# US 5,351,116 A · Velocimeters

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

- Number: US 5,351,116 A
- Document ID: US5351116A
- Status: Granted
- Kind: A
- Application number: 07/961,905
- Filed: 1993-01-06
- Granted: 1994-09-27
- Earliest claimed: 1990-07-06
- Inventors: James S. Barton; William K. D. Borthwick; David Harvey; Julian D. C. Jones; Roy McBride
- Web page: https://patentgrep.com/patent/US5351116A

## CPC

- G01P 3/366: {by using diffraction of light (for measuring speed of fluids G01P5/26)}
- G01P 5/26: by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
- 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 differential laser Doppler velocimeter is based on the use of a modified fibre optic Sagnac Interferometer 1,2. The interferometer phase is dependent not on the target displacement, but on its velocity. The output intensity of the interferometer may be modulated by control means PC which controls loop birefringence introducing a phase bias and polarization offset between counter-propagating beams.

## Claims

### Claim 1

Apparatus for measuring velocity comprising:
an interferometer including a loop of fibre optic radiation guide;
means for launching optical signals from a source of radiation in opposite directions around said loop;
probe means located within said loop and adapted to launch said optical signals from said radiation guide towards a moveable target, and to receive said optical signals after reflection from said target, and to re-direct said received optical signals into said radiation guide.

### Claim 2 (depends on 1)

Apparatus as claimed in claim 1 further comprising phase control means to create a phase difference between said optical signals, wherein said phase control means comprises means to control birefringence in said loop of fibre optic radiation guide.

### Claim 3 (depends on 2)

Apparatus as claimed in claim 2 wherein said phase control means comprises means to control birefringence in said loop of fibre optic radiation guide.

### Claim 4 (depends on 1)

Apparatus as claimed in claim 1 wherein said phase control means is adapted to introduce a phase bias of substantially .pi./2 between said optical signals.

### Claim 5 (depends on 1)

Apparatus as claimed in claim 1 including polarization control means to substantially maintain phase quadrature in said loop.

### Claim 6 (depends on 1, 2, 3, 4, 5)

Apparatus as claimed in any one of claims 1, 2, 3, 4 or 5 wherein the source of radiation is isolated from the interferometer by means of a polarizer and a quarter-wave plate.

### Claim 7 (depends on 1)

Apparatus as claimed in claim 1 wherein means is provided to focus beams from two fibre ends on to overlapping beam waists.

### Claim 8 (depends on 1)

Apparatus as claimed in claim 1 wherein beams from two fibre ends are collimated.

### Claim 9 (depends on 1)

Apparatus as claimed in claim 1 further comprising:
coupler means for coupling radiation from opposing arms of said probe means; and
focussing means provided to launch and receive radiation from one only of said opposing arms.

### Claim 10 (depends on 1)

Apparatus as claimed in claim 1 further comprising directional coupler means for measuring radiation reflected from said target and for measuring a power of radiation entering said loop.