SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased array

Abstract

The invention discloses a SiN-Si-SiN three-layer low-crosstalk waveguide array for an optical phased array. The SiN-Si-SiN three-layer low-crosstalk waveguide array comprises an upper-layer SiN waveguide, a middle-layer Si waveguide and a bottom-layer SiN waveguide. An SOI substrate in the array comprises a substrate silicon layer and a buried oxide layer, a SiN-Si-SiN waveguide layer is located above the buried oxide layer, and the upper layer of the SiN-Si-SiN waveguide layer is covered with SiO2. By designing waveguide width distribution, the mode matching degree between adjacent waveguides is reduced so as to reduce crosstalk between the waveguides, and a waveguide array with small spacing and low crosstalk is realized. The upper SiN waveguide layer and the lower SiN waveguide layer are arranged in a staggered mode, energy is transferred into the Si waveguide layers through interlayer coupling, crosstalk is further reduced, and meanwhile the smaller waveguide distance is achieved. The tail end of the SiN waveguide layer and the front end of the Si waveguide layer are subjected to tip treatment, and coupling loss is reduced. In addition, the advantages of low transmission loss of the SiN waveguide and high refractive index of the Si waveguide are combined, and low-loss optical transmission can be achieved while low crosstalk is achieved.

Description

Technical Field

[0001] This invention relates to the field of low crosstalk transmission waveguide technology, and more particularly to a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays. Background Technology

[0002] Optical phased array (OPA), as a novel beam control and scanning technology, has advantages such as small system size, high resolution, wide field of view, fast response speed, and good beam quality. Compared with traditional methods, it does not have a cumbersome mechanical structure and is a promising solution for optical detection and ranging.

[0003] The principle of optical phased arrays is to control the phase of multiple optical antennas (or transmitting units) to form a controllable beam in the far field using the principle of coherent superposition. Its core lies in adjusting the phase delay of each transmitting unit to achieve constructive interference (phase consistency) of the beam in a specific direction, while destructive interference occurs in other directions, thereby forming a directional or scanning beam.

[0004] For optical phased arrays with uniform antenna spacing, the scanning range is inversely proportional to the antenna spacing. Therefore, achieving a large scanning field of view often requires a smaller antenna spacing. However, excessively small antenna spacing can lead to uncontrollable coupling crosstalk between antennas, meaning light can couple and leak into other antennas, causing phase plane deviations and ultimately affecting the overall scanning performance and beam quality of the phased array. How to reduce crosstalk while simultaneously decreasing antenna spacing has become a major technical challenge for optical phased arrays.

[0005] In addition, the transmission waveguides currently used in optical phased arrays are mainly made of two materials: Si and SiN. Si waveguides have a high refractive index and strong mode field confinement ability, making it easier to achieve low crosstalk transmission. SiN waveguides have a lower refractive index and weaker mode field confinement ability, but their transmission loss is significantly lower than that of Si waveguides. Therefore, combining Si waveguides and SiN waveguides to give full play to their advantages has become another research direction for optical phased arrays. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays. This solves the problem that crosstalk makes it difficult to achieve small-pitch arrays in existing technologies, thereby further expanding the scanning field of view of phased arrays.

[0007] The objective of this invention is achieved through the following technical solution: a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays, the array comprising: The SOI substrate, from bottom to top, includes at least a substrate silicon layer and a buried oxide layer; SiN waveguide array, with SiN waveguides located above the buried oxide layer, arranged in two staggered layers, covered with a SiO2 protective layer; The Si waveguide array has Si waveguides located in the middle of a double-layer SiN waveguide, and the waveguide positions correspond one-to-one with the SiN waveguides. The ends of the SiN waveguides and the front ends of the Si waveguides are tip-processed and are both non-uniform width waveguide arrays. The tip width and tip length parameters are determined by simulation using the finite-difference time-domain method based on FDTD, and the crosstalk between waveguides is used as an evaluation index to optimize the waveguide width distribution.

[0008] Furthermore, the light is first transmitted between the upper and lower SiN waveguides, and then the energy is transferred to the Si layer through interlayer coupling.

[0009] Furthermore, the interlayer coupling incorporates waveguide tip processing, wherein the SiN waveguide, as the coupling front end, gradually narrows at its waveguide end, while the Si waveguide, as the coupling back end, widens at its waveguide front end, thereby achieving a smooth transition of the effective refractive index of the waveguide and reducing interlayer coupling loss.

[0010] Furthermore, the waveguide width distribution of the Si and SiN waveguide arrays used is optimized based on the finite-difference time-domain method of FDTD to reduce the mode matching degree between waveguides, thereby achieving low crosstalk transmission of light.

[0011] Furthermore, by adjusting the phase difference of the input light in each SiN waveguide of the waveguide array, the beam direction can be adjusted and scanned using the interference effect, which can be applied to the transmission system of optical phased array.

[0012] Furthermore, the SiN-Si-SiN three-layer low crosstalk waveguide array consists of three horizontally arranged waveguides with SiO2 filling the interlayer spaces.

[0013] The beneficial effects of this invention are as follows: The SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased arrays provided by this invention primarily uses SiN waveguides for transmission at the front end to reduce transmission loss, while employing a double-layer staggered structure to reduce transmission crosstalk. Near the transmitting end, energy is transmitted to the Si waveguides through interlayer coupling. The high refractive index of the Si waveguides further reduces the spacing and crosstalk, achieving low-crosstalk, small-pitch array antenna output, ultimately expanding the scanning field of view of the phased array. Furthermore, the SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased arrays provided by this invention uses non-uniform width waveguide layers for both the SiN and Si waveguides. According to coupled-mode theory, compared to uniform width waveguides, non-uniform width waveguides have significantly lower coupling efficiency due to their different propagation constants, thus achieving low-crosstalk transmission. Therefore, this invention uses the waveguide width distribution as an optimization parameter, the crosstalk obtained by the FDTD time-domain finite difference method simulation as an evaluation value, and uses an algorithm (such as particle swarm optimization) for optimization, thereby obtaining a non-uniform width waveguide array with low crosstalk. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a SiN-Si-SiN three-layer low crosstalk waveguide array structure for optical phased arrays according to an embodiment of the present invention.

[0016] Figure 2 This is a top view of a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays according to an embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram of the interlayer structure of a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays according to an embodiment of the present invention.

[0018] Figure 4 This is a longitudinal cross-sectional view of a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays according to an embodiment of the present invention.

[0019] Figure 5 This is a flowchart of waveguide width distribution optimization based on the FDTD (Finite-Difference Time Domain) method according to an embodiment of the present invention.

[0020] Figure 6 This is a flowchart of the tip parameter optimization process based on the FDTD (Finite Difference Time Domain) method in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figures 1-4 As shown, this invention provides a SiN-Si-SiN three-layer low crosstalk waveguide array for optical phased arrays, comprising: The SOI substrate, from bottom to top, includes at least a substrate silicon layer 1 and a buried oxide layer 2; it may also include a metal electrode layer for a front-end phase shifter (such as a thermally tunable TiN layer and an electrically tunable lithium niobate layer). The SiN waveguides are located above the buried oxide layer and consist of two layers (a lower SiN layer 4 and an upper SiN layer 5) that are staggered and located above and below the Si waveguide layer 8, respectively. The two waveguide arrays are equally spaced but misaligned by half a spacing. They are covered with a SiO2 protective layer 3. The staggered arrangement of the SiN waveguides reduces mode overlap between adjacent SiN waveguides, thereby reducing the coupling efficiency between SiN waveguides and reducing crosstalk. The Si waveguide layer 8 is located in the middle of the two SiN waveguides, and the waveguide positions correspond one-to-one with the upper and lower SiN waveguides. The upper input light 7 and the lower input light 6 are input through a double-layer SiN waveguide, and then transferred to the middle Si waveguide layer through interlayer coupling, and then transformed into output light 9.

[0023] Optical waveguide arrays are used to transmit light beams and can be applied to many optical devices, such as phased array lidar. Specifically, the optical waveguide array is an electronic device integrated on a CMOS semiconductor material, the most commonly used of which is an SOI substrate. The material and thickness of each layer of the SOI substrate from bottom to top can be customized according to different requirements. For ease of description, the following embodiments will use the aforementioned standard CMOS process SOI substrate as an example to integrate the optical waveguide array of the present invention.

[0024] The SOI substrate includes a three-layer SiN-Si-SiN waveguide array, with two SiN waveguide layers staggered and serving as the input, while the Si waveguide layers are located between the two SiN waveguide layers and correspond one-to-one with each SiN waveguide.

[0025] A low crosstalk waveguide array is composed of three layers of non-uniform width pointed waveguides spaced apart, such as... Figure 2 As shown, the tip width of the SiN waveguide is smaller than the waveguide width, and the tip width of the Si waveguide is smaller than the waveguide width. The specific tip width and tip length parameters are determined by simulation using the finite-difference time-domain method based on FDTD. The specific procedure is described in [reference needed]. Figure 6 Taking a 0.5 μm wide Si waveguide and a 1 μm wide SiN waveguide as an example, after parameter scanning optimization, the tip width of the SiN waveguide is set to 0.2 μm and the tip width of the Si waveguide is set to 0.32 μm, achieving a final interlayer coupling efficiency of 98.6%. The SiN-Si-SiN three-layer waveguide antenna array with tip processing can improve interlayer coupling efficiency by introducing a gradual change in effective refractive index. According to the Fresnel formula, the smaller the refractive index difference between interfaces, the lower the reflectivity. Therefore, achieving a smooth transition of the effective refractive index from the low refractive index of SiN to the high refractive index of Si through tip processing can reduce coupling loss. The tip length mainly affects the refractive index transition process; a longer tip length results in a smoother refractive index transition, which is beneficial for reducing coupling loss. However, an excessively long tip length may lead to uncontrollable crosstalk between Si waveguides. Therefore, the overall tip length needs to be determined by simulation using the finite-difference time-domain method based on FDTD.

[0026] Optical waveguide arrays are used to transmit light waves. Because light waves vary greatly in wavelength, a single design cannot satisfy all light waves. Even if the same design concept is used, the parameters will need to vary depending on the wavelength of the light wave being transmitted, for example, 1.5–1.6 μm. For ease of explanation, the following embodiments will use a wavelength of 1.5–1.6 μm as an example.

[0027] Based on the above embodiments, the waveguide array is further described as a SiN-Si-SiN three-layer non-uniform width waveguide array. The first problem to be solved in reducing antenna spacing is crosstalk between adjacent waveguides, and the essence of crosstalk is mode coupling. That is, when two waveguides are close to each other, their respective guided modes are no longer isolated; their electromagnetic fields overlap, forming "coupled modes." If the widths of the two waveguides are different, their propagation constants will also be different. For waveguide arrays, the propagation constant of optical wave transmission is related to the waveguide width. According to coupled-mode theory, compared to uniform width waveguides, non-uniform width waveguides have significantly lower coupling efficiency due to their different propagation constants, thus achieving low crosstalk transmission. Therefore, this invention uses the waveguide width distribution as an optimization parameter, and the crosstalk obtained from FDTD (Finite-Difference Time-Domain) simulation as an evaluation value. Algorithms (such as particle swarm optimization) are used for optimization, thereby obtaining a low-crosstalk non-uniform width waveguide array. The specific optimization process is described in [reference needed]. Figure 5 .

[0028] Furthermore, the transmission waveguides currently used in optical phased arrays are mainly made of two materials: Si and SiN. Si waveguides have a high refractive index and strong mode confinement capability, making it easier to achieve low crosstalk transmission. SiN waveguides have a lower refractive index and weaker mode confinement capability, but their transmission loss is significantly lower than that of Si waveguides. By dividing the SiN waveguide array into two staggered waveguide layers, the longitudinal spacing is introduced to reduce mode overlap between the SiN waveguides, thereby effectively suppressing mode coupling between the upper and lower SiN waveguides and reducing transmission crosstalk. Simultaneously, inserting a Si waveguide between the two SiN waveguide layers couples the light into the Si waveguide for transmission, leveraging the high refractive index of Si material to further confine the transmission mode field, thus reducing transmission crosstalk. Overall, this SiN-Si-SiN three-layer waveguide array retains the low transmission loss advantage of SiN waveguides while also leveraging the high refractive index advantage of Si waveguides, enabling low-crosstalk and low-loss optical transmission.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SiN-Si-SiN three-layer low-cross-talk waveguide array for optical phased arrays, characterized in that, The array comprises: An SOI substrate comprising at least a substrate silicon layer and a buried oxide layer from bottom to top; An SiN waveguide array, the SiN waveguide being located above the buried oxide layer and staggered in two layers, and a SiO2 protective layer being covered thereon; An Si waveguide array, the Si waveguide being located in the middle of the double-layer SiN waveguide and corresponding to the SiN waveguide in position; the end of the SiN waveguide and the front end of the Si waveguide are both non-equal-width waveguide arrays after tip processing, and the tip width and the tip length parameters are determined by FDTD-based time-domain finite difference method simulation, and the crosstalk between the waveguides is taken as an evaluation index to optimize the waveguide width distribution.

2. The SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased array according to claim 1, wherein, Light is first transmitted in the upper and lower SiN waveguides, and then transferred to the Si layer through interlayer coupling.

3. The SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased array according to claim 2, wherein, The interlayer coupling introduces waveguide tip processing, in which the waveguide end of the SiN waveguide as the front end of the coupling gradually narrows, and the waveguide front end of the Si waveguide as the rear end of the coupling gradually widens, thereby realizing smooth transition of the effective refractive index of the waveguide and reducing the interlayer coupling loss.

4. The SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased array according to claim 1, wherein, The waveguide width distribution of the Si and SiN waveguide arrays is optimized based on the FDTD-based time-domain finite difference method, which reduces the mode matching degree between the waveguides to realize low-crosstalk transmission of light.

5. The SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased array according to claim 1, wherein, By adjusting the phase difference of the input light of each SiN waveguide in the waveguide array, the directional adjustment and scanning of the light beam can be realized by using the interference effect, which is applied to the emission system of the optical phased array.

6. The SiN-Si-SiN three-layer low-crosstalk waveguide array for optical phased array of claim 1, wherein, The SiN-Si-SiN three-layer low-crosstalk waveguide array is a three-layer horizontally arranged waveguide, and the interlayer is filled with SiO2.

Images