Thin film lithium niobate polarizer, photonic chip, and optical quantum computer

Abstract

This application relates to a thin-film lithium niobate polarizer, a photonic chip, and an optical quantum computer. The thin-film lithium niobate polarizer includes: a beam splitter, a first bent waveguide, a second bent waveguide, a first straight waveguide, a second straight waveguide, a third bent waveguide, a fourth bent waveguide, and a beam combiner; the first bent waveguide is connected to the third bent waveguide through the first straight waveguide, and the second bent waveguide is connected to the fourth bent waveguide through the second straight waveguide; the first, second, third, and fourth bent waveguides have the same shape and are arranged centrally symmetrically; the first and second straight waveguides have the same shape and are arranged parallel to each other; wherein, all waveguides are shallowly etched waveguides.

Description

Technical Field

[0001] This application relates to the field of integrated photonics technology, and in particular to a thin-film lithium niobate polarizer, a photonic chip, and an optical quantum computer. Background Technology

[0002] In recent years, the maturity of thin-film lithium niobate (TFLN) technology has made it possible to realize high-density, low-loss, and high-efficiency photonic integrated circuits on chips. Furthermore, polarization multiplexing technology also requires selective processing of different polarization states on the chip. Therefore, developing high-performance, easily integrated on-chip polarizers on the thin-film lithium niobate platform has significant application value.

[0003] Traditional techniques disclose polarizers based on bent waveguides, which employ multiple bent structures with adjacent structures bending in opposite directions to degrade unwanted modes at the bends (TE and TM modes exhibit different losses at bends), thus enabling polarizers to pass only a specific mode. However, while bent structures can significantly degrade unwanted modes, they also incur losses for desired modes, resulting in high overall polarizer loss. Summary of the Invention

[0004] Based on this, and in response to the aforementioned technical problems, this application provides a thin-film lithium niobate polarizer, a photonic chip, and an optical quantum computer that can reduce losses.

[0005] In a first aspect, this application proposes a thin-film lithium niobate polarizer, comprising:

[0006] The beam splitter includes a beam splitting input waveguide, a first output waveguide, and a second output waveguide.

[0007] A first curved waveguide, one end of which is connected to a first output waveguide;

[0008] A second curved waveguide, one end of which is connected to a second output waveguide;

[0009] The first straight waveguide, one end of which is connected to the other end of the first curved waveguide;

[0010] A second straight waveguide, one end of which is connected to the other end of a second curved waveguide;

[0011] The third curved waveguide has one end connected to the other end of the first straight waveguide;

[0012] The fourth curved waveguide is connected at one end to the other end of the second straight waveguide;

[0013] A beam combiner includes a first input waveguide, a second input waveguide, and a beam combiner output waveguide. The first input waveguide is connected to the other end of a third curved waveguide, and the second input waveguide is connected to the other end of a fourth curved waveguide.

[0014] The first, second, third, and fourth curved waveguides have the same shape and are arranged in a centrally symmetrical manner; the first and second straight waveguides have the same shape and are arranged in parallel.

[0015] All waveguides are shallowly etched.

[0016] In one embodiment, the beam splitter, the first bent waveguide, the second bent waveguide, the third bent waveguide, the fourth bent waveguide, the first straight waveguide, the second straight waveguide, and the beam combiner are all ridge waveguides on a lithium niobate layer, the lithium niobate layer having a thickness of 400 nanometers to 600 nanometers, and the etching depth of the lithium niobate layer being 60 nanometers to half the thickness of the lithium niobate layer.

[0017] In one embodiment, the etching depth of the lithium niobate layer is approximately 100 nanometers.

[0018] In one embodiment, the spacing between the first straight waveguide and the second straight waveguide is the same as the width of the first straight waveguide and the second straight waveguide.

[0019] In one embodiment, the width of both the first and second straight waveguides is 0.8 micrometers to 1.1 micrometers, and the length of both the first and second straight waveguides is 20 micrometers to 40 micrometers.

[0020] In one embodiment, the beam splitter further includes: a first multimode waveguide region, one end of which is connected to the beam splitting input waveguide, and the other end of which is connected to the first output waveguide and the second output waveguide, respectively.

[0021] In one embodiment, the beam-splitter input waveguide, the first output waveguide, and the second output waveguide are all configured as tapered waveguides. The wide ends of the beam-splitter input waveguide, the first output waveguide, and the second output waveguide are all connected to the first multimode waveguide region. The narrow end widths of the beam-splitter input waveguide, the first output waveguide, and the second output waveguide are 0.8 micrometers to 1.1 micrometers, and the wide end widths of the beam-splitter input waveguide, the first output waveguide, and the second output waveguide are 2 micrometers to 2.4 micrometers. The length of the tapered waveguide is 8 micrometers to 16 micrometers, the length of the first multimode waveguide region is 23 micrometers to 30 micrometers, and the width of the first multimode waveguide region is 2.4 micrometers to 3.4 micrometers.

[0022] In one embodiment, the beam combiner further includes a second multimode waveguide region, one end of which is connected to the first input waveguide and the second input waveguide, and the other end of which is connected to the beam combiner output waveguide.

[0023] In one embodiment, the shapes of the first, second, third, and fourth curved waveguides are all set as cubic Bézier curves.

[0024] In one embodiment, the length of the cubic Bézier curve is set to 20 to 30 micrometers, and the width of the cubic Bézier curve is set to less than 1 micrometer.

[0025] Secondly, this application also proposes a photonic chip, including the thin-film lithium niobate polarizer of the first aspect embodiment described above.

[0026] Thirdly, this application also proposes an optical quantum computer, including the photonic chip of the second aspect embodiment described above.

[0027] The aforementioned thin-film lithium niobate polarizer, photonic chip, and optical quantum computer split the input light using a beam splitter. Then, the spacing between the output waveguides is increased using a first and second bent waveguide, and the light is input into a first and second straight waveguide. The dual-waveguide structure formed by the first and second straight waveguides supports only the TE00 mode and not the TM mode, thus naturally providing polarization. Therefore, the mode transmitted on each straight waveguide is the TE0 mode. Finally, the light passes through a third and fourth bent waveguide into a beam combiner for output. At this point, only the TE0 mode remains in the output light, completing the polarization of the input light. Compared to traditional polarizers with two bent structures in opposite directions, the thin-film lithium niobate polarizer of this application does not cause additional loss to the TE0 mode. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of a thin-film lithium niobate polarizer in one embodiment;

[0030] Figure 2 This is a schematic diagram of a ridge waveguide in one embodiment;

[0031] Figure 3 This is a schematic diagram of the first and second straight waveguides in one embodiment;

[0032] Figure 4 This is a schematic diagram of a beam splitter in one embodiment;

[0033] Figure 5This is a schematic diagram of a beam combiner in one embodiment;

[0034] Figure 6 This is a schematic diagram of a cubic Bézier curve in one embodiment.

[0035] Explanation of reference numerals in the attached figures:

[0036] 110. Beam splitter; 120. First curved waveguide; 130. Second curved waveguide; 140. First straight waveguide; 150. Second straight waveguide; 160. Third curved waveguide; 170. Fourth curved waveguide; 180. Beam combiner; 111. Beam splitter input waveguide; 112. First output waveguide; 113. Second output waveguide; 114. First multimode waveguide region; 181. First input waveguide; 182. Second input waveguide; 183. Beam combiner output waveguide; 184. Second multimode waveguide region. Detailed Implementation

[0037] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0039] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another.

[0040] Spatial relation terms such as “below,” “under,” “below,” “below,” “above,” “over,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, an element or feature described as “below,” “under,” or “below” other elements or features would be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both upper and lower orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein are interpreted accordingly.

[0041] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. Furthermore, in the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if there is an exchange of electrical signals or data between the connected objects.

[0042] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0043] In traditional technology, adjacent curved structures bend in opposite directions to reduce unwanted modes at the bend (TE and TM modes have different losses at the bend), thus enabling a polarizer to transmit only a specific mode. While this type of curved structure can reduce unwanted modes to a large extent, it also reduces the modes that need to be transmitted.

[0044] In addition, some related technologies employ a scheme based on upper and lower layer coupling structures and beam combiners. This scheme first converts the TM0 mode of the input light, which contains both TE0 and TM0 modes, into TE1 mode. Then, through mode matching, the TE1 mode is coupled to the upper TE0 mode. The original TE0 mode still passes through the lower waveguide. Subsequently, the TE0 modes from the upper and lower waveguides are passed through the upper and lower arms of an interferometer, respectively, to compensate the phase of the two TE0 beams to be identical before beam combining. The TM0 mode that has not been converted to TE1 will still be output from the lower waveguide. Furthermore, the interferometer's manufacturing tolerance is small, making it difficult to achieve perfect phase compensation, which may reduce the output optical power of the TE0 mode. The reduced output optical power of the TE0 mode, combined with the residual TM0 mode, lowers the polarization extinction ratio. Therefore, this type of polarizer based on coupling structures and beam combiners suffers from large size and a low polarization extinction ratio.

[0045] Based on this, embodiments of the present disclosure provide a thin-film lithium niobate polarizer, a photonic chip, and an optical quantum computer.

[0046] In one embodiment, a thin-film lithium niobate polarizer is provided, comprising: a beam splitter, the beam splitter including a beam-splitting input waveguide, a first output waveguide, and a second output waveguide; a first bent waveguide, one end of which is connected to the first output waveguide; a second bent waveguide, one end of which is connected to the second output waveguide; a first straight waveguide, one end of which is connected to the other end of the first bent waveguide; a second straight waveguide, one end of which is connected to the other end of the second bent waveguide; and a third bent waveguide, one end of which is connected to the first straight waveguide. The other end; a fourth curved waveguide, one end of which is connected to the other end of the second straight waveguide; a beam combiner, which includes a first input waveguide, a second input waveguide, and a beam combiner output waveguide, the first input waveguide being connected to the other end of the third curved waveguide, and the second input waveguide being connected to the other end of the fourth curved waveguide; the first curved waveguide, the second curved waveguide, the third curved waveguide, and the fourth curved waveguide have the same shape and are arranged in a centrally symmetrical manner; the first straight waveguide and the second straight waveguide have the same shape and are arranged in parallel; wherein, all waveguides are shallowly etched waveguides.

[0047] Figure 1 A schematic diagram of a thin-film lithium niobate polarizer provided according to an embodiment of the present disclosure is shown.

[0048] In one embodiment, such as Figure 1 As shown, a thin-film lithium niobate polarizer is provided, including: a beam splitter 110, a first bent waveguide 120, a second bent waveguide 130, a first straight waveguide 140, a second straight waveguide 150, a third bent waveguide 160, a fourth bent waveguide 170, and a beam combiner 180.

[0049] Beam splitter 110 includes a beam-splitting input waveguide 111, a first output waveguide 112, and a second output waveguide 113. One end of a first curved waveguide 120 is connected to the first output waveguide 112. One end of a second curved waveguide 130 is connected to the second output waveguide 113. One end of a first straight waveguide 140 is connected to the other end of the first curved waveguide 120. One end of a second straight waveguide 150 is connected to the other end of the second curved waveguide 130. One end of a third curved waveguide 160 is connected to the other end of the first straight waveguide 140. One end of a fourth curved waveguide 170 is connected to the other end of the second straight waveguide 150.

[0050] The combiner 180 includes a first input waveguide 181, a second input waveguide 182, and a combiner output waveguide 183. The first input waveguide 181 is connected to the other end of the third curved waveguide 160, and the second input waveguide 182 is connected to the other end of the fourth curved waveguide 170. The first curved waveguide 120, the second curved waveguide 130, the third curved waveguide 160, and the fourth curved waveguide 170 have the same shape and are arranged centrally symmetrically. The first straight waveguide 140 and the second straight waveguide 150 have the same shape and are arranged in parallel. All waveguides here are shallowly etched waveguides.

[0051] Beam splitter 110 splits the input optical signal into beams. The beam splitting input waveguide 111 receives the input optical signal, and the first output waveguide 112 and the second output waveguide 113 output the split optical signal. Depending on the specific application requirements, beam splitter 110 can employ various physical structures, such as a Y-type beam splitter or a multimode interference coupler.

[0052] One end of the first curved waveguide 120 is connected to the first output waveguide 112, and the other end of the first curved waveguide 120 is connected to one end of the first straight waveguide 140. One end of the second curved waveguide 130 is connected to the second output waveguide 113, and the other end of the second curved waveguide 130 is connected to one end of the second straight waveguide 150. The first curved waveguide 120 and the second curved waveguide 130 are used to adjust the spacing of the output waveguides and input the split optical signal into the dual waveguide structure containing the first straight waveguide 140 and the second straight waveguide 150.

[0053] The first straight waveguide 140 and the second straight waveguide 150 are identical in shape and arranged in parallel. The dual-waveguide structure containing both the first straight waveguide 140 and the second straight waveguide 150 is used for polarization filtering. By precisely adjusting the cross-sectional dimensions (such as width and thickness) of the straight waveguides and the spacing between the two straight waveguides, the dual-waveguide structure can be made to support only TE polarization filtering. 00 The mode of optical signal transmission, while TM 00 The effective refractive index of the mode is lower than that of TE. 00 The refractive index of the mode cannot be effectively confined, resulting in radiation leakage.

[0054] One end of the third curved waveguide 160 is connected to the other end of the first straight waveguide 140, and the other end of the third curved waveguide 160 is connected to the first input waveguide 181. One end of the fourth curved waveguide 170 is connected to the other end of the second straight waveguide 150, and the other end of the fourth curved waveguide 170 is connected to the second input waveguide 182. The third curved waveguide 160 and the fourth curved waveguide 170 are used to adjust the spacing of the input waveguides and to combine the polarization-filtered split beam signals into a smooth input beam combiner 180.

[0055] Beam combiner 180 is used to combine the input optical signals. The first input waveguide 181 and the second input waveguide 182 are used to receive the split optical signals after polarization filtering, and the beam combiner output waveguide 183 is used to output the combined optical signal. Since only TE remains in the first straight waveguide 140 and the second straight waveguide 150... 00The optical signal is a TM mode, therefore, in the optical signal output after beam combining by beam combiner 180, the TM mode has been completely stripped, and only the TE mode is retained. Depending on the specific application requirements, beam combiner 180 can adopt various physical structures, such as a Y-type beam combiner, a multimode interference coupler, etc. The structures of beam combiner 180 and beam splitter 110 can be the same or different.

[0056] The first curved waveguide 120, the second curved waveguide 130, the third curved waveguide 160 and the fourth curved waveguide 170 have the same shape and are arranged in a centrally symmetrical manner. This symmetrical arrangement ensures that the two optical signals experience exactly the same bending loss and phase change when turning, thereby maintaining the optical path difference and phase balance between the two arms.

[0057] When the waveguide thickness (i.e., etching depth) is large, it becomes impossible for the waveguide structure to support only TE. 00 The TM mode can also be transmitted.

[0058] It should be noted that this application describes the TE0 mode and TE. 00 The TE0 mode is for transverse electric modes in a single waveguide, while the TE... 00 The pattern is also known as the even-symmetric supermodel, TE. 00 The mode refers to the TE0 mode where the two waveguides have the same phase. That is, in this application, the mode TE or TM followed by a single number and followed by two numbers correspond to a single waveguide and a dual waveguide, respectively. Furthermore, the TE0 mode can also be represented as TE0 mode, TE... 00 The mode can also be represented as TE00 mode, TE1 mode can also be represented as TE1 mode, TM0 mode can also be represented as TM0 mode, and so on.

[0059] In this embodiment, all curved waveguides do not employ a 90-degree bend structure, thus avoiding additional losses to the TEO mode. Furthermore, all waveguides in this embodiment are manufactured using shallow etching, meaning the waveguide thickness or etching thickness is less than or equal to half the thickness of the lithium niobate layer.

[0060] In the thin-film lithium niobate polarizer provided in this embodiment, the first bent waveguide 120, the first straight waveguide 140, and the third bent waveguide 160 can be considered as "one" waveguide, and the second bent waveguide 130, the second straight waveguide 150, and the fourth bent waveguide 170 can be considered as "another" waveguide. These two waveguides form a dual-waveguide structure. The symmetrically arranged shallow-etched dual-waveguide structure allows the polarizer to support only TE. 00 The passage of the mode filters out the TM mode, thus achieving the effect of having only a single polarization state (TE). In addition, the single-layer thin-film lithium niobate polarizer provided in this application has a simple structure, which can filter out the TM mode by utilizing only the characteristics of the waveguide itself. It is not only easy to implement but also low in cost.

[0061] In one embodiment, the beam splitter 110, the first bent waveguide 120, the second bent waveguide 130, the third bent waveguide 160, the fourth bent waveguide 170, the first straight waveguide 140, the second straight waveguide 150, and the beam combiner 180 are all ridge waveguides on a lithium niobate layer. The thickness of the lithium niobate layer is 400 nm to 600 nm, and the etching depth of the lithium niobate layer is 60 nm to half the thickness of the lithium niobate layer. Preferably, when the thickness of the lithium niobate layer is 400 nm, the etching depth of the lithium niobate layer is 60 nm to 150 nm (inclusive). More preferably, when the thickness of the lithium niobate layer is 400 nm, the etching depth of the lithium niobate layer is approximately 100 nm.

[0062] Figure 2 A schematic diagram of a mid-ridge waveguide provided according to an embodiment of the present disclosure is shown.

[0063] like Figure 2 As shown, the polarizer in this embodiment can be designed using a 400 nm to 600 nm TFLN (thin-film lithium niobate) platform. The thickness of the lithium niobate layer is 400 nm to 600 nm, i.e., 400 nm ≤ D1 ≤ 600 nm. For the thin-film lithium niobate wafer, a ridge waveguide is formed on the lithium niobate layer after exposure and etching (such as ICP etching). The etching depth of the lithium niobate layer is 60 nm to half the thickness of the lithium niobate layer, i.e., 60 nm ≤ D2 ≤ D1 / 2. Subsequently, a silicon oxide layer is deposited on the ridge waveguide to protect the waveguide in the thin-film lithium niobate layer, for example, a silicon oxide layer with a thickness of more than 2 micrometers.

[0064] In traditional technologies, polarizer structures composed of straight and curved polarizing waveguides can only be applied to 300 nm TFLN platforms (i.e., lithium niobate layers with a thickness of 300 nm) to achieve quasi-TE polarization. 00 The stable transmission of the mode is not feasible because its structure cannot be adapted to the 400nm to 600nm TFLN platform.

[0065] This application utilizes a beam splitter 110, a first bent waveguide 120, a second bent waveguide 130, a third bent waveguide 160, a fourth bent waveguide 170, a first straight waveguide 140, a second straight waveguide 150, and a beam combiner 180 with shallowly etched ridge waveguide structures to form a polarizer that filters out TM modes on TFLN platforms above 400 nm, with relatively low polarizer loss.

[0066] In one embodiment, the spacing between the first straight waveguide 140 and the second straight waveguide 150 is the same as the width of the first straight waveguide 140 and the second straight waveguide 150.

[0067] As an illustration. Figure 2 Only a cross-section of a single ridge waveguide is shown, not the entire cross-section. Figure 1 The cross-sectional view of the curved waveguide region is shown.

[0068] Figure 3 A schematic diagram of a first straight waveguide and a second straight waveguide provided according to an embodiment of the present disclosure is shown.

[0069] like Figure 3 As shown, the first straight waveguide 140 and the second straight waveguide 150 have the same shape. Therefore, the width of the first straight waveguide 140 is the same as the width of the second straight waveguide 150, i.e., W1=W2. At the same time, the spacing between the first straight waveguide 140 and the second straight waveguide 150 is also the same as the width of the first straight waveguide 140 and the second straight waveguide 150, i.e., G1=W1=W2.

[0070] In one embodiment, such as Figure 3 As shown, the widths of the first straight waveguide 140 and the second straight waveguide 150 are both 0.8 μm to 1.1 μm, i.e., 0.8 μm ≤ W1 = W2 ≤ 1.1 μm. The lengths of the first straight waveguide 140 and the second straight waveguide 150 are both 20 μm to 40 μm, i.e., 20 μm ≤ L1 ≤ 40 μm.

[0071] Figure 4 A schematic diagram of a beam splitter provided according to an embodiment of the present disclosure is shown.

[0072] In one embodiment, such as Figure 4 As shown, the beam splitter 110 further includes a first multimode waveguide region 114, one end of which is connected to the beam-splitting input waveguide 111, and the other end of which is connected to the first output waveguide 112 and the second output waveguide 113, respectively. In this embodiment, the beam splitter 110 employs a multimode interference coupler structure. The first multimode waveguide region 114 is the core region for beam splitting, and its width is generally much larger than that of a single-mode waveguide, thus enabling it to support multiple modes simultaneously. The multimode interference coupler utilizes the difference in propagation constants of multiple modes in a wide waveguide to induce interference. By precisely controlling the waveguide length, constructive interference occurs at the output end face of the input light field, thereby self-imaged multiple light spots of equal intensity, achieving uniform distribution of optical power. Compared to using a Y-type beam splitter, the multimode interference coupler has lower losses.

[0073] In one embodiment, such as Figure 4As shown, the beam-splitting input waveguide 111, the first output waveguide 112, and the second output waveguide 113 are all configured as tapered waveguides, and their wide ends are connected to the first multimode waveguide region 114. The narrow end widths of the beam-splitting input waveguide 111, the first output waveguide 112, and the second output waveguide 113 are 0.8 μm to 1.1 μm, i.e., 0.8 μm ≤ Wn ≤ 1.1 μm. The wide end widths of the beam-splitting input waveguide 111, the first output waveguide 112, and the second output waveguide 113 are 2 μm to 2.4 μm, i.e., 2 μm ≤ Ww ≤ 2.4 μm. The lengths of the beam-splitting input waveguide 111, the first output waveguide 112, and the second output waveguide 113 are 8 μm to 16 μm, i.e., 8 μm ≤ Lt ≤ 16 μm. The length of the first multimode waveguide region 114 is 23 μm to 30 μm, i.e., 23 μm ≤ Lmmi ≤ 30 μm. The width of the first multimode waveguide region 114 is 2.4 μm to 3.4 μm, i.e., 2.4 μm ≤ Wmmi ≤ 3.4 μm.

[0074] Figure 5 A schematic diagram of a bundle combiner provided according to an embodiment of the present disclosure is shown.

[0075] In one embodiment, such as Figure 5 As shown, the beam combiner 180 further includes a second multimode waveguide region 184. One end of the second multimode waveguide region 184 is connected to the first input waveguide 181 and the second input waveguide 182, respectively, and the other end of the second multimode waveguide region 184 is connected to the beam-combining output waveguide 183. In this embodiment, the beam combiner 180 also adopts a multimode interference coupler structure. Two optical signals are simultaneously injected into the second multimode waveguide region 184 from the first input waveguide 181 and the second input waveguide 182, respectively. After entering the second multimode waveguide region 184, these two optical signals will also excite multiple lateral propagation modes within the second multimode waveguide region 184. When these two optical signals propagate in the second multimode waveguide region 184 for the same specific length as the beam splitter 110, their interference result will reconstruct the image of the input light field at the other end of the second multimode waveguide region 184, thereby realizing the physical merging of the two optical signals. Since the light reaching the beam combiner 180 is already a pure TE after being filtered by a straight waveguide... 00 Therefore, the multimode interference coupler structure can perfectly combine two co-polarized beams with extremely low loss, avoiding additional losses caused by mode mismatch. Furthermore, compared to the Y-type beam combiner 180, the multimode interference coupler structure has no geometrical abrupt change at the merging node, resulting in lower loss and less stringent manufacturing requirements.

[0076] In one embodiment, such as Figure 5As shown, the first input waveguide 181, the second input waveguide 182, and the beam combiner output waveguide 183 are all configured as tapered waveguides. The wide ends of the first input waveguide 181, the second input waveguide 182, and the beam combiner output waveguide 183 are all connected to the second multimode waveguide region 184. The narrow end widths of the first input waveguide 181, the second input waveguide 182, and the beam combiner output waveguide 183 are 0.8 μm to 1.1 μm, the wide end widths of the first input waveguide 181, the second input waveguide 182, and the beam combiner output waveguide 183 are 2 μm to 2.4 μm, and the lengths of the first input waveguide 181, the second input waveguide 182, and the beam combiner output waveguide 183 are 20 μm to 30 μm. The length of the second multimode waveguide region 184 is 60 μm to 70 μm, and the width of the second multimode waveguide region 184 is 4.4 μm to 6 μm.

[0077] In one embodiment, the shapes of the first bent waveguide 120, the second bent waveguide 130, the third bent waveguide 160, and the fourth bent waveguide 170 are all set as cubic Bézier curves. Optical waveguides are extremely sensitive to bending. If there is a bend (abrupt curvature) at the connection between the bent section and the straight waveguide, it will lead to severe radiation loss and mode crosstalk. By adjusting the control points of the Bézier curve so that its tangents at the start and end points are collinear with the connected straight waveguide, a smooth curvature transition can be perfectly achieved, minimizing optical field leakage and thus reducing loss.

[0078] Figure 6 A schematic diagram of a cubic Bézier curve provided according to an embodiment of the present disclosure is shown.

[0079] like Figure 6 As shown, a cubic Bézier curve is defined by four points P0, P1, P2, and P3. P0 and P3 are the start and end points of the curve, respectively, and the curve must pass through these two points. P1 and P2 are control points, which the curve usually does not pass through and are used to guide the shape of the curve.

[0080] In one embodiment, such as Figure 6 As shown, the length L of the cubic Bézier curve is set to 20 to 30 micrometers, i.e., 20 μm ≤ L ≤ 30 μm. The width h of the cubic Bézier curve is set to less than 1 micrometer, i.e., h < 1 μm. The starting point P0 is defined as (0,0), and the ending point P3 is defined as (L,h). Optionally, control point P1 is set at (L / 4,0), and control point P2 is set at (3L / 4,h).

[0081] The thin-film lithium niobate polarizer provided in this application is an on-chip polarizer, suitable for the O-band of 1260nm~1360nm. By adopting the structure of the thin-film lithium niobate polarizer of this application and only adjusting the dimensions of each part, the polarizer can be applied to the C-band.

[0082] In one embodiment, this application also provides a photonic chip, including the thin-film lithium niobate polarizer described in the above embodiments. The photonic chip can be any photonic chip that utilizes a polarizer, such as a programmable photonic integrated circuit, an optical computing chip, an optical switch, an optical phased array, or a tunable laser.

[0083] In one embodiment, this application also provides an optical quantum computer, including the photonic chip described in the above embodiment. The optical quantum computer performs computational tasks by manipulating the quantum states (such as polarization and path) of photons in the photonic chip, thereby completing quantum computing.

[0084] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," and "specific embodiment" refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example that is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0085] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A thin-film lithium niobate polarizer, characterized in that, include: The beam splitter includes a beam splitting input waveguide, a first output waveguide, and a second output waveguide. A first curved waveguide, one end of which is connected to the first output waveguide; A second curved waveguide, one end of which is connected to the second output waveguide; The first straight waveguide, one end of which is connected to the other end of the first curved waveguide; A second straight waveguide, one end of which is connected to the other end of the second curved waveguide; A third curved waveguide, one end of which is connected to the other end of the first straight waveguide; A fourth curved waveguide, one end of which is connected to the other end of the second straight waveguide; A beam combiner, comprising a first input waveguide, a second input waveguide, and a beam combiner output waveguide, wherein the first input waveguide is connected to the other end of the third curved waveguide, and the second input waveguide is connected to the other end of the fourth curved waveguide; The first curved waveguide, the second curved waveguide, the third curved waveguide, and the fourth curved waveguide have the same shape and are arranged in a centrally symmetrical manner; the first straight waveguide and the second straight waveguide have the same shape and are arranged in parallel. All waveguides are shallowly etched.

2. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The beam splitter, the first curved waveguide, the second curved waveguide, the third curved waveguide, the fourth curved waveguide, the first straight waveguide, the second straight waveguide, and the beam combiner are all ridge waveguides on a lithium niobate layer. The thickness of the lithium niobate layer is 400 nanometers to 600 nanometers, and the etching depth of the lithium niobate layer is 60 nanometers to half the thickness of the lithium niobate layer.

3. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The spacing between the first straight waveguide and the second straight waveguide is the same as the width of the first straight waveguide and the second straight waveguide.

4. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The width of both the first straight waveguide and the second straight waveguide is 0.8 micrometers to 1.1 micrometers, and the length of both the first straight waveguide and the second straight waveguide is 20 micrometers to 40 micrometers.

5. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The beam splitter further includes: a first multimode waveguide region, one end of which is connected to the beam splitting input waveguide, and the other end of which is connected to the first output waveguide and the second output waveguide, respectively.

6. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The beam combiner further includes a second multimode waveguide region, one end of which is connected to the first input waveguide and the second input waveguide, and the other end of which is connected to the beam combiner output waveguide.

7. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The shapes of the first, second, third, and fourth curved waveguides are all set as cubic Bézier curves.

8. The thin-film lithium niobate polarizer according to claim 7, characterized in that, The length of the cubic Bézier curve is set to 20 to 30 micrometers, and the width of the cubic Bézier curve is set to less than 1 micrometer.

9. A photonic chip, characterized in that, Including the thin-film lithium niobate polarizer as described in any one of claims 1 to 8.

10. An optical quantum computer, characterized in that, Including the photonic chip as described in claim 9.

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