S-resonator with an end reflector

An S-resonator with an end reflector (SRER) is analyzed in terms of its res onance conditions and directional properties. An S-resonator has a main fib er ring to which is attached an S-shaped fiber by means of two couplers, Co mpared to the basic S-resonator (BSR), the SRER has a highly reflecting ref lector at a free end of one of the coupler ports. Because of the complex re circulating routes in the two resonators, their characteristics depend stro ngly on the coupling coefficients of the couplers; the phase resonance cond ition for the subcavity can even be shifted from an even to an odd integer of pi, or vice versa, The new resonator can offer a higher clockwise lover counterclockwise circulating intensity ratio. This can be very useful in th e design of a ring fiber laser without an isolator.