Isosceles Trapezoid Optical Coupler for Retinal Displays
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Solution Overview
Problem
Current retinal projection displays face challenges with optical axis misalignment of different wavelengths, leading to complex light control and a lack of integration with visible light modulators, particularly with lithium niobate films, and struggle to achieve single-mode emission necessary for efficient light propagation.
Innovation Solution
A Y-branch type optical coupler with an isosceles trapezoidal shape is designed, where input-side optical waveguides are symmetrically disposed and inclined at specific angles, allowing for efficient coupling of lights with different wavelengths into a single output waveguide, enabling single-mode emission and integration with lithium niobate-based modulators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple optical waveguides are placed close to each other at the emission part without coupling, then the structure is simple, but the optical axis for each wavelength becomes different and light control becomes complicated
Solution Approach 1:
The patent merges multiple optical waveguides carrying different wavelengths (R, G, B) into a single optical waveguide through an optical coupling part. This combining approach maintains structural simplicity while achieving unified optical axis control, as all wavelengths are coupled into one waveguide that can be controlled as a single unit.
Solution Approach 2:
The optical coupling part acts as an intermediary component between the multiple input waveguides and the single output waveguide. This mediator enables the transition from multiple separate optical paths to a unified path, solving the contradiction by providing a mechanism that combines waveguides while maintaining control simplicity.
2Reliability
If directional couplers made of glass-based material are used, then stability is excellent, but coupling length becomes long and miniaturization is not possible
Solution Approach 1:
The patent changes the material parameter from conventional glass-based materials to lithium niobate material. This material substitution fundamentally alters the coupling characteristics, enabling much shorter coupling lengths while maintaining stability. The lithium niobate material's optical properties allow for compact coupler design without sacrificing reliability.
Solution Approach 2:
The invention employs lithium niobate as a specialized material that combines the stability characteristics of glass-based materials with enhanced coupling efficiency. This material choice enables the coupler to achieve both short coupling length and high stability, resolving the contradiction between size and reliability.
3Productivity
If multimode interferometers are used for RGB couplers, then coupling is achieved, but multi-mode light causes mode dispersion and higher propagation loss
Solution Approach 1:
The patent applies different structural characteristics to different parts of the optical coupling system. The optical coupling part has specific geometric features (trapezoidal shape with angled surfaces) that are optimized to couple light while maintaining single-mode propagation. This localized structural design ensures that mode control is achieved at the coupling region, preventing mode dispersion and reducing propagation loss.
Solution Approach 2:
The invention changes the operational parameter from multi-mode to single-mode light propagation through careful design of the waveguide dimensions and coupling geometry. By controlling the waveguide width, height, and coupling angle, the system maintains single-mode operation throughout the coupling process, eliminating mode dispersion and reducing propagation loss while achieving efficient coupling.
4Volume of moving object
If optical coupler is designed for small size to be mounted in glasses-type terminal, then integration is improved, but achieving single-mode emission becomes difficult
Solution Approach 1:
The patent achieves single-mode emission in a compact coupler by optimizing geometric parameters including waveguide width, height, length, and coupling angles. The lithium niobate material properties combined with precise dimensional control enable single-mode operation in a small footprint, making the coupler suitable for glasses-type terminals while maintaining reliable single-mode performance.
Solution Approach 2:
The use of lithium niobate material enables the coupler to achieve both small size and single-mode emission reliability. The material's high refractive index and optical properties allow for compact waveguide design with controlled mode propagation, resolving the contradiction between miniaturization and single-mode performance.
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 effectively curbs high-order modes, reduces propagation loss, and enables efficient single-mode light emission, facilitating the integration of the optical coupler with lithium niobate-based modulators, enhancing the performance of retinal projection displays.
Implementation Method 1
an optical coupling part to which a plurality of input-side optical waveguides through which the plurality of lights propagate, and one output-side optical waveguide are connected
Implementation Method 2
at least two input-side optical waveguides among the plurality of input-side optical waveguides are disposed symmetrically with respect to a symmetry axis of the isosceles trapezoid, are inclined at a second angle that is different from the first angle
Data Source
AI summary
A Y-branch type optical coupler includes an optical coupling part to which a plurality of input-side optical waveguides through which the plurality of lights propagate, and one output-side optical waveguide are connected, wherein the optical coupling part has an isosceles trapezoid shape of which the width is narrowed in a taper shape at a first angle α from the input side to the output side (a traveling direction of light) in a plan view, at least two input-side optical waveguides among the plurality of input-side optical waveguides are disposed symmetrically with respect to a symmetry axis of the isosceles trapezoid, are inclined at a second angle θ that is different from the first angle α, and are connected to a lower bottom portion of the isosceles trapezoid, and the difference between the first angle and the second angle is 0.9° or more and 14.8° or less.