A small low half-wave voltage thin film lithium niobate Y waveguide

Abstract

A small low half-wave voltage thin film lithium niobate Y waveguide, comprising an optical path structure composed of an input end face coupler, an input waveguide, a beam splitter, a modulation arm, an output waveguide and an output end face coupler connected in sequence and a modulation electrode; the modulation arm comprises two parallel and equidistant waveguide components, each waveguide comprising a clockwise rotating rectangular spiral waveguide, an S-shaped bending waveguide and a counterclockwise rotating rectangular spiral waveguide connected in sequence; in the modulation electrode, the branch electrodes are connected with the corresponding main electrodes according to the required polarity, and are distributed in the middle and both sides of the two waveguides of the modulation arm, so that the two waveguide components of the modulation arm are only subjected to electric field modulation in one direction; the application breaks the restriction of chip miniaturization on the length of the waveguide by improving the waveguide optical path of the modulation arm and connecting the modulation electrodes in parallel, and ensures the phase change accumulation caused by the applied electric field by reasonably matching the polarity of the electrodes on both sides of the waveguide, thereby improving the modulation length and effectively reducing the size and half-wave voltage of the Y waveguide.

Description

Technical Field

[0001] This invention belongs to the field of integrated optical waveguides and relates to a small, low half-wave voltage thin-film lithium niobate Y waveguide. Background Technology

[0002] Fiber optic gyroscopes are fiber optic sensors used in inertial navigation, widely applied in aerospace, marine, defense industries, and autonomous intelligent systems. In recent years, the size, weight, and cost of fiber optic gyroscopes have become increasingly insufficient to meet the demands of lightweight, compact, and high-precision applications. The Y-waveguide is a core component of the optical path in a fiber optic gyroscope system and a crucial factor determining its performance.

[0003] The design and fabrication of Y-waveguide modulators using single-crystal lithium niobate (LNiO) materials are relatively mature, but they face significant bottlenecks in terms of size and modulation efficiency. Optical waveguides made from LNiO materials using titanium diffusion or proton exchange techniques have weak optical confinement and a large minimum bending radius. To prevent metal absorption losses, a large gap exists between the waveguide and the electrodes, making it difficult to reduce chip size and half-wave voltage. The emergence of thin-film LNiO materials offers a possibility for the development of high-performance Y-waveguide modulators. Thin-film LNiO waveguides have strong optical confinement, overcoming the shortcomings of single-crystal LNiO materials, and can reduce Y-waveguide size and improve modulation efficiency. However, the half-wave voltage of a Y-waveguide is inversely proportional to the modulation length. Due to chip size limitations, the waveguide length in one direction is limited. To further reduce the half-wave voltage, it is necessary to overcome the constraint of chip length on modulation efficiency. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a small, low half-wave voltage thin-film lithium niobate Y-waveguide, thereby improving the modulation efficiency of the Y-waveguide with a very small chip length and reducing the chip size while lowering the half-wave voltage.

[0005] The solution of the present invention is:

[0006] A small, low half-wave voltage thin-film lithium niobate Y-waveguide includes an optical path structure and a modulation electrode. The optical path structure includes an input end-face coupler, an input waveguide, a beam splitter, a modulation arm, an output waveguide, and an output end-face coupler connected in sequence.

[0007] The modulation arm consists of two parallel and equidistant waveguide components. Each waveguide component includes a clockwise rotating rectangular helical waveguide, an S-shaped curved waveguide, and a counterclockwise rotating rectangular helical waveguide connected in sequence. The entire structure of the modulation arm is centrally symmetrically distributed, and the modulation arm rotates the output direction of the waveguide component relative to the input direction by n*90°, where n≥1 and n∈natural numbers. The modulation electrodes include a main circuit signal electrode, a main circuit ground electrode, and branch electrodes. The branch electrodes are connected to the main circuit signal electrode or the main circuit ground electrode according to the required polarity and are distributed in the middle and on the upper and lower sides of the horizontal section of the two waveguide components of the modulation arm. They work in a push-pull manner to ensure that each of the two waveguide components of the modulation arm is modulated by an electric field in only one direction.

[0008] Preferably, the clockwise and counterclockwise rotating rectangular helical waveguides in the modulation arm are both formed by alternating straight waveguides and 90° arc waveguides; in the clockwise or counterclockwise rotating rectangular helical waveguides, the length of the straight waveguide connected to the S-shaped curved waveguide is less than the length of the other horizontal straight waveguide segments.

[0009] Preferably, the S-shaped curved waveguide in the modulation arm is formed by connecting two circular arcs with the same central angle.

[0010] Preferably, the branch electrodes in the modulation electrode are multiple parallel coplanar waveguide structures, which are equally spaced in the middle and upper and lower sides of each horizontal straight waveguide segment of the two parallel equidistant waveguide components of the modulation arm, and the branch electrodes on both sides have the same polarity, while the branch electrodes in the middle have different polarities from those on both sides.

[0011] Preferably, the polarity of the branch electrodes in the modulation electrode is related to the light transmission direction in the modulation arm. The branch electrodes in the middle of each horizontal straight waveguide segment with the same light transmission direction have the same polarity, while the branch electrodes in the middle of horizontal straight waveguide segments with opposite light transmission directions have different polarities.

[0012] Preferably, the beam splitter is one of a Y-branch, a multimode interference coupler, or a directional coupler.

[0013] Preferably, the mode size of the input end face coupler and the output end face coupler matches the mode size of a common single-mode fiber.

[0014] Preferably, the substrate material of the low half-wave voltage thin-film lithium niobate Y-waveguide chip consists of a silicon substrate layer, a silicon oxide layer, and a lithium niobate layer from bottom to top. After etching out the waveguide optical path structure, a silicon oxide cladding layer is grown on the surface.

[0015] Preferably, the modulation electrode is fabricated on a silicon oxide cladding layer.

[0016] The advantages of this invention compared to the prior art are:

[0017] This invention is based on the fabrication of optical waveguides on thin-film lithium niobate substrates, breaking through the bottleneck of single-crystal lithium niobate materials. By etching subwavelength waveguides, the chip size is reduced and the modulation efficiency is improved.

[0018] This invention discloses a small, low half-wave voltage thin-film lithium niobate Y-waveguide. The modulation arm waveguide employs a rectangular spiral design, overcoming the limitations imposed on waveguide length by chip miniaturization. For complex transmission optical paths, multiple coplanar waveguide electrodes are connected in parallel. By rationally matching the polarities of the electrodes on both sides of the waveguide, the accumulation of phase transition caused by the applied electric field is ensured, thereby increasing the modulation length. The improved structure effectively reduces the half-wave voltage within a smaller chip size, meeting the requirements for application in miniaturized fiber optic gyroscopes, which helps reduce power consumption and improve the stability of the fiber optic gyroscope. Attached Figure Description

[0019] Figure 1 This is a top view schematic diagram of a small, low half-wave voltage thin-film lithium niobate Y-waveguide according to Embodiment 1 of the present invention;

[0020] Figure 2 This is a top view schematic diagram of a small low half-wave voltage thin-film lithium niobate Y-waveguide according to Embodiment 2 of the present invention;

[0021] Figure 3 This is a schematic diagram of a two-dimensional cross-section of a small, low half-wave voltage thin-film lithium niobate Y-waveguide modulation electrode according to Embodiment 1 of the present invention.

[0022] Figure 4 This is a graph showing the variation of half-wave voltage with modulation length in a small, low half-wave voltage thin-film lithium niobate Y-waveguide according to Embodiment 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0024] This invention proposes a small, low half-wave voltage thin-film lithium niobate Y-waveguide, comprising an optical path structure consisting of an input end-face coupler 1, an input waveguide 2, a beam splitter 3, a modulation arm 4, an output waveguide 5, and an output end-face coupler 6 connected in sequence, as well as a modulation electrode.

[0025] The modulation arm 4 consists of two parallel and equidistant waveguide components. Each waveguide component includes a clockwise rotating rectangular helical waveguide 4-1, an S-shaped curved waveguide 4-2, and a counterclockwise rotating rectangular helical waveguide 4-3 connected in sequence. The entire structure of the modulation arm 4 is centrally symmetrically distributed, and the modulation arm 4 rotates the output direction of the waveguide component relative to the input direction by n*90°, where n≥1 and n∈natural numbers. The modulation electrode 7 includes a main circuit signal electrode 7-1, a main circuit ground electrode 7-3, and a branch electrode 7-2. The branch electrode 7-2 is connected to the main circuit signal electrode 7-1 or the main circuit ground electrode 7-3 according to the required polarity, and is distributed in the middle and on the upper and lower sides of the horizontal section of the two waveguide components of the modulation arm 4. It works in a push-pull manner to ensure that each of the two waveguide components of the modulation arm is modulated by an electric field in only one direction.

[0026] The clockwise rotating rectangular helical waveguide 4-1 and the counterclockwise rotating rectangular helical waveguide 4-3 in the modulation arm 4 are both composed of alternating straight waveguides and 90° curved waveguides, and the output direction of the rectangular helical waveguide is rotated n*90° relative to the input direction. In either the clockwise rotating rectangular helical waveguide 4-1 or the counterclockwise rotating rectangular helical waveguide 4-3, the length of the straight waveguide connected to the S-shaped curved waveguide 4-2 is less than the length of the other horizontal straight waveguide segments.

[0027] The S-shaped curved waveguides 4-2 in the modulation arm 4 are all formed by connecting two arcs with the same central angle.

[0028] The branch electrodes 7-2 in the modulation electrode 4 form multiple parallel coplanar waveguide structures, which are distributed at equal intervals in the middle and upper and lower sides of each horizontal straight waveguide section composed of two parallel equidistant waveguide components in the modulation arm, and the polarity of the branch electrode in the middle of the waveguide is different from that on both sides of the waveguide.

[0029] The polarity of the branch electrodes in the modulation electrode is related to the light transmission direction in the modulation arm. The branch electrodes in the middle of the horizontal straight waveguide sections with the same light transmission direction have the same polarity, while the branch electrodes in the middle of the horizontal straight waveguide sections with opposite light transmission directions have different polarities, so as to ensure that the two waveguides of the modulation arm are each modulated by an electric field in only one direction.

[0030] The beam splitter can be a Y-branch, multimode interference coupler, directional coupler, etc. The mode size of the input and output end-face couplers matches the mode size of a typical single-mode fiber. The thin-film lithium niobate material used in the chip substrate consists of a silicon substrate layer, a silicon oxide layer, and a lithium niobate layer from bottom to top. After etching out the waveguide optical path, a silicon oxide cladding layer is grown on the surface. The modulation electrode is fabricated on top of the silicon oxide cladding layer.

[0031] Example 1:

[0032] Reference Figure 1 ,3 4. This embodiment provides a small, low half-wave voltage thin-film lithium niobate Y-waveguide, which mainly includes an optical path structure consisting of an input end-face coupler 1, an input waveguide 2, a beam splitter 3, a modulation arm 4, an output waveguide 5, and an output end-face coupler 6 connected in sequence, as well as a modulation electrode 7.

[0033] The modulation arm 4 consists of two parallel and equidistant waveguide components. Each waveguide component includes a clockwise rotating rectangular helical waveguide 4-1, an S-shaped curved waveguide 4-2, and a counterclockwise rotating rectangular helical waveguide 4-3, which are connected in sequence. The modulation electrode 7 includes a main line signal electrode 7-1, a main line ground electrode 7-3, and a branch electrode 7-2. The branch electrode 7-2 is connected to the corresponding main line electrode according to the required polarity and is distributed in the middle and on the upper and lower sides of the two horizontal waveguide sections of the modulation arm 4, working in a push-pull manner.

[0034] The clockwise rotating rectangular spiral waveguide 4-1 and the counterclockwise rotating rectangular spiral waveguide 4-3 in the modulation arm 4 are both composed of multiple straight waveguides and 90° arc waveguides connected alternately, which ultimately rotates the output direction of the rectangular spiral waveguide by 180° relative to the input direction.

[0035] The S-shaped curved waveguide 4-2 in the modulation arm 4 is composed of two circular arcs with a central angle of 90° connected together.

[0036] The modulation arm 4 has a centrally symmetrical distribution.

[0037] The branch electrodes 7-2 in the modulation electrode 7 form multiple parallel coplanar waveguide structures, which are distributed at equal intervals in the middle and on both sides of each horizontal straight waveguide section composed of two parallel equidistant waveguide components in the modulation arm 4. The polarity of the branch electrode 7-2 in the middle of the waveguide is different from that on both sides of the waveguide.

[0038] The polarity of the branch electrode 7-2 in the modulation electrode 7 is related to the light transmission direction in the modulation arm 4. The branch electrodes 7-2 in the middle of the horizontal straight waveguide sections with the same light transmission direction have the same polarity, while the branch electrodes 7-2 in the middle of the horizontal straight waveguide sections with opposite light transmission directions have different polarities. This ensures that each of the two waveguides in the modulation arm 4 is modulated by an electric field in only one direction.

[0039] In this embodiment, the main signal electrode 7-1 is connected to the positive terminal of the power supply, and the main ground electrode 7-3 is connected to the negative terminal of the power supply. One waveguide component of the modulation arm 4 is only modulated by an upward electric field in the entire optical transmission direction, and the other waveguide component is only modulated by a downward electric field in the entire optical transmission direction, so as to ensure the accumulation of phase transition caused by the modulation of multiple coplanar waveguide electrodes and improve the modulation efficiency.

[0040] In this embodiment, the width of all branch electrodes 7-2 is 15μm, the spacing between the middle and side branch electrodes 7-2 of the two waveguides of the modulation arm 4 is 3μm, and the electrode thickness is 0.9μm.

[0041] In this embodiment, the total length of the multi-segment coplanar waveguide electrode composed of branch electrodes 7-2 is 2cm, referring to... Figure 4 The half-wave voltage of the Y-waveguide can be reduced to 1.2V.

[0042] In this embodiment, the beam splitter 3 adopts a 1×2 multimode interference coupler structure.

[0043] Preferably, in this embodiment, the mode size of the input end face coupler 1 and the output end face coupler 6 is matched with the mode size of ordinary single-mode fiber, thereby reducing the coupling loss with the input and output fibers.

[0044] Furthermore, in this embodiment, the thin-film lithium niobate material used in the chip substrate consists of a silicon substrate layer 8, a silicon oxide layer 9, and a lithium niobate layer 10 from bottom to top. After etching out the waveguide optical path, a 1μm silicon oxide cladding layer 11 is grown on the surface. The waveguide width in the modulation arm 4 is 2.5μm, and the ridge height is 0.3μm. The modulation electrode 7 is fabricated on the silicon oxide cladding layer 11.

[0045] Example 2:

[0046] Reference Figure 1 , 2 In this embodiment 2, based on embodiment 1, the clockwise rotating rectangular spiral waveguide 4-1 and the counterclockwise rotating rectangular spiral waveguide 4-3 in the modulation arm 4 are both composed of multiple straight waveguides and 90° arc waveguides connected alternately, ultimately causing the output direction of the rectangular spiral waveguide to rotate 360° relative to the input direction.

[0047] Furthermore, in this embodiment, the total length of the multi-segment coplanar waveguide electrode composed of branch electrodes 7-2 is 3cm, referring to... Figure 4 The half-wave voltage of the Y-waveguide can be reduced to 0.8V.

[0048] This invention improves the waveguide optical path of the modulation arm and sets up modulation electrodes in parallel, breaking the constraint of chip miniaturization on waveguide length. By reasonably matching the polarity of the electrodes on both sides of the waveguide, it ensures the accumulation of phase transition caused by the applied electric field, increases the modulation length, and effectively reduces the size of the Y waveguide and half-wave voltage.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any changes and improvements made by those skilled in the art within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A small low half-wave voltage thin film lithium niobate Y waveguide, characterized by: The optical path structure comprises an input end face coupler (1), an input waveguide (2), a beam splitter (3), a modulation arm (4), an output waveguide (5) and an output end face coupler (6) connected in sequence, and a modulation electrode (7) is arranged on the modulation arm (4). The modulation arm (4) is composed of two parallel equidistant waveguide assemblies, each waveguide assembly comprises a clockwise rotating rectangular spiral waveguide (4-1), an S-shaped bending waveguide (4-2) and an anticlockwise rotating rectangular spiral waveguide (4-3) connected in sequence, the whole structure of the modulation arm (4) is centrally symmetrically distributed, and the modulation arm (4) rotates the output direction of the waveguide assembly by n*90° relative to the input direction, n≥1, n∈natural number. The modulation electrode (7) comprises a trunk signal electrode (7-1), a trunk ground electrode (7-3) and a branch electrode (7-2), the branch electrode (7-2) is connected with the trunk signal electrode (7-1) or the trunk ground electrode (7-3) according to the required polarity, and is distributed in the middle and on the upper and lower sides of the horizontal section of the two waveguide assemblies of the modulation arm (4) to work in a push-pull mode, so as to ensure that each of the two waveguide assemblies of the modulation arm is subjected to electric field modulation in only one direction.

2. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The clockwise rotating rectangular spiral waveguide (4-1) and the anticlockwise rotating rectangular spiral waveguide (4-3) in the modulation arm (4) are both formed by alternately connecting straight waveguides and 90° arc waveguides; the length of the straight waveguide connected with the S-shaped bending waveguide (4-2) in the clockwise rotating rectangular spiral waveguide (4-1) or the anticlockwise rotating rectangular spiral waveguide (4-3) is less than the length of the straight waveguide in the remaining horizontal sections.

3. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The S-shaped bending waveguide (4-2) in the modulation arm (4) is connected by two circular arcs with the same central angle.

4. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The branch electrode (7-2) in the modulation electrode (7) is a plurality of parallel coplanar waveguide structures, and is distributed in the middle and on the upper and lower sides of each horizontal straight waveguide section of the two parallel equidistant waveguide assemblies of the modulation arm (4) at equal intervals, the polarities of the branch electrodes on the two sides are the same, and the polarity of the branch electrode in the middle is different from the polarities of the branch electrodes on the two sides.

5. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The polarity of the branch electrode (7-2) in the modulation electrode (7) is related to the light transmission direction in the modulation arm (4), the polarities of the branch electrodes in the middle of each horizontal straight waveguide section with the same light transmission direction are the same, and the polarities of the branch electrodes in the middle of the horizontal straight waveguide sections with opposite light transmission directions are different.

6. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The beam splitter (3) is one of a Y branch, a multimode interference coupler and a directional coupler.

7. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The mode spot size of the input end face coupler (1) and the output end face coupler (6) matches the mode spot size of a common single-mode optical fiber.

8. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The low half-wave voltage thin film lithium niobate Y waveguide chip substrate material is sequentially composed of a silicon substrate layer (8), a silicon oxide layer (9) and a lithium niobate layer (10) from bottom to top, and after etching the waveguide optical path structure, a silicon oxide upper cladding layer (11) is grown on the surface.

9. The small low-voltage-swing thin-film lithium niobate Y waveguide according to claim 1, wherein: The modulation electrode (7) is prepared on the silicon oxide upper cladding layer (11).

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