Diode Laser Lateral Structure for Flat Field Distribution
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Solution Overview
Problem
Current diode laser structures, both single elements and arrays, face inefficiencies in field distribution, leading to increased threshold current, reduced slope efficiency, and mode switching issues due to suboptimal coupling of field distributions with excitation patterns, particularly with cosine or hyperbolic-cosine field distributions in the active core segments.
Innovation Solution
The design incorporates a lateral structure with reflecting-filter or adjusted attenuator systems to achieve flat or quasi-flat field distributions in single elements and arrays, utilizing segment systems with specific refractive index profiles and segment arrangements to enhance mode selection and discrimination, ensuring optimal coupling and reduced modal gain for non-preferred modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stripe diode laser structures (etched ridge, buried, gain-guided) are used, then lateral single mode operation can be achieved, but the field distribution follows a cosine or half-cosine pattern that couples poorly with uniform excitation, resulting in increased threshold current and reduced slope efficiency
Solution Approach 1:
The patent applies local quality by creating non-uniform refractive index profiles within the lateral structure. Specifically, it uses index-guided sections with higher refractive index and gain-guided sections with lower refractive index, creating localized regions with different optical properties. This allows the field distribution to be shaped locally to match the excitation profile, improving coupling efficiency while maintaining lateral single mode operation.
Solution Approach 2:
The patent changes the refractive index parameter spatially across the lateral structure. By varying the refractive index in different sections (index-guided vs gain-guided) and adjusting the width ratios of these sections, the patent transforms the field distribution from a conventional cosine pattern to a more uniform pattern, thereby improving the coupling with uniform current excitation and reducing threshold current.
2Power
If multiple lateral segments are combined to form arrays, then higher power output is achieved, but mode coupling between elements creates complex field distributions that lead to mode switching and reduced operational stability
Solution Approach 1:
The patent applies segmentation by dividing the lateral structure into distinct sections: index-guided segments, gain-guided segments, and inter-element coupling regions. Each segment has specific optical properties designed for its function. The index-guided segments confine modes locally, while the gain-guided segments provide controlled coupling between elements, preventing unwanted mode switching in arrays.
Solution Approach 2:
The patent introduces gain-guided sections as intermediary regions between index-guided sections and between array elements. These intermediary regions with lower refractive index act as coupling zones that control the interaction between adjacent lateral modes, stabilizing the mode distribution in arrays while maintaining high power output capability.
3Reliability
If the field distribution is confined to a narrow core segment, then lateral single mode operation is achieved, but the overlap with the broader excitation region is reduced, decreasing coupling efficiency
Solution Approach 1:
The patent merges two different guiding mechanisms: index-guiding and gain-guiding. The index-guided sections provide strong lateral confinement for single mode operation, while the gain-guided sections extend the effective interaction region with the excitation current. This combination allows the field distribution to be both confined (for single mode) and broadly overlapping with excitation (for high coupling efficiency).
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 approach results in improved coupling efficiency, reduced threshold current, increased slope efficiency, and enhanced stability against mode switching by ensuring flat or equal field amplitudes across elements, thereby optimizing laser performance.
Implementation Method 1
The ridge structure operates based on a real and positive difference in the effective refractive index in the lateral direction from the ridge-segment to the surrounding segments. Etching part of the surrounding segments top claddings, reduces the effective refractive index in these segments compared with that in non-etched core segment.
Implementation Method 2
The design incorporates a lateral structure with reflecting-filter or adjusted attenuator systems to achieve flat or quasi-flat field distributions in single elements and arrays
Data Source
AI summary
Diode lasers type of devices with good coupling between field distribution and gain are disclosed. A single element has a flat field distribution that couples with the uniform current injection in a contact region. A multi element array having almost flat field distribution in each element and almost equal amplitude for the field intensity in all elements is provided. Injection by multiple contacts couples well with the overall field distribution. Also, the lasers are stable against filament formation and mode switching.