JP5935465B2 - Optical device - Google Patents

Description

  The present invention relates to an optical device that couples an optical component such as a plurality of single core fibers to an optical element such as a multicore fiber.

  Conventionally, a multi-core fiber coupling device that couples a plurality of single-core fibers to a multi-core fiber is known. For example, Patent Document 1 below discloses an apparatus in which a lens is interposed between a multi-core fiber having two core regions and two single-core fibers in order to branch the multi-core fiber. The lens in this apparatus deflects a plurality of beams emitted from the multicore fiber in a direction inclined with respect to the optical axis of the multicore fiber so as to be separated from each other.

JP 60-212710 A

  In the prior art described above, since the beam of the multicore fiber is tilted by the lens, it is necessary to tilt the single core fiber so as to match the tilt. In this case, it is very difficult to adjust and align the angle between the multi-core fiber and the single-core fiber, which is not practical.

  Therefore, the inventors have studied a device as shown in FIG. 1 as a more practical device. The apparatus shown in FIG. 1 deflects a lens 11 (focal length f1) that separates a plurality of beams of the multicore fiber 10 from each other and a plurality of beams separated from each other by the lens 11 in a direction parallel to the optical axis of the multicore fiber. A lens l2 (focal length f2). Therefore, since it is not necessary to incline the single core fiber 20 with respect to the multicore fiber 10, angle adjustment is unnecessary, and high practicality can be realized.

Here, the interval between the plurality of beams of the multi-core fiber 10 is expanded by the lens l1, and the interval expansion rate m is f2 / f1. On the other hand, according to Lagrange's law used in optics, it is known that the beam divergence angle θ is proportional to the reciprocal of the interval expansion rate. That is, in the apparatus of FIG. 1, when the beam divergence angle θ _OUT at the end face of the multicore fiber is set, the divergence angle (condensing angle) θ _IN at the end face of the single core fiber is θ _OUT / m.

When the beam emitted from the multi-core fiber is a Gaussian beam, the beam has a beam radius w _OUT at the end face of the multi-core fiber and a spread angle θ _{OUT according} to the following equation when the wavelength is λ.

  θ = λ / (π · w)

Note that π is the circumference ratio. The above equation is also applied to the incident beam into a single core fiber. The divergence angle θ _IN of the incident beam to the single core fiber is θ _IN / m according to the Lagrangian law. In this case, the beam radius w _IN at the end face of the single core fiber is multiplied by m in accordance with the above formula to m · w _OUT . Therefore, there is a problem that the coupling loss of light to the single core fiber becomes large.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical device in which coupling loss is reduced while improving practicality.

  An optical device according to the present invention is an optical device that couples an optical element having a plurality of light input / output units having optical axes parallel to each other to another optical component, and is provided for the plurality of light input / output units of the optical element. A first optical system that is positioned on the optical axes of a plurality of incoming and outgoing beams and that is separated from each other by making the optical axes of the beams different from each other, and the first optical system side And a second optical system that sets optical axes of a plurality of beams that are in a state different from being parallel to each other in a substantially parallel state to each other.

  In this optical apparatus, the plurality of beams separated from each other by the first optical system are made substantially parallel to each other by the second optical system. For this reason, the other optical components do not need to be inclined with respect to the optical element, and angle adjustment is unnecessary, so that high practicality can be realized. Further, the coupling loss can be reduced.

  The second optical system may be configured to collect a plurality of beams on another optical component.

  The optical element may be a multi-core fiber, and the other optical component may be a plurality of single-core fibers, and the focal length of the first optical system may be equal to the focal length of the second optical system. Thereby, the coupling loss of light to the single core fiber is reduced.

  In the optical device, the aberration of the second optical system may be correctable. In this case, for example, a part of the second optical system may be changed in position relative to other optical components from the other part, and the aberration of the second optical system may be corrected. Further, the first and second optical systems may be integrally configured as one optical component. Further, at least one of the first and second optical systems may be a GRIN lens.

  According to the present invention, it is possible to reduce the coupling loss while improving the practicality.

FIG. 1 is a schematic configuration diagram illustrating a multi-core fiber coupling device according to the related art. FIG. 2 is a schematic configuration diagram illustrating the multi-core fiber coupling device according to the first embodiment. FIG. 3 is a diagram showing a mode in which the beam interval is enlarged on the end face of the multi-core fiber. FIG. 4 is a schematic configuration diagram illustrating a multi-core fiber coupling device according to the second embodiment. FIG. 5 is a diagram showing a positional shift of the lens of the second optical system in the multi-core fiber coupling device shown in FIG. FIG. 6 is a schematic configuration diagram illustrating a multi-core fiber coupling device according to the third embodiment. FIG. 7 is a partially enlarged cross-sectional view of the second optical system in the multi-core fiber coupling device shown in FIG. FIG. 8 is a diagram showing an aspect different from the second optical system shown in FIG. FIG. 9 is a schematic configuration diagram illustrating a multi-core fiber coupling device according to the fourth embodiment. FIG. 10 is a diagram illustrating a first optical system according to the fifth embodiment. FIG. 11 is a partial enlarged view of the first optical system shown in FIG. FIG. 12 is a schematic configuration diagram illustrating a multi-core fiber coupling device according to a sixth embodiment.

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

[First Embodiment]
First, the optical device 100 according to the first embodiment will be described with reference to FIG.

  As shown in FIG. 2, the optical device 100 is a device that combines a multi-core fiber 10 (optical element) and a single-core fiber 20 (other optical components) in order to propagate a single-mode optical signal. An optical system S1 and a second optical system S2 are provided. Hereinafter, an optical device included in the present invention using a multi-core fiber as an optical element is referred to as a multi-core fiber coupling device.

  The multi-core fiber 10 used in the present embodiment is an optical element having a plurality of light input / output units having optical axes parallel to each other, specifically, having seven core regions, and from its emission end face 10a. 7 beams are emitted (only three beams are shown in FIG. 2 when viewed from the side). More specifically, the seven core regions are at the positions of the regular hexagonal apex and the center point of the end face 10a, and the interval between adjacent core regions (that is, the beam interval on the exit end face 10a) is the same, for example, 0 It is about 045mm. The clad diameter of the multi-core fiber 10 is about 0.15 mmφ.

  On the other hand, as many single core fibers 20 as the number of core regions of the multicore fiber 10 (that is, seven) are prepared, and each light receiving end face 20a is parallel to the emission end face 10a of the multicore fiber 10 and on the same plane. Has been placed. That is, seven single-core fibers 20 (only three single-core fibers 20A, 20B, and 20C are shown in FIG. 2 as viewed from the side) are inclined at least with respect to the multi-core fiber 10. Instead, the multi-core fiber 10 is arranged in parallel to the extending direction, and the optical axis of the multi-core fiber 10 and the optical axis of each single-core fiber 20 are parallel to each other. The single core fiber 20 can be appropriately changed to a TEC fiber (Thermally-diffused Expanded Core Fiber) in which the mode field diameter (MFD) at the end is locally expanded in order to increase tolerance at the time of mounting. .

  The first optical system S1 is positioned on the optical axes of a plurality of beams entering and exiting the plurality of light input / output units of the multi-core fiber 10, and by making the optical axes of the beams different from each other. , They are separated from each other. The first optical system S1 is located on the multi-core fiber 10 side, and is composed of one condenser lens L1. The condensing lens L <b> 1 is disposed so as to face the end surface 10 a of the multicore fiber 10 on the axis of the emission end of the multicore fiber 10. As shown in FIG. 2, the condensing lens L1 is disposed at a position away from the end face 10a of the multi-core fiber 10 by the focal length f1 of the condensing lens L1. The plurality of beams that have passed through the condenser lens L1 are once separated from each other and then separated from each other, and the distance between the beams is increased as the distance from the first optical system S1 is increased.

  The second optical system S2 sets the optical axes of a plurality of beams that are different from being parallel to each other on the first optical system S1 side to be substantially parallel to each other. The second optical system S2 is located on the single core fiber 20 side, and is composed of one condenser lens L2 and seven condenser lenses L3. Although the condensing lens L3 is shown as being spatially separated in FIG. 2, it may be configured integrally as a lens array.

  Like the condensing lens L1, the condensing lens L2 is arrange | positioned so that the end surface 10a of the multicore fiber 10 may be faced on the axis line of the emission end part of the multicore fiber 10. As shown in FIG. 2, the condenser lens L2 is disposed at a position away from the condenser lens L1 by the sum (f1 + f2) of the focal length f1 of the condenser lens L1 and the focal length f2 of the condenser lens L2. . The plurality of beams transmitted through the condenser lens L2 are all separated from each other by the condenser lens L1 in a direction parallel to the optical axis of the multicore fiber 10 (that is, with the end surface 10a of the multicore fiber 10). It is deflected in the direction of the orthogonal axis, the facing direction of the end surface 10a of the multicore fiber 10 and the end surface 20a of the single core fiber 20.

  The seven condenser lenses L3 are arranged so as to face the condenser lens L2 on the optical axis of each deflected beam so as to collect each of the deflected beams. As shown in FIG. 2, the condenser lens L3 is disposed at a position away from the condenser lens L2 by a predetermined distance d. This distance d is determined by the focal length f3 of the condenser lens L3. That is, the distance d and the focal length f3 are set so that the focal length f1 of the condenser lens L1 described above is equal to the combined focal length f of the condenser lens L2 and the condenser lens L3.

The combined focal length f of the condenser lens L2 and the condenser lens L3 follows the following formula.
1 / f = 1 / f2 + 1 / f3-d / (f2 / f3)

Then, by making the focal length f1 of the condenser lens L1 equal to the combined focal length f of the condenser lens L2 and the condenser lens L3, the beam transmitted through the condenser lens L3 enters the single core fiber 20. The spread angle (condensing angle) θ _IN is equal to the beam spread angle θ _OUT when emitted from the multicore fiber 10. As a result, a very low coupling loss (for example, 0.5 dB) can be realized in the coupling between the multicore fiber 10 and the single core fiber 20.

  As described above, in the multi-core fiber coupling device 100, the plurality of beams of the multi-core fiber 10 separated from each other by the condensing lens L1 of the first optical system S1 is the condensing lens L2 of the second optical system S2. , L3 is deflected in a direction parallel to the optical axis of the multi-core fiber 10 (the direction of the axis orthogonal to the end face 10a). Therefore, the single-core fiber 20 does not need to be inclined with respect to the multi-core fiber 10, and angle adjustment is unnecessary, so that high practicality is realized.

  In the configuration of the present embodiment in which the optical element is the multi-core fiber 10 and the other optical components are a plurality of single-core fibers 20, a plurality of multi-core fibers 10 separated from each other by the condenser lens L1 of the first optical system S1. The condensing lenses L2 and L3 of the second optical system S2 that collect the beam of No. 1 in the core region of each single core fiber 20 corresponding to each beam have a combined focal length f of the lens of the first optical system S1. It is equal to the focal length f1 of L1. Therefore, the coupling loss of light to the single core fiber 20 is reduced.

  In the embodiment described above, the plurality of beams of the multi-core fiber 10 are separated from each other by the lens L1 of the first optical system S1, but the plurality of beams can be separated from each other also in the mode shown in FIG. Is possible. In FIG. 3 (a), the end surface 10a is subjected to end surface processing (not shown) so that the beams are adjusted in the beam emission directions that are separated from each other. More specifically, the end surface 10a is curved or chamfered so that the end surface of the core region at the peripheral position is inclined with respect to the end surface of the core region at the center position, thereby adjusting the beam emission direction. Is done. At this time, adjacent beams do not intersect if the inclination angle of the end face of each core region is set to an angle that is twice or more the beam divergence angle.

  Or, as shown in FIG. 3 (b), six glass blocks (two glass blocks G1 and G2 in FIG. 3 as viewed from the side) are arranged corresponding to the core region in the peripheral position, It is possible to refract the beam from the core region at the peripheral position in each glass block and to separate the plurality of beams of the multi-core fiber 10 from each other. For example, when the glass block G1 or G2 has a beam interval of 0.045 mm and a numerical aperture (NA) of 0.1, the inclination angle θ can be set to 30 degrees and the glass block length D can be set to about 10 μm.

[Second Embodiment]
Next, a multi-core fiber coupling device 100A according to the second embodiment will be described with reference to FIG.

  As shown in FIG. 4, the multi-core fiber coupling device 100A differs from the multi-core fiber coupling device 100 according to the first embodiment described above only in the configuration of the second optical system S2.

  The second optical system S2 of the multicore fiber coupling device 100A includes lens arrays L4 to L6. The lens array includes seven lenses (only three lenses L4 to L6 are shown in FIG. 4 as viewed from the side) so as to correspond to the seven beams. The seven lenses L4 to L6 of the second optical system S2 all have a focal length of f1, which is equal to the focal length of the condensing lens L1 of the first optical system S1.

Therefore, the divergence angle θ _OUT at the end face 10 a of the multicore fiber 10 and the divergence angle θ _IN at the end face of the single core fiber 20 are equal, and the same as in the first embodiment. In coupling, very low coupling losses can be realized.

  In the second embodiment, the same beam deflection as that of the condensing lens L2 of the first embodiment is performed. More specifically, in the second embodiment, the deflection of the beam is realized by shifting the position of the lens L as shown in FIG. That is, as shown in FIG. 5A, the beam is not deflected in such a positional relationship that the center line of the beam (middle line in FIG. 5) passes through the center point C of the lens L, but FIG. As shown in FIG. 5, by shifting the center line of the beam from the center point C of the lens L, the beam is deflected in a direction parallel to the optical axis of the multi-core fiber 10 like the beam transmitted through the condenser lens L2. The direction in which the lens L is shifted is the direction in which the center point C approaches the principal ray of the center beam (that is, the direction closer to the center lens L5). When the lenses are in contact with each other and it is difficult to shift the position, a lens piece obtained by excising a part of the lens may be used.

  Therefore, in the multi-core fiber coupling device 100A according to the second embodiment, the same or equivalent effect as the multi-core fiber coupling device 100 according to the first embodiment described above can be obtained.

[Third Embodiment]
Next, a multi-core fiber coupling device 100B according to a third embodiment will be described with reference to FIGS.

  As shown in FIG. 6, the multi-core fiber coupling device 100B is different from the multi-core fiber coupling device 100A according to the second embodiment described above in the configuration of the second optical system S2. That is, the second optical system S2 of the multi-core fiber coupling device 100B is configured by one lens array in which seven lens pieces L7 to L9 are combined instead of the seven lenses L4 to L6.

  Also in such a multi-core fiber coupling device 100B, the same or equivalent effect as the multi-core fiber coupling device 100 according to the first embodiment described above can be obtained.

  Here, when considering a more practical lens instead of an ideal lens, it is necessary to consider the aberration of the lens.

  As shown in FIG. 7, the plurality of beams transmitted through the lens arrays L7 to L9 of the second optical system S2 do not form the focal point F on the same plane (that is, the end face 20a of the single core fiber 20). Specifically, when the lens arrays L7 to L9 are arranged so that the beam transmitted through the central lens piece L8 forms a focal point F at the end face 20a of the single core fiber 20, the peripheral lens pieces L7 and L9 are arranged. Is the focal point F before the end face 20 a of the single core fiber 20.

  In such a case, in order to correct the aberration, it is preferable to use the lens configuration shown in FIG.

  That is, the central lens piece L8 'and the peripheral lens pieces L7, L9 are relatively shifted in the direction of the optical axis of the multicore fiber 10. As a result, all the beams transmitted through the lens arrays L7, L8 ', and L9 of the second optical system S2 are focused on the same plane. In the second optical system S2, the correction of the aberration may be performed by changing the relative position of a part of the lens array including the lenses L7 to L9 with the single core fiber 20 as described above in the second optical system S2. The aberration may be corrected by changing the surface shape of the integral lens. In addition, the aberration may be corrected by making the refractive index of the integrated lens different between the central portion and the lateral portion located laterally from the central portion.

[Fourth Embodiment]
Next, a multi-core fiber coupling device 100C according to the fourth embodiment will be described with reference to FIG.

  As shown in FIG. 9, the multi-core fiber coupling device 100 </ b> C is different from the multi-core fiber coupling device 100 </ b> B according to the third embodiment described above in that an integrated member 30 is provided. The integrated member 30 integrally configures the first optical system S1 and the second optical system S2 as one optical component, and the relative position between the first optical system S1 and the second optical system S2. Is a member for keeping the constant. The integrated member 30 may be a hollow case in which air is interposed between the first optical system S1 and the second optical system S2, and the first optical system S1 and the second optical system S2. It may be a solid member with a translucent material interposed between them. In the case of a solid member, the first optical system S1, the integrated member 30, and the second optical system S2 can be integrally molded.

[Fifth Embodiment]
The first optical system S1 in the first to fourth embodiments described above can be appropriately replaced with a GRIN lens (refractive index distribution type lens) L10 as shown in FIG.

  As can be seen from the optical path diagrams of FIGS. 10 and 11, the multiple beams of the multi-core fiber 10 are separated from each other by the GRIN lens L10, as in the first optical system S1 in the first to fourth embodiments.

  Thus, when the GRIN lens L10 is used as the first optical system S1, since the beam does not propagate in the air, the reflection loss at the interface between the glass and the air is significantly reduced. Further, by polishing the end face 10a of the multi-core fiber 10 and the end face of the GRIN lens L10 in advance perpendicular to the optical axis, it is not necessary to adjust the angles of the multi-core fiber 10 and the GRIN lens L10. There is a merit that it only needs to be adjusted.

  The GRIN lens can be used not only for the first optical system S1 but also for the second optical system S2.

[Sixth Embodiment]
Even if the glass block 40 is arranged so that no air is interposed between the first optical system S1 and the second optical system S2, as in the multi-core fiber coupling device 100D according to the sixth embodiment shown in FIG. Good.

  As described above, when the glass block 40 interposed between the first optical system S1 and the second optical system S2 is used, since the beam does not propagate in the air, the reflection loss at the interface between the glass and the air is reduced. Significantly reduced.

  Of the multi-core fiber coupling device according to the above-described embodiment, specific dimensions of each element will be described using the multi-core fiber coupling device 100D according to the sixth embodiment as an example. Here, a mode in which a plurality of beams are emitted from the end face 10a of the multicore fiber 10 at a beam interval of 0.045 mm and incident on the end face 20a of the single core fiber 20 at a beam interval of 0.25 mm will be described.

  The lengths of the first optical system S1 (GRIN lens), the glass block 40, and the second optical system S2 are 1.5 mm, 3.9 mm, and 1 mm, respectively, and the overall length is about 6.4 mm.

  The exit beam from the end face 10a of the multi-core fiber 10 (incident beam to the coupling device) has a beam interval of 0.045 mm, and NA corresponds to 0.1.

  The GRIN lens of the first optical system S1 has n (r) of 1.5-0.8 × r2, L of 1.5 mm, and a diameter of 0.66 mm.

Glass block 40 is composed of SiO _2, L is 3.9 mm, a diameter of 0.66 mm.

The lens of the second optical system S2 is made of a material equivalent to SiO ₂ , has a focal length of 0.7 mm, a radius of curvature of 0.312 mm, and L of 1 mm.

  The incident beam (outgoing beam from the coupling device) to the end face 20a of the single core fiber 20 has a beam interval of 0.25 mm, and NA corresponds to 0.1.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above-described embodiment, the optical element having a plurality of light input / output units having optical axes parallel to each other is exemplified as a multi-core fiber in which a plurality of cores are included in one fiber. A fiber array in which a plurality of fibers are arranged in a one-dimensional array, a fiber bundle in which a plurality of optical fibers having a single core are bundled so that the core is arranged in a two-dimensional manner, It is also possible to apply the optical element (for example, VCSEL array, PD array, etc.) in which the light emitting part and the light receiving part are arranged two-dimensionally to the above-described embodiment as the same as the above-described multi-core fiber 10. In addition, an optical element in which a plurality of light emitting units and light receiving units are two-dimensionally arranged can also be applied to other optical components. A GRIN lens may be used for the second optical system S2.

  In the above-described embodiments, the light emitted from the multicore fiber is described as a coupling device that enters the single core fiber. On the contrary, the light emitted from the single core fiber is incident on the multicore fiber. It can also be used as a coupling device. Further, the number of core regions of the multi-core fiber and the number of single-core fibers are not limited to seven, and can be increased or decreased as necessary. Furthermore, the specific dimensions and materials of the above-described elements can also be changed as necessary.

  DESCRIPTION OF SYMBOLS 10 ... Multi-core fiber, 20, 20A, 20B, 20C ... Single core fiber, 100, 100A, 100B, 100C, 100D, 200 ... Multi-core fiber coupling device, S1 ... 1st optical system, S2 ... 2nd optical system.

Claims (6)

An optical device for coupling an optical element having a plurality of light input / output units having optical axes parallel to each other to another optical component,
Located on the optical axes of a plurality of beams entering and exiting the plurality of light input / output portions of the optical element, and further separated from each other by making the optical axes of the beams different from each other. A first optical system,
A second optical system that sets the optical axes of the plurality of beams that are different from being parallel to each other on the first optical system side to be substantially parallel to each other ;
The second optical system is disposed at a position where the plurality of beams emitted from the first optical system and separated from each other are incident, and a plurality of the plurality of beams for individually condensing the plurality of beams. An optical apparatus comprising a lens, wherein all the focal points of the plurality of beams are formed on the same plane . The optical element is a multi-core fiber;
The other optical components, the optical device according to claim 1, wherein the Ah Turkey a plurality of single-core fiber. The optical apparatus according to claim 1, wherein each of the plurality of lenses has the same focal length. Each of the plurality of lenses connects all the focal points of the plurality of beams on the same plane by adjusting the relative positions of the emission positions of the plurality of beams and the other optical components to correct aberrations. The optical device according to any one of claims 1 to 3, wherein The optical device according to claim 1, wherein the plurality of lenses are integrated.   6. The optical apparatus according to claim 1, wherein the first and second optical systems are integrally configured as one optical component.

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