A polarization independent mode converter

Abstract

The application relates to a polarization-independent mode converter and belongs to the technical field of wireless communication semiconductor devices. The application comprises, from bottom to top, a wafer substrate, a buried oxygen layer of the wafer, a device layer and a SiO2 upper cladding layer of the device, wherein the device layer comprises an input waveguide, a polarization beam splitting rotator, a phase shifter, an optical beam splitter assembly, an optical beam combiner assembly and a micro-ring resonator. The polarization beam splitting rotator is used for converting TM mode into TE mode in the optical signal passing through the polarization rotation beam splitter, the phase shifter is used for ensuring that the phase difference of two rows of waves of the beam combination is 0, the optical beam splitter assembly is used for optical power division, the optical beam combiner assembly is used for combining two rows of TE mode optical signals, and the micro-ring resonator realizes output of the combined wave from an output end. The mode converter provided by the application has a simple structure, is used for realizing TE mode conversion of an arbitrary polarization state input, reduces coupling loss, improves coupling efficiency, and obtains a mode converter device with excellent polarization-independent performance.

Description

Technical Field

[0001] This invention relates to a polarization-independent mode converter, belonging to the field of wireless communication semiconductor device technology. Background Technology

[0002] With continuous advancements in technology in recent years, optoelectronic devices in optical communication are gradually moving towards integration. Compared to systems built from traditional discrete optical components, integrated optoelectronic devices offer several significant advantages, such as smaller footprint, reduced manufacturing costs, and improved performance stability by packaging different devices onto a single chip, thus avoiding interference from external factors and making them suitable for developing high-efficiency, multifunctional optoelectronic products. However, a technical challenge remains in the application of this technology: the materials, structure, or design of the devices can affect the polarization state of light. The mode field distribution, effective refractive index, and waveguide loss of the two polarization states, TE and TM, differ in the waveguide. When the performance of photonic devices is affected by the polarization state of the input light, it can lead to problems such as polarization-dependent loss, polarization mode dispersion, and polarization dependence of the operating wavelength. In fiber optic communication systems, optical transmission modules typically use ordinary optical fibers as the transmission medium. This makes it difficult to guarantee the polarization state of the input light when coupling light from ordinary optical fibers to rectangular waveguides on silicon-based integrated devices. The uncertainty of the input light polarization state makes the performance of optical devices highly unstable; therefore, solving the polarization dependence of optical devices is a significant challenge.

[0003] Currently reported photonic devices based on silicon-in-spar (SOI) for polarization beam splitting and rotation are mainly divided into mode-coupled polarization beam splitters and mode-evolutionary polarization beam splitters. Polarization beam splitters based on mode coupling generally employ an asymmetric directional coupler structure to excite hybrid supermodes and achieve mode conversion and separation through interference. These devices have the advantage of small size, which is beneficial for large-scale chip integration. However, such polarization beam splitters based on directional coupling structures require strict phase matching conditions to achieve mode coupling and conversion, making them sensitive to wavelength and process technology, with small operating bandwidth and small process tolerance. Polarization beam splitters based on mode evolution first convert the input TM0 mode into a higher-order TE1 mode, then separate it from the input TE0 mode and convert the TE1 mode back into a TE0 mode. The higher-order mode conversion occurs in the mode mixing region of the waveguide. Therefore, this type of polarization beam splitter has a more complex structure, but its bandwidth and manufacturing tolerances are larger. The polarization-independent mode converter proposed in this invention can effectively compensate for the defects of polarization beam rotators based on mode coupling principle and polarization beam rotators based on mode evolution principle, and obtain a high-performance mode converter that is independent of polarization. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of current polarization beam rotators based on mode coupling and mode evolution principles: 1. Mode coupling-based polarization beam rotators require strict phase matching conditions to achieve mode coupling and conversion, thus being sensitive to wavelength and manufacturing processes, with small operating bandwidth and low manufacturing tolerance; 2. Mode evolution-based polarization beam rotators have a complex structure, but their bandwidth and manufacturing tolerances are relatively large. This invention proposes a polarization-independent mode converter that effectively overcomes the defects of both mode coupling-based and mode evolution-based polarization beam rotators, meeting the application requirements of randomly polarized input light and achieving a high-performance mode converter that is independent of polarization.

[0005] The technical solution of this invention is: a polarization-independent mode converter, comprising, from bottom to top, a wafer substrate, a buried oxide layer of the wafer, a device layer and a SiO2 cladding layer of the device, the device layer including an input waveguide; a polarization beam splitter rotator 100, a phase shifter 200, an optical beam splitter assembly 300, an optical beam combiner assembly 400 and a microring resonator 500.

[0006] The optical beam splitter assembly 300 includes a first optical beam splitter 310 and a second optical beam splitter 320;

[0007] The optical beam combiner assembly 400 includes a first optical beam combiner 410 and a second optical beam combiner 420;

[0008] The input waveguide is connected to the input optical fiber;

[0009] The input waveguide is connected to the input end of the polarization beam splitter rotator 100; the straight-through end of the polarization beam splitter rotator 100 is connected to the input end of the phase shifter 200, the output end of the phase shifter 200 is connected to the input end of the first optical beam splitter 310, the cross end of the polarization beam splitter rotator 100 is connected to the input end of the second optical beam splitter 320, the lower output end of the first optical beam splitter 310 and the upper output end of the second optical beam splitter 320 are respectively connected to the upper and lower input ends of the first optical beam combiner 410, the upper output end of the first optical beam splitter 310 and the lower output end of the second optical beam splitter 320 are respectively connected to the upper and lower input ends of the second optical beam combiner 420, the output end of the first optical beam combiner 410 is connected to the upper input waveguide of the micro-ring resonator 500, and the output end of the second optical beam combiner 420 is connected to the lower input waveguide of the micro-ring resonator 500.

[0010] As a further embodiment of the present invention, the optical signal input from the input optical fiber passes sequentially through the direct end of the polarization beam splitter 100, the phase shifter I 200, and the input end of the first optical beam splitter 310; the optical signal output from the crossover end of the polarization beam splitter 100 is sent to the input end of the second optical beam splitter 320; the two optical signals output from the lower output end of the first optical beam splitter 310 and the upper output end of the second optical beam splitter 320 respectively enter the first optical combiner 410; the two optical signals output from the upper output end of the first optical beam splitter 310 and the lower output end of the second optical beam splitter 320 respectively enter the second optical combiner 420; the first optical combiner 410 outputs... The optical signal is coupled into the upper input terminal of the microring resonator 500, and the optical signal output from the second optical combiner 420 is coupled into the lower input waveguide of the microring resonator 500. The optical signal input into the lower input waveguide of the microring resonator 500 is first coupled into the microring of the microring resonator 500, passes through half of the microring, and is then coupled into the output waveguide of the microring resonator 500. The optical signal coupled into the upper input waveguide of the microring resonator 500 is then output from the output terminal. There is a path difference of half the circumference of the microring resonator's ring waveguide between the optical signal in the upper input waveguide and the optical signal in the lower input waveguide of the microring resonator 500.

[0011] As a further embodiment of the present invention, the polarization beam splitter rotator 100 is used to realize the higher-order conversion from TM0 mode to TE1 mode and the conversion and separation from TE1 mode to TE0 mode. The input light polarization mode of the input optical waveguide is TE mode, TM mode or a mixture of TE mode and TM mode, and the output is TE mode. The mode conversion of the input light wave is performed in the polarization beam splitter rotator 100, which together with the waveguides at both ends forms a mode transmission and conversion region.

[0012] As a further aspect of the present invention, there may be a phase difference between the optical signals transmitted at the input ports of the first optical beamsplitter 310 and the second optical beamsplitter 320, which may cause loss during beam combining. Therefore, an optical phase shifter 200 is loaded at the through port of the polarization beam rotator 100. The phase shifter 200 is an electro-optic phase shifter or a thermo-optic phase shifter. By changing the phase of the optical signal, a phase difference of zero or 2nπ is generated between the two optical signals to achieve beam combining interference enhancement, and finally the phase of the optical signals at the input ports of the first optical beamsplitter 310 and the second optical beamsplitter 320 is made consistent.

[0013] As a further embodiment of the present invention, the optical beam splitter assembly 300 is a 1×2 multimode interference coupler with dimensions of 3.2 μm in length and 2.4 μm in width; the optical beam splitter assembly 300 can split a beam of light into two beams proportionally. The first optical beam splitter 310 and the second optical beam splitter 320 have the same structure and can both be used for accurate power splitting.

[0014] As a further embodiment of the present invention, the first optical combiner 410 and the second optical combiner 420 adopt Y-shaped branch optical waveguides or multimode interference couplers, and both are 2×1 structures. When the first optical combiner 410 and the second optical combiner 420 are Y-shaped branch optical waveguides, the tilt angle θ of the two Y-shaped branch optical waveguides is 2°. The optical signals at the two input ends of the first optical combiner 410 and the second optical combiner 420 are in phase, and the two beams of light with the same phase but different intensities are combined. The interference of the two light waves at the two input ends of the Y-shaped branch optical waveguide is regarded as the superposition of the polarization-independent mode converter modes.

[0015] As a further aspect of the present invention, mode conversion is based on the principle of mode coupling, that is, satisfying the phase matching condition.

[0016] The superposition of modes can be considered as the interference of two light waves at the two input ends of the Y-shaped branched optical waveguide.

[0017] Coherent light waves can be represented as

[0018]

[0019]

[0020] Where E a0 and E b0 These represent the peak values ​​of the amplitudes of the two light waves, respectively. and Let represent their respective phases, and ω be the angular frequency. According to the principle of light wave interference, the synthesized light wave can be represented as:

[0021]

[0022] The amplitude E0 can be obtained from the following equation

[0023]

[0024] The amplitude of the superimposed light waves depends on the phase difference at the point where the two light waves superimpose. At that time, the amplitude E0 reaches its maximum.

[0025] As a further aspect of the present invention, the coupling gap of the micro-ring resonator 500 is 0.2 μm, the ring radius is 15 μm, and the free spectral range is set to 3.2 nm. The micro-ring resonator 500 can achieve efficient injection of optical signals. This requires injecting two coherent optical signals with the same wavelength and intensity into the resonator through the upper and lower input waveguides. Therefore, an optical beamsplitter assembly 300 and an optical beam combiner assembly 400 are connected sequentially to the front end of the micro-ring resonator 500 to achieve proportional distribution of the optical signals. The relationship between the transmitted electromagnetic field and wavelength is described by the following equation:

[0026]

[0027] In the formula, α, E i and Φ i These represent the transmission coefficient, coupling coefficient, loss coefficient of the microring resonator, electric field of the input signal, and phase, respectively.

[0028] As a further aspect of the present invention, the desired light is coupled into the resonator by adjusting the coupling coefficient of the directional coupler in the micro-ring resonator 500 to form a resonance phenomenon, thereby enhancing the optical signal of a specific frequency and outputting it through the output waveguide, while preventing unwanted light from being emitted from the output port.

[0029] As a further aspect of the present invention, two optical signals with the same intensity but a phase difference are injected through the two input ports of a dual-injection microring resonator. The optical signals propagate within the silicon microring and transmit around the ring waveguide. These photons undergo multiple orbits within the microring, forming a resonance phenomenon that amplifies the optical signal at a specific frequency, and are then output through the output waveguide. θ is the accumulated phase of the light as it passes through the ring in a steady state, expressed by the formula:

[0030]

[0031] In the formula, λ is the wavelength, and L Ring Let n be the circumference of the microring. eff The effective refractive index of the propagating mode.

[0032] The beneficial effects of this invention are:

[0033] 1. Compared with existing polarization beam rotators based on mode coupling principle and polarization beam rotators based on mode evolution principle, this invention effectively reduces coupling loss, improves coupling efficiency, and obtains a high-performance mode switching device that is independent of polarization.

[0034] 2. This invention is based on mature CMOS process fabrication. By utilizing existing technologies, it has low operating costs and can achieve mass production. Due to the maturity of existing technologies, its production efficiency is high, giving it a competitive advantage.

[0035] 3. When the optical signal in the input waveguide of this invention passes through the polarization rotating beam splitter, the TM mode in the optical signal is converted to the TE mode; the phase shifter component makes the phase difference between the two multimode interference couplers that enter the optical beam splitter component zero; the optical beam splitter component is used for optical power splitting; the signal passes through the optical beam combiner component and is combined at the micro-ring resonator and output from the output end.

[0036] 4. The mode converter proposed in this invention has a simple structure and can realize TE mode conversion for inputs with arbitrary polarization states. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a polarization-independent mode converter structure according to the present invention;

[0038] Figure 1 Labels: 100 - Polarization beam splitter rotator, 200 - Phase shifter, 300 - Optical beam splitter assembly, 310 - First optical beam splitter, 320 - Second optical beam splitter, 400 - Optical beam combiner assembly, 410 - First optical beam combiner, 420 - Second optical beam combiner, 500 - Microring resonator, input1 - Upper input waveguide, input2 - Lower input waveguide, output - Output waveguide

[0039] Figure 2 This is a schematic diagram of the micro-ring resonator 500 structure of the mode converter of the present invention;

[0040] Figure 3 This is a schematic diagram of mode conversion for a polarization-independent mode converter with mixed-mode input according to the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0042] In the description of this invention, it should be noted that terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," "first to fourth," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0043] Example 1: As Figure 1 As shown, a polarization-independent mode converter includes, from bottom to top, a wafer substrate, a buried oxide layer of the wafer, a device layer and a SiO2 cladding layer of the device, the device layer including an input waveguide; a polarization beam splitter rotator 100, a phase shifter 200, an optical beam splitter assembly 300, an optical beam combiner assembly 400 and a microring resonator 500.

[0044] The optical beam splitter assembly 300 includes a first optical beam splitter 310 and a second optical beam splitter 320;

[0045] The optical beam combiner assembly 400 includes a first optical beam combiner 410 and a second optical beam combiner 420;

[0046] The input waveguide is connected to the input optical fiber;

[0047] The input waveguide is connected to the input end of the polarization beam splitter rotator 100; the straight-through end of the polarization beam splitter rotator 100 is connected to the input end of the phase shifter 200, the output end of the phase shifter 200 is connected to the input end of the first optical beam splitter 310, the cross end of the polarization beam splitter rotator 100 is connected to the input end of the second optical beam splitter 320, the lower output end of the first optical beam splitter 310 and the upper output end of the second optical beam splitter 320 are respectively connected to the upper and lower input ends of the first optical beam combiner 410, the upper output end of the first optical beam splitter 310 and the lower output end of the second optical beam splitter 320 are respectively connected to the upper and lower input ends of the second optical beam combiner 420, the output end of the first optical beam combiner 410 is connected to the upper input waveguide of the micro-ring resonator 500, and the output end of the second optical beam combiner 420 is connected to the lower input waveguide of the micro-ring resonator 500.

[0048] As a further embodiment of the present invention, the optical signal input from the input optical fiber passes sequentially through the direct end of the polarization beam splitter 100, the phase shifter I 200, and the input end of the first optical beam splitter 310; the optical signal output from the crossover end of the polarization beam splitter 100 is sent to the input end of the second optical beam splitter 320; the two optical signals output from the lower output end of the first optical beam splitter 310 and the upper output end of the second optical beam splitter 320 respectively enter the first optical combiner 410; the two optical signals output from the upper output end of the first optical beam splitter 310 and the lower output end of the second optical beam splitter 320 respectively enter the second optical combiner 420; the first optical combiner 410 outputs... The optical signal is coupled into the upper input terminal of the microring resonator 500, and the optical signal output from the second optical combiner 420 is coupled into the lower input waveguide of the microring resonator 500. The optical signal input into the lower input waveguide of the microring resonator 500 is first coupled into the microring of the microring resonator 500, passes through half of the microring, and is then coupled into the output waveguide of the microring resonator 500. The optical signal coupled into the upper input waveguide of the microring resonator 500 is then output from the output terminal. There is a path difference of half the circumference of the microring resonator's ring waveguide between the optical signal in the upper input waveguide and the optical signal in the lower input waveguide of the microring resonator 500.

[0049] As a further embodiment of the present invention, the polarization beam splitter rotator 100 is used to realize the higher-order conversion from TM0 mode to TE1 mode and the conversion and separation from TE1 mode to TE0 mode. The input light polarization mode of the input optical waveguide is TE mode, TM mode or a mixture of TE mode and TM mode, and the output is TE mode. The mode conversion of the input light wave is performed in the polarization beam splitter rotator 100, which together with the waveguides at both ends forms a mode transmission and conversion region.

[0050] As a further aspect of the present invention, there may be a phase difference between the optical signals transmitted in the input ports of the first optical beamsplitter 310 and the second optical beamsplitter 320, which will cause loss during beam combining. Therefore, an optical phase shifter 200 is loaded at the through port of the polarization beam splitter. The phase shifter 200 is an electro-optic phase shifter or a thermo-optic phase shifter. By changing the phase of the optical signal, a phase difference of zero or 2nπ is generated between the two optical signals to achieve beam combining interference enhancement, and finally make the phase of the optical signals at the input ports of the first optical beamsplitter 310 and the second optical beamsplitter 320 consistent.

[0051] As a further embodiment of the present invention, the optical beam splitter assembly 300 is a 1×2 multimode interference coupler with dimensions of 3.2 μm in length and 2.4 μm in width; the optical beam splitter assembly 300 can split a beam of light into two beams proportionally. The first optical beam splitter 310 and the second optical beam splitter 320 have the same structure and can both be used for accurate power splitting.

[0052] As a further embodiment of the present invention, the first optical combiner 410 and the second optical combiner 420 adopt Y-shaped branch optical waveguides or multimode interference couplers, and both are 2×1 structures. When the first optical combiner 410 and the second optical combiner 420 are Y-shaped branch optical waveguides, the tilt angle θ of the two Y-shaped branch optical waveguides is 2°. The optical signals at the two input ends of the first optical combiner 410 and the second optical combiner 420 are in phase, and the two beams of light with the same phase but different intensities are combined. The interference of the two light waves at the two input ends of the Y-shaped branch optical waveguide is regarded as the superposition of the polarization-independent mode converter modes.

[0053] As a further aspect of the present invention, mode conversion is based on the principle of mode coupling, that is, satisfying the phase matching condition.

[0054] The superposition of modes can be considered as the interference of two light waves at the two input ends of the Y-shaped branched optical waveguide.

[0055] Coherent light waves can be represented as

[0056]

[0057]

[0058] Where E a0 and E b0 These represent the peak values ​​of the amplitudes of the two light waves, respectively. and Let represent their respective phases, and ω be the angular frequency. According to the principle of light wave interference, the synthesized light wave can be represented as:

[0059]

[0060] The amplitude E0 can be obtained from the following equation

[0061]

[0062] The amplitude of the superimposed light waves depends on the phase difference at the point where the two light waves superimpose. At that time, the amplitude E0 reaches its maximum.

[0063] As a further aspect of the present invention, the input waveguide and output waveguide used in the present invention are 500 nm wide and 220 nm high; the coupling gap of the micro-ring resonator 500 is 0.2 μm, the ring radius is 15 μm, and the free spectral range is set to 3.2 nm; the micro-ring resonator 500 can achieve efficient injection of optical signals, requiring two coherent optical signals with the same wavelength and intensity to be injected into the resonator through the upper and lower input waveguides of the micro-ring resonator 500. Therefore, an optical beam splitter assembly 300 and an optical beam combiner assembly 400 are connected sequentially to the front end of the micro-ring resonator 500 to achieve proportional distribution of optical signals. The relationship between the transmitted electromagnetic field and the wavelength is described by the following formula:

[0064]

[0065] In the formula, α, E i and Φ i These represent the transmission coefficient, coupling coefficient, loss coefficient of the microring resonator, electric field of the input signal, and phase, respectively.

[0066] As a further aspect of the present invention, the desired light is coupled into the resonator by adjusting the coupling coefficient of the directional coupler in the micro-ring resonator 500 to form a resonance phenomenon, thereby enhancing the optical signal of a specific frequency and outputting it through the output waveguide, while preventing unwanted light from being emitted from the output port.

[0067] As a further aspect of the present invention, two optical signals with the same intensity but a phase difference are injected through the two input ports of a dual-injection microring resonator. The optical signals propagate within the silicon microring and transmit around the ring waveguide. These photons undergo multiple orbits within the microring, forming a resonance phenomenon that amplifies the optical signal at a specific frequency, and are then output through the output waveguide. θ is the accumulated phase of the light as it passes through the ring in a steady state, expressed by the formula:

[0068]

[0069] In the formula, λ is the wavelength, and L Ring Let n be the circumference of the microring. eff The effective refractive index of the propagating mode.

[0070] This invention can be applied to the polarization modulation process of optical signals. In this invention, the optical signal input from the input optical fiber passes sequentially through a polarization beam splitter rotator 100, a phase shifter 200, a first optical beam splitter 310, a second optical beam splitter 320, a first optical beam combiner 410, a second optical beam combiner 420, and a micro-ring resonator 500. This enables the conversion of any input polarization state to TEO mode, which is beneficial for on-chip integration. Thus, this invention can achieve the effect of inputting any polarization state and outputting a single polarization TEO mode.

[0071] Example 2: Figures 1-3 As shown, a polarization-independent mode converter is described. This embodiment has the same structure as Embodiment 1. Assuming that the input optical field is a mixed optical signal with 60% of the input optical field in TE0 mode and 40% in TM0 mode, after passing through the polarization-independent mode converter, the output port only outputs TE0 mode.

[0072] The polarization beam splitter rotator 100 is connected to the input optical fiber via the input waveguide, and inputs an optical signal of 60% TE0 + 40% TM0.

[0073] The optical signal of 60% TE0 + 40% TM0 is transmitted in the input optical fiber to the polarization rotating beam splitter 100. The polarization rotating beam splitter 100 converts the optical signal of 40% TM0 mode in the input optical fiber into TE1 mode with the same phase and intensity. The directional coupler of the polarization rotating beam splitter 100 converts the TE1 mode into TE0 mode.

[0074] The 60% TEO mode output from the direct end of the polarization rotating beam splitter 100 enters the phase shifter 200. The phase shifter 200 changes the phase of the optical signal at the direct end in an electro-optical / thermo-optical manner, so that it is in phase with the optical signal at the input end of the second optical beam combiner 420 when it is input to the first optical beam combiner 410.

[0075] The 60% TE0 beam is split into two 30% TE0 beams in the first optical beam splitter 310, and the 40% TE0 beam is split into two 20% TE0 beams in the second optical beam splitter 320. The two sets of 30% TE0 and 20% TE0 beams are combined with the second optical beam combiner 420 in the first optical beam combiner 410 to form two equally proportioned optical signals, which are then injected into the microring resonator 500.

[0076] By adjusting the coupling coefficient of the directional coupler in the micro-ring resonator 500, two beams of light are coupled to the resonator for beam combining, such as... Figure 2 As shown, two beams of light with the same intensity but a phase difference are introduced from the upper and lower input waveguides, respectively, and then output from the output waveguide of the micro-ring resonator 500.

[0077] Based on the device structure and CMOS fabrication process of this invention, a polarization-independent mode converter proposed in this invention can be fabricated. The main integration process flow is as follows:

[0078] Step 1: First, perform surface pretreatment on the SOI wafer: For an SOI wafer with a structure including a silicon core layer thickness of 220nm and a silicon dioxide buried layer thickness of 2um, rinse with a 1:100 hydrofluoric acid solution for 10 seconds to remove the natural oxide layer on the surface. Then, rinse with deionized water for 10 minutes. Next, clean the organic matter and metal impurities on the silicon substrate surface with a concentrated sulfuric acid and hydrogen peroxide SPM solution. Rinse again with deionized water for 10 minutes. Finally, bake to remove moisture.

[0079] Step 2: Using plasma-enhanced chemical vapor deposition (PECVD), a 50nm thick layer of silicon dioxide is deposited on the silicon wafer surface as a hard mask for etching the silicon waveguide. Then, a layer of photoresist is uniformly coated onto the silicon wafer surface. Photoresists can be classified as positive or negative depending on the parameter requirements of the fabricated device. During exposure and development, positive photoresist dissolves in the developer, undergoing a chain-breaking reaction, resulting in a remaining pattern identical to the exposed pattern; negative photoresist does not dissolve in the developer, undergoing a cross-linking reaction, resulting in a remaining pattern opposite to the exposed pattern. The coated silicon wafer is then baked on a hot plate, causing the solvent in the photoresist to evaporate, ensuring adhesion between the silicon wafer and the photoresist, and guaranteeing that subsequent photolithography will achieve the desired effect.

[0080] Step 3: Using electron beam lithography, the photoresist and silicon wafer are acted upon by a focused electron beam spot to write the pattern.

[0081] Step 4: Place the exposed silicon wafer in the specified developer to remove unwanted photoresist solvent. Then, bake the photolithographically completed silicon wafer on a hot plate to remove residual photoresist solvent. The purpose is to improve the adhesion between the silicon wafer and the photoresist. Insufficient post-baking can lead to problems such as rough waveguide sidewalls or photoresist float in subsequent etching steps.

[0082] Step 5: Add a certain amount of ammonium fluoride as a buffer to the hydrofluoric acid etching solution to form a buffered hydrofluoric acid etching solution (BHF). Use the buffered hydrofluoric acid etching solution to remove silicon dioxide from the silicon waveguide surface. Since organic matter can cover part of the silicon wafer surface, making some contaminants difficult to remove, the RCA standard cleaning method is used to remove residual impurities from the silicon waveguide surface.

[0083] Step 6: A silicon dioxide layer with a thickness of 3μm is formed on the silicon substrate using the PECVD process.

[0084] Step 7: Cut the sample, use chemical mechanical planarization (CMP) to form a smooth surface, and then clean it to obtain the designed device structure.

[0085] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A polarization-independent mode converter, comprising, from bottom to top, a wafer substrate, a buried oxide layer of the wafer, a device layer, and a SiO2 cladding layer of the device, characterized in that: The device layer includes an input waveguide; a polarization beam splitter rotator (100); a phase shifter (200); an optical beam splitter assembly (300); an optical beam combiner assembly (400); and a microring resonator (500). The optical beam splitter assembly (300) includes a first optical beam splitter (310) and a second optical beam splitter (320); The optical beam combiner assembly (400) includes a first optical beam combiner (410) and a second optical beam combiner (420); The input waveguide is connected to the input optical fiber; The input waveguide is connected to the input end of the polarization beam splitter (100); the through end of the polarization beam splitter (100) is connected to the input end of the phase shifter (200), the output end of the phase shifter (200) is connected to the input end of the first optical beam splitter (310), the cross end of the polarization beam splitter (100) is connected to the input end of the second optical beam splitter (320), and the lower output end of the first optical beam splitter (310) and the upper output end of the second optical beam splitter (320) are respectively... The upper and lower input terminals of the first optical beam combiner (410) are connected to each other. The upper output terminal of the first optical beam splitter (310) and the lower output terminal of the second optical beam splitter (320) are connected to the upper and lower input terminals of the second optical beam combiner (420), respectively. The output terminal of the first optical beam combiner (410) is connected to the upper input waveguide of the micro-ring resonator (500). The output terminal of the second optical beam combiner (420) is connected to the lower input waveguide of the micro-ring resonator (500).

2. The polarization-independent mode converter according to claim 1, characterized in that: The optical signal input from the optical fiber passes sequentially through the straight-through end of the polarization beam splitter (100), phase shifter I (200), and the input end of the first optical beam splitter (310); the optical signal output from the cross-end of the polarization beam splitter (100) is sent to the input end of the second optical beam splitter (320); the two optical signals output from the lower output end of the first optical beam splitter (310) and the upper output end of the second optical beam splitter (320) respectively enter the first optical combiner (410); the two optical signals output from the upper output end of the first optical beam splitter (310) and the lower output end of the second optical beam splitter (320) respectively enter the second optical combiner (420); the optical signal output from the first optical combiner (410)... The signal is coupled into the upper input terminal of the microring resonator (500), and the optical signal output by the second optical combiner (420) is coupled into the lower input waveguide of the microring resonator (500). The optical signal input into the lower input waveguide of the microring resonator (500) is first coupled into the microring of the microring resonator (500), passes through half of the microring, and is then coupled into the output waveguide of the microring resonator (500). The optical signal coupled into the upper input waveguide of the microring resonator (500) is then output from the output terminal. There is a path difference of half the circumference of the microring resonator's ring waveguide between the optical signal in the upper input waveguide and the optical signal in the lower input waveguide of the microring resonator (500).

3. A polarization-independent mode converter according to claim 1, characterized in that: The polarization beam splitter (100) is used to realize the high-order conversion from TM0 mode to TE1 mode and the conversion and separation from TE1 mode to TE0 mode. The input light polarization mode of the input optical waveguide is TE mode, TM mode or a mixture of TE mode and TM mode. The output is TE mode. The mode conversion of the input light wave is performed in the polarization beam splitter (100) and forms a mode transmission and conversion region with the waveguides at both ends.

4. A polarization-independent mode converter according to claim 1, characterized in that: The phase shifter (200) is an electro-optic phase shifter or a thermo-optic phase shifter. By changing the phase of the optical signal, a phase difference of zero or 2nπ is generated between the two optical signals to achieve enhanced wave combining interference, and finally make the phase of the optical signals at the input ports of the first optical beam splitter (310) and the second optical beam splitter (320) consistent.

5. A polarization-independent mode converter according to claim 1, characterized in that: The optical beam splitter assembly (300) is a 1×2 multimode interference coupler with a length of 3.2μm and a width of 2.4μm. The optical beam splitter assembly (300) can split a beam of light into two beams of light in equal proportion.

6. A polarization-independent mode converter according to claim 1, characterized in that: The first optical combiner (410) and the second optical combiner (420) adopt Y-shaped branch optical waveguides or multimode interference couplers, and both are 2×1 structures. When the first optical combiner (410) and the second optical combiner (420) are Y-shaped branch optical waveguides, the tilt angle θ of the two Y-shaped branch optical waveguides is 2°. The optical signals at the two input ends of the first optical combiner (410) and the second optical combiner (420) are in phase. The two beams of light with the same phase but different intensities are combined. The interference of the two light waves at the two input ends of the Y-shaped branch optical waveguide is regarded as the superposition of the polarization-independent mode converter modes.

7. A polarization-independent mode converter according to claim 1, characterized in that: The coupling gap of the microring resonator (500) is 0.2 μm, the ring radius is 15 μm, and the free spectral range is set to 3.2 nm. An optical beam splitter assembly (300) and an optical beam combiner assembly (400) are connected to the front end of the microring resonator (500) to achieve proportional distribution of optical signals.

8. A polarization-independent mode converter according to claim 1, characterized in that: By adjusting the coupling coefficient of the directional coupler in the micro-ring resonator (500), the desired light is coupled into the resonator to form a resonance phenomenon, which enhances the optical signal of a specific frequency and outputs it through the output waveguide, while preventing unwanted light from being emitted from the output port.

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