A polarization independent conversion device

Abstract

The application relates to a polarization-independent conversion device and belongs to the technical field of semiconductor waveguide communication 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. 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 TM mode in the optical signal in the input optical waveguide into TE mode; the phase shifter assembly makes the phase difference of the optical waves entering the two multimode interference coupler input ends of the optical beam splitting assembly be 0; the optical beam splitting assembly is used for optical equal power division; the Y-branch waveguide superimposes signals, and finally outputs TE mode. The application realizes that, no matter whether the polarization state of the input light is TE mode or TM mode, the output is TE mode, a polarization conversion independent of the input polarization state is realized, and the device structure is excellent in performance, simple in structure and small in size.

Description

TECHNICAL FIELD

[0001] The application relates to a polarization-independent conversion device and belongs to the technical field of semiconductor waveguide communication devices. BACKGROUND

[0002] Optical networks have been widely used, but the current optical network components are different material systems, so that the devices in the current network system are difficult to integrate, the cost is high, the volume is large, and the maintenance is difficult. 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. Because the refractive index of silicon material is large, the silicon photonic communication device based on silicon material has a relatively dense structure; and the process of the silicon photonic communication device is completely compatible with the existing CMOS process, which can realize the on-chip integration of the silicon photonic communication device and the integrated circuit on the silicon substrate, not only effectively reducing the cost of the device, but also reducing the size of the device and improving the reliability of the device. Optical communication system has attracted widespread attention due to its potential in meeting the increasing demand for bandwidth. In addition to the inherent ultra-high bandwidth, optical communication also provides mode division multiplexing (MDM), which increases the channel capacity by multiplexing different mode signals in a single optical waveguide.

[0003] Silicon-based integrated optical technology has been proved to be a major method to meet the requirements of optical communication through miniaturized optical elements and circuits on a planar substrate. However, there is still a technical problem in the application of this method, that is, the material, structure or design of the device may affect the polarization state of light. The mode field distribution, effective refractive index and waveguide loss of the two polarization states TE and TM modes in the waveguide are different, and the performance of the photonic device is affected by the input light polarization state, which will cause polarization-dependent loss, polarization mode dispersion and polarization dependence of the working wavelength.

[0004] In optical fiber communication system, optical transmission module usually uses ordinary optical fiber as transmission medium, which will cause difficulty in guaranteeing the polarization state of input light when coupling light from ordinary optical fiber to rectangular waveguide on silicon-based integrated device. The uncertainty of input light polarization state will make the performance of optical device very unstable, so solving the polarization dependence of optical device is an important challenge. At present, the reported SOI-based photonic devices for polarization beam splitting and rotation include two categories based on mode coupling and mode evolution. But these structures have their own shortcomings, which affect the final performance of the device. The polarization beam splitting and rotation device based on mode coupling principle realizes the transformation of mode through directional coupler structure, and the separation and conversion of mode can be realized by one-step cross-polarization coupling. The device has the advantage of small size, which is conducive to the realization of large-scale integration of chip. But this kind of polarization beam splitting and rotation device based on directional coupling structure needs strict phase matching condition to achieve mode coupling and conversion, so it is sensitive to wavelength and process, has small working bandwidth and small process tolerance.

[0005] The polarization beam splitting and rotation device based on mode evolution principle converts the input TM0 mode into high-order TE1 mode first, then separates the input TE0 mode, and converts TE1 into TE0 mode. The high-order conversion of mode occurs in the mode mixing area of waveguide. Therefore, this kind of polarization beam splitting and rotation device has complex structure, but has the characteristics of large bandwidth and large tolerance. SUMMARY

[0006] In view of the problems and deficiencies of the prior art, the polarization-independent conversion device can effectively compensate for the defects of the polarization beam splitting and rotation device based on mode coupling principle and the polarization beam splitting and rotation device based on 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 scheme of the present application is: a polarization-independent conversion device, from bottom to top, including a wafer substrate, a buried oxygen layer of the wafer, a device layer and a SiO2 upper cladding layer of the device layer. The device layer includes an input optical waveguide, a polarization beam splitting and rotation device 100, a phase shifter assembly 200, an optical beam splitting 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 splitting rotator 100 is connected with an input optical fiber;

[0012] The through end of the polarization beam splitting rotator 100 is connected with the input end of the phase shifter I 210, and the output end of the phase shifter I 210 is connected with the input end of the multimode interference coupler I 310. The cross end of the polarization beam splitting rotator 100 is connected with 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 with 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 output end of the Y branch waveguide I 410 are respectively connected with 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 with 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 with 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 with the upper input end and the lower input end of the Y branch waveguide III 430. The output end of the Y branch waveguide III 430 is connected with an output optical waveguide.

[0013] As a further scheme of the present application, the optical signal input by the input optical fiber is sequentially input to the through end of the polarization beam splitting rotator 100, the phase shifter I 210 and the multimode interference coupler I 310. The optical signal output by the cross end of the polarization beam splitting rotator 100 is input to the multimode interference coupler II 320. The two optical signals output by the upper output end of the multimode interference coupler II 320 and the lower output end of the multimode interference coupler I 310 are input to the Y branch waveguide I 410 to realize first superposition output. The optical signal output by the upper output end of the multimode interference coupler I 310 and the first superposition optical signal output by the output end of the Y branch waveguide I 410 are respectively input to the upper port and the left port of the cross waveguide 500. The optical signals output by 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 second superposition output. The optical signal output by the right port of the cross waveguide 500 is input to the input end of the phase shifter II 220. The optical signal output by the output end of the phase shifter II 220 and the second superposition optical signal output by the output end of the Y branch waveguide II 420 are respectively input to the upper input end and the lower input end of the Y branch waveguide III 430 to realize third superposition output. The third superposition optical signal output by the output end of the Y branch waveguide III 430 is input to the output optical waveguide.

[0014] As a further scheme of the present application, the polarization beam splitting rotator 100 is realized by an asymmetric directional coupling structure composed of two ridge waveguides with different widths to realize the conversion and separation of TM mode to TE mode, the conversion principle is based on the mode coupling principle, the effective refractive index of TM0 mode in the multimode waveguide is equal to the effective refractive index of TE0 mode in the waveguide coupler, that is, the phase matching condition is satisfied to realize the separation of the multimode hybrid region, 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, so whether the input mode of the polarization beam splitting rotator 100 is a single TE mode, a single TM mode or a mixed input of TE mode and TM mode, the output optical waveguide finally outputs TE mode, and the output channels are different, and the polarization beam splitting rotator realized by using the asymmetric directional coupling structure can realize a device structure with excellent performance, simple structure and small size.

[0015] As a further scheme of the present application, by setting the phase shifter I 210, the phase shifter II 220 or the waveguide length difference, the phase difference of the optical signals input from 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, and the phase of the optical signals input from the input ends of the multimode interference coupler I 310 and the multimode interference coupler II 320 is the same, and the optical signals are TE modes.

[0016] As a further scheme of the present application, the waveguide length connecting the upper input ports of the Y branch waveguide I 410, the Y branch waveguide II 420 and the Y branch waveguide III 430 needs to satisfy that the transmission of the optical wave from the upper input port experiences an integer number of periods compared with the transmission of the optical wave from the lower input port of the Y branch waveguide I 410, the Y branch waveguide II 420 and the Y branch waveguide III 430, and the mode conversion of the polarization independent conversion device is based on the mode coupling principle, that is, the phase matching condition is satisfied. The Y branch waveguide I 410, the Y branch waveguide II 420 and the Y branch waveguide III 430 should satisfy the best position of the phase difference being 0, that is, the interference is enhanced, and the amplitude of the resultant wave is the sum of the amplitudes of the coherent light waves, which can be represented as:

[0017]

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

[0019]

[0020] The amplitude calculation formula of the resultant wave is as follows

[0021]

[0022] wherein is the square of the amplitude of the resultant wave. The amplitude of the superimposed light waves depends on the phase difference of the two light waves at the superimposition position. When the phase difference is zero, the amplitude E0 reaches a maximum value.

[0023] The phase of the light waves changes with the change of the propagation path, so the appropriate superimposition position must be determined to improve the mode coupling ratio:

[0024]

[0025] As a further scheme of the present application, the Y-branch waveguide I 410, Y-branch waveguide II 420, Y-branch waveguide III 430 satisfy the phase difference of 0, i.e. the optimal position of interference enhancement, and the amplitude of the resultant wave is the sum of the amplitudes of the coherent light waves; the light intensities input from the upper input end and the lower input end of the Y-branch waveguide I 410, Y-branch waveguide II 420, Y-branch waveguide III 430 are inconsistent, and according to the interference principle of light waves, the light intensity output from the output end of the Y-branch waveguide I 410, Y-branch waveguide II 420, Y-branch waveguide III 430 is still 1.

[0026] As a further scheme of the present application, the phase shifter I 210 is used to adjust the phase of the TE mode wave directly output from the polarization beam splitter 100, and one output channel is selected from each of the output channels of the multimode interference coupler I 310 and the multimode interference coupler II 320 to be connected to the Y-branch waveguide I 410 through two waveguides in the same way, the phase difference of the waves 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, and according to the interference enhancement principle of coherent waves, the waves input to the Y-branch waveguide I 410 are superimposed for the first time with a phase difference of zero.

[0027] As a further scheme of the present application, the multimode interference coupler I 310 and the multimode interference coupler II 320 are both 1x2 ports, used to divide a light beam into two light beams, the light signal is transmitted from the upper output end of the multimode interference coupler I 310 to the upper input end of the Y-branch waveguide II 420 through the cross waveguide 500; and the light signal is transmitted from the lower output port of the multimode interference coupler II 320 to the lower input end of the Y-branch waveguide II 420.

[0028] The upper output of the multimode interference coupler 310 and the lower output port of the multimode interference coupler 320 use the same two waveguides, only the length is different, one of which satisfies the transmission of the light wave to experience an integer number of cycles of the light wave of the other, that is, the length of the waveguide connected to the upper input port of the Y branch waveguide 420 satisfies the transmission of the light wave to experience an integer number of cycles of the light wave of the lower input of the Y branch waveguide 420, to ensure that the Y branch waveguide II 420 can be superimposed for the second time with a phase difference of zero.

[0029] As a further scheme of the application, the waveguide output by the Y branch waveguide I 410 is first connected to the phase shifter II 220 and then connected to the waveguide output by 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 light waveguide to output TE mode.

[0030] As a further scheme of the application, the mode input by the polarization-independent conversion device is a single TE mode, a single TM mode or a mixed input of TE mode and TM mode, and finally outputs TE mode in the output light waveguide.

[0031] The beneficial effects of the application are:

[0032] 1. In the application, the polarization beam splitting rotator converts the TM mode in the input light waveguide into TE mode; the phase shifter assembly makes the phase difference of the light waves entering the input ends of the two multimode interference couplers in the light splitting assembly 0; the light splitting assembly performs equal power splitting of light; the Y branch waveguide superimposes the signals and finally outputs TE mode;

[0033] 2. The application can effectively compensate for the defects caused by the polarization beam splitting rotator based on the mode coupling principle and the polarization beam splitting rotator based on the mode evolution principle, and obtain a polarization-independent mode converter with excellent performance;

[0034] 3. The mode input by the input light waveguide of the application can be TE mode, TM mode or mixed input of TE mode and TM mode, and finally TE mode is output in the output light waveguide;

[0035] 4. The polarization beam splitting rotator realized by using the asymmetric directional coupling structure in the application can realize a device structure with excellent performance, simple structure and small size;

[0036] 5. The application has the advantages of low optical loss, low crosstalk and high conversion efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a structural schematic view of a polarization-independent conversion device of the application;

[0038] Figure 2Structure diagram of Y-branch waveguide in the example of the present application;

[0039] In the figure: 100-polarization beam splitting 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 solutions of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0041] In the description of the present application, it should be noted that the directions or positional relationships described based on the drawings, such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the ordinal numbers (such as "first and second", "first to fourth", etc.) are used to distinguish objects and are not limited to the order, and cannot be understood as indicating or implying relative importance.

[0042] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

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

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

[0045] Embodiment 1: as Figure 1As shown, a polarization-independent conversion device comprises, from bottom to top, a substrate of a wafer, a buried oxide layer of the wafer, 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 splitting rotator 100, a phase shifter assembly 200, an optical beam splitting assembly 300, a Y-branch waveguide assembly 400, a cross waveguide 500, and an output optical waveguide.

[0046] The phase shifter assembly 200 comprises a phase shifter I 210 and a phase shifter II 220.

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

[0048] 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.

[0049] The polarization beam splitting rotator 100 is connected to an input optical fiber.

[0050] The polarization beam splitting rotator 100 is connected to an input optical fiber. The straight-through end of the polarization beam splitting 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 splitting 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 output end of the Y-branch waveguide I 410 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 input end and the lower input end of the Y-branch waveguide III 430. The output end of the Y-branch waveguide III 430 is connected to an output optical waveguide.

[0051] The input optical fiber input light signal, in turn, through the polarization beam splitter rotator 100 straight through end, phase shifter I 210, multimode interference coupler I 310; polarization beam splitter rotator 100 cross end output light signal to multimode interference coupler II 320, multimode interference coupler II 320 on the output end, multimode interference coupler I 310 lower output end output two beams of light signal into Y branch waveguide I 410 to realize the first superposition output, multimode interference coupler I 310 upper output end output signal and Y branch waveguide I 410 output end output first superposition light signal is input to the cross waveguide 500 upper port and left port respectively; cross waveguide 500 lower port and multimode interference coupler II 320 lower output end output light signal is input to Y branch waveguide II 420 upper input end, lower input end to realize the second superposition output; cross waveguide 500 right port output light signal is input to the phase shifter II 220 input end, phase shifter II 220 output end output light signal and Y branch waveguide II 420 output end output second superposition light signal is input to Y branch waveguide III 430 upper, lower input end to realize the third superposition output; Y branch waveguide III 430 output end output third superposition light signal is input to the output optical waveguide.

[0052] The polarization beam splitter rotator 100 is realized by the asymmetric directional coupling structure of two ridge waveguiders with different widths to realize the conversion and separation of TM mode to TE mode, the conversion principle is based on the mode coupling principle, the effective refractive index of TM0 mode in multimode waveguide is equal to the effective refractive index of TE0 mode in waveguide coupler, that is, the phase matching condition is satisfied to realize the separation of multimode mode hybridization area, TE mode is output from one of the output ends, TM mode is converted into the corresponding TE mode in waveguide coupler and output from the other output end, so whether the polarization beam splitter rotator 100 input mode is single TE mode, TM mode or TE mode and TM mode mixed input, the output optical waveguide finally outputs TE mode, and the output channels are different, and the polarization beam splitter rotator realized by using asymmetric directional coupling structure can realize excellent performance, simple structure and small size device structure.

[0053] The phase difference of light signals on the upper and lower input ends of Y branch waveguide I 410, Y branch waveguide II 420 and Y branch waveguide III 430 is 0 by setting phase shifter I 210, phase shifter II 220 or waveguide length difference, the phase of light signals on the input ends of multimode interference coupler I 310 and multimode interference coupler II 320 is the same, and the light signals are TE mode.

[0054] The length of the connecting waveguide of the upper input end of the Y-branch waveguide I 410, the Y-branch waveguide II 420 and the Y-branch waveguide III 430 needs to satisfy that the transmission of the optical wave compared with the optical wave of the lower input end of the Y-branch waveguide I 410, the Y-branch waveguide II 420 and the Y-branch waveguide III 430 experiences an integer number of periods, and the mode conversion of the polarization-independent conversion device is based on the principle of mode coupling, that is, the phase matching condition is satisfied. The phase difference at the Y-branch waveguide I 410, the Y-branch waveguide II 420 and the Y-branch waveguide III 430 should satisfy the best position of interference enhancement, and the amplitude of the synthesized wave is the amplitude of the coherent light wave added, which can be represented as:

[0055]

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

[0057]

[0058] The amplitude of the synthesized wave is calculated as follows

[0059]

[0060] In the formula, E is the square of the amplitude of the synthesized wave. The amplitude of the superimposed light wave depends on the phase difference of the two column light waves at the superposition position. When the phase difference is 0, the amplitude E0 reaches the maximum value.

[0061] The phase of the optical wave changes with the change of the propagation path, so it is necessary to determine the appropriate cascade position to improve the mode coupling ratio:

[0062]

[0063] The Y-branch waveguide I 410, the Y-branch waveguide II 420 and the Y-branch waveguide III 430 satisfy the best position of interference enhancement, that is, the phase difference is 0, and the amplitude of the synthesized wave is the amplitude of the coherent light wave added. The light intensity input from the upper input end and the lower input end of the Y-branch waveguide I 410, the Y-branch waveguide II 420 and the Y-branch waveguide III 430 is inconsistent. According to the principle of optical wave interference, the light intensity output from the output end of the Y-branch waveguide I 410, the Y-branch waveguide II 420 and the Y-branch waveguide III 430 is still 1.

[0064] The phase shifter 210 is used to adjust the phase of the TE mode wave directly from the polarization beam splitter 100, and each of the output channels of the multimode interference coupler 310 and the multimode interference coupler 320 is connected to the Y branch waveguide 410 by using two identical waveguides, the phase difference of the waves input to the upper input end and the lower input end of the Y branch waveguide 410 from the lower output end of the multimode interference coupler 310 and the upper output end of the multimode interference coupler 320 is zero, and the waves input to the upper input end of the Y branch waveguide 410 are superimposed for the first time with a phase difference of zero according to the interference enhancement principle of coherent waves.

[0065] The multimode interference coupler 310 and the multimode interference coupler 320 are both 1x2 ports, and are used to divide a beam of light into two beams of light, the upper output end of the multimode interference coupler 310 transmits the optical signal to the upper input end of the Y branch waveguide 420 through the cross waveguide 500, and the lower output end of the multimode interference coupler 320 transmits the optical signal to the lower input end of the Y branch waveguide 420.

[0066] The upper output end of the multimode interference coupler 310 and the lower output end of the multimode interference coupler 320 use two identical waveguides, and the difference between the two waveguides is only in length, one of the waveguides satisfies that the transmission of the light wave experiences an integer number of periods compared with the transmission of the light wave of the other waveguide, that is, the length of the waveguide connected to the upper input end of the Y branch waveguide 420 satisfies that the transmission of the light wave experiences an integer number of periods compared with the transmission of the light wave of the lower input end of the Y branch waveguide 420, so as to ensure that the waves output by the Y branch waveguide 420 can be superimposed for the second time with a phase difference of zero.

[0067] The waveguide output by the Y branch waveguide 410 is connected to the phase shifter 220 first and then connected to the waveguide output by the Y branch waveguide 420 to the Y branch waveguide 430, so as to ensure that the waves can be superimposed for the third time with a phase difference of zero, and finally connected to the output optical waveguide to output the TE mode.

[0068] The mode input by the polarization-independent conversion device is a single TE mode, a single TM mode or a mixed input of the TE mode and the TM mode, and finally the TE mode is output in the output optical waveguide.

[0069] The preparation method of the polarization-independent conversion device is a conventional method, and the specific process is as follows:

[0070] Step one: first, the SOI wafer is surface pretreated: the SOI wafer with a silicon core layer thickness of 220 nm and a buried silicon dioxide layer thickness of 2 μm is washed with a hydrofluoric acid solution with a proportion of 1:100 for 10 s, then cleaned with deionized water for 10 minutes after the natural oxide layer on the surface is removed, then the SPM solution of concentrated sulfuric acid and hydrogen peroxide is used to clean the organic matter and metal impurities on the silicon surface, then deionized water is used again for 10 minutes, and finally the water is removed by baking.

[0071] Step two: using PEVCD process, depositing 50nm thickness of silicon dioxide on the surface of silicon wafer as hard mask for etching silicon waveguide, then coating photoresist. After accurate alignment of the design on the mask and SOI wafer, exposure is performed, and the patterns of polarization beam splitter 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, etc. on the mask are transferred to the photoresist.

[0072] Step three: removing residual photoresist and cleaning, etching the top layer of silicon of the silicon-based wafer, so as to transfer the exposed patterns on the photoresist to the thin film material, obtaining the preliminary structure of polarization beam splitter 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.

[0073] Step four: using PEVCD to deposit dielectric thin film silicon dioxide again, chemically polishing the surface of the obtained silicon dioxide layer to obtain a smooth plane, and then cleaning; using LPVCD technology to deposit a silicon layer, polishing, then photoetching, including photoresist coating, exposure, development, drying, etching, and finally removing photoresist and cleaning, obtaining complete ridge waveguide and strip waveguide structure, completing the preparation of polarization beam splitter 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 structure.

[0074] Step five: to ensure stable operation of the device, using PEVCD to deposit dielectric thin film silicon dioxide with a thickness of 3μm. After using chemical mechanical planarization (CMP) process to form a smooth plane, cleaning is performed to obtain the final structure.

[0075] The specific embodiments of the application are described in detail above with reference to the accompanying drawings, but the application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the application.

Claims

1. A polarization-independent conversion device, comprising, from bottom to top, a wafer substrate, a buried oxide layer of the wafer, a device layer, and a SiO2 cladding layer on 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-shaped waveguide (500), and an output optical waveguide. The phase shifter assembly (200) includes phase shifter I (210) and phase shifter II (220); The optical beam splitter assembly (300) includes a multimode interference coupler I (310) and a multimode interference coupler II (320); The Y-branch waveguide assembly (400) includes Y-branch waveguide I (410), Y-branch waveguide II (420), and Y-branch waveguide III (430); The input end of the polarization beam splitter (100) is connected to the input optical fiber; The direct end of the polarization beam splitter (100) is connected to the input end of phase shifter I (210), and the output end of phase shifter I (210) is connected to the input end of multimode interference coupler I (310); the cross end of the polarization beam splitter (100) is connected to the input end of multimode interference coupler II (320); the lower output end of multimode interference coupler I (310) and the upper output end of multimode interference coupler II (320) are respectively connected to the upper and lower input ends of Y-branch waveguide I (410); the upper output end of multimode interference coupler I (310) and the output end of Y-branch waveguide I (410) are connected to the lower input end of Y-branch waveguide I (410). The output ends are connected to the upper and left ports of the cross-shaped waveguide (500) respectively; the lower port of the cross-shaped waveguide (500) and the lower output end of the multimode interference coupler II (320) are connected to the upper and lower input ends of the Y-branch waveguide II (420) respectively; the right port of the cross-shaped 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 connected to the upper and lower input ends of the Y-branch waveguide III (430) respectively; the output end of the Y-branch waveguide III (430) is connected to the output optical waveguide.

2. The polarization-independent conversion device according to claim 1, characterized in that: The optical signal input from the input fiber passes sequentially through the direct end of the polarization beam splitter (100), phase shifter I (210), and multimode interference coupler I (310). The optical signal output from the cross end of the polarization beam splitter (100) is sent to multimode interference coupler II (320). The two optical signals output from the upper output end of multimode interference coupler II (320) and the lower output end of multimode interference coupler I (310) enter Y-branch waveguide I (410) to achieve the first superposition output. The output signal from the upper output end of multimode interference coupler I (310) and the first superposition optical signal output from the output end of Y-branch waveguide I (410) are respectively input to the upper port of the cross-shaped waveguide (500). The optical signals output from the lower port of the cross-shaped waveguide (500) and the lower output of the multimode interference coupler II (320) are respectively input to the upper and lower inputs of the Y-branch waveguide II (420) to achieve a second superposition output; the optical signal output from the right port of the cross-shaped waveguide (500) is input to the input of the phase shifter II (220), and the optical signal output from the output of the phase shifter II (220) and the second superposition optical signal output from the output of the Y-branch waveguide II (420) are respectively input to the upper and lower inputs of the Y-branch waveguide III (430) to achieve a third superposition output; the third superposition optical signal output from the output of the Y-branch waveguide III (430) is input to the output optical waveguide.

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

4. The polarization-independent conversion device according to claim 1, characterized in that: By setting phase shifter I (210), phase shifter II (220) or waveguide length difference, the phase difference of the optical signals at the upper and lower input ends of Y-branch waveguide I (410), Y-branch waveguide II (420) and Y-branch waveguide III (430) is 0, the phase of the optical signals at the input ends of multimode interference coupler I (310) and multimode interference coupler II (320) is 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 optimal positions for interference enhancement, where the phase difference is 0 at Y-branch waveguide I (410), Y-branch waveguide II (420), and Y-branch waveguide III (430), are where the synthesized wave amplitude is the sum of the amplitudes of the coherent light waves. The light intensities input to the upper and lower input terminals of Y-branch waveguide I (410), Y-branch waveguide II (420), and Y-branch waveguide III (430) are inconsistent. According to the principle of light wave interference, the light intensity output at the output terminals of Y-branch waveguide I (410), Y-branch waveguide II (420), and Y-branch waveguide III (430) is 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 that comes directly from the polarization beam splitter (100). The phase difference between 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 and lower input ends of the Y-branch waveguide I (410) is zero. According to the principle of interference enhancement 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: Both the multimode interference coupler I (310) and the multimode interference coupler II (320) are 1×2 ports, used to split a beam of light into two beams. The upper output of the multimode interference coupler I (310) transmits the optical signal to the upper input of the Y-branch waveguide II (420) through the cross-shaped waveguide (500); the lower output port of the multimode interference coupler II (320) transmits the optical signal to the lower input of the Y-branch waveguide II (420). The upper output port of the multimode interference coupler (310) and the lower output port of the multimode interference coupler (320) use two identical waveguides, differing only in length. The length of one waveguide satisfies that the light wave travels an integer number of cycles compared to the light wave in the other waveguide. That is, the length of the waveguide connecting the upper input port of the Y-branch waveguide (420) satisfies that the light wave travels an integer number of cycles compared to the light wave at the lower input port of the Y-branch waveguide (420), ensuring that the second superposition can be performed in the Y-branch waveguide II (420) with a phase difference of zero.

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

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