Double line and tubular depressed cladding waveguides written by femtosecond laser irradiation in PTR glass

Depressed cladding concepts such as double line depressed index and tubular low index cladding waveguide structures were fabricated in bulk photo-thermo-refractive glass using femtosecond laser pulses. Effects of the writing laser power, waveguide geometrical structures and heat treatment on the light guiding properties were investigated. The results show that depressed cladding tubular waveguide design exhibits better guiding performances than double line waveguides in PTR glass. For the tubular cladding waveguide, single and multimode fields can be obtained for a wide processing parameter window. The simulations agree well with the experiment results. Moreover, the normalized frequency can be tuned and the quality of the depressed cladding tubular waveguide can be improved by eliminating uneven stress distribution after heat treatment.