An alternative light source for coherent anti-Stokes Raman scattering (CARS) microspectroscopy based on red-shifted solitons in a polarization-maintaining photonic crystal fiber (PM-PCF) is experimentally demonstrated. By coupling femtosecond pulses into the anomalous dispersion region of the fundamental mode of a PM-PCF along the slow and fast axes, the red-shifted solitons generated can be used as the Stokes beams when the pump pulses are chosen as the pump beams. Through the process of red-shift, the frequency differences of the pump-Stokes beams are tunable in the ranges of 0 to 4068 cm−1 and 0 to 4594 cm−1, respectively. Moreover, because of the well maintained polarization states of the pump and Stokes beams and the high output powers of the solitons, CARS microspectroscopy using the proposed source will have a high signal-to-noise ratio and short data acquisition time. CARS microspectroscopy based on the proposed all-fiber light source can be used for studying a wide range of vibrational Raman spectra.
We develop a simple iterative model to simulate a laser with homogeneous gain and intensity dependent loss. Simulation
results show that a laser with homogenous gain can operate at multiple wavelengths if the intensity-dependent loss
exhibits saturable transmitter characteristics. Our results also show that for nonlinear losses that have both saturable
transmitter and saturable absorber characteristics, such as arises from nonlinear optical loss mirrors (NOLM) or
nonlinear polarization rotation (NPR), the multiwavelength output power spectrum can become very flat. The laser can
also exhibit periodic and chaotic behaviors. We find that the same theoretical model can also be used to describe multipulsing
dynamics of mode-locked lasers when the cavity energy increases. Near the multi-pulsing transitions, both
periodic and chaotic behavior can be observed as operating states of the laser cavity. Our iterative model provides a
simple geometrical description of the entire multi-pulsing transition behavior as a function of increasing cavity energy.
The model captures all the key features observed in experiments, including the periodic and chaotic mode-locking
regions, and further provides valuable insight into laser cavity engineering for maximizing performance.