CN102681091A - Tunable optical delay line based on coupled optical waveguides - Google Patents

Abstract

The invention discloses an adjustable optical delay line based on coupling optical waveguides, which is composed of two optical waveguides parallel or perpendicular to each other. When the two waveguides are close to each other to 0.3-0.8 μm, they are coupled with each other through evanescent waves. It is mainly composed of two optical waveguides with different dispersion curves, and the dispersion curves of the two waveguides intersect at the phase-matched wavelength nodes. The two waveguides are coupled to each other, and the group velocity of the coupled mode undergoes a rapid jump at the intersection point, resulting in a delay. Through the adjustment of the thermo-optic effect, the optical signal can achieve low-distortion transmission and adjustable delay in a wide range. Effect.

Description

Adjustable optical delay line based on coupled optical waveguide

technical field

The invention relates to an adjustable optical delay line based on a coupling optical waveguide, belonging to the field of silicon-based photonics. the

Background technique

Silicon-based photonic devices are a research hotspot in recent years. Many passive and active photonic devices have been proposed by researchers, including buffers, filters, switches, modulators, detectors and lasers. These discrete devices or hybrid integrations can be used for on-chip optical signal processing. Delaying (or buffering) of optical signals is a basic function in time-domain optical signal processing. Photons cannot be stored, so the method of optical caching is to delay the optical signal for a period of time in the light-guiding medium, which can be considered in terms of slowing down the propagation speed of light and extending the length of the transmission medium. At present, two types of optical buffering methods are proposed: slow optical type and optical fiber delay line type. For slow-light optical buffer structures, silicon-based microring resonators and photonic crystal waveguides are widely used. Adjusting the dispersion of the corresponding waveguide or device is an effective way to achieve delay. In addition to microrings and photonic crystals, waveguide coupling is also an effective way to adjust waveguide transmission and dispersion performance. the

Based on the reported types of slow-light optical buffers, in terms of waveguide structure and device principles, it is necessary to expand and innovate to meet the application requirements. the

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, and propose an adjustable optical delay line based on coupling optical waveguides. The coupling optical waveguides are composed of two optical waveguides with different dispersion characteristics. The coupling caused by the dispersion of the structure, the group velocity of the coupled mode undergoes a rapid jump at the phase-matched wavelength node, resulting in a delay. After adding the thermal electrode, through the adjustment of the thermo-optic effect, the optical signal can achieve low-distortion transmission and adjustable delay in a wide range. The strength of waveguide coupling determines the sensitivity of thermo-optic effect to group velocity adjustment. the

Technical solution of the present invention is as follows:

A dimmable optical delay line based on coupled optical waveguides is characterized in that: the adjustable optical delay line is composed of two mutually parallel or perpendicular optical waveguides, when the two waveguides are close to each other to 0.3-0.8 μm, are coupled to each other by evanescent waves.

The two optical waveguides are optical waveguides with different dispersion curves, and the dispersion curves intersect at phase-matched wavelength nodes. the

The two optical waveguides are respectively a ridge silicon waveguide and a slot waveguide, a ridge silicon waveguide and a ridge silicon nitride waveguide, two ridge silicon waveguides or a ridge silicon waveguide and a photonic crystal waveguide. the

The two optical waveguides are coupled to each other, and the group velocity of the coupled mode jumps at the intersection point. the

Compared with the prior art, the beneficial effect of the present invention is that the two waveguides are coupled to each other, and the group velocity of the coupled mode undergoes a rapid jump at the intersection point, resulting in time delay. Through the adjustment of the thermo-optic effect, the optical signal can achieve low-distortion transmission and adjustable delay in a wide range. the

Description of drawings

FIG. 1 is a schematic diagram of the horizontal structure of two waveguides (ridge silicon (Si) waveguide and slot silicon waveguide) in the first embodiment of the present invention. the

Figure 2 is a diagram of the effective refractive index of a coupled optical waveguide. the

Fig. 3 is a mode distribution diagram of the excited symmetric mode in the coupling optical waveguide. the

Figure 4 is a schematic diagram of the structure of the thermal electrode. the

Figure 5 is a group velocity dispersion diagram of coupled optical waveguides. the

Figure 6 is the group velocity dispersion diagram and the corresponding pulse delay diagram under the two modes of the coupled optical waveguide

Fig. 7 is a schematic structural diagram of horizontal coupling of two waveguides (coupling of ridge silicon (Si) waveguide and ridge silicon nitride (Si ₃ N ₄ ) waveguide) in the second embodiment of the present invention.

Fig. 8 is a schematic structural diagram of vertical coupling of two waveguides (coupling of ridge silicon (Si) waveguide and ridge silicon nitride (Si ₃ N ₄ ) waveguide) in the third embodiment of the present invention.

FIG. 9 is a schematic structural diagram of the horizontal coupling of two waveguides (two ridge-shaped silicon (Si) waveguides coupling with different sizes) in the fourth embodiment of the present invention. the

Fig. 10 is a schematic structural diagram of the horizontal coupling of two waveguides (ridge silicon (Si) waveguide and photonic crystal waveguide coupling) in the fifth embodiment of the present invention. the

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited thereto. the

FIG. 1 is a schematic diagram of the horizontal structure of two waveguides (ridge silicon (Si) waveguide and slot silicon waveguide) in the first embodiment of the present invention. As shown in the figure, the adjustable optical delay line is composed of a ridge silicon (Si) waveguide 1 and a slot waveguide 2 parallel to each other. When the two waveguides are close to each other (approximately 0.3-0.8 μm), they are coupled to each other by evanescent waves. The coupled waveguide structure can support two coupled optical waveguide modes, symmetric and antisymmetric. At the phase-matched wavelength node, the group velocity of the two coupled modes undergoes a rapid jump, resulting in a large amount of delay variation. FIG. 2 is a diagram corresponding to the effective refractive index of the coupled optical waveguide of FIG. 1. FIG. Among them, the cross-sectional area of the ridge silicon (Si) waveguide is 300 nm×340 nm, the cross-sectional area of the slot optical waveguide is 440 nm×340 nm, the gap width is 20 nm, and the distance between the two waveguides is 500 nm. Silicon and The refractive indices of the oxide layer materials are 3.478 and 1.444, respectively. It can be seen from the figure that in the short wavelength range, the symmetric mode is close to the ridge optical waveguide mode, and the antisymmetric mode is close to the slot optical waveguide mode; in the long wavelength range, the symmetric mode is close to the slot optical waveguide mode, and the antisymmetric mode is close to the ridge waveguide mode. type optical waveguide mode. Figure 3 shows the mode distribution diagram of the excited symmetric mode in the coupling optical waveguide under different wavelength conditions, and the energy distribution is consistent with Figure 2 . The structural dispersion of coupled optical waveguides can be compensated by cascading two coupled waveguides that respectively excite different coupled modes, resulting in a low dispersion effect. the

Figure 4 shows a schematic diagram of the thermode structure. First deposit a layer of silicon oxide (oxide) in the finished waveguide, and then deposit metal tungsten (W) as a hot electrode. The hot electrode is made of high resistivity materials, such as tungsten (W), chromium (Cr), titanium nitride (TiN), etc. In order to compromise the response speed and the absorption of the light field by the top metal, the thickness h of silicon oxide (oxide) needs to be moderate, generally 0.5-1 μm. Too thick silicon oxide will affect the response speed of the device, and too thin silicon oxide will affect the absorption of the light field by the top metal. In this embodiment, the thickness h of the oxide is selected to be 0.9 μm, and the width w of the hot electrode is selected to be 12.5 μm. the

Fig. 5 is the group velocity dispersion diagram corresponding to Fig. 1, when the temperature increases, the position of the phase-matching wavelength node redshifts. As shown in Figure 5, as the temperature increases, when the optical signal is loaded on the carrier of the symmetrical mode, the delay of the signal increases; when the optical signal is loaded on the carrier of the anti-symmetrical mode, the delay of the signal decreases, So as to achieve the effect of adjustable delay. The strength of waveguide coupling determines the sensitivity of thermo-optic effect or electro-optic effect to group velocity adjustment. the

Fig. 6 is the group velocity dispersion diagram and the corresponding pulse delay diagram of the coupling optical waveguide in two modes corresponding to Fig. 1 . Although the group delay is very sensitive to temperature changes at the phase-matched wavelength node, the corresponding group delay dispersion is very large. The length of the coupling optical waveguide is designed to be 10 cm. Figure 6(a) shows the group delay dispersion of the symmetric mode in the coupling optical waveguide, and Figure 6(b) shows a Gaussian pulse loading with half maximum width of 10 ps In the case of symmetric mode transmission, a delay increase of about 190 ps is obtained when the temperature increases by 50 ^o C. Figure 6(c), (d) shows an asymmetrical pattern as the carrier, and the delay caused by increasing the temperature decreases. Through the thermo-optic effect, the delay amount of this coupled optical waveguide is adjustable. Figure 6(e) shows the dispersion curves of the cascade of two coupled optical waveguides with a length of 5 cm that respectively excite different coupled modes. The dispersion can be compensated by this method, resulting in a low dispersion effect, as shown in Figure 6(f ) shown. From Figure 6 (a) and (b), it can be seen that the dispersion curves of the two coupled modes are complementary, therefore, as shown in Figure 6 (e) and (f), the dispersion can excite two coupled optical waveguides of different coupled modes by cascading To compensate, the variation of the optical signal delay of the two coupling structures is reduced, resulting in the effect of low dispersion.

Fig. 7 is a schematic diagram of the horizontal coupling structure of two waveguides, a ridge silicon (Si) waveguide and a ridge silicon nitride (Si ₃ N ₄ ) waveguide, in the second embodiment of the present invention. The coupling waveguide can cause the overall structural dispersion, and achieve the effect of adjustable delay under the adjustment of thermo-optic effect. Fig. 8 is a schematic structural diagram of vertical coupling of two waveguides (coupling of ridge silicon (Si) waveguide and ridge silicon nitride (Si ₃ N ₄ ) waveguide) in the third embodiment of the present invention. Figure 9 is a schematic diagram of the horizontal coupling of two waveguides (two ridge-shaped silicon (Si) waveguides of different sizes) in the fourth embodiment of the present invention. The order modes are coupled with each other, which can achieve the effect of adjustable delay. Fig. 10 is a schematic structural diagram of the horizontal coupling of two waveguides (ridge silicon (Si) waveguide and photonic crystal waveguide coupling) in the fifth embodiment of the present invention, which can also achieve the effect of adjustable delay.

Claims (3)

1. tunable optical delay line based on coupling optical waveguide, its characteristics are: this tunable optical delay line is made up of two parallel to each other or vertical optical waveguides, when two waveguides each other near the time to 0.3-0.8 μ m, be coupled mutually through evanescent wave.

2. the tunable optical delay line based on coupling optical waveguide as claimed in claim 1 is characterized in that: described two one optical waveguides are the optical waveguides with different dispersion curves, and dispersion curve intersects at the wavelength node place of phase matching.

3. the tunable optical delay line based on coupling optical waveguide as claimed in claim 2; It is characterized in that: described two one optical waveguides are respectively the waveguide of a ridge silicon and gap waveguide, the waveguide of a ridge silicon and a ridge silicon nitride waveguides, waveguide of two ridge silicon or the waveguide of a ridge silicon and a photon crystal wave-guide.

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