GB2209603A - Precision angle and wavelength measurement apparatus using an acousto-optic cell - Google Patents
Precision angle and wavelength measurement apparatus using an acousto-optic cell Download PDFInfo
- Publication number
- GB2209603A GB2209603A GB8821701A GB8821701A GB2209603A GB 2209603 A GB2209603 A GB 2209603A GB 8821701 A GB8821701 A GB 8821701A GB 8821701 A GB8821701 A GB 8821701A GB 2209603 A GB2209603 A GB 2209603A
- Authority
- GB
- United Kingdom
- Prior art keywords
- acousto
- optic cell
- wavelength
- array
- cell
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000005259 measurement Methods 0.000 title claims description 5
- 230000003287 optical effect Effects 0.000 claims abstract description 9
- 230000005855 radiation Effects 0.000 claims 1
- 230000010355 oscillation Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 1
- 230000008713 feedback mechanism Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/28—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with deflection of beams of light, e.g. for direct optical indication
- G01D5/30—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with deflection of beams of light, e.g. for direct optical indication the beams of light being detected by photocells
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
Abstract
Apparatus for measuring angular deflection or a change in wavelength of a light source consists of a photosensitive array SP linked to an acousto-optic cell, with this array providing electrical feedback to the cell in order to return a deflected light spot to a null position. The apparatus also comprises collimating and beam deflecting optics L1, L2, M and electronic signal generators and amplifiers. The difference between the initial signal to the acousto-optic cell and that required to return the deflected light spot to the null position gives a measure of the angular deflection or change in optical wavelength. <IMAGE>
Description
PRECISION ANGLE AND WAVELENGTH NEASUREMENT APPARATUS
USING AN ACOUSTO-OPTIC
Description
This invention relates to an apparatus which can be configured to measure angular changes or wavelength changes.
The need to make precision measurements of variables such as changes in angle or wavelength is a prime requirement in several branches of physical science and engineering.
This invention uses an acousto-optic cell as
active element in a dynamic system where an excursion of a light spot, initially deflected by the acousto-optic cell then further deviated by a change in angular orientation of some reflecting body, or of optical wavelength, is returned to some central position by a dynamically applied feedback generated initially in a photosensitive array and translated into a signal suitable for application to the acousto-optic deflecting cell by
signal processing.
The use of an acousto-optic cell in such a closed, dynamically operating feedback apparatus is believed to be a novel way of measuring angular deflections or changes in wavelength of the light source (which may be a laser).
Specific embodiments of the apparatus will now be given. Reference should be made to the accompanying diagram and the following equation-
(1) Angular Measurement. Light passes through the Acousto-optic cell which is pre-driven at some frequency f. A portion of the light is deflected and allowed to
on a mirror mounted on the equipment the rotation of which is to be measured.
From the mirror the light spot is reflected onto a photosensitive array, wired in such a way that the light spot
on some pre-specified portion gives a null electrical output. However if the light spot falls away from this arbitrary central position a signal, either positive or negative and scaled in size proportionately to the size of the misalignment, is generated from the array.
Using a voltage controlledhdrive the Acousto-optic cell enables the oscillator frequency to be controlled by the feedback signal generated by the photosensitive array. By suitably scaling the feedback circuitry, the spot can be driven back to the centre of the photosensitive array. Thus, if after initially being set up, the equipment bearing the mirror rotates, the reflected spot attempts to translate across the photosensitive array but in doing so automatically generates a voltage of such a sign (+ or -) and magnitude that the oscillation frequency of the voltage controlled oscillator is changed so that the initial deflection through the
Acousto-optic cell is also changed to exactly oppose the change impressed by rotation of the apparatus.
Measuring the initial and final drive frequencies being emitted by the voltage controlled oscillator thus gives a measure of the extent of the angular rotation.
(2) Optical Wavelength Measurement. The voltage controlled oscillator is again used to drive the Acousto-optic cell. Light is passed through the cell and a portion is deflected onto the photosensitive array. The feedback mechanism is exactly as detailed above.
If the interaction geometry remains fixed, then inspection of the
equation reveals that a change in optical wavelength X must cause a change in the angle of deflection because the acoustic wavelength is fixed.
However this change in angular deflection then manifests itself as a translation of the diffracted spot across the photosensitive array. This in turn gives rise to an electronic feedback signal which when applied to the voltage controlled oscillator acts in a sense to change the oscillation frequency, in turn changing the acoustic wavelength in the call and hence the deflection angle, so as to centre the deflected light spot again.
Similarly to case (1) above, the extent of the change in optical wavelength can be measured by noting the initial and final drive frequencies generated by the voltage controlled oscillator.
Claims (5)
1. An apparatus comprising an optical light source, an acousto
optic cell, photosensing array, and electronic feedback
and control circuitry by which means deflections of a spot
of light, caused by rotation of some body, or changes in
optical wavelength, can be controlled and/or measured.
2. An apparatus as claimed in claim 1 where more than one
illuminating source and photosensing apparatus may be
involved in deflections, e.g. for calibration purposes.
3. An apparatus as claimed in claim 1 where the photosensing
array is placed beyond the output plane of the device and
connection to the array is made by optical fibres.
4. An apparatus as claimed in claim 1 where the optical
light source is a laser or LED emitting visible or
ultra-violet or infra red radiation.
5. An apparatus substantially as described herein with
reference to the accompanying figure.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB878721029A GB8721029D0 (en) | 1987-09-08 | 1987-09-08 | Precision angle measurement |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8821701D0 GB8821701D0 (en) | 1988-10-19 |
| GB2209603A true GB2209603A (en) | 1989-05-17 |
| GB2209603B GB2209603B (en) | 1992-05-06 |
Family
ID=10623403
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB878721029A Pending GB8721029D0 (en) | 1987-09-08 | 1987-09-08 | Precision angle measurement |
| GB8821701A Expired - Lifetime GB2209603B (en) | 1987-09-08 | 1988-09-05 | Precision angle and wavelength measurement apparatus using an acousto-optic cell |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB878721029A Pending GB8721029D0 (en) | 1987-09-08 | 1987-09-08 | Precision angle measurement |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8721029D0 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1992018845A2 (en) * | 1991-04-12 | 1992-10-29 | British Technology Group Limited | Methods of and apparatus for measurement using acousto-optic devices |
| US5583643A (en) * | 1991-04-12 | 1996-12-10 | British Technology Group Ltd. | Methods of and apparatus for measurement using acousto-optic devices |
-
1987
- 1987-09-08 GB GB878721029A patent/GB8721029D0/en active Pending
-
1988
- 1988-09-05 GB GB8821701A patent/GB2209603B/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1992018845A2 (en) * | 1991-04-12 | 1992-10-29 | British Technology Group Limited | Methods of and apparatus for measurement using acousto-optic devices |
| WO1992018845A3 (en) * | 1991-04-12 | 1992-12-23 | British Tech Group | Methods of and apparatus for measurement using acousto-optic devices |
| US5583643A (en) * | 1991-04-12 | 1996-12-10 | British Technology Group Ltd. | Methods of and apparatus for measurement using acousto-optic devices |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8721029D0 (en) | 1987-10-14 |
| GB8821701D0 (en) | 1988-10-19 |
| GB2209603B (en) | 1992-05-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20030905 |