Phase change material (PCM)-based actively tunable mid-wave IR filters have broad imaging and sensing applications—from probing molecular vibrations in chemical species to detecting radiant thermal signatures. We introduce the Phase-change actively tunable filter (P-ACTIVE) project lead by NASA Langley Research Center with collaborators MIT and the University of Cambridge. It covers background science, experimental and theoretical device performance, as well as recent results obtained from a MISSE-14 mission for space qualification of active metasurface optics and constituent PCM. We conclude with a prospective view of the technology and discuss the potential for these filters to serve multiple NASA missions.
Optical metasurfaces are planar subwavelength nanoantenna arrays engineered to provide on-demand manipulation of light, thereby enabling ultra-compact flat optics with high performance, small form-factor and new functionalities. When integrated with active elements, the pixelated, thin device architecture further facilitates dynamic tuning of local and global optical responses. Leveraging advanced materials, designs and architectures, we develop novel active and passive meta-optics capable of transforming a variety of optical systems that are traditionally bulky and complicated.
We report the results of the effect of prolonged low-Earth orbit exposure on phase-change materials (PCMs) and PCM-based metasurfaces. During a 6-month exposure as part of the Materials on the International Space Station Experiment (MISSE-14) test campaign led by NASA Langley Research Center, Ge2Sb2Te5 (GST) and GST-based metasurface spectral filters were monitored for their response to extreme temperature cycles, UV and ionizing radiation fluences, and atomic oxygen fluences. Upon return to Earth, the samples were characterized and compared to their pre-flight condition to glean insight into the effects of the space environment on metasurface performance and PCM optical and structural properties.
In this work, we introduce actively tunable PCM-FP (Fabry-Perot) and PCM-PNA (Plasmonic Nanohole Array) bandpass filters that possess high-speed tunability (MHz), narrow spectral bandwidth, high-transmissivity, broad tuning range, in an all solid-state design in a wide variety of imaging and spectroscopic applications. We also present the results from a Materials International Space Station Experiment (MISSE-14) in which chalcogenide phase change material (PCM) optical components are exposed and tested in Low Earth Orbit to determine their suitability for space applications. Our samples including Ge2Sb2Te5, Ge2Sb2Se4Te1, Sb2S3 thin-films and PCM-FP were delivered aboard the ISS by Northrop Grumman (NG-15) in Feb. 2021 for 6 months of exposure testing, including: temperature, vacuum, atomic oxygen, UV exposure and solar illumination effects. Our MISSE-14 PCM study will provide valuable information on the limitations and suitability of PCMs in harsh space environments.
The mid-wave infrared (MWIR) waveband (3-5 µm) contains numerous invaluable spectral /thermal signatures. Tunable MWIR filters are thus highly desirable in a variety of imaging and spectroscopic applications. We introduce phase-change tunable filters (PCTFs) which enable actively tunable spectral filtering across the MWIR waveband from a single solid-state element. This is achieved through the integration of the chalcogenide phase-change material GeSbTe (GST) into a plasmonic nanohole metasurface. We demonstrate polarization-insensitive PCTFs with >70% transmittance, 60nm bandwidth, and high-speed switching (MHz-GHz) across the MWIR waveband using a nanosecond laser pulse. We further show PCTF-based multispectral thermal imaging and dynamic gas sensing.
Tunable mid-wave infrared (MWIR) filters are highly desirable in a wide variety of imaging and spectroscopic applications; with the waveband containing numerous invaluable spectral absorption signatures. We demonstrate spectrally-tunable, all solid-state, thin-film bandpass filters operating across the MWIR by utilizing the phase-change material (PCM) Ge2Sb2Te5 as a tunable cavity medium between two Bragg mirrors. The induced PCM refractive index modulation increases the cavity’s optical path length, thereby tuning the filter passband. Our filters have 300 nm spectral tunability, ~70% transmission efficiencies, and ~60 nm passbands. We further show multispectral thermal imaging and dynamic CO2 gas plume sensing using the filters.
Tunable mid-wave infrared (MWIR) filters are highly desirable in a wide variety of imaging and sensing applications. Here, we demonstrate a solid-state, actively tunable, narrowband MWIR transmission filter based on a plasmonic nanohole array (PNA) design integrated with the phase change material GeSbTe (GST). Through finite-difference time domain simulations and experimental results, we show narrowband (~100nm), high-efficiency (~90%) transmission filtering, tunable across the entire MWIR spectrum (1~10µm). The active tunability of the GST/PNA filter has been experimentally demonstrated by single-shot pulsed laser irradiation-induced phase transformation and the device shows consistent behavior across a number of phase change cycles.
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