A lithium niobate-based hetero-integrated on-chip polarization-rotating beam splitter and a preparation method thereof

Abstract

A heterogeneous integrated on-chip polarization rotating beamsplitter based on GeSbS-loaded lithium niobate and its fabrication method are disclosed, relating to the field of integrated photonic chip technology. The heterogeneous integrated on-chip polarization rotating beamsplitter includes a lithium niobate thin film layer and a waveguide loading structure heterogeneously integrated on the lithium niobate thin film layer. The waveguide loading structure, from the input end to the output end, sequentially includes an input single-mode waveguide region, a mode converter region, an asymmetric directional coupler region, and an output port. The mode converter region is a tapered structure with an increasing cross-section along the direction from the input end to the output end. The asymmetric directional coupler region includes a through waveguide strip and a coupling waveguide strip, the coupling waveguide strip having a tapered structure with an increasing cross-section along the output direction. This invention eliminates the need for etching the lithium niobate thin film and simultaneously enables efficient and broadband mode conversion and polarization beam splitting of the input orthogonal polarization (TE0 and TM0) into two independent TE0 mode output channels.

Description

Technical Field

[0001] This invention relates to the field of integrated photonic chip technology, and in particular to a heterogeneous integrated on-chip polarization rotating beam splitter based on GeSbS-loaded lithium niobate and its fabrication method. Background Technology

[0002] Thin-film lithium niobate (TFLN) has attracted widespread attention due to its excellent electro-optic and nonlinear properties, as well as its wide transparency window. The lithium niobate platform is considered one of the promising material systems to become "optical silicon" due to its excellent electro-optic coefficient, wide transparency window, high nonlinear effect, and fabrication potential compatible with CMOS processes. Among them, on-chip polarization beamsplitters of lithium niobate (LiNbO3) are key devices in integrated photonics. They are used to separate or control the polarization state of light in optical communication, quantum information processing, and sensing, laying the foundation for future on-chip polarization multiplexing (PDM) technology.

[0003] However, lithium niobate materials exhibit strong anisotropy (birefringence), leading to significant differences in the propagation characteristics of TE and TM modes in the waveguide. Traditional silicon-based polarization beam splitters often face the following challenges on the TFLN platform: 1. Mode hybridization: TE and TM modes are prone to coupling in the waveguide, resulting in polarization-dependent losses and wavelength dependence. 2. Small phase mismatch: In TFLN waveguides, the effective refractive index difference between TE and TM modes is small (typically <0.02), making efficient polarization separation difficult. 3. Poor process compatibility: TFLN waveguides typically have tilted sidewalls (60°-70°), resulting in large waveguide spacing, low coupling efficiency, and difficulties in interfacing with existing photonic integrated devices (such as modulators and detectors). 4. Large device size: Traditional structures, such as adiabatic graded waveguides or long couplers, often reach hundreds of micrometers in length, which is not conducive to high integration.

[0004] To address these challenges, researchers have proposed various polarization beamsplitters based on TFLN in recent years. For example, patent application CN117555075A proposes a polarization beamsplitter based on lithium niobate thin film. By covering the lithium niobate thin film waveguide with a silicon nitride layer and employing a three-waveguide asymmetric directional coupler structure, TM polarized light and TE polarized light are coupled into the first waveguide. The second waveguide enhances the effective refractive index of TM polarized light through the silicon nitride layer, thereby increasing the phase mismatch of TM polarized light in the first and second waveguides. This prevents TM polarized light in the first waveguide from coupling, while TE polarized light in the first waveguide is coupled into the second waveguide, achieving separation between TM polarized light and TE polarized light and avoiding the incompatibility problem between other dual-waveguide structures and ordinary lithium niobate waveguides. Furthermore, to improve device integration, patent application CN116520493A describes a polarization beamsplitter chip based on thin-film lithium niobate for TE and TM mode separation. This chip etches symmetrical dual-branch ridge waveguides into the lithium niobate substrate, including an input straight waveguide, an output straight waveguide, a sine-type bent waveguide (replacing the traditional 90° bent waveguide to reduce device size), and a directional coupling region straight waveguide (achieving polarization selection by controlling the coupling length). It combines the ridge waveguide structure with a directional coupler, achieving efficient TE / TM separation by optimizing waveguide dimensions and coupling length. However, these solutions all require direct etching of the lithium niobate thin film to form the waveguide structure, and the polarization beamsplitter only achieves spatial separation of TE and TM polarized light, lacking integrated design for complete rotation and spatial routing of polarization states.

[0005] In recent years, thanks to advancements in dicing technology, single-crystal submicron-scale lithium niobate thin films can now be obtained via ion slicing. These films are then bonded to low-refractive-index insulator substrates using benzocyclobutene bonding or crystal bonding methods, resulting in lithium niobate on insulator (LNOI) platforms similar to silicon-on-insulator (SOI) platforms. However, due to its chemical inertness, obtaining high-quality lithium niobate waveguides through direct etching is not easy. First, existing photoresists limit the etching depth of lithium niobate to higher levels. Furthermore, lithium contamination issues make its processing technology incompatible with complementary metal-oxide-semiconductor (CMOS) technology. Moreover, the ribbed waveguide geometry with its sloping sidewall profile in TFLN waveguides restricts their application in situations requiring strong coupling or sensitive to sidewall effects. Therefore, the existing technology of etching lithium niobate thin films to form waveguide structures inevitably encounters the following technical problems: tilted sidewalls and high surface roughness, introducing additional scattering losses; lithium elements are prone to escape during the etching process, affecting the luminescence efficiency of rare earth ions; and poor compatibility with CMOS processes limits large-scale integration. Therefore, developing an etching-free, high-efficiency, broadband polarization rotation and beam splitting on-chip polarization beam splitter based on lithium niobate has practical application value. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects and shortcomings of the prior art and provide a heterogeneous integrated on-chip polarization rotating beam splitter with efficient mode conversion and polarization beam splitting, excellent broadband operating characteristics, and no need to etch the lithium niobate film.

[0007] Another objective of this invention is to provide a method for fabricating a heterogeneous integrated on-chip polarization rotating beam splitter.

[0008] Another object of the present invention is to provide an application of the above-mentioned heterogeneous integrated on-chip polarization rotating beam splitter in optical communication systems, quantum information processors or optical sensing devices.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: This invention provides a heterogeneous integrated on-chip polarization rotating beam splitter, comprising a lithium niobate thin film layer and a waveguide loading structure heterogeneously integrated on the lithium niobate thin film layer. The waveguide loading structure includes, from the input end to the output end, an input single-mode waveguide region, a mode converter region, an asymmetric directional coupler region, and an output port. The mode converter area is a tapered structure with an increasing cross-section along the direction from the input end to the output end, used to adiabatically convert the input TM0 mode to the TE1 mode; The asymmetric directional coupler region includes a through waveguide strip and a coupling waveguide strip. The coupling waveguide strip has a tapered structure with an increased cross-section along the output direction. The through waveguide strip is connected to the mode converter region. The coupling waveguide strip and the through waveguide strip are optically coupled to meet the phase matching condition, which is used to convert the TE1 mode to the TE0 mode. The output ports include a first output port and a second output port. The first output port is connected to the through waveguide strip, and the second output port is connected to the coupling waveguide strip.

[0010] In some embodiments, a waveguide displacement structure is also included, which is S-shaped and connected to the output end of the through waveguide strip and the first output port, respectively.

[0011] In some embodiments, the waveguide loading structure is made of amorphous chalcogenide glass, and the refractive index of the waveguide loading structure is 1.8-2.5 at a wavelength of 1470-1570 nm.

[0012] In some embodiments, the waveguide loading structure is made of at least one selected from germanium-antimony-sulfur (GeSbS) glass, Ge-Sb-Se glass, and As-S glass. Preferably, the waveguide loading structure is made of GeSbS glass.

[0013] In some embodiments, the thickness of the lithium niobate thin film layer is 400-700 nm; preferably, the thickness of the lithium niobate thin film layer is 550-650 nm.

[0014] In some embodiments, the refractive index of the lithium niobate thin film layer material is no=2.211, ne=2.137.

[0015] In some embodiments, the thickness of the waveguide loading structure is 300-500 nm; preferably, the thickness of the waveguide displacement structure is 350-450 nm, more preferably 380-420 nm.

[0016] In some embodiments, the width of the input single-mode waveguide region is 1.0-2.5 μm; preferably, the width of the input single-mode waveguide region is 1.6-1.8 μm, and more preferably, the width is 1.65-1.75 μm.

[0017] In some embodiments, the thickness of the lithium niobate thin film layer is 550-650 nm, the thickness of the waveguide displacement structure is 380-420 nm, and when the waveguide loading structure material is GeSbS glass, the width of the input single-mode waveguide region is 1.6-1.8 μm. This waveguide width can maintain single-mode transmission characteristics while maximally confining the optical mode field within the lithium niobate layer, achieving efficient overlap between pump light and signal light.

[0018] In some embodiments, the width of the input single-mode waveguide region is 1.6-1.8 μm, and the tapered structure of the mode converter region has an initial width the same as the width of the input single-mode waveguide region, an ending width of 2.1-2.3 μm, and a tapered length ≥ 600 μm. Preferably, the initial width is 1.65-1.75 μm, the ending width is 2.1-2.2 μm, and the tapered length is 600-700 μm.

[0019] In some embodiments, in the asymmetric directional coupler region, the width of the through waveguide strip is the same as the termination width of the mode converter region (the width is selected from 2.1-2.2 μm), the starting width of the coupling waveguide strip is 0.72-0.76 μm, the termination width is 0.82-0.86 μm, and the coupling length is ≥210 μm.

[0020] Preferably, the coupling gap between the through waveguide strip and the coupling waveguide strip is 1.3-1.5 μm. Preferably, the coupling length is 210-250 μm.

[0021] In some embodiments, the bottom surface of the lithium niobate thin film layer and the surface of the waveguide loading structure are respectively provided with cladding, and the material of the cladding is preferably silicon dioxide.

[0022] This invention provides a method for fabricating a heterogeneous integrated on-chip polarization rotating beam splitter, comprising the following steps: taking a substrate including a lithium niobate thin film layer, depositing an amorphous chalcogenide glass waveguide layer on the surface of the lithium niobate thin film layer, etching the amorphous chalcogenide glass waveguide layer to form a waveguide loading structure, thereby obtaining the heterogeneous integrated on-chip polarization rotating beam splitter.

[0023] In some embodiments, the deposition process of the amorphous chalcogenide glass waveguide layer can be achieved by magnetron sputtering or thermal evaporation.

[0024] In some embodiments, the etching process for the amorphous chalcogenide glass waveguide layer includes: forming a waveguide pattern by ultraviolet lithography or electron beam exposure, and then etching a waveguide loading structure by reactive ion etching (RIE) or inductively coupled plasma etching (ICP).

[0025] Specifically, the fabrication method of the heterogeneous integrated on-chip polarization rotating beam splitter includes the following steps: (1) Provide a Z-cut lithium niobate thin film substrate; from bottom to top, it consists of a silicon substrate (400-600 μm), silicon oxide (3-5 μm), and a lithium niobate thin film layer (400-700 nm), without the need for any etching process on the lithium niobate; (2) GeSbS thin film (thickness 300-500 nm) is deposited on the surface of lithium niobate thin film on the substrate by magnetron sputtering or thermal evaporation; at the same time, the deposited film is annealed to eliminate internal stress and reduce material absorption loss. (3) The waveguide pattern is formed by ultraviolet lithography or electron beam exposure, and the GeSbS thin film is patterned into the designed strip waveguide by reactive ion etching (RIE) or inductively coupled plasma etching (ICP) process to form the waveguide loading structure.

[0026] This invention provides an application of the heterogeneous integrated on-chip polarization rotating beam splitter in optical communication systems, quantum information processors, or optical sensing devices.

[0027] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a heterogeneous integrated on-chip polarization rotating beam splitter. Employing a heterogeneous integrated structure, it eliminates the need for etching the lithium niobate film, avoiding issues such as sidewall tilting, surface roughness, and lithium efflux, significantly reducing process complexity and device losses. Through a cascaded design of a tapered mode converter and an asymmetric directional coupler, a TM0→TE0 conversion efficiency >90% is achieved in the 1480-1570 nm wavelength band, exhibiting good wavelength insensitivity. Simultaneously, it can physically separate the input orthogonal polarizations (TE0 and TM0) into two independent TE0 mode output channels, laying a crucial structural foundation for subsequent system-level applications such as dual-channel polarization-insensitive optical amplification and independent polarization multiplexing signal control. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the heterogeneous integrated on-chip polarization rotating beam splitter of Embodiment 1 of the present invention.

[0029] Figure 2 For the present invention Figure 1 Front view of a heterogeneous integrated on-chip polarization rotating beam splitter.

[0030] Figure 3 For the present invention Figure 1 A cross-sectional view of a heterogeneous integrated on-chip polarization rotating beam splitter.

[0031] Figure 4This is a comparison diagram of the relationship between the effective refractive index and waveguide width of different modes in the cone-shaped mode converter of Experimental Example 1 of the present invention.

[0032] Figure 5 This is a graph showing the relationship between the TE0 and TM0 modes and the conversion efficiency as a function of the cone length in the cone-mode converter of Experimental Example 1 of this invention.

[0033] Figure 6 The graph shows the TM0→TE1 conversion efficiency of the tapered asymmetric directional coupler of Experiment 1 of this invention at different wavelengths.

[0034] Figure 7 This is a graph showing the relationship between the effective refractive index and waveguide width for different modes of the tapered asymmetric directional coupler in Experimental Example 2 of this invention.

[0035] Figure 8 This is the mode field diagram of the coupling between TE1 and TE0 of the conical asymmetric directional coupler in Experimental Example 2 of the present invention.

[0036] Figure 9 This is the mode field diagram of the coupling between TE0 and TE0 of the conical asymmetric directional coupler in Experimental Example 2 of the present invention.

[0037] Figure 10 The diagram shows the TE1→TE0 conversion efficiency of the tapered asymmetric directional coupler in Experiment Example 2 of this invention at different wavelengths. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way.

[0039] In the description of the embodiments of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc. (if present), indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the embodiments of this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. Furthermore, the terms "first," "second," and "third" are used only for descriptive purposes such as distinguishing similar objects, and should not be construed as indicating or implying relative importance or order.

[0040] Example 1 A heterogeneous integrated on-chip polarization rotating beam splitter, such as Figure 1-3 As shown, it includes a lithium niobate thin film layer (LiNbO3) and a waveguide loading structure heterogeneously integrated on the lithium niobate thin film layer. The bottom surface of the lithium niobate thin film layer and the surface of the waveguide loading structure are respectively provided with a silicon dioxide lower cladding layer and a silicon dioxide upper cladding layer.

[0041] Specifically, the lithium niobate thin film layer is a Z-cut lithium niobate thin film with a thickness of 600 nm and a refractive index of 2.2 at 1550 nm.

[0042] The thickness of the lower silica cladding is 4 μm, and the thickness of the upper silica cladding is 2 μm.

[0043] The waveguide loading structure is made of GeSbS material with a thickness of 400 nm and a refractive index of approximately 2.28 at 1550 nm. From the input end to the output end, the waveguide loading structure sequentially includes an input single-mode waveguide region 1, a mode converter region 2, an asymmetric directional coupler region 3, and an output port.

[0044] The single-mode waveguide region 1 has a width of 1.7 μm. While maintaining single-mode transmission characteristics, the waveguide maximally confines the optical mode field within the lithium niobate layer, achieving efficient overlap of the pump light and signal light for input fundamental transverse electric mode (TE0) and fundamental transverse magnetic mode (TM0). This structure completely avoids direct etching of the lithium niobate film, fundamentally circumventing the sidewall tilting and lithium contamination problems associated with lithium niobate waveguides.

[0045] The mode converter area 2 is a conical mode converter, which has a tapered structure with an increasing cross-section along the direction from the input end to the output end. It has a starting width of 1.7 μm, an ending width of 2.1 μm, and a tapered length of 600 μm. It is used to adiabatically convert the input TM0 mode to the TE1 mode. This achieves a mode conversion efficiency of approximately 96% from TM0 to TE1, and the TE0 mode does not undergo mode conversion within the same conical structure, maintaining low-loss direct transmission.

[0046] The asymmetric directional coupler region 3 is a tapered asymmetric directional coupler design, including a main waveguide and a coupling waveguide. The main waveguide is a straight-through waveguide with a constant width (W1) of 2.1 μm, carrying the TE1 mode converted by the tapered mode converter region 2. The coupling waveguide has a tapered structure with an increasing cross-section along the output direction, and the initial width (W1) of the coupling waveguide is... 2b The median width (W2) is 0.74 μm, and the median width (W2) is 0.79 μm. This is the most suitable coupling width for a wavelength of 1530 nm. In this embodiment, the coupling waveguide strip is tapered from the median width (W2) to the terminal width (W... 2eThe coupling length of the main waveguide strip is 0.84 μm to carry the TE0 mode, and the coupling length of the coupling waveguide strip is 210 μm. The cooperation between the main waveguide strip and the coupling waveguide strip ensures that the TE1 mode in the wide waveguide (main waveguide strip) and the TE0 mode in the narrow waveguide (coupled waveguide strip) meet strict phase matching conditions at the target wavelength (1470-1570 nm).

[0047] In this embodiment, when the coupling gap between the through waveguide strip and the coupled waveguide strip is 1.4 μm, the coupling length is determined to be 210 μm based on coupled-mode theory. This achieves a near 100% TE1→TE0 conversion efficiency in the tapered asymmetric directional coupler region 3, with extremely low crosstalk to the original through TE0 channel.

[0048] The output ports include a first output port and a second output port; the straight-through waveguide strip terminates the coupling state through an S-shaped curved waveguide displacement structure and stabilizes the output optical power, then connects to the first output port for outputting TEO mode. The coupling waveguide strip connects to the second output port for outputting TEO mode.

[0049] Based on the above-described heterogeneous integrated on-chip polarization rotating beam splitter design, in this embodiment, the optical signal containing TE0 and TM0 modes (as well as the 1480 nm pump light) enters the chip from the 1.7 μm wide GeSbS single-mode waveguide region 1 at the input port. The TE0 mode passes directly and with low loss through the tapered mode converter region 2, and continues sequentially along the main waveguide strip and waveguide displacement structure of the asymmetric directional coupler region 3 to the first output port. The TM0 mode first completes the TM0→TE1 mode conversion in the 600 μm long tapered mode converter region 2, and then the TE1 mode, carrying all the energy of the TM channel, is fully coupled to the adjacent waveguide in the tapered asymmetric directional coupler region 3 and converted to the TE0 mode, realizing the TE1→TE0 mode conversion, and is then split and transmitted to the second output port. Thus, the input orthogonal polarization states (TE0 / TM0) are efficiently separated and converted into two spatially independent beams, both with the polarization state TE0.

[0050] The fabrication method of the heterogeneous integrated on-chip polarization rotating beam splitter in this embodiment includes the following steps: (1) Provide a Z-cut lithium niobate thin film substrate, which consists of a silicon substrate (500 μm), silicon oxide (4 μm), and lithium niobate thin film layer (600 nm) from bottom to top, without the need for any etching process on the lithium niobate; (2) A 400 nm thick GeSbS film was deposited on the surface of the lithium niobate film on the substrate by thermal evaporation; at the same time, the deposited film was annealed to eliminate internal stress and reduce material absorption loss. (3) Waveguide patterns are formed by electron beam exposure and reactive ion etching (RIE) etching (ICP) process to pattern the GeSbS thin film into the designed strip waveguide to form the waveguide loading structure. (4) A 2μm thick silicon oxide film is deposited on the waveguide surface after photolithography by thermal evaporation to form a cladding layer; (5) Perform optical-grade polishing on the chip end face to reduce the coupling loss between the optical fiber and the waveguide.

[0051] Example 2 A heterogeneous integrated on-chip polarization rotating beam splitter differs from Embodiment 1 in that: in the mode converter region 2 of the waveguide loading structure of this embodiment, the starting width of the tapered structure is 1.7 μm, the ending width is 2.2 μm, and the tapered length is 600 μm.

[0052] Example 3 A heterogeneous integrated on-chip polarization rotating beam splitter differs from Embodiment 1 in that: in the mode converter region 2 of the waveguide loading structure of this embodiment, the starting width of the tapered structure is 1.7 μm, the ending width is 2.1 μm, and the tapered length is 700 μm.

[0053] Example 4 A heterogeneous integrated on-chip polarization rotating beam splitter differs from Embodiment 1 in that: in the mode converter region 2 of the waveguide loading structure of this embodiment, the starting width of the tapered structure is 1.7 μm, the ending width is 2.1 μm, and the tapered length is 900 μm.

[0054] Example 5 A heterogeneous integrated on-chip polarization rotating beam splitter differs from Embodiment 1 in that: in the asymmetric directional coupler region 3 of the waveguide loading structure of this embodiment, the width (W1) of the main waveguide strip is 2.1 μm; the initial width (W1) of the coupling waveguide strip... 2b The value is 0.74 μm, and the termination width (W) is... 2e The diameter of the waveguide is 0.88 μm, and the coupling length is 210 μm; the coupling gap between the through waveguide and the coupling waveguide is 1.4 μm.

[0055] Example 6 A heterogeneous integrated on-chip polarization rotating beam splitter differs from Embodiment 1 in that: in the asymmetric directional coupler region 3 of the waveguide loading structure of this embodiment, the width (W1) of the main waveguide strip is 2.1 μm; the initial width (W1) of the coupling waveguide strip... 2b The value is 0.74 μm, and the termination width (W) is... 2eThe diameter of the waveguide is 0.84 μm, and the coupling length is 250 μm; the coupling gap between the through waveguide and the coupling waveguide is 1.4 μm.

[0056] Experiment Example 1: Design Optimization of a Cone-Mode Converter 1.1 Width Optimization of the Conical Mode Converter This experiment is based on the lithium niobate thin film layer (thickness 600 nm) and GeSbS material waveguide loading structure (thickness 400 nm) of Example 1; it studies the effective refractive index (n) of different modes (TE0, TE1, TM0, TM1). eff The relationship between waveguide width and waveguide width is shown in the following figure. Figure 4 As shown.

[0057] The results show that the effective refractive indices of the TM0 and TE1 modes overlap when the waveguide width is about 1.9 μm, satisfying the phase matching condition and achieving mode hybridization. When the waveguide width is tapered to 2.1 μm, the effective refractive indices of the modes are completely separated, thereby achieving efficient mode conversion. The devices in Embodiments 1-2 of this invention have high TM0 to TE1 mode conversion efficiency when the waveguide width at the input end is adiabatically widened from the single-mode condition (1.7 μm) to 2.1-2.2 μm through the tapered transition region.

[0058] 1.2 Length Optimization of the Conical Mode Converter This experiment further optimizes the cone length using the Eigenmode Expansion (EME) method, and studies the effect of the cone length on the transmission and conversion efficiency of the TE0 and TM0 modes as the cone length changes.

[0059] like Figure 5 As shown, when the cone length reaches 600 μm, the mode conversion efficiency from TM0 to TE1 can reach about 96%; this proves that the devices in Examples 1 and 3-4 have high mode conversion efficiency, and the TE0 mode does not undergo mode conversion in the same cone structure, maintaining low-loss direct transmission.

[0060] like Figure 6 As shown, the finite-difference time-domain (FDTD) simulation results further confirm that the TM0→TE1 conversion efficiency of this tapered mode converter remains above 95.7% in a wide wavelength range of 1470-1570 nm, demonstrating excellent broadband operating characteristics.

[0061] Experiment Example 2: Design of a Conical Asymmetric Directional Coupler like Figure 7As shown, in the tapered asymmetric directional coupler design of Example 1, the TE1 mode in the wide waveguide and the TE0 mode in the narrow waveguide satisfy a strict phase-matching condition at the target wavelength. Specifically, at a wavelength of 1530 nm, the effective refractive index of the TE1 mode in the 2.1 μm wide waveguide is 2.078, which is equal to that of the 0.79 μm narrow waveguide, satisfying the phase-matching condition of the two modes at this wavelength. In the device of Example 1 of this invention, the narrow waveguide gradually increases in width from 0.74 μm to 0.84 μm, which is beneficial for achieving broadband mode switching. When the coupling gap between the two waveguides is set to 1.4 μm, the fully coupled length is calculated to be 210 μm using coupled-mode theory. The device of Example 6 also satisfies the coupling length requirement and has comparable performance to that of Example 1, and will not be described further.

[0062] like Figure 8-10 As shown, FDTD simulation results indicate that, within a wide wavelength range of 1470-1570 nm, the TE1→TE0 conversion efficiency of the tapered mode converter in Example 1 remains above 87%. Specifically, near the 1530 nm wavelength, this tapered asymmetric directional coupler achieves a near 100% TE1→TE0 conversion efficiency with extremely low crosstalk to the original through-path TE0 channel.

[0063] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. 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. A heterogeneously integrated on-chip polarization-rotating beam splitter, comprising: The structure includes a lithium niobate thin film layer and a waveguide loading structure heterogeneously integrated on the lithium niobate thin film layer. The waveguide loading structure is made of amorphous chalcogenide glass. The waveguide loading structure includes, from the input end to the output end, an input single-mode waveguide region (1), a mode converter region (2), an asymmetric directional coupler region (3), and an output port. The mode converter area (2) is a tapered structure with an increasing cross-section along the direction from the input end to the output end, used to adiabatically convert the input TM0 mode into TE1 mode; The asymmetric directional coupler region (3) includes a through waveguide and a coupling waveguide. The coupling waveguide has a tapered structure with an increased cross-section along the output direction. The through waveguide is connected to the mode converter region (2). The coupling waveguide and the through waveguide are optically coupled to meet the phase matching condition, which is used to convert the TE1 mode to the TE0 mode. The output ports include a first output port (4) and a second output port (5), the first output port (4) being connected to the through waveguide strip and the second output port (5) being connected to the coupling waveguide strip.

2. The heterogeneously integrated on-chip polarization-rotating beam splitter of claim 1, wherein, It also includes a waveguide displacement structure, which is S-shaped and connected to the output end of the straight waveguide strip and the first output port (4).

3. The heterogeneously integrated on-chip polarization-rotating beam splitter of claim 1, wherein, The waveguide loading structure has a refractive index of 1.8-2.5 at a wavelength of 1470-1570 nm.

4. The heterogeneously integrated on-chip polarization-rotating beam splitter of claim 1, wherein, The waveguide loading structure is made of at least one of GeSbS glass, GeSbSe glass, and AsS glass.

5. The heterogeneously integrated on-chip polarization-rotating beam splitter of claim 1, wherein, The thickness of the lithium niobate thin film layer is 400-700 nm, and the thickness of the waveguide loading structure is 300-500 nm.

6. The heterogeneous integrated on-chip polarization rotating beam splitter according to claim 1, characterized in that, The width of the input single-mode waveguide region (1) is 1.0-2.5μm.

7. The heterogeneous integrated on-chip polarization rotating beam splitter according to any one of claims 4-6, characterized in that, When the waveguide loading structure material is GeSbS glass, the width of the input single-mode waveguide region (1) is 1.6-1.8μm, and the starting width of the tapered structure of the mode converter region (2) is the same as the width of the input single-mode waveguide region (1), the ending width is 2.1-2.3μm, and the tapered length is ≥600 μm.

8. The heterogeneous integrated on-chip polarization rotating beam splitter according to claim 7, characterized in that, In the asymmetric directional coupler region (3), the width of the through waveguide strip is the same as the termination width of the mode converter region (2). In the coupling waveguide strip, the starting width is 0.72-0.76μm, the termination width is 0.82-0.86μm, and the coupling length is ≥210μm. The coupling gap between the through waveguide strip and the coupling waveguide strip is 1.3-1.5μm.

9. A method for fabricating a heterogeneous integrated on-chip polarization rotating beam splitter according to any one of claims 1-8, characterized in that, Includes the following steps: A substrate including a lithium niobate thin film layer is taken, and an amorphous chalcogenide glass waveguide layer is deposited on the surface of the lithium niobate thin film layer. The amorphous chalcogenide glass waveguide layer is etched to form a waveguide loading structure, thereby obtaining the heterogeneous integrated on-chip polarization rotating beam splitter.

10. The application of the heterogeneous integrated on-chip polarization rotating beam splitter according to any one of claims 1-8 in an optical communication system, a quantum information processor, or an optical sensing device.

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