Corrugated-Sidewall DFB ICL Waveguides for Single-Wavelength Lasing
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Solution Overview
Problem
Distributed feedback interband cascade lasers (DFB ICLs) face challenges in lasing at a single wavelength due to wide ridge widths that support higher order modes, making it difficult to suppress optical losses and confinement factors, and existing solutions like step-shape waveguides and sidewall gratings are either ineffective or impractical for volume production.
Innovation Solution
Implementing a ridge waveguide with alternating regions and a sampled grating structure combined with a partially-corrugated sidewall, which increases waveguide losses for higher order lateral modes while maintaining the fundamental mode, thereby ensuring single-wavelength operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a wide ridge width is used in DFB ICL, then the waveguide can be easily fabricated with good yield, but the structure supports multiple higher order modes instead of single fundamental mode
Solution Approach 1:
The patent introduces a narrow stripe region within the wider ridge waveguide structure. This narrow stripe region (width: 1-3 μm) is localized in the center of the ridge and provides strong optical confinement for the fundamental mode, while the wider ridge (total width: 4-10 μm) maintains ease of fabrication. The local quality change in the narrow stripe region suppresses higher order modes without sacrificing overall fabrication yield.
2Stability of the object's composition
If the ridge width is reduced to suppress higher order modes, then single-wavelength operation is achieved, but the fabrication yield and manufacturing precision deteriorate
Solution Approach 1:
The ridge waveguide is segmented into two functional regions: a narrow stripe region (1-3 μm width) that provides optical confinement and suppresses higher order modes, and a wider ridge region (4-10 μm total width) that ensures easy fabrication. This segmentation allows each region to optimize its function independently, achieving both single-wavelength operation and high fabrication yield.
3Stability of the object's composition
If a step-shape waveguide structure is used to suppress higher order modes, then single-mode operation is achieved, but the device complexity increases and manufacturing becomes more difficult
Solution Approach 1:
The patent employs an asymmetric ridge waveguide structure with a narrow stripe region centered within a wider ridge. This asymmetric geometry creates different optical confinement conditions for fundamental and higher order modes. The narrow central stripe provides strong confinement for the fundamental mode while the wider sides allow higher order modes to experience increased losses, achieving single-mode operation without complex step-shape structures.
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 solution effectively suppresses high order lateral modes, allowing DFB ICLs to lase at a single wavelength, improving manufacturing yield and reducing current spreading, as demonstrated by waveguide simulations and SEM pictures showing successful single-mode operation across various currents and temperatures.
Implementation Method 1
DFB lasers operate by introducing a wavelength-selective grating into the device structure in order to achieve single-wavelength operation
Implementation Method 2
A ridge waveguide is created by etching parallel trenches in the laser material to create an isolated stripe of gain material
Data Source
Figure 1
Figure 2~3
Figure 4A~4C
AI summary
An interband cascade laser including: a ridge waveguide having alternating first and second regions; wherein the first region has a constant width, and the second region has a width that matches that of the first region at boundaries between the first region and the second region, and the width of the second region increases to a maximum that is larger than the width of the first region, such that a partially-corrugated sidewall along each side of the ridge waveguide is formed; wherein the first region comprises a grating structure, and due to periodic nature of the first region, the grating structure is in a form of a sampled grating; and wherein the partially-corrugated sidewall increases waveguide losses for radiation in higher order lateral modes as compared to the fundamental waveguide mode.