The authors report the experimental demonstration of single-wavelength latching circuits using two 58-angstrom MQW (multiple-quantum-well) bistable etalons operating in both the transmission (AND gate or OR gate) and the reflection (NAND gate or NOR gate) mode. With milliwatt power, these devices operate at room temperature with latching times of approx.1 μs in duration thermal switch-down, which implies that they could be used as latching logic gates in a high-speed photonic switching system. Despite the fact that the etalons are not optimized, and no special procedure is taken to stabilize the laser power, a differential power gain of 4 still obtained. Large contrast is also observed. Calculations for nonsteady-state operations have shown that the differential energy gain vanishes as the pulse duration decreases and approaches the carrier lifetime. This suggests that a reduction of the carrier lifetimes is needed to achieve high-speed, single-wavelength, and cascadable optical logic operations.