General filter architecture using co-and counterpropagation signals are studied. A specific configuration based on a Sagnac loop within a ring resonator is analyzed. Novel tuning, apart from conventional tuning,is achieved by changing the coupling ratio of a coupler through the adjustment of the equivalent loop length. Full equations describing the filter behavior in passive and active configurations, and simple closed-form formulas to compute the tuning, tolerance, and full-width at half-maximum are reported. The performance of these devices is discussed for their application as selective or channel-dropping ultra-narrow-band filters. The effect of losses and their dispersion properties are also discussed. These devices can be conveniently implemented, using silicon-or InP-integrated optic technology, for they have high free spectral ranges.
© 2005 IEEE
Carmen Vázquez, Salvador Elías Vargas, and José Manuel Sánchez Pena, "Sagnac Loop in Ring Resonators for Tunable Optical Filters," J. Lightwave Technol. 23, 2555- (2005)