Ring-Cavity Quantum Cascade Laser Phase Shifter Beam Quality
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Solution Overview
Problem
Ring-cavity surface-emitting quantum cascade lasers (RCSE-QCLs) exhibit a central node in their beam profile due to destructive interference and non-optimum distributed feedback (DFB) grating periods, leading to high divergence and non-Gaussian beam quality, which is undesirable for various applications.
Innovation Solution
The implementation of a ring-shaped phase shifter with a spiraled surface and nested concentric ring-cavity structures, where the phase shifter's optical thickness varies to match the operational wavelength, and the use of spiral wedges to eliminate the central node and achieve a more uniform radiation pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a ring-cavity surface-emitting quantum cascade laser is used, then the laser can emit radiation perpendicular to the substrate surface with potential for high power output, but the spatial distribution exhibits a central node with non-Gaussian beam quality and high divergence
Solution Approach 1:
The patent introduces an asymmetric spiral phase shifter element within the ring-cavity structure. This spiral component creates an asymmetric phase distribution that transforms the symmetric ring-mode emission into a Gaussian-like beam profile, eliminating the central node while preserving the surface-emitting geometry and high power capability
Solution Approach 2:
The patent employs a spiral phase shifter that introduces azimuthal phase curvature to the ring-cavity emission. This curved phase front transforms the planar ring-mode wavefront into a spherical-like Gaussian beam profile, improving beam quality and reducing divergence while maintaining the perpendicular emission geometry
2Reliability
If distributed feedback gratings are used for wavelength control, then the laser achieves wavelength stability, but non-optimum grating periods cause destructive interference and central node formation
Solution Approach 1:
The patent introduces a spiral phase shifter as an intermediary element between the distributed feedback grating and the emission facet. This intermediate component compensates for the destructive interference patterns created by the grating, transforming the non-Gaussian beam profile into a Gaussian-like profile while preserving the wavelength stability provided by the DFB mechanism
3Ease of operation
If ring-shaped ridges are etched to form waveguides, then the laser achieves surface emission perpendicular to the substrate, but the circular geometry creates a central node in the radiation pattern
Solution Approach 1:
The patent breaks the symmetric circular geometry of the ring waveguide by introducing an asymmetric spiral phase shifter. This asymmetric element transforms the symmetric ring-mode emission pattern into an asymmetric Gaussian-like profile, eliminating the central node while preserving the surface-emitting capability perpendicular to the substrate
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 results in a power-scalable, high-power RCSE-QCL with improved beam quality, achieving a beam quality factor of M2 < 1.2 and enabling output powers over 15 W CW through a single aperture with a radially smooth intensity profile.
Implementation Method 1
a ring-shaped phase shifter aligned with the radiation emitting facet and having a spiraled surface... The ring-shaped phase shifter may have an optical thickness that varies from a first value to a second value greater than the first value based upon an azimuthal position
Data Source
AI summary
A ring-cavity surface emitting quantum cascade laser (RCSE-QCL) may include a ring-shaped active region having first and second opposing facets. One of the first and second opposing facets may define a radiation emitting facet. The RCSE-QCL may also include a ring-shaped phase shifter aligned with the radiation emitting facet and having a spiraled surface.