JP2006243039A - Magneto-optic optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magneto-optic optical component such as a variable optical attenuator, the magneto-optic optical component being small-sized and low in power consumption. <P>SOLUTION: The magneto-optic optical component has optical fiber couples (31a, 32a) to (31d, 32d) which are arranged in parallel in ±X directions, a Faraday rotator 20 which has a plurality of light transmission regions transmitting lights from the optical fibers 31a to 31d respectively, a magnetic domain A constituted with magnetism in a direction not parallel to a light incidence/projection surface, a magnetic domain B constituted with magnetism in the opposite direction from the magnetization direction of the magnetic domain A, and a magnetic domain wall as a border between the magnetic domain A and magnetic domain B, one permanent magnet 55 which applies a designated magnetic field to the Faraday rotator 20, and electromagnets 51a to 51d arranged corresponding to the optical fiber couples (31a, 32a) to (31d, 32d) which apply variable magnetic fields to the Faraday rotator 20 to change the position of the magnetic domain wall nearby the plurality of light transmission regions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magneto-optical component such as a variable optical attenuator used in an optical communication system.

  As a variable optical attenuator, a so-called magneto-optical variable optical attenuator is known that controls the attenuation of light by changing the Faraday rotation angle according to the intensity of an applied magnetic field. The magneto-optic variable optical attenuator has the advantage that it has high mechanical reliability and is easy to miniaturize because there is no mechanical moving part. The magneto-optic variable optical attenuator has a magneto-optic crystal and an electromagnet that applies a magnetic field to the magneto-optic crystal. By controlling the intensity of the magnetic field applied to the magneto-optic crystal by changing the amount of current flowing through the electromagnet, the Faraday rotation angle can be controlled by changing the magnetization intensity of the magneto-optic crystal.

  In Patent Document 1, a plurality of first optical fibers, a plurality of second optical fibers optically coupled to each of the first optical fibers by a light beam, and each light beam pass therethrough. Discloses a magnetization rotation type optical attenuator provided with a magneto-optical crystal provided on the magnetic field and a magnetic field application unit for applying a predetermined magnetic field to the magneto-optical crystal. The magnetic field application unit has one permanent magnet that saturates the magnetization of the magneto-optic crystal and a plurality of electromagnets that rotate the direction of magnetization in each part of the magneto-optic crystal. By rotating the direction of magnetization in each part of the magneto-optical crystal, the magnitude of the component parallel to the light beam of the magnetization vector changes, and an arbitrary Faraday rotation angle can be given to each light beam. In this optical attenuator, since a common magneto-optic crystal is used for a plurality of channels, the apparatus configuration can be simplified.

JP 11-119178 A JP 2004-133387 A

  However, in the optical attenuator disclosed in Patent Document 1, it is necessary to apply a strong magnetic field by an electromagnet in order to rotate the magnetization direction of the magneto-optical crystal in the saturation magnetization state. For this reason, it is necessary to use a large electromagnet or to pass a large current through the coil of the electromagnet. Therefore, there arises a problem that it is difficult to reduce the size and power consumption of the optical attenuator.

  An object of the present invention is to provide a magneto-optic optical component such as a variable optical attenuator having a small size and low power consumption.

  The above object includes two optical waveguide portions that are aligned with each other, and a plurality of optical waveguide pairs arranged in parallel in a predetermined parallel direction, and one optical waveguide portion of the plurality of optical waveguide portion pairs. A plurality of light transmitting regions through which each of the light passes, a magnetic domain A configured by magnetization in a direction not parallel to the light incident / exit surface, and a magnetic domain configured by magnetization in a direction opposite to the magnetization direction of the magnetic domain A B and a domain wall that becomes a boundary between the magnetic domain A and the magnetic domain B, and at least one of the magnetic domain A and the magnetic domain B continuously exists in the vicinity of each of the plurality of light transmission regions; A first magnetic field application system that applies a predetermined magnetic field to the magneto-optic crystal and a plurality of optical waveguide pairs are respectively disposed, and a variable magnetic field is applied to the magneto-optic crystal to transmit the plurality of light beams. The position of the domain wall in the vicinity of the region It is achieved by the magneto-optical device characterized by having a plurality of second magnetic field application system to variably in a direction substantially perpendicular to the parallel direction.

  In the magneto-optical component according to the present invention, each of the domain walls in the vicinity of the plurality of light transmission regions is substantially planar.

  In the magneto-optical component according to the present invention, the domain walls in the vicinity of the plurality of light transmission regions are substantially parallel to a plane including the parallel direction and the light traveling direction.

  According to the present invention, a magneto-optical component such as a variable optical attenuator with a small size and low power consumption can be realized.

  A magneto-optical component according to an embodiment of the present invention will be described with reference to FIGS. First, the operation principle of the magneto-optical component according to this embodiment will be described with reference to FIGS. FIGS. 1 to 3 show a state in which a magnetic field is applied to the Faraday rotator 20 that is a magneto-optic crystal under different conditions. FIG. 1A, FIG. 2A, and FIG. 3A show a state in which the Faraday rotator 20 is viewed in a direction perpendicular to the light incident / exit surface. Here, in optics, the “light incident surface” may be defined as a surface that includes the incident ray and the normal of the boundary surface, but the “light incident / exit surface” in this specification is not this definition, but Faraday rotation. It means a surface on which light is incident / exited in the child 20 (or other optical element). Two regions arranged in the vertical direction in the figure surrounded by two circles near the center of the Faraday rotator 20 are light transmission regions C1 and C2 through which two light beams having the same traveling direction pass. For example, two linearly polarized lights separated from each other by a birefringent plate and having orthogonal polarization directions and traveling from the front of the paper to the rear of the paper are incident on the light transmission regions C1 and C2 of the Faraday rotator 20, respectively. Then, the polarization azimuth is rotated by a predetermined angle and is emitted to the rear side of the paper. A magnetic field having a predetermined distribution is applied to the Faraday rotator 20 by a permanent magnet or an electromagnet described later.

  1 (b), FIG. 2 (b), and FIG. 3 (b) were cut along the DD line shown in FIG. 1 (a), FIG. 2 (a), and FIG. 3 (a), respectively. The magnetic domain structure in the cross section of the Faraday rotator 20 is typically shown. 1 (c), 2 (c), and 3 (c) show the direction and strength of the magnetic field applied in a direction parallel to the optical axis (direction perpendicular to the light incident / exit surface of the Faraday rotator 20). This is schematically represented by the direction and length of the arrow. In FIG. 1C, FIG. 2C, and FIG. 3C, the horizontal direction corresponds to the horizontal position of the cross section of the Faraday rotator 20, and the vertical direction represents the direction parallel to the optical axis. Yes.

  FIGS. 1A to 1C show a state in which a magnetic field is applied to the Faraday rotator 20 using only permanent magnets arranged at predetermined positions, for example. As shown in FIG. 1C, a magnetic field is applied to the left side of the Faraday rotator 20 in the drawing (in other words, in the direction toward the rear of the page in FIG. 1A). On the other hand, a magnetic field is applied to the right side portion of the Faraday rotator 20 in the downward direction in the figure (that is, the direction toward the front of the page in FIG. 1A). The magnetic field component applied to the Faraday rotator 20 changes monotonously in a predetermined direction within the light incident / exit surface. As shown by the arrow in the Faraday rotator 20 in FIG. 1B, the direction of magnetization in the Faraday rotator 20 is the same as the direction of the magnetic field applied to the Faraday rotator 20. Inside the Faraday rotator 20, an upward magnetic field, that is, a magnetic field in the same direction as the light traveling direction becomes dominant. In a region to which a magnetic field having a strength equal to or greater than the saturation magnetic field is applied, a magnetic domain in which magnetization is uniformly set in one direction is formed. Therefore, as shown in FIG. 1B, in the Faraday rotator 20, the region of the magnetic domain A in which the magnetization is uniformly upward (in the same direction as the light traveling direction) is uniformly downward in magnetization. It becomes more dominant than the region of the magnetic domain B (in the direction opposite to the light traveling direction). Thereby, as shown in FIG. 1 (c), the plane of the magnetic domain A and the magnetic domain B as shown in FIGS. 1 (a) and 1 (b) at the position O where the magnetic field perpendicular to the light incident / exit surface becomes zero. A boundary (hereinafter referred to as “domain wall I”) is formed.

  In order to maintain the domain wall I in a substantially flat shape, the position near the position O where the perpendicular magnetic field with respect to the light incident / exit surface shown in FIGS. 1 (c), 2 (c), and 3 (c) becomes zero. It is sufficient that the gradient of the magnetic field strength is sufficiently large. Further, by applying a uniform vertical magnetic field so that the position O is linear in the light incident surface, the domain wall I can be stably moved with good reproducibility. As a result, a magneto-optical optical component having excellent reproducibility can be realized without causing hysteresis of the magnetic domain structure.

  In the state shown in FIGS. 1A to 1C, both the light transmission regions C1 and C2 are completely included in the region of the magnetic domain A. Further, the distance between the light transmission region C1 and the domain wall I (the distance between the center position of the light beam transmitted through the light transmission region C1 and the domain wall I) and the distance between the light transmission region C2 and the domain wall I (transmission through the light transmission region C2). The distance between the center position of the light beam and the domain wall I) is substantially equal. Here, the Faraday rotation angle when the light transmission regions C1 and C2 are in the magnetic domain A region is defined as + θfs (saturated Faraday rotation angle). That is, the two linearly polarized light beams that have entered the Faraday rotator 20 from the front side of the paper and transmitted through the light transmission regions C1 and C2 are both emitted from the paper surface with their polarization directions rotated by + θfs.

  2A to 2C show a state in which a coil of an electromagnet is energized and a magnetic field in the direction opposite to the light traveling direction is applied in addition to the magnetic field generated by the permanent magnet. In this state, as shown in FIG. 2 (c), the position O moves to the left in the figure, and is located approximately at the center of the Faraday rotator 20. As a result, in the Faraday rotator 20, an upward magnetic field (the same direction as the light traveling direction) is applied to the left half, and a downward magnetic field (opposite to the light traveling direction) is applied to the right half. Become. Therefore, as shown in FIG. 2B, the domain wall I also moves in the left direction in the figure and is positioned at the approximate center of the Faraday rotator 20. The Faraday rotator 20 includes a domain A in which the magnetization is uniformly upward (the same direction as the light traveling direction) and a magnetic domain B in which the magnetization is uniformly downward (opposite to the light traveling direction). A region is formed on the left and right halves with a central domain wall I as a boundary. As a result, as shown in FIG. 2A, in the light transmission regions C1 and C2, the domain of the magnetic domain A and the domain of the magnetic domain B exist almost in half, and both magnetic domains are included evenly. Both the Faraday rotation angles θf are 0 °. That is, the two linearly polarized light beams that have entered the Faraday rotator 20 from the front side of the paper and transmitted through the light transmission regions C1 and C2 are emitted to the rear side of the paper without being rotated in the polarization direction.

  FIGS. 3A to 3C show a state where a larger current is passed through the coil of the electromagnet and a magnetic field in the direction opposite to the light traveling direction is further applied. In this state, as shown in FIG. 3C, the position O further moves to the left in the drawing. Thereby, in the Faraday rotator 20, a downward magnetic field (opposite to the light traveling direction) in the figure becomes dominant. Therefore, as shown in FIG. 3B, in the Faraday rotator 20, the region of the magnetic domain B in which the magnetization is uniformly directed downward (opposite to the traveling direction of light) is directed upward in the magnetization. It becomes dominant from the region of the magnetic domain A (in the same direction as the light traveling direction). Thereby, as shown in FIG. 3A, both the light transmission regions C1 and C2 are completely included in the region of the magnetic domain B. The Faraday rotation angle when the light transmission regions C1 and C2 are in the domain of the magnetic domain B is −θfs. That is, the two linearly polarized light beams that have entered the Faraday rotator 20 from the front side of the paper and transmitted through the light transmission regions C1 and C2 are both emitted from the back of the paper with the polarization azimuth rotated by −θfs.

  Thus, by controlling the current flowing through the coil of the electromagnet, the magnetic domain structure in the light transmission regions C1 and C2 of the Faraday rotator 20 by moving the domain wall I is shown in FIG. 1 and in FIG. It can be gradually changed between the states or between the state shown in FIG. 1 and the state shown in FIG. Thereby, the Faraday rotation angle in the light transmission regions C1 and C2 can be continuously changed.

  When the distance between the light transmission region C1 and the domain wall I and the distance between the light transmission region C2 and the domain wall I are different from each other, the magnetic domain structures in the light transmission regions C1 and C2 may be different from each other. For this reason, the Faraday rotation angles in the light transmission regions C1 and C2 are different from each other, and there is a problem that the polarization dependency of the magneto-optical component is increased. On the other hand, as shown in FIGS. 1 to 3, when the distance between the light transmission region C1 and the domain wall I and the distance between the light transmission region C2 and the domain wall I are substantially equal, the light transmission regions C1, C2 The magnetic domain structure is almost the same in any state, and the Faraday rotation angles for the two light beams respectively transmitted through the light transmission regions C1 and C2 are the same in any state. Can be realized.

  FIG. 4 shows a schematic configuration of a variable optical attenuator array 1 in which four transmissive variable optical attenuators 2a to 2d are arrayed as a magneto-optical optical component according to this embodiment. In FIG. 4, the Z axis is taken in the light traveling direction, and the X axis and the Y axis are taken in two directions perpendicular to each other in a plane perpendicular to the Z axis. 4A shows a configuration of the variable optical attenuator array 1 viewed in the −X direction, and FIG. 4B shows a configuration of the variable optical attenuator array 1 viewed in the + Y direction. As shown in FIGS. 4A and 4B, the variable optical attenuator array 1 is arranged on the −Z side and optical fibers (optical waveguide portions) 31a to 31d with input side lenses to which light from the outside is input. And four optical fiber pairs (optical waveguide pairs) (31a, 32a) provided with output side lens-attached optical fibers (optical waveguide portions) 32a to 32d that are arranged on the + Z side and output light to the outside. To (31d, 32d) corresponding to the four channels CH1 to CH4. Four optical fiber pairs (31a, 32a) to (31d, 32d) are arranged in parallel in the ± X directions. The optical fibers 31a to 31d with input side lenses have a configuration in which, for example, a graded index (GI) fiber 42 coaxial with the optical fiber 41 is fused to the tip of the single mode optical fiber 41. The optical fibers 32a to 32d with output side lenses have the same configuration as the optical fibers 31a to 31d with input side lenses, and are aligned and connected to the optical fibers 31a to 31d with input side lenses.

  The variable optical attenuator array 1 has optical elements shared by the channels CH1 to CH4 between the optical fibers 31a to 31d with input side lenses and the optical fibers 32a to 32d with output side lenses. As an optical element, for example, one birefringent plate 10, one half-wave plate 14, one Faraday rotator 20, and one birefringent plate 12 are arranged in this order in the light traveling direction. Has been. The birefringent plates 10 and 12 linearly move the ordinary light component of the light from the input side lens-attached optical fibers 31a to 31d and deviate the abnormal light component by, for example, a predetermined axis deviation amount in the + X direction. Yes. The half-wave plate 14 rotates the polarization direction of incident light by 45 ° in a predetermined direction. The Faraday rotator 20 is manufactured using a magnetic garnet single crystal film. The magnetic garnet single crystal film is grown by, for example, a liquid phase epitaxial (LPE) method, and has a perpendicular magnetic property in which an easy axis of magnetization appears in a direction perpendicular to the film growth surface. The Faraday rotator 20 has, for example, a light incident / exit surface parallel to the film growth surface and perpendicular to the easy magnetization axis.

  Furthermore, the variable optical attenuator array 1 includes the same number (four) of electromagnets (magnetic field application systems) 51a to 51d (four sets in this example) as the number of optical fiber pairs (31a, 32a) to (31d, 32d). 4b) (not shown). One electromagnet 51a to 51d is arranged corresponding to each of the optical fiber pairs (31a, 32a) to (31d, 32d). The electromagnets 51a to 51d include C-shaped yokes 52a to 52d extending relatively long in the directions along the optical fiber pairs (31a, 32a) to (31d, 32d), and a coil 53a wound around the yokes 52a to 52d. To 53d. The yokes 52a to 52d are manufactured using a material such as electromagnetic soft iron or permalloy. Both end portions of the yokes 52a to 52d are opposed to each other with the −Y side end portion of the Faraday rotator 20, for example, interposed therebetween. A variable magnetic field component in the ± Z direction parallel to the easy magnetization axis is applied to the Faraday rotator 20 by adjusting the currents flowing through the coils 53a to 53d.

  The yokes 52a to 52d have permanent magnets 54a to 54d magnetized in the −Z direction (the direction of magnetization is indicated by arrows in FIG. 4A) in part. By providing the permanent magnets 54a to 54d, the yokes 52a to 52d are magnetized even when the coils 53a to 53d are not energized. As a result, in the region on the −Y side of the Faraday rotator 20, the magnetic field component (bias magnetic field) in the −Z direction parallel to the easy magnetization axis is greater than or equal to the saturation magnetic field even when the coils 53 a to 53 d are not energized. It is designed to be applied with strength.

  In the + Y direction of the Faraday rotator 20, a smaller number (for example, one) of permanent magnets (magnetic field application systems) 55 than the number of optical fiber pairs (31a, 32a) to (31d, 32d) (4 groups) are arranged. Has been. The permanent magnet 55 is magnetized in the −Z direction. The permanent magnet 55 applies a magnetic field component in the + Z direction parallel to the easy magnetization axis to the + Y side region of the Faraday rotator 20 with a strength higher than the saturation magnetic field. Here, as the permanent magnets 54a to 54d, 55, a samarium cobalt magnet, a neodymium iron boron magnet, a ferrite magnet, a bond magnet, a semi-hard magnet, or the like can be used.

  In the region to which a magnetic field having a strength equal to or greater than the saturation magnetic field is applied, a magnetic domain in which the magnetization is uniformly set in one direction is formed. Therefore, the Faraday rotator 20 has a two-domain structure. FIG. 5 shows an example of the magnetic domain structure of a part (channels CH1 and CH2) of the Faraday rotator 20 in a state where no current is passed through the coils 53a to 53d. As shown in FIG. 5, in the + Y side region of the Faraday rotator 20 to which a magnetic field in the + Z direction is applied by the permanent magnet 55, the magnetization in the + Z direction is parallel to the easy magnetization axis and not parallel to the light incident / exit surface. Is formed. On the other hand, in the -Y side region of the Faraday rotator 20 to which a magnetic field in the -Z direction is applied by the yokes 52a to 52d partially including the permanent magnets 54a to 54d, the -Z direction opposite to the magnetic domain A is provided. A magnetic domain B constituted by the magnetization of is formed. A domain wall I is formed at the boundary between the magnetic domain A and the magnetic domain B. The domain wall I generally extends substantially parallel to a plane (XZ plane) including the parallel direction of the optical fiber pairs (31a, 32a) to (31d, 32d) and the light traveling direction, and the yokes 52a to 52d. It protrudes to the + Y side in the vicinity of each region sandwiched between both ends. Here, if the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + θfs (for example, + 45 °), the Faraday rotation angle of the magnetic domain B is −θfs (for example, −45 °).

  In the vicinity of the two light transmission regions C1 and C2 (Cch1) through which the two lights of the channel CH1 separated by the birefringent plate 10 are transmitted through the Faraday rotator 20, respectively, the yoke 52a (permanent magnet 54a) is used in the −Z direction. The magnetic field is dominant. That is, the domain wall I is located on the + Y side of the light transmission regions C1 and C2 (Cch1), and almost all of the light transmission regions C1 and C2 (Cch1) are included in the domain of the magnetic domain B. Further, in the vicinity of the two light transmission regions C1 and C2 (Cch2) through which the two lights of the channel CH2 are transmitted through the Faraday rotator 20, a magnetic field in the −Z direction is dominant by the yoke 52b (permanent magnet 54b). It has become. In other words, the domain wall I is located on the + Y side of the light transmission regions C1 and C2 (Cch2), and almost all of the light transmission regions C1 and C2 (Cch2) are included in the domain of the magnetic domain B. The magnetic domain A and the magnetic domain B are continuously present in the vicinity of the light transmission regions Cch1 and Cch2 of a plurality of channels (channels CH1 and CH2 in FIG. 5). The domain wall I is substantially planar in the vicinity of the light transmission regions C1 and C2, and is substantially parallel to the XZ plane. Further, in the light transmission regions C1 and C2 of the light emitted from the same optical fiber with the input side lens, the distance between the light transmission region C1 and the domain wall I (the center position of the light beam transmitted through the light transmission region C1 and the domain wall I). And the distance between the light transmission region C2 and the domain wall I (the distance between the center position of the light beam transmitted through the light transmission region C2 and the domain wall I) are substantially equal.

  By causing a current in the direction of decreasing the magnetization of the yokes 52a to 52d to flow through the coils 53a to 53d and applying to the −Y side region of the Faraday rotator 20 −the magnetic field intensity in the −Z direction is weakened, the domain wall I becomes − Moving in the Y direction, the domain B domain decreases. In FIG. 5, the domain wall I ′ moved to the −Y side from the light transmission regions C <b> 1 and C <b> 2 by flowing predetermined currents through the coils 53 a and 53 b is indicated by broken lines. In this state, almost the entire area of each of the light transmission regions C1 and C2 is included in the region of the magnetic domain A. By adjusting the currents flowing through the coils 53a to 53d, the positions of the domain walls I in the vicinity of the light transmission regions C1 and C2 are independently determined for the channels CH1 to CH4, and the optical fiber pairs (31a, 32a) to (31d, 32d) is variable in the ± Y direction substantially perpendicular to the parallel direction. Thereby, the magnetic domain structure in the light transmission regions C1 and C2 can be adjusted independently for each of the channels CH1 to CH4.

  FIG. 6 shows another example of the magnetic domain structure of the Faraday rotator 20. As shown in FIG. 6, depending on the distribution of the magnetic field applied to the Faraday rotator 20, only one magnetic domain (magnetic domain A) exists continuously in the vicinity of the light transmission regions Cch1 and Cch2 of the plurality of channels. The other magnetic domain (magnetic domain B) may be formed independently for each channel. At this time, the domain wall I is separated for each channel. Even in such a case, the position of the domain wall I in the vicinity of the light transmission regions C1 and C2 can be varied independently in the ± Y direction for each of the channels CH1 to CH4 by adjusting the currents flowing through the coils 53a to 53d. Thus, the magnetic domain structure in the light transmission regions C1 and C2 can be adjusted independently for each of the channels CH1 to CH4.

  Next, the operation of the variable optical attenuator array 1 according to this embodiment will be described. 7 and 8 show an example of the operation of the variable optical attenuator 2a in the variable optical attenuator array 1. FIG. 7A and 7B show a first state in which the light transmission region is completely included in the magnetic domain B region. The first state is a state where no current is passed through the coil 53a, for example. As shown in FIGS. 7A and 7B, the light emitted from the light exit end of the input-side lens-attached optical fiber 31a enters the birefringent plate 10 as light L1. In FIG. 7B, the direction of the optical axis of the birefringent plate 10 is indicated by a double arrow. The light L1 incident on the birefringent plate 10 is separated into ordinary light L2a and extraordinary light L2b. That is, the ordinary light component light L2a travels straight through the birefringent plate 10, and the extraordinary light component light L2b deviates from the birefringent plate 10 by a predetermined amount in the + X direction. The two lights L2a and L2b emitted from the birefringent plate 10 are incident on the half-wave plate 14 and the polarization direction is rotated by 45 ° in a predetermined direction and emitted from the half-wave plate 14.

  The two lights L2a and L2b emitted from the half-wave plate 14 enter the Faraday rotator 20. Here, the light transmission region where the light L2a transmitted through the birefringent plate 10 as ordinary light passes through the Faraday rotator 20, and the light transmission region where the light L2b transmitted through the birefringent plate 10 as abnormal light passes through the Faraday rotator 20. Are both included in the domain B. For this reason, the two lights L2a and L2b incident on the Faraday rotator 20 are both emitted from the Faraday rotator 20 with the polarization direction rotated by 45 ° in a predetermined direction. That is, the light L2a and the light L2b are transmitted through the half-wave plate 14 and the Faraday rotator 20, so that both polarization directions are rotated by 90 °. The two lights L2a and L2b emitted from the Faraday rotator 20 enter the birefringent plate 12. Since the direction of the optical axis of the birefringent plate 12 is the same as the direction of the optical axis of the birefringent plate 10, the light L2a transmitted through the birefringent plate 10 as ordinary light and rotated by 90 ° in the polarization direction passes through the birefringent plate 12. The light L2b that is transmitted as extraordinary light, transmitted through the birefringent plate 10 as extraordinary light, and whose polarization orientation is rotated by 90 ° is transmitted through the birefringent plate 12 as ordinary light. Therefore, the light L2a is offset by a predetermined amount of offset in the + X direction at the birefringent plate 12, and the light L2b travels straight through the birefringent plate 12. Since the amount of axial deviation at the birefringent plate 10 is equal to the amount of axial deviation at the birefringent plate 12, the two lights L2a and L2b are combined and emitted from the birefringent plate 12 as light L3. The light L3 is coupled to the light incident end of the output-side lens-attached optical fiber 32a and output to the outside. In the first state, all the light input from the outside to the optical fiber 31a with the input side lens is output to the outside from the optical fiber 32a with the output side lens without depending on the polarization. Therefore, in the first state, the amount of light attenuation is minimum (almost 0).

  FIG. 8 shows a second state in which the light transmission region is completely included in the region of the magnetic domain A. The second state is a state in which a predetermined current is passed through the coil 53a, for example. As shown in FIG. 8, the light input from the outside and emitted from the light exit end of the optical fiber 31a with the input side lens enters the birefringent plate 10 as light L4. The light L4 incident on the birefringent plate 10 is separated into ordinary light L5a and extraordinary light L5b and emitted from the birefringent plate 10. That is, the ordinary light component light L5a travels straight through the birefringent plate 10, and the extraordinary light component light L5b deviates from the birefringent plate 10 by a predetermined amount in the + X direction. The two lights L5a and L5b emitted from the birefringent plate 10 are incident on the half-wave plate 14 and rotated from the half-wave plate 14 by rotating the polarization direction by 45 ° in a predetermined direction.

  The two lights L5a and L5b emitted from the half-wave plate 14 enter the Faraday rotator 20. Here, the light transmission region where the light L5a transmitted through the birefringent plate 10 as ordinary light passes through the Faraday rotator 20 and the light L5b transmitted through the birefringent plate 10 as extraordinary light and misaligned through the Faraday rotator 20 are transmitted. Both of the light transmission regions are included in the domain of the magnetic domain A. For this reason, the two lights L5a and L5b incident on the Faraday rotator 20 are both emitted from the Faraday rotator 20 with their polarization directions rotated by 45 ° in the opposite directions. That is, the lights L5a and L5b are transmitted through the half-wave plate 14 and the Faraday rotator 20 without being rotated as a result. The two lights L5a and L5b emitted from the Faraday rotator 20 enter the birefringent plate 12. Since the direction of the optical axis of the birefringent plate 12 is the same as the direction of the optical axis of the birefringent plate 10, the light L5a transmitted through the birefringent plate 10 as ordinary light also transmits through the birefringent plate 12 as ordinary light. The light L5b that has passed through 10 as extraordinary light also passes through the birefringent plate 12 as extraordinary light. Therefore, the light L5a travels straight through the birefringent plate 12, and the light L5b is off-axis by a predetermined amount of off-axis in the + X direction again at the birefringent plate 12. Therefore, the two lights L5a and L5b are emitted from the birefringent plate 12 onto different optical paths without being combined. These lights L5a and L5b are not coupled to the light incident end of the optical fiber 32a with an output side lens and are not output to the outside. The light input from the outside to the optical fiber 31a with the input side lens in the second state does not depend on the polarization and is not output at all from the optical fiber 32a with the output side lens. Therefore, in the second state, the amount of light attenuation is maximized.

  In the domain wall motion system as in the present embodiment, the direction of magnetization of the Faraday rotator 20 is not uniform, and the optical characteristics are different in the in-plane direction. Therefore, it may be difficult to reduce the polarization dependence. However, in the present embodiment, the axis deviation direction in the birefringent plate 10 is the + X direction, and the domain wall I is parallel to the XZ plane. Further, as shown in FIG. 7A, the optical paths of the two lights L2a and L2b projected onto the YZ plane perpendicular to the domain wall I are the same. Although not shown, even if the two lights L5a and L5b in the second state are similarly projected onto the YZ plane, the two optical paths match. Since the off-axis direction of the birefringent plate 10 and the domain wall I are parallel, the two separated lights L2a and L2b (L5a and L5b) pass through the same magnetic domain of the Faraday rotator 20 and have the same optical effect. To receive. Therefore, according to this embodiment, a variable optical attenuator with small polarization dependence can be realized.

  As described above, the variable optical attenuator 2a has a light attenuation amount of approximately 0 in the first state and a maximum light attenuation amount in the second state. By controlling the current flowing through the coil 53a of the electromagnet 51a to move the domain wall I in the ± Y direction, the magnetic domain structure in the light transmission region is gradually changed between the first state and the second state. Can be continuously changed. In the present embodiment, the domain walls I in the vicinity of the two light transmission regions through which the two separated lights L2a and L2b (L5a and L5b) pass through the Faraday rotator 20 are planar, and the two light transmission regions are domain walls. Since the distance to I is substantially equal to each other, the two light transmission regions have substantially the same magnetic domain structure in any state. For this reason, the two lights L2a and L2b (L5a and L5b) are subjected to the same optical effect. Therefore, according to this embodiment, a variable optical attenuator with small polarization dependence can be realized. If the magnetic domain structure of the two light transmission regions changes substantially uniformly when the current passed through the coil 53a is changed, the domain wall I may be a curved surface instead of a flat surface. When the variable optical attenuator array 1 is actually manufactured, for example, the position of the yoke 52a with respect to the variable optical attenuator 2a is adjusted in the XY plane, and the yoke 52a is fixed at the position having the least polarization dependence. . In the present embodiment, since the optical path lengths of the light L2a and the light L2b are equal, the polarization mode dispersion is extremely small. Since the operations of the other variable optical attenuators 2b to 2d are the same as the operation of the variable optical attenuator 2a, description thereof is omitted.

  In the above description, the state in which no current is passed through the coil 53a is the first state. However, the present invention is not limited to this, and the state in which no current is passed through the coil 53a may be the second state. A third state (Faraday rotation angle θf is 0 °) in which the magnetic domain A and the magnetic domain B are approximately half each in the light transmission region may be employed. For example, when the state in which no current flows through the coil 53a is the third state, the first and second states can be obtained by flowing positive and negative currents. In this case, since the maximum value of the absolute value of the current in the first and second states can be halved, the power consumption can be reduced to ¼. Further, when the second state is a state in which no current is flowing, the first state can be achieved by flowing a current in a direction opposite to that described above. However, since the yoke 52a is magnetized by the permanent magnet 54a, there is a problem that the magnetization of the yoke 52a is likely to be saturated when a current is passed in the direction in which the magnetization of the yoke 52a increases. Therefore, as described above, there is an advantage that a wider variable width can be ensured by passing a current in the direction of decreasing the magnetization of the yoke 52a.

  In the present embodiment, a domain wall movement method is used in which the domain structure in the light transmission regions C1 and C2 is changed by moving the domain wall I instead of the magnetization rotation method in which the magnetization is uniformly rotated. For this reason, the small electromagnets 51a-51d can be used, or the electric current sent through the coils 53a-53d can be made small. Therefore, according to this embodiment, it is possible to realize a variable optical attenuator array 1 that is small and consumes low power. In general, the response speed of the variable optical attenuator is limited by the inductance of the electromagnet. In the present embodiment, since the electromagnets 51a to 51d can be reduced in size, the inductance can be reduced and the response speed can be increased.

  Furthermore, in the present embodiment, the permanent magnet 55 and the optical elements (birefringent plates 10, 12, 1/2 wavelength plate 14, Faraday rotator 20) are made to be variable light as compared with a configuration in which four variable optical attenuators are simply combined. It can be shared by the attenuators 2a to 2d. Therefore, the number of parts can be reduced, and the variable optical attenuator array 1 can be reduced in size and price. Further, by sharing all the optical elements, the optical axes of the optical fibers 31a to 31d with input side lenses and the optical fibers 32a to 32d with output side lenses can be integrated, so that the variable optical attenuator array 1 The assembly can be simplified.

  Here, a variable optical attenuator array using a multi-domain structure of a Faraday rotator has been proposed in Japanese patent applications (Japanese Patent Application Nos. 2004-15851 and 2004-161413) filed by the present applicant. In the variable optical attenuator array proposed in the above patent application, a plurality of domain walls substantially perpendicular to a plane including the parallel direction of the plurality of variable optical attenuators and the light traveling direction are formed corresponding to each variable optical attenuator. Yes. However, since the variable optical attenuator array proposed in the above patent application requires a relatively large number of permanent magnets and optical elements, it may be difficult to reduce the size and the cost. On the other hand, the variable optical attenuator array 1 according to the present embodiment has a smaller number of permanent magnets and optical elements than the variable optical attenuator array proposed in the above patent application, and thus can be easily reduced in size and price. Can be realized.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above-described embodiment, the optical fibers with a lens 31a to 31d and 32a to 32d including the GI fiber 42 are given as examples of the optical waveguide unit. However, the present invention is not limited to this, and the optical fiber and the lens are used. It may be provided separately, or an optical waveguide may be used instead of the optical fiber. Also, an optical fiber with a lens in which a spherical lens is fused to the tip of the optical fiber can be used.

It is a figure explaining the principle of operation of the magneto-optic optical component by the 1st Embodiment of this invention. It is a figure explaining the principle of operation of the magneto-optic optical component by the 1st Embodiment of this invention. It is a figure explaining the principle of operation of the magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows schematic structure of the magneto-optical optical component by one embodiment of this invention. It is a figure which shows the magnetic domain structure of a part of Faraday rotator. It is a figure which shows the other example of the one part magnetic domain structure of a Faraday rotator. It is a figure which shows operation | movement of the magneto-optical optical component by one embodiment of this invention. It is a figure which shows operation | movement of the magneto-optical optical component by one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Variable optical attenuator array 2a-2d Variable optical attenuator 10, 12 Birefringence plate 14 1/2 wavelength plate 20 Faraday rotator 31a-31d Optical fiber 32a-32d with input side lens Optical fiber 41 with output side lens 41 Single mode optical fiber 42 GI fibers 51a to 51d Electromagnets 52a to 52d Yokes 53a to 53d Coils 54a to 54d, 55 Permanent magnets

Claims (3)

A plurality of optical waveguide pairs each provided with two optical waveguides aligned with each other and arranged in parallel in a predetermined parallel direction;
A plurality of light transmission regions through which light from one of the plurality of optical waveguide portions is transmitted, a magnetic domain A configured by magnetization in a direction not parallel to the light incident / exit surface, and the magnetic domain A A magnetic domain B formed by magnetization in a direction opposite to the magnetization direction, and a domain wall that is a boundary between the magnetic domain A and the magnetic domain B, wherein at least one of the magnetic domain A and the magnetic domain B is a plurality of light transmission regions. A magneto-optic crystal that continuously exists in the vicinity of each, and
A first magnetic field application system for applying a predetermined magnetic field to the magneto-optical crystal;
The magnetic wall is disposed corresponding to the plurality of optical waveguide pairs, and a variable magnetic field is applied to the magneto-optic crystal to position the domain walls in the vicinity of the plurality of light transmission regions in a direction substantially perpendicular to the parallel direction. And a plurality of second magnetic field application systems that are variable. The magneto-optic optical component according to claim 1,
The magneto-optical component according to claim 1, wherein the domain walls in the vicinity of the plurality of light transmission regions are each substantially planar. The magneto-optic optical component according to claim 2,
The magneto-optical component according to claim 1, wherein the domain walls in the vicinity of the plurality of light transmission regions are substantially parallel to a plane including the parallel direction and the traveling direction of the light.

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