Buried-Heterostructure Semiconductor Laser for Wider Single-Mode Mesa
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Solution Overview
Problem
Semiconductor lasers with buried heterostructures face challenges in maintaining high optical coupling efficiency and reliability due to the large optical confinement coefficient and limited design flexibility of the n-InGaAsP guide layer, which affects the spread angle of the far field pattern and the appearance of higher-order transverse modes.
Innovation Solution
Incorporating a high refractive index layer with a higher refractive index than the first cladding layer but not absorbing light, positioned under the mesa structure and buried layer, expands the distribution of light, increasing the higher-order transverse-mode cut-off width, thereby improving output characteristics and reliability by reducing the spread angle of the far field pattern and increasing the area of the near field pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the optical confinement coefficient to the mesa structure is large, then the aspect ratio of output light is close to 1, but the area of near field pattern becomes small, leading to large spread angle of far field pattern and decreased optical coupling tolerance
Solution Approach 1:
A low refractive index layer is introduced as an intermediary between the high refractive index guide layer and the cladding layer. This intermediary layer reduces the abrupt refractive index difference, allowing the optical confinement coefficient to be reduced while maintaining light distribution control, thereby increasing the near field pattern area and reducing the far field spread angle without compromising the aspect ratio
2Reliability
If the mesa width is increased to reduce current density, then higher power output and reliability are achieved, but higher-order transverse modes appear when exceeding the cut-off width
Solution Approach 1:
The refractive index distribution is modified by introducing the low refractive index layer, which changes the optical confinement parameters. This allows the cut-off width for higher-order transverse modes to be increased, enabling broader mesa widths to be used without generating harmful higher-order modes, thus reducing current density while maintaining single-mode operation
3Measurement precision
If the n-InGaAsP guide layer is used to fill the diffraction grating, then optical properties are determined, but design flexibility is reduced and the cut-off width is narrowed
Solution Approach 1:
The guide layer structure is segmented into a high refractive index layer (n-InGaAsP) for maintaining optical properties and a low refractive index layer for providing design flexibility. This segmentation allows the diffraction grating to be filled with the high refractive index material for optimal optical performance while the low refractive index layer below it enables broader design options and wider cut-off width without compromising optical characteristics
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 enhances the power output and reliability of semiconductor lasers by broadening the cut-off width, reducing the current density, and improving optical coupling tolerance without increasing the optical confinement coefficient, allowing for broader mesa widths without generating high-order modes.
Implementation Method 1
a high refractive index layer configured to not absorb light oscillating in the multi-quantum well layer
Implementation Method 2
the high refractive index having a higher refractive index than the first cladding layer
Implementation Method 3
a diffraction grating layer at least partially constituting a diffraction grating capable of diffracting the light oscillating in the multi-quantum well layer
Data Source
AI summary
A semiconductor laser includes: a multi-quantum well layer in a mesa structure; a buried layer comprising a semi-insulating semiconductor, the buried layer being in contact with each of both sides of the mesa structure; a first cladding layer with a first conductivity type, the first cladding layer having a lower refractive index than the multi-quantum well layer; a high refractive index layer configured to not absorb light oscillating in the multi-quantum well layer, the high refractive index layer having a higher refractive index than the first cladding layer; a diffraction grating layer at least partially constituting a diffraction grating capable of diffracting the light oscillating in the multi-quantum well layer, the diffraction grating layer not contacting the high refractive index layer; a substrate with the first conductivity type; and a second cladding layer with a second conductivity type above the multi-quantum well layer.