Z-cut Lithium Niobate Ridge Waveguide Polarizer
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Solution Overview
Problem
Existing waveguide-type polarizers for lithium niobate optical modulators face challenges in efficiently transmitting extraordinary light while minimizing light loss and manufacturing complexity, particularly due to the need for separate thin films and increased chip size, which affects productivity and integration capabilities.
Innovation Solution
A waveguide-type polarizer is designed with a Z-cut lithium niobate substrate and optical waveguides having a ridge structure, incorporating a low refractive index film and a high refractive index film, where the thickness and width of these films are optimized to ensure extraordinary light transmission without altering the distribution of extraordinary light, and the ridge angle is less than 90 degrees, allowing for stable integration without complex manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a film-shaped polarizer is attached to the connection portion between chip and fiber, then extraordinary light transmission is achieved, but light loss increases and productivity decreases
Solution Approach 1:
The patent merges the polarizer function directly into the waveguide structure by forming a ridge waveguide on the Z-cut lithium niobate substrate. The ridge structure itself acts as the polarizer, eliminating the need for separate film-shaped polarizers attached at connection portions. This integration reduces light loss by maintaining continuous waveguide structure and improves productivity by enabling batch fabrication of polarized waveguides.
Solution Approach 2:
The ridge structure serves as an intermediary element that selectively guides extraordinary light while blocking ordinary light. By creating a specific ridge geometry with controlled width and height, the waveguide acts as a mediator that exploits the anisotropic electro-optical properties of lithium niobate to achieve polarization filtering without requiring additional polarizing components.
2Reliability
If separate thin films are formed for polarizer and electrode buffer layer, then polarizer function is achieved, but manufacturing complexity increases and productivity decreases
Solution Approach 1:
The patent combines the polarizer structure with the waveguide structure into a single ridge waveguide formation process. The ridge is formed by selective removal of the lithium niobate substrate, creating both the waveguide confinement and the polarization filtering function simultaneously. This eliminates the need for separate thin film deposition steps for polarizers and buffer layers, significantly improving manufacturing efficiency.
Solution Approach 2:
The ridge structure performs multiple functions simultaneously: it provides optical confinement for the waveguide, serves as the polarization filtering element, and acts as the structural support. This multi-functional design eliminates the need for separate dedicated components for each function, reducing manufacturing steps and improving productivity while maintaining reliable polarizer performance.
3Adaptability or versatility
If region for polarizer is added to LN chip, then polarizer function is integrated, but chip size increases
Solution Approach 1:
The patent integrates the polarizer function directly into the existing waveguide region without requiring additional dedicated space. The ridge structure is formed within the same area where the waveguide propagates, utilizing the anisotropic properties of the lithium niobate substrate along the Z-cut orientation. This allows polarization filtering to be achieved within the existing chip footprint, avoiding any increase in chip size.
4Adaptability or versatility
If Ti-diffused optical waveguide with ridge structure is used, then both extraordinary light and ordinary light are guided, but ordinary light removal becomes necessary
Solution Approach 1:
The patent exploits the local anisotropic properties of the Z-cut lithium niobate substrate by creating a ridge structure with specific orientation and dimensions. The ridge is formed along a direction that maximizes the difference in effective refractive index between extraordinary and ordinary modes. This local structural modification creates strong polarization dependence, allowing the waveguide to selectively guide extraordinary light while naturally suppressing ordinary light without requiring additional filtering components.
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
This configuration enables stable and efficient transmission of extraordinary light, reducing light loss and manufacturing errors, thereby improving the integration of polarizer functions into optical waveguides without increasing chip size or complicating the manufacturing process.
Implementation Method 1
A low refractive index film with a thickness satisfying 0≦n×t/λ≦0.3742... and a high refractive index film with a thickness satisfying 0.089≦n×t/λ... are formed on the side of the ridge structure
Implementation Method 2
an optical waveguide that has a ridge structure and is formed on the substrate... the width of the ridge structure is a ridge width where the distribution of ordinary light of light waves propagated through the optical waveguide changes and the distribution of the extraordinary light of light waves does not change
Implementation Method 3
an optical waveguide element having an electro-optical effect, such as a lithium niobate (LN) substrate... Since LN has anisotropy in the electro-optical effect, light polarized in a specific direction is incident on the LN optical modulator
Data Source
AI summary
The waveguide-type polarizer includes: a Z-cut lithium niobate substrate; an optical waveguide having a ridge structure and formed on the substrate; a low refractive index film formed with a thickness satisfying 0≦n·t/λ≦0.3742 (where n is a refractive index, t (μm) is the thickness of the film, and λ (μm) is the wavelength of a light wave) on the side of the ridge structure; and a high refractive index film formed with a thickness satisfying 0.089≦n·/λ on the low refractive index film. The width of the ridge structure is a ridge width where the distribution of ordinary light of the light waves propagated through the optical waveguide changes and the distribution of extraordinary light of the light waves does not change, the angle of the ridge structure is less than 90°, and the waveguide-type polarizer has a function of transmitting extraordinary light.