Asymmetric Semiconductor Laser Vertical Divergence
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Solution Overview
Problem
Existing semiconductor lasers face challenges in reducing vertical far-field divergence while maintaining high output power and minimizing optical loss and threshold current, as previous methods often result in poor performance or increased ohmic resistance and optical loss.
Innovation Solution
A semiconductor laser structure with an asymmetric refractive index profile is designed, where the n-cladding layer has a higher refractive index than the p-cladding layer, and the n-cladding layer thickness is adjusted between 3 to 6 micrometers to control the vertical far-field divergence without expanding the near-field mode size, ensuring the peak of the lasing optical mode remains within the active region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the n-cladding layer thickness is increased to reduce vertical far-field divergence, then beam divergence is reduced, but optical loss and threshold current increase
Solution Approach 1:
The patent applies local quality by creating an asymmetric refractive index distribution specifically in the cladding layers. The n-cladding layer has a higher refractive index than the p-cladding layer, which locally modifies the optical mode confinement in a specific region (the n-cladding area) to reduce vertical divergence without uniformly affecting the entire laser structure and causing excessive optical loss.
Solution Approach 2:
The patent directly applies asymmetry by designing an asymmetric layer structure where the n-cladding layer thickness (3-6 μm) and refractive index are deliberately made different from the p-cladding layer. This asymmetric configuration creates an asymmetric optical mode distribution that reduces vertical far-field divergence while maintaining acceptable optical loss characteristics.
2Shape
If the n-cladding layer thickness is increased to reduce vertical far-field divergence, then beam divergence is reduced, but lasing threshold current increases
Solution Approach 1:
The asymmetric refractive index distribution in the n-cladding layer locally modifies optical confinement to reduce vertical divergence. This localized modification achieves beam shaping without requiring a uniform increase in all layer dimensions that would otherwise be necessary to maintain low threshold current.
Solution Approach 2:
The asymmetric structure with thicker, higher-index n-cladding layer creates an optimized optical mode distribution that reduces vertical divergence. The asymmetry allows the optical mode to be confined more effectively in the vertical direction while maintaining horizontal confinement, thereby reducing threshold current compared to symmetric designs with equivalent divergence reduction.
3Shape
If symmetric layer structure is used to expand optical mode, then vertical far-field divergence is reduced, but ohmic resistance increases
Solution Approach 1:
The patent replaces the symmetric layer structure with an asymmetric one, where the n-cladding layer has different thickness and refractive index characteristics compared to the p-cladding layer. This asymmetry achieves optical mode expansion and vertical divergence reduction while allowing independent optimization of the electrical contact regions, thereby avoiding the increased ohmic resistance associated with symmetric 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
This approach significantly reduces the vertical far-field divergence from 20 to 13 degrees while maintaining constant confinement factor and lasing threshold, achieving improved laser beam quality and efficient fiber coupling.
Implementation Method 1
selecting a refractive index of the n-cladding and the p-cladding layer, so that in operation, a lasing optical mode of the semiconductor laser is asymmetric, the majority of the lasing optical mode shifting towards the n-cladding layer
Implementation Method 2
The refractive index of the n-cladding layer is lower than the indices of the quantum well and the waveguide layers
Data Source
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AI summary
The invention relates to a method of reducing vertical divergence of a high-power semiconductor laser with a negligible threshold current and conversion efficiency penalty. The low divergence is achieved by increasing the thickness of the n-cladding layer in an asymmetric laser diode stack structure, to a value ranging from 1 to 4 times the laser mode size measured at 10% level. The divergence may be tuned by adjusting the n-cladding layer parameters in an area of the tail the optical mode, measuring 0.03% or less of the maximal optical power density of said optical mode.