On-Chip Photonic MEMS Coupled-Cavity Spectrometer

This letter introduces a monolithically integrated microspectrometer based on triple cavities operating in a coupled configuration. Two scanning cavities are sandwiching a static one, where the latter is displaced using an electrostatic comb-drive actuator. The whole structure is self-aligned by photolithography and etched on silicon-on-insulator substrate using deep etching technology. The input light is injected into the chip and the output light is captured using an extended InGaAs photo detector. Thanks to the low-finesse cavities and proper design dimensions, the device is configured as a Fourier Transform Infra-Red (FTIR) spectrometer. A spectral range of 1250–2600 nm is achieved with a spectral resolution of 16 nm at
$1.55~\mu \text{m}$
wavelength. The proposed configuration requires only one third of the actuator travel range compared to the conventional Michelson interferometer with the same spectral resolution. Moreover, the footprint of the cavities is very compact occupying an area of 0.37 mm
²
only.