Semiconductor Laser With External Reflector for Beam Quality
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Solution Overview
Problem
High-power semiconductor lasers face challenges in maintaining high spatial beam quality and narrow spectral line width while achieving high output power, as increasing the lateral width of the active material leads to gain in higher order spatial modes, reducing beam quality and increasing spectral line width.
Innovation Solution
A semiconductor laser is optically coupled with a narrow spectral and spatial bandwidth reflector having a three-dimensional pattern of refractive index variations, providing selective feedback to enhance the gain of desired modes and stabilize the laser light, thereby improving spatial beam quality and reducing spectral line width without compromising output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the lateral width of the active material is increased to achieve high output power, then the output power is improved, but the spatial beam quality deteriorates due to gain in higher order spatial modes
Solution Approach 1:
The patent introduces an external reflector that provides selective feedback to the laser cavity. The reflector has wavelength- and angular-dependent reflectivity that preferentially reflects light at specific angles corresponding to the fundamental spatial mode, while allowing higher order modes to escape. This feedback mechanism enhances the gain for the desired mode and suppresses higher order modes, enabling high power output with improved spatial beam quality
Solution Approach 2:
The external reflector implements local quality by having different reflectivity properties for different spatial modes. The reflector is designed with specific optical characteristics that provide high reflectivity for the fundamental mode at certain angles and wavelengths, while providing lower reflectivity for higher order modes. This spatially selective feedback allows the system to optimize performance for specific modes while suppressing others
2Power
If the lateral width of the active material is increased to achieve high output power, then the output power is improved, but the spectral line width increases
Solution Approach 1:
The external reflector provides wavelength-selective feedback that enhances the gain for specific longitudinal modes while suppressing others. The reflector's wavelength-dependent reflectivity creates a feedback loop that stabilizes the laser emission at desired wavelengths, resulting in narrowed spectral line width even when operating at high power levels with wide stripe emitters
Solution Approach 2:
The system changes the optical feedback parameters by introducing an external reflector with specific wavelength- and angle-dependent reflectivity characteristics. This modifies the resonant conditions in the laser cavity, creating preferential gain for specific wavelengths and modes, thereby narrowing the spectral line width while maintaining high output power
3Power
If multiple wide stripe emitters are combined in an array to increase output power, then the output power is improved, but the spatial beam quality of the combined beam deteriorates
Solution Approach 1:
The patent combines multiple wide stripe emitter arrays with external reflectors, where each emitter's output is reflected and redirected by its associated external reflector. The reflectors are positioned and oriented to overlap the reflected beams from multiple emitters, creating a combined output beam. This merging approach allows the system to achieve high total power while the external reflectors maintain spatial beam quality by selecting for fundamental modes from each emitter
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 allows for high-power, high-beam quality, and narrow line width operation by discriminating against higher order modes, maintaining brilliance and reducing thermal and current dependence, while enabling efficient beam combining and stabilization of the output wavelength.
Implementation Method 1
The reflector can be a volume diffractive grating
Implementation Method 2
reflector having a three-dimensional pattern of refractive index variations within the reflector
Implementation Method 3
a portion of the light in the output beam is reflected back into the laser by the reflector
Implementation Method 4
The reflector can be a volume Bragg grating
Data Source
AI summary
A light source includes a semiconductor laser diode and a narrow spectral and spatial bandwidth reflector in optical communication with respect to the semiconductor diode laser and aligned with the output beam of the diode laser, such that a portion of the light in the output beam is reflected back into the laser.