Cascade Raman soliton 1.34-1.65-μm fiber lasers

Abstract

Exploitation of highly efficient stimulated Raman scattering in optical fibers has given rise through a soliton shaping mechanism to a simple source of femtosecond high-power pulses from simple fiber ring laser systems, synchronously pumped by the 100-ps pulses from a cw mode-locked Nd:YAG laser at 1.32 μm.1 Principally, the operation has been limited to the first Stokes band around 1.4 μm (Ar 440 cm-1). The soliton pulse shaping mechanism giving rise to pulses of 100 fs, which as a result of the short interaction length is unable to generate efficiently the higher Raman orders in cascade. By using a dispersion shifted fiber, so that the first Stokes band and the fundamental are in the positive group velocity dispersion regime, highly efficient Raman generation (>50%) is possible in fiber spans 100s of meters. This technique then permits efficient generation of the second Stokes component (centered around 1.5 μm), which if in the region of negative group velocity dispersion can undergo a solitonlike pulse compression.2 In a dispersion shifted fiber ring laser geometry, pulses as short as 170 fs with peak powers of ~4 kW around 1.5 μm have been generated. Further cascade into the third Stokes per mitted similar operation with pulses of ~200 fs.