JPH01311204A - Optical fiber sensor device - Google Patents

Abstract

PURPOSE:To maintain measurement accuracy even if the abrupt variation of the light intensity level of interference light or the phase shift is <=1 wavelength 2pi by extracting a pulse signal according to a signal from which mutually 90 deg. out-of-phase DC components are removed. CONSTITUTION:Opposite-phase interference light beams which are 180 deg. out of phase as to light intensity variation are extracted from two kinds of interference light by an optical means (opposite-phase photodetectors 38, 42, etc.). Further, the couple of opposite-phase photodetectors 38 and 42 output opposite-phase electric signals MBS1b and MBS2b corresponding to the opposite-phase interference light beams and differential amplifiers 70 and 72 amplify the opposite-phase electric signals MBS1b and MBS2b and electric signals MBS1a and MBS2a differentially to obtain two kinds of signals which are 90 deg. out of phase with each other and have DC components removed. Then those two kinds of signals are converted by comparators which have, for example, a voltage zero V as its threshold value into pulse signals, which are inputted to an up/down counter, etc., to measure the quantity of the phase shift of the interference light.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to an optical fiber sensor device that performs measurement based on the amount of phase change of interference light, and in particular, the present invention relates to an optical fiber sensor device that performs measurement based on the amount of phase change of interference light. The present invention relates to a device that does not impair measurement accuracy even when

BACKGROUND OF THE INVENTION Optical fiber sensor devices that utilize light interference are widely used to measure the moving distance, rotation angle, surface roughness, pressure, gas concentration, etc. of an object to be measured. One type of such optical fiber sensor device includes (a) a single polarization optical fiber that transmits light in two transmission modes whose polarization planes are orthogonal to each other, and (b) transmission using the polarization constant optical fiber. The reference light and measurement light are extracted based on the
By combining the measurement light whose phase has been changed depending on the measurement object with the reference light, the light intensity changes in accordance with the change in phase, and the phase of the change in light intensity is shifted by 90 degrees. (C) an optical sensor head unit for inputting two types of interference 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 (C) light for extracting the reference light and measurement light. an optical transmitting/receiving unit that detects the two types of interference light that is input into the constant polarization optical fiber and returns through the constant polarization optical fiber and converts it into an electrical signal, and converts the electrical signal into a pulse signal. There is a type that measures the amount of phase change of the interference light by converting it into .

For example, the patent application No. 62-335 filed earlier by the applicant
The device described in No. 242 is one example.

By the way, in such an optical fiber sensor device,
The two types of electrical signals corresponding to the above two types of interference light can be approximated by A cosΦ(t
) +B, A sinΦ(1)10B, and the DC component B is usually removed and converted into a pulse signal by a comparator with a threshold of 0. For example, FIG. 5 shows an example of such a DC component removal circuit, in which the measurement signal MB
SI and MBS2 correspond to the above two types of electrical signals. Further, FIG. 6 shows the waveforms of the measurement signals MBSI and MBS2° and the signals 331 to 5SIO of each part in FIG. 5.

In these figures, the measurement signals MBSI and MBS2
is differentially amplified by the differential amplifier 210, and the signal S
Comparator 2 which takes voltage 0■ as dark value based on SI
12 and the monostable multi-bi break 214, when the signal SSI crosses the 0 point, a pulse signal SS4 generated when the phase Φ(1) of the interference light is represented by (π/4+nπ) in FIG. 6 is extracted. The pulse signal S3
4 is supplied to AND circuits 220 and 222 together with a pulse signal SS5 obtained by a differential amplifier 216 and a comparator 218 whose dark value is voltage O. By ANDing these signals, a sample and hold signal is generated. Trigger pulse signals SS6 and SS8 are obtained. The pulse signal SS5 applied to the AND circuit 222 is N
It is inverted by the OT circuit 224, and the trigger pulse signal SS6 has a phase Φ(1) of (z/4+2nπ).
The trigger pulse signal SS is generated when represented by
8 is generated when the phase Φ(1) is expressed as (5π/4+2nπ). Note that the above n is an integer.

On the other hand, the measurement signals MBS1 and MBS2 are sent to the inverting adder 2.
26 and the signal SS2 becomes a minimum when the phase Φ(1) is expressed as (z/4+2nπ), and becomes a maximum when the phase Φ(1) is expressed as (5π/4+2nπ). Therefore, the sample & hold circuit 2 to which this signal SS2 and the trigger pulse signal SS6 are supplied
At 28, the minimum value of the signal SS2 is sampled and held, and a signal SS7 representing the minimum value is output to the 174 inverting and averaging circuit 230. Further, in the sample and hold circuit 232 to which the signal SS2 and the trigger pulse signal SS8 are supplied, the maximum value of the signal S32 is sampled and held, and a signal SS9 representing the maximum value is output to the 174 inverting and averaging circuit 230. . Then, the 174 inverting and averaging circuit 230 inverts the supplied signals SST and SS9, adds them, and divides by 4 to obtain the DC component B, and outputs the dark value signal 5SIO representing the DC component B. do.

The dark value signal 5SIO is the measurement signal MBSI and MB
This corresponds to a threshold value for removing a DC component when converting S2 into a pulse signal, and the measurement signal MBS1 is converted into a pulse signal PS by the differential amplifier 216 and the comparator 218.
It is converted to l. The pulse signal SS5 is the same as the pulse signal PS1 of q. In addition, the measurement signal MBS2
is converted into a pulse signal PS2 by a differential amplifier 234 and a comparator 236 whose threshold is the voltage Ov. In addition, at the beginning of operation, the dark value signal 5S indicating the accurate dark value
Since IO cannot be obtained, the dark value signal obtained by the smoothing circuit 238 is supplied to the differential amplifiers 216 and 234 by switching the changeover switch SW. For example, the changeover switch SW has a threshold value signal 5SI.
It is configured to be switched when the voltage value of O and the voltage value of the smoothing circuit 238 become approximately equal.

Then, the pulse signals PSt and PSt obtained in this way are
Since the phases of S2 are shifted by 90° from each other,
For example, by inputting common A-phase signals and B-phase signals to a reversible up-down counter in a rotary encoder, etc., the amount of change in the phase Φ(t) of the interference light is measured based on the pulse edges of these signals. be done.

Problems to be Solved by the Invention However, in such a conventional optical fiber sensor device, if the light intensity level of the interference light changes sharply or the amount of phase change of the interference light is less than 2π per wavelength, Dark value signal 5SIO cannot be obtained accurately,
Pulse signal Psi.

There is a problem in that the pulse width of PS2 becomes narrower or wider, which impairs measurement accuracy.

That is, since the dark value signal 5S10 is updated by sampling the maximum and minimum values of the signal S52, the measurement light may be diffusely reflected or the interference rate may fluctuate during surface roughness measurement etc., resulting in interference light. If the light intensity level of the light changes rapidly, the update of the threshold signal 5SIO may not be able to keep up. Additionally, if the amount of phase change of the interference light is smaller than 2π per wavelength due to interruption of measurement or small irregularities in surface roughness, the minimum and maximum values of the two signals SS2 may not be obtained. Accurate darkness value signal 5SI even if the light intensity level of interference light changes in
O cannot be obtained.

For example, the pulse signals PS1 and PS2 are
When input to the divided up/down counter, when the dark value signal 5sio is accurately determined as shown by the solid line in FIG.
, PS2 becomes as shown in Fig. 2, and the measured value by the up-down counter shows that the phase Φ(1) of the interference light is π
The maximum error is about π/4, which is about half of π/2, with respect to the true value shown by the dashed line in FIG. 2. but,
When the dark value signal 5sto deviates as shown by the dashed line in FIG. 7, the pulse signals Psi, P
As shown in FIG. 8, the pulse width of S2 becomes narrower, and the error in the measured value by the up/down counter increases accordingly. Note that if the dark value signal 5310 deviates significantly as shown by the two-dot chain line in FIG. There may be cases where the up/down counter becomes inverted due to no longer being counted.

Further, if the dark value signal 5S10 deviates as described above, the generation of the pulse signal SS5 is impaired, so the trigger pulse signal SS6 or SS8 may no longer be generated, and the measurement failure state may continue.

The present invention was made against the background of the above circumstances, and its purpose is to prevent measurement accuracy from being impaired even when the light intensity level of interference light changes sharply or when the amount of phase change is less than 2π per wavelength. The goal is to make sure that there is no such thing.

Means for Solving the Problems In order to achieve the object, the present invention provides the following: (a) a single polarization constant optical fiber; (b) an optical sensor head section;
(C) an optical fiber sensor device of the type that includes an optical transmitter/receiver section and performs measurement by converting the electric signal into a pulse signal to determine the amount of phase change of the interference light; (d) the two types of interference light; The phase of the light intensity change is 180
an optical means for extracting the two types of negative phase interference light shifted by degrees; (e) an optical fiber for transmitting the two types of negative phase interference light to the optical transmitter/receiver; and (f) an optical means provided in the optical transmitter/receiver. , a pair of anti-phase photodetectors that respectively detect the two types of anti-phase interference light and output anti-phase electrical signals whose phases are shifted by 90 degrees from each other; A pair of differential amplifiers that differentially amplify two types of electrical signals are provided, and based on the two types of signals obtained by the differential amplifiers, the phases of which are shifted by 90 degrees from each other and the DC component is removed. The present invention is characterized in that the pulse signal is extracted.

Operation and Effects of the Invention In such an optical fiber sensor device, the phase of the light intensity change for the two types of interference light is 180 degrees.
The reverse phase interference light shifted by 1 is extracted by an optical means, and a pair of reverse phase photodetectors output a reverse phase electrical signal corresponding to the reverse phase interference light, and the reverse phase electrical signal and the electrical signal are outputted by a pair of reverse phase photodetectors. By differentially amplifying the two signals using a differential amplifier, two types of signals whose phases are shifted by 90 degrees from each other and whose direct current components are removed are obtained. and,
The amount of phase change of the interference light is measured by converting these two types of signals into pulse signals by a comparator whose dark value is, for example, a voltage of 0.times., and then inputting the pulse signals to an up/down counter or the like.

Here, the above two types of signals are obtained by differentially amplifying electrical signals whose phases differ by 180 degrees, so compared to the conventional case of calculating the dark value and removing the DC component. Therefore, the configuration of the signal processing section is greatly simplified. In addition, even if the optical intensity level of the interference light changes sharply or the amount of phase change is less than 2π per wavelength, differential amplification correctly removes the DC component, making it possible to always obtain accurate pulse signals. measurement accuracy is improved.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 1, a monochromatic laser beam emitted from a laser light source 10 such as a He-N e laser is transmitted to a polarizing beam splitter 12 rotated by 45 degrees around the optical axis.
．． Faraday rotator 14. After passing through the polarizing beam splitter 16 , the light beam is made incident on the end face of the first polarization-constant optical fiber 20 by the condenser lens 18 . Said polarizing beam splitter 12° Faraday rotator 14. The polarizing beam splitter 16 also functions as an optical isolator, and prevents the reflected light returned through the polarization constant optical fiber 20 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.
The light reflected by 6 is made incident on the first photosensor 24 by the condensing lens 22, and the polarization plane of the light that has passed through the polarizing beam splitter 16 is rotated by 45 degrees around the optical axis by the Faraday rotator 14, resulting in polarized light. Beam splitter 1
After being reflected by the light beam 2, the light beam is made incident on the second optical sensor 28 by the condensing lens 26. On the other hand, the reflected light returned through the second polarization constant optical fiber 30 is reflected by the condensing lens 32.
The polarizing beam splitter 34 converts the beam into parallel light.
The light that is separated according to the plane of polarization and reflected by the polarizing beam splitter 34 is made incident on the third optical sensor 38 by the condensing lens 36, and the light that has passed through the polarizing beam splitter 34 is converted into fourth light by the condensing lens 40. The light is made incident on the sensor 42. An optical transmitter/receiver 200 is constituted by the optical elements and optical sensors described above, and a fixed polarization optical fiber 20.3 is attached to the machine frame (not shown) of the optical transmitter/receiver 200.
One end of 0 is fixed.

The polarization constant optical fibers 20.30 are exactly the same, and include a core 44, a pair of stress applying parts 46 sandwiching the core 44,
For example, the HE++X
Polarized light is transmitted while preserving the plane of polarization in two transmission modes: mode and HE mode, . The other ends of these constant polarization optical fibers 20 and 30 are fixed to the machine frame (not shown) of the optical sensor head section 202, and the laser light incident on one end of the constant polarization optical fiber 20 is The linearly polarized light that has passed through the polarization beam splitter 16 is transmitted to the optical sensor head section 202 in one of the two transmission modes of the constant polarization optical fiber 20 .

The optical sensor head section 2 is
The laser beam transmitted up to 02 is converted into parallel light by a condenser lens 50, and separated into reference light Lm and measurement light LH by a non-polarizing beam splitter 52. The measurement light beam 8 that has passed through the non-polarized beam splitter 52 rotates the plane of polarization of the linearly polarized light by 45 degrees by passing it back and forth twice 174
Passed through the wave plate 54 and directed toward one of the pair of first corner cube prism 58 and second corner cube prism 60 mounted on the measurement target 56, for example, the first corner cube prism 58. Projected.

In addition, the reference light reflected by the non-polarizing beam splitter 52 passes through a 178 wavelength plate 62 that converts linearly polarized light into circularly polarized light by transmitting it twice back and forth, and then is direction-changed by a mirror 64, so that it is not The other of the first corner cube prism 58 and the second corner cube prism 60 that are parallel to the measurement light LM that has passed through the polarizing beam splitter 52 and are mounted on the measurement object 56;
That is, it is projected toward the second corner cube prism 60. Note that the first corner cube prism 58
The reflective surface of the second corner cube prism 60 is coated with metal to prevent the polarization characteristics from being changed by reflection.

Further, the measurement object 56 is a first corner cube prism 58
and the second corner cube prism 60, and accordingly the optical path lengths and phases of the measuring beam 4 and the reference beam LR are changed.

Here, the measurement light reflected by the first Nacube prism 5 is transmitted through the 174-wave plate 54 again and converted into linearly polarized light tilted at 45 degrees with respect to the outgoing polarization plane. , second corner cube prism 6
The reference light LR reflected by 0 is again passed through the 1/8 wavelength plate 62
The optical axis of the 174-wave plate 54 is the outgoing measurement light LM.
This is because the optical axis of the 178-wave plate 62 is inclined at 45 degrees with respect to the polarization plane of the forward reference light LR. be.

The measurement light LH and the reference light I, which have been made into linearly polarized light and circularly polarized light in this way, are each split into two by a non-polarized beam splitter 52, and the measurement light LH and the reference light I, which have been transmitted through the non-polarized beam splitter 52, are The reference light reflected by the non-polarized beam splitter 52 passes through the condenser lens 50 and is directed to the first polarization constant optical fiber 2.
0. At this time, the measurement light L1 and the reference light are equally distributed and made incident on two types of transmission modes HE, `` and HE, ,'' of the polarization optical fiber 20, and the optical path accompanying the rotation of the measurement object 56 is By changing the length, the phases of the measurement light 1.l and the reference light are changed, so that they interfere with each other.

In addition, since the measurement light LH is linearly polarized light whose polarization plane is tilted by 45 degrees with respect to the above two types of transmission modes, it is distributed to these two types of transmission modes HE, ``,'' and HE + + ' with the same phase. However, when the circularly polarized reference light LR is distributed to the transmission modes HE, ``,'' and HE++', their phases are shifted by 90 degrees from each other. Therefore, transmission mode H
The phase of the change in the light intensity of the interference light transmitted in the transmission mode HE+I' is shifted by 90 degrees from each other.

Further, the measurement light Ls reflected by the non-polarizing beam splitter 52 and the reference light transmitted through the non-polarizing beam splitter 52 are reflected by a mirror 66 and then passed through the condensing lens 68 to the second polarization constant optical fiber 30. is made incident on. In this case as well, the measurement light is made incident on the constant polarization optical fiber 30.

and the reference beam are made to interfere with each other, and the phases of the optical intensity changes of the interference beams transmitted in the two types of transmission modes HE, , X and HE,' are shifted by 90° from each other.

Furthermore, the measurement light LM incident on the second polarization constant optical fiber 30 is reflected by the non-polarization beam splitter 52, so that the measurement light LM is reflected by the non-polarization beam splitter 52.
The two types of interference light transmitted by this polarization-controlled optical fiber 30 are shifted in phase by 180° with respect to the measurement light beam 8 that passes through the first polarization-controlled optical fiber 20.
1 for each of the two types of interference light transmitted by
The phase is shifted by 80°. The interference light transmitted by the second polarization-constant optical fiber 30 corresponds to anti-phase interference light, and the interference light is transmitted by the non-polarization beam splitter 52. mirror 66
, condenser lens 68. and a second polarization constant optical fiber 30
An optical means for extracting two types of anti-phase interference light is configured. Further, the polarization constant optical fiber 30 has two
This corresponds to an optical fiber that transmits different types of anti-phase interference light to the optical transmitter/receiver 200. - The above-mentioned two types of interference light and anti-phase interference light are each transmitted to the optical transmitting/receiving unit 200 by the polarization-controlled optical fiber 20, 30 with the phases of the light intensity changes shifted by 90 degrees from each other, and then The two types of interference light transmitted by the constant polarization optical fiber 20 are separated by the polarization beam splitter 16 and sent to the first optical sensor 24. Second optical sensor 28
is made to be incident on. In addition, the second polarization constant optical fiber 30
The two types of anti-phase interference light transmitted by the polarizing beam splitter 34 are separated by the third optical sensor 38.
．． The light is made incident on the fourth optical sensor 42.

The optical sensors 24 and 28 output two types of electrical signals, ie, measurement signals MBSLa and MBS2a, whose phases are shifted by 90° in response to changes in the light intensity of the two types of interference light. Further, the optical sensors 38 and 42 constitute a pair of reverse phase photodetectors, which generate two types of reverse phase electrical signals whose phases are shifted by 90 degrees in response to changes in the light intensity of the two types of reverse phase interference light. That is, measurement signals MBS1b and MBS2b are output. The phases of the measurement signals MBS1b and MBS2b are also 18% with respect to the measurement signals MBS1a and MBS2a, respectively.
It is shifted by 0°.

The measurement signals MBSla and MBSlb, MBS2a and MBS2b whose phases are shifted by 180° from each other are respectively supplied to differential amplifiers 70 and 72 and differentially amplified.
As a result, two types of measurement signals R31 and R32 whose phases are shifted by 90° from each other and whose DC components are removed are obtained. These measurement signals R3I and R32 are sent to comparators 74.7 each having a voltage Ov as a threshold value.
6, the pulse signals Psi and PS2 repeat generation and disappearance of pulses every time the phase of the interference light changes by 1/2 phase π, and whose phases are shifted by 90° from each other.
is converted to

The pulse signals Psi and PS2 correspond to the A-phase signal and B-phase signal of a rotary encoder, etc., and are supplied to the reversible up-down counter 7B, thereby changing the amount of change in the phase Φ(1) of the interference light. Furthermore, the rotation angle of the measurement object 56 is measured, and the measured value is displayed on the display 80. In the case of a counter that increases or decreases the measured value each time it changes, the measured value is output by the pulse signal P as shown in FIG.
Each time the pulse edges of Sl and PS2 are detected, they are updated stepwise, and their increase or decrease is performed according to Table 1, depending on the direction of the pulse edge determined by the direction of phase change and the sign of the other pulse signal.

Table 1 Here, the measurement signals R3I and R32, which are the sources of the pulse signals Psi and PS2, are obtained by differentially amplifying the measurement signals MBS1a and MBSlb, MBS2a and MBS2b, which have phases different by 180°, respectively. Therefore, the configuration of the signal processing section is greatly simplified compared to the case where the dark value is determined and the DC component is removed from the measurement signals MBSI and MBS2 as shown in FIG. . In addition, even if the optical intensity level of the interference light changes sharply or the amount of change in the phase Φ(1) is less than the monthly wavelength 2π, the DC component is correctly removed by differential amplification, so the pulse signal Psi is always accurate. Since PS2 can now be obtained, measurement accuracy is improved.

That is, for example, when the rotation of the measurement object 56 stops, the phase Φ(1) does not change, so the dark value signal 5sio in FIG. If the light intensity level of the interference light becomes significantly higher or lower when the measurement object 56 starts to move after that, the correct pulse signals Psi and PS2 cannot be obtained depending on the darkness value signal 5SIO. ,
According to the optical fiber sensor device of this embodiment, the measurement object 5
6. Always correct pulse signal Psi regardless of whether it is rotating or stopping.
PS2 is obtained and the up/down counter 78 is allowed to count normally.

Next, another embodiment of the present invention will be described. In the following embodiments, parts substantially common to those in the above embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 3 is a sectional view showing the optical sensor head section 204 when the optical fiber sensor device of the present invention is applied to a surface roughness meter, 82 is a mirror that reflects the reference light I, and 84 is a mirror that reflects the reference light I. This is an objective lens for condensing the measurement light beam 14 onto the surface 88 of the measurement target 86. In this case, surface 8
For example, if the displacement amount of 8 is smaller than 1/2 of the wavelength λ of the measurement light, the phase of the interference light due to the unevenness of the surface 88 Φ(
The amount of change in 1) is less than 2π for one phase, and the amount of change in the fifth
In contrast to the case where the dark value signal 5S10 in the DC component removal circuit shown in the figure is not updated, in this embodiment, the first
By the same signal processing as in the embodiment, correct pulse signals Psi and PS2 can always be obtained regardless of the size of the irregularities on the surface 88. This is also effective when the laser beam is diffusely reflected by the unevenness of the surface 88 and the light intensity level of the interference light changes instantaneously.

In the embodiment shown in FIG. 4, the measurement light LM reflected by the non-polarizing beam splitter 52 and the reference light LR transmitted through the non-polarizing beam splitter 52 are polarized and separated by a polarizing beam splitter 90. , As a result, the measurement light L9 and the reference light I are caused to interfere with each other, and the phases of the light intensity changes of the interference lights are shifted by 90 degrees from each other. The non-polarized beam LH is also reflected by the splitter 52, so that the non-polarized beam splitter 52
The phase is 18o with respect to the measurement light Lx passing through.

The two types of interference light transmitted by the first polarization-constant optical fiber 20 are shifted in phase by 180 degrees from each other. In this embodiment, the interference light interfered by the polarizing beam splitter 90 corresponds to the opposite phase interference light, and the polarizing beam splitter 9o and the non-polarizing beam splitter 52 are used to extract two types of opposite phase interference light. Optical means are configured.

Then, the negative phase interference light reflected by the polarizing beam splitter 90 is made incident on the multimode optical fiber 92 by the condensing lens 68, transmitted to the optical transmitter/receiver 200, and made incident on the fourth optical sensor 42. on the other hand,
The anti-phase interference light that has passed through the polarizing beam splitter 90 is reflected by the mirror 66 and then inputted into the multimode optical fiber 96 by the condensing lens 94, and transmitted to the optical transmitting/receiving section 200, where it is transmitted to the third optical sensor 38. is made to be incident on. The core diameter of the multimode optical fiber 92.96 is generally about 50 to 100 μm or less, which is larger than the core diameter of about 4 μm or less of the polarization constant optical fiber. assembly becomes easy. A pair of multimode optical fibers 92.96 are
It corresponds to an optical fiber that transmits two types of antiphase interference light.

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.

For example, in the embodiment described above, in order to obtain anti-phase interference light whose phase is shifted by 180 degrees, the non-polarizing beam splitter 52 and the polarization-controlled optical fiber 30. Alternatively, although the polarizing beam splitter 90 is used, other optical means such as a polarizing prism such as a Wollaston prism may also be employed.

In addition, in the above embodiment, the up/down counter 7 is divided into four parts.
8 was explained, but by creating a new measurement signal by using a two-divided up/down counter or by differentially amplifying or adding measurement signals R3I and R32,
It is also possible to employ a high division up/down counter such as 8 divisions or 16 divisions.

Furthermore, in the above embodiment, the present invention was applied to a device that measures the rotation angle of the measurement object 56 and the surface roughness of the measurement object 86, but it can also be applied to a device that measures moving distance, gas concentration, pressure, etc. The present invention can be similarly applied.

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

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the configuration of an optical fiber sensor device that is an embodiment of the present invention. FIG. 2 is a diagram illustrating the operation of the up/down counter in the optical fiber sensor device of FIG. 1. FIG. 3 is a sectional view showing an optical sensor head section when the present invention is applied to a surface roughness needle. Fourth
The figure is a diagram illustrating the configuration of another embodiment of the present invention. FIG. 5 is an electrical circuit diagram showing an example of a conventional DC component removal circuit. FIG. 6 is a diagram showing signal waveforms at various parts in the electric circuit shown in FIG. FIG. 7 is a diagram illustrating cases in which the dark value determined by the DC component removal circuit in FIG. 5 is correct and cases in which it is incorrect. FIG. 8 is a diagram illustrating the operation of the up/down counter when the darkness value is incorrect. 20: Constant polarization optical fiber 30: Constant polarization optical fiber (optical fiber) 38. 42: Optical sensor (reverse phase photodetector) 52: Non-polarizing beam splitter 56. 86: Measurement object 66: Mirror 68: Condensing lens 70 , 72: Differential amplifier 90:
Polarizing beam splitter 92.96: Multimode optical fiber (optical fiber) 200
: Optical transmitting/receiving section 202.204: Optical sensor head section Lo: Measurement light L8: Reference light MBS1a,
MBS2a: electrical signal MBS1b, MBS2b: reverse phase electrical signal 1'S1. P.S.
2: Pulse signal applicant Brother Industries, Ltd. 0 Jozuki 6

Claims (1)

[Claims] A single polarization-controlled optical fiber that transmits light in two transmission modes whose polarization planes are orthogonal to each other, and a reference light and a measurement light are extracted based on the light transmitted by the polarization-controlled optical fiber. By combining the measurement light whose phase has been changed depending on the measurement object and the reference light, the light intensity changes in accordance with the change in phase, and the phase of the change in light intensity is shifted by 90 degrees. an optical sensor head unit that inputs the two types of interference 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; an optical transmitting/receiving unit that detects each of the two types of interference light that is input to a constant polarization optical fiber and returns through the constant polarization optical fiber and converts it into an electrical signal, and converts the electrical signal into a pulse signal. In an optical fiber sensor device of the type that performs measurement by determining the amount of phase change of the interference light, two types of anti-phase interference are provided in which the phase of the light intensity change is shifted by 180 degrees with respect to the two types of interference light. an optical means for extracting light; an optical fiber for transmitting the two types of negative phase interference light to the optical transmitting and receiving section; a pair of anti-phase photodetectors that output anti-phase electrical signals shifted by 90 degrees, and a pair of differential amplifiers that differentially amplify the two types of anti-phase electrical signals and the two types of electrical signals, respectively. An optical fiber sensor device characterized in that the pulse signal is extracted based on two types of signals obtained by the differential amplifier and whose phases are shifted by 90 degrees from each other and whose DC components are removed.