Phase shifter and preparation method thereof

Abstract

The invention belongs to the technical field of optical communication, and particularly discloses a phase shifter and a preparation method thereof, and the phase shifter comprises a waveguide layer and a phase change material layer. The phase change material layer half wraps the periphery of the waveguide layer; the half wrapping is that the top end or the bottom end of the waveguide layer is fully covered on the cross section of the waveguide layer, and the side wall of the waveguide layer is partially covered; the length of the phase-change material layer is less than or equal to that of the waveguide layer; the parameter design of the phase shifter meets the condition that the difference value between the # imgabs0 # TE and the # imgabs1 # TM is smaller than a threshold value; wherein the # imgabs2 # TE is the effective refractive index difference of a TE mode optical signal in the phase shifter, and the # imgabs3 # TM is the effective refractive index difference of a TM mode optical signal in the phase shifter; the effective refractive index difference refers to the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively. According to the invention, the phase shifter with the polarization insensitive characteristic is provided.

Description

Technical Field

[0001] The present application belongs to the field of optical communication technology, and more specifically, relates to a phase shifter and a method for preparing the same. Background Art

[0002] Integrated circuits are a crucial cornerstone of modern information technology. Over the past few decades, they have experienced rapid development, aligning with Moore's Law. However, in recent years, the linewidth of individual transistors in integrated circuits has increasingly approached its physical limits, making it difficult to further increase circuit integration to meet the growing demands for information processing and storage. Optical communications offer a new approach to addressing this "electronic bottleneck" in traditional circuits. Compared to traditional electrical communications, optical communications offer advantages in high speed, high bandwidth, and low power consumption. Silicon-based phase shifters are a key component in optical communications technology.

[0003] Currently, most silicon-based phase shifters are implemented by changing the refractive index of an optical waveguide, such as those based on carrier dispersion and thermo-optic effects. Chalcogenide phase change materials (PCMs) can rapidly and repeatedly switch between crystalline and amorphous states, a process known as phase change. The electrical and optical properties of PCMs differ significantly between their crystalline and amorphous states. Therefore, combining PCMs with optical waveguides can create silicon-based phase shifters. Furthermore, the phase change material does not require additional power to maintain its state, which helps address the challenges of size, power consumption, and volatility in phase shifters.

[0004] However, phase shifters formed by directly covering waveguides with phase change materials often have different refractive indices for light of different polarization states and are more sensitive to polarization. This reduces the reliability of communication systems and increases the need for phase calibration. In order to reduce the polarization sensitivity of phase change material phase shifters, optimization and innovation in the phase shifter structure are needed. Summary of the Invention

[0005] In view of the defects of the prior art, the purpose of this application is to provide a phase shifter and a preparation method thereof, aiming to solve the problem of high polarization sensitivity of the existing phase shifter.

[0006] To achieve the above objectives, in a first aspect, the present application provides a phase shifter, comprising: a waveguide layer and a phase change material layer; The phase change material layer is semi-wrapped around the waveguide layer; the semi-wrapping means that, in the cross section of the waveguide layer, the top or bottom of the waveguide layer is fully covered, and the side wall of the waveguide layer is partially covered; the phase change material layer covering the top or bottom of the waveguide layer is continuous with the phase change material layer covering the side wall of the waveguide layer, and the corresponding top or bottom of the waveguide layer is completely wrapped; The length of the phase change material layer is less than or equal to the length of the waveguide layer; The parameters of the phase shifter are designed to meet the following requirements: TE and TM The difference is less than the threshold; TE is the effective refractive index difference of the TE mode optical signal in the phase shifter, TM is the effective refractive index difference of the TM mode optical signal in the phase shifter; the effective refractive index difference refers to: the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively.

[0007] In a possible implementation, a coverage height of the phase-change material layer on the side wall of the waveguide layer is smaller than a height of the side wall of the waveguide layer.

[0008] In a possible implementation manner, the phase change material layer symmetrically covers two side walls of the waveguide layer.

[0009] In a possible implementation, the thickness of the phase change material layer covering the top or bottom of the waveguide layer is the same as the thickness of the phase change material layer covering the sidewall of the waveguide layer.

[0010] In one possible implementation, when TE and TM When the difference is less than the threshold, the phase difference when the phase shifter transmits the TE mode optical signal and the TM mode optical signal respectively does not exceed the preset value; and / or the threshold is determined according to the preset value; and / or the preset value is less than or equal to 0.02π.

[0011] In a possible implementation manner, the cross section of the waveguide layer is rectangular.

[0012] In a possible implementation, the phase shifter further includes: an insulating layer; The insulating layer is arranged on the periphery of the phase change material layer and the waveguide layer, and covers the periphery of the phase change material layer and the waveguide layer that is not wrapped by the phase change material layer.

[0013] In a second aspect, the present application provides a method for preparing the phase shifter described in the first aspect or any possible implementation of the first aspect, comprising: Depositing an insulating layer of a first thickness on a substrate; providing a waveguide layer of a first height, a first width, and a first length on the substrate; wherein the first thickness is greater than or equal to the first height; removing the insulating layer exceeding the first height so that the top of the waveguide layer is exposed; Etching the periphery of two sidewalls of the waveguide layer to form two trenches, wherein the etching depth of the trenches is less than the first height, and the etching length is less than or equal to the first length; A phase change material layer is prepared on the top of the waveguide layer and the two channels to half-wrap the waveguide layer; The parameters of the phase shifter are designed to meet the following requirements: TE and TM The difference is less than the threshold; TE is the effective refractive index difference of the TE mode optical signal in the phase shifter, TM is the effective refractive index difference of the TM mode optical signal in the phase shifter; the effective refractive index difference refers to: the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively.

[0014] In a possible implementation, the waveguide layer material is Si3N4, and the phase change material layer material is Sb2Se3.

[0015] In a possible implementation, the height of the waveguide layer is 800 nm and the width is 800 nm; the thickness of the phase change material layer is 8 nm, and the height of the phase change material layer covering the two side walls of the waveguide layer is 550 nm ± 100 nm. h nm; h is determined by the threshold value.

[0016] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies: This application provides a phase shifter and a method for fabricating the same. This application proposes a method for adjusting the polarization sensitivity of the phase shifter by employing a phase change material layer with incomplete sidewall coverage, thereby reducing the phase shifter's sensitivity to polarization. Furthermore, this application designs the phase shifter's parameters based on the effective refractive index difference when the phase shifter transmits TE mode optical signals and TM mode optical signals, respectively. This ensures that the effective refractive index change between the TE mode and TM mode states is as consistent as possible, resulting in nearly identical effective refractive index and π phase shift length in the TE and TM modes, demonstrating polarization insensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the cross-sectional structure of the phase shifter provided in an embodiment of the present application; Figure 2 is an overall structural diagram of the phase shifter provided in an embodiment of the present application; Figure 3 is a flow chart of a method for preparing a phase shifter provided in an embodiment of the present application; Figure 4 1 is a schematic diagram of a process flow for preparing a phase shifter provided in an embodiment of the present application; Figure 5 This embodiment of the present application provides Curve graph showing changes with H; Figure 6 Schematic diagram of the change of the effective refractive index difference of the phase shifter provided by an embodiment of the present application along with the input optical signal; Figure 7 This is a schematic diagram showing how the π phase shift length of a phase shifter varies with the input optical signal, provided in a specific embodiment of the present application; Figure 8 This is a schematic diagram of waveguide size scanning provided by an embodiment of the present application; Figure 9 Schematic diagram of the effective refractive index difference of the phase shifter when the sidewalls are fully covered with phase change material according to an embodiment of the present application; Figure 10 The phase shifter under different polarization states when the sidewall phase change material is fully covered is provided in the embodiment of the present application. Schematic diagram of phase shift length. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0019] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0020] In order to solve the problems of poor performance of traditional phase shifters in terms of size, power consumption, volatility and polarization sensitivity, the present application provides a polarization-insensitive phase shifter based on phase change materials. On the one hand, Figure 1 As shown, the provided phase shifter includes: a waveguide layer, a phase change material layer and an insulating layer.

[0021] Specifically, the phase change material layer is semi-wrapped around the waveguide layer; the semi-wrapping means that, in the cross section of the waveguide layer, the top or bottom of the waveguide layer is fully covered, and the side wall of the waveguide layer is partially covered; the phase change material layer covering the top or bottom of the waveguide layer is continuous with the phase change material layer covering the side wall of the waveguide layer, and completely wraps the corresponding top or bottom of the waveguide layer; the insulating layer is arranged around the phase change material layer and the waveguide layer, covering the portion of the phase change material layer and the waveguide layer that is not wrapped by the phase change material layer.

[0022] Wherein, the length of the phase change material layer is less than or equal to the length of the waveguide layer.

[0023] Furthermore, the parameters of the phase shifter are designed to meet the following requirements: TE and TM The difference is less than the threshold; TEis the effective refractive index difference of the TE mode optical signal in the phase shifter, TM is the effective refractive index difference of the TM mode optical signal in the phase shifter; the effective refractive index difference refers to: the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively.

[0024] For example, the phase change material layer covers the sidewalls of the waveguide layer to a height less than the height of the sidewalls of the waveguide layer. Furthermore, the phase change material layer covers two symmetrical parts of the sidewalls of the waveguide layer.

[0025] Optionally, the thickness of the top (or bottom) phase change material layer close to the waveguide is equal to the thickness of the phase change material layer close to the sidewall of the waveguide.

[0026] Optionally, when TE and TM When the difference is less than the threshold, the phase difference when the phase shifter transmits the TE mode optical signal and the TM mode optical signal respectively does not exceed the preset value; and / or the above threshold is determined according to the preset value; and / or the preset value can be set to be less than or equal to 0.02π.

[0027] Optionally, the cross section of the waveguide layer is rectangular. For a detailed overall structure diagram, see Figure 2 shown.

[0028] On the other hand, taking the phase change material layer half-wrapping the waveguide layer and fully wrapping the top of the waveguide layer as an example, the present application provides a method for preparing a phase shifter, such as Figure 3 As shown, the following steps are included: Step S101, depositing an insulating layer of a first thickness on a substrate; a waveguide layer of a first height, a first width, and a first length is provided on the substrate; the first thickness is greater than or equal to the first height; Step S102, removing the insulating layer exceeding the first height so that the top of the waveguide layer is exposed; Step S103, etching the periphery of two sidewalls of the waveguide layer to form two trenches, wherein the etching depth of the trenches is less than the first height, and the etching length is less than or equal to the first length; Step S104, preparing a phase change material layer on the top of the waveguide layer and the two channels to half-wrap the waveguide layer; Among them, the parameter design of the phase shifter satisfies: TE and TM The difference is less than the threshold; TE is the effective refractive index difference of the TE mode optical signal in the phase shifter, TM is the effective refractive index difference of the TM mode optical signal in the phase shifter; the effective refractive index difference refers to: the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively.

[0029] For example, the waveguide has a substantially square cross-section, although variations in shape may occur in practice. The material used may be Si3N4, although Si or SiO2 may also be used. The phase-change material layer, which is in close contact with the waveguide layer, may use the chalcogenide compound Sb2Se3, although chalcogenide materials such as GST may also be used.

[0030] For example, the phase change material layer covers the top or bottom layer of the waveguide and the side wall of the waveguide, and the phase change material layer on the side wall does not completely cover the waveguide, while the phase change materials on the top (or bottom) layer and the side wall are connected to each other.

[0031] It is understandable that the coverage of the phase change material layer on the waveguide in the length direction (perpendicular to the cross section) can be to completely cover the same structure or to cover a certain length as required.

[0032] For example, the designed cross-sectional size of the square waveguide is 800 nm×800 nm, and the actual size may deviate.

[0033] For example, the designed thickness of the phase change material layer is 8 nm, and the actual size may vary.

[0034] For further example, the height of the phase change material layer covering the two side walls of the waveguide layer is 550nm± h nm; h is determined by the threshold value.

[0035] The above height is based on the designed phase shifter TE and TM The difference can be less than the threshold value. The specific value can be determined by referring to the simulation and experiment before the corresponding design.

[0036] In a more specific embodiment, the above preparation method may include the following steps: (1) A silicon dioxide lower cladding layer with a thickness of about 3 µm is deposited on a silicon-based substrate, and an 800 nm thick silicon nitride film is deposited on the surface of the lower cladding layer; then, photoresist is spin-coated on the surface of the silicon nitride film, and the mask pattern is transferred to the substrate using an electron beam lithography (EBL) device. Then, a developer is used to react with the photoresist to reveal the waveguide pattern; then, dry etching ICP technology is used to react and remove the silicon nitride material not covered by the photoresist to form a waveguide structure. Finally, after the etching is completed, the photoresist is washed away using acetone and alcohol solutions.

[0037] (2) Based on step (1), a layer of 800 nm thick silicon dioxide is deposited using chemical vapor deposition (PECVD). Since there is already an 800 nm thick silicon nitride waveguide on the substrate, the total thickness of the waveguide and its surrounding areas will exceed 800 nm. Therefore, chemical mechanical polishing (CMP) is used to smooth the area exceeding 800 nm, so that the surface of the connection area between silicon dioxide and silicon nitride is sufficiently flat.

[0038] (3) Use dry etching ICP technology to etch silicon dioxide. Since silicon dioxide and silicon nitride have an extremely high etching selectivity ratio (>50:1), the reaction gas of silicon dioxide has little effect on silicon nitride. The photolithography step can be skipped and etching can be performed directly. The etching depth is the expected filling height of the side wall of the phase change material.

[0039] (4) Spin-coat the photoresist and use a maskless photolithography process to carve out the pattern of the phase change material based on the previous step, and use a developer to react with the photoresist in the exposed area; then use a magnetron sputtering process to deposit the phase change material on the substrate surface. The phase change material will evenly cover the sidewalls and surface of the waveguide, and the appropriate phase change material deposition thickness is set according to the design requirements of polarization insensitivity.

[0040] (5) On the basis of step (4), a layer of silicon dioxide is deposited as a protective layer of the phase shifter structure. Then, a heating structure of the phase shifter can be prepared on this basis according to actual needs to drive the phase change material to switch back and forth between the crystalline state and the amorphous state. The process flow diagram of the above steps is as follows Figure 4 shown.

[0041] This application uses silicon dioxide as the substrate and upper cladding, fabricating an 800 nm-tall Si3N4 waveguide on the substrate. Sb2Se3 phase-change material is then applied to the waveguide's upper surface and sidewalls to create a phase shifter. When the phase-change material changes state, the effective refractive index of the phase shifter also changes, achieving a phase shifting effect. The fabrication process employed in this application is simple, compatible with conventional CMOS processes, easily integrated, and suitable for large-scale production. This has significant implications for the development of optical interconnect systems, optical signal processing, and silicon-based optoelectronics.

[0042] Generally speaking, covering the waveguide top and sidewalls with phase change material can achieve the effect of a phase shifter. However, since the effective refractive index of light with different polarization states in the phase shifter is often different, this also makes the phase shifter polarization sensitive. Therefore, this application proposes a solution in which the sidewalls are not completely covered with phase change material to adjust the polarization sensitivity of the phase shifter. The cross-sectional view of the phase shifter is shown above. Figure 1 and Figure 2 As shown in Figure 2. The phase shifter is fabricated on a silicon dioxide substrate.

[0043] The following describes the design details of the phase shifter in detail using a specific embodiment. In this embodiment, the phase change material is Sb2Se3, the waveguide material is Si3N4, the film thickness is designed to be 8 nm, and the design requires the phase shifter to operate in the wavelength band of 1520 nm-1610 nm.

[0044] Specifically, polarization-insensitive phase shifters require transverse electric (TE) and transverse magnetic (TM) modes. The phase shift length is the same. This condition is equivalent to the effective refractive index change between the TE mode and the TM mode being the same, that is: TE = TM .

[0045] By scanning the height H of the sidewall Sb2Se3, the effective refractive index in the TE and TM modes satisfies the following formula group:

[0046]

[0047]

[0048] In the above formula Indicates that the optical signal passes through the same length (where ) The phase difference between the phase shifter and the non-phase shifter waveguide is specifically controlled The method is to let two light signals pass through two identical phase shifters respectively, control the phase change material of one phase shifter to crystallize and the phase change material of the other phase shifter to amorphize; Formula (2) shows that the phase difference is designed to be , formula (3) indicates that under the same conditions (except for the polarization mode of the optical signal), the phase difference between the transmitted TE mode and TM mode optical signals is required to be no more than (This value can be designed according to the actual situation. If the polarization insensitivity needs to be further reduced, the value can be further reduced.) By substituting the refractive index information of the specific material, the scanning height H is obtained in the simulation software. For the H curve, see Figure 5 .Depend on Figure 5 It can be seen that when the phase change material layer sidewall coverage height is 550 nm, the phase difference between the transmitted TE mode and TM mode optical signals is the smallest. Therefore, the height of the Sb2Se3 layer covering the phase shifter sidewall can be set to 550 nm.

[0049] When the sidewall coverage height of the phase change material layer is 550 nm, the effective refractive index and propagation loss of the phase shifter are calculated using the FDE algorithm, and the data in Tables 1 and 2 are obtained. It can be seen that the effective refractive index difference between the phase shifter in TE and TM modes ( ) is very close, such as Figure 6 As shown; at the same time TE, TM mode Phase shift length L π Almost the same as Figure 7 As shown, it shows that the phase shifter is polarization insensitive.

[0050] Table 1. Phase shifter effective refractive index

[0051] Table 2. Phase shifter propagation loss and Phase shift length

[0052] Using the FDE solver, we calculated the insertion loss and wavelength-dependent loss of a 41µm-long phase shifter at a central wavelength of 1560 nm within the design wavelength band of 1520 nm to 1610 nm. The insertion loss is 0.01 dB, and the wavelength-dependent loss is 0.0005 dB.

[0053] To meet manufacturability requirements, the phase shifter first undergoes tolerance analysis. Key process-dependent dimensional parameters include the main waveguide width and height, the phase-change material film thickness, and the sidewall fill height (the remaining height after subtracting the phase-change material height from the waveguide sidewall height). Tolerance analysis of these three parameters primarily assesses their impact on crosstalk.

[0054] (1) Regarding the sidewall filling height, according to the process flow, the sidewall needs to be filled with 800 nm–550 nm=250 nm of SiO2 as a dielectric layer. Usually, the process error of material deposition is about 3%, and the expected film thickness is 250±7.5 nm. The thickness of the dielectric layer that meets the crosstalk requirements of this design is between 800 nm–530 nm=270 nm and 800 nm–570 nm=230 nm, which is expected to meet the project requirements.

[0055] (2) Regarding the PCM material film thickness, the design thickness for this project is 8 nm. Based on the 5% process error, the expected deposited film thickness is 8 nm ± 0.04 nm. As for the effect of scanning film thickness on polarization correlation, experimental research found that when the phase change material sidewall coverage thickness is 550 nm or near it, there is a certain PCM thickness that can meet the polarization insensitivity condition. The acceptable PCM thickness is 6 nm-12 nm, and the expected process can meet the design requirements.

[0056] (3) For the waveguide size, the width and height are equal. Scanning the size range of 750 nm-850 nm can meet the polarization requirements. Figure 8 shown.

[0057] The above experiments show that when the cross-sectional dimensions of the silicon nitride waveguide are set to 800 nm × 800 nm, the thickness of the phase change material is 8 nm, and the sidewall coverage height is scanned using Lumerical MODE software, when the sidewall coverage height is 550 nm, the effective refractive index and π phase shift length of the TE and TM modes are almost the same, indicating that the phase shifter at this time has polarization-insensitive characteristics. In the traditional phase shifter preparation process, the phase change material is often completely covered on the sidewall of the waveguide. Such a structure is often more sensitive to polarization. When the cross-sectional dimensions of the silicon nitride waveguide are 800 nm × 800 nm, and the upper surface and sidewalls are completely covered with 8nm thick phase change material, the simulated effective refractive index difference of the phase shifter in the TE and TM modes is as follows: Figure 9 As shown, under this condition, the π phase shift length of the phase shifter is as follows Figure 10 As shown in Figure 3, the π phase shift lengths in the TE and TM modes differ greatly and are more sensitive to polarization.

[0058] In summary, this application discloses a polarization-insensitive phase shifter structure based on phase-change material. The phase shifter's main structure consists of a waveguide layer and a phase-change material layer, which are tightly connected. The phase-change material layer partially wraps around the waveguide. From a cross-sectional perspective, the phase-change material covers the top (or bottom) and sidewalls of the waveguide layer, completely covering the waveguide at the top and partially covering the sidewalls. The thickness of the phase-change material at the top and sidewalls is essentially the same. From a perpendicular perspective, the phase-change material can completely cover the waveguide or cover a certain length as needed. This phase shifter utilizes an external electrode structure to adjust the crystallization state of the phase-change material using electrical pulses, thereby changing the overall effective refractive index. This alters the relative phase of an optical signal after passing through a waveguide of equal length (non-phase-shifter structure) and the phase shifter, achieving phase shifting. The phase shifter provided in this application features polarization insensitivity to the optical signal, low loss, wide wavelength adaptability, high process tolerance, and multi-level adjustable phase difference.

[0059] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0060] In addition, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0061] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after the connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0062] In addition, in the embodiments of the present application, the mathematical concepts mentioned include symmetry, equality, parallelism, and perpendicularity. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense. A small amount of deviation is allowed, and it is possible to be approximately symmetric, approximately equal, approximately parallel, or approximately perpendicular. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0063] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A phase shifter, characterized in that: include: a waveguide layer and a phase change material layer; The phase change material layer is semi-wrapped around the waveguide layer; the semi-wrapping means that, in the cross section of the waveguide layer, the top or bottom of the waveguide layer is fully covered, and the side wall of the waveguide layer is partially covered; the phase change material layer covering the top or bottom of the waveguide layer is continuous with the phase change material layer covering the side wall of the waveguide layer, and the corresponding top or bottom of the waveguide layer is completely wrapped; The length of the phase change material layer is less than or equal to the length of the waveguide layer; The parameters of the phase shifter are designed to meet the following requirements: TE and TM The difference is less than the threshold; TE is the effective refractive index difference of the TE mode optical signal in the phase shifter, TM is the effective refractive index difference of the TM mode optical signal in the phase shifter; the effective refractive index difference refers to: the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively.

2. The phase shifter according to claim 1, wherein: The covering height of the phase change material layer on the side wall of the waveguide layer is smaller than the height of the side wall of the waveguide layer.

3. The phase shifter according to claim 2, wherein: The phase change material layer symmetrically covers two side walls of the waveguide layer.

4. The phase shifter according to claim 1, wherein: The thickness of the phase change material layer covering the top or bottom of the waveguide layer is the same as the thickness of the phase change material layer covering the sidewall of the waveguide layer.

5. The phase shifter according to claim 1, wherein: when TE and TM When the difference is less than the threshold, the phase difference when the phase shifter transmits the TE mode optical signal and the TM mode optical signal respectively does not exceed the preset value; and / or the threshold is determined according to the preset value; and / or the preset value is less than or equal to 0.02π.

6. The phase shifter according to any one of claims 1 to 5, characterized in that: The cross section of the waveguide layer is rectangular.

7. The phase shifter according to any one of claims 1 to 5, characterized in that: Also includes: Insulation layer; The insulating layer is arranged on the periphery of the phase change material layer and the waveguide layer, and covers the periphery of the phase change material layer and the waveguide layer that is not wrapped by the phase change material layer.

8. A method for preparing the phase shifter according to any one of claims 1 to 7, characterized in that: include: Depositing an insulating layer of a first thickness on a substrate; a waveguide layer of a first height, a first width and a first length is provided on the substrate; The first thickness is greater than or equal to the first height; removing the insulating layer exceeding the first height so that the top of the waveguide layer is exposed; Etching the periphery of two sidewalls of the waveguide layer to form two trenches, wherein the etching depth of the trenches is less than the first height, and the etching length is less than or equal to the first length; A phase change material layer is prepared on the top of the waveguide layer and the two channels to half-wrap the waveguide layer; The parameters of the phase shifter are designed to meet the following requirements: TE and TM The difference is less than the threshold; TE is the effective refractive index difference of the TE mode optical signal in the phase shifter, TM is the effective refractive index difference of the TM mode optical signal in the phase shifter; the effective refractive index difference refers to: the change value of the effective refractive index of the phase shifter when the phase change material layer is in the crystalline state and the amorphous state respectively.

9. The method according to claim 8, characterized in that The waveguide layer material is Si3N4, and the phase change material layer material is Sb2Se3.

10. The method according to claim 8 or 9, characterized in that The height of the waveguide layer is 800 nm and the width is 800 nm; the thickness of the phase change material layer is 8 nm, and the height of the phase change material layer covering the two side walls of the waveguide layer is 550 nm ± h nm; h is determined by the threshold value.

Images