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CN-122018219-A - Frequency conversion device based on lithium niobate ridge waveguide on insulator and preparation method

CN122018219ACN 122018219 ACN122018219 ACN 122018219ACN-122018219-A

Abstract

The embodiment of the application provides a frequency conversion device based on a lithium niobate ridge waveguide on an insulator and a preparation method thereof, belonging to the fields of integrated optics, nonlinear optics and optoelectronic devices. The device comprises a silicon substrate layer, a silicon dioxide buffer layer, an x-cut lithium niobate thin film layer and a silicon dioxide cladding layer from bottom to top, wherein a ridge waveguide with periodically-changing width is arranged on the x-cut lithium niobate layer, and light in the waveguide propagates along the y-axis direction. According to the application, the waveguide with the width periodically changed is prepared on the lithium niobate thin film, so that quasi-phase matching is realized, and the second harmonic conversion efficiency is greatly improved. By changing the period of the waveguide, the second-order nonlinear phase matching conditions under different wavelengths, such as the phase matching conditions of second harmonic generation, sum frequency generation and difference frequency generation, can be satisfied. Correspondingly, the waveguide structure with the width periodically changing can be formed by a single etching process, and a complex ferroelectric domain inversion step is not needed. The application has the advantages of simple process, controllable shape and flexible design.

Inventors

  • LI ZHIYUAN
  • He Linye
  • LI XIAONI

Assignees

  • 华南理工大学

Dates

Publication Date
20260512
Application Date
20260210

Claims (10)

  1. 1. A lithium niobate ridge waveguide-on-insulator-based frequency conversion device comprising: A substrate layer; a silicon dioxide buffer layer on the substrate layer; An x-cut lithium niobate thin film layer on the silicon dioxide buffer layer; a ridge waveguide which is positioned on the lithium niobate thin film layer and periodically changes in width along the light propagation direction; The periodical change of the ridge waveguide width is used for compensating phase mismatch in the nonlinear frequency conversion process, so that quasi-phase matching is realized.
  2. 2. The frequency conversion device according to claim 1, wherein the periodic variation of the width of the ridge waveguide along its length is sinusoidal, rectangular or zigzag.
  3. 3. The frequency conversion device according to claim 1 or 2, wherein the ridge waveguide has a width that varies sinusoidally along its length, and the coordinates of its upper surface boundary satisfy the relation: Wherein, the For the reference width of the waveguide, In order to vary the amplitude of the width variation, In order to vary the period of time, Is the coordinate along the light propagation direction.
  4. 4. A frequency conversion device according to claim 3, wherein the The range of the value of the optical fiber is 1 μm to 10 μm, and the optical fiber is used for compensating the phase mismatch between the fundamental frequency light and the frequency doubling light.
  5. 5. The frequency conversion device of claim 1, wherein the total thickness of the lithium niobate thin film layer is 300-600 nm a and the ridge waveguide has an etch depth of 180-300 a nm a.
  6. 6. The frequency conversion device according to claim 1, wherein a mode field converter is connected to both ends of the ridge waveguide for coupling in light and out light.
  7. 7. The frequency conversion device of claim 6, wherein the mode field converter is an inverted cone end coupler.
  8. 8. The frequency conversion device of claim 1, further comprising a silica cladding layer covering the ridge waveguide.
  9. 9. A method of manufacturing a frequency conversion device according to any one of claims 1 to 8, comprising the steps of: providing a lithium niobate thin film substrate on an insulator, which comprises a substrate layer, a silicon dioxide buffer layer and an x-cut lithium niobate thin film layer; forming a patterned mask on the lithium niobate thin film layer, wherein the pattern of the mask defines a ridge waveguide structure with the width periodically changing along a preset direction; etching the exposed lithium niobate thin film by taking the mask as an etching barrier layer to form the ridge waveguide; the mask is removed.
  10. 10. The method of claim 9, further comprising the step of depositing a silicon dioxide cladding layer on the device surface after removing the mask.

Description

Frequency conversion device based on lithium niobate ridge waveguide on insulator and preparation method Technical Field The application relates to the field of integrated optics, nonlinear optics and optoelectronic devices, in particular to a frequency conversion device based on a lithium niobate ridge waveguide on an insulator and a preparation method thereof. Background Nonlinear frequency conversion (such as second harmonic generation, sum frequency generation and difference frequency generation) is a core technology for expanding laser wavelength, realizing all-optical signal processing, generating quantum light sources and the like. Lithium niobate crystals are considered as ideal platforms for achieving efficient nonlinear processes due to their extremely large second order nonlinear coefficients and excellent electro-optical properties. In recent years, the technology of 'lithium niobate on insulator' (Lithium Niobate on Insulator, LNOI) is to make lithium niobate into a film with submicron thickness, and combine with a low refractive index substrate (such as silicon dioxide), so that the optical field is strongly limited in the waveguide, the interaction between light and substances is greatly enhanced, and a foundation is laid for realizing high-efficiency and miniaturized integrated nonlinear devices. However, achieving efficient nonlinear frequency conversion in the waveguide must meet stringent phase matching conditions. Due to material dispersion and waveguide dispersion, fundamental frequency light and converted light (such as frequency-doubled light) generally propagate at different phase velocities, generating phase mismatch, resulting in periodic oscillation of conversion efficiency during propagation, which cannot be continuously increased. On a thin film lithium niobate platform, the dominant technology for achieving quasi-phase matching is periodically poled lithium niobate. The technology performs periodic inversion on ferroelectric domains of lithium niobate through an external electric field to form nonlinear coefficients distributed periodically, so as to compensate phase mismatch. However, the technical route has the obvious defects that 1) the process is complex, high-voltage polarization is required to be carried out by depositing electrodes, the process is complicated, the cost is high, 2) the domain inversion morphology is difficult to control accurately, the problems of rough side wall, uneven duty ratio and the like are easy to occur, the performance and the yield of the device are influenced, 3) the structure with the period less than 4 microns is difficult to prepare due to the fact that the polarization electric field precision is limited, and the application of the structure in the scenes of short-wavelength conversion and the like is limited. Therefore, there is an urgent need in the art for a lithium niobate thin film nonlinear frequency conversion device and a preparation method thereof that are simpler in process, lower in cost, and capable of achieving high-precision phase matching. Disclosure of Invention The embodiment of the application mainly aims to provide a frequency conversion device based on a lithium niobate ridge waveguide on an insulator and a preparation method thereof, and aims to solve the problems of complex process, high cost, low yield, difficult domain structure control, limitation of a technology to a polarizable material system and the like of a nonlinear frequency conversion device based on periodically polarized lithium niobate in the prior art. To achieve the above object, an aspect of an embodiment of the present application provides a frequency conversion device based on a lithium niobate ridge waveguide on an insulator, including: A substrate layer; a silicon dioxide buffer layer on the substrate layer; An x-cut lithium niobate thin film layer on the silicon dioxide buffer layer; a ridge waveguide which is positioned on the lithium niobate thin film layer and periodically changes in width along the light propagation direction; The periodical change of the ridge waveguide width is used for compensating phase mismatch in the nonlinear frequency conversion process, so that quasi-phase matching is realized. In some embodiments, the periodic variation of the width of the ridge waveguide along its length is sinusoidal, rectangular or zigzagged. In some embodiments, the ridge waveguide has a sinusoidal variation in width along its length, and the coordinates of its upper surface boundary satisfy the relationship: Wherein, the For the reference width of the waveguide,In order to vary the amplitude of the width variation,In order to vary the period of time,Is the coordinate along the light propagation direction. In some embodiments, theThe range of the value of the optical fiber is 1 μm to 10 μm, and the optical fiber is used for compensating the phase mismatch between the fundamental frequency light and the frequency doubling light. In some embodi