N x N optical switch array and optical switch chip based on polarization-independent mach-zehnder optical switch

Abstract

The application relates to a polarization-independent N*N Mach-Zehnder optical switch array, and 2*2 polarization-independent MZ optical switch units are connected according to a certain topological structure. Any link passes through a plurality of 2*2 polarization-independent MZ optical switch units, a polarization-independent waveguide cross junction and a TE0-TM0 mode switcher. A TE0-TM0 mode switcher is arranged in the middle stage of each link of the array, and is used for converting TE0 and TM0 mode optical signals transmitted by the first half stage of the switch array into TM0 and TE0 modes respectively to continue transmission in the second half stage of the switch array, so that polarization-dependent loss and differential group delay of the polarization-independent optical switch array are effectively reduced, and polarization independence of the switch array on TE0 and TM0 modes is ensured. Moreover, the switch array can be designed and realized on multiple integrated platforms including a 220nm thick SOI platform.

Description

Technical Field

[0001] This invention relates to the field of optical communication device technology, specifically to an N×N optical switch array and optical switch chip based on a polarization-independent Mach-Zehnder optical switch. Background Technology

[0002] In recent years, large-scale integrated optical switch chips have been widely reported on various platforms. In comparison, the integrated SOI platform, with its advantages of compact structure, low power consumption, and CMOS compatibility, better meets the design requirements for realizing large-scale integrated optical switch chips. In particular, the 220nm thick SOI platform has been the most widely researched and applied. However, because integrated optical waveguides generally have birefringence characteristics, most integrated optical switch chips exhibit significant polarization dependence, meaning they typically only support on-chip transmission of light in transverse electric mode (TE). Eliminating the polarization dependence of integrated optical switch chips can not only improve the signal transmission quality in practical applications but also enable the chip to support polarization-multiplexed signal transmission, thereby increasing system capacity. This is of great significance for enhancing the application value of optical switch chips.

[0003] Currently, there are three main technical approaches to realizing polarization-independent switch array chips: polarization diversity, on-chip polarization control, and on-chip polarization insensitivity. Among them, a research team at the Advanced Industrial Science and Technology Research Institute (AIST) in Japan reported a non-replicable 32×32 polarization-independent optical switch chip [K. Suzuki, R. Konoike, N. Yokoyama, M. Seki, M. Ohtsuka, S. Saitoh, S. Suda, H. Matsuura, K. Yamada, S. Namiki, H. Kawashima, K. Ikeda, J. Lightwave Technol. 2020, 38, 226.]. This scheme utilizes the characteristic of the PILOSS structure that has a pair of redundant routing links in any routing state, allowing the optical signal to be split into two polarization components by a polarization beam splitter before entering the chip, and rotating the TM0 component into a TE0 component. The two components are then routed through a pair of redundant links provided by the chip before being combined by another polarization beam splitter to complete the output. A research team from Shanghai Jiao Tong University also reported an 8×8 polarization-independent micro-ring optical switch chip [X.Li,W.Gao,L.Lu,J.Chen,L.Zhou,Photon.Res.2023,11,712.], which consists of cascaded dual micro-ring units connected in a Crossbar structure. The difference lies in the use of an off-chip polarization rotating beam splitter. Both schemes can achieve polarization-independent optical routing using a single chip. However, on the one hand, as the chip size increases, complex on-chip delay compensation is required to ensure that the delay and loss of the redundant links are close; on the other hand, this scheme is only suitable for specific topologies, and PILOSS and Crossbar type switch arrays also struggle to guarantee low-loss and low-crosstalk switching performance as the switch size increases. A research team from Shanghai Jiao Tong University reported a polarization-independent 4×4 optical switch chip based on an on-chip polarization control scheme [X.Li,L.Lu,W.Gao,X.Li,J.Chen,L.Zhou,Chinese.Opt.Lett.2021,19,101302.]. The basic principle of this scheme is to insert an on-chip polarization controller before each input waveguide of the switch array. With the help of optimization algorithms and matched driving circuits, the optical signal of the input array is automatically adjusted to the TE0 mode in real time. Although this scheme is simple in design and compact in structure, it is challenging to realize a high-speed and concise automatic polarization control system. In addition, this scheme does not support polarization multiplexing signal routing.A research team from Zhejiang University [S.Wang, D.Dal.Opt.Lett.2018,43,2531.] and Sun Yat-sen University [H.Yang, Y.Kuan, T.Xiang, Y.Zhu, X.Cai, L.Liu,Opt.Express.2018,26,14340.] reported the realization of a polarization-insensitive optical switch chip using an on-chip polarization-insensitive structure. They implemented a 2×2 polarization-independent 3dB beam splitter and phase shifter on 340nm and 500nm thick silicon platforms, respectively, enabling the optical switching unit to support both TE and TM modes of routing simultaneously. However, on the one hand, the device size of the thick silicon platform is relatively large, which is a disadvantage in the context of large-scale integration requirements. Although a research team from Zhejiang University [Y.Wu, X.Liu, T.Chu, Arxiv:2312.06146, 2023] recently reported a 4×4 polarization-independent switch array on a 340nm thick silicon platform, its size is relatively large and there is still significant room for improvement in the static performance of the switches. Currently, another research team from Zhejiang University [S.Zhao, J.Chen, D.Dai, Y.Shi, APL Photon.2023, 8, 116109.] reported a polarization-independent optical switch unit on a 220nm thick SOI platform, but no arrays on this platform have been reported yet. Furthermore, for polarization-independent optical switch chips constructed from on-chip polarization-insensitive structures, the polarization-dependent loss and differential group delay of any routing path continuously increase with the link length (array size expansion), severely impairing the switching performance of polarization-multiplexed signals. Currently, there is no system design scheme to reduce polarization-dependent loss and differential group delay.

[0004] In summary, the current research status of the three technical approaches to realizing polarization-independent optical switch chips is insufficient to meet the actual needs of large-scale optical switch chips. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention proposes an N×N polarization-independent Mach-Zehnder (MZ) optical switch array chip, which can support implementation on any integrated platform, including a 220nm thick SOI platform, and effectively reduces polarization-dependent loss and differential group delay, supporting high-performance routing of high-speed polarization multiplexed optical signals.

[0006] The technical solution of the present invention is as follows:

[0007] On one hand, this invention provides an N×N optical switch array based on polarization-independent Mach-Zehnder (MZ) optical switches, characterized in that it is composed of several 2×2 polarization-independent MZ units connected according to a specific topology. The N×N optical switch array includes N optical input ports and N optical output ports, with a routing link formed between any two optical input ports and any two optical output ports. This routing link passes through several 2×2 polarization-independent MZ optical switch units, several polarization-independent waveguide cross-junctions, and one TEO-TMO mode switch.

[0008] Furthermore, the 2×2 polarization-independent MZ optical switch unit is used to synchronously switch the TEO / TMO mode optical signals supported by the waveguide.

[0009] Furthermore, the polarization-independent waveguide cross junction is used to synchronously and with low loss transmit TEO / TMO mode optical signals supported by the waveguide through the two cross waveguides.

[0010] Furthermore, the TE0-TM0 mode switch is used to simultaneously convert the TE0 (TM0) mode optical signal of the input waveguide into TM0 (TE0) mode with low loss.

[0011] Furthermore, the topologies include, but are not limited to, PILOSS, Butterfly, Benes and improved Benes, DLN or improved DLN, S&S, Crossbar, etc.

[0012] Furthermore, each routing link is composed of several 2×2 polarization-independent MZ optical switch units and polarization-independent waveguide cross-junctions connected in series via waveguides. A TE0-TM0 mode switch is inserted in the middle stage of each link. The number of 2×2 polarization-independent MZ optical switch units, the number of polarization-independent waveguide cross-junctions, and the length of the connecting waveguides are kept consistent on both sides of the TE0-TM0 mode switch.

[0013] Furthermore, the 2×2 polarization-independent MZ optical switch unit is characterized by comprising an input waveguide I1, an input waveguide I2, an output waveguide O1, an output waveguide O2, a first polarization-independent 3dB coupler, a polarization-independent phase shifter, and a second polarization-independent 3dB coupler. When light is input from the input waveguide I1 (or input waveguide I2) in TE0 (or TM0) mode, it is uniformly split into two beams by the polarization-independent 3dB coupler and then polarization-independent phase shifters are applied to each beam. The two polarization-independent phase shifters simultaneously generate a phase of 0 or π for the TE0 / TM0 modes. After the phase difference, the two beams are combined by a second polarization-independent 3dB coupler. When the polarization-independent phase shifter generates a 0 phase difference, the two beams interfere constructively at the output waveguide O2 (or output waveguide O1) of the 2×2 polarization-independent MZ optical switch unit, thus making the 2×2 polarization-independent MZ optical switch unit work in the crossover state. When the polarization-independent phase shifter generates a π phase difference, the two beams interfere constructively at the output waveguide O1 (or output waveguide O2) of the 2×2 polarization-independent MZ optical switch unit, thus making the 2×2 polarization-independent MZ optical switch unit work in the through state.

[0014] Furthermore, the 2×2 polarization-independent MZ optical switch unit is characterized in that the first polarization-independent 3dB coupler and the second polarization-independent 3dB coupler are adiabatic couplers, multimode interferometers, or cascaded directional couplers.

[0015] Furthermore, the 2×2 polarization-independent MZ optical switch unit is characterized in that the polarization-independent phase shifter is implemented based on the thermo-optic effect or the carrier dispersion effect.

[0016] Furthermore, the polarization-independent waveguide cross junction is characterized by including, but not limited to, two identical nonlinearly broadened waveguides, piecewise linearly broadened waveguides, and vertical intersections of linearly broadened waveguides in a plane. It also includes spatial intersections between multiple waveguides.

[0017] Furthermore, the TE0-TM0 mode switch is characterized by including, but not limited to, various technical approaches such as active mode switching, reverse design, passive mode evolution polarization rotator, passive mode hybrid polarization rotator, and combination of passive TE0-TE1 mode rotator and TE1-TM0 mode converter.

[0018] On the other hand, the N×N optical switch array based on polarization-independent Mach-Zehnder optical switches is characterized in that its design and fabrication platform includes, but is not limited to, silicon (SOI), silicon nitride, (doped) silicon oxide, silicon oxynitride, thin-film lithium niobate, or indium phosphide.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) This invention not only achieves low loss and polarization independence characteristics of arbitrary routing links in N×N optical switch arrays, but also proposes a high-performance on-chip routing scheme for polarization multiplexed signals. By introducing a passive TEO-TMO mode switch in the symmetrical switch array, the TEO and TMO mode optical signals transmitted in the first half of the switch array are converted into TMO and TEO modes respectively, and then transmitted in the second half of the switch array. This allows the TEO / TMO components in the input signal to be routed to the output port with similar loss and delay, reducing the polarization-dependent loss and differential group delay of the chip, enabling the N×N optical switch array to support high-performance routing of high-speed polarization multiplexed signals.

[0021] 2) The key components included in this invention have high process tolerance in their design, including polarization-independent optical switching units, polarization-independent waveguide cross junctions, and TEO-TMO mode switches. This supports the design and implementation of large-scale polarization-independent optical switching systems.

[0022] 3) The N×N polarization-independent optical switch array proposed in this invention can overcome the limitations of the integrated platform, especially the 220nm SOI integrated platform, and can maximize the advantages of the platform such as CMOS compatibility, small size and low loss to achieve large-scale polarization-independent on-chip optical switching. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the N×N optical switch array based on the polarization-independent Mach-Zehnder optical switch of the present invention;

[0024] Figure 2 This is a schematic diagram of the structure of a 2×2 polarization-independent MZ optical switch unit in an N×N optical switch array based on polarization-independent Mach-Zehnder optical switches according to the present invention.

[0025] Figure 3 This is a schematic diagram of the polarization-independent waveguide crossing in the N×N optical switch array based on the polarization-independent Mach-Zehnder optical switch of the present invention. (a) is a schematic diagram of the waveguide crossing structure, (b) is a cross-sectional electric field distribution diagram of TE0 mode, (c) is the transmission and crosstalk spectrum of TE0 mode, (d) is a cross-sectional electric field distribution diagram of TM0 mode, and (e) is the transmission and crosstalk spectrum of TM0 mode.

[0026] Figure 4 This is a schematic diagram of the TE0-TM0 mode switch in the N×N optical switch array based on the polarization-independent Mach-Zehnder optical switch of the present invention;

[0027] Figure 5 This is a schematic diagram of the mode conversion structure in the TE0-TM0 mode switch of this invention;

[0028] Figure 6The diagram shows the operating state and transmission spectrum of the mode conversion structure under TE0 and TM0 mode input conditions, where (a) is the electric field distribution diagram of the mode conversion structure under TE0 mode input, (b) is the transmission and crosstalk spectrum under TE0 mode input, (c) is the electric field distribution diagram of the mode conversion structure under TM0 mode input, and (d) is the transmission and crosstalk spectrum under TM0 mode input.

[0029] Figure 7 The cross-sectional electric field distribution and simulated transmission spectrum of the TE0-TE1 mode switch are shown, where (a) is the structure of the mode switch, (b,c) are the cross-sections of electric field intensity and electric field y-component intensity under TE0 mode input, (d) are the transmission and crosstalk spectrum under TE0 mode input, (e,f) are the cross-sections of electric field intensity and electric field y-component intensity under TE1 mode input, and (g) are the transmission and crosstalk spectrum under TE1 mode input.

[0030] Figure 8 The cross-sectional electric field distribution and simulated transmission spectrum of the TE0-TM0 mode switch are shown, where (a) is the cross-sectional electric field of the mode switch under TE0 mode input, (b) is the transmission and mode crosstalk spectrum under TE0 mode input, (c) is the cross-sectional electric field of the mode switch under TM0 mode input, and (d) is the transmission and mode crosstalk spectrum under TM0 mode input.

[0031] Figure 9 This is a schematic diagram of an embodiment of a 4×4 polarization-independent Mach-Zehnder optical switch array.

[0032] In the picture:

[0033] 1.1 2×2 polarization-independent MZ optical switch unit E N,N Input waveguide I N Output waveguide O N 2.1 Input waveguide I1, 2.2 Input waveguide I2, 2.3 Output waveguide O1, 2.4 Output waveguide O2, 2.5 Vibration-independent 3dB coupler, 2.6 Polarization-independent phase shifter

[0034] 1.2 Polarization-independent waveguide cross junction ME N-1 It is formed by two identical nonlinearly broadened waveguides intersecting perpendicularly in a plane;

[0035] 1.3 TE0-TM0 Mode Switch: 4.1 Mode Conversion Structure, 4.2 TE0-TE1 Mode Switch, 4.3 Mode Conversion Structure Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments, but should not be construed as limiting the scope of protection of the present invention.

[0037] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of an N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to the present invention. In this example, an N×N polarization-independent Mach-Zehnder optical switch array is constructed using a PILOSS structure, as shown in the figure, including N 2 One 2×2 polarization-independent MZ optical switch unit 1.1, (N-1) 2 1.2 One polarization-independent waveguide cross junction and 2N TEO-TMO mode switches 1.3.

[0038] In this embodiment, the N×N polarization-independent Mach-Zehnder optical switch array chip is implemented on a silicon-based 220nm conventional waveguide process platform. The ridge waveguide is 90nm thick and supports transverse electric mode (TEO) and transverse magnetic mode (TMO) transmission. It also supports implementation on platforms with other thicknesses, such as SOI, silicon nitride, (doped) silicon oxide, silicon oxynitride, thin-film lithium niobate, and indium phosphide.

[0039] In this embodiment, the N×N polarization-independent Mach-Zehnder optical switch array is formed by cascading 2×2 polarization-independent MZ optical switch units 1.1 in a PILOSS structure, consisting of N 2 The 2×2 polarization-independent MZ optical switch units 1.1 are arranged into an N-row N-column switch matrix. For any routing link, it needs to pass through (N-1) 2×2 polarization-independent MZ optical switch units 1.1 in the cross state, 1 2×2 polarization-independent MZ optical switch unit 1.1 in the bar state, (N-1) polarization-independent waveguide cross junctions (1.2), and 1 TEO-TMO mode switch 1.3. By changing the position of the switch unit (1.1) in the bar state, the routing link of the chip can be switched. The switch array can also be constructed from switch units (1.1) using classic topologies such as Butterfly, Benes and improved Benes, DLN and improved DLN, S&S, Crossbar, and PILOSS.

[0040] Figure 2This is a schematic diagram of the structure of a 2×2 polarization-independent MZ optical switch unit in an N×N optical switch array based on polarization-independent Mach-Zehnder optical switches according to the present invention. As shown in the figure, the 2×2 polarization-independent MZ optical switch unit 1.1 consists of two input waveguides I1 (2.1) and I2 (2.2), two output waveguides O1 (2.3) and O2 (2.4), a polarization-independent 3dB coupler (2.5), and a polarization-independent phase shifter (2.6). When light is input into waveguide (2.1) (or 2.2) from I1 (or I2) in TE0 (TM0) mode, it is uniformly split into two beams by the first polarization-independent 3dB coupler (2.5) and then input into polarization-independent 3dB phase shifters (2.6). The two polarization-independent phase shifters (2.6) simultaneously generate a phase difference of 0 or π for TE0 / TM0 modes, and then the beams are combined by the second unbalanced polarization-independent 3dB coupler (2.5). When the polarization-independent phase shifter (2.6) generates a phase difference of 0, the two beams interfere constructively at the output waveguide (2.4) (or 2.3) of the switch unit (1.1), and the switch unit operates in the cross state. When the polarization-independent phase shifter (2.6) generates a phase difference of π, the two beams interfere constructively at the output waveguide (2.3) (or 2.4) of the switch unit (1.1), and the switch unit operates in the bar state. The polarization-independent 3dB coupler (2.5) can be implemented by adiabatic couplers, multimode interferometers, cascaded directional couplers, etc.; the polarization-independent phase shifter (2.6) can be implemented based on effects including but not limited to thermo-optical effects and carrier dispersion effects.

[0041] The polarization-independent waveguide cross junction (1.2) in the embodiment is as follows: Figure 3 As shown, it is formed by two identical nonlinearly broadened waveguides (3.1–3.2) perpendicularly intersecting in a plane. Figure 3 The paper also presents the cross-sectional electric field distribution, transmission loss, and crosstalk for TE0 and TM0 modes. The polarization-independent waveguide cross junction (1.2) can also be implemented based on schemes such as combined linearly broadened waveguides and spatial multilayer waveguide cross junctions. The polarization-independent waveguide cross junction (1.2) can also be designed and implemented based on silicon-silicon nitride multilayer waveguide platforms.

[0042] The TE0-TM0 mode switch (1.3) in the embodiment is as follows: Figure 4 As shown, it consists of two mode switching structures (4.1) and (4.3) cascaded together with a TE0-TE1 mode switch (4.2). Figure 5The structure of the mode conversion structure (4.1) and (4.3) is given, which includes a mode converter (5.1) and an adiabatic tapered waveguide (5.2). The mode converter (5.1) has an input cross-section of 220nm × 500nm in a strip waveguide, a gradually linearly transitioning ridge waveguide with dimensions of 220nm × 600nm, and a planar layer size of 90nm × 600nm. The adiabatic tapered waveguide (5.2) has an input cross-section of 220nm × 600nm in a ridge waveguide, a planar layer size of 90nm × 600nm, and a gradually linearly transitioning ridge waveguide with dimensions of 220nm × 1μm. When the TE0 mode is input to the mode conversion structure, the TE0 mode output is maintained; when the TM0 mode is input to the mode conversion structure, the output is gradually converted to the TE1 mode. Figure 6 Simulated transmission spectra of one design example of this structure are presented. The TE0-TE1 mode switch (4.2) is implemented by an axisymmetric, nonlinearly variable width multimode waveguide. Figure 7 The cross-sectional electric field distribution and simulated transmission spectrum of the TE0-TE1 mode switch (4.2) are presented, which can convert the TE0 / TE1 modes of the input waveguide to TE0 / TE1 modes respectively. In summary, Figure 8 The cross-sectional electric field distribution of the TE0-TM0 mode switch 1.3 in the TE0 / TM0 mode input scenario is presented on the simulated transmission spectrum. The TE0-TM0 mode switch can also be designed and implemented based on schemes including reverse design, mode switching, passive mode evolution polarization rotator, and passive mode hybrid polarization rotator.

[0043] Figure 9 This is a schematic diagram of an embodiment of a 4×4 polarization-independent Mach-Zehnder optical switch array. The working principle of the polarization-independent Mach-Zehnder optical switch array is explained below, using N=4 as an example:

[0044] like Figure 9 As shown, a 4×4 optical switch array based on polarization-independent Mach-Zehnder optical switches consists of 4 2 Each link consists of three 2×2 polarization-independent MZ optical switch units connected in a cross-sectional topology. Each link passes through three 2×2 polarization-independent MZ optical switch units in waveguide crossover mode and one 2×2 polarization-independent MZ optical switch unit in waveguide straight-through mode. A TE0-TM0 mode switch is located in the intermediate stage of each link, and a polarization-independent waveguide crossover junction is located at each waveguide crossover point.

[0045] A polarization-multiplexed optical signal containing TE0 and TM0 modes is input from the I1 port into a 4×4 optical switch array, and passes through the polarization-independent MZ switch unit E. 11 E 22After routing, the signal enters the TE0-TM0 mode switch ME3, where the TE0 (TM0) component of the input signal is converted to the TM0 (TE0) component, and then passed through E... 13 and E 14 After routing, the signal is output from port O1 of the switch array. Thus, the TE0 component of the optical signal input from port I1 passes through the first two switch units E in TE0 mode. 11 E 22 With one waveguide cross junction, after passing through the mode switch ME3, it is converted to TM0 mode and then passed through the next two switching units E 13 E 14 And one waveguide cross junction; simultaneously, the TM0 component of the optical signal input from port I1 passes through the first two switching units E in TM0 mode. 11 E 22 With one waveguide cross junction, after passing through the mode switch ME3, it is converted to TE0 mode and then passed through the next two switching units E 13 E 14 And one waveguide cross junction. Since the switching units and waveguide cross junctions are polarization-independent, and all waveguides connecting adjacent switching units have equal lengths, the losses and delays experienced by the TE0 and TM0 components of the input signal from port I1 to port O1 are essentially the same. This effectively reduces the polarization-dependent loss and differential group delay of the polarization-independent optical switch array, enabling it to support the routing of high-speed polarization-multiplexed signals.

Claims

1. An N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch, characterized in that, The N×N optical switch array is composed of several 2×2 polarization-independent MZ units connected according to a topology. It includes N optical input ports and N optical output ports, and a routing link is formed between any optical input port and any optical output port. Each of the routing links passes through several 2×2 polarization-independent MZ optical switch units, several polarization-independent waveguide cross junctions, and one TEO-TMO mode switch. The TE0-TM0 mode switch is located in the middle stage of the routing link to convert the TE0 mode optical signal transmitted in the first half of the routing link into TM0 mode and the TM0 mode optical signal into TE0 mode, so that the TE0 component and TM0 component in the input optical signal experience the same transmission path in the routing link. The number of 2×2 polarization-independent MZ optical switch units, the number of polarization-independent waveguide cross junctions, and the length of the connecting waveguides are kept consistent on both sides of the TE0-TM0 mode switch.

2. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 1, characterized in that, The 2×2 polarization-independent MZ optical switch unit is used to synchronously switch the TEO / TMO mode optical signals supported by the waveguide.

3. The N×N optical switch array based on polarization-independent Mach-Zehnder optical switches according to claim 1, characterized in that, The polarization-independent waveguide cross junction is used to synchronously and with low loss allow TEO / TMO mode optical signals supported by the waveguides to pass through the two cross waveguides.

4. The N×N optical switch array based on polarization-independent Mach-Zehnder optical switches according to claim 1, characterized in that, The TE0-TM0 mode switch is used to simultaneously convert the TE0 (TM0) mode optical signal of the input waveguide into TM0 (TE0) mode with low loss.

5. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 1, characterized in that, The topologies include PILOSS, Butterfly, Benes or improved Benes, DLN or improved DLN, S&S, and Crossbar.

6. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 1, characterized in that, Any routing link is composed of several 2×2 polarization-independent MZ optical switch units and polarization-independent waveguide cross junctions connected in series via waveguides, with a TE0-TM0 mode switch inserted in the middle stage of each link.

7. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 1, characterized in that, When N=2, the system includes input waveguide I1, input waveguide I2, output waveguide O1, output waveguide O2, a first polarization-independent 3dB coupler, a polarization-independent phase shifter, and a second polarization-independent 3dB coupler. When light enters from input waveguide I1 (or input waveguide I2) in TE0 (or TM0) mode, it is uniformly split into two beams by the polarization-independent 3dB coupler and then polarization-independent phase shifters. The two polarization-independent phase shifters simultaneously generate a phase difference of 0 or π for the TE0 / TM0 modes, and then the second polarization-independent 3dB coupler... When the dB coupler combines the beams, and the polarization-independent phase shifter generates a 0-phase difference, the two beams interfere constructively at the output waveguide O2 (or output waveguide O1) of the 2×2 polarization-independent MZ optical switch unit, thus enabling the 2×2 polarization-independent MZ optical switch unit to operate in a crossover state; when the polarization-independent phase shifter generates a π-phase difference, the two beams interfere constructively at the output waveguide O1 (or output waveguide O2) of the 2×2 polarization-independent MZ optical switch unit, thus enabling the 2×2 polarization-independent MZ optical switch unit to operate in a through state.

8. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 7, characterized in that, The first polarization-independent 3dB coupler and the second polarization-independent 3dB coupler can be thermally adiabatic couplers, multimode interferometers, or cascaded directional couplers.

9. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 7, characterized in that, The polarization-independent phase shifter is implemented based on the thermo-optic effect or the carrier dispersion effect.

10. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 1, characterized in that, The polarization-independent waveguide cross junction includes two identical nonlinearly broadened waveguides, piecewise linearly broadened waveguides, and vertical crossovers of linearly broadened waveguides in a plane; it also includes spatial crossovers between multiple waveguides.

11. The N×N optical switch array based on a polarization-independent Mach-Zehnder optical switch according to claim 1 is characterized in that, The TE0-TM0 mode switch includes various technical approaches, such as active mode switching, passive Nanobeam waveguide, passive mode evolution polarization rotator, passive mode hybrid polarization rotator, and combination of passive TE0-TE1 mode rotator and TE1-TM0 mode converter.

Images