Direct-write waveguides and structural modification by femtosecond laser pulses

Embedded waveguides and their optical properties in bulk silicate glasses fabricated by femtosecond (fs) laser pulses (800 nm, <120 fs, at 1 kHz) are reported. Experimental results show that there is a narrow operating window for our system to produce low loss waveguides. An angular dependence of light transmission measured between two crossed polarizers on these laser-modified regions suggests that these regions possess an optical birefrigent property. Furthermore, the optical axes of laser-induced birefringence can be controlled by the polarization direction of the fs laser. Permanent optical birefringence induced by the fs laser pulses can be produced in amorphous silica, and borosilicate glass. Raman spectroscopy of the modified glass shows a densification and reconstruction of silica network in the glass. Results show that the amount of laser-induced birefringence depends on pulse energy level and the number of accumulated pulses. Mechanisms that contribute to the observed laser induced birefringence behavior are discussed.