Actively Tunable Filter Components (ATFCs) Using Phase Change Materials (PCM) for Scientific Instrumentation

Abstract:

The presentation addresses the challenge in improving the key scientific component metrics of Size, Weight, and Power (SWaP) associated with active tuning filter components (ATFCs). The team at NASA LaRC, working with collaborators, developed an ATFC, an all-solid-state tunable filter, based on a Phase Change Material (PCM) which can operate across the visible and infrared spectrum. Optical filters are critical components in a plethora of NASA Earth and Space science missions.

The challenge: The optical filter wheel, when combined with multiple Fabry-Perot filters are used for many NASA missions including SAGE-IV and SCIFLI (Scientifically Calibrated In-Flight Imagery). Conventional Fabry-Perot filters offer discrete, static passbands, thus requiring laser filter wheels to accommodate many individual filters. The filter wheel has moving parts, has slow response times and/or provides limited spectral resolution.

Our solution: The ATFC is a single-component tunable filter which has the advantage of a robust and continuous tuning bandwidth, allowing for a single component to replace the multiple filters required by the filter wheel. Our major advances include:
• A new design concept marrying two distinct physical phenomena: PCM and extraordinary optical transmission are independently well-known. However, by combining their specific benefits in a single novel design, unexplored capabilities have been demonstrated.
• Continuously tunable, reversible, operation across the spectral band of interest: The utilization of optically switched, partially crystalline phases of PCM allows for a near continuum of states over the MWIR waveband.
• Spectrally agnostic, robust design: A straightforward design modification permits operation from the visible to the MWIR spectral bands, with no major design modifications required; the design is spectrally agnostic.
• High transmission efficiency and narrowband performance: Our devices have unrivalled optical performance characteristics.
• Real-time thermal imaging using our filters: Using a conventional IR-camera, real-world applicability is shown through tunable multispectral thermal imaging.

Future direction: The reduction in volume and weight of the ATFC will enable an instrument to fit within a SmallSat configuration, freeing up available space for other components and reducing the overall cost of the payload. Therefore, the ATFC would become a central component for future Earth science measurement instrumentation. Additionally, the ATFC is applicable to wider multi-and hyper-spectral imaging; from applications in chemical sensing, astronomy, radiometry, and biomedical diagnosis. In the presentation, customizable wavelength filters and their applications will be discussed as well as the future direction of the technology.

The team: Mr. Scott Bartram, Mr. Stephen Borg, Dr. Matthew Julian, and Dr. Calum Williams comprise the team. The team acknowledges support from the NASA LaRC FY19 and FY20 CIF/IRAD Program.

Presenters: Dr. Hyun Jung Kim