Lateral Bragg Mirror Electrode Layout for Low-Loss Quantum Cascade Lasers
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Solution Overview
Problem
Existing lateral DFB-structured quantum cascade lasers suffer from inefficient electron injection and increased optical losses due to lateral structuring of the active region, which disrupts electron scattering and increases the laser threshold.
Innovation Solution
The laser design incorporates lateral corrugations on the top electrode instead of the active region, forming a distributed Bragg mirror that enhances electrical injection and minimizes optical losses, while maintaining effective optical feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lateral corrugations are formed on the active region to create a distributed Bragg mirror, then optical feedback is achieved, but electron injection efficiency deteriorates and optical losses increase
Solution Approach 1:
The patent introduces a distributed Bragg reflector as an intermediary component formed by lateral corrugations on the electrode rather than directly on the active region. This mediator provides the necessary optical feedback while isolating the active region from direct structural modification, thereby preserving electron injection efficiency and minimizing optical losses.
Solution Approach 2:
The patent transitions from vertical optical feedback structures to lateral corrugations on the electrode surface. By moving the Bragg mirror structure to a lateral dimension on the electrode rather than vertically through the active region, the design achieves optical feedback without disrupting the vertical electron transport path, thus maintaining injection efficiency.
2Reliability
If lateral corrugations are formed on the active region, then distributed Bragg reflection is achieved, but optical losses increase
Solution Approach 1:
The electrode serves as an intermediary layer where the distributed Bragg reflector is formed, rather than modifying the active region directly. This intermediary positioning allows the corrugations to provide optical feedback while minimizing direct interaction with the optical mode in the active region, thereby reducing optical losses.
3Reliability
If lateral structuring is applied to the active region, then Bragg reflection is achieved, but laser threshold increases
Solution Approach 1:
The patent relocates the lateral structuring from the active region to the electrode surface. This dimensional relocation allows the Bragg reflection to be achieved through lateral corrugations on the electrode while preserving the integrity of the active region, thereby maintaining low laser threshold and avoiding the power penalty associated with direct active region structuring.
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 design improves electron injection efficiency and reduces optical losses, achieving enhanced performance and controlled far-field emission in quantum cascade lasers.
Implementation Method 1
The distributed Bragg reflector is a mirror that can reflect light radiation with a given wavelength λ with a reflectivity R greater than 99%. Such a mirror typically comprises periodic corrugations with different refractive indices. For a grating pitch of the order of Λ=m·λ/2n, where n is the effective refractive index and m is the grating order, the partial reflections combine by constructive interference
Implementation Method 2
the partial reflections combine by constructive interference, and the corrugations 'distributed' along the grating act as a high-quality mirror
Implementation Method 3
the active region of the laser is electrically polarised via electrodes, such that electrons are injected. This active region typically comprises a multiplicity of quantum wells wherein an electron will successively lose part of its energy, in a cascade, while emitting a photon of given energy each time
Implementation Method 4
This light radiation propagates in a guided manner inside the optical cavity of the laser. This optical cavity is typically bounded by bottom and top layers called LOC (acronym for 'Low Optical Confinement'), and at least one Bragg reflector. The LOC layers help to better confine the optical mode in the active region
Data Source
AI summary
A laser is provided, including: a distributed Bragg mirror; a waveguide, the laser to emit light radiation along a longitudinal direction x, and the waveguide formed at least in part in a stack of layers made of III-V materials including at least one active region to emit the light radiation, the mirror including lateral corrugations distributed periodically along the direction x in a period Λ, the corrugations being carried by at least a lateral plane xz defined by the direction x and a first transverse direction z normal to the direction x, the corrugations having a dimension d along a second transverse direction y normal to the direction x; and a top electrode arranged on the waveguide along the direction z, the corrugations being partly located at lateral flanks of the top electrode, extending parallel to the plane xz, and extending only on the lateral flanks of the top electrode.