# US 7,692,746 B2 · Digitally-switchable bandpass filter

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 7,692,746 B2
- Document ID: US7692746B2
- Status: Granted
- Kind: B2
- Application number: 11/161,376
- Filed: 2005-08-01
- Published: 2007-02-01
- Granted: 2010-04-06
- Earliest claimed: 2005-08-01
- Assignees: Real D
- Inventors: Gary D. Sharp
- Web page: https://patentgrep.com/patent/US7692746B2

## CPC

- G02F 1/13363: Birefringent elements, e.g. for optical compensation
- G02F 1/133528: {Polarisers}
- G02F 1/13473: {for wavelength filtering or for colour display without the use of colour mosaic filters}
- G02F 2203/055: wavelength filtering
- G02F 2413/08: with a particular optical axis orientation
- 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

## Abstract

Disclosed are digitally-switchable bandpass filters combining non-tunable retarder stacks with switchable liquid crystal cells. The disclosed filter embodiments function like a filter wheel with no moving parts that may provide faster switching, better image registration, compact size, and lower electrical power consumption. These benefits are attractive in portable handheld devices, such as bio-hazard sensors or glucose monitors.

## Claims

### Claim 1

An optical filter for filtering a beam of light passing through it, the optical filter comprising:
a retarder stack, the retarder stack comprising at least three retarder layers wherein the retarder layers have substantially the same retardance values, and the retarder angles of the retarder layers are substantially symmetric relative to the middle of the retarder stack;
a liquid crystal cell adjacent to the retarder stack, the liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the light beam passing through the optical filter; and
first and second polarizers on opposite sides of the adjacent retarder stack and liquid crystal cell such that polarization of the beam of light remains substantially unchanged between the liquid crystal cell and the one of the first and second polarizers that is adjacent to the liquid crystal cell.

### Claim 2 (depends on 1)

The optical filter of claim 1 wherein retarder stack has an even number (1 to M) of retarder layers and wherein the middle of the stack is between the M/2 layer and the M/2+1 layer.

### Claim 3 (depends on 1)

The optical filter of claim 1 wherein retarder stack has an odd number (1 to M) of retarder layers and wherein the middle of the stack is the middle of the M/2 layer.

### Claim 4 (depends on 1)

The optical filter of claim 1, wherein the first and second polarizers are oriented orthogonally to each other.

### Claim 5 (depends on 1)

The optical filter of claim 1 wherein a certain wavelength band of the light beam is polarization converted.

### Claim 6 (depends on 5)

The optical filter of claim 5 wherein the retarder stack has an odd number of films and wherein the light beam has a polarization that is retarded by half of the wavelength in the certain wavelength band.

### Claim 7 (depends on 5)

The optical filter of claim 5 wherein the retarder stack has an even number of films and wherein the light beam has a polarization that is substantially purely rotated in the certain wavelength band.

### Claim 8 (depends on 1)

The optical filter of claim 1, wherein the retarder angle of each of the retarder layers is less than approximately ±7° with respect to the input polarization.

### Claim 9 (depends on 1)

The optical filter of claim 1, wherein the optical filter is a bandpass filter when the liquid crystal cell receives the certain input voltage signal and wherein the optical filter comprises a “notch” filter when the liquid crystal cell is driven with another input voltage.

### Claim 10 (depends on 1)

The optical filter of claim 1, and further comprising:
another retarder stack;
another liquid crystal cell, the another liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the light beam passing through the optical filter,
the another retarder stack and another liquid cell positioned adjacent to each other and collectively adjacent to one of the first and second polarizers; and
a third polarizer positioned such that the collectively adjacent another retarder stack and another liquid crystal cell are interposed between the third polarizer and the one of the first and second polarizers.

### Claim 11 (depends on 10)

The optical filter of claim 10, wherein the retarder stack, the liquid crystal cell, and the first and second polarizers comprise a first filter stage and wherein the another retarder stack, the another liquid crystal cell, the one of the first and second polarizers, and the third polarizer comprise a second filter stage.

### Claim 12 (depends on 11)

The optical filter of claim 11, wherein the filter is operable to receive a first set of input voltage signals at the voltage inputs of the liquid crystal cell and the another liquid crystal cell, and wherein one of the first and second filter stages is a bandpass filter when its respective liquid crystal cell receives one of the first set of input voltage signals and wherein the other filter stage comprises a “notch” filter when its respective liquid crystal cell is driven with another input voltage signal.

### Claim 13 (depends on 12)

The optical filter of claim 12, wherein the filter is further operable to receive a second set of input voltage signals at the voltage inputs whereby the other of the first and second filter stages is a bandpass filter and the one of the first and second filter stages comprises a “notch” filter.

### Claim 14 (depends on 13)

The optical filter of claim 13, wherein the respective notches of the first and second filters are substantially nonoverlapping.

### Claim 15 (depends on 1)

The optical filter of claim 1, wherein the liquid crystal cell is of a construction selected from the group consisting of twisted nematic, electrically controlled birefringence, pi-cell, ferroelectric, and vertically aligned nematic.

### Claim 16 (depends on 1)

The optical filter of claim 1, wherein the liquid crystal cell is a twisted nematic cell comprised of two transparent electrodes and a liquid crystal material interposed between the two electrodes, the two transparent electrodes each having an alignment layer with a rub direction, wherein the retarder angle of each of the retarder layers is less than approximately ±45° with respect to the rubbing direction of one of the alignment layers.

### Claim 17 (depends on 1)

A filter according to claim 1, wherein the retarder angles of each of the retarder layers is clustered about an input polarization direction of the incoming beam of light.

### Claim 18

An optical filter for filtering a beam of light passing through it, the optical filter comprising:
a first retarder stack, the first retarder stack comprising at least three retarder layers wherein the retarder layers have substantially the same retardance values, and the retarder angles of the retarder layers are substantially symmetric relative to the middle of the retarder stack;
a first liquid crystal cell adjacent to the first retarder stack, the first liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter;
first and second polarizers on opposite sides of the adjacent first retarder stack and first liquid crystal cell;
a second retarder stack;
a second liquid crystal cell, the second liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter,
the second retarder stack and second liquid cell positioned adjacent to each other and collectively adjacent to one of the first and second polarizers; and
a third polarizer positioned such that the collectively adjacent second retarder stack and second liquid crystal cell are interposed between the third polarizer and the one of the first and second polarizers, and such that polarization of the beam of light remains substantially unchanged between the second liquid crystal cell and the third polarizer.

### Claim 19 (depends on 18)

The optical filter of claim 18, wherein the filter is operable to receive a first set of input voltage signals at the voltage inputs of the first and second liquid crystal cells, and wherein one of the first and second filter stages is substantially achromatic when its respective liquid crystal cell receives one of the first set of input voltage signals and wherein the other filter stage comprises a “notch” filter when its respective liquid crystal cell is driven with another of the set of input voltage signals.

### Claim 20 (depends on 19)

The optical filter of claim 19, wherein the filter is further operable to receive a second set of input voltage signals at the voltage inputs whereby the other of the first and second filter stages is substantially achromatic and the one of the first and second filter stages comprises a “notch” filter.

### Claim 21

A digitally tuned optical filter having digitally tuned optical filtering characteristics, the digitally tuned optical filter comprising:
a first retarder stack, the first retarder stack comprising at least three retarder layers wherein the retarder layers have substantially the same retardance values, and the retarder angles of the retarder layers are substantially symmetric relative to the middle of the retarder stack;
a first liquid crystal cell adjacent to the first retarder stack, the first liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of a beam of light passing through the optical filter;
first and second polarizers on opposite sides of the adjacent first retarder stack and first liquid crystal cell;
a second retarder stack;
a second liquid crystal cell, the second liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter,
the second retarder stack and second liquid cell positioned adjacent to each other and collectively adjacent to one of the first and second polarizers;
a third polarizer positioned such that the collectively adjacent second retarder stack and second liquid crystal cell are interposed between the third polarizer and the one of the first and second polarizers, and such that polarization of the beam of light remains substantially unchanged between the second liquid crystal cell and the third polarizer; and
a controller in electrical communication with the first and second liquid crystal cells, the controller operable to apply at least first and second sets of input voltage signals to the first and second liquid crystal cells to thereby tune the filtering characteristics of the optical filter.

### Claim 22

A spectrometry system for measuring a signature light from a sample to be measured, the spectrometry system comprising:
a light source;
optical components operable to focus light from the light source onto the sample to be measured;
a digitally tuned optical filter having digitally tuned optical filtering characteristics, comprising:
a first retarder stack, the first retarder stack comprising at least three retarder layers wherein the retarder layers have substantially the same retardance values, and the retarder angles of the retarder layers are substantially symmetric relative to the middle of the retarder stack;
a first liquid crystal cell adjacent to the first retarder stack, the first liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter;
first and second polarizers on opposite sides of the adjacent first retarder stack and first liquid crystal cell;
a second retarder stack;
a second liquid crystal cell, the second liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter,
the second retarder stack and second liquid cell positioned adjacent to each other and collectively adjacent to one of the first and second polarizers;
a third polarizer positioned such that the collectively adjacent second retarder stack and second liquid crystal cell are interposed between the third polarizer and the one of the first and second polarizers, and such that polarization of the beam of light remains substantially unchanged between the second liquid crystal cell and the third polarizer; and
a controller in electrical communication with the first and second liquid crystal cells, the controller operable to apply at least first and second sets of input voltage signals to the first and second liquid crystal cells to thereby tune the filtering characteristics of the optical filter; and
an optical sensor positioned to receive light from the sample.

### Claim 23 (depends on 22)

The spectrometry system of claim 22 where the light received from the sample is fluoresced by the sample.

### Claim 24 (depends on 22)

The spectrometry system of claim 22 where digital filter is positioned optically after the sample.

### Claim 25 (depends on 22)

The spectrometry system of claim 22 where the digital filter is positioned optically before the sample.

### Claim 26 (depends on 22)

The spectrometry system of claim 22 where the digital filter scans through optical wavelength spectra.

### Claim 27

An optical imaging system using a digitally tuned filter comprising:
optical components operable to focus light from a light source; and
a digitally tuned optical filter having digitally tuned optical filtering characteristics, comprising:
a first retarder stack, the first retarder stack comprising at least three retarder layers wherein the retarder layers have substantially the same retardance values, and the retarder angles of the retarder layers are substantially symmetric relative to the middle of the retarder stack;
a first liquid crystal cell adjacent to the first retarder stack, the first liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter;
first and second polarizers on opposite sides of the adjacent first retarder stack and first liquid crystal cell;
a second retarder stack;
a second liquid crystal cell, the second liquid crystal having a voltage input and operable at least at a certain input voltage signal at its voltage input to impart no change of the state of polarization of the beam of light passing through the optical filter,
the second retarder stack and second liquid cell positioned adjacent to each other and collectively adjacent to one of the first and second polarizers;
a third polarizer positioned such that the collectively adjacent second retarder stack and second liquid crystal cell are interposed between the third polarizer and the one of the first and second polarizers, and such that polarization of the beam of light remains substantially unchanged between the second liquid crystal cell and the third polarizer; and
a controller in electrical communication with the first and second liquid crystal cells, the controller operable to apply at least first and second sets of input voltage signals to the first and second liquid crystal cells to thereby tune the filtering characteristics of the optical filter.

### Claim 28 (depends on 27)

The optical imaging system of claim 27 and further comprising an optical sensor upon which the optical components are operable to focus the light from the light source.

### Claim 29 (depends on 27)

The optical imaging system of claim 27 and further comprising an image plane upon which the optical components are operable to focus the light from the light source.

### Claim 30 (depends on 27)

The optical imagining system of claim 27 and further comprising the light source.

### Claim 31 (depends on 27)

The optical imaging system of claim 27 wherein the digital filter is operable under control of the controller to scan through optical wavelength spectra.

### Claim 32 (depends on 31)

The optical imaging system of claim 31 wherein the digital filter is positioned after the optical components to scan through the optical wavelength spectra of the received light.

### Claim 33 (depends on 31)

The optical imaging system of claim 31 wherein the digital filter is positioned before the optical components to scan through the optical wavelength spectra of the light from the light source.

### Claim 34 (depends on 31)

The optical imaging system of claim 31 wherein the optical imaging system is a CMOS or CCD detector array.

### Claim 35 (depends on 31)

The optical imaging system of claim 31 wherein the optical imaging system is an image projection system.