Coherence-preserved amplification of spectral peaked optical frequency comb using fiber Raman amplifier

Spectral peaking, which converts sharp intensity or phase modulation into an intense spectral peak, is a useful phenomenon for comb mode selection, which is important for highly sensitive spectroscopy. However, the optical power of the selected peak is small, and power scaling is an important technical issue. In this work, we investigated the power scaling of a spectral peaked optical frequency comb at 1.65 μm using a fiber Raman amplifier. A 1 km length of Raman fiber was used as the gain fiber, and the fundamental characteristics of amplification were examined for a CW beam, a spectral peaked comb, and a conventional pulsed comb. Coherence-preserved, low-noise amplification with 22 dB gain was achieved for the spectral peaked comb. Low-noise similariton-like amplification was demonstrated for the comb pulse input both experimentally and numerically. As far as we know, this is the first power scaling of an optical frequency comb using a fiber Raman amplifier. This technique can be applied to a wide wavelength band, and is very useful for spectroscopic applications.