Femtosecond pulse squeezing limited by stimulated Raman process in optical fibers

Optical fiber-based squeezing with transmission characteristics in the positive, zero, and negative group-velocity dispersion regions was studied, using a femtosecond Cr4+:YAG laser and reflection-type interferometers. The squeezing was limited by a stimulated Raman process-related phenomenon in all the dispersion regions. The primary limiting factor was a phase variation between a Raman soliton and other spectral components that were taken in the soliton through the stimulated Raman process. The maximum squeezing was −3.3 dB, which was obtained within a positive group-velocity dispersion region. Although a polarization-maintaining fiber is generally required as a squeezer, polarization non-maintaining fibers with a small amount of polarization-maintaining fiber are also utilizable.