Study On Group Velocity Manipulation In Optical Fibers

Slow and fast light have some important applications in all optical communication, optical sensor, enhancement of nonlinear effect and optical phase array antenna, etc. Controlling the group velocity in fiber has been attracted much attention for it has some advantages such as work at room temperature, compatible with fiber communication systems and so on.The techniques of tunable slow and fast light have been widely studied. However, all of these techniques are still far from practical application.We have studied the slow and fast light in fiber. We proposed several new approaches to generate slow and fast light. Compare with other techniques, each of these new schemes has its advantages and more applicable to practical systems.We first proposed controllable self-induced SBS fast-light enhanced in an optical fiber ring. By circulate the Stokes light back into the cavity for Brillouin oscillation, larger advancement and slope efficiency have been obtained. Our experiments show that the largest advancement of 10 ns when the pump power increasing to 16.25 dBm. The advancement is almost propotional to the input power, the advancement per pump power is about 1.67 ns/dBm.We first experimentally demonstrated tunable slow light in active fiber Bragg grating. When we vary the pump power, the group delay variation which caused by the variation of the imaginary part of the gain coefficient is negligible. In active fiber grating, the real part of the gain coefficient is varying with the pump power. Thus, the detuning is varying with the pump power. If the central wavelength of the signal light is set near the side band of the grating, we can obtain large group delay variation when we varying the pump power. In the experiment, up to 0.9 ns group delay variation has been obtained. We believe this simple, feasible, cost-effective slow light approach will have a great future in developing optical data synchronization and optical phase array antenna. We first demonstrated group velocity manipulation in active fibers using cross gain modulation: from ultraslow to superluminal propagation.We first demonstrated group delay variation with the modulation phase difference between the signal light and the saturating light. We observed ultraslow propagation with a small group velocity of 1.69×106 m/s and superluminal propagation with a negative group velocity of ?3 .3×105 m/s in a 14 m 400 ppm Er doped fiber when the modulation frequency is 20 kHz. In addition, we experimentally demonstrated equidirectional XGM slow light and analyzed the group delay variation with the modulation phase difference at different modulation frequencies. Our approach has advantages such as larger signal bandwidth, larger fractional delay, and working at any wavelength in EDF gain band.We first analyzed slow and fast light in active fiber ring resonator. Compare with other schemes, our method has some advantages such as more convenient, wider bandwidth, higher output power and so on.