# US 7,466,424 B2 · Displacement sensor based on photonic crystal waveguides

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- Number: US 7,466,424 B2
- Document ID: US7466424B2
- Status: Granted
- Kind: B2
- Application number: 11/274,132
- Filed: 2005-11-16
- Published: 2006-05-18
- Granted: 2008-12-16
- Earliest claimed: 2004-11-17
- Assignees: Ramot at Tel-Aviv University Ltd.
- Inventors: Menachem Nathan; Ben Zion Steinberg; Oren Levy; Amir Boag
- Web page: https://patentgrep.com/patent/US7466424B2

## CPC

- G02B 6/1225: {comprising photonic band-gap structures or photonic lattices}
- B82Y 20/00: Nanooptics, e.g. quantum optics or photonic crystals
- G01D 5/266: {by interferometric means (G01D5/353 takes precedence)}
- G01P 15/0802: {Details}
- G01P 15/093: by photoelectric pick-up
- G01P 2015/0828: {the mass being of the paddle type being suspended at one of its longitudinal ends}
- G02B 6/3508: {Lateral or transverse displacement of the whole waveguides, e.g. by varying the distance between opposed waveguide ends, or by mutual lateral displacement of opposed waveguide ends}
- G02B 6/3594: {Characterised by additional functional means, e.g. means for variably attenuating or branching or means for switching differently polarized beams}
- G02B 6/3596: {With planar waveguide arrangement, i.e. in a substrate, regardless if actuating mechanism is outside the substrate}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})

## Abstract

A displacement sensor comprising at least one pair of co-planar photonic crystal waveguide (PCWG) sections aligned along or parallel to a common axis and separated by a gap, one PCWG section of a pair operative to perform a displacement relative to the other section of the pair. In some embodiments, the sensor is linear, comprising two PCWG sections seperated by a gap that forms a cross PCWG, the displacement sensing performed preferrably differentially between two edges of the cross PCWG. In other embodiments, the sensor includes Mach Zehnder Interferometer (MZI) configurations with gaps between fixed and moving PCWG sections. Displacement induced changes in the gap widths are reflected in changes in an output parameter of the MZI.

## Claims

### Claim 1

An optical displacement sensor comprising:
a. a first photonic crystal waveguide (PCWG);
b. a second PCWG co-planar with and operative to perform a displacement relative to the first PCWG, wherein the first and second PCWGs are parallel to a common axis and separated by a gap that serves as a cross PCWG, and
c. an optical detection mechanism operative to provide an optical measurement correlated with the relative displacement between the first and second PCWGs.

### Claim 2 (depends on 1)

The optical displacement sensor of claim 1, wherein the optical detection mechanism includes a first detector positioned proximate to one end of the cross PCWG and a second detector positioned proximate to another end of the cross PCWG, and wherein the optical measurement includes a differential optical measurement performed by the first and second detectors.

### Claim 3 (depends on 1)

The optical displacement sensor of claim 1, wherein the PCWGs are selected from the group consisting of one-dimensional (1D) ridge PCWGs, PCWGs formed in a 1D photonic crystal, PCWGs formed in a 2D photonic crystal and PCWGs formed in a 3D photonic crystal.

### Claim 4 (depends on 1)

The optical displacement sensor of claim 1, wherein each PCWG segment includes an array of dielectric posts surrounded by air.

### Claim 5 (depends on 1)

The optical displacement sensor of claim 1, wherein each PCWG is selected from the group consisting of a W1-type waveguide and a CCW waveguide.

### Claim 6

A method for sensing mechanical displacements optically, comprising the steps of:
a. providing a first photonic crystal waveguide (PCWG);
b. providing a second PCWG coplanar with and operative to perform a displacement relative to the first PCWG, wherein the first and second PCWGs are parallel to a common axis and separated by a gap that serves as a cross PCWG, and
c. performing an optical measurement correlated with the relative displacement between the first and second PCWGs, thereby obtaining a displacement value.

### Claim 7 (depends on 6)

The method of claim 6, wherein the steps of providing first and second PCWGs include providing first and second Mach Zelnder Interferometer (MZI) PCWG segments, wherein each MZI PCWG segment includes two, first and second arms, wherein the first arms of the first and second MZI PCWGs are separated by a first gap and wherein the second arms of the first and second MZI PCWGs are separated by a second gap.

### Claim 8 (depends on 6)

The method of claim 6, wherein the step of performing an optical measurement correlated with the relative displacement between the first and second PCWGs includes positioning a first detector proximate to one end of the cross PCWG and positioning a second detector proximate to another end of the cross PCWG, and using the first and second detectors to perform a differential optical measurement correlated with the relative displacement.

### Claim 9 (depends on 6)

The method of claim 6, wherein the relative displacement includes a displacement that changes the first gap in a first direction and changes the second gap equally in an opposite direction to the first direction, and wherein the step of performing an optical measurement correlated with the relative displacement includes performing an interference measurement that is correlated with the gap changes.