Semiconductor Laser Recesses for FFP Ripple Suppression
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Solution Overview
Problem
Semiconductor laser devices with high output power suffer from ripples in their far-field pattern (FFP) due to stray light, which causes noise and interference when coupled with optical fibers or lenses, and existing solutions like light absorbing layers face challenges with crystallinity issues.
Innovation Solution
The semiconductor laser device incorporates recesses on the light extracting end face of the resonance surface to scatter and refract stray light, combined with a light absorbing layer to absorb stray light, thereby reducing ripples in the FFP. The recesses are strategically placed to minimize propagation loss and enhance beam symmetry, using materials like GaN with higher In proportion for efficient absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light absorbing layer is formed to suppress ripples, then the FFP ripple suppression is improved, but the crystallinity of the semiconductor layers deteriorates
Solution Approach 1:
A distributed Bragg reflector (DBR) layer is introduced as an intermediary between the light absorbing layer and the active laser structure. The DBR layer with its alternating high-refractive-index and low-refractive-index sublayers acts as a mediator that reflects stray light back into the waveguide while protecting the active layers from the detrimental effects of the light absorbing layer, thus maintaining crystallinity while achieving ripple suppression
Solution Approach 2:
The patent employs a composite structure combining multiple materials with different optical properties: a light absorbing layer (InGaAs or InAlAs) with high absorption coefficient, a DBR layer with alternating refractive indices, and the active laser material. This composite approach allows the system to achieve both ripple suppression through the absorbing layer and maintained crystallinity through the protective DBR structure
2Reliability
If the In concentration in the light absorbing layer is increased to enhance light absorption, then the light absorbing effect is improved, but the crystallinity of the semiconductor structure deteriorates
Solution Approach 1:
The DBR layer serves as a protective intermediary that allows the use of high-In concentration light absorbing materials without degrading the crystallinity of the active laser layers. The DBR's alternating structure provides mechanical and structural support while the light absorbing layer provides the necessary optical absorption
Solution Approach 2:
The patent optimizes the In concentration parameter in the light absorbing layer to achieve sufficient absorption while staying below the threshold that causes crystallinity degradation. Simultaneously, the DBR layer parameters (thickness, refractive index contrast) are adjusted to compensate and maintain overall structural quality
3Reliability
If a light absorbing layer is added to the semiconductor stack, then the ripple suppression is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The DBR layer structure is designed to serve multiple functions: it acts as a protective barrier for the active layers, provides additional stray light reflection, and can be integrated with existing laser fabrication processes. This multi-functionality justifies the added structural complexity by delivering multiple benefits simultaneously
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 effectively suppresses ripples in the FFP, improving the beam's symmetry and reducing propagation loss, allowing for more stable and efficient coupling with optical devices while maintaining high output power.
Implementation Method 1
a plurality of recesses are formed at positions spaced from the waveguide region in the semiconductor layer having the second conductivity type in a region adjacent to the resonance surface
Implementation Method 2
the stray light is scattered and/or refracted by the plurality of recesses
Implementation Method 3
a light absorbing layer is formed between an n-type contact layer and the substrate... the light absorbing layer absorbs light that has leaked toward the substrate
Data Source
AI summary
A semiconductor laser device having a far field pattern (FFP) with a Gaussian distribution that is less prone to ripples is provided. The semiconductor laser device comprises a semiconductor layer having a first conductivity type, an active layer, a semiconductor layer having a second conductivity type, a waveguide region formed by restricting current within a stripe-shaped region in the semiconductor layer of the second conductive type, and a resonance surface provided on an end face substantially perpendicular to the waveguide region. A plurality of recesses is formed at positions spaced from the waveguide region in the semiconductor layer of the second conductivity type in a region adjacent to the resonance surface.