Thin film lithium niobate electro-optical modulator with stepped electrodes

Abstract

The invention relates to the technical field of optical fiber communication, in particular to a thin-film lithium niobate electro-optical modulator of a stepped electrode, which comprises a substrate, a buffer layer, an optical waveguide, a metal electrode and a transition layer, the optical waveguide is an X-shaped or Y-shaped cutting LN film, a traditional ridge-shaped structure is adopted, the optical waveguide is bonded to the thick SiO2 buffer layer on the substrate, the film can be prepared through various technologies such as ion implantation, wafer bonding and hot slicing, and in order to improve the electro-optical overlapping coefficient and reduce light absorption loss, a silicon dioxide transition layer is used for connecting the metal electrode and the optical waveguide. The metal electrode is of a stepped structure, the electrode can effectively reduce electrical loss and obtain high bandwidth, and the electrode is used for generating an electric field in the aspect of photoelectric efficiency; the electric field is used for changing the functional characteristics of the thin-film lithium niobate layer and further changing the optical transmission characteristics of the waveguide, so that electro-optical modulation is realized. Therefore, the problem that an existing electro-optical modulator is low in modulation efficiency is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber communication, and in particular to a thin-film lithium niobate electro-optic modulator with a stepped electrode. Background Art

[0002] Electro-optic modulators are widely used at the transmitting end of optical communication systems. They alter the amplitude, phase, and other information of the optical carrier wave by applying an external electrical signal, enabling high-speed conversion between electrical and optical signals. As user demands for data throughput and communication network bandwidth increase, higher requirements are placed on the performance and integration of electro-optical modulators. Thin-film lithium niobate modulators, with their low power consumption, wide bandwidth, compact size, and relatively mature fabrication technology, offer promising solutions for the future development of integrated optical circuits. Summary of the Invention

[0003] The present invention aims to provide a thin-film lithium niobate electro-optic modulator with stepped electrodes, aiming to solve the problem of low modulation efficiency of existing electro-optic modulators.

[0004] To achieve the above object, the present invention provides a thin-film lithium niobate electro-optic modulator with a stepped electrode, comprising a substrate, a buffer layer, an optical waveguide, a metal electrode and a transition layer;

[0005] The buffer layer is located on the top of the substrate, the optical waveguide is located on the top of the buffer layer, the transition layer is located on a side of the optical waveguide away from the buffer layer, the metal electrode is located on the top of the transition layer, and the transition layer connects the metal electrode and the optical waveguide.

[0006] Wherein, the metal electrode has a stepped structure.

[0007] Wherein, the optical waveguide is an X-shaped cut lithium niobate film with a ridge-shaped structure.

[0008] Wherein, the metal electrode is a gold electrode with a stepped structure.

[0009] Wherein, the transition layer is a silicon dioxide cladding.

[0010] The present invention discloses a thin-film lithium niobate electro-optical modulator with a stepped electrode, comprising a substrate, a buffer layer, an optical waveguide, a metal electrode, and a transition layer. The buffer layer is located on top of the substrate, the optical waveguide is located on top of the buffer layer, the transition layer is located on the side of the optical waveguide away from the buffer layer, and the metal electrode is located on top of the transition layer. The middle electrode is a signal electrode, and the electrodes on both sides are ground electrodes. The transition layer connects the metal electrode and the optical waveguide. The optical waveguide is an X-cut lithium niobate thin film with a ridge-like structure. The optical waveguide is bonded to the thick SiO2 buffer layer on the substrate. The metal electrode is a stepped gold electrode, which effectively reduces electrical loss and achieves high bandwidth. In terms of photoelectric efficiency, the stepped metal electrode enhances the effect on the optical waveguide, effectively improving modulation efficiency. The metal electrodes are periodically arranged along the Y-axis of the optical waveguide. The high-dielectric cladding and isolation layer reduce optical loss while changing the electric field intensity distribution, significantly increasing the electric field intensity in the waveguide and enhancing the overlap between the electric and optical fields, thereby improving modulation efficiency. A stepped traveling-wave electrode lithium niobate electro-optic modulator achieves a half-wave voltage-length product of 0.99 V·cm at an optical absorption loss of 0.25 dB / cm, providing important guidance for the design of electro-optic modulators. This solves the low modulation efficiency problem of existing electro-optic modulators. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 FIG. 1 is a top view of a thin-film lithium niobate electro-optic modulator with stepped electrodes according to a first embodiment of the present invention.

[0013] Figure 2 FIG. 1 is a cross-sectional view of a thin-film lithium niobate electro-optic modulator with stepped electrodes according to the first embodiment of the present invention.

[0014] Figure 3 FIG. 1 is an electric field distribution diagram of a thin-film lithium niobate electro-optic modulator with stepped electrodes according to the second embodiment of the present invention.

[0015] Figure 4 This is a light spot diagram of a thin-film lithium niobate electro-optic modulator with stepped electrodes according to the second embodiment of the present invention.

[0016] Figure 5 This is a comparison diagram of the half-wave voltage-length product of the structure of the stepped traveling-wave electrode lithium niobate electro-optical modulator according to the second embodiment of the present invention and the structure of a common traveling-wave electrode.

[0017] Figure 6 This is a comparison diagram of the light absorption loss of the structure of the stepped traveling-wave electrode lithium niobate electro-optical modulator according to the second embodiment of the present invention and that of a common traveling-wave electrode structure.

[0018] In the figure: 101 - substrate, 102 - buffer layer, 103 - optical waveguide, 104 - transition layer, 105 - metal electrode. DETAILED DESCRIPTION

[0019] The following describes embodiments of the present invention in detail, examples of which 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 invention, and are not to be construed as limiting the present invention.

[0020] The first embodiment of this application is:

[0021] See also Figures 1 to 2 , Figure 1 FIG. 1 is a top view of a stepped traveling-wave electrode lithium niobate electro-optic modulator according to a first embodiment of the present invention. Figure 2 1 is a cross-sectional view of a stepped traveling-wave electrode lithium niobate electro-optic modulator according to a first embodiment of the present invention.

[0022] The present invention provides a thin-film lithium niobate electro-optic modulator with a stepped electrode, comprising a substrate 101, a buffer layer 102, an optical waveguide 103, a metal electrode 105 and a transition layer 104;

[0023] The buffer layer 102 is located on the top of the substrate 101, the middle electrode is a signal electrode, and the electrodes on both sides are ground electrodes. The optical waveguide 103 is located on the top of the buffer layer 102, and the transition layer 104 is located on the side of the optical waveguide 103 away from the buffer layer 102. The metal electrode 105 is located on the top of the transition layer 104, and the transition layer 104 connects the metal electrode 105 and the optical waveguide 103.

[0024] The metal electrode 105 has a stepped structure.

[0025] The optical waveguide 103 is an X-cut lithium niobate thin film with a ridge-shaped structure.

[0026] The metal electrode 105 is a gold electrode with a stepped structure.

[0027] The transition layer 104 is a silicon dioxide cladding layer.

[0028] In this embodiment, the optical waveguide 103 is an X-cut LN thin film with a ridge structure. The optical waveguide 103 is bonded to a thick SiO2 buffer layer 102 on a Si substrate 101. The thin film can be fabricated using a variety of processes, such as ion implantation, wafer bonding, and thermal slicing. The metal electrode 105 is a stepped metal electrode 105. Near the optical waveguide 103, the stepped electrode forms a progressively wider pattern from top to bottom. The lower end is closer to the optical waveguide 103, significantly enhancing the electric field strength near the optical waveguide 103, while the upper end is further away from the optical waveguide 103, reducing optical absorption loss and improving modulation efficiency. The transition layer 104 significantly reduces optical loss. The transition layer 104 connects the metal electrode 105 and the optical waveguide 103.

[0029] The second embodiment of this application is:

[0030] Based on the first embodiment, please refer to Figures 3 to 6 ,in, Figure 3 This is a diagram of the electric field distribution in the cross section of the stepped traveling-wave electrode lithium niobate electro-optic modulator according to the second embodiment of the present invention. Figure 4 This is the light spot diagram of the ridge waveguide during single-mode transmission of the stepped traveling-wave electrode lithium niobate electro-optical modulator according to the second embodiment of the present invention. Figure 5 and Figure 6 The modulation efficiency and light absorption loss of the structure of the present invention and the common traveling wave electrode structure are compared respectively. Figure 5 、 6 As shown, the half-wave voltage-length product of the structure of the present invention is more advantageous, and the light absorption loss is also maintained at a low value, which has important guiding significance for the design of electro-optical modulators.

[0031] The stepped traveling wave electrode lithium niobate electro-optic modulator provides a new approach to increasing the bandwidth of the electro-optic modulator and improving the photoelectric efficiency, and has important guiding significance for the design of the electro-optic modulator.

[0032] Furthermore, the present invention is further described by optimizing the design:

[0033] Using COMSOL simulation software, the half-wave voltage-length product and optical absorption loss of the electro-optic modulator with different electrode spacing are studied.

[0034] The environment settings are as follows:

[0035] Modeling process: A 2D model of the electro-optic modulator's modulation region cross-sectional structure was created in the software according to the design, including the buffer layer, optical waveguide, metal electrode, isolation layer, and high-dielectric cladding. The SiO2 buffer layer is 4.7μm thick; the lithium niobate waveguide is a ridge structure with a top surface width of 1.5μm, a sidewall tilt angle of 60°, and an etch depth of 0.25μm; the metal electrode is a three-layer stepped electrode structure, with the first and second layers being 0.5μm thick and the third layer being 0.2μm thick; and the SiO2 isolation layer is 0.2μm thick.

[0036] Material Settings: Based on the properties of the X-cut lithium niobate material, the relative permittivity and refractive index were set anisotropically in the waveguide direction. The diagonal elements of the refractive index matrix were set to (2.1376, 2.2111, 2.2111), and the diagonal elements of the relative permittivity matrix were set to (27.9, 44.3, 44.3).

[0037] Physical field settings: electrostatic field and electromagnetic wave frequency domain field are used. In the electrostatic field, the ground electrode and signal electrode are given voltage terminal types, where the ground electrode voltage is 0V and the signal electrode voltage is 1V.

[0038] Study setup: Add an electrostatic field solver, set the modeled electrodes as signal electrodes and ground electrodes, and apply the corresponding voltages.

[0039] Add solution settings: solve the effective mode refractive index of the waveguide and the corresponding electric field distribution in the optical waveguide area.

[0040] Parameter sweep setting: While fixing other parameters, sweep the overall electrode gap from 3 μm to 7 μm to obtain calculation results under different electrode gaps.

[0041] Results: As Figure 4 As shown, it is verified that the fundamental mode of the waveguide is the TE mode, the feasibility of the structure is determined, and the electrode spacing between the signal electrode and the ground electrode is optimized by parameter scanning.

[0042] Formula calculation: Refer to the calculation formula of half-wave voltage-length product to calculate the half-wave voltage-length product under different electrode spacing. The calculation results of half-wave voltage-length product and light absorption loss are as follows: Figure 5 、 Figure 6 shown.

[0043]

[0044] In formula (1), n e is the optical refractive index of lithium niobate crystal in the z direction, γ 33 is the electro-optic coefficient of lithium niobate crystal in the z direction, E0(x,z) is the electric field intensity of TE mode, E z(x,z) is the electric field along the z-axis.

[0045] Software simulations of the modulation efficiency and loss of the structure of the present invention show that, compared with traditional electro-optic modulators, a smaller half-wave voltage-length product can be achieved at the same optical absorption loss. This electro-optic modulator can achieve a half-wave voltage-length product of 1.2 V·cm with an optical loss of 0.2 dB / cm, demonstrating excellent performance.

[0046] The above disclosure is only a preferred embodiment of a thin-film lithium niobate electro-optical modulator with a stepped electrode of the present invention. Of course, this cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that implementing all or part of the processes of the above embodiment and making equivalent changes in accordance with the claims of the present invention still fall within the scope of the invention.

Claims

1. A thin-film lithium niobate electro-optic modulator with a stepped electrode, characterized in that: including a substrate, a buffer layer, an optical waveguide, a metal electrode and a transition layer; The buffer layer is located on the top of the substrate, the optical waveguide is located on the top of the buffer layer, the transition layer is located on a side of the optical waveguide away from the buffer layer, the metal electrode is located on the top of the transition layer, and the transition layer connects the metal electrode and the optical waveguide.

2. The thin-film lithium niobate electro-optic modulator with stepped electrodes according to claim 1, wherein: The metal electrode has a stepped structure.

3. The thin-film lithium niobate electro-optic modulator with stepped electrodes according to claim 1, wherein: The optical waveguide is an X-shaped cut lithium niobate film with a ridge structure.

4. The thin-film lithium niobate electro-optic modulator with stepped electrodes according to claim 1, wherein: The metal electrode is a gold electrode with a stepped structure.

5. The thin-film lithium niobate electro-optic modulator with stepped electrodes according to claim 1, wherein: The transition layer is a silicon dioxide cladding layer.

Images