Polarization-independent conversion device

Abstract

The invention relates to a polarization-independent conversion device, and belongs to the technical field of semiconductor waveguide communication 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. The device layer comprises an input optical waveguide, a polarization beam splitting rotator, a phase shifter assembly, an optical beam splitting assembly, a Y-branch waveguide, a cross waveguide and an output optical waveguide. The polarization beam splitting rotator is used for converting a TM mode in an optical signal input into the optical waveguide into a TE mode; the phase shifter assembly enables the phase difference of light waves entering the input ends of the two multimode interference couplers in the light beam splitting assembly to be 0; the light beam splitting assembly is used for equal-power splitting of light; and the Y branch waveguide superposes the signals, and finally outputs a TE mode. No matter whether the polarization state of input light is a TE mode or a TM mode, output is the TE mode, polarization conversion irrelevant to the input polarization state is achieved, and the device structure is excellent in performance, simple in structure and small in size.

Description

Technical Field

[0001] The invention relates to a polarization-independent conversion device, belonging to the technical field of semiconductor waveguide communication devices. Background Art

[0002] Optical networks have been widely used, but the various components of the current optical networks are made of different material systems, which makes it difficult to integrate the various devices in the current network system. The cost is high, the size is large, and it is difficult to maintain. Based on the current optical network situation, in order to reduce the cost and size of the device, silicon-based photonic devices have been greatly developed. Due to the large refractive index of silicon materials, silicon photonic communication devices based on silicon materials have a denser structure; and the process of silicon photonic communication devices is fully compatible with the existing CMOS process, which can realize on-chip integration of silicon photonic communication devices and integrated circuits on silicon, which not only effectively reduces the cost of devices, but also reduces the size of devices and improves the reliability of devices. Optical communication systems have attracted widespread attention due to their potential in meeting the growing bandwidth demand. In addition to the inherent ultra-high bandwidth, optical communication also provides mode division multiplexing (MDM), which increases channel capacity by multiplexing signals of different modes in a single optical waveguide.

[0003] Silicon-based integrated optics technology has been proven to be a major approach to meet optical communication requirements by miniaturizing optical components and circuits on planar substrates. However, this approach still faces a technical challenge in its application, namely that 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 distributions, effective refractive indices, and waveguide losses in the waveguide. When the performance of photonic devices is affected by the polarization state of the input light, it will lead to problems such as polarization-dependent loss, polarization mode dispersion, and polarization dependence of the operating wavelength.

[0004] In optical fiber communication systems, optical transmission modules usually use ordinary optical fibers as transmission media, which makes it difficult to ensure 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 polarization state of the input light will make the performance of optical devices very unstable, so solving the polarization correlation of optical devices is an important challenge. Currently, there are two types of photonic devices based on silicon on insulator (SOI) reported for polarization beam splitting and rotation: those based on mode coupling and those based on mode evolution. However, these structures have their own shortcomings, which affect the final performance of the device. The polarization beam splitter rotator based on the mode coupling principle realizes mode conversion through a directional coupler structure. The mode separation and conversion can be achieved through one-step cross-polarization coupling. 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 a 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 has a small process tolerance.

[0005] Based on the principle of mode evolution, the polarization beam splitter rotator converts the input TM0 mode into a high-order TE1 mode, 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, this type of polarization beam splitter rotator has a complex structure, but has the characteristics of large bandwidth and large tolerance. Summary of the invention

[0006] In view of the problems and shortcomings of the above-mentioned prior art, the present invention provides a polarization-independent conversion device that can effectively compensate 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, and obtain a polarization-independent mode converter with excellent performance. The device has the advantages of low optical loss, low crosstalk and high conversion efficiency.

[0007] The technical solution of the present invention is: a polarization-independent conversion device, 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 layer, wherein the device layer includes an input optical waveguide, a polarization beam splitter rotator 100, a phase shifter assembly 200, an optical beam splitter assembly 300, a Y-branch waveguide assembly 400, a cross waveguide 500, and an output optical waveguide;

[0008] The phase shifter assembly 200 includes a phase shifter I 210 and a phase shifter II 220;

[0009] The optical beam splitting assembly 300 includes a multimode interference coupler I 310 and a multimode interference coupler II 320;

[0010] The Y-branch waveguide assembly 400 includes a Y-branch waveguide I 410 , a Y-branch waveguide II 420 , and a Y-branch waveguide III 430 ;

[0011] The input end of the polarization beam splitter rotator 100 is connected to the input optical fiber;

[0012] The through end of the polarization beam splitter rotator 100 is connected to the input end of the phase shifter I210, and the output end of the phase shifter I210 is connected to the input end of the multimode interference coupler I310; the cross end of the polarization beam splitter rotator 100 is connected to the input end of the multimode interference coupler II320; the lower output end of the multimode interference coupler I310 and the upper output end of the multimode interference coupler II320 are respectively connected to the upper input end and the lower input end of the Y branch waveguide I410; the upper output end of the multimode interference coupler I310 and the output end of the Y branch waveguide I410 are respectively connected to the input end of the multimode interference coupler I310 and the output end of the Y branch waveguide I410. The ends are respectively connected to the upper port and the left port of the cross waveguide 500; the lower port of the cross waveguide 500 and the lower output end of the multimode interference coupler II 320 are respectively connected to the upper input end and the lower input end of the Y branch waveguide II 420; the right port of the cross waveguide 500 is connected to the input end of the phase shifter II 220, and the output end of the phase shifter II 220 and the output end of the Y branch waveguide II 420 are respectively connected to the upper and lower input ends of the Y branch waveguide III 430; the output end of the Y branch waveguide III 430 is connected to the output optical waveguide.

[0013] As a further solution of the present invention, the optical signal input by the input optical fiber passes through the straight end of the polarization beam splitter rotator 100, the phase shifter I210, and the multimode interference coupler I310 in sequence; the cross end of the polarization beam splitter rotator 100 outputs an optical signal to the multimode interference coupler II320, and the two optical signals output from the upper output end of the multimode interference coupler II320 and the lower output end of the multimode interference coupler I310 enter the Y branch waveguide I410 to achieve the first superposition output, and the output signal of the upper output end of the multimode interference coupler I310 and the first superposition optical signal output from the output end of the Y branch waveguide I410 are respectively input into the cross waveguide 50 0; the optical signals output from the lower port of the cross waveguide 500 and the lower output end of the multimode interference coupler II 320 are respectively input to the upper input end and the lower input end of the Y branch waveguide II 420 to realize the second superposition output; the optical signal output from the right port of the cross waveguide 500 is input to the input end of the phase shifter II 220, and the optical signal output from the output end of the phase shifter II 220 and the second superposition optical signal output from the output end of the Y branch waveguide II 420 are respectively input to the upper and lower input ends of the Y branch waveguide III 430 to realize the third superposition output; the third superposition optical signal output from the output end of the Y branch waveguide III 430 is input to the output optical waveguide.

[0014] As a further solution of the present invention, the polarization beam splitter rotator 100 is composed of an asymmetric directional coupling structure composed of two ridge waveguides of different widths to realize the conversion and separation of TM mode to TE mode. The conversion principle is based on the mode coupling principle, so that the effective refractive index of the TM0 mode in the multimode waveguide is equal to the effective refractive index of the TE0 mode in the waveguide coupler, that is, the phase matching condition is met to realize the separation of the multimode mode hybridization zone, the TE mode is output from one of the output ends, and the TM mode is converted into the corresponding TE mode in the waveguide coupler and output from the other output end. Therefore, no matter whether the input mode of the polarization beam splitter rotator 100 is a single TE mode, a TM mode, or a mixed input of a TE mode and a TM mode, the output optical waveguide finally outputs a TE mode, and the output channels are different. At the same time, the polarization beam splitter rotator realized by the asymmetric directional coupling structure can realize a device structure with excellent performance, simple structure and small size.

[0015] As a further solution of the present invention, by setting the phase shifter I210, the phase shifter II220 or the waveguide length difference, the phase difference of the optical signals at the upper and lower input ends of the Y-branch waveguide I410, the Y-branch waveguide II420, and the Y-branch waveguide III430 is 0, the phases of the optical signals at the input ends of the multimode interference coupler I310 and the multimode interference coupler II320 are the same, and the optical signals are all TE mode.

[0016] As a further solution of the present invention, the waveguide length of the upper input port connecting the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 needs to satisfy that the transmission of the light wave experiences an integer number of cycles compared to the light wave at the lower input end of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430, and the mode conversion of the polarization-independent conversion device is based on the mode coupling principle, that is, it satisfies the phase matching condition. The Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 should satisfy the phase difference of 0, that is, the optimal position for interference enhancement, and the amplitude of the synthetic wave is the sum of the amplitudes of the coherent light waves. The coherent light waves can be expressed as:

[0017]

[0018] Where E a0 is the peak value of the amplitude of the first wave, E b0 is the peak value of the amplitude of the second wave, is the phase of the first wave, is the phase of the second wave, and ω is the angular frequency. According to the principle of light wave interference, the superimposed light wave can be expressed as:

[0019]

[0020] The formula for calculating the synthetic wave amplitude is as follows

[0021]

[0022] In the formula is the square of the amplitude of the composite wave. The amplitude of the superimposed light wave depends on the phase difference between the two light waves at the superimposed position. When , the amplitude E0 reaches its maximum value.

[0023] The phase of the light wave changes as the propagation path changes, so the appropriate cascade position must be determined to improve the mode coupling ratio:

[0024]

[0025] As a further solution of the present invention, the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 satisfy the optimal position where the phase difference is 0, i.e., interference enhancement, and the synthetic wave amplitude is the sum of the amplitudes of the coherent light waves; the light intensities input to the upper input end and the lower input end of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 are inconsistent. According to the interference principle of light waves, the light intensity output from the output end of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 is still 1.

[0026] As a further solution of the present invention, the phase shifter I210 is used to adjust the phase of the TE mode wave directly coming out of the polarization beam splitter rotator 100. An output channel is selected from each of the output channels of the multimode interference coupler 310 and the multimode interference coupler 320 to connect to the Y-branch waveguide 410 with two completely identical waveguides. The phase difference of the waves input from the lower output end of the multimode interference coupler I310 and the upper output end of the multimode interference coupler II320 to the upper input end and the lower input end of the Y-branch waveguide I410 is zero. According to the interference enhancement principle of coherent waves, the wave at the input end of the Y-branch waveguide I410 is superimposed for the first time with a phase difference of zero.

[0027] As a further solution of the present invention, the multimode interference coupler I310 and the multimode interference coupler II320 are both 1×2 ports, which are used to split a beam of light into two beams of light. The upper output end of the multimode interference coupler I310 transmits the optical signal to the upper input end of the Y branch waveguide II420 through the cross waveguide 500; the lower output port of the multimode interference coupler II320 transmits the optical signal to the lower input end of the Y branch waveguide II420;

[0028] The upper output of the multimode interference coupler 310 and the lower output port of the multimode interference coupler 320 use exactly the same two waveguides, with only a difference in length. The length of one waveguide satisfies that the light wave is transmitted through an integer number of cycles compared to the light wave of the other waveguide, that is, the length of the waveguide connected to the upper input port of the Y-branch waveguide 420 satisfies that the light wave is transmitted through an integer number of cycles compared to the light wave of the lower input port of the Y-branch waveguide 420, so as to ensure that the second superposition can be performed with a phase difference of zero in the Y-branch waveguide II 420.

[0029] As a further solution of the present invention, the waveguide output by the Y-branch waveguide I410 is first connected to the phase shifter II220 and then connected together with the waveguide output by the Y-branch waveguide II420 to the Y-branch waveguide III430 to ensure that a third superposition can be performed with a phase difference of zero, and finally connected to the output optical waveguide to output the TE mode.

[0030] As a further solution of the present invention, the input mode of the polarization-independent conversion device is a single TE mode, a TM mode, or a mixture of a TE mode and a TM mode, and finally the TE mode is output in the output optical waveguide.

[0031] The beneficial effects of the present invention are:

[0032] 1. In the present invention, the polarization beam splitter rotator converts the TM mode in the optical signal in the input optical waveguide into the TE mode; the phase shifter component makes the phase difference of the light waves entering the two multimode interference coupler input ends in the optical beam splitting component to be 0; the optical beam splitting component performs equal power division of light; the Y-branch waveguide superimposes the signal and finally outputs the TE mode;

[0033] 2. The present invention can effectively make up for the defects of polarization beam splitters based on the mode coupling principle and polarization beam splitters based on the mode evolution principle, and obtain a polarization-independent mode converter with excellent performance;

[0034] 3. The input mode of the optical waveguide of the present invention can be TE mode, TM mode or a mixture of TE and TM mode, and finally the output optical waveguide outputs TE mode;

[0035] 4. The polarization beam splitter rotator implemented by the present invention using an asymmetric directional coupling structure can achieve a device structure with excellent performance, simple structure and small size;

[0036] 5. The present invention has the advantages of low light loss, low crosstalk and high conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic structural diagram of a polarization-independent conversion device of the present invention;

[0038] Figure 2A schematic diagram of the structure of a Y-branch waveguide in an example of the present invention;

[0039] The numbers in the figure are: 100-polarization beam splitter rotator, 200-phase shifter assembly, 210-phase shifter I, 220-phase shifter II, 300-optical beam splitting assembly, 310-multimode interference coupler I, 320-multimode interference coupler II, 400-Y branch waveguide assembly, 410-Y branch waveguide I, 420-Y branch waveguide II, 430-Y branch waveguide III, 500-cross waveguide, input1-upper input end; input2-lower input end; output-output end. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] 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.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0045] Example 1: Figure 1As shown, a polarization-independent conversion device 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 layer, characterized in that: the device layer includes an input optical waveguide, a polarization beam splitter rotator 100, a phase shifter assembly 200, an optical beam splitter assembly 300, a Y-branch waveguide assembly 400, a cross waveguide 500, and an output optical waveguide;

[0046] The phase shifter assembly 200 includes a phase shifter I 210 and a phase shifter II 220;

[0047] The optical beam splitting assembly 300 includes a multimode interference coupler I 310 and a multimode interference coupler II 320;

[0048] The Y-branch waveguide assembly 400 includes a Y-branch waveguide I 410 , a Y-branch waveguide II 420 , and a Y-branch waveguide III 430 ;

[0049] The input end of the polarization beam splitter rotator 100 is connected to the input optical fiber;

[0050] The through end of the polarization beam splitter rotator 100 is connected to the input end of the phase shifter I210, and the output end of the phase shifter I210 is connected to the input end of the multimode interference coupler I310; the cross end of the polarization beam splitter rotator 100 is connected to the input end of the multimode interference coupler II320; the lower output end of the multimode interference coupler I310 and the upper output end of the multimode interference coupler II320 are respectively connected to the upper input end and the lower input end of the Y branch waveguide I410; the upper output end of the multimode interference coupler I310 and the output end of the Y branch waveguide I410 are respectively connected to the input end of the multimode interference coupler I310 and the output end of the Y branch waveguide I410. The ends are respectively connected to the upper port and the left port of the cross waveguide 500; the lower port of the cross waveguide 500 and the lower output end of the multimode interference coupler II 320 are respectively connected to the upper input end and the lower input end of the Y branch waveguide II 420; the right port of the cross waveguide 500 is connected to the input end of the phase shifter II 220, and the output end of the phase shifter II 220 and the output end of the Y branch waveguide II 420 are respectively connected to the upper and lower input ends of the Y branch waveguide III 430; the output end of the Y branch waveguide III 430 is connected to the output optical waveguide.

[0051] The optical signal input by the input optical fiber passes through the straight end of the polarization beam splitter rotator 100, the phase shifter I210, and the multimode interference coupler I310 in sequence; the cross end of the polarization beam splitter rotator 100 outputs an optical signal to the multimode interference coupler II320, and the two optical signals output from the upper output end of the multimode interference coupler II320 and the lower output end of the multimode interference coupler I310 enter the Y branch waveguide I410 to achieve the first superposition output, and the output signal of the upper output end of the multimode interference coupler I310 and the first superposition optical signal output from the output end of the Y branch waveguide I410 are respectively input to the upper port and the lower port of the cross waveguide 500. Left port; the optical signals output from the lower port of the cross waveguide 500 and the lower output end of the multimode interference coupler II 320 are respectively input into the upper input end and the lower input end of the Y branch waveguide II 420 to realize the second superposition output; the optical signal output from the right port of the cross waveguide 500 is input into the input end of the phase shifter II 220, and the optical signal output from the output end of the phase shifter II 220 and the second superposition optical signal output from the output end of the Y branch waveguide II 420 are respectively input into the upper and lower input ends of the Y branch waveguide III 430 to realize the third superposition output; the third superposition optical signal output from the output end of the Y branch waveguide III 430 is input into the output optical waveguide.

[0052] The polarization beam splitter rotator 100 is composed of an asymmetric directional coupling structure composed of two ridge waveguides of different widths to realize the conversion and separation of TM mode to TE mode. The conversion principle is based on the mode coupling principle, so that the effective refractive index of the TM0 mode in the multimode waveguide is equal to the effective refractive index of the TE0 mode in the waveguide coupler, that is, the phase matching condition is met to realize the separation of the multimode mode hybridization zone, the TE mode is output from one of the output ends, and the TM mode is converted into the corresponding TE mode in the waveguide coupler and output from the other output end. Therefore, no matter whether the input mode of the polarization beam splitter rotator 100 is a single TE mode, a TM mode or a mixed input of a TE mode and a TM mode, the output optical waveguide finally outputs a TE mode, and the output channels are different. At the same time, the polarization beam splitter rotator realized by the asymmetric directional coupling structure can realize a device structure with excellent performance, simple structure and small size.

[0053] By setting the phase shifter I210, the phase shifter II220 or the waveguide length difference, the phase difference of the optical signals at the upper and lower input ends of the Y-branch waveguide I410, the Y-branch waveguide II420, and the Y-branch waveguide III430 is 0, the phases of the optical signals at the input ends of the multimode interference coupler I310 and the multimode interference coupler II320 are the same, and the optical signals are all in TE mode.

[0054] The connecting waveguide length of the upper input end of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 needs to satisfy the transmission of the light wave at the lower input end of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430. The mode conversion of the polarization-independent conversion device is based on the mode coupling principle, that is, it satisfies the phase matching condition. The Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 should meet the phase difference of 0, that is, the optimal position for interference enhancement, and the amplitude of the synthetic wave is the sum of the amplitudes of the coherent light waves. The coherent light waves can be expressed as:

[0055]

[0056] Where E a0 is the peak value of the amplitude of the first wave, E b0 is the peak value of the amplitude of the second wave, is the phase of the first wave, is the phase of the second wave, and ω is the angular frequency. According to the principle of light wave interference, the superimposed light wave can be expressed as:

[0057]

[0058] The formula for calculating the synthetic wave amplitude is as follows

[0059]

[0060] In the formula is the square of the amplitude of the composite wave. The amplitude of the superimposed light wave depends on the phase difference between the two light waves at the superimposed position. When , the amplitude E0 reaches its maximum value.

[0061] The phase of the light wave changes as the propagation path changes, so the appropriate cascade position must be determined to improve the mode coupling ratio:

[0062]

[0063] The Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 satisfy the optimal position where the phase difference is 0, i.e., interference enhancement, and the synthetic wave amplitude is the sum of the amplitudes of the coherent light waves; the light intensities input to the upper input end and the lower input end of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 are inconsistent. According to the interference principle of light waves, the light intensity output from the output ends of the Y-branch waveguide I410, Y-branch waveguide II420, and Y-branch waveguide III430 is still 1.

[0064] The phase shifter I 210 is used to adjust the phase of the TE mode wave directly coming out of the polarization beam splitter rotator 100. An output channel is selected from each of the output channels of the multimode interference coupler 310 and the multimode interference coupler 320 to connect to the Y branch waveguide 410 with two completely identical waveguides. The phase difference of the waves input from the lower output end of the multimode interference coupler I 310 and the upper output end of the multimode interference coupler II 320 to the upper input end and the lower input end of the Y branch waveguide I 410 is zero. According to the interference enhancement principle of coherent waves, the wave at the input end of the Y branch waveguide I 410 is superimposed for the first time with a phase difference of zero.

[0065] The multimode interference coupler I 310 and the multimode interference coupler II 320 are both 1×2 ports, which are used to split a beam of light into two beams of light. The upper output end of the multimode interference coupler I 310 transmits the optical signal to the upper input end of the Y branch waveguide II 420 through the cross waveguide 500; the lower output port of the multimode interference coupler II 320 transmits the optical signal to the lower input end of the Y branch waveguide II 420;

[0066] The upper output of the multimode interference coupler 310 and the lower output port of the multimode interference coupler 320 use exactly the same two waveguides, with only a difference in length. The length of one waveguide satisfies that the light wave is transmitted through an integer number of cycles compared to the light wave of the other waveguide, that is, the length of the waveguide connected to the upper input port of the Y-branch waveguide 420 satisfies that the light wave is transmitted through an integer number of cycles compared to the light wave of the lower input port of the Y-branch waveguide 420, so as to ensure that the second superposition can be performed with a phase difference of zero in the Y-branch waveguide II 420.

[0067] The waveguide output from the Y-branch waveguide I 410 is first connected to the phase shifter II 220 and then connected together with the waveguide output from the Y-branch waveguide II 420 to the Y-branch waveguide III 430 to ensure that the third superposition can be performed with a phase difference of zero, and finally connected to the output optical waveguide to output the TE mode.

[0068] The polarization-independent conversion device inputs a single TE mode, a TM mode, or a mixture of a TE mode and a TM mode, and finally outputs a TE mode in an output optical waveguide.

[0069] The method for preparing a polarization-independent conversion device described in this embodiment is a conventional method, and the specific process is as follows:

[0070] 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 2μm. 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.

[0071] Step 2: Using the PEVCD process, 50nm thick silicon dioxide is deposited on the surface of the silicon wafer as a hard mask for etching the silicon waveguide, and then photoresist is applied. The mask designed on the SOI wafer is precisely aligned and then exposed, and the polarization beam rotator 100, phase shifter I 210, phase shifter II 220, multimode interference coupler I 310, multimode interference coupler II 320, Y branch waveguide I 410, Y branch waveguide II 420, Y branch waveguide III 430, cross waveguide 500 and other patterns designed on the mask are transferred to the photoresist.

[0072] Step three: remove the residual photoresist and clean it, and perform an etching process on the top silicon of the silicon-based wafer to transfer the exposed pattern on the photoresist to the thin film material, thereby obtaining the preliminary structure of the polarization beam rotator 100, phase shifter I210, phase shifter II220, multimode interference coupler I310, multimode interference coupler II320, Y-branch waveguide I410, Y-branch waveguide II420, Y-branch waveguide III430, and cross waveguide 500.

[0073] Step 4: Use PEVCD to deposit silicon dioxide as a dielectric thin film, chemically polish the surface of the obtained silicon dioxide layer to obtain a smooth plane, and then clean it; use LPVCD technology to deposit a silicon layer, polish it, and then perform photolithography. The photolithography includes spinning, exposure, development, drying, etching, and finally debonding and cleaning to obtain a complete ridge waveguide and strip waveguide structure, and complete the preparation of the polarization beam splitter rotator 100, phase shifter I210, phase shifter II220, multimode interference coupler I310, multimode interference coupler II320, Y-branch waveguide I410, Y-branch waveguide II420, Y-branch waveguide III430, and cross waveguide 500 structures.

[0074] Step 5: To ensure stable operation of the device, PEVCD is used to deposit dielectric thin film silicon dioxide with a deposition thickness of 3 μm. A chemical mechanical planarization (CMP) process is used to form a smooth surface and then clean it to obtain the final structure.

[0075] 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 conversion device, 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 layer, characterized in that: The device layer comprises an input optical waveguide, a polarization beam splitter rotator (100), a phase shifter component (200), an optical beam splitter component (300), a Y-branch waveguide component (400), a cross waveguide (500) and an output optical waveguide; The phase shifter assembly (200) comprises a phase shifter I (210) and a phase shifter II (220); The optical beam splitting component (300) comprises a multimode interference coupler I (310) and a multimode interference coupler II (320); The Y-branch waveguide assembly (400) comprises a Y-branch waveguide I (410), a Y-branch waveguide II (420), and a Y-branch waveguide III (430); The input end of the polarization beam splitter rotator (100) is connected to an input optical fiber; The through end of the polarization beam splitter rotator (100) is connected to the input end of the phase shifter I (210), and the output end of the phase shifter I (210) is connected to the input end of the multimode interference coupler I (310); the cross end of the polarization beam splitter rotator (100) is connected to the input end of the multimode interference coupler II (320); the lower output end of the multimode interference coupler I (310) and the upper output end of the multimode interference coupler II (320) are respectively connected to the upper input end and the lower input end of the Y branch waveguide I (410); the upper output end of the multimode interference coupler I (310) and the input end of the Y branch waveguide I (410) are respectively connected to the input end of the multimode interference coupler I (310). The output end is respectively connected to the upper port and the left port of the cross waveguide (500); the lower port of the cross waveguide (500) and the lower output end of the multimode interference coupler II (320) are respectively connected to the upper input end and the lower input end of the Y branch waveguide II (420); the right port of the cross waveguide (500) is connected to the input end of the phase shifter II (220); the output end of the phase shifter II (220) and the output end of the Y branch waveguide II (420) are respectively connected to the upper and lower input ends of the Y branch waveguide III (430); the output end of the Y branch waveguide III (430) is connected to the output optical waveguide.

2. A polarization-independent conversion device according to claim 1, characterized in that: The optical signal inputted by the input optical fiber passes through the straight-through end of the polarization beam splitter (100), the phase shifter I (210), and the multimode interference coupler I (310) in sequence; the cross end of the polarization beam splitter (100) outputs the optical signal to the multimode interference coupler II (320); the two optical signals outputted from the upper output end of the multimode interference coupler II (320) and the lower output end of the multimode interference coupler I (310) enter the Y-branch waveguide I (410) to realize the first superposition output; the output signal of the upper output end of the multimode interference coupler I (310) and the first superposition optical signal outputted from the output end of the Y-branch waveguide I (410) are respectively inputted into the upper port of the cross waveguide (500) and left port; the optical signals output from the lower port of the cross waveguide (500) and the lower output end of the multimode interference coupler II (320) are respectively input into the upper input end and the lower input end of the Y branch waveguide II (420) to realize the second superposition output; the optical signal output from the right port of the cross waveguide (500) is input into the input end of the phase shifter II (220), the optical signal output from the output end of the phase shifter II (220) and the second superposition optical signal output from the output end of the Y branch waveguide II (420) are respectively input into the upper and lower input ends of the Y branch waveguide III (430) to realize the third superposition output; the third superposition optical signal output from the output end of the Y branch waveguide III (430) is input into the output optical waveguide.

3. The polarization-independent conversion device according to claim 1, characterized in that: The polarization beam splitter rotator (100) realizes conversion and separation of TM mode to TE mode by an asymmetric directional coupling structure composed of two ridge waveguides of different widths. The conversion principle is based on the mode coupling principle. The input mode of the polarization beam splitter rotator (100) is a single TE mode, a TM mode, or a mixed input of a TE mode and a TM mode. The output optical waveguide finally outputs a TE mode, and the output channels are different.

4. The polarization-independent conversion device according to claim 1, characterized in that: By setting the phase shifter I (210), the phase shifter II (220) or the waveguide length difference, the phase difference of the optical signals at the upper and lower input ends of the Y-branch waveguide I (410), the Y-branch waveguide II (420) and the Y-branch waveguide III (430) is 0, the phases of the optical signals at the input ends of the multimode interference coupler I (310) and the multimode interference coupler II (320) are the same, and the optical signals are all in TE mode.

5. The polarization-independent conversion device according to claim 1, characterized in that: The Y-branch waveguide I (410), Y-branch waveguide II (420) and Y-branch waveguide III (430) are at the optimal position where the phase difference is 0, i.e., interference enhancement is achieved, and the amplitude of the synthetic wave is the sum of the amplitudes of the coherent light waves; the light intensities input to the upper input end and the lower input end of the Y-branch waveguide I (410), Y-branch waveguide II (420) and Y-branch waveguide III (430) are inconsistent, and according to the interference principle of light waves, the light intensities output from the output ends of the Y-branch waveguide I (410), Y-branch waveguide II (420) and Y-branch waveguide III (430) are still 1.

6. The polarization-independent conversion device according to claim 1, characterized in that: The phase shifter I (210) is used to adjust the phase of the TE mode wave directly output from the polarization beam splitter (100). The phase difference of the waves respectively input to the upper input end and the lower input end of the Y branch waveguide I (410) from the lower output end of the multimode interference coupler I (310) and the upper output end of the multimode interference coupler II (320) is zero. According to the interference enhancement principle of coherent waves, the waves at the input end of the Y branch waveguide I (410) are superimposed for the first time with a phase difference of zero.

7. The polarization-independent conversion device according to claim 1, characterized in that: The multimode interference coupler I (310) and the multimode interference coupler II (320) are both 1×2 ports, used to split a beam of light into two beams of light, the upper output end of the multimode interference coupler I (310) transmits the optical signal to the upper input end of the Y branch waveguide II (420) through the cross waveguide (500); the lower output port of the multimode interference coupler II (320) transmits the optical signal to the lower input end of the Y branch waveguide II (420); The upper output of the multimode interference coupler 310 and the lower output port of the multimode interference coupler 320 use two identical waveguides, with only a difference in length. The length of one waveguide satisfies that the light wave is transmitted through an integer number of cycles compared to the light wave of the other waveguide, that is, the length of the waveguide connected to the upper input port of the Y-branch waveguide 420 satisfies that the light wave is transmitted through an integer number of cycles compared to the light wave of the lower input port of the Y-branch waveguide 420, so as to ensure that the second superposition can be performed with a phase difference of zero in the Y-branch waveguide II (420).

8. The polarization-independent conversion device according to claim 1, characterized in that: The waveguide output from the Y-branch waveguide I (410) is first connected to the phase shifter II (220) and then connected together with the waveguide output from the Y-branch waveguide II (420) to the Y-branch waveguide III (430) to ensure that the third superposition can be performed with a phase difference of zero, and finally connected to the output optical waveguide to output the TE mode.

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