Large-area, actively tunable, asymmetric Fabry-Perot cavities for colorimetric sensing and optical switching
Inventors
Palinski, Timothy J. • Hunter, Gary W. • Zhang, John
Assignees
Dartmouth College • National Aeronautics and Space Administration NASA
Publication Number
US-11243159-B1
Publication Date
2022-02-08
Expiration Date
2040-02-06
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Abstract
A tunable colorimetric sensor/optical filter is based on a lithography-free, asymmetric Fabry-Perot cavity. The sensor has a thin-film structure formed by a lossy, porous nanoplasmonic top film deposited on an actively tunable spacer middle layer, and a reflective base layer (either a metal or semiconductor). The structure is fabricated using wafer-scale PVD processes, and the middle layer responds to the presence of a stimulus in the local environment, by expanding in thickness resulting in a shift in resonance wavelength and thus an obvious change in color of the sensor, which color change is detectable by the naked-eye. Such layered geometries exhibit vibrant, macroscopic structural coloration owing to the broadband optical absorption of the top film, enabling the change in spacer thickness to be transduced visually, circumventing the need for sophisticated optical equipment for signal readout to observe the presence of the environmental stimulus.
Core Innovation
The invention describes a tunable colorimetric sensor and optical filter based on a lithography-free, asymmetric Fabry-Perot cavity. This sensor is a thin-film structure comprising a lossy, porous nanoplasmonic top film deposited on an actively tunable spacer middle layer, and a reflective base layer which can be metal or semiconductor. The middle layer responds to a stimulus by expanding in thickness, causing a shift in resonance wavelength and producing an observable color change in the sensor visible to the naked eye. This enables visual detection of the presence of the environmental stimulus without sophisticated optical equipment.
The problem addressed is that while nanostructured metal-insulator-metal (MIM) plasmonic metasurfaces and asymmetric Fabry-Perot cavities have shown capabilities in light control and sensing, existing colorimetric sensors often require spectrometers for readout and complicated fabrication techniques. Prior sensors that respond to stimuli with resonance shifts lacked naked-eye readability and were not easily fabricated over large areas economically. The invention solves this by combining a lossy plasmonic nanoisland film top layer with a stimuli-responsive dielectric middle layer to produce vibrant, additive reflective structural colors observable directly by the naked eye using large-area, lithography-free fabrication.
Claims Coverage
The patent includes one independent claim which covers a thin-film sensor with key structural and functional components. The following are the main inventive features disclosed by the claim.
Tunable thin-film sensor configuration
The sensor comprises an optically reflective base layer, a lossy, discontinuous plasmonic metal film top layer arranged over the base layer, and a stimulus-responsive dielectric film middle layer arranged between the base and top layers. The middle layer has an optical path length configured to reversibly change upon exposure to a stimulus, producing a reversible change in the visible color of reflected light. The top layer is at or near a percolation threshold.
The independent claim concentrates the inventive concept on a multilayer thin-film sensor structure incorporating a stimulus-responsive dielectric spacer whose optical path length changes reversibly upon stimulus exposure, combined with a specialized discontinuous lossy plasmonic top layer near percolation, enabling naked-eye visible reversible color changes.
Stated Advantages
Enables sensitive, naked-eye, colorimetric sensing without the need for sophisticated optical readout equipment.
Allows large-area, lithography-free fabrication using economical wafer-scale deposition processes.
Produces vibrant, additive (band-pass) reflective structural colors with high saturation and low angular sensitivity (iridescence-free).
Exhibits fast and fully reversible color-tuning response to environmental stimuli.
Offers tunability via the base layer material choice, top layer thickness and morphology, and middle layer optical properties, thus optimizing sensor performance.
Applicable for low-cost, on-chip bio/chemical sensing with potential medical diagnostics and environmental monitoring use.
Documented Applications
Colorimetric sensors for detecting chemical analytes such as organic solvents and ethanol vapors.
Bio/chemical sensing, including incorporation of bio-recognition elements for selective sensing.
Environmental monitoring such as breath analysis, bacterial species identification, and detection of explosives.
Optical switching devices with fast and reversible tuning of reflected color and light absorption.
Tunable color filtering and resonant optical cavities for enhanced light emission, molecular vibrational experiments, and lasing/spontaneous emission applications.
Potential application in astronaut health monitoring and resource-limited diagnostic settings requiring simple, reliable readout.
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