Abstract
The optical sources with high spectral brightness enhance the signal-to-noise ratio which is helpful in spectroscopic application. The spectral compression in a single mode fiber was first observed and it was later satisfactorily explained where the cause of spectral narrowing was attributed to self-phase modulation acting on a negative-chirped pulse. Our approach for spectral compression is using a linear ramp dispersion-increasing fiber (DIF), which is reverse processes of adiabatic soliton temporal compression. However, the feasibility for spectral compression would be seemingly limited by the dispersion ramp of DIF. In our numerical analysis, it would be possible that the real spectral compression ratio exceeds the ideal fiber limitation. In experiment, we prove that a stretch-pulse mode locked fiber laser with 112fs pulse width reaches the spectral compression ratio of 28.6 which the number is beyond ideal ratio of 22.5. Recently, the waveform-dependent spectral compression within a normal dispersive photonic crystal fiber was addressed. In our calculation, we analyze the feasibility for spectral compression over various waveform pulses and point out that all-normal dispersion (ANDi) fiber laser pulses could give higher spectral compression ratio than hyperbolic secant and Gaussian pulses. Using a home-made ANDi laser as optical source, the spectral compression ratio of 45 can be achieved experimentally.