Thin film electro-optic phase modulator based on non-coplanar electrode structure and method of manufacturing the same

Abstract

This invention relates to a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method, belonging to the field of integrated photonic device technology. It solves the problem of limited modulation performance and bandwidth loss in the prior art. The modulator includes, from bottom to top, the following: a silicon and a silicon dioxide substrate; a thin-film lithium niobate waveguide layer, including a planar portion and a ridge portion protruding from the planar portion and extending longitudinally; a silicon dioxide upper cladding layer, which covers the ridge portion of the thin-film lithium niobate waveguide layer; a ground electrode and a signal electrode, which are symmetrically disposed on the outer surface of the silicon dioxide upper cladding layer, forming a double-layer non-coplanar structure.

Description

Technical Field

[0001] This invention relates to the field of integrated photonic device technology, and more specifically to a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method. Background Technology

[0002] Optical modulators are key components in information optics. Their main function is to modulate and process light transmitted in waveguide links, thereby converting the information to be transmitted from electrical signals into optical signals. Based on the different physical properties of the information carried by light, modulators can be divided into three categories: intensity modulators, phase modulators, and polarization modulators. Among them, phase modulators, benefiting from the inherently stable nature of their phase, possess excellent anti-interference capabilities. Furthermore, their high modulation depth allows for higher data capacity. Therefore, phase modulators are widely used in high-precision, long-distance, and high-speed optical transmission systems.

[0003] The mainstream method for modulating optical phase utilizes the electro-optic effect of crystals. Compared to thermo-optic, acousto-optic, optomechanical, and nonlinear effects, the electro-optic effect offers faster modulation speeds, more precise modulation depths, and more mature technology, resulting in better performance parameters for electro-optic phase modulators. However, the electro-optic effect places stringent requirements on materials, necessitating a large electro-optic coefficient and good thermal stability.

[0004] Traditional lithium niobate electro-optic modulators use bulk lithium niobate. Waveguides fabricated using ion diffusion or proton exchange techniques have a low refractive index contrast, resulting in weak light confinement and large device size, making them difficult to integrate into on-chip optical systems. Recently, with advancements in materials processing technology, particularly the maturity of crystal ion cutting and polishing techniques, thin-film lithium niobate has become possible. Thin-film lithium niobate overcomes the shortcomings of bulk lithium niobate, enhancing the waveguide's light confinement and reducing device size. Furthermore, the reduced device size allows for a lower modulator driving voltage, further improving modulator performance.

[0005] Thin-film lithium niobate phase modulators are active devices that control and change the phase of incident light. To enhance the interaction between the electromagnetic and microwave fields in the modulator and improve its performance, in addition to using suitable materials, the modulation region of the modulator also needs a suitable structure. For the electric field to effectively act on the optical waveguide, the signal electrode and ground electrode of the modulator need to be symmetrically placed on both sides of the waveguide. Currently, the electrode structures used in thin-film lithium niobate phase modulators are mainly divided into two types: rectangular electrodes and T-shaped electrodes, both of which are coplanar electrode structures.

[0006] A rectangular electrode structure refers to a waveguide where the signal electrode and ground electrode on both sides are rectangular in shape in both the cross-section perpendicular to the light transmission direction and in the plane of the material. Figure 1a and Figure 1b As shown. A T-type electrode is created by adding a T-shaped electrode to the side of a rectangular electrode closer to the waveguide, such as... Figure 2a and Figure 2b As shown. Both of these electrode structures require the electrode and the waveguide to be on the same plane, and therefore are collectively referred to as coplanar electrode structures.

[0007] Electro-optic phase modulators with coplanar electrode structures suffer from problems such as uneven electric field distribution and low modulation efficiency. The technical reason for these problems can be attributed to insufficient overlap between the electric field generated by the coplanar electrode structure and the optical field inside the optical waveguide, i.e., a low overlap factor between the photoelectric fields. The coplanar electrodes, limited by the width of the silicon dioxide cladding, cannot be close enough to the optical waveguide, resulting in a weak electric field component in the modulation direction. This makes it difficult to effectively influence the optical waveguide embedded within the cladding, leading to limited modulation depth and low modulation performance. To achieve the desired phase modulation effect, a higher driving voltage must be applied to compensate for the insufficient overlap between the electric and optical fields. This not only increases energy consumption but also places higher voltage requirements on the circuit, increasing system complexity and cost.

[0008] Secondly, electro-optic phase modulators suffer from a limitation between modulation performance and bandwidth. This is due to the constraint between the modulation electric field strength within the waveguide and the electromagnetic transmission loss within the electrodes, and is directly related to the electrode structure design of the phase modulator. When the electrode spacing of the modulator decreases, the modulation electric field within the waveguide strengthens, enhancing modulation performance. However, this also results in larger parasitic capacitances on the electrodes, especially during high-speed modulation. Large capacitance leads to an increase in the RC time constant (the response time of capacitor charging), limiting the modulator's bandwidth and preventing it from meeting the demands of high-speed communication. Currently, on-chip integrated thin-film lithium niobate phase modulators with rectangular electrode structures still cannot overcome this limitation, preventing further performance improvements in rectangular electrode devices.

[0009] like Figure 2a and Figure 2bAs shown, the on-chip integrated thin-film lithium niobate phase modulator with a T-shaped electrode structure adds a small T-shaped electrode structure near the waveguide side to the rectangular electrode. This makes the modulation efficiency determined by the electrode spacing of the small electrode, while the bandwidth and loss are determined by the spacing of the main electrode, breaking the limitations of single-electrode modulation performance and bandwidth loss. However, because the T-shaped electrode structure modulator requires a very small size of the T-shaped electrode on the main electrode, it places higher demands on the precision of the fabrication process. In addition, the excessively small structure also increases the device's susceptibility to process errors, posing significant challenges to device yield and uniformity.

[0010] Existing technologies mostly optimize electrodes by modifying the shape of electrodes in the same plane. The advantage of doing so is that it can ensure as few processing steps as possible. However, as the performance requirements of modulators continue to increase, the shape of coplanar electrode structures is becoming more and more complex, and the processing difficulty of coplanar electrode structures is also constantly increasing.

[0011] Therefore, this technical field needs to further optimize the electrode structure and fabrication process to meet the application requirements of phase modulators with high modulation efficiency, low transmission loss, and low processing difficulty. Summary of the Invention

[0012] To address the aforementioned problems, this invention provides a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method. This invention aims to avoid the problem of excessively complex single-layer electrode shapes leading to excessively high processing precision requirements. By changing the electrode structure from coplanar to non-coplanar, and through longitudinally superimposed electric fields, the driving voltage required by the modulator is reduced, thereby improving modulation efficiency.

[0013] According to one embodiment of the present invention, a thin-film electro-optic phase modulator based on a non-coplanar electrode structure includes, from bottom to top, the following: a silicon and a silicon dioxide substrate; a thin-film lithium niobate waveguide layer including a planar portion and a ridge portion protruding from the planar portion and extending longitudinally; a silicon dioxide upper cladding layer covering the ridge portion of the thin-film lithium niobate waveguide layer; a ground electrode and a signal electrode symmetrically disposed on the outer surface of the silicon dioxide upper cladding layer, forming a double-layer non-coplanar structure.

[0014] Optionally, the ridge portion of the thin-film lithium niobate waveguide layer has a trapezoidal cross-sectional shape.

[0015] Optionally, the ground electrode and the signal electrode are made of gold.

[0016] Optionally, the grounding electrode is formed in a Z-shaped structure or an inverted Z-shaped structure; the signal electrode is formed in a Z-shaped structure or an inverted Z-shaped structure; and the grounding electrode and the signal electrode are arranged symmetrically to each other.

[0017] Optionally, the grounding electrode includes: a flat upper surface, a flat lower surface, and a side surface connecting the upper and lower surfaces, wherein the upper surface is attached to the top surface of the silicon dioxide cladding, the lower surface is attached to the planar portion of the thin-film lithium niobate waveguide layer, and the side surface is attached to the side surface of the silicon dioxide cladding; the signal electrode includes: a flat upper surface, a flat lower surface, and a side surface connecting the upper and lower surfaces, wherein the upper surface is attached to the top surface of the silicon dioxide cladding, the lower surface is attached to the planar portion of the thin-film lithium niobate waveguide layer, and the side surface is attached to the side surface of the silicon dioxide cladding.

[0018] Optionally, the longitudinal length of the ridge portion of the thin-film lithium niobate waveguide layer ranges from 0.4 cm to 2 cm; the distance between the upper surface of the ground electrode of the ground electrode and the upper surface of the signal electrode of the signal electrode ranges from 1 μm to 2 μm.

[0019] Optionally, two sets of parallel modulation arm structures are formed in the modulation region. Each set of modulation arm structures includes: a longitudinally extending ridge, a silicon dioxide cladding covering the ridge, and symmetrical grounding electrodes and signal electrodes disposed on the outer surface of the silicon dioxide cladding. The two sets of modulation arm structures are merged at the input position before the modulation region and the output position after the modulation region. A beam splitter is provided at the input position where the two sets of modulation arm structures are merged, and a beam combiner is provided at the output position.

[0020] Optionally, a set of modulation arm structures is formed in the modulation region. The modulation arm structure includes: a longitudinally extending ridge, a silicon dioxide cladding covering the ridge, and symmetrical ground electrodes and signal electrodes disposed on the outer surface of the silicon dioxide cladding.

[0021] A method for manufacturing a thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to another embodiment of the present invention includes the following steps:

[0022] Step S1: Deposit a layer of silicon dioxide on a silicon wafer to form a silicon and silicon dioxide substrate;

[0023] Step S2: A thin film lithium niobate layer is bonded on a silicon and silicon dioxide substrate, and the bonded thin film lithium niobate layer is processed into a thin film lithium niobate optical waveguide layer including a planar portion and a longitudinally extending ridge portion using dry etching or wet etching technology.

[0024] Step S3: Deposit a silicon dioxide layer on the surface of the thin-film lithium niobate waveguide layer, such that the silicon dioxide layer completely covers the ridge region of the thin-film lithium niobate waveguide layer.

[0025] Step S4: Etch away the silicon dioxide material outside the longitudinal sides of the ridge portion to expose the planar portion of the thin film lithium niobate optical waveguide layer, and obtain the silicon dioxide upper cladding covering the ridge portion.

[0026] Step S5: Subsequently, using photolithography lift-off technology, gold is vapor-deposited onto the planar portion of the silicon dioxide cladding and thin-film lithium niobate waveguide layer to form an electrode structure including a ground electrode and a signal electrode.

[0027] Step S6: Deposit a silicon dioxide protective layer on the uppermost surface of the structure obtained above to obtain a thin-film electro-optic phase modulator based on a non-coplanar electrode structure.

[0028] Optionally, in step S2, the bonded thin-film lithium niobate layer is processed into a thin-film lithium niobate optical waveguide layer comprising a planar portion and two longitudinally parallel ridge portions using dry etching or wet etching techniques.

[0029] The thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method provided by the present invention are used to integrate optical gyroscopes and have the advantages of miniaturization, high modulation efficiency, large bandwidth, low transmission loss and easy processing.

[0030] Compared with the prior art, the thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method provided according to embodiments of the present invention have at least the following advantages:

[0031] 1. Compared with the traditional coplanar rectangular electrode structure in the prior art, the present invention adopts a non-coplanar electrode structure and utilizes the superposition of electric fields by double-layer capacitors to break the limitation between modulation performance and bandwidth loss of the modulator, thereby improving the overall performance of the thin-film lithium niobate phase modulator.

[0032] 2. Compared with the existing coplanar T-type electrode structure, the present invention avoids the introduction of special microstructures while ensuring modulation performance, reduces the requirements for processing precision, and increases the tolerance for process errors, which is conducive to improving the yield and reliability of the modulator and effectively reducing the manufacturing cost of the device.

[0033] 3. The thin-film electro-optic phase modulator based on a non-coplanar electrode structure provided by the present invention can make full use of the space on the integrated gyroscope chip, which is beneficial to the miniaturization design of the integrated gyroscope, and has strong feasibility and practicality. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly introduced below. The features and advantages of the present invention can be more clearly understood by referring to the accompanying drawings. The accompanying drawings are schematic and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1a This is a schematic diagram of a thin-film lithium niobate phase modulator with a rectangular electrode structure, as described in the prior art.

[0036] Figure 1b This is a cross-sectional view of one arm structure of a thin-film lithium niobate phase modulator with a rectangular electrode structure in the prior art.

[0037] Figure 2a This is a schematic diagram of a thin-film lithium niobate phase modulator with a T-shaped electrode structure, as described in the prior art.

[0038] Figure 2b This is a cross-sectional view of one arm structure of a thin-film lithium niobate phase modulator with a T-shaped electrode structure in the prior art.

[0039] Figure 3a This is a top view of a thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to a first embodiment of the present invention.

[0040] Figure 3b A cross-sectional view of a modulation arm structure of a thin-film electro-optic phase modulator based on a non-coplanar electrode structure provided according to a first embodiment of the present invention.

[0041] Figure 4a This is a top view of a thin-film electro-optic phase modulator with a non-coplanar electrode structure according to a second embodiment of the present invention.

[0042] Figure 4b A cross-sectional view of a thin-film electro-optic phase modulator with a non-coplanar electrode structure provided according to a second embodiment of the present invention.

[0043] Figure label:

[0044] 1-Silicon and silicon dioxide substrate;

[0045] 2-Thin-film lithium niobate optical waveguide layer;

[0046] 21-Planar part;

[0047] 22- Ridge-shaped part;

[0048] 31-Band splitter;

[0049] 32- Bundle combiner;

[0050] 4-Grounding electrode;

[0051] 41 - Upper surface of the grounding electrode;

[0052] 42 - Side of grounding electrode;

[0053] 43 - Lower surface of the grounding electrode;

[0054] 5 - Signal electrode;

[0055] 51 - Upper surface of the signal electrode;

[0056] 52 - Side of signal electrode;

[0057] 53 - Lower surface of the signal electrode;

[0058] 6-Silica overcoating;

[0059] 7-Silica protective layer. Detailed Implementation

[0060] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0061] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0062] The following detailed description, with reference to the accompanying drawings, illustrates a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method according to an embodiment of the present invention.

[0063] like Figure 3a and Figure 3bAs shown, a thin-film electro-optic phase modulator based on a non-coplanar electrode structure, according to a first embodiment of the present invention, is used for integrating an optical gyroscope. It includes, from bottom to top: a silicon and silicon dioxide substrate 1; a thin-film lithium niobate waveguide layer 2, including a planar portion 21 and a ridge portion 22 protruding from the planar portion 21 and extending longitudinally; a silicon dioxide upper cladding layer 6, which covers the ridge portion 22 of the thin-film lithium niobate waveguide layer 2; a ground electrode 4 and a signal electrode 5, which are symmetrically disposed on the outer surface of the silicon dioxide upper cladding layer 6, forming a double-layer non-coplanar structure. The ridge portion 22 of the thin-film lithium niobate waveguide layer 2 constitutes a ridge waveguide for transmitting light. The ridge portion 22 of the thin-film lithium niobate waveguide layer 2 is formed into a longitudinally extended shape with a trapezoidal cross-section. The ground electrode 4 and the signal electrode 5 may be formed of gold. Optionally, the ground electrode 4 and signal electrode 5 can be formed by removing the silicon dioxide material from both sides of the longitudinal direction of the ridge portion 22 of the thin-film lithium niobate waveguide layer 2 after covering it with silicon dioxide material, leaving only the silicon dioxide upper cladding 6 covering the ridge portion 22. The ground electrode 4 and signal electrode 5 are then disposed on the outer surface of this silicon dioxide upper cladding 6, forming a double-layer non-coplanar structure with a height difference between the ground electrode 4 and signal electrode 5. The silicon dioxide upper cladding 6 can be a longitudinally extending cuboid structure covering the ridge portion 22.

[0064] like Figure 3a As shown, in this first embodiment, the thin-film electro-optic phase modulator based on a non-coplanar electrode structure has a symmetrical dual-arm structure, including two sets of parallel modulation arm structures (hereinafter referred to as arm structures) in the modulation region. These are Mach-Zehnder modulators, and the two sets of modulation arm structures are merged at the input position before the modulation region and the output position after the modulation region. Each modulation arm structure includes: a longitudinally extending ridge 22 of thin-film lithium niobate, a silicon dioxide cladding 6 covering the ridge 22, and symmetrical ground electrode 4 and signal electrode 5 disposed on the outer surface of the silicon dioxide cladding 6. The ground electrode 4 can be disposed on the outer side of the two arm structures, and the signal electrode 5 can be disposed on the inner side between the two arm structures. In this embodiment, a beam splitter 31 and a beam combiner 32 can also be disposed at the input and output positions where the two sets of modulation arm structures are merged.

[0065] like Figure 3bAs shown, in this first embodiment, the ground electrode 4 of one arm of the thin-film electro-optic phase modulator based on a non-coplanar electrode structure can be formed into an inverted Z-shaped structure, and the signal electrode 5 can be formed into a Z-shaped structure, and they are symmetrical to each other (it should be understood that in the other symmetrical arm structure, the Z-shaped structures formed by the ground electrode 4 and the signal electrode 5 are in opposite directions), thereby forming a double-layer non-coplanar structure different from the straight-line coplanar structure. The ground electrode 4 forming the inverted Z-shape includes a flat upper ground electrode surface 41, a flat lower ground electrode surface 43, and a ground electrode side surface 42 connecting the upper and lower surfaces. The upper ground electrode surface 41 is attached to the top surface of the silicon dioxide upper cladding 6, the lower ground electrode surface 43 is attached to the planar portion 21 of the thin-film lithium niobate waveguide layer 2, and the ground electrode side surface 42 is attached to the side surface of the silicon dioxide upper cladding 6. The upper ground electrode surface 41 and the lower ground electrode surface 43 of the ground electrode 4 form a double-layer structure with a height difference. The Z-shaped signal electrode 5 includes a flat upper signal electrode surface 51, a flat lower signal electrode surface 53, and a side signal electrode surface 52 connecting the upper and lower signal electrode surfaces. The upper signal electrode surface 51 is attached to the top surface of the silicon dioxide cladding 6, the lower signal electrode surface 53 is attached to the planar portion 21 of the thin-film lithium niobate waveguide layer 2, and the side signal electrode surface 52 is attached to the side of the silicon dioxide cladding 6. The upper signal electrode surface 51 and the lower signal electrode surface 53 of the signal electrode 5 form a double-layer structure with a height difference. In this embodiment, the lower surface 53 of the signal electrode 5 of the two sets of parallel modulation arm structures can be formed as an integral structure extending on the planar portion 21 between the two sets of modulation arm structures. That is, the lower surface 53 of the signal electrode 5 can be formed to extend from the inside of one set of modulation arm structures to the other set of modulation arm structures on the planar portion 21 of the thin-film lithium niobate waveguide layer 2, so that the signal electrodes 5 of the two sets of modulation arm structures can be formed integrally.

[0066] Continue to refer to Figure 3a and Figure 3bIn this first embodiment, the electrode portions of the thin-film electro-optic phase modulator based on a non-coplanar electrode structure, namely the ground electrode 4 and the signal electrode 5, have an inverted Z-shaped or Z-shaped structure, such that the upper and lower surfaces of the electrodes are located on different planes with a height difference. When an external electric field is applied to the signal electrode 5, the upper surface 41 of the ground electrode 4 and the upper surface 51 of the signal electrode 5 form a top capacitor, generating the main electric field, while the lower surface 43 of the ground electrode 4 and the lower surface 53 of the signal electrode 5 form a bottom capacitor, generating a secondary electric field. Thus, the top and bottom capacitors form a double-layer capacitor. Therefore, in this thin-film electro-optic phase modulator based on a non-coplanar electrode structure, the total electric field applied to the ridge portion 22 of the thin-film lithium niobate waveguide layer 2 is composed of the superposition of the sub-fields formed by the upper and lower capacitors. This allows the driving voltage applied to the signal electrode 5 to be reused multiple times, thereby effectively reducing the required driving voltage and improving the modulation efficiency of the modulator while ensuring the modulation effect remains unchanged. Furthermore, this non-coplanar electrode structure breaks away from the traditional modulator's reliance on altering electrode spacing to affect modulation efficiency. It avoids the limitations imposed by electrode spacing on modulation efficiency and bandwidth loss, thus improving modulation efficiency without reducing modulator bandwidth. Additionally, the non-coplanar electrode structure does not require special microstructures or high-precision manufacturing processes, making it insensitive to fabrication errors and contributing to improved device yield and uniformity.

[0067] See Figure 3b In this first embodiment, the thin-film electro-optic phase modulator based on the non-coplanar electrode structure may further include a silicon dioxide protective layer 7 covering the uppermost layer. The uppermost cladding layer of the on-chip thin-film electro-optic phase modulator based on the non-coplanar electrode structure may be made of silicon dioxide, which can effectively protect the device structure and at the same time have a large refractive index difference with the thin-film lithium niobate waveguide layer 2, thereby improving device performance.

[0068] In this embodiment, a wafer of suitable size and high surface flatness can be obtained using crystal ion cutting technology as the substrate layer of the aforementioned silicon and silicon dioxide substrate 1. The main function of this substrate layer is to provide mechanical support for the entire thin-film electro-optic phase modulator based on a non-coplanar electrode structure. In the on-chip integrated thin-film electro-optic phase modulator of this embodiment, silicon material can be used as the substrate layer. To improve the beam characteristics of the waveguide, a thick silicon dioxide thin film is first deposited on the silicon substrate layer as the lower cladding layer, thereby forming the silicon and silicon dioxide substrate 1. The material of the thin-film lithium niobate optical waveguide layer 2 is thin-film lithium niobate. The geometric parameters of the waveguide can be designed before processing, and the excess thin-film lithium niobate material is removed by dry or wet etching technology, with the remaining part forming the waveguide structure. The electrode layers of the ground electrode 4 and the signal electrode 5 can be fabricated by photolithography and metal deposition technology. The electric field generated by the ground electrode 4 and the signal electrode 5 will act on the thin-film lithium niobate optical waveguide layer 2, which is the core of the interaction between the microwave field and the electromagnetic field. Therefore, by using the grounding electrode 4 and the signal electrode 5, the effect of efficient interaction between the light field and the electric field can be achieved.

[0069] Depending on the performance focus of the modulator, the structural parameters of the thin-film electro-optic phase modulator based on a non-coplanar electrode structure provided in the first embodiment can be modified and adjusted. These structural parameters may include: modulation region length, electrode spacing, etching depth, etc. The modulation region length is the longitudinal length of the ridge portion 22 of the thin-film lithium niobate optical waveguide layer 2 (i.e., the longitudinal length of the silicon dioxide cladding 6, and the ground electrode 4 and signal electrode 5), ranging from 0.4 cm to 2 cm, and optionally, 0.75 cm. A longer modulation region length results in stronger modulation performance, but also leads to a decrease in bandwidth due to increased impedance. The above range provides both good modulation performance and optimal bandwidth. The electrode spacing is the distance between the upper surface 41 of the ground electrode 4 and the upper surface 51 of the signal electrode 5, ranging from 1 μm to 2 μm. Smaller electrode spacing results in greater modulation performance, but also leads to greater transmission loss. Furthermore, when the spacing is less than 1 μm, the requirements for the manufacturing process will be further increased. The above range provides both good modulation performance and low loss, and is easier to process. The etching depth is the height of the ridge 22 of the thin-film lithium niobate waveguide layer 2 relative to the planar portion 21, ranging from 0.1 μm to 0.5 μm, and can be set to 0.3 μm. The etching depth affects modulation performance and transmission loss. As the etching depth increases, the localization capability of the thin-film lithium niobate waveguide layer 2 for the optical mode field is enhanced, thus reducing loss. However, it also weakens the effect of the electric field on the optical field, thereby reducing modulation performance. Furthermore, the distance between the two parallel ridges 22 of the two-arm structure of the thin-film electro-optic phase modulator based on a non-coplanar electrode structure provided in this first embodiment can be 0.5 cm. The ground electrode 4 and the signal electrode 5 can be formed of gold material with a thickness of 0.2 μm to 0.9 μm.

[0070] See Figure 3a and Figure 3bThe following provides structural parameters for an embodiment of a thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to the first embodiment. This embodiment of the thin-film electro-optic phase modulator has a symmetrical structure with two arms; for ease of description, only the structural parameters of one arm are described here. The silicon wafer layer of the silicon and silicon dioxide substrate 1 is relatively thick and is negligible here; the thickness of the silicon dioxide layer can be set to 2 μm. The thin-film lithium niobate waveguide layer 2 uses a 0.6 μm thick thin-film lithium niobate cut along a plane perpendicular to the x-axis, with an etching depth of 0.3 μm, forming a ridge portion 22 of the thin-film lithium niobate waveguide layer 2. The ridge portion 22 of the thin-film lithium niobate waveguide layer 2 is formed with a trapezoidal cross-sectional shape, a width of 2 μm at its widest point at the bottom, and the bottom corner of the trapezoid is the etching angle, which can be set to 75°. The silicon dioxide cladding layer 6 is generally cuboid in shape, with a total thickness of 0.8 μm and a width of 7 μm. The ground electrode 4 and signal electrode 5 can be formed of gold material with a thickness of 0.45 μm. The width of the lower surface 43 of the ground electrode is 5 μm, the width of the upper surface 41 of the ground electrode is 2.8 μm, the width of the lower surface 53 of the signal electrode is approximately 0.5 cm, close to the distance between the two ridges 22 (this actual distance is the distance between the two ridges 22 minus the width of the silicon dioxide cladding 6 and the thickness of the gold), the width of the upper surface 52 of the signal electrode is 2.8 μm, and the distance between the upper surface 41 of the ground electrode 4 and the upper surface 51 of the signal electrode 5 is 1.2 μm. In the above description, length refers to the dimension along the longitudinal direction of the arm structure or ridge 22, width refers to the dimension in the horizontal plane perpendicular to the longitudinal direction, and height refers to the dimension in the vertical direction perpendicular to the horizontal plane.

[0071] A method for using a thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to a first embodiment of the present invention for phase modulation includes the following steps.

[0072] Step S1: The light emitted from the light source passes through the end-face coupler or grating coupler (not shown in the figure) outside the thin-film electro-optic phase modulator based on a non-coplanar electrode structure and enters the beam splitter 31. The beam splitter 31 then guides the input light into the ridge portion 22 of the thin-film lithium niobate waveguide layer 2 in the modulation region. In embodiments with a single-arm structure single-waveguide modulator, the light emitted from the light source directly enters the ridge portion 22 of the thin-film lithium niobate waveguide layer 2 in the modulation region through the end-face coupler or grating coupler, without the need for a beam splitter.

[0073] Step S2: Apply steady-state or alternating current to signal electrode 5 and ground ground electrode 4.

[0074] In step S3, the input light is modulated by the ridge portion 22 of the thin-film lithium niobate ridge waveguide layer 2 and output via the beam combiner 32 to obtain output light. This output light is input to a photodetector, processed by the photodetector, and output as an electrical signal. This electrical signal is then input to an oscilloscope. The photodetector is connected to a power meter or a modulation / demodulation circuit. By analyzing the power of the electrical signal displayed by the power meter and the electrical signal output by the modulation / demodulation circuit, the phase of the output light can be obtained and compared with the phase of the input light introduced by the beam splitter to determine the change in phase. Similarly, in the embodiment with a single-arm structure single-waveguide modulator, the output light is directly input to the photodetector from the ridge portion 22 without the need for a beam combiner.

[0075] Step S4: Determine whether the obtained phase change meets the preset requirements. If the preset requirements are not met, return to step S2 and adjust the steady-state or alternating current applied to the signal electrode 5. If the preset requirements are met, the process ends and the output light that meets the phase requirements after phase modulation is obtained. It can be used for integrated optical gyroscopes or other required devices.

[0076] Considering the application of phase modulators in different systems, another embodiment of the present invention may also have a single modulation arm structure, which may reduce the modulation performance of the modulator. However, for some simple systems or scenarios with strict size requirements, thin-film electro-optic phase modulators with a single modulation arm structure still have great application potential.

[0077] like Figure 4a and Figure 4b As shown, a second embodiment of the present invention provides a thin-film electro-optic phase modulator based on a non-coplanar electrode structure, which is a single-waveguide modulator with a single modulation arm structure. As shown in the figure, in this embodiment, the lower surface 43 of the ground electrode 4 and the lower surface 53 of the signal electrode 5 are completely symmetrical. In this embodiment, a beam splitter and beam combiner are not required. Apart from this, the single modulation arm structure in this second embodiment of the single-waveguide thin-film electro-optic phase modulator based on a non-coplanar electrode structure is essentially the same as one modulation arm structure in the first embodiment of the dual modulation arm structure thin-film electro-optic phase modulator based on a non-coplanar electrode structure, and will not be described again here.

[0078] The method for manufacturing a thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to a third embodiment of the present invention includes the following steps.

[0079] Step S1: Deposit a layer of silicon dioxide on a silicon wafer to form a silicon and silicon dioxide substrate 1.

[0080] In step S2, a thin film lithium niobate layer is bonded onto the silicon and silicon dioxide substrate 1, and the bonded thin film lithium niobate layer is processed into a thin film lithium niobate optical waveguide layer 2 comprising a planar portion 21 and longitudinally extending ridge portions 22 using dry etching or wet etching techniques. Optionally, in step S2, the bonded thin film lithium niobate layer can be processed into a thin film lithium niobate optical waveguide layer 2 comprising a planar portion 21 and two longitudinally parallel ridge portions 22.

[0081] Step S3: Deposit a silicon dioxide layer on the surface of the thin-film lithium niobate waveguide layer 2, such that the silicon dioxide layer completely covers the ridge portion 22 of the thin-film lithium niobate waveguide layer 2, i.e. the light transmission mode region.

[0082] In step S4, the silicon dioxide material outside the longitudinal sides of the ridge portion 22 is etched away to expose the planar portion 21 of the thin-film lithium niobate optical waveguide layer 2, and a silicon dioxide upper cladding layer 6 covering the ridge portion 22 is obtained. Optionally, the silicon dioxide material extending outward from each side of the ridge portion 22 beyond a range of 3.5 μm can be removed.

[0083] In step S5, gold is then deposited onto the planar portion 21 of the silicon dioxide cladding layer 6 and the thin-film lithium niobate waveguide layer 2 using photolithography lift-off technology to form an electrode structure including a ground electrode 4 and a signal electrode 5.

[0084] Because the ridge portion 22 of the ridge-shaped thin-film lithium niobate optical waveguide layer 2 is covered with a silicon dioxide upper cladding layer 6, and the silicon dioxide material on both sides of the ridge portion 22 of the thin-film lithium niobate optical waveguide layer 2 is etched away to expose the planar portion 21 of the thin-film lithium niobate optical waveguide layer 2, there is a height difference between the planar portion 21 of the thin-film lithium niobate optical waveguide layer 2 and the top surface of the silicon dioxide upper cladding layer 6. Therefore, the ground electrode 4 and the signal electrode 5 formed are non-coplanar due to the height difference, forming a double-layer capacitor, and the whole presents a Z-shape.

[0085] Step S6: Deposit a silicon dioxide protective layer 7 on the uppermost surface of the structure obtained above, and the thin-film electro-optic phase modulator based on the non-coplanar electrode structure is thus completed.

[0086] Optionally, in the above embodiment, step S2 may further include setting a beam splitter 31 and a beam combiner 32 at the input and output positions of the ridge portion 22 of the thin-film lithium niobate optical waveguide layer 2, respectively.

[0087] As described above, the embodiments of the present invention provide a solution different from the traditional coplanar electrode scheme, namely, a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and its manufacturing method. The invention is characterized by miniaturization, high modulation efficiency, large bandwidth, low transmission loss, and ease of fabrication, solving the limitations in modulation performance and bandwidth loss inherent in current on-chip integrated thin-film lithium niobate electro-optic modulators.

[0088] All of the above-mentioned optional technical solutions can be combined in any way to form the optional embodiments of this application, and will not be described in detail here.

[0089] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0090] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A thin-film electro-optic phase modulator based on a non-coplanar electrode structure, characterized in that, Including those set from bottom to top: Silicon and silicon dioxide substrates; A thin-film lithium niobate waveguide layer, comprising a planar portion and a ridge portion protruding from the planar portion and extending longitudinally; A silicon dioxide overlay covers the ridge portion of the thin-film lithium niobate waveguide layer; The ground electrode has a Z-shaped or inverted Z-shaped cross section perpendicular to the light transmission direction, and the signal electrode has a Z-shaped or inverted Z-shaped cross section perpendicular to the light transmission direction. The ground electrode and the signal electrode are symmetrically arranged on the outer surface of the silicon dioxide cladding to form a double-layer non-coplanar structure. The grounding electrode includes: a flat upper surface of the grounding electrode, a flat lower surface of the grounding electrode, and a side surface of the grounding electrode connecting the upper surface and the lower surface. The upper surface of the grounding electrode is attached to the top surface of the silicon dioxide cladding, the lower surface of the grounding electrode is attached to the planar portion of the thin-film lithium niobate waveguide layer, and the side surface of the grounding electrode is attached to the side surface of the silicon dioxide cladding. The signal electrode includes: a flat upper surface of the signal electrode, a flat lower surface of the signal electrode, and a side surface of the signal electrode connecting the upper surface of the signal electrode and the lower surface of the signal electrode. The upper surface of the signal electrode is attached to the top surface of the silicon dioxide cladding, the lower surface of the signal electrode is attached to the planar portion of the thin-film lithium niobate waveguide layer, and the side surface of the signal electrode is attached to the side surface of the silicon dioxide cladding. The distance between the upper surface of the grounding electrode and the upper surface of the signal electrode of the signal electrode is between 1 μm and 2 μm. The width of the upper surface of the grounding electrode is 2.8 μm; The width of the upper surface of the signal electrode is 2.8 μm; The ridge portion of the thin-film lithium niobate waveguide layer has a trapezoidal cross-sectional shape, the widest part of the bottom of the trapezoidal cross-sectional shape is 2μm, the base angle of the trapezoidal cross-sectional shape is 75°, and the etching depth of the ridge portion is 0.1μm to 0.5μm; The silica cladding is rectangular in shape, with a total thickness of 0.8 μm and a width of 7 μm; The longitudinal length of the ridge portion of the thin-film lithium niobate waveguide layer ranges from 0.4 cm to 2 cm.

2. The thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that, The grounding electrode and signal electrode are made of gold.

3. The thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that: Two sets of parallel modulation arm structures are formed in the modulation region. Each set of modulation arm structures includes: a longitudinally extending ridge, a silicon dioxide cladding covering the ridge, and symmetrical grounding electrodes and signal electrodes disposed on the outer surface of the silicon dioxide cladding. The two sets of modulation arm structures are merged at the input position before the modulation region and the output position after the modulation region. A beam splitter is set at the input position where the two sets of modulation arm structures are merged, and a beam combiner is set at the output position.

4. The thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that, A set of modulation arm structures is formed in the modulation region. The modulation arm structure includes: a longitudinally extending ridge, a silicon dioxide cladding covering the ridge, and symmetrical ground electrodes and signal electrodes disposed on the outer surface of the silicon dioxide cladding.

5. The method for manufacturing a thin-film electro-optic phase modulator based on a non-coplanar electrode structure according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: Deposit a layer of silicon dioxide on a silicon wafer to form a silicon and silicon dioxide substrate; Step S2: A thin film lithium niobate layer is bonded on a silicon and silicon dioxide substrate, and the bonded thin film lithium niobate layer is processed into a thin film lithium niobate optical waveguide layer including a planar portion and a longitudinally extending ridge portion using dry etching or wet etching technology. Step S3: Deposit a silicon dioxide layer on the surface of the thin-film lithium niobate waveguide layer, such that the silicon dioxide layer completely covers the ridge region of the thin-film lithium niobate waveguide layer. Step S4: Etch away the silicon dioxide material outside the longitudinal sides of the ridge portion to expose the planar portion of the thin film lithium niobate optical waveguide layer, and obtain the silicon dioxide upper cladding covering the ridge portion. Step S5: Subsequently, using photolithography lift-off technology, gold is vapor-deposited onto the planar portion of the silicon dioxide cladding and the thin-film lithium niobate optical waveguide layer to form an electrode structure including a ground electrode and a signal electrode. The cross-section of the ground electrode perpendicular to the light transmission direction is a Z-shaped structure or an inverted Z-shaped structure, and the cross-section of the signal electrode perpendicular to the light transmission direction is a Z-shaped structure or an inverted Z-shaped structure. Step S6: Deposit a silicon dioxide protective layer on the uppermost surface of the structure obtained above to obtain a thin-film electro-optic phase modulator based on a non-coplanar electrode structure; In step S2, the ridge portion forming the thin-film lithium niobate waveguide layer has a trapezoidal cross-sectional shape, the width of the widest part of the bottom of the trapezoidal cross-sectional shape is 2μm, the base angle of the trapezoidal cross-sectional shape is 75°, and the etching depth of the ridge portion is 0.1μm to 0.5μm; In step S4, the silicon dioxide cladding is formed in a cuboid shape with a total thickness of 0.8 μm and a width of 7 μm; In step S5, forming a ground electrode includes: a flat upper surface of a ground electrode, a flat lower surface of a ground electrode, and a side surface of a ground electrode connecting the upper and lower surfaces. The upper surface of the ground electrode is attached to the top surface of the silicon dioxide cladding, the lower surface of the ground electrode is attached to the planar portion of the thin-film lithium niobate waveguide layer, and the side surface of the ground electrode is attached to the side surface of the silicon dioxide cladding. Forming a signal electrode includes: a flat upper surface of a signal electrode, a flat lower surface of a signal electrode, and a side surface of a signal electrode connecting the upper and lower surfaces. The upper surface of the signal electrode is attached to the top surface of the silicon dioxide cladding, the lower surface of the signal electrode is attached to the planar portion of the thin-film lithium niobate waveguide layer, and the side surface of the signal electrode is attached to the side surface of the silicon dioxide cladding. The width of the upper surface of the ground electrode is 2.8 μm, the width of the upper surface of the signal electrode is 2.8 μm, and the distance between the upper surface of the ground electrode and the upper surface of the signal electrode is between 1 μm and 2 μm.

6. The manufacturing method according to claim 5, characterized in that, In step S2, the bonded thin-film lithium niobate layer is processed into a thin-film lithium niobate optical waveguide layer including a planar portion and two longitudinally parallel ridge portions using dry etching or wet etching techniques.

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