Tunable micro-integrated narrow linewidth extended cavity diode laser at 780nm

A compact and tunable micro-integrated extended cavity diode laser (ECDL) on AlN ceramic template in butterfly packaging has developed for rubidium (780.2 nm) atom interferometry. Moveable parts are strictly omitted to provide maximum mechanical stability and reliability. The micro-integrated ECDL uses a volume holographic Bragg grating (VHBG) with a diffraction efficiency of 20% at 780.2 nm and a FWHM bandwith 70 pm based on a littrow configuration possessing an extended cavity length of 5.5 mm. The gain chip in ECDL has curved stripe with high reflecting (99%) on normal side and deep antireflecting (AR) on the tilted one. The curved stripe together with deep AR-coating provides extremely low reflection (<10(-5)) allowing suppression of self lasing and minimizing of gain ripples. The divergent beam from the gain chip is collimated by a fast and a slow axis collimator lens to be able to optimize both axis separately. The VHBG is thermally stabilized by means of a micro-thermoelectric cooler and a micro-temperature sensor to control the emission frequency of the laser module. Coarse tuning is hence accomplished by tuning the temperature of the VHBG, which provides an overall tuning range of > 65 GHz for a temperature range of 25 K with a tuning factor at 2.6 GHz/K. Continuous laser frequency tuning is achieved by sweeping the injection current to the Gain chip for 8.8GHz at -557 MHz/mA. The device provides a short term full-width-half-maximum (FWHM) linewidth of significantly less than 100 kHz and an optical power in excess of 120 mW.