JP2010085148A - Minute displacement measuring device, minute displacement measuring method, and minute displacement measuring program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize a measuring device by constituting an interferometer with the minimum constitution, in minute displacement measurement utilizing laser light. <P>SOLUTION: Light emitted from a semiconductor laser oscillation element 2 is split by the first optical coupler 15 into irradiation light guided through the second optical fiber 5 and reference light guided through the fourth optical fiber 7. Light reflected by a measuring object 30 passes through the third optical fiber, and interferes mutually with the reference light in the second optical coupler 17. Light intensity of interference light is detected by a photodetector 10. A refractive index changer 16 for changing a refractive index is installed in the second optical fiber 5. A photodetection signal from the photodetector 10 is transferred to an arithmetic unit 25 through an amplifier 23 and an A/D converter 24, and a control signal to be applied to the refractive index changer 16 is generated there. The control signal is applied to the refractive index changer 16 through a D/A converter 21 and a refractive index changeable control means 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a minute displacement measuring apparatus, a minute displacement measuring method, and a minute displacement measuring program for measuring minute displacement such as minute vibration of an object, and in particular, a laser beam and an optical fiber that guides the laser beam. The present invention relates to a minute displacement measuring apparatus, a minute displacement measuring method, and a minute displacement measuring program for measuring minute displacement.

2. Description of the Related Art Conventionally, a displacement measuring apparatus that measures the displacement of an object using laser light has been used in various fields because it can measure with high accuracy. Usually, a conventional minute displacement measuring apparatus using optical interference combines a half mirror, a polarizing beam splitter or the like and a wave plate to split a laser beam into two optical paths and use one of the beams as reference light. The other light is applied to the object to be measured and used as measurement light. When the reflected lights are combined again, the intensity change of the interference light that occurs according to the phase difference between the two causes The difference in the optical path distance, that is, the displacement of the object to be measured is detected.
A micro displacement measuring apparatus using optical components such as an optical fiber and a beam splitter is disclosed in Patent Document 1. FIG. 15 is a block diagram of the minute displacement measuring apparatus disclosed in Patent Document 1. In FIG. 15, 201 is a frequency stabilized quadrature laser source, 204 is a mirror, 205 is an analyzer, and 206 is a photodiode. , 207 is a signal processing circuit, 210 is a heterodyne interference optical system, 211 and 221 are polarization beam splitters, 212 and 213 are corner cubes, 222 and 225 are coupling lenses, 223 and 226 are polarization-maintaining optical fibers, 224 and 227 Is a collimating lens, and f ₀ and f ₁ are the frequencies of laser beams whose polarizations are orthogonal to each other. As shown in FIG. 15, the light emitted from the laser light source 201 is branched into two by the polarization beam splitter 221, one is the reference light, and the other is the measurement light reflected by the corner cube 213 fixed to the object to be measured. Become. Further, the reference light and the measurement light interfere with each other by the polarization beam splitter 211 to form interference light. By measuring the light intensity of the interference light with the photodiode 206, the displacement of the corner cube 218 according to the light intensity of the interference light is measured.

Further, Patent Document 2 discloses a minute displacement measuring device using an optical fiber and an optical waveguide. FIG. 16 is a configuration diagram of the minute displacement measuring device disclosed in Patent Document 2. In FIG. 16, 301 is a broadband light source, 302 is an optical fiber, 303 is a depolarizer, 304 is an input optical fiber, and 305 is a single unit. One-mode optical fiber type 3dB coupler, 306 is a reference optical fiber, 307 is an optical waveguide phase modulation element, 308 is an input / output port, 309 is a capillary, 310 is an optical waveguide, 311 is a mirror, 312 is an optical fiber for measurement light, 313, 318 is an end surface, 314 and 319 are lenses, 315 is a signal optical fiber, 316 is a light receiver, 317 is a phase modulation electrode, 320 is a narrowband filter, 321 is a light receiving element, and R1, R2, M1, and M2 are reflected light waves. It is. As shown in FIG. 16, the light wave emitted from the broadband light source 301 is depolarized by the depolarizer 303 and guided to the single mode optical fiber type 3 dB coupler 305, where it is divided into two. One of the halved light waves returns from the object to be measured to the 3 dB coupler 305 via the lens 314 as reference light. Signal light (interference light) corresponding to the phase difference between the reference light and the measurement light is sent to the light receiver 316, passes through the narrow band filter 320, and enters the light receiving element 321. Then, by making the optical path length difference between the reference light and the measurement light equal to or less than the interference length determined by the bandwidth of the narrow band filter 320, the end faces of the optical waveguide 310 and the optical fibers 306 and 312 can be made vertical without being processed obliquely. It has come to be finished.
Japanese Patent Laid-Open No. 11-101608 Japanese Patent Laid-Open No. 10-232109

However, the micro displacement measuring devices disclosed in Patent Documents 1 and 2 have some problems.
First, the first problem of Patent Document 1 is that the optical components used in the apparatus are composed of an optical fiber, a polarization beam splitter, a laser oscillator, a photodetector, and the like, and there are many components and the volume for housing them increases. For this reason, the apparatus becomes larger and more expensive. If the apparatus becomes large and the number of components increases, the time required for assembling the apparatus becomes long. Also, the apparatus of Patent Document 1 has the disadvantage of requiring adjustment work such as alignment of the optical axis at the time of assembly. There was a problem that increased. The second problem is that a corner cube is fixed to the object to be measured, and the incident light enters the corner cube, and the reflected light passes through the polarization beam splitter and reaches the reference light detector. This means that a long distance is propagated through the optical component, and a considerable loss is incurred. If the light from the object to be measured is lost and the intensity is reduced, there is a disadvantage that the sensitivity of the photodetector is deteriorated and accurate detection cannot be performed. The third problem is that the reference light is intentionally reflected by a fixed corner cube. There is an inconvenience that the number of components increases by one and the assemblability deteriorates. The fourth problem is that the reference beam and the measurement beam are branched by passing through the polarization beam splitter from the laser light source, so that the respective light intensities are almost the same. Therefore, the measurement light emitted from the measurement light path is reflected by the movable corner cube, and the light loss while returning to the measurement light path again, and the reference light emitted from the reference light path is reflected by the fixed corner cube. Considering the light loss while returning to the reference light path again, the measurement light may have a light intensity lower than that of the reference light. In this case, the sensitivity is deteriorated with respect to the displacement of the object to be measured, and as a result, there is a disadvantage that the measurement accuracy is adversely affected.

  In addition, the problem (fifth problem) of the micro displacement meter disclosed in Patent Document 2 is that the reference light is generated by forming a mirror at the edge of the substrate in order to produce the reference light. is there. There is an inconvenience that the number of processes for manufacturing the substrate is increased and the component cost is increased. Also in the case of Patent Document 2, the inconvenience of the fourth problem occurs. That is, the light splitting between the reference light and the irradiation light is performed by a single-mode optical fiber type 3 dB coupler, and the branching ratio is 50:50. In this case as well, the irradiation light emitted from the optical waveguide is covered. Since light loss occurs while being reflected by the measurement object and returning to the optical waveguide, the measurement light has a light intensity that is lower than that of the reference light, and the sensitivity to the displacement of the measurement object is reduced. This results in inconvenience that the measurement accuracy is adversely affected.

  An object of the present invention is to solve the above-described problems of the prior art, and its purpose is to increase the manufacturing efficiency, size reduction, simplified configuration, and simplicity of a measurement device in a minute displacement measurement using laser light. Realization of operation and high-sensitivity and highly reliable measurement in consideration of loss of irradiation light and reference light so that the intensity of light from the object to be measured reaches the photodetector becomes stronger. Is to do.

  To achieve the above object, according to the present invention, a semiconductor laser oscillation element, a first optical fiber that receives light from the semiconductor laser oscillation element, and light guided through the first optical fiber as reference light. A first optical fiber type coupler that branches into the irradiation light; the second optical fiber that guides the irradiation light that irradiates the object to be measured; and a third optical fiber that is incident after the irradiation light is reflected by the object to be measured; A fourth optical fiber guided by the reference light branched by the first optical fiber coupler, a second optical fiber that interferes with the irradiation light guided by the third optical fiber and the reference light guided by the fourth optical fiber. Optical fiber coupler, a fifth optical fiber for guiding the interference light interfered by the second optical fiber coupler, and an interference light guided by the fifth optical fiber. A photodetector for detecting intensity; a refractive index variable device that is provided in at least one of the second optical fiber, the third optical fiber, or the fourth optical fiber, and changes an effective refractive index of the optical fiber; A variable refractive index control unit that controls the operation of the refractive index variable unit, and a calculation that generates a control signal to be transmitted to the variable refractive index control unit based on the detection result of the photodetector and detects the displacement of the object to be measured. And a minute displacement measuring apparatus comprising the means.

  Preferably, the spectral ratio of the first optical fiber coupler is set so that the light intensity of the irradiated light is higher than that of the reference light. Alternatively, preferably, the spectral and coupling ratios of the first and second optical fiber couplers are such that the light intensity of the reflected light and the reflected light of the irradiation light that interferes in the second optical fiber coupler is higher than that of the reference light. It is set to be higher than that.

  In order to achieve the above object, according to the present invention, reference is made to a semiconductor laser oscillation device, a first optical fiber that receives light from the semiconductor laser oscillation device, and light that is guided through the first optical fiber. A first optical fiber coupler that branches into light and irradiated light; the second optical fiber that guides the irradiated light that irradiates the object to be measured; and a third optical fiber that is incident after the irradiated light is reflected by the measured object And the fourth optical fiber guided by the reference light branched by the first optical fiber coupler, the irradiation light guided by the third optical fiber, and the reference light guided by the fourth optical fiber interfere with each other. A second optical fiber coupler, a fifth optical fiber for guiding the interference light interfered by the second optical fiber coupler, and a waveguide guided by the fifth optical fiber. A photodetector for detecting the light intensity of the light, and a refractive index variable device that is provided in at least one of the second optical fiber, the third optical fiber, or the fourth optical fiber and changes an effective refractive index of the optical fiber; And a refractive index variable control unit that controls the operation of the refractive index variable unit, and a control signal that is transmitted to the variable refractive index control unit based on a detection result by the photodetector and generates a displacement of the object to be measured. And a laser beam irradiation step for irradiating an object to be measured with a laser beam from a semiconductor laser oscillation element via an optical fiber; An interference light detection step for detecting an intensity change of interference light between the irradiation light from the object irradiated with the laser light and the reference light from the semiconductor laser oscillation element; The refractive index variable control step for variably controlling the refractive index of the refractive index variable device based on the detection result of the interference light detection step, and the change amount of the refractive index of the refractive index variable device caused by the refractive index variable control step. And a displacement detection step for detecting the displacement of the object to be measured based on the measurement result. In the variable refractive index control step, the detection result of the measurement light detection step is monitored, and the intensity of the detection light is preset. There is provided a minute displacement measuring method, characterized in that the refractive index of the refractive index variable device is variably controlled so as to be a value.

  In order to achieve the above object, according to the present invention, reference is made to a semiconductor laser oscillation device, a first optical fiber that receives light from the semiconductor laser oscillation device, and light that is guided through the first optical fiber. A first optical fiber coupler that branches into light and irradiated light; the second optical fiber that guides the irradiated light that irradiates the object to be measured; and a third optical fiber that is incident after the irradiated light is reflected by the measured object And the fourth optical fiber guided by the reference light branched by the first optical fiber coupler, the irradiation light guided by the third optical fiber, and the reference light guided by the fourth optical fiber interfere with each other. A second optical fiber coupler, a fifth optical fiber for guiding the interference light interfered by the second optical fiber coupler, and a waveguide guided by the fifth optical fiber. A photodetector for detecting the light intensity of the light, and a refractive index variable device that is provided in at least one of the second optical fiber, the third optical fiber, or the fourth optical fiber and changes an effective refractive index of the optical fiber; And a refractive index variable control unit that controls the operation of the refractive index variable unit, and a control signal that is transmitted to the variable refractive index control unit based on a detection result by the photodetector and generates a displacement of the object to be measured. A computer program for operating a minute displacement measuring device comprising: an arithmetic means for detecting the intensity value of the interference light detected by the photodetector in a computer that controls the operation of the minute displacement measuring device. Measurement light level acquisition processing for capturing the light and a refractive index variable control processing for controlling the operation of the refractive index variable device so that the intensity value of the interference light becomes a preset value. And a displacement calculation process for calculating the displacement of the object to be measured based on the amount of change in the effective refractive index of the optical fiber caused by the operation of the refractive index variable device. Program.

[Action]
According to the minute displacement measuring apparatus of the present invention, the optical fiber type measuring apparatus can be simply configured with a small number of parts, the apparatus can be downsized, the assembling work can be simplified, and the cost can be reduced. Therefore, it is possible to provide a highly accurate minute displacement measuring device at low cost. According to such an optical fiber type minute displacement measuring apparatus and a minute displacement measuring method using the same, an optical path is formed by an optical fiber, and a minute displacement can be measured by installing only an optical fiber that irradiates a measurement object even in a very small space. It is possible to increase the possibility of displacement measurement. In addition, by constructing an optical fiber that minimizes light loss in the optical path so that the reflected light from the object to be measured is relatively larger than the irradiated light, the sensitivity of the object to be measured is increased. In addition, it is resistant to disturbances such as thermal expansion and vibration, so that it is possible to reduce the loss received by the measurement light, and a highly accurate and reliable measurement result can be obtained.
Further, in the above-described optical fiber type micro displacement measuring apparatus, the above-mentioned calculating means may control the refractive index of the refractive index variable device so that the intensity of the interference light by the photodetector becomes the maximum value or the minimum value. Good. In this way, instead of obtaining the displacement of the object to be measured from the detected intensity change of the light, the intensity of the interference light between the irradiation light from the object to be measured and the reference light from the semiconductor laser oscillation element is the maximum value or Adjustment is performed so as to maintain the minimum value, and the displacement of the object to be measured is obtained from the amount of change in the refractive index. Therefore, even a relatively large displacement of the object can be detected.
Further, in the above-described optical fiber type micro displacement measuring apparatus, the above-described calculating means controls the refractive index of the refractive index variable device so that the intensity of the interference light by the photodetector becomes an average value of the maximum value and the minimum value. You may do it. In this way, the displacement of the object to be measured is not obtained from the detected intensity change of the light, but the intensity of the interference light between the irradiation light from the object to be measured and the reference light from the semiconductor laser oscillation element is the rate of change. Adjustment is performed so as to maintain a high value, and the displacement of the object to be measured is obtained from the amount of change in the refractive index, so that the displacement of the object can be detected with high accuracy.
However, the calculation means described above controls the refractive index of the refractive index variable device so that the intensity of the light detected by the photodetector is not limited to the maximum value, the minimum value, or the average value thereof, but may be an arbitrary value. May be.

  The minute displacement measuring apparatus of the present invention is configured such that the interferometer is constituted by an optical fiber, and the reference light is guided through the optical fiber and directly incident on the photodetector, so that the number of components can be reduced and produced. As a result, downsizing and cost reduction can be realized. Further, by increasing the light intensity of the measurement light as compared with the reference light, it is possible to realize highly accurate measurement.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
FIG. 1 is a schematic diagram showing the configuration of the optical fiber type micro displacement measuring apparatus according to the first embodiment of the present invention. The minute displacement measuring apparatus of the present embodiment includes a power source 1, a semiconductor laser oscillation element 2 that oscillates laser light when a current is applied from the power source 1, and a first optical fiber 3 that receives light from the semiconductor laser oscillation element 2. A first optical fiber coupler 15 for branching light guided through the first optical fiber 3 into reference light and irradiation light, a second optical fiber 5 for guiding irradiation light irradiated to the object to be measured, and irradiation The third optical fiber 6 incident after the light is reflected by the object to be measured, the fourth optical fiber 7 guided by the reference light branched from the first optical fiber coupler 15, and the third optical fiber 6 are guided. A second optical fiber type coupler 17 in which the measurement light and the reference light guided through the fourth optical fiber 7 interfere, and a fifth light in which the interference light interfered by the second optical fiber type coupler 17 is guided. A fiber 8, a photodetector 10 for detecting the light intensity of interference light guided through the fifth optical fiber 8, and a refractive index variable device 16 provided in the second optical fiber 5 for changing the refractive index of the optical fiber; From the amplifier 23 that amplifies the current signal from the photodetector 10 and converts it into a voltage signal, the A / D converter 24 that converts the analog voltage signal from the amplifier 23 into a digital signal, and the A / D converter 24 The control device 25 generates a control signal to be applied to the refractive index variable device 16 based on the digital voltage signal, and calculates the displacement of the device under test 30, and displays the displacement of the device under test 30 calculated by the device 25. The displacement display device 26, the D / A converter 21 for converting the digital control signal calculated by the arithmetic device 25 into an analog signal, and the refractive index based on the control signal output by the D / A converter 21. It comprises a variable refractive index control means 22 supplies to the variable 16, and the displacement display device 26 for displaying the displacement of the measurement target object 30 that is calculated by the arithmetic unit 25. In FIG. 1, reference numerals 4 and 9 denote sixth and seventh optical fibers attached to the first and second optical fiber couplers, respectively.
Here, the arithmetic unit 25 controls the refractive index variable unit 16 via the refractive index variable control unit 22 so that the detected light intensity of the photodetector 10 becomes a predetermined value (set value). That is, when the position of the device under test 30 changes and the output of the photodetector 10 changes, the arithmetic unit 25 adjusts the refractive index of the refractive index variable device 16, that is, adjusts the optical path length of the illumination light. Control is performed so that the output of the photodetector 10 returns to the set value. Accordingly, the displacement of the object to be measured 30 corresponds to the change in the refractive index of the refractive index variable device 16 at this time. Can know. This change in refractive index is based on the amount of energy supplied to the refractive index variable device 16 by the variable refractive index control unit 22 based on a command from the arithmetic device 25, so that the displacement of the object 30 to be measured eventually becomes the arithmetic device. 25 is reflected in the amount of energy indicated.

Here, the optical fiber will be briefly described. The optical fiber has a triple structure of a core part called a core, a part called a clad or cladding layer outside the core part, and a coating covering the clad from the outside. By making the refractive index of the core higher than that of the cladding, light is propagated only to the core in the central portion as much as possible by total reflection and refraction. Both the core and the cladding are made of quartz glass or plastic, which has a very high transmittance for light. An optical fiber uses light refractive index to guide light with high straightness. That is, the optical fiber is suitable for constructing a three-dimensional optical path.
The optical loss rate of an optical fiber is about 10 ⁻⁶ dB / cm. In addition, devices with various functions can be connected between optical fibers, and these functions can be given to optical fibers. For example, the refractive index variable device described above is one of those functions.

  Now, the configuration of the minute displacement measuring apparatus according to the present embodiment will be described in more detail. Any laser beam that oscillates may be used as long as it is stable coherent light and propagates through the optical fiber in a single mode. The power source 1 applies a current to the semiconductor laser oscillation element 2 so that the semiconductor laser oscillation element 2 oscillates and outputs laser light. The laser light emitted from the semiconductor laser oscillation element 2 is incident on the first optical fiber 3, guided therethrough, and is present in the second optical fiber 5 and the fourth optical fiber 7 by the first optical fiber coupler 15. Branches at a specific branching ratio. The light guided through the second optical fiber 5 passes through the refractive index variable device 16 and is emitted from one end surface of the second optical fiber 5, and the light is irradiated to the object to be measured 30 and reflected. The reflected light is incident on the third optical fiber 6.

The second optical fiber 5 and the third optical fiber 6 are configured so that the loss of light when the light emitted from the second optical fiber 5 returns from the object to be measured and enters the third optical fiber 6 is minimized. A two-core fiber collimator is formed. In the two-core fiber collimator, the second optical fiber 5 and the third optical fiber 5 and the third optical fiber are reflected so that the light reflected from the object to be measured 30 enters the third optical fiber with almost no loss as shown in FIG. The distance 2d between the axes of the optical fiber 6, the angle θ, and the focal length and position of the collimator lens 29 are optimally selected. For example, the closer the distance a from the collimator lens 29 to the object to be measured 30 is, the closer the focal length of the collimator lens 29 is, the better the optical coupling efficiency and the smaller the optical loss. Placed in position.
The light reflected by the device under test 30 enters the third optical fiber 6 and is guided to the second optical fiber coupler 17. On the other hand, the light branched to the fourth optical fiber 7 by the first optical fiber coupler 15 is guided to the second optical fiber coupler 17 by the fourth optical fiber 7. The light guided by the second optical fiber coupler 17 from the third optical fiber 6 (measurement light) and the light guided by the fourth optical fiber 7 (reference light) interfere with each other by the second optical fiber coupler 17. Then, it becomes interference light and is guided through the fifth optical fiber 8. The interference light guided through the fifth optical fiber 8 is incident on the photodetector 10, and the light intensity is detected by the photodetector 10. On the other hand, of the light guided through the fourth optical fiber and the light guided through the third optical fiber 6, the light guided to the seventh optical fiber 9 by the second optical fiber coupler 17, that is, the light outside the interference light is Escape to the right place. Specifically, the light guided by the end face of the seventh optical fiber is reflected and incident again on the seventh optical fiber, so that the operation of the second optical fiber coupler 17 is not affected. For example, a non-reflective terminator or the like is attached, or the seventh optical fiber 9 is made an extremely small ring to attenuate the guided light.
In FIG. 1, the refractive index variable device 16 is installed in the second optical fiber, but may be provided in either the third optical fiber or the fourth optical fiber, or a plurality of these optical fibers. You may install in the place. When the refractive index variable device 16 is provided at a plurality of locations, the number of refractive index variable control means 22 is required by the number of the refractive index variable devices 16.
A signal corresponding to a predetermined refractive index is sent from the arithmetic unit 25 to the refractive index variable device 16 via the refractive index variable control means 22 to change the optical path length to a predetermined refractive index.

  Here, the optical fiber coupler will be described with reference to the drawings. FIGS. 9A and 9B are diagrams showing examples of optical fiber couplers. In general, an optical fiber type coupler includes a coupler (1 × 2 coupler) for branching one optical fiber at two branch ratios, and two optical fibers each having one optical fiber at a branch ratio. There is an optical fiber (2x2 coupler) that branches to an optical fiber and the other optical fiber also splits into two optical fibers with a certain branching ratio. FIG. 9A shows a 1 × 2 coupler, and FIG. 9B shows a 1 × 2 coupler. In each case, an example of the branching ratio is indicated by a number. By the way, in the case of a 50:50 branching ratio, it is called a 3 dB coupler, in the case of a 60:40 branching ratio, it is called a 4 dB coupler, and in the case of a 70:30 branching ratio, it is called a 5 dB coupler.

Thus, the difference in optical loss between the light guided through the fourth optical fiber 7 branched by the first optical fiber coupler 15 and the light guided through the third optical fiber returned from the object to be measured is calculated. It is desirable to determine the branching ratio between the first optical fiber coupler 15 and the second optical fiber coupler 17 in order to make a prediction based on experience and increase the sensitivity of the displacement of the object to be measured. In order to improve the sensitivity of the displacement of the object to be measured 30, the light (measurement light) guided through the third optical fiber 6 is replaced with the fourth optical fiber 7 when interference is caused by the second optical fiber coupler 17. This is because it is necessary to make the detection light more sensitive to the displacement of the object to be measured 30 than the light that guides the light (reference light). Here, it is desirable that the branching ratio of the first optical fiber coupler 15 is such that the light branched to the second optical fiber side is stronger than the fourth optical fiber side.
The first optical fiber coupler 15 and the second optical fiber coupler 17 may be configured by any means or method as long as they have a function of branching light into a plurality of parts.

Next, parts other than the components of the optical fiber of the minute displacement measuring apparatus of the present embodiment will be described. The intensity of the interference light guided through the fifth optical fiber 8 is measured by the photodetector 10, and a current signal corresponding to the intensity is output. The photocurrent output from the photodetector 10 is amplified by the amplifier 23 and converted into a voltage signal. The analog voltage signal output from the amplifier 23 is converted into a digital signal by the A / D converter 24.
The arithmetic device 25 calculates a control signal to be applied to the refractive index variable device 16 based on the digital voltage signal from the A / D converter 24 and outputs the control signal to the D / A converter 21. The control signal converted into an analog signal by the D / A converter 21 is transmitted to the variable refractive index control unit 22, and the refractive index variable control unit 22 supplies predetermined energy to the refractive index variable unit 16 based on the control signal. To do.
The displacement display device 26 displays the displacement of the device under test 30 calculated by the calculation device 25. The display format is to display the displacement amount as a number, to display the light intensity before and after the displacement as a waveform, to display the refractive index change before and after the displacement as a numerical value, and to display any value or waveform that shows the displacement amount. It doesn't matter.
The minute displacement measuring apparatus according to the present invention is configured so that the optical waveguide is formed of an optical fiber and the displacement can be measured by emitting light with only the tip of the optical fiber directed toward the object to be measured. But displacement measurement is possible, and the miniaturization and weight reduction of the measuring device are remarkably improved.

[Description of waveguide]
Next, the waveguide of the minute displacement measuring apparatus according to the present embodiment will be described in more detail. First, how to determine the branching ratio in the first optical fiber coupler 15 and the second optical fiber coupler 17 will be described. As described above, the loss experienced by light when guided through each optical fiber is 10 ⁻⁶ dB / cm, and the length of the optical fiber is about 1 m at the maximum, which is negligibly small. Therefore, the loss that the light from the first optical fiber receives in the optical fiber is the time until the light guided through the second optical fiber 5 is emitted toward the object to be measured 30 and enters the third optical fiber 6. The biggest among them. So, assuming that the above loss is 2dB,
The relationship between light loss and light intensity is
Light loss = 10 · log (output light intensity / input light intensity)
Therefore, if optical loss is -2,
Output light intensity / input light intensity = 10 ^ (light loss / 10) = 10 ^ (-0.2) = 0.631
Thus, the output light intensity is reduced to 63.1% of the original light intensity.

Therefore, if the intensity of light guided through the first optical fiber 3 is A and the ratio of the light branched into the second optical fiber 5 by the first optical fiber coupler 15 is α, the light is guided to the third optical fiber 6. The light intensity to be transmitted is A · 0.631 · α, and the light intensity guided to the fourth optical fiber 7 is A · (1-α).
Further, when the ratio of the light guided through the fourth optical fiber 7 to the fifth optical fiber 8 is β, the light from the third optical fiber 6 is also taken into account when the light from the third optical fiber 6 is taken into consideration. The light is A · (1−α) · β + A · 0.631 · α · (1−β). Here, the ratio at which the light from the third optical fiber 6 is guided to the fifth optical fiber 8 is (1-β).
Therefore, in order to make the intensity of the light guided through the third optical fiber 6 out of the light guided through the fifth optical fiber 8 larger than the intensity of the light guided to the fourth optical fiber 7,
A ・ 0.631 ・ α ・ (1-β)> A ・ (1-α) ・ β
And it is sufficient.
Since the branching ratio of the optical fiber coupler is generally determined as 50:50, 60:40, 70:30, 80:20, 90:10, the first optical fiber coupler 15 and the second optical fiber from the above formula. Combination candidates for the mold coupler 17 are obtained. However, since a specific branching ratio can be produced arbitrarily, branching ratios other than these branching ratios can be used if necessary. By selecting the branching ratio so as to satisfy the above equation, the displacement of the object to be measured 30 can be detected with high sensitivity, and accurate measurement can be performed.

The length of the refractive variable 16 is calculated from the difference between the optical path lengths of the irradiation light and the reflected light, the phase amount to be changed, and the amount of change in the refractive index that varies with the amount of energy that can be applied per unit length of the refractive variable 16. can do.
As the material of the optical fiber, typical quartz which is a thermo-optic material is generally used. Therefore, specifically, a heater is used for the refractive index variable device 15, and the refractive index variable control unit is a heater control unit. A control signal (analog signal) corresponding to a predetermined temperature is sent from the heater control unit to the heater to heat a part of the optical fiber to a predetermined temperature and change the refractive index of the optical fiber.

The refractive index variable device 16 may be any one that changes the effective refractive index of the optical fiber, and a so-called phase shifter can be used.
As described above, the phase shifter includes, as described above, an optical fiber whose refractive index is changed by a heater, an electro-optical material such as lithium niobate that changes its refractive index by voltage, and an acousto-optic material. Some lithium tantalate, lithium niobate, and the like whose refractive index is changed by acoustic vibration can be used.
When a phase shifter using an electro-optic material or an acousto-optic material is employed, an optical fiber such as the third optical fiber 5 is cut and the phase shifter is inserted there. When using a phase shifter of an electro-optic material, an electro-optic element provided with an electrode is disposed between the optical fibers, and a control signal is applied to the electrode from the variable refractive index control unit 22. When using a phase shifter of an acoustooptic material, an acoustooptic element provided with a transducer is disposed between optical fibers, and a control signal is applied to the transducer from the variable refractive index control unit 22. When such an electro-optic element or acousto-optic element is used as a phase shifter, the optical fiber and the phase shifter are optically connected via an optical connector, or optically directly using a method such as fusion. Connected. Use optical connectors with low loss.

Next, with reference to FIGS. 7 (a), 7 (b), and 7 (c), a specific example in the case where a phase shifter is configured by an optical fiber that is a thermo-optic material will be described. In FIG. 7A, the second optical fiber 5 is fixed to the optical fiber fixing plate 43 on the Peltier effect element 41, and a thermistor 42 is used as a temperature detector of the Peltier effect element 41. The second optical fiber 5 is heated by the Peltier effect element 41 to change the refractive index of the second optical fiber 5. Further, in order to control the temperature of the Peltier effect element 41 with high accuracy, feedback control is performed using a thermistor 42 as a temperature detector. As the temperature detector, a temperature sensor such as a thermocouple may be used instead of the thermistor 42. However, the thermistor 42 is more compact and more convenient for forming a phase shifter.
FIG. 7B shows a case where a nichrome wire 44 is wound around the second optical fiber 5 and a thermistor 41 is used as a temperature detector. Also in this configuration, the thermistor 41 detects the temperature and feedback-controls the temperature of the nichrome wire 44. As the temperature detector, a temperature sensor such as a thermocouple can be used instead of the thermistor 42.
FIG. 7C shows a case where the thermistor 41 is used as a temperature detector through the second optical fiber 5 through the heater 45. In this configuration, the thermistor 41 also detects the temperature and feedback controls the temperature of the heater. As the temperature detector, a temperature sensor such as a thermocouple can be used instead of the thermistor 42.
In addition, the refractive index variable device 16 may be anything other than the one described above as long as it has a similar function.

[Description of operation]
Next, the operation of the first embodiment will be described. The light emitted from the semiconductor laser oscillation element 2 enters the first optical fiber, is branched by the first optical fiber coupler 15, and one enters the fourth optical fiber 7 and is guided to the second optical fiber coupler 17. Waved. The light guided through the other second optical fiber 5 passes through the refractive index variable device 16 whose refractive index is modulated, and its optical path length is adjusted. Next, the light is emitted from one end face of the second optical fiber, and the light is irradiated to the object to be measured 30 and reflected. The reflected light enters the third optical fiber 6 and is guided to the second optical fiber coupler 17.
The light guided from the fourth optical fiber 7 (reference light) and the light guided by the third optical fiber 6 (irradiation light / measurement light) interfere with each other by the second optical fiber coupler 17 and Become. Further, the interference light is guided through the fifth optical fiber 8 and then emitted from one end face toward the photodetector 10, and the light intensity of the interference light is detected by the photodetector 10.
The light intensity detected by the photodetector 10 is digitized through the amplifier 23 and the A / D converter 24 and is subjected to arithmetic processing by the arithmetic device 25. When a certain amount of energy is supplied to the refractive index variable unit 16 in the second optical fiber 5 by the control signal generated in the arithmetic unit 25, the temperature of the second optical fiber 5 in the refractive index variable unit 16 changes and there. The refractive index of can be changed. Therefore, the entire optical path length of the irradiation light can be changed, and the phase difference from the reference light can be freely controlled.

Using this principle, the refractive index of the waveguide is adjusted, and the object to be measured 30 is resonated by matching the phase of the reflected light with the phase of the irradiated light at the initial position (position before displacement). It is also possible to make the light intensity weakest, or it is possible to adjust to an arbitrary light intensity. The light intensity set in this way becomes the set value.
The light detector 10 that detects the interference light observes the interference state, and the light intensity of the interference light can be observed by forming an interferometer.

  Next, when a minute displacement is given to the device under test 30, the reflected position changes when reflected by the device under test 30, so that the interference light changes from the initial light intensity (set value). Also at this time, the interference light intensity after the change can be detected by observing the signal from the photodetector 10. Then, by feeding back the signal from the photodetector 10 to the signal to be sent to the refractive index variable control unit 22, the refractive index of the second optical fiber 5 can be further changed to return the interference light to the initial light intensity again. it can. Therefore, the amount of displacement of the device under test 30 can be determined according to the amount of change in the refractive index of the optical fiber before and after the device under test 30 is displaced. However, it is necessary to obtain the relationship between the refractive index change amount and the displacement amount in advance.

Next, the relationship between irradiation light and reflected light and interference between reference light and reflected light will be described. FIG. 11A is a diagram schematically showing an incident state of the reference light on the second optical fiber coupler 17 which is an interference part, and FIG. 11B is a second optical fiber coupler of the reflected light. It is a figure which shows typically the incident condition to 17. One of the lights (reference light) emitted from the semiconductor laser oscillation element 2 is guided through the first optical fiber 3 and the fourth optical fiber 7 and reaches a second optical fiber type coupler 17 at a certain phase. It is in the position.
On the other hand, the light (irradiated light) guided through the first optical fiber 3 and the second optical fiber 5 is irradiated to the object to be measured 30 and reflected at a certain phase. Here, the phase of the light is inverted. The reflected light travels through the third optical fiber 6 and reaches the second optical fiber coupler 17. The reached light also has a certain phase. The reference light having a phase different from the irradiation light having the phase which is the second optical fiber type coupler 17 interferes to have a certain light intensity. If the phase difference between the two is 1/2 of the wavelength, they cancel each other and the light intensity is the weakest. Further, when the phase difference between the two is zero, they are strengthened to each other and become in a resonance state, and the light intensity is the strongest.

Here, the above phenomenon can be expressed mathematically as follows. First, let λ be the wavelength of light from the semiconductor laser oscillation element 2. With respect to the irradiation light, if the total optical path length of the first optical fiber 3 and the fourth optical fiber 7 is L1, and the phase of the irradiation light at the interference unit 9 (length below the wavelength) is Δ1, the following equation holds.
m ・ λ + Δ1 = L1 (1)
Further, when the optical path length L1 is expressed by the refractive index n1 and the geometric distance d1, the equation (2) is established.
L1 = n1 ・ d1 (2)
From (1) and (2),
m ・ λ + Δ1 = n1 ・ d1 (3)
It becomes. Here, m is the number of waves of one wavelength existing in the optical path length L1.

Similarly, for the reflected light, the optical path length is the total geometric distance d2 of the first optical fiber 3, the second optical fiber 5 and the third optical fiber 6, the average refractive index n2 in the optical path, and the object to be measured. When the phase is reflected by 30 (the length below the wavelength) Δr, and the phase of the reflected light at the interference unit 9 (the length below the wavelength) Δ2,
n ・ λ + Δ2 + 2 ・ Δr = n2 ・ d2 (4)
Here, n is the number of waves of one wavelength existing in the total optical path length of the first optical fiber 3, the second optical fiber 5, and the third optical fiber 6.
When subtracting equation (4) from equation (3),
(mn) ・ λ + Δ1-Δ2-2 ・ Δr = n1 ・ d1-n2 ・ d2 (5)
Furthermore, since m, n, λ, Δ1, n1, and d1 are constant and do not change,
When formula (5) is simplified,
Δ2 + 2, Δr-n2, d2 = constant (6)
It becomes.

From Expression (6), when the position of the object to be measured 30 is changed and the geometric distance d2 is changed, Δr and Δ2 are changed. Therefore, by changing n2, that is, by changing the refractive index by the refractive index variable device 16, the expression (6) can be satisfied.
Therefore, when the refractive index is changed by the refractive index variable device 16, the phase difference between the two lights changes, and when the phase difference becomes zero, the interference light becomes a resonance state, and the phase difference becomes 1 / wavelength. 2 is the weakest light. Furthermore, an arbitrary interference state can be created by arbitrarily adjusting this phase difference.

Here, the interference between the two lights will be further described with reference to FIG. In FIG. 12 (a), when the phase difference between the two lights is zero, that is, when the phases coincide with each other, if the upper and lower lights interfere with each other, the two lights are combined. As described above, the light intensity is the highest, that is, the resonance state.
On the other hand, in FIG. 12 (b), the phase difference between the two lights is π (1/2 of the wavelength), and when the upper and lower lights interfere with each other, they weaken each other as shown by the waveform under the arrow. The strength is the smallest.
Therefore, by changing the refractive index with the refractive index variable device 16, the phase difference between the irradiation light (measurement light) and the reference light changes, and the light intensity detected by the photodetector 10 changes.

Further, the displacement of the object to be measured 30 and the light intensity of the interference light are indicated by a sine wave in which the intensity of light appears in a λ / 2 period as shown in FIG. This is because light is reflected by the object to be measured 30 and a phase twice as large as the displacement of the object to be measured is generated. Therefore, the displacement of the object to be measured shows the intensity of light in a λ / 2 period. Become.
Therefore, the arithmetic unit 25 first specifies any one point on the sine wave shown in FIG. 13 and sets the light intensity value at that point as a set value, and when the device under test 30 is in the initial position, A command is given to the refractive index variable control unit 22 so that the detection light of the detector 10 becomes a set value. The refractive index variable control unit 22 controls the operation of the refractive index variable device 16 according to a command from the arithmetic unit 25 and adjusts the refractive index of the second optical fiber 5 to set the light intensity of the interference light to a set value. . The light intensity is observed by the photodetector 10 that detects the light intensity of the interference light.

When a minute displacement occurs in the object to be measured 30, the optical path length of the irradiation light changes, and the detection light level received by the photodetector 10 changes. Therefore, the arithmetic unit 25 sets the detection light level to a set value. The variable refractive index control unit 22 that issues a command and adjusts the refractive index of the second optical fiber 5 so that the detected light level is set to a set value.
In this way, it is possible to see whether or not the optical path length has changed by observing the signal from the photodetector 10, and the signal from the photodetector 10 is fed back to the signal sent to the variable refractive index control unit 22. Thus, the detected light level can always be set to the set value. In this case, the refractive index changes according to the amount of energy applied to the refractive index variable device 16 of the second optical fiber 5 before and after the measurement object 30 is displaced, and the optical path length of the irradiation light changes, and the measurement object 30. Therefore, the amount of displacement of the object to be measured 30 can be obtained from the amount of energy applied to the refractive index variable device 16 or the refractive index change of the refractive index variable device 16.
The arithmetic device 25 shown in FIG. 1 has a function as a displacement detection unit that detects the displacement of the object to be measured based on the refractive index of the waveguide. Further, the arithmetic unit 25 holds in advance data indicating the relationship between the amount of energy applied to the refractive index variable device 16 or the refractive index change of the refractive index variable device 16 and the displacement amount of the device under test 30.
Here, the computing device 25 in the present embodiment is the relationship between the amount of energy applied to the refractive index variable device 16 of the second optical fiber 5 or the refractive index change of the refractive index variable device 16 and the displacement amount of the device under test 30. Is stored in advance so that a reliable measurement result can be calculated using actual laser light data. However, the present invention is not limited to this, and the wavelength of the laser light from the semiconductor laser oscillation element 2 is displaced. If the measurement accuracy is known to the extent that there is no problem, the amount of energy applied to the refractive index variable device 16 of the second optical fiber 5 or the change in the refractive index of the refractive index variable device 16 and the amount of displacement of the object to be measured 30 are calculated. Data indicating the relationship may not be held in advance.
Therefore, in the present embodiment, the arithmetic unit 25 does not measure the displacement of the object to be measured from the light intensity as in the conventional case, but passes through the reference light from the semiconductor laser oscillation element 2 and the object to be measured 30. The refractive index variable unit 16 changes the refractive index of the second optical fiber 5 so that the interference light level with the reflected light always becomes a set value, and the refractive index variable unit 16 of the second optical fiber 5 is changed accordingly. The displacement of the device under test 30 is measured from the amount of energy applied or the change in the refractive index of the refractive index variable device 16.

The most desirable setting value for the detected light level is the light intensity value at point B having the largest rate of change on the sine wave shown in FIG. However, if the light intensity value at the point C or the point D is set as a set value, even if the displacement amplitude of the object to be measured 30 exceeds 1/4 of the measurement light wavelength, the number of detection light peaks is not counted. The displacement can be detected accurately. Therefore, the arithmetic unit 25 according to the present embodiment sets the value at the point B, that is, the average value of the maximum level and the minimum level when measuring with high accuracy, and when measuring a relatively large displacement. It is assumed that the value at point C or point D, that is, the maximum level or the minimum level is set as a set value, and a command is issued to the refractive index variable control unit 22 so that the detection light of the photodetector 10 becomes the set value. However, as a matter of course, the setting value of the detection light level is not limited to the maximum value, the minimum value, or the average value of the detection light intensity, and any value may be used.
As for the functions of the arithmetic device in the present embodiment described above, the function contents may be programmed and executed by a computer. Data indicating the amount of energy applied to the refractive index variable device 16 or the relationship between the refractive index change of the refractive index variable device 16 and the amount of displacement of the object to be measured 30 is stored in a storage device of a computer. Also good.

[Flow of minute displacement measurement]
Next, the overall operation of the minute displacement measuring apparatus according to the present embodiment will be described. Here, the minute displacement measuring method is also described simultaneously with showing each step. FIG. 14 is a flowchart showing the overall operation of the minute displacement measuring apparatus of the present embodiment. First, when the power source 1 supplies a current to the semiconductor laser oscillation element 2, the semiconductor laser oscillation element 2 oscillates laser light (step S1), the laser light is incident on the first optical fiber 3, and the first optical fiber type Through the coupler 15, one is reflected as a reference light to the second optical fiber type coupler 17, and the other is reflected by the object to be measured and guided to the second optical fiber type coupler 17 as irradiation light. In this way, an interferometer is formed.
Subsequently, first, the photodetector 10 detects a change in the light intensity of the interference light (step S2). The detected light intensity change is digitized through the amplifier 23 and the A / D converter 24 and is subjected to arithmetic processing in the arithmetic unit 25 to generate a control signal to the refractive index variable device 16. Then, the refractive index variable control unit 22 adjusts the operation of the refractive index variable device 16 based on a command from the arithmetic device 25. Therefore, the refractive index variable control unit 22 adjusts the amount of energy applied to the refractive index variable device 16 so that the detected light intensity shows a preset value. That is, the interference light is set to the set value at the initial position of the DUT 30 (step S3). Then, when a minute displacement occurs in the object to be measured 30 and the optical path length of the irradiation light changes and the intensity of the interference light changes (Yes in step S4), the refractive index variable device 16 is in the second optical fiber 5. The amount of energy is supplied, the refractive index of the second optical fiber 5 is adjusted, and the interference light is returned to the original intensity again (step S5).
Then, the arithmetic unit 25 calculates the displacement amount of the device under test 30 according to the refractive index change amount of the refractive index variable device 16 before and after the device under test 30 is displaced (step S6).
In this way, the arithmetic unit 25 feeds back the signal from the photodetector 10 to the signal sent to the refractive index variable control unit 22 to change the refractive index of the second optical fiber 5, and the light intensity of the interference light is always set. The displacement of the device under test 30 is detected so as to be a value.

  Since the minute displacement measuring apparatus of the present embodiment is configured as described above, a measuring apparatus having high flexibility is realized by forming the interferometer with an optical fiber. Further, instead of measuring the displacement of the object to be measured from the light intensity as in the prior art, the refractive index of the second optical fiber 5 is changed so that the light intensity of the interference light at the interferometer always becomes a set value. Since the displacement of the object to be measured is measured from the amount of change in the refractive index of the second optical fiber 5 due to the change, if the maximum value or the minimum value is set as the set value, the displacement amplitude of the object to be measured is 1 / wavelength of the measurement light wavelength. Even when the number exceeds 4, the displacement can be accurately detected without counting the number of peaks of the detection light.

[Second Embodiment]
FIG. 2 is a schematic diagram showing the configuration of the minute displacement measuring apparatus according to the second embodiment of the present invention. In the first embodiment shown in FIG. 1, a 2 × 2 coupler is used as the first optical fiber coupler 15, but the micro displacement measuring apparatus of the present embodiment is configured using a 1 × 2 optical fiber coupler. is doing. Thereby, the obtained effect is the same as that of the first embodiment.

[Third Embodiment]
FIG. 3 is a schematic diagram showing the configuration of the minute displacement measuring apparatus according to the third embodiment of the present invention. In the first embodiment, the light emitted from the second optical fiber 5 to the object to be measured and reflected from the object to be measured 30 is guided to the third optical fiber 6. In this minute displacement measuring apparatus, an optical fiber coupler (third optical fiber coupler 18) is guided to the third optical fiber 6. However, in this case, since the third optical fiber coupler has a branching ratio, the light reflected from the object to be measured 30 is guided to the third optical fiber 6 by the third optical fiber coupler 18 by the branching ratio. The wave light is subject to loss. Accordingly, the first optical fiber coupler 15, the second optical fiber coupler 17, and the second optical fiber coupler 17 are set so that the intensity of the interference light is greater than the intensity of the reference light in consideration of the branching ratio of the third optical fiber coupler 18. It is necessary to determine the branching ratio of the three optical fiber couplers 18.

[Fourth Embodiment]
FIG. 4 is a schematic diagram showing the configuration of a minute displacement measuring apparatus according to the fourth embodiment of the present invention. In the third embodiment, a 2 × 2 coupler is used as the first optical fiber coupler. However, the minute displacement measuring apparatus of the present embodiment is configured using a 1 × 2 optical fiber coupler. Thereby, the obtained effect is the same as in the case of the third embodiment.
The relationship between the first embodiment and the second embodiment and the relationship between the third embodiment and the fourth embodiment are the same.

[Fifth Embodiment]
FIG. 5 is a schematic diagram showing the configuration of a minute displacement measuring apparatus according to the fifth embodiment of the present invention. In the third and fourth embodiments, the light emitted from the second optical fiber 5 to the object to be measured and reflected from the object to be measured 30 is reflected by the third optical fiber type coupler 18 to the third optical fiber. However, since the third optical fiber coupler has a branching ratio, the light reflected from the object to be measured 30 is reflected by the third optical fiber coupler 18 according to the branching ratio of the third optical fiber coupler 18. The light guided through the optical fiber 6 is subject to loss due to branching. In order to avoid the loss, the circulator 19 is used in place of the third optical fiber coupler 18 in the minute displacement measuring apparatus of the present embodiment.
In the circulator used in the present embodiment, as shown in FIG. 10, the light from P0 is 100% guided to P1, and the light from P1 is 100% guided to P2. (Light is guided in the direction of the arrow in FIG. 10)
By using the circulator 19, the light reflected from the device under test 30 is guided to the third optical fiber 6 without being lost. The effects obtained by this configuration are almost the same as those in the first and second embodiments.

[Sixth Embodiment]
FIG. 6 is a schematic diagram showing the configuration of a minute displacement measuring apparatus according to the sixth embodiment of the present invention. In the minute displacement measuring apparatus of this embodiment, the 2 × 2 coupler used for the first optical fiber coupler in the fifth embodiment is a 1 × 2 optical fiber coupler. The relationship between the first embodiment and the second embodiment, the relationship between the third embodiment and the fourth embodiment, and the relationship between the fifth embodiment and the sixth embodiment. The relationships are the same. And the effect acquired by this structure is the same as that of the case of 5th Embodiment.

  The minute displacement measuring apparatus of the present invention can be used as a displacement sensor alone as a measuring instrument, or in a production facility for mounting a semiconductor laser element, a semiconductor element or the like on a substrate, and when nano-positioning the element with respect to the substrate is performed. It can be used for metric order displacement measurement. And since the measuring apparatus is miniaturized, it is possible to measure even an object that has been difficult to measure conventionally.

Schematic which shows the structure of 1st Embodiment of the micro displacement apparatus of this invention. Schematic which shows the structure of 2nd Embodiment of the micro displacement apparatus of this invention. Schematic which shows the structure of 3rd Embodiment of the micro displacement apparatus of this invention. Schematic which shows the structure of 4th Embodiment of the micro displacement apparatus of this invention. Schematic which shows the structure of 5th Embodiment of the micro displacement apparatus of this invention. Schematic which shows the structure of 6th Embodiment of the micro displacement apparatus of this invention. The figure which shows the specific example of the refractive index variable device used for the micro displacement apparatus of this invention. Explanatory drawing of the 2 core fiber collimator used for the micro displacement apparatus of this invention. Explanatory drawing of the optical fiber type coupler used for the micro displacement apparatus of this invention. Explanatory drawing of the circulator used for the micro displacement apparatus of this invention. The figure explaining the relationship between the optical path length in the micro displacement apparatus of this invention, and interference of light. The figure explaining optical interference. The figure which showed the relationship between the displacement of the to-be-measured object of the micro displacement apparatus of this invention, and the light intensity of interference light. The flowchart which showed the operation | movement of the whole micro displacement apparatus of the 1st Embodiment of this invention. The figure which shows the structure of a 1st conventional micro displacement measuring apparatus. The figure which shows the structure of the 2nd conventional micro displacement measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 2 Semiconductor laser oscillation element 3 1st optical fiber 4 6th optical fiber 5 2nd optical fiber 6 3rd optical fiber 7 4th optical fiber 8 5th optical fiber 9 7th optical fiber 10 Photodetector 15 1st Optical fiber coupler 16 Refractive index variable device 17 Second optical fiber type coupler 18 Third optical fiber type coupler 19 Circulator 21 D / A converter 22 Refractive index variable control unit 23 Amplifier 24 A / D converter 25 Computing device 26 Displacement display Device 29 Collimator lens 30 DUT 41 Peltier effect element 42 Thermistor (temperature sensor)
43 Optical fiber fixing plate 44 Nichrome wire 45 Heater 201 Frequency stabilized quadrature laser light source 204 Mirror 205 Analyzer 206 Photodiode 207 Signal processing circuit 210 Heterodyne interference optical system 211 Polarizing beam splitter 212, 213 Corner cube 221 Polarizing beam splitter 222, 225 Coupling lenses 223 and 226 Polarization plane preserving optical fibers 224 and 227 Collimating lens 301 Broadband light source 302 Optical fiber 303 Depolarizer 304 Input optical fiber 305 Single mode optical fiber type 3 dB coupler 306 Reference light optical fiber 307 Optical waveguide phase modulation element 308 Input / output port 309 Capillary 310 Optical waveguide 311 Mirror 312 Optical fibers 313 and 318 for measurement light End surfaces 314 and 319 Lens 3 5 signal optical fiber 316 photodetector 317 phase modulation electrode 320 narrowband filter 321 receiving element

Claims (15)

A semiconductor laser oscillation element; a first optical fiber that receives light from the semiconductor laser oscillation element; a first optical fiber coupler that branches light guided through the first optical fiber into reference light and irradiation light; The second optical fiber that guides the irradiation light that irradiates the object to be measured, the third optical fiber that enters after the irradiation light is reflected by the object to be measured, and the reference light branched by the first optical fiber coupler are guided. A fourth optical fiber to be waved, a second optical fiber coupler in which irradiation light guided through the third optical fiber and a reference light guided through the fourth optical fiber interfere with each other, and the second optical fiber coupler. A fifth optical fiber for guiding the interfered interference light; a photodetector for detecting the light intensity of the interference light guided through the fifth optical fiber; and the second optical fiber. Eber, a refractive index variable device that is provided in at least one of the third optical fiber and the fourth optical fiber and changes the effective refractive index of the optical fiber, and a refractive index variable control that controls the operation of the refractive index variable device And a calculation means for generating a control signal to be transmitted to the variable refractive index control unit based on a detection result by the photodetector and detecting a displacement of the object to be measured. measuring device. 2. The minute displacement measuring apparatus according to claim 1, wherein the spectral ratio of the first optical fiber coupler is set so that the light intensity of the irradiated light is higher than that of the reference light. The spectral and coupling ratios of the first and second optical fiber couplers are such that the light intensity of the internally reflected light of the irradiation light and the reflected light interfering with each other in the second optical fiber coupler is higher than that of the reference light. The minute displacement measuring device according to claim 1, wherein the minute displacement measuring device is set. The control unit controls the refractive index variable unit via the refractive index variable control unit so that the intensity of light detected by the photodetector becomes a maximum value or a minimum value. 4. The micro displacement measuring device according to any one of 3 above. The computing means controls the refractive index variable device via the refractive index variable control unit so that the intensity of the light detected by the photodetector becomes an average value of a maximum value and a minimum value. The micro displacement measuring device according to any one of claims 1 to 3. 6. The minute displacement measuring device according to claim 1, wherein the second optical fiber and the third optical fiber are coupled by a two-core optical fiber collimator. 6. The minute displacement measuring device according to claim 1, wherein the second optical fiber and the third optical fiber are coupled by an optical fiber type optical coupler. 6. The minute displacement measuring apparatus according to claim 1, wherein the second optical fiber and the third optical fiber are coupled by a circulator. 9. The minute displacement measuring apparatus according to claim 1, wherein the refractive index variable device changes a refractive index of the optical fiber by heating or cooling a part of the optical fiber. The micro displacement measuring apparatus according to claim 9, wherein the heating or cooling means of the refractive index variable device is a heater or a Peltier effect element. 9. The minute displacement according to any one of claims 1 to 8, wherein the refractive index variable device is configured by an electro-optic element that is installed between the optical fibers and uses an electro-optic material as a waveguide. measuring device. The micro displacement according to any one of claims 1 to 8, wherein the refractive index variable device is configured by an electro-optical element that is installed between the optical fibers and uses an acousto-optic material for a waveguide. measuring device. The micro displacement measuring apparatus according to claim 1, wherein the calculation unit has a function of detecting a displacement of the object to be measured. A semiconductor laser oscillation element; a first optical fiber that receives light from the semiconductor laser oscillation element; a first optical fiber coupler that branches light guided through the first optical fiber into reference light and irradiation light; The second optical fiber that guides the irradiation light that irradiates the object to be measured, the third optical fiber that enters after the irradiation light is reflected by the object to be measured, and the reference light branched by the first optical fiber coupler are guided. A fourth optical fiber to be waved, a second optical fiber coupler in which irradiation light guided through the third optical fiber and a reference light guided through the fourth optical fiber interfere with each other, and the second optical fiber coupler. A fifth optical fiber for guiding the interfered interference light; a photodetector for detecting the light intensity of the interference light guided through the fifth optical fiber; and the second optical fiber. Eber, a refractive index variable device that is provided in at least one of the third optical fiber and the fourth optical fiber and changes the effective refractive index of the optical fiber, and a refractive index variable control that controls the operation of the refractive index variable device And a micro displacement measuring device including a calculation unit that generates a control signal to be transmitted to the variable refractive index control unit based on a detection result by the photodetector and detects a displacement of the object to be measured. A method for measuring a minute displacement, a laser light irradiation step for irradiating a measurement object with a laser beam from a semiconductor laser oscillation element via an optical fiber, and an irradiation light from the measurement object irradiated with the laser light and the semiconductor An interference light detection step for detecting an intensity change of interference light with the reference light from the laser oscillation element, and a detection result based on the detection result by the interference light detection step. A refractive index variable control step for variably controlling the refractive index of the refractive index variable device, and a displacement for detecting the displacement of the object to be measured based on the amount of change in the refractive index of the refractive index variable caused by the refractive index variable control step. A step of detecting, and in the variable refractive index control step, the detection result of the measurement light detection step is monitored, and the refractive index of the refractive index variable device is adjusted so that the intensity of the detection light becomes a preset value. A minute displacement measuring method, wherein the rate is variably controlled. A semiconductor laser oscillation element; a first optical fiber that receives light from the semiconductor laser oscillation element; a first optical fiber coupler that branches light guided through the first optical fiber into reference light and irradiation light; The second optical fiber that guides the irradiation light that irradiates the object to be measured, the third optical fiber that enters after the irradiation light is reflected by the object to be measured, and the reference light branched by the first optical fiber coupler are guided. A fourth optical fiber to be waved, a second optical fiber coupler in which irradiation light guided through the third optical fiber and a reference light guided through the fourth optical fiber interfere with each other, and the second optical fiber coupler. A fifth optical fiber for guiding the interfered interference light; a photodetector for detecting the light intensity of the interference light guided through the fifth optical fiber; and the second optical fiber. Eber, a refractive index variable device that is provided in at least one of the third optical fiber and the fourth optical fiber and changes the effective refractive index of the optical fiber, and a refractive index variable control that controls the operation of the refractive index variable device Operating a minute displacement measuring apparatus comprising: a control unit for generating a control signal to be transmitted to the variable refractive index control unit based on a detection result by the photodetector and detecting a displacement of the object to be measured. A measurement light level acquisition process for fetching the intensity value of the interference light detected by the photodetector into a computer that controls the operation of the micro displacement measuring device, and the intensity value of the interference light A refractive index variable control process for controlling the operation of the refractive index variable so as to have a preset value, and the optical flux generated by the operation of the refractive index variable. Small displacement measuring program for the displacement calculating process for calculating a displacement of the object to be measured based on the amount of change in the effective refractive index of Iba, characterized in that to the execution.

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