Dispersionless slow light using gap solitons

The ability to slow down and delay optical pulses is an intriguing physical phenomenon with significant applications, such as in telecommunications. It is essential for these applications that the phenomenon has enough bandwidth, so that it can respond sufficiently fast to the very short light pulses that will carry the information in future telecommunications systems. However, typical slow-light systems exhibit dispersion, which distorts the pulses on propagation, leading to loss of information, thereby limiting the bandwidth. This limitation imposes a trade-off between the acquired delay and the system's bandwidth. By introducing nonlinearity, however, the pulse can travel slowly and also remain undistorted over arbitrarily long propagation lengths by the formation of a soliton. We observe such solitons in a fibre Bragg grating, and show that subnanosecond pulses travel at 16% of the speed of light, without broadening.