An interlayer vertical coupling polarization filtering structure

Abstract

This invention discloses an interlayer vertically coupled polarization filter structure, comprising an input silicon waveguide, an interlayer coupler, a separating waveguide structure, a mode transmission and absorption structure, and an output silicon waveguide. One end of the interlayer coupler is connected to the input silicon waveguide, which couples the TM and TE polarization modes from the optical fiber. The interlayer coupler converts the TM0 mode in the silicon waveguide layer into the TM0 mode in the thin-film lithium niobate waveguide layer, while the TE fundamental mode in the silicon waveguide layer remains the TE0 mode. The separating waveguide structure then vertically separates the TM0 mode in the thin-film lithium niobate waveguide layer and the TE0 mode in the silicon waveguide layer. The mode transmission and absorption structure transmits the TE0 mode and absorbs unwanted TM0 modes. Finally, the output silicon waveguide outputs the TE0 mode. The advantages of this invention are that, while ensuring low insertion loss and high operating bandwidth, the overall length is only tens of micrometers, making it small in size and conducive to on-chip integration.

Description

Technical Field

[0001] This invention relates to an interlayer vertically coupled polarization filter structure for use in silicon photonic integrated chips, belonging to the field of optoelectronic materials and devices technology. Background Technology

[0002] In mainstream integrated photonic platforms (such as silicon-on-insulator (SOI) platforms or silicon-silicon nitride (SiN) multilayer platforms), waveguides often exhibit strong birefringence due to the high refractive index contrast and asymmetrical geometric cross-sections of the waveguide materials. This means that the effective refractive index and electromagnetic field distribution of transverse electric (TE) and transverse magnetic (TM) modes differ significantly when propagating in the waveguide. To ensure stable optical signal transmission, most core components in integrated optical paths (such as modulators, microring resonators, and arrayed waveguide gratings) are typically designed to operate only in a single polarization state (usually the TE mode). If non-target polarization states (such as the TM mode) are mixed into the input optical signal, not only will polarization-dependent loss (PDL) be introduced, but it will also lead to severe mode dispersion and signal crosstalk, resulting in performance degradation of the entire chip system. Therefore, introducing a high-performance polarization filter structure into the optical path to efficiently filter out unwanted polarization modes is a necessary prerequisite for realizing high-density integrated optical paths.

[0003] Currently, most existing polarization filter structures employ single-layer planar two-dimensional designs, such as planar asymmetric directional couplers, multimode interference couplers (MMIs), or subwavelength gratings (SWGs). However, these traditional planar polarization filter structures face the following bottlenecks: 1. Excessive chip area occupation. Planar directional couplers rely on evanescent wave coupling between waveguides within the same plane, often requiring a long coupling region (typically tens to hundreds of micrometers) to achieve polarization state separation, significantly wasting valuable chip area and hindering the development of higher-density integration of optical chips. 2. Extreme sensitivity to photolithography processes. The coupling efficiency of planar structures is highly dependent on the gap size between waveguides in the same layer. Limited by the precision of current photolithography processes, a waveguide width or gap deviation of a few nanometers can cause severe phase mismatch, leading to a significant decline in the device's polarization extinction ratio (PER), making it difficult to guarantee device yield.

[0004] To overcome the two-dimensional spatial limitations of planar structures, the industry has recently begun exploring three-dimensional integrated architectures using interlayer vertical coupling to achieve polarization filtering. This involves placing the input waveguide and the filter waveguide on different material layers (e.g., two layers of silicon, or a lower silicon layer and an upper silicon nitride / polymer layer), and controlling the interlayer spacing using thin-film deposition processes. Since the thickness control precision of thin-film deposition (typically at the sub-nanometer level) is far superior to the linewidth control precision of planar lithography, this interlayer vertical structure theoretically offers better process tolerance and significantly saves planar area. However, existing interlayer vertical polarization coupling structures still have unresolved technical drawbacks. These drawbacks may result in: accidentally damaging the target polarized light while filtering out unwanted polarized light, leading to high insertion loss in the target polarized light; and, due to the fixed interlayer coupling coefficient, the operating bandwidth of the device is typically narrow, and it is highly sensitive to alignment deviations between the two waveguides in the vertical projection.

[0005] Therefore, the field of integrated circuits urgently needs a novel interlayer vertically coupled polarization filter structure. This structure needs to further break through the refractive index matching limitations of the original structure while saving area by utilizing the three-dimensional interlayer space, in order to achieve high-performance polarization filtering with high polarization extinction ratio, low insertion loss, wide operating bandwidth, and ease of chip integration. Summary of the Invention

[0006] The purpose of this invention is to propose an interlayer vertically coupled polarization filter structure, and the technical solution adopted is as follows:

[0007] An interlayer vertically coupled polarization filter structure includes an input silicon waveguide, an interlayer coupler, a separated waveguide structure, a mode transmission and absorption structure, and an output silicon waveguide.

[0008] One end of the interlayer coupler is connected to the input silicon waveguide, which couples the TM and TE polarization modes in the optical fiber. The interlayer coupler converts the TM0 mode in the silicon waveguide layer into the TM0 mode in the thin-film lithium niobate waveguide layer, while the TE fundamental mode in the silicon waveguide layer remains the TE0 mode. The separation waveguide structure then separates the TM0 mode in the thin-film lithium niobate waveguide layer and the TE0 mode in the silicon waveguide layer in the vertical direction. The mode transmission and absorption structure transmits the TE0 mode and absorbs the unwanted TM0 mode. Finally, the output silicon waveguide outputs the TE0 mode.

[0009] In a further preferred embodiment of the technical solution of the present invention, the interlayer coupler includes a first coupling waveguide and a second coupling waveguide. One end of the first coupling waveguide is connected to the input silicon waveguide. The first coupling waveguide transmits the TEO mode and couples the TMO mode energy into the second coupling waveguide, converting it into the TMO mode in the second coupling waveguide. The first coupling waveguide is a silicon waveguide, and the second coupling waveguide is a thin-film lithium niobate waveguide.

[0010] In a further preferred embodiment of the technical solution of the present invention, the separated waveguide structure includes a silicon straight waveguide I and a curved thin-film lithium niobate waveguide, one end of the silicon straight waveguide I is connected to the other end of the first coupling waveguide, and one end of the curved thin-film lithium niobate waveguide is connected to the other end of the second coupling waveguide.

[0011] A further preferred embodiment of the technical solution of the present invention includes a thin-film lithium niobate tapered waveguide, a silicon doped block, and a silicon straight waveguide II. The first end of the thin-film lithium niobate tapered waveguide is connected to the other end of the bent thin-film lithium niobate waveguide. The silicon doped block is constructed in the silicon waveguide layer at the tail end of the thin-film lithium niobate tapered waveguide. One end of the silicon straight waveguide II is connected to the other end of the silicon straight waveguide I. One end of the output silicon waveguide is connected to the other end of the silicon straight waveguide II. The other end of the output silicon waveguide outputs the TEO mode. The width of the thin-film lithium niobate tapered waveguide gradually decreases with the transmission length.

[0012] In a further preferred embodiment of the technical solution of the present invention, the thin-film lithium niobate tapered waveguide is a thin-film lithium niobate tapered helical waveguide, and the line shape of the thin-film lithium niobate tapered helical waveguide is any one of an equiangular helix, a hyperbolic helix, an Archimedean helix, and other two-dimensional helices.

[0013] In a further preferred embodiment of the technical solution of the present invention, all waveguides are strip waveguides.

[0014] In a further preferred embodiment of the technical solution of the present invention, the silicon doped block is any one of the following shapes: circular, elliptical, square, rectangular, polygonal, and other irregular shapes.

[0015] In a further preferred embodiment of the technical solution of the present invention, the silicon doped block can be P-type doped or N-type doped.

[0016] A further preferred embodiment of the technical solution of the present invention is an interlayer vertically coupled polarization filter structure, which, from bottom to top, comprises: a substrate layer, a silicon waveguide layer, and a thin-film lithium niobate waveguide layer, all surrounded by silicon oxide. The sidewall tilt angle of the silicon waveguide layer is β, the sidewall tilt angle of the thin-film lithium niobate waveguide layer is α, the thickness of the thin-film lithium niobate waveguide layer ranges from 200 nanometers to 1 micrometer, the thickness of the silicon waveguide layer ranges from 100 nanometers to 500 nanometers, the width of the thin-film lithium niobate waveguide layer ranges from 200 nanometers to 4 micrometers, and the width of the silicon waveguide layer ranges from 100 nanometers to 2 micrometers.

[0017] In a further preferred embodiment of the technical solution of the present invention, the thickness of silicon oxide between the thin-film lithium niobate waveguide layer and the silicon waveguide layer is 200 nanometers to 800 nanometers, and the thickness of the silicon oxide cladding layer above the thin-film lithium niobate waveguide layer is 1 micrometer to 6 micrometers; the sidewall tilt angle β of the silicon waveguide layer cross section ranges from 70° to 90°, and the sidewall tilt angle α of the thin-film lithium niobate waveguide layer cross section ranges from 50° to 90°.

[0018] The advantages of this invention compared to the prior art are as follows:

[0019] The interlayer vertically coupled polarization filter structure of this invention, through the design of the interlayer coupling structure, ensures that after the TM0 mode couples, its energy is transferred to the thin-film lithium niobate waveguide and absorbed, while the TE0 mode does not couple and continues to propagate in the silicon waveguide. This structure only requires adjusting the widths of the silicon waveguide and the thin-film lithium niobate waveguide, without the need for complex structural design.

[0020] The interlayer vertically coupled polarization filter structure of this invention gradually reduces the confinement of the TMO mode by narrowing the width of the thin-film lithium niobate tapered waveguide. Then, the mode energy is absorbed by the silicon dopant. The thin-film lithium niobate tapered waveguide is designed as a spiral to increase the overlap area with the silicon dopant above, so that the TMO mode is completely absorbed. This structure can ensure that unwanted modes are completely absorbed without reflection. Moreover, the silicon dopant is a mature silicon photonics process in silicon waveguide layers, avoiding the dilemma that it is impossible to construct silicon dopant to absorb excess mode energy in thin-film lithium niobate waveguide layers.

[0021] The interlayer vertically coupled polarization filter structure of the present invention has a simple structural design. Each waveguide layer only needs to be etched once, which reduces the risk of parameter deviation introduced by multiple etching, reduces the complexity of the etching process, and makes the overall process more stable, thereby improving the device yield from the design level.

[0022] The interlayer vertically coupled polarization filter structure of the present invention has a small overall length of only tens of micrometers while ensuring low insertion loss and high operating bandwidth, which is conducive to chip integration. Attached Figure Description

[0023] Figure 1 This is a top view of the interlayer vertically coupled polarization filter structure of the present invention;

[0024] Figure 2 This is a side view of the interlayer vertically coupled polarization filter structure of the present invention.

[0025] Figure 3 This is a cross-sectional view of the interlayer vertically coupled polarization filter structure of the present invention;

[0026] Figure 4This is a curve showing the effective refractive index of the inner mode of the thin-film lithium niobate waveguide (second coupling waveguide) in the interlayer coupler obtained by simulation in an embodiment of the present invention, which varies with the waveguide width.

[0027] Figure 5 This is a curve showing the effective refractive index of the mode within the silicon waveguide (first coupled waveguide) of the interlayer coupler as a function of the waveguide width, obtained through simulation in an embodiment of the present invention.

[0028] Figure 6 This is a simulation of the interlayer coupler obtained in this embodiment of the invention, under the condition of effective refractive index matching of the mode, showing the change curve of the TMO mode energy in the thin film lithium niobate waveguide coupled to the thin film lithium niobate waveguide, and the change of TMO mode energy with wavelength in the thin film lithium niobate waveguide.

[0029] Figure 7 The curves showing the insertion loss of the TM0 and TE0 modes at the output port of the mode transmission and absorption structure 3 obtained in the simulation of this embodiment of the invention are as follows:

[0030] Wherein, 1-interlayer coupler, 101-first coupling waveguide, 102-second coupling waveguide, 2-separated waveguide structure, 201-silicon straight waveguide I, 202-bent thin-film lithium niobate waveguide, 3-mode transmission and absorption structure, 301-thin-film lithium niobate tapered waveguide, 302-silicon doped block, 303-silicon straight waveguide II, 4-input silicon waveguide, 5-output silicon waveguide, 6-silicon waveguide layer, 7-thin-film lithium niobate waveguide layer, 8-substrate layer. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figures 1-7 The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] like Figure 1 , 2 As shown in Figure 3, this embodiment proposes an interlayer vertically coupled polarization filter structure. This structure has a simple overall design, requiring only a single etching operation for each layer, resulting in higher process stability. The overall device length is only tens of micrometers, making it small in size and easy to integrate. In terms of performance, it achieves low insertion loss for TE mode and an extinction ratio greater than 17 dB in the wavelength range above 60 nm.

[0034] like Figure 1 , 2As shown in Figure 3, the interlayer vertically coupled polarization filter structure includes, from bottom to top: a substrate layer 8, a silicon waveguide layer 6, and a thin-film lithium niobate waveguide layer 7. The waveguide is surrounded by silicon oxide. The sidewall tilt angle of the silicon waveguide layer 6 is β, which ranges from 70° to 90°. The sidewall tilt angle of the thin-film lithium niobate waveguide layer 7 is α, which ranges from 50° to 90°.

[0035] like Figure 1 , 2 As shown in Figure 3, this invention proposes an interlayer vertically coupled polarization filter structure for integrated chips, comprising an input silicon waveguide 4, an interlayer coupler 1, a separated waveguide structure 2, a mode transmission and absorption structure 3, and an output silicon waveguide 5. The interlayer coupler 1 includes a first coupling waveguide 101 and a second coupling waveguide 102. The separated waveguide structure 2 includes a section of straight silicon waveguide I 201 and a section of curved thin-film lithium niobate waveguide 202. The mode transmission and absorption structure 3 includes a section of thin-film lithium niobate tapered waveguide 301, a silicon doped block 302, and a section of straight silicon waveguide II 303. All waveguides are strip waveguides.

[0036] Input silicon waveguide 4 is used to input the TE fundamental mode (i.e., TE0 mode) and the TM fundamental mode (i.e., TM0 mode).

[0037] Interlayer coupler 1 includes a first coupling waveguide 101 and a second coupling waveguide 102. The first coupling waveguide 101 is a silicon waveguide, and the second coupling waveguide 102 is a thin-film lithium niobate waveguide. One end of the first coupling waveguide 101 is connected to the input silicon waveguide 4.

[0038] The first coupling waveguide 101 is used to convert the TM0 mode in the silicon waveguide (first coupling waveguide 101) into the TM0 mode in the thin-film lithium niobate waveguide (second coupling waveguide 102) for transmission in the second coupling waveguide 102, while the TE0 mode in the silicon waveguide (first coupling waveguide 101) still transmits along the first coupling waveguide 101.

[0039] The separated waveguide structure 2 includes a silicon straight waveguide I 201 and a bent thin-film lithium niobate waveguide 202. One end of the silicon straight waveguide I 201 is connected to the other end of the first coupling waveguide 101, and one end of the bent thin-film lithium niobate waveguide 202 is connected to the other end of the second coupling waveguide 102. The separated waveguide structure 2 is used to separate the TM0 mode in the thin-film lithium niobate waveguide (second coupling waveguide 102) and the TE0 mode in the silicon waveguide (first coupling waveguide 101) in the vertical direction, so as to prevent the mode from being recoupled from the thin-film lithium niobate waveguide (second coupling waveguide 102) back to the silicon waveguide (first coupling waveguide 101).

[0040] The mode transmission and absorption structure 3 includes a thin-film lithium niobate tapered waveguide 301, a silicon doped block 302, and a silicon straight waveguide II 303, used to transmit the TEO mode and absorb unwanted TMO modes; the output silicon waveguide 5 is used to output the TEO mode. Specifically, the first end of the thin-film lithium niobate tapered waveguide 301 is connected to the other end of the bent thin-film lithium niobate waveguide 202, the silicon doped block 302 is constructed in the silicon waveguide layer 6 at the tail end of the thin-film lithium niobate tapered waveguide 301, one end of the silicon straight waveguide II 303 is connected to the other end of the silicon straight waveguide I 201, one end of the output silicon waveguide 5 is connected to the other end of the silicon straight waveguide II 303, and the other end of the output silicon waveguide 5 outputs the TEO mode; the width of the thin-film lithium niobate tapered waveguide 301 gradually decreases with the transmission length.

[0041] Furthermore, the thin-film lithium niobate tapered waveguide 301 is a thin-film lithium niobate tapered helical waveguide, and the line shape of the thin-film lithium niobate tapered helical waveguide is any one of an equiangular helix, a hyperbolic helix, an Archimedean helix, and other two-dimensional helices.

[0042] Furthermore, the silicon doped block 302 can be circular, elliptical, square, rectangular, polygonal, or any other irregular shape. The silicon doped block 302 can be P-type doped or N-type doped.

[0043] Within the integrated chip, the steps for implementing the polarization filtering function using the interlayer vertical coupling polarization filter structure in this embodiment are as follows:

[0044] S1. First, the polarization mode in the optical fiber is coupled into the chip through the input silicon waveguide 4. To ensure that only the TE fundamental mode (i.e., TE0 mode) is transmitted in the silicon waveguide layer 6, the existing TM fundamental mode (i.e., TM0 mode) needs to be effectively filtered out. For example... Figure 1 As shown.

[0045] S2. Next, the TM0 mode in the silicon waveguide layer 6 is converted to the upper thin-film lithium niobate waveguide layer 7 via an interlayer coupler 1. Specifically, by designing the width and height of the silicon waveguide layer 6 and the thin-film lithium niobate waveguide layer 7, the effective refractive indices of the TM0 mode in the two waveguide layers are matched, so that the energy of the TM0 mode in the silicon waveguide layer 6 is completely coupled to the upper thin-film lithium niobate waveguide layer 7, such as... Figure 1 As shown. Furthermore, the TE0 mode in silicon waveguide layer 6 does not satisfy the phase-matching condition for mode coupling and still propagates forward within silicon waveguide layer 6. At this time, the TM0 mode propagates in the upper thin-film lithium niobate waveguide layer 7, and the TE0 mode propagates in the lower silicon waveguide layer 6. As... Figure 2 As shown

[0046] S3. Finally, the upper thin-film lithium niobate waveguide layer 7 connects to a curved thin-film lithium niobate waveguide 202 and a thin-film lithium niobate tapered spiral waveguide (thin-film lithium niobate tapered waveguide 301). A silicon doped block 302 is placed below the tail end of the thin-film lithium niobate tapered spiral waveguide. The curved thin-film lithium niobate waveguide 202 can quickly create a lateral positional difference with the lower silicon straight waveguide I201, preventing mode energy from coupling back into the lower silicon waveguide (first coupling waveguide 101). The width of the thin-film lithium niobate tapered waveguide 301 gradually narrows, reducing the confinement of the modes within it and allowing the modes to diffuse into space. The silicon doped block 302 at the tail end can effectively absorb the mode energy in the lithium niobate waveguide. The spiral design increases the overlap area with the silicon doped block 302, making the absorption more thorough. In this way, the TM0 mode in the thin-film lithium niobate waveguide layer 7 will be completely absorbed, while the TEO mode in the lower silicon waveguide layer 6 will continue to propagate unaffected. Figure 2 As shown, the device implements on-chip polarization filtering.

[0047] To better understand this invention, the following details an application example of an interlayer vertically coupled polarization filter structure for integrated chips proposed in this invention. Specific Implementation Example 1:

[0049] An embodiment of the present invention relates to an interlayer vertically coupled polarization filter structure, comprising an input silicon waveguide 4, an interlayer coupler 1, a separated waveguide structure 2, a mode transmission and absorption structure 3, and an output silicon waveguide 5, as shown below. Figure 1 , 2 As shown in Figure 3.

[0050] The on-chip polarization filtering function of the entire structure can be described as follows: the polarization modes in the optical fiber are coupled into the chip through the input silicon waveguide 4. To ensure that only the TE0 mode is transmitted in the silicon waveguide layer 6, the TM0 mode energy in the silicon waveguide layer 6 is first transferred to the upper thin-film lithium niobate waveguide layer 7 via an interlayer coupler 2. Subsequently, the TM0 mode in the thin-film lithium niobate waveguide layer 7 is gradually and completely absorbed by the lower silicon doped block 302 through a thin-film lithium niobate tapered helical waveguide (thin-film lithium niobate tapered waveguide 301). The TE0 mode continues to transmit in the silicon waveguide layer 6 without coupling. In this way, the TM0 mode in the silicon waveguide layer 6 is filtered out, and only the TE0 mode is transmitted, thus realizing the polarization filtering function.

[0051] The material parameters, structural parameters, and simulation results set in this embodiment are as follows:

[0052] First, the refractive index of the thin-film lithium niobate waveguide layer 7 was set to 2.14, and its thickness was 450 nm. The refractive index of the silicon waveguide layer 6 was set to 3.47, and its thickness was 220 nm. The sidewall tilt angle β of the silicon waveguide layer 6 and the sidewall tilt angle α of the thin-film lithium niobate waveguide layer 7 were both set to 90°. The thickness of the silicon oxide layer between the thin-film lithium niobate waveguide layer 7 and the silicon waveguide layer 6 was 400 nm. The thickness of the silicon oxide layer covering the thin-film lithium niobate waveguide layer 7 was 1 μm, and the thickness of the silicon oxide layer below the silicon waveguide layer 6 was 3 μm. The refractive index of the silicon oxide was set to 1.44. The curves of the effective refractive index of each mode in the thin-film lithium niobate waveguide layer 7 as a function of waveguide width were obtained by width scanning, as shown below. Figure 4 As shown. The curves of the effective refractive index of each mode within silicon waveguide layer 6 as a function of waveguide width were obtained through width scanning, as shown below. Figure 5 As shown. Comparison Figure 4 and Figure 5 It can be observed that the effective refractive index of the TM0 mode in the thin-film lithium niobate waveguide layer 7 at a waveguide width of 2.5 micrometers is comparable to that of the TM0 mode in the silicon waveguide layer 6 at a waveguide width of around 0.5 micrometers.

[0053] Next, in the interlayer coupler 1 section, a thin-film lithium niobate waveguide (second coupling waveguide 102) with a width of 2.5 micrometers and a silicon waveguide (first coupling waveguide 101) with a width of 480 nanometers are set. The centers of the two waveguide cross-sections coincide in the vertical direction, and the overlap length of the waveguides is 28.2 micrometers. When mode propagation occurs in the silicon waveguide (first coupling waveguide 101), the TM0 mode undergoes mode coupling due to effective refractive index matching, and the mode energy is transferred to the TM0 mode of the upper thin-film lithium niobate waveguide (second coupling waveguide 102), as shown in the schematic diagram. Figure 6 As shown in the illustration. From Figure 6 It can be observed that the conversion efficiency of the TM0 mode in both waveguides (thin-film lithium niobate waveguide (second coupling waveguide 102) and silicon waveguide (first coupling waveguide 101)) is greater than 0.978 in the wavelength range of interest, achieving excellent coupling efficiency.

[0054] Then, as Figure 1As shown, in the two-part separated waveguide structure, a thin-film lithium niobate waveguide (second coupling waveguide 102) is connected to a curved waveguide (curved thin-film lithium niobate waveguide 202), rapidly creating a lateral positional difference with the underlying silicon waveguide (first coupling waveguide 101). This prevents the TM0 mode in the thin-film lithium niobate waveguide (second coupling waveguide 102) from recoupled back into the silicon waveguide (first coupling waveguide 101). The tapered spiral portion of the thin-film lithium niobate waveguide has an initial width of 2.5 μm and an ending width of 300 nm. The spiral is a freely configured spiral shape without a fixed function. The silicon doped block 302 is circular with a diameter of 40 μm and is p-doped (boron ion implantation) to ensure complete absorption of mode energy in the thin-film lithium niobate waveguide (second coupling waveguide 102). The width of the underlying silicon waveguide (first coupling waveguide 101) remains 480 nm.

[0055] Finally, the insertion loss curves of the TM0 and TE0 modes obtained at the silicon waveguide output port of the polarization filter structure described in this embodiment as a function of wavelength are attached. Figure 7 As shown, this device exhibits almost no loss for the TEO mode within the wavelength range of interest (1520 nm to 1580 nm), and the extinction ratio between the two polarization modes is greater than 17 dB. This indicates that after the interlayer vertical coupling polarization filter structure of this invention passes through the fiber-coupled input silicon waveguide 4, only the TEO mode is transmitted in the silicon waveguide layer 6, while the TEO mode is filtered out, thus completing the on-chip polarization filtering function.

[0056] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An interlayer vertically coupled polarization filter structure, characterized in that, The input silicon waveguide (4), interlayer coupler (1), split waveguide structure (2), mode transmission and absorption structure (3), and output silicon waveguide (5). One end of the interlayer coupler (1) is connected to the input silicon waveguide (4). The input silicon waveguide (4) couples the two polarization modes TM and TE in the optical fiber into the input. After passing through the interlayer coupler (1), the TM0 mode in the silicon waveguide layer (6) is converted into the TM0 mode in the thin film lithium niobate waveguide layer (7). The TE fundamental mode in the silicon waveguide layer (6) is still the TE0 mode. Then, the TM0 mode in the thin film lithium niobate waveguide layer (7) and the TE0 mode in the silicon waveguide layer (6) are separated in the vertical direction by the separation waveguide structure (2). The TE0 mode is transmitted and the unwanted TM0 mode is absorbed by the mode transmission and absorption structure (3). Finally, the TE0 mode is output by the output silicon waveguide (5).

2. The interlayer vertically coupled polarization filter structure according to claim 1, characterized in that, The interlayer coupler (1) includes a first coupling waveguide (101) and a second coupling waveguide (102). One end of the first coupling waveguide (101) is connected to the input silicon waveguide (4). The first coupling waveguide (101) transmits the TEO mode and couples the TEO mode energy into the second coupling waveguide (102), converting it into the TEO mode in the second coupling waveguide (102). The first coupling waveguide (101) is a silicon waveguide, and the second coupling waveguide (102) is a thin-film lithium niobate waveguide.

3. The interlayer vertically coupled polarization filter structure according to claim 2, characterized in that, The separated waveguide structure (2) includes a silicon straight waveguide I (201) and a curved thin-film lithium niobate waveguide (202). One end of the silicon straight waveguide I (201) is connected to the other end of the first coupling waveguide (101), and one end of the curved thin-film lithium niobate waveguide (202) is connected to the other end of the second coupling waveguide (102).

4. The interlayer vertically coupled polarization filter structure according to claim 3, characterized in that, The mode transmission and absorption structure (3) includes a thin-film lithium niobate tapered waveguide (301), a silicon doped block (302), and a silicon straight waveguide II (303). The first end of the thin-film lithium niobate tapered waveguide (301) is connected to the other end of the bent thin-film lithium niobate waveguide (202). The silicon doped block (302) is constructed in the silicon waveguide layer (6) at the tail end of the thin-film lithium niobate tapered waveguide (301). One end of the silicon straight waveguide II (303) is connected to the other end of the silicon straight waveguide I (201). One end of the output silicon waveguide (5) is connected to the other end of the silicon straight waveguide II (303). The other end of the output silicon waveguide (5) outputs the TEO mode. The width of the thin-film lithium niobate tapered waveguide (301) gradually decreases with the transmission length.

5. The interlayer vertically coupled polarization filter structure according to claim 4, characterized in that, The thin-film lithium niobate tapered waveguide (301) is a thin-film lithium niobate tapered helical waveguide, and the line shape of the thin-film lithium niobate tapered helical waveguide is any one of equiangular helix, hyperbolic helix, Archimedean helix and other two-dimensional helices.

6. The interlayer vertically coupled polarization filter structure according to claim 4, characterized in that, All waveguides are strip waveguides.

7. The interlayer vertically coupled polarization filter structure according to claim 4, characterized in that, The silicon doped block (302) can be any of the following shapes: circular, elliptical, square, rectangular, polygonal, or other irregular shapes.

8. The interlayer vertically coupled polarization filter structure according to claim 7, characterized in that, The silicon doped block (302) can be P-type doped or N-type doped.

9. The interlayer vertically coupled polarization filter structure according to claim 1, characterized in that, The interlayer vertically coupled polarization filter structure, from bottom to top, includes: a substrate layer (8), a silicon waveguide layer (6), and a thin-film lithium niobate waveguide layer (7), all surrounded by silicon oxide. The sidewall tilt angle of the silicon waveguide layer (6) is β, the sidewall tilt angle of the thin-film lithium niobate waveguide layer (7) is α, the thickness of the thin-film lithium niobate waveguide layer (7) ranges from 200 nanometers to 1 micrometer, the thickness of the silicon waveguide layer (6) ranges from 100 nanometers to 500 nanometers, the width of the thin-film lithium niobate waveguide layer (7) ranges from 200 nanometers to 4 micrometers, and the width of the silicon waveguide layer (6) ranges from 100 nanometers to 2 micrometers.

10. The interlayer vertically coupled polarization filter structure according to claim 9, characterized in that, The thickness of the silicon oxide between the thin-film lithium niobate waveguide layer (7) and the silicon waveguide layer (6) is 200 nm to 800 nm, and the thickness of the silicon oxide cladding above the thin-film lithium niobate waveguide layer (7) is 1 μm to 6 μm; the sidewall tilt angle β of the silicon waveguide layer (6) is in the range of 70° to 90°, and the sidewall tilt angle α of the thin-film lithium niobate waveguide layer (7) is in the range of 50° to 90°.

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