JPS6138505A - Optical measuring instrument - Google Patents

Abstract

PURPOSE:To measure variation in physical quantity to be measured accurately by removing intensity variation as a noise and extracting only a phase shift by the measuring device which utilizes a Mach-Zehnder interferometer using an optical fiber as an optical path. CONSTITUTION:A branch means 12 branches coherent light from a light source 10 into two pieces of luminous flux, which are distributed to a sensor optical path 14 and a reference optical path 16. The center part of the sensor optical path 14 is placed as a measurement part in an atmosphere to be measured and converts variation in physical value to be measured into variation of propagation characteristics. A detector 26 performs square-law detection by superposing light beams which are passed through the optical paths 14 and 16 and reflected by half-mirrors 18 and 20 respectively to output an interference signal S1. The detectors 24 and 28 perform square-law detection as to transmitted light beams from the mirrors 18 and 20 and output intensity signals S2 and S3 respectively. An arithmetic device 30 performs specific arithmetic on the basis of output signals of those detectors and remove intensity variation elements except intensity variation due to interference from an interference signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a device for measuring various physical quantities, and particularly to an optical measuring device using a Matsuhatsu Enda interferometer.

[Prior art]

A method using an optical interferometer is known as one method for precisely measuring changes in physical quantities.

Among such optical interferometers, the Matsuhatsu Enda interferometer is typical, and many others have been proposed that use optical crystals or optical fibers as well as spatial propagation optical paths.

A measurement device using a Matsuhatsu Enda interferometer using an optical fiber uses one of two optical paths (sensor optical path).
is located in the measuring section, and this sensor optical path and the other optical path (
This causes the output light of each light beam passing through the reference optical path) to interfere with each other, and when the physical conditions (temperature, pressure, etc.) around the sensor optical path change, the propagation characteristics of the sensor optical path change accordingly. This method takes advantage of the fact that the state of interference changes.

In other words, when the output lights of the respective light fluxes passing through the two optical paths are matched and observed, the bright and dark stripes move spatially due to changes in the physical conditions around the sensor optical path. It is possible to know changes in the physical quantity that is the object of measurement. Note that changes in physical quantities can be similarly measured by observing temporal changes in brightness and darkness at one point instead of observing the movement of bright and dark stripes.

By the way, in this type of device, changes in the physical quantity to be measured change the state of interference because changes in the physical quantity affect the refractive index and optical path length of the optical fiber that is the sensor optical path, and the propagation related to the phase of the sensor optical path. This is because it induces a change in the characteristics, but in reality, it is often accompanied by other changes in the propagation characteristics, such as changes in the electromagnetic field vibration plane, mode conversion of the propagation mode, and intensity changes based on these changes.

In this type of device, the occurrence of a change in intensity due to a factor other than interference means that the contrast of bright and dark interference fringes changes, which acts as noise. In particular, when observing temporal changes in brightness and darkness at one point, it is difficult to distinguish whether the change in brightness is due to the influence of interference or to factors other than interference, and it is difficult to strictly measure changes in physical quantities. It was not possible to take full advantage of the characteristics of this type of device, which is the ability to

[Summary of the invention]

The present invention has been made in view of the above-mentioned problems, and its purpose is to remove intensity changes as noise and change the phase in a measurement device using a Matsuhatsu Enda interferometer with an optical fiber as the optical path. The object of the present invention is to provide a device that can accurately detect changes in physical quantities to be measured.

In order to achieve such an object, the present invention uses a Matsuhatsu Enda interferometer that uses an optical fiber as an optical path, and extracts the intensity of each light passing through a sensor optical path and a reference optical path as a first intensity signal and a second intensity signal, respectively. , the intensity of the light passing through the sensor optical path and the reference optical path is made to interfere with each other, and the intensity of the light is extracted as an interference signal, and the interference signal and the first . By performing a predetermined calculation based on the second intensity signal, intensity change elements other than the intensity change due to interference are removed from the interference signal.

Hereinafter, the present invention will be described in detail along with examples.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention.

A light source 10 emits coherent light. The branching means 12 branches the coherent light from the light source 10 into two beams, and distributes them into a sensor optical path 14 and a reference optical path 16, respectively.

Both the sensor optical path 14 and the reference optical path 16 are constructed of optical fibers, and the other end faces half mirrors 18 and 20.

The central portion of the sensor/sample optical path i4 is placed in the atmosphere to be measured as the measurement unit 22, and converts changes in the physical quantity to be measured into changes in the propagation characteristics of the optical path.

On the other hand, the reference optical path 16 has the same optical path length as the sensor optical path 14 and is placed in a stable atmosphere.

The half mirror 18 receives the light emitted from the sensor optical path 14 and divides it into transmitted light and reflected light, and sends the transmitted light to the detector 24.
The reflected light is projected onto the detector 26.

Similarly, the half mirror 20 receives the light emitted from the reference optical path 16 and divides it into transmitted light and reflected light, projects the transmitted light to the detector 28 , and projects the reflected light to the detector 26 .

In the detector 26, the reflected light from the half mirror 18 and the reflected light from the half mirror 20 are superimposed, and the detector 26 performs square law detection of this superimposed light to detect the intensity of this light and generate an interference signal. Output as S1. However, this interference signal includes not only an intensity change based on interference, that is, an intensity change based on the phase difference between the two light beams, but also an intensity change due to a direct influence in the measurement unit 22.

The detectors 24 and 28 receive the transmitted light from the half mirrors 1B and 20, perform square law detection, detect the intensity thereof, and output the detected light as an intensity signal 52°S3.

The output signal lines of the detectors 24, 26 and 28 are all connected to an arithmetic unit 30, and the arithmetic unit 30 performs a predetermined operation described below based on the output signals of these detectors, and determines whether the light passes through different optical paths. A signal indicating only a change in the phase difference between the two light beams is output.

Next, the operation of this embodiment will be explained focusing on the calculation process in the calculation device 30.

If the complex amplitude of the light at the end of the reference optical path 16 on the half mirror 20 side is Aexp(jφ''), the complex amplitude of the light at the end of the sensor optical path I4 on the half mirror 18 side is different from the phase and In response to a change in intensity, KAexp(jφS) is obtained, where A is a constant determined by the light source, φr and φS are phases, and are intensity change factors in the measuring section 22.

Since reflected light from both the half mirrors 18 and 20 enters the detector 26, the complex amplitude of the incident light here is ('A Aexp (jφr) + 'A K Aexp
(jφs)).

To find the intensity of light with a complex amplitude Δexp(jφ), Aexp(jφ) and its complex conjugate Aexp(−jφ)
It is nothing but taking the product of .

Therefore, the complex amplitude (HAexp(jφr) + 'A K Aexp(j
The strength ■1 of φs)) is as follows.

1+= ((%Aexp(jφr) + 'A K A
exp(jφ5))X ('A Aexp(-jφr)
+ 'A K Aexp (-jφS)] = (!4
A)"X-(exp(jφr) + Kexp(jφ5
)) x (cxp(-jφr) + Kexp(-jφ
, )) = (HA)”X (1+K” +K (exp
(j(φr-φS)+exp(-j(φr-φ5))
) = (〃AνX (1+K” + 2 Kcos(φr−
φs))・・・・・(1) On the other hand, the complex amplitude of the light incident on the detector 24 is 'AK
Since Aexp(jφS), its intensity I2 is I
z=1/4 A"-K"...(
2), and the complex amplitude of the light incident on the detector 28 is %
Since Aexp(jφr), its strength ■, is I,
=174 Az ・ ・ ・
・(3) becomes.

Interference signal St and intensity signal S2 manually input to the calculation device 30
．． Since S3 is a signal that indicates the strength T, It, and 13, respectively, ■ If we multiply S3 by 4 and take its square root, we can calculate A. ■ If we divide S2 by 33 and take its square root, we can calculate K. can be calculated, and after destroying S2 and S3 from S1, use the results of ■■! By dividing by 4A''K, cos (φr−φS) can be calculated.

cos (φr−φS) is the cosine of the one-order difference between the light passing through the sensor optical path 14 and the reference optical path 16, and only the intensity change due to interference can be known from the change in this value. It is possible to accurately detect changes in physical quantities in .

FIG. 2 is a schematic configuration diagram when the device of this embodiment is used for temperature detection, and the same parts as in FIG. 1 are denoted by the same reference numerals.

The optical fiber 14 serving as the sensor optical path is shown wound into a coil and inserted into the measuring section 22. The purpose of winding the sensor optical path into a coil in this way is to increase the length of the optical path placed in the atmosphere to be measured, and by doing so, the detection power can be increased.

The reason why the optical fiber 16 serving as the reference optical path is wound into a coil is to make the optical path length equal to that of the sensor optical path.

FIG. 3 is a partial configuration diagram when the device of this embodiment is used for pressure detection.

In the measurement unit 22, a pressure change can be measured by applying a microventure to the optical fiber 14, which is a resensor optical path, according to the pressure to be measured, and detecting a change in propagation characteristics due to the microvent.

FIG. 4 is a block diagram showing another embodiment of the present invention.

In this figure, the same or corresponding parts as in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In this implementation (i), optical shutters 40 and 42 are provided in the sensor optical path 14 and the reference optical path 16, and
This optical shutter 40. /12 to generate the interference signal St.
and intensity signal S2. This is to detect S3 in a time-division manner.

The control calculation unit 44 includes a shutter driver 441. Timing control means 442. Buffer 443 and arithmetic unit 444
Equipped with.

The shutter driver 441 drives the optical shutters 40.42 in response to a signal from the timing control means 442. First, when both optical shutters 40.42 are opened, the two beams of light interfere with each other on the detector 26, and are detected. The receiver 26 outputs the interference signal St to the buffer 443.

Next, the optical shutter 40 is left open and only the optical shutter 42 is closed. Then, since only the light that has passed through the sensor optical path 14 is irradiated onto the light receiving section of the detector 26, the output signal of the detector 26 is input to the buffer 443 as the intensity signal S2 of the light that has passed through the sensor optical path 14.

Next, when the optical shutter 40 is closed and the ξ optical shutter 42 is opened, the output signal of the detector 26 is input to the buffer 443 as the intensity signal S3 of the light passing through the reference optical path 16.

With this, one cycle of photodetection operation is completed, and the interference signal S12 intensity signal S2. By inputting S3 to the arithmetic unit 444 and performing the same arithmetic operation as the arithmetic operation in the arithmetic unit 30 of the first embodiment described above, c
The value of os(φr−φS) can be calculated. However, in this embodiment, the interference signal SL, the intensity signal S2.
S3 is the interference signal S1.S3 in the first embodiment described above. Each of the intensity signals is 22 times, or 4 times, the intensity signal S2.33.

Similar to the first embodiment, it is possible to know the change in the physical quantity in the measuring section 22 from this value.

In addition, if a mechanical shutter is used as the optical shutter, the distance will be several meters.
Switching of s is easy and is sufficient to detect changes in normal physical quantities, but to measure even faster decreases, an optical switch or optical modulator can be used in the optical shack. For example, an acousto-optic modulator can be used to According to the method, switching time of about 1 μs is possible.

〔Effect of the invention〕

As explained above, according to the optical measuring device of the present invention, the intensity of each light passing through the sensor optical path and the reference optical path is extracted as an intensity signal, and the lights passing through the sensor optical path and the reference optical path are caused to interfere with each other. By extracting the intensity of the light as an interference signal and performing a predetermined calculation based on the interference signal and the intensity signal, intensity change elements other than the intensity change due to interference are removed from the interference signal, so the light passing through the sensor optical path is It is possible to extract the cosine of the phase difference between the light passing through the reference optical path and the reference optical path, and it is possible to detect changes in various physical quantities extremely accurately.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a schematic configuration diagram when the device of this embodiment is used for temperature detection, and Fig. 3 is a block diagram of the device of this embodiment used for pressure detection. FIG. 4 is a partial block diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 10... Light source, 12... Branching means, 14... Sensor optical path, 16... Reference optical path, 18.20...
・Half mirror 122...measuring part, 24, 26.28
...Detector, 30,444...Arithmetic device, 40.4
2... Optical shutter.

Claims (2)

[Claims] (1) In a Mach-Zehnder interferometer with an optical fiber as the optical path, the intensity of each light passing through the sensor optical path and the reference optical path is extracted as a first intensity signal and a second intensity signal, respectively, and the light passes through the sensor optical path and the reference optical path. The intensity of the light produced by interfering with each other is extracted as an interference signal, and by performing a predetermined calculation based on the interference signal and the first and second intensity signals, intensity change factors other than the intensity change due to interference are extracted from the interference signal. An optical measuring device characterized by removing. (2) The optical measuring device according to claim 1, wherein the interference signal and the first and second intensity signals are extracted in a time-division manner by the same detector.