Retroreflective optical system and methods
Inventors
Wayne, David T. • Neuner, III, Burton H.
Assignees
Publication Number
US-10598592-B1
Publication Date
2020-03-24
Expiration Date
2039-02-20
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Abstract
A retroreflective optical system for creating a passive optical tag in an absence of electrical power, involving: a retroreflector having a surface and a retroreflective element disposed in relation to the surface, the retroreflective element configured to: passively impart a unique signature in relation to incoming light by using at least one of spectral filtration and color filtration, whereby a plasmonic response is effectible; and reflect outgoing light having the unique signature; and an optical device having an input aperture, the optical device disposed at a distance from the retroreflector and configured to transmit the incoming light and the outgoing light.
Core Innovation
The invention involves a retroreflective optical system designed to create a passive optical tag that operates without electrical power. The system includes a retroreflector having a surface and a retroreflective element disposed in relation to the surface. This retroreflective element is configured to passively impart a unique signature in relation to incoming light through spectral filtration or color filtration, effecting a plasmonic response, and to reflect outgoing light having the unique signature. An optical device with an input aperture is positioned a distance from the retroreflector and is configured to transmit both the incoming and outgoing light.
The problem being solved arises from limitations of related art devices used for tagging objects at standoff distances for identification and tracking. Existing devices typically require electrical power to actively generate unique optical signatures or operate in the radio-frequency spectrum, which suffers from vulnerabilities such as jamming and spectrum allocation issues. The reliance on electrical power restricts the usability on objects intended for tagging due to the need for modules requiring energy to modulate light sources actively. Therefore, there is a need to improve object identification processes while reducing or eliminating the power requirements.
The disclosed retroreflective optical system overcomes these challenges by eliminating the need for electrical power, utilizing a retroreflective element that spectrally filters the reflected beam to reflect only selected light, thereby enabling unique identification of tagged objects. The system employs plasmonic techniques, including surface plasmon-polaritons or surface phonon-polaritons, which are electromagnetic surface waves excited at interfaces between materials of opposite permittivity signs. Coupling techniques such as gratings or prisms are used to excite these modes. The retroreflector can have configurations like corner cube retroreflectors that are operable over wide fields of view and insensitive to orientation and jitter, facilitating robust passive tagging and identification.
Claims Coverage
The patent includes two independent claims covering a passive optical tag and a method of fabricating a retroreflective optical system, each detailing several inventive features related to plasmonic thin films, retroreflector configurations, and spectral signature functionalities.
Passive optical tag with plasmonic thin film imparting unique spectral signature
The passive optical tag comprises a retroreflector with at least one reflective surface where a plasmonic thin film of uniform thickness with negative permittivity is disposed. This thin film produces a plasmonic response that spectrally filters incoming light during reflection at each surface, imparting a unique spectral signature upon the outgoing light that distinguishes the tag among similar tags with different spectral signatures.
Retroreflector configurations for broad spectral and operational range
The retroreflector is provided in a solid configuration, specifically a corner cube configuration, constructed from materials chosen from UV-spectrum-transparent, visible-spectrum-transparent, near-IR-spectrum-transparent, mid-IR-spectrum-transparent, or far-IR-spectrum-transparent materials. It operates independently of orientation, maintains reflection of outgoing light at the same angle as incoming light, possesses a large field of view approximately −85 to 85 degrees, and is insensitive to platform jitter.
Fabrication method involving plasmonic thin films and optical device
The method for fabricating the retroreflective optical system includes providing a retroreflector with at least one reflective surface bearing a uniform thickness plasmonic thin film having negative permittivity for spectral filtration and unique spectral signature generation. It further includes providing an optical device positioned at a distance to receive outgoing light for remote identification of the passive optical tag based on its unique spectral signature.
Plasmonic thin film properties and spectral signature customization
The plasmonic thin film is sufficiently thin to allow an evanescent electric field to extend through it, exciting a plasmonic response at an outer interface for at least one specific wavelength. This response attenuates internal reflection at that wavelength, tailoring the outgoing light's spectral signature. Parameters such as refractive index, material purity, film thickness, presence or absence of protective dielectric overcoats, and dielectric material permittivity are selected to customize different spectral signatures among similar optical tags.
Utilization of polar crystal plasmonic thin films for IR spectral filtering
The plasmonic thin film can be a polar crystal, such as silicon carbide (SiC), exhibiting negative permittivity in the infrared range. This produces plasmonic responses from surface phonon polaritons at the film's outer interface, enabling spectral filtering and imparting unique infrared spectral signatures in the outgoing light.
System for remote identification based on spectral signatures
A system comprising a plurality of similar optical tags each imparting different spectral signatures, an optical detector to receive outgoing light from the retroreflective element, and a signal processor that matches the detected unique spectral signature to identify a specific passive optical tag remotely among the plurality of tags.
The independent claims cover a passive optical tag with a plasmonic thin film providing unique spectral signatures, retroreflector structures supporting broad operational parameters, fabrication methods incorporating these features, and systems enabling remote identification based on spectral differentiation.
Stated Advantages
Elimination of the need for electrical power to generate unique optical signatures, enabling passive operation.
Improved standoff object identification through distinctive spectral signatures imparted by spectral filtration using plasmonic responses.
Orientation-independent operation with a large field of view and insensitivity to platform jitter, enhancing robustness and usability in varying conditions.
Customization of spectral signatures via selectable material properties and thin film parameters, allowing unique tagging and identification among similar tags.
Capability to operate over various spectral bands, including visible, near-infrared, mid-infrared, and far-infrared, by selection of materials and coatings.
Documented Applications
Tagging objects at standoff distances for remote identification and tracking without electrical power.
Military thermal imaging and biochemical sensing implementations using mid-infrared and far-infrared spectral ranges.
Surface phonon-polariton excitation applications enabled by polar crystal plasmonic thin films.
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