# US 9,752,932 B2 · Tunable electro-optic filter stack

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- Number: US 9,752,932 B2
- Document ID: US9752932B2
- Status: Granted
- Kind: B2
- Application number: 13/881,608
- Filed: 2011-10-29
- Published: 2014-12-04
- Granted: 2017-09-05
- Earliest claimed: 2010-10-29
- Assignees: Drexel University
- Applicants: Adam K. Fontecchio; Sameet K. Shriyan; Alyssa Bellingham
- Inventors: Adam K. Fontecchio; Sameet K. Shriyan; Alyssa Bellingham
- Web page: https://patentgrep.com/patent/US9752932B2

## CPC

- G01J 3/0237: {Adjustable, e.g. focussing}
- G01J 3/502: {using a dispersive element, e.g. grating, prism}
- G01J 3/51: using colour filters
- G02B 27/0103: {comprising holographic elements}
- G02F 1/13342: {Holographic polymer dispersed liquid crystals}
- G02F 1/13476: {in which at least one liquid crystal cell or layer assumes a scattering state}
- G03F 7/20: Exposure; Apparatus therefor (photographic printing apparatus for making copies G03B27/00)
- G03F 7/26: Processing photosensitive materials; Apparatus therefor (G03F7/12 - G03F7/24 take precedence)
- G02F 2203/055: wavelength filtering
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

A holographic polymer dispersed liquid crystal (HPDLC) tunable filter exhibits switching times of no more than 20 microseconds. The HPDLC tunable filter can be utilized in a variety of applications. An HPDLC tunable filter stack can be utilized in a hyperspectral imaging system capable of spectrally multiplexing hyperspectral imaging data acquired while the hyperspectral imaging system is airborne. HPDLC tunable filter stacks can be utilized in high speed switchable optical shielding systems, for example as a coating for a visor or an aircraft canopy. These HPDLC tunable filter stacks can be fabricated using a spin coating apparatus and associated fabrication methods.

## Claims

### Claim 1

A hyperspectral imaging system comprising:
a hyperspectral imager that includes a holographic polymer dispersed liquid crystal (HPDLC) tunable optical filter through which light passes, the hyperspectral imager configured to acquire and spectrally multiplex hyperspectral imaging data, wherein:
the HPDLC tunable optical filter comprises a stacked assembly of two or more HPDLC thin film elements, each HPDLC thin film element being switchable between a light reflecting state and a transparent or semitransparent state with a switching time of no more than twenty microseconds; and
each HPDLC thin film element, when in its light reflecting state, reflects a different Bragg wavelength than the other HPDLC thin film elements such that when exposed to incident light and in its respective reflecting state, each HPDLC thin film element allows a different spectrum of incident light to be transmitted through the stack,
the collective sets of spectra of incident light from the plurality of HPDLC thin film elements being the hyperspectral imaging data.

### Claim 2 (depends on 1)

The hyperspectral imaging system of claim 1, wherein a first holographic polymer dispersed liquid crystal thin film of the plurality abuts a first surface of an intervening conductive layer and a second holographic polymer dispersed liquid crystal thin film of the plurality abuts an opposed second surface of the intervening conductive layer.

### Claim 3 (depends on 1)

The hyperspectral imaging system of claim 1, wherein each of the plurality of holographic polymer dispersed liquid crystal thin films abuts a surface of a conductive element disposed adjacent to the holographic polymer dispersed liquid crystal thin film element.

### Claim 4 (depends on 1)

The hyperspectral imaging system of claim 1, wherein the holographic polymer dispersed liquid crystal tunable filter comprises a stack of alternating holographic polymer dispersed liquid crystal thin film elements and conductive elements.

### Claim 5 (depends on 4)

The hyperspectral imaging system of claim 4, wherein the conductive elements comprise respective discrete layers of PEDOT:PSS.

### Claim 6 (depends on 1)

The hyperspectral imaging system of claim 1, wherein each of the holographic polymer dispersed liquid crystal thin film elements comprises a film thickness of no more than twenty microns.

### Claim 7 (depends on 1)

The hyperspectral imaging system of claim 1, wherein the holographic polymer dispersed liquid crystal tunable filter is capable of facilitating the acquisition of hyperspectral imaging data throughout a wavelength range of approximately 780 nm to approximately 3 μm.

### Claim 8 (depends on 1)

The hyperspectral imaging system of claim 1, further comprising a transmitter configured to transmit the acquired hyperspectral imaging data.

### Claim 9 (depends on 1)

The hyperspectral imaging system of claim 1, further comprising a platform configured to carry the hyperspectral imager, the platform configured to facilitate airborne collection of the hyperspectral imaging data.

### Claim 10 (depends on 1)

The operating hyperspectral imaging system of claim 1, wherein each HPDLC thin film element is individually biased between its respective light reflecting and transparent or semitransparent states.

### Claim 11 (depends on 1)

The hyperspectral imaging system of claim 1, wherein each HPDLC thin film element, when in its light reflecting state, reflects a different Bragg wavelength with a resolution of less than 10nm.

### Claim 12 (depends on 1)

The hyperspectral imaging system of claim 1, wherein the reflection wavelength of each HPDLC thin film element has a full width at half maximum (FWHM) in a range of from 5 to 20nm.

### Claim 13

An operating hyperspectral imaging system comprising:
a hyperspectral imager that includes a holographic polymer dispersed liquid crystal (HPDLC) tunable filter, the hyperspectral imager acquiring and spectrally multiplexing hyperspectral imaging data from the tunable filter, wherein:
the HPDLC tunable filter comprises a stacked assembly of two or more HPDLC thin film elements, each HPDLC thin film element being switched during operation between a light reflecting state and a transparent or semitransparent state with a switching time of no more than twenty microseconds;
each HPDLC thin film element is designed to reflect a different Bragg wavelength across an operating bandwidth; and
when exposed to incident light and in its respective light reflecting state, each HPDLC thin film element is generating a unique set of spectral data,
the collective sets of spectral data from the plurality of HPDLC thin film elements being the hyperspectral imaging data.

### Claim 14 (depends on 13)

The operating hyperspectral imaging system of claim 13, wherein the holographic polymer dispersed liquid crystal tunable filter comprises a stack of alternating holographic polymer dispersed liquid crystal thin film elements and conductive elements.

### Claim 15 (depends on 13)

The operating hyperspectral imaging system of claim 13, wherein each HPDLC thin film element, when in its light reflecting state, is reflecting a different Bragg wavelength with a resolution of less than 10nm.

### Claim 16 (depends on 13)

The operating hyperspectral imaging system of claim 13, wherein each HPDLC thin film element is individually biased between its respective light reflecting and transparent or semitransparent states.

### Claim 17 (depends on 13)

The operating hyperspectral imaging system of claim 13, further comprising a transmitter that is transmitting the acquired hyperspectral imaging data.