Characteristics of spectral peaking in optical fibers

Abstract

We investigated multiple spectral peak generation during a coherent supercontinuum generation process with normal-dispersion highly nonlinear fibers both numerically and experimentally. Wideband multiple spectral peak generation was achieved in the 1.6–1.7 μm range using an ultrashort-pulse fiber laser, a CH4 gas cell, and highly nonlinear fiber. The maximum signal-to-background ratio was ∼8.4. Thanks to the normal-dispersion fibers, the induced phase shifts in the absorption spectra were clearly observed on the spectra during the spectral peak generation. The intensity and phase noise properties of the generated spectral peaks were examined, and low noise properties were confirmed. The spectral peaking phenomenon was investigated experimentally in a fiber amplifier. Periodical spectral peaking was successfully observed for a soliton pulse with Kelly sidebands, and the optical pulse experienced absorption in HCN gas. It is expected that spectral peaking occurs for pulses that experience absorption in many different kinds of gas species or those with spectral peaks. This light source and phenomenon will be useful for developing novel optical frequency comb techniques and optical wavelength standards.