Lithium Niobate Optical Coupling Structure for Mode Mismatch
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Solution Overview
Problem
Conventional lithium niobate devices face issues with low coupling efficiency due to mismatched mode fields between lithium niobate optical waveguides and single-mode optical fibers, primarily caused by differences in cross-sectional areas and refractive indices, leading to increased optical loss and poor process consistency.
Innovation Solution
An optical coupling structure is developed, featuring a silicon dioxide core layer and cladding layer formed on the lithium niobate optical waveguide, with a rectangular or trapezoidal end face area matching the single-mode optical fiber's cross-sectional area, and an adhesive with a refractive index close to the core layer to minimize refractive index differences, along with a photoetching process to improve consistency and reduce Fresnel reflection loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lithium niobate devices are prepared by high-temperature proton exchange, then the devices can be manufactured, but the device volume becomes large and process consistency deteriorates
Solution Approach 1:
The patent changes the manufacturing process parameters from high-temperature proton exchange to low-temperature photolithography and etching processes. This parameter change enables precise control of waveguide dimensions (reducing device volume) while maintaining excellent process consistency through standard semiconductor fabrication techniques.
Solution Approach 2:
The patent replaces the chemical proton exchange process with physical photolithography and etching processes. This substitution allows for precise geometric control of the waveguide structure, achieving both small device volume and high process consistency through mask-defined patterns.
2Productivity
If the cross-sectional area of lithium niobate optical waveguide is kept small (square microns), then the device integration is improved, but the mode field matching with single-mode optical fiber deteriorates, leading to low coupling efficiency
Solution Approach 1:
The patent extends the waveguide structure in the vertical dimension by adding multiple layers (buffer layer, lower cladding layer, core layer, upper cladding layer). This dimensional extension increases the effective coupling area without increasing the planar footprint, thereby maintaining device integration while improving mode field matching with optical fibers.
Solution Approach 2:
The patent uses composite material structure with different refractive index layers (TiO2 core layer with n=2.3, SiO2 cladding layers with n=1.45). This composite structure creates an optimized mode field distribution that better matches the optical fiber mode field, improving coupling efficiency while maintaining small device footprint.
3Manufacturing precision
If standard photolithography and etching processes are used, then manufacturing precision is improved, but additional process steps are required compared to conventional methods
Solution Approach 1:
The patent segments the waveguide structure into multiple functional layers (buffer layer, lower cladding layer, core layer, upper cladding layer) that can be fabricated using standard sequential photolithography and etching processes. Each layer is precisely controlled through separate mask patterns, achieving high manufacturing precision through modular fabrication.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances coupling efficiency by reducing mode mismatch loss and optical loss, improving the consistency of the optical coupling structure, and eliminating sensitivity to light polarization, thus increasing the efficiency and reliability of the coupling process.
Implementation Method 1
a silicon dioxide core layer formed on peripheral walls of the lithium niobate optical waveguide and enclosing the lithium niobate optical waveguide; and a silicon dioxide cladding layer formed on peripheral walls of the silicon dioxide core layer and enclosing the silicon dioxide core layer
Implementation Method 2
an adhesive; where the adhesive is provided on end faces of the silicon dioxide core layer and the silicon dioxide cladding layer in a light transmission direction, and a difference value between a refractive index of the adhesive and a refractive index of the silicon dioxide core layer is less than 0.5
Data Source
AI summary
An optical coupling structure, an optical coupling system and a method for preparing the optical coupling structure are provided. The method includes: step S101: preparing a base substrate; step S102: forming a lithium niobate optical waveguide on the base substrate; step S103: forming a silicon dioxide core layer enclosing the lithium niobate optical waveguide on peripheral walls of the lithium niobate optical waveguide; step S104: forming a silicon dioxide cladding layer enclosing the silicon dioxide core layer on peripheral walls of the silicon dioxide core layer. The optical coupling structure alleviates a technical problem of low coupling efficiency between the lithium niobate optical waveguide and the single-mode optical fiber in the related art, and achieves a technical effect of improving the coupling efficiency between the lithium niobate optical waveguide and the single-mode optical fiber.