Velocimeters

Details Velocimeters Velocimeters

1993-01-06

1994-09-27

Buczinski, Stephen C.

Optics: measuring and testing

Velocity or velocity/height measuring

With light detector

356350, G01P 336, G01B 902

Patent

active

053511166

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to velocimeters and, in particular, to differential laser Doppler velocimeters based on the use of a modified fibre optic Sagnac interferometer. A feature of the invention is that the interferometer phase is dependent not on the target displacement, but on its velocity.


BACKGROUND OF THE RELATED ART

Unlike interferometers used to measure a Doppler frequency shift directly, the practical use of the Sagnac is not restricted to very high velocities. It finds particular advantage in the measurement of high frequency oscillatory velocities, where the direct response to velocity effectively discriminates against unwanted low frequency components. To optimize the sensitivity of the interferometer, we have introduced a .pi./2 phase bias between the two beams, using a passive technique based on control of the birefringence of the fibre loop.
Fibre optic techniques in laser velocimetry are known (Jackson, D. A., Jones, J. D. C. 1986 Fibre Optic Sensors. Optica Acta 33, 1469, Jackson, D. A., Jones, J. D. C. 1986 Extrinsic fibre optic sensors for remote measurement: parts one and two. Opt. and Laser Tech. 18, 243, 299). Many commercial instruments are now available which use fibres to form flexible waveguides between a source/detector module and a remote probe. It is thus appropriate to consider further applications of fibre optics in which their properties are exploited to facilitate optical signal processing of the Doppler signal. In particular, the use of fibres and fibre components allows the implementation of interferometer configurations which are impractical using conventional optics.


SUMMARY OF THE INVENTION

In the present work, we have considered interferometer arrangements in which the detected optical phase is a function of target velocity, rather than the more usual situation in which an optical intensity is amplitude modulated with a frequency proportional to target velocity. He have thus sought to transfer the signal processing step of frequency discrimination from the electronic to the optical domain.
Direct measurement of velocity is of particular value in measurements on oscillatory targets or flows. For example, consider the use of a conventional reference beam laser velocimeter (such as one having the configuration of a Michelson interferometer, in which the target is effectively one mirror of the interferometer) used to measure out of plane vibration. The phase of the interferometer is dependent on the displacement of the target surface, and hence for a given velocity the amplitude of the phase modulation declines as the oscillation frequency is increased. Hence the measurement of high frequency oscillations is difficult, and it is generally necessary to use active phase modulation techniques to recover the high frequency signal in the presence of unwanted larger amplitude low frequency ambient vibrations.
According to the present invention there is provided a velocimeter comprising an interferometer including a loop of fibre optic radiation guide, means for launching optical signals 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, to receive said signals after reflection from said target and to re-direct said signals into said radiation guide.


BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
FIG. 1 shows a fibre optic Sagnac interferometer used in one embodiment of the invention,
FIG. 2 shows an experimental layout,
FIGS. 3(a) through 3(d) illustrate various probe configurations,
FIG. 4 is a graphical representation of measurements of signal amplitude,
FIG. 5 is a display of a network analyzer trace, and
FIG. 6 is an oscilloscope trace.


DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 2 of the drawings, this shows a new approach based on the fibre Sagnac interferometer. Classical interferometers have

REFERENCES:
patent: 4470696 (1984-09-01), Ballard
patent: 4571080 (1986-02-01), Papuchon et al.
patent: 4885462 (1989-12-01), Dakin
patent: 4902127 (1990-02-01), Byer et al.
patent: 4906092 (1990-03-01), O'Meara
Optics and Laser Technology, vol. 18, No. 5, Oct. 1986, Butterworth & Co. (Publishers) Ltd., (London, GB) D. A. Jackson et al.: "Extrinsic fibre-optic sensors for remote measurement: part one", pp. 243-252, see p. 243, line 1-p. 244, col. 1, line 37; FIG. 5 (cited in the application).
Optics and Laser Technology, vol. 1, No. 6, Dec. 1986, Butterworth & Co. (Publishers) Ltd., (London, GB) D. A. Jackson et al.: "Extrinsic Fibre-optic sensors for remote measurement: part two", pp. 299-307, see abstract, p. 229; FIG. 2-6 (cited in the application).

Affiliated with

Also associated with

Rating

Velocimeters does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Velocimeters, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Velocimeters will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1268915