Polarization-independent mode converter

Abstract

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

Description

Technical Field

[0001] The invention relates to a polarization-independent mode converter, belonging to the technical field of wireless communication semiconductor devices. Background Art

[0002] With the continuous advancement of technology in recent years, optoelectronic devices in optical communications are gradually developing in the direction of integration. Compared with the system built by traditional discrete optical devices, integrated optoelectronic devices have some obvious advantages, such as less space occupation, lower production cost, and by packaging different devices on a chip, avoiding interference from some external factors, making the performance more stable, suitable for the development of high-efficiency and multifunctional optoelectronic products. However, there is still a technical difficulty in the application of this technology, that is, the material, structure or design of the device may affect the polarization state of light. The two polarization states TE and TM modes have different mode field distribution, effective refractive index and waveguide loss in the waveguide. After the performance of the photonic device is affected by the polarization state of the input light, it will lead to polarization-related loss, polarization mode dispersion and polarization correlation of the working wavelength. In the optical fiber communication system, the optical transmission module usually uses ordinary optical fiber as the transmission medium, which will make it difficult to ensure the polarization state of the input light when coupling light from ordinary optical fiber to the rectangular waveguide on the silicon-based integrated device. The uncertainty of the polarization state of the input light will make the performance of the optical device very unstable, so solving the polarization correlation of the optical device is an important challenge.

[0003] Currently, the photonic devices based on silicon on insulator (SOI) reported for polarization beam splitting rotation are mainly divided into mode coupling polarization beam splitting rotation devices and mode evolution polarization beam splitting rotation devices. Polarization beam splitters based on the mode coupling principle generally use an asymmetric directional coupler structure to excite hybrid supermodes and interfere to achieve mode conversion and separation. The device has the advantage of small size, which is conducive to large-scale integration of chips. However, this type of polarization beam splitter rotator based on the directional coupling structure requires strict phase matching conditions to achieve mode coupling and conversion, so it is sensitive to wavelength and process, has a small working bandwidth, and a small process tolerance. The polarization beam splitter rotator based on the mode evolution principle first converts the input TM0 mode into a high-order TE1 mode, then separates it from the input TE0 mode, and converts TE1 into TE0 mode. The high-order conversion of the mode occurs in the mode mixing region of the waveguide. Therefore, the structure of this type of polarization beam splitter rotator is relatively complex, but its bandwidth and manufacturing tolerance are relatively large. A polarization-independent mode converter proposed in the present invention can effectively make up for the defects of a polarization beam splitter rotator based on a mode coupling principle and a polarization beam splitter rotator based on a mode evolution principle, thereby obtaining a polarization-independent mode converter with excellent performance. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the problems and shortcomings of the current polarization beam splitter rotator based on the mode coupling principle and the polarization beam splitter rotator based on the mode evolution principle: 1. The polarization beam splitter rotator based on the mode coupling principle requires strict phase matching conditions to achieve mode coupling and conversion, so it is sensitive to wavelength and process, has a small working bandwidth and a small process tolerance; 2. The structure of the polarization beam splitter rotator based on the mode evolution principle is relatively complex, but its bandwidth and manufacturing tolerance are large. The polarization-independent mode converter proposed in the present invention can effectively make up for the defects of the polarization beam splitter rotator based on the mode coupling principle and the polarization beam splitter rotator based on the mode evolution principle, meet the application requirements of the input light being randomly polarized light, and obtain a polarization-independent mode converter with excellent performance.

[0005] The technical solution of the present invention is: a polarization-independent mode converter, which includes, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer and a SiO2 upper cladding layer of the device, wherein 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;

[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 input end and the lower input end of the first optical 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 input end and the lower input end of the second optical beam splitter 420, the output end of the first optical beam splitter 410 is connected to the upper input waveguide of the microring resonator 500; the output end of the second optical beam splitter 420 is connected to the lower input waveguide of the microring resonator 500.

[0010] As a further solution of the present invention, the optical signal input by the input optical fiber passes through the through end of the polarization beam splitter rotator 100, the phase shifter I 200, and the input end of the first optical beam splitter 310 in sequence; the cross end of the polarization beam splitter rotator 100 outputs the optical signal to the input end of the second optical beam splitter 320; the two optical signals outputted from the lower output end of the first optical beam splitter 310 and the upper output end of the second optical beam splitter 320 enter the first optical combiner 410; the two optical signals outputted from the upper output end of the first optical beam splitter 310 and the lower output end of the second optical beam splitter 320 enter the second optical combiner 420; the output of the first optical combiner 410 The optical signal is coupled into the upper input end 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 from the lower input waveguide of the microring resonator 500 is first coupled into the microring of the microring resonator 500, and then coupled to the output waveguide output of the microring resonator 500 after passing through half of the microring, and the optical signal coupled into the upper input waveguide of the microring resonator 500 is then output from the output end, and there is a path difference of half the circumference of the microring resonator ring waveguide between the optical signal of the upper input waveguide of the microring resonator 500 and the optical signal of the lower input waveguide.

[0011] As a further solution of the present invention, the polarization beam splitter rotator 100 is used to achieve high-order conversion from TM0 mode to TE1 mode and 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 mixed input 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, and it forms a mode transmission and conversion region with the waveguides at both ends.

[0012] As a further solution of the present invention, there may be a difference in the phase of the optical signals transmitted in the input ports of the first optical beam splitter 310 and the second optical beam splitter 320, which will cause loss during wave combining. Therefore, an optical phase shifter 200 is loaded on the through port of the polarization beam splitter rotator 100. The phase shifter 200 is an electro-optical phase shifter or a thermo-optical 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 wave combining interference enhancement, and finally the phases of the optical signals at the input ports of the first optical beam splitter 310 and the second optical beam splitter 320 are consistent.

[0013] As a further solution of the present invention, the optical beam splitter assembly 300 is a multimode interference coupler with a 1×2 structure, and its size is 3.2 μm in length and 2.4 μm in width; the optical beam splitter assembly 300 can split a beam of light waves into two beams of light waves in equal proportion. 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 division.

[0014] As a further solution 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 inclination angles θ of the two Y-shaped branch optical waveguides are both 2°, and the optical signals at the two input ends of the first optical combiner 410 and the second optical combiner 420 are consistent in phase, and two beams of light with the same phase but different intensities are combined, and the interference of the two columns of 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 mode.

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

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

[0017] The coherent light wave can be expressed as

[0018]

[0019]

[0020] Where E a0 and E b0 Represent the peak values ​​of the two light wave amplitudes, and Respectively represent their respective phases, and ω is the angular frequency. According to the principle of light wave interference, the synthesized light wave can be expressed as:

[0021]

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

[0023]

[0024] The amplitude of the superimposed light wave depends on the phase difference at the position where the two light waves are superimposed. When , the amplitude E0 reaches its maximum.

[0025] As a further solution of the present invention, the coupling gap of the microring resonator 500 is 0.2 μm, the ring radius is 15 μm, and the free spectrum range is set to 3.2 nm; the microring resonator 500 can realize efficient injection of optical signals, requiring that two mutually coherent optical signals with the same wavelength and light intensity be injected into the resonator at the upper input waveguide and the lower input waveguide of the microring resonator 500, so the optical beam splitter component 300 and the optical beam combiner component 400 are successively connected at the front end of the microring resonator 500 to realize the proportional distribution of the optical signal, and the relationship between the transmission electromagnetic field and the wavelength is given by the following formula:

[0026]

[0027] In the formula, α, E i and Φ i They are the transmission coefficient and coupling coefficient of the directional coupler, the loss coefficient of the microring resonator, the electric field of the input signal and its phase.

[0028] As a further solution of the present invention, by adjusting the coupling coefficient of the directional coupler in the microring resonator 500, the desired light is coupled into the resonator to form a resonance phenomenon, enhance the optical signal of a specific frequency, and output it through the output waveguide, while preventing unnecessary light from being emitted from the output port.

[0029] As a further solution of the present invention, two light signals with the same intensity and phase difference are injected through the two input ports of the double-injection microring resonator. The light signals propagate in the silicon microring and are transmitted around the ring waveguide. These photons circulate multiple times inside the microring, forming a resonance phenomenon, enhancing the light signal of a specific frequency, and outputting it through the output waveguide. θ is the accumulated phase of light passing through the ring in a stable state, which is expressed by the formula:

[0030]

[0031] Where λ is the wavelength, L Ring is the circumference of the microring, n eff is the effective refractive index of the propagating mode.

[0032] The beneficial effects of the present invention are:

[0033] 1. Compared with the existing polarization beam splitter rotator technology based on the mode coupling principle and the polarization beam splitter rotator technology based on the mode evolution principle, the present invention effectively reduces the coupling loss, improves the coupling efficiency, and obtains a polarization-independent mode conversion device with excellent performance;

[0034] 2. The present invention is prepared based on mature CMOS technology. By utilizing existing technology, its operating cost is low and batch production can be realized. Due to the maturity of existing technology, its production efficiency is high and it has competitive advantages;

[0035] 3. When the optical signal in the input waveguide of the present invention passes through the polarization rotation beam splitter, the TM mode in the optical signal is converted into the TE mode; the phase shifter component makes the phase difference of the light waves entering the two multimode interference couplers in the optical beam splitting component respectively 0, the optical beam splitting component is used for optical power division, and the signal passes through the optical beam combining component, and is combined in the microring resonator and output from the output end;

[0036] 4. The mode converter proposed in the present invention has a simple structure and can realize TE mode conversion of any polarization state input. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the structure of a polarization-independent mode converter of the present invention;

[0038] Figure 1 The numbers in the figure are: 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 It is a schematic structural diagram of a microring resonator 500 of a mode converter of the present invention;

[0040] Figure 3 A schematic diagram of mode conversion of a polarization-independent mode converter mixed mode input of the present invention. DETAILED DESCRIPTION

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

[0042] In the description of the present invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are based on the directions or positional relationships described in the drawings, and are only for the convenience of describing the present invention and simplifying the description, 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 limiting the present invention. In addition, the use of ordinal numbers (e.g., "first and second", "first to fourth", etc.) is to distinguish objects, and is not limited to this order, and cannot be understood as indicating or implying relative importance.

[0043] Example 1: Figure 1 As shown, a polarization-independent mode converter includes, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer, and a SiO2 upper cladding layer of the device, wherein 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;

[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 input end and the lower input end of the first optical 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 input end and the lower input end of the second optical beam splitter 420, the output end of the first optical beam splitter 410 is connected to the upper input waveguide of the microring resonator 500; the output end of the second optical beam splitter 420 is connected to the lower input waveguide of the microring resonator 500.

[0048] As a further solution of the present invention, the optical signal input by the input optical fiber passes through the through end of the polarization beam splitter rotator 100, the phase shifter I 200, and the input end of the first optical beam splitter 310 in sequence; the cross end of the polarization beam splitter rotator 100 outputs the optical signal to the input end of the second optical beam splitter 320; the two optical signals outputted from the lower output end of the first optical beam splitter 310 and the upper output end of the second optical beam splitter 320 enter the first optical combiner 410; the two optical signals outputted from the upper output end of the first optical beam splitter 310 and the lower output end of the second optical beam splitter 320 enter the second optical combiner 420; the output of the first optical combiner 410 The optical signal is coupled into the upper input end 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 from the lower input waveguide of the microring resonator 500 is first coupled into the microring of the microring resonator 500, and then coupled to the output waveguide output of the microring resonator 500 after passing through half of the microring, and the optical signal coupled into the upper input waveguide of the microring resonator 500 is then output from the output end, and there is a path difference of half the circumference of the microring resonator ring waveguide between the optical signal of the upper input waveguide of the microring resonator 500 and the optical signal of the lower input waveguide.

[0049] As a further solution of the present invention, the polarization beam splitter rotator 100 is used to achieve high-order conversion from TM0 mode to TE1 mode and 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 mixed input 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, and it forms a mode transmission and conversion region with the waveguides at both ends.

[0050] As a further solution of the present invention, there may be a difference in the phase of the optical signals transmitted in the input ports of the first optical beam splitter 310 and the second optical beam splitter 320, which will cause loss during wave combining. Therefore, an optical phase shifter 200 is loaded on the through port of the polarization beam splitter rotator. The phase shifter 200 is an electro-optical phase shifter or a thermo-optical 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 wave combining interference enhancement, and finally the phases of the optical signals at the input ports of the first optical beam splitter 310 and the second optical beam splitter 320 are consistent.

[0051] As a further solution of the present invention, the optical beam splitter assembly 300 is a multimode interference coupler with a 1×2 structure, and its size is 3.2 μm in length and 2.4 μm in width; the optical beam splitter assembly 300 can split a beam of light waves into two beams of light waves in equal proportion. 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 division.

[0052] As a further solution 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 inclination angles θ of the two Y-shaped branch optical waveguides are both 2°, and the optical signals at the two input ends of the first optical combiner 410 and the second optical combiner 420 are consistent in phase, and two beams of light with the same phase but different intensities are combined, and the interference of the two columns of 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 mode.

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

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

[0055] The coherent light wave can be expressed as

[0056]

[0057]

[0058] Where E a0 and E b0 Represent the peak values ​​of the two light wave amplitudes, and Respectively represent their respective phases, and ω is the angular frequency. According to the principle of light wave interference, the synthesized light wave can be expressed as:

[0059]

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

[0061]

[0062] The amplitude of the superimposed light wave depends on the phase difference at the position where the two light waves are superimposed. When , the amplitude E0 reaches its maximum.

[0063] As a further solution of the present invention, the input waveguide and output waveguide used in the present invention are 500nm wide and 220nm high; the coupling gap of the microring resonator 500 is 0.2μm, the ring radius is 15μm, and the free spectrum range is set to 3.2nm; the microring resonator 500 can realize efficient injection of optical signals, requiring that two mutually coherent optical signals with the same wavelength and light intensity be injected into the resonator at the upper input waveguide and the lower input waveguide of the microring resonator 500, so the optical beam splitter component 300 and the optical beam combiner component 400 are successively connected at the front end of the microring resonator 500 to realize the proportional distribution of the optical signal, and the relationship between the transmission electromagnetic field and the wavelength is given by the following formula:

[0064]

[0065] In the formula, α, E i and Φ i They are the transmission coefficient and coupling coefficient of the directional coupler, the loss coefficient of the microring resonator, the electric field of the input signal and its phase.

[0066] As a further solution of the present invention, by adjusting the coupling coefficient of the directional coupler in the microring resonator 500, the desired light is coupled into the resonator to form a resonance phenomenon, enhance the optical signal of a specific frequency, and output it through the output waveguide, while preventing unnecessary light from being emitted from the output port.

[0067] As a further solution of the present invention, two light signals with the same intensity and phase difference are injected through the two input ports of the double-injection microring resonator. The light signals propagate in the silicon microring and are transmitted around the ring waveguide. These photons circulate multiple times inside the microring, forming a resonance phenomenon, enhancing the light signal of a specific frequency, and outputting it through the output waveguide. θ is the accumulated phase of light passing through the ring in a stable state, which is expressed by the formula:

[0068]

[0069] Where λ is the wavelength, L Ring is the circumference of the microring, n eff is the effective refractive index of the propagating mode.

[0070] The present invention can be applied to the polarization modulation process of optical signals; in the present invention, the optical signal input by the input optical fiber passes through the polarization beam splitter rotator 100, the phase shifter 200, the first optical beam splitter 310, the second optical beam splitter 320, the first optical combiner 410, the second optical combiner 420, and the microring resonator 500 in sequence, which can realize the conversion of the input arbitrary polarization state to the TE0 mode, which is beneficial to on-chip integration. Therefore, the present invention can achieve the effect of arbitrary polarization state input and single polarization TE0 mode output.

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

[0072] The polarization beam splitter rotator 100 is connected to the input optical fiber through the input waveguide, and inputs the 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 rotation beam splitter 100. The polarization rotation beam splitter 100 converts the optical signal of 40% TM0 mode in the input optical fiber into the TE1 mode with the same phase and intensity. The directional coupler of the polarization rotation beam splitter 100 converts the TE1 mode into the TE0 mode.

[0074] The 60% TE0 mode output from the through end of the polarization rotation beam splitter 100 enters the phase shifter 200, and the phase shifter 200 changes the phase of the through end optical signal in the form of electro-optical / thermo-optical, so that when it is input into the first optical combiner 410, the phase of the optical signal at the input end of the second optical combiner 420 is consistent.

[0075] The 60% TE0 light beam is split into two 30% TE0 light beams by the first beam splitter 310, and the 40% TE0 light beam is split into two 20% TE0 light beams by the second beam splitter 320. The two groups of light with 30% TE0 and 20% TE0 are respectively combined by the first optical combiner 410 and the second optical combiner 420 to form two equal-proportional light signals to be injected into the microring resonator 500.

[0076] By adjusting the coupling coefficient of the directional coupler in the microring resonator 500, two beams of light are coupled into the resonator for wave combination, such as Figure 2 As shown, two beams of light with the same light intensity and a phase difference are respectively output from the upper input waveguide and the lower input waveguide, and then output from the output waveguide of the microring resonator 500.

[0077] Based on the device structure and CMOS manufacturing process of the present invention, a polarization-independent mode converter proposed by the present invention can be prepared. The main integration process flow can be as follows:

[0078] Step 1: First, pre-treat the surface of the SOI wafer: The structure includes a silicon core layer with a thickness of 220nm and a silicon dioxide buried layer with a thickness of 2um. Rinse with a hydrofluoric acid solution with a ratio of 1:100 for 10s, remove the natural oxide layer on the surface, and then wash with deionized water for 10 minutes. Then use a SPM solution of concentrated sulfuric acid and hydrogen peroxide to clean the organic matter and metal impurities on the silicon surface, and then use deionized water to wash again for 10 minutes, and finally bake to remove moisture.

[0079] Step 2: Use plasma enhanced chemical vapor deposition (PECVD) process to deposit 50nm thick silicon dioxide on the surface of the silicon wafer as a hard mask for etching silicon waveguides. Then evenly apply a layer of photoresist on the surface of the silicon wafer. Photoresists can be divided into positive and negative according to the parameter requirements of the device preparation. During the exposure and development process, the positive photoresist dissolves in the developer, that is, a chain breaking reaction occurs, and the remaining pattern is the same as the exposure pattern; the negative photoresist is insoluble in the developer, that is, a cross-linking reaction occurs, and the remaining pattern is opposite to the exposure pattern; the silicon wafer after the glue is baked on a hot plate, and the solvent in the photoresist evaporates, ensuring the adhesion between the silicon wafer and the photoresist, and ensuring that the subsequent photolithography can achieve the desired effect.

[0080] Step 3: Using electron beam lithography technology, the photoresist and the silicon wafer are acted upon by the concentrated electron beam spot to implement pattern writing.

[0081] Step 4: Place the exposed silicon wafer in the designated developer to remove unnecessary photoresist solvents. Then bake the photolithography-finished silicon wafer on a hot plate to remove the residual photoresist solvents. The purpose is to improve the adhesion between the silicon wafer and the photoresist. If the post-baking effect is not good enough, it will lead to problems such as rough waveguide sidewalls or floating glue in the 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), and use the buffered hydrofluoric acid etching solution to remove the silicon dioxide on the surface of the silicon waveguide. Since organic matter will cover part of the silicon wafer surface, making some contamination difficult to remove, the RCA standard cleaning method is used to remove the impurities remaining on the surface of the silicon waveguide.

[0083] Step 6: Use PECVD process to form a silicon dioxide layer on the silicon substrate with a deposition thickness of 3 μm.

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

[0085] The specific embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A polarization-independent mode converter, comprising, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer, and a SiO2 upper 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 component (300), an optical beam combiner component (400) and a microring resonator (500); The optical beam splitter assembly (300) comprises a first optical beam splitter (310) and a second optical beam splitter (320); The optical beam combiner assembly (400) comprises 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); 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 optical waveguide (200) is connected to the upper input end and the lower input end 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 input end and the lower input end 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 microring resonator (500); and the output end of the second optical beam combiner (420) is connected to the lower input waveguide of the microring resonator (500).

2. A polarization-independent mode converter according to claim 1, characterized in that: An optical signal inputted from an input optical fiber passes through the through end of the polarization beam splitter (100), the phase shifter I (200), and the input end of the first optical beam splitter (310) in sequence; the cross end of the polarization beam splitter (100) outputs an optical signal to the input end of the second optical beam splitter (320); two optical signals outputted 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 beam combiner (410); two optical signals outputted 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 beam combiner (420); the optical signals outputted from the first optical beam combiner (410) The signal is coupled into the upper input end 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 to the output waveguide of the microring resonator (500), and the optical signal coupled into the upper input waveguide of the microring resonator (500) is then output from the output end, and there is a path difference of half the circumference of the microring resonator's annular waveguide between the optical signal of the upper input waveguide of the microring resonator (500) and the optical signal of the lower input waveguide.

3. The polarization-independent mode converter according to claim 1, characterized in that: The polarization beam splitter rotator (100) is used to realize high-order conversion from TM0 mode to TE1 mode and 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 mixed input of TE mode and TM mode, and the output is TE mode. The mode conversion of the input light wave is carried out in the polarization beam splitter rotator (100), and the polarization beam splitter rotator (100) and the waveguides at both ends form a mode transmission and conversion region.

4. The polarization-independent mode converter according to claim 1, characterized in that: The phase shifter (200) is an electro-optical phase shifter or a thermo-optical phase shifter, which changes the phase of the optical signal so as to generate a phase difference of zero or 2nπ between the two optical signals to achieve combined wave interference enhancement, and ultimately makes the phases of the optical signals at the input ports of the first optical beam splitter (310) and the second optical beam splitter (320) consistent.

5. The polarization-independent mode converter according to claim 1, characterized in that: The optical beam splitter components (300) are all multi-mode interference couplers with a 1×2 structure, and their dimensions are 3.2 μm in length and 2.4 μm in width. The optical beam splitter components (300) can split a beam of light waves into two beams of light waves in equal proportion.

6. The polarization-independent mode converter according to claim 1, characterized in that: The first optical combiner (410) and the second optical combiner (420) adopt a Y-shaped branch optical waveguide or a multimode interference coupler, and both have a 2×1 structure. When the first optical combiner (410) and the second optical combiner (420) are Y-shaped branch optical waveguides, the inclination angles θ of the two Y-shaped branch optical waveguides are both 2°, and the optical signals at the two input ends of the first optical combiner (410) and the second optical combiner (420) are consistent in phase, and two beams of light with the same phase but different intensities are combined, and the interference of the two columns of 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 mode.

7. The 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 spectrum range is set to 3.2 nm; the optical beam splitter component (300) and the optical beam combiner component (400) are successively connected to the front end of the microring resonator (500) to achieve equal-proportional distribution of optical signals.

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

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