Semiconductor Laser Low Reflection Film for Stable Reflectance
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Solution Overview
Problem
Conventional semiconductor laser devices face challenges in precisely controlling the reflectance at the emission facet due to variations in the thickness and refractive index of dielectric films, leading to reduced yield and instability in high-power bluish purple semiconductor lasers with short wavelengths like 405 nm.
Innovation Solution
A semiconductor laser device is designed with a reflection film composed of alternately laminated first and second dielectric films of different materials, forming four or more layers, where the refractive indexes and thicknesses of the films are carefully controlled to maintain stable reflectance across variations, using materials like aluminum oxide and silicon oxide to achieve a desired reflectance range of 5-17%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layered dielectric film is used for the low reflection film at the front facet, then the film structure is simple and easy to manufacture, but the reflectance control precision deteriorates due to thickness variations
Solution Approach 1:
The single-layered dielectric film is divided into multiple layers (first dielectric film and second dielectric film with different refractive indexes) to achieve better reflectance control. The segmentation allows each layer to contribute differently to the overall optical properties, compensating for thickness variations and improving manufacturing precision.
Solution Approach 2:
The patent uses composite dielectric film structures combining materials with different refractive indexes (such as Al2O3 and SiO2) to create a low reflection film with stable reflectance characteristics. The composite structure leverages the optical properties of each material to achieve precise reflectance control despite variations in film thickness.
2Length of moving object
If the film thickness is reduced to achieve shorter wavelength operation (405 nm), then the laser wavelength is shortened, but the reflectance control becomes more difficult and yield decreases
Solution Approach 1:
The dielectric film is segmented into multiple layers with different refractive indexes, allowing the overall optical thickness to be reduced for shorter wavelength operation while maintaining precise reflectance control through the combined optical properties of each layer.
Solution Approach 2:
The patent changes the optical parameters by using multiple dielectric layers with different refractive indexes and thicknesses, enabling precise control of reflectance at shorter wavelengths (405 nm) where single-layer films would require extremely precise thickness control.
3Ease of manufacture
If vacuum deposition or sputtering is used for film formation with thickness control of ±5%, then the manufacturing process is simple, but the reflectance control accuracy of 6±1% cannot be achieved
Solution Approach 1:
The film structure is segmented into multiple layers, which reduces the sensitivity of overall reflectance to individual layer thickness variations. This allows conventional deposition processes with ±5% thickness control to achieve the required 6±1% reflectance accuracy.
Solution Approach 2:
The composite dielectric film structure with materials of different refractive indexes provides inherent compensation for thickness variations, enabling accurate reflectance control using standard vacuum deposition or sputtering processes without requiring ultra-precise thickness control.
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
This configuration allows for stable and reproducible control of reflectance, suppressing variations to 1% or less even with ±5% thickness variations, enhancing the yield and reliability of semiconductor laser devices by maintaining reflectance stability across different film thicknesses.
Implementation Method 1
a reflection film is provided at one of facets of the resonator, and the reflection film is formed of a first dielectric film and a second dielectric film, made of materials different from each other, which are alternately laminated in four or more layers
Data Source
AI summary
A semiconductor laser device comprises a GaN substrate having a refractive index of 3.5 or below, a semiconductor layer laminated on the substrate, and a pair of facets forming a resonator and in face-to-face-relation to each other in a direction perpendicular to the direction of the laminated layer. One of the facets of the resonator includes a low reflection film, of a first dielectric film, a second dielectric film, a third dielectric film, and a fourth dielectric film. When the refractive indexes of these films are taken as n1, n2, n3, and n4, n1=n3 and n2=n4. The following relationship between the first dielectric film and the third dielectric film, and between the second dielectric film and the fourth dielectric film is established, nd+n′d′=pλ/4, where p is an integer, and λ is oscillation wavelength of a laser beam generated by the semiconductor laser device.