JP4544359B2 - Optical parts - Google Patents

Description

  The present invention relates to an optical component that adjusts the power of light propagating from a first optical path to a second optical path.

In optical communication, an optical component for adjusting the power of an optical signal, for example, a variable optical attenuator or an optical switch is often used. In an example of such an optical component, a mirror is disposed on the optical path between two optical waveguides, and the amount of reflected light is changed by moving the mirror, thereby propagating from one optical waveguide to the other optical waveguide. The light power is adjusted (see Non-Patent Document 1).
C. Marxer et al., "Micro-Opto-Mechanical 2x2 Switch for Single Mode Fibers based on Plasma-Etched Silicon Mirror and Electrostatic Actuation" (preceding 11th IEEE Workshop on Micro-Electro-Mechanical System, 1998, 233-237)

  FIG. 10 is a schematic plan view showing an example of a variable optical attenuator using a mirror. The variable optical attenuator 50 includes a planar lightwave circuit (PLC) 10, a mirror 20, and a mirror driving device 30. The optical waveguides 11 and 12 in the PLC 10 have end portions arranged mirror-symmetrically with respect to the plane 13. These end portions have end faces 11a and 12a aligned on the same plane. The mirror 20 has a reflecting surface 20a parallel to these end surfaces 11a and 12a. The mirror driving device 30 can move the mirror 20 along the directions indicated by the arrows 32 and 33. The light from the optical waveguide 11 is reflected toward the optical waveguide 12 when entering the reflection surface 20a. Thereby, light propagates from the optical waveguide 11 to the optical waveguide 12. On the other hand, when the light from the optical waveguide 11 does not enter the reflecting surface 20a, the light does not enter the optical waveguide 12.

  As shown in FIG. 10, the reflecting surface 20 a has an edge 20 b that moves across the plane 13 as the mirror 20 moves. At the edge 20b, incident light is scattered in various directions due to a diffraction phenomenon. For this reason, part of the light from the optical waveguide 11 returns to the optical waveguide 11 and propagates again in the optical waveguide 11. This light is the return light to the optical waveguide 11. Such return light may distort the waveform of the signal light propagating in the optical waveguide 11 and cause a communication error.

  Therefore, an object of the present invention is to reduce the return light to the first optical path in an optical component that adjusts the power of light propagating from the first optical path to the second optical path.

  FIG. 11 shows the relationship between the position of the mirror edge 20b and the coupling efficiency in the variable optical attenuator 50 shown in FIG. When the mirror edge position is 0 μm, the edge 20 b is located on the plane 13 between the optical waveguides 11 and 12. In FIG. 11, the solid line indicates the coupling efficiency of light traveling from the optical waveguide 11 to the optical waveguide 12, the alternate long and short dash line indicates the coupling efficiency of light returning from the optical waveguide 11 to the optical waveguide 11, and the two-dot chain line indicates the optical waveguide. The coupling efficiency of light returning from 12 to the optical waveguide 12 is shown. In FIG. 11, the one-dot chain line and the two-dot chain line overlap. As shown in FIG. 11, the variable optical attenuator 50 has a high coupling efficiency of return light to the optical waveguides 11 and 12. Therefore, the waveform of the signal light in the optical waveguide is relatively easily distorted.

  As a method for preventing the distortion of the signal light waveform, it is conceivable to connect isolators 51 and 52 to the optical waveguides 11 and 12 as shown in FIG. When the signal light 55 propagating through the optical waveguide 11 is reflected by the mirror 20, it enters the optical waveguide 12 and propagates through the optical waveguide 12. Return light 56 to the optical waveguide 11 generated by scattering at the edge portion 20 b of the mirror 20 is blocked by an isolator 51 connected to the optical waveguide 11. In addition, the isolator 52 connected to the optical waveguide 12 blocks the return light 57 from the external device connected to the variable optical attenuator 50, thereby preventing incidence on the variable optical attenuator 50. Therefore, generation of light returning from the optical waveguide 12 to the optical waveguide 12 is also prevented. Note that a typical allowable value of the coupling efficiency of the return light is −45 dB, but the allowable value varies depending on the system in which the variable optical attenuator is used.

  If the isolator is used as described above, it is possible to suppress the influence of the return light on the signal light in the optical communication system using the variable optical attenuator. However, since it is necessary to connect the isolator to the optical waveguide, the construction of the system becomes complicated, and the manufacturing cost of the system also increases. Therefore, the present inventors have devised another optical component and mirror that can reduce the return light.

  In one aspect, the present invention provides a first optical path having a first optical axis, a second optical path having a second optical axis that is non-parallel to the first optical axis, and a first optical axis. And a mirror that moves across the bisector of the angle formed by the second optical axis. On the surface of the mirror, there is provided a reflecting portion that receives light from the first optical path and reflects the light to the second optical path.

  The reflection part may have an edge including a straight line part arranged on a plane substantially perpendicular to the bisector. The straight line portion may be inclined with respect to the normal line of the plane including the first and second optical axes. Alternatively, the reflection part may have an edge including a curved part arranged on a plane substantially perpendicular to the bisector.

  These straight portions and curved portions are non-parallel to the normal line of the plane including the first and second optical axes. This non-parallel portion on the edge of the reflecting surface suppresses a component in the first optical axis direction of scattered light generated when light from the first optical path enters the portion. Thereby, the return light to the first optical path is reduced.

  In order to further reduce the return light to the first optical path, the acute angle φ is preferably 5 ° or more.

In addition, the reflecting portion has an edge including a portion disposed on a plane substantially perpendicular to the bisector, and the portion is expressed by the following formula:
Rav (X) = ∫R (X, Y) · Φ (Y) dY / ∫Φ (Y) dY (where X is the intersection of the plane including the first and second optical axes and the reflecting portion) The X-axis coordinate extending along the Y-axis, Y is the Y-axis coordinate extending perpendicularly to the X-axis on the reflector, R (X, Y) is the reflectance distribution on the XY plane, and Φ (Y) is the first The function Rav (X) defined by the Y-direction intensity distribution of light incident on the reflecting portion from the optical path may have a distribution that varies from at least 10% to 90% between two different X coordinates. .

  The part giving such a distribution function Rav (X) at the edge of the reflection surface of the mirror suppresses the component in the first optical axis direction of the scattered light generated when the light from the first optical path enters the part. . Thereby, the return light to the first optical path is reduced.

  In order to further reduce the return light to the first optical path, the interval between the two X coordinates at which the function Rav (X) changes from 10% to 90% is the X direction of the light incident on the reflector from the first optical path. It is preferably 3% or more of the mode field diameter.

  The optical component of the present invention may further include at least one of an optical waveguide optically coupled to the first optical path and an optical waveguide optically coupled to the second optical path. The optical waveguide may be a planar waveguide or an optical fiber.

  In another aspect, the present invention is a movable mirror device including a reflective surface and a driving device capable of moving the reflective surface along a predetermined movement path. The travel path extends parallel to a plane that intersects the reflective surface substantially perpendicularly. The reflection surface has an edge that moves while intersecting the plane in accordance with the movement of the reflection surface along the movement path. The edge may include a straight line portion inclined with respect to the normal line of the plane. The acute angle formed by the straight line portion and the normal line is preferably 5 ° or more. Alternatively, the edge may include a curved portion.

  These straight portions and curved portions are not parallel to the normal line of the plane parallel to the movement path of the reflecting surface. This non-parallel portion on the edge of the reflecting surface suppresses the component in the optical axis direction of the scattered light generated when the light on the optical path having the optical axis arranged on the plane enters the portion. Thereby, the return light to the optical path is reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the return light to a 1st optical path can be reduced in the optical component which adjusts the power of the light which propagates from a 1st optical path to a 2nd optical path.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  (First Embodiment) FIG. 1 is a schematic plan view showing an optical component of the first embodiment. This optical component is a variable optical attenuator 100. The variable optical attenuator 100 includes a planar lightwave circuit (PLC) 10, a mirror 21, and a mirror driving device 30. The mirror 21 and the mirror driving device 30 constitute a movable mirror device 40.

  The PLC 10 has two optical waveguides 11 and 12. The optical waveguides 11 and 12 are planar waveguides extending parallel to the paper surface of FIG. The optical waveguides 11 and 12 are made of, for example, quartz glass. The ends of the optical waveguides 11 and 12 closer to the mirror 21 may intersect with each other and overlap each other, or may be separated from each other.

  The mirror 21 is a light reflector having a reflecting surface 21a. The reflecting surface 21a is substantially flat and has an extremely high reflectance (for example, 90% or more) with respect to light of a predetermined wavelength propagating through the optical waveguides 11 and 12. The reflecting surface 21a has a substantially uniform reflectance. The reflection surface 21a is provided on the surface of the mirror 21 and extends in a direction perpendicular to the paper surface of FIG. The mirror 21 moves so that the reflecting surface 21 a faces the end surfaces of the optical waveguides 11 and 12. A gap between the reflecting surface 21a and these end faces may be filled with a refractive index matching material. Details of the mirror 21 will be described later.

  The mirror driving device 30 moves the mirror 21 substantially parallel to the ZX plane, as indicated by arrows 32 and 33. In response to this, the reflecting surface 21 a of the mirror 21 moves along the movement path 46. The movement of the mirror 21 is reversible. The movement path 46 extends in parallel to a plane (for example, the paper surface of FIG. 1) that crosses the reflecting surface 21a substantially perpendicularly. In the present embodiment, the movement path 46 is a straight line extending substantially in the X direction. Therefore, in the vicinity of the end faces of the optical waveguides 11 and 12, the reflecting surface 21a moves substantially parallel to the end faces of the optical waveguides 11 and 12, as indicated by arrows 32 and 33. An example of the mirror driving device 30 is an electrostatic actuator as described in Non-Patent Document 1 above.

  The movement path 46 may be curved. If the curvature is sufficiently large, the reflecting surface 21a can be moved substantially in the X direction in the vicinity of the end faces of the optical waveguides 11 and 12.

  In FIG. 1, an XYZ rectangular coordinate system is drawn for convenience of explanation. The X axis extends along the intersection of the plane including the optical axes of both the waveguides 11 and 12 and the reflecting surface 21a. The Y axis extends perpendicular to the X axis in a plane perpendicular to the bisector of the angle formed by the optical axes of both waveguides 11 and 12. The Z axis extends parallel to the bisector.

  Hereinafter, the mirror 21 will be described in more detail with reference to FIGS. 2 and 3. FIG. 2 is a schematic perspective view showing the mirror 21. FIG. 3 is a diagram showing the reflecting surface 21a of the mirror 21 as seen from an angle different from that in FIG.

  As shown in FIG. 2, the variable optical attenuator 100 has optical paths 26 and 27 for sending light from the optical waveguide 11 to the optical waveguide 12 through the mirror 21. Optical paths 26 and 27 are optically coupled to optical waveguides 11 and 12, respectively. The reflecting surface 21 a of the mirror 21 moves so as to intersect the optical path 26. The optical paths 26 and 27 extend between the end surfaces of the optical waveguides 11 and 12 and the reflecting surface 21a. The light 41 emitted from the optical waveguide 11 travels on the optical path 26 toward the mirror 21, is reflected by the reflecting surface 21 a, and travels on the optical path 27 toward the optical waveguide 12. Optical paths 26 and 27 have optical axes 16 and 17, respectively. The optical axes 16 and 17 are arranged on a plane parallel to the paper surface of FIG. The optical axes 16 and 17 are non-parallel and intersect at an angle θ. The bisector 18 of angle θ extends on the plane containing the optical axes 16 and 17. Reference numeral 14 in FIG. 2 indicates a plane including the optical axes 16 and 17. Hereinafter, the plane 14 is referred to as a reference plane. The reference plane 14 is substantially parallel to the movement path 46 of the reflecting surface 21a and crosses the reflecting surface 21a substantially vertically.

  As shown in FIG. 2, the reflecting surface 21a of the mirror 21 has a trapezoidal shape. The reflecting surface 21 a has a linear edge 21 b that moves so as to cross the bisector 18 as the mirror 21 moves. The edge 21 b moves while intersecting the reference plane 14 in accordance with the movement of the reflecting surface 21 a along the movement path 46. The reflecting surface 21a and the edge 21b are substantially located on the XY plane. Further, as described above, the bisector 18 is parallel to the Z axis. Therefore, the edge 21 b is disposed on a plane substantially perpendicular to the bisector 18. The edge 21 b is inclined with respect to the normal line 15 of the reference plane 14, and forms an acute angle φ with the normal line 15.

  In order to efficiently couple light between the optical waveguides 11 and 12 through the reflecting surface 21a, it is desirable that the reflecting surface 21a and the edge 21b are completely perpendicular to the bisector 18. However, in practice, it is sufficient if the angle formed by the projection line of the bisector 18 onto the reflecting surface 21a and the bisector 18 is 85 ° or more and 90 ° or less, more desirably 89 ° or more and 90 ° or less. High coupling efficiency can be obtained.

  When the reflection surface 21 a receives the light 41 traveling along the optical axis 16 of the optical path 26 from the optical waveguide 11, the reflection surface 21 a reflects the light 41 along the optical axis 17 of the optical path 27. As a result, the light 41 from the optical waveguide 11 enters the optical waveguide 12 along the optical axis 17 and propagates through the optical waveguide 12. On the other hand, when the light from the optical waveguide 11 does not enter the reflecting surface 21 a, the light does not enter the optical waveguide 12.

  In FIG. 3, the cross section of the beam 44 of the incident light 41 is illustrated in an enlarged manner. As shown in FIG. 3, when light incident on the reflection surface 21a from the optical waveguide 11 is distributed on the edge 21b, the incident light is scattered at the edge 21b due to the diffraction phenomenon. A part of the scattered light is coupled to the optical waveguide 12 and propagates in the optical waveguide 12. When the mirror 21 moves from the position shown in FIG. 3 in the direction of the arrow 32, the incident light is reflected by a narrower portion on the reflecting surface 21a, so that the coupling efficiency from the optical waveguide 11 to the optical waveguide 12 is improved. descend. On the contrary, when the mirror 21 moves from the position shown in FIG. 3 in the direction of the arrow 33, the incident light is reflected by the wider part on the reflecting surface 21a. The coupling efficiency is increased. Therefore, the power of light propagating from the optical waveguide 11 to the optical waveguide 12 can be changed according to the movement of the mirror 21. This is the operating principle of the variable optical attenuator 100.

  Part of the scattered light at the edge 21 b returns to the optical waveguide 11. This is the return light to the optical waveguide 11. In the present embodiment, since the edge 21b is inclined with respect to the normal 15 of the reference plane 14, the return light is reduced. Hereinafter, with reference to FIGS. 2 and 13, reduction of return light by the mirror 21 of the present embodiment will be described in comparison with the mirror 20 shown in FIG. 10.

  FIG. 13 is a schematic perspective view showing the mirror 20 shown in FIG. The reflection surface 20a of the mirror 20 has an edge 20b. The edge 20 b is a straight line portion parallel to the normal line 15 of the reference plane 14. That is, the edge 20 b is perpendicular to the reference plane 14. Theoretically, when light enters the edge 20b along the optical axis 16 on the reference plane 14 which is substantially perpendicular to the edge 20b, light scattering occurs in the plane 14 and the scattered light 43 is incident on the plane 14. Proceed along. In FIG. 13, the scattered light does not occur outside the plane 14 because the light component reflected by the portion of the reflecting surface 20 a located above the reference plane 14 and the reflecting surface 20 a located below the reference plane 14. This is because the light components reflected by the portions cancel each other according to Huygens' principle. When light scattering occurs in the plane 14 perpendicular to the edge 20b, a part of the scattered light 43 is relatively easily coupled to the optical waveguide 11 having the optical axis 16 on the same plane 14. Thus, return light to the optical waveguide 11 is generated.

  On the other hand, as shown in FIG. 2, the mirror 21 of the present embodiment has an edge 21 b inclined with respect to the normal 15 of the reference plane 14. Therefore, the reference plane 14 is not perpendicular to the edge 21b. For this reason, even if light enters the edge 21 b along the optical axis 16 on the reference plane 14, light scattering occurs in a plane that is not parallel to the reference plane 14. Thereby, since the coupling efficiency of the scattered light to the optical waveguide 11 is reduced, the return light to the optical waveguide 11 can be reduced.

  Below, the effect of this embodiment is confirmed, referring FIG. FIG. 4 shows the relationship between the inclination angle φ of the edge 21 b and the coupling efficiency of return light to the optical waveguide 11 with respect to various values of the crossing angle θ of the optical axes 16 and 17. Here, it is assumed that the incident light 41 is a beam having a wavelength of 1.55 μm in vacuum and having a Gaussian distribution with the optical axis 16 as the center. The MFD (mode field diameter) in the horizontal direction of the incident light 41 is 20 μm, and the MFD in the vertical direction is 10 μm. Here, the horizontal direction and the vertical direction indicate the major axis direction and the minor axis direction of the elliptical cross section 44 of the incident light beam shown in FIG. 3, which are equal to the X direction and the Y direction, respectively. It is assumed that the gap between the end faces of the optical waveguides 11 and 12 and the reflecting surface 21a is filled with a refractive index matching material having a refractive index of 1.45.

  As shown in FIG. 4, the return light coupling efficiency is reduced with an increase in the inclination angle φ of the edge 21b under any θ value. In addition, the larger the θ, the greater the effect of reducing the coupling efficiency. In particular, when θ is 45 ° or more, the coupling efficiency of return light can be greatly suppressed to −40 dB or less under an inclination angle φ of 5 ° or more.

  The angle formed by the ends of the optical waveguides 11 and 12 facing the mirror 21 is determined according to the angle θ between the optical axes 16 and 17. When planar waveguides are used as the optical waveguides 11 and 12 as in the present embodiment, the curvature of the optical waveguides 11 and 12 tends to increase when θ is large. In this case, there is a high possibility that light leaks at the bent portions of the optical waveguides 11 and 12 and loss occurs. Although depending on the configuration of the system using the variable optical attenuator 100, when it is necessary to particularly suppress the leakage light, the angle θ is appropriate to be 30 ° or less, and the inclination angle φ of the edge 21b is 10 ° or more. desirable. In the present embodiment in which the reflecting surface 21a moves along the movement path 46 substantially parallel to the reference plane 14, the inclination angle φ is desirably 75 ° or less. As the angle φ increases, the moving distance of the reflecting surface 21a required to change the power of light propagating from the optical waveguide 11 to the optical waveguide 12 by a predetermined amount also increases. Therefore, if the angle φ is too large, it is difficult to reduce the size of the variable optical attenuator 100.

  In addition, in order to efficiently reflect the light 41 by the reflecting surface 21a, the length of the edge 21b is preferably larger than the MFD in the direction along the edge 21b of the incident light 41.

  (Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a schematic perspective view showing the mirror 22 used in the second embodiment. The optical component of the present embodiment is a variable optical attenuator obtained by replacing the mirror 21 with the mirror 22 shown in FIG. 5 in the variable optical attenuator 100 shown in FIG. The variable optical attenuator of this embodiment has the same configuration as the variable optical attenuator 100 except for the mirror.

  The mirror 22 is a light reflector having a reflecting surface 22a. The reflection surface 22a is substantially flat and has an extremely high reflectance (for example, 90% or more) with respect to light of a predetermined wavelength propagating through the optical waveguides 11 and 12. The reflecting surface 22a has a substantially uniform reflectance. The mirror 22 moves so that the reflection surface 22 a faces the end surfaces of the optical waveguides 11 and 12. The gap between the reflecting surface 22a and these end faces may be filled with a refractive index matching material.

  As shown in FIG. 5, the reflecting surface 22a has a curved edge 22b. The edge 22b moves so as to cross the bisector 18 as the mirror 22 moves. The reflecting surface 22a and the edge 22b are substantially located on the XY plane. Further, as described above, the bisector 18 is parallel to the Z axis. Therefore, the edge 22 b is arranged on a plane substantially perpendicular to the bisector 18. Of course, the edge 22b is not parallel to the normal 15 of the reference plane.

  In order to efficiently couple light between the optical waveguides 11 and 12 through the reflecting surface 22a, it is desirable that the reflecting surface 22a and the edge 22b are completely perpendicular to the bisector 18. However, in practice, it is sufficient if the angle formed by the projection line of the bisector 18 onto the reflecting surface 22a and the bisector 18 is 85 ° or more and 90 ° or less, more desirably 89 ° or more and 90 ° or less. High coupling efficiency can be obtained.

  When the reflecting surface 22 a receives the light 41 traveling along the optical axis 16 of the optical path 26 from the optical waveguide 11, the reflecting surface 22 a reflects the light 41 along the optical axis 17 of the optical path 27. As a result, the light 41 from the optical waveguide 11 enters the optical waveguide 12 along the optical axis 17 and propagates through the optical waveguide 12. On the other hand, when the light from the optical waveguide 11 does not enter the reflecting surface 22a, the light does not enter the optical waveguide 12.

  When light incident on the reflecting surface 22a from the optical waveguide 11 is distributed on the edge 22b, the incident light is scattered at the edge 22b due to a diffraction phenomenon. A part of the scattered light is coupled to the optical waveguide 12 and propagates in the optical waveguide 12. When the mirror 22 moves from the position shown in FIG. 5 in the direction of the arrow 32, the incident light is reflected by a narrower portion on the reflection surface 22a, so that the coupling efficiency from the optical waveguide 11 to the optical waveguide 12 is improved. descend. On the contrary, when the mirror 22 moves from the position shown in FIG. 3 in the direction of the arrow 33, the incident light is reflected by the wider part on the reflection surface 22a. Increases coupling efficiency. Therefore, the power of light propagating from the optical waveguide 11 to the optical waveguide 12 can be changed according to the movement of the mirror 22. This is the operating principle of the variable optical attenuator of this embodiment.

  As shown in FIG. 5, the curved edge 22 b is not perpendicular to the reference plane 14. For this reason, even if light enters the edge 21 b along the optical axis 16 on the reference plane 14, light scattering occurs in a plane that is not parallel to the reference plane 14. Thereby, since the coupling efficiency of the scattered light to the optical waveguide 11 is reduced, the return light to the optical waveguide 11 can be reduced.

  More generally, the edge of the mirror extending in a curved line in a plane perpendicular to the bisector 18 has a portion extending in a direction non-perpendicular to the reference plane 14 regardless of the specific shape of the edge. Must be included. Therefore, at least a part of the light scattering occurs in a plane that is not parallel to the reference plane 14. For this reason, the mirror having the curved edge is less likely to couple the scattered light generated at the edge to the optical waveguide 11 than the mirror 20 having the edge 20b composed only of a straight line perpendicular to the reference plane 14. Therefore, by using a mirror having curved edges, the coupling efficiency of return light can be reduced.

  (Third Embodiment) Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a schematic plan view showing the mirror 23 used in the third embodiment. The optical component of this embodiment is a variable optical attenuator obtained by replacing the mirror 21 with the mirror 23 shown in FIG. 6 in the variable optical attenuator 100 shown in FIG. The variable optical attenuator of this embodiment has the same configuration as the variable optical attenuator 100 except for the mirror.

  The mirror 23 is a light reflector having a reflecting surface 23a. The reflecting surface 23a is substantially flat and has an extremely high reflectance (for example, 90% or more) with respect to light of a predetermined wavelength propagating through the optical waveguides 11 and 12. The reflecting surface 23a has a substantially uniform reflectance. The mirror 23 moves so that the reflection surface 23 a faces the end surfaces of the optical waveguides 11 and 12. A gap between the reflecting surface 23a and these end faces may be filled with a refractive index matching material.

  As shown in FIG. 6, the reflecting surface 23a has a sawtooth edge 23b. The edge 23b has a configuration in which straight portions 23c and 23d are alternately connected. In FIG. 6, the straight line portion 23c extends downward and the straight line portion 23d extends upward. The bisector of the angle formed by the adjacent straight line portion 23c and the straight line portion 23d is parallel to the X axis.

  The edge 23b moves so as to cross the bisector 18 of the angle formed by the optical axes 16 and 17 as the mirror 23 moves. The reflecting surface 23a and the edge 23b are substantially located on the XY plane. The bisector 18 is parallel to the Z axis. Therefore, the edge 23 b is arranged on a plane substantially perpendicular to the bisector 18. The normal 15 of the reference plane 14 is parallel to the Y axis. The straight portions 23 c and 23 d constituting the edge 23 b are both inclined with respect to the normal 15 of the reference plane 14. These straight portions 23 c and 23 d form an acute angle φ with the normal 15.

  In order to efficiently couple light between the optical waveguides 11 and 12 via the reflecting surface 23a, it is desirable that the reflecting surface 23a and the edge 23b are completely perpendicular to the bisector 18. However, in practice, it is sufficient if the angle formed by the projection line of the bisector 18 onto the reflecting surface 23a and the bisector 18 is 85 ° or more and 90 ° or less, and more desirably 89 ° or more and 90 ° or less. High coupling efficiency can be obtained.

  In FIG. 6, each of the sawtooth teeth on the reflecting surface 23a is represented by reference numeral 23e. Each saw tooth 23e has a height H along the X direction. These saw teeth 23e are arranged at intervals D along the Y direction.

  When the reflecting surface 23 a receives the light 41 traveling along the optical axis 16 of the optical path 26 from the optical waveguide 11, the reflecting surface 23 a reflects the light 41 along the optical axis 17 of the optical path 27. As a result, the light 41 from the optical waveguide 11 enters the optical waveguide 12 along the optical axis 17 of the optical waveguide 12 and propagates through the optical waveguide 12. On the other hand, when the light 41 from the optical waveguide 11 does not enter the reflecting surface 23 a, the light 41 does not enter the optical waveguide 12.

  When light incident on the reflecting surface 23a from the optical waveguide 11 is distributed on the edge 23b, the incident light is scattered at the edge 23b due to a diffraction phenomenon. A part of the scattered light is coupled to the optical waveguide 12 and propagates in the optical waveguide 12. Here, it is assumed that a beam of incident light is irradiated around the origin of the XYZ coordinate system shown in FIG. When the mirror 23 moves from the position shown in FIG. 6 in the direction of the arrow 32, the incident light is reflected by a narrower portion on the reflecting surface 23a, so that the coupling efficiency from the optical waveguide 11 to the optical waveguide 12 is improved. descend. Conversely, when the mirror 23 moves from the position shown in FIG. 6 in the direction of the arrow 33, incident light is reflected by a wider portion on the reflecting surface 33 a, so that the light from the optical waveguide 11 to the optical waveguide 12 is reflected. The coupling efficiency is increased. Therefore, the power of light propagating from the optical waveguide 11 to the optical waveguide 12 can be changed according to the movement of the mirror 23. This is the operating principle of the variable optical attenuator of this embodiment.

  Similar to the first embodiment, the edge 23b is composed of the straight portions 23c and 23d inclined with respect to the ZX plane, that is, the normal line 15 of the reference plane 14, so that the return light to the optical waveguide 11 is reduced. Can do. However, since the scattered light generated in the plurality of linear portions 23c and 23d interfere with each other, the conditions required to achieve a sufficient reduction in the return light are different from those in the first embodiment.

Therefore, hereinafter, the reduction of the return light in the present invention will be described from another viewpoint. In this description, the following formula
Rav (X) = ∫R (X, Y) ・ Φ (Y) dY / ∫Φ (Y) dY (1)
The function Rav (X) defined in is used. As shown in FIG. 2, X is a coordinate in the X-axis direction extending along the intersection of the reference plane 14 and the reflecting surface of the mirror, and Y is perpendicular to the X-axis in a plane parallel to the reflecting surface of the mirror. It is a coordinate of direction. R (X, Y) is a reflectance distribution in the XY plane. Here, the reflectance at the XY coordinates where the reflecting surface 23a exists is 100%, and the reflectance at the XY coordinates where the reflecting surface 23a does not exist is 0%. Φ (Y) is the Y direction intensity distribution of the light incident on the reflecting surface 23 from the optical waveguide 11.

  The function Rav (X) represents the reflectance distribution of the reflecting surface averaged with the Y-direction distribution of the incident light beam. In the interpretation of return light suppression using Rav (X), return light is determined according to the distribution of Rav (X) regardless of the shape of the edge of the mirror. Therefore, first, description will be made using the mirror 21 of FIG. Rav (X) relating to the mirror 21 (see FIG. 2) when Φ (Y) is a Gaussian distribution with an MFD (mode field diameter) of 10 μm and the inclination angle φ of the linear portion 21b is 0 °, 20 ° and 45 °. Is shown in FIG. In FIG. 7, the position where Rav (X) is 50% is the origin of the X coordinate.

  As shown in FIG. 7, when φ = 0 °, Rav (X) = 0% when X> 0, and Rav (X) = 100% when X <0. That is, Rav (X) is discontinuous at the origin of the X coordinate. When φ = 0 °, the edge 21b is no longer inclined with respect to the normal line 15 of the reference plane 14, and becomes a straight line parallel to the normal line 15 like the edge 20b shown in FIG. On the other hand, when φ = 20 ° and 45 °, Rav (X) is continuous at the origin of the X coordinate and changes smoothly near the origin.

  As shown in FIG. 7, the change in Rav (X) near the origin of the X coordinate becomes gentler as the inclination angle φ increases. Accordingly, considering that the edge 21b corresponding to φ> 0 ° has less return light than the edge 20b corresponding to φ = 0 °, the condition necessary for reducing the return light is the function Rav (X ) Is considered to change slowly. When φ = 0 °, Rav changes from 0% to 100% in a single X coordinate of X = 0. From this, the inventor compared with the mirror 20 having the edge 20b if Rav (X) varies between at least 10% and 90%, more preferably 0% to 100%, between two different X coordinates. Thus, it was considered that the return light to the optical waveguide 11 can be sufficiently reduced.

  Note that it is sufficient if the change in Rav (X) is more gradual than in the case of φ = 0 °, and therefore Rav (X) does not necessarily change continuously. For example, even when Rav (X) changes stepwise from 10% to 90% between two X coordinates, a sufficient return light reduction effect can be obtained. However, the finer the stairs, the greater the effect of reducing the return light.

  Hereinafter, the width in the X direction in which Rav (X) changes from 10% to 90% is referred to as an edge width. When the horizontal axis in FIG. 4 described above is replaced with the MFD in the X direction of the edge width / incident light beam, FIG. 4 is redrawn as shown in FIG. Here, the incident light beam has a Gaussian distribution, the MFD in the X direction is 20 μm, and the MFD in the Y direction is 10 μm.

  In the interpretation of return light suppression using Rav (X), the return light is determined according to the distribution of Rav (X) regardless of the shape of the edge of the mirror. Therefore, FIG. 4 is obtained with respect to the edge 21b having the shape shown in FIG. 2, but FIG. 8 obtained by redrawing this is applicable to edges having other shapes.

  As shown in FIG. 8, when the angle θ between the optical axes 16 and 17 is 45 ° or more, the value on the horizontal axis in FIG. 8, that is, (edge width / MFD in the X direction) is 0.03 or more. In addition, the coupling efficiency of return light can be greatly suppressed to -40 dB or less. In the sawtooth edge 23b shown in FIG. 6, the edge width is substantially equal to the height H of the sawtooth 23e. Therefore, if the height H of the saw tooth 23e is 3% or more of the MFD in the X direction, the return light can be greatly suppressed.

  When the optical waveguides 11 and 12 are planar waveguides as in the present embodiment, the curvature of the optical waveguides 11 and 12 tends to increase when θ is large. When it is necessary to particularly suppress the leakage light of the optical waveguide, the angle θ is suitably 30 ° or less, and the inclination angle φ of the edge 21b is desirably 10 ° or more. At this time, the edge width is desirably 6% or more of the MFD in the X direction.

  Below, the manufacturing method of the mirror of the said embodiment is demonstrated, referring Fig.9 (a) and (b). FIGS. 9A and 9B are schematic perspective views showing examples of the mirror 23.

  As shown in FIG. 9A, the mirror 23 can be manufactured by processing one end portion of the substrate 23f into a sawtooth shape and then coating the upper surface of the substrate 23f with a highly reflective material 23g. . Similarly, the other mirrors 21 and 22 can be manufactured by processing the edge of the substrate into a desired shape and then coating the upper surface of the substrate with a highly reflective material.

  Further, as shown in FIG. 9B, the mirror 23 can also be manufactured by coating the upper surface of the substrate 23h with a highly reflective material 23i so as to have a sawtooth-shaped end portion. Similarly, the other mirrors 21 and 22 can be manufactured by coating the upper surface of the substrate with a highly reflective material so as to have a desired shape. In this manufacturing method, a portion that is not covered by the highly reflective material exists on the upper surface of the substrate. In order to reduce reflection at this part, either apply an anti-reflection coating on the top surface of the substrate and then apply a highly reflective material, or move the mirror in a refractive index matching material that has the same refractive index as the substrate. It is desirable to make it.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

  In the above embodiment, a variable optical attenuator is cited as an example of the optical component of the present invention. However, the present invention may be any other optical component that changes the power of light propagating from one optical path to another. For example, in the variable optical attenuator of the above embodiment, the power of light propagating from the optical waveguide 11 to the optical waveguide 12 can be made almost zero by moving the mirror. Therefore, these variable optical attenuators can be used as 1 × 1 optical switches that turn on and off the light propagating from the optical waveguide 11 to the optical waveguide 12.

  The optical component of the above embodiment has an optical waveguide as an optical path. However, the optical component of the present invention may include an optical path formed in a medium (for example, air) by an arbitrary optical system such as a lens, instead of the optical waveguide. The optical waveguide used as the optical path is not limited to the planar waveguide in the above embodiment, and may be any other optical waveguide, for example, an optical fiber.

  In the above embodiment, the reflecting surface of the mirror is flat. However, in the present invention, a reflective surface including a curved surface portion may be employed.

  In the above embodiment, the mirror moves linearly in the direction perpendicular to the bisector 18. However, the movement of the mirror may not be linear. For example, the mirror may be moved by fixing the mirror to one end of a straight bar-like arm and turning the arm around the other end of the arm. In this case, the movement path of the mirror is a substantially arc-shaped curve. If the radius of curvature of the movement path is sufficiently large, the movement path is approximately a straight line.

  In the optical component of the present invention, the thickness in the direction perpendicular to the reflecting surface of the mirror is arbitrary. For example, the mirror may have a uniform thickness in a direction perpendicular to the reflecting surface.

  In the optical component of the present invention, the mirror or the mirror driving device may be manufactured by using a micro electro mechanical system (MEMS) technology. Examples of the mirror driving device include an electrostatic actuator, an electromagnetic actuator using electromagnetic force, and an actuator using thermal deformation. For example, the electrostatic actuator has a movable electrode portion and a fixed electrode portion, and a mirror is installed on the movable electrode portion. By generating an electrostatic force between the two electrodes, the movable electrode portion is moved, and the mirror moves accordingly.

  In the third embodiment, the plurality of saw teeth have the same height and width. However, the reflecting surface of the mirror may have a plurality of saw teeth whose height and / or width are different from each other.

  In the above embodiment, a desirable Rav (X) is obtained by an appropriate shape of the edge of the reflecting surface having a uniform reflectance. However, instead of this, the desired Rav (X) may be achieved by the reflectance distribution on the reflecting surface. For example, the reflectance distribution may be realized by changing the thickness of the high reflectance material coated on the reflective surface according to the position.

It is a schematic plan view which shows the variable optical attenuator of 1st Embodiment. It is a schematic perspective view which shows the mirror of 1st Embodiment. It is a figure which shows the reflective surface of the mirror seen from the angle different from FIG. It is a figure which shows the coupling efficiency of the return light according to edge angle. It is a schematic perspective view which shows the mirror of 2nd Embodiment. It is a schematic plan view which shows the mirror of 3rd Embodiment. It is a figure which shows function Rav (X). It is a figure which shows the coupling efficiency of the return light according to (edge width / MFD of X direction). It is a schematic perspective view which shows the example of the mirror of 3rd Embodiment. It is a schematic plan view which shows an example of a variable optical attenuator. It is a figure which shows the relationship between the position of the edge of a mirror, and coupling efficiency. It is the schematic which shows one method of reducing a return light. It is a schematic perspective view which shows a mirror.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Planar lightwave circuit (PLC), 11 and 12 ... Optical waveguide, 14 ... Plane containing two optical axes, 15 ... Plane normal containing two optical axes, 16 and 17 ... Optical axes, 18 ... Two Bisector of angle formed by optical axis, 21-23 ... mirror, 21a-23a ... reflecting surface, 21b-23b ... edge, 23c and 23d ... straight line part, 23e ... sawtooth, 26 and 27 ... optical path, 30 ... Mirror driving device, 32 and 33... Mirror moving direction, 40... Mirror moving device, 46.

Claims (2)

A first optical waveguide optically coupled to a first optical path having a first optical axis and an optical second optical path having a second optical axis that is non-parallel to the first optical axis A planar lightwave circuit having a coupled second optical waveguide;
A mirror that moves in a direction intersecting a bisector of an angle formed by the first optical axis and the second optical axis;
With
The surface of the mirror is provided with a substantially flat reflecting portion that receives light from the first optical path and reflects the light to the second optical path,
The reflecting portion is a curved edge disposed on a plane substantially perpendicular to the bisector, and is a plane including the first optical axis and the second optical axis. The edge having a portion extending in a non-perpendicular direction,
The mirror moves so that the portion of the edge extending in the non-vertical direction crosses the bisector;
Optical components for optical communications. The optical component according to claim 1, wherein the optical component is a variable optical attenuator.

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