Nonlinear Spectrum Compression of Negatively Chirped Picosecond Pulses in Dispersion-Shifted Telecom Fiber

We investigated both experimentally and numerically self-phase modulation-induced spectrum compression dynamics of negatively chirped picosecond Gaussian pulses in the low-loss dispersion-shifted telecom fiber near its zero dispersion wavelength (ZDW). It was experimentally observed linearly interpolated monotonous increase in spectrum compression ratio (SCR) with negative chirp growth of the incident pulse in the range from -5.9 to -91.9. According to numerical simulations, despite its small values in the vicinity of ZDW, fiber dispersion limits both SCR growth and spectrum compression quality expressed in terms of time-bandwidth product value and energy confinement ratio at larger chirp values (|C| > 100), in a combined action with self-phase modulation (SPM). Having optimized fiber length and pulse energy, we achieved record 49.2-fold spectrum compression of 38.3-ps, 2.08 nJ negatively chirped Gaussian pulses with compressed spectrum FWHM of 0.23 nm and ≈50% energy confinement at 1560 nm wavelength, leading to ≈13.3-times spectral brightness magnification. We believe that results obtained can be promising for ultra-short pulse laser systems development with enhanced spectral brightness.