JP2007205939A - Displacement sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a displacement sensor having high sensitivity by making assembling easy. <P>SOLUTION: The displacement sensor is provided with: an optical fiber 3 for emitting introduced detection light from a first end face 3b; a first condensing element 4 for irradiating the first end face with reflection light by irradiating an object face 5 with light emitted from the first end face; detection signal output means 6-8 for outputting a signal indicating displacement of the object face on the basis of the reflection light incident on the optical fiber from the first end face; an emitting part 1 for emitting the detection light; and a second condensing element 2 for introducing the detection light by irradiating a second end face 3a of the optical fiber with light from the emitting part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a displacement in which the displacement of the target surface is detected through an optical signal by guiding detection light to the target surface using an optical fiber and observing the reflected light through the optical fiber. The present invention relates to a detection device. This displacement detection apparatus is suitable for converting mechanical vibration of an object, particularly vibration of a diaphragm caused by sound pressure into an electric signal.

  Conventionally, as a displacement detection device that includes an optical fiber that guides the radiated light from the light emitting unit to the target and guides the reflected light from the target to the light receiving unit, converts the mechanical vibration of the target into an optical signal, and detects it. There is known one in which at least a pair of optical fibers are arranged at a predetermined angle with respect to an object (see, for example, Patent Document 1). Further, there is known a configuration in which an outer periphery of a light projecting optical fiber group having a plurality of optical fibers is covered with a light receiving optical fiber group and disposed so as to face an object (for example, Patent Document 2). reference).

  According to these displacement detection devices, the object can be set at an arbitrary location away from the light emitting unit and the light receiving unit. In addition, since there is no part that operates electrically from the light emitting unit side end surface of the optical fiber to the light receiving unit side end surface through the object, the part that operates electrically is in an electromagnetic environment or an explosion-proof environment. It is possible to accurately detect the displacement of the target object even in a place where it may be affected by the surrounding environment or may affect the surrounding environment.

JP-A-8-297011 Japanese Patent Laid-Open No. 2005-203954

  However, according to the displacement detection device in which the optical fiber is arranged at a predetermined angle with respect to the object, the light emitted from the light projecting optical fiber is projected so that it can be received well by the light receiving optical fiber. It is necessary to accurately arrange the optical fiber for light and the optical fiber for light reception with respect to the object. For this reason, there is a problem that the assembly of the apparatus is very complicated.

  In addition, according to the displacement detection device in which the outer periphery of the light projecting optical fiber group is covered with the light receiving optical fiber group, although it is easy to assemble, only a change in the reflected light amount equal to or less than the amount of displacement of the object is obtained. I can't. For this reason, there exists a problem that desired sensitivity cannot be obtained.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a displacement detection device that is easy to assemble and has high sensitivity.

  In order to achieve the above object, a displacement detection device according to a first aspect of the present invention irradiates a target surface with an optical fiber that emits introduced detection light from the first end face, and light emitted from the first end face. And a detection signal output means for outputting a signal indicating the displacement of the target surface based on the reflected light incident on the optical fiber from the first end surface; It is characterized by comprising.

  Here, as a displacement detection apparatus, what is used for an optical microphone, for example corresponds. Since “displacement” is a change in position, the displacement detection device detects the position of the target surface by detecting the displacement of the target surface with respect to the reference position, or continuously detects the displacement of the target surface. The present invention can be applied to detecting vibration of the target surface. For example, a convex lens corresponds to the condensing element.

  In this configuration, when the introduced detection light is emitted from the first end face of the optical fiber, the emitted light is irradiated onto the target surface by the first light collecting element, and the reflected light is reflected from the first light collecting element. To irradiate the first end face. At this time, if the first end surface, the first condensing element, and the target surface are at the in-focus position, the amount of reflected light incident on the first end surface is minimal because the reflected light beam at the first end surface is minimal. Is the maximum. As the target surface moves away from the in-focus position in one direction or the other direction, the luminous flux of the reflected light at the first end surface increases, and the amount of reflected light incident on the first end surface decreases. That is, the amount of reflected light incident from the first end surface can be used as a parameter indicating the displacement or position of the target surface. Therefore, the detection signal output means can output a signal indicating the displacement of the target surface as a signal indicating a change in the amount of light based on the reflected light incident on the optical fiber from the first end surface.

  The displacement detection device according to a second aspect of the present invention is characterized in that, in the first aspect, the target surface is a surface of a diaphragm that is displaced according to sound pressure.

  According to a third aspect of the present invention, in the first or second aspect, the optical fiber is a single mode fiber or a graded index fiber.

  According to a fourth aspect of the invention, in the first to third aspects of the invention, the displacement detection device irradiates the second end face of the optical fiber with the light emitting unit that emits the detection light and the light from the light emitting unit. And a second light collecting element for introducing detection light.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the light emitting unit is a semiconductor laser.

  According to a sixth aspect of the present invention, in the fifth aspect, the semiconductor laser is driven at an oscillation start current or less.

  According to a seventh aspect of the present invention, in the displacement detection device according to any one of the fourth to sixth aspects, the second condensing element has an NA (numerical aperture) on the light emitting unit side that is equal to or greater than an emission angle of the light emitting unit The side NA is equal to or less than the NA of the second end face of the optical fiber.

  According to an eighth aspect of the present invention, in the displacement detection device according to any one of the fourth to seventh aspects, the detection signal output means is provided between the second end face and the second light collecting element and is emitted from the second end face. It has a branching element for branching the reflected light, a third light collecting element for collecting the branched reflected light, and a photoelectric conversion means for converting the collected reflected light into an electric signal. As the photoelectric conversion means, for example, an optical sensor can be used.

  According to a ninth aspect of the present invention, in the displacement detection device according to any one of the first to seventh aspects, the optical fiber is branched, so that a part of the reflected light incident from the first end face is branched. The detection signal output means condenses light emitted from the third end face by a fourth light collecting element and a fourth light collecting element. And photoelectric conversion means for converting the emitted light into an electrical signal.

  In any one of the first to ninth inventions, the displacement detection device according to the tenth aspect of the present invention is such that if the NA on the optical fiber side in the first condensing element is k and the NA on the target surface side is m, m ≧ k.

  According to the present invention, the optical fiber is commonly used for light projection for guiding the detection light to the target surface and for light reception for guiding the reflected light from the target surface to the detection signal output means. An easy displacement detection device can be provided. In addition, as a first condensing element that condenses the light emitted from the optical fiber on the target surface and makes the reflected light from the target surface enter the optical fiber, the NA on the optical fiber side is k, and the NA on the target surface side is By using m that satisfies m ≧ k when m, the displacement amount of the target surface can be acquired with a sensitivity of m / k times, and displacement detection with high sensitivity can be performed.

  FIG. 1 is a block diagram showing a configuration of a displacement detection apparatus according to the first embodiment of the present invention. In the figure, 1 is a light emitting unit that emits light for detection, 2 is a condensing element that condenses light from the light emitting unit 1, and 3 is provided with a light emitting unit side end surface 3a and an object side end surface 3b. An optical fiber 4 that emits light from the condensing element 2 incident on 3a from the object-side end surface 3b, and 4 irradiates the surface of the object 5 with light emitted from the object-side end surface 3b, and reflects the reflected light. A condensing element for irradiating the object-side end surface 3b, 6 is provided between the light emitting unit side end surface 3a and the condensing element 2, and a branching element for branching the reflected light emitted from the light emitting unit side end surface 3a, 7 is branched. A condensing element for condensing the reflected light, and a light receiving unit 8 for converting the collected reflected light into an electric signal.

  That is, the diverging light emitted from the light emitting unit 1 is incident on the light emitting unit side end surface 3 a of the optical fiber 3 through the light collecting element 2. The light incident on the optical fiber 3 is radiated from the object-side end face 3b, and then collected and reflected on the object 5 via the condensing element 4. The reflected light again enters the object-side end surface 3 b of the optical fiber 3 through the condensing element 4. The reflected light incident on the optical fiber 3 is radiated from the light emitting unit side end face 3 a, then the path is changed by the branch element 6, and is condensed on the light receiving element 8 by the light collecting element 7. That is, the optical fiber 3 is commonly used as the forward path and the return path for the detection light.

  The object 5 is capable of reflecting light emitted from the object-side end face 3b of the optical fiber 3 and making it incident on the object-side end face 3b of the optical fiber 3 again. If it is such a thing, it may be a liquid level, for example. Specifically, a diaphragm that is displaced according to sound pressure can be used as the object 5. In this case, the displacement of the diaphragm due to the sound pressure can be accurately detected even at an arbitrary location away from the light emitting unit 1 and the light receiving unit 8. In addition, since there is no part that operates electrically between the light emitting part side end surface 3a of the optical fiber 3 and the diaphragm, the part that operates electrically is affected by the surrounding environment such as an electromagnetic environment or an explosion-proof environment. The displacement of the diaphragm can be accurately detected even in a place where it may be affected or the surrounding environment may be affected.

  As the optical fiber 3, a single mode fiber, a multimode fiber, a plastic fiber, or the like can be used. However, some multimode fibers and plastic fibers have a large loss of light transmitted through the optical fiber, making long-distance transmission difficult. When used in an electromagnetic environment, an explosion-proof environment, or the like, it is also conceivable to detect the displacement of the object 5 installed at a location several hundred meters or more away. Therefore, it is desirable to use a single mode fiber or a graded index fiber as the optical fiber 3. Alternatively, a holey fiber having a hole structure and low transmission loss and strong bending can be used.

  As the light emitting unit 1, an LED or a semiconductor laser can be used. However, since the LED is an optical surface light source, it is difficult to efficiently make the emitted light incident on the optical fiber 3 according to the LED, even though the LED is interposed through the light condensing element 2. In this case, if a multimode fiber or a plastic fiber having a large fiber diameter is used as the optical fiber 3, the efficiency can be improved to some extent. However, according to these optical fibers, since the loss during transmission in the optical fiber is large as described above, transmission over a long distance becomes impossible. It is also possible to increase the incident efficiency somewhat by using an LED having an aperture of several tens to several hundreds of micrometers. However, since the light emitting part of the semiconductor laser is about several micrometers and is considered as an optical point light source, it is desirable to use a semiconductor laser as the light emitting part 1.

  As the condensing element 2, one having an NA (numerical aperture) on the light emitting unit 1 side that is equal to or larger than the radiation angle of the light emitting unit 1 and an NA on the optical fiber 3 side that is less than or equal to the NA on the light emitting unit side end surface 3 a Is preferred. This is because the emitted light from the light emitting unit 1 can be taken in without loss and incident on the light emitting unit side end surface 3a of the optical fiber 3 without loss. Specifically, the NA on the light emitting unit 1 side is preferably 0.2 or more, and more preferably 0.3 or more. The NA on the optical fiber 3 side is preferably 0.3 or less, more preferably 0.2 or less.

  If the NA on the optical fiber 3 side of the condensing element 4 is k and the NA on the object 5 side is m, the optical magnification on the object-side end surface 3b of the optical fiber 3 is m / k. A displacement of 5 can be obtained with a sensitivity of m / k times. Therefore, in order to detect the displacement amount of the object 5 with high sensitivity, it is desirable to use a condensing element 4 having NA on the optical fiber 3 side and the object 5 side such that m ≧ k. .

  The operation of the displacement detection device will be described. The diverging light radiated from the light emitting unit 1 has a light emitting unit 1 side NA greater than or equal to the emission angle of the light emitting unit 1 and an optical fiber 3 side NA less than or equal to the NA of the light emitting unit side end face 3a of the optical fiber 3. 2 refracts in the direction of convergence. A part of the refracted light is branched by the branch element 6, but the other part is transmitted through the branch element 6 and is incident on the light emitting portion side end face 3 a of the optical fiber 3.

  When the optical fiber 3 is a single mode fiber or a graded index fiber, the light incident on the optical fiber 3 is transmitted to at least several hundred meters or more with a minimum loss of light. Radiated from the side end face 3b. The diverging light radiated from the object-side end face 3b is reflected by the condensing element 4 having an NA that satisfies m ≧ k when the NA on the optical fiber 3 side is k and the NA on the object 5 side is m. It is condensed on the object 5.

  The light condensed on the object 5 is reflected by the object 5, is condensed again by the light condensing element 4, and enters the object-side end surface 3b of the optical fiber 3. The reflected light incident on the object-side end surface 3b is transmitted through the same path as the forward path, and is radiated from the light-emitting part-side end surface 3a of the optical fiber 3. A part of the reflected light radiated from the light emitting unit side end face 3 a passes through the branch element 6. The other part is branched by the branch element 6 and condensed on the light receiving element 8 by the light collecting element 7.

  In this state, when the object 5 is displaced in a direction parallel to the optical axis of the light collecting element 4 by mechanical vibration, the diameter of the light beam on the object 5 and the object on the object side end surface 3b of the optical fiber 3 The diameter of the luminous flux of the reflected light from the object 5 changes, and the amount of light incident on the object-side end surface 3b changes. Incident light whose amount of light has changed is transmitted by the optical fiber 3 and detected by the light receiving element 8. Thereby, the amount of displacement of the object 5 can be detected as a change in the intensity of the optical signal incident on the light receiving element 8.

  At this time, if the NA on the optical fiber 3 side of the condensing element 4 is k and the NA on the object 5 side is m, the optical magnification on the object-side end surface 3b of the optical fiber 3 on the object 5 is m / k. Therefore, the change amount of the light beam diameter on the object side end surface 3b with respect to the change amount of the light beam diameter on the object 5 is acquired with a sensitivity of m / k times, and the displacement amount of the object 5 is detected with high sensitivity. be able to.

  In addition, when using a semiconductor laser as the light emission part 1, it has been confirmed that there exists a phenomenon in which composite resonance occurs due to return light returning to the semiconductor laser and distortion occurs in the output signal. This phenomenon does not pose a problem when the amount of return light returning to the semiconductor laser is sufficiently small, but has been remarkably confirmed when the semiconductor laser is used at an oscillation start current or higher. Therefore, by driving the semiconductor laser below the oscillation start current, it is possible to reduce the amount of return light that is fed back to the semiconductor laser and to avoid the occurrence of distortion of the output signal that occurs due to complex resonance. The same effect can also be obtained by reducing the amount of return light returning to the semiconductor laser by an optical isolator.

  Moreover, when the surface of the object side end surface 3b, the condensing element 4, and the object 5 is in a focus position, the light quantity of the reflected light which injects into the object side end surface 3b becomes the maximum, and the object 5 has the position It decreases as it moves away from both sides in the optical axis direction. The amount of decrease is the same if the distances on both sides are the same. However, since the change in the amount of light is not linear in the vicinity of the in-focus position, the reference position of the object 5 is set to be shifted from the in-focus position to either side, and the amount of light with respect to the change in the position of the object 5 is set. It is adjusted so that the displacement of the object 5 can be detected in a range in which the change substantially shows a monotone increase or a monotone decrease.

  According to the present embodiment, the optical fiber 3 is commonly used for light projection for guiding detection light to the object 5 and for light reception for guiding reflected light from the object 5 to the light receiving unit 8. It is possible to provide a displacement detection device that can be easily assembled. In addition, as the condensing element 4 that condenses the light emitted from the optical fiber 3 on the object 5 and makes the reflected light from the object 5 enter the optical fiber 3, the NA on the optical fiber 3 side is k, and the object By using the one that satisfies m ≧ k when the NA on the 5th side is m, the displacement amount of the object 5 can be acquired with a sensitivity of m / k times, and highly sensitive displacement detection can be performed.

  FIG. 2 is a block diagram showing a configuration of a displacement detection apparatus according to the second embodiment of the present invention. In the figure, elements denoted by the same reference numerals as those in FIG. 1 are the same elements as in FIG. Reference numeral 9 in FIG. 2 denotes an optical fiber having a branch point on the optical path. That is, the optical fiber 9 includes a light emitting unit side end surface 9a, an object side end surface 9b, and a light receiving unit side end surface 9c, and emits light from the light collecting element 2 incident on the light emitting unit side end surface 9a from the object side end surface 9b. At the same time, the light from the condensing element 4 incident from the object side end face 9b is branched at the branch point between the light emitting part side end face 9a and the object side end face 9b, and the light receiving part side end face 9c is directed to the light collecting element 8. It is comprised so that it may inject toward.

  In the embodiment of FIG. 1, the reflected light from the object 5 is branched and detected between the condensing element 2 and the optical fiber 3, whereas in the present embodiment, the reflected light is optical fiber. In FIG. 9, the light is branched and emitted from the light receiving portion side end face 9c to be detected. The other points are the same as in the embodiment of FIG.

  In other words, in the displacement detection device of the present embodiment, the divergent light emitted from the light emitting unit 1 is incident on the light emitting unit side end surface 9 a of the optical fiber 9 through the light condensing element 2. The incident light is radiated from the object-side end face 9 b, and then collected on the object 5 via the light condensing element 4 and reflected by the object 5. The reflected light again enters the object-side end surface 9 b of the optical fiber 9 through the condensing element 4. The incident reflected light is branched at the branch point of the optical fiber 9, is emitted from the light receiving unit side end face 9 c, and is then condensed on the light receiving element 8 by the light collecting element 7.

  The object 5 may be, for example, a liquid surface as long as it can reflect the light emitted from the object-side end surface 9b of the optical fiber 9 and enter the object-side end surface 9b of the optical fiber 9 again. It doesn't matter. Specifically, a diaphragm that is displaced according to sound pressure can be used as the object 5. In this case, the displacement of the diaphragm due to the sound pressure can be accurately detected even at an arbitrary location away from the light emitting unit 1 and the light receiving unit 8. In addition, since there is no part that operates electrically on the path from the light incident on the light emitting unit side end surface 9a of the optical fiber 9 to the light receiving unit side end surface 9c of the optical fiber 9 through the diaphragm, It is possible to accurately detect the displacement of the diaphragm even in places where the operating part is affected by the surrounding environment such as electromagnetic environment or explosion-proof environment or may affect the surrounding environment. .

  As the optical fiber 9, a single mode fiber, a multimode fiber, a plastic fiber, or the like can be used. However, some multimode fibers and plastic fibers have a large loss of light transmitted through the optical fiber, making long-distance transmission difficult. When used in an electromagnetic environment, an explosion-proof environment, or the like, it is also conceivable to detect the displacement of the object 5 installed at a location several hundred meters or more away. For this reason, it is desirable to use a single mode fiber or a graded index fiber as the optical fiber 9. Alternatively, a holey fiber having a hole structure, low transmission loss, and strong bending can be used.

  As the light emitting unit 1, an LED or a semiconductor laser can be used. However, since the LED is an optical surface light source, according to the LED, it is difficult to efficiently make the emitted light incident on the optical fiber 9 even though the LED is disposed through the light condensing element 2. In this case, if a multimode fiber or a plastic fiber having a large fiber diameter is used as the optical fiber 9, the efficiency can be improved to some extent. However, according to these optical fibers, since the loss during transmission is large as described above, transmission over a long distance becomes impossible. It is also possible to increase the incident efficiency somewhat by using an LED having an aperture of several tens to several hundreds of micrometers. However, since the light emitting portion of the semiconductor laser is about several micrometers and is optically considered as a point light source, it is desirable to use a semiconductor laser as the light emitting portion 1.

  As the condensing element 2, it is preferable to use an element having an NA on the light emitting unit 1 side that is equal to or larger than an emission angle of the light emitting unit 1 and an NA on the optical fiber 9 side that is less than or equal to NA on the light emitting unit side end face 9 a of the optical fiber 9. This is because the emitted light from the light emitting unit 1 can be taken in without loss and incident on the light emitting unit side end face 9a without loss. Specifically, the NA on the light emitting unit 1 side is preferably 0.2 or more, and more preferably 0.3 or more. The NA on the optical fiber 9 side is preferably 0.3 or less, more preferably 0.2 or less.

  If the NA on the optical fiber 9 side of the condensing element 4 is k and the NA on the object 5 side is m, the optical magnification on the object-side end surface 9b of the optical fiber 9 is m / k. A displacement of 5 can be obtained with a sensitivity of m / k times. Therefore, in order to detect the displacement amount of the object 5 with high sensitivity, it is desirable to use a condensing element 4 having NA on the optical fiber 9 side and the object 5 side such that m ≧ k. .

  The operation of the displacement detection device will be described. The diverging light emitted from the light emitting unit 1 includes a light emitting unit side NA that is greater than or equal to the emission angle of the light emitting unit 1 and an optical fiber 9 side NA that is less than or equal to the NA of the light emitting unit side end face 9a of the optical fiber 9. And is incident on the light emitting portion side end surface 9 a of the optical fiber 9.

  When the optical fiber 9 is a single mode fiber or a graded index fiber, the light incident on the optical fiber 9 is transmitted to at least several hundred meters or more with a minimum loss of light. Radiated from the side end face 9b. The diverging light radiated from the object-side end face 9b is reflected by the condensing element 4 having an NA that satisfies m ≧ k when the NA on the optical fiber 9 side is k and the NA on the object 5 side is m. It is condensed on the object 5.

  The light condensed on the object 5 is reflected by the object 5, is condensed again by the condensing element 4, and enters the object-side end surface 9 b of the optical fiber 9. The reflected light that has entered the object-side end surface 9 b is branched at the branch point on the optical fiber 9 and is emitted from the light-receiving-unit-side end surface 9 c of the optical fiber 9. The reflected light emitted from the light receiving unit side end face 9 c is collected on the light receiving element 8 by the light collecting element 7.

  In this state, when the object 5 is displaced in a direction parallel to the optical axis of the light collecting element 4 due to mechanical vibration, the diameter of the light beam on the object 5 and the object on the object side end surface 9b of the optical fiber 9 are detected. The diameter of the luminous flux of the reflected light from the object 5 changes, and the amount of light incident on the object-side end surface 9b changes. Incident light whose amount of light has changed is transmitted through the optical fiber 9, and the path is branched along the way to be detected by the light receiving element 8. Thereby, the amount of displacement of the object 5 can be detected as a change in the intensity of the optical signal incident on the light receiving element 8.

  At this time, assuming that the NA on the optical fiber 9 side of the condensing element 4 is k and the NA on the object 5 side is m, the optical magnification on the object-side end surface 9b of the optical fiber 9 on the object 5 is m / k. Therefore, the change amount of the light beam diameter on the object side end surface 9b with respect to the change amount of the light beam diameter on the object 5 is acquired with a sensitivity of m / k times, and the displacement amount of the object 5 is detected with high sensitivity. be able to.

  In addition, when using a semiconductor laser as the light emission part 1, it has been confirmed that there exists a phenomenon in which composite resonance occurs due to return light returning to the semiconductor laser and distortion occurs in the output signal. This phenomenon does not pose a problem when the amount of return light returning to the semiconductor laser is sufficiently small, but has been remarkably confirmed when the semiconductor laser is used at an oscillation start current or higher. Therefore, by driving the semiconductor laser below the oscillation start current, it is possible to reduce the amount of return light that is fed back to the semiconductor laser, and to avoid the distortion of the output signal that occurs due to the complex resonance. A similar effect can also be obtained by reducing the amount of return light that returns to the semiconductor laser using an optical isolator.

  Further, when the surface of the object side end surface 9b, the light condensing element 4 and the object 5 are in the in-focus position, the amount of reflected light incident on the object side end surface 9b is maximized, and the object 5 is positioned at that position. It decreases as it moves away from both sides in the optical axis direction. The amount of decrease is the same if the distances on both sides are the same. However, since the change in the amount of light is not linear in the vicinity of the in-focus position, the reference position of the object 5 is set to be shifted from the in-focus position to either side, and the amount of light with respect to the change in the position of the object 5 is set. It is adjusted so that the displacement of the object 5 can be detected in a range in which the change substantially shows a monotone increase or a monotone decrease.

  According to the present embodiment, the optical fiber 9 is commonly used for light projection for guiding detection light to the object 5 and for light reception for guiding reflected light from the object 5 to the light receiving unit 8. It is possible to provide a displacement detection device that can be easily assembled. Further, as the condensing element 4 that condenses the light emitted from the optical fiber 9 on the object 5 and makes the reflected light from the object 5 enter the optical fiber 9, the NA on the optical fiber 9 side is k, and the object By using the one that satisfies m ≧ k when the NA on the 5th side is m, the displacement amount of the object 5 can be acquired with a sensitivity of m / k times, and highly sensitive displacement detection can be performed.

It is a block diagram which shows the structure of the displacement detection apparatus which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the displacement detection apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Light emission part, 2: Light collection element, 3: Optical fiber, 3a: Light emission part side end surface, 3b: Object side end surface, 4: Light collection element, 5: Object, 6: Branch element, 7: Light collection Element: 8: Light receiving unit, 9: Two-branched optical fiber, 9a: Light emitting unit side end surface, 9b: Object side end surface, 9c: Light receiving unit side end surface

Claims (8)

An optical fiber for emitting the introduced detection light from the first end face;
Irradiating the target surface with light emitted from the first end face, and irradiating the reflected light on the first end face;
And a detection signal output means for outputting a signal indicating the displacement of the target surface based on the reflected light incident on the optical fiber from the first end face.   The displacement detection device according to claim 1, wherein the target surface is a surface of a diaphragm that is displaced according to sound pressure.   The displacement detection device according to claim 1, wherein the optical fiber is a single mode fiber or a graded index fiber. A light emitting unit for emitting the detection light;
4. The apparatus according to claim 1, further comprising: a second condensing element that irradiates the second end face of the optical fiber with light from the light emitting unit and introduces the detection light. The displacement detection device according to item.   The second condensing element is characterized in that the NA on the light emitting unit side is equal to or larger than the radiation angle of the light emitting unit, and the NA on the optical fiber side is equal to or smaller than the NA on the second end face of the optical fiber. The displacement detection apparatus according to claim 4. The detection signal output means includes
A branch element that is provided between the second end face and the second light collecting element and branches the reflected light emitted from the second end face;
A third condensing element for condensing the branched reflected light;
6. The displacement detection device according to claim 4, further comprising photoelectric conversion means for converting the collected reflected light into an electric signal. The optical fiber is branched, whereby a part of the reflected light incident from the first end surface is emitted from the third end surface of the branched optical fiber portion,
The detection signal output means includes
A fourth condensing element that condenses light emitted from the third end surface;
The displacement detection apparatus according to claim 1, further comprising: a photoelectric conversion unit that converts light collected by the fourth light collecting element into an electric signal. 8. The relationship according to claim 1, wherein m ≧ k, where k is the NA on the optical fiber side of the first light collecting element and m is the NA on the target surface side. Displacement detector.

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