JP2005352038A - Optical branching module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical branching module suitable for miniaturization and superior in branching extension. <P>SOLUTION: The optical branching module comprises an optical branching element 10 for forming branching signal light by reflecting a part of the incident signal light, and provided with a plurality of translucent layers 13a, 13b and 13c transmitting the residual part of the incident signal light at an interval; an incident means (optical fiber cord 15) for making the incident signal light obliquely incident on the translucent layers 13a, 13b and 13c; and a multiple reflection prevention means for preventing multiple reflection overlapped on the optical path of the branching signal light reflected on one translucent layer, by the optical path of sub-reflection light generated by being reflected again in the inside of the optical branching element 10 by a part of the branching signal light reflected on the other translucent layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical branching module.

  An optical branching module that splits the power of one incident light into a plurality (N) is a subscriber unit in a system that draws an optical fiber into various buildings such as FTTH (fiber to the home) or FTTP (fiber to the premises). In addition to being used as an optical module for branching light into a large number of light before this, it is widely used in various optical line systems for branching optical power into a plurality of parts, such as in an optical LAN or measuring equipment. As such an optical branching module, for example, an optical fiber coupler type obtained by fusing and stretching a plurality of optical fibers is well known.

The following Patent Document 1 relates to a wavelength multiplexer / demultiplexer that separates multiplexed light including a plurality of lights having different wavelengths into light of each wavelength, and a plurality of light that selectively reflects light of a predetermined wavelength and transmits the remainder. A structure in which the wavelength selective filter layers are arranged at intervals is disclosed.
The invention described in Patent Document 1 and the present invention are common in that a plurality of films having a light reflection and transmission function (for example, the wavelength selection filter) are provided at intervals. Whereas the invention is an optical branching module that branches the power of incident light of an arbitrary wavelength into a plurality, the invention described in Patent Document 1 is a wavelength multiplexer / demultiplexer that separates multiplexed light for each wavelength. Different. In such a wavelength multiplexer / demultiplexer, a plurality of separated lights have different wavelengths, so there is no problem even if multiple reflections occur inside the module.
JP 2002-169054 A

In recent years, with the increase in the density of optical transmission, the demand for downsizing and increasing the capacity of various optical components is increasing. However, the optical fiber coupler type optical branch module is difficult to downsize, and There was a problem that the branch expandability for increasing the number of branches (N) was poor.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical branching module that is suitable for downsizing and has excellent branching expandability.

  In order to achieve the above object, the optical branching module of the present invention reflects a part of the incident signal light to form the branched signal light, and includes a plurality of semi-transmissive layers that transmit the remainder of the incident signal light. , Optical branching elements provided at a distance from each other, incident means for making the incident signal light incident obliquely on the semi-transmissive layer, and part of the branched signal light reflected by one semi-transmissive layer Is provided with multiple reflection preventing means for preventing multiple reflections in which the optical path of the sub-reflected light that is reflected again inside the optical branching element overlaps the optical path of the branched signal light reflected by the other semi-transmissive layer. It is characterized by.

It is preferable that the plurality of semi-transmissive layers are parallel to each other.
As the multiple reflection preventing means, there is a configuration in which the intervals between adjacent semi-transmissive layers are formed non-uniformly.
Alternatively, as the multiple reflection preventing means, the light branching element comprises a laminated block in which the semi-transmissive layer and a solid medium layer that transmits the transmitted light of the semi-transmissive layer are alternately laminated, A part of the outer surface of the block is inclined with respect to the semi-transmissive layer, and the branched signal light reflected by one semi-transmissive layer is transmitted through the inclined surface before reaching the other semi-transmissive layer. There is a configuration to do.
A solid medium block that transmits the branched signal light transmitted through the inclined surface may be joined to the inclined surface of the laminated block.
The solid medium block may be provided with a reflection layer that reflects the branched signal light transmitted through the inclined surface.
The incident means may include an optical path changing means for changing a traveling direction of incident signal light.

  According to the present invention, an optical branching module that is suitable for downsizing and excellent in branching expandability can be obtained.

FIG. 1 is a schematic configuration diagram illustrating a first embodiment of the optical branching module of the present invention in partial cross-sectional view. The optical branching module of this embodiment includes a block-shaped optical branching element 10, an optical fiber cord 15 (incident means) provided to face the incident surface of the optical branching element 10, and an output surface of the optical branching element 10. The optical fiber array 17 is provided oppositely, and the lens array 16 is provided between the optical fiber array 17 and the optical branching element 10. In FIG. 1, the optical branching element 10 shows a cross section, and the optical fiber array 17 shows a partial cross section. The alternate long and short dash line in the figure indicates the optical axis.
The optical branching element 10 includes a laminated block 11 and a solid medium block 14 joined on an inclined surface 11a of the laminated block 11, and the whole is formed in a rectangular parallelepiped shape. The incident surface and the exit surface of the light branching element 10 form two opposing surfaces of the outer surface of the light branching element 10.

The laminated block 11 is a rectangular parallelepiped in which light-transmitting solid medium layers 12a, 12b, 12c, and 12d and semi-transmissive layers 13a, 13b, and 13c that reflect a part of incident signal light and transmit the remaining light are alternately laminated. Alternatively, a cubic block is formed in a shape cut by an inclined surface 11a that intersects the semi-transmissive layers 13a, 13b, and 13c at a predetermined constant angle. The relationship between the angle of inclination of the inclined surface 11a (indicated by A in the figure) and the incident angle α of incident signal light to the laminated block 11 to be described later is determined in consideration of the refractive index of the material of the laminated block 11. For example, the inclination angle A is set approximately equal to the value of (α / 1.5).
In the laminated block 11, the outermost layers at both ends in the lamination direction (indicated by X in the figure) of the semi-transmissive layers 13a, 13b, and 13c are all composed of solid medium layers 12a and 12d.
Further, in a direction perpendicular to the stacking direction (X) and perpendicular to the surface facing the inclined surface 11a from the inclined surface 11a (indicated by Y in the figure, hereinafter sometimes referred to as the width direction). The width of the laminated block 11 gradually increases from the incident surface side to the outgoing surface side in the direction along the lamination direction (X).
In addition, when the direction perpendicular to both the X direction and the Y direction in the figure is the Z direction, the inclined surface 11a is a surface parallel to the Z direction.

The solid medium layers 12a, 12b, 12c, and 12d are configured by using a substrate made of a transparent material such as glass, for example, and each layer is preferably configured by the same material. The thicknesses of the solid medium layers 12a, 12b, 12c, and 12d are uniform, and the plurality of semi-transmissive layers 13a, 13b, and 13c are parallel to each other. In the present embodiment, the different solid medium layers 12a, 12b, 12c, and 12d are formed to have the same thickness. The thickness of each of the solid medium layers 12a, 12b, 12c, and 12d is not particularly limited, but the distance D between the optical paths of the plurality of branched signal lights emitted from the optical branching element 10 can vary depending on the thickness. In the present embodiment, the thickness of each solid medium layer 12a, 12b, 12c, 12d is preferably set to about 1.5 to 2.5 mm. Note that the thickness of the solid medium layer 12a that forms the outermost layer on the incident side does not affect the distance D between the optical paths of the outgoing branched signal light, and therefore has a different thickness from the other solid medium layers 12b, 12c, and 12d. You can also

The semi-transmissive layers 13a, 13b, and 13c can be formed of, for example, a metal thin film, a semiconductor film, a dielectric multilayer film made of TiO ₂ and SiO ₂ , or a dielectric multilayer film made of Ta ₂ O ₅ and SiO _2. . The reflectance in each of the semi-transmissive layers 13a, 13b, and 13c can be appropriately set according to the branching ratio of light to be obtained.
A non-reflective layer (not shown) is provided on the outer surface 11b on the incident side of the laminated block 11, that is, the outer surface on the incident side of the solid medium layer 12a that forms the outermost layer on the incident side. In addition, a reflective layer (not shown) is provided on the outer surface 11c on the output side of the laminated block 11, that is, on the outer surface on the output side of the solid medium layer 12d that forms the outermost layer on the output side. The reflectance of the outer surface 11c on the emission side of the laminated block 11 is preferably about 98 to 100%.

The solid medium block 14 is formed in a shape in which a rectangular parallelepiped or a cube having the same size in the stacking direction (X) direction as the stacked block 11 is cut by an inclined surface having the same angle as the inclined surface 11 a of the stacked block 11. . The solid medium block 14 is preferably made of the same material as the solid medium layers 12a, 12b, 12c, and 12d of the laminated block 11, and is made of a transparent material such as glass.
A reflective layer (not shown) is provided on the outer surface 14 b on the incident side of the solid medium block 14. The reflection layer on the outer surface 14b is parallel to the transmission layers 13a, 13b, and 13c, and the reflectance is preferably about 98 to 100%. Further, a non-reflective layer (not shown) is provided on the outer surface 14 c on the emission side of the solid medium block 14.

  The laminated block 11 and the solid medium block 14 may be joined by using an adhesive, but in order to prevent reflection at the interface between them, the solid medium block 14 and the laminated block 11 have the same refractive index of light. It is preferable to use a light-transmitting adhesive having a degree. It is also preferable that both the inclined surface 11a of the laminated block 11 and the inclined surface of the solid medium block 14 are polished to a surface accuracy of λ / 4 or less, and both surfaces are joined by optical contact.

The optical fiber cord 15 includes an optical fiber 15a and a lens 15b provided at the emission end thereof. The optical fiber cord 15 is arranged so that incident signal light emitted from the optical fiber 15 a is incident obliquely on the outer surface 11 b on the incident side of the laminated block 11. That is, the incident direction of the incident signal light is set so as to be perpendicular to the Z direction and incident at an acute angle with respect to the outer surface 11 b on the incident side of the laminated block 11.
As the incident angle α of the incident signal light increases, insertion (passage) loss and polarization-dependent loss increase. Therefore, it is preferably close to 0 ° in that respect, but if it is too small, the transflective layers 13a, 13b, and 13c The distance D between the optical paths of the reflected branched signal lights is reduced, and as a result, interference occurs between the branched signal lights. Therefore, although it depends on the size of the interval between the semi-transmissive layers 13a, 13b, and 13c, for example, α is preferably set to about 10 to 20 °.
The position where the incident signal light enters the outer surface 11b on the incident side of the laminated block 11 is a semi-transmissive layer if the distance from the incident position to the inclined surface 11a of the laminated block 11 (shown by B in the figure) is too large. Since the branched signal light reflected by 13a, 13b, and 13c reaches another semi-transmissive layer before reaching the inclined surface 11a, it is set in a range in which such inconvenience does not occur.

In the optical fiber array 17, a plurality of optical fibers 17a are led out from the end of a tape-like optical fiber cable 17c, and a fiber array guide 17b is provided at the tip of the leaded optical fiber 17a. 17a are arranged in parallel to each other and at equal intervals. The lens array 16 only needs to have a function of focusing a plurality of lights without changing the direction of each optical axis, and a general lens array can be used.
The optical fiber array 17 and the lens array 16 are arranged such that their optical axes coincide with the optical axis of the branched signal light emitted from the optical branching element 10. That is, the optical axes of the optical fiber array 17 and the lens array 16 are inclined with respect to the outer surface 11 c on the emission side of the optical axis laminated block 11.

In the optical branching module of the present embodiment, incident signal light emitted from the optical fiber cord 15 is incident obliquely on the laminated block 11 of the optical branching element 10. The incident signal light incident on the laminated block 11 passes through the solid medium layer 12a that forms the outermost layer on the incident side, reaches the first semi-transmissive layer 13a, and a part thereof is reflected to be the first branched signal. It becomes light, and the remaining part is transmitted through the first semi-transmissive layer 13a.
The first branched signal light reflected by the first semi-transmissive layer 13 a is transmitted through the inclined surface 11 a of the laminated block 11, further transmitted through the solid medium block 14, and the outer surface 14 b on the incident side of the solid medium block 14. Then, the light is reflected from the reflection layer provided on the outer side of the light branching element 10 from the outer surface 14 c on the emission side of the solid medium block 14.
On the other hand, the signal light transmitted through the first semi-transmissive layer 13a reaches the second semi-transmissive layer 13b, a part of which is reflected to become the second branched signal light, and the remaining part is the second semi-transmissive layer 13b. Transparent.
The second branched signal light reflected by the second semi-transmissive layer 13b passes through the inclined surface 11a of the laminated block 11 through an optical path substantially parallel to the first branched signal light, and is incident on the solid medium block 14. The light is reflected by the reflective layer on the outer surface 14 b on the side, and is emitted from the outer surface 14 c on the emission side of the solid medium block 14.
On the other hand, the signal light transmitted through the second semi-transmissive layer 13b reaches the third semi-transmissive layer 13c, a part of which is reflected to become the third branched signal light, and the remaining part is the third semi-transmissive layer 13c. Transparent.

The third branched signal light reflected by the third semi-transmissive layer 13c is also emitted from the optical branching element 10 through an optical path substantially parallel to the first and second branched signal lights.
On the other hand, the signal light transmitted through the third semi-transmissive layer 13c is reflected by the outer surface 11c on the emission side of the laminated block 11 to become the fourth branched signal light, and an optical path substantially parallel to the first to third branched signal lights. Then, the light is emitted from the optical branching element 10 in the same manner.
In this way, the four branched signal lights are emitted in a state in which the optical paths are parallel to each other from the outer surface 14 c on the emission side of the solid medium block 14 of the optical branching element 10. In the present embodiment, the intervals between the first to third semi-transmissive layers 13a, 13b, and 13c, and the interval between the third semi-transmissive layer 13c and the outer surface 11c on the emission side of the laminated block 11 are all formed equal. Therefore, the distance D between the optical paths (optical axes) of these four branched signal lights is equal to each other.
The four branched signal lights emitted from the optical branching element 10 are respectively converged by the lens array 16 and are incident on four of the plurality of optical fibers 17a constituting the optical fiber array 17, respectively.

Here, it is necessary to configure so that the optical axes of the four branched signal lights emitted from the optical branching element 10 coincide with the optical axes of any four optical fibers 17a in the optical fiber array 17. However, for example, the distance D between the optical axes of the four branched signal lights can be adjusted by the thickness of the three solid medium layers 12b, 12c, and 12d on the emission side among the four solid medium layers. Alternatively, it can be adjusted by changing the setting of the incident angle α of the incident signal light to the optical branching element 10.
Or you may set the space | interval of the optical fiber 17a in the optical fiber array 17 according to the space | interval D of the optical axes of branch signal light.

  Note that the inclination angle A of the inclined surface 11a and the incident angle α of the incident signal light are determined before the branched signal light reflected by the semi-transmissive layers 13a, 13b, and 13c reaches the semi-transmissive layer different from itself. It is possible to change within the range.

The optical branching module of the present embodiment can split the power of one incident signal light into four by the optical branching element 10 and emit each as branched signal light. Since the branched signal light emitted from the optical branching element 10 is obtained in a state where the optical axes are parallel to each other and the distance D between the optical axes is equal, it can be easily incident on the optical fiber 17a of the optical fiber array 17. .
Further, the light branching element 10 has a block shape, and it is easy to change the thickness of the solid medium layers 12a, 12b, 12c, and 12d and the number of the semi-transmissive layers 13a, 13b, and 13c. Therefore, it is suitable for downsizing and the number of branches can be easily expanded. Further, by achieving miniaturization of the optical branching module, it is possible to realize a reduction in loss and an improvement in temperature stability.

In particular, in the optical branching module of the present embodiment, one of the outer surfaces of the laminated block 11 constituting the optical branching element 10 is an inclined surface 11a, so that the branched signal light reflected by one semi-transmissive layer is used. By setting the incident position so as to transmit through the inclined surface 11a before reaching the other semi-transmissive layer, multiple reflection in the optical branching element 10 can be prevented.
Here, the multiple reflection means, for example, as shown in FIG. 4, a part of the branched signal light (shown by a solid line in the figure) reflected by one semi-transmissive layer (for example, the first semi-transmissive layer 13a). The optical path of the sub-reflected light (indicated by a broken line in the figure) that is reflected again inside the optical branching element 40 is reflected by another semi-transmissive layer (for example, the second semi-transmissive layer 13b). It means overlapping with the optical path. In FIG. 4, the same constituent elements as those in FIG.

  In addition, in the optical branching element 10, when the solid medium block 14 is not bonded on the inclined surface 11 a of the laminated block 11, the branched signal light reflected by the semi-transmissive layers 13 a, 13 b, and 13 c is reflected on the laminated block 11. The inclined surface 11a of the light branching element is transmitted through the interface between the inclined surface 11a and the atmosphere of the light branching element (for example, air) and emitted to the outside of the light branching element. When the incident angle of the branched signal light with respect to the interface becomes small and exceeds the critical angle, the branched signal light is totally reflected at the interface and is not emitted outside the optical branching element. On the other hand, in the configuration in which the solid medium block 14 is bonded onto the inclined surface 11a of the laminated block 11 as in the present embodiment, the solid medium layers 12b, 12c, and 12d of the laminated block 11; By making the refractive index substantially the same as that of the solid medium block 14, total reflection at the interface between the two can be effectively suppressed. Therefore, the incident angle α of the incident signal light to the optical branching element 10 can be set small. It becomes possible. By reducing the incident angle α, insertion loss and polarization dependent loss can be reduced.

In the optical branching module of the present embodiment, the reflection layer is provided on the outer surface 14 b on the incident side of the solid medium block 14 constituting the optical branching element 10, so that the branched signal light is transmitted to the incident side of the optical branching element 10. Can be emitted to the opposite side.
Further, since the reflective layer provided on the outer surface 14b of the solid medium block 14 is parallel to the semi-transmissive layers 13a, 13b, 13c, the optical axis direction of the incident signal light and the optical axis direction of the branched signal light are parallel. Alignment of the optical axes of components and the like is easy, which is preferable in assembly work.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the optical branching module of the present invention in partial cross-sectional view. The optical branching module of the present embodiment is provided with a prism 28 (optical path changing means), a lens array 16 and an optical fiber array 17 in order from the optical branching element 20 side so as to face one surface of the block-shaped optical branching element 20. It has been. The light branching element 20 and the prism 28 are integrally provided on the base 29. In the present embodiment, the optical system including the prism 28, the lens array 16, and the optical fiber array 17 includes incident means for making incident signal light incident on the optical branching element 20, and branched signal light emitted from the optical branching element 20. It also serves as means for transmitting by being incident on the optical fiber 17a.
In FIG. 2, the optical branching element 20 shows a cross section. The alternate long and short dash line in the figure indicates the optical axis. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

The optical branching element 20 in the present embodiment is different from the optical branching element 10 in the first embodiment in that the surface of the solid medium block 24 joined to the inclined surface 11a of the laminated block 11 that faces the prism 28 ( Hereinafter, the light exit surface 24b) is provided with a non-reflective layer (not shown) without providing a reflective layer.
Further, in the optical branching element 20 of the present embodiment, the branched signal light is emitted to the side on which the incident signal light is incident, and the surface facing the prism 28 of the laminated block 11 is referred to as “incident surface 11b”. The surfaces facing each other are referred to as “reflecting surfaces 11c”, and the configurations of these surfaces are the same as the incident-side surface 11b and the emitting-side surface 11c in the first embodiment, respectively.

In the present embodiment, the optical fiber array 17 is arranged so that the optical axis of the optical fiber 17 a is perpendicular to the incident surface 11 b of the laminated block 11.
The prism 28 changes the traveling direction of the incident signal light emitted from the optical fiber 17 a of the optical fiber array 17 so as to be inclined with respect to the incident surface 11 b of the laminated block 11, and the emission surface of the solid medium block 24. The traveling direction of the branched signal light emitted obliquely from 24b is changed to be parallel to the optical axis of the optical fiber 17a.
The incident angle α and the incident position of the incident signal light with respect to the incident surface 11b of the laminated block 11 can be set in the same manner as in the first embodiment.

In the optical branching module of the present embodiment, incident signal light emitted from one of the optical fibers 17a constituting the optical fiber array 17 is obliquely incident on the laminated block 11 of the optical branching element 20. .
The incident signal light incident on the laminated block 11 passes through the solid medium layer 12a that forms the outermost layer on the incident side, reaches the first semi-transmissive layer 13a, and the first branched signal light reflected here is Then, the light passes through the inclined surface 11 a of the laminated block 11, further passes through the solid medium block 24, and is emitted from the emission surface 24 b to the outside of the optical branching element 20.
The signal light transmitted through the first semi-transmissive layer 13a reaches the second semi-transmissive layer 13b, and the second branched signal light reflected here passes through an optical path substantially parallel to the first branched signal light. Then, the light passes through the inclined surface 11 a of the laminated block 11 and is emitted from the emission surface 24 b of the solid medium block 24.
The signal light transmitted through the second semi-transmissive layer 13b reaches the third semi-transmissive layer 13c, and the third branched signal light reflected here is an optical path substantially parallel to the first and second branched signal lights. Then, the light is emitted from the optical branching element 20 in the same manner.
The signal light transmitted through the third semi-transmissive layer 13c is reflected by the reflecting surface 11c of the laminated block 11 to become the fourth branched signal light, and the optical signal passes through the optical path substantially parallel to the first to third branched signal lights. The light is emitted from the optical branching element 20.
As described above, the four branched signal lights are emitted from the emission surface 24b of the solid medium block 24 of the optical branching element 20 with their optical paths being parallel to each other. The distances D between the optical paths (optical axes) of these four branched signal lights are equal to each other.
The four branched signal lights emitted from the optical branching element 20 are respectively converged by the lens array 16 and are incident on four of the plurality of optical fibers 17 a constituting the optical fiber array 17.

  Also in the present embodiment, as in the first embodiment, the optical axes of the four branched signal lights emitted from the optical branching element 20, and the optical axes of any four optical fibers 17a in the optical fiber array 17 Are configured to match.

In this embodiment as well, as in the first embodiment, the inclination angle A of the inclined surface 11a is such that the branched signal lights reflected by the semi-transmissive layers 13a, 13b, and 13c are transmitted to different semi-transmissive layers. It can be set in a range up to the inclined surface 11a before reaching.
In the present embodiment, the light branching element 20 and the prism 28 are integrally provided on the base 29, but the prism 28 may be separated from the light branching element 20. The prism 28, the lens array 16 and the optical fiber array 17 may be provided integrally.

  In the optical branching module of the present embodiment, the same operational effects as those of the first embodiment can be obtained, and in particular, the branched signal light is transmitted through the emission surface 24b of the solid medium block 24 constituting the optical branching element 20. Therefore, the branched signal light can be emitted to the incident side of the optical branching element 10. Accordingly, it is possible to transmit incident signal light and branch signal light with one optical fiber array 17, which is preferable in reducing the size of the module.

FIG. 3 is a cross-sectional view showing an optical branching element 30 in the third embodiment of the optical branching module of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.
The light branching element 30 in the present embodiment is different from the light branching element 10 in the first embodiment in that the light branching element 30 is a rectangular parallelepiped and has a laminated block that does not have the inclined surface 11a, and a different solid medium layer. 32a, 32b, 32c, and 32d have different thicknesses.
In the optical branching element 30 of this embodiment, the branched signal light is emitted to the side on which the incident signal light is incident. Therefore, the surface on which the incident signal light is incident and the branched signal light is emitted is referred to as an “incoming / outgoing surface 31b”, and a surface opposite to the surface is referred to as a “reflecting surface 31c”. This is the same as the outer surface 11b on the incident side and the outer surface 11c on the outgoing side of the laminated block 11 in the first embodiment.

In the present embodiment, the solid medium layers 32a, 32b, 32c, and 32d are configured such that the thickness of each layer gradually increases from the incident / exit surface 31b toward the reflective surface 31c. Within each layer, the thickness is uniform. Therefore, the plurality of semi-transmissive layers 13a, 13b, and 13c are parallel to each other, and the intervals between the adjacent semi-transmissive layers are not uniform.
The thickness of each of the solid medium layers 32a, 32b, 32c, and 32d is not particularly limited, but the distance D between the optical axes of the plurality of branched signal lights emitted from the optical branching element 30 can change depending on the thickness. Moreover, multiple reflection can be prevented by providing a difference in the thickness of each layer. In the present embodiment, the thickness of each solid medium layer 32a, 32b, 32c, 32d is preferably set within a range of, for example, about 0.5 to 5 mm, and the difference in thickness between different solid medium layers is 1 to 3 mm. It is preferably set within a range of the degree.

In the optical branching module of this embodiment, the incident signal light is incident on the optical branching element 30 obliquely with respect to the semi-transmissive layers 13a, 13b, and 13c, and the branched signal light emitted from the optical branching element 30 is The means for transmitting is not particularly limited. For example, an optical system in which the optical fiber cord 15, the optical fiber array 17, the lens array 16, and an optical path changing unit such as a prism as necessary are appropriately combined in the first embodiment can be used.
The incident angle α of the incident signal light with respect to the incident / exit surface 31b of the light branching element 30 can be set in the same manner as in the first embodiment. The incident position of the incident signal light can be arbitrarily set.

In the optical branching module of the present embodiment, incident signal light is incident on the incident / exit surface 31 b of the optical branching element 30 obliquely.
The incident signal light incident on the optical branching element 30 passes through the solid medium layer 32a that forms the outermost layer on the incident side, reaches the first semi-transmissive layer 13a, and is reflected here by the first branched signal light. Is emitted from the incident / exit surface 31b to the outside of the optical branching element 30.
The signal light transmitted through the first semi-transmissive layer 13a reaches the second semi-transmissive layer 13b, and the second branched signal light reflected here passes through an optical path substantially parallel to the first branched signal light. The light is emitted from the incident / exit surface 31b.
The signal light transmitted through the second semi-transmissive layer 13b reaches the third semi-transmissive layer 13c, and the third branched signal light reflected here is an optical path substantially parallel to the first and second branched signal lights. Then, the light is emitted from the optical branching element 30 in the same manner.
The signal light that has passed through the third translucent layer 13c is reflected by the reflecting surface 31c to become the fourth branched signal light, and passes through an optical path substantially parallel to the first to third branched signal lights. 30.
In the present embodiment, the four branched signal lights emitted from the incident / exit surface 31b of the optical branching element 30 have parallel optical paths, but the distance D between the optical paths (optical axes) of the branched signal lights is mutually different. Is different.

The optical branching module of the present embodiment can branch the power of one incident signal light into four by the optical branching element 30 and emit the branched signal light as parallel to each other.
Further, the optical branching element 30 has a block shape as in the first embodiment, and is easy to change in design. Therefore, the optical branching element 30 is suitable for downsizing and the number of branches can be easily expanded. Further, by achieving miniaturization of the optical branching module, it is possible to realize a reduction in loss and an improvement in temperature stability.

In particular, in the optical branching module of this embodiment, the intervals between the semi-transmissive layers 13a, 13b, and 13c adjacent to each other in the optical branching element 30 are formed non-uniformly. Reflection can be prevented.
That is, in this embodiment, as shown in FIG. 3, a part of the branched signal light (shown by a solid line in the figure) reflected by one semi-transmissive layer (for example, the first semi-transmissive layer 13a) is optically branched. Even if sub-reflected light (indicated by a broken line in the figure) is reflected again inside the element 30, the semi-transmissive layers 13a, 13b, and 13c are formed with non-uniform intervals. Is not overlapped with the optical path of the branched signal light reflected by another semi-transmissive layer (for example, the second semi-transmissive layer 13b), and multiple reflection is prevented.
In addition, since the light branching element 30 is composed only of a laminated block having no inclined surface, the light branching element 30 is easily manufactured and has an advantage that the degree of freedom of the incident position is high.

In each of the embodiments described above, an example in which the number of semi-transmissive layers is three has been described. However, the number of semi-transmissive layers can be appropriately changed according to the number of branched signal lights to be obtained.
Further, in each of the above embodiments, the plurality of semi-transmissive layers are parallel to each other. However, the light transmission may be performed in a similar manner even if they are not necessarily parallel. Multiple reflections can also be prevented by a configuration in which the semi-transmissive layers are substantially parallel. In order to obtain a plurality of branched signal lights in a mutually parallel state, it is preferable that the plurality of semi-transmissive layers are parallel to each other.
In each of the above embodiments, the case where light is branched using the optical branching module according to the present invention has been described. However, if the traveling direction of the signal light is reverse, a plurality of lights are combined into one light. Is done. That is, the optical branching module of the present invention can be used as an optical coupling module with the traveling direction of signal light reversed. It can also be used as a wavelength branching element that separates wavelengths.

Example 1
An optical branching module having the configuration shown in FIG. 1 was configured.
First, on one surface of a glass plate having a thickness of 2.14 mm (solid medium layer), a dielectric multilayer film made of _Ta 2 _{O 5} and SiO ₂ (semi-transparent layer) one formed by ion-assisted deposition, Three glass plates and dielectric multilayer films were laminated so as to be alternated and adhered to each other, and the glass plate was laminated and adhered on the outermost dielectric multilayer film to produce a block body. The block body was cut at an inclined surface 11a inclined with respect to the dielectric multilayer film to produce a laminated block 11.
Separately, a glass block was cut along an oblique inclined surface to produce a solid medium block 14 having the same outer shape as the laminated block 11.
The inclined surface 11a of the obtained laminated block 11 and the inclined surface of the solid medium block 14 were joined and integrated with a transparent adhesive to produce a rectangular parallelepiped light branching element 10.
In the optical branching element 10, the inclination angle A of the inclined surface 11a was 6.65 °. Further, in order from the incident side, the reflectance of the first semi-transmissive layer 13a is 25%, the reflectance of the second semi-transmissive layer 13b is 25%, and the reflectance of the third semi-transmissive layer 13c is 25%. did.
A reflective film made of Ta ₂ O ₅ and SiO ₂ was formed on the outer surface 11c on the emission side of the laminated block 11 by ion-assisted vapor deposition, and the reflectance was 99%. A reflective film made of Ta ₂ O ₅ and SiO ₂ was formed on the outer surface 14b on the incident side of the solid medium block 14 by ion-assisted vapor deposition, and the reflectance was set to 99%.
As the optical fiber array 17, eight optical fibers 17 a are arranged in parallel and in a line, and the distance between the optical axes of adjacent optical fibers 17 a is 500 μm.
The incident angle α of the incident signal light emitted from the optical fiber cord 15 to the laminated block 11 of the optical branching element 10 was 10 °, and the distance B from the incident position to the inclined surface 11a was 0.5 mm.

Using the optical branching module having such a configuration, incident signal light was branched. That is, light having a wavelength of 1550 nm was incident on the optical branching element 10 from the laser light source, and the output intensity of each of the four branched signal lights emitted from the optical branching element 10 was measured with an optical power meter. The insertion loss at 25 ° C. was as follows when the four branched signal lights were branched signal lights 1, 2, 3, and 4 from the side closer to the inclined surface 11a. The following insertion loss values are values excluding the theoretical branching loss (6 dB).
Branch signal light 1 0.32 dB
Branch signal light 2 0.51 dB
Branch signal light 3 0.75 dB
Branch signal light 4 0.89 dB
Further, the fluctuation range (temperature dependence) of the output intensity when the ambient temperature of the optical branching module was changed in the range of 0 to 65 ° C. was as follows.
Branch signal light 1 0.12 dB
Branch signal light 2 0.10 dB
Branch signal light 3 0.15 dB
Branch signal light 4 0.20 dB

(Example 2)
In the light branching element 10 manufactured in Example 1, the light having the configuration shown in FIG. 2 is similarly obtained except that the reflecting film is not provided on the incident-side outer surface 14b of the solid medium block 14 and a non-reflective layer is provided instead. The branch element 20 was produced.
As the optical fiber array 17, eight optical fibers 17a are arranged in parallel and in a line, and the distance between the optical axes of the adjacent optical fibers 17a is 500 μm.
The incident angle α of the incident signal light emitted from the optical fiber array 17 to the laminated block 11 of the optical branching element 20 and the distance B from the incident position to the inclined surface 11a are the same as in the first embodiment.

Using the optical branching module having such a configuration, incident signal light was branched. The four branched signal lights emitted from the optical branching element 20 were evaluated in the same manner as in Example 1.
The results of measuring insertion loss at 25 ° C. are shown below.
Branch signal light 1 0.26 dB
Branch signal light 2 0.45 dB
Branch signal light 3 0.62 dB
Branch signal light 4 0.75 dB
Moreover, the result of having measured the temperature dependence (variation width) of output intensity similarly to Example 1 is shown below.
Branch signal light 1 0.10 dB
Branch signal light 2 0.11 dB
Branch signal light 3 0.12 dB
Branch signal light 4 0.15 dB

(Comparative example)
Using an optical fiber coupler type optical branching device (product name: 1 × 4 Coupler, manufactured by Sumitomo Osaka Cement Co., Ltd.) formed by fusing and stretching a plurality of optical fibers, the incident signal light was branched into four. The four branched signal lights emitted from the optical branching device were evaluated in the same manner as in Example 1.
The results of measuring insertion loss at 25 ° C. are shown below.
Branch signal light 1 0.35 dB
Branch signal light 2 0.62 dB
Branch signal light 3 0.47 dB
Branch signal light 4 0.55 dB
Moreover, the result of having measured the temperature dependence (variation width) of output intensity similarly to Example 1 is shown below.
Branch signal light 1 0.15 dB
Branch signal light 2 0.22 dB
Branch signal light 3 0.16 dB
Branch signal light 4 0.25 dB

It is a schematic block diagram which shows 1st Embodiment of the optical branching module concerning this invention. It is a schematic block diagram which shows 2nd Embodiment of the optical branching module concerning this invention. It is a schematic block diagram which shows 3rd Embodiment of the optical branching module concerning this invention. It is explanatory drawing of multiple reflection.

Explanation of symbols

10, 20, 30, 40 ... optical branching element, 11, 31 ... laminated block, 11a ... inclined surface,
12a, 12b, 12c, 12d, 32a, 32b, 32c, 32d ... solid medium layer,
13a, 13b, 13c ... semi-transmissive layer, 14, 24 ... solid medium block,
15 ... Optical fiber cord (incident means), 28 ... Prism (optical path changing means).

Claims (7)

A part of incident signal light is reflected to form a branched signal light, and a plurality of semi-transmissive layers that transmit the remainder of the incident signal light are provided with an interval therebetween,
An incident means for obliquely entering the incident signal light with respect to the semi-transmissive layer;
The optical path of the sub-reflected light that is generated when a part of the branched signal light reflected by one semi-transmissive layer is reflected again inside the optical branching element is the optical path of the branched signal light reflected by the other semi-transmissive layer. An optical branching module comprising multiple reflection preventing means for preventing overlapping multiple reflections.   The optical branching module according to claim 1, wherein the plurality of semi-transmissive layers are parallel to each other.   The optical branching module according to claim 2, wherein the multiple reflection preventing means is formed with non-uniform intervals between adjacent semi-transmissive layers.   As the multiple reflection preventing means, the light branching element is composed of a laminated block in which the semi-transmissive layer and a solid medium layer that transmits the transmitted light of the semi-transmissive layer are alternately laminated. A part of the outer surface is inclined with respect to the semi-transmissive layer so that the branched signal light reflected by one semi-transmissive layer is transmitted through the inclined surface before reaching the other semi-transmissive layer. It is comprised by these, The optical branching module as described in any one of Claims 1-3 characterized by the above-mentioned.   5. The optical branching module according to claim 4, wherein a solid medium block that transmits the branched signal light transmitted through the inclined surface is joined to the inclined surface of the laminated block.   The optical branching module according to claim 5, wherein the solid medium block is provided with a reflection layer for reflecting the branched signal light transmitted through the inclined surface. The optical branching module according to claim 1, wherein the incident unit includes an optical path changing unit that changes a traveling direction of incident signal light.

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