We have proposed channel drop filters based on a combination of Fabry–Perot (F–P) resonators in a two-dimensional photonic crystal with a triangular lattice of air holes. By tuning the separation, the radii of air holes between F–P resonators, and the length of two F–P resonators, we can selectively improve filter characteristics and obtain a forward-dropping efficiency of 95% and a backward-dropping efficiency of 90% at desired resonance frequencies. For the case where two F–P resonators are directly connected without separation, it forms a ring behavior and has a backward-dropping efficiency of 75% at resonance. Moreover, we investigate the dependence of optical bistability in one of the optimized resonators on initial frequency detunings. A switching speed of 2ps is obtained. By decreasing the initial frequency detuning, overshoot on the switching-on power can be greatly suppressed.