VECSEL Partially Reflecting Element Reduces Pump Power
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Surface emitting lasers, particularly those in the III-nitride material system, face challenges in achieving sufficient power output due to high pump power requirements, which limits their efficiency and effectiveness in various applications.
Innovation Solution
Incorporating a partially reflecting element (PRE) within the laser optical cavity of vertical external cavity surface emitting lasers (VECSELs), which enhances the recycling of laser radiation and increases the electric field intensity in the active region, thereby reducing the threshold power needed for lasing and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional VECSEL structure without a PRE is used, then the device complexity is low, but the pump power requirement is high and lasing efficiency is poor
Solution Approach 1:
A partially reflecting element (PRE) is introduced as an intermediary component within the optical cavity, positioned between the gain element and the external out-coupling reflector. The PRE has reflectivity of 30-70% at both pump and lasing wavelengths, serving as a mediator that recycles both pump and laser radiation back into the active region, thereby reducing the threshold pump power requirement while maintaining manageable device complexity through a single additional optical element
Solution Approach 2:
The optical cavity parameters are modified by introducing the PRE with specific reflectivity characteristics (30-70% at pump wavelength and 30-70% at lasing wavelength). This parameter change transforms the cavity's energy recycling behavior, allowing sustained oscillation at lower pump power levels by adjusting the balance between coupling efficiency and internal recycling without fundamentally redesigning the entire device architecture
2Power
If pump power is increased to achieve sufficient power output, then the power output increases, but heat-related damage risk increases and efficiency decreases
Solution Approach 1:
The PRE enables continuous recycling of both pump radiation and lasing radiation back into the active region, creating a sustained useful action that maintains lasing at lower average power levels. This continuous recycling mechanism ensures that photons multiple-pass through the gain medium, extracting more energy per unit of input pump power and reducing waste heat generation
Solution Approach 2:
The PRE creates an optical feedback mechanism where a portion of the lasing radiation is reflected back into the active region, reinforcing the stimulated emission process. This feedback loop allows the system to maintain stable oscillation at lower pump power thresholds, reducing the need to operate at high power levels that would generate excessive heat
3Illumination intensity
If a PRE with high reflectivity is used, then the electric field intensity in the active region increases, but the pump radiation absorption decreases
Solution Approach 1:
The PRE reflectivity parameters are optimized to specific ranges (30-70% at pump wavelength and 30-70% at lasing wavelength) to balance two competing requirements: sufficient reflection to build up electric field intensity for low threshold operation, and sufficient transmission to allow pump radiation to reach and be absorbed by the active region. This parameter optimization resolves the contradiction by finding the optimal middle ground
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 introduction of a partially reflecting element within the VECSEL cavity reduces the required pump power for lasing, enhances the electric field intensity, and increases lasing efficiency, allowing for more effective power output while minimizing heat-related damage.
Implementation Method 1
The partially reflecting element (PRE) has reflectivity of between about 30% and about 70% for radiation at the lasing wavelength and reflectivity of between about 30% and about 70% for radiation at the pump wavelength
Implementation Method 2
an active region arranged between the DBR and the out-coupling reflector, the active region configured to emit radiation at a lasing wavelength, λlase
Implementation Method 3
The PRE comprises a distributed Bragg reflector comprising a number of layer pairs, each layer pair comprising a first layer of AlGaN and a second layer of GaN
Data Source
AI summary
Surface emitting laser structures that include a partially reflecting element disposed in the laser optical cavity are disclosed. A vertical external cavity surface emitting laser (VECSEL) structure includes a pump source configured to emit radiation at a pump wavelength, λpump, an external out-coupling reflector, a distributed Bragg reflector (DBR,) and an active region arranged between the DBR and the out-coupling reflector. The active region is configured to emit radiation at a lasing wavelength, λlase. The VECSEL structure also includes partially reflecting element (PRE) arranged between the gain element and the external out-coupling reflector. The PRE has reflectivity of between about 30% and about 70% for the radiation at the lasing wavelength and reflectivity of between about 30% and about 70% for the radiation at the pump wavelength.