Surface-Emitting Laser Electrode Design for Stable High-Output Operation
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Solution Overview
Problem
Surface emitting lasers face challenges in achieving high output power while maintaining stable transverse mode and efficient current injection due to limitations in resonator length and carrier density distribution, leading to issues like gain saturation and multimode oscillation.
Innovation Solution
A surface emitting laser design with a pair of electrodes that inject carriers with different current densities, a semiconductor layer laminated body with varying area density, and fine holes or resistive layers to adjust carrier distribution, along with an external mirror for increased resonator length, ensuring uniform carrier distribution and stable transverse mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the resonator length is increased to obtain sufficient gain, then the output power is improved, but the device structure becomes more complex and the manufacturing difficulty increases
Solution Approach 1:
The resonator is segmented into a semiconductor substrate portion and a separate external mirror portion, allowing the resonator length to be effectively increased while keeping the semiconductor substrate structure simple and manageable. The external mirror is positioned at a distance from the substrate to create the extended resonator cavity.
Solution Approach 2:
An external mirror serves as an intermediary element to extend the resonator length without directly modifying the semiconductor substrate structure. The external mirror reflects light back into the active layer, providing the necessary optical feedback for lasing while maintaining a simple substrate design.
2Power
If the beam cross-section is increased to achieve high output power, then the output power is improved, but the transverse mode becomes multimode leading to reduced beam quality and oscillation efficiency
Solution Approach 1:
The lower electrode is designed with non-uniform area density, having a first area density in a first region and a second area density in a second region. This local variation in electrode properties allows for optimized current distribution that maintains single-mode operation while achieving high output power through increased beam cross-section.
Solution Approach 2:
The area density parameter of the lower electrode is changed across different regions to control the current density distribution. By adjusting this parameter, the patent achieves uniform carrier distribution in the active layer, preventing spatial hole burning and maintaining stable single-mode oscillation at high power levels.
3Power
If the driving current is increased to obtain high output power, then the output power is improved, but gain saturation occurs due to spatial hole burning preventing high output operation
Solution Approach 1:
The area density parameter of the lower electrode is modified to change the current density distribution pattern. This parameter change ensures that current is distributed more uniformly across the active layer, preventing the formation of high-current-density regions that cause spatial hole burning and gain saturation.
Solution Approach 2:
Different regions of the lower electrode are assigned different area densities to create a tailored current distribution profile. This local optimization prevents uniform current overload that leads to spatial hole burning, allowing sustained high-power operation without gain saturation.
4Reliability
If uniform carrier distribution is achieved through divided electrodes, then the transverse mode stability is improved, but the device structure and current injection system become more complex
Solution Approach 1:
The lower electrode is designed with spatially varying area density rather than being divided into separate electrodes. This approach achieves uniform carrier distribution through continuous variation in electrode properties, maintaining transverse mode stability while avoiding the structural complexity of multiple discrete electrodes.
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 design achieves high-output characteristics with stable transverse mode, efficient current injection, and reduced speckle noise, enabling applications in high-power laser projectors and optical systems with improved reliability and power efficiency.
Implementation Method 1
a pair of electrodes for injecting carriers into the active layer; injection of current from one electrode into the active layer is carried out with different current densities
Implementation Method 2
an external mirror for increased resonator length
Implementation Method 3
an active layer disposed on a semiconductor substrate; when a driving voltage is applied between the upper electrode and the lower electrode and a current is injected into the active layer, light is generated in the active layer
Data Source
AI summary
A surface emitting laser includes an active layer disposed on a semiconductor substrate, and a pair of upper and lower electrodes for injecting carriers into the active layer. The plane surface of the lower electrode is shaped into a star so that injection of current into the active layer from the lower electrode is carried out with a high density at the center of the lower electrode and with a low density at its periphery part. In the surface emitting laser, the density distribution of the carriers injected into the active layer corresponds to the power distribution of light inside the active layer. Thereby, hole burning due to an increase in the current density in the region of the active layer corresponding to the peripheral part of the electrode is avoided, and the transverse mode stability during high output operation is significantly enhanced to improve high-output characteristic.