Demonstration of critical coupling in microfiber loops wrapped around a copper rod

The authors demonstrate critical coupling condition in microfiber loops wrapped around a copper rod. The critical coupling condition is achieved by tuning the coupling coefficient to balance the circulation loss. A maximum extinction of 30 dB has been obtained around the critical coupling point with a quality factor of about 4000. The resonance wavelength can be tuned by applying an electric current through the copper rod. The copper rod, usually deemed as a high-loss medium for handling light at optical frequency, serves as a low-index robust support for achieving critical coupling in the microfiber loops with acceptable loss. (C) 2007 American Institute of Physics.