Spectral broadening in femtosecond laser written waveguides in chalcogenide glass

Nonlinear spectral broadening to 200 nm, from an initial width of 50 nm, has been demonstrated in galliumlanthanum sulphide glass waveguides from 1540 nm, 200 fs pulses at 30 nJ/pulse. A formation mechanism ispresented for these femtosecond laser written waveguides, based on optical characterization and comparisonsto previous work. Two different types of waveguide are identified. One has a characteristic long narrow structureand is formed through filamentation caused by self-focusing. The other has a characteristic “teardrop”structure, which is formed by a type IIA photosensitivity mechanism and cumulative heating of glass arounda central laser-exposed region