Polarization insensitive type 2*2 Mach-Zehnder optical switch based on silicon nitride waveguide device

Abstract

The invention provides a polarization insensitive 2 * 2 Mach-Zehnder optical switch based on a silicon nitride waveguide device. The silicon nitride waveguide layer comprises two optical input waveguides, two 2 * 2 bent waveguide type 3dB directional couplers, two symmetric Mach-Zehnder interference (MZI) arms and two optical output waveguides; two light input waveguides are respectively coupled with two input ports of a first 2 * 2 3dB directional coupler, through two paths of symmetrical MZI arms, a straight waveguide of one MZI arm is attached with a thermode to carry out optical signal phase modulation, output light of the two paths of MZI arms is input to a second 2 * 2 3dB directional coupler, so that the output light of the two paths of MZI arms is combined and interfered, and the output light of the two paths of MZI arms is output to the second 2 * 2 3dB directional coupler. And two paths of output waveguides are respectively led out. Based on the silicon nitride square waveguide and the 2 * 2 bent waveguide type 3dB directional coupler, the directional coupler has the advantages of being insensitive to polarization, large in bandwidth, low in insertion loss, high in extinction ratio and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical communication, and in particular relates to a polarization-insensitive 2×2 Mach-Zehnder switch based on a silicon nitride waveguide device. Background Art

[0002] An optical switch is an optical device with one or more optional transmission ports. Its function is to physically switch or logically operate the optical signal in the optical transmission line or integrated optical circuit. It is a key component of the reconfigurable optical add-drop multiplexing system. Among various types of optical switches, optical switches based on integrated optical waveguide devices have attracted widespread attention due to their compactness, reliability and scalability. As one of the most functionally representative integrated optical switches, the Mach-Zehnder optical switch (MZS) has gradually become a research hotspot.

[0003] In the prior art, Dai Daoxin et al. proposed a low-loss, large-bandwidth silicon thermal Mach-Zehnder switch in 2016, which uses a silicon-on-insulator (SOI) waveguide with a cross-section of 220nm×510nm, with a 140nm operating bandwidth, a loss of less than 1dB, and an extinction ratio greater than 20dB. However, this switch has the disadvantage of polarization sensitivity; in 2024, Shi Yaocheng et al. proposed an ultra-low-loss silicon thermal Mach-Zehnder switch based on a compact fast quasi-adiabatic coupler, which uses a 220nm SOI waveguide, has a loss of 0.25dB and an extinction ratio greater than 17dB in the C+L+S band (1460nm-1625nm), but this switch also exhibits strong polarization dependence. The integration of this device in the system link requires additional polarization management units, which increases the complexity of the system. Compared with silicon waveguides, when the thickness of silicon nitride waveguides can be greater than 600nm, single-mode silicon nitride waveguides with square cross-sections can be prepared. This symmetric property can be used to intuitively realize polarization-insensitive waveguide structures.

[0004] Therefore, it is necessary to further research and develop high-performance MZS based on silicon nitride waveguides to improve its working bandwidth and polarization independence and other indicators to meet higher fiber-optic communication requirements. Summary of the invention

[0005] The present invention provides a polarization-insensitive MZS based on a silicon nitride waveguide device, which is used to solve the problems of small working bandwidth, polarization sensitivity and the like of the MZS based on SOI waveguide in the prior art.

[0006] To achieve the above purpose and other purposes, the present invention provides a polarization-insensitive MZS based on a silicon nitride square waveguide device, wherein the silicon nitride waveguide layer configuration includes two optical input waveguides, two 2×2 bent waveguide type 3dB directional couplers, two symmetrical MZI arms and two optical output waveguides; the two optical input waveguides are respectively connected to two input ports of the input region waveguide of the first 2×2 3dB directional coupler, through two symmetrical MZI arms, one of which is a straight waveguide of the MZI arm with an additional hot electrode to perform optical signal phase modulation, and the output lights of the two MZI arms are input to the second 2×2 3dB directional coupler, so that the output lights of the two MZI arms are combined and interfered, and the two output optical waveguides are respectively led out.

[0007] In the structure, the cross-sections of all waveguide structures are square, and this shape ensures that the waveguide has nearly equal effective refractive index for transverse electric (TE) and transverse magnetic (TM) modes, thereby ensuring polarization independence.

[0008] In the structure, the first 2×2 curved waveguide type 3dB directional coupler includes: two optical input waveguides are respectively coupled with two input ports of the input zone waveguide of the first 2×23dB directional coupler, and the two output ports of the input zone waveguide are respectively connected with the two input ports of two parallel coupled curved waveguides, and the input zone waveguide is used to couple the input light of a certain optical input waveguide into the coupled curved waveguide. The two output ports of the coupled curved waveguide are respectively connected to the two input ports of the output zone waveguide, and the coupled curved waveguide is used to divide the input light into two beams of light with equal intensity and a phase difference of 90°. The output zone waveguide leads out a straight-through output port and a cross output port respectively, and the output zone waveguide is used to avoid crosstalk of the output light. Among them, the input zone waveguide and the output zone waveguide are left-right symmetrical with respect to the coupled curved waveguide.

[0009] In the structure, the two symmetrical MZI arms include: the through output port and the cross output port of the first 2×2 curved waveguide type 3dB directional coupler are respectively connected to the input ports of the two input S curved waveguides that are symmetrical up and down. The output ports of the two input S curved waveguides are respectively connected to the two input ports of two parallel straight waveguides, wherein one of the straight waveguides is attached with an electrode, and the voltage applied by the electrode changes the phase difference of the two MZI straight waveguide interference arm lights. The two output ports of the straight waveguide are respectively connected to the input ports of the two output S curved waveguides that are symmetrical up and down, and lead out the output ports of the two output S curved waveguides.

[0010] In the structure, the second 2×2 curved waveguide type 3dB directional coupler includes: the output ports of the two symmetrical MZI arms are respectively connected to the two input ports of the input zone waveguide of the second 2×2 3dB directional coupler. The two output ports of the input zone waveguide are respectively connected to the two input ports of two parallel coupled curved waveguides, and the input zone waveguide is used to couple the light passing through the two symmetrical MZI arms into the coupled curved waveguide. The two output ports of the coupled curved waveguide are respectively connected to the two input ports of the output zone waveguide, and the coupled curved waveguide is used to merge and interfere the two symmetrical MZI arm lights. The straight-through output port and the cross output port of the output zone waveguide are respectively connected to the input ports of the two output optical waveguides, and the output zone waveguide is used to avoid crosstalk of the output light. Among them, the input zone waveguide and the output zone waveguide are left-right symmetrical with respect to the coupled curved waveguide.

[0011] After passing through the first 2×2 curved waveguide type 3dB directional coupler, the input light is split into two beams with equal intensity and a 90° phase difference. The light intensities of the two output ports of the coupler are:

[0012] P1(L)=P in -P2(L)

[0013]

[0014] Among them, P in is the input light intensity, P1(L) and P2(L) are the light intensities at the through output port and the cross output port of the 2×2 3dB directional coupler respectively; k is the coupling coefficient, is the phase mismatch between the two waveguides, L = θR is the length of the coupling region, R and θ are the bending radius and angle of the coupled curved waveguide, respectively. Polarization insensitivity is achieved using a square cross-section silicon nitride waveguide; on this basis, by selecting the coefficient The desired cross-coupling ratio is obtained, wavelength-insensitive operation is achieved at the length corresponding to the peak of the sinusoidal term, wavelength sensitivity is reduced, and thus the working bandwidth is increased.

[0015] When passing through the two MZI arm straight waveguides, the voltage applied by the electrode changes the phase difference of the interference arm light of the two MZI straight waveguides. When passing through the second 2×2 3dB directional coupler, the two symmetrical MZI arm lights are combined and interfered to obtain two output lights.

[0016] The light intensities of the two output ports are:

[0017]

[0018] Among them, P bar and P crossare the light intensities at the MZS straight output port and the cross output port, respectively, and ΔΦ is the phase shift applied by the straight waveguide modulation arm with electrodes. When no voltage control is applied, ΔΦ = 0, and all light is output from the cross output port; when the same voltage is applied to one of the straight waveguide interference arms to achieve a π phase shift, both TE and TM polarized light will be switched to the straight output port for output.

[0019] Compared with the prior art, the advantages of the present invention are as follows: This paper adopts a single-mode silicon nitride waveguide with a square cross-section, and realizes a polarization-insensitive waveguide structure in a relatively simple way. Compared with the polarization-insensitive optical switch based on the Mach Zehnder interferometer structure proposed by Xu Hongnan in 2021, which adds a polarization rotator to realize polarization-insensitive output, the device structure is simpler and saves costs. This paper adopts silicon nitride waveguide. Compared with the silicon waveguide used in a polarization-insensitive silicon-based optical switch proposed by Wang Shipeng in 2020, the silicon nitride waveguide has a moderate refractive index contrast and can achieve large working bandwidth performance; in addition, this paper adopts a bent waveguide directional coupler, which has a smaller insertion loss than the multi-mode interference (MMI) 3dB coupler used in a polarization-insensitive silicon-based optical switch, and obtains the desired cross-coupling ratio by selecting appropriate coefficients, realizing wavelength-insensitive operation at the length corresponding to the peak of the sine term, reducing wavelength sensitivity and increasing the working bandwidth. This paper proposes a polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide devices. In the C+L+S band (1460nm-1625nm), when the switch is on or off, the TE / TM extinction ratio is greater than 18dB and the insertion loss is less than 0.3dB, realizing a polarization-insensitive, large-bandwidth, low-insertion-loss, and high-extinction-ratio 2×2 Mach-Zehnder optical switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown is a schematic structural diagram of a polarization-insensitive 2×2 Mach-Zehnder optical switch based on a silicon nitride waveguide device according to an embodiment of the present invention.

[0021] Figure 2 Shown is a schematic structural diagram of a 2×2 bent waveguide type 3dB coupler in a polarization-insensitive 2×2 Mach-Zehnder optical switch based on a silicon nitride waveguide device according to this embodiment and a port description.

[0022] Figure 3 The optical field diagram of the TE mode of the 2×2 3dB coupler in the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device of this embodiment is shown. The waveguide is a square waveguide with a cross section of 800nm×800nm.

[0023] Figure 4The optical field diagram of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device in this embodiment under the 2×2 3dB coupler TM mode is shown. The waveguide is a square waveguide with a cross section of 800nm×800nm.

[0024] Figure 5 Shown are the splitting ratios of the 2×2 3dB coupler in different polarization states in the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide devices of this embodiment.

[0025] Figure 6 The figure shows the insertion loss of a 2×2 3dB coupler in a polarization-insensitive 2×2 Mach-Zehnder optical switch based on a silicon nitride waveguide device in this embodiment under different polarization states.

[0026] Figure 7 Shown is the extinction ratio of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on the silicon nitride waveguide device of this embodiment under different polarization states in the off state (without additional phase shift).

[0027] Figure 8 The figure shows the insertion loss of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device of this embodiment under different polarization states in the off state (without additional phase shift).

[0028] Fig. 9 Shown is the extinction ratio of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on the silicon nitride waveguide device of this embodiment in different polarization states when in the on state (with additional π phase shift).

[0029] Fig.10 The insertion loss of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device of this embodiment in different polarization states when in the on state (with additional π phase shift) is shown.

[0030] In the figure:

[0031] 10 Light input waveguide,

[0032] 101 Optical input waveguide,

[0033] 102 2×2 3dB coupler,

[0034] 103 2×2 3dB coupler 102 input zone waveguide,

[0035] 104 2×2 3dB coupler 102 bent coupled waveguide,

[0036] 105 2×2 3dB coupler 102 output zone waveguide,

[0037] 20MZI arm,

[0038] 201MZI arm two input S-bend waveguide,

[0039] 202 MZI arm two straight waveguides,

[0040] 203 MZI arm straight waveguide additional electrode,

[0041] 204MZI arm two output S-bend waveguide,

[0042] 30 2×2 3dB coupler,

[0043] 301 2×2 3dB Coupler 30 Input Zone Waveguide,

[0044] 302 2×2 3dB Coupler 30 Bend Coupled Waveguide,

[0045] 303 2×2 3dB Coupler 30 Output Zone Waveguide,

[0046] 40 straight output optical waveguide,

[0047] 401 Cross output optical waveguide. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0049] Example 1: Figure 1As shown, through photolithography and etching processes, the 2×2 Mach-Zehnder optical switch silicon nitride waveguide configuration layer includes two optical input waveguides 10, 101, a 2×2 curved waveguide type 3dB coupler 102, two MZI arms 20, a 2×2 curved waveguide type 3dB coupler 30, and a straight output optical waveguide 40 and a cross output optical waveguide 401. The two optical input waveguides 10, 101 are respectively coupled with two input ports of the 2×2 3dB coupler 102, and through the two MZI arms 20, one of which is provided with an electrode 203 for optical signal phase modulation, the output light of the two MZI arms is input to the 2×2 3dB directional coupler 30, so that the output light of the two MZI arms 20 is combined and interfered, and the straight output optical waveguide 40 and the cross output optical waveguide 401 are respectively led out. The 2×2 3dB directional coupler 102 and the 2×2 3dB directional coupler 30 are arranged in a central symmetric manner to realize a symmetrical MZI. The 2×2 3dB coupler 102 further includes an input region waveguide 103, a coupled curved waveguide 104, and an output region waveguide 105. The 2×2 3dB coupler 30 also includes an input region waveguide 301, a coupled curved waveguide 302, and an output region waveguide 303. The MZI arm 20 includes two input S-curved waveguides 201, two straight waveguides 202 of the MZI arm, an MZI arm straight waveguide additional electrode 203, and two output S-curved waveguides 204.

[0050] In the structure 1, the 2×2 curved waveguide type 3dB directional coupler 102 comprises:

[0051] The two optical input waveguides 10 and 101 are respectively connected to the two input ports of the input area waveguide 103. The two output ports of the input area waveguide 103 are connected to the two input ports of two parallel coupled curved waveguides 104. The input area waveguide 103 is used to couple the input light into the coupled curved waveguide 104. The two output ports of the coupled curved waveguide 104 are respectively connected to the two input ports of the output area waveguide 105. The coupled curved waveguide 104 is used to divide the input light into two beams with equal intensity and a phase difference of 90°. The output area waveguide 105 leads to a straight-through output port and a cross output port respectively. The output area waveguide 105 is used to avoid crosstalk of the output light. The input area waveguide 103 and the output area waveguide 105 are bilaterally symmetrical with respect to the coupled curved waveguide 104.

[0052] In the structure 1, the two MZI arms 20 respectively include:

[0053] The through-end output port and the cross-end output port of the 2×2 curved waveguide type 3dB directional coupler 102 are respectively connected to the input ports of the two-way input S curved waveguide 201 which are symmetrical up and down. The output ports of the two-way input S curved waveguide 201 are respectively connected to the two-way input ports of two parallel straight waveguides 202, wherein one of the straight waveguides is attached with an electrode 203, and the voltage applied by the electrode 203 changes the phase difference of the light of the two-way MZI straight waveguide interference arm 202. The two-way output ports of the straight waveguide 202 are respectively connected to the input ports of the two-way output S curved waveguide 204 which are symmetrical up and down, and lead out the output ports of the two-way output S curved waveguide 204.

[0054] In the structure 1, the 2×2 curved waveguide type 3dB directional coupler 30 comprises:

[0055] The output ports of the two symmetrical MZI arms 20 are respectively connected to the two input ports of the input zone waveguide 301 of the 2×2 3dB directional coupler 30. The two output ports of the input zone waveguide 301 are respectively connected to the two input ports of two parallel coupled curved waveguides 302, and the input zone waveguide 301 is used to couple the light passing through the two symmetrical MZI arms 20 into the coupled curved waveguide 302. The two output ports of the coupled curved waveguide 302 are respectively connected to the two input ports of the output zone waveguide 303, and the coupled curved waveguide 302 is used to combine and interfere the light of the two symmetrical MZI arms 20. The straight-through output port and the cross output port of the output zone waveguide 303 are respectively connected to the input ports of the straight-through output optical waveguide 40 and the cross output optical waveguide 401, and the output zone waveguide 303 is used to avoid crosstalk of the output light. The input zone waveguide 301 and the output zone waveguide 303 are bilaterally symmetrical with respect to the coupled curved waveguide 302.

[0056] In this embodiment, the cross section of the silicon nitride waveguide is a square waveguide with a size of 800nm×800nm, which is wrapped in silicon dioxide. The structural parameters of the 2×2 curved waveguide type 3dB directional coupler are: w1=w2=800nm, gap=300nm, R1=56.65μm, θ1=28.8°, R2=57.75μm, θ2=14.4°, R3=R4=R1=56.65μm. The waveguide spacing in the coupling area is 300nm, and the coupling length is L=14.24μm.

[0057] Figure 3-Figure 4 The figure shows the waveguide light field diagram of the silicon nitride waveguide in different polarization states in this embodiment. Figure 3 This is the 1550nm wavelength optical field diagram in TE mode, and the corresponding effective refractive index is 1.711597; Figure 4 This is the light field diagram at a wavelength of 1550nm in TM mode, and the corresponding effective refractive index is 1.711597.

[0058] Figure 5 The figure shows the splitting ratio of the 2×2 curved waveguide type 3dB coupler in different polarization states. In the wavelength range of 1400nm to 1700nm, the TE / TM splitting ratio is maintained in the range of 45%-55% with an optical bandwidth of nearly 170nm, showing the good wavelength independence and polarization independence of the curved waveguide type 3dB coupler.

[0059] Figure 6 The insertion loss of the 2×2 curved waveguide type 3dB coupler in this embodiment under different polarization states is shown. In the wavelength range of 1400nm-1700nm, the insertion loss of TE / TM is less than 0.06dB. Therefore, the MZS composed of them also has extremely low insertion loss.

[0060] Figure 7 The extinction ratio of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device in this embodiment in the off state (without additional phase shift) under different polarization states is shown. In the wavelength range of 1460nm-1630nm, the TE / TM extinction ratio is greater than 20dB. Figure 8 The insertion loss of the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide devices of this embodiment in different polarization states when in the off state (without additional phase shift) is shown. In the wavelength range of 1450nm-1650nm, the insertion loss of TE / TM is less than 0.2dB.

[0061] Fig. 9 The extinction ratio of the polarization-insensitive 2×2 Mach-Zehnder switch based on silicon nitride devices in this embodiment in the on state (with additional π phase shift) under different polarization states is shown. In the wavelength range of 1470nm-1635nm, the extinction ratio of TE / TM is greater than 20dB, and in the wavelength range of 1460nm-1650nm, the extinction ratio of TE / TM is greater than 18dB. Fig.10 The insertion loss of the polarization-insensitive 2×2 Mach-Zehnder switch based on silicon nitride devices in this embodiment in different polarization states when in the on state (with additional π phase shift) is shown. In the wavelength range of 1460nm-1635nm, the insertion loss of TE / TM is less than 0.3dB.

[0062] Based on the above design, this embodiment realizes a polarization-insensitive, large-bandwidth, low-insertion-loss, and high-extinction-ratio Mach-Zehnder optical switch in the C+L+S band (1460nm-1625nm).

[0063] As described above, the polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device of the present invention has the following beneficial effects:

[0064] The present invention uses square silicon nitride waveguides and 2×2 curved waveguide type 3dB directional couplers to realize a polarization-insensitive, large bandwidth, low insertion loss, and high extinction ratio 2×2 Mach-Zehnder optical switch. The device reduces the system polarization management overhead and can be widely used in complex on-chip systems such as passive optical networks and optical computing.

[0065] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device, characterized in that: The silicon nitride waveguide device configuration of the 2×2 Mach-Zehnder switch includes two optical input waveguides, two 2×2 curved waveguide type 3dB directional couplers, two symmetrical MZI arms and two optical output waveguides, and the cross sections of all waveguides are square; the two optical input waveguides are respectively coupled with the two input ports of the first 2×2 3dB directional coupler, and through two symmetrical MZI arms, one of which is provided with an electrode for optical signal phase modulation, the output light of the two MZI arms is input to the second 2×23dB directional coupler, so that the output light of the two MZI arms is combined and interfered, and two output optical waveguides are respectively led out, The first 2×2 curved waveguide type 3dB directional coupler and the second 2×2 curved waveguide type 3dB directional coupler are arranged in a central symmetric manner to compensate for the difference in waveguide lengths of the couplers.

2. The polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride devices according to claim 1, characterized in that: The first 2×2 bent waveguide type 3dB directional coupler comprises: Two optical input waveguides are respectively connected to two input ports of the input area waveguide of the first 2×2 3dB directional coupler, and two output ports of the input area waveguide are connected to two input ports of two parallel coupled curved waveguides. The input area waveguide is used to couple input light of a certain optical input waveguide into the coupled curved waveguide, and the two output ports of the coupled curved waveguide are respectively connected to the two input ports of the output area waveguide of the first 2×2 3dB directional coupler. The coupled curved waveguide is used to divide the input light into two beams of light with equal intensity and a phase difference of 90°. The output area waveguide leads out a straight-through output port and a cross output port respectively, and the output area waveguide is used to avoid crosstalk of the output light, wherein the input area waveguide and the output area waveguide are bilaterally symmetrical with respect to the coupled curved waveguide.

3. The polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device according to claim 1, characterized in that: The two symmetrical MZI arms include: The through output port and the cross output port of the first 2×2 curved waveguide type 3dB directional coupler are respectively connected to the input ports of two vertically symmetrical input S-curved waveguides, and the output ports of the two input S-curved waveguides are respectively connected to the two input ports of two parallel straight waveguides, wherein one of the straight waveguides is attached with a thermocouple, and the thermocouple is used to apply a voltage to change the phase difference of the interference arm light of the two MZI straight waveguides, and the two output ports of the straight waveguides are respectively connected to the input ports of the two vertically symmetrical output S-curved waveguides, and the output ports of the two output S-curved waveguides are led out.

4. The polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device according to claim 1, characterized in that: The second 2×2 3dB directional coupler comprises: The output ports of the two symmetrical MZI arms are respectively connected to the two input ports of the input zone waveguide of the second 2×2 3dB directional coupler, the two output ports of the input zone waveguide are respectively connected to the two input ports of two parallel coupled curved waveguides, the input zone waveguide is used to couple the light passing through the two symmetrical MZI arms into the coupled curved waveguide of the second 2×2 3dB directional coupler, the two output ports of the coupled curved waveguide are respectively connected to the two input ports of the output zone waveguide, the coupled curved waveguide is used to merge and interfere the two symmetrical MZI arm lights, the straight-through output port and the cross output port of the output zone waveguide are respectively connected to the input ports of the two optical output waveguides, the output zone waveguide is used to avoid crosstalk of the output light, wherein the input zone waveguide and the output zone waveguide are bilaterally symmetrical with respect to the coupled curved waveguide.

5. The polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device according to claim 4, characterized in that: After passing through the first 2×2 curved waveguide type 3dB directional coupler, the input light is divided into two beams with equal intensity and a 90° phase difference. The light intensities of the two output ports of the coupler are: P1(L)=P in -P2(L) Among them, P in is the input light intensity, P1(L) and P2(L) are the light intensities at the through output port and the cross output port of the 2×2 3dB directional coupler respectively; k is the coupling coefficient, is the phase mismatch between the two waveguides, L = θR is the length of the coupling region, R and θ are the bending radius and angle of the coupled curved waveguide, respectively, and a square cross-section silicon nitride waveguide is used to achieve polarization insensitivity; on this basis, by selecting the coefficient The desired cross-coupling ratio is obtained, wavelength-insensitive operation is achieved at the length corresponding to the peak of the sinusoidal term, wavelength sensitivity is reduced, and thus the working bandwidth is increased.

6. The polarization-insensitive 2×2 Mach-Zehnder optical switch based on silicon nitride waveguide device according to claim 5, characterized in that: When passing through the two MZI arm straight waveguides, the electrode applies voltage to change the phase difference of the two MZI straight waveguide interference arm lights. When passing through the second 2×2 3dB directional coupler, the two symmetrical MZI arm lights are combined and interfered to obtain two output lights. The light intensities of the two output ports are: Among them, P bar and P cross are the light intensities at the MZS straight output port and the cross output port, respectively. ΔΦ is the phase shift applied by the straight waveguide modulation arm with electrodes. When no voltage control is applied, ΔΦ=0, and all light is output from the cross output port. When the same voltage is applied to control one of the straight waveguide interference arms to achieve a π phase shift, both TE and TM polarized light will be switched to the straight output port for output.

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