Chirped VCSEL Reflector for Stable Single-Mode Output
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Solution Overview
Problem
Conventional Vertical Cavity Surface Emitting Lasers (VCSELs) face limitations in achieving stable single mode power due to mode competition, spatial hole burning, and gain clamping, resulting in reduced maximal power and unstable fundamental modes.
Innovation Solution
Incorporating a chirped pattern reflector with a concave central portion and a convex outer portion to selectively stabilize the fundamental mode while diverging higher order modes, enhancing reflectivity and mode stability through a curved effective mirror configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional VCSEL with flat mirrors is used, then the device structure is simple and easy to manufacture, but the fundamental mode stability is poor and higher order modes cannot be effectively suppressed
Solution Approach 1:
The patent applies curvature to the reflector surface by creating a chirped pattern where the grating period varies spatially. This results in an effective curved mirror that focuses fundamental modes while defocusing higher order modes, thereby stabilizing the fundamental mode without requiring a physically complex external cavity structure.
Solution Approach 2:
The chirped pattern reflector implements local quality by having different grating periods in different regions. The grating period is optimized locally to provide different reflectivity characteristics for different modes: constructive interference for fundamental modes and destructive interference for higher order modes, achieving mode selectivity through spatially varying local properties.
2Power
If external cavity with curved mirror is used to shape waveform and collimate beam, then single mode power increases, but fabrication and control becomes difficult for industrial applications
Solution Approach 1:
The patent merges the functions of the external curved cavity with the VCSEL's top mirror by integrating the chirped grating pattern directly into the top mirror structure. This combination eliminates the need for separate external cavity components while maintaining the mode-selective focusing effect, thereby increasing single mode power without compromising manufacturability.
Solution Approach 2:
Instead of using a physical curved mirror that is difficult to fabricate, the patent creates an effective curved mirror by copying the curvature effect through a planar chirped grating pattern. The varying grating period replicates the optical path differences of a curved surface, achieving the same mode-selective effect through a manufacturable planar structure.
3Reliability
If a chirped pattern reflector with varying grating period is implemented, then mode selectivity and fundamental mode stability improve, but the reflector design and fabrication complexity increases
Solution Approach 1:
The patent employs parameter changes by systematically varying the grating period across the reflector surface according to a chirped pattern. This controlled parameter variation creates the desired phase modulation that enhances fundamental mode stability and suppresses higher order modes, achieving reliable mode selection through precise parameter control.
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 chirped pattern reflector increases the stability of the fundamental mode and reduces the quality factor of higher order modes, leading to improved electro-optic performance and increased single mode power in VCSELs.
Implementation Method 1
The chirped pattern reflector includes: a central portion structured to present a concave portion of an effective mirror to the active region, and an outer portion structured to present a convex portion of the effective mirror to the active region
Data Source
AI summary
A vertical cavity surface emitting laser (VCSEL) may include an active region (e.g., one or more quantum wells) and a chirped pattern reflector. The active region may be configured to be electrically pumped such that the active region generates light having a fundamental mode and a higher order mode. The chirped pattern reflector may include a first portion presenting to the active region as a first portion of an effective mirror having a concave shape and a second portion presenting to the active region as a second portion of the effective mirror having a convex shape.