Abstract

Researchers have generally agreed that stimulated Raman scattering (SRS) must be avoided if high-quality fiber-and-grating pulse compression is to be achieved. We investigate depletion of 1.06-μm pulses by multiple-order SRS in single-mode fibers and carefully examine the implications for subseqeunt pulse compression. Intense SRS (with walk-off) clamps the pump pulse energy and steepens its rising edge; subsequent self-phase modulation results in nonsymmetric spectral broadening and a nonlinear chirp. Attempts at compression lead to asymmetric compressed pulses with broad energetic wings. As the laser power is increased, group velocity dispersion helps to linearize the frequency chirp; at powers high enough for third Stokes generation (1.9 W in our 400-m fiber), more than 80 % of the spectrum is compressible. In these conditions highly stable transform-limited pulses as short as 600 fs are obtained. We describe the evolution of the power spectrum and frequency chirp and the role of group velocity dispersion as a function of optical power in the fiber. Pulse compressibility is discussed, and stabilization due to multiple-order Raman scattering is emphasized. Finally, we discuss high-resolution picosecond pulse shaping and encoding made possible by Raman stabilized pulse compression and propose that such encoding could be utilized for an optical code-division multiple-access self-routing switch.

© 1987 Optical Society of America