By directly writing with a femtosecond laser, researchers at the University of California–Davis and the Missouri University of Science and Technology (Rolla, MO) have tested several types of zinc phosphate glass to see if they are suitable substrates for laser-writing of waveguides. The beam from a Ti:sapphire laser emitting 180 fs pulses at a 1 kHz repetition rate, and with pulse energies ranging from 0.2 to 4 µJ, was focused by a 0.40 NA microscope lens into the glass and laterally scanned at a 50 µm/s speed. One glass out of the five tested, a glass with an oxygen-to-phosphorus ratio of 3.25 (60ZnO-40P2O5 glass), worked well for the process, showing a positive refractive-index change of up to 5 × 10-4.
The laser-written areas were examined in white light under a microscope, revealing an obvious waveguide structure only in the one glass candidate. Under both white light and 660 nm transmission, the waveguide showed a circular Gaussian near-field profile. The far-field profile at 660 nm was circular. A loss of 6.69 dB over 3 mm was observed, likely caused by pre-existing flaws in the glass sample, say the researchers.
Contact Luke Fletcher at [email protected].
