GaN DFB Laser Grating Structure for Single-Mode UV SHG Output
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Solution Overview
Problem
There is a need for a semiconductor laser element that can produce high output in a longitudinal single mode, specifically to convert 444 nm light into 222 nm second harmonic for safer ultraviolet sterilization applications, as existing GaN-based materials face challenges in achieving sufficient refractive index difference and optical coupling coefficient.
Innovation Solution
A distributed feedback semiconductor laser element with a multi-layered structure including a GaN substrate, conductivity-type semiconductor layers, and a light emitting layer, featuring a ridge waveguide and a first diffraction grating with a depth of 50 nm to 200 nm and a duty ratio within a specific range, optimized to achieve a high optical coupling coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a GaN-based material is used as a semiconductor light emitting element, then light emission in ultraviolet or visible wavelength band is achieved, but it is difficult to obtain sufficient refractive index difference and increase optical coupling coefficient
Solution Approach 1:
The patent uses a composite structure combining GaN-based semiconductor layers with a distributed feedback grating pattern. The multi-layered GaN structure with alternating high-refractive-index and low-refractive-index layers creates enhanced optical coupling through the composite material architecture, overcoming the limitation of insufficient refractive index difference in single-material GaN systems.
Solution Approach 2:
The patent changes the structural parameters of the semiconductor layer by creating a periodic distributed feedback grating with specific duty ratios (0.3 to 0.7) and depth ratios (0.1 to 0.5). This parameter optimization modifies the optical properties to achieve sufficient optical coupling coefficient without changing the base GaN material composition.
2Power
If a distributed feedback laser diode is used to achieve longitudinal single-mode operation, then high output is obtained, but the conversion efficiency of SHG waves is insufficient without proper grating optimization
Solution Approach 1:
The patent optimizes the duty ratio of the distributed feedback grating to be between 0.3 and 0.7, and the depth ratio to be between 0.1 and 0.5. These parameter changes maximize the optical coupling coefficient, enabling efficient longitudinal single-mode operation and high SHG conversion efficiency simultaneously.
Solution Approach 2:
The patent implements a periodic distributed feedback grating structure within the semiconductor layer. This periodic modulation of the refractive index creates constructive interference for the desired wavelength, enhancing the optical coupling and enabling efficient frequency doubling through periodic nonlinear optical interaction.
3Object-affected harmful factors
If KrCl excimer lamp is used for 222 nm ultraviolet sterilization, then safer sterilization is achieved, but the system size is large and noise is high
Solution Approach 1:
The patent replaces the mechanical KrCl excimer lamp system with a solid-state GaN-based semiconductor laser system. This substitution eliminates the mechanical components, high voltage power supplies, and acoustic noise associated with excimer lamps, while maintaining the safe 222 nm sterilization capability through frequency doubling of the 444 nm laser output.
Solution Approach 2:
The patent utilizes nonlinear optical phase matching in a frequency doubling crystal to convert 444 nm fundamental wave light into 222 nm second harmonic light. This phase transition in the optical frequency domain enables compact sterilization without requiring direct generation of 222 nm radiation by the semiconductor laser itself.
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 the semiconductor laser element to operate in a longitudinal single mode with high output, effectively converting 444 nm light into 222 nm second harmonic, thus addressing the safety concerns and efficiency requirements for ultraviolet sterilization applications.
Implementation Method 1
a first diffraction grating formed adjacent to and on both sides of the ridge waveguide
Implementation Method 2
GaN-based materials are widely used as semiconductor light emitting elements that emit light in a wavelength band of ultraviolet light or visible light
Implementation Method 3
a method of converting 444 nm light into 222 nm second harmonic (SHG: second harmonic generation wave) using harmonic generation by a wavelength conversion element
Data Source
AI summary
In a distributed feedback semiconductor laser element, a multi-layered structure includes a GaN substrate, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, and a ridge waveguide is formed. A first diffraction grating is formed adjacent to and on both sides of the ridge waveguide. A depth d of a groove of the first diffraction grating is included in the range of 50 nm d≤200 nm, and a duty ratio duty is included in the range of an inequality (1) using constants a, b, c, and n defined for the order of the diffracted light.-d-can+b≦duty≦d-can+b(1)