The influence of the different parameters used for the production of double line waveguides in Nd3+ doped TeO2-ZnO glasses by fs laser writing

Abstract

Nd3+ doped TeO2-ZnO glasses with double line waveguides produced by femtosecond (fs) laser writing technique are presented. The waveguides are written directly into these glasses using a femtosecond (fs) Ti:Sapphire laser, operating at 800 nm, delivering 30 fs pulses at 10 kHz repetition rate. Each written line is formed by several collinearly overlapping lines. When double line waveguides are produced, the light is guided in between the two lines and a negative refractive index change is produced in the region of the fs laser’s focus. However, as the absorption of the material at 800 nm (4 I9/2 → 4 F 5/2 + 2 H9/2 transition of Nd3+) is in resonance with the fs laser, the heating of the material makes writing difficult. In this context, the use of several overlapping lines represents a good alternative as the velocity of the writing can be increased to avoid, heating. We report results of output mode profile, beam quality factor M2 and refractive index change for, different parameters used for the fs laser writing. Pulse energies were 15μJ for 4 and 8 overlapping lines and 30 μJ for 2, 4 and 8 overlapping lines and the writing speed was 0.5 mm/s. The present investigation evaluates the best condition for the waveguides inscription, studying the influence of different parameters used in the writing process aiming at future photonic applications.