WO2015012094A1

WO2015012094A1 - Optical interference sensor, and measurement system using same

Info

Publication number: WO2015012094A1
Application number: PCT/JP2014/068039
Authority: WO
Inventors: 吉田　稔; 穆之高原; 義治平山; 元史加志
Original assignee: 白山工業株式会社
Priority date: 2013-07-25
Filing date: 2014-07-07
Publication date: 2015-01-29
Also published as: JPWO2015012094A1; JP6002329B2

Abstract

[Problem] To provide a high-resolution optical interference sensor which, not having component-connecting joints, is easily processed with MEMS technology and can be formed as a single body, is capable of continuous measurement even in high-temperature environments, and can measure physical quantities with a high dynamic range and a high sampling frequency; and to provide a measurement system using said sensor. [Solution] An oscillator supported by a spring member in the vibration direction is provided inside of the sensor main body. A displacement surface is arranged on the front surface of the oscillator in the oscillation direction, and a reference surface is arranged coaxially with the displacement surface on the rear surface of the oscillator. The sensor is further provided with a first optical path system which irradiates the reference surface with light and receives light reflected from the reference surface, a second optical path system which irradiates the displacement surface with light and receives light reflected from the displacement surface, and a delay unit which is inserted between the first optical path system and the second optical path system. By multiplexing the light received in the first optical path system and the second optical path system, it becomes possible to measure the optical path difference of the reference surface and the displacement surface.

Description

Optical interference sensor and measurement system using the same

The present invention uses a light (laser light) interferometry (homodyne interference or Mach-Zehnder interference) to accurately and physically reduce the physical quantity such as the velocity and acceleration of the sensor object, and to further increase the dynamic range and height. The present invention relates to an optical interference sensor that measures at a sampling frequency and a measurement system using the same.

Conventionally, as a sensor for measuring physical quantities such as acceleration and velocity, a dynamic coil method in which a vibrator having a coil wound inside a magnetic force of a permanent magnet is freely vibrated to measure an electromagnetic induction current, or a coil is wound inside a magnetic force. There is a servo method in which control is performed so as not to generate displacement of the vibrator and measurement, or a capacitance type in which a capacitor is formed of two metal plates and acceleration is measured from a change in capacitance. In these systems, the time change of the displacement of the vibrator is converted into an electric signal such as an electromagnetic induction current or a capacitance, and then the velocity or the acceleration is obtained.

In these methods, the design of the response characteristics of the vibrator (the vibrator that continuously displaces from a small acceleration to a large acceleration in the target frequency range) and the improvement in the accuracy of digitization of the electric signal corresponding to the change Within the above limitations, sensors are made. For example, when observing earthquake motion, a vibrator capable of obtaining a large displacement in a frequency band (0.01 Hz to 100 Hz) corresponding to earthquake motion is not suitable for practical use because the size of a pendulum or a spring is large. In response to this problem, a servo-type accelerometer has been developed, and a high dynamic range is realized with a structure with a small displacement by providing a current that offsets the displacement.

However, even with this method, the dynamic range is limited when measuring electrical signals (the lower one is 1 / f noise or thermal noise of the amplifier and the higher one is the operating voltage limit of the electronic circuit), so the voltage range is about 1 μV The resolution is limited to about 140 dB at ± 5 V, and 146 to 150 dB is said to be the limit even if low noise or devising an electronic circuit. At the same time, in this method, the electrical design and the mechanical design are complicated to improve the accuracy, which makes the handling delicate and expensive, making the sensor unsuitable for practical use.

On the other hand, in order to realize a low-cost and compact acceleration sensor, a capacitive sensor using MEMS (Micro Electro Mechanical Systems) technology has been developed. It consists of a capacitor with a small gap between the two plates in order to detect small changes in displacement in response to small accelerations, and the vibration changes the distance of the gap between the capacitors and the plates This is a method of detecting a change in capacitance due to a change in area of a capacitor or the like by sliding.

Although this method realizes a compact and low-cost acceleration sensor, the dynamic range is about 100 dB from the limit of capacitance measurement.

JP, 2010-71939, A JP, 2011-202961, A Japanese Patent Application Publication No. 2008-500547 JP, 2011-185943, A Patent No. 5118004 gazette Patent No. 5118246 gazette Patent No. 4153464

In order to increase the sensitivity, the above-mentioned capacitive acceleration sensor is required to reduce the distance between the electrodes or to increase the area of the electrodes. On the other hand, in order to measure even larger vibrations, it is required that the movable region of the movable electrode be large. Therefore, development is in progress in the direction of increasing the area of the electrode. Due to such trade-off, the dynamic range of the capacitive MEMS acceleration sensor is only about 100 dB.

Further, in the conventional light interference method, relative displacement with respect to the reflecting mirror placed on the measurement object (displacement surface) is calculated with the reflecting mirror connected to the optical fiber as a fixed point. Such a conventional method has a problem that it is not possible to remove an error factor inside the optical fiber system such as a minute displacement of the optical fiber and an influence of temperature up to the fixing point as well as the displacement of the object.

On the other hand, it has been difficult to increase the sensitivity when trying to create a capacitive sensor using conventional MEMS technology. For example, in Japanese Patent Application Publication No. 2008-550547 (Patent Document 3) or Japanese Patent Application Publication No. 2011-185943 (Patent Document 4), the electrode surface of the capacitor is slid to create a highly sensitive capacitive MEMS accelerometer. By changing the area of the electrode plate to change the capacitance. Furthermore, an intermediate frame is provided to avoid vibrations other than the vibration direction while inserting a soft spring to lower the natural period. However, even if an intermediate frame is inserted, the direction in which the inter-electrode distance is changed can not be completely prevented. Therefore, it is necessary to distinguish between the capacitance change due to the displacement of the electrode plate and the capacitance change due to the inter-electrode distance change. There is a problem that you can not

Furthermore, it is strongly demanded that the sensor can continuously and accurately measure even in a high temperature environment of 300 ° C. or higher.

The present invention has been made under the circumstances as described above, and it is an object of the present invention to provide a sensor which is easy to process by MEMS technology and can be integrally molded without a joint part connecting parts, and operates with no power By this, continuous measurement is possible even in high temperature environments of 300 ° C. or higher, physical quantities can be measured with a high dynamic range and high sampling frequency, and an optical interference sensor having a high resolution of about 160 dB and a measurement system using the same It is.

The present invention relates to an optical interference type sensor, and the above object of the present invention is characterized in that the inside of the sensor main body is provided with a vibrator supported by a spring member in the vibration direction, A displacement surface provided and a reference surface provided coaxially with the displacement surface are provided on the rear surface of the vibrator, and light is irradiated to the reference surface and light reflected from the reference surface is received. A second optical path system that irradiates the light to the displacement surface and receives reflected light from the displacement surface, and the first optical path system or the second optical path system. By measuring the optical path difference between the reference surface and the displacement surface by combining the light received by the first optical path system and the second optical path system with the interposed delay unit. To be achieved.

The present invention relates to a measurement system, and the above object of the present invention is to provide each of the optical interference type sensors and a measurement light signal generation unit which generates intensity modulated and phase modulated measurement light signals as light for irradiation. And a sensor signal arithmetic processing unit that receives a time division multiplexed signal of the received light, converts it into an electrical signal and digitizes it, and outputs a phase variation signal based on the measurement light, the reference light and the interference light as a sensor signal This is achieved by providing

For example, a conventional acceleration sensor selects electronic components that operate even at high temperature for a certain period, incorporates it in a heat insulation box, etc., and measures acceleration at 200 ° C for several months while cooling with a Peltier element. There is no sensor that operates continuously for more than one year. However, the optical interference type sensor of the present invention is a homodyne interference type or Mach-Zehnder type optical interference type sensor fabricated by processing from Si single crystal or SiO ₂ single crystal by MEMS technology, and the relative displacement of both sides of the vibrator is The velocity and acceleration are calculated by obtaining at a high sampling frequency of 1 MHz or more. The optical interference sensor does not need a power supply, so there is no need to consider the influence of temperature by the electronic components, and it operates in high temperature environment with Si or SiO ₂ optical fiber, sensor body, spring, reflective surface In addition, it is possible to fabricate a sensor that operates normally even at high temperatures for a long time. Since Si single crystal has a melting point of 1400 ° C at normal pressure, and low temperature quartz structure up to about 500 ° C at normal pressure, SiO ₂ single crystal has physical properties without any layer transition at about 300 ° C. It changes continuously.

Also, conventionally, although there are accelerometers that operate with no power supply using optical interferometry, the measurement range is limited to a range up to half the laser light wavelength, and the dynamic range is limited to 100 dB. Met. However, in the optical interference type sensor and measurement system of the present invention, a laser beam having a wavelength of, for example, 1.55 μm is used as a light pulse of 1 to 10 nsec, and the light pulse is irradiated with a light pulse whose phase is shifted by 90 °. In this method, the change in relative displacement is detected by light-to-electrical conversion of the interference light and digitization. Therefore, there is no limitation of 1⁄2 of the wavelength of the laser light, and it is possible to continuously detect displacement exceeding 10,000 times (7.7 mm) of the half wavelength while maintaining the resolution of 1 pm to 10 nm. Thus, for example, in the mode of measuring the displacement up to 2 mm at a resolution of 0.1 nm at 1 MHz, a dynamic range of 144 dB can be realized.

In the conventional optical interferometry, the relative displacement with the reflecting mirror placed on the object (displacement surface) is detected by using the reflecting mirror connected to the optical fiber as a fixed point (reference plane) different from the sensor object It has become. Such a conventional method has a problem that it is not possible to remove an error factor inside the optical fiber system, such as minute displacement of the optical fiber and the influence of temperature up to the fixed point, as well as the displacement of the sensor object. On the other hand, in the optical interference type sensor of the present invention, the reference surface is provided inside the object (sensor main body), and the relative displacement of the displacement surface within the motion system of the object is directly measured. The measured value indicates only the displacement due to the vibration characteristic of the vibrator. Therefore, there is an advantage that it is not affected by measurement errors due to minute vibrations or temperature of the fiber system.

In the present invention, not a metal spring material such as phosphor bronze but a Si single crystal or SiO ₂ single crystal suitable for MEMS processing is used as the material of the vibrator or the spring. The Si single crystal and the SiO ₂ single crystal have a temperature coefficient and a Young's modulus smaller than that of a metal material, and behave as a completely elastic body with respect to a minute acceleration. On the other hand, a metal material such as phosphor bronze may not cause displacement or fly displacement when it receives a microacceleration due to the lattice defect of the crystal structure or the variation of the adhesion of grain boundaries. However, by using the Si single crystal or the SiO ₂ single crystal, the homogeneity of the material is maintained, and the linearity at the time of the minute displacement by the minute acceleration is maintained, and the minute acceleration (eg, 1 nG) is measured by measuring the minute displacement. ) To large accelerations (e.g. 10 G) can be detected. In the present invention, in order to realize micro displacement measurement (0.1 nm or less in resolution), a vibrator of Si single crystal or SiO ₂ single crystal is adopted, which is suitable as a method for detecting micro displacement.

It is a block diagram for demonstrating the principle of an optical interference type sensor (1st patent). It is a time chart which shows the operation example of an optical interference type sensor (the 1st patent). It is a figure which shows the example of a characteristic of an optical interference type sensor (1st patent). It is a block diagram for demonstrating the principle of an optical interference type | mold sensor (2nd patent). It is a time chart which shows the operation example of an optical interference type sensor (the 2nd patent). It is a figure which shows the example of a characteristic of an optical interference type sensor (2nd patent). It is a plane block diagram showing the example of wire connection and structure of a 1st embodiment of an optical interference type sensor concerning the present invention. It is a plane block diagram showing the example of wire connection and structure of a 2nd embodiment of an optical interference type sensor concerning the present invention. It is a block block diagram which shows the structural example (system 1st Embodiment) of the measurement system which used two or more optical interference type sensors (homodyne type | mold) which concern on this invention. It is a block block diagram which shows the structural example (system 2nd Embodiment) of the measurement system which used two or more optical interference type sensors (Mach-Zehnder type | mold) which concern on this invention. It is a plane block diagram showing the example of wire connection and structure of a 3rd embodiment of an optical interference type sensor concerning the present invention. It is a plane block diagram showing the example of wire connection and structure of a 4th embodiment of an optical interference type sensor concerning the present invention. It is a plane block diagram showing the example of wire connection and structure of a 5th embodiment of an optical interference type sensor concerning the present invention. It is sectional drawing which shows a part of 5th Embodiment in detail.

The optical interference sensor according to the present invention is manufactured by etching a single crystal substrate of Si or SiO ₂ (quartz) by MEMS (Micro Electro Mechanical Systems) technology, and sealing the space between the spring member and the vibrator (shield) It is processed to make it a closed space. One of the vibrators provided in the space in the sensor body is the displacement surface (light reflection surface), and the other is the reference surface (light reflection surface). The relative displacement of the displacement surface with respect to the reference surface is in the range of 1 nm to 10 mm. For example, by measuring the light interference method using a sampling frequency of 1 MHz to 100 MHz with a resolution of 1 pm to 1 nm, for example, a large dynamic range (for example, 140 dB to It is a sensor that can be obtained at 170 dB). The measurement data obtained by the optical interference type sensor can be easily used as a speed sensor or an acceleration sensor by performing arithmetic processing at a high sampling frequency.

From the displacement data of the displacement surface of the transducer measured at high sampling frequency (1 MHz to 100 MHz), the resolution of relative displacement is increased to 10 pm in the process of decimating to the sampling frequency (10 Hz to 10 kHz) determined by vibration measurement. Perform decimation filter processing to obtain acceleration. As a result, the relative displacement of the displacement surface of the vibrator with respect to the reference surface is measured with a resolution of 10 pm in a range of ± 1 mm, and a velocity sensor and an acceleration sensor with a dynamic range of 166 dB can be realized at a sampling frequency of 1 kHz.

When the optical interference type sensor of the present invention is applied to an acceleration sensor, it responds accurately to minute accelerations (about 1 nG) to large accelerations (about 10 G) and outputs corresponding displacements in the range of ± 10 pm to ± 1 mm The structure of the vibrator is used. In the conventional capacitive MEMS acceleration sensor, measurement is performed by a change in distance between electrode plates or a change in electrode plate area due to sliding of the electrode plate, but there are electrical limitations, etc. I could not take the range. However, the present invention is characterized in that there is no electrode surface, and a large displacement can be accurately measured together with a small displacement.

In the present invention, a method of measuring the physical quantity using optical interferometry, with relative displacement of the displacement surface and the reference surface and the associated physical quantities, with the both surfaces of the vibrator as displacement surfaces and reference surfaces (for example, patent No. , Patent No. 5118246 (second patent)). Specifically, a single-axis spring portion is formed inside the sensor body, and both surfaces of the vibrator supported by the spring portion are respectively used as a displacement surface and a reference surface, and a reflection mirror of laser light is provided on each surface. . The displacement amount (acceleration, velocity) of the vibrator due to the external force is obtained by deriving the optical path difference from the interference signal of each reflected light.

In the uniaxial supporting type in which the vibrator is displaced in one axial direction of the vibration direction, the light irradiated to the reference surface and the displacement surface is reflected from the reflecting surface in the same direction, and based on the interference signal of homodyne interference or Mach-Zehnder interference The optical path difference can be determined.

The vibrator and the spring member have a symmetrical shape with respect to the center (center line) of the sensor body in the vibration direction, and a closed space is formed by the spring member seamlessly connecting the vibrator and the sensor body. It has a damper effect along with the vibration of.

The present invention uses the principle of optical interferometry disclosed in Japanese Patent No. 5118004 (first patent) and Japanese Patent No. 5118246 (second patent) to the present applicant, and the outline thereof will be described first.

FIG. 1 is a schematic configuration of an optical interference type sensor (homodyne interference) disclosed in Japanese Patent No. 5118004 (first patent), and a reference light R of an optical pulse as shown in FIG. The light is incident on the optical coupler 10 and irradiated (reference light R) from the optical fiber 12, and the irradiated light is reflected from the reference reflection surface 14. Also, measurement light S of an optical pulse as shown in FIG. 2 (B) is incident from the optical fiber 11 to the optical coupler 10 and is irradiated from the optical fiber 13 with a delay time t / 2, and the irradiated light (measurement light S) is reflected from the measurement reflection surface 15. In this example, the reference reflection surface 14 is irradiated with the reference light R and the reflected light is received by the same optical fiber 12, and the measurement reflection surface 15 is irradiated with the measurement light S as well. The light reception is also performed by the same optical fiber 13, and it is called a homodyne interference type in which light emission and reception are performed by one optical fiber. The light reflected from the reference reflecting surface 14 and the measurement reflecting surface 15 is multiplexed by the optical coupler 10 and emitted from the incident optical fiber 11 as reflected light R, I, S. Since the input light pulse is short, it is considered that the light level does not change during that time.

As shown in FIG. 2C, the reflected light multiplexed by the optical coupler 10 includes the reference light R and the measurement light S, as well as the interference light I in which the reference light R and the measurement light S interfere with each other. The phase difference θ between the light R and the measurement light S, that is, the phase difference θ between the reference surface (the reference reflection surface 14) and the measurement surface (the measurement reflection surface 15), is expressed by the following equation 1. The measurement light S is irradiated in the same path, and the reflected light S also travels in the same path, so the total delay time is t / 2 + t / 2 = t.

Then, the characteristic of cos θ with respect to the phase change is as shown in FIG. 3, and the interference light I of the reflected light, the reference light R, and the measurement light S are measured to obtain cos θ. An optical interference sensor can be configured.

FIG. 4 is a schematic configuration of an optical interference type sensor (homodyne interference) shown in Japanese Patent No. 5118246 (second patent), and the phase difference 90 ° between the regions # 1 and # 2 as shown in FIG. 5 (A). While the reference light R of the light pulse having the following is input from the optical fiber 21 to the optical coupler 20 and is irradiated from the optical fiber 22 (reference light R), the irradiation light is reflected from the reference reflection surface 24 and is transmitted to the optical fiber 22. It will be incident. Also, measurement light S of an optical pulse having a phase difference of 90 ° in the regions # 1 and # 2 as shown in FIG. 5B is made incident from the optical fiber 21 to the optical coupler 20, and the optical fiber has a delay time t / 2. While being irradiated from 23, the irradiation light (measurement light S) is reflected from the measurement reflection surface 25 and enters the optical fiber 23. The time ratio of the regions # 1 and # 2 is 2 to 1 in any pulse. The light reflected from the reference reflection surface 24 and the measurement reflection surface 25 is multiplexed by the optical coupler 20 and emitted from the optical fiber 21 as the reflected light R, I1, I2, and S.

The light irradiated to the reference reflection surface 24 and the measurement reflection surface 25 is both reflected, so the reflected light is, as shown in FIG. 5C, the reference light R, the measurement light S, the reference light R and the measurement light. Since S contains two different interference lights I1 and I2 that interfere, interference outputs of a plurality of different phases are obtained.

In the first patent, when the phase difference between the reference light and the measurement light is 90 degrees, the maximum measurable phase is only ± 90 ° (half wavelength), and it is the principle that it exceeds this Although not possible, in the second patent, it is possible to measure over the wall by inputting an optical pulse whose phase is shifted by 90 ° at a constant frequency (for example, 1 MHz).

FIG. 6 shows a state of continuous measurement by cos θ1 and cos θ2 having a 90 ° phase difference. Of the two values, the measured value is always selected between 1 / √2 and -1 / √2. The fluctuation direction of the phase is determined from the difference from the phase measured immediately before. This makes it possible to measure the displacement beyond the half wavelength length.

In the present invention, the measurement principle of the first and second patents described above is applied to construct an optical interference type sensor described below and a measurement system using the same.

FIG. 7 is a plan view and a connection diagram showing a structural example (sensor first embodiment) of the homodyne interference type, single-axis support type light interference type sensor 100 according to the present invention, which is a sensor to be measured The main body 110 is integrally manufactured from the Si crystal substrate or the SiO ₂ crystal substrate by the MEMS technology, and the sensor main body 110 has four rectangular hollow portions 111 and four U-shaped straight springs 112A. , 112B, 113A, 113B are provided in the cavity 111. The vibrator 114 and the springs 112A to 113B are also manufactured by MEMS technology. The vibrator 114, the

springs

112A and 112B, and the

springs

113A and 113B are symmetrical with respect to the center line CL1 in the vibration direction (X direction in the drawing), and the vibrator 114 has negligible change in the Y direction. It stays at the center of the structure and is displaced to one axis in the X direction. A mirror surface processed flat reflective surface (displacement surface) 115 is provided at the center of the front surface of the vibrator 114, and a mirror surface processed flat reflective surface (reference surface) is provided at the center of the back surface of the transducer 114. 116 are provided. The sensor body 110 may be, for example, 10 mm in length and width, 400 μm in thickness, and the reflecting surfaces 115 and 116 may be mirrors.

Although not shown, the hollow portion 111 is sealed by a borosilicate glass plate or the like after MEMS processing to form a closed space. That is, the vibrator 114 and the springs 112A to 113B are disposed in the closed space. The inside of the closed space may be a vacuum or may be filled with a gas.

Although the measurement system 300 will be described later, the measurement system 300 is connected to an optical fiber 101A for transmitting light (laser light) to be irradiated, and an optical fiber 101C for entering reflected light from the optical circulator 101. An optical coupler 102 is connected to the optical fiber 101 through an optical fiber 101B. In the optical coupler 102, the reflecting surface 116 serving as the reference surface is irradiated with light, the optical fiber 102A for receiving the reflected light, and the reflecting surface 115 serving as the displacement surface is irradiated with light via the delay portion 103, and the reflection thereof An optical fiber 102B for receiving light is connected. Further, collimators 104A and 104B for reliably performing parallel irradiation and parallel light reception of light are provided at the respective tips of the

optical fibers

102A and 102B, but this is not essential.

In such a configuration, the measurement light signal generated by the measurement system 300 passes through the optical fiber 101A, the optical circulator 101, the optical fiber 101B, the optical coupler 102, the optical fiber 102A, the collimator 104A, and the reflection surface 116 of the reference surface. It is irradiated. The reflection surface 116 is a plane, and the reflected light reflected from the reflection surface 116 passes the collimator 104A, the optical fiber 102A, the optical coupler 102, the optical fiber 101B, the optical circulator 101, and the optical fiber 101C to the measurement system 300. It is incident. The measurement light signal demultiplexed by the optical coupler 102 passes through the optical fiber 102B provided with the delay unit 103 and the collimator 104B and is irradiated to the reflection surface 115 to be a displacement surface, and the reflection light reflected from the reflection surface 115 is reverse. Through the collimator 104B, the optical fiber 102B, the optical coupler 102, the optical fiber 101B, and the optical circulator 101, and enters the measurement system 300 from the optical fiber 101C.

In this embodiment, since the vibrator 114 is symmetrical with respect to the center line CL1 and is equally supported by the four springs 112A to 113B, the vibrator 114 vibrates in the vibration direction (X Displacement in the other direction (eg, Y direction), and negligible displacement. As a result, the reflection surface 115 of the displacement surface is also displaced only in the vibration direction (X direction), so that the optical path difference can be measured reliably and accurately. In the present embodiment, since the reference surface 116 and the displacement surface 115 are on the same line and integral with the vibrator 114, it is possible to measure the optical path difference as twice the displacement amount of the vibrator.

FIG. 8 is a plan view and a connection diagram showing a structural example (sensor second embodiment) of the Mach-Zehnder interference type, single-axis support type light interference type sensor 120 according to the present invention, which is an object to be measured As in the first embodiment, the sensor body 130 is integrally manufactured from a Si crystal substrate or a SiO ₂ crystal substrate by MEMS technology, and the sensor body 130 has a rectangular cavity 131 and is U-shaped. The vibrator 134 supported by four

springs

132A, 132B, 133A, and 133B formed in a straight line is provided in the hollow portion 131. As in the first embodiment of the sensor, the vibrator 134, the

springs

132A and 132B, and the

springs

133A and 133B have a symmetrical shape with respect to the center line CL2 in the vibration direction (X direction in the drawing). The displacement is negligible in the Y direction, and is displaced along one axis in the X direction. A reflective surface (displacement surface) 135 having a reflection characteristic in the shape of a V-shaped mirror-processed cross-section is provided at the center on the front surface of the vibrator 134, and a mirror processing is provided at the center on the back surface of the vibrator 134. A reflecting surface (reference surface) 136 having retroreflective characteristics is provided in a V-shaped cross section. Also in this example, after the MEMS processing, the hollow portion 134 is shielded and sealed by a borosilicate glass plate or the like to form a closed space. The reflecting surface (displacement surface) 135 and the reflecting surface (reference surface) 136 may be V-shaped mirrors.

The measurement system 300 is connected to an optical fiber 121 for transmitting light to be irradiated (laser light) and an optical fiber 126 for receiving reflected light. The optical fiber 121 is connected to an optical coupler 122 for dividing the irradiation light, and the optical fiber 126 is connected to an optical coupler 127 for multiplexing the reflected light. The optical coupler 122 is connected to an optical fiber 123A for irradiating light to the reflection surface 136 serving as a reference surface, and an optical fiber 123B for irradiating light via the delay unit 124 to the reflection surface 135 serving as a displacement surface. Further, the optical coupler 127 is connected to an optical fiber 128A that receives the reflected light from the reflecting surface 136 and an optical fiber 128B that receives the reflected light from the reflecting surface 13. In addition,

collimators

125A, 125B and 129A, 129B are provided at each end of the

optical fibers

123A, 123B and 128A, 128B for reliably performing parallel irradiation and parallel reception of light, but this is not essential. .

The reflecting surfaces 135 and 136 have a V-shaped (orthogonal) shape, and the light irradiated to one of the surfaces is changed in direction and reflected from the other surface in the same direction as the incident light. It has the property of recursion. In addition to the V-shaped (orthogonal) shape, it is also possible to use a prism to form a reflective surface of similar retrograde characteristics.

In such a configuration, the measurement optical signal generated by the measurement system 300 is split by the optical coupler 122 through the optical fiber 121, and one of the split optical signals is transmitted through the optical fiber 123A and the collimator 125A to the reflective surface 136 of the reference surface. The other is irradiated to the reflective surface 135 of the displacement surface through the optical fiber 123B and the collimator 125B. The reflected light from the reflecting surface 136 is incident on the optical coupler 127 through the collimator 129A and the optical fiber 128A, and the reflected light from the reflecting surface 135 is incident on the optical coupler 127 through the collimator 129B and the optical fiber 128B. The light combined by the optical coupler 127 is incident on the measurement system 300 through the optical fiber 126.

In the sensor embodiment 2 as well as the sensor embodiment 1, the vibrator 134 is symmetrical with respect to the center line CL2 and is equally supported back and forth by the four springs 132A to 133B. Thus, the vibrator 134 is displaced only in the vibration direction (X direction) and negligible in the other directions (for example, Y direction). As a result, the reflection surface 135 of the displacement surface is also displaced only in the vibration direction (X direction), so that the optical path difference can be measured reliably and accurately. In the present embodiment, the reference surface 136 and the displacement surface 136 are colinear and integral with the vibrator, and are reflected twice by the V-shaped reference surface 136 and the displacement surface 136, so the optical path difference is 4 It can measure by the amount of displacement of double.

In the homodyne interference type and the Mach-Zehnder interference type single-axis support sensor, the spring member and the vibrator both constitute a sealed closed space shielded by the ceiling plate and the bottom plate, and the left and right Due to the change in space volume, the viscosity of the filling gas brings about a damper effect. As a result, the collision between the vibrator and the sensor main body when a large acceleration is applied is avoided, and durability is provided. The vibrator and the spring member are structured to be symmetrical with respect to the vibration direction, and the effect of reducing the sensitivity of the other axes other than the vibration direction is large.

Next, a configuration example of a measurement system using the above-described optical interference type sensor will be described with reference to the drawings.

The measurement system of FIG. 9 is a homodyne interference type shown in the first embodiment of the sensor, using a plurality (three in this example) of single-axis support type optical interference type sensors 100, such as acceleration applied to each sensor The example (system 1st Embodiment) which measures a physical quantity is shown. The sensors # 1 to # 3 have the same structure, and are the same as the contents described in FIG. In FIG. 9, the sensor # 3 is omitted.

The measurement system 300 includes a measurement light signal generation unit 310 and a sensor signal calculation processing unit 320. The measurement light signal generation unit 310 intensity-modulates the continuous laser light generated by the highly stable laser light source 311. A light intensity modulation unit 312 that generates a light pulse and an optical phase modulation unit 313 that shifts the phase of the light pulse by 90 ° (π / 2) and outputs the light pulse. The measurement light signal generation unit 310 generates a measurement signal and a reference signal used as a reference for measurement. The measurement light signal (light pulse) from the light phase modulation unit 313 is incident on the optical circulator 101 through the optical fiber 101A, and is further incident on the optical coupler 160 through the optical fiber 101B. The measurement light signal generation unit 310 outputs a measurement light signal with a pulse width of 3 t at a cycle T. The 3t pulse is configured to be phase modulated such that the front 2t width and the rear 1t width are 90 ° out of phase (orthogonal phase). The optical signal for measurement is demultiplexed by the optical coupler 160, and one is irradiated to the reflecting portion of the sensor # 1 through the optical coupler CP1 of the sensor # 1 as described above, and the other is the optical fiber 161A having the delaying portion 161B. The light passes through the light coupler 162. One of the lights demultiplexed by the optical coupler 162 passes through the optical coupler CP2 of the sensor # 2 and is irradiated to the reflecting portion of the sensor # 2, and the other light passes through the optical fiber 163A including the delaying portion 163B and the sensor # 3. The light is incident on the optical coupler CP3 of the sensor # 3 and is irradiated to the reflection part of the sensor # 3.

The light irradiated to the reflecting surface of each reference surface of sensors # 1 to # 3 and the reflecting mirror of each displacement surface is received by the same optical fiber, and the light received by sensor # 3 is combined by optical coupler CP3 The combined light is input to the optical coupler 162 through the optical fiber 163A. The light received by the sensor # 2 is multiplexed by the optical coupler CP2, the multiplexed light is multiplexed by the optical coupler 162, and the multiplexed light is incident on the optical coupler 160 through the optical fiber 161A. The light received by the sensor # 1 is multiplexed by the optical coupler CP1, the multiplexed light is multiplexed by the optical coupler 160, and the multiplexed light is incident on the optical circulator 101 through the optical fiber 101B. Further, the light is incident on the sensor signal processing unit 320 in the measurement system 300 through the optical fiber 101C. The optical signals of the sensors # 1, # 2, and # 3 incident on the sensor signal processing unit 320 are time division multiplexed optical signals, and in the signals of the respective sensors, there is no optical signal (Z), reference The light portion (R), the interference light portions (I1, I2), and the measurement light portion (S) are included.

When a plurality of sensors are observed, the timing of the incident pulse and the delay amount by the

delay units

162B and 163B shown in FIG. 9 are combined, and when incident, interference light by sensor # 1, interference light by sensor # 2, sensor The interference light due to # 3 is received (analyzed at different reception timings) independently by the sensor signal processing unit 320 and analyzed.

The sensor signal processing unit 320 inputs light signals (R, I1, I2, S) for the sensors # 1 to # 3, converts them into electric signals by the light-electric conversion unit (O / E) 321, and converts the electric signals into analog signals. A / D converter 322 digitizes the signal. The digitized signal is limited in the necessary frequency band respectively by the R filter 323A, the I1 filter 323B, the I2 filter 323C, and the S filter 323D, and is input to the cos operation unit 324. After zero correction of the reference light R, the interference lights I1 and I2, and the measurement light S with a portion having no signal as a zero point, cos θ1 and cos θ2 are calculated according to the following equations (2) and (3).

However, since the interference light I1 and the interference light I2 are in quadrature, cos θ1 and cos θ2 are in a phase relationship of 90 ° apart.

The cos θ1 and cos θ2 calculated by the cos calculation unit 324 are input to the difference calculation unit 325, the θ1, θ2, Δθ1 and Δθ2 are calculated, and the calculated difference Δθ is input to the integration calculation unit 326 with a period T. The difference calculation unit 325 executes the following processes (1) to (7) using cos θ1 and cos θ2.
(1) With respect to cos θ1 and cos θ2, one having an absolute value close to 0 is identified.
(2) The magnitudes of cos θ1 and cos θ2 are compared and identified.
(3) Two cos θ positions are determined on the cosine curve from two large and small conditions on the basis that the cos θ 1 and cos θ 2 are 90 ° apart in the reference light phase and the absolute value is close to 0 side.
(4) From the cos θ1 and cos θ2 positions defined on the cosine curve, the angles θ1 and θ2 are determined.
(5) Let θ1a and θ2a be the angles obtained from cos θ1 and cos θ2 one cycle before.
(6) The difference Δθ of the phase change with one cycle before is obtained as Δθ1 = θ1−θ1a, Δθ2 = θ2−θ2a.
(7) From the differences Δθ1 and Δθ2, the difference with cos θ1 and cos θ2 on the side closer to the absolute value of 0 is selected as Δθ and output.

The difference Δθ calculated by the difference calculation unit 325 is input to the integration calculation unit 326, the difference calculation unit 326 integrates the difference Δθ, and the integrated value is output as the displacement sensor signal θs.

Although three light interference sensors 100 (# 1 to # 3) are provided in this example, one may be used or four or more sensors may be similarly applied. In addition, although A / D conversion is performed on the electrical signal that has been subjected to optical-to-electrical conversion, and then digital filtering is performed. However, the electrical signal is subjected to analog filtering processing and then A / D conversion to be digitized. Also good.

Next, an example of measuring a physical quantity such as acceleration applied to each sensor using a plurality of (three in this example) optical interference type sensors 120 of the Mach-Zehnder interference type described in FIG. The second embodiment will be described with reference to FIG. The sensors # 1 to # 3 have the same structure, and are the same as the contents described in FIG. Further, the measurement system 300 is also the same as the system first embodiment of FIG. 9, so the description is omitted, and the sensor # 3 is omitted in FIG.

The measurement optical signal from the measurement optical signal generation unit 310 in the measurement system 300 is incident on the optical coupler 170 through the optical fiber 101A, and one of the lights demultiplexed by the optical coupler 170 passes through the optical fiber 170A and the sensor The light is input to the # 1 optical coupler CP11, and the other is input to the optical coupler 172 through the optical fiber 170B including the delay unit 170C. One of the lights demultiplexed by the optical coupler 172 is incident on the optical coupler CP21 of the sensor # 2 through the optical fiber 172A, and the other is incident on the optical coupler CP31 of the sensor # 3 through the optical fiber 172B including the delay unit 172C. Be done.

The two reflected lights from the sensor # 3 are multiplexed by the optical coupler CP32, and the multiplexed light is incident on the optical coupler 178 through the optical fiber 178B. Further, the two reflected lights from the sensor # 2 are multiplexed by the optical coupler CP22, and the multiplexed light is incident on the optical coupler 178 through the optical fiber 178A. The light multiplexed by the optical coupler 178 is incident on the optical coupler 176 through the optical fiber 176B, the two reflected lights from the sensor # 1 are multiplexed by the optical coupler CP12, and the multiplexed light is transmitted to the optical fiber 176A. The light passes through the light coupler 176. The light coupled by the optical coupler 176 is incident on the sensor signal processing unit 320 in the measurement system 300 through the optical fiber 101C. The optical signals of the sensors # 1, # 2, and # 3 incident on the sensor signal processing unit 320 are time division multiplexed optical signals, and there are no optical signal (Z) in each sensor signal, the reference light portion (R), interference light portions (I1, I2), measurement light portion (S) are included.

In the present embodiment, although three photosensors 120 (# 1 to # 3) are described, one photosensor may be used, or four or more sensors may be similarly applied. In this Mach-Zehnder interference, by causing the reflected light to be incident on the optical fiber for reflected light different from the optical fiber for irradiation, the interference between the reflected light and the irradiation light does not occur, and the result of continuously irradiating the irradiation light pulse Interference light generated can be transmitted continuously. This enables connection of a large number of sensors by one optical fiber as compared to homodyne interference.

Hereinafter, although the other embodiment of the optical interference type | mold sensor which concerns on this invention is described, the said measurement system is applicable similarly about these sensors.

In each of the embodiments of the optical interference type sensor described above, the reference plane is disposed on the same axial line (center line) of the back surface of the transducer, but as shown in the third embodiment (homodyne interference) of FIG. Alternatively, the mirror surface-treated reflecting surface (reference surface) 116 may be provided in a fixed portion close to the center line CL1 of the sensor main body 110 together with the hollow portion. Light is irradiated from the optical fiber 102A to the reflection surface (reference surface) 116 through the collimator 104A, and light reflected from the reflection surface (reference surface) 116 is incident to the optical fiber 102A through the collimator 104A.

Further, in the fourth embodiment (Mach-Zehnder interference) of FIG. 12, a V-shaped reflection surface (reference surface) 136 mirror-processed is provided on the fixed portion near the center line CL2 of the sensor body 130 together with the cavity portion. It has a structure. Light is irradiated from the optical fiber 1129A to the reflection surface (reference surface) 136 through the collimator 125A, and the reflected light V-reflected by the reflection surface (reference surface) 136 is incident to the optical fiber 128A through the collimator 129A. As described above, even if the reference surface fixed to the sensor main body is provided, the displacement of the sensor can be measured by the change of the optical path length.

The sensor 160 according to the fifth embodiment shown in FIG. 13 corresponds to the second embodiment shown in FIG. 8 and is provided on the side of the sensor main body 130 and has a plurality of V-shaped mirror surfaces 161 provided with a plurality of V-shaped mirror surfaces; A jagged mirror 162 provided with a plurality of V-shaped mirrors is provided as a reference surface and a displacement surface so that the unevenness is opposite to the jagged mirror 161 and is oppositely provided. For example, the facing relationship of the jagged mirror surfaces 161 and 162 on the displacement surface is as shown in FIG. 14, and the light LG1 emitted from the collimator 125B is reflected one after another by each V-shaped mirror and finally the vibrator The light LG19 reflected by the side mirror surface is incident on the collimator 129B. By thus reflecting light n times (an integer of 2 or more) by the jagged mirror surfaces 161 and 162 a plurality of times, the optical path difference can be made n times.

Next, the dynamic range will be described.

The measurement repetition period is 1 MHz (1 μsec), and the wavelength of light for measurement is 1.55 μm. Assuming that the half amplitude of the measurement target is 1.55 mm, which is 1000 times of 1.55 μm, it can be obtained 4000 times at 2000 wavelengths and 1/2 wavelength in a round trip. Therefore, 72 dB can be obtained at 4000 times 1 μsec. 60 dB can be obtained by A / D sampling the half wavelength with 10 bits. The white noise irrelevant to the displacement signal included in the obtained measurement data can be reduced by narrowing the signal extraction band from 0.01 Hz to 50 Hz. Decimating the sampling frequency from 1 MHz to 125 Hz, √ (1/8000) = 1/89 is 39 dB. From the above, the dynamic range may be about 72 + 60 + 39 = 171 dB.

The main features of the present invention will be listed and described below.

Because it uses optical measurement and MEMS technology, it does not use electronic components, is environmentally friendly, and is suitable for high temperature environments with no power supply. Because it uses light measurement and MEMS technology, it is small, about 10 mm square. In addition, it is a vibrator that responds to minute acceleration because a micro-oscillator of Si single crystal or SiO ₂ single crystal (lattice defect minimum, spring of 20 μm thickness and 5 mm length by micro processing) is fabricated by MEMS technology. .

Since only the relative displacement of the reference surface and the tip of the transducer is extracted by providing a retroreflecting surface on the displacement surface of the reference surface of the transducer and the displacement surface of the tip of the transducer, it is possible to Light measurement that captures deformation is possible.

Conventionally, sensors that measure physical quantities such as acceleration and velocity include a dynamic coil type, a servo type, and a capacitance type, but these all convert physical quantities into electrical signals and measure them, so the upper limit and lower limit Both have limits. With regard to the lower limit of measurement, in the present method, displacement is not converted into an electrical signal, but is handled only by light measurement. Therefore, a minute signal can be measured regardless of the limit inherent to the electrical signal. In this method, since the measurement upper limit only depends on the magnitude of displacement of the vibrator, a dynamic range of 140 dB can be realized if there is a vibrator having a displacement of ± 1 mm.

In addition, the acceleration sensor in the conventional light measurement is limited to displacement measurement within a half wavelength, and the dynamic range up to 100 dB is the limit. According to this method, the produced vibrator has a displacement of up to ± 1 mm, and the vibration can be captured as a relative displacement between the reference surface of the sensor body and the displacement surface of the front surface of the vibrator. The acceleration measurement of 140 dB can be realized by using a sensor device capable of measuring the relative displacement of ± 1 mm by using the measurement method based on the optical interference method shown in Patents 5118004 and 5118246. In addition, by controlling the measurement light pulse by time division, interference light of time division multiplexing can be captured and processed, so that the configuration of a multipoint measurement system in which a plurality of sensors are connected to an optical fiber becomes possible.

Since the optical interference type sensor according to the present invention does not use an electronic circuit in the sensor unit, all parts except the measurement system unit operate with no power. Accordingly, the present invention can be used for a non-power 4D observation network for resource exploration in a submarine environment where stable operation is required for a long time under a high temperature environment where electronic circuits do not operate, and a submarine earthquake observation network.

In addition, it can be applied to a sensorless network without a power source for constructing a seafloor seismic observation network, a microminiature sensor as a microdevice for minimally invasive medical treatment, and a microminiature multipoint connection sensor for incorporating an articulated robot.

10, 20

Optical couplers

14, 24 Reflecting surface (reference surface)
15, 25 reflective surface (measurement surface)
100 Optical interference sensor (homodyne type)
DESCRIPTION OF SYMBOLS 101

Optical circulator

102, 122, 127 Optical coupler 116, 136 Reflection surface (reference surface)
115, 135 Reflective surface (displacement surface)
120 Optical interference sensor (Mach-Zehnder type)
200 Optical interference sensor (Mach-Zehnder type)
211, 221 optical coupler 231 reflective surface (reference surface)
233 Reflective surface (displacement surface)
300 Measurement System 310 Measurement Optical Signal Generator 311 Laser Light Source 312 Light Intensity Modulator 313 Optical Phase Modulator 320 Sensor Signal Arithmetic Processor 321 Optical-Electric Converter (O / E)
324 cos operation unit 325 difference operation unit 326 integration operation unit

Claims

Inside the sensor main body, a vibrator supported by a spring member in the vibration direction is provided, and a displacement surface disposed on the front surface of the vibrator in the vibration direction and a rear surface of the vibrator are provided. And a reference surface disposed coaxially with the displacement surface,
A first optical path system that irradiates light to the reference surface and receives reflected light from the reference surface, and irradiates the light to the displacement surface and second that receives the reflected light from the displacement surface And a delay unit interposed in the first optical path system or the second optical path system,
Optical interference characterized in that the optical path difference between the reference surface and the displacement surface can be measured by combining the light received by the first optical path system and the second optical path system. Expression sensor.
The optical interference sensor according to claim 1, wherein the spring member supports the vibrator back and forth with respect to the vibration direction and on both sides with respect to the center.
The light interference type sensor according to claim 1 or 2, wherein a collimator is provided in an irradiation unit and a light receiving unit of the first optical path system and the second optical path system.
Inside the sensor body, a vibrator supported by a spring member in the vibration direction is provided, and a V-shaped displacement surface of the vibrator disposed in the front direction in the vibration direction, and a rear surface of the vibrator And a V-shaped reference surface disposed coaxially with the displacement surface,
A first optical path system for emitting light to one of the reference surfaces;
A second optical path system that receives the reflected light from the other of the reference planes that has been changed in direction from one of the reference planes;
A third optical path system for irradiating the light to one of the displacement surfaces;
A fourth optical path system that receives reflected light from one of the displacement surfaces that has been directionally converted from one of the displacement surfaces;
And a delay unit interposed in any one of the first to fourth optical path systems,
Optical interference characterized in that the optical path difference between the reference surface and the displacement surface can be measured by combining the light received by the second optical path system and the fourth optical path system. Expression sensor.
The V-shaped reference surface and the V-shaped displacement surface are in a jagged shape having a plurality of V-shaped shapes, and have a plurality of V-shaped shapes so as to face the reference surfaces and the displacement surfaces. Two jagged reflective surfaces are provided,
The light irradiated to one of the reference surfaces is reflected a plurality of times by the reference surface and the opposite reflecting surface and is incident on the second optical path, and the light irradiated to one of the displacement surfaces is the displacement surface 5. The optical interference sensor according to claim 4, wherein the light is reflected a plurality of times by the opposing displacement surface and is incident on the fourth light path.
Inside the sensor main body, a vibrator supported by a spring member in the vibration direction is provided, and a displacement surface disposed on the front surface of the vibrator in the vibration direction and a rear surface of the vibrator are provided. And a reference surface disposed coaxially with the displacement surface,
A first optical path system that irradiates light to the reference surface and receives reflected light from the reference surface, and irradiates the light to the displacement surface and second that receives the reflected light from the displacement surface And a delay unit interposed in the first optical path system or the second optical path system,
An optical interference sensor that combines the light received by the first optical path system and the second optical path system;
A measurement light signal generation unit that generates a measurement light signal that is intensity-modulated and phase-modulated and that is the light for irradiation;
A sensor signal arithmetic processing unit that receives a time division multiplexed signal of the received light, converts it into an electrical-to-electrical conversion and digitizes it, and outputs a phase variation signal based on measurement light, reference light and interference light as a sensor signal;
The measurement system characterized by comprising.
7. The measurement according to claim 6, wherein a plurality of the interference sensors are provided, and the plurality of the interference sensors are connected to the measurement light signal generation unit and the sensor signal processing unit via an optical circulator and an optical coupler. system.
Inside the sensor body, a vibrator supported by a spring member in the vibration direction is provided, and a V-shaped displacement surface of the vibrator disposed in the front direction in the vibration direction, and a rear surface of the vibrator And a V-shaped reference surface disposed coaxially with the displacement surface,
A first optical path system for emitting light to one of the reference surfaces;
A second optical path system that receives the reflected light from the other of the reference planes that has been changed in direction from one of the reference planes;
A third optical path system for irradiating the light to one of the displacement surfaces;
A fourth optical path system that receives reflected light from one of the displacement surfaces that has been directionally converted from one of the displacement surfaces;
And a delay unit interposed in any one of the first to fourth optical path systems,
An interferometric sensor that combines the light received by the second optical path system and the fourth optical path system;
A measurement light signal generation unit that generates a measurement light signal that is intensity-modulated and phase-modulated and that is the light for irradiation;
A sensor signal arithmetic processing unit that receives a time division multiplexed signal of the received light, converts it into an electrical-to-electrical conversion and digitizes it, and outputs a phase variation signal based on measurement light, reference light and interference light as a sensor signal;
The measurement system characterized by comprising.
The measurement system according to claim 8, wherein a plurality of the interference sensors are provided, and the plurality of interference sensors are connected to the measurement light signal generation unit and the sensor signal arithmetic processing unit via an optical coupler.