Photonic microwave time delay using slow- and fast-light effects in optically injected semiconductor lasers

This study numerically and experimentally investigates a photonic approach for microwave time delay, which takes advantage of the redshift of the laser cavity resonance induced by external optical injection in a semiconductor laser. The strong enhancement around the redshifted cavity resonance not only amplifies the power, but also shifts the phase of the microwave signals carried by the optical injection. Such a microwave phase shift is approximately linear over a few gigahertz, leading to a constant microwave time delay over the frequency range. A different time delay can be achieved by simply adjusting the injection power or frequency. For the microwave frequencies up to 40 GHz investigated in this Letter, a continuously tunable range of more than 80 ps in time delay is achieved over an instantaneous bandwidth of approximately 7 GHz. The quality of the data carried by the microwave signals is mostly preserved after time delay. Thus, a bit-error ratio down to 10^-9 at 2.5 Gb/s is achieved with a possible detection sensitivity improvement of 5 dB.