Average optical power monitoring in micromirrors

The thermal properties of tip-tilt micromirrors have been analyzed theoretically and measured experimentally for devices operated in air and in vacuum. Typical micromirror thermal conductances are shown to range from 10^-3 W/K for devices operated close to the substrate in air to 10^-5 W/K for devices operated in a vacuum. These results demonstrate that micromirror temperatures are extremely sensitive to the average optical signal incident upon them and can be used as probes of incident power in much the same way as thermal infrared detectors. This has been experimentally demonstrated using a λ = 661 nm diode laser with polysilicon micromirrors, and sensitivities reaching below 70 nW of absorbed optical power, limited by the Johnson and 1/f noise of the micromirrors and measurement system. Average optical power monitoring could be useful in large cross connects or other applications, where the additional integration of a tap/beamsplitter plus photodiode assembly is undesirable