Electro-optical modulator based on thin film lithium niobate and preparation method thereof

Abstract

The invention discloses an electro-optical modulator based on thin film lithium niobate and a preparation method thereof. The electro-optical modulator comprises a substrate layer; the resin layer is arranged on one side of the substrate layer; the film lithium niobate layer is arranged on the side, away from the substrate layer, of the resin layer, and an optical waveguide is arranged on the surface of the part, close to the resin layer, of the film lithium niobate layer; the metal electrode layer is arranged on the partial surface, close to the resin layer, of the thin film lithium niobate layer; and the protective layer is arranged on one side, far away from the resin layer, of the thin-film lithium niobate layer. The substrate layer and the thin film lithium niobate layer with the optical waveguide structure are bonded through the resin layer, so that the modulation structure of the electro-optical modulator is completely covered with resin, the resin layer can play a role in protecting and constraining an optical field, and low-loss coupling is achieved; and the resin in the resin layer can effectively isolate the optical waveguide on the thin-film lithium niobate layer from the metal electrode layer, so that the lower optical transmission loss is ensured while the electrode distance is reduced and the modulation efficiency is improved, and the efficient modulation is realized.

Description

Technical Field

[0001] The present application relates to the technical field of lithium niobate thin film electro-optic modulators, and more specifically, to an electro-optic modulator based on thin film lithium niobate and a method for preparing the same. Background Art

[0002] With the rapid development of communication network technology, new generation information technologies such as 5G, Internet, artificial intelligence, and cloud computing have increasingly higher requirements for optical communication networks. Traditional optical communication technology has gradually failed to meet the requirements of high-speed communication and large-capacity data transmission. Electro-optical modulators are important devices in the field of photonic high-speed communication. They convert high-speed electronic signals in communication equipment into optical signals through phase modulation, intensity modulation, etc. The performance of the modulator itself determines the data transmission capacity of the system.

[0003] Lithium niobate is one of the most widely used photonic application materials due to its excellent optical properties, such as strong electro-optic effect, high second-order optical nonlinearity, wide optical transparent window, and low material loss. With the rapid development of single-crystal lithium niobate thin films manufactured by ion implantation and wafer bonding technology, photonic devices based on thin-film lithium niobate have many important applications in optical communications, optical sensing, optical computing, etc. In the field of optical communications, electro-optic modulators based on thin-film lithium niobate have great potential to achieve high modulation efficiency and large modulation bandwidth and are widely studied. At present, the lithium niobate on insulator (LNOI) platform is widely used to prepare electro-optic modulators. Through the "Smart-Cut" technology, sub-micron-thick lithium niobate single-crystal thin films are combined on silicon dioxide insulating layers and silicon substrates. The waveguide formed by dry etching on the lithium niobate thin film has a large refractive index contrast and strong optical confinement, making efficient and compact densely integrated devices possible.

[0004] However, the relative dielectric constant of silicon-based substrates is relatively large, which affects the high-speed modulation performance of electro-optic modulators. Using quartz substrates with lower relative dielectric constants can ensure the matching of microwave and light wave speeds, while taking into account transmission line impedance matching and modulation of low drive voltage. However, the current lithium niobate thin film modulators based on quartz substrates usually adopt the process method of thin film first and then structure, which has a more complicated preparation process and faces problems such as difficult processing and high process requirements. Summary of the invention

[0005] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the purpose of the present application is to propose an electro-optic modulator based on thin-film lithium niobate and a method for preparing the same. The present application uses a resin layer to bond the substrate layer to the thin-film lithium niobate layer with an optical waveguide structure, so that the modulation structure of the electro-optic modulator is completely covered in the resin. The resin layer can protect and bind the light field to achieve low-loss coupling; and the resin in the resin layer can effectively isolate the optical waveguide on the thin-film lithium niobate layer from the metal electrode layer, while reducing the electrode spacing to improve the modulation efficiency, ensuring low light transmission loss and achieving efficient modulation.

[0006] In a first aspect of the present application, an electro-optic modulator based on thin-film lithium niobate is proposed. According to an embodiment of the present application, the electro-optic modulator based on thin-film lithium niobate comprises:

[0007] substrate layer;

[0008] a resin layer, the resin layer being arranged on one side of the substrate layer;

[0009] A thin-film lithium niobate layer, wherein the thin-film lithium niobate layer is arranged on a side of the resin layer away from the substrate layer, and an optical waveguide is arranged on a portion of the surface of the thin-film lithium niobate layer close to the resin layer;

[0010] A metal electrode layer, the metal electrode layer being disposed on a portion of the surface of the thin-film lithium niobate layer close to the resin layer;

[0011] A protective layer is disposed on a side of the thin-film lithium niobate layer away from the resin layer.

[0012] According to the electro-optic modulator based on thin-film lithium niobate in the above-mentioned embodiment of the present application, a resin layer is used to bond the substrate layer to the thin-film lithium niobate layer with an optical waveguide structure, so that the modulation structure of the electro-optic modulator is completely covered in the resin. The resin layer can protect and bind the light field, and during the mode field diffusion process, it ensures that the light does not escape into the air, thereby achieving low-loss coupling; and the resin in the resin layer can effectively isolate the optical waveguide on the thin-film lithium niobate layer from the metal electrode layer. The resin plays an isolating role between the metal electrode and the optical waveguide, and while reducing the electrode spacing to improve the modulation efficiency, it ensures a low light transmission loss, thereby achieving efficient modulation.

[0013] At the same time, the electro-optic modulator of the present application is prepared on a resin layer and a substrate layer with a low dielectric constant, and adopts a coplanar traveling wave electrode structure with a mature process to efficiently achieve matching of microwave phase velocity and light wave group velocity, while achieving impedance matching and low modulation half-wave voltage, thereby realizing a high-performance and high-speed electro-optic modulator.

[0014] In addition, the electro-optic modulator based on thin-film lithium niobate according to the above embodiment of the present application may also have the following additional technical features:

[0015] In some embodiments of the present application, the thickness of the resin layer is 3 μm to 500 μm; and / or the refractive index of the resin layer is in the range of 1.4 to 1.6.

[0016] In some embodiments of the present application, the optical waveguide includes an input spot converter, a beam splitter, two optical waveguides, a beam combiner and an output spot converter connected to each other.

[0017] In some embodiments of the present application, the input spot converter and the output spot converter respectively include a double-layer lithium niobate conical waveguide structure, the resin layer covers the double-layer lithium niobate conical waveguide structure, and the length range of the double-layer lithium niobate conical waveguide structure is 0.3μm to 1μm; and / or, the beam splitter and the beam combiner respectively include a multimode interference coupler structure, and the interference area length range of the multimode interference coupler structure is 50μm to 100μm.

[0018] In some embodiments of the present application, the metal electrode layer includes a traveling wave signal electrode and two traveling wave ground electrodes, and the two traveling wave ground electrodes are arranged in parallel on opposite sides of the traveling wave signal electrode; the two optical waveguides are respectively arranged in parallel between the two traveling wave ground electrodes and the traveling wave signal electrode.

[0019] In some embodiments of the present application, the traveling wave ground electrode and the optical waveguide, and the optical waveguide and the traveling wave signal electrode are respectively isolated by the resin in the resin layer; and / or the width of the traveling wave signal electrode ranges from 3μm to 30μm; and / or the spacing between the traveling wave signal electrode and the traveling wave ground electrode ranges from 4μm to 10μm; and / or the width of a single optical waveguide is from 1μm to 3μm.

[0020] In some embodiments of the present application, the thickness of the thin film lithium niobate layer is 200nm to 1000nm; and / or the etching depth of the optical waveguide is 100nm to 700nm; and / or the thickness of the metal electrode layer ranges from 0.2μm to 2μm.

[0021] In some embodiments of the present application, the substrate layer includes at least one of a quartz substrate layer and a silicon substrate layer.

[0022] In some embodiments of the present application, the protective layer includes at least one of silicon dioxide and resin; and / or the protective layer has a thickness of 1 μm to 10 μm.

[0023] In a second aspect of the present application, a method for preparing an electro-optic modulator based on thin-film lithium niobate is proposed. According to an embodiment of the present application, the method comprises:

[0024] Etching an optical waveguide on a lithium niobate substrate;

[0025] forming a metal electrode layer in the modulation region of the optical waveguide to obtain a Mach-Zehnder modulation structure on the lithium niobate substrate;

[0026] The plane where the optical waveguide of the lithium niobate substrate is located is bonded upside down on the substrate layer by resin, and the lithium niobate substrate is thinned on the side of the lithium niobate substrate away from the resin to form a thin-film lithium niobate layer;

[0027] A protective layer is formed on the side of the thin-film lithium niobate layer away from the resin to obtain the electro-optical modulator based on thin-film lithium niobate.

[0028] According to the method for preparing an electro-optic modulator based on thin-film lithium niobate according to the above-mentioned embodiment of the present application, the method proposes for the first time a reverse manufacturing process of preparing the structure first and then thinning the lithium niobate, that is, first using resin to bond the substrate layer to the lithium niobate substrate with an optical waveguide structure, and then thinning the lithium niobate substrate, which simplifies the preparation process and effectively solves the problem of complex process flow of lithium niobate thin film modulators based on quartz substrates, and facilitates the mass production of high-speed lithium niobate thin film modulators in the future. In addition, the method simplifies the process while also achieving speed matching, impedance matching, efficient modulation and other requirements.

[0029] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0031] Figure 1 A schematic diagram of the structure of an electro-optic modulator based on thin-film lithium niobate according to an embodiment of the present application;

[0032] Figure 2 This is a schematic diagram of the structure of a thin film lithium niobate layer according to an embodiment of the present application;

[0033] Figure 3 A cross-sectional schematic diagram of an electro-optic modulator based on thin-film lithium niobate according to an embodiment of the present application;

[0034] Figure 4 This is a modulation electric field diagram of the lithium niobate thin film electro-optic modulator of Example 1 of the present application;

[0035] Figure 5 This is a characteristic impedance comparison diagram of the lithium niobate thin film modulator of Example 1 of the present application;

[0036] Figure 6 This is a comparison diagram of the microwave refractive index and the light wave group refractive index of the lithium niobate thin film modulator of Example 1 of the present application.

[0037] Among them, 1-substrate layer, 2-resin layer, 3-thin film lithium niobate layer, 4-metal electrode layer, 5-protective layer, 6-input spot mode converter, 7-beam splitter, 8-traveling wave signal electrode, 9-traveling wave ground electrode, 10-beam combiner, 11-output spot mode converter, 12-optical waveguide. DETAILED DESCRIPTION

[0038] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0039] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred elements must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present application.

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0041] In this application, unless otherwise clearly specified and limited, the terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0042] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0043] In the first aspect of the present application, an electro-optic modulator based on thin film lithium niobate is proposed. According to an embodiment of the present application, referring to the attached Figure 1 and attached Figure 3 The electro-optic modulator based on thin-film lithium niobate includes: a substrate layer 1; a resin layer 2, which is arranged on one side of the substrate layer 1; a thin-film lithium niobate layer 3, which is arranged on the side of the resin layer 2 away from the substrate layer 1, and an optical waveguide is arranged on the surface of the thin-film lithium niobate layer 3 close to the resin layer 2 (the optical waveguide is etched on the thin-film lithium niobate layer 3); a metal electrode layer 4, which is arranged on the surface of the thin-film lithium niobate layer 3 close to the resin layer 2 (that is, the metal electrode layer 4 relies on the thin-film lithium niobate layer 3); a protective layer 5, which is arranged on the side of the thin-film lithium niobate layer 3 away from the resin layer 2.

[0044] It should be noted that in the attached Figures 1 to 3 In FIG. 1 , X represents the length direction of the electro-optic modulator, Y represents the width direction of the electro-optic modulator, and Z represents the thickness direction of the electro-optic modulator.

[0045] The beneficial effects that can be achieved by the thin-film lithium niobate electro-optic modulator proposed in this application are described in detail below:

[0046] The present application uses a resin layer 2 with a low dielectric constant to bond the substrate layer 1 to the thin-film lithium niobate layer 3 with an optical waveguide structure, so that the modulation structure of the electro-optical modulator is completely covered in the resin. The resin layer 2 can protect and bind the light field. During the mode field diffusion process, it ensures that the light does not escape into the air, thereby achieving low-loss coupling; and the resin in the resin layer 2 can effectively isolate the optical waveguide on the thin-film lithium niobate layer 3 from the metal electrode layer 4. The resin plays an isolating role between the metal electrode and the optical waveguide, while reducing the electrode spacing and improving the modulation efficiency, it ensures low light transmission loss and achieves efficient modulation.

[0047] At the same time, the electro-optic modulator of the present application is prepared on a resin layer 2 with a low dielectric constant and a substrate layer 1, and adopts a coplanar traveling wave electrode structure with a mature process to efficiently achieve matching of microwave phase velocity and light wave group velocity, while achieving impedance matching and low modulation half-wave voltage, thereby realizing a high-performance and high-speed electro-optic modulator.

[0048] In the embodiment of the present application, the substrate layer 1 is used for speed matching of microwaves and light waves. The protective layer 5 is covered on the thin film lithium niobate layer 3 for protection and buffering.

[0049] According to some specific embodiments of the present application, the thickness of the resin layer 2 is 3μm to 500μm, for example, it can be 3μm, 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, etc. By limiting the thickness of the resin layer 2 within the above range, it can be further ensured that the resin layer 2 effectively bonds the substrate layer 1 with the thin film lithium niobate layer 3 with the optical waveguide structure, further ensures that the modulation structure of the electro-optical modulator is completely covered in the resin, further ensures that the resin layer 2 plays a role in protecting and binding the light field, and further ensures that the resin in the resin layer 2 can effectively isolate the optical waveguide on the thin film lithium niobate layer 3 from the metal electrode layer 4.

[0050] According to some further specific embodiments of the present application, the refractive index of the resin layer 2 is in the range of 1.4 to 1.6, for example, it may be 1.4 / 1.44 / 1.48 / 1.52 / 1.56 / 1.6, etc., thereby further ensuring the above-mentioned properties of the resin layer 2.

[0051] In the embodiments of the present application, the specific type of material of the above-mentioned resin layer 2 is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific embodiments, the material of the above-mentioned resin layer 2 includes at least one of epoxy acrylate, polyurethane acrylic resin, polyester acrylic resin, amino acrylic resin, acryloxy resin, methacryloxy resin, vinyl resin and allyl resin.

[0052] According to some specific embodiments of the present application, refer to the attached Figure 2 , the optical waveguide includes a connected input spot converter 6, a beam splitter 7, two optical waveguides 12, a combiner 10 and an output spot converter 11. Among them, the input spot converter 6 is terminated with the input optical fiber for spot matching of the input light. The 1×2 beam splitter 7 divides the input light into two equal-power light paths through a multimode interference coupler structure and transmits them to the Mach-Zehnder modulation structure part. The 2×1 combiner 10 combines the two modulated lights. The output spot converter 11 is connected to the output optical fiber for spot matching of the output light and output. The optical fiber is directly terminated at the spot converters at the input and output ends of the electro-optic modulator.

[0053] According to some specific embodiments of the present application, refer to the attached Figure 2 The metal electrode layer 4 includes a traveling wave signal electrode 8 and two traveling wave grounding electrodes 9, and the two traveling wave grounding electrodes 9 are arranged in parallel on opposite sides of the traveling wave signal electrode 8; the two optical waveguides 12 are respectively arranged in parallel between the two traveling wave grounding electrodes 9 and the traveling wave signal electrode 8. Among them, the two optical waveguides 12, the traveling wave signal electrode 8, and the two traveling wave grounding electrodes 9 together form a Mach-Zehnder modulation structure, and a modulation signal is applied to the metal electrode to perform electro-optical modulation on the two lights. The metal electrode is connected to the external electrode through the opening above the thin film lithium niobate layer 3 and the protective layer 5. Through the metal lead, the traveling wave signal electrode 8 is connected to the external electrode signal end, and the traveling wave grounding electrode 9 is connected to the external electrode ground end. The metal electrode structure is a coplanar traveling wave electrode, which adopts a push-pull voltage drive.

[0054] According to some other specific embodiments of the present application, the input spot converter 6 and the output spot converter 11 respectively include a double-layer lithium niobate tapered waveguide structure, and the resin layer 2 covers the double-layer lithium niobate tapered waveguide structure, and the double-layer tapered waveguide structure is used to achieve low-loss conversion from the large mode field of the optical fiber to the small mode field of the waveguide of the thin-film lithium niobate layer 3. Further, the length of the double-layer lithium niobate tapered waveguide structure ranges from 0.3μm to 1μm, for example, it can be 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, etc.

[0055] According to some further specific embodiments of the present application, the beam splitter 7 and the beam combiner 10 respectively include a multimode interference coupler structure, and the interference region length of the multimode interference coupler structure ranges from 50 μm to 100 μm.

[0056] According to some further specific embodiments of the present application, the traveling wave ground electrode 9 and the optical waveguide 12 , and the optical waveguide 12 and the traveling wave signal electrode 8 are isolated by the resin in the resin layer 2 .

[0057] According to some other specific embodiments of the present application, the width of the traveling wave signal electrode 8 ranges from 3 μm to 30 μm, for example, 3 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc.

[0058] According to some other specific embodiments of the present application, the spacing between the traveling wave signal electrode 8 and the traveling wave ground electrode 9 is in the range of 4 μm to 10 μm, for example, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0059] According to some further specific embodiments of the present application, the width of a single optical waveguide 12 is 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc.

[0060] According to some other specific embodiments of the present application, the thickness of the thin film lithium niobate layer 3 is 200nm~1000nm (for example, it can be 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc.), the etching depth of the optical waveguide is 100nm~700nm (for example, it can be 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, etc.), and the thickness of the metal electrode layer 4 ranges from 0.2μm to 2μm (for example, it can be 0.2μm, 0.5μm, 1μm, 1.5μm, 2μm, etc.).

[0061] According to some other specific embodiments of the present application, the substrate layer 1 includes at least one of a quartz substrate layer 1 and a silicon substrate layer 1, preferably a quartz substrate layer 1 with a lower dielectric constant. Using a quartz substrate with a lower relative dielectric constant can ensure the matching of microwave and light wave velocities, while taking into account transmission line impedance matching and modulation of low drive voltage. The electro-optic modulator of the present application is prepared on a resin layer 2 with a lower dielectric constant and a quartz substrate layer 1, and adopts a coplanar traveling wave electrode structure with a mature process to efficiently achieve microwave phase velocity and light wave group velocity matching, while achieving impedance matching and low modulation half-wave voltage, and realizing a high-performance and high-speed electro-optic modulator.

[0062] According to some further specific embodiments of the present application, the protective layer 5 includes at least one of silicon dioxide and resin, preferably silicon dioxide.

[0063] According to some other specific embodiments of the present application, the thickness of the protective layer 5 is 1 μm to 10 μm (for example, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, etc.), thereby further ensuring the protection and buffering effect of the protective layer 5.

[0064] In the embodiment of the present application, the specific process of performing electro-optical modulation using the electro-optical modulator of the present application is as follows:

[0065] The input spot mode converter is terminated with the input optical fiber, and a double-layer tapered waveguide structure is used to achieve low-loss conversion from the large mode field of the optical fiber to the small mode field of the lithium niobate thin film waveguide; the converted input light first enters the beam splitter, and through the multimode interference coupler structure, one light is divided into two light paths with equal power and transmitted to the optical waveguide of the Mach-Zehnder modulation part. Then a modulation signal is applied to the metal electrode to perform electro-optical modulation on the two light paths, specifically, the traveling wave signal electrode is connected to the signal end of the external electrode, and the traveling wave ground electrode is connected to the ground end of the external electrode. The two modulated light paths are combined into one light output through a beam combiner, using a multimode interference coupler structure; the output light passes through the output spot mode converter, and through the double-layer tapered waveguide structure, the small mode field light in the lithium niobate thin film waveguide is diffused, and terminated with the output optical fiber to achieve low-loss coupling.

[0066] In a second aspect of the present application, a method for preparing the above-mentioned electro-optic modulator based on thin-film lithium niobate is proposed. According to an embodiment of the present application, the method comprises:

[0067] S100: Etching an optical waveguide on a lithium niobate substrate;

[0068] In this step, an optical waveguide is etched on a lithium niobate substrate.

[0069] According to some specific embodiments of the present application, Figure 3 , the optical waveguide includes an input spot converter, a beam splitter, two optical waveguides, a combiner and an output spot converter, which are connected in sequence. Among them, the input spot converter is terminated with the input optical fiber for spot matching of the input light. The 1×2 beam splitter divides the input light into two equal-power light paths through a multimode interference coupler structure and transmits them to the Mach-Zehnder modulation structure part. The 2×1 combiner combines the two modulated lights. The output spot converter is connected with the output optical fiber for spot matching of the output light and output. The optical fiber is directly terminated from the spot converter at the input and output ends of the electro-optic modulator.

[0070] S200: forming a metal electrode layer in a modulation region of the optical waveguide to obtain a Mach-Zehnder modulation structure on a lithium niobate substrate;

[0071] In this step, a metal electrode layer is deposited in the modulation region of the optical waveguide to obtain a Mach-Zehnder modulation structure on a lithium niobate substrate.

[0072] According to some further specific embodiments of the present application, refer to the attached Figure 3 The metal electrode layer includes a traveling wave signal electrode and two traveling wave grounding electrodes. The two traveling wave grounding electrodes are arranged in parallel on opposite sides of the traveling wave signal electrode; the two optical waveguides are respectively arranged in parallel between the two traveling wave grounding electrodes and the traveling wave signal electrode. Among them, the two optical waveguides, the traveling wave signal electrode, and the two traveling wave grounding electrodes together form a Mach-Zehnder modulation structure, and the modulation signal is applied to the metal electrode to perform electro-optical modulation on the two light paths. The metal electrode is connected to the external electrode through the thinned thin film lithium niobate layer and the opening above the protective layer. Through the metal lead, the traveling wave signal electrode is connected to the signal end of the external electrode, and the traveling wave grounding electrode is connected to the ground end of the external electrode. The metal electrode structure is a coplanar traveling wave electrode, which adopts a push-pull voltage drive.

[0073] S300: bonding the plane where the optical waveguide of the lithium niobate substrate is located to the substrate layer by means of resin, and thinning the lithium niobate substrate on the side of the lithium niobate substrate away from the resin to form a thin film lithium niobate layer;

[0074] In this step, the plane where the optical waveguide of the lithium niobate substrate is located is bonded to the substrate layer by resin flip-down, and the traveling wave ground electrode and the optical waveguide, and the optical waveguide and the traveling wave signal electrode are isolated by resin respectively. Then, the lithium niobate substrate is thinned on the side of the lithium niobate substrate away from the resin to form the final thin-film lithium niobate layer.

[0075] S400: forming a protective layer on a side of the thin-film lithium niobate layer away from the resin.

[0076] In this step, a protective layer is deposited on the side of the thin-film lithium niobate layer away from the resin to obtain an electro-optic modulator based on the thin-film lithium niobate.

[0077] According to some further specific embodiments of the present application, the protective layer includes at least one of silicon dioxide and resin, preferably silicon dioxide.

[0078] According to the method for preparing an electro-optic modulator based on thin-film lithium niobate according to the above-mentioned embodiment of the present application, the method proposes for the first time a reverse manufacturing process of preparing the structure first and then thinning the lithium niobate, that is, first using resin to bond the substrate layer to the lithium niobate substrate with an optical waveguide structure, and then thinning the lithium niobate substrate, which simplifies the preparation process and effectively solves the problem of complex process flow of lithium niobate thin film modulators based on quartz substrates, and facilitates the mass production of high-speed lithium niobate thin film modulators in the future. In addition, the method simplifies the process while also achieving speed matching, impedance matching, efficient modulation and other requirements.

[0079] At the same time, the method uses a resin with a low dielectric constant to bond the substrate layer to the lithium niobate layer with the optical waveguide structure, so that the modulation structure of the electro-optic modulator is completely covered in the resin. The resin can protect and bind the light field. During the mode field diffusion process, it ensures that the light does not escape into the air, thereby achieving low-loss coupling; and the resin can effectively isolate the optical waveguide on the lithium niobate layer from the metal electrode layer. The resin plays an isolating role between the metal electrode and the optical waveguide, while reducing the electrode spacing and improving the modulation efficiency, it ensures low light transmission loss and achieves efficient modulation.

[0080] In addition, the electro-optic modulator of the present application is prepared on a resin layer and a substrate layer with a low dielectric constant, and adopts a coplanar traveling wave electrode structure with a mature process to efficiently achieve microwave phase velocity and light wave group velocity matching, while achieving impedance matching and low modulation half-wave voltage, thereby realizing a high-performance and high-speed electro-optic modulator.

[0081] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. In addition, unless otherwise explicitly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to this article or known methods, and the reaction conditions not listed are also easily available to those skilled in the art.

[0082] Example 1

[0083] This embodiment provides an electro-optic modulator based on thin-film lithium niobate, and the preparation method thereof is as follows:

[0084] 1) First, an optical waveguide structure is prepared on a lithium niobate substrate, including: etching an input spot converter, a beam splitter, modulating two optical waveguides, a beam combiner and an output spot converter.

[0085] 2) Depositing metal electrode layers on both sides of the two optical waveguides, including a traveling wave signal electrode and two traveling wave grounding electrodes, wherein the two traveling wave grounding electrodes are arranged in parallel on opposite sides of the traveling wave signal electrode; and the two optical waveguides are arranged in parallel between the two traveling wave grounding electrodes and the traveling wave signal electrode.

[0086] 3) Then, the lithium niobate layer with the structure is bonded to the quartz substrate by means of epoxy acrylate resin, the lithium niobate substrate is thinned to a film thickness, and the epoxy acrylate resin forms an epoxy acrylate resin layer.

[0087] 4) Finally, a silicon dioxide layer is grown on the surface of the thinned lithium niobate layer, a hole is opened in the metal lead part, connected to the external electrode, and optical fibers are coupled at the input and output ends to complete the preparation of the lithium niobate thin film electro-optic modulator.

[0088] Among them, the thickness of the epoxy acrylate resin layer is 5μm; the thickness of the silicon dioxide layer is 3μm; the thickness of the thinned lithium niobate film layer is 700nm, of which the depth of the etched lithium niobate waveguide is 300nm; the widths of the two optical waveguides are 2μm respectively, and under the isolation of the resin layer with a refractive index of 1.5, the electrode spacing between the traveling wave signal electrode and the traveling wave ground electrode is reduced to 5.6μm, the thickness of the metal electrode is 0.5μm, and a traveling wave signal electrode with a width of 20μm and a traveling wave ground electrode with a width of 120μm are used to reduce microwave loss; the input mode spot converter structure waveguide length and the output mode spot converter structure waveguide length are 0.5μm respectively.

[0089] Example 2

[0090] This embodiment provides an electro-optic modulator based on thin-film lithium niobate, and its preparation method is basically the same as that of Embodiment 1, except that:

[0091] The thickness of the epoxy acrylate resin layer is 10 μm; the thickness of the silicon dioxide layer is 2 μm; the thickness of the thinned lithium niobate film layer is 600 nm, wherein the depth of the etched lithium niobate waveguide is 300 nm.

[0092] Example 3

[0093] This embodiment provides an electro-optic modulator based on thin-film lithium niobate, and its preparation method is basically the same as that of Embodiment 1, except that:

[0094] The thickness of the epoxy acrylate resin layer is 20 μm; the thickness of the silicon dioxide layer is 5 μm; the thickness of the thinned lithium niobate film layer is 400 nm, wherein the depth of the etched lithium niobate waveguide is 200 nm.

[0095] Example 4

[0096] This embodiment provides an electro-optic modulator based on thin-film lithium niobate, and its preparation method is basically the same as that of Embodiment 1, except that:

[0097] The thickness of the epoxy acrylate resin layer is 30 μm; the thickness of the silicon dioxide layer is 4 μm; the thickness of the thinned lithium niobate film layer is 500 nm, wherein the etching depth of the lithium niobate waveguide is 250 nm.

[0098] Example 5

[0099] This embodiment provides an electro-optic modulator based on thin-film lithium niobate, and its preparation method is basically the same as that of Embodiment 1, except that:

[0100] The widths of the two optical waveguides are 1.5μm respectively. Under the isolation of the resin layer with a refractive index of 1.5, the electrode spacing between the traveling wave signal electrode and the traveling wave ground electrode is reduced to 5μm. The thickness of the metal electrode is 0.8μm. A traveling wave signal electrode with a width of 10μm and a traveling wave ground electrode with a width of 120μm are used to reduce microwave loss. The length of the input spot converter structure waveguide and the length of the output spot converter structure waveguide are 0.3μm respectively.

[0101] Example 6

[0102] This embodiment provides an electro-optic modulator based on thin-film lithium niobate, and its preparation method is basically the same as that of Embodiment 1, except that:

[0103] The widths of the two optical waveguides are 2.4μm respectively. Under the isolation of the resin layer with a refractive index of 1.5, the electrode spacing between the traveling wave signal electrode and the traveling wave ground electrode is reduced to 6.5μm. The thickness of the metal electrode is 1μm. A traveling wave signal electrode with a width of 15μm and a traveling wave ground electrode with a width of 120μm are used to reduce microwave loss. The length of the input mode spot converter structure waveguide and the length of the output mode spot converter structure waveguide are 1μm respectively.

[0104] The electric field was modulated on the thin-film lithium niobate electro-optic modulators prepared in Examples 1 to 6 respectively. The metal electrode structure was a coplanar traveling wave electrode, and a push-pull voltage drive was adopted. A positive voltage of 1V was applied to the traveling wave signal electrode, and the traveling wave ground electrode was grounded.

[0105] Figure 4 The modulation electric field diagram of the lithium niobate thin film electro-optic modulator of Example 1 of the present application is shown in Figure 1. A positive voltage of 1V is applied to the traveling wave signal electrode, and the traveling wave ground electrode is grounded. The lithium niobate thin film modulator of Example 1 has a transmission loss of less than 0.1dB / cm and a half-wave voltage-length product of less than 2.5V.cm within the parameter range.

[0106] Figure 5 This is a characteristic impedance comparison diagram of the lithium niobate thin film modulator of Example 1 of the present application, Figure 6 This is a comparison chart of the microwave refractive index and the light wave group refractive index of the lithium niobate thin film modulator of Example 1 of the present application. Figure 5 and Figure 6 As shown, the lithium niobate thin film modulator of Example 1 has a characteristic impedance close to 50Ω in the high frequency range, which meets the requirement of matching the characteristic impedance of the transmission line with the impedance of the external driving circuit and the load. At the same time, in the high frequency range, the microwave refractive index is close to the refractive index of the light wave group, which meets the speed matching requirement and has the conditions for realizing high-speed modulation.

[0107] The modulated electric field diagrams, characteristic impedance comparison diagrams, and microwave refractive index and light wave group refractive index comparison diagrams of Examples 2 to 6 are similar to those of Example 1 and are not repeated here. It can be seen from the modulated electric field diagrams, characteristic impedance comparison diagrams, and microwave refractive index and light wave group refractive index comparison diagrams of Examples 2 to 6 that the lithium niobate thin film modulators of Examples 2 to 6 have a characteristic impedance close to 50Ω in the high frequency range, meeting the requirement that the characteristic impedance of the transmission line matches the impedance of the external driving circuit and the load, and at the same time, in the high frequency range, the microwave refractive index is close to the light wave group refractive index, meeting the speed matching requirement, and having the conditions for realizing high-speed modulation.

[0108] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0109] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. An electro-optic modulator based on thin film lithium niobate, characterized in that: include: substrate layer; a resin layer, the resin layer being arranged on one side of the substrate layer; A thin-film lithium niobate layer, wherein the thin-film lithium niobate layer is arranged on a side of the resin layer away from the substrate layer, and an optical waveguide is arranged on a portion of the surface of the thin-film lithium niobate layer close to the resin layer; A metal electrode layer, the metal electrode layer being disposed on a portion of the surface of the thin-film lithium niobate layer close to the resin layer; A protective layer is disposed on a side of the thin-film lithium niobate layer away from the resin layer.

2. The electro-optic modulator based on thin film lithium niobate according to claim 1, characterized in that: The thickness of the resin layer is 3 μm to 500 μm; And / or, the refractive index of the resin layer is in the range of 1.4 to 1.

6.

3. The electro-optic modulator based on thin film lithium niobate according to claim 1, characterized in that: The optical waveguide comprises an input spot mode converter, a beam splitter, two optical waveguides, a beam combiner and an output spot mode converter which are connected to each other.

4. The electro-optic modulator based on thin-film lithium niobate according to claim 3, characterized in that: The input spot converter and the output spot converter respectively include a double-layer lithium niobate tapered waveguide structure, the resin layer covers the double-layer lithium niobate tapered waveguide structure, and the length of the double-layer lithium niobate tapered waveguide structure ranges from 0.3 μm to 1 μm; And / or, the beam splitter and the beam combiner respectively include a multimode interference coupler structure, and the interference region length of the multimode interference coupler structure ranges from 50 μm to 100 μm.

5. The electro-optic modulator based on thin film lithium niobate according to claim 3, characterized in that: The metal electrode layer includes a traveling wave signal electrode and two traveling wave grounding electrodes, and the two traveling wave grounding electrodes are arranged in parallel on opposite sides of the traveling wave signal electrode; The two optical waveguides are respectively arranged in parallel between the two traveling wave ground electrodes and the traveling wave signal electrode.

6. The electro-optic modulator based on thin-film lithium niobate according to claim 5, characterized in that: The traveling wave ground electrode and the optical waveguide, and the optical waveguide and the traveling wave signal electrode are isolated by the resin in the resin layer respectively; And / or, the width of the traveling wave signal electrode ranges from 3 μm to 30 μm; And / or, the distance between the traveling wave signal electrode and the traveling wave ground electrode ranges from 4 μm to 10 μm; And / or, the width of a single optical waveguide is 1 μm to 3 μm.

7. The electro-optic modulator based on thin-film lithium niobate according to any one of claims 1 to 6, characterized in that: The thickness of the thin film lithium niobate layer is 200nm to 1000nm; And / or, the etching depth of the optical waveguide is 100nm to 700nm; And / or, the thickness of the metal electrode layer is in the range of 0.2 μm to 2 μm.

8. The electro-optic modulator based on thin-film lithium niobate according to any one of claims 1 to 6, characterized in that: The substrate layer includes at least one of a quartz substrate layer and a silicon substrate layer.

9. The electro-optic modulator based on thin-film lithium niobate according to any one of claims 1 to 6, characterized in that: The protective layer includes at least one of silicon dioxide and resin; And / or, the protective layer has a thickness of 1 μm to 10 μm.

10. A method for preparing an electro-optic modulator based on thin-film lithium niobate according to any one of claims 1 to 9, characterized in that: include: Etching an optical waveguide on a lithium niobate substrate; forming a metal electrode layer in the modulation region of the optical waveguide to obtain a Mach-Zehnder modulation structure on the lithium niobate substrate; The plane where the optical waveguide of the lithium niobate substrate is located is bonded upside down on the substrate layer by resin, and the lithium niobate substrate is thinned on the side of the lithium niobate substrate away from the resin to form a thin-film lithium niobate layer; A protective layer is formed on the side of the thin-film lithium niobate layer away from the resin to obtain the electro-optical modulator based on thin-film lithium niobate.

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