Femtosecond laser written 16.5 mm long glass-waveguide amplifier and laser with 5.2 dB cm−1 internal gain at 1534 nm

A 16.5 mm long, heavily doped erbium–ytterbium phosphate glass-waveguide amplifier was fabricated by the femtosecond laser (fs-laser) inscription technique. The femtosecond laser inscription of waveguides was carried out at 500 kHz repetition rate using a 0.68 NA aspheric lens. The energy deposition profile in the dielectric material was initially simulated using a generalized adaptive fast-Fourier evolver (GAFFE) algorithm. The size and shape of the guiding structures were carefully controlled by the slit shaping technique to reduce the coupling losses, with achievable values down to less than 0.1 dB. Rigorous simulations of the response of the active waveguides were carried out to optimize their performance as optical amplifiers. A maximum of 8.6 dB internal gain at 1534 nm was obtained upon bidirectional laser pumping at 976 nm, leading to a gain per unit length of 5.2 dB cm−1. Laser action was also achieved for both ring and linear cavity configurations. (letter)