Liquid Crystal Guided-Mode Extraction With Intermediate Waveguide Coupling
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Solution Overview
Problem
Existing active extraction structures for guided modes in integrated waveguides suffer from undesirable diffraction patterns leading to light losses and lack of directivity, resulting in bulky and inefficient optical devices.
Innovation Solution
A guided mode extraction structure with a support substrate, main and intermediate waveguides, and electrodes that control the refractive index of liquid crystal to enable evanescent coupling and reflective deflection, minimizing losses and enhancing directivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If surface diffraction gratings are used for light extraction, then light extraction is achieved, but extraction efficiency is fixed and device size increases
Solution Approach 1:
The patent applies liquid crystal material to the diffraction grating structure, enabling dynamic control of the refractive index through voltage application. This transforms the static extraction grating into a dynamic structure that can switch between extraction and non-extraction states, resolving the contradiction between fixed extraction efficiency and controllability.
Solution Approach 2:
The patent changes the refractive index parameter of the liquid crystal layer through voltage control, which directly modulates the diffraction grating's coupling efficiency. By varying this physical parameter, the system achieves controllable light extraction while maintaining a compact form factor.
2Adaptability or versatility
If active extraction structures with liquid crystal are used, then controllability is achieved, but diffraction patterns cause light losses and reduced directivity
Solution Approach 1:
The patent introduces an intermediate waveguide layer between the main waveguide and the liquid crystal grating. This intermediary structure acts as a buffer that reduces the strength of evanescent field coupling, thereby minimizing unwanted diffraction effects and energy losses while preserving the controllable extraction functionality.
Solution Approach 2:
The patent extracts the problematic diffraction grating function from direct contact with the main waveguide by placing it in a separate intermediate waveguide layer. This separation removes the source of harmful diffraction patterns while maintaining the essential light extraction capability through controlled coupling.
3Illumination intensity
If liquid crystal refractive index is modified to enable extraction, then light extraction is achieved, but device complexity increases
Solution Approach 1:
The patent merges multiple functions into the liquid crystal layer: it serves as both the refractive index modulation medium and the diffraction grating structure. This consolidation reduces the number of separate components needed, thereby simplifying the overall device structure despite the added functionality.
Solution Approach 2:
The liquid crystal layer performs multiple roles simultaneously: it acts as the active medium for refractive index modulation, forms the diffraction grating structure, and enables both extraction and non-extraction states. This multi-functionality reduces device complexity by eliminating the need for separate components for each function.
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 structure achieves efficient light extraction with minimal losses and improved directivity, resulting in a brighter and more compact optical device.
Implementation Method 1
a first electrode and a second electrode, arranged with respect to the core of the intermediate waveguide so as to cause a refractive index of the liquid crystal to switch, in a coupling portion of the core of the intermediate waveguide, from a first level to a second level, according to the polarization direction, when a variation of an electrical potential difference is applied between the first and second electrodes
Implementation Method 2
The first level, the second level and the arrangement of the coupling portion relative to the main waveguide are such that the guided mode, when present, is coupled at least in part, by evanescent coupling of the main waveguide to the coupling portion only when the refractive index of the coupling portion is equal to the second level
Implementation Method 3
a flat surface opposite the exit face, reflective at wavelength λ, making a non-zero angle with the upper face of the support substrate
Data Source
Figure 1A~1B
Figure 2~3
Figure 4A~4B
AI summary
The invention relates to a structure for extracting a linearly polarized guided mode of wavelength λ, comprising: a primary waveguide capable of guiding the guided mode; an intermediate liquid crystal waveguide, capable of guiding a coupled mode, extending parallel to the upper surface of a substrate; a flat reflective surface opposite an exit face of the intermediate waveguide, making a non-zero angle with the substrate; and first and second electrodes arranged relative to the core of the intermediate waveguide so as to shift the refractive index of the liquid crystal from a first level to a second level when a variation in the electrical potential difference is applied between the first and second electrodes. The guided mode is coupled by evanescent coupling only when the refractive index of the liquid crystal is equal to the second level.