JPS5937404A - Strain gage using optical fiber for retaining polarization plane - Google Patents

Abstract

PURPOSE:To improve the accuracy in strain measurement by juxtaposing an optical fiber for retaining polarization plane for a reference and an optical fiber for retaining polarization plane for measurement. CONSTITUTION:A light source part 7 contg. a laser diode 4, a half mirror 3a, capacitors 2a, 2b and an optical fiber keep plate 12a, etc. and a photodetection part 8 contg. a photoelectric detector 5, a half mirror 3b, collimators 6a, 6b and an optical fiber keep plate 12b, etc. are provided at both ends of an installation plate 9. An optical fiber 1a for retaining polarization plane for a reference and an optical fiber 1b for retaining polarization plane for measurement are guided by means of fiber guides 13 and are laid between said parts. A containing cover 14 formed with plural slits 10 for moving and plural holes 11 for drawing out are formed to the plate 9 disposed in such a way. The upper parts of the guides 13 are projected from the slits 10 and the strain applying parts S of the fiber 1b are drawn out of the holes 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain meter that uses optical interference, and particularly to a strain meter that performs interference using polarization-maintaining optical fibers.

FIG. 1 is a system diagram of a conventional strain meter that utilizes optical interference. LA and LB are both polarization maintaining optical fibers,
A strain applying section S is provided in a portion of lb.

The monochromatic light emitted from the L/--ff Io F' (LD) 4 is split into two by a half mirror 3a tilted at 45 degrees, and the reflected light is sent to a polarization-maintaining optical fiber by a condenser 2a. The transmitted light is focused on the end face of each 1a, and the transmitted light is connected to a polarization-maintaining optical fiber by a condenser 2b.
The beams are focused and incident on the end faces of each 1b.

The light beam propagating through each polarization-maintaining optical fiber (la, lb) and emitted from the opposite end face is turned into a parallel light flux by a collimator 6a6b installed so that the exit end face becomes the focal position, and is converted into a parallel light flux by a half mirror 3b. The amount of light is alternately detected by the photoelectric detector 5 and compared. In the method of detecting light alternately using the same photoelectric detector 5 and the method of 1 to 1, polarization preserving optical fibers 1 t+ and 1 b are used to rotate polarized light whose polarization planes are orthogonal to each other. Photon II'Ii1
This can be achieved by alternately detecting the intensity of the light, or by alternately causing the light flux to enter the photoelectric detector 5 by mechanical adjustment.

The strain meter configured in this way is capable of measuring f of the strain of the polarization-preserving optical fibers (l a , l h), interference in the standard state, and changes due to temperature changes, mechanical pressure, etc. From the changes in the state of interference when given, the temperature and pressure of 8 parts are 1 liter.
Although it has the advantage of being able to determine the temperature of the wavefront, since the wavefront preserving optical fibers are installed at different locations, temperature differences occur, reducing measurement accuracy. Also,
If a measurer accidentally touches one of the polarization preserving optical fibers 1 during measurement, the amount of measured light tends to change, resulting in insufficient reliability.

The present invention eliminates the drawbacks of the prior art, improves measurement accuracy by keeping the reference and measurement polarization-maintaining optical fibers always in the same temperature state, and provides a polarization-maintaining optical fiber that is small and easy to handle. The purpose is to provide a strain meter using Phi A12, and its features are that a reference line and a measurement line are fixed to a movably installed Phi A guide, and a flat horizontal storage container is installed. In addition to laying it in a wavy manner,
When the measurement line is pulled out and the strain applying section is installed at the place where the strain occurs, the Phi and F guides are moved so that they are laid in a lower wave shape.

Figure 2 shows a polarization-maintaining optical fiber, which is an embodiment of the present invention.
2 is a perspective view of a strain meter using a variety of devices, and the same parts as in FIG. 1 are given the same reference numerals. Figure 3 is still the storage lid 1 shown in Figure 2.
FIG. 4 is a perspective view showing the internal arrangement with part 4 removed. Laser diode 14, No.7 mirror 3a, capacitor 2a
. In between, a reference polarization-maintaining optical fiber 1a and a measurement polarization-maintaining optical fiber 1b are guided by a fiber guide 113 and laid.

Multiple moving slits 1 are installed on the installation stand arranged in this way.
When the storage lid 14 having a plurality of extraction holes 11 is attached, the state shown in FIG. 2 is obtained.

At this time, a part of the fiber guide 13 protrudes from the moving slit 10 to the 11th position, and a part of the extraction hole 11 is used to pull out the strain applying part S of the polarization-maintaining optical fiber for measurement.
ing.

FIG. 4 is a perspective view of the fiber guide r1a of FIG. 2. The protruding portion of this fine guide that slides through the moving slit 10 is provided with a slot 17. This slot +7 makes it easy to insert the polarization-maintaining optical fiber for measurement into the horizontal hole 16, and also improves the contact between the moving slit 1o and the fine guide 13.

The storage lid 14 may be made of either a metal plate or a synthetic resin plate. There is a horizontal hole 16 at the bottom of this Phi-gai la.
is equipped with a polarization maintaining optical fiber for measurement.
The downward holding pin 18 with J412p attached to the side surface through which b passes through holds the reference polarization plane optical fiber 1a.5
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FIG. 5 is an enlarged view of the main part of FIG. 3, showing the arrangement of a pair of polarization-maintaining optical fibers la and lb. The reference polarization-maintaining optical fibers 1a are fixed to the holding pin 18 and are always wound around the outside of the fiber guide 13, and the measurement polarization-maintaining optical fibers 1b are connected to the fiber ζ guide 1.
The cable is installed through the horizontal hole 16 of No. 3, but in this state it is covered with the storage lid 14 and cannot be seen from above. This Phino-Q guide 13 is guided in the direction of the arrow by a moving slit lO of the accommodation flap 14, so that it can be easily moved.

FIG. 6 is an enlarged plan view of the main part of FIG. 2. One fin guide 13 is installed in each moving slit lO, and the measurement polarization-maintaining optical fiber 1b is meanderingly laid through the fin guide r13, and the reference polarization-maintaining light Phi and la are stopped by the holding pin 18 of the Noainoζ guide 13 and meander. This situation can be seen from the extraction hole 11, but the reference polarization-maintaining optical fibers 1a are always arranged to pass outside the fiber ζ guide 13.

Fig. 7 is a sectional view taken along line A-11 in Fig.'X6. A Noaino ζ guide 13 and polarization preserving optical fibers 1a and 1b are housed in an installation base 9 formed in a shallow groove shape, and a storage lid 14 is attached to two sides of the base 9 with screws 19. Note that the measurement polarization-maintaining optical fibers 1b are arranged on the reference polarization-maintaining optical fiber 61a so as to be easily installed. Therefore, as shown in FIG. 2, it becomes easy to pull out the polarization-maintaining optical fiber 9111 for measurement from the extraction holes 1 to 11.

The strain meter constructed in this way is the Phi S Guide 1.
3 to the center of the moving slit IO as shown by the arrow in Fig. 5, the length of the polarization-maintaining optical fiber Zlb for measurement can be made longer, so pull it out from the extraction hole 11 and use it as a strain applying section. becomes extremely easy. However, even in this case, the reference polarization-maintaining optical fiber .la is located at the lower level as shown in FIG. 7, so it will not become entangled. Further, when the measurement is finished, the state shown in FIG. 6 can be easily returned by moving the fine guide 13 to its original position.

The strain meter using the polarization-maintaining optical fiber of this embodiment has the following effects.

(1) Since the reference polarization-maintaining optical fiber ζla and the measurement polarization-maintaining optical fiber ζlb are arranged in parallel, there is no temperature difference between the two, improving strain measurement accuracy.

(2) All parts of the strain meter are housed in a small and thin storage box, so there is no difference between the strain gauge and the outside temperature, improving the reliability of the measured values.

(3) The polarization-maintaining optical fibers for measurement can be freely taken out from any location and stored in their original state very easily and in a short time.

(4) Since the optical fibers are installed in the storage box and the only exposed part is the strain applying section, they are sufficiently protected and highly reliable.

(5) The length of the strain applying section to be taken out can be freely adjusted by adjusting the position of the phi and ζ guides.

FIG. 8 is a system diagram of a strain meter using polarization-maintaining optical fibers according to another embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals. When used as a strain meter, a set of at least two polarization-maintaining optical fibers is required, one of which is for reference and the other one for measurement. Distortion is measured by comparing the change in the difference between the two. therefore,
As shown in FIG. 8, by installing 5 to 10 lines of polarization preserving optical fins 1, it is possible to measure the amount of strain at the strain applying portions S at five locations. In this case, the five reference polarization-maintaining optical fibers 1b are installed at once, and the remaining measurement polarization-maintaining optical fibers 1b are installed using multiple fibers.
It is also possible to install the cables all at once using multiple cables and cables.

FIG. 9 is a plan view showing the state in which the measurement polarization-maintaining optical fibers 1b of FIG. 8 are installed all at once. There is. In this case as well, the length of the strain applying section S is adjusted by movably installing a plurality of fiber optics r13.

The strain meter using polarization-maintaining optical fibers of this example is constructed by separately installing multiple pairs of polarization-maintaining optical fibers for reference and measurement purposes. This provides the advantage of being able to measure state changes at multiple locations.

The above has mainly explained that mechanical strain is measured by changes in the polarization propagation performance of polarization-maintaining optical fibers due to the strain of the strain applied is, but if the strain applying part S is installed in the heating part, It can be applied to a wide range of measurements, including temperature measurement.

The strain meter using the polarization maintaining optical fiber of the present invention has the advantage of being easy to handle, small in size, and highly accurate.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a conventional strain meter that uses optical interference;
The figure is a perspective view of a strain meter using a polarization-maintaining optical fiber ζ, which is an embodiment of the present invention. Figure 4 is a perspective view of the fiber guide in Figure 2, Figure 5 is an enlarged view of the main parts in Figure 3,
6 is an enlarged plan view of the main part of FIG. 2, FIG. 7 is a sectional view taken along line A-B in FIG. 6, and FIG. 8 is a polarization-maintaining optical fiber according to another embodiment of the present invention. FIG. 9, which is a system diagram of the strain meter used, is a plan view showing the state in which the polarization-maintaining optical fibers for measurement shown in FIG. 10-8 are installed all at once. 1...Polarization maintaining optical fiber, 2...Condenser, 3...Half mirror 14...Laser diode 1,
5... Photogravitational detector, 6... Collimator, 7... Light source section, 8... Light receiving section, 0... Installation stand, lO... Slit for movement, 11... Extraction 1~ Hole, 12...Optical fiber holder, 13...Fine guide 14...
・Storage lid, 15... Presser bottle, 16... Horizontal hole, 1
7... Slot, 18... Presser pin, 19... Screw.

Claims (2)

[Claims] (1) At least one pair of polarization-maintaining optical fibers constitutes a measurement line provided with a strain applying section and a reference line, and polarized light passing through the reference line and polarized light passing through the measurement line In a strain meter that uses polarization-preserving optical fibers that detect the state of the strain applying section based on the interference situation with When pulling out the measurement line and installing the strain applying section at the place where strain occurs, move the fiber guide and lay it in a wave shape in a flat and horizontally long storage container. A strain meter using a polarization-preserving optical fiber. (2) Claim 1, wherein the flat and horizontally long storage container has a storage lid in which movement slits and removal holes for the fiber guide are alternately formed in a direction transverse to the longitudinal direction. A strain meter using the polarization-preserving optical fiber described in Section 1.