Sub-MHz Linewidth UV Laser Diode for Metrological Applications

Compact highly coherent visible light sources are cornerstones for metrological applications such as the implementation of integrated atomic clocks. Footprint reduction of photonic components relies on the availability of integrated narrow-linewidth lasers [1]. At short wavelengths from ultraviolet (UV) to blue, laser diodes are commercially available but they often exhibit a multimode longitudinal spectrum detrimental to the above mentioned applications. Optical feedback consists in the use of an external cavity to filter out a narrow part of the initial spectrum and to drive the laser diode at the filter central wavelength [2]. The optical properties of the laser diode can be drastically enhanced in term of threshold, linewidth and stability. In this paper, we propose a compact sub-MHz linewidth UV laser diode laser (UV FGL) based on a 2 cm fiber Bragg grating external cavity.