CN100464696C - A spectral domain OCT imaging method and system based on optical scanning delay line - Google Patents

Abstract

The invention discloses a spectral domain OCT (optical coherence tomography) imaging method and system based on an optical scanning delay line. The optical scanning delay line is introduced in the reference arm of the spectral domain OCT system, which can realize the dispersion-free phase shift of the reference light and the system dispersion compensation at the same time. In particular, when the dual-grating-based optical scanning delay line is introduced, a large range of group velocity dispersion and third-order dispersion can be generated for any symbol combination, which can accurately match the dispersion of the reference arm and the sample arm in the spectral domain OCT system. . Through dispersion-free phase shift and dispersion compensation, coherent noise can be eliminated while ensuring the axial resolution of the spectral domain OCT system, and the imaging depth of the system can be doubled. The invention is of great significance to the ultra-high resolution complex spectrum domain OCT system.

Description

A spectral domain OCT imaging method and system based on optical scanning delay line

technical field

The invention relates to optical coherence tomography (OCT) technology, in particular to a spectral domain OCT imaging method and system based on optical scanning delay lines.

Background technique

Optical Coherence Tomography (OCT) is an emerging optical imaging technology, which can realize non-contact, non-invasive, high-resolution imaging of the tissue structure and physiological functions inside the living body, and can be used for early detection of diseases. And in the field of body biopsy has a wide range of applications.

The spectral domain OCT system uses a high-speed CCD to collect the spectral components of the interference signal in parallel, and can obtain the depth information of the sample without axial scanning, which has the characteristics of fast and high sensitivity. However, the disadvantage of spectral domain OCT lies in its inherent coherent noise such as mutual interference signals between layers of the sample and self-coherent interference signals of the light source. At the same time, due to the inverse Fourier transformation of the interference spectrum collected on the CCD to obtain depth information, the result of the Fourier transformation of the real function is Hermitian conjugated, resulting in symmetric information items, thus limiting the spectral domain. The detection depth of the OCT system.

The method to eliminate the coherent noise of spectral domain OCT and expand its detection depth is realized by forming complex spectral interference signals. Usually, the piezoelectric ceramic driver is used to move the mirror of the reference arm to achieve phase shifting. Usually, a five-step phase shifting method is used to reconstruct the interference signal between the sample and the reference arm through the interference spectrum signal obtained after each phase shift. The complex value of the spectral component of , and then perform inverse Fourier transformation, thereby eliminating coherent noise and doubling the imaging depth.

Since the OCT system uses a broadband light source to obtain micron-level axial resolution, the spectral domain OCT system that uses a piezoelectric ceramic driver to achieve phase shift inevitably has the problem of dispersion, which will lead to the reconstruction of the complex signal of the interference spectrum after phase shift. error, which is more pronounced in super-resolution spectral domain OCT systems. At the same time, in order to avoid reducing the axial resolution due to system dispersion, the spectral domain OCT system using the phase shift method uses the subsequent numerical dispersion compensation algorithm to match the dispersion of the reference arm and the sample arm to achieve the best resolution. In software dispersion compensation, an iterative process is used to maximize a predefined image sharpness function, at which point the system dispersion is considered to be compensated. However, due to the limitations of the iterative algorithm, the real-time performance of the software dispersion compensation algorithm is not good, and the software dispersion compensation algorithm can only compensate the system dispersion within a small range.

Contents of the invention

The object of the present invention is to provide a spectral domain OCT imaging method and system based on an optical scanning delay line. At the reference arm of the spectral domain OCT system, a fast optical scanning delay line is used to achieve dispersion-free phase modulation, and at the same time, the fast optical scanning delay line is used as a dispersion compensation element to match the dispersion of the reference arm and the sample arm. In particular, when using a fast optical scanning delay line based on double gratings, the system dispersion can be compensated to the third order in a large range.

The purpose of the present invention is achieved through the following technical solutions:

1. A spectral domain OCT imaging method based on an optical scanning delay line:

A fast optical scanning delay line system is introduced into the reference arm of the spectral domain OCT system to achieve phase modulation of the reference light and compensation for the dispersion of the system; The optical scanning delay line can accurately compensate the system dispersion in a wider range; the specific steps are as follows:

1) Synchronize the vibrating mirror in the optical scanning delay line in the reference arm, the scanning probe of the sample arm and the linear array CCD in the detection unit through a synchronous timing circuit to collect interference spectrum signals;

2) By adjusting the distance x ₀ between the rotating axis of the galvanometer and the optical axis in the optical scanning delay line and the defocus amount Δz of the grating, the system dispersion is compensated while performing dispersion-free phase modulation on the reference light; When scanning the delay line, adjusting the distance between the two gratings can produce group velocity dispersion and third-order dispersion of any symbol combination with a larger variation range than single-grating optical scanning delay line, so that the reference arm and sample arm in the spectral domain OCT system Dispersion is precisely matched;

3) In one scanning cycle of the vibrating mirror in the optical scanning delay line, the linear array CCD is controlled by the synchronous sequential circuit to collect the interference spectrum signal at the same time interval, and the signal is transmitted to the PC through a dedicated interface; in the PC, through the existing various A phase-shifting algorithm uses three-step, four-step and five-step methods to reconstruct the complex expression of the interference spectrum signal, and then obtains the information of an axial scan through the inverse Fourier transform.

2. A spectral domain OCT imaging system based on optical scanning delay line:

Including broadband light source, optical isolator, broadband fiber coupler, four polarization controllers, scanning probe, detection unit and optical scanning delay line; the low coherent light from the broadband light source is incident through the first polarization controller and optical isolator To the broadband fiber coupler, after splitting, one path passes through the second polarization controller and enters the reference arm formed by the optical scanning delay line, the other path passes through the third polarization controller and enters the scanning probe, and the two returned light interferes through the fourth polarization controller connected to the detection unit, and finally processed in the computer to reconstruct the image.

The scanning probe includes a collimating lens, a scanning vibrating mirror and a focusing lens; the optical signal entered by the third polarization controller is irradiated onto the sample through the collimating lens, the scanning vibrating mirror and the focusing lens.

The detection unit: includes a first collimating mirror, a transmission grating, a double-glued achromatic lens and a linear array CCD; the interference light signal entered by the fourth polarization controller passes through the first collimating mirror, the transmission grating, the double-glued After the achromatic lens, focus on the linear array CCD; the electrical signal generated on the linear array CCD is transmitted to the computer through the image acquisition card.

The optical scanning delay line: includes a first blazed grating, a second collimating mirror, a first plane mirror, a first Fourier transform lens and a first scanning galvanometer; wherein the first blazed grating is parallel to the first Fourier transform lens , the distance from its front focal plane is an adjustable defocus amount Δz; the first scanning galvanometer is located on the back focal plane of the first Fourier transform lens; The included angle of the normal line of a blazed grating is the blaze angle of the first blazed grating; the second collimating mirror is located directly above the first plane reflector; the distance between the rotating axis of the first scanning galvanometer and the optical axis is an adjustable variable x ₀ .

The optical scanning delay line: includes a second blazed grating, a third blazed grating, a third collimating mirror, a second plane mirror, a second Fourier transform lens, and a second scanning galvanometer; wherein the third blazed grating and the first The two Fourier transform lenses are parallel, and the distance from its front focal plane is an adjustable defocus amount Δz; the second scanning galvanometer is located on the back focal plane of the second Fourier transform lens; the distance between the second scanning galvanometer rotating shaft and the optical axis is An adjustable variable x ₀ ; the second blazed grating and the third blazed grating are parallel to each other, and their reticle lines are also parallel to each other, and the distance between them is an adjustable amount d; the third collimating mirror and the second blazed grating The included angle of the normal line of the grating is an adjustable inclination angle, and its size is adjusted to make the light with a center wavelength of λ ₀ exit along the optical axis after being diffracted by the second blazed grating and the third blazed grating; the third collimating mirror is located at Directly above the second plane mirror; the distance between the rotation axis of the second scanning galvanometer and the optical axis is an adjustable variable x ₀ .

Compared with background technology, the beneficial effect that the present invention has is:

1. Realize phase shift without dispersion. The dispersion-free phase shift of the reference light can be performed by optically scanning the delay line, which eliminates the phase shift error caused by the bandwidth of the light source, thereby avoiding subsequent algorithm errors. With a dispersion-free phase shift, a complex form of interference light between the sample and reference arms can be constructed. spectral signal, thereby eliminating coherent noise and doubling the imaging depth.

2. Hardware compensation system dispersion. In the optical scanning delay line, the system dispersion is compensated by adjusting the defocus amount of the grating. Especially when the optical scanning delay line with double gratings is used, the independent variable of the grating spacing is increased, which can produce group velocity dispersion and third-order dispersion that vary in a large range, so that the system dispersion can be compensated to the third order. It is of great significance in the ultra-high resolution spectral domain OCT system.

3. Dispersion-free phase shift and dispersion compensation are realized through optical scanning delay line at the same time. The compactness and reliability of the spectral domain OCT system can be achieved.

Description of drawings

Fig. 1 is a system schematic diagram of a specific embodiment of the spectral domain OCT imaging method based on an optical scanning delay line according to the present invention, wherein the reference arm is a single-grating optical scanning delay line;

Fig. 2 is a schematic diagram of the structure of the reference arm when the reference arm of the spectral domain OCT system is a double-grating optical scanning delay line;

Fig. 3 is a block diagram of the control system of the spectral domain OCT system based on the optical scanning delay line used in the present invention.

In the figure: 1. Broadband light source, 2. Optical isolator, 3. Broadband fiber coupler, 4. Polarization controller, 5. Collimator lens, 6. Scanning mirror, 7. Focusing lens, 8. Sample, 9. Blazed grating, 10. Collimating mirror, 11. Plane mirror, 12. Fourier transform lens, 13. Scanning mirror, 14. Collimating mirror, 15. Transmission grating, 16. Double cemented achromatic lens, 17. Linear array CCD, 18, blazed grating, 19, blazed grating, 20, image acquisition card, 21, computer, 22, scanning probe, 23, optical scanning delay line, 24, detection unit.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

As shown in Figure 1, the present invention comprises a broadband light source 1, an optical isolator 2, a broadband fiber coupler 3, four polarization controllers 4, a scanning probe 22, a detection unit 24 and an optical scanning delay line 23; The low-coherence light is incident on the broadband fiber coupler 3 through the first polarization controller 4 and the optical isolator 2, and after splitting, one path passes through the second polarization controller 4 and enters the reference arm formed by the optical scanning delay line 23, and the other path passes through The third polarization controller 4 enters the scanning probe 22 , and the two returned light interferences pass through the fourth polarization controller 4 to connect to the detection unit 24 , and finally processed by the computer 21 to reconstruct the image.

The scanning probe 22: includes a collimating lens 5, a scanning vibrating mirror 6 and a focusing lens 7; the optical signal entered by the third polarization controller 4 is irradiated to the On sample 8.

The detection unit 24: includes a first collimating mirror 14, a transmission grating 15, a double-glued achromatic lens 16 and a linear array CCD17; the interference light signal entered by the fourth polarization controller 4 passes through the first collimating mirror 14 , transmission grating 15, double glued achromatic lens 16, focus on the linear array CCD17;

The optical scanning delay line 23: includes the first blazed grating 9, the second collimating mirror 10, the first plane mirror 11, the first Fourier transform lens 12 and the first scanning galvanometer 13; wherein the first blazed grating 9 Parallel to the first Fourier transform lens 12, the distance from its front focal plane is an adjustable defocus amount Δz; the first scanning galvanometer 13 is located on the back focal plane of the first Fourier transform lens 12; the second collimating mirror 10 And the angle between the normal of the first plane mirror 11 and the normal of the first blazed grating 9 is the blaze angle of the first blazed grating 9; the second collimating mirror 10 is positioned directly above the first plane mirror 11; The distance between the rotation axis and the optical axis of a scanning galvanometer 13 is an adjustable variable x ₀ .

As shown in Figure 2, the optical scanning delay line 23: includes the second blazed grating 18, the third blazed grating 19, the third collimating mirror 10, the second plane mirror 11, the second Fourier transform lens 12 and the first Two scanning vibrating mirrors 13; wherein the third blazed grating 19 is parallel to the second Fourier transform lens 12, and the distance from its front focal plane is an adjustable defocus amount Δz; the second scanning vibrating mirror 13 is located at the second Fourier transform lens 12 on the rear focal plane; the distance between the rotating axis of the second scanning galvanometer 13 and the optical axis is an adjustable variable x ₀ ; the second blazed grating 18 and the third blazed grating 19 are parallel to each other, and their scribed lines are also parallel to each other. The distance between them is an adjustable amount d; the angle between the third collimating mirror 10 and the normal line of the second blazed grating 18 is an adjustable inclination angle, and its size is adjusted to make the light with a center wavelength of λ ₀ pass through the second The blazed grating 18 and the third blazed grating 19 are diffracted and emitted along the direction of the optical axis; the third collimating mirror 10 is located directly above the second plane mirror 11; the distance between the second scanning galvanometer 13 rotating shaft and the optical axis is adjustable variable x ₀ .

As shown in Figure 1, the low-coherence light emitted from the broadband light source 1 enters the broadband fiber coupler 3 through the polarization controller 4 and the optical isolator 2, and enters the reference arm and the sample arm through the polarization controller 4 after splitting. After being collimated by the collimating mirror 10, the light of the arm is split by the blazed grating, and each spectral component is focused on the scanning lens 13 through the Fourier transform lens 12, and after being modulated by the scanning lens 13, it returns to the blazed grating 9 through the Fourier transform lens 12 again, and After being diffracted again by the blazed grating 9, it is projected on the plane mirror 11. Each spectral component reflected by the plane mirror 11 returns along the original path, and finally synthesizes the same beam of light and returns to the broadband fiber coupler 3. After interference with the light returned by the sample arm, it enters the detection unit 24 and is divided into various wavelengths by the transmission grating 15. , and then focus on the linear array CCD17 by the double cemented achromatic lens 16. Finally, these interference spectral components are transmitted to the computer 21 through the image acquisition card 20 for processing.

In Fig. 1, after the reference light passes through the optical scanning delay line 23, the phase change amount of the light wave with wavelength λ is:

φ(k)＝2kδ+2kΔz cos β+2kx ₀ θ-2kθ f sin β (1)

Wherein k is a wave number and k=2π/λ, δ is an initial optical path difference, it can be considered that δ=0, θ is the rotation angle of the scanning galvanometer 13, f is the focal length of the Fourier transform lens 12, and β is formed by psinβ=m(λ -λ ₀ ), p is the grating constant, λ ₀ is the center wavelength, and the Taylor expansion of φ(k) is:

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; !</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; !</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;z</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;z</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;m\&theta;f</span>}}{{\mathrm{<span\; class="notranslate">\; pk</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; !</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; !</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

的大小，从而可以对系统中的群速度色散(GVD)和三阶色散(TOD)进行补偿。在样本臂放置一个平面反射镜，对干涉光谱信号做逆傅立叶变换，得到A-scan的值，此时通过调节Δz来改变包络的宽度，当包络的半宽度与宽带光源1的相干长度基本匹配时，可以认为此时的Δz补偿了系统的色散。同时调节x₀＝-mfλ₀/p，此时φ(k)≈2x₀θk₀+2Δzkin ${\mathrm{D.}}_k=-8{\mathrm{\&pi;}}^2{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C200710068210E00091.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\mathrm{\&Delta;z}/p^2{k_0}^3$ ${\mathrm{D.}}_k^{\&prime;}=\mathrm{twenty\; four}{\mathrm{\&pi;}}^2{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C200710068210E00091.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\mathrm{\&Delta;z}/p^2{k_0}^4,$ By changing Δz, D _k and

, so that the group velocity dispersion (GVD) and third order dispersion (TOD) in the system can be compensated. Place a plane reflector on the sample arm, and perform inverse Fourier transform on the interference spectrum signal to obtain the value of A-scan. At this time, the width of the envelope is changed by adjusting Δz. When the half width of the envelope is equal to the coherence length of the broadband light source 1 When basically matching, it can be considered that Δz at this time compensates the dispersion of the system. At the same time adjust x ₀ =-mfλ ₀ /p, at this time φ(k)≈2x ₀ θk ₀ +2Δzk

After dispersion compensation, the interference signal is split by the transmission grating 15, and focused on the linear array CCD17 by the double-glued achromatic lens 16. The interference spectrum signal collected by any pixel of the linear array CCD17 is:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; kz</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="i"\; filenames="C200710068210E00091.png"\; state="\{\{state\}\}">i</figure-callout></span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&NotEqual;</span>\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}<span\; class="notranslate">\; )</span>$

                         

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; k\&Delta;z</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; kz</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; coherent\; noises</span>}$

It can be seen from the above formula that the interference spectrum component between the reference arm and the sample arm has a phase term 4x ₀ k ₀ θ that does not vary with k, thus achieving phase modulation without dispersion. Simultaneously, the scanning vibrating mirror 6 of the reference arm, the scanning vibrating mirror 13 in the optical scanning delay line 23, and the exposure time of the linear CCD17 in the detection unit are controlled by a synchronous circuit to collect signals. For example, the frequency of the scanning vibrating mirror 6 in the sample arm is set to 30 Hz, and the frequency of the scanning vibrating mirror 13 in the optical scanning delay line 23 is set to 500 Hz. The linear array CCD17 collects 5 interference spectrum signals at equal intervals to obtain the interference spectrum signal values under different phase shift amounts. At this time, the existing five-step phase shift algorithm can be used to calculate the phase and amplitude of the interference spectrum signals, and The interference spectrum signal in complex form is:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; k\&Delta;z</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; kz</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>$

At this time, the inverse Fourier transform of the obtained complex interference spectrum signal can be obtained to obtain the depth information of an A-scan that eliminates the image and coherent noise, and the detection depth is doubled.

As shown in FIG. 2 , it is a schematic diagram of an optical scanning delay line whose reference arm is a double grating. Wherein the blazed grating 18 and the blazed grating 19 are placed in parallel, and their scribed lines are parallel to each other. Compared with the single-grating optical scanning delay line shown in the reference arm in Fig. 1, the reference light enters the optical scanning delay line through the collimating mirror 10, passes through the blazed grating 18 and the blazed grating 19 to split the light, and then passes through the Fourier transform lens 12 in turn , scanning the vibrating mirror 13, and returning to the broadband fiber coupler 3 along the original path after being reflected by the plane mirror 11. The phase change φ(k) of the light wave with wavenumber k is related to the distance d between two blazed gratings. The double-grating optical scanning delay line can produce a larger range of dispersion compensation than the single-grating optical scanning delay line by adjusting the grating spacing d and the grating defocus amount Δz, and can simultaneously compensate the system's group velocity dispersion (GVD) and third-order Dispersion (TOD).

As shown in Fig. 3, it is a block diagram of the control system of the spectral domain OCT system based on the optical scanning delay line. The interference spectrum signal collected by the linear array CCD17 is transmitted to the computer 21 through the image acquisition card 20 . The computer 21 simultaneously generates synchronous timing to control the scanning galvanometer 13 in the optical scanning delay line 23 and the scanning probe 22 of the sample arm. In one scanning period of the scanning vibrating mirror 13 of 23 in the optical scanning delay line, computer 21 controls the linear array CCD17 to collect 5 interference spectrum signals at the same time interval, and after one scanning period of scanning vibrating mirror 13 finishes, computer 21 controls The scanning probe 22 scans the next lateral position.

Claims (1)

1. A spectral domain OCT imaging method based on an optical scanning delay line, characterized in that: a fast optical scanning delay line system is introduced into the reference arm of the spectral domain OCT system, and the phase modulation of the reference light and the dispersion of the system are realized at the same time Compensation; when using a double-grating fast optical scanning delay line, compared with a single-grating optical scanning delay line, it can accurately compensate the system dispersion in a larger range; the specific steps are as follows: 1) Synchronize the vibrating mirror in the optical scanning delay line in the reference arm, the scanning probe of the sample arm and the linear array CCD in the detection unit through a synchronous timing circuit to collect interference spectrum signals; 2) By adjusting the distance x0 between the rotating axis of the galvanometer and the optical axis in the optical scanning delay line and the defocus amount Δz of the grating, the system dispersion is compensated while performing dispersion-free phase modulation on the reference light; when the fast optical scanning of double gratings is used For the delay line, adjust the distance between the two gratings to produce group velocity dispersion and third-order dispersion with a larger range than the single-grating optical scanning delay line, so that the dispersion of the reference arm and the sample arm in the spectral domain OCT system can be accurately matched; 3) In one scanning cycle of the vibrating mirror in the optical scanning delay line, the linear array CCD is controlled by the synchronous sequential circuit to collect the interference spectrum signal at the same time interval, and the signal is transmitted to the PC through a dedicated interface; in the PC, through the existing various A phase-shifting algorithm uses three-step, four-step and five-step methods to reconstruct the complex expression of the interference spectrum signal, and then obtains the information of an axial scan through the inverse Fourier transform.

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