# US 2008/0187011 A1 · Tuning optical cavities

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- Number: US 2008/0187011 A1
- Document ID: US20080187011A1
- Status: Published application
- Kind: A1
- Application number: 11/702,320
- Filed: 2007-02-05
- Published: 2008-08-07
- Earliest claimed: 2007-02-05
- Assignees: Palo Alto Research Center Incorporated
- Inventors: Peter Kiesel; Oliver Schmidt; Michael Bassler; Uma Srinivasan
- Web page: https://patentgrep.com/patent/US20080187011A1

## CPC

- H01S 3/08081: {Unstable resonators}
- G01J 3/26: using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
- H01S 3/105: by controlling the mutual position or the reflecting properties of the reflectors of the cavity {, e.g. by controlling the cavity length}({H01S3/10076}, H01S3/13 take precedence)
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- 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)

## Abstract

An inhomogeneous optical cavity is tuned by changing its shape, such as by changing reflection surface positions to change tilt angle, thickness, or both. Deformable components such as elastomer spacers can be connected so that, when deformed, they change relative positions of structures with light-reflective components such as mirrors, changing cavity shape. Electrodes can cause deformation, such as electrostatically, electromagnetically, or piezoelectrically, and can also be used to measure thicknesses of the cavity. The cavity can be tuned, for example, across a continuous spectrum, to a specific wavelength band, to a shape that increases or decreases the number of modes it has, to a series of transmission ranges each suitable for a respective light source, with a modulation that allows lock-in with photosensing for greater sensitivity, and so forth. The optical cavity can be a linear variable filter fabricated on the photosensitive surface of a photosensing component such as a photosensor array or a position-sensitive detector.

## Claims

### Claim 1

An optical cavity device comprising:
first and second structures that can move relative to each other, the first and second structures including first and second light-reflective components, respectively;
between the first and second light-reflective components, an inhomogeneous optical cavity; and
connected to the first and second structures, a set of one or more tuning structures that can tune the optical cavity by changing relative positions of the first and second light-reflective components; at least one of the tuning structures in the set including:
first and second electrodes connected to the first and second structures, respectively, the first and second electrodes being connectible to receive electrical tuning signals; and
a deformable component between the first and second electrodes; the deformable component being deformable in response to the electrical tuning signals received by the first and second electrodes.

### Claim 2 (depends on 1)

The device of claim 1 in which the first and second electrodes of each tuning structure in the set are on facing surfaces of the first and second structures, respectively.

### Claim 3 (depends on 1)

The device of claim 1 in which the deformable component includes at least one of:
dielectric elastomer material that is deformed in response to an electrostatic field between electrodes;
nonmagnetic elastomer material that is deformed by electromagnetic attraction or repulsion between electrodes; and
piezoelectric material that expands or contracts in response to electrical signals received through the electrodes.

### Claim 4 (depends on 1)

The device of claim 1 in which the set of tuning structures, by changing relative positions of the first and second light-reflective components, changes the optical cavity's shape by doing at least one of changing a tilt angle and changing an optical distance.

### Claim 5 (depends on 1)

The device of claim 1 in which the optical cavity has an exit surface at which it provides output light, the device further comprising:
a photosensing component connected to the exit surface to receive the output light.

### Claim 6 (depends on 1)

A system that comprises the device of claim 1, the system further comprising:
one or more sensing components that can sense a feature of the relative position of the first and second light-reflective components and provide feature signals indicating the sensed feature; and
control circuitry connected to receive the feature signals; in response to the feature signals, the control circuitry providing the electrical tuning signals to the set of tuning structures.

### Claim 7 (depends on 6)

The system of claim 6 in which the control circuitry comprises a processor, the processor providing the electrical tuning signals based on the feature signals and on calibration data.

### Claim 8 (depends on 6)

The system of claim 6 in which the sensing components can sense distance between the first and second light-reflective components.

### Claim 9

A method of making optical cavity devices, the method comprising:
producing an optical cavity device that includes:
first and second structures that can move relative to each other and that include first and second light-reflective components, respectively;
an inhomogeneous optical cavity between the first and second light-reflective components; and
connected to the first and second structures, a set of one or more tuning structures that can tune the optical cavity by changing relative positions of the first and second light-reflective components;
the act of producing the optical cavity device comprising:
producing the set of tuning structures so that at least one of the tuning structures in the set includes:
first and second electrodes connected to the first and second structures, respectively, the first and second electrodes being connectible to receive electrical tuning signals; and
a deformable component between the first and second electrodes; the deformable component being deformable in response to electrical signals to the first and second electrodes, causing change in relative positions of the first and second structures.

### Claim 10 (depends on 9)

The method of claim 9 in which the act of producing the optical cavity device further comprises:
operating the set of tuning structures to change the shape of the optical cavity to an initial shape.

### Claim 11 (depends on 10)

The method of claim 10 in which the act of producing the optical cavity device further comprises:
illuminating the optical cavity with a known light source and photosensing a laterally varying intensity distribution of the optical cavity's output light to obtain photosensing results; and
monitoring the photosensing results while operating the set of tuning structures.

### Claim 12 (depends on 9)

The method of claim 9 in which the act of producing the optical cavity device comprises:
fabricating the optical cavity device on a photosensitive surface of a photosensing IC; in use, the photosensitive surface receiving output light from the optical cavity.

### Claim 13

A method of using an optical cavity with a changeable shape; the method comprising:
tuning the optical cavity by changing its shape; and
operating the optical cavity to provide output light with a laterally varying intensity distribution that depends on the optical cavity's shape.

### Claim 14 (depends on 13)

The method of claim 13 in which the act of tuning is performed before the act of operating.

### Claim 15 (depends on 14)

The method of claim 14 in which the act of tuning determines a photon energy range in which the optical cavity transmits light; the output light being within the photon energy range.

### Claim 16 (depends on 14)

The method of claim 14 in which the act of tuning changes the number of modes in which the optical cavity provides output light.

### Claim 17 (depends on 13)

The method of claim 13 in which the act of tuning and the act of operating are performed concurrently.

### Claim 18 (depends on 17)

The method of claim 17 in which the act of tuning comprises:
continuously changing the optical cavity's shape while performing the act of operating.

### Claim 19 (depends on 18)

The method of claim 18, further comprising:
photosensing the output light at a photosensitive surface;
the act of tuning further comprising:
modulating the optical cavity's shape at a frequency to perform a lock-in operation.

### Claim 20 (depends on 17)

The method of claim 17 in which the act of tuning comprises:
incrementally changing the optical cavity's shape while performing the act of operating.

### Claim 21 (depends on 13)

The method of claim 13 in which the act of tuning and the act of operating are performed alternately.

### Claim 22 (depends on 21)

The method of claim 21 in which the act of operating includes a series of operations during each of which the optical cavity receives input light from a respective light source; the act of tuning including, after each operation in the series, an act of changing the optical cavity's shape for the next operation.

### Claim 23 (depends on 13)

The method of claim 13, further comprising:
providing input light to the optical cavity and photosensing output light provided by the optical cavity in response to the input light to obtain sensing results; the act of providing input light and photosensing output light comprising:
providing tuning signals causing the optical cavity to have a sequence of one or more shapes; for each shape, the photosensed output light having a respective laterally varying intensity distribution; the sensing results including information resulting from the laterally varying intensity distribution.

### Claim 24 (depends on 23)

The method of claim 23 in which the act of providing tuning signals further comprises:
providing a sequence of tuning signals so that the sensing results indicate a derivative of one of absorption and dispersion with respect to wavelength.

### Claim 25 (depends on 23)

The method of claim 23 in which the photosensed output light includes a light spot on a photosensitive surface; the act of providing tuning signals comprising:
providing tuning signals that cause the optical cavity's output energy function to vary periodically with a constant frequency; in response, the light spot moving periodically over the photosensitive surface with the constant frequency.

### Claim 26 (depends on 25)

The method of claim 25, further comprising:
using the photosensing results to obtain a differential quantity indicating the light spot's position on the photosensitive surface; and
performing a lock-in operation to increase the precision of the light spot's position as indicated by the differential quantity.

### Claim 27

A system comprising:
a tunable optical cavity device that includes an inhomogeneous optical cavity, the device responding to tuning signals by changing the inhomogeneous optical cavity's energy output function;
a photosensing component having one or more photosensitive surfaces; and
control circuitry that operates the inhomogeneous optical cavity; the control circuitry providing tuning signals causing the optical cavity to have a sequence of one or more laterally varying energy output functions; for each laterally varying energy output function, the optical cavity providing respective output light having a respective laterally varying intensity distribution on the photosensitive surfaces;
in response to each energy output function's output light, the photosensing component providing sensing results including information resulting from the output light's laterally varying intensity distribution.