MMI Optical Coupler for RGB Axis Alignment in XR Glasses
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Solution Overview
Problem
Existing retina projection type displays face challenges with optical axis misalignment for different wavelengths, complex light control, and the need for an optical coupler that can integrate with a visible light modulator using a lithium niobate film, while conventional couplers are large and have high light loss.
Innovation Solution
An optical coupler design utilizing a multimode interference (MMI) structure with specific MMI type optical coupling elements and tapered waveguides, integrated with a lithium niobate film, to align and couple laser light beams of different wavelengths efficiently, reducing size and light loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a directional coupler made of glass material is used for visible light coupling, then stability is excellent, but when a lithium niobate substrate with large Δn is used, the coupling length becomes long and size reduction is not possible
Solution Approach 1:
The patent changes the refractive index parameter by using lithium niobate material with large Δn (refractive index difference) instead of conventional glass materials. This parameter change enables shorter coupling length while maintaining coupling effectiveness, resolving the contradiction between stability and size.
Solution Approach 2:
The patent employs composite material structure combining lithium niobate substrate with specific waveguide layers. This composite approach leverages the high refractive index difference of lithium niobate to achieve compact coupling length while maintaining the stability required for visible light modulation applications.
2Ease of manufacture
If optical waveguides are simply brought close to each other at the emission unit, then integration is simple, but the optical axis for each wavelength differs and control of the emitted light becomes complicated
Solution Approach 1:
The patent implements preliminary action by pre-aligning the optical axes of multiple wavelengths at the input end of the waveguides. The coupling structure is designed to maintain this alignment throughout propagation, ensuring that all wavelengths exit along a common optical axis without requiring complex control mechanisms.
Solution Approach 2:
The patent creates a universal coupling structure that simultaneously handles multiple wavelengths (RGB) with a single integrated design. The waveguide configuration and coupling mechanism work universally for all wavelengths, simplifying both manufacturing and light control while achieving wavelength-independent optical axis alignment.
3Adaptability or versatility
If conventional optical couplers are used for RGB coupling, then coupling function is achieved, but the device size is large and light loss is high
Solution Approach 1:
The patent replaces conventional mechanical or glass-based coupling structures with an integrated photonic waveguide system. This substitution eliminates the need for large-scale mechanical alignment components, achieving compact size while maintaining effective RGB light coupling through evanescent field interaction in the waveguides.
Solution Approach 2:
The patent transitions from three-dimensional bulk optical coupling to two-dimensional planar waveguide coupling. By confining light propagation to the waveguide mode in the transverse dimension, the coupling interaction is enhanced over a shorter length, reducing the overall device volume while maintaining coupling functionality.
4Adaptability or versatility
If conventional optical couplers are used for RGB coupling, then coupling function is achieved, but light loss is high
Solution Approach 1:
The patent replaces lossy conventional coupling interfaces with low-loss integrated waveguide coupling. The evanescent field coupling mechanism in the waveguides minimizes scattering and absorption losses compared to conventional couplers, achieving efficient RGB light coupling with reduced energy loss.
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 proposed optical coupler enables compact integration with a visible light modulator, effectively aligning and coupling RGB light beams with reduced loss, suitable for XR glasses applications.
Implementation Method 1
The MMI type optical coupler receives a plurality of input signals using a plurality of waveguide ports on the light input side, uses a single waveguide port for the output signal on the light output side, couples all input signals, and outputs them as an output signal. The MMI type optical coupler is an optical coupler that utilizes a characteristic that a plurality of modes generated for each wavelength within a wide optical coupler interfere with each other, and an image is formed (converges) at a specific position.
Data Source
AI summary
An optical coupler of the present disclosure couples laser light beams with a plurality of different wavelengths, and includes an MMI connected optical coupling unit formed by connecting a first MMI type optical coupling element that shifts an incidence position and a second MMI type optical coupling element having a width wider than the width of the first MMI type optical coupling element, one or more first light input side optical waveguides that are connected to the first MMI type optical coupling element, one or more second light input side optical waveguides that are connected to the second MMI type optical coupling element and one light output side optical waveguide that is connected to the second MMI type optical coupling element.