JP2005049610A - Optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical component providing excellent optical characteristics as an optical component used for an optical communication system. <P>SOLUTION: The optical component has a lens 4 changing divergent light to nearly parallel beams, a double refraction wedge plate 6 separating incident light into normal light and abnormal light and respectively emitting the incident light to two optical paths different from each other, and a Faraday rotator 8 equipped with a prescribed optical function for the light made incident from two optical paths. In the optical component, a YZ plane exists which is parallel with the center axis of the lens 4 and to which two optical paths are projected in an overlapped state, and the Faraday rotator 8 is arranged to have the distribution of the optical characteristic in a direction D nearly parallel with the light incident and emitting surface of the Faraday rotator 8 on the YZ plane. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical component used in an optical communication system.

  In optical communication systems, small and low cost optical components are required. Optical components are broadly divided into transmission types and reflection types. The transmission type optical component generally has a configuration in which an optical fiber, a lens, an optical element, a lens, and an optical fiber are arranged in this order. In contrast, a reflective optical component generally has a configuration in which a two-core fiber, a lens, an optical element, and a reflective film are arranged in this order. The reflection type optical component can substantially reduce the number of components compared to the transmission type, and can reduce the thickness of the optical element by half. For this reason, a reflection type optical component is promising as an optical component that realizes a small size and a low price.

  FIG. 12 shows a configuration of a reflective variable optical attenuator described in Patent Document 1. As shown in FIG. 12, the variable optical attenuator has a two-core ferrule 103 including an input optical fiber 101 and an output optical fiber 102. In the traveling direction of light emitted from the light exit end 111 of the input optical fiber 101, a lens 104, a birefringent wedge plate 106, a Faraday rotator 108, and a reflective film 110 are arranged in this order. The variable optical attenuator includes a magnetic field applying unit 120 that applies a magnetic field to the Faraday rotator 108 and an adjustment unit 122 that changes the magnetic field based on a control signal.

  FIG. 13 shows a configuration in the vicinity of the Faraday rotator 108 and the magnetic field application unit 120. As shown in FIG. 13, the magnetic field application unit 120 includes two permanent magnets 130A and 130B. The permanent magnet 130 </ b> A has a plate shape, and the reflective film 110 is in close contact between the flat surface that provides one pole (S pole in the drawing) and the Faraday rotator 108. The permanent magnet 130B has an annular shape having an opening, and the input beam IB and the reflected beam RB pass through the opening. In order to provide the Faraday rotator 108 with a constant magnetic field substantially parallel to the input beam IB and the reflected beam RB by the permanent magnets 130A and 130B, the end surface corresponding to the north pole of the permanent magnet 130B has a permanent magnetic field of the Faraday rotator 108. It is fixed to the end surface opposite to the magnet 130A. The magnetic field applying unit 120 includes an electromagnet in which a coil 134 is wound around a yoke (electromagnetic yoke) 132. One end of the yoke 132 is disposed close to one end surface perpendicular to the light incident / exit surface of the Faraday rotator 108, and the other end of the yoke 132 is disposed close to the other end surface facing the one end surface of the Faraday rotator 108. Has been.

  That is, a first magnetic field is applied to the Faraday rotator 108 by an electromagnet in the direction indicated by the broken arrow F in FIGS. 12 and 13, and the direction perpendicular to the direction in which the first magnetic field is applied (on the light incident / exit surface). The second magnetic field is applied by the permanent magnets 130A and 130B in the vertical direction).

  FIG. 14 schematically shows the arrangement of the optical elements constituting the variable optical attenuator shown in FIG. 12 and the optical path of light that passes through or reflects them. Although the light beam has a certain width, in the present application, the optical path is indicated by the central axis of the beam. In FIG. 14, the central axis of the lens 104 of the variable optical attenuator is the Z axis, and 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. 14A shows an optical path projected onto the XZ plane, and FIG. 14B shows an optical path projected onto the YZ plane. In FIG. 14A, the arrangement of the electromagnet yoke 132 is also shown. As shown in FIGS. 14A and 14B, the input optical fiber 101 and the output optical fiber 102 of the variable optical attenuator are arranged adjacent to each other in parallel to the Z axis in the YZ plane. A lens 104, a birefringent wedge plate 106, a Faraday rotator 108, and a reflective film 110 are arranged in this order in the traveling direction (Z-axis direction) of light emitted from the light emitting end 111 of the input optical fiber 101. .

  The light incident / exit end face of the two-core ferrule 103 is polished so as to be inclined at an inclination angle θ3 with respect to the X axis in the XZ plane so that the reflected light at the end face does not return to the original optical path. The birefringent wedge plate 106 is disposed at a predetermined inclination angle with respect to the X axis in the XZ plane corresponding to the inclination of the light incident / exit end face of the two-core ferrule 103. The Faraday rotator 108 is inclined at an inclination angle θ4 with respect to the X axis in the XZ plane corresponding to the inclination of the light incident / exit end face of the two-core ferrule 103 and the birefringent wedge plate 106.

  As shown in FIGS. 14A and 14B, the light beam emitted from the light exit end 111 of the input optical fiber 101 passes through the optical path L11, enters the lens 104, and is converted from a divergent ray bundle into a parallel ray bundle. And emitted onto the optical path L12. The light beam passing on the optical path L12 enters the birefringent wedge plate 106 and is separated into ordinary light and extraordinary light. The ordinary light emitted from the birefringent wedge plate 106 travels to the optical path L13o, and the extraordinary light travels to an optical path L13e different from the ordinary light path L13o. Light traveling along the optical paths L13o and L13e is incident on different positions of the Faraday rotator 108, respectively. The Faraday rotator 108 shown in FIGS. 14A and 14B is saturated and magnetized in a direction perpendicular to the light incident / exit surface by applying a saturation magnetic field from the permanent magnets 130A and 130B shown in FIG. Further, a variable magnetic field is applied to the Faraday rotator 108 in the direction substantially along the X axis (the direction indicated by the broken double arrow F in FIG. 14A) by the electromagnet shown in FIG. By rotating the saturation magnetization direction of the Faraday rotator 108 in the direction of the combined magnetic field of the saturation magnetic field and the variable magnetic field, and controlling the strength of the magnetization component in the direction perpendicular to the light incident / exit surface, the Faraday rotation angle θf (For example, 0 ° <θf ≦ 45 °) is changed.

  The two lights incident on the light incident / exit surface of the Faraday rotator 108 from the optical paths L13o and L13e are reflected by the reflective film 110, pass through the Faraday rotator 108 twice, and exit from the light incident / exit surface. When the Faraday rotation angle θf is 45 °, the ordinary light incident from the optical path L13o rotates the polarization plane by 90 °, exits the Faraday rotator 108, and proceeds to the optical path L14e. The light on the optical path L14e passes through the birefringent wedge plate 106 as abnormal light and proceeds to the optical path L15e. On the other hand, the extraordinary light incident from the optical path L13e also has its polarization plane rotated by 90 °, exits the Faraday rotator 108, and proceeds to the optical path L14o. The light on the optical path L14o passes through the birefringent wedge plate 106 as ordinary light and proceeds to the optical path L15o. Since the optical paths L15e and L15o are both parallel to the optical path L12 in the XZ plane shown in FIG. 14A, the light incident on the lens 104 through the optical paths L15e and L15o becomes a convergent beam bundle, respectively. It passes through L16o and is coupled to the light incident end 112 of the output optical fiber 102 of the two-core ferrule 103. Therefore, when the Faraday rotation angle θf is 45 °, the light emitted from the light emitting end 111 of the input optical fiber 101 can be incident on the light incident end 112 of the output optical fiber 102 without being attenuated.

  On the other hand, when the Faraday rotation angle θf is about 0 °, ordinary light incident from the optical path L13o exits the Faraday rotator 108 without rotating the polarization plane, and proceeds to the optical path L14e. The light on the optical path L14e passes through the birefringent wedge plate 106 as ordinary light and travels to an optical path (not shown) shifted in the + X direction from the optical path L15e. On the other hand, abnormal light incident from the optical path L13e also exits the Faraday rotator 108 without rotating the plane of polarization, and proceeds to the optical path L14o. The light on the optical path L14o passes through the birefringent wedge plate 106 as extraordinary light and travels to an optical path (not shown) shifted in the −X direction from the optical path L15o. These optical paths do not become parallel to the optical path L12 in the XZ plane shown in FIG. 14A, and the convergent light beam transmitted through the lens 104 is not coupled to the light incident end 112 of the output optical fiber 102 of the two-core ferrule 103. . Therefore, when the Faraday rotation angle θf is about 0 °, the light emitted from the light emitting end 111 of the input optical fiber 101 can be attenuated to the maximum. In this variable optical attenuator, the optical transmission loss from the input optical fiber 101 to the output optical fiber 102 is controlled by changing the Faraday rotation angle θf between about 0 ° and 45 °, and the desired attenuation is obtained. It will be obtained.

  By the way, the variable light attenuator separates the ordinary light and the extraordinary light into the optical paths L13o and L13e by the birefringent wedge plate 106. Therefore, the two separated lights are Faraday in the direction of the broken line double arrow F in FIG. The light enters the rotor 108 at different positions. Accordingly, the two separated lights pass through different optical paths in the Faraday rotator 108. However, the magnetic field applied to the Faraday rotator 108 by the permanent magnets 130A and 130B and the electromagnet is not uniform and generally has a distribution. In the example shown in FIGS. 12 to 14, a variable magnetic field is applied by an electromagnet in the direction indicated by the broken line double arrow F, but it is difficult to make the intensity of the variable magnetic field uniform in the direction of the broken line double arrow F. Accordingly, a slight shift occurs in the direction of the combined magnetic field, and a distribution occurs in the Faraday rotation angle θf in the direction of the broken-line double arrow F. For this reason, the rotation angle of the polarization plane of the light incident on the Faraday rotator 108 from the optical path L13o and the rotation angle of the polarization plane of the light incident on the Faraday rotator 108 from the optical path L13e do not coincide with each other. A difference arises and the problem that polarization dependence becomes large arises. As described above, if a distribution occurs in the optical characteristics of the Faraday rotator 108 in the in-plane direction including two different optical paths, the characteristics of the polarization-independent variable optical attenuator using the birefringent plate are deteriorated. Problem arises.

If it is a transmission type optical component, the position of the input optical fiber 101 and the output optical fiber 102 can be adjusted independently. However, in the reflection type optical component, since the normal input optical fiber 101 and the output optical fiber 102 are integrated as a two-core ferrule 103, the degree of freedom of adjustment is halved. For this reason, it is difficult to make light incident under optimum conditions, particularly with respect to the Faraday rotator 108 in which the distribution of optical characteristics occurs. Therefore, the reflection type optical component has a problem that it is difficult to obtain stable optical characteristics as compared with the transmission type.
Japanese Patent Laid-Open No. 10-161076 JP 2000-28967 A JP 2002-258229 A JP 2003-107420 A

  An object of the present invention is to provide an optical component capable of obtaining good optical characteristics.

  The purpose is different from each other by separating the incident light into ordinary light and extraordinary light, which are arranged in at least one of the front and rear of the lens as viewed in the light traveling direction, and the lens that makes the diverging light substantially parallel light An optical component having a birefringent element that respectively exits into two optical paths and an optical element having a predetermined optical function for light incident from the two optical paths, the optical component being parallel to the central axis of the lens, There is at least one virtual plane projected by overlapping two optical paths, and the optical element has a distribution of optical characteristics in a direction substantially parallel to the light incident / exit surface of the optical element in a plane parallel to the virtual plane. It is achieved by an optical component characterized in that it is arranged to have

  The optical component according to the invention is characterized in that the optical component further includes a reflective film that reflects the light that has passed through the optical element and reenters the optical element.

  The optical component according to the present invention is characterized in that the two optical paths substantially coincide with the central axis of the lens when projected onto the virtual plane.

  The optical component of the present invention, wherein the optical element is a magneto-optical crystal having a Faraday effect, and a magnetic domain A configured by magnetization in a direction substantially perpendicular to the light incident / exit surface, and a magnetization direction of the magnetic domain A And a magnetic domain B having optical characteristics different from that of the magnetic domain A, and a domain wall that is a boundary surface between the magnetic domain A and the magnetic domain B.

  The optical component according to the present invention is characterized in that the domain wall is formed substantially perpendicular to the virtual plane.

  The optical component according to the invention is characterized in that the domain wall is movable in a direction parallel to the virtual plane and substantially parallel to the light incident / exit surface.

  The optical component according to the invention is characterized in that the two optical paths are substantially parallel to the domain wall at least in the optical element when projected onto the virtual plane.

  In the optical component of the present invention, the optical element is a magneto-optical crystal having a Faraday effect, and is arranged in a direction substantially parallel to the light incident / exit surface of the magneto-optical crystal in a plane parallel to the virtual plane. The first magnetic field is applied, and the second magnetic field is applied in a direction different from the first magnetic field.

  According to the present invention, it is possible to realize an optical component with good optical characteristics.

  An optical component according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 schematically shows the arrangement of optical elements constituting the variable optical attenuator according to the present embodiment and the optical path of light that passes through or reflects them. In FIG. 1, the central axis of the lens is the Z axis, and the X axis and the Y axis are taken in two directions orthogonal to each other in a plane orthogonal to the Z axis. 1A shows an optical path projected onto the XZ plane, and FIG. 1B shows an optical path projected onto the YZ plane. In FIG. 1B, the arrangement of the electromagnet yoke 32 is also shown.

  As shown in FIGS. 1A and 1B, the variable optical attenuator has a two-core ferrule 3 including an input optical fiber 1 and an output optical fiber 2. The input optical fiber 1 and the output optical fiber 2 are disposed adjacent to each other in parallel to the Z axis in the YZ plane. In the traveling direction (Z-axis direction) of the light emitted from the light exit end (input port) 11 of the input optical fiber 1, there are a lens 4, a birefringent wedge plate (birefringent element) 6, and a Faraday rotator (optical element). 8 and the reflective film 10 are arranged in this order. The Faraday rotator 8 has a substantially rectangular parallelepiped shape, and has a light incident / exit surface on which light is incident and an opposing surface facing the light incident / exit surface. The Faraday rotator 8 has two side end faces that are substantially perpendicular to the XZ plane and two side end faces that are substantially perpendicular to the YZ plane. The reflective film 10 is formed on the opposite surface of the Faraday rotator 8 by depositing a dielectric multilayer film or a metal thin film such as aluminum. Note that, on the opposite surface side of the Faraday rotator 8, for example, a reflection mirror deposited on a glass substrate surface as a reflection film with a dielectric thin film or a metal thin film such as aluminum may be disposed. Although not shown in the drawing, an annular permanent magnet having a path of a light beam incident on the Faraday rotator 8 is disposed on the light incident / exit surface side of the Faraday rotator 8. A plate-like permanent magnet is disposed on the back side of the reflective film 10. One end portion of a yoke 32 having a “C” -shaped cross section is disposed in the vicinity of one end face that is substantially perpendicular to the YZ plane of the Faraday rotator 8 as shown in FIG. The other end portion of the yoke 32 is disposed in the vicinity of the other end surface substantially perpendicular to the YZ plane of the Faraday rotator 8. Here, the cross section parallel to the XZ plane at both ends of the yoke 32 is sufficiently larger than, for example, the Faraday rotator 8. Thereby, the distribution of the magnetic field in the direction of the dashed double-pointed arrow E in FIG. 1A becomes uniform to such an extent that no practical problem occurs.

  That is, in the plane parallel to the YZ plane, the first magnetic field (variable magnetic field) is applied to the Faraday rotator 8 by the electromagnet in the direction of the broken line double arrow D substantially parallel to the light incident / exit surface. The second magnetic field is applied by a permanent magnet in a direction substantially perpendicular to the application direction (direction perpendicular to the light incident / exit surface). The first magnetic field applied to the Faraday rotator 8 is substantially uniform in the direction of the broken line double arrow E, and a predetermined distribution is generated in the direction of the broken line double arrow D, for example. The second magnetic field is substantially uniform within the light incident / exit surface of the Faraday rotator 8.

  The light incident / exit end face of the two-core ferrule 3 is polished so as to be inclined at an inclination angle θ1 with respect to the X axis in the XZ plane so that the reflected light from the end face does not return to the original optical path. The birefringent wedge plate 6 is disposed at a predetermined inclination angle with respect to the X axis in the XZ plane corresponding to the inclination of the light incident / exit end face of the two-core ferrule 3. Further, the Faraday rotator 8 is inclined at an inclination angle θ2 with respect to the X axis in the XZ plane corresponding to the inclination of the light incident / exit end face of the two-core ferrule 3 and the birefringent wedge plate 6. As shown in FIG. 1B, in the projection onto the YZ plane, the light incident / exit end surface of the two-core ferrule 3, the light emitting end 11 of the input optical fiber 1, and the light incident end 12 of the output optical fiber 2 are , Almost perpendicular to the Z axis. Further, the end surfaces of the lens 4, the birefringent wedge plate 6, the Faraday rotator 8, and the reflective film 10 are substantially perpendicular to the Z axis.

  As shown in FIGS. 1A and 1B, the light beam emitted from the light exit end 11 of the input optical fiber 1 passes through the optical path L1, enters the lens 4, and is converted from a divergent ray bundle into a parallel ray bundle. And emitted onto the optical path L2. The light beam passing on the optical path L2 enters the birefringent wedge plate 6 and is separated into ordinary light and extraordinary light. The ordinary light emitted from the birefringent wedge plate 6 travels to the optical path L3o, and the extraordinary light travels to an optical path L3e different from the ordinary light optical path L3o. Light traveling along the optical paths L3o and L3e is incident on different positions of the Faraday rotator 8, respectively. The Faraday rotator 8 shown in FIGS. 1A and 1B is saturated and magnetized in a direction perpendicular to the light incident / exit surface by applying a saturation magnetic field from a permanent magnet. Further, the direction along the Y axis with respect to the Faraday rotator 8 by the electromagnet (the direction perpendicular to the paper surface indicated by ◎ D in FIG. 1A and the direction indicated by the broken double arrow D in FIG. 1B). A variable magnetic field is applied to. As a result, the optical characteristics of the Faraday rotator 8 in the direction substantially along the X axis (the direction indicated by the double-pointed arrow E in FIG. 1A) are maintained substantially constant. By rotating the saturation magnetization direction of the Faraday rotator 8 in the direction of the combined magnetic field of the saturation magnetic field and the variable magnetic field, and controlling the strength of the magnetization component perpendicular to the light incident / exit surface, the Faraday rotation angle θf ( For example, 0 ° <θf ≦ 45 °) is changed.

  The two lights incident on the light incident / exit surface of the Faraday rotator 8 from the optical paths L3o, L3e are reflected by the reflection film 10 and pass through the Faraday rotator 8 twice to be emitted from the light incident / exit surface. When the Faraday rotation angle θf is 45 °, the ordinary light incident from the optical path L3o is rotated by 90 ° on the polarization plane, exits the Faraday rotator 8, and proceeds to the optical path L4e. The light on the optical path L4e passes through the birefringent wedge plate 6 as abnormal light and proceeds to the optical path L5e. On the other hand, the extraordinary light incident from the optical path L3e also has its polarization plane rotated by 90 °, exits the Faraday rotator 8, and proceeds to the optical path L4o. The light on the optical path L4o passes through the birefringent wedge plate 6 as ordinary light and proceeds to the optical path L5o. Since the optical paths L5e and L5o are both parallel to the optical path L2 in the XZ plane shown in FIG. 1A, the light incident on the lens 4 through the optical paths L5e and L5o becomes a convergent beam bundle, respectively. It passes through L6o and is coupled to the light incident end (output port) 12 of the output optical fiber 2 of the two-core ferrule 3. Therefore, when the Faraday rotation angle θf is 45 °, the light emitted from the light emitting end 11 of the input optical fiber 1 can be incident on the light incident end 12 of the output optical fiber 2 without being attenuated. As shown in FIG. 1B, the optical paths L3o and L3e, the optical paths L4o and L4e, and the optical paths L5o and L5e are substantially overlapped when projected onto the YZ plane.

  On the other hand, when the Faraday rotation angle θf is about 0 °, ordinary light incident from the optical path L3o exits the Faraday rotator 8 without rotating the polarization plane, and proceeds to the optical path L4e. The light on the optical path L4e passes through the birefringent wedge plate 6 as ordinary light and travels to an optical path (not shown) shifted in the + X direction from the optical path L5e. Also, abnormal light incident from the optical path L3e is emitted from the Faraday rotator 8 without rotating the plane of polarization, and proceeds to the optical path L4o. The light on the optical path L4o passes through the birefringent wedge plate 6 as extraordinary light and travels to an optical path (not shown) shifted in the −X direction from the optical path L5o. These optical paths are not parallel to the optical path L2 in the XZ plane shown in FIG. 1A, and the convergent light beam transmitted through the lens 4 is not coupled to the light incident end 12 of the output optical fiber 2 of the two-core ferrule 3. . Therefore, when the Faraday rotation angle θf is about 0 °, the light emitted from the light emitting end 11 of the input optical fiber 1 can be attenuated to the maximum. In this variable optical attenuator, the optical transmission loss from the input optical fiber 1 to the output optical fiber 2 is controlled by changing the Faraday rotation angle θf between about 0 ° and 45 °, and the desired attenuation is obtained. It will be obtained.

  By the way, this variable optical attenuator separates ordinary light and extraordinary light into optical paths L3o and L3e by the birefringent wedge plate 6, so that the two separated lights are Faraday in the direction of the broken line double arrow E in FIG. The light enters the different positions of the rotor 8. Accordingly, the two separated lights pass through different optical paths in the Faraday rotator 8. However, in the present embodiment, a substantially uniform magnetic field is applied in the direction of the broken line double arrow E in a plane parallel to the XZ plane shown in FIG. The optical characteristics of No. 8 are maintained almost constant. Therefore, no subtle shift occurs in the direction of the combined magnetic field, and no distribution of the Faraday rotation angle θf occurs in the direction of the broken-line double arrow E. For this reason, since the rotation angle of the polarization plane of the light incident on the Faraday rotator 8 from the optical path L3o and the rotation angle of the polarization plane of the light incident on the Faraday rotator 8 from the optical path L3e are exactly the same, the operating current of the electromagnet Can be controlled to obtain a desired attenuation.

  In this way, by preventing the optical characteristics of the Faraday rotator 8 from being distributed in the in-plane direction in which the two optical paths are projected without overlapping, a polarization-independent variable using a birefringent plate is possible. It becomes possible to suppress the characteristic deterioration of the optical attenuator. On the other hand, in the plane parallel to the YZ plane, the distribution of the Faraday rotation angle θf occurs in the Faraday rotator 8, but the projections of the two optical paths in the Faraday rotator 8 overlap and are common as shown in FIG. Therefore, they are not affected by different optical characteristics. Therefore, according to the variable optical attenuator of the present embodiment, there is almost no difference in optical characteristics depending on the polarization, so that good optical characteristics with small polarization dependence can be obtained with high reproducibility.

  Next, an optical component according to a second embodiment of the present invention will be described with reference to FIGS. First, the operation principle of the optical component according to this embodiment will be described with reference to FIGS. 2 to 4 show a state in which a magnetic field is applied to the Faraday rotator 8 under different conditions. 2 (a), 3 (a), and 4 (a) show the Faraday rotator 8 viewed in a direction perpendicular to the light incident / exit surface. A region surrounded by a substantially central circle of the Faraday rotator 8 is a light transmission region C. 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 8, and the polarization direction is rotated by a predetermined angle and is emitted rearward of the paper. On both sides of the Faraday rotator 8, permanent magnets M1 and M2 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 disposed farther from the central portion of the light transmission region C of the Faraday rotator 8 than the permanent magnet M1.

  2 (b), FIG. 3 (b), and FIG. 4 (b) were cut along the lines XX shown in FIG. 2 (a), FIG. 3 (a), and FIG. 4 (a), respectively. A magnetic domain structure in a cross section of the Faraday rotator 8 is schematically shown. The XX ray crosses the center of the light transmission region C. 2B, 3B, and 4B, the magnetic flux inside the permanent magnet M1 is shown downward in the figure, and the magnetic flux inside the permanent magnet M2 is shown upward in the figure.

  2 (c), 3 (c), and 4 (c) show the direction and magnitude 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 8). This is schematically represented by the direction and length of the arrow. In the drawing, the horizontal direction corresponds to the horizontal position of the cross section of the Faraday rotator 8, and the vertical direction represents a direction parallel to the optical axis.

  2A, 2B, and 2C show a state in which a magnetic field is applied to the Faraday rotator 8 only by the permanent magnets M1 and M2. As shown in FIG. 2 (c), the magnetic field is applied upward in the figure (that is, toward the rear of the page in FIG. 2 (a)) in the left portion of the Faraday rotator 8 near the permanent magnet M1, while On the right side near the magnet M2, the magnetic field is applied downward in the figure (that is, toward the front of the page in FIG. 2A). The magnitude of the magnetic field component applied to the Faraday rotator 8 changes monotonously in a predetermined direction within the light incident / exit surface. As shown by the arrow in the Faraday rotator 8 in FIG. 2B, the direction of magnetization in the Faraday rotator 8 is the same as the direction of the magnetic field applied to the Faraday rotator 8 by the permanent magnet M1 and the permanent magnet M2. become. The permanent magnets M1 and M2 have substantially the same magnetic field strength, but the magnetic poles are opposite to each other and the distance from the Faraday rotator 8 is closer to the permanent magnet M1. As shown in (c), an upward magnetic field, that is, a magnetic field in the same direction as the traveling direction of light incident from the outside becomes dominant. Therefore, as shown in FIG. 2B, the Faraday rotator 8 has a magnetic domain A region having an upward magnetization (in the same direction as the light traveling direction) facing downward (opposite to the light traveling direction). It becomes more dominant than the region of the magnetic domain B having the magnetization of. As a result, as shown in FIG. 2C, at the position O where the magnetic field in the direction perpendicular to the light incident / exit surface becomes 0, the magnetic domain A and the magnetic domain B as shown in FIG. 2A and FIG. A boundary surface (hereinafter referred to as a domain wall I) is formed, and the light transmission region C is completely included in the region of the magnetic domain A. 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).

  Here, the permanent magnet M1 is moved closer to the Faraday rotator 8 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 and disposing the two so as to be approximately equidistant from the Faraday rotator 8. 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, when an electromagnet (not shown) is energized and a magnetic field in the direction opposite to the traveling direction of light is further applied in addition to the magnetic field generated by the permanent magnets M1 and M2, the magnetic field in the direction perpendicular to the light incident / exit surface is zero. O moves to the left in the figure and comes to be positioned approximately at the center of the Faraday rotator 8. As a result, as shown in FIG. 3 (c), the Faraday rotator 8 is in a state where an upward magnetic field is applied to the left half and a downward magnetic field is applied to the right half. Therefore, as shown in FIG. 3B, the domain wall I also moves in the left direction in the figure, and the Faraday rotator 8 includes a domain A having an upward magnetization and a domain B having a downward magnetization. Is formed on the left and right halves with the center as the boundary. As a result, as shown in FIG. 3A, 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.

  Subsequently, when a further magnetic field is applied to the electromagnet (not shown) to further apply a magnetic field in the direction opposite to the traveling direction of the light, the position O where the magnetic field in the direction perpendicular to the light incident / exit surface becomes 0 is further leftward in the figure. Move to. As a result, as shown in FIG. 4C, a downward magnetic field in the figure becomes dominant in the Faraday rotator 8. Therefore, as shown in FIG. 4B, in the Faraday rotator 8, the domain B having the downward magnetization is more dominant than the domain A having the upward magnetization. Thereby, as shown in FIG. 4A, 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 magnetic domain B region is −θfs.

  FIG. 5 shows the state of the domain wall I between the magnetic domains A and B generated in the Faraday rotator 8 when the above operating principle is used. FIG. 5 shows a part of the vicinity (inside a circle) of the domain wall I, and the domain wall I is linearly formed as shown in the figure. In the photograph shown in FIG. 5, regions in which the magnetization is partially reversed in the thickness direction appear in the left and right magnetic domains A and B of the domain wall I. Even if such a region exists, its existence is allowed if it does not cause deterioration of reproducibility. As described above, when the above operating principle is used, the magnetic field strength applied to the Faraday rotator 8 is controlled so that the domain wall I is linear. In order to obtain such a linear domain wall structure, it is necessary to apply a magnetic field having a sufficiently large gradient. FIG. 6 shows a part of the vicinity (inside a circle) of the domain wall I when the magnetic field gradient is small. As shown in the figure, the domain wall I is formed in a non-linear shape.

  When the domain wall I is not linear, the magnetic field (H1 <H2 <H3) applied to the Faraday rotator 8, for example, is gradually increased to H1, H2, H3, H2, and H1, as shown from left to right in FIG. If changed to, even if the magnetic field is restored from another magnetic field, the original magnetic domain structure is not restored and reproducibility cannot be obtained. For example, the left end and the right end in FIG. 6 show the same magnetic field H1 applied state, but the magnetic domain structures of the two are different. Therefore, the shape of the domain wall I is non-linear and the shapes of the two are different. Similarly, even in the application state of the same magnetic field H2 shown in the left and right of the figure before and after the application of the magnetic field H3 in the center of the figure, the magnetic domain structure is not reproducible and the shape of the domain wall I is non-linear and the shapes of the two are different. For this reason, in the operation principle shown in FIGS. 2 to 4, when the domain wall I having the shape as shown in FIG. 6 is used, the reproducibility of the optical characteristics is lowered, which causes a practical problem.

  On the other hand, as shown in FIG. 5, when the domain wall I that is the boundary surface between the magnetic domains A and B is maintained substantially linear, the domain wall in the same magnetic field can be obtained even if the applied magnetic field is changed and the domain wall I is moved. The shape of I hardly changes and good reproducibility is obtained.

  In order to maintain the domain wall I in a substantially straight line shape, the position near the position O where the perpendicular magnetic field with respect to the light incident / exit surface shown in FIGS. 2 (c), 3 (c), and 4 (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 / exit plane, 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.

  The magnitude of the magnetic field required to maintain the domain wall I substantially linearly depends on the characteristics of the magneto-optical crystal such as perpendicular magnetic anisotropy, saturation magnetization, exchange energy, and the like. At least at both ends of the magneto-optic crystal, it is necessary to apply a magnetic field having a magnitude greater than or equal to the saturation magnetic field and having a different orientation. Experimentally, for example, it is possible to find a condition that the domain wall I is almost linear by gradually increasing the gradient of the magnetic field.

  The Faraday rotator 8 of the variable optical attenuator according to the present embodiment is formed by polishing a garnet single crystal film grown by, for example, an LPE (liquid phase epitaxial) method. The garnet single crystal film has a perpendicular magnetic domain structure perpendicular to the film surface, and the Faraday rotator 8 has a magnetic domain structure when a magnetic field smaller than the saturation magnetic field is applied, and diffraction loss occurs.

  The variable optical attenuator according to the present embodiment forms a state where only the magnetic domain A exists in the light transmission region C and a state where both the magnetic domain A and the magnetic domain B are included in the light transmission region C. The amount of light transmitted from 1 to the output optical fiber 2 is continuously changed. For example, when a magnetic field component in the vertical direction is applied to the light incident / exit surface of the Faraday rotator 8 by a permanent magnet and no current flows through the coil of the electromagnet, the Faraday rotator 8 has a wider area than the magnetic domains B and B. And a magnetic domain A. At this time, the light transmission region C is completely included in, for example, the magnetic domain A region. The saturation Faraday rotation angle is θfs, where θfs is set to about 45 °. The magnetization direction of the magnetic domain B is opposite to the magnetization direction of the magnetic domain A. Therefore, the Faraday rotation angle for light that has passed through the magnetic domain A twice is + 90 °, and the Faraday rotation angle for light that has passed the magnetic domain B twice is −90 °. As a result, the phase of the light that has passed through the magnetic domain A twice and the phase of the light that has passed through the magnetic domain B twice are shifted by a half wavelength, so the two lights condensed at the light incident end 12 of the output optical fiber 2 cancel each other. Fit. When the magnetic domain A region and the magnetic domain B region are halved in the light transmission region C, the two lights collected at the light incident end 12 of the output optical fiber 2 are not coupled at all, and the maximum attenuation is achieved. A quantity is obtained. If the magnetic field generated by the electromagnet is changed so that only the magnetic domain A exists in the light transmission region C, the magnetic domain A region is gradually decreased and the magnetic domain B region is gradually increased. Can be changed continuously.

  As described above, the variable optical attenuator of the present embodiment differs from the conventional variable optical attenuator using the change in the Faraday rotation angle in that it uses the light diffraction effect without using the change in the Faraday rotation angle. It has characteristics.

  In order to construct a variable optical attenuator similar to that of the first embodiment using the operating principle of the present embodiment, the domain wall I in FIGS. 1A and 1B is substantially parallel to the XZ plane. That is, the moving direction of the domain wall I is the direction along the Y-axis (the direction perpendicular to the paper surface indicated by ◎ D in FIG. 1A and the direction indicated by the broken line double arrow D in FIG. 1B). As shown, a permanent magnet and an electromagnet (not shown) may be disposed on the Faraday rotator 8. By arranging in this way, a characteristic with small polarization dependence can be obtained as in the first embodiment. However, in the presence of a domain wall, a problem other than the polarization dependence also occurs.

  FIG. 7 shows the relationship between the light incident on the Faraday rotator 8 and the domain wall I. As shown in FIG. 7, a part of the parallel light beam incident on the magnetic domain B obliquely with respect to the domain wall I passes through the magnetic domain A across the domain wall I. For this reason, even if the region of magnetic domain A and the region of magnetic domain B exist almost in half in the light reflection region C, diffraction is not completely performed. Therefore, there is a problem in that a sufficient amount of attenuation cannot be obtained even when the operating principle of the present embodiment is applied to a variable optical attenuator having the same configuration as that of the first embodiment.

  FIG. 8 shows a variable optical attenuator according to the present embodiment that solves the above-described problems, and schematically shows the arrangement of optical elements constituting the attenuator and the optical path of light that is transmitted or reflected by them. Yes. In FIG. 8, the central axis of the lens is the Z axis, and 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. 8A shows an optical path projected onto the XZ plane, and FIG. 8B shows an optical path projected onto the YZ plane.

  As shown in FIGS. 8A and 8B, the variable optical attenuator has a two-core ferrule 3 including an input optical fiber 1 and an output optical fiber 2. The input optical fiber 1 and the output optical fiber 2 are arranged adjacent to each other in parallel to the Z axis in the XZ plane. In the traveling direction (Z-axis direction) of light emitted from the light emitting end 11 of the input optical fiber 1, the lens 4, the birefringent wedge plate 6, the Faraday rotator 8, and the reflective film 10 are arranged in this order. . The reflective film 10 is formed on the opposite surface of the Faraday rotator 8 opposite to the surface of the two-core ferrule 3 side. The light incident / exit end face of the two-core ferrule 3 is polished so as to be inclined at an inclination angle θ1 with respect to the X axis in the XZ plane so that the reflected light from the end face does not return to the original optical path. The birefringent wedge plate 6 is disposed at a predetermined inclination angle with respect to the X axis in the XZ plane corresponding to the inclination of the light incident / exit end face of the two-core ferrule 3. Further, the Faraday rotator 8 is inclined at an inclination angle θ2 with respect to the X axis in the XZ plane corresponding to the inclination of the light incident / exit end face of the two-core ferrule 3 and the birefringent wedge plate 6. As shown in FIG. 8B, in the projection onto the YZ plane, the light incident / exit end surface of the two-core ferrule 3, the light emitting end 11 of the input optical fiber 1, and the light incident end 12 of the output optical fiber 2 are , Almost perpendicular to the Z axis. Further, the end surfaces of the lens 4, the birefringent wedge plate 6, the Faraday rotator 8, and the reflective film 10 are substantially perpendicular to the Z axis. As described above, in the Faraday rotator 8, the permanent magnet, and the electromagnet, the domain wall I is substantially parallel to the XZ plane, and the direction of movement of the domain wall I is the direction along the Y axis (in FIG. They are arranged so as to be in a direction perpendicular to the paper surface to be shown and a direction indicated by a broken line double arrow D in FIG. As a result, the Faraday rotator 8 has a distribution of Faraday rotation angles in the direction along the Y axis in the YZ plane (the direction of the dashed arrow D) (the Faraday rotation angle in the domain A domain is + 45 ° and the domain B domain) The Faraday rotation angle at -45 °). On the other hand, in the XZ plane, since only the magnetic domain A or only the magnetic domain B exists in the Faraday rotator 8, no distribution of the Faraday rotation angle occurs. 8A and 8B, at least the optical path of the light passing through the Faraday rotator 8 is substantially parallel to the domain wall I in the projection of the optical path onto the YZ plane. In this example, almost all the optical paths coincide with the Z axis in the projection onto the YZ plane.

  9 and 10 show the relationship between the light incident on the Faraday rotator 8 and the domain wall I. FIG. 9 shows a state in which only the magnetic domain A exists in the light transmission region C, and FIG. 10 shows a state in which the region of the magnetic domain A and the region of the magnetic domain B exist in the light transmission region C almost in half. As shown in FIGS. 9 and 10, in the present embodiment, at least the optical path of the light passing through the Faraday rotator 8 is substantially parallel to the domain wall I. Therefore, the light incident on the magnetic domain A of the Faraday rotator 8 passes through only the magnetic domain A without traversing the domain wall I and exits from the Faraday rotator 8. The light incident on the magnetic domain B of the Faraday rotator 8 passes through the domain wall I. The Faraday rotator 8 is ejected through only the magnetic domain B without crossing.

  8A and 8B, the light beam emitted from the light exit end 11 of the input optical fiber 1 passes through the optical path L1, enters the lens 4, and is converted from a divergent ray bundle into a parallel ray bundle. It is emitted on the optical path L2. The light beam passing on the optical path L2 enters the birefringent wedge plate 6 and is separated into ordinary light and extraordinary light. The ordinary light emitted from the birefringent wedge plate 6 travels to the optical path L3o, and the extraordinary light travels to an optical path L3e different from the ordinary light optical path L3o. Light traveling along the optical paths L3o and L3e is incident on different positions on the light incident / exit surface of the Faraday rotator 8, respectively. The two lights incident on the light incident / exiting surface of the Faraday rotator 8 are reflected by the reflection film 10 and pass through the Faraday rotator 8 twice to be emitted from the light incident / exiting surface.

  When the saturated Faraday rotation angle θfs is 45 °, the Faraday rotation angle of the magnetic domain A is + 45 °, and the Faraday rotation angle of the magnetic domain B is −45 °. The ordinary light and the extraordinary light that have passed through the magnetic domain A of the Faraday rotator 8 twice are rotated by + 90 ° and emitted from the Faraday rotator 8. The ordinary light and the extraordinary light which have passed through the magnetic domain B of the Faraday rotator 8 twice are emitted from the Faraday rotator 8 by rotating the plane of polarization by −90 °. That is, the ordinary light incident on the Faraday rotator 8 from the optical path L3o is rotated by 90 ° or −90 ° on the plane of polarization, exits the Faraday rotator 8, and proceeds to the optical path L4e. The extraordinary light incident on the Faraday rotator 8 from the optical path L3e is rotated by 90 ° or −90 ° on the plane of polarization, exits the Faraday rotator 8, and proceeds to the optical path L4o. The light on the optical path L4e passes through the birefringent wedge plate 6 as abnormal light and proceeds to the optical path L5e. On the other hand, the light on the optical path L4o passes through the birefringent wedge plate 6 as ordinary light and proceeds to the optical path L5o. The light incident on the lens 4 through the optical paths L5e and L5o passes through the optical paths L6e and L6o to converge on the light incident end 12 of the output optical fiber 2, respectively.

  Here, the phase of the light passing through the magnetic domain A twice and the phase of the light passing through the magnetic domain B twice are shifted by a half wavelength. For this reason, the two lights (ordinary light) traveling on the optical path L24o and condensed on the light incident end 12 of the output optical fiber 2 cancel each other, travel on the optical path L24e, and converge on the light incident end 12 of the output optical fiber 2. The two lights (abnormal light) cancel each other. When the magnetic domain A region and the magnetic domain B region are halved in the light transmission region C, the two lights collected at the light incident end 12 of the output optical fiber 2 are not coupled at all, and the maximum attenuation is achieved. A quantity is obtained. If the magnetic field generated by the electromagnet is changed so that only the magnetic domain A exists in the light transmission region C, the magnetic domain A region is gradually decreased, and the magnetic domain B region is gradually increased. Can be changed continuously.

  FIG. 11 shows a modification of the configuration of the variable optical attenuator according to this embodiment. As shown in FIG. 11, in this modification, instead of the birefringent wedge plate 6 disposed between the lens 4 and the Faraday rotator 8, the light emitting end 11 and the output optical fiber of the input optical fiber 1 are used. The birefringent parallel flat plate 7 disposed between the two light incident ends 12 and the lens 4 is characterized. The birefringent parallel flat plate 7 is arranged at a predetermined inclination angle with respect to the X axis in the XZ plane corresponding to the inclination angle of the light incident / exit end face of the two-core ferrule 3. The optical axis of the birefringent parallel plate 7 is in the XZ plane. In the projection onto the YZ plane, the light incident / exit end surface of the two-core ferrule 3, the light emitting end 11 of the input optical fiber 1, and the light incident end 12 of the output optical fiber 2 are substantially perpendicular to the Z axis. . Further, each end face of the birefringent parallel flat plate 7, the lens 4, the Faraday rotator 8, and the reflective film 10 is substantially perpendicular to the Z axis. With this configuration, at least the optical path of the light passing through the Faraday rotator 8 is substantially parallel to the domain wall I in the projection of the optical path onto the YZ plane. In this example, almost all the optical paths coincide with the Z axis in the projection onto the YZ plane.

  The light beam emitted from the light exit end 11 of the input optical fiber 1 enters the birefringent parallel plate 7 and is separated into ordinary light and extraordinary light. The ordinary light emitted from the birefringent parallel plate 7 travels to the optical path L21o, and the extraordinary light travels to an optical path L21e different from the ordinary light optical path L21. Light traveling along the optical paths L21o and L21e is incident on the lens 4 and emitted onto the optical paths L22o and L22e, respectively. The light traveling along the optical paths L22o and L22e is incident on different positions on the light incident / exit surface of the Faraday rotator 8, respectively. The two lights incident on the light incident / exiting surface of the Faraday rotator 8 are reflected by the reflection film 10 and pass through the Faraday rotator 8 twice to be emitted from the light incident / exiting surface.

  When the saturated Faraday rotation angle θfs is 45 °, the Faraday rotation angle of the magnetic domain A is + 45 °, and the Faraday rotation angle of the magnetic domain B is −45 °. The ordinary light and the extraordinary light that have passed through the magnetic domain A of the Faraday rotator 8 twice are rotated by + 90 ° and emitted from the Faraday rotator 8. The ordinary light and the extraordinary light which have passed through the magnetic domain B of the Faraday rotator 8 twice are emitted from the Faraday rotator 8 by rotating the plane of polarization by −90 °. That is, the ordinary light incident on the Faraday rotator 8 from the optical path L22o is rotated by 90 ° or −90 ° on the polarization plane, exits the Faraday rotator 8, and proceeds to the optical path 23e. The extraordinary light incident on the Faraday rotator 8 from the optical path L22e is rotated by 90 ° or −90 ° on the plane of polarization, exits the Faraday rotator 8, and proceeds to the optical path L23o. The light on the optical paths L23e and L23o is incident on the lens 4, converted into convergent light beams, and travels to the optical paths L24e and L24o. The light on the optical path L24e passes through the birefringent parallel plate 7 as extraordinary light, and is condensed on the light incident end 12 of the output optical fiber 2. The light on the optical path L24o passes through the birefringent parallel plate 7 as ordinary light and is condensed on the light incident end 12 of the output optical fiber 2.

  Here, the phase of the light passing through the magnetic domain A twice and the phase of the light passing through the magnetic domain B twice are shifted by a half wavelength. For this reason, the two lights (ordinary light) traveling on the optical path L24o and condensed on the light incident end 12 of the output optical fiber 2 cancel each other, travel on the optical path L24e, and converge on the light incident end 12 of the output optical fiber 2. The two lights (abnormal light) cancel each other. When the magnetic domain A region and the magnetic domain B region are halved in the light transmission region C, the two lights collected at the light incident end 12 of the output optical fiber 2 are not coupled at all, and the maximum attenuation is achieved. A quantity is obtained. If the magnetic field generated by the electromagnet is changed so that only the magnetic domain A exists in the light transmission region C, the magnetic domain A region is gradually decreased, and the magnetic domain B region is gradually increased. Can be changed continuously.

  In the present embodiment, the domain wall I is substantially parallel to the XZ plane, and the moving direction of the domain wall I is the direction along the Y axis (perpendicular to the paper surface indicated by ◎ in FIG. 8A or 11A). The Faraday rotator 8, the permanent magnet, and the electromagnet are arranged so as to be in the direction and the direction indicated by the broken-line double arrow D in FIG. 8B or FIG. 11B. For this reason, the optical characteristics of the Faraday rotator 8 are not distributed in the in-plane direction projected so that the two optical paths do not overlap. Therefore, the polarization dependence of the polarization-independent variable optical attenuator using the birefringent plate can be suppressed. On the other hand, in the YZ plane, although the distribution of the Faraday rotation angle θf occurs in the Faraday rotator 8 with the domain wall I as a boundary, as shown in FIGS. 8B and 11B, two Faraday rotators 8 in the Faraday rotator 8 Since the projection of the optical path overlaps and is shared, ordinary light and extraordinary light are not affected by different optical characteristics.

  In the present embodiment, at least the optical path of the light passing through the Faraday rotator 8 is substantially parallel to the domain wall I in the projection of the optical path onto the YZ plane. Therefore, the light incident on the magnetic domain A of the Faraday rotator 8 passes through only the magnetic domain A without traversing the domain wall I and exits from the Faraday rotator 8. The light incident on the magnetic domain B of the Faraday rotator 8 passes through the domain wall I. The Faraday rotator 8 is ejected through only the magnetic domain B without crossing. Thereby, when the region of the magnetic domain A and the region of the magnetic domain B exist almost in half in the light reflection region C, diffraction is almost completely performed. Therefore, according to the variable optical attenuator of the present embodiment, it is possible to easily obtain a desired attenuation amount, which is not inferior to that of a transmissive optical component, and to obtain good optical characteristics with high reproducibility.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above embodiment, the reflection type variable optical attenuator has been described as an example. However, the present invention is not limited to this, and can be applied to a transmission type variable optical attenuator and other optical components. In particular, when applied to an optical component including an optical element in which an optical boundary surface such as the domain wall I of the Faraday rotator 8 of the second embodiment is formed, the same as the second embodiment. The effect is obtained.

  In the above embodiment, for example, the Faraday rotator 8 in which the distribution of optical characteristics does not occur in the direction of the broken-line double-pointed arrow E in FIGS. 1A and 1B has been described as an example. I can't. For example, even in the case of the Faraday rotator 8 in which the distribution of optical characteristics is generated in both the broken-line double-headed arrows D and E in FIGS. 1A and 1B, the distribution of the optical characteristics generated in the Faraday rotator 8 is measured in advance. If the Faraday rotator 8 (and permanent magnets and electromagnets) is arranged so that a more uniform direction of optical characteristics is arranged in the direction of the broken-line double-headed arrow E, the same effect as in the above embodiment can be obtained.

It is a figure which shows the structure of the variable optical attenuator as an optical component by the 1st Embodiment of this invention. It is FIG. (1) explaining the operation principle of the variable optical attenuator as an optical component by the 2nd Embodiment of this invention. It is FIG. (2) explaining the operation principle of the variable optical attenuator as an optical component by the 2nd Embodiment of this invention. It is FIG. (3) explaining the operation principle of the variable optical attenuator as an optical component by the 2nd Embodiment of this invention. It is a figure which shows the state of the domain wall I between the magnetic domains A and B which arise in the Faraday rotator by the 2nd Embodiment of this invention. It is a figure which shows the state of the domain wall I between the magnetic domains A and B produced when a magnetic field gradient is small. It is a figure which shows the relationship between the light which injects into a Faraday rotator, and the domain wall. It is a figure which shows the structure of the variable optical attenuator as an optical component by the 2nd Embodiment of this invention. It is a figure which shows the relationship between the light which injects into a Faraday rotator, and the domain wall. It is a figure which shows the relationship between the light which injects into a Faraday rotator, and the domain wall. It is a figure which shows the modification of a structure of the variable optical attenuator as an optical component by the 2nd Embodiment of this invention. It is a figure which shows the structure of the conventional variable optical attenuator. It is a figure which shows the structure of the magnetic field application unit of the conventional variable optical attenuator. It is a figure which shows the structure of the conventional variable optical attenuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input optical fiber 2 Output optical fiber 3 Two-core ferrule 4 Lens 6 Birefringent wedge plate 7 Birefringent parallel plate 8 Faraday rotator 10 Reflective film 11 Light emitting end 12 Light incident end 32 York

Claims (8)

A lens that makes divergent light substantially parallel light and at least one of the front and rear of the lens as viewed in the light traveling direction, and separates the incident light into ordinary light and extraordinary light and separates them into two different optical paths. An optical component having a birefringent element that respectively emits and an optical element having a predetermined optical function with respect to light incident from the two optical paths,
There is at least one virtual plane parallel to the central axis of the lens and projected by overlapping the two optical paths,
The optical component is disposed so as to have a distribution of optical characteristics in a direction substantially parallel to a light incident / exit surface of the optical element within a plane parallel to the virtual plane. The optical component according to claim 1,
An optical component, further comprising a reflective film that reflects light that has passed through the optical element and reenters the optical element. The optical component according to claim 1 or 2,
The optical component, wherein the two optical paths substantially coincide with a central axis of the lens when projected onto the virtual plane. The optical component according to any one of claims 1 to 3,
The optical element is a magneto-optical crystal having a Faraday effect, and is composed of a magnetic domain A configured by magnetization in a direction substantially perpendicular to the light incident / exit surface, and magnetization in a direction opposite to the magnetization direction of the magnetic domain A. An optical component comprising: a magnetic domain B having optical characteristics different from that of the magnetic domain A; and a domain wall that is a boundary surface between the magnetic domain A and the magnetic domain B. The optical component according to claim 4,
The optical component is characterized in that the domain wall is formed substantially perpendicular to the virtual plane. The optical component according to claim 4 or 5,
The optical component is capable of moving in a direction substantially parallel to the light incident / exit surface within a plane parallel to the virtual plane. The optical component according to any one of claims 4 to 6,
The optical component characterized in that the two optical paths are substantially parallel to the domain wall at least in the optical element when projected onto the virtual plane. The optical component according to any one of claims 1 to 3,
The optical element is a magneto-optical crystal having a Faraday effect;
A first magnetic field is applied in a direction substantially parallel to the light incident / exit surface of the magneto-optic crystal within a plane parallel to the virtual plane;
An optical component, wherein the second magnetic field is applied in a direction different from the first magnetic field.

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