GaN Nano-Grating Structure for Circularly Polarized Lasers
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Solution Overview
Problem
Gallium nitride-based lasers emitting linearly polarized light require conversion to circularly polarized light, which is typically achieved using bulk quarter-wave plates that are large in size, hindering device miniaturization and integration, and metal gratings suffer from high absorption loss leading to low energy efficiency.
Innovation Solution
A gallium nitride nano superstructure comprising a substrate, dielectric film layer, and nano-grating structure is used to convert linearly polarized light into circularly polarized light, with grating parameters optimized for high efficiency and minimal energy loss, and integrated at the laser's light-emitting end face.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a bulk quarter-wave plate is used to convert linearly polarized light to circularly polarized light, then the polarization conversion function is achieved, but the device volume becomes large, hindering miniaturization and integration
Solution Approach 1:
The bulk quarter-wave plate is segmented into a nano-grating structure consisting of multiple periodic sub-wavelength elements. Each grating unit acts as a localized phase modulator, collectively achieving the wave plate function while reducing the overall footprint to the diffraction limit scale.
Solution Approach 2:
The solution transitions from a three-dimensional bulk optical element to a two-dimensional planar nano-grating structure. By confining the optical function to a planar geometry with vertical sub-wavelength features, the device achieves wave plate functionality with dramatically reduced lateral dimensions suitable for on-chip integration.
2Volume of moving object
If a metal grating structure is used to achieve circularly polarized light emission, then the device size is reduced, but the absorption loss increases, leading to low energy efficiency
Solution Approach 1:
The material parameter is changed from metal to dielectric (gallium nitride). This fundamental material substitution eliminates the high absorption losses inherent in metal structures while maintaining the sub-wavelength grating geometry that enables compact size. The dielectric material provides the necessary refractive index contrast for grating operation without the parasitic absorption of metals.
Solution Approach 2:
The structure employs a composite design combining dielectric gallium nitride material with optimized nano-grating geometry. This composite approach integrates the low-loss properties of dielectrics with the size-reduction capabilities of sub-wavelength grating structures, achieving both compact dimensions and high energy efficiency.
3Volume of moving object
If the grating size is reduced for miniaturization, then the device can be integrated, but the grating parameters become extremely small, increasing manufacturing difficulty
Solution Approach 1:
The grating parameters are optimized to fall within the 100-300 nm range, which represents a sweet spot achievable with contemporary semiconductor fabrication techniques such as electron-beam lithography and reactive ion etching. This parameter selection balances miniaturization goals with manufacturing capabilities, avoiding dimensions that would be prohibitively difficult to fabricate.
Solution Approach 2:
The manufacturing approach replaces traditional optical lithography with electron-beam lithography or focused ion beam techniques. These methods provide the necessary sub-100 nm resolution for defining the grating features, enabling precise fabrication of the nano-scale structures required for miniaturized operation.
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 nano superstructure achieves high-efficiency circularly polarized light output with minimal energy loss, enabling compact device integration and stability under extreme conditions.
Implementation Method 1
N. F. Yu etc. used metal grating structure to realize circularly polarized light-emitting laser in mid-infrared band based on surface plasmon effect
Implementation Method 2
N. F. Yu etc. used metal grating structure to realize circularly polarized light-emitting laser in mid-infrared band based on surface plasmon effect
Implementation Method 3
The biggest problem of using metal grating to prepare circularly polarized light-emitting laser is the large absorption loss of metal, which leads to the low energy efficiency of the light
Implementation Method 4
spin coating a photoresist on the film, photoetching and developing to prepare a photoresist grating pattern
Data Source
AI summary
The present invention relates to a gallium nitride nano superstructure and a preparation method thereof. The gallium nitride nano superstructure is used for realizing circularly polarized light output of the gallium nitride-based laser. The gallium nitride nano superstructure comprises, from bottom to top, a substrate, a dielectric film layer and a nano-grating structure layer, a grating material of the nano-grating structure layer comprising one of gallium nitride, N-type gallium nitride and P-type gallium nitride, a grating period being in a range of 100 nm-280 nm, a grating height being in a range of 100 nm-300 nm, and a grating line width being in a range of 50 nm-200 nm. The gallium nitride nano superstructure of the present invention can be applied to a gallium nitride-based laser to realize the circularly polarized light output of the gallium nitride-based laser.