Stable coherent coupling of laser diodes by a volume Bragg grating in photothermorefractive glass

Abstract

Two separate laser diodes emitting near 980 nm were coupled by a thick volume Bragg grating recorded in a photothermorefractive glass. The coupled diodes emitted at the same wavelength with a spectral width narrowed to below the resolution of the spectrum analyzer (<30 pm). Coherent emission at a pumping level greater than five times above the threshold was observed for several months with near-unity visibility of the interference pattern.

Nonlinear photosensitivity of photo-thermo-refractive glass by high intensity laser irradiation

“…High efficiency diffractive optical elements recorded in PTR glass have shown robustness under harsh conditions of utilization such as elevated temperatures and high power laser irradiation. These elements have been used for spectral beam combining [3], selection of transverse and longitudinal modes in different laser resonators [4], high brightness semiconductor lasers [5], etc. However, all of these diffractive optical elements were recorded via linear excitation of Ce 3+ (photo-sensitizer in PTR glass) within its spectrum of photosensitivity (280-350 nm).…”

High-Power Fiber Lasers

“…VHGs recorded in glass have been first suggested for use in coherent coupling of diode lasers in Refs. [37,38]. The basic idea of this approach is to use volume Bragg gratings to create extremely dispersive external resonators for coherently combining individual lasers.…”

“…The VHG is acting within this approach as a common output coupler. Venus et al [37,38] coherently coupled two 980-nm diode lasers and produced single wavelength output for both diodes with spectral width narrowed to \30 pm. Similar technology can be applied for high-power fiber lasers using coherent beam combining and is potentially capable of achieving 100-kW level of coherent fiber laser radiation.…”

Volume Bragg Gratings in PTR glass – New Optical Elements for Laser Design

“…A new approach to this problem was demonstrated in publications [22,23] where extremely narrow-band PTR VBGs were used for radiation exchange between two laser diodes. It was demonstrated that coherent radiation from two laser diodes placed at separated stages could be observed for a year at driving current exceeding 4 thresholds.…”