JPS5977306A - Interferometer type measuring device - Google Patents

Abstract

PURPOSE:To make a device compact, by splitting the light from a light source into a light beam, which is inputted to a Bragg cell, and a light beam, which is inputted to an object to be measured, through a half mirror. CONSTITUTION:Part of light 100 having a frequency f0, which is outputted from a laser light source 1, is reflected by a half mirror 5 and inputted to a Bragg cell 2. Then, a first modulated light beam having a frequency of f0+f1 is obtained. The light beam is reflected by a reflecting mirror 4 and inputted to a light receivig device 7 through the Bragg cell 2 and the mirror 5 again. Meanwhile, the rest of the light 100, which has passed the mirror 5, is projected to a reflecting mirror 6, which is attached to an object to be measured. The light reflected by the mirror 6 becomes the light having a frequency of f0+DELTAf. The light is reflected by the mirror 5 and merged with the light 103. The result reaches the light receiving device 7. An electric signal 105 of f1+ or -DELTAf is obtained from the light receiving device. The signal 105 and an electric signal 106 having a frequency f1 from a driving circuit 3 are inputted to a measuring circuit 8, and a moving distance l is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION a) Technical Field The present invention relates to a four-measurement device for measuring the distance of a moving object;
In particular, the present invention relates to an optical interference type measuring device using an acousto-optic element.

b) Technical Background and Problems It is well known that the frequency of light can be shifted by the frequency of sound waves using an acousto-optic device such as a Bragg cell. This frequency-shifted light interferes with the original frequency,
The amount of displacement of various objects to be measured can be detected from the difference frequency signals generated at this time. This technique is called a heterogain detection method, and has the characteristic that information (one frequency change, one phase change) is converted into a signal 42 whose frequency is reduced to a difference frequency, and the displacement of the object to be measured (one frequency change, one phase change).

Figure 1 is a block II diagram of a conventional optical interference type measuring device 9 for measuring moving distance.

Frequency f emitted from laser light source 1. The light 100 is emitted from the Bragg cell 2 (two people).
. The current θ dimension 102, the frequency is f. First-order modulated light 103 shifted by 100 m, the frequency is f. The light of the secondary light control 104 etc. shifted to +2 is separated and output.

Primary modulated light 103): l, reflected by the reflecting mirror 4, no.
The light passes through the fumirror 5 and reaches the light receiver 7. On the other hand, the zero-order light 102 passes through the mirror 5 and is emitted toward the measurement target, is reflected by the reflecting mirror 6 attached thereto, and is reflected back to the mirror 5 (= return), where it is reflected at 90
'The light changes direction and merges with the primary modulated light 103 and reaches the light receiver 7 (secondary modulated light 103).

Here, when the object to be measured moves at a speed V, the frequency of the O-order light 102 reflected by the reflecting mirror 6 changes by a frequency Δf corresponding to the speed V due to the Doppler effect, and becomes ±Δf.

Δ〕=knee=2v ・・・・・・+1)272
However, λ is the wavelength of the output light of the O-order light 102.

At the output of the photodetector 7, a magnetic signal 105 having a frequency of L±Δf, which is reduced to a frequency equal to that of the heterodyne detection method described above, is obtained. This electrical signal 105 and drive circuit 3
The circuit 8 measures the electrical signal 106 of the frequency given by the circuit 8.
(The movement distance l is detected by two people using the method described below. In other words, the measuring circuit 8 is a reversible pulse signal (two-way addition and subtraction) corresponding to the frequency of the electric signals 105 and 106. Equipped with a counting circuit, it counts a period of +2 from time t1.This counted value N means 2Vλ from the relationship in equation (2), and the moving distance l can be measured by transforming it as shown in equation (3). .

2 = T(X2 xt) = Tl --(2)
In the conventional configuration as described above (2), there is a problem that the deflection angle φ of the primary modulated light 103 from the Bragg cell 2 is extremely small. For example, the deflection angle φ is about 14 milliradians, and this value is Even if the beams 102 and 103 are separated by a distance of 1 meter, they will be separated by only 14 mm.
This is a problem that limits the physical shape of the mirror i, making it extremely difficult to install them, and hindering miniaturization of the optical interferometric measuring device 9.

C) Purpose of the Invention The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an optical interference type measuring device that can be made smaller by changing the optical system.

d) 1 Existing Summary of the Invention The present invention includes a laser light source that outputs a first optical signal of a first frequency, and an ultrasonic wave L that outputs a drive signal of a frequency of a conduit 2.
1 (The optical signal of two frequencies interferes with the dynamic circuit and the acousto-optic element which is energized by the drive signal and outputs the optical signal by changing the frequency of the IZ2 and deflecting the Kojin Kai No. 8 of the first frequency. a light-receiving circuit that outputs a magnetic signal having a difference frequency, and a second optical signal that reflects a part of the tenth optical signal and enters the acousto-optic element, and transmits a fourth optical signal for measurement. Obtain a third optical signal to be emitted twice - reflect the primary modulated light of the second optical signal that has been deflected and output from the acousto-optic element and travel backward along the original optical path again. The light is transmitted through the acousto-optic element and transmitted through the -11 mirror to receive the light in the i-path (the reflecting mirror that emits the two beams), and the third optical signal is transmitted to the measuring object (which is irradiated with the two beams and subjected to the Doppler effect) whose position changes. It is a block configuration diagram of an example of how the reflected light is reflected by the -11 mirror and interferes with the linear variable V4B0.The same reference numerals as in Figure 2 and 1 indicate the same functions. In the optical interferometric measurement device 10 shown in Figure 2, a part of the light 100 with a frequency f. emitted from the laser light source 1 is reflected by the Bragg cell 2 (two people irradiated). The black cell 2 is energized by an ultrasonic signal of frequency f1 from the drive circuit 3 to obtain 01st modulated light 103 with frequency f.+f.
The light is reflected by the reflecting mirror 4 and returned to the original optical path, passes through the Bragg cell 2 again, and then passes through the mirror 5 and is guided to the light receiver 7 (two configurations).

On the other hand, the frequency f emitted from the laser light source 1. A part of the light 100 passes through the -7 mirror 5 and is emitted toward the measurement target (two reflecting mirrors 6).The light reflected by the reflecting mirror 6 is affected by the Doppler effect as described above. (From second f. The light with the frequency of ±Δf is reflected by the synoof mirror 5, merges with the primary modulated light 103, and reaches the light receiver 7. The light with the frequency of A±Δf from the light receiver 7 The moving distance l can be detected in the same manner as in FIG.

FIG. 3 shows a detailed configuration of the optical system shown in FIG. 2.

In the figure, light 100 at a frequency that is incident on the -.-7 mirror 5 from the laser light source is partially reflected and enters the Bragg cell 2. The Bragg cell 2 is driven by the drive circuit 3 from the left side as shown in the figure with an ultrasonic signal of frequency f,
The incident light causes a negative Doppler effect, A - f,
primary modulated light 103 having a frequency of is obtained. This primary modulated light 1
03 is the 0th order light 1 where the incident light goes straight and passes through.
The angle φ is on the left side as in the optical path 107 with respect to the optical path 108 of 02.
only deflected. The reflecting mirror 4 has a reflecting surface that receives the primary modulated light 1.
03 so that the reflected light passes through the optical path 107 and returns to the original position C2 of the Bragg cell 2. (In this case, the reflected light of the 0th order light 102 is shifted from the original position of the Bragg cell 2 by 1 to 2 millimeters (backward). This reflected light is prevented from entering the Bragg cell 2 (it may be blocked). The optical path The primary modulated light 103 that has returned through 107 is not frequency modulated again, goes straight through the Bragg cell 2, passes through the optical path 109, passes through the nof mirror 5, and enters the light receiver 7.

On the other hand, a part of the incident light 100 having a frequency f which passes through the -11 mirror 5 and faces the measurement object (two directions) is reflected at a reflection angle α by the reflection mirror 6 that moves together with the measurement object, and is reflected at a frequency fo±.
The light of Δf passes through the optical path 110) and returns to the first mirror 5, where it is reflected and merges with the transmitted light of the optical path 109 to reach the light receiver 7 (2). L±
Optical signals of two frequencies having a frequency difference of Δf interfere and enter, and as described above, an electric signal 105 of a frequency of h±Δf is obtained, and the moving distance of the object to be measured can be measured.

In the configuration shown in FIG. 3 (2), in order to match the beams of light of two frequencies toward the receiver 7, the condition α = φ is required according to the principle of geometric optics. The optical paths 109 and 110 must have a symmetrical relationship (-) with respect to
2, the beams of reflected light on the optical path 1100 are shifted from their original positions and no longer match. However, the effective diameter of the laser beam is around 1 φ, and in addition, the above-mentioned through angle α is equal to φ, which is an extremely small angle, and the distance of movement of the object to be measured is limited. As long as the diameter of the laser beam in the optical path 110 is large, the beam width will not be a problem and the desired purpose can be achieved and a sufficiently comprehensive measurement can be performed. The range can be expanded further.

It goes without saying that the optical interferometric measuring device of the present invention is effective in measuring vibration amplitude.

f) Other Embodiments of the Invention The optical interferometric measurement device of the present invention is not limited to one that measures displacement in spatial distance, but may also be one that detects changes in the optical path length of an optical fiber. FIG. 4 shows an alternative method according to the present invention in which the optical input/output conditions for the optical fiber 11 are set so as to be equal to the reflection angle α of the reflector 6 (2) shown in FIG. 3, and changes in the optical path length of the optical fiber 11 are measured. This is an optical interference measuring device according to an embodiment of the present invention.

As mentioned above, it can be measured with an accuracy of the unit of light wavelength λ, so it is possible to measure slight expansion and contraction of optical fibers, and it can also be applied to the measurement of other physical quantities that have a correlation with the expansion and contraction of optical fibers. can.

g) Effects of the Invention According to the present invention, it is possible to obtain a miniaturized optical interference type measuring device using an acousto-optic element such as a Bragg cell.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional photon waveform measurement device.
Figure 2 is a schematic diagram of the block 41 of the interferometric measuring device d according to the present invention, Figure 3 is a detailed diagram of the optical system shown in Figure 2, IB4
tl diagram, 4th (unfortunately, the optical interferometer σI11 device II't component diagram C of other embodiments of this invention is required. 1... Laser light source 2... Bragg cell (fr J optical element) 3...j
lXl rotation 4.6...Reflector 5...-7 Mirror 7...Receiver 8...NJi constant circuit 11...Optical fiber 102...0th order light 103... Primary modulated light (7317) Agent Patent attorney Norihiro Chika Right (and 1 other person) Figure 2, 1C, 3

Claims (1)

[Claims] a laser light source that outputs a first optical signal at a first frequency;
an ultrasonic drive circuit that outputs a drive signal of a second frequency;
An acousto-optic element energized by the drive signal changes the optical input signal of the first frequency by the second frequency, deflects it, and outputs it; a light-receiving circuit that outputs an electric signal; and a light-receiving circuit that reflects a part of the first optical signal and transmits it as a second optical signal to the acousto-optic element and emits it for m111 constant.
a half mirror that reflects the optical signal; and a half mirror that reflects the primary modulated light of the second optical signal that is deflected and output from the acousto-optic element to reverse the original optical path and pass through the acousto-optic element again. The third optical signal is transmitted through the half mirror to the light receiving circuit (two reflecting mirrors) and the third optical signal is irradiated to the measurement target (two, and the reflected light is reflected by the half mirror to be modulated by the first modulation). An optical interference type measuring device characterized in that the light is made to enter the light receiving circuit in such a manner as to interfere with the light.