Observation of Slow Light in Dot-Bragg Grating Waveguides Inscribed by Femtosecond Laser

We demonstrate the slow-light characteristics in a first -order dot-Bragg grating (DBG) waveguide inscribed in bulk glass using a femtosecond laser. The light-guiding waveguide is fabricated using a two-laser-passes inscription process, with center distance and offset optimization to enhance the dot array-waveguide interaction, leading to improved transmission spectrum. Experimental results show that the DBG achieves a maximum transmission dip of 12.5 dB, with a group delay of ~43 ps and a slow-down factor of 1.45.