Enhanced fast light in microfiber ring resonator with a Sagnac loop reflector.

We fabricate a microfiber knot-type ring resonator with a Sagnac loop reflector, and control the light velocity using the device. In this structure, light is reflected by the Sagnac loop and passes through the ring resonator twice. Thus, it possesses doubled transmission and group delay comparing with the microfiber ring resonator without the Sagnac loop. We experimentally demonstrate pulse advancement in an under-coupled microfiber knot-type ring resonator with a Sagnac loop reflector. In the experiment, a maximum of approximately 25 ps pulse advancement was achieved for a 5-Gb/s RZ signal.