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

Abstract

The invention relates to a film electro-optic phase modulator based on a non-coplanar electrode structure and a manufacturing method of the film electro-optic phase modulator, belongs to the technical field of integrated photonic devices, and solves the problem that modulation performance and bandwidth loss are limited in the prior art. The thin-film lithium niobate waveguide layer comprises a plane part and a ridge-shaped part which protrudes from the plane part and extends longitudinally; the silicon dioxide upper cladding layer covers the ridge-shaped part of the thin-film lithium niobate waveguide layer; and the grounding electrode and the signal electrode are symmetrically arranged on the outer surface of the silicon dioxide upper cladding to form a double-layer non-coplanar structure.

Description

Technical Field

[0001] The invention relates to the technical field of integrated photonic devices, and in particular to a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and a manufacturing method thereof. Background Art

[0002] The optical modulator is a key device in information optics. Its main function is to modulate and process the light transmitted in the waveguide link, thereby converting the information to be transmitted from the electrical signal to the optical signal. According to the different physical properties of the information carried by light, modulators can be divided into three categories: intensity, phase, and polarization modulators. Among them, the phase modulator has good anti-interference ability due to the fact that the phase itself is not easy to change. At the same time, the modulation depth of the phase is high, which makes the phase modulator have a higher data capacity. Therefore, phase modulators are widely used in high-precision, long-distance and high-speed optical transmission systems.

[0003] The mainstream method of modulating the optical phase is to use the electro-optic effect of crystals. Compared with the thermo-optic effect, acousto-optic effect, optomechanical effect and nonlinear effect, the electro-optic effect has a faster modulation speed, more precise modulation depth and more mature technology, so the performance parameters of the electro-optic phase modulator are better. However, the electro-optic effect also has more stringent requirements for materials. It requires the material to have a large electro-optic coefficient and good thermal stability.

[0004] Traditional lithium niobate electro-optic modulators use bulk lithium niobate. This waveguide prepared based on ion diffusion or proton exchange technology has a very low refractive index contrast, which leads to weak light binding ability of the waveguide and a large device size, making it difficult to apply to on-chip integrated optical systems. Recently, with the advancement of material processing technology, thanks to the maturity of crystal ion cutting and grinding and polishing technology, lithium niobate in a thin film state has been prepared. Thin-film lithium niobate makes up for the shortcomings of bulk lithium niobate, enhancing the waveguide's ability to bind light and reducing the size of the device. And because the device size is reduced, the driving voltage of the modulator is also reduced, which further improves the performance of the modulator.

[0005] Thin Film Lithium Niobate Phase Modulator is an active device that controls and changes the phase of incident light. In order to increase the interaction between the electromagnetic field and the microwave field in the modulator and improve the performance of the modulator, in addition to using suitable materials, the modulation area of ​​the modulator also needs to be designed with a suitable structure. In order for the electric field to act effectively on the optical waveguide, the signal electrode and the ground electrode of the modulator need to be symmetrically placed on both sides of the waveguide. At present, the electrode structures used in thin film lithium niobate phase modulators are mainly divided into two types, the first is a rectangular electrode, and the second is a T-type electrode, both of which are coplanar electrode structures.

[0006] The rectangular electrode structure means that the signal electrodes and ground electrodes on both sides of the waveguide are rectangular in shape in the cross section perpendicular to the light transmission direction and in the cross section in the material plane direction, such as Figure 1a and Figure 1b As shown. The T-shaped electrode is a rectangular electrode with a T-shaped electrode added on the side of the electrode close to the waveguide, as shown Figure 2a and Figure 2b Both electrode structures require that the electrode and the waveguide are on the same plane, so they are also collectively referred to as coplanar electrode structures.

[0007] The electro-optic phase modulator with a coplanar electrode structure has problems such as uneven electric field distribution and low modulation efficiency. The technical reasons for these problems can be attributed to the insufficient overlap between the electric field generated by the electro-optic phase modulator with a coplanar electrode structure and the optical field inside the optical waveguide, that is, the overlap factor of the optical electric field is low. The coplanar electrode is limited by the width of the silicon dioxide upper cladding and cannot be close enough to the optical waveguide, so that the component of the electric field in the modulation direction is weak, and it is difficult to effectively affect the optical waveguide buried in the upper cladding, resulting in limited modulation depth and low modulation performance. In order to achieve the desired phase modulation effect, a higher driving voltage must be applied to compensate for the lack of overlap between the electric field and the optical field. This not only increases energy consumption, but also places higher voltage requirements on the circuit, increasing the complexity and cost of the system.

[0008] Secondly, there is a limitation between modulation performance and bandwidth in the electro-optic phase modulator. This is caused by the restrictive relationship between the modulation electric field strength in the waveguide and the electromagnetic transmission loss in the electrode, 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 in the waveguide is enhanced, and the modulation performance is enhanced. However, at the same time, it will cause the electrode to have a large parasitic capacitance. Especially in high-speed modulation, the large capacitance will cause the RC time constant (the response time of capacitor charging) to increase, which limits the bandwidth of the modulator and makes it unable to meet the needs of high-speed communication. At present, the on-chip integrated thin-film lithium niobate phase modulator with a rectangular electrode structure still cannot break this limitation, which makes it impossible to further improve the performance of rectangular electrode devices.

[0009] like Figure 2a and Figure 2bAs shown in the figure, the on-chip integrated thin-film lithium niobate phase modulator with a T-type electrode structure is based on a rectangular electrode, and a small T-type electrode structure is added on the side close to the waveguide. This makes the modulation efficiency determined by the electrode spacing of the small electrode, while the bandwidth and loss are determined by the main electrode spacing, breaking the limitations of the modulation performance and bandwidth loss of a single electrode. However, since the modulator with a T-type electrode structure requires the size of the T-type electrode on the main electrode to be very small, higher requirements are placed on the accuracy of the processing technology. In addition, the overly small structure also makes the device more susceptible to process errors, and the device yield and uniformity face huge challenges.

[0010] The existing technology for optimizing electrodes is mostly to modify the shape of the electrodes in the same plane. The advantage of this is that it can ensure as few processing steps as possible. However, with the continuous improvement of modulator performance requirements, the electrode shape of the coplanar structure has become more complex, and the processing difficulty of the coplanar electrode structure has also been increasing.

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

[0012] In order to solve the above problems, the present invention provides a thin film electro-optic phase modulator based on a non-coplanar electrode structure and a manufacturing method thereof. The present invention hopes to avoid the problem that the shape of a single-layer electrode is too complicated and the processing accuracy is too high, thereby changing the electrode structure from coplanar to non-coplanar, and reducing the driving voltage required by the modulator by longitudinally superimposing the electric field, thereby improving the modulation efficiency.

[0013] A thin-film electro-optic phase modulator based on a non-coplanar electrode structure provided according to one embodiment of the present invention includes, arranged in order from bottom to top: a silicon and silicon dioxide substrate; a thin-film lithium niobate waveguide layer, including a planar portion and a ridge-shaped portion protruding from the planar portion and extending longitudinally; a silicon dioxide upper cladding layer, which covers the ridge-shaped portion of the thin-film lithium niobate waveguide layer; a ground electrode and a signal electrode, which are symmetrically arranged on the outer surface of the silicon dioxide upper cladding layer to form 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 material.

[0016] Optionally, the ground electrode is formed into a Z-shaped structure or an inverted Z-shaped structure; the signal electrode is formed into a Z-shaped structure or an inverted Z-shaped structure; and wherein the ground electrode and the signal electrode are symmetrically arranged with respect to each other.

[0017] Optionally, the ground electrode includes: a flat ground electrode upper surface, a flat ground electrode lower surface and a ground electrode side surface connecting the upper surface and the lower surface, wherein the ground electrode upper surface is bonded to the top surface of the silica upper cladding, the ground electrode lower surface is bonded to the planar portion of the thin film lithium niobate waveguide layer, and the ground electrode side surface is bonded to the side surface of the silica upper cladding; the signal electrode includes: a flat signal electrode upper surface, a flat signal electrode lower surface and a signal electrode side surface connecting the signal electrode upper surface and the signal electrode lower surface, wherein the signal electrode upper surface is bonded to the top surface of the silica upper cladding, the signal electrode lower surface is bonded to the planar portion of the thin film lithium niobate waveguide layer, and the signal electrode side surface is bonded to the side surface of the silica upper cladding.

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

[0019] Optionally, two groups of parallel modulation arm structures are formed in the modulation area, each group of modulation arm structures includes: a longitudinally extending ridge portion, a silicon dioxide upper cladding covering the ridge portion, and symmetrical ground electrodes and signal electrodes arranged on the outer surface of the silicon dioxide upper cladding; the two groups of modulation arm structures are merged at the input position before the modulation area and the output position after the modulation area, and a beam splitter is arranged at the input position where the two groups of modulation arm structures are merged, and a beam combiner is arranged at the output position.

[0020] Optionally, a group of modulation arm structures are formed in the modulation area, and the modulation arm structures include: a longitudinally extending ridge portion, a silicon dioxide upper cladding layer covering the ridge portion, and symmetrical ground electrodes and signal electrodes arranged on the outer surface of the silicon dioxide upper cladding layer.

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

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

[0023] Step S2, bonding a thin-film lithium niobate layer on a silicon and silicon dioxide substrate, and processing the bonded thin-film lithium niobate layer into a thin-film lithium niobate optical waveguide layer including a planar portion and a longitudinally extending ridge portion by dry etching or wet etching technology;

[0024] Step S3, depositing a silicon dioxide layer on the surface of the thin-film lithium niobate optical waveguide layer, so that the silicon dioxide layer completely covers the ridge portion of the thin-film lithium niobate waveguide layer;

[0025] Step S4, etching away the silicon dioxide material other than the two longitudinal sides of the ridge portion to expose the planar portion of the thin-film lithium niobate optical waveguide layer and obtain a silicon dioxide upper cladding layer covering the ridge portion;

[0026] Step S5, then using a photolithography lift-off technique, evaporating gold on the planar portion of the silicon dioxide upper cladding layer and the thin-film lithium niobate optical waveguide layer to form an electrode structure including a ground electrode and a signal electrode;

[0027] Step S6, depositing 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 including a planar portion and two longitudinally parallel ridge portions by using dry etching or wet etching technology.

[0029] The thin-film electro-optic phase modulator based on a non-coplanar electrode structure and the manufacturing method thereof provided by the present invention are used for an integrated optical gyroscope 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 the non-coplanar electrode structure and the manufacturing method thereof provided according to the embodiments of the present invention have at least the following beneficial effects:

[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 double-layer capacitance on the electric field to break the limitation between the modulation performance and bandwidth loss of the modulator, thereby improving the comprehensive performance of the thin-film lithium niobate phase modulator.

[0032] 2. Compared with the coplanar T-type electrode structure in the prior art, the present invention avoids introducing special microstructures while ensuring modulation performance, reduces the requirements for processing accuracy, and increases the tolerance for process errors, which is beneficial 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 the non-coplanar electrode structure provided by the present invention can fully utilize the space on the integrated gyroscope sheet, is conducive to the miniaturized design of the integrated gyroscope, and has strong feasibility and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use 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 drawings. The drawings are schematic and should not be understood as limiting the present invention in any way. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

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

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

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

[0039] Figure 3a A top view 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.

[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 A top 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.

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

[0043] Reference numerals:

[0044] 1-Silicon and silicon dioxide substrates;

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

[0046] 21- plane part;

[0047] 22-ridge;

[0048] 31- beam splitter;

[0049] 32- beam combiner;

[0050] 4- Ground electrode;

[0051] 41- upper surface of ground electrode;

[0052] 42- side of the grounding electrode;

[0053] 43- lower surface of ground electrode;

[0054] 5-Signal electrode;

[0055] 51- signal electrode upper surface;

[0056] 52- side of the signal electrode;

[0057] 53- signal electrode lower surface;

[0058] 6-silicon dioxide upper cladding;

[0059] 7-Silicon dioxide protective layer. DETAILED DESCRIPTION

[0060] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0061] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0062] A thin-film electro-optic phase modulator based on a non-coplanar electrode structure and a manufacturing method thereof according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0063] like Figure 3a and Figure 3bAs shown, a thin-film electro-optic phase modulator based on a non-coplanar electrode structure is provided according to the first embodiment of the present invention, which is used for an integrated optical gyroscope, and includes, arranged in order 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 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 arranged on the outer surface of the silicon dioxide upper cladding 6 to form 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 can be formed of a gold material. Optionally, the ground electrode 4 and the signal electrode 5 may be formed by, after the silicon dioxide material is covered on the thin-film lithium niobate waveguide layer 2, removing the silicon dioxide material other than the longitudinal sides of the ridge portion 22 of the thin-film lithium niobate waveguide layer 2, leaving only the silicon dioxide upper cladding layer 6 covering the ridge portion 22, and then arranging the ground electrode 4 and the signal electrode 5 on the outer surface of the silicon dioxide upper cladding layer 6, so that the ground electrode 4 and the signal electrode 5 form a double-layer non-coplanar structure with a height difference. The silicon dioxide upper cladding layer 6 may be a longitudinally extending rectangular parallelepiped structure covering the ridge portion 22.

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

[0065] like Figure 3bAs shown, in the first embodiment, the ground electrode 4 of one arm structure of the thin film electro-optic phase modulator based on the 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 formed into an inverted Z-shaped structure includes a flat ground electrode upper surface 41, a flat ground electrode lower surface 43, and a ground electrode side surface 42 connecting the upper surface and the lower surface, the ground electrode upper surface 41 is attached to the top surface of the silicon dioxide upper cladding layer 6, the ground electrode lower surface 43 is attached to the plane portion 21 of the thin film lithium niobate waveguide layer 2, and the ground electrode side surface 42 is attached to the side of the silicon dioxide upper cladding layer 6. The ground electrode upper surface 41 and the ground electrode lower surface 43 of the ground electrode 4 form a double-layer structure with a height difference. The signal electrode 5 forming a Z-shape includes a flat signal electrode upper surface 51, a flat signal electrode lower surface 53, and a signal electrode side surface 52 connecting the signal electrode upper surface and the signal electrode lower surface. The signal electrode upper surface 51 is attached to the top surface of the silicon dioxide upper cladding layer 6, the signal electrode lower surface 53 is attached to the plane portion 21 of the thin-film lithium niobate waveguide layer 2, and the signal electrode side surface 52 is attached to the side of the silicon dioxide upper cladding layer 6. The signal electrode upper surface 51 and the signal electrode lower 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 groups of parallel modulation arm structures can be formed as an integral structure extending on the plane portion 21 between the two groups of modulation arm structures. That is, the lower surface 53 of the signal electrode 5 can be formed to extend from the inner side of one group of modulation arm structures to the other group of modulation arm structures on the plane portion 21 of the thin-film lithium niobate waveguide layer 2, so that the signal electrodes 5 of the two groups of modulation arm structures can be formed integrally.

[0066] Continue to refer Figure 3a and Figure 3bThe electrode part of the thin film electro-optic phase modulator based on the non-coplanar electrode structure of the first embodiment, namely the ground electrode 4 and the signal electrode 5, is an inverted Z-shaped or Z-shaped structure, so that the upper surface and the lower surface of the electrode are located on different planes above and below, and have a height difference. When an external electric field is applied to the signal electrode 5, the ground electrode upper surface 41 of the ground electrode 4 and the signal electrode upper surface 51 of the signal electrode 5 constitute a top capacitor, generating a primary electric field, and the ground electrode lower surface 43 of the ground electrode 4 and the signal electrode lower surface 53 of the signal electrode 5 constitute a bottom capacitor, generating a secondary electric field. Thus, the top capacitor and the bottom capacitor form a double-layer capacitor. Therefore, in the thin film electro-optic phase modulator based on the 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 partial electric fields formed by the upper and lower capacitors, which can make the driving voltage applied to the signal electrode 5 be used multiple times, thereby effectively reducing the required driving voltage and improving the modulation efficiency of the modulator while ensuring that the modulation effect remains unchanged. In addition, the electrodes of the non-coplanar structure break the single method of the traditional modulator to affect the modulation efficiency by changing the electrode spacing, avoiding the limitation of the electrode spacing on the modulation efficiency and bandwidth loss, thus improving the modulation efficiency without reducing the bandwidth of the modulator. In addition, the electrodes of the non-coplanar structure do not require special microstructures, do not require special process accuracy requirements, are insensitive to errors in the processing technology, and help improve the yield and uniformity of the device.

[0067] See also Figure 3b In the 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 top layer. The topmost cladding layer of the thin film electro-optic phase modulator based on the non-coplanar electrode structure on the integrated chip may be made of silicon dioxide material, which can effectively protect the device structure and has a large refractive index difference with the thin film lithium niobate waveguide layer 2, thereby improving the device performance.

[0068] In this embodiment, a wafer of suitable size and high surface flatness can be obtained by using crystal ion cutting technology as the substrate layer of the above-mentioned silicon and silicon dioxide substrate 1. The main function of the 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 thin film electro-optic phase modulator integrated on a chip of this embodiment, silicon material can be used as the substrate layer. In order to improve the beam characteristics of the waveguide, a thick silicon dioxide film is first deposited on the silicon substrate layer as a lower cladding layer, thereby forming a 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. The excess thin film lithium niobate material can be removed by dry or wet etching technology, and the remaining part forms a waveguide structure. The electrode layer of the ground electrode 4 and the signal electrode 5 can be made by photolithography technology and metal deposition technology. The electric field induced 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, through the ground electrode 4 and the signal electrode 5, the effect of efficient interaction between the optical field and the electric field can be achieved.

[0069] According to the different emphasis of the modulator performance, the structural parameters of the thin film electro-optic phase modulator based on the non-coplanar electrode structure provided in the first embodiment can be modified and adjusted. The structural parameters may include: modulation zone length, electrode spacing, etching depth, etc. The modulation zone length is the longitudinal length of the ridge portion 22 of the thin film lithium niobate optical waveguide layer 2 (that is, the longitudinal length of the silicon dioxide upper cladding layer 6, and the ground electrode 4 and the signal electrode 5), which can range from 0.4cm to 2cm, and can be optionally set to 0.75cm. The longer the modulation zone length, the stronger the modulation performance, but the bandwidth will also decrease due to the increase in impedance. The above range can provide better modulation performance and better bandwidth. The electrode spacing is the spacing distance between the ground electrode upper surface 41 of the ground electrode 4 and the signal electrode upper surface 51 of the signal electrode 5, which can range from 1μm to 2μm. The smaller the electrode spacing, the greater the modulation performance, but it will also bring greater transmission loss, and when the spacing is less than 1μm, the requirements for the process will also be further improved. The above range can provide better modulation performance with less loss and is easy to process. The etching depth is the height of the ridge portion 22 of the thin-film lithium niobate waveguide layer 2 relative to the plane portion 21, which can range from 0.1μm to 0.5μm, and can be set to 0.3μm. The etching depth will affect the modulation performance and transmission loss. When the etching depth increases, the localization ability of the thin-film lithium niobate optical waveguide layer 2 for the optical mode field is enhanced, so the loss will be reduced, but at the same time it will also weaken the effect of the electric field on the optical field, thereby reducing the modulation performance. In addition, the distance between the two parallel ridge portions 22 of the two-arm structure of the thin-film electro-optic phase modulator based on the non-coplanar electrode structure provided in the first embodiment can be 0.5cm. The ground electrode 4 and the signal electrode 5 can be formed of a gold material with a thickness of 0.2μm to 0.9μm.

[0070] See also Figure 3a and Figure 3b,The following provides the structural parameters of an embodiment of a thin film electro-optic phase modulator based on a non-coplanar electrode structure applying the first embodiment. The thin film electro-optic phase modulator of this embodiment has a symmetrical structure with two arms. For the convenience of description, only the structural parameters of one of the arms are described here. The thickness of the silicon wafer layer of the silicon and silicon dioxide substrate 1 is relatively thick, which is ignored here, and the thickness of the silicon dioxide layer can be set to 2μm. The thin film lithium niobate waveguide layer 2 uses a thin film lithium niobate with a thickness of 0.6μm cut along a plane perpendicular to the x-crystal axis, and the etching depth is 0.3μm to form 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 to have a trapezoidal cross-sectional shape, the width of the widest part of the bottom is 2μm, and the bottom angle of the trapezoid is the etching angle, which can be set to 75°. The silicon dioxide upper cladding layer 6 is generally in the shape of a rectangular parallelepiped, with a total thickness of 0.8μm and a width of 7μm. The ground electrode 4 and the signal electrode 5 can be formed of a 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 close to the distance between the two ridges 22 (the actual distance is the distance between the two ridges 22, minus the width of the silicon dioxide upper cladding 6 and the thickness of gold) is 0.5 cm, 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, the length refers to the dimension along the longitudinal direction of the arm structure or the ridge 22, the width refers to the dimension in the direction perpendicular to the longitudinal direction in the horizontal plane, and the height refers to the dimension in the vertical direction perpendicular to the horizontal plane.

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

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

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

[0074] Step S3, the input light is modulated by the ridge portion 22 of the thin-film lithium niobate ridge waveguide layer 2 and outputted by the beam combiner 32 to obtain the output light, which is inputted into the photodetector, and the photodetector processes and outputs an electrical signal, which is inputted into the oscilloscope. The photodetector is connected to a power meter or a modulation and demodulation circuit, and the phase of the output light can be obtained by analyzing the power of the electrical signal displayed by the power meter and the electrical signal outputted by the modulation and demodulation circuit, and compared with the phase of the input light introduced by the beam splitter to obtain the phase change of the light. As above, in the embodiment of the single-waveguide modulator with a single-arm structure, the output light is directly inputted into 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 not, return to step S2 and adjust the steady-state or alternating current applied to the signal electrode 5. If it meets the preset requirements, end the process and obtain output light that meets the phase requirements after phase modulation, which can be used for an integrated optical gyroscope or other required devices.

[0076] Taking into account 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 a lot of application space.

[0077] like Figure 4a and Figure 4b As shown, according to the second embodiment of the present invention, a thin film electro-optic phase modulator based on a non-coplanar electrode structure is provided, which is a single waveguide modulator having a single modulation arm structure. As shown in the figure, in this embodiment, the ground electrode lower surface 43 of the ground electrode 4 and the signal electrode lower surface 53 of the signal electrode 5 are completely symmetrical. In this embodiment, a beam splitter and a beam combiner may not be provided. In addition, in the thin film electro-optic phase modulator based on a non-coplanar electrode structure in the single waveguide form of the second embodiment, the single modulation arm structure is basically the same as one modulation arm structure in the thin film electro-optic phase modulator based on a non-coplanar electrode structure with a dual modulation arm structure of the first embodiment above, and will not be repeated here.

[0078] A method for manufacturing a thin-film electro-optic phase modulator based on a non-coplanar electrode structure provided in accordance with a third embodiment of the present invention includes the following steps.

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

[0080] Step S2, a thin-film lithium niobate layer is bonded on 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 including a planar portion 21 and a longitudinally extending ridge portion 22 by dry etching or wet etching technology. Optionally, in this step S2, the bonded thin-film lithium niobate layer can be processed into a thin-film lithium niobate optical waveguide layer 2 including a planar portion 21 and two longitudinally extending parallel ridge portions 22.

[0081] Step S3, depositing a silicon dioxide layer on the surface of the lithium niobate thin film optical waveguide layer 2, so that the silicon dioxide layer completely covers the area of ​​the ridge portion 22 of the lithium niobate thin film waveguide layer 2, that is, the light-transmitting mode area.

[0082] 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 obtain the silicon dioxide upper cladding layer 6 covering the ridge portion 22. Optionally, the silicon dioxide material outside the range of 3.5 μm extending outward from both sides of the ridge portion 22 can be removed.

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

[0084] Since the ridge portion 22 of the ridge-type 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 removed by etching to expose the plane portion 21 of the thin-film lithium niobate optical waveguide layer 2, there is a height difference between the plane 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, due to the height difference, the formed ground electrode 4 and the signal electrode 5 form a non-coplanar structure, forming a double-layer capacitor, and presenting a Z shape as a whole.

[0085] Step S6, depositing 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 completed.

[0086] Optionally, in the above embodiment, step S2 may further include arranging 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 solution, namely, a thin-film electro-optic phase modulator based on a non-coplanar electrode structure and a manufacturing method thereof. The invention is characterized by miniaturization, high modulation efficiency, large bandwidth, low transmission loss, and easy processing, which solves the limited modulation performance and bandwidth loss problems of the current on-chip integrated thin-film lithium niobate electro-optic modulator.

[0088] All the above optional technical solutions can be arbitrarily combined to form optional embodiments of the present application, which will not be described one by one here.

[0089] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean 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 embodiment of the present invention.

[0090] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A thin film electro-optic phase modulator based on a non-coplanar electrode structure, characterized in that: Including from bottom to top: Silicon and silicon dioxide substrates; A thin-film lithium niobate waveguide layer includes a planar portion and a ridge portion protruding from the planar portion and extending longitudinally; A silicon dioxide upper cladding layer covering a ridge-shaped portion of the thin-film lithium niobate waveguide layer; The ground electrode and the signal electrode are symmetrically arranged on the outer surface of the silicon dioxide upper cladding to form a double-layer non-coplanar structure.

2. The thin film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that: The ridge portion of the thin-film lithium niobate waveguide layer has a trapezoidal cross-sectional shape.

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

4. The thin film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that: The ground electrode is formed into a zigzag structure or a reverse zigzag structure; The signal electrode is formed into a zigzag structure or an inverted zigzag structure; And wherein, the ground electrode and the signal electrode are arranged symmetrically to each other.

5. The thin film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 4, characterized in that: The ground electrode comprises: a flat ground electrode upper surface, a flat ground electrode lower surface, and a ground electrode side surface connecting the upper surface and the lower surface, wherein the ground electrode upper surface is bonded to the top surface of the silicon dioxide upper cladding layer, the ground electrode lower surface is bonded to the planar portion of the thin-film lithium niobate waveguide layer, and the ground electrode side surface is bonded to the side surface of the silicon dioxide upper cladding layer; The signal electrode includes: a flat signal electrode upper surface, a flat signal electrode lower surface, and a signal electrode side surface connecting the signal electrode upper surface and the signal electrode lower surface, wherein the signal electrode upper surface is bonded to the top surface of the silicon dioxide upper cladding layer, the signal electrode lower surface is bonded to the planar portion of the thin film lithium niobate waveguide layer, and the signal electrode side surface is bonded to the side surface of the silicon dioxide upper cladding layer.

6. The thin film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 5, characterized in that: The longitudinal length of the ridge portion of the thin-film lithium niobate optical waveguide layer ranges from 0.4 cm to 2 cm; The spacing distance between the ground electrode upper surface of the ground electrode and the signal electrode upper surface of the signal electrode ranges from 1 μm to 2 μm.

7. The thin film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that: Two groups of parallel modulation arm structures are formed in the modulation area, each group of modulation arm structures includes: a longitudinally extending ridge portion, a silicon dioxide upper cladding layer covering the ridge portion, and symmetrical ground electrodes and signal electrodes arranged on the outer surface of the silicon dioxide upper cladding layer; The two groups of modulation arm structures are combined at an input position before the modulation region and an output position after the modulation region, and a beam splitter is arranged at the input position where the two groups of modulation arm structures are combined, and a beam combiner is arranged at the output position.

8. The thin film electro-optic phase modulator based on a non-coplanar electrode structure according to claim 1, characterized in that: A group of modulation arm structures are formed in the modulation area, and the modulation arm structures include: a longitudinally extending ridge portion, a silicon dioxide upper cladding layer covering the ridge portion, and symmetrical grounding electrodes and signal electrodes arranged on the outer surface of the silicon dioxide upper cladding layer.

9. 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 8, characterized in that: The following steps are involved: Step S1, depositing a layer of silicon dioxide on a silicon wafer to form a silicon and silicon dioxide substrate; Step S2, bonding a thin-film lithium niobate layer on a silicon and silicon dioxide substrate, and processing the bonded thin-film lithium niobate layer into a thin-film lithium niobate optical waveguide layer including a planar portion and a longitudinally extending ridge portion by dry etching or wet etching technology; Step S3, depositing a silicon dioxide layer on the surface of the thin-film lithium niobate optical waveguide layer, so that the silicon dioxide layer completely covers the ridge portion of the thin-film lithium niobate waveguide layer; Step S4, etching away the silicon dioxide material other than the two longitudinal sides of the ridge portion to expose the planar portion of the thin-film lithium niobate optical waveguide layer and obtain a silicon dioxide upper cladding layer covering the ridge portion; Step S5, then using a photolithography lift-off technique, evaporating gold on the planar portion of the silicon dioxide upper cladding layer and the thin-film lithium niobate optical waveguide layer to form an electrode structure including a ground electrode and a signal electrode; Step S6, depositing 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.

10. The manufacturing method according to claim 9, 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 by using dry etching or wet etching technology.

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