JP2016024357A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical isolator capable of stably operating due to lower temperature dependency.SOLUTION: An optical isolator 1 includes a pair of polarizers 31 and 34, a Faraday rotator 32 arranged between the pair of polarizers 31 and 34, and a magnetism application unit 40 for applying a magnetic field to the Faraday rotator 32. The intensity of the magnetic field applied to the Faraday rotator 32 is changed according to the temperature change of the Faraday rotator 32 so as to suppress the change of the Faraday rotation angle which is caused by the temperature change of the Faraday rotator 32.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical isolator, and is particularly suitable when the temperature of the optical isolator changes.

  Laser devices are used in various fields such as a processing field and a medical field. However, the light reflected by the object to be processed may enter the laser device again as return light. In order to prevent the laser device from being damaged by the return light, an optical isolator may be used. An optical isolator is an optical device in which the loss of light differs greatly depending on whether light travels in the forward direction or in the reverse direction.

  However, the isolation of the optical isolator has a characteristic that varies with temperature. Therefore, even when sufficient isolation is obtained at a certain temperature, the isolation may be reduced due to a change in the environmental temperature where the optical isolator is placed or due to its own heat generation. The main cause is that the Faraday rotation angle of the Faraday rotator used in the optical isolator varies with temperature.

  Patent Documents 1 and 2 below describe optical isolators that suppress the temperature dependence of isolation. This optical isolator rotates a light output side polarizer in accordance with an ambient temperature among a pair of polarizers sandwiching a Faraday rotator along an optical path. In the optical isolator described in Patent Document 1, bimetals are fixed at two opposite positions on the side surface of the polarizer to be rotated, and the polarizer is rotated by the bimetal warp caused by temperature change. For this reason, the polarizer rotates around the optical path. Further, in the optical isolator described in Patent Document 2, a bimetal is fixed at one place on the side surface of the polarizer to be rotated, and the polarizer rotates while moving perpendicularly to the optical path by the bimetal warp caused by temperature change.

JP 2003-202521 A Japanese Patent No. 2721879

  However, as in the optical isolator described in Patent Document 1, if the bimetal is fixed to the two side surfaces of the polarizer and the polarizer is rotated, the configuration becomes complicated. In general, it is difficult to rotate the polarizer without changing the optical axis of the polarizer, and if the optical axis of the polarizer changes, the operation may become unstable. Similarly, the optical isolator described in Patent Document 2 rotates while the polarizer moves perpendicularly to the optical path, so that the position of the light transmitted through the polarizer may change and the operation may become unstable.

  Therefore, an object of the present invention is to provide an optical isolator that has a small temperature dependency and can be stably operated.

  In order to solve the above problems, the present invention includes a pair of polarizers, a Faraday rotator disposed between the pair of polarizers, and a magnetic application unit that applies a magnetic field to the Faraday rotator. The intensity of the magnetic field applied to the Faraday rotator varies according to the temperature change so as to suppress a change in Faraday rotation angle due to a temperature change of the Faraday rotator. It is what.

  In this optical isolator, the temperature dependence of the Faraday rotation angle is suppressed by changing the magnetic field applied to the Faraday rotator with the temperature change of the Faraday rotator. In other words, in the state where the Faraday rotation angle is changed by a temperature change as in Patent Documents 1 and 2, the Faraday rotation angle that causes the temperature change of the isolation is not performed by compensating for the isolation by rotating the polarizer. Suppresses changes due to temperature. For this reason, it is not necessary to rotate a polarizer, and the instability of the operation | movement accompanying the rotation operation | movement of an element is prevented. Thus, according to the optical isolator of the present invention, the temperature dependence of the isolation is small and the operation can be stably performed.

  The driving device further includes a driving member that relatively moves the Faraday rotator and the magnetic application unit along the optical path direction, and the magnetic application unit is configured along the optical path direction of light propagating through the Faraday rotator. Applying a magnetic field of varying intensity, and the driving member includes the Faraday rotator and the magnetic application unit according to the temperature change so as to suppress a change in Faraday rotation angle due to a temperature change of the Faraday rotator. It is preferable to move it relatively.

  As such a magnetic application part, a permanent magnet can be mentioned, for example. Therefore, by relatively moving the permanent magnet and the Faraday rotator, the strength of the magnetic field applied to the Faraday rotator can be adjusted without using an electromagnet. Thus, by not using an electromagnet, the cost required for manufacturing an optical isolator can be reduced.

  The position of the magnetic application unit may be fixed, and the driving member may move the Faraday rotator.

  A Faraday rotator generally has a smaller mass than a magnet. Accordingly, by moving the Faraday rotator, the Faraday rotator can be easily moved relative to the magnetic application unit. Even in this case, since the operation of rotating the element is not involved, it is possible to suppress the operation of the optical isolator from becoming unstable.

  When the Faraday rotator is moved in this manner, it is preferable that the Faraday rotator further includes a fixing member to which the Faraday rotator is fixed, and the driving member moves the fixing member.

  Therefore, even if stress is applied from the drive unit by moving the Faraday rotator via the fixed member, the stress can be applied to the fixed member and the stress applied to the Faraday rotator can be suppressed. For this reason, it is possible to suppress degradation of isolation caused by stress.

  It is preferable that the pair of polarizers are fixed to the fixing member together with the Faraday rotator.

  The relative positions of the polarizer and the Faraday rotator do not change because each polarizer moves together with the Faraday rotator. Therefore, changes in optical characteristics can be suppressed.

  Alternatively, the Faraday rotator is preferably fixed in position, and the driving member moves the magnetic application unit.

  By moving the magnet, it is not necessary to move the element through which light propagates. For this reason, it is possible to suppress the optical path from becoming unstable and the operation of the optical isolator from becoming unstable.

  The driving member may be a bimetal whose one end is fixed, and the Faraday rotator and the magnetic application unit may move relatively by displacement of the other end of the bimetal due to the temperature change. preferable.

  Bimetal has a simple structure and a large amount of variation due to temperature changes. For this reason, the Faraday rotator and the magnetic application unit can be moved relatively stably.

  It is preferable that the magnetic application unit includes an electromagnet, further includes a voltage application unit that applies a voltage to the electromagnet, and the voltage application unit changes the voltage according to the temperature change.

  The intensity of the magnetic field applied by the electromagnet to the Faraday rotator can be changed by changing the voltage of the voltage application unit. In this case, it is not necessary to change the position of at least one of the Faraday rotator and the magnetic application unit. Since there is no portion to be moved in this way, an optical isolator having excellent durability can be obtained.

  As described above, according to the present invention, there is provided an optical isolator having a small temperature dependency and capable of operating stably.

It is a figure which shows the optical isolator which concerns on 1st Embodiment of this invention. It is a figure which shows a mode that light is radiate | emitted. It is a figure which shows a mode that transmission of the reflected return light from a process target object is suppressed. It is a figure which shows the relationship between the temperature change of a general Faraday rotator, and a Faraday rotation angle. It is a figure which shows the temperature dependence of the isolation in a common isolator. It is a figure which shows the relationship in the setting temperature of the distance from the center of the magnetic application part in the optical isolator of FIG. 1 to the center position of a Faraday rotator, and a Faraday rotation angle. It is a figure which shows the operation | movement by the temperature change of the optical isolator of FIG. It is a figure which shows the relationship between the temperature change of the Faraday rotator in the optical isolator shown in FIG. 1, and a Faraday rotation angle. It is a figure which shows the temperature dependence of the isolation of the optical isolator of FIG. It is a figure which shows the optical isolator which concerns on 2nd Embodiment of this invention. It is a figure which shows the optical isolator which concerns on 3rd Embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an optical isolator according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing an optical isolator according to the present embodiment. As shown in FIG. 1, the optical isolator 1 of the present embodiment includes a housing 10, a tube 20, a first beam shift plate 31, a Faraday rotator 32, a polarization rotator 33, and a second beam shift plate 34. The magnetic application unit 40 and the drive unit 50 are provided as main components.

  The casing 10 has an outer shape having a pair of surfaces facing each other, and has an outer shape that is, for example, a rectangular parallelepiped or a cylinder. Each of the pair of surfaces of the housing 10 is formed with an opening through which light can pass, one of which is a light entrance 11 and the other is a light exit 12. This opening may be, for example, glass when the casing 10 is made of aluminum, or a hole in which nothing is physically disposed.

  On the inner side surface of the housing 10, a tube support portion 16 that surrounds the entrance port 11 and a tube support portion 17 that surrounds the exit port 12 are provided. Further, on the inner side surface of the housing 10, a driving unit fixing portion 18 is provided on a surface orthogonal to the surface on which the entrance 11 is formed and the surface on which the exit 12 is formed.

  In the present embodiment, the magnetic application unit 40 is constituted by a cylindrical permanent magnet. Accordingly, the magnetic application unit 40 applies a magnetic field in the direction in which the optical elements are arranged in the through hole and in the vicinity of the through hole. The strength of the magnetic field is greatest at the center in the through hole of the magnetic application unit 40. The magnet 20 is fixed to the housing 10 by means (not shown), and the tube 20 is inserted into the through hole in this state.

  The tube 20 has a cylindrical shape, and a notch 28 is formed. In addition, the tube 20 has an incident side surface portion 26 which is a planar portion perpendicular to the longitudinal direction and located at one end portion of the tube 20, and a longitudinal direction located at the other end portion of the tube 20. The exit side surface portion 27, which is a planar portion perpendicular to the tube, is connected so as to close the through hole of the tube 20. In addition, an incident port 21 that is an opening through which light can be transmitted is formed in the incident side surface portion 26, and an output port 22 that is an opening through which light can be transmitted is formed in the output side surface portion 27.

  In the state where the tube 20 is inserted through the through hole of the magnetic application unit 40 as described above, the incident port 21 and the incident port 11 of the housing 10 overlap, and the emission port 22 and the emission port 22 of the housing 10 are connected. The tube supports 16 and 17 are supported so as to overlap each other. In this state, the tube 20 is movable in the longitudinal direction.

  A first beam shift plate 31, a Faraday rotator 32, a polarization rotator 33, and a second beam shift plate 34 are fixed in the through hole of the tube 20. That is, the tube 20 can be understood as a fixing member that is disposed on the optical path and fixes an optical element necessary for light isolation.

  The first beam shift plate 31 is disposed at a position adjacent to the incident side surface portion 26 in the through hole of the tube 20. The first beam shift plate 31 is a birefringent element, and separates light into ordinary light and extraordinary light whose polarizations are different from each other by 90 degrees when random polarized light enters. Thus, the first beam shift plate is an element that uses polarized light and is called a polarizer.

Examples of the material constituting the first beam shift plate 31 include yttrium orthovanadate (YVO ₄ ), calcite (CaCO ₃ ), and rutile (TIO ₂ ).

The Faraday rotator 32 is disposed at a position adjacent to the first beam shift plate 31 in the through hole of the tube 20. Specifically, in the present embodiment, the Faraday rotator 32 is such that the center C _F of the Faraday rotator 32 is incident from the axial center C _M of the through hole of the magnetic application unit 40 at a set temperature determined by design. It is unevenly distributed on the side surface portion 26 side. In FIG. 1, the center C _M in the axial direction of the through hole is indicated by a line perpendicular to the axial direction. The Faraday rotator 32 rotates the polarization direction of incident light by +45 degrees and emits it.

Examples of the material constituting the Faraday rotator 32 include terbium gallium garnet type single crystal (TGG: Tb ₃ Ga ₅ O ₁₂ ), terbium aluminum garnet type single crystal (TAG: Tb ₃ Al ₅ O ₁₂ ), terbium. scandium aluminum garnet-type single crystal _{(TSAG: Tb 3 Sc 2 Al} 3 O 12) , and the like.

  The polarization rotator 33 is disposed at a position adjacent to the Faraday rotator 32 in the through hole of the tube 20. The polarization rotator 33 rotates the polarization direction of the light incident from the incident port 11 side by +45 degrees and emits it, and emits the polarization direction of the light incident from the output port 12 side by −45 degrees.

  Examples of the material constituting the polarization rotator 33 include quartz.

  The second beam shift plate 34 is disposed at a position adjacent to the polarization rotator 33 in the through hole of the tube 20. The side opposite to the polarization rotator 33 side of the second beam shift plate 34 is adjacent to the emission side surface portion 27. The second beam shift plate 31 is the same element as the first beam shift plate 31. Therefore, the second beam shift plate is also called a polarizer.

  The drive unit 50 is made of bimetal in the present embodiment. A bimetal is a plate-like member in which two metals having different thermal expansion coefficients are laminated, and has a property that it tends to a member having a small thermal expansion coefficient as the temperature rises. In the present embodiment, the metal side of the bimetal which is the drive unit 50 is arranged such that the metal side having a large thermal expansion coefficient faces the incident side surface portion 26 side, and the metal side having a small thermal expansion coefficient faces the emission side surface portion 27 side, and one end of the bimetal is driven. It is fixed to the part fixing part 18. Therefore, the other end of the bimetal moves from the incident side face part 26 side to the outgoing side face part 27 side as the temperature rises. The other end of the bimetal is fitted in the notch 28 of the tube 20. As described above, the tube 20 is movable in the longitudinal direction while being supported by the tube support portions 16 and 17, and therefore moves with the movement of the other end of the bimetal.

  Next, the optical operation of the optical isolator 1 shown in FIG. 1 will be described.

  FIG. 2 is a diagram showing how light is emitted, and FIG. 3 is a diagram showing how transmission of reflected light is suppressed. 2 and 3, the notch 28, the casing 10, the magnetic application unit 40, and the drive unit 50 of the tube 20 are omitted. 2 and 3, the state of propagation of ordinary light is indicated by a solid line, and the state of propagation of abnormal light having a polarization direction different from that of ordinary light by 90 degrees is indicated by a broken line. In addition, the polarization direction of ordinary light is formally indicated by a solid line double arrow, and the polarization direction of extraordinary light is formally indicated by a broken line double arrow.

  As shown in FIG. 2, random polarized light enters from the entrance 21 through the entrance 11 of the housing 10. The respective lights are refracted in different directions by the first beam shift plate 31 and are emitted from different positions of the first beam shift plate 31. Each emitted light enters the Faraday rotator 32, and the polarization direction rotates +45 degrees and exits from the Faraday rotator 32. Each light emitted from the Faraday rotator 32 enters the polarization rotator 33, and the polarization direction is further rotated by +45 degrees. Each light emitted from the polarization rotator 33 enters the second beam shift plate 34. Each light is refracted in different directions by the second beam shift plate 34 and is emitted from the same position of the second beam shift plate 34. This is due to the following reason. That is, in the first beam shift plate 31, for example, it is assumed that ordinary light is refracted in a specific direction and abnormal light is refracted in another specific direction different from the normal light. Each light emitted from the polarization rotator 33 is rotated by +90 degrees from the state in which the polarization direction is incident on the first beam shift plate 31. Therefore, in the second beam shift plate having the same configuration as the first beam shift plate 31, the extraordinary light is refracted in a specific direction in which the ordinary light is refracted by the first beam shift plate 31, and the ordinary light is extraordinary by the first beam shift plate 31. Refracts in the other specific direction where it is refracted. Thus, as shown in FIG. 2, ordinary light and extraordinary light are emitted from the same location of the second beam shift plate 34. Each light emitted from the second beam shift plate 34 is emitted from the emission port 22 and emitted from the emission port 12 of the housing 10.

  Light may enter from the exit port 22 through the exit port 12 of the housing 10. Examples of such a case include an example in which the optical isolator 1 is disposed in a fiber laser device, and light emitted from the fiber laser device is reflected by a workpiece or the like and is incident on the fiber laser device again. . As shown in FIG. 3, the random polarized light incident from the emission port 22 is refracted in different directions by the second beam shift plate 34 and is emitted from different positions of the second beam shift plate 34. Each light emitted from the second beam shift plate 34 is rotated by the polarization rotator 33 by −45 degrees. Each light emitted from the polarization rotator 33 enters the Faraday rotator 32, and the polarization direction rotates +45 degrees and exits from the Faraday rotator 32. That is, the polarization state of the two lights separated by the first beam shift plate 31 is the same as the polarization direction of the second beam shift plate 34. Accordingly, each light emitted from the Faraday rotator 32 is refracted in the first beam shift plate 31 in the same manner as the second beam shift plate 34. For this reason, each light cannot be emitted from the same location of the first beam shift plate 31, and further cannot be emitted from the entrance 21 as shown in FIG. In this way, light is isolated.

  Next, the temperature dependence and suppression of the isolation of the optical isolator will be described.

  FIG. 4 is a diagram illustrating an example of a relationship between a temperature change of a general Faraday rotator and a Faraday rotation angle. As shown in FIG. 4, the Faraday rotator provided in the optical isolator has temperature dependence on the Faraday rotation angle. That is, at the design set temperature, the Faraday rotator rotates the polarization direction of light by +45 degrees as described above, but when the temperature change occurs in the Faraday rotator, the Faraday rotation angle changes. In a general Faraday rotator, the Faraday rotation angle decreases when the temperature is higher than a set temperature. In this case, for example, when reflected light enters the optical isolator, light having a polarization direction between normal light and abnormal light enters the first beam shift plate 31 from the Faraday rotator 32. Then, the first beam shift plate does not refract as designed, and a part of light may be emitted from the entrance 21 as indicated by a dotted line in FIG.

  FIG. 5 is a diagram showing the temperature dependence of the isolation of a general optical isolator. As described above, when the Faraday rotation angle changes with temperature change, a general optical isolator has temperature dependency in isolation as shown in FIG. That is, the isolation tends to deteriorate as the temperature rises or falls from the set temperature.

  Therefore, in the optical isolator of this embodiment, the temperature dependence of isolation is suppressed as described below.

  FIG. 6 is a diagram illustrating the relationship between the distance from the center of the magnetic application unit 40 to the center position of the Faraday rotator 32 and the Faraday rotation angle in the optical isolator 1 of FIG. The Faraday rotation angle of the Faraday rotator 32 varies depending on the strength of the applied magnetic field. In the optical isolator 1 of this embodiment, when the center of the Faraday rotator 32 is located at the center of the magnetic application unit 40 where the intensity of the magnetic field applied to the entire Faraday rotator 32 is the largest, the Faraday rotation angle is about 53. Degree. As apparent from FIG. 5, in the optical isolator 1 of the present embodiment, the center of the Faraday rotator 32 is shifted from the center of the magnetic application unit 40 by about 3.5 mm in order for the Faraday rotation angle to be 45 degrees at the set temperature. It will be in the state which will be in the position. For this reason, as described above, the Faraday rotator 32 is arranged such that the center of the Faraday rotator 32 is unevenly distributed on the incident side surface portion 26 side than the center of the magnetic application unit 40 at the set temperature. The size of this uneven distribution is about 3.5 mm. Thus, the Faraday rotator 32 of the optical isolator 1 rotates the polarization direction of the incident light at the set temperature by +45 degrees.

  FIG. 7 is a diagram illustrating a behavior of the optical isolator 1 due to a temperature change. When the optical isolator 1 is used, for example, as a component such as a fiber laser device, the temperature of the optical isolator 1 may increase as the temperature in the fiber laser device increases due to the use of the fiber laser device. In this case, the temperature of the Faraday rotator 32 rises, and the Faraday rotation angle becomes small as described above due to the temperature dependence of the Faraday rotation angle. However, as shown in FIG. 7, the other end of the bimetal that is the drive unit 50 of the optical isolator 1 moves from the incident side surface 26 side to the emission side surface portion 27 side as the temperature rises as described above. With this movement, the center of the Faraday rotator 32 together with the tube 20 moves toward the center of the magnetic application unit 40. As the Faraday rotator 32 moves, the strength of the magnetic field applied to the Faraday rotator 32 increases and the Faraday rotation angle increases. The decrease in the Faraday rotation angle due to the temperature increase of the Faraday rotator 32 and the increase in the Faraday rotation angle due to the increase in the strength of the magnetic field applied to the Faraday rotator 32 cancel each other. The temperature dependence of the Faraday rotation angle is suppressed.

  FIG. 8 is a diagram showing the temperature dependence of the Faraday rotation angle of the present embodiment. For reference, a line indicating the temperature dependence of the Faraday rotation angle of the general Faraday rotator shown in FIG. 4 is indicated by a broken line. As shown in FIG. 8, the Faraday rotator 32 of the present embodiment moves relative to the magnetic application unit 40 as the temperature changes as described above, so that the temperature dependence of the Faraday rotation angle is suppressed. Further, when the environmental temperature of the optical isolator 1 becomes lower than the set temperature, the Faraday rotation angle increases, but at this time, the bimetal is on the opposite side to the above temperature rise. Therefore, the strength of the magnetic field applied from the magnetic application unit 40 to the Faraday rotator 32 is reduced. For this reason, even when the temperature is decreased, the increase in the Faraday rotation angle due to the temperature decrease and the decrease in the strength of the applied magnetic field cancel each other, and the Faraday rotation of the Faraday rotator 32 as shown in FIG. The temperature dependence of the corners is suppressed.

  FIG. 9 is a diagram showing the temperature dependence of the isolation of the optical isolator 1. In FIG. 9, the isolation of the general optical isolator shown in FIG. 4 is indicated by a broken line. As shown by the solid line in FIG. 9, according to the optical isolator 1, even if the temperature changes, the change in isolation can be suppressed more than a general optical isolator. This is because the temperature dependence of the Faraday rotation angle of the Faraday rotator 32 is suppressed as described above.

つまり、バイメタルの他端の変位量は温度変化と一次の関係となる。 As is apparent from FIG. 6, in the optical isolator 1 of the present embodiment, if the deviation of the center of the Faraday rotator 32 from the center of the magnetic application unit 40 is 1.5 mm to 4.5 mm, the amount of the deviation. A line indicating the relationship between the angle of rotation and the Faraday rotation angle is substantially a straight line. That is, if the amount of deviation is within a range, the amount of movement of the Faraday rotator and the Faraday rotation angle are in a primary relationship. Further, when a bimetal whose one end is fixed is used as the driving unit 50, the displacement amount of the other end of the bimetal is D [mm], and the bimetal bending coefficient is k [K ⁻¹ ]. Is ΔT [K], the length of the displaceable portion of the bimetal is L [mm], and the thickness of the bimetal is t [mm], the displacement amount D at the other end is expressed by the following equation (1). Indicated.

That is, the displacement amount of the other end of the bimetal has a linear relationship with the temperature change.

  As described above, the amount of movement of the Faraday rotator 32 by the bimetal has a primary relationship with the amount of change in temperature, and the Faraday rotation angle is in a range where the amount of movement of the Faraday rotator has a primary relationship as described above. The magnitude of the change in the Faraday rotation angle has a linear relationship with the amount of change in temperature. Therefore, if the temperature change range of these optical isolators is within the range that satisfies these relationships, the change in isolation due to the temperature change of the optical isolator can be more accurately suppressed.

  As described above, according to the optical isolator 1 of the present embodiment, the temperature dependence of the Faraday rotation angle is suppressed by changing the magnetic field applied to the Faraday rotator 32 with a temperature change. For this reason, the temperature dependence of isolation can be suppressed. For this reason, it is not necessary to rotate the first beam shift plate 31 and the second beam shift plate 34 which are polarizers. Therefore, the optical isolator 1 of the present invention can operate stably.

  Further, in the optical isolator 1 of the present embodiment, the Faraday rotator 32 and the magnetic application unit 40 are relatively moved with the temperature change, and the change of the Faraday rotation angle is suppressed with this movement. For this reason, the magnetic field applied to the Faraday rotator 32 can be changed without using an electromagnet, and a permanent magnet can be used as the magnetic application unit. For this reason, the cost required for manufacturing the optical isolator can be reduced.

  In the optical isolator 1 of the present embodiment, the position of the magnetic application unit 40 is fixed, and the drive unit 50 moves the Faraday rotator 32. Since the Faraday rotator generally has a smaller mass than the magnet, the Faraday rotator 32 and the magnetic application unit 40 can be easily moved relative to each other by moving the Faraday rotator.

  Moreover, since the drive part 50 is moving the Faraday rotator 32 by moving the tube 20, it can suppress that a stress is given to the Faraday rotator 32 from the drive part 50. FIG. For this reason, it is possible to suppress degradation of isolation caused by stress.

  Since the first beam shift plate 31 and the second beam shift plate 34 which are a pair of polarizers are fixed to the tube 20 together with the Faraday rotator 32, the first beam is moved along with the movement of the Faraday rotator 32. The relative positions of the shift plate 31 and the second beam shift plate 34 and the Faraday rotator 32 do not change. Therefore, even if the Faraday rotator 32 moves, the optical characteristics of the optical isolator 1 can be prevented from changing.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or equivalent, except the case where it demonstrates especially, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 10 is a diagram illustrating the optical isolator according to the present embodiment. As shown in FIG. 10, in the optical isolator 2 of the present embodiment, the tube 20 is fixed to the tube support portions 16 and 17, and the magnetic application unit 40 is not fixed to the housing and can move along the longitudinal direction of the tube 20. The point that the other end of the drive unit 50 is fixed to the magnetic application unit 40 is mainly different from the optical isolator 1 of the first embodiment.

  The relative positions of the Faraday rotator 32 and the magnetic application unit 40 at the set temperature are the same as the relative positions in the optical isolator 1 of the first embodiment. The bimetal constituting the drive unit 50 moves from the exit side surface 27 side of the light tube 20 to the entrance side surface portion 26 side when the temperature of the optical isolator 2 rises at the other end that is not fixed to the drive fixing unit 18. It is supposed to be configured. That is, the metal side of the bimetal which is the drive unit 50 having a large coefficient of thermal expansion faces the emission side part 27 side, the metal side having a small coefficient of thermal expansion faces the incident side part 26 side, and one end of the bimetal is arranged at the drive part fixing part. 18 is fixed.

  In this optical isolator 2, when the environmental temperature rises from the set temperature, the magnetic application unit 40 moves to the incident side surface 26 side, so that the relative position between the Faraday rotator 32 and the magnetic application unit 40 is shown in FIG. 7. These are the same as those relative positions in the optical isolator 1 of the first embodiment. Therefore, the change in the Faraday rotation angle due to the temperature dependency of the Faraday rotator 32 and the change in the Faraday rotation angle due to the change in the magnetic field applied to the Faraday rotator cancel each other, and the optical isolator 2 has the temperature dependency of isolation. Is suppressed. Further, when the environmental temperature of the optical isolator 2 becomes lower than the set temperature, the magnetic application unit 40 moves to the emission side surface 27 side, so that the Faraday rotation angle increases due to the temperature decrease and the strength of the applied magnetic field decreases. Cancel each other, and the temperature dependence of the isolation of the optical isolator 2 is suppressed.

  According to the optical isolator 2 of the present embodiment, it is not necessary to move an element that propagates light. For this reason, it is possible to suppress the optical path from becoming unstable and the operation of the optical isolator 2 from becoming unstable.

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or equivalent, except the case where it demonstrates especially, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 11 is a diagram showing an optical isolator according to this embodiment. As shown in FIG. 11, in the optical isolator 3 of this embodiment, the tube 20 is fixed to the tube support portions 16 and 17, the magnetic application unit 40 is an electromagnet, the drive unit 50 is not provided, the temperature sensor 42 and the voltage application are performed. The main difference from the optical isolator 1 of the first embodiment is that the portion 45 is provided.

  The voltage application unit 45 applies a voltage to the magnetic application unit 40, and the magnetic application unit 40, which is an electromagnet, generates a magnetic field applied to the Faraday rotator when the voltage is applied.

  The temperature sensor 42 detects the temperature in the housing 10 and inputs information about the temperature to the voltage applying unit 45. The voltage applying unit 45 applies a predetermined voltage to the magnetic applying unit 40 that is an electromagnet so that a magnetic field is applied to the Faraday rotator 32 so that the Faraday rotation angle is 45 degrees at the set temperature. .

  In such an optical isolator 3, when the temperature in the housing 10 rises, the voltage applying unit 45 receives information about the temperature from the temperature sensor 42, and the strength of the magnetic field applied to the Faraday rotator 32 increases. As described above, the voltage applied to the magnetic application unit 40 is increased. As described above, when the temperature of the Faraday rotator 32 increases, the Faraday rotation angle decreases. Therefore, the decrease in the Faraday rotation angle due to the temperature dependence of the Faraday rotator 32 and the increase in the Faraday rotation angle due to the increase in the strength of the magnetic field applied from the electromagnet to the Faraday rotator cancel each other. The temperature dependence of the isolation 3 is suppressed. In addition, when the environmental temperature of the optical isolator 3 becomes lower than the set temperature, the voltage applying unit 45 receives information on the temperature from the temperature sensor 42, so that the magnetic field strength applied to the Faraday rotator 32 is reduced. The voltage applied to the application unit 40 is reduced. Therefore, the increase in the Faraday rotation angle due to the temperature decrease and the decrease in the Faraday rotation angle due to the decrease in the strength of the magnetic field applied from the electromagnet cancel each other, and the temperature dependence of the isolation of the optical isolator 3 is suppressed.

  According to the optical isolator 3 of the present embodiment, it is not necessary to change the positions of the Faraday rotator and the magnetic application unit. Since there is no portion to be moved in this way, an optical isolator having excellent durability can be obtained. Further, since the optical element does not move, the optical path is stabilized, and the operation of the optical isolator 3 can be suppressed from becoming unstable.

  The present invention has been described above by taking the first and second embodiments as examples, but the present invention is not limited to these.

  For example, in the said embodiment, the 1st, 2nd beam shift plates 31 and 34 were used as a polarizer. However, for example, a polarizing plate that transmits only polarized light polarized in a specific direction may be used as the polarizer, and the optical isolator may be configured such that the Faraday rotator is disposed between the pair of polarizing plates. In this case, each polarizing plate is arranged so that the light transmitted through one polarizing plate and the light transmitted through the other polarizing plate are polarized in directions different from each other by 90 degrees.

  In the first embodiment and the second embodiment, a bimetal is used as the drive unit 50. However, the present invention is not limited to this. For example, the tube 20 and the magnetic application unit 40 may be moved by thermal expansion or thermal contraction using a member that thermally expands or contracts in a direction connecting the incident port 21 side and the exit port 22 side.

  In the first embodiment, the tube 20 is moved in order to move the Faraday rotator 32. However, the optical isolator of the present invention may have a configuration in which the tube 20 is not provided and the Faraday rotator 32 is directly moved by the driving unit 50, for example. Even when the Faraday rotator 32 is fixed to the tube and moved together with the tube, the other optical elements may not be fixed to the tube.

  Further, the shape of the permanent magnet or the electromagnet is not particularly limited as long as the Faraday rotation angle of the Faraday rotator 32 becomes a predetermined rotation angle.

  As described above, according to the present invention, it is possible to provide an optical isolator having a small temperature dependency and capable of operating stably, and can be used in industrial fields such as fiber laser devices and optical communications.

DESCRIPTION OF SYMBOLS 1, 2, 3 ... Optical isolator 10 ... Case 11 ... Incident port 12 ... Outlet port 16, 17 ... Tube support part 18 ... Drive part fixing | fixed part 20 ... Tube DESCRIPTION OF SYMBOLS 31 ... 1st beam shift plate 32 ... Faraday rotator 33 ... Polarization rotator 34 ... 2nd beam shift plate 40 ... Magnetic application part 42 ... Temperature sensor 45 ... Voltage provision 50: Drive unit

Claims (8)

A pair of polarizers, a Faraday rotator disposed between the pair of polarizers, and a magnetic application unit that applies a magnetic field to the Faraday rotator,
An optical isolator comprising:
The optical isolator, wherein the intensity of the magnetic field applied to the Faraday rotator changes according to the temperature change so as to suppress a change in Faraday rotation angle due to a temperature change of the Faraday rotator. A drive member that relatively moves the Faraday rotator and the magnetic application unit along the optical path direction;
The magnetic application unit applies a magnetic field whose intensity changes along the optical path direction of light propagating through the Faraday rotator,
The driving member relatively moves the Faraday rotator and the magnetic application unit according to the temperature change so as to suppress a change in Faraday rotation angle due to a temperature change of the Faraday rotator. The optical isolator according to claim 1. The position of the magnetic application unit is fixed,
The optical isolator according to claim 2, wherein the driving member moves the Faraday rotator. A fixing member to which the Faraday rotator is fixed;
The optical isolator according to claim 3, wherein the driving member moves the fixing member. The optical isolator according to claim 4, wherein the pair of polarizers are fixed to the fixing member together with the Faraday rotator. The Faraday rotator is fixed in position,
The optical isolator according to claim 2, wherein the driving member moves the magnetic application unit. The drive member is a bimetal with one end fixed in position,
The optical isolator according to any one of claims 3 to 6, wherein the Faraday rotator and the magnetic application unit move relatively by displacement of the other end of the bimetal due to the temperature change. . The magnetic application unit is composed of an electromagnet,
A voltage application unit for applying a voltage to the electromagnet;
The optical isolator according to claim 1, wherein the voltage application unit changes the voltage according to the temperature change.

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