JP6002329B2 - Optical interference sensor and measurement system using the same - Google Patents

Description

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

  Conventional sensors for measuring physical quantities such as acceleration and speed include a moving coil method in which an electromagnetic induction current is measured by freely vibrating a vibrator wound with a coil within the magnetic force of a permanent magnet, or a coil wound within a magnetic force. There are a servo system that controls and measures so as not to cause displacement of the vibrator, or a capacitance type that measures acceleration from a change in capacitance by forming a capacitor with two metal plates. In these methods, a change in the displacement of the vibrator over time is converted into an electric signal such as an electromagnetic induction current or a capacitance, and then the speed and acceleration are obtained.

  In these methods, the design of the response characteristics of the vibrator (vibrator that continuously displaces from a small acceleration to a large acceleration in the target frequency range) and the improvement of the accuracy of digitization of the electrical signal corresponding to the change Within the above limitations, sensors are made. For example, when observing seismic motion, a vibrator that can take a large displacement in a frequency band (0.01 Hz to 100 Hz) corresponding to the seismic motion is not suitable for practical use because the size of the pendulum and the spring is large. In response to this problem, servo accelerometers have been developed, and a high dynamic range is realized with a structure with little displacement by applying a current that cancels the displacement.

  However, even with this method, the dynamic range is limited when measuring an electrical signal (lower is the 1 / f noise and thermal noise of the amplifier, and the higher is the limit of the operating voltage of the electronic circuit), so the voltage range is about 1 μV to The limit is about ± 5 V and the resolution is about 140 dB, and even if low noise or an electronic circuit is devised, it is said that the limit is 146 to 150 dB. At the same time, this method complicates both the electrical design and the mechanical design to improve accuracy, making the sensor delicate and costly and unsuitable for practical use.

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

  Although this method can realize a small and low-cost acceleration sensor, the dynamic range is about 100 dB due to the limit of capacitance measurement.

JP 2010-71939 A JP 2011-202961 A Special table 2008-500547 gazette JP 2011-185943 A Japanese Patent No. 5111804 Japanese Patent No. 5118246 Japanese Patent No. 4153464

  In order to increase the sensitivity of the above-described capacitance type acceleration sensor, it is required to decrease the distance between the electrodes or increase the area of the electrodes. On the other hand, if a measurement that can be measured even with a larger vibration is attempted, the movable region of the movable electrode is required to be large. For this reason, development is proceeding in the direction of increasing the electrode area. Due to such a trade-off, the dynamic range of the capacitive MEMS acceleration sensor is only about 100 dB.

  In the conventional optical interference method, a relative displacement with respect to a reflecting mirror installed on a measurement object (displacement surface) is calculated with a reflecting mirror connected to an optical fiber as a fixed point. In such a conventional method, there is a problem in that error factors inside the optical fiber system such as not only the displacement of the object but also the minute displacement of the optical fiber and the influence of the temperature to the fixed point cannot be removed.

  On the other hand, it has been difficult to increase the sensitivity when creating a capacitive sensor using conventional MEMS technology. For example, in Japanese translations of PCT publication No. 2008-500547 (Patent Document 3) or JP 2011-185943 (Patent Document 4), the electrode surface of a capacitor is slid to create a high-sensitivity capacitive MEMS accelerometer. By doing so, the capacitance is changed by changing the area of the electrode plate. 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 of changing the distance between the electrodes cannot be completely prevented. Therefore, it is necessary to distinguish between changes in capacitance due to electrode plate displacement and changes in capacitance due to changes in the distance between electrodes. There is a problem that can not be.

  Furthermore, there is a strong demand for sensors to be able to measure continuously and accurately even in high temperature environments of 300 ° C. or higher.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a sensor that does not have a joint portion for connecting parts, can be easily formed by MEMS technology, can be integrally formed, and operates without a power source. Provides an optical interference sensor capable of continuous measurement even in a high temperature environment of 300 ° C or higher, capable of measuring physical quantities with a high dynamic range and high sampling frequency, and having a high resolution of about 160 dB and a measurement system using the same. There is.

  The present invention relates to an optical interference sensor, and the object of the present invention is to provide a vibrator supported by a spring member in the vibration direction inside the sensor body, and to the front surface of the vibrator toward the vibration direction. A displacement surface disposed on the rear surface of the vibrator; a reference surface disposed coaxially with the displacement surface; and irradiating the reference surface with light and receiving reflected light from the reference surface. A first optical path system that irradiates the displacement surface with the light, a second optical path system that 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 plane and the displacement plane by combining the light received by the first optical path system and the second optical path system. Achieved.

  The present invention relates to a measurement system, and the object of the present invention is to provide an optical signal generator for measurement that generates each optical interference sensor and an intensity-modulated and phase-modulated measurement optical signal as the irradiation light. And a sensor signal arithmetic processing unit that receives the time-division multiplexed signal of the received light, digitizes it by photoelectric conversion, and outputs a phase variation signal based on measurement light, reference light, and interference light as a sensor signal; It is achieved by comprising.

For example, a conventional acceleration sensor selects electronic components that operate for a certain period of time even at high temperatures and incorporates them in a heat insulation box, etc., and measures acceleration at 200 ° C for several months while cooling with a Peltier device. 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 processed by MEMS technology from a Si single crystal or SiO ₂ single crystal, and the relative displacement of both sides of the vibrator is measured. The speed and acceleration are calculated by obtaining at a high sampling frequency of 1 MHz or higher. The optical interference sensor does not require a power supply, so there is no need to consider the temperature effect of electronic components. Optical fiber, sensor body, spring, reflecting surface (reflecting mirror) with Si or SiO ₂ operating in high temperature environment Therefore, a sensor that operates normally for a long time even at high temperatures can be manufactured. Si single crystals have a melting point of 1400 ° C at normal pressure, and SiO ₂ single crystals have a low-temperature quartz structure up to about 500 ° C at normal pressure. It changes continuously.

  Conventionally, there are accelerometers that use optical interferometry and operate without a power supply, but the measurement range is limited to the region up to half the laser beam wavelength, and the dynamic range is limited to 100 dB. Met. However, in the optical interference sensor and measurement system of the present invention, for example, a laser beam with a wavelength of 1.55 μm is converted into an optical pulse of 1 to 10 nsec, and the reflection surface is irradiated with a light pulse whose phase is shifted by 90 °. The method employs a method of detecting a change in relative displacement by photoelectrically converting the interference light with the light and further digitizing it. Therefore, there is no restriction of 1/2 of the wavelength of the laser beam, and displacement exceeding 10,000 times half wavelength (7.7 mm) can be continuously detected while maintaining a resolution of 1 pm to 10 nm. Thereby, for example, in a mode in which a displacement of up to 2 mm is measured at 1 MHz with a resolution of 0.1 nm, a dynamic range of 144 dB can be realized.

  In the conventional optical interferometry, the reflection mirror connected to the optical fiber is used as a fixed point (reference surface) different from the sensor object, and the relative displacement with the reflection mirror installed on the object (displacement surface) is detected. It has become. In such a conventional method, there is a problem in that error factors inside the optical fiber system such as not only the displacement of the sensor object but also the minute displacement of the optical fiber and the influence of the temperature up to the fixed point cannot be removed. On the other hand, in the optical interference sensor of the present invention, a reference surface is provided inside the object (sensor body), and the relative displacement of the displacement surface inside the motion system of the object is directly measured. The measured value indicates only the displacement due to the vibration characteristics 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, a Si single crystal or SiO ₂ single crystal suitable for MEMS processing is used as the material of the vibrator and the spring, not a metal spring material such as phosphor bronze. Si single crystal and SiO ₂ single crystal have a smaller temperature coefficient and Young's modulus than metal materials, and behave as a complete elastic body against minute acceleration. On the other hand, metallic materials such as phosphor bronze may not cause displacement or may cause jump displacement when subjected to minute acceleration due to lattice defects in the crystal structure and variations in the fixing force of grain boundaries. However, by using Si single crystal or SiO ₂ single crystal, the homogeneity of the material is maintained, and the linearity at the time of minute displacement by minute acceleration is retained, and minute acceleration (for example, 1 nG) is measured by measuring minute displacement. ) To a large acceleration (for example, 10G) can be detected. In the present invention, in order to realize a minute displacement measurement (with a resolution of 0.1 nm or less), a Si single crystal or SiO ₂ single crystal vibrator is employed, which is suitable as a method for detecting a minute 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 (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 sensor (2nd patent). It is a time chart which shows the operation example of an optical interference type sensor (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 which shows the connection and the structural example of 1st Embodiment of the optical interference type sensor which concerns on this invention. It is a plane block diagram which shows the connection and the structural example of 2nd Embodiment of the optical interference type sensor which concerns on this invention. 1 is a block configuration diagram showing a configuration example (system first embodiment) of a measurement system using a plurality of optical interference sensors (homodyne type) according to the present invention. It is a block block diagram which shows the structural example (system 2nd Embodiment) of the measurement system using two or more optical interference type sensors (Mach-Zehnder type) which concern on this invention. It is a plane block diagram which shows the connection and the structural example of 3rd Embodiment of the optical interference type sensor which concerns on this invention. It is a plane block diagram which shows the connection and the structural example of 4th Embodiment of the optical interference type sensor which concerns on this invention. It is a plane block diagram which shows the connection and the structural example of 5th Embodiment of the optical interference type sensor which concerns on this invention. It is sectional drawing which shows a part of 5th Embodiment in detail.

The optical interference sensor according to the present invention is produced by etching a single crystal substrate of Si or SiO ₂ (quartz) using MEMS (Micro Electro Mechanical Systems) technology, and sealing the space between the spring member and the vibrator (shield). Processed into a closed space. One of the vibrators provided in the space inside the sensor body is the displacement surface (light reflection surface) and the other is the reference surface (light reflection surface). For example, by measuring with optical interferometry using a sampling frequency of 1 MHz to 100 MHz with a resolution of 1 pm to 1 nm, the physical quantity that the displacement surface of the vibrator receives due to external force can be accurately and at high speed, with a large dynamic range (e.g., 140 dB to It is a sensor that can be obtained at 170 dB). By processing the measurement data obtained by the optical interference sensor at a high sampling frequency, it can be easily used as a speed sensor or an acceleration sensor.

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

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

  In the present invention, both sides of the vibrator are used as a displacement surface and a reference surface, and the relative displacement between the displacement surface and the reference surface and the accompanying physical quantity are measured using a physical quantity measurement method (for example, Japanese Patent No. 5118004 (first patent) ), Patent No. 5118246 (second patent)). Specifically, a uniaxial spring portion is formed inside the sensor body, and both surfaces of the vibrator supported by the spring portion are used as a displacement surface and a reference surface, respectively, and a laser beam reflecting mirror is provided on each surface. . The amount of displacement (acceleration, speed) of the vibrator due to external force is obtained by deriving the optical path difference from the interference signal of each reflected light.

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

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

  The present invention uses the principle of the optical interferometry disclosed in Japanese Patent No. 5118004 (first patent) and Japanese Patent No. 5118246 (second patent) according to the present applicant.

  FIG. 1 is a schematic configuration of an optical interference sensor (homodyne interference) disclosed in Japanese Patent No. 5118004 (first patent). Reference light R of an optical pulse as shown in FIG. Is incident on the optical coupler 10 and irradiated from the optical fiber 12 (reference light R), and the irradiated light is reflected from the reference reflecting surface 14. Further, the measurement light S of an optical pulse as shown in FIG. 2B enters the optical coupler 10 from the optical fiber 11 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 reflecting surface 15. In this example, irradiation of the reference light R and reception of the reflected light are performed on the standard reflection surface 14 by the same optical fiber 12, and the measurement light S is irradiated on the measurement reflection surface 15 by the reflected light. Light reception is also performed by the same optical fiber 13, which is referred to as a homodyne interference type in which light is projected and received by a single optical fiber. The light reflected from the reference reflection surface 14 and the measurement reflection surface 15 is combined by the optical coupler 10 and emitted from the incident optical fiber 11 as reflected light R, I, and 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 combined by the optical coupler 10 includes the reference light R and the measurement light S, and the interference light I with which the reference light R and the measurement light S interfere. The phase difference θ between the light R and the measurement light S, that is, the phase difference θ between the reference surface (reference reflection surface 14) and the measurement surface (measurement reflection surface 15) is expressed by the following equation (1). The measurement light S is irradiated through the same path, and the reflected light S also passes through the same path, so that the total delay time is t / 2 + t / 2 = t.

そして、位相変化に対するcosθの特性は図３に示すようになり、反射光の干渉光Ｉ，参照光Ｒ，計測光Ｓを計測してcosθを求めることにより、光信号レベル変動の影響を受けない光干渉型センサを構成することができる。

The characteristics of cosθ with respect to the phase change are as shown in FIG. An optical interference sensor can be configured.

  FIG. 4 is a schematic configuration of an optical interference sensor (homodyne interference) shown in Japanese Patent No. 5118246 (second patent), and a phase difference of 90 ° in regions # 1 and # 2 as shown in FIG. The reference light R of the optical pulse having the above is incident on the optical coupler 20 from the optical fiber 21 and irradiated (reference light R) from the optical fiber 22, and the irradiated light is reflected from the reference reflecting surface 24 and is applied to the optical fiber 22. Incident. Further, the 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 incident on the optical coupler 20 from the optical fiber 21, and has an optical fiber having a delay time t / 2. In addition, the irradiation light (measurement light S) is reflected from the measurement reflection surface 25 and enters the optical fiber 23. The time ratio between the regions # 1 and # 2 is 2 to 1 for both pulses. The light reflected from the reference reflection surface 24 and the measurement reflection surface 25 is combined by the optical coupler 20 and emitted from the incident optical fiber 21 as reflected light R, I1, I2, and S.

  Since both the light applied to the standard reflecting surface 24 and the measuring reflecting surface 25 are reflected, the reflected light is the reference light R and measuring light together with the reference light R and measuring light S as shown in FIG. Two different interference lights I1 and I2 with which S interferes are included, and a plurality of interference outputs having different phases are obtained.

  According to the first patent, when the phase relationship between the reference beam and the measuring beam is 90 degrees, the maximum measurable phase is only ± 90 ° (half wavelength), and it is the principle that it exceeds this. However, in the second patent, by inputting an optical pulse whose phase is shifted by 90 ° at a constant frequency (for example, 1 MHz), it is possible to measure over the wall.

  FIG. 6 shows a state of continuous measurement using cos θ1 and cos θ2 having a phase difference of 90 °. The measurement value is always selected between 1 / √2 and -1 / √2 among the two values. The phase fluctuation direction 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 above-described measurement principles of the first and second patents are applied to construct an optical interference sensor described below and a measurement system using the same.

FIGS. 7A and 7B are a plan configuration diagram and a connection diagram showing a structural example (sensor first embodiment) of a homodyne interference type single-axis support type optical interference sensor 100 according to the present invention, and a sensor that is a measurement object The main body 110 is integrally manufactured from a Si crystal substrate or a SiO ₂ crystal substrate by MEMS technology, and the sensor main body 110 has a square cavity 111 and four springs 112A formed by U-shaped straight lines. , 112B, 113A, 113B are provided in the cavity 111. The vibrator 114 and the springs 112A to 113B are also produced by MEMS technology. The vibrator 114, the springs 112A and 112B, and the springs 113A and 113B have a symmetrical shape with respect to the center line CL1 in the vibration direction (X direction in the drawing), and the vibrator 114 has a negligible change in the Y direction. However, it has a structure that is displaced to one axis in the X direction. A mirror-processed flat reflecting surface (displacement surface) 115 is provided at the center of the front surface of the vibrator 114, and a mirror-treated flat reflecting surface (reference surface) is provided at the center of the rear surface of the vibrator 114. 116 is provided. The sensor main body 110 may be, for example, 10 mm in length and width and 400 μm in thickness, and the reflecting surfaces 115 and 116 may be mirrors.

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

  Although the measurement system 300 will be described later, the measurement system 300 is connected to an optical fiber 101A that transmits light to be irradiated (laser light) and an optical fiber 101C that receives reflected light from the optical circulator 101. An optical coupler 102 is connected to 101 via an optical fiber 101B. The optical coupler 102 is irradiated with light through a delay portion 103 to an optical fiber 102A that receives the reflected light 116, which receives the reflected light, and the reflecting surface 115 that serves as a displacement surface, and reflects the reflected light. An optical fiber 102B that receives light is connected. Further, collimators 104A and 104B for reliably performing parallel light irradiation and parallel light reception are provided at the tips of the optical fibers 102A and 102B, but this is not essential.

  In such a configuration, the measurement optical signal generated in 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, and the collimator 104A, and is reflected on the reflection surface 116 of the reference surface. Irradiated. The reflection surface 116 is a flat surface, and the reflected light reflected from the reflection surface 116 passes through the collimator 104A, the optical fiber 102A, the optical coupler 102, the optical fiber 101B, and the optical circulator 101, and then passes from the optical fiber 101C to the measurement system 300. Incident. The measurement optical signal demultiplexed by the optical coupler 102 is applied to the reflecting surface 115 serving as a displacement surface via the optical fiber 102B provided with the delay unit 103 and the collimator 104B, and the reflected light reflected from the reflecting surface 115 is reversed. Then, the light enters the measurement system 300 from the optical fiber 101C via the collimator 104B, the optical fiber 102B, the optical coupler 102, the optical fiber 101B, and the optical circulator 101.

  In the present embodiment, the vibrator 114 is symmetrical with respect to the center line CL1 and is equally supported by the four springs 112A to 113B in the front-rear direction. (Direction) and is negligible in other directions (for example, Y direction). As a result, the reflecting 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 this embodiment, since the reference surface 116 and the displacement surface 115 are on the same line and integrated with the vibrator 114, the optical path difference can be measured as twice the displacement amount of the vibrator.

FIG. 8 is a plan configuration diagram and a connection diagram showing a structural example (sensor second embodiment) of a Mach-Zehnder interference type uniaxial support type optical interference sensor 120 according to the present invention, which is a measurement object. Similar to the first embodiment of the sensor, the sensor main body 130 is integrally manufactured from the Si crystal substrate or the SiO ₂ crystal substrate by MEMS technology, and the sensor main body 130 has a rectangular cavity 131 and is U-shaped. An oscillator 134 supported by four springs 132A, 132B, 133A, 133B formed by straight lines is provided in the cavity 131. Similar to the sensor first embodiment, 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 (the X direction in the drawing). The displacement is negligible in the Y direction, and is displaced to one axis in the X direction. A reflection surface (displacement surface) 135 having a V-shaped cross-section that has been mirror-finished and having recursive characteristics is provided at the center of the front surface of the vibrator 134. A reflecting surface (reference surface) 136 having a V-shaped cross section and having recursive characteristics is provided. In this example as well, the cavity 134 is sealed and sealed with a borosilicate glass plate or the like after MEMS processing, thereby forming a closed space. The reflection surface (displacement surface) 135 and the reflection surface (reference surface) 136 may be V-shaped mirrors.

  Connected to the measurement system 300 are an optical fiber 121 that transmits light to be irradiated (laser light) and an optical fiber 126 that receives reflected light. An optical coupler 122 that demultiplexes irradiation light is connected to the optical fiber 121, and an optical coupler 127 that combines reflected light is connected to the optical fiber 126. Connected to the optical coupler 122 are an optical fiber 123A for irradiating light to a reflecting surface 136 serving as a reference surface, and an optical fiber 123B for irradiating light to a reflecting surface 135 serving as a displacement surface via a delay unit 124. The optical coupler 127 is connected to an optical fiber 128 </ b> A that receives reflected light from the reflecting surface 136 and an optical fiber 128 </ b> B that receives reflected light from the reflecting surface 13. Further, collimators 125A, 125B and 129A, 129B are provided at the tips of the optical fibers 123A, 123B and 128A, 128B to ensure parallel irradiation and light reception of light, but this is not essential. .

  The reflecting surfaces 135 and 136 are V-shaped (orthogonal), and the light irradiated to one surface is changed in direction and reflected from the other surface in the same direction as incident. Has recursive properties. In addition to the V-shaped (orthogonal) shape, it is also possible to form a reflective surface having similar recursive characteristics using a prism.

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

  Similarly to the sensor embodiment 1, the sensor embodiment 2 is symmetrical with respect to the center line CL2 and is equally supported by the four springs 132A to 133B. Thus, the vibrator 134 is displaced only in the vibration direction (X direction) and is negligible in other directions (for example, the Y direction). As a result, the reflecting 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 this embodiment, the reference surface 136 and the displacement surface 136 are on the same line and integrated with the vibrator, and are reflected twice by the V-shaped reference surface 136 and the displacement surface 136, so that the optical path difference is 4 It can be measured with double displacement.

  In the homodyne interference type and Mach-Zehnder interference type single-axis support sensors, both the spring member and the vibrator constitute a sealed closed space where the ceiling plate and the bottom plate are shielded, By changing the spatial volume, a damper effect is brought about by the viscosity of the filling gas. This avoids a collision between the vibrator and the sensor body when a large acceleration is applied, and provides durability. The vibrator and the spring member have a structure having a symmetric shape with respect to the vibration direction, and the effect of lowering the sensitivity of other axes other than the vibration direction is great.

  Next, a configuration example of a measurement system using the above-described optical interference 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, and uses a plurality of (three in this example) uniaxial support type optical interference 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 with reference to FIG. In FIG. 9, sensor # 3 is omitted.

  The measurement system 300 includes a measurement optical signal generation unit 310 and a sensor signal calculation processing unit 320. The measurement optical signal generation unit 310 intensity-modulates continuous laser light generated by a highly stable laser light source 311. The optical intensity modulation unit 312 that generates the optical pulse and the optical phase modulation unit 313 that outputs the optical pulse with the phase shifted by 90 ° (π / 2). The measurement optical signal generator 310 generates a measurement signal and a reference signal used as a measurement reference. An optical signal for measurement (optical pulse) from the optical phase modulator 313 is incident on the optical circulator 101 via the optical fiber 101A, and further incident on the optical coupler 160 via the optical fiber 101B. The measurement optical signal generator 310 outputs a measurement optical signal with a period T and a pulse width 3t. The 3t pulse has a configuration in which the front 2t width and the rear 1t width are phase-modulated so that the phases are different by 90 ° (orthogonal phase). The optical signal for measurement is demultiplexed by the optical coupler 160, one of which passes through the optical coupler CP1 of the sensor # 1 and irradiates the reflection part of the sensor # 1 as described above, and the other passes through the optical fiber 161A including the delay unit 161B. Then, the light enters the optical coupler 162. One of the lights demultiplexed by the optical coupler 162 is irradiated to the reflection part of the sensor # 2 via the optical coupler CP2 of the sensor # 2, and the other light is sent to the sensor # 3 via the optical fiber 163A including the delay part 163B. Is incident on the optical coupler CP3 and is applied to the reflecting portion of the sensor # 3.

  The light irradiated to the reflecting surfaces of the reference surfaces and the reflecting mirrors of the displacement surfaces of the sensors # 1 to # 3 is received by the same optical fiber, and the light received by the sensor # 3 is multiplexed by the optical coupler CP3. The combined light is incident on the optical coupler 162 through the optical fiber 163A. The light received by the sensor # 2 is combined by the optical coupler CP2, and the combined light is combined by the optical coupler 162, and the combined light enters the optical coupler 160 via the optical fiber 161A. The light received by the sensor # 1 is combined by the optical coupler CP1, the combined light is combined by the optical coupler 160, and the combined light is incident on the optical circulator 101 through the optical fiber 101B. Further, the light enters the sensor signal calculation 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 arithmetic processing unit 320 are time-division multiplexed optical signals, and each sensor signal includes a portion (Z) where there is no optical signal, reference The optical part (R), the interference light part (I1, I2), and the measurement light part (S) are included.

  When observing a plurality of sensors, the timing of incident pulses and the delay amounts of the delay units 162B and 163B shown in FIG. 9 are combined, and when incident, the interference light by sensor # 1, the interference light by sensor # 2, and the sensor Interference light from # 3 is received and analyzed by the sensor signal calculation processing unit 320 independently (shifting the reception timing).

  The sensor signal calculation processing unit 320 inputs optical signals (R, I1, I2, S) for the sensors # 1 to # 3, converts them into electric signals by an optical-electric conversion unit (O / E) 321 and outputs the analog electric signals. The signal is digitized by the A / D converter 322. The digitized signal is subjected to frequency band restrictions required by the R filter 323A, the I1 filter 323B, the I2 filter 323C, and the S filter 323D, and is input to the cos arithmetic unit 324. After correcting the zero point of the reference light R, the interference lights I1 and I2, and the measurement light S with the portion where there is no signal as the zero point, cos θ1 and cos θ2 are calculated according to the following equations 2 and 3.

ただし、干渉光Ｉ１と干渉光Ｉ２は直交位相にあることから、ｃｏｓθ１とｃｏｓθ２は90°離れた位相関係にある。

ｃｏｓ演算部３２４で演算されたｃｏｓθ１及びｃｏｓθ２が、差分演算部３２５に入力され、θ１、θ２、Δθ１、Δθ２が演算され、演算された差分Δθが周期Ｔで積算演算部３２６に入力される。差分演算部３２５では、ｃｏｓθ１とｃｏｓθ２を用いて次の（１）〜（７）の処理を実行する。
（１）ｃｏｓθ１、ｃｏｓθ２について、絶対値が０に近い方を識別する。
（２）ｃｏｓθ１、ｃｏｓθ２について、その大小を比較して識別する。
（３）ｃｏｓθ１、ｃｏｓθ２が参照光位相で90°離れていること、絶対値が０に近い側を基準として、２つの大小の条件から、余弦曲線上に２つのｃｏｓθ位置を定める。
（４）余弦曲線上の定められたｃｏｓθ１、ｃｏｓθ２位置より、その角度θ１、θ２を求める。
（５）１周期前のｃｏｓθ１、ｃｏｓθ２より得られた角度をθ１ａ、θ２ａとする。
（６）１周期前との位相変化の差分ΔθをΔθ１＝θ１−θ１ａ、Δθ２＝θ２−θ２ａとして求める。
（７）差分Δθ１、Δθ２より、ｃｏｓθ１、ｃｏｓθ２で、絶対値が０に近い側の差分をΔθとして選択し、出力する。

差分演算部３２５で演算された差分Δθは積算演算部３２６に入力され、積算演算部３２６で差分Δθが積算され、積算値が変位センサ信号θｓとして出力される。

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

The cos θ1 and cos θ2 calculated by the cos calculation unit 324 are input to the difference calculation unit 325, θ1, θ2, Δθ1, and Δθ2 are calculated, and the calculated difference Δθ is input to the integration calculation unit 326 at a period T. The difference calculation unit 325 executes the following processes (1) to (7) using cos θ1 and cos θ2.
(1) For cos θ1 and cos θ2, the one whose absolute value is closer to 0 is identified.
(2) The cos θ1 and cos θ2 are identified by comparing their magnitudes.
(3) Two cos θ positions are determined on the cosine curve based on two large and small conditions on the basis that cos θ1 and cos θ2 are 90 ° apart from each other in the reference light phase and the absolute value is close to zero.
(4) The angles θ1 and θ2 are obtained from the determined cos θ1 and cos θ2 positions on the cosine curve.
(5) The angles obtained from cos θ1 and cos θ2 one cycle before are θ1a and θ2a.
(6) The difference Δθ in phase change from the previous cycle is obtained as Δθ1 = θ1-θ1a and Δθ2 = θ2-θ2a.
(7) From the differences Δθ1 and Δθ2, the difference on the side of the cos θ1 and cos θ2 whose absolute value is close to 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 Δθ is integrated by the integration calculation unit 326, and the integration value is output as the displacement sensor signal θs.

  In this example, the three optical interference sensors 100 (# 1 to # 3) are installed, but one may be used, or the same applies to four or more sensors. In addition, A / D conversion is applied to the electrical signal that has been converted from light to electricity, and then digital filtering is performed. However, the electrical signal is subjected to analog filtering and then A / D converted to digitization. Also good.

  Next, an example of measuring a physical quantity such as acceleration applied to each sensor by using a plurality of Mach-Zehnder interference type optical interference sensors 120 (three in this example) of the Mach-Zehnder interference type described in FIG. A 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. Also, the measurement system 300 is the same as that of the first embodiment of the system shown in FIG. 9, and the description thereof is omitted. In FIG. 10, the sensor # 3 is omitted.

  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 is transmitted through the optical fiber 170A. The light enters the # 1 optical coupler CP11 and the other light enters the optical coupler 172 via the optical fiber 170B including the delay unit 170C. One of the lights demultiplexed by the optical coupler 172 enters the optical coupler CP21 of the sensor # 2 via the optical fiber 172A, and the other enters the optical coupler CP31 of the sensor # 3 via the optical fiber 172B including the delay unit 172C. Is done.

  The two reflected lights from the sensor # 3 are combined by the optical coupler CP32, and the combined light enters the optical coupler 178 via the optical fiber 178B. The two reflected lights from the sensor # 2 are combined by the optical coupler CP22, and the combined light is incident on the optical coupler 178 via the optical fiber 178A. The light combined by the optical coupler 178 enters the optical coupler 176 via the optical fiber 176B, the two reflected lights from the sensor # 1 are combined by the optical coupler CP12, and the combined light passes through the optical fiber 176A. Then, the light enters the optical coupler 176. The light combined by the optical coupler 176 enters the sensor signal calculation 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 calculation processing unit 320 are time-division multiplexed optical signals, and each sensor signal has no optical signal (Z) and a reference optical part. (R), interference light part (I1, I2), and measurement light part (S) are included.

  In this example, three optical sensors 120 (# 1 to # 3) are described. However, one may be used, or the same applies to four or more sensors. In this Mach-Zehnder interference, the reflected light is incident on an optical fiber for reflected light different from the optical fiber for irradiation, so that interference between the reflected light and the irradiated light does not occur, and the irradiation light pulse is continuously irradiated. The generated interference light can be continuously transmitted. Thereby, compared to homodyne interference, a large number of sensors can be connected by one optical fiber.

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

  In each of the embodiments of the optical interference sensor described above, the reference plane is arranged on the same axis (center line) of the rear surface of the transducer, but as shown in the third embodiment (homodyne interference) of FIG. A structure in which a mirror-finished reflection surface (reference surface) 116 is provided together with a hollow portion in a fixed portion of the sensor body 110 close to the center line CL1. The reflection surface (reference surface) 116 is irradiated with light from the optical fiber 102A through the collimator 104A, and the reflected light from the reflection surface (reference surface) 116 enters the optical fiber 102A through the collimator 104A.

  Further, in the fourth embodiment (Mach-Zehnder interference) of FIG. 12, a mirror-shaped V-shaped reflecting surface (reference surface) 136 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. The reflection surface (reference surface) 136 is irradiated with light from the optical fiber 1129A through the collimator 125A, and the reflected light reflected by the reflection surface (reference surface) 136 is incident on the optical fiber 128A through the collimator 129A. As described above, even when the reference surface fixed to the sensor body is provided, the displacement of the sensor can be measured by the change in the optical path length as described above.

  A sensor 160 of the fifth embodiment shown in FIG. 13 corresponds to the second embodiment shown in FIG. 8, is provided on the sensor body 130 side, and has a jagged mirror surface 161 having a plurality of V-shaped mirror surfaces. A jagged mirror surface 162 provided with a plurality of V-shaped mirror surfaces is provided as a reference surface and a displacement surface, respectively, so that the uneven surface is oppositely opposed to the jagged mirror surface 161. For example, the opposing relationship between 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 on each V-shaped mirror surface, and finally the vibrator The light LG19 reflected by the side mirror surface enters the collimator 129B. Thus, the light path difference can be made n times by reflecting the light n times (integer of 2 or more) times by the jagged mirror surfaces 161 and 162 a plurality of times.

Next, the dynamic range will be described.

  The measurement repetition cycle is 1 MHz (1 μsec), and the wavelength of light for measurement is 1.55 μm. If the amplitude of the measurement target is 1.55 mm, which is 1000 times 1.55 μm, 2000 round trips and 4000 rounds at 1/2 wavelength can be obtained. Therefore, 72 dB is obtained at 4000 times 1 μsec. 60 dB can be obtained by A / D sampling the half wavelength at 10 bits. White noise unrelated to the displacement signal contained in the obtained measurement data can be reduced by narrowing the signal extraction band from 0.01 Hz to 50 Hz. When the sampling frequency is decimated 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 optical measurement and MEMS technology, it is as small as 10mm square. In addition, it is a vibrator that responds to minute acceleration because it uses a MEMS technology to produce a micro-vibrator of Si single crystal or SiO ₂ single crystal (minimum lattice defects, micro-processed spring with a thickness of 20μm and a length of 5mm). .

  A retroreflecting surface is provided on the reference surface of the transducer and the displacement surface at the tip of the transducer, and only the relative displacement between the reference surface and the transducer tip is extracted by interfering the reflected light from each. Optical measurement that captures deformation is possible.

  Conventionally, sensors that measure physical quantities such as acceleration and speed include moving coil type, servo type, and electrostatic capacity type, but these all convert physical quantities into electrical signals for measurement. Both have limitations. With respect to the lower limit of measurement, in this method, the displacement is not corrected to an electric signal, but is handled only by optical measurement, so that a minute signal can be measured regardless of the limit specific to the electric signal. In this method, the upper limit of measurement only depends on the magnitude of the displacement of the transducer, so a dynamic range of 140 dB can be realized if there is a transducer with a displacement of ± 1 mm.

  In addition, the conventional acceleration sensor for optical measurement is limited to displacement measurement within 1/2 wavelength, and the dynamic range up to 100 dB is the limit. According to this method, the manufactured vibrator has a displacement of up to ± 1 mm, and the vibration can be regarded as a relative displacement between the reference plane of the sensor body and the displacement plane of the front face of the vibrator. Using the measurement method based on the optical interferometry shown in Japanese Patent No. 5118004 and Japanese Patent No. 5118246, an acceleration measurement of 140 dB can be realized by using the sensor device capable of measuring the relative displacement of ± 1 mm. In addition, by controlling the measurement light pulse in a time division manner, signal processing can be performed by capturing time division multiplexed interference light, so that a multi-point measurement system in which a plurality of sensors are connected to an optical fiber can be configured.

  Since the optical interference sensor according to the present invention does not use an electronic circuit for the sensor part, all parts except the measurement system part operate with no power supply. Accordingly, the present invention can be used for a non-power source 4D observation network for resource exploration and a submarine seismic observation network under a high temperature environment where an electronic circuit does not operate and under a sea bottom environment where long-term stable operation is required.

  It can also be applied to non-powered sensor networks for constructing submarine seismic observation networks, ultra-small sensors as minimally invasive medical microdevices, and ultra-small multi-point connection sensors built in multi-joint robots.

10, 20 Optical coupler 14, 24 Reflecting surface (reference surface)
15, 25 Reflective surface (measurement surface)
100 Optical interference sensor (homodyne type)
101 Optical circulators 102, 122, 127 Optical couplers 116, 136 Reflecting surface (reference surface)
115, 135 Reflecting surface (displacement surface)
120 Optical interference sensor (Mach-Zehnder type)
200 Optical interference sensor (Mach-Zehnder type)
211, 221 Optical coupler 231 Reflecting surface (reference surface)
233 Reflecting surface (displacement surface)
300 Measurement System 310 Optical Signal Generation Unit for Measurement 311 Laser Light Source 312 Optical Intensity Modulation Unit 313 Optical Phase Modulation Unit 320 Sensor Signal Calculation Processing Unit 321 Optical-Electric Conversion Unit (O / E)
324 cos calculation unit 325 difference calculation unit 326 integration calculation unit

Claims (4)

A sensor body is provided with a vibrator supported by a spring member with respect to the vibration direction, a V-shaped displacement surface disposed in front of the vibrator 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 irradiating one of the reference planes with light;
A second optical path system for receiving reflected light from the other of the reference planes whose direction has been changed;
A third optical path system for irradiating one of the displacement surfaces with the light;
A fourth optical path system for receiving reflected light from the other of the displacement surfaces, the direction of which is changed from the other;
A delay unit interposed in any of the first to fourth optical path systems,
The optical interference characterized in that the optical path difference between the reference plane and the displacement plane can be measured by multiplexing the light received by the second optical path system and the fourth optical path system. Type sensor. The V-shaped reference surface and the V-shaped displacement surface are jagged shapes 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 arranged,
The light irradiated to one of the reference surfaces is reflected a plurality of times by the reference surface and the opposing reflecting surface, is incident on the second optical path, and the light irradiated to one of the displacement surfaces is the displacement surface. The optical interference sensor according to claim 4, wherein the optical interference sensor is reflected a plurality of times by the opposing displacement surfaces and is incident on the fourth optical path. A sensor body is provided with a vibrator supported by a spring member with respect to the vibration direction, a V-shaped displacement surface disposed in front of the vibrator 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 irradiating one of the reference planes with light;
A second optical path system for receiving reflected light from the other of the reference planes whose direction has been changed;
A third optical path system for irradiating one of the displacement surfaces with the light;
A fourth optical path system for receiving reflected light from the other of the displacement surfaces, the direction of which is changed from the other;
A delay unit interposed in any of the first to fourth optical path systems,
An interference sensor for combining lights received by the second optical path system and the fourth optical path system;
An optical signal generator for measurement that generates intensity-modulated and phase-modulated optical signals for measurement and is used as the irradiation light; and
Receiving a time-division multiplexed signal of the received light, digitizing by photoelectric conversion, and outputting a phase variation signal based on measurement light, reference light and interference light as a sensor signal; and
A measurement system 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 optical signal generation unit and the sensor signal calculation processing unit via an optical coupler.

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