C) [<a href="#B60-jmmp-08-00054" class="html-bibr">60</a>,<a href="#B61-jmmp-08-00054" class="html-bibr">61</a>].</p> Full article ">Figure 19
<p>Effect of annealing temperature on the tensile strength and breaking elongation of L-PBF (<b>a</b>) Cu-1.3Cr and (<b>b</b>) Cu-2.5Cr alloys fabricated in parallel (0°) and perpendicular (90°) to the stacking directions, and SEM images taken from the fractured surfaces of the L-PBF Cu-1.3Cr alloy fabricated in (<b>c</b>) parallel (0°) and (<b>d</b>) perpendicular (90°) directions schematically shown in (<b>e</b>), and (<b>f</b>) a vertical cross-section image showing the crack propagation in the as-printed Cu-1.3Cr L-PBF sample (Reprinted with permission from [<a href="#B62-jmmp-08-00054" class="html-bibr">62</a>]).</p> Full article ">Figure 20
<p>(<b>a</b>,<b>b</b>) Elongation, (<b>c</b>,<b>d</b>) yield strength, and (<b>e</b>,<b>f</b>) tensile strength of L-PBF Cu-Cr alloys manufactured by CuCr0.3 [<a href="#B63-jmmp-08-00054" class="html-bibr">63</a>], CuCr0.3 mixed with 0.05 wt.% carbon nano-particle [<a href="#B63-jmmp-08-00054" class="html-bibr">63</a>], carburized CuCr1 [<a href="#B65-jmmp-08-00054" class="html-bibr">65</a>], and nitrided CuCr1 [<a href="#B64-jmmp-08-00054" class="html-bibr">64</a>] before and after different heat treatments. (Note: AB, S+A, and DA stand for as-built, solutionized+aged, and directly aged, respectively.).</p> Full article ">Figure 21
<p>(<b>a</b>) Relative density of Cu-0.8Cr + 0.2 wt.% TiC and virgin Cu-0.8Cr samples manufactured by L-PBF process with laser power of 320 W and various scan speeds of 500 mm/s, 600 mm/s, 700 mm/s, 800 mm/s, and 1000 mm/s; (<b>b</b>) UTS, Rp0.2, and elongation of L-PBF samples fabricated by laser power of 320 W and scan speed of 600 mm/s. Fracture morphologies of (<b>c</b>,<b>d</b>) Cu-0.8Cr and (<b>e</b>,<b>f</b>) Cu-0.8Cr + 0.2 wt.% TiC tensile samples (Reprinted with permission from [<a href="#B66-jmmp-08-00054" class="html-bibr">66</a>]).</p> Full article ">Figure 22
<p>(<b>a</b>) Corrosion potential (E_corr) and (<b>b</b>) corrosion current density (i_corr) of the L-PBF Cu-0.5Cr samples before and after different heat treatments in 3.5 wt.% NaCl solution (applied heat treatments: direct aging at 480 °C, solutioning at 1020 °C, and solutioning at 1020 °C + aging at 480 °C) [<a href="#B61-jmmp-08-00054" class="html-bibr">61</a>].</p> Full article ">Figure 23
<p>Microstructure of L-DED CuCr30 samples (<b>a</b>) before and (<b>b</b>) after the extrusion process, along with the corresponding EBSD analysis (<b>c</b>) before and (<b>d</b>) after the extrusion process. (<b>e</b>,<b>f</b>) Bright field TEM images taken from the L-DED CuCr30 alloy after the extrusion process indicate the formation of twins (Reprinted with permission from [<a href="#B80-jmmp-08-00054" class="html-bibr">80</a>]).</p> Full article ">Figure 24
<p>(<b>a</b>) Electrical conductivity, (<b>b</b>) density, and (<b>c</b>) tensile strength of vacuum casted, as-printed L-DED, and L-DED +extruded CuCr30 alloy [<a href="#B80-jmmp-08-00054" class="html-bibr">80</a>,<a href="#B81-jmmp-08-00054" class="html-bibr">81</a>].</p> Full article ">Figure 25
<p>(<b>a</b>) Low-magnification SEM image taken from the EBM-fabricated Cu-25Cr alloy. (<b>b</b>,<b>c</b>) EDS elemental analysis taken from areas A and B. (<b>d</b>) A high-resolution FIB-SEM image taken from an EBM-fabricated Cu-25Cr alloy (Reprinted with permission from [<a href="#B84-jmmp-08-00054" class="html-bibr">84</a>]).</p> Full article ">Figure 26
<p>Typical microstructure of Cu-Cr alloys fabricated using different AM methods (Reprinted with minor edits with permission from [<a href="#B60-jmmp-08-00054" class="html-bibr">60</a>,<a href="#B67-jmmp-08-00054" class="html-bibr">67</a>,<a href="#B80-jmmp-08-00054" class="html-bibr">80</a>,<a href="#B84-jmmp-08-00054" class="html-bibr">84</a>]).</p> Full article ">Figure 27
<p>Effect of pre/post-printing processes on the electrical conductivities and tensile strengths of different Cu-Cr alloys fabricated by traditional manufacturing and AM methods.</p> Full article ">Figure 28
<p>Microstructure of the L-PBF-fabricated Cu81-Ni19 alloy (labeled as a 3D model) and the substrate in the annealed state (labeled as a monolith) (Reprinted with permission from [<a href="#B88-jmmp-08-00054" class="html-bibr">88</a>]).</p> Full article ">Figure 29
<p>SEM images of L-PBF Cu-Ni alloy (Cu76-Ni14.8-Sn7-Pb1.6) with laser scan speeds of (<b>a</b>) 100 mm/s, (<b>b</b>) 200 mm/s, and (<b>c</b>) 300 mm/s (layer thickness: 20 μm) [<a href="#B86-jmmp-08-00054" class="html-bibr">86</a>].</p> Full article ">Figure 30
<p>Thickness and mass density of L-PBF Cu-Ni monolayers (Cu71-Ni22.8-Sn4.7-Pb1.43) fabricated at (<b>a</b>,<b>b</b>) laser power of 190 W with different scan speeds of 25, 50, and 80 mm/s, and (<b>c</b>,<b>d</b>) at different laser powers of 190 and 260 W with the scan speed of 80 mm/s [<a href="#B89-jmmp-08-00054" class="html-bibr">89</a>].</p> Full article ">Figure 31
<p>After-corrosion (in NaCl) topography of the L-PBF-fabricated Cu76-Ni14.8-Sn7-Pb1.6 alloy with a layer thickness of (<b>a</b>–<b>c</b>) 20 μm and different laser scan speeds of (<b>a</b>) 100 mm/s, (<b>b</b>) 200 mm/s, and (<b>c</b>) 300 mm/s, and a layer thickness of 60 μm and different laser scan speeds of (<b>d</b>) 100 mm/s, (<b>e</b>) 200 mm/s, and (<b>f</b>) 300 mm/s (Reprinted with permission from [<a href="#B86-jmmp-08-00054" class="html-bibr">86</a>]).</p> Full article ">Figure 32
<p>Tensile strength of L-PBF Cu-Ni (Cu71-Ni22.8-Sn4.7-Pb1.43) monolayers fabricated at (<b>a</b>) laser power of 190 W with different scan speeds and (<b>b</b>) different laser powers with a scan speed of 80 mm/s (Reprinted with permission from [<a href="#B89-jmmp-08-00054" class="html-bibr">89</a>]).</p> Full article ">Figure 33
<p>(<b>a</b>) The order of the deposition and (<b>b</b>) a photographic view of the as-built structure of the graded Cu-Ni alloy fabricated by the L-DED process (Reprinted with permission from [<a href="#B33-jmmp-08-00054" class="html-bibr">33</a>]).</p> Full article ">Figure 34
<p>Surface morphology of L-DED-fabricated (<b>a</b>) pure Ni and (<b>b</b>) Cu-Ni alloy. The porosity distribution at the interface of (<b>c</b>) Ni-CuNi75, (<b>d</b>) CuNi75-CuNi50, and (<b>e</b>) CuNi50-CuNi25. (<b>f</b>) The XRD patterns of a L-DED-deposited graded Cu-Ni alloy (Reprinted with permission from [<a href="#B33-jmmp-08-00054" class="html-bibr">33</a>]).</p> Full article ">Figure 35
<p>Microstructure of the L-DED-deposited graded Cu-Ni alloy at different locations of (<b>a</b>) the bottom layer, (<b>b</b>,<b>c</b>) the middle layers, and (<b>d</b>) the top layer (Reprinted with permission from [<a href="#B33-jmmp-08-00054" class="html-bibr">33</a>]).</p> Full article ">Figure 36
<p>(<b>a</b>–<b>h</b>) EBSD data and (<b>i</b>–<b>l</b>) TEM analysis of WAAM-fabricated Cu-Ni alloy (the composition of filler: Cu-Si(0.082), Mn(0.89), S(0.01), P(0.04), Fe(0.64), Ti(0.25), and Ni(30.13) (wt.%)) (Reprinted with permission from [<a href="#B85-jmmp-08-00054" class="html-bibr">85</a>]).</p> Full article ">Figure 37
<p>As-deposited microstructures of the L-DED-fabricated copper-nickel alloy using different elemental powder blends of (<b>a</b>) blend 1, (<b>b</b>) blend 2, (<b>c</b>) blend 3, and (<b>d</b>) blend 4, which are listed in <a href="#jmmp-08-00054-t004" class="html-table">Table 4</a> (Reprinted with permission from [<a href="#B92-jmmp-08-00054" class="html-bibr">92</a>]).</p> Full article ">Figure 38
<p>Optical micrographs of the as-deposited microstructure of the L-DED-fabricated copper-nickel alloys using different sets of powder blends of pure copper and Delero-22 alloy, including (<b>a</b>) blend 1, (<b>b</b>) blend 2, (<b>c</b>) blend 3, (<b>d</b>) blend 4, and (<b>e</b>) blend 5, which are listed in <a href="#jmmp-08-00054-t005" class="html-table">Table 5</a> (Reprinted with permission from [<a href="#B92-jmmp-08-00054" class="html-bibr">92</a>]).</p> Full article ">Figure 39
<p>(<b>a</b>) L-DED nozzle used for mixing and melting Cu-Ni powders to produce samples shown in (<b>b</b>). (<b>c</b>) The SEM-EDS of an area from the B1S1 sample (see <a href="#jmmp-08-00054-t006" class="html-table">Table 6</a>) (Reprinted with permission from [<a href="#B94-jmmp-08-00054" class="html-bibr">94</a>]).</p> Full article ">Figure 40
<p>Microhardness variations along the building direction for two samples of L-DED-graded Cu-Ni alloy and pure Ni-Cu joint (Reprinted with permission from [<a href="#B33-jmmp-08-00054" class="html-bibr">33</a>]).</p> Full article ">Figure 41
<p>Mechanical properties of Cu–Ni alloy fabricated by the WAAM process (the composition of filler: Cu-Si(0.082), Mn(0.89), S(0.01), P(0.04), Fe(0.64), Ti(0.25), and Ni(30.13) (wt.%)) [<a href="#B85-jmmp-08-00054" class="html-bibr">85</a>].</p> Full article ">Figure 42
<p>Mechanical properties of miniature tensile Cu-Ni alloy samples manufactured by the L-DED process using various blends of copper-nickel powders listed in <a href="#jmmp-08-00054-t005" class="html-table">Table 5</a> (Reprinted with permission from [<a href="#B92-jmmp-08-00054" class="html-bibr">92</a>]).</p> Full article ">Figure 43
<p>Variation in Vickers hardness values (HV_0.2) along the height of the L-DED-deposited copper-nickel-graded material. (<b>a</b>,<b>c</b>,<b>e</b>): Hardness plots on set 1, set 2, and set 3 deposits of 100/0 (Ni/Cu) on 30/70 (Ni/Cu), respectively. (<b>b</b>,<b>d</b>,<b>f</b>): Hardness plots of set 1, set 2, and set 3 deposits of 30/70 (Ni/Cu) on 100/0 (Ni/Cu) (solid circles are the spot measurement, and the red dotted line is the moving average trend line with four measurements as the period) (Reprinted with permission from [<a href="#B93-jmmp-08-00054" class="html-bibr">93</a>]).</p> Full article ">Figure 44
<p>(<b>a</b>) It represents 0.2% offset yield strength, (<b>b</b>) ultimate tensile strength, and (<b>c</b>) strain to break for the miniature tensile Cu-Ni alloy samples manufactured by L-DED using different sets of power and duty cycles (Reprinted with permission from [<a href="#B93-jmmp-08-00054" class="html-bibr">93</a>]).</p> Full article ">Figure 45
<p>Resistivity and thermal conductivity along (<b>a</b>,<b>b</b>) x, y (in-plane), and z (cross-plane) directions from the same block of the L-DED-fabricated Cu-Ni sample (B1S2 in <a href="#jmmp-08-00054-t006" class="html-table">Table 6</a>), and (<b>c</b>,<b>d</b>) in the cross-plane direction measured for different blocks of the L-DED samples listed in <a href="#jmmp-08-00054-t006" class="html-table">Table 6</a> (Reprinted with permission from [<a href="#B94-jmmp-08-00054" class="html-bibr">94</a>]).</p> Full article ">Figure 46
<p>(<b>a</b>) PDP and (<b>b</b>,<b>c</b>) EIS results for the Cu–Ni alloy fabricated by WAAM process (Reprinted with permission from [<a href="#B85-jmmp-08-00054" class="html-bibr">85</a>]).</p> Full article ">Figure 47
<p>(<b>a</b>) XRD patterns of L-PBF and cast Cu–10Sn alloy, along with the corresponding SEM images taken from the microstructure of (<b>b</b>–<b>d</b>) L-PBF and (<b>e</b>) cast Cu–10Sn alloy, and (<b>f</b>) the corresponding stress–strain curves (Reprinted with permission from [<a href="#B104-jmmp-08-00054" class="html-bibr">104</a>]).</p> Full article ">Figure 48
<p>(<b>a</b>,<b>b</b>) Bright-field TEM images, (<b>c</b>) higher resolution TEM image, and (<b>d</b>,<b>e</b>) EDS elemental maps taken from L-PBF-fabricated Cu-13Sn alloy. (<b>f</b>) A comparison between the mechanical properties of the L-PBF Cu-13Sn alloy (denoted as the present study) and other tin-bronzes fabricated by L-PBF or other fabrication methods (Reprinted with permission from [<a href="#B110-jmmp-08-00054" class="html-bibr">110</a>]).</p> Full article ">Figure 49
<p>Effect of laser energy density on the (<b>a</b>) hardness and relative density, (<b>b</b>) yield strength, (<b>c</b>) tensile strength, and (<b>d</b>) ductility of L-PBF Cu-10Sn alloy, along with (<b>e</b>) the corresponding stress–strain curves. Microstructure of L-PBF Cu-10Sn parts fabricated at energy densities of (<b>f</b>) 210, (<b>g</b>) 220, and (<b>h</b>) 230 J/mm² (Reprinted with permission from [<a href="#B115-jmmp-08-00054" class="html-bibr">115</a>]).</p> Full article ">Figure 50
<p>(<b>a</b>) Effect of laser energy density at different laser powers on the relative density of the L-PBF Cu-15Ni-8Sn alloy. SEM images at different magnifications taken from the microstructure of the L-PBF Cu-15Ni-8Sn alloy fabricated with a laser power of 340 W and energy densities of (<b>b</b>,<b>e</b>) 142 J/mm³, (<b>c</b>,<b>f</b>) 70 J/mm³, and (<b>d</b>,<b>g</b>) 142 J/mm³ (Reprinted with permission from [<a href="#B117-jmmp-08-00054" class="html-bibr">117</a>]).</p> Full article ">Figure 51
<p>Schematic illustration from the formation sequence of the L-PBF-fabricated Cu-15Sn alloy: (<b>a</b>) the initial deposited track in each layer, (<b>b</b>) the adjacent deposited track in the same layer, (<b>c</b>) the first deposited track in the subsequent layer, and (<b>d</b>) the effect of temperature gradient on the supercooling [<a href="#B8-jmmp-08-00054" class="html-bibr">8</a>]. SEM images showing the microstructure of an L-PBF fabricated Cu-10Sn alloy at (<b>e</b>) low-magnification side view and high-magnification images from (<b>f</b>) region 1, (<b>g</b>) region 2, and (<b>h</b>) region 3 (Reprinted with permission from [<a href="#B118-jmmp-08-00054" class="html-bibr">118</a>]).</p> Full article ">Figure 52
<p>XRD patterns of the raw Cu-10Sn pre-alloyed powders, L-PBF part in the as-fabricated (AF) condition, and annealed samples at 600 and 800 °C in horizontal and vertical directions (Reprinted with permission from [<a href="#B118-jmmp-08-00054" class="html-bibr">118</a>]).</p> Full article ">Figure 53
<p>(<b>a</b>) XRD patterns of the raw Cu-15Sn pre-alloyed powders, the L-PBF-fabricated part, and the annealed sample at 600 °C for 4 h, along with the (<b>b</b>–<b>e</b>) microstructure of the as-printed and (<b>f</b>,<b>g</b>) annealed L-PBF Cu-15Sn samples (Reprinted with permission from [<a href="#B8-jmmp-08-00054" class="html-bibr">8</a>]).</p> Full article ">Figure 54
<p>EBSD-IPF maps of L-PBF Cu-10Sn samples: (<b>a</b>) as-printed-horizontal, (<b>b</b>) as-printed-vertical, (<b>c</b>) annealed at 600 °C-horizontal, (<b>d</b>) annealed at 600 °C-vertical, (<b>e</b>) annealed at 800 °C-horizontal, and (<b>f</b>) annealed at 800 °C-vertical (Reprinted with permission from [<a href="#B118-jmmp-08-00054" class="html-bibr">118</a>]).</p> Full article ">Figure 55
<p>(<b>a</b>) Stress–strain curves of the conventionally fabricated QSn15-1-1 bar, as-printed, and annealed L-PBF Cu-15Sn samples at 500, 600, and 700 °C, along with the fractured surfaces of (<b>b</b>,<b>c</b>) as-printed and (<b>d</b>,<b>e</b>) annealed L-PBF Cu-15Sn samples at 600 °C for 4 h (Reprinted with permission from [<a href="#B8-jmmp-08-00054" class="html-bibr">8</a>]).</p> Full article ">Figure 56
<p>Summary of the mechanical properties of various tin-bronzes, produced through different conventional and AM methods.</p> Full article ">Figure 57
<p>(<b>a</b>) Thermal conductivity of the L-PBF Cu-10Sn alloy in the as-fabricated (AF) and annealed samples at 600 and 800 °C. (<b>b</b>) Effect of Sn content on the thermal conductivity of tin-bronzes and (<b>c</b>) effect of δ phase percentage on the Sn content in the α phase and thermal conductivity of tin-bronzes (Reprinted with permission from [<a href="#B118-jmmp-08-00054" class="html-bibr">118</a>]).</p> Full article ">Figure 58
<p>(<b>a</b>) Weight loss versus immersion time curves of AF and annealed L-PBF Cu-10Sn samples at 600 and 800 °C, and (<b>b</b>) XRD results of the corroded surfaces after 11 days of immersion in a 3.5 wt.% NaCl water solution. The results of (<b>c</b>) OCP and (<b>d</b>) PDP tests of the AF and annealed L-PBF Cu-10Sn samples at 600 and 800 °C. SEM images taken from the corroded surfaces of the L-PBF Cu-10Sn alloy after immersion testing of (<b>e</b>) the sample annealed at 800 °C and (<b>f</b>,<b>g</b>) the AF sample (Reprinted with permission from [<a href="#B118-jmmp-08-00054" class="html-bibr">118</a>]).</p> Full article ">Figure 59
<p>The pros and cons of different AM methods employed in bimetallic material fabrication [<a href="#B39-jmmp-08-00054" class="html-bibr">39</a>,<a href="#B128-jmmp-08-00054" class="html-bibr">128</a>,<a href="#B129-jmmp-08-00054" class="html-bibr">129</a>,<a href="#B130-jmmp-08-00054" class="html-bibr">130</a>,<a href="#B131-jmmp-08-00054" class="html-bibr">131</a>,<a href="#B132-jmmp-08-00054" class="html-bibr">132</a>,<a href="#B133-jmmp-08-00054" class="html-bibr">133</a>].</p> Full article ">Figure 60
<p>(<b>a</b>–<b>c</b>) Schematic illustration of the L-PBF Cu10Sn-Ti6Al4V bimetallic structure with different interface processing strategies. Cross-section of L-PBF Cu10Sn-Ti6Al4V bimetallic structure fabricated using (<b>a1</b>,<b>a2</b>) direct boding strategy, (<b>b1</b>,<b>b2</b>) remelting method, and (<b>c1</b>,<b>c2</b>) FGM strategy (Reprinted with permission from [<a href="#B139-jmmp-08-00054" class="html-bibr">139</a>]).</p> Full article ">Figure 61
<p>(<b>a1</b>–<b>e3</b>) Microstructural features of the interface between Cu10Sn and Ti6Al4V sides of the bimetallic structure fabricated by L-PBF with direct bonding strategy, remelting method, and FGM techniques (Reprinted with permission from [<a href="#B139-jmmp-08-00054" class="html-bibr">139</a>]).</p> Full article ">Figure 62
<p>(<b>a</b>) L-PBF bimetallic 316L/CuSn10 structure and (<b>b</b>) the schematic illustrations of the interlayer staggered scanning strategy (<b>left</b>) and island scanning strategy (<b>right</b>). (<b>c</b>) The entire interfacial microstructure of L-PBF bimetallic 316L/CuSn10, (<b>d</b>) magnified area A of (<b>c</b>), (<b>e</b>) magnified area B of (<b>c</b>), (<b>f</b>) magnified area C of (<b>c</b>), (<b>g</b>) magnified area D of (<b>e</b>), and (<b>h</b>) a schematic illustration of the nucleation site and propagation direction of the cracks (Reprinted with permission from [<a href="#B145-jmmp-08-00054" class="html-bibr">145</a>]).</p> Full article ">Figure 63
<p>XRD patterns taken from the L-PBF bimetallic 316L/CuSn10 structure in different regions, including the 316L side, CuSn10 side, and interface region (Reprinted with permission from [<a href="#B145-jmmp-08-00054" class="html-bibr">145</a>]).</p> Full article ">Figure 64
<p>Stress–strain curves of single parts of (<b>a</b>) 316L SS, (<b>b</b>) CuSn10, and (<b>c</b>) horizontally combined and (<b>d</b>) vertically combined 316L/CuSn10 bimetallic materials fabricated by L-PBF (Reprinted with permission from [<a href="#B145-jmmp-08-00054" class="html-bibr">145</a>]).</p> Full article ">Figure 65
<p>A schematic illustration showing the FDM process (Reprinted with permission from [<a href="#B150-jmmp-08-00054" class="html-bibr">150</a>]).</p> Full article ">Figure 66
<p>Optical microscopy images showing the porosity distribution in FDM-fabricated Cu-10Sn bronze sintered at temperatures of (<b>a</b>) 850 °C, (<b>b</b>) 875 °C, and (<b>c</b>) 900 °C. (<b>d</b>) Stress–strain curves of the FDM-produced Cu-10Sn bronze sintered at temperatures of 850 °C, 875 °C, and 900 °C (Reprinted with permission from [<a href="#B150-jmmp-08-00054" class="html-bibr">150</a>]).</p> Full article ">Figure 67
<p>A summary of microstructural features observed in NAB alloys fabricated using different conventional and AM methods [<a href="#B19-jmmp-08-00054" class="html-bibr">19</a>,<a href="#B155-jmmp-08-00054" class="html-bibr">155</a>,<a href="#B165-jmmp-08-00054" class="html-bibr">165</a>,<a href="#B167-jmmp-08-00054" class="html-bibr">167</a>,<a href="#B171-jmmp-08-00054" class="html-bibr">171</a>].</p> Full article ">Figure 68
<p>An overview of the mechanical properties exhibited by NAB alloys fabricated by diverse conventional and AM methods.</p> Full article ">Figure 69
<p>Microstructure of the cast NAB using (<b>a</b>) optical and (<b>b</b>) SEM images. TEM images taken from the microstructure of WAAM-fabricated NAB alloy: (<b>c</b>) low-magnification image showing the general microstructure, and (<b>d</b>,<b>e</b>) high-magnification images showing the intermetallic phases (Reprinted with permission from [<a href="#B152-jmmp-08-00054" class="html-bibr">152</a>]).</p> Full article ">Figure 70
<p>Bright-field TEM images indicating (<b>a</b>) Cu matrix along with the corresponding SAED pattern confirming the presence of α phase and κ_IV intermetallic, (<b>b</b>) globular κ_II phases characterized as Fe₃Al, and (<b>c</b>) lamellar κ_III phases characterized as NiAl (Reprinted with permission from [<a href="#B152-jmmp-08-00054" class="html-bibr">152</a>]).</p> Full article ">Figure 71
<p>Microstructure of heat-treated WAAM-produced NAB in three different conditions: (<b>a</b>,<b>b</b>) 350 °C for 2 h (HT-1), (<b>c</b>,<b>d</b>) 550 °C for 4 h (HT-2), and (<b>e</b>,<b>f</b>) 675 °C for 6 h (HT-3) (Reprinted with permission from [<a href="#B154-jmmp-08-00054" class="html-bibr">154</a>]).</p> Full article ">Figure 72
<p>(<b>a</b>) Macrostructure of WAAM-fabricated NAB alloy (Cu-8Al-2Ni-2Fe-2Mn), microstructural features at (<b>b</b>) the bottom area of the first deposited layer, (<b>c</b>) transition from dendritic structure to cellular grains in the first deposited layer, (<b>d</b>,<b>e</b>) low- and high-magnification micrographs taken from the first interlayer band area, and (<b>f</b>,<b>g</b>) low- and high-magnification micrographs taken from the second interlayer band area (Reprinted with permission from [<a href="#B156-jmmp-08-00054" class="html-bibr">156</a>]).</p> Full article ">Figure 73
<p>Top view of the microstructure of WAAM-fabricated NAB alloy (Cu-8Al-2Ni-2Fe-2Mn) taken from different locations of (<b>a</b>–<b>c</b>) bottom area, (<b>d</b>,<b>e</b>) top area, and (<b>f</b>) the very last deposited layer, confirming the microstructural coarsening from the bottom to the top regions (Reprinted with permission from [<a href="#B156-jmmp-08-00054" class="html-bibr">156</a>]).</p> Full article ">Figure 74
<p>Effect of ultrasonic vibration on the columnar structure of WAAM NAB, (<b>a</b>) without ultrasonic vibration and (<b>b</b>) with ultrasonic vibration (Reprinted with permission from [<a href="#B157-jmmp-08-00054" class="html-bibr">157</a>]).</p> Full article ">Figure 75
<p>CMT Twin torch along with the first deposited layer of NAB using a CMT Twin torch (Reprinted with permission from [<a href="#B158-jmmp-08-00054" class="html-bibr">158</a>]).</p> Full article ">Figure 76
<p>(<b>a</b>) Engineering stress–strain curves of the cast and WAAM-NABs (Reprinted with permission from [<a href="#B152-jmmp-08-00054" class="html-bibr">152</a>]). (<b>b</b>) Stress–strain curves of the WAAM NAB in as-built and heat-treated conditions of HT-1 (350 °C for 2 h), HT-2 (550 °C for 4 h), and HT-3 (675 °C for 6 h) (Reprinted with permission from [<a href="#B154-jmmp-08-00054" class="html-bibr">154</a>]).</p> Full article ">Figure 77
<p>(<b>a</b>) Wear depth and (<b>b</b>) weight loss of the WAAM and cast NABs during wear testing. (<b>c</b>) Microhardness profile showing the transition from the cast substrate to WAAM-fabricated NAB (Reprinted with permission from [<a href="#B22-jmmp-08-00054" class="html-bibr">22</a>]).</p> Full article ">Figure 78
<p>Stress–strain curves of the cast NAB counterpart (C95220 alloys), and the WAAM NAB samples under different conditions (U2 and U3 are with ultrasonic vibration, and C3 is without ultrasonic vibration) (Reprinted with permission from [<a href="#B157-jmmp-08-00054" class="html-bibr">157</a>]).</p> Full article ">Figure 79
<p>Mechanical properties of a WAAM-fabricated NAB alloy, including (<b>a</b>) tensile strength, (<b>b</b>) yield strength, (<b>c</b>) elongation, and (<b>d</b>) the standard deviation of tensile strength values. (Note: QT = quenching and tempering, and AF = as-fabricated.) (Reprinted with permission from [<a href="#B153-jmmp-08-00054" class="html-bibr">153</a>]).</p> Full article ">Figure 80
<p>PFs of the WAAM-fabricated NAB alloy in different conditions of As-fabricated (AF), quenched (Q), quenched and tempered (QT), and directly tempered (T) (Reprinted with permission from [<a href="#B159-jmmp-08-00054" class="html-bibr">159</a>]).</p> Full article ">Figure 81
<p>Microstructure of the (<b>a</b>) cast, (<b>b</b>) wrought, and (<b>c</b>,<b>d</b>) L-PBF-fabricated NAB counterparts (Reprinted with permission from [<a href="#B165-jmmp-08-00054" class="html-bibr">165</a>]).</p> Full article ">Figure 82
<p>Microstructure of the L-PBF-fabricated NAB samples after different post-printing heat treatment cycles, including (<b>a</b>,<b>b</b>) 600 °C for 1 hour, (<b>c</b>,<b>d</b>) 700 °C for 1 hour, (<b>e</b>,<b>f</b>) 800 °C for 1 h, (<b>g</b>,<b>h</b>) 900 °C for 1 h (Reprinted with permission from [<a href="#B165-jmmp-08-00054" class="html-bibr">165</a>]).</p> Full article ">Figure 83
<p>(<b>a</b>) Stress–strain curves of the as-printed and heat-treated L-PBF NAB samples, and (<b>b</b>) a comparison with the mechanical properties of cast and wrought counterparts. (<b>c</b>) Mass loss measurements after seawater exposure for 3 and 6 months in the as-printed and heat-treated L-PBF NAB alloy compared with the cast and wrought counterparts (Reprinted with permission from [<a href="#B165-jmmp-08-00054" class="html-bibr">165</a>]).</p> Full article ">Figure 84
<p>Microstructure of as-built and heat-treated L-PBF NAB alloys using different feedstocks, including (<b>a</b>,<b>b</b>) C63000 and (<b>c</b>,<b>d</b>) C95800. (<b>e</b>) Stress–strain curves of L-PBF-fabricated NAB alloys using two feedstocks of C63000 and C95800 in the as-built and heat-treated conditions, respectively, along with the cast and forged counterparts (Reprinted with permission from [<a href="#B163-jmmp-08-00054" class="html-bibr">163</a>]).</p> Full article ">Figure 85
<p>PDP curves of the as-built and heat-treated L-PBF NAB alloys, using different feedstocks of (<b>a</b>,<b>b</b>) C63000 and (<b>c</b>,<b>d</b>) C95800 (Reprinted with permission from [<a href="#B163-jmmp-08-00054" class="html-bibr">163</a>]).</p> Full article ">Figure 86
<p>(<b>a</b>) As-fabricated EBM NAB cylindrical parts with a diameter of 25 mm, (<b>b</b>) IPF map of the as-fabricated sample, (<b>c</b>) the corresponding grain boundary map, (<b>d</b>) SEM image showing uniform distribution of precipitates, (<b>e</b>) the IPF map taken from the white square selected areas showing the formation of precipitates on both intergranular and intragranular areas, and (<b>f</b>–<b>i</b>) the corresponding EDS elemental maps of Cu, Al, Ni, and Fe (Reprinted with permission from [<a href="#B166-jmmp-08-00054" class="html-bibr">166</a>]).</p> Full article ">Figure 87
<p>(<b>a</b>–<b>c</b>) TEM images at different magnifications and the corresponding SAED patterns taken from the melt pool center of the L-DED NAB part; (<b>d</b>–<b>g</b>) the corresponding EDS elemental maps of Cu, Al, Fe, and Ni’ (<b>h</b>,<b>i</b>) TEM images and the corresponding SAED patterns of α and β* taken from the melt pool boundary; (<b>j</b>) HRTEM image taken from α; (<b>k</b>) HRTEM image taken from β*; and (<b>l</b>–<b>o</b>) EDS elemental maps taken from the inset in (<b>h</b>) (Reprinted with permission from [<a href="#B171-jmmp-08-00054" class="html-bibr">171</a>]).</p> Full article ">Figure 88
<p>(<b>a</b>) Stress–strain curve of the L-DED NAB part fabricated with different process parameters (S1–S8) and (<b>b</b>) summary of the obtained mechanical properties. (<b>c</b>) A comparison between the mechanical properties of the L-DED NAB part and the counterparts fabricated by other manufacturing processes, including WAAM, L-PBF, and cast before and after heat treatment (Reprinted with permission from [<a href="#B171-jmmp-08-00054" class="html-bibr">171</a>]).</p> Full article ">Figure 89
<p>(<b>a</b>) SEM image taken from the interface between WAAM NAB and the 316L SS substrate, showing the formation of cracks in the HAZ of the SS side, and (<b>b</b>) higher magnification SEM image, showing the penetration of liquid NAB into the intergranular regions of the SS side (Reprinted with permission from [<a href="#B160-jmmp-08-00054" class="html-bibr">160</a>]).</p> Full article ">Figure 90
<p>(<b>a</b>) Interface of the WAAM-fabricated NAB/316L bimetal, and (<b>b</b>–<b>d</b>) the corresponding EDS elemental analysis (Reprinted with permission from [<a href="#B161-jmmp-08-00054" class="html-bibr">161</a>]).</p> Full article ">Figure 91
<p>Microstructural features of (<b>a</b>,<b>b</b>) interfacial region of the L-DED-fabricated CuNi2SiCr/NAB bimetal part, (<b>c</b>) NAB substrate, (<b>d</b>) CuNi2SiCr-deposited layers, (<b>e</b>) HAZ region, and (<b>f</b>) diluted region (Reprinted with permission from [<a href="#B169-jmmp-08-00054" class="html-bibr">169</a>]).</p> Full article ">Figure 92
<p>After-immersion surface morphology of the (<b>a</b>–<b>d</b>) NAB substrate and (<b>e</b>–<b>h</b>) deposited layers at different immersion times: (<b>a</b>,<b>e</b>) 1 day, (<b>b</b>,<b>f</b>) 5 days, (<b>c</b>,<b>g</b>) 14 days, and (<b>d</b>,<b>h</b>) 28 days (Reprinted with permission from [<a href="#B170-jmmp-08-00054" class="html-bibr">170</a>]).</p> Full article ">Figure 93
<p>(<b>a</b>) Schematic illustration showing the L-DED fabrication process of NAB/15-5 PH bimetal samples; (<b>b</b>) a representative of the as-fabricated part showing the tensile sample preparation; (<b>c</b>) a prototype of a bimetal NAB/15-5 PH part; (<b>d</b>) low-magnification confocal image, covering the last layer of 15-5 PH side, interface, and the first layer of NAB side; (<b>e</b>–<b>g</b>) higher magnification images taken from zones 1, 2, and 3 of (<b>d</b>), respectively; and (<b>h</b>) EDS elemental line scan covering NAB side, interface, and 15-5 PH side (Reprinted with permission from [<a href="#B168-jmmp-08-00054" class="html-bibr">168</a>]).</p> Full article ">Figure 94
<p>Schematic illustration of stress concentration at the tips of Fe_xAl dendrites during tensile loading in (<b>a</b>) longitudinal and (<b>b</b>) transverse directions in the L-DED-fabricated NAB/15-5 PH bimetal part (Reprinted with permission from [<a href="#B168-jmmp-08-00054" class="html-bibr">168</a>]).</p> Full article ">Figure 95
<p>Corrosion properties of the L-DED bimetal NAB/15-5 PH part: (<b>a</b>) PDP curves, and (<b>b</b>) Nyquist plots resulted from EIS testing. Surface profiles of (<b>c</b>) NAB and (<b>d</b>) 15-5 PH after 72 h of immersion. SEM images taken from the corroded surfaces of (<b>e</b>) NAB and (<b>f</b>) 15-5 PH after 72 h of immersion. (<b>g</b>) The depth of the corrosion pits in the NAB and 15-5 PH (Reprinted with permission from [<a href="#B168-jmmp-08-00054" class="html-bibr">168</a>]).</p> Full article ">Figure 96
<p>(<b>a</b>) TiO₂-TiC-coated diamond particles produced by the molten salt method, (<b>b</b>) Raman spectra of TiO₂-TiC powder taken from the selected area of interest, (<b>c</b>) schematic illustration showing the L-DED process, and (<b>d</b>) SEM image of the copper/diamond powder mixture (Reprinted with permission from [<a href="#B175-jmmp-08-00054" class="html-bibr">175</a>]).</p> Full article ">Figure 97
<p>(<b>a</b>–<b>c</b>) SEM images taken from the surface of L-DED-fabricated copper-diamond composites with different energy densities, (<b>d</b>) effect of process parameters on the quality of the printed parts, (<b>e</b>) effect of laser energy density on the density of the printed parts, (<b>f</b>) schematic illustration showing the process of particle ejection during the deposition process, and (<b>g</b>) effect of interphase on the thermal conductivity (TC) of copper-diamond composites when using no interphase (black bar), only TiC interphase (red bar), and TiO₂-TiC interphase (green bar) (Reprinted with permission from [<a href="#B175-jmmp-08-00054" class="html-bibr">175</a>]).</p> Full article ">Figure 98
<p>(<b>a</b>,<b>b</b>) SEM images of the L-DED-fabricated copper-diamond surface, (<b>c</b>) cross-sectional view of copper-(TiO₂-TiC)-diamond, (<b>d</b>) copper/TiO₂ interface, (<b>e</b>) TiO₂/TiC interface, and (<b>f</b>–<b>h</b>) HR-TEM micrographs of copper, TiO₂, and TiC, respectively (Reprinted with permission from [<a href="#B175-jmmp-08-00054" class="html-bibr">175</a>]).</p> Full article ">Figure 99
<p>SEM images taken from (<b>a</b>) the original diamond particle, (<b>b</b>) the TiO₂-TiC-coated diamond particle before L-DED printing, and (<b>c</b>) after L-DED printing. (<b>d</b>) The corresponding Raman spectra from the powders at different states and (<b>e</b>) full width at half maximum (FWHM) and the diamond peak’ position in different states of the powders (Reprinted with permission from [<a href="#B175-jmmp-08-00054" class="html-bibr">175</a>]).</p> Full article ">Figure 100
<p>(<b>a</b>) XRD results of a BJT-fabricated copper-diamond composite in the (a₁) green state, (a₂) after sintering at 800 °C, and (a₃) after sintering at 900 °C, along with the (<b>b</b>) relative density of the samples fabricated with different volume fractions of diamond and different sintering temperatures (Reprinted with permission from [<a href="#B182-jmmp-08-00054" class="html-bibr">182</a>]).</p> Full article ">Figure 101
<p>(<b>a</b>) An schematic illustration showing the effect of sintering temperature on the BJT-fabricated copper-diamond composite sample, along with the fracture surfaces of the samples sintered at (<b>b</b>) 800 °C and (<b>c</b>) 900 °C (Reprinted with permission from [<a href="#B182-jmmp-08-00054" class="html-bibr">182</a>]).</p> Full article ">Figure 102
<p>SEM images taken from (<b>a</b>) mixed composite powder before the L-PBF process and (<b>b</b>) surface of the L-PBF-fabricated Cu-GO composite specimen, along with the (<b>c</b>) stress–strain curves of as-printed samples in vertical and horizontal directions (Reprinted with permission from [<a href="#B23-jmmp-08-00054" class="html-bibr">23</a>]).</p> Full article ">Figure 103
<p>(<b>a</b>,<b>b</b>) Unpolished top view of the L-PBF-fabricated copper-carbon composite, (<b>c</b>,<b>d</b>) the corresponding polished (unetched) samples, and (<b>e</b>,<b>f</b>) the corresponding etched samples (Reprinted with permission from [<a href="#B177-jmmp-08-00054" class="html-bibr">177</a>]).</p> Full article ">Figure 104
<p>(<b>a</b>,<b>b</b>) Virgin CuCr0.3 alloy powder, (<b>c</b>,<b>d</b>) mixed CuCr0.3 powder and carbon nano-particles, along with the SEM images taken from the top view of the L-PBF-fabricated (<b>e</b>) CuCr0.3 alloy, and (<b>f</b>) carbon-mixed CuCr0.3 composite used for L-PBF fabrication of copper-carbon composite (Reprinted with permission from [<a href="#B63-jmmp-08-00054" class="html-bibr">63</a>]).</p> Full article ">Figure 105
<p>SEM image taken from the powder mixture used for the L-DED fabrication of the copper-ZrB₂ in-situ composite (Reprinted with permission from [<a href="#B178-jmmp-08-00054" class="html-bibr">178</a>]).</p> Full article ">Figure 106
<p>(<b>a</b>) Microstructure and elemental distribution maps of Zr, Cu, and Ni taken from the L-DED-fabricated copper-ZrB₂ in-situ composite and (<b>b</b>) the corresponding XRD results (Reprinted with permission from [<a href="#B178-jmmp-08-00054" class="html-bibr">178</a>]).</p> Full article ">Figure 107
<p>(<b>a</b>) XRD analysis and (<b>b</b>) SEM images taken from the SLS processed copper-ceramic composite using ZrB₂ reinforcing particles (Reprinted with permission from [<a href="#B179-jmmp-08-00054" class="html-bibr">179</a>]).</p> Full article ">Figure 108
<p>(<b>a</b>) An overview of the ODS-Cu powder used for SEBM-fabrication of copper-alumina composite, (<b>b</b>) a low-magnification cross-sectional view, and (<b>c</b>) a high-magnification SEM image showing the uniform dispersion of Al₂O₃ with an approximate size of 35 nm (Reprinted with permission from [<a href="#B180-jmmp-08-00054" class="html-bibr">180</a>]).</p> Full article ">Figure 109
<p>Longitudinal cross-sectional overview of SEBM-fabricated copper-alumina composite showing a porous structure in (<b>a</b>–<b>c</b>) all different sets of process parameters, along with (<b>d</b>–<b>f</b>) higher magnification SEM images showing the occurrence of phase separation in the microstructure of the as-printed specimens, that is, region (1) consists of pure copper, region (2) reveals copper/alumina structure, and region (3) contains alumina (Reprinted with permission from [<a href="#B180-jmmp-08-00054" class="html-bibr">180</a>]).</p> Full article ">Figure 110
<p>Different feedstock powders used for SLS fabrication of Cu-tin alloy, including (<b>a</b>) virgin Cu powders, (<b>b</b>) mechanically mixed Cu and Sn powders, and (<b>c</b>,<b>d</b>) cross-section and surface of composite Cu-Sn powders, respectively (Reprinted with permission from [<a href="#B181-jmmp-08-00054" class="html-bibr">181</a>]).</p> Full article ">Figure 111
<p>SEM images at different magnifications taken from the SLS-fabricated Cu-based sample using (<b>a</b>,<b>b</b>) mechanically mixed Cu and Sn powders, (<b>c</b>,<b>d</b>) composite Cu-Sn powders, along with (<b>e</b>,<b>f</b>) a detailed microstructural feature showing the necking between two Cu particles in the presence of a Sn-rich interparticle layer (Reprinted with permission from [<a href="#B181-jmmp-08-00054" class="html-bibr">181</a>]).</p> Full article ">

Figure 1
<p>Example excitation spectra and emission spectra for fluorophores in a multicolor, multiphoton imaging experiment. On the x-axes, we show (from top to bottom) the wavelength corresponding to single-photon excitation and emission, 2-photon excitation, and 3-photon excitation, respectively.</p> Full article ">Figure 2
<p>(<b>a</b>) Brightfield and (<b>b</b>) widefield epifluorescence images (composite of 405/440 (blue), 488/520 (green), and 560/605 (red) (excitation/emission filter central wavelength)) of a thin <span class="html-italic">S. aizunensis</span> sample (~3 µL of sample sandwiched between a microscope slide and cover slip), showing the filaments formed in the cultures. The strong scattering from this sample causes a significant blur, even when the focal plane is directly below the cover slip. Scale bars: 100 µm.</p> Full article ">Figure 3
<p>Schematic of our laser and microscope system. The repetition rate of the laser was controlled by choosing an appropriate divisor to the oscillator pulse train with the timing electronics. The detection electronics’ sampling rate was set with the oscillator pulse train, and then synchronized to the amplifier output pulses.</p> Full article ">Figure 4
<p>Characterization of the output beam from our femtosecond fiber laser. The pulses were characterized using second-harmonic frequency-resolved optical gating (<b>a</b>,<b>b</b>), showing a pulse duration of 180 fs with minimal satellite pulses. (<b>c</b>) The far-field beam profile, measured with a beam profiler camera. The profile is nearly perfectly Gaussian, owing to only the fundamental mode being launched in the large-mode area final amplifier stage.</p> Full article ">Figure 5
<p>Three-dimensional measurement of the 2P and 3P PSF. (<b>a</b>,<b>b</b>) Projections of the 3D measurement along the <span class="html-italic">z</span>-axis of the orange (2P) and blue (3P) fluorescence, respectively, from a 500 nm bead. (<b>d</b>,<b>e</b>) Projections along the <span class="html-italic">y</span>-axis of the orange and blue fluorescence, respectively, of the same 500 nm bead, to visualize the <span class="html-italic">z</span>-profiles of the PSFs. (<b>c</b>) Linear lateral cross-sections of the 2P and 3P PSFs. The solid lines represent the <span class="html-italic">x</span> cross-sections and the dashed lines show the <span class="html-italic">y</span> cross-sections of the 3P (blue) and 2P (red) PSFs. The magenta and cyan lines show the lateral cross-sections of the calculated 2P and 3P PSFs, convoluted with a 500 nm sphere, respectively. (<b>f</b>) Linear axial cross-sections of the measured 2P (red line) and 3P (blue line) PSFs. The magenta and cyan lines show the axial cross-section of the calculated 2P and 3P PSF convoluted with a 500 nm sphere, respectively.</p> Full article ">Figure 6
<p>Simulated signal-to-background ratio vs. scattering length and imaging depth for (<b>a</b>) 2P excited fluorescence and (<b>b</b>) 3P fluorescence. Contour lines (iso-values for signal-to-background ratio) and color coding are the same for both panels. Contour lines are labeled where possible. Beyond a signal-to-background ratio of 1:20, contour lines are drawn at 1:50 and 1:100. Obviously, those last contours represent situations where image quality is so gravely compromised that imaging is practically impossible.</p> Full article ">Figure 7
<p>Characterization of the nonlinearity of the fluorescence in different detection spectral windows. Panel (<b>a</b>) shows a composite image (76 µm × 76 µm) of the measurements in all 3 detection channels at the highest laser power shown in panel (<b>b</b>). Scale bars: 10 µm. A region where the no sample movement was detected between all measurements was chosen to extract the signal vs. background. Panel (<b>b</b>) shows the power dependence of the fluorescence signal in the red (570–640 nm), green (490–560 nm), and blue (400–480 nm) detection channels.</p> Full article ">Figure 8
<p>Measurement of 2P and 3P fluorescence vs. depth (76 µm × 76 µm × 570 µm) in a Streptomyces sample. (<b>a</b>) Red (570–640 nm), green (490–560 nm), and blue (400–480 nm) fluorescence channels (top row—<span class="html-italic">xy</span> slice 90 µm below top surface; middle row—central <span class="html-italic">xz</span> cut; bottom row—<span class="html-italic">xy</span> slice 390 µm below top surface; horizontal (<span class="html-italic">xy</span>) scale bar: 10 µm; vertical (<span class="html-italic">z</span>) scale bar: 30 µm). (<b>b</b>) Signal minus background vs. depth normalized to maximum value (solid dots and solid lines) and, accordingly, scaled background vs. depth (dashed lines) for the red, green, and blue channels. (<b>c</b>) Signal-to-background ratio vs. depth for the red, green, and blue detection channels.</p> Full article ">Figure 9
<p>Measurement of 2P and 3P fluorescence vs. depth (76 µm × 76 µm × 270 µm) in a dense <span class="html-italic">Streptomyces</span> bacterial community sample. (<b>a</b>) Red (570–640 nm), green (490–560 nm), and blue (400–480 nm) fluorescence channels (Top row—<span class="html-italic">xy</span> slice 10 µm below top surface. Middle row—<span class="html-italic">xz</span> slide 160 µm below top surface. Bottom row—<span class="html-italic">xy</span> slice 270 µm below top surface. Scale bar: 10 µm.). (<b>b</b>) Center <span class="html-italic">xz</span> cut; scale bar: 10 µm.</p> Full article ">Figure 10
<p>(<b>a</b>) Signal minus background vs. depth corresponding to the stack shown in <a href="#sensors-24-00667-f007" class="html-fig">Figure 7</a>, normalized to maximum value (close to 150 µm depth; solid dots and lines) and, accordingly, scaled background vs. depth (dashed lines) for the red, green, and blue channels. (<b>b</b>) Signal-to-background ratio vs. depth for the red, green, and blue detection channels.</p> Full article ">Figure 11
<p>Images (76 µm × 76 µm) obtained at 780 µm below the sample surface in a medium-dense sample (with 120 µm effective attenuation length), i.e., at 6.5 scattering lengths below the surface; (<b>a</b>) 3P excited fluorescence signal detected in the 400–480 nm spectral window; (<b>b</b>) 2P excited fluorescence signal detected in the 570–640 nm spectral window. <span class="html-italic">Streptomyces</span> filaments are clearly recognized in the 3P image but cannot be resolved in the 2P image due to the overwhelming background. Scale bars: 10 µm.</p> Full article ">

Figure 1
<p>(<b>A</b>) Experimental setup for measuring the fluorescence excitation–emission matrices of calculi; (<b>B</b>) experimental setup for recording the diffuse light reflection spectra of calculi.</p> Full article ">Figure 2
<p>FTIR spectra for different types of stones. The dotted lines represent the band characteristics of each type (chemical composition) of calculus.</p> Full article ">Figure 3
<p>(<b>A</b>–<b>C</b>) The normalized average fluorescence emission spectra for the three types of stones at excitation wavelengths of 340, 380 and 420 nm, respectively. The translucent areas depict the magnitude of the standard deviation. (<b>D</b>–<b>F</b>) The characteristic EEMs of the three types of stones.</p> Full article ">Figure 4
<p>(<b>A</b>) The normalized fluorescence spectrum of averaged over five measurement points from a single calculi. (<b>B</b>) The normalized fluorescence spectrum of all the calculi. The translucent areas depict the magnitude of the standard deviation. The excitation wavelength was 380 nm.</p> Full article ">Figure 5
<p>(<b>A</b>) Average optical density (OD) spectra of three types of stones with OD subtracted at 600 nm. Translucent areas indicate the magnitude of the standard deviation. (<b>B</b>) Box plots of the slope of the OD spectra for the three types of stones. The rhombus depicts the outlying OD spectrum detected from one of the oxalate stones. (<b>C</b>) Characteristic appearance of a urate calculus, oxalates and hydroxyapatites from top to bottom, respectively.</p> Full article ">Figure 6
<p>The confusion matrix (<b>A</b>) of the train subset for the classifier using EEM data (<b>B</b>) of the test subset for the classifier also using solely EEM data; (<b>C</b>) of the train subset for the classifier that uses both EEM and DRS data; and (<b>D</b>) of the test subset for a classifier that uses both EEM and DRS data.</p> Full article ">

Figure 1
<p>Fundamentals and types of multiphoton microscopy (MPM). (<b>a</b>) A femtosecond laser generates ultrashort pulses, which are sent to galvanometric (xy) scanning mirrors to scan the beam on the back aperture of the objective with the help of scan and tube lenses. The dichroic mirror helps to transmit the excitation wavelength and reflects the emitted light from the mouse brain. Since the beam fills most of the back aperture of the objective lens, the beam is focused to a micrometer level beam size on the focal plane of the objective. The emitted light is directed to the highly sensitive photon multiplier tubes (PMTs) by using two dichroic mirrors and two band-pass filters depending on the type of MPM. (<b>b</b>) Energy-level diagrams of different kinds of MPMs, such as 2PEF, SHG, 3PEF, and THG. <math display="inline"><semantics> <mrow> <mi>h</mi> <mi>ω</mi> </mrow> </semantics></math> is the excitation photon energy, <math display="inline"><semantics> <mi>λ</mi> </semantics></math> denotes wavelength.</p> Full article ">Figure 2
<p>The recent developments in the field of ultra-fast fiber lasers. (<b>a</b>) Ring laser cavity design. Insets: Longitudinal modes in a simple laser cavity: gain medium of the laser, cavity longitudinal modes are equally spaced by <math display="inline"><semantics> <mfrac> <mi>c</mi> <mrow> <mn>2</mn> <mi>L</mi> </mrow> </mfrac> </semantics></math>, the modes whose corresponding frequencies fall within the gain bandwidth of the laser will be amplified and lased out. (<b>b</b>) Pulse shaping regimes of the mode-locked fiber lasers. (<b>c</b>) Different categories of saturable absorbers: Optical phenomena-based, and material-based. (<b>d</b>) Tunable repetition rate and wavelength source for MPM imaging.</p> Full article ">Figure 3
<p>Various configurations of ultrafast lasers. (<b>a</b>) Schematic representation of the mode-locked Yb-doped fiber laser ring cavity. The total cavity length is 4.8 m. A polarizing beam splitter (PBS) is used to split the fast and slow axis light and helps to measure the pulsed output. Half-wave and quarter-wave plates are used to varying the polarization state of the light which helps to obtain the phase and mode-locking. The use of the birefringent filter plate (BRF) allows for control of the spectral bandwidth in the cavity. Col.1 and Col.2 indicate the collimators [<a href="#B26-photonics-10-01307" class="html-bibr">26</a>]. (<b>b</b>) Experimental configuration of circularly polarized solitons generation: QWP, quarter-wave plate; L, lens; LPF, long-pass filter [<a href="#B50-photonics-10-01307" class="html-bibr">50</a>]. (<b>c</b>) Experimental view of Cr:F laser setup. FC: fiber collimator; PL: pump lens; CM: Concave mirror; DCM: double-chirped mirror; PL: pump lens; OC: output coupler; BD: beam dump [<a href="#B51-photonics-10-01307" class="html-bibr">51</a>]. (<b>d</b>) Schematic of the 1.8 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m femtosecond fiber laser system, Stage 1: Er-doped amplifier, Stage 2: Tm:ZBLAN pre-amplifier and power amplifier [<a href="#B16-photonics-10-01307" class="html-bibr">16</a>].</p> Full article ">Figure 4
<p>Different configurations of fiber amplifiers. (<b>a</b>) System diagram for a basic CPA system (<b>b</b>) different building blocks of the MOPA system, (<b>c</b>) schematic representation of GMNA.</p> Full article ">Figure 5
<p>All−fiber mode−locked oscillator output characteristics. (<b>a</b>) Wavelength spectrum of the laser. (<b>b</b>) Mode−locked laser pulse train. (<b>c</b>) Measured RF spectrum repetition rate centered at 21.35 MHz. (<b>d</b>) Oscillator output before and after compression. Adapted from [<a href="#B52-photonics-10-01307" class="html-bibr">52</a>].</p> Full article ">Figure 6
<p>Characteristics of different stage amplifier output. (<b>a</b>) Optical spectrum of pre−amplifier. (<b>b</b>) Optical spectrum of the power−amplifier. (<b>c</b>) The power amplifier ASE spectrum. (<b>d</b>) The relationship between input and output power. Adapted from [<a href="#B52-photonics-10-01307" class="html-bibr">52</a>].</p> Full article ">Figure 7
<p>Two-photon functional mouse brain imaging with fiber lasers. (<b>a</b>) Dual color neuronal (jRGECO1a) and axonal (jYCaMP1s) imaging at 1040 nm wavelength with 31.25 MHz repetition rate. (<b>Top left</b>) The average image of both colors, (<b>top right</b>) pixel-wise covariance of response amplitudes in each color. (<b>Bottom</b>) jYCaMP (yellow) and jRGECO (red) recordings from the button site. Gray lines represent the visual stimulus onsets. Adapted from [<a href="#B27-photonics-10-01307" class="html-bibr">27</a>]. (<b>b</b>) Comparison of spontaneous activity of neurons at a 680 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m depth with or without AES by two-photon microscopy. (<b>Top left</b>) Structural image of neurons without AES. (<b>Top right</b>) structural image of neurons with AES. (<b>Bottom left</b>) Spontaneous activity traces acquired without AES. (<b>Bottom right</b>) Spontaneous activity traces acquired with AES. Adapted from [<a href="#B59-photonics-10-01307" class="html-bibr">59</a>].</p> Full article ">Figure 8
<p>Two-photon fluorescence structural mouse brain imaging with fiber lasers. (<b>a</b>) Dual color neuronal (green, YFP mice) and microvasculature (red, Texas Red dye) imaging at 1060 nm wavelength with 40 MHz repetition rate up to a 750 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m depth. (<b>left</b>) Microvasculature imaging with Texas-red dye, (<b>right</b>) neuronal imaging with YFP transgenic mice. Adapted from [<a href="#B26-photonics-10-01307" class="html-bibr">26</a>]. (<b>b</b>) Neuronal and brain vasculature imaging by exciting the mouse brain with a Yb amplifier-based fiber laser and a Raman laser simultaneously. (<b>Top</b>) Maximum intensity projections ranging from the surface to a 750 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m depth for neurons (<b>left</b>, tdTomato, 1060 nm excitation), vasculature (<b>right</b>, Alexafluor 647, 1250 nm excitation), and overlaid to each other (<b>middle</b>). (<b>Bottom</b>) Side view for the same stacks from neurons (<b>left</b>), vasculature (<b>right</b>), and overlaid to each other (<b>middle</b>) Adapted from [<a href="#B60-photonics-10-01307" class="html-bibr">60</a>]. (<b>c</b>) (<b>Left</b>) 3D reconstruction of 2-photon fluorescence image stack of mouse brain vasculature labeled with ICG (red), and third-harmonic generation images of myelinated axons (green) delineating the white matter. (<b>Right</b>) Representative 2D two-photon fluorescence images at the depth from the brain surface, as indicated. Adapted from [<a href="#B50-photonics-10-01307" class="html-bibr">50</a>].</p> Full article ">Figure 9
<p>Three-photon fluorescence functional mouse and Drosophila brain imaging with fiber lasers. (<b>a</b>) Video-rate imaging of neural activity in Kenyon cells labeled with GCaMP7f during electric shocks. The blue and orange lines show single Kenyon cell activity under rest and electric shock, respectively. Red shade areas represent the periods of electric shocks. Inset: a single Kenyon cell. Scale bar is 80 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m. Adapted from [<a href="#B51-photonics-10-01307" class="html-bibr">51</a>]. (<b>b</b>) (<b>Top</b>) Structural images of neurons without AES (<b>left</b>), and with AES (<b>right</b>). (<b>Bottom</b>) Spontaneous activity of neurons without AES (<b>left</b>), and with AES (<b>right</b>). With AES, the spontaneous traces have higher SNR than those without AES. Reproduced with permission from [<a href="#B59-photonics-10-01307" class="html-bibr">59</a>].</p> Full article ">Figure 10
<p>Examples of three-photon structural brain imaging. (<b>a</b>) Schematic illustration of in vivo imaging of neurons expressing TurboFP635. TurboFP635 was expressed in cortical neurons of a mouse (C57BL/6N) and was excited by 3-photon excitation at 1.8 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m (<b>left</b>), 3D reconstruction of 700 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m z-stack (<b>right</b>). Reproduced with permission from Ref. [<a href="#B16-photonics-10-01307" class="html-bibr">16</a>]. (<b>b</b>) Comparison of 3P and 2P excitation for imaging mouse brain tissue (<b>left</b>); 3PEF (<b>top</b>) and 2PEF (<b>bottom</b>) imaging of a tdTomato-labeled fixed mouse brain cortex at depths of 200 and 600 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m. (<b>right</b>) Dual-color 3PEF imaging for several combinations of green–red fluorescent proteins in HEK cells (<b>top</b>) and mouse brain tissue at a depth of 500 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m (<b>bottom</b>). Reproduced with permission from Ref. [<a href="#B49-photonics-10-01307" class="html-bibr">49</a>].</p> Full article ">Figure 11
<p>Simultaneous three-photon fluorescence (3PEF) and third-harmonic generation (THG) imaging of fixed Rainbow-3 mouse brain cortex and brain stem. (<b>a</b>–<b>c</b>) Simultaneous THG (<b>a</b>) and 3PEF (<b>b</b>) imaging of a fixed mouse brain cortex. (<b>c</b>) In the cortex, THG imaging provides contrast similar to that of brain vasculature, as confirmed by overlaying the 3PEF signal acquired through tdTomato. (<b>d</b>–<b>f</b>) Simultaneous THG (<b>d</b>) and 3PEF (<b>e</b>) imaging of a fixed mouse brain stem; (<b>f</b>) 3PEF highlights the brain vasculature and THG highlights myelinated axons and cell bodies so that the overlapping of these two signals is minimal. Reproduced with permission from [<a href="#B63-photonics-10-01307" class="html-bibr">63</a>].</p> Full article ">Figure 12
<p>Several fiber laser advancement prospects as well as potential future innovations.</p> Full article ">

Figure 1
<p>Structure of SMF-MMF-SMF filter [<a href="#B8-micromachines-14-02026" class="html-bibr">8</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) Tunable Yb-doped fiber laser based on SMF-MMF-SMF filter; (<b>b</b>) Tunable results of the dissipative soliton fiber laser [<a href="#B10-micromachines-14-02026" class="html-bibr">10</a>].</p> Full article ">Figure 3
<p>(<b>a</b>) Tuning principle of SMF-MMF-SMF filter by bending; (<b>b</b>) Experimental setup diagram of the tunable fiber laser; (<b>c</b>) Output spectra of the interval-adjustable dual-wavelength fiber laser; (<b>d</b>) Output spectra of the tunable single-wavelength fiber laser [<a href="#B20-micromachines-14-02026" class="html-bibr">20</a>].</p> Full article ">Figure 4
<p>(<b>a</b>) Experimental setup diagram of the tunable mode-locked fiber laser; (<b>b</b>) Output spectra of the tunable mode-locked fiber laser [<a href="#B24-micromachines-14-02026" class="html-bibr">24</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) Experimental setup diagram of the Tm-doped fiber laser; (<b>b</b>) Measured spectra of the single-wavelength laser by adjusting the PC and rotating the MMF [<a href="#B26-micromachines-14-02026" class="html-bibr">26</a>].</p> Full article ">Figure 6
<p>Structure of the SMF-NCF-SMF filter [<a href="#B29-micromachines-14-02026" class="html-bibr">29</a>].</p> Full article ">Figure 7
<p>(<b>a</b>) Structure of the tunable SMF-NCF-SMF filter; (<b>b</b>) Experimental setup diagram of the tunable Tm-doped fiber laser; (<b>c</b>) Tuning results of the Tm-doped fiber laser [<a href="#B31-micromachines-14-02026" class="html-bibr">31</a>].</p> Full article ">Figure 8
<p>(<b>a</b>) Structure of the SMF-NCF-SMF filter based on index-matching liquid; (<b>b</b>) Experimental setup diagram of the tunable erbium-doped fiber laser; (<b>c</b>) Tuning results [<a href="#B32-micromachines-14-02026" class="html-bibr">32</a>].</p> Full article ">Figure 9
<p>(<b>a</b>) Cross-section of the two-core fiber [<a href="#B33-micromachines-14-02026" class="html-bibr">33</a>]; (<b>b</b>) The structure of the interference filter based on two-core fiber [<a href="#B33-micromachines-14-02026" class="html-bibr">33</a>]; (<b>c</b>) Structure of the interference filter based on tapered seven-core fiber [<a href="#B35-micromachines-14-02026" class="html-bibr">35</a>].</p> Full article ">Figure 10
<p>(<b>a</b>) The field distribution and normalized power in a tapered seven-core fiber simulated by Rsoft software; (<b>b</b>) Transmission spectra of tapered seven-core fiber simulated by Rsoft software [<a href="#B35-micromachines-14-02026" class="html-bibr">35</a>].</p> Full article ">Figure 11
<p>(<b>a</b>) Cross-section of the seven-core fiber; (<b>b</b>) Working principle of the interference filter based on seven-core fiber [<a href="#B39-micromachines-14-02026" class="html-bibr">39</a>].</p> Full article ">Figure 12
<p>(<b>a</b>) Experimental setup diagram of the tunable erbium-doped fiber laser based on tapered seven-core fiber filter; (<b>b</b>) Spectra of the tunable fiber laser [<a href="#B35-micromachines-14-02026" class="html-bibr">35</a>].</p> Full article ">Figure 13
<p>Power transfer number versus FSR measured (blue circles) and simulated (red stars) at λ₀ = 1.55 μm for tapers assuming different elongations. Inset shows an experimental example of normalized transfer power versus taper elongation [<a href="#B42-micromachines-14-02026" class="html-bibr">42</a>].</p> Full article ">Figure 14
<p>(<b>a</b>) Schematic diagram of the tapered fiber filter; (<b>b</b>) Tunable fiber laser based on tapered fiber filter; (<b>c</b>) Tuning results of the fiber laser [<a href="#B44-micromachines-14-02026" class="html-bibr">44</a>].</p> Full article ">Figure 15
<p>Schematic diagram of the double-cone MZI filter [<a href="#B50-micromachines-14-02026" class="html-bibr">50</a>].</p> Full article ">Figure 16
<p>(<b>a</b>) Experimental setup diagram of the tunable fiber laser based on a double-cone MZI filter; (<b>b</b>) Tuning results after annealing [<a href="#B50-micromachines-14-02026" class="html-bibr">50</a>].</p> Full article ">Figure 17
<p>(<b>a</b>) The cross-section of the FLCSCF; (<b>b</b>) Schematic diagram of the FLCSCF filter; (<b>c</b>) Experimental setup of the fiber laser based on FLCSCF filter; (<b>d</b>) Tunable single-wavelength lasing output [<a href="#B59-micromachines-14-02026" class="html-bibr">59</a>].</p> Full article ">Figure 18
<p>Diagram of two cascaded up-taper joints structure [<a href="#B60-micromachines-14-02026" class="html-bibr">60</a>].</p> Full article ">Figure 19
<p>(<b>a</b>) The cross-section of the PCF; (<b>b</b>) Schematic diagram of the SMF-PCF-SMF filter [<a href="#B55-micromachines-14-02026" class="html-bibr">55</a>]; (<b>c</b>) Experimental setup of the tunable fiber laser; (<b>d</b>) Tuning results of the single-wavelength output spectrum [<a href="#B63-micromachines-14-02026" class="html-bibr">63</a>].</p> Full article ">Figure 20
<p>(<b>a</b>) Schematic diagram of the core-offset structure filter; (<b>b</b>) Experimental setup of the tunable fiber laser; (<b>c</b>) Spectral response against temperature [<a href="#B62-micromachines-14-02026" class="html-bibr">62</a>].</p> Full article ">Figure 21
<p>(<b>a</b>) Experimental setup diagram of the tunable mode-locked fiber laser based on tapered seven-core fiber filter; (<b>b</b>) Spectra of the tunable dissipative soliton fiber laser; (<b>c</b>) Spectra of the tunable amplifier similariton fiber laser [<a href="#B41-micromachines-14-02026" class="html-bibr">41</a>].</p> Full article ">

Figure 1
<p>Evolution of LRPON (based on Figure 1 from [<a href="#B19-photonics-10-00923" class="html-bibr">19</a>]).</p> Full article ">Figure 2
<p>OLT and ONUs discovery and communication protocol. The contention zone is the period where multiple ONUs engage in competition to register with the OLT, ensuring collision avoidance.</p> Full article ">Figure 3
<p>Flowchart of the DWDBA algorithm.</p> Full article ">Figure 4
<p>DWDBA Algorithm Sequence Diagram.</p> Full article ">Figure 5
<p>Throughput for scenario 1 where the ONUs are placed between 50 km and 75 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 6
<p>Throughput for scenario 2 where the ONUs are placed between 70 km and 100 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 7
<p>Throughput for scenario 3 where the ONUs are placed between 17 km and 100 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 8
<p>Throughput for scenario 4 where the ONUs are placed between 50 km and 100 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 9
<p>Queue delay for scenario 1 where the ONUs are placed between 50 km and 75 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 10
<p>Queue delay for scenario 2 where the ONUs are placed between 70 km and 100 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 11
<p>Queue delay for scenario 3 where the ONUs are placed between 17 km and 100 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">Figure 12
<p>Queue delay for ONUs placed between 50 km and 100 km from OLT for DWDBA (<b>left</b>) and IPACT (<b>right</b>).</p> Full article ">

Figure 1
<p>The experimental setup of the multiwavelength SOA fiber laser.</p> Full article ">Figure 2
<p>Multiwavelength emission from SOA fiber laser at different pump currents.</p> Full article ">Figure 3
<p>The emitted wavelength peaks vs. the pump current.</p> Full article ">Figure 4
<p>The multiwavelength SOA fiber laser outputs optical power.</p> Full article ">Figure 5
<p>The multiwavelength SOA fiber laser tunability operating regimes at different SOA temperatures.</p> Full article ">Figure 6
<p>Output optical power stability over 6 h.</p> Full article ">Figure 7
<p>The multiwavelength peaks stability at pump current of 300 mA over 3 h.</p> Full article ">