An efficient mm-wave photomodulator is designed based on coupled Fabry–Perot modes in a low-lifetime silicon wafer and an adjacent cavity formed from a transparent reflector, such as indium tin oxide. The modulation of a reflected beam using this coupled-cavity design is increased by a factor of 7 compared with that from an isolated silicon wafer, while also introducing a degree of tunability and maintaining low angular dispersion. For the particular design built and tested, a modulation of 32% is achieved for an extremely low optical illumination of just 0.006 W / cm 2 and with a maximum operation rate of more than 3 kHz. The large increase in modulation, coupled with the flexibility of the design and the fact that all components can be industrially manufactured, makes this photomodulator a promising candidate for many communication, imaging, and sensing applications.

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