Lithium Niobate Waveguide Mode Converter for Visible Light Polarization
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Solution Overview
Problem
Existing optical elements fail to efficiently convert the polarization mode of visible light, particularly for applications in retinal projection devices and near-eye wearable devices, as they are designed primarily for infrared wavelengths and do not consider visible light conversion.
Innovation Solution
An optical element comprising a substrate with a core layer and a metal body in parallel configuration, utilizing surface plasmons to convert the polarization mode of visible light from TE to TM or vice versa, enhancing conversion efficiency by optimizing the edge overlap and distance between the waveguide and metal body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an InGaAsP ridge waveguide with metal layer is used for polarization rotation, then the polarization mode conversion works for 1.55 μm infrared light, but it does not work for visible light wavelengths
Solution Approach 1:
The patent changes the material parameters of the waveguide from InGaAsP/InP (infrared optimized) to lithium niobate (visible light optimized). This material substitution enables the waveguide to effectively guide and convert polarization modes of visible light wavelengths while maintaining the plasmonic metal layer configuration for effective polarization rotation.
Solution Approach 2:
The patent creates a composite structure combining lithium niobate waveguide material with a metal layer (such as gold or silver). This composite configuration leverages the high refractive index and electro-optic properties of lithium niobate for visible light guidance, while the metal layer provides surface plasmon resonance for effective polarization mode conversion across visible wavelengths.
2Productivity
If the metal body is placed close to the waveguide to excite surface plasmons, then polarization conversion efficiency improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements partial overlap between the metal body edge and the waveguide, where the metal edge extends partially over the waveguide region. This partial overlap configuration provides sufficient surface plasmon excitation for high conversion efficiency while maintaining a relaxed tolerance range for manufacturing variations, avoiding the need for precise full-edge alignment.
Solution Approach 2:
The patent applies the metal layer selectively in specific regions adjacent to and overlapping portions of the waveguide, rather than uniformly covering the entire waveguide. This localized metal placement creates the necessary surface plasmon conditions for polarization conversion while reducing the overall manufacturing complexity and positioning requirements.
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 enables efficient conversion of visible light polarization modes, improving image projection quality in retinal projection devices and near-eye wearable devices without requiring large drive currents, and reducing manufacturing complexity.
Implementation Method 1
Since the metal body has a negative dielectric constant, surface plasmons are excited on the surface of the metal body. Therefore, the polarization mode of the visible light propagating through the waveguide interacts with the surface plasmons, and is rotated in accordance with the position of the edge of the metal body.
Implementation Method 2
a core layer provided on the main surface and made of a material having an electro-optic effect, the core layer including a waveguide extending in a first direction along the main surface
Data Source
AI summary
An optical element includes: a substrate including a main surface; a core layer provided on the main surface and made of a material having an electro-optic effect, the core layer including a waveguide extending in a first direction along the main surface; and a metal body extending in the first direction and provided in parallel with the waveguide. The waveguide and the metal body constitute a mode converter that converts a polarization mode of visible light from a first polarization mode, which is one polarization mode among a TE mode and a TM mode, to a second polarization mode, which is another polarization mode among the TE mode and the TM mode. The metal body includes an edge in a second direction intersecting the first direction and along the main surface. The edge overlaps the waveguide when viewed from a third direction intersecting the main surface.