JP2009216638A - Minute displacement measuring device and measuring method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily-manufacturable and miniaturizable minute displacement measuring device having high precision and a simple constitution, in minute displacement measurement utilizing laser light. <P>SOLUTION: Optical waveguides 4, 5, 6, 7, 8, 9, 12 constituting an interferometer are formed on a planar lightwave circuit substrate 3, and a refractive index changer 11 for changing a refractive index of a part of the optical waveguides is provided. Light intensity of interference light 9 between reflected light 6 from a measuring object 30 when a measuring object 30 is displaced and reference light 7 is detected by a photodetector 10, and the refractive index of the optical waveguides is changed by the refractive index changer 11 so that the light intensity is returned to an initial value, and a displacement of the measuring object 30 is calculated from a variation of the refractive index at that time. This device is hardly influenced by an optical loss of detection light, and performs highly-accurate measurement of displacement of the measuring object. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a micro displacement measuring apparatus for measuring micro displacement such as micro vibration of an object, a measuring method thereof, and a program for measuring micro displacement, and more particularly, an apparatus for measuring micro displacement of an object to be measured using laser light. And a method.

  2. Description of the Related Art Conventionally, a displacement measuring apparatus that measures the displacement of an object using a laser beam is used in various fields because it can measure with high accuracy. Usually, a conventional micro displacement measuring apparatus using optical interference combines a half mirror or a polarizing beam splitter and a wave plate to split a laser beam into two optical paths, and refer to one of the beams as a reference beam. Irradiate the mirror for light, the other light irradiates the object to be measured as measurement light, and from the change in the intensity of the interference light that occurs according to the phase difference between the two reflected light again, The difference between the two optical paths, that is, the displacement of the object to be measured is detected.

Further, a micro displacement measuring device using an optical waveguide formed on a crystal substrate is disclosed in Patent Document 1 and Patent Document 2 below.
As shown in FIG. 11, the apparatus disclosed in Patent Document 1 is a substrate on which an optical fiber 230 having a laser oscillator 240 and a photodetector 250 attached on one end side and an optical waveguide 212 branched in a Y shape is formed. 211. A reflection member 216 is attached to the end portion of the optical waveguide 214 that guides the reference light on the substrate 211, and electrodes 215 for controlling the phase of the reference light are formed on both sides of the optical waveguide 214. A predetermined voltage is applied to the electrode 215 from the phase control unit 260.
In this apparatus, the laser light oscillated from the laser oscillator 240 enters the optical waveguide 212 through the optical fiber 230 and is branched into the reference light and the irradiation light irradiated on the object to be measured 280. Irradiation light is reflected by the object to be measured 280, reference light is reflected by the reflecting member 216, and interference light obtained by combining these reflected lights enters the photodetector 250 through the optical fiber 230. The photodetector 250 detects the light intensity of the interference light. In addition, the phase control unit 260 adjusts the phase difference between the reference light that generates the interference light in the initial state and the irradiation light to be, for example, π / 2, that is, the light intensity of the interference light is zero. To do. By controlling the operating point in this way, the displacement of the device under test 280 can be accurately measured.

The apparatus disclosed in Patent Document 2 includes a crystal substrate 301 on which optical waveguides 302 and 303 are formed, as shown in FIG. A part of these optical waveguides 302 and 303 are close to each other to form a directional coupler 306. Laser light output from the light source 312 is incident on the optical waveguide 302 via the optical fiber 313, and part of this laser light is propagated to the optical waveguide 305 side by the directional coupler 306, and irradiated light As shown, the object to be measured 309 is irradiated through the condenser lens 308. The remaining laser light travels through the optical waveguide 304 as reference light and is reflected by the reference light mirror 307. The reflected reference light propagates to the optical waveguide 303 side by the directional coupler 306 and is combined with the irradiation light reflected by the object 309 to generate an interference wave. The interference wave enters the photodetector 316 through the optical waveguide 303 and the optical fiber 315, and the light intensity is detected. Further, on both sides of the optical waveguide 304, as in Patent Document 1, electrodes 314 for controlling the phase of the reference light are provided.
Further, electrodes 310 and 311 are provided at both ends of the substrate 301, and the displacement of the object 309 to be measured is measured in a state where an alternating electric field is applied to the electrodes 310 and 311 to slightly vibrate the substrate 301. .
Japanese Patent Laid-Open No. 11-37718 JP-A-7-159114

However, the minute displacement measuring devices disclosed in Patent Documents 1 and 2 have some problems.
In these apparatuses, when the laser light incident on the substrate is divided into the reference light and the irradiation light, the branching ratio is set to 50:50. However, the irradiation light is emitted from the optical waveguide of the substrate and the measurement target is measured. Since light loss occurs until the reflected light returns to the optical waveguide of the substrate again, the light intensity becomes weaker than that of the reference light. In these devices, the displacement of the object to be measured is calculated based on the change in the light intensity of the interference light in which the reflected irradiation light and the reference light are combined, so the light intensity of the irradiation light compared to the reference light If the value becomes weak, the sensitivity to the displacement of the object to be measured deteriorates, and there is a disadvantage that the measurement accuracy decreases.

Further, in these apparatuses for obtaining the displacement of the measurement target from the intensity change of the interference light, as described in Patent Document 1, when the displacement amplitude of the measurement target exceeds ¼ of the wavelength of the laser light. Therefore, it is necessary to count the number of peaks of the interference light, and to calculate the displacement of the object to be measured from the number and the intensity of the interference light when the displacement is completed.
In these apparatuses, since the mirror is provided on the end face of the substrate to obtain the reference light, the number of components increases by the amount of the mirror, and the assembling work becomes complicated.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and the object is to perform highly accurate and reliable measurement in minute displacement measurement using laser light. To provide a micro displacement measuring device that is simple in configuration, easy to manufacture, miniaturized, and easy to operate, and to provide a micro displacement measuring method and program thereof.

  In order to achieve the above object, according to the present invention, a semiconductor laser oscillation element that oscillates laser light and an optical waveguide through which the laser light propagates are irradiated with laser light oscillated from the semiconductor laser oscillation element. A planar lightwave circuit board that divides light into reference light, irradiates the object to be measured with the irradiation light, and generates interference light between the irradiation light reflected by the object to be measured and incident again. A refractive index variable device that changes a refractive index of the optical waveguide of the planar lightwave circuit board that guides the irradiation light or the reference light, a photodetector that detects the light intensity of the interference light, and the photodetector. Refractive index variable control means for controlling the operation of the refractive index variable so that the detected light intensity of the interference light becomes a preset value, and the refraction of the optical waveguide changed by the refractive index variable Rate change or change Displacement detecting means for detecting the displacement of the object to be measured based on the amount of change in energy applied to the refractive index variable device for obtaining is provided. .

  The planar lightwave circuit board has a first optical waveguide that guides the laser light oscillated from the semiconductor laser oscillation element, and the laser light guided by the first optical waveguide is referred to as irradiation light. A branching portion that divides the light into a light, a second optical waveguide that guides the irradiation light branched off at the branching portion to the irradiation position of the object to be measured, and the irradiation light that is reflected again by the object to be measured A third optical waveguide for guiding the reference light, a fourth optical waveguide for guiding the reference light divided by the branching portion, the irradiation light guided by the third optical waveguide, and the fourth optical light An interference part that interferes with the reference light guided by the waveguide and a fifth optical waveguide that guides the interference light interfered by the interference part are formed. It is provided in at least one of the optical waveguide, the third optical waveguide, and the fourth optical waveguide.

  The refractive index variable control means preferably has the refractive index so that the light intensity of the interference light detected by the photodetector becomes a maximum value or a minimum value, or an average value of the maximum value and the minimum value. Controls the operation of the transformer.

  Preferably, the laser light oscillated from the semiconductor laser oscillation element is divided on the planar lightwave circuit board so that the irradiation light is larger than the reference light.

  In order to achieve the above object, according to the present invention, the laser light oscillated from the semiconductor laser oscillation element is guided to the irradiation position of the object to be measured by the optical waveguide in the planar lightwave circuit board. A laser light irradiation step for irradiating the object to be measured, the reference light branched from the laser light, and the irradiation light reflected from the object to be measured are guided to an interference position by an optical waveguide in the planar lightwave circuit board. The interference light detection step of generating interference light and detecting the intensity change of the interference light and the detection result in the interference light detection step are monitored so that the light intensity of the interference light becomes a preset value. A refractive index variable control step for variably controlling the refractive index of the optical waveguide, and a change amount of the refractive index of the optical waveguide caused by the refractive index variable control step or a variable control of the refractive index in order to obtain the variation amount. Energy Small displacement measuring method characterized by comprising a displacement detection step of the detecting the displacement of the object to be measured based on the change amount of ghee, a, is provided.

  In order to achieve the above object, according to the present invention, there is provided a semiconductor laser oscillation element that oscillates a laser beam and an optical waveguide through which the laser beam propagates, and the laser beam oscillated from the semiconductor laser oscillation element. Is split into an irradiation light and a reference light, the irradiation light is irradiated onto the object to be measured, and a planar light wave that generates interference light between the irradiation light and the reference light reflected again by the object to be measured and incident again A circuit board; a refractive index variable device that changes a refractive index of an optical waveguide that guides the irradiation light or reference light of the planar lightwave circuit board; and a photodetector that detects a light intensity of the interference light. A measurement light for taking in the intensity value of the interference light detected by the photodetector into a computer that calculates the displacement of the object to be measured by controlling the operation of the refractive index variable device. Level acquisition processing and the interference light A refractive index variable control process for controlling the operation of the refractive index variable so that the degree value becomes a preset value, and a change amount of the refractive index of the optical waveguide caused by the operation of the refractive index variable or the change There is provided a micro displacement measurement program that executes a displacement calculation process for calculating a displacement of the object to be measured based on a change amount of energy applied to the refractive index variable device in order to obtain a quantity. The

The present invention does not calculate the displacement of the object to be measured from the detected change in the intensity of the interference light but measures the intensity of the interference light as a maximum value, for example, in a minute displacement measurement using laser light. The light intensity of the interference light is adjusted to the maximum value, and the displacement of the object to be measured is obtained from the change in refractive index at that time or the change in energy required for the adjustment. Therefore, the displacement of the object to be measured can be measured with high accuracy.
Further, in the present invention, even when the displacement amplitude of the object to be measured exceeds ¼ of the wavelength of the laser beam, it is not necessary to count the peak number of the interference light when measuring the displacement amplitude. Even when the displacement is relatively large, it can be measured with a simple operation.
In addition, since the minute displacement measuring apparatus of the present invention does not require a reference light reflecting mirror, it has a simple configuration, can be reduced in size and weight, and is easy to manufacture.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing the configuration of a minute displacement measuring apparatus according to the first embodiment of the present invention, and FIG. 10 is a flowchart showing the operation of this apparatus.
This apparatus has a semiconductor laser oscillation element 2 that oscillates laser light by applying a current from a power source 1 and an optical waveguide through which the laser light propagates, and divides the incident laser light into irradiation light and reference light. Then, the planar lightwave circuit board (hereinafter referred to as PLC (Planar Lightwave Circuit) board) that emits the interference light between the irradiated light and the reference light that is incident on the object 30 and reflected by the object 30 and incident again. 3), a refractive index variable device 11 that changes the refractive index of the optical waveguide that guides the irradiation light or reference light of the PLC substrate 3, and detects the light intensity of the interference light, and outputs a current signal corresponding to the detected light intensity. A photodetector 10, an amplifier 23 for amplifying a current signal from the photodetector 10 and converting it into a voltage signal, and an A / D converter 24 for converting an analog voltage signal output from the amplifier 23 into a digital voltage signal; A / D converter 24 The output digital voltage signal is calculated as a voltage value, the refractive index setting value (digital value) of the optical waveguide commanded to the refractive index variable device 11 is calculated, and the measured value is measured from the amount of change in the refractive index. An arithmetic device 25 that calculates the displacement of the object 30, a displacement display device 26 that displays the displacement of the object 30 calculated by the arithmetic device 25, and a refractive index setting value (digital value) output from the arithmetic device 25. A D / A converter 21 that converts an electrical signal (analog value) that can be applied to the refractive index variable device 11, and a refractive index variable control unit 22 that controls the refractive index variable device 11 using this electrical signal. I have.
The “refractive index variable control means” referred to in the claims is realized by the calculation device 25 and the refractive index variable control unit 22, and the “displacement detection means” is realized by the calculation device 25.

  Further, the PLC substrate 3 includes a first optical waveguide 4 that receives light from the semiconductor laser oscillation element 2 and a branch that divides the laser light guided by the first optical waveguide 4 into reference light and irradiation light. Part 8, second optical waveguide 5 through which the irradiation light irradiated to the object to be measured 30 is guided, and a third optical waveguide 6 in which the irradiation light is reflected by the object to be measured and enters the PLC substrate 3 again. A fourth optical waveguide 7 in which the reference light branched by the branching portion 8 is guided, an irradiation light guided by the third optical waveguide 6 and a reference guided by the fourth optical waveguide 7. An interference unit 9 that interferes with light and a fifth optical waveguide 12 that guides the interference light that interferes with the interference unit 9 are formed. The interference light guided by the fifth optical waveguide 12 enters the photodetector 10.

Here, the PLC substrate 3 uses a lithium niobate crystal, which is an electro-optic material whose refractive index varies with voltage. The length of one side of the PLC substrate 3 is several centimeters. The optical waveguide is a light path provided on the PLC substrate 3 in order to guide an optical signal using the difference in the refractive index of light. For example, Ti is thermally diffused along the optical waveguide pattern. Can do. Various methods for forming an optical waveguide are widely known, and in the present invention, any method may be used to form an optical waveguide.
Here, the branching portion 8 is constituted by an optical waveguide branched in a Y shape.
The second optical waveguide 5 and the third optical waveguide 6 form a folded optical waveguide at a position where the object to be measured 30 is irradiated with the irradiation light. In the folded optical waveguide, the light from the second optical waveguide 5 is incident on the third optical waveguide 6 after being irradiated onto the object to be measured 30, reflected, and receiving almost no loss.

Here, the interference unit 9 is formed of a directional coupler. As shown in FIG. 5, in the directional coupler, a part of two optical waveguides (here, a third optical waveguide 6 and a fourth optical waveguide 7 are shown) are parallel and close (generally In addition, a part of the laser light guided by one optical waveguide 6 propagates to the other optical waveguide 7 through the gap between the optical waveguides. Therefore, the reference light guided by the fourth optical waveguide 7 interferes with the irradiation light guided by the third optical waveguide 6, and the interference light travels through the fifth optical waveguide 12. In the directional coupler, if the length of the adjacent optical waveguides is 100 μm at the minimum, the two lights interfere sufficiently.
The light that has not propagated from the optical waveguide 6 to the optical waveguide 7 escapes to an appropriate place. Specifically, light is emitted from the end face of the PLC substrate 3 that does not affect the operation.

The refractive index variable device 11 is an electrode for applying a voltage to the optical waveguide when the material of the PLC substrate 3 is an electro-optical material, and this electrode is formed at a position sandwiching the optical waveguide of the PLC substrate 3. Further, in this case, the refractive index variable control unit 22 is a voltage controller, and a predetermined voltage signal (analog signal) is sent from the voltage controller to the electrode, and a predetermined voltage is applied to the optical waveguide in the PLC board 3. Is applied, and the refractive index of the optical waveguide changes.
The optical path length of light is represented by the path integral of the product of the physical optical path length and the optical path refractive index. Therefore, the optical path length of light can be changed by changing the refractive index of the optical waveguide.
Here, although the refractive index variable device 11 is disposed in the second optical waveguide 5, the refractive index variable device 11 may be disposed in the third optical waveguide 6 or the fourth optical waveguide 7. Alternatively, a plurality of optical waveguides among the second optical waveguide 5, the third optical waveguide 6, and the fourth optical waveguide 7 may be disposed. However, when a plurality of refractive index variable devices 11 are arranged, the same number of refractive index variable control units 22 is required.

Next, the operation of this minute displacement measuring apparatus will be described.
The laser light oscillated from the semiconductor laser oscillation element 2 enters the first optical waveguide 4 and is branched into reference light and irradiation light by the branching portion 8, and the reference light enters the fourth optical waveguide 7. Waveguided to the interference unit 9.
On the other hand, the irradiation light is guided by the second optical waveguide 5 and emitted from one end face of the PLC substrate 3. Further, the refractive index of the second optical waveguide 5 in the meantime is varied by the refractive index variable device 11 and the optical path length is adjusted. The light emitted from the second optical waveguide 5 irradiates the object to be measured 30, and the reflected light enters the third optical waveguide 6 and is guided to the interference unit 9.
In the interference unit 9, the irradiation light guided by the third optical waveguide 6 and the reference light guided by the fourth optical waveguide 7 interfere with each other and become interference light in the fifth optical waveguide 12. The light is guided, emitted from the end face of the PLC substrate 3, and enters the photodetector 10. The photodetector 10 detects the light intensity of the interference light.
The light intensity detected by the photodetector 10 is digitized through the amplifier 23, the A / D converter 24, and the arithmetic unit 25.

At this time, the optical path length of the irradiated light in the PLC substrate 3 is adjusted by adjusting the amount of energy applied to the refractive index variable device 11 to change the refractive index of a part of the second optical waveguide 5, thereby changing the optical path length of this part. It changes by doing. Therefore, the phase difference between the interfering reference light and the irradiation light can be freely set by controlling the amount of energy applied to the refractive index variable device 11 and changing the optical path length in the PLC substrate 3 of the irradiation light.
Using this principle, the refractive index of the optical waveguide is adjusted so that the measured light 30 has the same phase (zero phase difference) between the irradiation light and the reference light at the initial position (position before displacement). It can be set or the irradiation light and the reference light can be set to have opposite phases (phase difference π).

When the two lights interfere with each other, as shown in FIG. 8A, when the phase difference between the two lights is zero, the two lights interfere with each other, so that the light intensity is the highest. A state, that is, a resonance state. Therefore, the light intensity detected by the photodetector 10 is maximized. On the other hand, as shown in FIG. 8B, when the phase difference between the two lights is ½ of the wavelength, they weaken each other, so that the light intensity becomes the smallest. Accordingly, the light intensity detected by the photodetector 10 is minimized.
The arithmetic unit 25 is configured so that the numerical value of the light intensity detected by the photodetector 10 shows the maximum value or the minimum value at the initial position (position before displacement) of the DUT 30. Alternatively, it is set so as to indicate an average value of the maximum value and the minimum value, the voltage of the refractive index variable device 11 satisfying the set value is calculated, and the voltage is supplied to the refractive index variable device through the refractive index variable control unit 22. 11 is applied.

Next, when a minute displacement is given to the measurement object 30, the reflection position of the irradiation light reflected by the measurement object 30 changes. Therefore, the interference light changes from the initial light intensity (set value).
FIG. 7 is a diagram for explaining the change in the light intensity of the interference light, and schematically shows the waveforms of the reference light (a) and the irradiation light (b) in the PLC substrate 3.
As shown in FIG. 7A, the light serving as the reference light is emitted from the semiconductor laser oscillation element 2 and reaches the interference unit 9 through the first optical waveguide 4 and the fourth optical waveguide 7. Assuming that the geometric distance of the first optical waveguide 4 and the fourth optical waveguide 7 is d1 and the refractive index is n1, the optical path length L1 of this light in the PLC substrate 3 is L1 = n1 · d1. Further, the phase of the reference light that has reached the interference unit 9 (the length less than the wavelength) is represented by Δ1.

On the other hand, as shown in FIG. 7B, the light that becomes the irradiation light is emitted from the semiconductor laser oscillation element 2 and passes through the first optical waveguide 4, the second optical waveguide 5, and the third optical waveguide 6. It passes through and reaches the interference unit 9. If the geometric distance of the first optical waveguide 4, the second optical waveguide 5, and the third optical waveguide 6 is d2, and the average refractive index is n2, the optical path of this light in the PLC substrate 3 The length L2 is L2 = n2 · d2. The phase (the length below the wavelength) when this irradiation light reaches the interference portion 9 is represented by Δ2. In the case of irradiation light, a phase of 2 · Δr (length equal to or shorter than the wavelength) is generated when the light is reflected by the object to be measured 30 and returned.
The light intensity of the interference wave when the reference light and the irradiation light interfere with each other in the interference unit 9 is determined by Δ1 and Δ2. If Δ1−Δ2 = 0, the relationship between the reference light and the irradiation light at the time of incidence on the interference unit 9 is in the state shown in FIG. 8A, so that the light intensity of the interference wave becomes maximum, and Δ1−Δ2 = If λ / 2 (λ is the wavelength of the laser light oscillated from the semiconductor laser oscillation element 2), the state shown in FIG. 8B is obtained, and the light intensity of the interference wave is minimized.
Here, when the position of the object to be measured 30 is displaced, Δr changes, and the value of Δ2 changes accordingly, so the light intensity of the interference wave changes.

When the object to be measured 30 is displaced and the light intensity of the interference light deviates from the set value, the arithmetic unit 25 refracts necessary to return the light intensity of the interference light to the set value based on the current value of the light intensity. The voltage value of the refractive index variable device 11 is calculated, and the voltage is applied to the refractive index variable device 11 through the variable refractive index control unit 22. Further, the amount of displacement of the device under test 30 is calculated from the amount of change in voltage value before and after the displacement of the device under test 30. For this calculation, the calculation device 25 holds data indicating the relationship between the amount of energy applied to the refractive index variable device 11 and the amount of displacement of the device under test 30 in advance.
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.

Here, the relationship of FIG. 7 is expressed mathematically as follows.
First, for the reference light, if the number of wavelengths existing in the optical path length L1 is m, the following equation (1) is established.
m · λ + Δ1 = L1 (1)
Further, as described above, the optical path length L1 has the relationship of the following equation (2).
L1 = n1 · d1 (2)
From (1) and (2),
m · λ + Δ1 = n1 · d1 (3)
It becomes.
Similarly, with respect to the irradiation light, if the number of wavelengths existing in the optical path length L2 is n, the following expression (4) is established.
n · λ + Δ2 + 2 · Δr = n2 · d2 (4)
When subtracting equation (4) from equation (3),
(Mn) · λ + Δ1−Δ2-2 · Δr = n1 · d1−n2 · d2 (5)
Further, since m, n, λ, Δ1, n1, and d1 are constant and do not change, when the equation (5) is simplified,
Δ2 + 2 · Δr−n2 · d2 = constant (6)
It becomes.

From the equation (6), when the position of the object to be measured 30 is changed and Δr and Δ2 are changed, n2 is changed, that is, by changing the refractive index by the refractive index variable device 11, the equation (6) is obtained. ) 2 can be returned to the set value (that is, the light intensity of the interference light can be returned to the set value).
In such a case, since Δ2 is known, if only the amount of change in refractive index is measured, the amount of change in Δr, that is, the amount of displacement of the object to be measured 30 can be obtained from Equation (6).

As shown in FIG. 9, the relationship between the displacement of the object to be measured 30 and the light intensity of the interference light can be represented by a sine wave in which the intensity of light appears in a λ / 2 period. The reason why the period in this case is λ / 2 is that 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.
The most desirable setting value of the light intensity of the interference light detected by the photodetector 10 is the light intensity value at the 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, the number of peaks of the detected light can be counted even if the displacement amplitude of the object to be measured 30 exceeds 1/4 of the measurement light wavelength λ. Therefore, the displacement can be detected accurately.
Therefore, when measuring with high accuracy, the value at point B, that is, the average value of the maximum level and minimum level is set as the set value, and when measuring a relatively large displacement, the value at point C or point D is used. It is desirable to give a command to the variable refractive index control unit 22 so that the detection light of the photodetector 10 becomes a set value with the value, that is, the maximum level or the minimum level as a set value. Of course, any other value can be used as the set value of the detection light level.

Next, the overall operation of the minute displacement measuring apparatus will be described based on the flowchart of FIG.
First, when the power source 1 applies a current to the semiconductor laser oscillation element 2, the semiconductor laser oscillation element 2 oscillates a laser beam (step S1), and the laser beam enters the first optical waveguide 4 and enters the branching portion 8. Then, one is reflected to the interference unit 9 as reference light, the other is reflected by the object to be measured, and is guided to the interference unit 9 as irradiation light. In this way, an interferometer is formed.
Subsequently, the light intensity of the interference light is detected by the photodetector 10 (step S2, interference light detection step). The detected light intensity is digitized by the amplifier 23, the A / D converter 24, and the arithmetic unit 25. The arithmetic unit 25 adjusts the amount of energy (voltage value) applied to the refractive index variable device 11 through the refractive index variable control unit 22 so that the detected light intensity shows a preset setting value (step S3). .

When a minute displacement occurs in the object to be measured 30 and the intensity of the interference light changes from the set value (Yes in step S4), the arithmetic unit 25 changes the refractive index variable necessary for returning the intensity of the interference light to the set value. 11 is calculated and applied to the refractive index variable device 11 through the variable refractive index control unit 22. Thereby, the intensity of the interference light returns to the set value again (step S5, refractive index variable control step).
Then, the arithmetic unit 25 calculates the amount of displacement of the device under test 30 according to the voltage change amount of the refractive index variable device 11 before and after the device under test 30 is displaced (step S6, displacement detection step).
As described above, the arithmetic unit 25 controls the refractive index variable control unit 22 while controlling the refractive index variable control unit 22 so that the light intensity of the interference light always becomes the set value based on the signal from the photodetector 10 until the measurement is completed. The displacement of the measurement object 30 is detected (step 7).
Such processing procedures can be programmed and executed by a computer.

As described above, in this minute displacement measuring apparatus, the light intensity of the interference light when the object to be measured is displaced is maintained at the set value, and the amount of change in the refractive index (or the amount of change) before and after the displacement is obtained. Since the displacement of the object to be measured is obtained from the amount of change in energy applied to the refractive index variable device, compared to the conventional method of obtaining the displacement of the object to be measured from the detected intensity change of the interference light Less susceptible to light loss. Therefore, highly accurate measurement is possible.
Further, with this minute displacement measuring apparatus, even a relatively large displacement such that the displacement amplitude of the object to be measured exceeds 1/4 of the wavelength of the laser beam can be measured with a simple operation.
Further, in this minute displacement measuring apparatus, since the fourth optical waveguide 7 that guides the reference light is directly connected from the branching portion 8 to the interference portion 9, a mirror for reference light reflection is unnecessary, and the configuration is It is simple. In addition, the manufacturing process can be simplified, the productivity can be improved, and the price can be reduced.
In addition, this minute displacement measuring apparatus can be highly integrated and miniaturized by mounting a semiconductor laser element and a photodetector on a PLC substrate on which an optical waveguide is formed. With this high integration and miniaturization, the distance until reflected light from the object to be measured reaches the photodetector can be shortened, minimizing optical loss in the optical waveguide, and increasing the sensitivity of displacement measurement. Can be raised. Further, the loss received by the measurement light due to disturbance such as thermal expansion and vibration can be reduced, and a highly reliable measurement result can be obtained.

In the configuration of FIG. 1, the semiconductor laser oscillation element 2 and the photodetector 10 are arranged on separate end faces of the PLC substrate 3, but these are arranged on the same end face of the PLC substrate 3 as shown in FIG. 2. You may arrange | position and you may arrange | position in any places.
Here, as the electro-optic material used for the PLC substrate 3, a typical lithium niobate is used, but other electro-optic materials may be used. In addition, materials other than electro-optic materials can be used as long as they can change the refractive index of the optical waveguide formed on the substrate.
For example, a thermo-optic material whose refractive index changes with heat can be used for the PLC substrate 3. A typical example of the thermo-optic material is quartz. In this case, the refractive index variable device 11 serves as a heater, and the refractive index variable control unit 22 serves as a heater controller. The heater heats the optical waveguide in the PLC substrate 3 to a predetermined temperature by a signal (analog signal) sent from the heater controller, and changes the refractive index of the optical waveguide.
In addition, an acousto-optic material whose refractive index changes with stress can be used for the PLC substrate 3. A typical example of the acoustooptic material is lithium niobate. In this case, the refractive index variable device 11 serves as a transducer, and the refractive index variable control unit 22 serves as a transducer controller. The transducer applies a predetermined stress to the optical waveguide in the PLC substrate 3 due to distortion caused by the piezoelectric signal (analog signal) sent from the transducer controller, and changes the refractive index of the optical waveguide.
The length of the refractive variable device 11 is the difference between the optical path lengths of the irradiation light and the reflected light, the phase amount to be changed, the amount of change in the refractive index that changes depending on the amount of energy per unit length that can be applied to the refractive variable device 11, etc. Can be calculated based on

Further, here, the branching portion 8 is constituted by an optical waveguide branched in a Y shape, but any means can be used as long as it has a function of branching one light into a plurality of parts. .
Further, here, the second optical waveguide and the third optical waveguide form a folded optical waveguide, but the irradiation light guided by the second optical waveguide is derived toward the object to be measured, Any means can be used as long as it has a function of deriving the irradiation light reflected by the object to be measured to the third optical waveguide.
Here, the interference unit 9 is formed of a directional coupler, but any means can be used as long as it has a function of combining the reference light and the irradiation light.
The laser light is stable coherent light, and there is no limitation on the type and wavelength of the laser as long as it propagates through the optical waveguide in the PLC substrate 3 in a single mode.
Here, it is assumed that the arithmetic unit 25 holds in advance data indicating the relationship between the amount of energy applied to the refractive index variable device 11 and the amount of displacement of the object to be measured 30, but the semiconductor laser oscillator 2 If the wavelength of the laser beam from is known to the extent that there is no problem in the measurement accuracy of the displacement, this data need not be held in advance.

(Second Embodiment)
FIG. 3 is a diagram showing a configuration of a minute displacement measuring apparatus according to the second embodiment of the present invention, and FIG. 6 is a diagram showing a configuration of a branching portion of this apparatus.
In this minute displacement measuring apparatus, in order to improve the measurement sensitivity of the displacement of the object to be measured, the branching portion for branching the laser light is configured so that the amount of irradiation light is divided more than the reference light. Thereby, the influence by the optical loss of irradiation light can be reduced.
The configuration of the minute displacement measuring apparatus shown in FIG. 3 is the same as that of the first embodiment (FIG. 1) except for the branching section 8.

As shown in an enlarged view in FIG. 6, the branching portion 8 has a branching ratio when the laser light guided by the first optical waveguide 4 is branched into the second optical waveguide 5 and the fourth optical waveguide 7. Branching ratio control units 14 (a) and 14 (b) are controlled. The branching ratio controllers 14 (a) and 14 (b) are refractive index variable devices that change the refractive indexes at the entrances of the second optical waveguide 5 and the fourth optical waveguide 7. As described in the first embodiment, the refractive index variable device can be realized by a configuration in which voltage, heat, or stress is applied to a corresponding portion of the PLC substrate 3.
There is a phenomenon in which light is attracted to a higher refractive index, and the branching ratio control units 14 (a) and 14 (b) use this phenomenon to make the refractive index of the second optical waveguide 5 the fourth. It is set to be higher than the refractive index of the optical waveguide 7, and the amount of irradiation light guided in the second optical waveguide 5 is greater than the reference light guided in the fourth optical waveguide 7. It is controlled to increase.

Next, how to obtain an appropriate branching ratio in this case will be described.
The loss received by the light propagating through each optical waveguide of the PLC substrate 3 is 10 ⁻⁶ dB / cm, and the length of the PLC substrate 3 is several cm. Therefore, the optical loss in the PLC substrate 3 is negligible. small. Therefore, the loss that the light incident on the first optical waveguide 4 of the PLC substrate 3 receives in the PLC substrate is that the light guided by the second optical waveguide 5 is emitted from the PLC substrate 3 to the device under test 30. The loss received before entering the third optical waveguide 6 again is the largest.
Therefore, assuming that the above loss is 2 dB, a relational expression between the optical loss and the optical intensity,
Light loss = 10 · log (light intensity)
From the above, when the light intensity is calculated as light loss = −2,
Light intensity = 10 ^ (light loss / 10) = 10 ^ (− 0.2) = 0.630
It becomes. This means that the light intensity drops to 63.1% of the original light intensity.
Accordingly, if the intensity of light guided by the first optical waveguide 4 is A and the ratio of the light branched to the second optical waveguide 5 at the branching portion 8 is α, the third optical waveguide 6 The light intensity of the irradiated light that is guided and reaches the interference section 9 is:
A ・ 0.631 ・ α
Thus, the light intensity of the reference light guided by the fourth optical waveguide 7 and reaching the interference unit 9 is
A ・ (1-α)
It becomes.

For this reason, the light intensity of the irradiation light guided by the second optical waveguide 5 and guided by the third optical waveguide 6 through the device under test 30 is guided by the fourth optical waveguide 7. The condition for making it larger than the light intensity is
A · 0.631 · α> A · (1-α)
When the above equation is solved, α> 0.613.
Therefore, the minimum value of the branching ratio between the second optical waveguide 5 and the fourth optical waveguide 7 can be calculated as 61.3: 38.7.
In the branching section 8, when the branching ratio control section 14 controls the refractive indexes of the second optical waveguide 5 and the fourth optical waveguide 7 so as to achieve this branching ratio, the light is guided through the third optical waveguide 6. Until the light loss is 2 dB, the light intensity of the irradiation light guided by the third optical waveguide 6 is higher than the light intensity of the reference light guided by the fourth optical waveguide 7, The displacement of the measurement object 30 can be detected with high sensitivity, and the accuracy of the displacement measurement can be increased.

In addition, as shown in FIG. 4, the branch portion in which the branch ratio control unit 14 is provided so that the branch ratio of the Y-shaped branch waveguide can be adjusted is shown in FIG. It can also be used at a location where the waveguide 6 is connected. In this branching section 15, the branching ratio control section is adjusted so that a large amount of reflected light from the device under test 30 that has entered from the sixth optical waveguide 13 flows toward the third optical waveguide 6.
In the PLC substrate 3 having the branch portion 15, the light guided by the second optical waveguide 5 is guided by the sixth optical waveguide 13 through the branch portion 15 and emitted to the object to be measured 30. . The light reflected by the device under test 30 enters the sixth optical waveguide 13 again and is branched into the second optical waveguide 5 and the third optical waveguide 6 according to the branching ratio set in the branching section 15.

Such branching ratio control is also possible in a directional coupler. As shown in FIG. 5, in the directional coupler in which the two optical waveguides 6 and 7 are arranged close to each other, the coupling strength between the optical waveguides is parallel to the distance between the optical waveguides and the refractive index between the optical waveguides. It depends on the length of the optical waveguide. Therefore, the amount of light propagating from the optical waveguide 6 to the optical waveguide 7 can be adjusted by arranging a refractive index variable device to vary the refractive index of the gap between the optical waveguides.
A directional coupler having such a branching ratio adjusting function can be used for the branching section 14, the branching section 15, or the interference section 9 of the PLC substrate 3.

The minute displacement measuring apparatus of the present invention can measure displacement on the order of nanometers and can be extremely miniaturized by high integration. For this reason, for example, it can be used for production equipment for mounting a semiconductor laser element, a semiconductor element, or the like on a substrate and used for alignment of the element with respect to the substrate.
Further, it can be used as a single measuring instrument and can be used for measuring the displacement of an object that has been too large to measure with conventional displacement sensors.

  The micro displacement measuring apparatus of the present invention has high accuracy, can be miniaturized, and can be used in a wide range of fields such as manufacturing fields of various products that require precision, measuring instruments, medical devices, and experimental devices that require high precision. Can be used.

The figure which shows the structure of the micro displacement measuring apparatus which concerns on the 1st Embodiment of this invention. The figure which shows the other structure of the micro displacement measuring apparatus which concerns on the 1st Embodiment of this invention. The figure which shows the structure of the micro displacement measuring apparatus which concerns on the 2nd Embodiment of this invention. The figure which shows the other structure of the micro displacement measuring apparatus which concerns on the 2nd Embodiment of this invention. The figure which shows an example of the directional coupler used with the micro displacement measuring apparatus which concerns on embodiment of this invention The figure which shows the branch part provided with the branch ratio controller used with the micro displacement measuring apparatus which concerns on the 2nd Embodiment of this invention. The figure explaining the mode of propagation of light in the minute displacement measuring device concerning an embodiment of the invention Diagram explaining light interference The figure which shows the relationship between the displacement of the to-be-measured object in the micro displacement measuring apparatus which concerns on embodiment of this invention, and the light intensity of interference light The flowchart which shows operation | movement of the micro displacement measuring apparatus which concerns on embodiment of this invention. The figure which shows the structure of the conventional minute displacement measuring device The figure which shows the other structure of the conventional minute displacement measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 2 Semiconductor laser oscillation element 3 Planar light wave circuit board (PLC board)
DESCRIPTION OF SYMBOLS 4 1st optical waveguide 5 2nd optical waveguide 6 3rd optical waveguide 7 4th optical waveguide 8 Branching part 9 Interference part 10 Photodetector 11 Refractive index variable device 12 5th optical waveguide 13 6th light guide Waveguide 14 Branch ratio controller 15 Branch section 21 D / A converter 22 Variable refractive index control section 23 Amplifier 24 A / D converter 25 Arithmetic unit 26 Displacement display unit 30 Device under test 211 Substrate 212 Y-shaped branch optical waveguide 214 Optical waveguide 215 Electrode 216 Reflecting member 230 Optical fiber 240 Laser oscillator 250 Photo detector 260 Phase control unit 280 Object to be measured 301 Crystal substrate 302 Optical waveguide 303 Optical waveguide 304 Optical waveguide 305 Optical waveguide 306 Directional coupler 307 Reference optical mirror 308 Condensing lens 309 Measured object 310 Electrode 311 Electrode 312 Light source 313 Optical fiber 314 Electric Pole 315 optical fiber 316 photodetector

Claims (17)

A semiconductor laser oscillation element that oscillates laser light;
An optical waveguide through which the laser light propagates, the laser light oscillated from the semiconductor laser oscillation element is divided into irradiation light and reference light, and the object to be measured is irradiated with the irradiation light; A planar lightwave circuit board that generates interference light between the reference light and the irradiation light reflected again at
A refractive index variable device that changes a refractive index of an optical waveguide of the planar lightwave circuit board that guides the irradiation light or the reference light;
A photodetector for detecting the light intensity of the interference light;
Refractive index variable control means for controlling the operation of the refractive index variable device so that the light intensity of the interference light detected by the photodetector becomes a preset value;
The displacement of the object to be measured is detected based on the change amount of the refractive index of the optical waveguide changed by the refractive index variable device or the change amount of energy applied to the refractive index variable device to obtain the change amount. Displacement detecting means for
A micro displacement measuring device comprising:   The micro displacement measuring apparatus according to claim 1, wherein the planar lightwave circuit board includes a first optical waveguide that guides a laser beam oscillated from the semiconductor laser oscillation element, and the first optical waveguide. A branching unit that divides the guided laser light into irradiation light and reference light; a second optical waveguide that guides the irradiation light branched by the branching unit to an irradiation position on the object to be measured; Guided by the third optical waveguide that guides the incident light reflected again by the measurement object, the fourth optical waveguide that guides the reference light divided by the branch portion, and the third optical waveguide. An interference part where the waved irradiation light and the reference light guided by the fourth optical waveguide interfere with each other, and a fifth optical waveguide for guiding the interference light interfered by the interference part, The refractive index variable device includes at least one of the second optical waveguide, the third optical waveguide, and the fourth optical waveguide. Minute displacement measuring apparatus, characterized in that provided in or.   2. The minute displacement measuring apparatus according to claim 1, wherein the refractive index variable control means is configured to change the refractive index so that the light intensity of the interference light detected by the photodetector becomes a maximum value or a minimum value. A micro-displacement measuring device for controlling the operation of a vessel.   2. The minute displacement measuring apparatus according to claim 1, wherein the refractive index variable control means is configured such that the light intensity of the interference light detected by the photodetector becomes an average value between a maximum value and a minimum value. A micro displacement measuring apparatus for controlling the operation of the refractive index variable device. 2. The minute displacement measuring apparatus according to claim 1, wherein the refractive index variable control means is configured so that the light intensity of the interference light detected by the photodetector has an arbitrary value. A minute displacement measuring device characterized by controlling operation.   2. The minute displacement measuring device according to claim 1, wherein the laser light oscillated from the semiconductor laser oscillation element is divided so that the irradiation light is larger than the reference light on the planar lightwave circuit board. A minute displacement measuring device characterized by being made.   3. The minute displacement measuring apparatus according to claim 2, wherein a branching ratio to the branching optical waveguide that guides the irradiation light in the branching portion is based on a branching ratio to the branching optical waveguide that guides the reference light. Is set so as to be larger.   3. The micro displacement measuring apparatus according to claim 2, wherein the branch portion is formed of a directional coupler in which two optical waveguides are arranged close to each other, and a gap between the optical waveguides guides the reference light. A minute displacement measuring device, wherein the branching ratio to the optical waveguide for guiding the irradiation light is set to be larger than the branching ratio to the waveguide.   3. The minute displacement measuring device according to claim 2, wherein the second optical waveguide and the third optical waveguide form a folded optical waveguide.   3. The micro displacement measuring apparatus according to claim 2, wherein the second optical waveguide and the third optical waveguide are connected to a branched optical waveguide and reflected by the object to be measured to the branched optical waveguide. A minute displacement measurement characterized in that the branching ratio of the branch optical waveguide is set so that the irradiated light that has entered is branched more toward the third optical waveguide than the second optical waveguide. apparatus.   3. The micro displacement measuring apparatus according to claim 2, wherein the second optical waveguide and the third optical waveguide constitute a directional coupler, and the directional coupler is reflected by the object to be measured. The gap between the optical waveguides of the directional coupler is set so that the irradiation light that has entered into the third optical waveguide branches more toward the third optical waveguide than the second optical waveguide. A micro displacement measuring device.   The micro displacement measuring apparatus according to any one of claims 1 to 11, wherein the optical waveguide is made of a thermo-optic material having a temperature dependency of a refractive index, and the refractive index variable device A part is heated to change the refractive index of the optical waveguide, and the displacement detecting means detects the displacement of the object to be measured based on the amount of change in heating applied to the optical waveguide by the refractive index variable device. A micro displacement measuring apparatus characterized by:   The micro displacement measuring apparatus according to any one of claims 1 to 11, wherein the optical waveguide is made of an electro-optic material having a voltage dependency of a refractive index, and the refractive index variable device A voltage is applied to a part to change the refractive index of the optical waveguide, and the displacement detection unit displaces the object to be measured based on a change amount of the voltage applied to the optical waveguide by the refractive index variable device. A minute displacement measuring device characterized by detecting the above.   The micro displacement measuring apparatus according to any one of claims 1 to 11, wherein the optical waveguide is made of an acousto-optic material having a stress dependence of refractive index, and the refractive index variable device includes the optical waveguide. A piezoelectric change is applied to a part to change a refractive index of the optical waveguide, and the displacement detection unit detects a displacement of the object to be measured based on a change amount of a voltage applied to the refractive index variable device. A micro displacement measuring device characterized by   2. The minute displacement measuring apparatus according to claim 1, wherein the semiconductor laser oscillation element and the photodetector are arranged on the planar lightwave circuit board. A laser light irradiation step of guiding laser light oscillated from the semiconductor laser oscillation element to an irradiation position on the object to be measured with an optical waveguide in a planar lightwave circuit board;
The reference light branched from the laser light and the irradiation light reflected from the object to be measured are guided to an interference position by an optical waveguide in the planar lightwave circuit board to generate interference light, and the intensity of the interference light An interference light detection step for detecting a change;
A detection result in the interference light detection step is monitored, and a refractive index variable control step for variably controlling the refractive index of the optical waveguide so that the light intensity of the interference light becomes a preset value;
A displacement for detecting the displacement of the object to be measured based on the amount of change in the refractive index of the optical waveguide caused by the variable refractive index control step or the amount of change in energy required for the variable control of the refractive index to obtain the amount of change. A detection step;
A minute displacement measuring method comprising: A semiconductor laser oscillation element that oscillates the laser light; and an optical waveguide through which the laser light propagates; the laser light oscillated from the semiconductor laser oscillation element is branched into irradiation light and reference light; A planar lightwave circuit board that generates interference light between the reference light and the irradiated light that has been irradiated onto the object to be measured, reflected by the object to be measured, and incident again, or the reference light or the planar lightwave circuit board. In a minute displacement measuring apparatus, comprising: a refractive index variable device that changes a refractive index of an optical waveguide that guides light; and a photodetector that detects the light intensity of the interference light, and the operation of the refractive index variable device A computer for calculating the displacement of the object to be measured by controlling
A measurement light level acquisition process for capturing an intensity value of the interference light detected by the photodetector;
A refractive index variable control process for controlling the operation of the refractive index variable device so that the intensity value of the interference light becomes a preset value;
The displacement of the object to be measured is calculated based on the amount of change in the refractive index of the optical waveguide caused by the operation of the refractive index variable or the amount of change in energy applied to the refractive index variable to obtain the amount of change. A program for measuring a minute displacement, characterized by executing a displacement calculation process.

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