JPH03181803A - Vacuum piston-type optical fiber length measuring instrument - Google Patents

Abstract

PURPOSE:To measure the length with high accuracy without influences of the air by accommodating optical paths of a measuring light of an optical sensor head part of an optical fiber sensor apparatus which measures with use of the interference of lights and a reference light within a vacuum container. CONSTITUTION:The optical paths of a measuring light LM of an optical sensor head part 104 and a reference light are accommodated within a vacuum container 114. The measuring light LM projected from the head part 104 is reflected two times within a roof prism 116 mounted to a piston 108 of a length measuring mechanism, and directed to a reflector 112. The light is reversed by the reflector 112 and returned again to the head part 104. Therefore, the light is changed in its optical path four times the advancing/retracting amount of the prism 108. Since the optical path of the reference light within the head 104 is constant, the change of the phase of the interference light is corresponding to the advancing/retracting amount of the piston 108. The piston 108 is equipped with metallic bellows 106a, 106b which expand outside and inside of the container 114. Even when the piston 108 and bellows 106a, 106b expand and shrink, the volume of the vacuum part of the container 114 is not changed, without influences by the atmospheric pressure.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a length measuring device of the length measuring device, and more specifically, the application of an optical fiber sensor device using interference of light to the length measuring device of the length measuring device of the length measuring device. This relates to a device that has been used.

[Prior Art] Conventionally, light is transmitted and received between an optical transmitting/receiving unit and an optical sensor head via an optical fiber, and based on a phase change of interference light obtained by interfering a reference light and a measurement light, There is a length measuring device that uses an optical fiber sensor device to perform measurements.

For example, patent application No. 62-3352 filed earlier by the applicant.
No. 42, Patent Application No. 1982-316497, Patent Application No. 1983-2
Among the embodiments of the optical fiber sensor device described in the specification of No. 9313, there is a length measuring device of a length measuring device, and in particular, it has a caliper type measuring mechanism proposed in Japanese Patent Application No. 1983-335242. The prototype machine achieved a resolution of 0.08 Ja.

[Problem to be Solved by the Invention] However, in order to obtain an accurate measurement value of five digits or more, the refractive index of the air at the time of measurement must be determined by some means, and the measurement value obtained from the above-mentioned length measuring device must be determined by some means. must be corrected by the refractive index of air, and the refractive index of air also depends on temperature, atmospheric pressure,
Since the refractive index of air changes from moment to moment depending on humidity, CO, and concentration, it is cumbersome that the refractive index of air must be constantly measured during the measurement period.

The present invention has been made to solve the above-mentioned problems, and as long as the wavelength of the laser light source in vacuum is known, there is no need to calculate the refractive index of air. The purpose is to provide a piston-type optical fiber length measuring device.

[Means for Solving the Problem] In order to achieve this object, the vacuum piston type optical fiber length measuring instrument of the present invention transmits and receives light between the optical transmitting and receiving section and the optical sensor head section via an optical fiber. At the same time, the amount of forward and backward movement of the piston of the measuring mechanism is measured by an optical fiber sensor device that measures based on the phase change of the reference light and the measurement light, and the piston is It is characterized in that it is attached to a vacuum container having a structure in which the volume of the vacuum part does not change, and is configured such that the optical path of the measurement light and reference light of the optical sensor head section is contained in the vacuum container. .

Further, a single polarization-controlled optical fiber for transmission transmits light in two transmission modes whose polarization planes are orthogonal to each other, and light for extracting reference light and measurement light having the same frequency is input into the polarization-controlled optical fiber. In addition, an optical transmitter/receiver unit detects the two types of interference light returned via the constant polarization optical fiber and converts them into electrical signals, and the reference light and the measurement light are detected based on the light transmitted by the constant polarization optical fiber. As the light is extracted, the phase of the measurement light is changed by advancing and retracting the piston of the measuring mechanism, and the phase of the light intensity change is changed, and the phases of the light intensity changes are shifted by 90'' from each other. and an optical sensor head section that inputs light into the constant polarization optical fiber so that the two types of interference light are transmitted in two transmission modes of the constant polarization optical fiber, and the two types of interference light are The amount of phase change of the interference light is determined based on the electric signals of the A phase and B phase of two groups whose phases are shifted by 90'' corresponding to the light, and the amount of forward and backward movement of the piston of the measuring mechanism is measured. It is configured as follows.

Further, a single polarization-controlled optical fiber for transmission transmits light in two transmission modes whose polarization planes are orthogonal to each other, and the reference light and the measurement light are made to enter the polarization-controlled optical fiber, and the reference light and the measurement light are incident on the polarization-controlled optical fiber. The measurement light is transmitted in one and the other of the two transmission modes, and interference light is generated based on the reference light and measurement light returned via the constant polarization optical fiber, and the interference light is generated. an optical transmitter/receiver that detects a change in intensity and converts it into an electrical signal, and changes the phase of the measurement light among the reference light and measurement light transmitted by the constant polarization optical fiber by moving a piston of a measuring mechanism forward and backward; It also includes an optical sensor head section that causes the reference light and measurement light to enter the polarization-controlled optical fiber so as to be transmitted in a transmission mode opposite to that of the forward path.

In addition, the vacuum piston type optical fiber length measuring device uses a constant polarization optical fiber for transmission that transmits light in two transmission modes with polarization planes that are orthogonal to each other, and two types of linearly polarized light that transmit light in two transmission modes whose polarization planes are orthogonal to each other and have different frequencies. is input into the polarization-controlled optical fiber, the two types of linearly polarized light are transmitted in one and the other of the two transmission modes, and the two types of interference returned in the two transmission modes of the polarization-controlled optical fiber are transmitted. an optical transmitter/receiver that detects each light and converts it into an electrical signal; and divides the two types of linearly polarized light transmitted by the constant polarization optical fiber into the reference light and measurement light, respectively, and determines the frequency of the measurement light. After changing the polarization plane of the two types of linearly polarized light included in either the reference light or the measurement light by 90' in opposite directions while changing it by advancing and retreating the piston of the measuring mechanism, It has an optical sensor head section that combines a reference light such as . The measuring mechanism is configured to measure the amount of forward and backward movement of the piston of the measuring mechanism based on the measuring mechanism.

[Function] In the vacuum piston type optical fiber 1111 GC device of the present invention having the above configuration, the optical path of the measurement light and reference light of the optical sensor head of the optical fiber sensor device that performs measurement using light interference is Since it is housed in a vacuum container, the amount of forward and backward movement of the piston of the measuring mechanism can be measured without being affected by air.

Further, since the volume of the vacuum portion does not change as the piston moves forward and backward, atmospheric pressure is not applied when the piston moves forward and backward.

Furthermore, in the polarization-controlled optical fiber, the light for extracting the reference light and measurement light is transmitted in one of two transmission modes on the outward path, and the phases of the light intensity changes are shifted by 90'' from each other on the return path. Different types of interference light 2
Since an optical fiber sensor device is used in which transmission is carried out in different transmission modes, phase changes in the interference light caused by temperature changes, vibrations, etc. of the polarization-constant optical fiber cancel each other out, and high measurement accuracy can be obtained.

Further, since an optical fiber sensor device is used in which the reference light and the measurement light transmitted in the constant polarization optical fiber are transmitted in mutually opposite transmission modes on the outward and return paths, the above-mentioned claims, Similar to the vacuum piston type optical fiber length measuring device (2), phase changes in the reference light and measurement light caused by temperature changes, vibrations, etc. of the constant polarization optical fiber are canceled out, and high accuracy can be obtained.

In addition, two types of linearly polarized light with orthogonal polarization planes and different frequencies transmitted through a constant polarization optical fiber are divided into a reference light and a total of 111F+ light in the optical sensor head, and these are the reference light and measurement light. The planes of polarization of the two types of linearly polarized light contained in either one are in opposite directions.
The reference light and the measurement light are then combined to obtain two types of interference light, which are returned to the optical transmitter/receiver in two transmission modes of the polarized optical fiber. By converting it into an electrical signal, the second
The amount of forward and backward movement of the piston is determined n1 based on the frequency difference between the different types of electrical signals. Therefore, in this case as well, the frequency shift given to the linearly polarized light during transmission in the constant polarization optical fiber is canceled out, and high measurement accuracy can be obtained.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

As shown in FIG. 1, laser light is transmitted and received between the optical transmitting/receiving unit 102 and the optical sensor head unit 104 via the polarization-controlled optical fiber 20, and the laser beam does not exit from the optical sensor head unit 104. In this configuration, the amount of forward and backward movement of the piston of the vernier mechanism is measured based on the phase change of the interference light obtained by interfering the reference light L3 and the measurement light LM. The measurement light LM is transmitted to the optical sensor head section 10.
4, is reflected twice within the roof prism 116 attached to the piston 108 of the vernier mechanism, is reversed in direction and directed to a reflector 112 such as a corner cube mirror, and is reversed in direction by the reflector 112. Since the light travels backward along the optical path and returns to the optical sensor head section 104 again, the optical path is changed by four times the amount of forward and backward movement of the piston 108. On the other hand, since the optical path of the reference light LR inside the optical sensor head 104 is constant, the phase change of the interference light corresponds to the amount of forward and backward movement of the piston. As mentioned above, the measurement light LM
Since the reference light LR and the reference light LR are located inside the vacuum container 114, they are not affected by the atmosphere. Also, the piston 10 of the vernier mechanism
8 is attached with a metal bellows 106a that extends toward the outside of the vacuum container 114 at one end, and a metal bellows 106b that extends toward the inside of the vacuum container 114 at the other end, and these two metal bellows 106a and b are the same. Therefore, as shown by the dotted line in the figure, the piston 10
Even if the metal bellows 8 and metal bellows 106a and 106b expand and contract, the volume of the vacuum part of the vacuum container 114 does not change. Therefore, no force due to atmospheric pressure is applied to the forward and backward movement of the piston. In addition, in the figure, only the metal bellows 1.06a and the piston 108 located outside the vacuum container 114 are shown in the case where the piston 108 moves forward for easy viewing.

In the following embodiments, parts that are substantially the same as those in the first embodiment are given the same reference numerals and explanations thereof will be omitted.

FIG. 2 shows a vacuum piston-type optical fiber length measuring instrument that has a different structure from that in FIG. This method uses a double O-ring 58. In this case as well, since the volume of the vacuum portion does not change as the piston 108 moves forward and backward, no force due to atmospheric pressure is applied to the movement of the piston 108 back and forth.

FIG. 3 shows the configuration of an optical fiber sensor device according to another embodiment, in which a monochromatic laser beam emitted from a laser light source 10 such as a semiconductor laser is arranged by rotating 45@ around the optical axis. After passing through the polarizing beam splitter 12, Faraday rotator 14, and polarizing beam splitter 16,
The light is made incident on the end face of the constant polarization optical fiber 20 by the condenser lens 18 . The polarizing beam splitter 12, Faraday rotator 14, and polarizing beam splitter 16 also function as optical isolators, and prevent reflected light from entering the laser light source 10. The polarizing beam splitter 16 also has a function of splitting the reflected light according to the plane of polarization, and the light reflected by the polarizing beam splitter 16 is passed through the condensing lens 22 to the first optical sensor 2.
4. In addition, the polarizing beam splitter 16
The reflected light that has passed through has its plane of polarization rotated by 45 degrees around the optical axis by the Faraday rotator 14 , so it is reflected by the polarizing beam splitter 12 and is made incident on the second photosensor 28 by the condensing lens 26 . In this example,
The above-described optical elements and optical sensors constitute the optical transmitting/receiving section 30 of the optical fiber sensor device, and one end of the constant polarization optical fiber 20 is fixed to a machine frame (not shown) of the optical transmitting/receiving section 30.

The polarization constant optical fiber 20 has a core 32 and a core 32.
The HE7. 'Mode and HE,
Light is transmitted while preserving the plane of polarization in two transmission modes: 1 and 2 modes. As mentioned above, since the light incident on one end of the polarization-controlled optical fiber 20 is linearly polarized light that has passed through the polarization beam splitter 16, the light is transmitted in one of the two transmission modes within the polarization-controlled optical fiber 20. For transmission, the polarization-constant optical fiber 20 is fixed with its orientation around the optical axis adjusted.

The other end of the constant polarization optical fiber 20 is fixed to a vacuum container 114, which is insulated from the atmosphere by a vacuum window 56 and an O-ring 58.
A machine frame 40 of the optical sensor head section 38 is fixed inside. The linearly polarized light transmitted in one of the two transmission modes of the constant polarization optical fiber 20 passes through the condenser lens 46 and is converted into parallel light, and then passes through the vacuum window 5.
6, and is separated into a reference light LR and a measurement light LM by a non-polarizing beam splitter 48. The measurement light L8 passes through the non-polarizing beam splitter 48 and passes through the 174-wave plate 54.
After passing through the roof prism 116 shown in FIG. 1 or 2, the direction is changed and the reflector 112 such as a corner cube mirror or cat's eye is reflected twice.
The reference beam reflected by the non-polarizing beam splitter 48 is directed by a mirror 60 after passing through a 1/8 wavelength plate 62, and is focused onto a mirror 66 by a condensing lens 64. be illuminated.

Then, the measurement light LM% reference light LR reflected by the reflector 112 and the mirror 66 is inputted into the polarization-controlled optical fiber 20 following optical paths opposite to the forward path, and is made to enter the polarization-controlled optical fiber 20.
Interference is caused according to the phase change caused by the forward and backward movement of the That is, the light intensity of this interference light does not change if the optical path length of the measurement light L%A is constant, but when the piston 108 moves forward or backward and the optical path length changes, the phase of the measurement light L□ changes accordingly. Varies depending on quantity.

On the other hand, the optical axis of the quarter-wave plate 54 is the outgoing measurement light LM.
Because it is tilted at 22.5 degrees with respect to the polarization plane of
The plane of polarization of the measurement light beam on the return path that has passed through the quarter-wave plate 54 twice is tilted by 45°. In addition, the above 1
Since the optical axis of the 78-wave plate 62 is tilted by 45@ with respect to the polarization plane of the outbound reference light LR, the return reference light LR that has passed through the 178-wave plate 62 twice is converted into circularly polarized light. be done. Therefore, the measurement light LM is transmitted in two types of transmission modes HE, , x and HE, , of the polarization-controlled optical fiber 20.
The plane of polarization is tilted 45″ with respect to Y, and they are 2tl
i-class transmission modes HE,, x and HE,.

However, when the circularly polarized reference light LR is distributed, its phases are shifted by 90' from each other when distributed.

Therefore, the phase of the light intensity change of the interference light transmitted in the transmission mode HE, ., X and the phase of the light intensity change of the interference light transmitted in the transmission mode HE, .

The above-mentioned interference light of type 2a is transmitted to the optical transmitter/receiver section 3 through the polarization-controlled optical fiber 20 with the phase of the change in light intensity shifted by 90''.
0, each of which is made into parallel light by a condenser lens 18, separated by a polarizing beam splitter 16, and sent to the first optical sensor 24. The light is made incident on the second optical sensor 28. The first optical sensor 24 and the second optical sensor 28 are
2FJ type electric signal whose phase is shifted by 90' in response to the change in the light intensity of the 2F type interference light, that is, the measurement signal MSl
, MS2 is output. These measurement signals MS1, , MS
2 are treated as a sine signal and a cosine signal, respectively, and in the measuring circuit 70, after the DC component is removed, a pulse is generated every time the phase of the interference light changes by 1/2 phase π by a comparator with the voltage Ov as a threshold value. , and are converted into A-phase and B-phase pulse signals whose phases are shifted by 90'' from each other, and the amount of phase change of the interference light is calculated with high precision by a reversible up-down counter δp1
determined. This amount of phase change corresponds to the amount of forward and backward movement of the piston 10g, and thereby the distance traveled by the piston can be measured with high accuracy.

On the other hand, in this embodiment, in the forward path, the reference light and the linearly polarized light for extracting the measurement light LM are transmitted through the constant polarization optical fiber 20 in one transmission mode, and in the subsequent path, two types of interference light are transmitted with constant polarization. Since the waves are transmitted in two transmission modes of the optical fiber 20, phase changes within the polarization optical fiber 20 caused by external stimuli such as temperature fluctuations, distortion, and vibration are canceled out, and high measurement accuracy is achieved. can get.

Further, since the vacuum container 114 and the optical sensor head section 38 are connected to the optical transmitter/receiver section 30 by one polarization-constant optical fiber 20, there is an advantage that the vacuum container 114 and the optical sensor head section are configured compactly.

FIG. 4 shows the configuration of an optical fiber sensor device used in the vacuum piston type optical fiber length measuring device according to claim (3), in which the laser light emitted from the laser light source 10 is polarized. After passing through the beam splitter 12, the Faraday rotator 14, the polarizing beam splitter 16, the non-polarizing beam splitter 74, and the wavelength plate 76, the light is made incident on the polarization-constant optical fiber 20 by the condensing lens 18.

The non-polarizing beam splitter 74 extracts a part of the reflected light without depending on the polarization component, and the light extracted from the non-polarizing beam splitter 74 is rotated by 45 degrees around the optical axis. The light beam is transmitted through the polarizing beam splitter 78 for extracting the signal component to form only the signal component, and is made incident on the first optical sensor 24 by the condensing lens 22. Further, the reflected light reflected by the polarizing beam splitter 16 is made incident on the second optical sensor 28 by the condensing lens 26. Furthermore, the 174-wave plate 76 has a crystal axis in the direction of the dashed arrow shown in the figure, and converts linearly polarized light into circularly polarized light. For this reason, the constant polarization optical fiber 2
0 two types of transmission modes HE II x and HE 11
In fact, 28 types of linearly polarized light having mutually different phase powers of 90'' are transmitted. These two types of linearly polarized light are the measurement light LM and the reference light L□.

In this embodiment, the optical element and optical sensor described above constitute the optical transmitter/receiver section 80 of the optical fiber sensor device. Note that the light emitted to the outside by the non-polarizing beam splitter 74 is used as a monitor of the output light of the laser light source 10.

The other end of the constant polarization optical fiber 20 is connected to a vacuum vessel 114.
The vacuum container 114 is insulated from the atmosphere by a vacuum window 56 and an O-ring 58.
A machine frame 83 of the optical sensor head section 82 is fixed within the frame 4. Measurement light emitted from the other end of the constant polarization optical fiber 20.

After the reference light LR is made into parallel light by the condensing lens 46, the plane of polarization is rotated by 45' by the Faraday rotator 84. After that, the measurement light and the reference light L
R is separated by a polarizing beam splitter 86, and the measurement light LM transmitted through the polarizing beam splitter 86 is reflected twice within the roof prism 116 shown in FIG. The reference light L8 is incident on the reflector 112 such as a cat's eye and reflected by the polarizing beam splitter 86, and after its direction is changed by the mirror 60, it is focused onto the mirror 66 by the condensing lens 64.

Total Al tip LMs reflected by reflector 112 and mirror 66
The reference beams LR are incident on the polarization-constant optical fiber 20 following optical paths opposite to the forward path, but their planes of polarization are each inverted by 180' due to reflection, and are also reversed by 45 degrees by the Faraday rotator 84. Since they are rotated, they are made to enter the transmission mode opposite to the forward path. Then, the optical transmitter/receiver 8 is connected to the fixed polarization optical fiber 20.
The measurement light LM and reference light LR transmitted to 0 are parallelized by the condensing lens 18 and then converted into right-handed circularly polarized light and left-handed circularly polarized light by the quarter-wave plate 76. Since the amplitudes of the LM and the reference light LR are approximately equal, the interference between the left and right circularly polarized light results in linearly polarized light, and the direction of the plane of polarization is determined by the phase difference between the measurement light and the reference light LR. For example, if the phase difference between the measurement light LM and the reference light LR is 2π, the linearly polarized light rotates once. This linearly polarized light is interference light obtained by interfering the total 11p1 light LM and the reference light LR.

Such linearly polarized light is split into two by the non-polarizing beam splitter 74 and detected by the first optical sensor 24 and the second optical sensor 28 through the polarizing beam splitters 78 and 16. Since the planes of polarization of the polarizing beam splitters 78 and 16 are inclined by 45'' with respect to each other, the phases of the linearly polarized light intensities detected by the first optical sensor 24 and the second optical sensor 28 are shifted by 90'' from each other. Therefore, in the measuring circuit 70, the distance traveled by the piston 108 is measured with high accuracy in the same manner as in the embodiment shown in FIG.

In this embodiment, the reference light LR and the measurement light LM are transmitted in opposite transmission modes in the polarization-controlled optical fiber 20 on the outward and return paths, so temperature fluctuations, distortion, vibration, etc. The phase change within the polarization-constant optical fiber 2o caused by the external stimulus is canceled out, and the same effect as the embodiment shown in FIG. 3 can be obtained.

In addition, in this embodiment, since the measurement light LM and the reference light LR are made to interfere with each other in the optical transmitting/receiving section 8o, it is possible to detect the phase difference between the measurement light LM and the reference light LR. If so, various methods can be adopted in addition to the above method of reading the amount of phase change from two types of measurement signals MS1 and MS2 with a phase shift of 90". It is also possible to use a heterodyne optical fiber sensor device that uses two different types of light as a reference light and a measurement light and performs measurement based on changes in the number of beats of their interference light.

Further, FIG. 5 shows still another embodiment, in which the laser light output from the laser light source 10 is transmitted to the optical frequency modulator 9.
0 into two types of linearly polarized light whose polarization planes are orthogonal to each other and whose frequencies are different, and then passed through a non-polarizing beam splitter 74 and a condensing lens 18 to a constant polarization optical fiber 2.
It is made incident on the end face of 0. The non-polarizing beam splitter 74 splits a part of the linearly polarized light by reflection and makes it incident on the monitoring optical sensor 94 through the condenser lens 92 .

Furthermore, the two types of interference light returned from the constant polarization optical fiber 20 are made into parallel light by the condensing lens 18 and reflected by the non-polarizing beam splitter 74, and then split into each polarization plane by the polarizing beam splitter 16. One of the interference lights is received by the first optical sensor 24 through the condenser lens 22, and the other interference light is received by the second optical sensor 28 through the condenser lens 26. In this embodiment, the optical element and optical sensor described above constitute the optical transmitter/receiver section 96 of the optical fiber sensor device.

Since the laser light incident on one end of the polarized optical fiber 20 is linearly polarized light having planes of polarization orthogonal to each other and different frequencies, the two types of transmission modes HEllx and HE occur within the polarized optical fiber 20. , ,Y. The other end of the constant polarization optical fiber 20 is fixed to a vacuum container 114, and the vacuum container 114 is insulated from the atmosphere by a vacuum window 56 and an O-ring 58.
The machine frame 83 of the optical sensor head section 98 is placed inside the vacuum container 114.
is fixed. The mutually orthogonal linearly polarized lights transmitted in the two transmission modes and emitted from the other end of the polarization-controlled optical fiber 20 are converted into parallel lights through a condenser lens 46, and then passed through a vacuum window 56. The non-polarized beam splitter 48 separates the reference light LR and measurement light, each of which contains the two types of linearly polarized light. The measurement light LM transmitted through the non-polarizing beam splitter 48 is reflected twice within the roof prism 116 shown in FIG. On the other hand, the reference light LR reflected by the non-polarizing beam splitter 48 is passed through the 1/4 wavelength plate 54, then its direction is changed by the mirror 60, and is focused onto the mirror 66 by the condensing lens 64.

The measurement light LM and the reference light reflected by the reflector 112 and the mirror 66 respectively follow optical paths opposite to the outgoing path and are combined by the non-polarizing beam splitter 48, but the two constituting the reference light LR The linearly polarized light is passed through the 1/4 wavelength plate 54 on its outward journey, and is converted into clockwise and counterclockwise circularly polarized light, respectively, with respect to the traveling direction, and is passed through the 1/4 wavelength plate 54 again on its return journey. This results in linearly polarized light whose polarization planes are rotated by 90″ in opposite directions with respect to the polarization plane of the outgoing path.

In other words, the two types of linearly polarized light whose polarization planes are perpendicular to each other and which constitute the reference light are transmitted back and forth through the quarter-wave plate 54, so that the polarization planes are opposite to each other on the outbound and return trips. .

The two types of linearly polarized light constituting the measurement light and the two types of linearly polarized light constituting the reference light LR are each combined by the non-polarizing beam splitter 48 and made to interfere, and the two types of interference light are Constant polarization optical fiber 20-2
The signals are transmitted in two transmission modes HE28, HE2, Y, and returned to the optical transmitter/receiver 96. Optical transmitter/receiver 96
, the above two types of interference light are reflected by the non-polarizing beam splitter 74, and then reflected by the polarizing beam splitter 16.
The beat signal BS is divided into two parts depending on the direction of the polarization plane by the first optical sensor 24 and the second optical sensor 28.
I and BS2.

Here, the frequencies of the two types of linearly polarized light output from the optical frequency modulator 90 are respectively flr f2, and the frequency shifts received from the polarization optical fiber 20 due to temperature changes, vibrations, etc. on the outward path are respectively Δft+ Δf2. The measurement light L changes due to the phase change as the piston 108 moves forward and backward.
If the frequency shift given to M is Δfa, and the frequency shift received from the polarization-controlled optical fiber 20 on the return trip due to temperature changes, vibrations, etc. is Δfl'+ Δf21, then the original frequency distributed to the measurement light LM is f. , the final frequency of linearly polarized light is f1+Δf1+Δfa+Δf
, /, the final frequency of the linearly polarized light whose original frequency is f2 distributed to the reference light LR which is made to interfere with the linearly polarized light is f2+Δf2+Δf.

The beat frequency of those interference lights, that is, the frequency fBI of one of the beat signals BSI and BS2 is expressed by the following equation (3). Also, the final frequency of the linearly polarized light whose original frequency is f distributed to the reference light L8 is f1+Δ
The final frequency of the linearly polarized light whose original frequency is f2 distributed to the measurement light t, A that is interfered with the linearly polarized light is f2+Δf2+Δfa+Δ(,/, and the beat of those interference lights is The frequency, that is, the other frequency f8□ of the beat signals BSI and BS2 is expressed as follows: The differential, that is, the frequency difference is detected, and the beat expressed by the following equation (5) is calculated by a counter that counts clock signals of a constant frequency through a gate that is opened for a time corresponding to the differential amount. The amount of differential between the signals BSI and BS2, that is, the distance the piston has moved, is measured with high accuracy.

Δfadt@... (5) In this embodiment, the reference light LR is
The frequencies of beat signals BSI and BS2 representing two types of interference light obtained by rotating the two types of linearly polarized light in opposite directions by 90 @ and combining the reference light and measurement light LM. Since the difference is measured, the frequency shifts Δf and Δf2 caused by the distortion of the core 32 that occurs in the forward polarization optical fiber 20 are canceled out, and the differences between the first and second embodiments are canceled. Similarly, high measurement accuracy can be obtained.

In this case, it is also possible to use different polarization-controlled optical fibers for the outbound and return routes.

Although several embodiments of the present invention have been described above in detail based on the drawings, the present invention can also be implemented in other embodiments.

Furthermore, the optical fiber sensor devices of the embodiments described above are merely examples, and various other optical fiber sensor devices can be used.

Although other examples are not given, the present invention can be implemented with various modifications and improvements within the knowledge of those skilled in the art.

[Effects of the Invention] As is clear from the detailed description above, the present invention provides a vacuum piston fiber length measuring device that can easily perform highly accurate length measurement without being affected by air.

[Brief explanation of drawings]

1 to 5 show embodiments embodying the present invention. FIG. 1 is a diagram explaining the configuration of a vacuum piston type optical fiber length measuring device, and FIG. 2 is a diagram showing another embodiment. FIG. 3 is a diagram explaining the configuration of an optical fiber sensor device used in another example, and FIG. 4 is a diagram explaining the configuration of an optical fiber sensor device used in another example. FIG. 5 is a diagram illustrating the configuration of an optical fiber sensor device used in yet another embodiment. In the figure, 20 is a (constant polarization) optical fiber, 102 is an optical transmitter/receiver, 104 is an optical sensor head, 108 is a piston, 1
08+106a and b have a structure where the volume of the vacuum part does not change,
114 is a vacuum container.

Claims (1)

[Claims] 1. Phase change of interference light obtained by transmitting and receiving light between the optical transmitting/receiving unit and the optical sensor head via an optical fiber and interfering the reference light and measurement light. means for measuring the amount of forward and backward movement of the piston of the measuring mechanism using an optical fiber sensor means that performs measurement based on the measurement mechanism; 1. A vacuum piston type optical fiber length measuring instrument, which is attached to a container, and the optical path of the measurement light and reference light of the optical sensor head section is contained in the vacuum container. 2. A single polarization-controlled optical fiber for transmission that transmits light in two transmission modes whose polarization planes are orthogonal to each other, and light for extracting reference light and measurement light having the same frequency is input into the polarization-controlled optical fiber. In addition, an optical transmitting/receiving unit detects the two types of interference light returned via the constant polarization optical fiber and converts them into electrical signals; As the light is extracted, the phase of the measurement light is changed by advancing and retracting the piston of the measuring mechanism, and the phase of the light intensity change is changed, and the phases of the light intensity change are shifted by 90 degrees from each other. and an optical sensor head section that inputs light into the polarization-controlled optical fiber so that the two types of interference light are transmitted in two transmission modes of the polarization-controlled optical fiber, and the two types of interference light are The amount of change in the phase of the interference light is determined based on two types of A-phase and B-phase electrical signals whose phases are shifted by 90 degrees corresponding to , and the amount of forward and backward movement of the piston of the measuring mechanism is measured. The vacuum piston type optical fiber length measuring device according to item 1. 3. A single polarization-controlled optical fiber for transmission that transmits light in two transmission modes whose polarization planes are orthogonal to each other, and the reference light and measurement light are input into the polarization-controlled optical fiber, and the reference light and measurement light are is transmitted in one and the other of the two transmission modes, generating interference light based on the reference light and measurement light returned via the constant polarization optical fiber, and detecting changes in light intensity of the interference light. an optical transmitting/receiving unit that converts the reference light into an electrical signal; and changing the phase of the measuring light among the reference light and the measuring light transmitted by the constant polarization optical fiber by advancing and retreating a piston of the measuring mechanism; 2. The vacuum piston type optical fiber measurement device according to claim 1, further comprising an optical sensor head portion that makes the reference light and measurement light enter the polarization-constant optical fiber so as to be transmitted in a transmission mode opposite to that of the forward path. Long vessels. 4. The optical fiber sensor device uses a fixed polarization optical fiber for transmission that transmits light in two transmission modes whose polarization planes are orthogonal to each other, and two types of linearly polarized light whose polarization planes are orthogonal to each other and have different frequencies. Inject the polarized light into the optical fiber, and
Light that transmits different types of linearly polarized light in one and the other of the two transmission modes, and detects and converts the two types of interference light returned in the two transmission modes of the polarization-controlled optical fiber into electrical signals. A transmitter/receiver unit distributes the two types of linearly polarized light transmitted by the constant polarization optical fiber into the reference light and measurement light, respectively, and changes the frequency of the measurement light by moving the piston of the measuring mechanism forward and backward. At the same time, the polarization planes of the two types of linearly polarized light included in either the reference light or the measurement light are moved in opposite directions by 90 degrees.
It has an optical sensor head that combines the reference light and the measurement light and inputs the same into the polarization-controlled optical fiber after rotating the reference light and the measurement light, and generates two types of electrical signals corresponding to the two types of interference light. 2. The vacuum piston type optical fiber length measuring instrument according to claim 1, wherein the amount of forward and backward movement of the piston of the length measuring mechanism is measured based on the frequency difference.