Performance of single- and double-ring resonators using 3*3 optical-fiber coupler

This paper investigates theoretically the transmission characteristics of single- and double-ring resonators using 3*3 optical-fiber couplers. Two configurations of a 3*3 coupler are considered: configuration A, with the three fibers centered at the vertices of an equilateral triangle, and configuration B, with their centers aligned in a straight line. It is found that a ring resonator using configuration A does not show any performance improvement over ring resonators using 2*2 couplers. On the other hand, a single-ring resonator using configuration B has a performance close to resonators using 2*2 couplers. It is also shown that a double-ring resonator using a 3*3 coupler exhibits resonance with a double peak, which may find application in the filtering of coherent frequency-shift keying (FSK) signals after optical amplification in an optical-fiber line repeater.>