Reverse-Tapered Quantum Cascade Lasers for Single-Mode High Power
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Solution Overview
Problem
Existing quantum cascade lasers (QCLs) operating in the 4.5-5.0 μm wavelength region face challenges in maintaining single-spatial-mode operation at high output powers, often requiring narrow element widths which limit power scalability and beam combining efficiency.
Innovation Solution
The implementation of reverse-tapered laser elements with distributed feedback (DFB) gratings configured to suppress specific longitudinal modes, combined with continuous ridge structures, ensures single-mode operation and high output powers, achieving a single-lobe far-field beam pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If narrow element width (5-6 μm) is used to maintain single-spatial-mode operation, then beam quality is improved, but output power is limited to 1.5-2.0 watts
Solution Approach 1:
The patent transitions from conventional narrow ridge waveguides to a tapered ridge structure where the ridge width varies along the propagation direction. This dimensional change allows the mode confinement to be maintained at the narrow end while the wider end provides increased optical mode area for higher power extraction, effectively decoupling the constraints between mode stability and power output.
Solution Approach 2:
The patent modifies the ridge width parameter along the propagation direction, creating a tapered profile rather than a uniform width. This parameter variation enables the optical mode to be confined at the narrow end for single-mode operation while expanding toward the wide end to support higher power levels, achieving both beam quality and high power output.
2Power
If higher CW output powers (5 W) are achieved, then power is improved, but multi-mode operation occurs with beam steering
Solution Approach 1:
By introducing a tapered dimension to the ridge structure, the patent creates a gradual expansion of the optical mode area along the propagation direction. This allows the mode to remain confined and stable at the narrow end while accommodating higher power at the wide end, preventing the transition to multi-mode operation that occurs in uniform narrow ridges at high power levels.
3Stability of the object's composition
If narrow ridge width is used for grating coupled surface-emitting QCLs, then single-lateral-mode operation is maintained, but device complexity and fabrication difficulty increase
Solution Approach 1:
The tapered ridge structure introduces a gradual width variation along the propagation direction, which relaxes the stringent fabrication tolerances associated with uniform narrow ridges. The gradual transition provides a buffer against manufacturing variations, making it easier to maintain single-lateral-mode operation while allowing for more practical fabrication processes.
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 achieves output powers at least twice that of existing QCL devices while maintaining beam quality, with increased fabrication tolerance and light outcoupling efficiency.
Implementation Method 1
quantum cascade active layer
Implementation Method 2
quantum cascade active layer, the upper cladding layer and the lower cladding layer define a guided optical mode
Implementation Method 3
distributed feedback grating
Implementation Method 4
distributed feedback grating configured to suppress specific longitudinal modes
Data Source
AI summary
Single-mode quantum cascade semiconductor lasers are provided. The lasers comprise a laser element, the laser element comprising a quantum cascade active layer; an upper cladding layer over the quantum cascade active layer; and a lower cladding layer under the quantum cascade active layer, wherein the quantum cascade active layer, the upper cladding layer and the lower cladding layer define a guided optical mode. The quantum cascade active layer and the upper and lower cladding layers are shaped in the form of a ridge structure having a front face, a back face opposite the front face, and a lasing face through which laser emission exits the ridge structure, the ridge structure configured such that the laser emission has a single-lobe, far-field beam pattern from the ridge structure comprising certain sections, including tapered sections, collateral sections, or both.