JP2015088615A - Piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric element which is used in a scanner of an optical scanning type endoscope to drive an optical fiber and improves the durability in a fixing part between a holding member and the piezoelectric element.SOLUTION: An optical fiber is inserted into a cylindrical piezoelectric element 50 and a tip of the optical fiber protrudes from a front end surface of the piezoelectric element 50. An insertion part 55 is formed on an outer peripheral surface near a rear end of the piezoelectric element 50 and the insertion part 55 is inserted into an annular holding member. An adhesive layer is provided between the insertion part 55 and the holding member. External surface electrodes 51X, 51Y for applying voltage to the piezoelectric element 50 are formed on an outer peripheral side surface of the piezoelectric element 50. The external surface electrodes 51X, 51Y are not formed on an entire surface of the insertion part 55.

Description

  The present invention relates to a piezoelectric element that is used in, for example, a scanner of an optical scanning endoscope and drives an optical fiber.

  The piezoelectric element for driving the optical fiber is formed into a cylindrical shape so that the optical fiber is inserted through the inside. With the technique described in Patent Document 1 for this cylindrical piezoelectric element, four driving electrodes are formed over the entire length in the longitudinal direction on the outer peripheral side surface of the piezoelectric element. The tip of the optical fiber protrudes from the front end surface of the piezoelectric element. The tip of the optical fiber is displaced in a plane perpendicular to the longitudinal axis, and this displacement forms a spiral when viewed from the longitudinal direction. The vicinity of the rear end of the piezoelectric element is inserted into an annular holding member, and the piezoelectric element is fixed in a cantilever state.

  In the technique described in Patent Document 2, the inner diameter of the holding member is slightly larger than the outer diameter of the cylindrical piezoelectric element, and an adhesive provided between the outer peripheral surface of the piezoelectric element and the inner peripheral surface of the holding member. The piezoelectric element is fixed to the holding member by the layer. In addition, when a voltage is applied to the electrodes formed on the piezoelectric element, one of the two portions located substantially on the diagonal line in the cross section of the piezoelectric element extends in the longitudinal direction and the other contracts in the longitudinal direction. As a result, the tip of the optical fiber is displaced in a spiral shape.

JP 2009-212519 A Special table 2008-504557 gazette

  However, in the piezoelectric element described in Patent Document 1, electrodes are formed over the entire length in the longitudinal direction on the outer peripheral side surface. Therefore, when a voltage is applied to the electrode, the insertion portion of the piezoelectric element into the holding member also tends to expand and contract in the longitudinal direction even though it does not substantially contribute to driving of the optical fiber. Here, as described in Patent Document 2, when an adhesive layer is provided between the outer peripheral surface of the piezoelectric element and the inner peripheral surface of the holding member, shear stress acts on the adhesive layer. When the electrode is formed over the entire length in the longitudinal direction on the outer peripheral side surface of the piezoelectric element, the adhesive layer is repeatedly subjected to stress and stress is concentrated at the bonding boundary portion. As a result, the adhesive layer or the interface between the adhesive layer and the holding member or the piezoelectric element may be destroyed, and the durability of the fixing portion between the holding member and the piezoelectric element may be reduced.

  The present invention is a piezoelectric element that is used in a scanner of an optical scanning endoscope and drives an optical fiber, and is a piezoelectric element that can improve durability at a fixing portion between a holding member and a piezoelectric element. The object is to provide an element.

  A piezoelectric element according to the present invention is a cylindrical piezoelectric element for displacing the tip of an optical fiber that is inserted inside and protrudes from a front end surface, and is formed on an outer peripheral surface near the rear end of the piezoelectric element. An insertion portion that is inserted into the holding member and supported by the holding member by an adhesive layer; and an electrode that is formed on an outer peripheral side surface of the piezoelectric element and applies a voltage to the piezoelectric element, and includes at least one of the insertion portions. The part is characterized in that no electrode is formed.

  Preferably, the rear end portion of the insertion portion is positioned in front of the rear end surface of the piezoelectric element, the insertion portion conductive layer formed in the insertion portion, and the rear end surface and the rear end portion of the outer peripheral side surface of the piezoelectric element. And an end conductive layer formed therebetween, and the end conductive layer is electrically connected to the electrode by the insertion portion conductive layer. Preferably, two or more longitudinal grooves extending in the longitudinal direction are formed on the outer peripheral side surface of the piezoelectric element, and no electrode is formed in the longitudinal groove. Preferably, the insertion portion includes a short groove provided in parallel with the long groove, two peripheral grooves provided with one end connected to both ends of the short groove and provided in parallel in the circumferential direction, and two peripheral grooves. The other end is connected and has a longitudinal groove adjacent to the longitudinal groove, and no electrode is formed in the short groove and the circumferential groove. Preferably, four longitudinal grooves are provided at positions that are 90 ° apart from each other in the circumferential direction of the cross section of the piezoelectric element.

  Preferably, no electrode is formed on the entire surface of the insertion portion. Preferably, the end conductive layer formed between the rear end surface and the rear end portion of the outer peripheral side surface of the piezoelectric element is located at a front end of the rear end surface of the piezoelectric element. Further prepare.

  The piezoelectric element according to the present invention is a cylindrical piezoelectric element for displacing the tip of an optical fiber that is inserted inside and protrudes from the front end surface, and is formed on the outer peripheral side surface of the piezoelectric element, and voltage is applied to the piezoelectric element. 2 or more, and two or more longitudinal grooves extending in the longitudinal direction are formed on the outer peripheral side surface of the piezoelectric element, and no electrode is formed in the longitudinal groove.

  ADVANTAGE OF THE INVENTION According to this invention, it is a piezoelectric element used with the scanner of an optical scanning endoscope, and drives an optical fiber, Comprising: It can improve durability in the fixing | fixed part between a holding member and a piezoelectric element. A piezoelectric element that can be obtained can be obtained.

It is a figure which shows the structure of the optical fiber scanner in the 1st Embodiment of this invention. It is a figure which shows the adhesive bond layer provided between an operation member and a piezoelectric element. It is sectional drawing which shows the AA cross section of FIG. It is a perspective view which shows a piezoelectric element. It is a figure which shows a mode that an adhesive agent is apply | coated to the longitudinal groove of the piezoelectric element before plating. It is a figure which shows a mode that the adhesive agent apply | coated to the longitudinal groove of the piezoelectric element before plating was hardened. It is a figure which shows a part of cross section of the piezoelectric element after plating. It is a figure which shows a mode that the adhesive agent hardened | cured from the longitudinal groove after plating is peeled. It is a figure which shows the end surface of a piezoelectric element. It is sectional drawing of the piezoelectric element in the state where the voltage is not applied. It is sectional drawing of the piezoelectric element in the state where the voltage was applied. It is a perspective view which shows the piezoelectric element in 2nd Embodiment. It is a figure which shows the structure of the optical fiber scanner which concerns on 3rd Embodiment. It is a perspective view which shows a piezoelectric element. It is detail drawing of the arrow D of FIG. It is a perspective view which shows the piezoelectric element in 4th Embodiment. It is detail drawing of the arrow F of FIG. It is detail drawing of the arrow G of FIG.

  The configuration of the piezoelectric element according to the first embodiment of the present invention will be described below with reference to the drawings. First, an outline of the optical fiber scanner mounted on the distal end portion of the optical scanning endoscope will be described. As shown in FIG. 1, the optical fiber scanner 10 includes an annular housing 20. An annular holding member 30 is fixed inside the housing 20, and a lens unit 40 is provided in the housing 20. A cylindrical piezoelectric element 50 is inserted into the holding member 30 and fixed by an adhesive layer described later. An optical fiber 60 is inserted into the piezoelectric element 50. The optical fiber 60 is held in a cantilever state with its tip protruding from the front end face of the piezoelectric element 50. The protruding portion of the optical fiber 60 is fixed by an adhesive 70. The optical fiber 60 is connected to a light source (not shown). In this specification, the direction toward the tip side of the optical fiber 60 is defined as the front.

  An insertion portion 55 is formed on the outer peripheral surface near the rear end of the piezoelectric element 50. As shown in FIG. 2, the insertion portion 55 is supported by the holding member 30 by the adhesive layer 58. The width of the insertion portion 55 in the longitudinal direction is equal to or greater than the width of the holding member 30.

  On the outer peripheral side surface of the piezoelectric element 50, a plurality of outer surface electrodes 51 </ b> X and 51 </ b> Y are formed on the distal end side with respect to the insertion portion 55. The plurality of outer surface electrodes 51X and 51Y are separated in the circumferential direction over the entire longitudinal direction. For convenience of explanation, as shown in the drawing, among the outer surface electrodes, those used for bending in the X direction are particularly referred to as outer surface electrodes 51X, and those used for bending in the Y direction are particularly referred to as outer surface electrodes 51Y. Represent. As shown in FIG. 1, a wire 80 is soldered to each of the separated outer surface electrodes 51 </ b> X and 51 </ b> Y near the front end of the holding member 30. As shown in FIG. 3, a notch 31 is formed on the outer peripheral surface of the annular holding member 30. A wire 80 is inserted through a gap between the notch 31 and the inner peripheral surface of the housing 20, and the wire 80 is drawn from the front to the rear of the holding member 30. Each wire 80 is connected to a power supply unit (not shown). The optical fiber 60 is fixed to the piezoelectric element 50 via the tube 90.

  The illumination light L transmitted from the light source is emitted to the subject via the optical fiber 60 and the lens unit 40. The piezoelectric element 50 is bent in the radial direction at its front portion from the holding member 30. The bending frequency is controlled to coincide with the resonance frequency of the flexural vibration at the tip of the optical fiber 60. As a result, the tip of the optical fiber 60 is greatly displaced in the X and Y directions as compared to the displacement of the optical fiber 60 in the vicinity of the piezoelectric element 50. The locus of this displacement forms a spiral when viewed from the Z direction. For example, even if the displacement of the optical fiber 60 near the adhesive 70 is several μm, the displacement of the tip of the optical fiber 60 is about 0.5 mm. In each figure, the Z direction is a direction along the optical axis of the lens unit 40, and the direction toward the distal end side of the optical fiber 60, that is, the front is positive. Further, the X and Y directions (see FIG. 9) are directions orthogonal to the Z direction and orthogonal to each other. The length of the piezoelectric element 50 is, for example, 1 to 10 mm. The number of poles of the outer surface electrodes 51X and 51Y is, for example, four.

  As shown in FIG. 4, the piezoelectric element 50 is manufactured by forming a conductive layer including outer surface electrodes 51 </ b> X and 51 </ b> Y on the outer peripheral side surface of the piezoelectric member 52. The piezoelectric member 52 is formed in a cylindrical shape in which longitudinal grooves 53 extending in the longitudinal direction are formed at four places in the circumferential direction. That is, four longitudinal grooves 53 are provided at positions that are 90 ° apart from each other in the circumferential direction of the cross section of the piezoelectric element 50. The cross section represents a cut surface when the piezoelectric element 50 is cut along a plane perpendicular to the longitudinal direction. The piezoelectric member 52 is made of a piezoelectric material and a binder powder. The molding method is, for example, extrusion molding. The piezoelectric material is, for example, PZT (lead zirconate titanate).

  A through hole 54 extending in the longitudinal direction is formed in the piezoelectric element 50. An inner surface electrode 56 is formed on the surface of the through hole 54. The insertion portion 55 is located near the rear end of the piezoelectric element 50. Therefore, the rear end portion of the insertion portion 55 is positioned in front of the rear end surface of the piezoelectric element 50.

  End conductive layers 57 </ b> X and 57 </ b> Y are formed between the rear end surface of the piezoelectric element 50 and the rear end of the insertion portion 55 on the outer peripheral side surface of the piezoelectric element 50. The outer surface electrodes 51X and 51Y and the end conductive layers 57X and 57Y are formed by a single plating process. In this plating step, the insertion portion 55 is masked with, for example, a tape, so that a conductive layer is not formed. That is, no electrode is formed on the entire surface of the insertion portion 55. The outer surface electrodes 51 </ b> X and 51 </ b> Y formed on the outer peripheral side surface of the piezoelectric element 50 are used for applying a voltage to the piezoelectric member 52. The end conductive layers 57 </ b> X and 57 </ b> Y are not used for applying a voltage to the piezoelectric member 52. In the drawings, a dot pattern indicates that a conductive layer including an electrode is not provided.

  Next, a method of processing the longitudinal groove 53 so that no electrode is formed will be described with reference to FIGS. First, the adhesive 100 (schematically shown in FIG. 5) is applied to the longitudinal groove 53. For example, the adhesive 100 is attached to the tip of a wire having an outer diameter smaller than the width of the longitudinal groove 53, and the tip of the wire is inserted into the longitudinal groove 53 and moved along the groove. Adhesive 100 is applied. The adhesive 100 is, for example, a thermoplastic resin, and has elasticity like rubber after being cured. As shown in FIG. 6, the adhesive 100 is cured and bulges from the opening of the longitudinal groove 53.

  Subsequently, a plating process is performed, and a conductive layer 110 is formed on the outer peripheral side surface of the piezoelectric member 52 and the exposed surface of the adhesive 100 as shown in FIG. Here, since the adhesive 100 is in close contact with the piezoelectric member 52, the conductive layer 110 is not directly formed in the longitudinal groove 53. The formation method of the conductive layer 110 may be based on curing of a conductive adhesive containing silver powder in addition to the plating treatment. Finally, as shown in FIG. 8, the adhesive 100 is peeled from the piezoelectric member 52. Thereby, the outer surface electrodes 51X and 51Y are formed in a separated state. The width of the longitudinal groove 53 is set so that a necessary spatial distance can be secured and the piezoelectric member 52 can be appropriately polarized.

  Unlike the outer surface electrodes 51X and 51Y, the inner surface electrode 56 is not separated into a plurality of poles as shown in FIG. In addition, the outer diameter in the cross section of the piezoelectric element 50 is 0.1-1 mm, for example.

  After the plating process, a high voltage is applied between the outer surface electrodes 51X and 51Y and the inner surface electrode 56 to polarize the piezoelectric member 52, and the piezoelectric element 50 is completed. That is, a high voltage is applied to the voltage application range 59 in FIG. The piezoelectric members 52 corresponding to all the outer surface electrodes 51X and 51Y are polarized so as to be appropriately displaced.

  Next, drive control when the piezoelectric element 50 is used in an optical fiber scanner of a scanning endoscope will be described. 10 and 11 each show an AA cross section of the piezoelectric element 50 shown in FIG. An AC voltage is applied between the two outer surface electrodes 51X and 51X and between the two outer surface electrodes 51Y and 51Y (not shown). Thus, by controlling the voltage applied to the outer surface electrodes 51X and 51Y, the tip of the optical fiber is driven in a spiral shape.

  Next, a mechanism for bending the piezoelectric element 50 will be described. When an AC voltage is applied between the outer surface electrodes 51X and 51X, as shown in FIG. 11, the portion corresponding to the outer surface electrode 51X in the left cross-sectional portion of the piezoelectric element 50 is elongated in the longitudinal direction due to the piezoelectric inverse effect. The portion corresponding to the outer surface electrode 51X in the right cross-sectional portion contracts in the longitudinal direction. As a result, the portion of the piezoelectric element 50 corresponding to the outer electrode 51X bends in the direction of the arrow B shown in FIG. 11, that is, in the X direction. On the other hand, in the piezoelectric element 50, portions corresponding to the insertion portion 55 and the end conductive layers 57X and 57Y are not bent because no voltage is applied thereto.

  As described above, in the present embodiment, the outer surface electrodes 51X and 51Y are not formed on the entire surface of the insertion portion 55. As a result, when the tip of the optical fiber 60 is driven in a spiral shape, a voltage is applied to the outer surface electrodes 51X and 51Y, but the insertion portion 55 in contact with the adhesive layer 58 does not expand or contract in the longitudinal direction. Is not subjected to shear stress due to expansion and contraction of the insertion portion 55. Therefore, since the repeated stress due to the shear stress does not occur, it is possible to avoid that the adhesive layer 58 or the interface thereof is broken and the durability of the fixing portion between the holding member and the piezoelectric element is lowered.

  Further, in the present embodiment, the adhesive 100 is applied to the longitudinal groove 53 and cured, and after the conductive layer 110 is formed on the outer peripheral side surface of the piezoelectric member 52 and the exposed surface of the adhesive 100, the adhesive 100 is added to the longitudinal groove 53. The outer surface electrodes 51X and 51Y are formed by being peeled off. Thereby, each outer surface electrode 51X, 51Y can be easily arranged in the state separated in the circumferential direction. On the other hand, in the prior art, when the outer surface electrode is separated in the circumferential direction, first, a convex portion extending in the longitudinal direction is formed on the cylindrical outer surface in the molding step. Next, a conductive layer is formed on the entire outer surface, and finally the convex portion is removed. However, in this case, it is difficult to stably form the convex portion. On the other hand, in this embodiment, since it is not necessary to provide a convex portion extending in the longitudinal direction on the cylindrical outer surface in the molding step, the outer surface electrodes 51X and 51Y can be stably separated and arranged in the circumferential direction.

  FIG. 12 shows a configuration of the piezoelectric element 150 of the second embodiment in which the insertion portion 155 is formed up to the rear end of the outer peripheral surface of the piezoelectric element 150. Except that the end conductive layers 57X and 57Y in FIG. 4 are not formed, the configuration of the piezoelectric element 150 in FIG. 12 is the same as that in the first embodiment. As described above, in the second embodiment, since the insertion portion 155 is formed up to the rear end of the outer peripheral surface of the piezoelectric element 150, masking in the plating process is relatively easy and the piezoelectric element 150 is fixed to the holding member 30. In this case, positioning in the longitudinal direction becomes easy.

  FIG. 13 shows a configuration of an optical fiber scanner 180 according to the third embodiment. In the piezoelectric element 200, insertion portion conductive layers 201X and 201Y are formed in the insertion portion. Further, the holding member 230 is not formed with the notch 31 of the holding member 30 in FIG. The wire 80 is soldered to the outer peripheral surface near the rear end of the piezoelectric element 50 behind the holding member 230. Other configurations of the optical fiber scanner 180 are the same as those in the first embodiment.

  As shown in FIGS. 14 and 15, insertion portion conductive layers 201 </ b> X and 201 </ b> Y are formed in the insertion portion of the piezoelectric element 200 in parallel with the longitudinal groove 53. In addition, piezoelectric member exposed portions 203X and 203Y are formed in the insertion portion of the piezoelectric element 200. The outer surface electrodes 51X and 51Y, the end conductive layers 57X and 57Y, and the insertion conductive layers 201X and 201Y are formed by a single plating process. In this plating step, the piezoelectric member exposed portions 203X and 203Y are masked with, for example, tape, so that no conductive layer is formed. In addition to what is shown in FIG. 14, the insertion portion conductive layers 201 </ b> X and 201 </ b> Y are also formed on the back side thereof, that is, at a position shifted in phase by 180 ° in the outer circumferential direction of the piezoelectric element 200. In the insertion portion, portions other than the portion where the insertion portion conductive layers 201X and 201Y are formed are masked. Note that an arrow D in FIG. 14 indicates a direction in which the piezoelectric element 200 is viewed from an intermediate direction between the X direction and the Y direction while being orthogonal to the longitudinal direction of the piezoelectric element 200. Further, as shown in FIG. 14, in the polarization process, a high voltage is applied to two voltage application ranges 205 and 205 separated in the longitudinal direction.

  In the third embodiment, since the insertion portion conductive layers 201X and 201Y are formed in the insertion portion, the wire 80 can be soldered to the outer peripheral surface near the rear end of the piezoelectric element 50 behind the holding member 230. For this reason, workability can be improved as compared with the case where soldering is performed in front of the holding member 230, and the wire 80 can be pulled out from the rear of the holding member 30, so that the wire 80 can be easily routed. . In addition, since no voltage is applied to the piezoelectric member exposed portions 203X and 203Y, the same effects as those of the first embodiment can be obtained.

  FIG. 16 shows a piezoelectric element according to a fourth embodiment having another configuration of a piezoelectric element in which insertion portion conductive layers 201X and 201Y are formed in the insertion portion. As shown in FIG. 17, in the piezoelectric element 300, another masking method is performed instead of the piezoelectric member exposed portions 203X and 203Y of the third embodiment. That is, the insertion portion 55 has short grooves 303X and 303Y and two circumferential grooves 305X, 305X, 305Y and 305Y for each pole. The short grooves 303 </ b> X and 303 </ b> Y are provided in parallel with the long groove 53. Two circumferential grooves 305X, 305X, 305Y, and 305Y for each pole are provided in parallel in the circumferential direction with one end thereof connected to both ends of the short grooves 303X and 303Y. In addition to what is shown in FIG. 17, the insertion portion conductive layers 201 </ b> X and 201 </ b> Y are also formed on the back side thereof, that is, at a position shifted in phase by 180 ° in the outer circumferential direction of the piezoelectric element 300. As shown in FIG. 18, the other ends of the circumferential grooves 305 </ b> X and 305 </ b> Y are connected to the longitudinal groove 53. Note that arrow F in FIG. 16 indicates a direction perpendicular to the longitudinal direction of the piezoelectric element 300 and the direction in which the piezoelectric element 300 is viewed from an intermediate direction between the X direction and the Y direction. An arrow G indicates a direction in which the piezoelectric element 300 is visually recognized from a direction whose phase is shifted by 90 ° from the direction of the arrow F in the circumferential direction of the piezoelectric element 300.

  In the short grooves 303X and 303Y and the circumferential grooves 305X and 305Y, no electrode is formed by the same process as that of the long groove 53 in the first embodiment. Since the short grooves 303X and 303Y and the circumferential grooves 305X and 305Y are difficult to be formed by extrusion, the piezoelectric element 300 is formed by injection molding, for example. The unused conductive layers 301X and 301Y surrounded by the short grooves 303X and 303Y, the circumferential grooves 305X and 305Y, and the long grooves 53 are formed by the same plating process as the insertion portion conductive layers 201X and 201Y. Other configurations of the piezoelectric element are the same as those in the third embodiment.

  In the fourth embodiment, electrodes are not formed in the short grooves 303X and 303Y and the circumferential grooves 305X and 305Y by the same process as the long grooves 53, and therefore, masking in the plating process can be performed only with an adhesive. Further, as in the second embodiment, the soldering workability can be improved and the wire 80 can be pulled out from the rear of the holding member 30, so that the wire 80 can be easily routed. Further, since no voltage is applied to the unused conductive layers 301X and 301Y, the same effects as those of the first embodiment are obtained.

  The above is the description of the embodiment of the present invention. In the first to fourth embodiments, four longitudinal grooves are formed, but two or more longitudinal grooves may be formed. In the fourth embodiment, the piezoelectric element is molded by injection molding. However, after the piezoelectric element is molded by extrusion molding, the short groove and the circumferential groove may be formed by a laser processing machine.

10, 180 Optical fiber scanner 30, 230 Holding member 50, 150, 200, 300 Piezoelectric element 51X, 51Y External electrode 53 Longitudinal groove 55, 155 Insert part 57X, 57Y End conductive layer 58 Adhesive layer 201X, 201Y Insert part conductive layer

Claims (8)

A cylindrical piezoelectric element for displacing the tip of an optical fiber that is inserted inside and protrudes from the front end surface,
Formed on the outer peripheral surface near the rear end of the piezoelectric element, and inserted into an annular holding member and supported by the holding member by an adhesive layer;
Formed on an outer peripheral side surface of the piezoelectric element, and an electrode for applying a voltage to the piezoelectric element,
The piezoelectric element, wherein the electrode is not formed on at least a part of the insertion portion. The rear end portion of the insertion portion is located in front of the rear end surface of the piezoelectric element,
An insertion portion conductive layer formed in the insertion portion;
An end conductive layer formed between the rear end surface and the rear end on the outer peripheral side surface of the piezoelectric element;
The piezoelectric element according to claim 1, wherein the end conductive layer is electrically connected to the electrode by the insertion portion conductive layer. Two or more longitudinal grooves extending in the longitudinal direction are formed on the outer peripheral side surface of the piezoelectric element,
The piezoelectric element according to claim 1, wherein the electrode is not formed in the longitudinal groove. The insertion portion includes a short groove provided in parallel to the longitudinal groove, two peripheral grooves provided at one end connected in parallel to the both ends of the short groove and provided in parallel in the circumferential direction, and the two other peripheral grooves. Having an end connected and a longitudinal groove adjacent to the longitudinal groove;
The piezoelectric element according to claim 3, wherein the electrode is not formed in the short groove and the circumferential groove.   4. The piezoelectric element according to claim 3, wherein four longitudinal grooves are provided at positions that are 90 ° apart from each other in a circumferential direction of a transverse section of the piezoelectric element.   The piezoelectric element according to claim 1, wherein the electrode is not formed on the entire surface of the insertion portion. The rear end portion of the insertion portion is located in front of the rear end surface of the piezoelectric element,
The piezoelectric element according to claim 6, further comprising an end conductive layer formed between the rear end face and the rear end on the outer peripheral side surface of the piezoelectric element. A cylindrical piezoelectric element for displacing the tip of an optical fiber that is inserted inside and protrudes from the front end surface,
Formed on the outer peripheral side surface of the piezoelectric element, comprising an electrode for applying a voltage to the piezoelectric element;
Two or more longitudinal grooves extending in the longitudinal direction are formed on the outer peripheral side surface of the piezoelectric element,
The piezoelectric element, wherein the electrode is not formed in the longitudinal groove.

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