Reliable refractive-index adjustment in Ge-doped silica-core planar waveguides by high-repetition rate femtosecond laser pulses Available to Purchase

Laser trimming of phase errors are becoming vitally important technologies for silica-based planar waveguide devices such as arrayed-waveguide gratings (AWGs), directional couplers, etc. for Dense Wavelength Division Multiplexing (DWDM). Conventional phase trimming technologies based on UV excimer lasers have serious problems such as delicate and time consuming preparation for hydrogen-loaded sensitization processes, requirement of mask-processes and difficulty in real time, high-speed phase-error correction, etc. This paper presents some representative features of our novel technology for rapid and reliable refractive-index adjustment in germanosilica-based planar waveguides utilizing high-repetition rate ultrashort laser pulses. Infrared (800nm), 200 kHz, 150 fs pulses were used to increase refractive index of the planar waveguides with 100 µm/s scanning speed. With increase in the irradiation power density, maximum refractive-index increase up to ~2 × 10⁻³ was obtained with distinct saturation at around 2.2 TW/cm². No decay in the refractive index change was observed even after annealing at 200°C for 100 hours. This highly stable refractive-index increase is in consistent with the phenomena of permanent refractive-index increase observed by Kondo, et al. in Ge-doped silica-core glass fibers irradiated by ultrashort laser pulses.