JP2005221644A - Magnetooptic optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide magnetooptical components, such as variable optical attenuators, which are used for optical communication systems, have the function of an optical shutter, are small in size, low in price and low in electric power consumption, and are high in speed. <P>SOLUTION: The magnetooptical components have Faraday rotators 20 and 21 respectively provided with polarizing glasses 30, 31 and 32, magnetic domains A constituted by magnetization in a direction perpendicular to light incident and exit surfaces, magnetic domains B constituted by magnetization in a direction reverse from the magnetization direction of the magnetic domains A, magnetic walls 1 serving as boundaries between the magnetic domains A and the magnetic domains B and light transmission regions transmitting light beams, and magnetic field applying mechanisms for respectively varying the positions of the magnetic walls 1 by applying variable magnetic fields to the Faraday rotators 20 and 21. The Faraday rotator 20 is arranged between the polarizing glass 30 and the polarizing glass 31 and the Faraday rotator 21 is arranged between the polarizing glass 31 and the Faraday rotator 32. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  One of magneto-optic optical components used in an optical communication system is a variable optical attenuator. 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 element (magneto-optic crystal) and an electromagnet that applies a magnetic field to the magneto-optic element. By controlling the intensity of the magnetic field applied to the magneto-optical element by changing the amount of current flowing through the coil of the electromagnet, the Faraday rotation angle can be controlled by changing the intensity of magnetization of the magneto-optical element.

  A method for controlling the magnetic field applied to the magneto-optical element is disclosed in Patent Document 1, for example. The magnetic field control method will be described with reference to FIG. FIG. 25A shows a variable optical attenuator, and the variable optical attenuator includes a Faraday rotator (magneto-optic element) 113 and a polarizer 112. The variable optical attenuator includes a permanent magnet 114 and an electromagnet 115 that apply a magnetic field in a direction orthogonal to the Faraday rotator 113, and a variable current source 116 that applies a drive current to the electromagnet 115.

  The direction of the magnetic field applied to the Faraday rotator 113 by the permanent magnet 114 is parallel to the transmission direction of the light beam 117 in the Faraday rotator 113, and the direction of the magnetic field applied to the Faraday rotator 113 by the electromagnet 115 is Faraday rotator. 113 is perpendicular to the magnetic field application direction by the permanent magnet 114 and the transmission direction of the light beam 117.

  In FIG. 25 (b), arrows 102 and 105 are vectors representing the magnetization direction and magnitude in the Faraday rotator 113, and arrows 101 and 103 are vectors representing the direction and magnitude of the applied magnetic field applied from the outside. The arrow 104 is a vector representing the direction and magnitude of the combined magnetic field of the arrows 101 and 103. In the figure, the Z direction is the propagation direction of light in the Faraday rotator 113, and the X direction is orthogonal to the Z direction. The Faraday rotator 113 is in a state of saturation magnetization 102 by the vertical magnetic field 101 by the external permanent magnet 114. Next, when the horizontal magnetic field 103 is applied by the electromagnet 115, the external magnetic field becomes a composite magnetic field 104, and the Faraday rotator 113 is in a state of magnetization 105. The magnitude of the magnetization 105 is the same as the magnitude of the saturation magnetization 102. Therefore, the Faraday rotator 113 is in a saturation magnetization state.

  As described above, a vertical magnetic field is applied in advance to the Faraday rotator 113 by the permanent magnet 114 so that the Faraday rotator 113 is in a saturation magnetization state, and the Faraday rotator 113 is horizontally aligned by the electromagnet 115 disposed in the in-plane direction. Apply a magnetic field. The magnitude of the magnetization component 106 in the Z direction is controlled by rotating the magnetization direction of the Faraday rotator 113 by the angle θ from the magnetization 102 to the magnetization 105 by the combined magnetic field 104 of the two magnetic fields. The Faraday rotation angle changes depending on the magnitude of the magnetization component 106. In the case of this method, since the Faraday rotator 113 is always used in the saturation magnetization region, there is no hysteresis, and the Faraday rotation angle can be changed with good reproducibility.

  However, in the magnetic field application method disclosed in Patent Document 1, it is necessary to increase the in-plane direction magnetic field applied by the electromagnet 115 in order to rotate the magnetization uniformly in a state where the vertical magnetic field is applied by the permanent magnet 114. There is. For this reason, it is necessary to use a large electromagnet 115 or to pass a large current through the coil of the electromagnet 115. Therefore, there is a problem that it is difficult to reduce the size and power consumption of the magneto-optical component.

  The variable optical attenuator as described above is used, for example, to adjust the light amount of each channel in a wavelength division multiplexing optical communication system. The range of attenuation used in practice is from 0 dB to 10 dB (or more). The variable optical attenuator is often used in combination with an optical isolator, but if the variable optical attenuator and the optical isolator are separately provided, the apparatus becomes large and expensive. In order to realize downsizing and cost reduction of the apparatus, a variable optical attenuator with an optical isolator function that integrates both is required. The function of the optical isolator largely depends on the system, but at least an isolation value of 15 dB or more is required. In addition, the variable optical attenuator is also required to have an optical shutter function that blocks light of each channel in wavelength multiplexing communication. The function of the optical shutter depends on the system, but an attenuation of about 40 dB or more is required.

  Several configurations are known in which the function of an optical isolator is added to a variable optical attenuator. Patent Document 2 discloses a variable optical attenuator with an optical isolator function that maintains a reverse loss at a constant value while rotating a polarizer or an analyzer by a motor to make the attenuation variable. In this configuration, a constant reverse loss can always be maintained, but a mechanism for rotating the polarizer or the analyzer is required. Therefore, not only the apparatus is increased in size but also has a problem in long-term reliability because it has a movable part.

  The variable optical attenuator with an optical isolator function disclosed in Patent Document 3 is obtained by adding an optical element having the function of an optical isolator to the optical attenuator. A saturation magnetic field is applied to the first magneto-optical crystal used in the portion functioning as the optical isolator, and a variable magnetic field is applied to the second magneto-optical crystal used in the portion functioning as the optical attenuator. Therefore, there is a problem that the first magneto-optic crystal and the second magneto-optic crystal cannot be arranged close to each other, and the apparatus becomes large. Further, no consideration is given to an optical shutter function that requires an attenuation of 40 dB or more.

  Further, Patent Documents 4 and 5 disclose optical attenuators using two or more magneto-optical crystals, but the optical isolator function is not considered at all. For example, the optical attenuator described in Patent Document 5 achieves an attenuation of 40 dB or more, but does not operate as an optical isolator.

  Patent Document 6 describes an optical attenuator using an optical isolator, but does not show a specific configuration for simultaneously realizing optical isolation and optical attenuation.

  Further, in Patent Document 7, although the Faraday rotation angle optimum for optical attenuation in the optical attenuator is considered, the optical isolator is not considered at all.

As described above, the conventional variable optical attenuator with an optical isolator function has a problem that it is difficult to reduce the size of the apparatus because the optical isolator is simply combined with the variable optical attenuator. Further, each of the above-mentioned patent documents merely discloses a variable optical attenuator, and does not mention any function of the optical isolator. Furthermore, each of the above patent documents does not mention any variable optical attenuator having both functions of an optical isolator and an optical shutter.
Japanese Patent No. 2815509 Japanese Patent No. 2518362 Japanese Patent Laid-Open No. 11-149065 JP-A-11-212043 JP 2001-330810 A JP 2001-526407 A JP-A-9-236784

  SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical optical component such as a variable optical attenuator having an optical shutter function, small size, low price, low power consumption and high speed. Another object of the present invention is to provide a magneto-optical component in which the function of an optical isolator is further added to the above variable optical attenuator and the like.

  The above-described object is that the first to third polarizers arranged in order on the optical path, the magnetic domain A configured by magnetization in a direction not parallel to the light incident / exit surface, and the magnetization direction of the magnetic domain A are opposite to each other First and second magneto-optical elements each including a magnetic domain B configured by magnetization in a direction, a planar magnetic domain wall that is a boundary between the magnetic domain A and the magnetic domain B, and a light transmission region through which a light beam is transmitted A magneto-optical optical component having a magnetic field applying mechanism that applies a variable magnetic field to the first and second magneto-optical elements to change the position of the domain wall, respectively. The second polarizer is disposed between the first polarizer and the second polarizer, and the second magneto-optical element is disposed between the second polarizer and the third polarizer. This is achieved by a magneto-optic optical component characterized in that.

  The magneto-optic optical component of the present invention, wherein the distance between the domain wall of the first magneto-optic element and the light beam, and the distance between the domain wall of the second magneto-optic element and the light beam. Are different from each other.

  The magneto-optic optical component of the present invention, wherein the distance between the domain wall of the first magneto-optic element and the light beam, and the distance between the domain wall of the second magneto-optic element and the light beam. The difference is that it is 0.8 times or more the beam diameter of light.

  Further, the object is to reflect a first polarizer that emits light incident from the outside as a first light beam, and to reflect the first light beam on a different optical path from the first light beam. A reflecting portion that emits as the second light beam traveling in a direction different from the traveling direction of the first light beam; a second polarizer that enters the second light beam and emits the same; A magnetic domain A constituted by magnetization in a direction not parallel to the plane, a magnetic domain B constituted by magnetization in a direction opposite to the magnetization direction of the magnetic domain A, and a planar shape serving as a boundary between the magnetic domain A and the magnetic domain B A magneto-optical element comprising a domain wall, a first light transmission region through which the first light beam is transmitted, and a second light transmission region through which the second light beam is transmitted; the magneto-optical element; A third polarizer disposed between the reflecting portion and the magneto-optical element can be used. It is achieved by the magneto-optical device characterized by having a magnetic field application mechanism by applying a magnetic field to vary the position of the domain wall.

  The magneto-optic optical component according to the invention is characterized in that the distance between the first light beam and the second light beam in the magneto-optical element is at least 0.8 times the beam diameter of the light. And

  According to the present invention, it is possible to realize a magneto-optical optical component such as a variable optical attenuator that has a function of an optical shutter and is small, low cost, low power consumption and high speed. Further, according to the present invention, it is possible to realize a magneto-optical component in which the function of an optical isolator is further added to the above variable optical attenuator or the like.

[First Embodiment]
A magneto-optical component according to the first 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. 1 to 3 show a state in which a magnetic field is applied to the Faraday rotator 20 that is a magneto-optical element 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). A region surrounded by a circle near the center of the Faraday rotator 20 is a light transmission region C through which the light beam is transmitted. For example, linearly polarized light traveling from the front of the paper toward the rear of the paper is incident on the light transmission region C of the Faraday rotator 20, and the polarization direction is rotated by a predetermined angle to exit the rear of the paper. The Faraday rotator 20 is grown by, for example, a liquid phase epitaxy (LPE) method, and is formed of a magnetic garnet single crystal film having a perpendicular magnetization property in which an easy axis of magnetization appears in a direction perpendicular to the film growth surface. On both sides of the Faraday rotator 20, permanent magnets M <b> 1 and M <b> 2 that constitute a magnetic field application mechanism together with an electromagnet described later are arranged. The two permanent magnets M1 and M2 have, for example, substantially the same magnetic force, and their magnetic poles are arranged in opposite directions (magnetization directions are opposite). For example, the magnetic flux inside the permanent magnet M1 is directed from the rear to the front, and the magnetic flux inside the permanent magnet M2 is directed from the front to the rear. Further, the permanent magnet M2 is arranged farther from the light transmission region C of the Faraday rotator 20 than the permanent magnet M1.

  1 (b), 2 (b), and 3 (b) were cut along the lines XX shown in FIGS. 1 (a), 2 (a), and 3 (a), respectively. The magnetic domain structure in the cross section of the Faraday rotator 20 is typically shown. In FIG. 1B, FIG. 2B, and FIG. 3B, the magnetic flux inside the permanent magnet M1 is downward, and the magnetic flux inside the permanent magnet M2 is upward.

  1 (c), 2 (c), and 3 (c) show the direction and strength of a 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 the figure, the horizontal direction corresponds to the horizontal position of the cross section of the Faraday rotator 20, and the vertical direction represents a direction parallel to the optical axis.

  1A to 1C show a state in which a magnetic field is applied to the Faraday rotator 20 only by the permanent magnets M1 and M2. As shown in FIG. 1C, the magnetic field is applied upward in the drawing (that is, toward the rear of the drawing in FIG. 1A) in the left portion of the Faraday rotator 20 near the permanent magnet M1. On the other hand, the magnetic field is applied downward in the drawing (that is, toward the front of the page in FIG. 1A) in the right portion near the permanent magnet M2. 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 by the permanent magnet M1 and the permanent magnet M2. become. The permanent magnets M1 and M2 have substantially the same magnetic force, but the magnetic poles are opposite to each other, and the distance from the Faraday rotator 20 is closer to the permanent magnet M1, and therefore, the Faraday rotator 20 has a configuration shown in FIG. As shown in c), 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 the magnetization is uniformly unidirectional 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 (the same direction as the light traveling direction) is uniformly downward. 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, and the light transmission region C is completely included in the region of the magnetic domain A.

  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, it is possible to realize a magneto-optic optical component having excellent reproducibility and free from hysteresis of the magnetic domain structure, which has been a problem in the past.

Here, the Faraday rotation angle when the light transmission region C is in the magnetic domain A region is defined as + θfs (saturated Faraday rotation angle). That is, the linearly polarized light that has entered the Faraday rotator 20 from the front of the paper and transmitted through the light transmission region C is rotated backward by + θfs and is emitted to the rear of the paper.
In the present embodiment, the magnetization directions of the magnetic domain A and the magnetic domain B are perpendicular to the light incident / exit surface (parallel to the light propagation direction). However, since the Faraday rotation angle of the Faraday rotator 20 varies depending on the light propagation direction component of the magnetization, the magnetization direction may be in another direction as long as it is not parallel to the light incident / exit surface (perpendicular to the light propagation direction). .

  Here, the permanent magnet M1 is moved closer to the Faraday rotator 20 than the permanent magnet M2, so that the light transmission region C enters the region of the magnetic domain A. For example, the magnetic force of the permanent magnet M1 is that of the permanent magnet M2. The light transmission region C may be placed in the region of the magnetic domain A by making it stronger so that the two are substantially equidistant with respect to the Faraday rotator 20. Alternatively, the light transmission region C may be placed in the region of the magnetic domain A using only the permanent magnet M1 without using the permanent magnet M2.

  Next, in FIGS. 2A to 2C, an electromagnet (not shown) 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 magnets M1 and M2. The position O at which the magnetic field perpendicular to the surface is 0 is moved to the left in the figure, and is positioned approximately at the center of the Faraday rotator 20. As a result, as shown in FIG. 2C, a magnetic field upward (in the same direction as the light traveling direction) in the figure is applied to the left half of the Faraday rotator 20 and downward (reverse to the light traveling direction) in the right half. Direction) is applied. 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 (in the same direction as the light traveling direction) and a magnetic domain B in which the magnetization is uniformly downward (in the opposite direction 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. 2B, in the light transmission region C, the region of the magnetic domain A and the region of the magnetic domain B exist almost in half, and both magnetic domains are included equally, so that the Faraday rotation is performed. The angle θf is 0 °. That is, the linearly polarized light that has entered the Faraday rotator 20 from the front side of the paper and has passed through the light transmission region C is emitted to the rear of the paper without rotating the polarization direction.

  Next, in FIGS. 3A to 3C, a larger current is applied to a coil of an electromagnet (not shown) to further apply a magnetic field in the direction opposite to the traveling direction of light, as shown in FIG. Then, the position O at which the magnetic field perpendicular to the light incident / exit surface is 0 is further moved to the left in the figure. As a result, as shown in FIG. 3C, a magnetic field in the downward direction (opposite to the traveling direction of light) is dominant in the Faraday rotator 20. 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 light traveling direction) is directed upward in the magnetization direction. 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. 3C, the light transmission region C is completely included in the region of the magnetic domain B. The Faraday rotation angle when the light transmission region C is in the region of the magnetic domain B is −θfs. That is, the linearly polarized light that has entered the Faraday rotator 20 from the front side of the paper and has passed through the light transmission region C is rotated backward by −θfs and is emitted to the rear of the paper.

  FIG. 4 schematically shows a main configuration of a transmissive variable optical attenuator as a magneto-optical component according to the present 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. Further, X = 0 on the central axis of the light beam. As shown in FIG. 4, the variable optical attenuator includes a polarizing glass (polarizer) 30, a Faraday rotator 20, a polarizing glass 31, and a Faraday rotation in order from the light incident port P <b> 1 (not shown) where light enters from the outside. It has a child 21 and a polarizing glass 32. Instead of the polarizing glasses 30, 31, 32, a wedge birefringent polarizer, a birefringent plate, or the like can be used. A magnetic field structure with a predetermined distribution is applied to the Faraday rotators 20 and 21 by a magnetic field application mechanism (not shown) to form a magnetic domain structure. The Faraday rotator 20 is, for example, a boundary between the magnetic domain A1 in which the magnetization direction is uniformly in the + Z direction, the magnetic domain B1 in which the magnetization direction is uniformly in the -X direction, and the magnetic domains A1 and B1. And a parallel domain wall I1. The Faraday rotator 21 includes a magnetic domain A2 in which the magnetization direction is uniformly the same as the magnetization direction of the magnetic domain A1, a magnetic domain B2 in which the magnetization direction is uniformly the same as the magnetization direction of the magnetic domain B1, and a magnetic domain A2. , B2 and a domain wall I2 substantially parallel to the domain wall I1. The domain wall I1 of the Faraday rotator 20 and the domain wall I2 of the Faraday rotator 21 can be moved in the ± X direction by controlling the current flowing through the coil of the electromagnet. The domain walls I1 and I2 are arranged in different planes. In the configuration shown in FIG. 4, the plane including the domain wall I1 is positioned in the + X direction from the plane including the domain wall I2.

  Here, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + θf1, and the Faraday rotation angle of the magnetic domain B is −θf1. Further, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 21 is + θf2, and the Faraday rotation angle of the magnetic domain B is −θf2. The relative angle between the optical axis of the polarizing glass 30 and the optical axis of the polarizing glass 31 is φ1, and the relative angle between the optical axis of the polarizing glass 31 and the optical axis of the polarizing glass 32 is φ2. Further, the X coordinate of the domain wall I1 of the Faraday rotator 20 is X1, and the X coordinate of the domain wall I2 of the Faraday rotator 21 is X2.

Assuming that the extinction ratio of the polarizing glasses 30, 31, 32 is sufficiently larger than the extinction ratio S of the Faraday rotators 20, 21, the light passing through the magnetic domain Ai passes through the forward (+ Z) transmittance Fai and the magnetic domain Ai. The reverse direction (−Z direction) transmittance Bai of the light is expressed by the following equation.
Fai = (1−S) cos ² (φi−θfi) + Ssin ² (φi−θfi)
Bai = (1−S) cos ² (−φi−θfi) + Ssin ² (−φi−θfi)

On the other hand, the forward transmittance Fbi of the light passing through the magnetic domain Bi and the reverse transmittance Bbi of the light passing through the magnetic domain Bi are expressed by the following equations.
Fbi = (1-S) cos ² (φi + θfi) + Ssin ² (φi + θfi)
Bbi = (1-S) cos ² (−φi + θfi) + Ssin ² (−φi + θfi)

  Here, i = 1 or 2. From these expressions, the relationship of Bai = Fbi and Bbi = Fai is established. For example, when φi = θfi = 45 ° and S = 0.001, Fai = Bbi = 0.999 and Fbi = Bai = 0.001.

The transmittance of light passing through the two Faraday rotators 20 and 21 is the product of the transmittance of each passing magnetic domain. For example, the forward transmittance of light passing through the magnetic domains A1 and A2 is Fa1 × Fa2, and the forward transmittance of light passing through the magnetic domains A1 and B2 is Fa1 × Fb2.
Here, assuming that the light beam is a Gaussian beam, the forward loss and the reverse loss of the variable optical attenuator in which the positions of the domain walls I1 and I2 (X coordinate) are variable while maintaining their relative positions are calculated. φ1 = θf1 = φ2 = θf2 = 45 °, and the extinction ratio of the Faraday rotators 20 and 21 was 0.001.
In the following, it is considered that the range of 0 to 10 dB in the forward loss is used for the light amount adjustment as the variable optical attenuator. Further, it was considered that a reverse loss (isolation) of at least 15 dB or more is necessary for the function of the optical isolator, and a forward loss of 40 dB or more is necessary for the function of the optical shutter.

  FIG. 5 shows the distance between the plane including the domain wall I1 and the plane including the domain wall I2 (the difference between the distance between the domain wall I1 and the central axis of the light beam and the distance between the domain wall I2 and the central axis of the light beam). It is a graph which shows the forward loss and reverse loss of the variable optical attenuator ((X1-X2) / (beam diameter) = 1.5) which is 1.5 times the beam diameter. The horizontal axis of the graph represents the X coordinate (X1 / (beam diameter)) of the domain wall I1 normalized by the beam diameter, and the vertical axis represents the loss (dB). As shown in FIG. 5, as the domain wall I1 moves in the + X direction, the forward loss increases and the reverse loss decreases. In the range where the forward loss is 0 to 10 dB, the backward loss is maintained at 30 dB or more. Therefore, this variable optical attenuator functions as an optical isolator. When the domain wall I1 further moves in the + X direction, the forward loss becomes 60 dB (≧ 40 dB), and this variable optical attenuator functions as an optical shutter. Note that this variable optical attenuator does not function as an optical isolator because the backward loss is small in the region where the forward loss is 40 dB or more. However, when functioning as an optical shutter, it suffices if light can be blocked, and there is no need to function as an optical isolator.

  FIG. 6 shows a variable optical attenuator ((X1-X2) / (beam diameter) = 0.8) in which the distance between the plane including the domain wall I1 and the plane including the domain wall I2 is 0.8 times the beam diameter. It is a graph which shows a forward direction loss and a reverse direction loss. As shown in FIG. 6, in the range where the forward loss is 0 to 10 dB, the reverse loss is maintained at a value of about 15 dB or more. Therefore, this variable optical attenuator functions as an optical isolator. When the domain wall I1 further moves in the + X direction, the forward loss becomes 60 dB (≧ 40 dB), and this variable optical attenuator functions as an optical shutter. This variable optical attenuator does not function as an optical isolator because the reverse loss is small in a region where the forward loss is 40 dB or more, but it does not cause a problem for the same reason as described above.

FIG. 7 is a graph showing the forward loss and the backward loss of the variable optical attenuator ((X1-X2) / (beam diameter) = 0) in which the domain wall I1 and the domain wall I2 are in the same plane. As shown in FIG. 7, when the forward loss is 10 dB, the reverse loss is 1 dB or less. Therefore, this variable optical attenuator does not function as an optical isolator.
Thus, if the distance between the plane including the domain wall I1 and the plane including the domain wall I2 is 0.8 times or more the beam diameter (| X1-X2 | / (beam diameter) ≧ 0.8), the optical isolator and A variable optical attenuator that functions as an optical shutter is obtained.

  FIG. 8 shows the configuration of the transmissive variable optical attenuator 1 according to this embodiment. As shown in FIG. 8, the variable optical attenuator 1 has an optical element in which a polarizing glass 30, a Faraday rotator 20, a polarizing glass 31, a Faraday rotator 21, and a polarizing glass 32 are arranged in this order on the optical path. doing.

  The variable optical attenuator 1 has permanent magnets 66, 67, 68, 69 for applying a saturation magnetic field to the Faraday rotators 20, 21 in a direction parallel to the optical axis, and an optical axis for the Faraday rotators 20, 21. And an electromagnet 70 that applies a variable magnetic field in a parallel direction. The electromagnet 70 has a U-shaped yoke 71 and a coil 72 wound around the yoke 71. A permanent magnet 66 is embedded in the upper part of the drawing at one end (left side in the figure) of the yoke 71, and a permanent magnet 67 is embedded in the lower part of the figure. A permanent magnet 68 is embedded in the upper part of the other end of the yoke 71 (right side in the figure), and a permanent magnet 69 is embedded in the lower part of the figure. The direction of the magnetic poles of the permanent magnets 66 and 68 is rightward in the figure, and the direction of the magnetic poles of the permanent magnets 67 and 69 is leftward in the figure. The permanent magnet 68 is closer to the optical axis than the permanent magnet 66, and the permanent magnet 67 is closer to the optical axis than the permanent magnet 69. By adjusting the positions of the permanent magnets 66, 67, 68 and 69, the positions of the domain wall I 1 of the Faraday rotator 20 and the domain wall I 2 of the Faraday rotator 21 can be adjusted.

  Light introducing windows 73 for transmitting light are provided at both ends of the yoke 71 of the electromagnet 70, respectively. The polarizing glass 30, the Faraday rotator 20, the polarizing glass 31, the Faraday rotator 21, and the polarizing glass 32 are located between both ends of the yoke 71. Light incident from the light introduction window 73 at one end of the yoke 71 passes through the optical axis of each optical element and exits from the light introduction window 73 at the other end of the yoke 71. By energizing the coil 72 of the electromagnet 70, a closed magnetic path passing through the optical element between the yoke 71 and both ends of the yoke 71 is formed, and for the Faraday rotators 20 and 21 to which a saturation magnetic field is applied in advance parallel to the optical axis. A desired magnetic field parallel to the optical axis can be applied. Thereby, the domain walls I1 and I2 of the Faraday rotators 20 and 21 can be moved in the ± X directions.

  Here, the operation of the variable optical attenuator 1 in which the distance between the plane including the domain wall I1 and the plane including the domain wall I2 is, for example, 1.0 times or more of the beam diameter will be described with reference to FIGS. 9 to 14 are views in which the polarization state of the light passing through each optical element constituting the variable optical attenuator 1 is viewed in the + Z direction. FIG. 9A to FIG. 14A show the polarization state of light on the light incident / exit surface Z1 on the −Z side of the polarizing glass 30 (see FIG. 4). FIG. 9B to FIG. 14B show the polarization state of light on the light incident / exit surface Z2 on the + Z side of the polarizing glass 30. FIG. FIG. 9C to FIG. 14C show the polarization state of light on the light incident / exit surface Z <b> 3 on the −Z side of the polarizing glass 31. FIG. 9D to FIG. 14D show the polarization state of the light on the light incident / exit surface Z 4 on the + Z side of the polarizing glass 31. (E) of FIG. 9 thru | or FIG. 14 has shown the polarization state of the light in the light entrance / exit surface Z5 by the side of -Z of the polarizing glass 32. FIG. (F) of FIG. 9 thru | or FIG. 14 has shown the polarization state of the light in the light entrance / exit surface Z6 of the + Z side of the polarizing glass 32. FIG.

  9 to 14 schematically show the polarizing glasses 30, 31, 32 and the Faraday rotators 20, 21 together in the + Z direction for easy understanding. Each of (a) to (f) shows a virtual grid in order to indicate the position of each light. The polarization direction of each light is indicated by a double arrow.

  First, the state of light incident from the light incident port P1 (1) in a state where the magnetic domain A is formed in the light transmission region of both the Faraday rotators 20 and 21 by the magnetic field application mechanism (not shown) (first state) Will be described with reference to FIG. As shown in FIG. 9A, the light L <b> 11 incident from the light incident port P <b> 1 (1) is incident on one surface of the polarizing glass 30. As shown in FIG. 9B, the polarization component parallel to the transmission axis of the polarizing glass 30 (indicated by a double-headed arrow in the drawing) of the light L11 is transmitted through the polarizing glass 30 and emitted as polarized light L12 from the other surface. To do. The light L12 enters the magnetic domain A of the Faraday rotator 20, and as shown in FIG. 9C, the light L12 is rotated from the Faraday rotator 20 as light L13 rotated 45 ° clockwise with respect to the Z axis when viewed in the + Z direction. Exit. Thereby, the polarization direction of the light L13 becomes parallel to the transmission axis of the polarizing glass 31. The light L13 is incident on one surface of the polarizing glass 31, is transmitted without being absorbed by the polarizing glass 31, and is emitted from the other surface as light L14 as shown in FIG. 9D. The light L14 enters the magnetic domain A of the Faraday rotator 21, and as shown in FIG. 9E, the light L14 is rotated from the Faraday rotator 21 as light L15 rotated by 45 ° clockwise about the Z axis when viewed in the + Z direction. Exit. Thereby, the polarization direction of the light L15 becomes parallel to the transmission axis of the polarizing glass 32. The light L15 enters one surface of the polarizing glass 32, is transmitted without being absorbed by the polarizing glass 32, and is emitted as light L16 from the other surface as shown in FIG. 9 (f). The light L16 enters the light exit port P2 (2) and exits to the outside. Therefore, the light incident on the light incident port P1 (1) is emitted from the light emitting port P2 (2).

  Next, the domain walls I1 and I2 are moved by a magnetic field application mechanism (not shown), the magnetic domain B is formed in the light transmission region of the Faraday rotator 20, and the magnetic domain A is formed in the light transmission region of the Faraday rotator 21. The state of light incident from the light incident port P1 (1) in the (second state) will be described with reference to FIG. As shown in FIG. 10A, the light L <b> 21 incident from the light incident port P <b> 1 (1) is incident on one surface of the polarizing glass 30. As shown in FIG. 10 (b), the polarized light component parallel to the transmission axis of the polarizing glass 30 in the light L21 is transmitted through the polarizing glass 30 and emitted as polarized light L22 from the other surface. The light L22 is incident on the magnetic domain B of the Faraday rotator 20, and as shown in FIG. 10C, the Faraday rotator 20 is obtained as light L23 having a polarization orientation rotated 45 ° counterclockwise about the Z axis when viewed in the + Z direction. Emanates from. Thereby, the polarization direction of the light L23 becomes perpendicular to the transmission axis of the polarizing glass 31. The light L23 is absorbed by the polarizing glass 31 and does not pass through the polarizing glass 31. Therefore, the light incident on the light incident port P1 (1) does not exit from the light exit port P2 (2).

  Next, the light incident port in a state (third state) in which the domain walls I1 and I2 are further moved by a magnetic field application mechanism (not shown) and the magnetic domain B is formed in the light transmission regions of both the Faraday rotators 20 and 21. The state of light incident from P1 (1) will be described with reference to FIG. As shown in FIG. 11A, the light L31 incident from the light incident port P1 (1) is incident on one surface of the polarizing glass 30. As shown in FIG. 11B, the polarized light component parallel to the transmission axis of the polarizing glass 30 in the light L31 passes through the polarizing glass 30 and is emitted as polarized light L32 from the other surface. The light L32 is incident on the magnetic domain B of the Faraday rotator 20, and as shown in FIG. 11C, the Faraday rotator 20 is obtained as light L33 whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the + Z direction. Emanates from. Thereby, the polarization direction of the light L33 becomes perpendicular to the transmission axis of the polarizing glass 31. The light L33 is absorbed by the polarizing glass 31 and does not pass through the polarizing glass 31. Therefore, the light incident on the light incident port P1 (1) does not exit from the light exit port P2 (2).

  Note that the light L23 in the second state and the light in the third state due to an error in the Faraday rotator 20, an angular shift in the Faraday rotation angle associated with a change in temperature wavelength, an angular shift in the optical axis of each optical element, or the like. The polarization direction of the light L33 may not be perpendicular to the transmission axis of the polarizing glass 31, and some light may pass through the polarizing glass 31. In the second state, the light transmitted through the polarizing glass 31 enters the light exit port P2 (2) and exits to the outside in the same manner as in the first state shown in FIGS. On the other hand, in the third state, the light transmitted through the polarizing glass 31 enters the magnetic domain B of the Faraday rotator 21 and rotates in the polarization direction so as to be perpendicular to the transmission axis of the polarizing glass 32. The light does not enter the port P2 (2). Therefore, in the third state, a higher attenuation can be obtained than in the second state.

  Next, the state of light incident from the light exit port P2 (2) in the first state will be described with reference to FIG. As shown in FIG. 12 (f), the light L 41 incident from the light exit port P 2 (2) is incident on one surface of the polarizing glass 32. As shown in FIG. 12 (e), the polarized light component parallel to the transmission axis of the polarizing glass 32 in the light L41 is transmitted through the polarizing glass 32 and emitted as polarized light L42 from the other surface. The light L42 enters the magnetic domain A of the Faraday rotator 21, and as shown in FIG. 12D, the light L42 is rotated from the Faraday rotator 21 as light L43 rotated 45 ° clockwise with respect to the Z axis when viewed in the + Z direction. Exit. Thereby, the polarization direction of the light L43 becomes perpendicular to the transmission axis of the polarizing glass 31. The light L43 is absorbed by the polarizing glass 31 and does not pass through the polarizing glass 31. Therefore, the light incident on the light exit port P2 (2) does not exit from the light entrance port P1 (1).

  Next, the state of light incident from the light emission port P2 (2) in the second state will be described with reference to FIG. As shown in FIG. 13 (f), the light L 51 incident from the light output port P 2 (2) enters one surface of the polarizing glass 32. As shown in FIG. 13 (e), the polarized light component parallel to the transmission axis of the polarizing glass 32 in the light L51 is transmitted through the polarizing glass 32 and emitted from the other surface as polarized light L52. The light L52 enters the magnetic domain A of the Faraday rotator 21, and as shown in FIG. 13 (d), the light L53 is rotated from the Faraday rotator 21 as light L53 rotated 45 ° clockwise with respect to the Z axis when viewed in the + Z direction. Exit. Thereby, the polarization direction of the light L53 becomes perpendicular to the transmission axis of the polarizing glass 31. The light L53 is absorbed by the polarizing glass 31 and does not pass through the polarizing glass 31. Therefore, the light incident on the light exit port P2 (2) does not exit from the light entrance port P1 (1).

  Next, the state of light incident from the light emission port P2 (2) in the third state will be described with reference to FIG. As shown in FIG. 14 (f), the light L 61 incident from the light exit port P 2 (2) is incident on one surface of the polarizing glass 32. As shown in FIG. 14E, the polarized light component parallel to the transmission axis of the polarizing glass 32 in the light L61 passes through the polarizing glass 32 and is emitted as polarized light L62 from the other surface. The light L62 is incident on the magnetic domain B of the Faraday rotator 21, and as shown in FIG. 14D, the Faraday rotator 21 is obtained as light L63 rotated by 45 ° counterclockwise with respect to the Z axis as viewed in the + Z direction. Emanates from. Thereby, the polarization direction of the light L63 is parallel to the transmission axis of the polarizing glass 31. The light L63 is incident on one surface of the polarizing glass 30, is transmitted without being absorbed by the polarizing glass 31, and is emitted as light L64 from the other surface as shown in FIG. The light L64 enters the magnetic domain B of the Faraday rotator 20, and as shown in FIG. 14 (b), the Faraday rotator 21 is obtained as light L65 having a polarization orientation rotated 45 ° counterclockwise about the Z axis when viewed in the + Z direction. Emanates from. Thereby, the polarization direction of the light L65 becomes parallel to the transmission axis of the polarizing glass 30. The light L65 is incident on one surface of the polarizing glass 30, is transmitted without being absorbed by the polarizing glass 30, and is emitted as light L66 from the other surface as shown in FIG. The light L66 enters the light incident port P1 (1) and exits to the outside. Therefore, the light incident on the light exit port P2 (2) exits from the light entrance port P1 (1).

  Here, in the second state, the light transmitted through the polarizing glass 31 due to the angular deviation of the Faraday rotation angle, the angular deviation of the optical axis of each optical element, or the like is the third state shown in FIGS. In the same manner as in the state, the light enters the light incident port P1 (1) and exits to the outside. On the other hand, in the first state, the light transmitted through the polarizing glass 31 enters the magnetic domain A of the Faraday rotator 20 and rotates in the polarization direction so as to be perpendicular to the transmission axis of the polarizing glass 30. The light does not enter the port P1 (1). Therefore, a higher attenuation can be obtained in the first state than in the second state.

  FIG. 15 schematically shows the configuration of a variable optical attenuator 1 'as a modification of the magneto-optical component according to this embodiment. As shown in FIG. 15, the permanent magnets 66, 67, 68 and 69 may be arranged away from the yoke 71 of the electromagnet 70 (not shown). Further, without providing the electromagnet 70, the domain walls I1 and I2 of the Faraday rotators 20 and 21 may be moved by making the positions of the permanent magnets 66, 67, 68 and 69 variable.

  FIG. 16 schematically shows a configuration of a variable optical attenuator 1 ″ as another modification of the magneto-optical component according to the present embodiment. As shown in FIG. 16, the polarizing glass 30, the Faraday rotator 20, the polarizing glass 31, the Faraday rotator 21, and the polarizing glass 32 are arranged so that the light incident / exit surface is inclined with respect to the optical path. In this example, each optical element is arranged such that the upper end in the figure is inclined to the right, and the respective light incident / exit surfaces are substantially parallel to each other. Since the light beam is refracted every time it enters each optical element, the optical path gradually moves downward in the figure. As a result, the light beam is incident on the Faraday rotator 20 in the region α at the center of the light incident / exit surface, while the Faraday rotator 21 is incident on the region β below the center of the light incident / exit surface. . A magnetic field is applied to the Faraday rotators 20 and 21 by common permanent magnets 66 and 67. However, the distance between the magnetic wall I1 of the Faraday rotator 20 and the light beam, and the magnetic wall I2 of the Faraday rotator 21 and the light beam. Are different from each other. By adjusting the tilt angle of each optical element, the difference between the distance between the domain wall I1 and the light beam and the distance between the domain wall I2 and the light beam can be adjusted. Further, by arranging each optical element so as to be inclined with respect to the optical path, it is possible to prevent the reflected return light from each optical element from being coupled to an optical waveguide mechanism (not shown) such as an optical waveguide. In this example, the light incident / exit surfaces of the optical elements are substantially parallel to each other, but the tilt direction and tilt angle of each optical element may be set independently. In addition, the tilt direction and tilt angle of each optical element may be adjusted so that the optical axes of the incident light and the emitted light coincide with each other. In this way, since, for example, two optical waveguide mechanisms that allow light to enter and exit each optical element can be arranged coaxially, the assembly of the magneto-optical component is facilitated.

  According to the variable optical attenuators 1, 1 ′, 1 ″ according to the present embodiment, the magnetic domain in the light transmission region C is moved by moving the domain wall I instead of the magnetization rotation method that rotates the magnetization of the magneto-optical element uniformly. Since the domain wall motion method for changing the structure is used, the Faraday rotation angle can be changed with a small electromagnet, and a small and low power consumption magneto-optic optical component can be realized. Further, the response speed is usually limited by L (inductance) of the electromagnet, and if the electromagnet can be miniaturized, L can be reduced, so that the response speed can be increased.

  Further, according to the variable optical attenuator 1, 1 ′, 1 ″ according to the present embodiment, the domain walls I of the Faraday rotators 20 and 21 are moved by the magnetic field applying mechanism, and the first state, the second state, and the second state. By gradually changing between the three states, the attenuation of the light incident on the light incident port P1 (1) can be continuously changed. The variable optical attenuators 1, 1 ′, and 1 ″ function as optical isolators because light incident on the light exit port P 2 (2) does not exit from the light entrance port P 1 (1) in the first and second states. It also has a function. Further, the variable optical attenuators 1, 1 ', 1' 'have a function as an optical shutter because a very high attenuation can be obtained in the third state. In the conventional optical attenuator, the range in which high attenuation can be obtained may be narrow, but in the variable optical attenuator 1, 1 ′, 1 ″, the attenuation is saturated in the high attenuation region as shown in FIGS. Therefore, the operation as an optical shutter is stable. In the variable optical attenuator 1, 1 ′, 1 ″, the position of the permanent magnet is changed to adjust the position of the domain wall I1 of the Faraday rotator 20 and the position of the domain wall I2 of the Faraday rotator 21, so that a current flows in the coil of the electromagnet. A so-called dark light attenuator that blocks light when no light is flowing can also be realized.

Generally, a high-attenuation magneto-optic variable optical attenuator having an optical shutter function is a two-stage configuration using two Faraday rotators, like the variable optical attenuators 1, 1 ′, 1 ″ of the present embodiment. is required. On the other hand, in order to add an optical isolator function to the variable optical attenuator, a three-stage configuration using three Faraday rotators is simply required.
In this embodiment, paying attention to the fact that it is not necessary to function as an optical isolator when blocking light, a multifunctional optical component is realized with a simple configuration of two-stage type. Since the variable optical attenuator 1, 1 ′, 1 ″ according to the present embodiment has a simple element configuration, it can be reduced in size and price.

[Second Embodiment]
Next, a magneto-optical component according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 17 schematically shows the configuration of the reflective variable optical attenuator 2 as a magneto-optical component according to this embodiment. In FIG. 17, the Z axis is taken in the light traveling direction, and the direction in which the light from the outside is directed to the two-surface reflector (reflecting portion) 38 provided in the reflective variable attenuator 2 is the + Z direction. Further, the X axis and the Y axis are taken in two directions orthogonal to each other in a plane orthogonal to the Z axis. FIG. 17A shows the configuration of the reflective variable optical attenuator 2 viewed in the + Y direction, and FIG. 17B shows the configuration of the reflective variable optical attenuator 2 viewed in the −X direction.

  As shown in FIGS. 17A and 17B, the reflective variable attenuator 2 is connected to two optical fibers 41 and 42. The −Z side end of the optical fiber 41 is a light incident port P1 (1) through which light enters from the outside. The + Z side end of the optical fiber 42 is a light emission port P2 (2) for emitting light to the outside. In the + Z direction of each of the optical fibers 41 and 42, lenses 51 and 52 for converting divergent light emitted from the optical fibers 41 and 42 into parallel light are respectively disposed.

  A polarizing glass 30 is disposed in the + Z direction of the lens 51, and a polarizing glass 32 is disposed in the + Z direction of the lens 52. The two polarizing glasses 30 and 32 are arranged adjacent to each other in parallel to the XY plane and have a light incident / exit surface perpendicular to the Z axis. A Faraday rotator 20 is disposed in the + Z direction of the polarizing glasses 30 and 32. A magnetic field structure having a predetermined distribution is applied to the Faraday rotator 20 by a magnetic field application mechanism (not shown) to form a magnetic domain structure. The domain wall I of the Faraday rotator 20 is parallel to the YZ plane, and can be moved in the ± X directions (indicated by arrows in the figure) by controlling the current flowing through the coil of the electromagnet.

  A polarizing glass 31 is arranged in the + Z direction of the Faraday rotator 20. On the + Z side of the polarizing glass 31, for example, a two-surface reflector 38 such as a right-angle prism is disposed. The two-surface reflector 38 has a function of changing the optical path by two-surface reflection. The dihedral reflector 38 may have a structure in which two reflecting mirrors are combined in addition to the right-angle prism as shown in FIG. In the Faraday rotator 20, a light transmission region through which light traveling in the + Z direction is transmitted and a light transmission region through which light reflected by the two-surface reflector 38 and transmitted in the −Z direction are transmitted are formed at different positions.

  Next, the operation of the reflective variable optical attenuator 2 according to this embodiment will be described. 18 to 23 are diagrams in which the polarization state of light passing through each optical element constituting the reflective variable attenuator 2 is viewed in the + Z direction. (A) of FIG. 18 thru | or FIG. 23 has shown the polarization state of the light in the light entrance / exit surface Z1 by the side of -Z of polarizing glass 30 and 32 (refer FIG. 17). (B) of FIG. 18 thru | or FIG. 23 has shown the polarization state of the light in the light entrance / exit surface Z2 of the + Z side of polarizing glass 30 and 32. FIG. (C) of FIG. 18 thru | or FIG. 23 has shown the polarization state of the light in the light entrance / exit surface Z3 of the -Z side of the polarizing glass 31. FIG. (D) of FIG. 18 thru | or FIG. 23 has shown the polarization state of the light in the light entrance / exit surface Z4 of the + Z side of the polarizing glass 31. FIG.

  18 to 23, for easy understanding, the polarizing glasses 30 and 32, the Faraday rotator 20, and the polarizing glass 31 are viewed in the + Z direction, and the two-surface reflector 38 is viewed in the -Y direction. The state is also schematically shown. Each of (a) to (d) shows a virtual grid in order to indicate the position of each light. The polarization direction of each light is indicated by a double arrow.

  First, the state of light incident from the light incident port P1 (1) when the magnetic domain A is formed in the Faraday rotator 20 by the magnetic field application mechanism (not shown) will be described with reference to FIG. To do. In the first state, the two light transmission regions where the light traveling in the + Z direction and the light traveling in the −Z direction are transmitted through the Faraday rotator 20 are both completely included in the domain A. As shown on the left side of FIG. 18A, the light L111 incident from the light incident port P <b> 1 (1) is incident on one surface of the polarizing glass 30. As shown on the left side of FIG. 18B, the polarization component parallel to the transmission axis of the polarizing glass 30 in the light L111 passes through the polarizing glass 30 and is emitted as polarized light L112 from the other surface. The light L 112 is incident on the magnetic domain A of the Faraday rotator 20. As shown on the left side of FIG. 18C, the light L112 is emitted from the Faraday rotator 20 as light L113 whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the + Z direction. Thereby, the polarization direction of the light L113 is parallel to the transmission axis of the polarizing glass 31. The light L113 is incident on one surface of the polarizing glass 31, is transmitted without being absorbed by the polarizing glass 31, and is emitted as light L114 from the other surface as shown on the left side of FIG. The light L114 is reflected by the two-surface reflector 38, and enters the other surface of the polarizing glass 31 as light L115 whose optical path has been changed, as shown on the right side of FIG.

  The light L115 is transmitted without being absorbed by the polarizing glass 31, and is emitted as the light L116 from the other surface of the polarizing glass 31, as shown on the right side of FIG. The light L 116 is incident on the magnetic domain A of the Faraday rotator 20. Since the Faraday rotator 20 has nonreciprocity, as shown on the right side of FIG. 18B, the light L116 is a light L117 whose polarization orientation is rotated by 45 ° clockwise about the Z axis when viewed in the + Z direction. Is emitted from the Faraday rotator 20. Thereby, the polarization direction of the light L117 is parallel to the transmission axis of the polarizing glass 32. The light L117 enters one surface of the polarizing glass 32, is transmitted without being absorbed by the polarizing glass 32, and is emitted as light L118 from the other surface as shown on the right side of FIG. The light L118 enters the light exit port P2 (2) and exits to the outside. Therefore, the light incident on the light incident port P1 (1) is emitted from the light emitting port P2 (2).

  Next, the domain wall I is moved in the + X direction by a magnetic field application mechanism (not shown), the magnetic domain A is formed in the + X side region of the Faraday rotator 20, and the magnetic domain B is formed in the −X side region ( The state of light incident from the light incident port P1 (1) in the second state will be described with reference to FIG. In the second state, the light transmission region in which the light traveling in the + Z direction is transmitted through the Faraday rotator 20 is completely included in the region of the magnetic domain A, and the light transmission in the −Z direction is transmitted through the Faraday rotator 20. The region is completely contained within the region of magnetic domain B. As shown on the left side of FIG. 19A, the light L <b> 121 incident from the light incident port P <b> 1 (1) is incident on one surface of the polarizing glass 30. As shown on the left side of FIG. 19B, the polarized light component parallel to the transmission axis of the polarizing glass 30 in the light L121 is transmitted through the polarizing glass 30 and emitted as polarized light L122 from the other surface. The light L122 is incident on the magnetic domain A of the Faraday rotator 20. As shown on the left side of FIG. 19 (c), the light L122 is emitted from the Faraday rotator 20 as light L123 having a polarization orientation rotated 45 ° clockwise about the Z axis when viewed in the + Z direction. Thereby, the polarization direction of the light L123 is parallel to the transmission axis of the polarizing glass 31. The light L123 is incident on one surface of the polarizing glass 31, is transmitted without being absorbed by the polarizing glass 31, and is emitted as light L124 from the other surface as shown on the left side of FIG. The light L124 is reflected by the two-surface reflector 38, and enters the other surface of the polarizing glass 31 as light L125 whose optical path has been changed, as shown on the right side of FIG.

  The light L125 is transmitted without being absorbed by the polarizing glass 31, and is emitted as the light L126 from the other surface of the polarizing glass 31, as shown on the right side of FIG. The light L126 is incident on the magnetic domain B of the Faraday rotator 20. As shown on the right side of FIG. 19B, the light L126 is emitted from the Faraday rotator 20 as light L127 whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the + Z direction. As a result, the polarization direction of the light L127 becomes perpendicular to the transmission axis of the polarizing glass 32. The light L127 is absorbed by the polarizing glass 32 and does not pass through the polarizing glass 32. Therefore, the light incident on the light incident port P1 (1) does not exit from the light exit port P2 (2).

  Next, the domain wall I is further moved in the + X direction by a magnetic field application mechanism (not shown), and is incident from the light incident port P1 (1) in the state where the magnetic domain B is formed in the Faraday rotator 20 (third state). The state of light will be described with reference to FIG. In the third state, the two light transmission regions in which the light traveling in the + Z direction and the light traveling in the −Z direction are transmitted through the Faraday rotator 20 are completely included in the domain B. As shown on the left side of FIG. 20A, the light L131 incident from the light incident port P <b> 1 (1) is incident on one surface of the polarizing glass 30. As shown on the left side of FIG. 20B, the polarized light component parallel to the transmission axis of the polarizing glass 30 in the light L131 is transmitted through the polarizing glass 30 and emitted as polarized light L132 from the other surface. The light L132 is incident on the magnetic domain B of the Faraday rotator 20. As shown on the left side of FIG. 20C, the light L132 is emitted from the Faraday rotator 20 as light L133 having a polarization orientation rotated 45 ° counterclockwise about the Z axis when viewed in the + Z direction. Thereby, the polarization direction of the light L133 becomes perpendicular to the transmission axis of the polarizing glass 31. The light L 133 is absorbed by the polarizing glass 31 and does not pass through the polarizing glass 31. Therefore, the light incident on the light incident port P1 (1) does not exit from the light exit port P2 (2).

  Note that the polarization direction of the light L127 in the second state is changed to the polarizing glass 32 due to a manufacturing error of the Faraday rotator 20, an angular shift of the Faraday rotation angle due to a temperature wavelength change, or an optical axis angular shift of each optical element. It is possible that some of the light passes through the polarizing glass 32 without being perpendicular to the transmission axis. In addition, the polarization orientation of the light L133 in the third state may not be perpendicular to the transmission axis of the polarizing glass 31, and some light may be transmitted through the polarizing glass 31. In the second state, the light transmitted through the polarizing glass 32 enters the light exit port P2 (2) and exits to the outside. On the other hand, in the third state, the light transmitted through the polarizing glass 31 is reflected by the two-surface reflector 38 and enters the magnetic domain B of the Faraday rotator 20 so as to be perpendicular to the transmission axis of the polarizing glass 32. Since the polarization azimuth is rotated, it does not enter the light exit port P2 (2). Therefore, in the third state, a higher attenuation can be obtained than in the second state.

  Next, the state of light incident from the light emission port P2 (2) in the first state will be described with reference to FIG. As shown on the right side of FIG. 21A, the light L <b> 141 that has entered from the light exit port P <b> 2 (2) enters one surface of the polarizing glass 32. As shown on the right side of FIG. 21B, the polarized light component parallel to the transmission axis of the polarizing glass 32 in the light L141 is transmitted through the polarizing glass 32 and emitted as polarized light L142 from the other surface. The light L 142 is incident on the magnetic domain A of the Faraday rotator 20. As shown on the right side of FIG. 21 (c), the light L142 is emitted from the Faraday rotator 20 as light L143 having a polarization orientation rotated 45 ° clockwise about the Z axis when viewed in the + Z direction. Thereby, the polarization direction of the light L143 becomes perpendicular to the transmission axis of the polarizing glass 31. The light L143 is absorbed by the polarizing glass 31 and does not pass through the polarizing glass 31. Therefore, the light incident on the light exit port P2 (2) does not exit from the light entrance port P1 (1).

  Next, the state of light incident from the light emission port P2 (2) in the second state will be described with reference to FIG. As shown on the right side of FIG. 22A, the light L <b> 151 that has entered from the light exit port P <b> 2 (2) enters one surface of the polarizing glass 32. As shown on the right side of FIG. 22B, the polarized light component parallel to the transmission axis of the polarizing glass 32 in the light L151 is transmitted through the polarizing glass 32 and is emitted as polarized light L152 from the other surface. The light L152 is incident on the magnetic domain B of the Faraday rotator 20. As shown on the right side of FIG. 22C, the light L152 is emitted from the Faraday rotator 20 as light L153 whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the + Z direction. As a result, the polarization direction of the light L 153 is parallel to the transmission axis of the polarizing glass 31. The light L153 is incident on one surface of the polarizing glass 31, is transmitted without being absorbed by the polarizing glass 31, and is emitted from the other surface as light L154 as shown on the right side of FIG. The light L154 is reflected by the two-surface reflector 38 and enters the other surface of the polarizing glass 31 as light L155 whose optical path has been changed, as shown on the left side of FIG.

  The light L155 is transmitted without being absorbed by the polarizing glass 31, and is emitted as light L156 from the other surface of the polarizing glass 31, as shown on the left side of FIG. The light L156 is incident on the magnetic domain A of the Faraday rotator 20. As shown on the left side of FIG. 22B, the light L156 is emitted from the Faraday rotator 20 as light L157 whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the + Z direction. Thereby, the polarization direction of the light L157 becomes perpendicular to the transmission axis of the polarizing glass 30. The light L157 is absorbed by the polarizing glass 30 and does not pass through the polarizing glass 30. Therefore, the light incident on the light exit port P2 (2) does not exit from the light entrance port P1 (1).

  Next, the state of light incident from the light emission port P2 (2) in the third state will be described with reference to FIG. As shown on the right side of FIG. 23A, the light L161 incident from the light exit port P2 (2) is incident on one surface of the polarizing glass 32. As shown on the right side of FIG. 23B, the polarized light component parallel to the transmission axis of the polarizing glass 32 in the light L161 passes through the polarizing glass 32 and is emitted as polarized light L162 from the other surface. The light L162 is incident on the magnetic domain B of the Faraday rotator 20. As shown on the right side of FIG. 23 (c), the light L162 is emitted from the Faraday rotator 20 as light L163 rotated 45 ° counterclockwise about the Z axis when the polarization direction is viewed in the + Z direction. Thereby, the polarization direction of the light L163 is parallel to the transmission axis of the polarizing glass 31. The light L163 is incident on one surface of the polarizing glass 31, is transmitted without being absorbed by the polarizing glass 31, and is emitted from the other surface as light L164 as shown on the right side of FIG. The light L164 is reflected by the two-surface reflector 38 and is incident on the other surface of the polarizing glass 31 as light L165 whose optical path has been changed, as shown on the left side of FIG.

  The light L165 is transmitted without being absorbed by the polarizing glass 31, and is emitted as the light L166 from the other surface of the polarizing glass 31, as shown on the left side of FIG. The light L166 is incident on the magnetic domain B of the Faraday rotator 20. As shown on the left side of FIG. 23B, the light L166 is emitted from the Faraday rotator 20 as light L167 whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the + Z direction. Thereby, the polarization direction of the light L167 becomes parallel to the transmission axis of the polarizing glass 30. The light L167 enters one surface of the polarizing glass 30, is transmitted without being absorbed by the polarizing glass 30, and is emitted as light L168 from the other surface as shown on the left side of FIG. The light L168 enters the light incident port P1 (1) and exits to the outside. Therefore, the light incident on the light exit port P2 (2) exits from the light entrance port P1 (1).

  In the light incident from the light incident port P1 (1), a portion where the light travels in the + Z direction (left side in FIGS. 18 to 20) and a portion where the light travels in the −Z direction (right side in FIGS. 18 to 20). When divided into two, in the first state shown in FIG. 18, both the portion where the light travels in the + Z direction and the portion where the light travels in the −Z direction are in a transmissive state. In the second state shown in FIG. 19, the light is transmitted in the + Z direction, but is not transmitted in the −Z direction. Here, even in the non-transmission state, there is a small amount of light that travels in the same optical path as in FIG. 18 due to the angular deviation of the polarizer, the wave plate, and the Faraday rotator due to wavelength temperature changes and fabrication errors. In the third state shown in FIG. 20, since both the portion where the light travels in the + Z direction and the portion where the light travels in the −Z direction are in a non-transmissive state, a very high attenuation can be obtained.

  Further, in the light incident from the light exit port P2 (2), a portion where the light travels in the + Z direction (right side in FIGS. 21 to 23) and a portion where the light travels in the −Z direction (left side in FIGS. 21 to 23). In the third state shown in FIG. 23, both the portion where the light travels in the + Z direction and the portion where the light travels in the −Z direction are in a transmissive state. In the second state illustrated in FIG. 22, the light is transmitted in the + Z direction, but is not transmitted in the −Z direction. Here, even in the non-transmission state, there is a small amount of light traveling on the same optical path as in FIG. In the first state shown in FIG. 21, both the portion where the light travels in the + Z direction and the portion where the light travels in the −Z direction are in a non-transmissive state, and thus a very high attenuation can be obtained.

  FIG. 24 schematically shows the configuration of a reflective variable optical attenuator 2 'as a modification of the magneto-optical component according to this embodiment. In FIG. 24, the coordinate system is taken as in FIG. FIG. 24A shows a configuration in which the reflective variable optical attenuator 2 'is viewed in the + Y direction, and FIG. 24B shows a configuration in which the reflective variable optical attenuator 2' is viewed in the -X direction. As shown in FIGS. 24A and 24B, in this modification, the reflective film 18 is disposed in place of the two-surface reflector 38 as compared with the reflective variable attenuator 2 shown in FIG. The reflective film 18 is formed, for example, on the + Z side surface of the polarizing glass 31. In this modification, the optical fibers 41 and 42 are disposed obliquely in the XZ plane with respect to the light incident / exit surfaces of the polarizing glasses 30 and 32 so that light is incident obliquely. The Faraday rotator 20 includes a light transmission region through which incident light traveling from the light incident port P1 (1) or the light emitting port P2 (2) toward the reflective film 18 is transmitted, and the incident light reflected by the reflective film 18 Are formed at different positions with light transmissive regions through which reflected light traveling in different directions on different optical paths is transmitted. Since the operation of the reflective variable optical attenuator 2 'is the same as the operation of the reflective variable optical attenuator 2 shown in FIGS.

  In the variable optical attenuator 2 ′ according to the present modification, since it is not necessary to use the two-surface reflector 38, it is possible to further reduce the size and cost of the variable optical attenuator 2 shown in FIG. 17.

  In the reflection type variable optical attenuators 2 and 2 ′ shown in FIGS. 17 and 24, the two Faraday rotators 20 and 21 included in the transmission type variable optical attenuator shown in FIG. 4 are configured by one Faraday rotator 20. Can be considered. Therefore, in the present embodiment, the distance between the center position of the light beam traveling in the + Z direction on the Faraday rotator 20 and the center position of the light beam reflected on the two-surface reflector 38 and traveling in the −Z direction on the Faraday rotator 20. However, it may be 0.8 times or more of the beam diameter of light. For example, in FIG. 18, a reflective variable optical attenuator that functions as an optical isolator and an optical shutter can be obtained by setting the distance between the light L112 and the light L117 to be 0.8 times or more the beam diameter of the light. In the reflective variable light attenuator 2 shown in FIG. 17, the distance between the two light transmission regions can be adjusted by changing the light incident position on the two-surface reflector 38. Further, in the reflection type variable light attenuator 2 ′ shown in FIG. 24, the distance between the two light transmission regions is changed by changing the incident angle of the light to the reflection film 18 and the distance between the reflection film 18 and the Faraday rotator 20. Can be adjusted.

  According to the variable optical attenuators 2 and 2 'according to the present embodiment, since the magnetic domain structure in the light transmission region is changed as in the first embodiment, a small size, low power consumption and high speed magneto-optics are achieved. Optical components can be realized.

  Further, according to the variable optical attenuators 2 and 2 ′ according to the present embodiment, the domain wall I is moved by the magnetic field application mechanism, and the magnetic domain structure of the Faraday rotator 20 is changed to the first state, the second state, and the third state. The amount of attenuation of light incident on the light incident port P1 (1) can be continuously changed. The variable optical attenuators 2 and 2 ′ also have a function of an optical isolator because light incident on the light exit port P 2 (2) does not exit from the light entrance port P 1 (1) in the first and second states. Furthermore, since the variable optical attenuators 2 and 2 'can obtain a very high attenuation in the third state, they also have an optical shutter function.

  Furthermore, the variable optical attenuators 2 and 2 ′ according to the present embodiment realize a two-stage configuration with only one Faraday rotator 20 as compared with the configuration of the transmission type variable optical attenuator 1 shown in FIG. At the same time, since the optical fibers 41 and 42 are disposed only on one side, the size and the cost can be further reduced.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above embodiment, a permanent magnet is used as the magnetic field application mechanism, but the present invention is not limited to this. For example, instead of the permanent magnet, a semi-hard magnet that has a smaller coercive force than the permanent magnet and can reverse the magnetization may be used.
In addition to the polarizing glass, any kind of polarizer can be used as the polarizer. For example, a birefringent crystal plate may be used.

  In the present specification, for example, a device having both an optical attenuator function and an optical isolator function is expressed as “a variable optical attenuator having an optical isolator function”, “a variable optical attenuator having an optical isolator function”, or the like. However, the present invention is not restricted by the device name, and can of course be applied to a device having an equivalent configuration having another name such as “optical isolator with variable optical attenuator function”.

It is a figure explaining the operation principle of the magneto-optical optical component by the 1st Embodiment of this invention. It is a figure explaining the operation principle of the magneto-optical optical component by the 1st Embodiment of this invention. It is a figure explaining the operation principle of the magneto-optical optical component by the 1st Embodiment of this invention. It is a figure which shows the principal part structure of the transmissive | pervious variable optical attenuator as a magneto-optical optical component by the 1st Embodiment of this invention. It is a graph which shows the forward loss and reverse loss of the variable optical attenuator whose distance of the plane containing the domain wall I1 and the plane containing the domain wall I2 is 1.5 times the beam diameter. It is a graph which shows the forward loss and reverse loss of the variable optical attenuator whose distance of the plane containing the domain wall I1 and the plane containing the domain wall I2 is 0.8 times the beam diameter. It is a graph which shows the forward direction loss and reverse direction loss of the variable optical attenuator in which the domain wall I1 and the domain wall I2 exist in the same plane. It is a figure which shows the structure of the transmissive | pervious variable optical attenuator as a magneto-optical optical component by the 1st Embodiment of this invention. It is a figure which shows operation | movement of the transmissive | pervious variable optical attenuator as a magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows operation | movement of the transmissive | pervious variable optical attenuator as a magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows operation | movement of the transmissive | pervious variable optical attenuator as a magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows operation | movement of the transmissive | pervious variable optical attenuator as a magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows operation | movement of the transmissive | pervious variable optical attenuator as a magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows operation | movement of the transmissive | pervious variable optical attenuator as a magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows the structure of a transmissive | pervious variable optical attenuator as a modification of the magneto-optical optical component by the 1st Embodiment of this invention. It is a figure which shows the structure of the transmissive | pervious variable optical attenuator as another modification of the magneto-optic optical component by the 1st Embodiment of this invention. It is a figure which shows the structure of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows operation | movement of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows operation | movement of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows operation | movement of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows operation | movement of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows operation | movement of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows operation | movement of a reflection type variable optical attenuator as a magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure which shows the structure of a reflection type variable optical attenuator as a modification of the magneto-optical optical component by the 2nd Embodiment of this invention. It is a figure explaining the schematic structure and operating principle of the conventional variable optical attenuator.

Explanation of symbols

1, 1 ′, 1 ″ transmission type variable optical attenuator 2, 2 ′ reflection type variable optical attenuator 18 reflective film 20, 21 Faraday rotator 30, 31, 32 polarizing glass 38 two-surface reflector 41, 42 optical fiber 51, 52 Lens 66, 67, 68, 69 Permanent magnet 70 Electromagnet 71 Yoke 72 Coil 73 Light introduction window

Claims (5)

First to third polarizers arranged in order on the optical path;
It becomes a boundary between the magnetic domain A and the magnetic domain B, and the magnetic domain A constituted by the magnetization in the direction opposite to the magnetization direction of the magnetic domain A First and second magneto-optical elements each having a planar domain wall and a light transmission region through which a light beam passes;
A magneto-optic optical component having a magnetic field application mechanism that applies a variable magnetic field to the first and second magneto-optical elements to vary the position of the domain wall.
The first magneto-optical element is disposed between the first polarizer and the second polarizer;
The magneto-optic optical component according to claim 1, wherein the second magneto-optical element is disposed between the second polarizer and the third polarizer. The magneto-optic optical component according to claim 1,
The distance between the magnetic wall of the first magneto-optical element and the light beam is different from the distance between the magnetic wall of the second magneto-optical element and the light beam. parts. The magneto-optic optical component according to claim 2,
The difference between the distance between the magnetic wall of the first magneto-optical element and the light beam and the distance between the magnetic wall of the second magneto-optical element and the light beam are 0. A magneto-optic optical component characterized by being 8 times or more. A first polarizer that emits light incident from the outside as a first light beam;
A reflecting unit that reflects the first light beam and emits the second light beam traveling in a direction different from the traveling direction of the first light beam on a different optical path from the first light beam;
A second polarizer that enters the second light beam and emits the second light beam; and
It becomes a boundary between the magnetic domain A and the magnetic domain B, and the magnetic domain A constituted by the magnetization in the direction opposite to the magnetization direction of the magnetic domain A A magneto-optical element comprising a planar domain wall, a first light transmission region through which the first light beam is transmitted, and a second light transmission region through which the second light beam is transmitted;
A third polarizer disposed between the magneto-optical element and the reflecting unit;
A magneto-optic optical component comprising: a magnetic field application mechanism that applies a variable magnetic field to the magneto-optical element to change a position of the domain wall. The magneto-optic optical component according to claim 4,
The magneto-optical component according to claim 1, wherein a distance between the first light beam and the second light beam in the magneto-optical element is 0.8 times or more a light beam diameter.

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