JP2005265901A - Optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical component such as a variable optical attenuator with a monitor function and a photodetection module with a variable attenuator, the optical component having both a variable optical attenuating function of variably attenuating light and a monitor function of monitoring the quantity of light. <P>SOLUTION: The optical component has: a birefringent crystal plate 11 which splits a light L1 into lights L2a and L2b and projects them on different optical paths; 1/2-wavelength plates 26 and 27 which rotates polarization azimuths of the lights to project them as lights L3a and L3b having the same polarization azimuth; a Faraday rotator 20 which variably rotates the polarization azimuths of the lights to project them as lights L4a and L4b; a polarizing glass 34 which absorbs specified polarized light components and projects lights L5a and L5b; 1/2-wavelength plates 28 and 29 which rotate the polarization azimuths of the lights to protect lights L6a and L6b having orthogonal polarization azimuths; a birefringent crystal plate 12 which multiplexes the lights to project a light L7; and a photodetecting element 32 which receives part of the light L7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical component such as a variable optical attenuator used in an optical communication system, a variable optical attenuator with a monitoring function, and a light receiving module with a variable attenuator.

  One of optical components used in an optical communication system is a variable optical attenuator (variable optical attenuator). As a variable optical attenuator, a so-called magneto-optical variable optical attenuator is known that controls the amount of light attenuation by changing the Faraday rotation angle according to the strength of an applied magnetic field. The magneto-optic variable optical attenuator has advantages that it has high mechanical reliability and is easy to miniaturize because there is no mechanical moving part. The magneto-optical variable optical attenuator includes a magneto-optical element (magneto-optical crystal) and an electromagnet that applies a variable magnetic field to the magneto-optical 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.

  The main purpose of use of the variable optical attenuator is light amount adjustment. For this reason, the variable optical attenuator is often used in combination with a light receiving element that monitors the amount of light. FIG. 6 shows a configuration of a conventional variable optical attenuator disclosed in Patent Document 1. As shown in FIG. 6, the variable optical attenuator 120 includes an optical fiber 110a, a lens 107a, a wedge-shaped birefringent crystal 108a, a Faraday rotator 109, a wedge-shaped birefringent crystal 108b, and a lens 107b. And an optical fiber 110b. Further, on the output side of the variable optical attenuator 120, an optical coupler 100 that branches a part of two birefringent light beams, a lens 102, an aperture 104 that passes one of the two birefringent light beams, A light receiver 106 that monitors the optical power that has passed through the aperture 104 is provided. A control circuit 122 is provided outside the variable optical attenuator 120. The control circuit 122 controls the amount of current that flows through the coil of the variable optical attenuator 120 so that the output power of the variable optical attenuator 120 becomes a predetermined value based on the electrical signal photoelectrically converted by the light receiver 106. It has become. As a result, the input power fluctuation to the variable optical attenuator 120 can be suppressed and the output power can be controlled to be constant.

  The light emitted from the wedge-shaped birefringent crystal 108b is composed of four beams having different angles (polarization directions) or optical paths. Two of the beams are coupled to the optical fiber 110b, and the remaining two beams are attenuation components that are not coupled to the optical fiber 110b. In order to monitor the output power, it is necessary to receive only two beams coupled to the optical fiber 110b by the light receiver 106. For this purpose, as shown in FIG. 6, the aperture 104 is used to remove unnecessary beams, or the light receiving surface of the light receiver 106 is made small so that only two beams coupled to the optical fiber 110b are received. It is necessary to align the optical axis of the light receiver 106.

  However, when the aperture 104 is used, the number of parts increases, and thus there is a problem that the manufacturing cost of the variable optical attenuator 120 increases. Further, there is a problem that the optical axis alignment of the light receiver 106 is extremely difficult. As described above, in an optical component such as the variable optical attenuator 120 using the birefringent crystals 108a and 108b as polarizers, unnecessary light that is not coupled to the optical fiber 110b is also received simply by providing the light receiver 106. Therefore, it is difficult to add a function for monitoring the amount of transmitted light.

JP-A-9-236784

  An object of the present invention is to provide an optical component having both a variable light attenuation function for variably attenuating light and a monitor function for monitoring the amount of light.

  The purpose is to split the light incident from the outside into first and second light beams whose polarization directions are substantially orthogonal to each other and to emit them on different optical paths, and among the first and second light beams Rotating at least one of the polarization directions, and variably converting the polarization state of the third and fourth lights, and a first polarization rotating unit that emits the third and fourth lights respectively having substantially the same polarization directions. Then, a variable polarization element that emits light as fifth and sixth light, respectively, and a polarizer that absorbs a predetermined polarization component of the fifth and sixth light and emits light as seventh and eighth light, respectively. And a second polarization rotating section that rotates at least one of the seventh and eighth lights and emits them as ninth and tenth lights whose polarization directions are substantially orthogonal to each other, and the ninth And combine the tenth light Is achieved by the optical component and having a polarization multiplexing device emitting as 11 of light.

  In the optical component of the present invention, the polarizer absorbs a polarization component that is not combined by the polarization multiplexing element.

  The optical component according to the present invention further includes an optical element that branches a part of the eleventh light and a light receiving element that receives a part of the eleventh light and detects the intensity. It is characterized by.

  The optical component of the present invention is characterized in that it further includes a light receiving element that receives the eleventh light and detects its intensity.

  In addition, the object is to separate the light incident from the outside into first and second light beams whose polarization directions are substantially orthogonal to each other and to emit the light beams on different optical paths, and the first and second light beams. The polarization rotator that rotates at least one of the polarization orientations and emits the third and fourth light beams having substantially the same polarization orientation, and variably converts the polarization states of the third and fourth lights. A variable polarization element that emits light as fifth and sixth light, respectively, and a polarizer that absorbs a predetermined polarization component of the fifth and sixth light and emits light as seventh and eighth light, respectively. It is achieved by an optical component comprising a light receiving element that receives the seventh and eighth lights and detects the intensity.

  In the optical component of the present invention, the variable polarization element variably rotates the polarization directions of the third and fourth lights.

  According to the present invention, an optical component having both a variable light attenuation function for variably attenuating light and a monitor function for monitoring the amount of light can be realized.

[First Embodiment]
An optical component according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 schematically shows a configuration of a variable optical attenuator 1 having a monitor function as an optical component according to the present embodiment. In FIG. 1, 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. As shown in FIG. 1, the variable optical attenuator 1 is connected to an optical fiber 41 disposed on the −Z direction side and an optical fiber 42 disposed on the + Z direction side. The end of the optical fiber 41 on the −Z side is a light incident port P1 (indicated as (1) in the drawing) through which light enters from the outside. The + Z side end of the optical fiber 42 is a light exit port P2 (indicated as (2) in the figure) through which light exits.

  In the + Z direction of the optical fiber 41, a lens 51 that converts divergent light emitted from the optical fiber 41 into parallel light is disposed. A birefringent crystal plate (polarization separation element) 11 is disposed in the + Z direction of the lens 51. The birefringent crystal plate 11 is configured to offset the extraordinary light component of the light traveling in the + Z direction by a predetermined amount of offset in the -Y direction. In the + Z direction of the birefringent crystal plate 11, two half-wave plates (first polarization rotation units) 26 and 27 are arranged. The half-wave plates 26 and 27 are arranged adjacent to each other in the ± Y direction. The half-wave plate 26 is arranged on the + Y side, and rotates the polarization direction of the light transmitted through the birefringent crystal plate 11 as ordinary light by + 45 °. The half-wave plate 27 is arranged on the −Y side, and rotates the polarization direction of the light transmitted through the birefringent crystal plate 11 as extraordinary light by −45 °. Thereby, the polarization direction of the light transmitted through the half-wave plate 26 and the polarization direction of the light transmitted through the half-wave plate 27 coincide. If the half-wave plate is arranged so that the polarization orientation of the light transmitted through the birefringent crystal plate 11 as ordinary light and the polarization orientation of the light transmitted through the birefringent crystal plate 11 as extraordinary light coincide with each other. Good. Therefore, for example, if a single half-wave plate 26 that rotates the polarization orientation by + 90 ° on the optical path of the light that has passed through the birefringent crystal plate 11 as ordinary light is arranged as the first polarization rotation unit, The half-wave plate 27 may not be disposed on the optical path of the light transmitted through the refractive crystal plate 11 as extraordinary light.

  In the + Z direction of the half-wave plates 26 and 27, a Faraday rotator 20 is arranged as a variable polarization element that variably changes the polarization state of light. The Faraday rotator 20 is produced by polishing a Bi-substituted rare earth iron garnet single crystal film grown by, for example, an LPE (liquid phase epitaxial) method. The single crystal film grown by the LPE method is usually a perpendicular magnetization film having perpendicular magnetization due to induced magnetic anisotropy. As will be described later, a perpendicular magnetization film is not suitable for the Faraday rotator 20 in the case where the magnetization rotation method in which the magnetization is rotated to control the Faraday rotation angle is used. For this reason, when the magnetization rotation method is used, the Bi-substituted rare earth iron garnet single crystal film used for the Faraday rotator 20 is heat-treated at a temperature of about 1000 ° C. for several hours or more in order to eliminate the induced magnetic anisotropy. Is given.

  A variable magnetic field is applied to the Faraday rotator 20 by a magnetic field application mechanism (not shown). The magnetic field application mechanism has, for example, a permanent magnet (or semi-hard magnet) and an electromagnet. The Faraday rotator 20 is in a state of saturation magnetization by a perpendicular magnetic field previously applied in the Z direction, for example, by a permanent magnet. Further, a variable horizontal magnetic field is applied to the Faraday rotator 20 by an electromagnet, for example, in the X direction. FIG. 2 shows the magnetization direction in the Faraday rotator 20 and its magnitude, and the direction and magnitude of the magnetic field applied to the Faraday rotator 20 from the outside. Arrows 82 and 85 are vectors representing the magnetization direction and the magnitude in the Faraday rotator 20, and arrows 81, 83 and 84 are vectors representing the direction and magnitude of the magnetic field applied to the Faraday rotator 20 from the outside. is there. In a state where no current is passed through the coil of the electromagnet, the Faraday rotator 20 is uniformly in a saturation magnetization 82 state by a vertical magnetic field 81 by a permanent magnet. At this time, the Faraday rotation angle (saturated Faraday rotation angle) θf of the Faraday rotator 20 is, for example, 90 °. When a current is passed through the coil of the electromagnet and the horizontal magnetic field 83 is applied by the electromagnet, the external magnetic field becomes the combined magnetic field 84 and the Faraday rotator 20 enters the state of magnetization 85. The magnitude of the magnetization 85 is the same as the magnitude of the saturation magnetization 82, and therefore the Faraday rotator 20 is in a saturation magnetization state.

  In this way, the Faraday rotator 20 is preliminarily applied to the Faraday rotator 20 by a permanent magnet so that the Faraday rotator 20 is in a saturation magnetization state, and a predetermined current is passed through the coil so that the Faraday rotator 20 can be changed by the electromagnet. A horizontal magnetic field 83 is applied. Then, the direction of magnetization of the light transmission region of the Faraday rotator 20 is uniformly rotated from the magnetization 82 to the magnetization 85 by the angle θ by the combined magnetic field 84 of the two magnetic fields 81 and 83, and the magnitude of the Z-direction component 86 of the magnetization. Is controlling. The Faraday rotation angle θf of the Faraday rotator 20 varies in the range of 0 ° <θf ≦ 90 ° depending on the magnitude of the Z-direction component 86. For example, when each optical element is arranged so that the attenuation amount is minimized when the Faraday rotation angle θf is 90 °, the maximum attenuation amount can be obtained when the Faraday rotation angle θf is about 0 °. Since the Faraday rotator 20 is always used in the saturation magnetization region, the Faraday rotation angle θf can be changed with good reproducibility without causing hysteresis. The saturated Faraday rotation angle is not limited to 90 °. For example, when the saturation Faraday rotation angle is 105 ° and each Faraday rotation angle θf is 15 °, the optical elements are arranged so that the attenuation is minimized, and the maximum Faraday rotation angle θf is 15 °. An attenuation amount may be obtained. In order to set the Faraday rotation angle θf to about 0 °, it is necessary to apply a very strong horizontal magnetic field by an electromagnet. Thus, it is possible to obtain the maximum attenuation at the Faraday rotation angle θf larger than 0 °. This is effective for reducing power consumption.

  Returning to FIG. 1, a polarizing glass (polarizer) 34 is disposed in the + Z direction of the Faraday rotator 20. The polarizing glass 34 absorbs light of a polarization component that is not coupled to the light exit port P2 out of the light from the light incident port P1. Two half-wave plates (second polarization rotating portions) 28 and 29 are arranged in the + Z direction of the polarizing glass 34, and a birefringent crystal plate (polarized light) is arranged in the + Z direction of the half-wave plates 28 and 29. (Multiplexing element) 12 is arranged. The half-wave plates 28 and 29 are arranged adjacent to each other in the ± Y direction. The half-wave plate 28 is arranged on the + Y side, and the polarization direction is rotated so that light transmitted through the birefringent crystal plate 11 as ordinary light enters the birefringent crystal plate 12 as extraordinary light. The half-wave plate 29 is arranged on the −Y side, and the polarization direction is rotated so that light transmitted through the birefringent crystal plate 11 as extraordinary light enters the birefringent crystal plate 12 as ordinary light. Yes. Similar to the birefringent crystal plate 11, the birefringent crystal plate 12 is arranged so that the extraordinary light component of the light traveling in the + Z direction is offset in the -Y direction. The amount of axial deviation of the birefringent crystal plates 11 and 12 is substantially the same. If the orientation of the birefringent crystal plate 12 is adjusted, only one of the half-wave plates 28 and 29 may be used. The birefringent crystal plates 11, 12, half-wave plates 26, 27, 28, 29, Faraday rotator 20, and polarizing glass 34 are, for example, parallel plate type optical elements, and light incident / exit substantially parallel to the XY plane. Has a surface. Here, in optics, a “light incident surface” may be defined as a surface including an incident light ray and a normal of a boundary surface. However, the “light incident / exit surface” in this specification is not defined as this, It means a surface where light enters / exits in an optical element.

  In the + Z direction of the birefringent crystal plate 12, a lens 52 that converts parallel light emitted from the birefringent crystal plate 12 into convergent light and enters the optical fiber 42 is disposed. Between the birefringent crystal plate 12 and the lens 52, a glass plate 30 which is an optical element for branching a part of light is disposed. For example, the glass plate 30 is arranged in parallel to a surface rotated 45 ° clockwise about the X axis when the XY plane is viewed in the + X direction, and reflects part of the light traveling in the + Z direction in the + Y direction. Yes. In the + Y direction of the glass plate 30, a light receiving element 32 that receives light reflected by the glass plate 30 and detects its intensity is disposed. By detecting the light intensity with the light receiving element 32, the amount of light transmitted through the variable optical attenuator 1 can be monitored.

  In this example, the variable optical attenuator 1 using the magnetization rotation method is taken as an example, but the present invention can also be applied to a variable optical attenuator using another method such as a domain wall motion method. For example, the Faraday rotator 20 of the variable optical attenuator using the domain wall motion method is manufactured using a magnetic garnet single crystal film having perpendicular magnetization. The Faraday rotator 20 is applied with a magnetic field monotonously changing in a predetermined direction in the light incident / exit surface by a magnetic field application mechanism, and a magnetic domain A composed of magnetization in a direction not parallel to the light incident / exit surface, A magnetic domain B constituted by magnetization opposite to the magnetization direction and a planar domain wall I serving as a boundary between the magnetic domain A and the magnetic domain B are formed. The Faraday rotation angle θf can be controlled by changing the position of the domain wall I by changing the magnetic field applied to the Faraday rotator 20 by the magnetic field application mechanism. In the variable optical attenuator using the domain wall motion method, the Faraday rotation angle θf with respect to the two lights L3a and L3b can be made the same if the domain wall I and the biaxial refraction plates 11 and 12 are made to be parallel to each other. Therefore, polarization independence can be realized.

  Next, the operation of the variable optical attenuator 1 according to this embodiment will be described. The light incident from the light incident port P1 enters the birefringent crystal plate 11 as light L1. The light L1 incident on the birefringent crystal plate 11 is separated into ordinary light L2a and extraordinary light L2b and emitted onto different optical paths. That is, the ordinary light component light L2a travels straight through the birefringent crystal plate 11, and the extraordinary light component light L2b deviates from the birefringent crystal plate 11 by a predetermined amount in the -Y direction. The light L2a emitted from the birefringent crystal plate 11 enters the half-wave plate 26, and the light L2b enters the half-wave plate 27. The light L2a incident on the half-wave plate 26 is emitted from the half-wave plate 26 as light L3a whose polarization orientation is rotated by + 45 °. The light L2b incident on the half-wave plate 27 exits the half-wave plate 27 as light L3b whose polarization direction is rotated by −45 °. Thereby, the polarization directions of the two lights L3a and L3b coincide with each other. The two lights L3a and L3b are incident on the Faraday rotator 20. The two lights L3a and L3b incident on the Faraday rotator 20 are emitted from the Faraday rotator 20 as lights L4a and L4b whose polarization azimuths are both rotated by a predetermined angle. The two lights L4a and L4b are incident on the polarizing glass 34. The light L4a and L4b incident on the polarizing glass 34 is attenuated and attenuated by the polarization component that is not coupled to the light output port P2, and is emitted from the polarizing glass 34 as light L5a and L5b, respectively. The transmission axis of the polarizing glass 34 is substantially parallel to the polarization azimuths of the lights L4a and L4b in a state where the attenuation amount is minimum when it is assumed that the polarizing glass 34 is not provided.

  The light L5a emitted from the polarizing glass 34 enters the half-wave plate 28, and the light L5b enters the half-wave plate 29. The light L5a incident on the half-wave plate 28 exits the half-wave plate 28 as light L6a whose polarization orientation has been rotated by + 45 °, and enters the birefringent crystal plate 12. The light L5b incident on the half-wave plate 29 exits the half-wave plate 29 as light L6b whose polarization orientation is rotated by −45 °, and enters the birefringent crystal plate 12. Thereby, the polarization directions of the two lights L6a and L6b are orthogonal to each other. The light L6a passes through the birefringent crystal plate 12 as extraordinary light, and the light L6b passes through the birefringent crystal plate 12 as ordinary light. That is, the extraordinary light component light L6a is offset by a predetermined amount in the -Y direction at the birefringent crystal plate 12, and the ordinary light component light L6b travels straight through the birefringent crystal plate 12. Since the birefringence crystal plates 11 and 12 have the same axis deviation direction and the same axis deviation amount, the two lights L6a and L6b are combined and emitted from the birefringence crystal plate 12 as light L7. Here, since the polarization component that is not multiplexed by the birefringent crystal plate 12 is absorbed by the polarizing glass 34, the polarized light component L6a that exits the half-wave plate 28 and passes through the birefringent crystal plate 12 as ordinary light. 'And the polarized light component L6b' that exits the half-wave plate 29 and passes through the birefringent crystal plate 12 as extraordinary light are hardly present. A part of the light L7 is reflected by the glass plate 30 and is incident on the light receiving element 32, and the other part is transmitted through the glass plate 30 and is incident on the light exit port P2 and is emitted to the outside.

  In the variable optical attenuator 1 of this embodiment, the magnetic field applied to the Faraday rotator 20 is gradually changed by the magnetic field application mechanism, and the magnitude of the polarization component coupled to the light exit port P2 is changed, thereby changing the light intensity. The attenuation can be continuously changed. Further, since the optical path lengths of the two lights are equal to each other, polarization mode dispersion does not occur.

  In the present embodiment, the polarization component that is not combined by the birefringent crystal plate 12 (the polarization component that is not coupled to the light output port P2) is absorbed by the polarization glass. For this reason, almost all of the light emitted from the birefringent crystal plate 12 is coupled to the light exit port P2, so that the optical axes of the glass plate 30 and the light receiving element 32 can be easily aligned, and the variable optical attenuator 1 The function of monitoring the amount of transmitted light can be easily added. Therefore, according to the present embodiment, it is possible to realize an optical component having both a variable light attenuation function for variably attenuating light and a monitor function for monitoring the amount of light.

  FIG. 3 schematically shows a configuration of a two-stage variable optical attenuator 1 ′ as a modification of the magneto-optical component according to the present embodiment. In FIG. 3, the coordinate system is taken as in FIG. As shown in FIG. 3, the variable optical attenuator 1 ′ has a birefringent crystal plate 11 and two half-wave plates 26 and 27 arranged in the + Z direction of the birefringent crystal plate 11. Yes. The half-wave plate 26 rotates the polarization direction of light transmitted through the birefringent crystal plate 11 as ordinary light by + 45 °, and the half-wave plate 27 changes the polarization direction of light transmitted through the birefringent crystal plate 11 as extraordinary light. -45 ° rotation. Thereby, the polarization direction of the light transmitted through the half-wave plate 26 and the polarization direction of the light transmitted through the half-wave plate 27 coincide. In the + Z direction of the half-wave plates 26 and 27, the Faraday rotator 20, the polarizing glass 34, the Faraday rotator 21, and the polarizing glass 35 are arranged in this order. The polarizing glasses 34 and 35 are configured to absorb light of a polarization component that is not coupled to the light exit port P2 out of the light from the light incident port P1 side. Two half-wave plates 28 and 29 are arranged in the + Z direction of the polarizing glass 35, and the birefringent crystal plate 12 is arranged in the + Z direction of the half-wave plates 28 and 29. The half-wave plate 28 rotates the polarization direction so that the light transmitted through the polarizing glass 35 enters the birefringent crystal plate 12 as extraordinary light. The half-wave plate 29 rotates the polarization direction so that light transmitted through the polarizing glass 35 enters the birefringent crystal plate 12 as ordinary light. A glass plate 30 is arranged in the + Z direction of the birefringent crystal plate 12. The glass plate 30 is arranged in parallel to a plane rotated 45 ° clockwise about the X axis when the XY plane is viewed in the + X direction, and reflects a part of the light traveling in the + Z direction in the + Y direction. . In the + Y direction of the glass plate 30, a light receiving element 32 that monitors light reflected by the glass plate 30 is disposed. By detecting the light intensity with the light receiving element 32, the amount of light transmitted through the variable optical attenuator 1 'can be monitored.

  In this modification, light that is not coupled to the light exit port P2 is absorbed by the polarizing glasses 34 and 35. Accordingly, similar to the configuration shown in FIG. 1, almost all of the light emitted from the birefringent crystal plate 12 is coupled to the light exit port P2, so that the amount of light transmitted through the variable optical attenuator 1 ′ is monitored. Becomes easier. In addition, the variable optical attenuator 1 ′ of this modification has a two-stage configuration in which two Faraday rotators 20 and 21 are used. Accordingly, since an extremely high attenuation amount can be obtained as compared with the configuration shown in FIG. 1, the variable optical attenuator 1 'also functions as an optical shutter.

[Second Embodiment]
Next, an optical component according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 shows the configuration of a light receiving module 2 with a variable attenuator as an optical component according to this embodiment. In FIG. 4, the coordinate system is taken as in FIG. As shown in FIG. 4, the light receiving module 2 is connected to an optical fiber 41 arranged in the −Z direction. The −Z side end of the optical fiber 41 is a light incident port P1 through which light enters from the outside. In the + Z direction of the optical fiber 41, a lens 51 that converts divergent light emitted from the optical fiber 41 into parallel light is disposed.

  The light receiving module 2 includes optical elements (birefringent crystal plate 11, half-wave plates 26 and 27, Faraday rotator 20, polarizing glass 34, half-wavelength) arranged in the same manner as the variable optical attenuator 1 shown in FIG. It has plates 28 and 29 and a birefringent crystal plate 12). The light receiving module 2 can be applied to a magnetization rotation method, a domain wall motion method, and the like, similarly to the variable optical attenuator 1 of the first embodiment. In the + Z direction of the birefringent crystal plate 12, for example, a light receiving element 32 that directly receives the light emitted from the birefringent crystal plate 12 is disposed.

  Next, the operation of the light receiving module 2 according to this embodiment will be described. Light incident from the light incident port P1 enters the birefringent crystal plate 11 as light L11. The light L11 incident on the birefringent crystal plate 11 is separated into ordinary light L12a and extraordinary light L12b and is emitted onto different optical paths. That is, the ordinary light component light L12a travels straight through the birefringent crystal plate 11, and the extraordinary light component light L12b deviates from the birefringent crystal plate 11 by a predetermined amount in the -Y direction. The light L12a emitted from the birefringent crystal plate 11 enters the half-wave plate 26, and the light L12b enters the half-wave plate 27. The light L12a incident on the half-wave plate 26 is emitted from the half-wave plate 26 as light L13a whose polarization direction is rotated by + 45 °. The light L12b incident on the half-wave plate 27 is emitted from the half-wave plate 27 as light L13b whose polarization direction is rotated by −45 °. As a result, the polarization directions of the two lights L13a and L13b coincide with each other. The two lights L13a and L13b are incident on the Faraday rotator 20. Lights L13a and L13b incident on the Faraday rotator 20 are emitted from the Faraday rotator 20 as light L14a and L14b whose polarization directions are rotated by a predetermined angle. The two lights L14a and L14b are incident on the polarizing glass 34. The light L14a and L14b incident on the polarizing glass 34 is attenuated by the polarization component that is not multiplexed by the birefringent crystal plate 12, and is emitted from the polarizing glass 34 as light L15a and L15b. The transmission axis of the polarizing glass 34 is substantially parallel to the polarization azimuths of the lights L14a and L14b in a state where the attenuation amount is minimum when it is assumed that the polarizing glass 34 is not provided.

  The light L15a emitted from the polarizing glass 34 enters the half-wave plate 28, and the light L15b enters the half-wave plate 29. The light L15a incident on the half-wave plate 28 exits the half-wave plate 28 as light L16a with the polarization orientation rotated by + 45 °, and enters the birefringent crystal plate 12. The light L15b incident on the half-wave plate 29 exits the half-wave plate 29 as light L16b whose polarization orientation is rotated by −45 °, and enters the birefringent crystal plate 12. Thereby, the polarization directions of the two lights L16a and L16b are orthogonal to each other. The light L16a passes through the birefringent crystal plate 12 as extraordinary light, and the light L16b passes through the birefringent crystal plate 12 as ordinary light. That is, the extraordinary light component light L16a is offset by a predetermined amount in the -Y direction at the birefringent crystal plate 12, and the ordinary light component light L16b travels straight through the birefringent crystal plate 12. Since the birefringent crystal plates 11 and 12 have the same axial deviation direction and axial deviation amount, the two lights L16a and L16b are combined and emitted as the light L17 from the birefringent crystal board 12. Here, since the polarization component that is not combined by the birefringent crystal plate 12 is absorbed by the polarizing glass 34, the polarized light component L16a that exits from the half-wave plate 28 and passes through the birefringent crystal plate 12 as ordinary light. 'And the polarization component light L16b' that exits the half-wave plate 29 and passes through the birefringent crystal plate 12 as extraordinary light are hardly present. The light L17 emitted from the birefringent crystal plate 12 directly enters the light receiving element 32.

  In the light receiving module 2 of the present embodiment, the amount of light attenuation is obtained by gradually changing the magnetic field applied to the Faraday rotator 20 by the magnetic field applying mechanism and changing the magnitude of the polarization component coupled to the light exit port P2. Can be changed continuously. Further, since the optical path lengths of the two lights are equal to each other, polarization mode dispersion does not occur.

  In the present embodiment, similarly to the first embodiment, the polarization component that is not combined by the birefringent crystal plate 12 is absorbed by the polarizing glass 34. For this reason, the optical axis alignment of the light receiving element 32 becomes unnecessary, and the light receiving module 2 with a variable attenuator can be easily realized. Therefore, according to the present embodiment, it is possible to realize an optical component having both a variable light attenuation function for variably attenuating light and a monitor function for monitoring the amount of light.

  FIG. 5 schematically shows a configuration of a light receiving module 2 ′ with a variable attenuator as a modification of the magneto-optical component according to the present embodiment. In FIG. 5, the coordinate system is taken as in FIG. As shown in FIG. 5, the light receiving module 2 ′ does not have the half-wave plates 28 and 29 and the birefringent crystal plate 12 and emits the polarizing glass 34 compared to the light receiving module 2 shown in FIG. 4. For example, the light receiving element 32 ′ that directly receives the two lights L15a and L15b.

  In the present modification, although the two lights L15a and L15b travel on different optical paths, the point that the intensity is already attenuated by a predetermined attenuation amount is used. Therefore, if the light receiving element 32 'has a light receiving surface capable of receiving both the light L15a and L15b, a light receiving module 2' with a variable attenuator can be realized with a simpler configuration than the light receiving module 2 shown in FIG.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above-described embodiment, the configuration using the Faraday rotator 20 that is a magneto-optic crystal as a variable polarization element has been described as an example. It can also be used as an element.

It is a figure which shows the structure of the optical component by the 1st Embodiment of this invention. It is a figure explaining the variable polarization element of the optical component by the 1st Embodiment of this invention. It is a figure which shows the modification of a structure of the optical component by the 1st Embodiment of this invention. It is a figure which shows the structure of the optical component by the 2nd Embodiment of this invention. It is a figure which shows the modification of a structure of the optical component by the 2nd Embodiment of this invention. It is a figure which shows the structure of the conventional variable optical attenuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'Variable optical attenuator 2, 2' Light reception module 11, 12 Birefringence crystal plate 20, 21 Faraday rotator 26, 27, 28, 29 1/2 wavelength plate 30 Glass plate 32 Light receiving element 34, 35 Polarizing glass 41, 42 Optical fiber 51, 52 Lens

Claims (6)

A polarization separation element that separates light incident from the outside into first and second light beams substantially orthogonal to each other in polarization direction and emits the light beams on different optical paths;
A first polarization rotator that rotates at least one of the first and second lights and emits them as third and fourth lights having substantially the same polarization orientation;
A variable polarization element that variably converts the polarization states of the third and fourth lights and emits them as fifth and sixth lights, respectively;
A polarizer that absorbs a predetermined polarization component of the fifth and sixth lights, respectively, and emits them as seventh and eighth lights;
A second polarization rotator that rotates at least one of the seventh and eighth lights and emits them as ninth and tenth lights that are substantially orthogonal to each other;
An optical component comprising: a polarization multiplexing element that multiplexes the ninth and tenth lights and emits them as eleventh light. The optical component according to claim 1,
The optical component according to claim 1, wherein the polarizer absorbs a polarization component that is not multiplexed by the polarization multiplexing element. The optical component according to claim 1 or 2,
An optical element for branching a part of the eleventh light;
An optical component, further comprising: a light receiving element that receives a part of the branched eleventh light and detects an intensity thereof. The optical component according to claim 1 or 2,
An optical component, further comprising: a light receiving element that receives the eleventh light and detects the intensity. A polarization separation element that separates light incident from the outside into first and second light beams substantially orthogonal to each other in polarization direction and emits the light beams on different optical paths;
A polarization rotation unit that rotates at least one polarization direction of the first and second lights and emits them as third and fourth lights having substantially the same polarization direction;
A variable polarization element that variably converts the polarization states of the third and fourth lights and emits them as fifth and sixth lights, respectively;
A polarizer that absorbs a predetermined polarization component of the fifth and sixth lights, respectively, and emits them as seventh and eighth lights;
An optical component comprising: a light receiving element that receives the seventh and eighth lights and detects intensity. An optical component according to any one of claims 1 to 5,
The optical component, wherein the variable polarization element variably rotates polarization directions of the third and fourth lights.

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