SU1693382A1 - Method of measuring change of phase shift of light waves - Google Patents

Abstract

The invention relates to a measuring and measuring technique. The purpose of the invention is to expand the measurement range by limiting the variation of the frequency of an electrical signal depending on the phase shift. The method consists in the photo mixing of the orders of the reference and measuring beams passing through the acousto-optic modulator, converting the optical signal into an electrical signal, changing the excitation frequency of the acousto-optic modulator depending on the frequency of the electrical signal and determining the moments of an abrupt change in the frequency of the electrical signal. 1 silt

Description

The invention relates to an instrumentation technique and can be used to control movements.

The purpose of the invention is to expand the measurement range by limiting the change in the frequency of the electrical signal depending on the phase shift.

The drawing shows the block diagram of the device that implements the method.

The device consists of an optically coupled laser 1, a Michelson interferometer made of a beam splitter 2, optically coupled by a beam splitter 2 of the measuring reflector 3 and a reference reflector 4, and a double optical wedge 5 located between the reflector 3 and the beam splitter 2 optically coupled to a beam splitter 2, lenses 6, an acousto-optic modulator 7 with an emitter 8 ultrasonic waves, a diaphragm 9, an optical unit 10 and a photodetector 11, a switch 12 connected between the output of the photodetector 11 and the input of the radiator 8, torus 13 harmonic oscillations, the output of which is connected to the second input of the switch 12, and the frequency detector 14, the input of which is connected to the output of the photodetector 11.

The method is carried out as follows.

The laser radiation 1, directed to the beam splitter 2, is divided into measuring and reference light beams. Reflected from the reflectors 3 and 4, the light fluxes Eu and E0p are spatially combined on the beam splitter 2 at a diffraction angle a given by the double optical wedge 5 and directed to the modulator 7, in which, by excitation of the generator 13, through the switch 12 of the emitter 8 a running ultrasound wave is created (Y38). After diffraction of the light waves Eu and E0p on V3B by the diaphragm 9, the spatially aligned orders of the diffraction spectrum are filtered onto the block 10: zero diffraction (L

WITH

about about with

00

go

pore before the measuring light wave Pu (o) and any of the first diffraction patterns of the reference light wave E0p (1). Block 10 allows you to adjust the offset angle of the diffraction spectrum, changing under the influence of positive feedback through the switch 12, providing the necessary spatial period between abrupt changes (breakdowns) in the output signal frequency, thereby making it possible to vary the resolution of the device.

Spatially aligned orders of the diffraction spectrum after block 10 are directed to a photodetector 11, which forms an electrical output signal with a frequency equal to the difference between the interacting frequencies of diffraction orders Eu (o) and E0n (1). The Uwig signal is fed to the input of the frequency detector 14, by means of which frequency breakdowns are detected, and via the positive feedback channel through the switch 12, to the excitation of the emitter 8. The harmonic oscillator 13 at the frequency f0 and the switch 12 serve to arrange positive feedback. Generator 12 provides excitation of the radiator at the time of the breakdown of the optical communication in the device and at the initial time of operation.

The essence of the method is as follows.

The light waves Eu and E0p after interaction with ultrasound B and spatial filtration are described by simplified expressions.

-j (± Ai o) t En (t) Eu (o) P, (3)

and the expression (2) on the basis of (3) is written as

Synthesize U0 sin (2 l (fM ± D f)) t, (A)

where ± Af ± v0 is the frequency shift of the output signal,

The presence of positive feedback with a change in the frequency of the output signal leads to a change in accordance with (4) of the frequency of the ultrasound in modulator 7 due to the final propagation velocity of the ultrasound Vy3B. reaching the coordinate of the interaction YO for the time determined by the formula

At

 Wo

V

bonds in

(five)

It has been established that between the frequency breakdowns of the output signal, there is a lanech / dependence on the measured phase shift 25, described by the expression

f KP rvh,

(6)

one

where KP - transmission coefficient KP -d-

The diffraction angle of the interfering light waves is determined as follows.

35

and arcsin

Eu (t,) Ei (o) I

- / it

Eon (t) Eop (1) P

-j (l-fm) t

where Eu (0) is the zero order of the diffraction of the light wave;

Eop (1) is the first order of diffraction of a light wave;

V0 is the optical frequency;

fM is the frequency of ultrasound V.

As a result of photo displacement of the optical optical components Eu (o) and Eop {1), an output signal is formed at the output of the photodetector, which is described as

ivyh081p2ltmt .. (2)

Taking into account that when a controlled object moves, a Doppler frequency shift (± Av0) of a measuring light wave occurs, the expression (1) for Ец (m.) Takes the form

Vv

where A is the length of the UT, A.

Tm

When the frequency of the output signal is varied according to (4), the frequency of the RAS, the length of the RAS, and the diffraction angle a. When the frequency of the output signal reaches a certain value of Af, a frequency breakdown occurs.

due to the departure of the reference light wave beyond the limits of stable photoreception. Block 10 allows you to set the spatial period between interruptions of the output frequency by adjusting the angle

shifts of diffraction orders.

The spatial period between the frequency breakdown of the output signal

55

I - ° ftf 4 n Vy, B

and the phase shifts of the light wave corresponding to the spatial period-DE

4, TL The invention The method for measuring the change in the phase shift of light waves, which consists of sending reference and measuring light waves to an acousto-optic modulator, combining the diffraction order of the output spectrum by photo-shifting, converting the optical signal into an electrical one in the photo-shifting zone, cha0

the frequency of the electrical signal and the excitation frequency of the acousto-optic modulator depending on the frequency of the electrical signal, varying heme. that, in order to extend the measurement range, the angle between the diffraction orders is chosen, based on the required measurement range, the breakdown of the oscillations of the frequency of the electrical signal is recorded, and the change in the phase shift of the measuring light wave is judged by the number of failures of the frequency oscillations.

Claims (1)

Claim A method of measuring the phase shift of light waves, which consists in sending the reference and measuring light waves to the acousto-optic modulator, combining the diffraction orders of the output spectrum by photographing, converting the optical signal into an electric signal in the photographic zone, measuring the frequency of the electric signal and changing the frequency of the acousto-optical modulator depending on the frequency of the electrical signal, different heme. 5 that, in order to expand the measurement range, the angle between the diffraction orders is selected based on the required measurement range, the stall of the oscillations of the frequency of the electric signal is recorded, and 10 about the change in the phase shift of the measuring light wave is judged by the number of stalls of the frequency oscillations.