Slowing down light to 300  km/s in a deuterium-loaded fiber Bragg grating

We report light propagation with a group velocity of only 300  km/s, a group index of 1010, and a group delay of 42 ns, in a strong apodized fiber Bragg grating 12.5 mm in length. The grating was fabricated in a deuterium-loaded fiber using a femtosecond laser and a phase mask, followed by annealing to reduce residual losses. Data analysis indicates a strong index modulation of 1.98×10(-3) and an ultra-low single-pass power loss of 0.010 dB.