1.5 μm high-power robust single-frequency waveguide laser

Single-frequency lasers at 1.5 μm are key elements for applications to several fields such as spectroscopy and optical sensing. In many cases device specifications may become very demanding in terms of power, compactness, insensitivity to environmental disturbance and high temporal coherence. Bulk laser cavities are able to provide high output powers but are generally quite sensitive to technical noise and are not compact devices. On the contrary, short fiber lasers and, in particular, waveguide lasers are compact devices with monolithic structures which have the potentialities to satisfy all the requirements previously outlined. However, looking at the literature up to now only few mW output level robust single-frequency waveguide laser were demonstrated. In this paper we demonstrate optimised laser configuration producing more than 20 mW in robust single-frequency operation by using an Er:Yb-doped phosphate glass waveguide only 9-mm long. We also found that single-frequency operation can be obtained by using cavity lengths of up to 60 mm that is, in our opinion, an upper limit value. We believe that 50 mm active waveguides could provide up to 100 mW output power and we report preliminary test. The cavity is formed by two butt coupled fiber-Bragg grating (FBG) mirrors. We conclude that ion-exchange technique is very promising to achieve 100-mW output power level.