This paper reports the generation of record low group velocities, large group delays, and high optical confinements in strong apodized fiber Bragg gratings (FBGs). The gratings were fabricated in deuterium-loaded fiber using an 806-nm femtosecond laser and a phase mask to produce strong apodized index-modulation profiles and low internal loss, followed by annealing to reduce residual losses. In a first FBG of this type with a length of ~25 mm and a non-saturated index modulation we measured a group delay–transmission product of 10.4 ns, the highest ever reported. In a stronger, shorter FBG (12.3 mm in length), a group delay of 42 ns was observed, corresponding to a group velocity of only ~290 km/s and a group index of 1020. In a still shorter and therefore lower loss device (~5 mm) we were able to observe the fundamental mode, and infer a Purcell factor as high as 25.5. These exceptional features are made possible in part by the gratings’ strong index modulation (~2x10^-3) and ultra-low single-pass loss (~0.01–0.015 dB/cm).

Date Published: 10 March 2015
PDF: 8 pages
Proc. SPIE 9378, Slow Light, Fast Light, and Opto-Atomic Precision Metrology VIII, 93780E (10 March 2015); doi: 10.1117/12.2081508

Published in SPIE Proceedings Vol. 9378:
Slow Light, Fast Light, and Opto-Atomic Precision Metrology VIII
Selim M. Shahriar; Jacob Scheuer, Editor(s)