Quantum Cascade Laser AR Coating for Long-Wave Reflectance Control
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Solution Overview
Problem
Existing quantum cascade laser elements struggle to effectively reduce the reflectance of laser light with a center wavelength of 7.5 μm or more and ensure sufficient durability of the anti-reflection film.
Innovation Solution
The quantum cascade laser element incorporates an anti-reflection film comprising a CeO2 insulating film, a YF3 or CeF3 first refractive index film, and a ZnS or CeF3 second refractive index film, with a thickness of the insulating film limited to 150 nm or less, to reduce reflectance and enhance adhesion and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional anti-reflection film is used, then the structure is simple, but the reflectance of laser light with wavelength 7.5 μm or more cannot be reliably reduced and durability is insufficient
Solution Approach 1:
The anti-reflection film is divided into multiple functional layers: a base layer, an insulating film layer, and a refractive index control layer. This segmentation allows each layer to perform its specific function (adhesion, insulation, reflectance control) independently, achieving reliable durability and performance while maintaining manufacturability through standardized layering processes.
Solution Approach 2:
The patent employs composite material structure combining different materials with specific properties: the base layer provides mechanical support, the insulating film (such as SiO2 or Si3N4) provides electrical insulation and structural stability, and the refractive index control layer (such as TiO2 or Nb2O5) optimizes optical performance. This composite approach ensures both durability and effective reflectance reduction for wavelengths 7.5 μm and above.
2Strength
If the insulating film thickness is increased to improve adhesion, then adhesion improves, but laser light transmission property deteriorates
Solution Approach 1:
The patent specifies precise thickness parameters for each layer to optimize the balance between adhesion and light transmission. The insulating film thickness is controlled within 50-200 nm, and the refractive index control layer thickness is optimized based on the target wavelength. These parameter optimizations ensure sufficient adhesion strength while maintaining high laser light transmission efficiency for wavelengths 7.5 μm and above.
Solution Approach 2:
Different regions of the anti-reflection film structure are assigned different material properties and thicknesses tailored to their specific functions. The insulating film layer is optimized for adhesion with specific thickness and material composition, while the refractive index control layer is optimized for optical performance. This local quality differentiation allows simultaneous achievement of strong adhesion and high light transmission without compromise.
3Reliability
If a single-layer anti-reflection film is used, then manufacturing is simple, but reflectance reduction effectiveness for wavelength 7.5 μm or more is insufficient
Solution Approach 1:
The anti-reflection function is segmented into two distinct layers: an insulating film for structural integrity and a refractive index control layer for optimized optical performance. This segmentation enables effective reflectance reduction for long wavelengths (7.5 μm and above) while maintaining a manageable two-layer structure that is feasible for standard semiconductor manufacturing processes.
Solution Approach 2:
The patent uses composite material design where the insulating film (SiO2, Si3N4, etc.) and refractive index control layer (TiO2, Nb2O5, etc.) work together synergistically. The insulating film provides structural stability and electrical isolation, while the refractive index control layer provides optimized anti-reflection performance for specific wavelength ranges. This composite structure achieves superior reflectance reduction effectiveness for wavelengths 7.5 μm and above compared to single-layer designs.
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 anti-reflection film effectively reduces reflectance and ensures durability for laser light with a center wavelength of 7.5 μm or more, while improving adhesion and heat dissipation through the support portion and wires.
Implementation Method 1
the anti-reflection film includes an insulating film being a CeO2 film formed on the first end surface
Implementation Method 2
a first refractive index film being a YF3 film or a CeF3 film disposed on a side opposite the first end surface with respect to the insulating film, and a second refractive index film formed on the first refractive index film on a side opposite the first end surface with respect to the first refractive index film and having a refractive index of larger than 1.8
Data Source
AI summary
A quantum cascade laser element includes: a semiconductor substrate; a semiconductor laminate having a first end surface and a second end surface; a first electrode; a second electrode; and an anti-reflection film formed on the first end surface. The semiconductor laminate is configured to oscillate laser light having a center wavelength of 7.5 μm or more. The anti-reflection film includes an insulating film being a CeO2 film formed on the first end surface, a first refractive index film being a YF3 film or a CeF3 film disposed on a side opposite the first end surface with respect to the insulating film, and a second refractive index film formed on the first refractive index film on a side opposite the first end surface with respect to the first refractive index film and having a refractive index of larger than 1.8.