Tapered semiconductor amplifiers for optical frequency combs in the near infrared

Abstract

A tapered semiconductor amplifier is injection seeded by a femtosecond optical frequency comb at 780nm from a mode-locked Ti:sapphire laser. Energy gains of more than 17dB(12dB) are obtained for 1mW(20mW) of average input power when the input pulses are stretched into the picosecond range. A spectral window of supercontinuum light generated in a photonic fiber has also been amplified. Interferometric measurements show sub-Hertz linewidths for a heterodyne beat between the input and amplified comb components, yielding no detectable phase-noise degradation under amplication. These amplifiers can be used to boost the infrared power in f-to-2f interferometers used to determine the carrier-to-envelope offset frequency, with clear advantages for stabilization of octave-spanning femtosecond lasers and other supercontinuum light sources.