S-resonator with an end reflector

An S-resonator with an end reflector (SRER) is analyzed in terms of its resonance conditions and directional properties. An S-resonator has a main fiber ring to which is attached an S-shaped fiber by means of two couplers. Compared to the basic S resonator (BSR), the SRER has a highly reflecting reflector at a free end of one of the coupler ports. Because of the complex recirculating routes in the two resonators, their characteristics depend strongly on the coupling coefficients of the couplers; the phase resonance condition for the subcavity can even be shifted from an even to an odd integer of /spl pi/, or vice versa. The new resonator can offer a higher clockwise over counterclockwise circulating intensity ratio. This can be very useful in the design of a ring fiber laser without an isolator.