Waveguide amplifiers and lasers written by femtosecond laser pulses

Abstract

The fabrication of telecom active devices, such as waveguide amplifiers and lasers, with femtosecond laser pulses is of great industrial interest due to the simplicity, low cost and 3D capabilities of this technology with respect to the standard ones. In this work we will present the various improvements that brought us to demonstrate net gain and the first waveguide laser fabricated with femtosecond laser pulses on an erbium-ytterbium-doped phosphate glass. The first results have been obtained with an amplified, low repetition rate (1 kHz), Ti:Sapphire system. The target of matching the mode field of the fabricated waveguides to that of standard telecom fibers pushed us to develop a novel astigmatic focusing of the writing beam to overcome the asymmetry of the waveguide transverse profile intrinsic in the transversal writing geometry. Despite the circularization of the transverse profile, the high coupling losses allowed only for internal gain in an all-fiber coupling configuration. The best results have been obtained with a very compact, unamplified, diode-pumped Yb:glass laser, with a higher repetition rate (166/505 kHz) and lower energy. In this case, the waveguides exhibited almost perfect mode matching with a telecom fiber allowing coupling losses as low as 0.18 dB and propagation losses of 0.5 dB/cm. Such figures enabled net gain when pumping with 980-nm laser diodes and laser action by terminating the waveguide with two fiber Bragg gratings. These results pave the way to a transfer of femtosecond waveguide writing into the industrial arena for the realization of practical telecom components.