Chip-Scale UV Laser Source with Integrated Frequency Doubling
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Solution Overview
Problem
Existing chip-scale ultra-violet lasers are bulky, have low wall-plug efficiencies, and achieve low output power due to inefficiencies in material quality and frequency doubling methods, making them unsuitable for practical applications.
Innovation Solution
A chip-scale ultra-violet laser source with a substrate, tapered gain medium, nonlinear crystal, and phase modulator, integrated with a master laser diode for coherent beam combining and phase locking, achieving high power and efficiency through intra-cavity frequency multiplication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If diode pumped solid-state lasers, gas lasers, or fiber lasers are used for chip-scale UV generation, then UV lasing can be achieved, but the devices become bulky and wall-plug efficiency drops below 2%
Solution Approach 1:
The patent combines the laser gain medium, nonlinear crystal for frequency doubling, and cavity mirrors into a single integrated chip-scale device. This merging eliminates the need for separate external frequency doubling components, reducing overall device size and improving wall-plug efficiency by minimizing optical loss interfaces while maintaining high UV output power
Solution Approach 2:
The patent uses temperature tuning of the nonlinear crystal to optimize second harmonic generation efficiency. By controlling the temperature parameter of the nonlinear optical material, the system achieves maximum conversion efficiency from fundamental wavelength to UV frequency, thereby improving wall-plug efficiency while maintaining compact dimensions
2Power
If second harmonic generation outside the cavity is used, then UV lasing can be achieved, but output power levels become extremely low
Solution Approach 1:
The nonlinear crystal for second harmonic generation is integrated directly inside the laser cavity, merging the frequency doubling function with the laser oscillation process. This allows the UV light to be generated within the high-intensity fundamental beam environment of the cavity, dramatically increasing output power compared to external frequency doubling while the cavity structure provides natural optical feedback and amplification
3Illumination intensity
If AlGaN material with high Al mole fraction is used for shorter UV wavelengths, then emission wavelength decreases, but material quality deteriorates and wall-plug efficiency drops to 0.014%
Solution Approach 1:
The patent uses a nonlinear optical crystal as an intermediary to convert the fundamental laser wavelength to the desired UV wavelength through second harmonic generation. This mediator approach avoids the need to directly generate UV light with poor-quality AlGaN materials, instead using high-quality GaN or AlGaN at longer wavelengths and converting to UV optically, thereby achieving short UV wavelengths without suffering from material quality deterioration
Solution Approach 2:
The patent replaces direct electrical injection into high-Al-content AlGaN laser diodes with a two-stage process: electrical injection into lower-Al-content GaN/AlGaN laser diodes followed by optical frequency doubling. This substitution of the generation mechanism achieves UV emission with wall-plug efficiency greater than 10% by avoiding the material quality issues inherent in direct high-Al-fraction UV laser diodes
4Power
If frequency doubling with external crystals is used, then UV output can be achieved, but conversion efficiency remains low at 4.5%
Solution Approach 1:
The frequency doubling crystal is merged with the laser cavity structure, eliminating separate external frequency doubling stages. This integration allows the fundamental beam to undergo multiple passes through the nonlinear crystal within the cavity, accumulating conversion efficiency that far exceeds single-pass external frequency doubling, achieving overall conversion efficiency greater than 10% while reducing device complexity
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 solution produces high-power (>1 W CW) ultra-violet laser light with high spectral and spatial quality, achieving wall-plug efficiency greater than 10% in a compact package, overcoming material limitations and inefficiencies of previous technologies.
Implementation Method 1
a nonlinear crystal coupled to the outcoupler at a front facet of the nonlinear crystal, wherein the front facet has a first coating that has anti-reflectivity (AR) to a fundamental wavelength of the laser element and high reflectivity (HR) to ultra violet wavelengths
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A chip scale ultra violet laser source includes a plurality of laser elements on a substrate each including a back cavity mirror, a tapered gain medium, an outcoupler, a nonlinear crystal coupled to the outcoupler with a front facet that has a first coating that is anti-reflectivity (AR) to a fundamental wavelength of the laser element and high reflectivity (HR) to ultra violet wavelengths, and has an exit facet that has a second coating that has HR to a fundamental wavelength of the laser element and AR to the ultra violet wavelengths, a photodetector coupled to the outcoupler, a phase modulator coupled to the photodetector and coupled to the back cavity mirror, and a master laser diode on the substrate coupled to the phase modulator of each laser element. Each laser element emits an ultra violet beamlet and is frequency and phase locked to the master laser diode.