We have derived the general condition to achieve 100% drop efficiency in the resonant tunneling-based channel drop filters of a three-port system with reflection feedback. According to our theoretical modeling based on the coupled mode theory in time, the condition is that the Q-factor due to coupling to a bus port should be twice as large as the Q-factor due to coupling to a drop port and the phase retardation occurring in the round trip between a resonator and a reflector should be a multiple of 2π. The theoretical modeling also shows that the reflection feedback in the three-port channel drop filters brings about relaxed sensitivity to the design parameters, such as the ratio between those two Q-factors and the phase retardation in the reflection path. Based on the theoretical modeling, a five-channel drop filter has been designed in a two-dimensional photonic crystal, in which only a single reflector is placed at the end of the bus waveguide. The performance of the designed filter has been numerically calculated using the finite-difference time domain method. In the designed filter, drop efficiencies larger than 96% in all channels have been achieved.
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