Spectral Filters – IR Region – Remote Thermal Imaging

High-performance wavelength discrimination in the long-wave infrared region (LWIR) of the electromagnetic spectrum (wavelength range from 8 microns to 12 microns) is desirable for civilian and military applications. Of particular importance is to achieve on-chip passive thermal imaging with spectral filters, allowing remote target recognition without requiring any light source for illumination since objects emit radiation in the LWIR spectral band simply due to their room temperature.

Microelectromechanical systems (MEMS) enable the development of lightweight field-portable spectroscopic devices for optical remote imaging and sensing. These systems hybridize MEMS-based Fabry-Pérot interferometers (FPIs) with either single-point infrared detectors or focal plane imaging arrays. FPIs provide a spectrometer architecture that is compatible with thin-film surface-micromachined MEMS. These FPIs consist of two mirrors (generally consist of a pair of distributed Bragg reflectors (DBRs), separated by an optical cavity in a MEMS implementation).

A new study gives further insights into the MEMS-based implementation of spectroscopic systems. A proof-of-concept for large-area narrowband MEMS-based fixed cavity FPIs operating in the LWIR region has application in developing portable micro-spectrometers. This work reports for the first time on using low-index BaF2 thin films in combination with Ge high-index thin films (spectral filters) for such applications. These MEMS devices are relevant to remote infrared imaging and spectroscopic sensing for target identification and space situation awareness.

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