Optical switch

Abstract

This optical switch comprises a connection part, a lens, and a reflection mirror array. The lens is disposed so that input light from one or more multi-core fibers connected to the connection part passes therethrough. The reflection mirror array is configured to reflect, toward an output destination, the input light propagating through the lens. Each of the one or more multicore fibers comprises a plurality of cores two-dimensionally arranged at a predetermined pitch so as to form a predetermined geometric pattern. The reflection mirror array comprises a plurality of reflection mirrors two-dimensionally arranged in an enlarged geometric pattern and at an enlarged pitch. Each of the plurality of reflection mirrors is configured to be capable of rotationally driving the reflection surface around two rotation axes.

Description

Optical switch

[0001] The present disclosure relates to optical switches.

[0002] In recent years, with the increasing speed of mobile communications, the amount of communication traffic in optical backbone networks has been increasing. Current optical links using single-mode fiber (SCF) are unable to keep up with the increasing traffic demand. For this reason, space-division multiplexing (SDM) networks using multimode fiber (MCF) have been proposed.

[0003] An SDM network includes a wavelength division multiplexing (WDM) layer using SCF, as well as an SDM layer that uses MCF-based spatial division channel routing. Recently, a simple and economical spatial cross-connect (SXC) architecture based on a core selection switch (CSS) has been proposed as an SXC architecture that uses MCF (see, for example, Non-Patent Document 1).

[0004] Masahiko Kamino et al., "Core selective switch with low insertion loss over ultra-wide wavelength range for spatial channel networks," Journal of Lightwave Technology, USA, March 15, 2022, Vol. 40, No. 6, pp. 1822-1828

[0005] The proposed core selection switch uses a tilt-type MEMS mirror as a switching element. The tilt angle of the MEMS mirror is controlled by controlling the voltage applied to the MEMS mirror. The core of the output multi-core fiber is selected through the control of the tilt angle.

[0006] Incidentally, in optical switches compatible with multi-core fibers, including the above-described core selection switch, the higher the core integration density of the multi-core fiber, the more restrictions there are on the arrangement of reflecting mirrors in the reflecting mirror array.

[0007] Therefore, according to one aspect of the present disclosure, it is desirable to provide an optical switch suitable for a multi-core fiber with a high core density.

[0008] According to one aspect of the present disclosure, there is provided an optical switch including a connection portion, a lens, and a reflecting mirror array, wherein one or more multi-core fibers are connected to the connection portion.

[0009] The lens is positioned to receive input light from one or more multicore fibers connected to the splice, and the reflective mirror array is configured to reflect the input light passing through the lens toward an output destination.

[0010] Each of the one or more multicore fibers comprises a plurality of cores arranged two-dimensionally at a predetermined pitch to form a predetermined geometric pattern, and the lens is positioned such that input light passing through the lens is incident on the reflective mirror array with an expanded geometric pattern and pitch.

[0011] The reflective mirror array includes a plurality of reflective mirrors arranged two-dimensionally with an expanded geometric pattern and pitch, each of which is configured such that its reflective surface can be rotated around two rotation axes.

[0012] In an optical switch configured in this manner, the reflective mirror array can receive input light from one or more multi-core fibers in an expanded geometric pattern and pitch, and reflect each of these input light toward a corresponding output destination.

[0013] Therefore, according to one aspect of the present disclosure, it is possible to provide an optical switch suitable for a multi-core fiber with a high core density.

[0014] According to one aspect of the present disclosure, the plurality of reflective mirrors may include a plurality of MEMS tilt mirrors. The MEMS tilt mirrors as switching elements have low optical loss, a wide bandwidth, and can operate with low power consumption.

[0015] According to one aspect of the present disclosure, each of the plurality of reflecting mirrors may include a main body having a reflective surface on its surface and an electrode pad for power supply. The electrode pad may be provided on the rear surface of the main body. This arrangement of the electrode pads allows a larger reflective surface to be provided on the surface compared to when the electrode pads are provided on the surface. Therefore, insertion loss caused by light incident on the reflecting mirror extending beyond the reflective surface can be reduced.

[0016] According to one aspect of the present disclosure, a reflective mirror array may include a substrate, and the reflective mirrors may be surface-mounted on the substrate via electrode pads.

[0017] According to one aspect of the present disclosure, the reflective mirror array may include, as a plurality of reflective mirrors, a plurality of MEMS devices configured as MEMS tilt mirrors, each having one reflective surface.

[0018] According to one aspect of the present disclosure, a reflective mirror may include a first structure and a second structure. The first structure may be a structure that is driven to rotate around two rotation axes. The second structure may have a front surface and a back surface, and may be connected to the first structure at the back surface. The front surface of the second structure may extend in a direction perpendicular to the normal direction so as to overlap the first structure in the normal direction. A reflective surface may be provided on the surface of the second structure.

[0019] By providing a reflecting surface on the surface of the second structure that overlaps with the rotationally driven first structure, it is possible to provide a larger reflecting surface on the second structure compared to when a reflecting surface is provided on the surface of the first structure, thereby making it possible to reduce insertion loss.

[0020] FIG. 1 is a diagram illustrating an example of installation of a core selection switch in an optical network. FIG. 2 is a diagram illustrating the optical configuration of the core selection switch. FIG. 3 is a diagram illustrating a controller that controls the core selection switch. FIG. 4 is a diagram conceptually illustrating optical switching in the core selection switch. FIG. 5A is a plan view showing a two-dimensional arrangement of multi-core fibers in a plane perpendicular to the optical axis, and FIG. 5B is a plan view showing a two-dimensional arrangement of MEMS tilt mirrors in a reflective mirror array. FIG. 6A is a plan view of a MEMS tilt mirror, and FIG. 6B is a bottom view of the MEMS tilt mirror. FIG. 8A is a plan view of a MEMS tilt mirror of a modified example, and FIG. 8B is a front view of the MEMS tilt mirror of the modified example.

[0021] 1...optical network, 10...core selection switch, 20...multicore fiber, 21...core, 30...MCF array, 40...microlens array, 41...microlens, 50...condenser lens, 80...reflecting mirror array, 81...substrate, 85...MEMS tilt mirror, 90...controller, 100...MEMS tilt mirror, 110...lower structure, 111...main body, 111A...opening, 111B...comb electrode, 113...frame, 113A...comb electrode, 113B...comb electrode, 115...plate, 115A...comb electrode, 119...electrode pad, 150...upper structure, 151...support, 155...support plate, 159...reflective surface, 850...main body, 851...reflective surface, 859...electrode pad.

[0022] Exemplary embodiments of the present disclosure will now be described with reference to the drawings.

[0023] The core selection switch (CSS) 10 of this embodiment shown in FIG. 1 is an optical switch installed in a node of an optical network 1 constructed using a multi-core fiber (MCF) 20 .

[0024] Each of the multi-core fibers 20 is an optical fiber having a plurality of cores 21 in one cladding. The core selection switch 10 is connected to the plurality of multi-core fibers 20. The core selection switch 10 is configured to be able to switch the propagation path of an optical signal on a core-by-core basis between an input MCF and an output MCF.

[0025] The input MCF is one or more multi-core fibers 20 among the multiple multi-core fibers 20 that input an optical signal to the core selection switch 10. The output MCF is one or more multi-core fibers 20 among the multiple multi-core fibers 20 that output an optical signal from the core selection switch 10 to the outside.

[0026] The core selection switch 10 shown in Fig. 2 includes an MCF array 30, a microlens array 40, a condenser lens 50, and a reflective mirror array 80. The dashed-dotted line in Fig. 2 conceptually represents the propagation of input light, i.e., an optical signal input from an input MCF, to the reflective mirror array 80.

[0027] 3, a controller 90 is connected to the core selection switch 10. The controller 90 is electrically connected to the reflecting mirror array 80 so as to be able to control the reflecting mirror array 80.

[0028] Fig. 4 conceptually illustrates optical switching realized in the core selection switch 10. The solid arrows in Fig. 4 conceptually represent the propagation of input light from the input MCF. The two-dot chain arrows in Fig. 4 conceptually represent the propagation of reflected light from the reflective mirror array 80 corresponding to the input light, which is output to the outside through the output MCF.

[0029] The MCF array 30 functions as a connection portion with the multi-core fibers 20. At least some of the multiple multi-core fibers 20 connected and fixed to the MCF array 30 function as the above-mentioned input MCF. At least some of the multiple multi-core fibers 20 function as the above-mentioned output MCF. The multiple multi-core fibers 20 may include a multi-core fiber 20 that functions as both the input MCF and the output MCF.

[0030] The microlens array 40 includes a plurality of microlenses 41. The plurality of microlenses 41 are two-dimensionally arranged in the microlens array 40. Specifically, the plurality of microlenses 41 are arranged in the microlens array 40 in a two-dimensional arrangement corresponding to the two-dimensional arrangement of the multi-core fibers 20 connected to the MCF array 30. Each microlens 41 functions as a collimator.

[0031] Each microlens 41 is associated with one of the multiple multi-core fibers 20. Each microlens 41 is arranged on a path along which input light from a corresponding one of the multiple multi-core fibers 20 or output light to the corresponding one multi-core fiber 20 propagates.

[0032] Input light from each core 21 of the input MCF is converted into collimated light by the corresponding microlens 41 and enters the condenser lens 50. The incident position on the condenser lens 50 differs for each core 21. In Fig. 4, of the three multi-core fibers 20 shown in the figure, one multi-core fiber 20 in the middle row corresponds to the input MCF.

[0033] The optical system of the core selection switch 10 is configured as a 4f optical system using a microlens array 40 and a condenser lens 50. Therefore, input light from the multicore fiber 20 is incident on the reflecting mirror array 80 at a pitch and beam diameter corresponding to f2 / f1 times the core pitch and core MFD (mode field diameter) of the multicore fiber 20. Here, f1 is the focal length of the microlens 41, and f2 is the focal length of the condenser lens 50.

[0034] The condenser lens 50 is arranged to form a telecentric optical system. Input light from the input MCF passes through the condenser lens 50 and is deflected so that the light after passing through the condenser lens 50 is parallel to the principal ray (principal axis) of the condenser lens 50, and is condensed to form a focus at the focal position of the condenser lens 50.

[0035] The reflective mirror array 80 is arranged so as to reflect the input light at this focal position. The reflective mirror array 80 is provided with a plurality of MEMS tilt mirrors 85 as MEMS type reflective mirrors on the surface of a substrate 81 arranged perpendicular to the principal ray.

[0036] A plurality of MEMS tilt mirrors 85 are provided on the image plane of the input light from the condenser lens 50. The reflecting mirror array 80 can include the same number of MEMS tilt mirrors 85 as the number of cores of the input MCF.

[0037] That is, each MEMS tilt mirror 85 is disposed at a position where it collects input light from a corresponding core 21 that propagates through the condenser lens 50. The multiple MEMS tilt mirrors 85 are two-dimensionally arranged on the substrate 81 in a pattern that is an enlarged version of the two-dimensional arrangement of the cores 21 of the input MCF.

[0038] 5A , in each multicore fiber 20, the multiple cores 21 are two-dimensionally arranged at a predetermined pitch so as to form a predetermined geometric pattern in the cladding. Input light incident on the reflecting mirror array 80 passes through the microlens array 40 and the condenser lens 50, and is incident on the reflecting mirror array 80 with a geometric pattern and pitch that are an enlargement of the geometric pattern and pitch of the multiple cores 21.

[0039] In the reflective mirror array 80, multiple MEMS tilt mirrors 85 are two-dimensionally arranged on a substrate 81 with an enlarged geometric pattern and pitch, as shown in Fig. 5B. Symbol D1 in Fig. 5B represents the spacing between adjacent MEMS tilt mirrors 85, i.e., the mirror pitch. The mirror pitch D1 is the distance between the centers of the reflective surfaces 851 of adjacent MEMS tilt mirrors 85. Symbol D2 in Fig. 5B represents the diameter of the reflective surface 851, i.e., the mirror diameter.

[0040] Fig. 6A is a plan view, in other words a top view, of MEMS tilt mirror 85 as seen from above reflective mirror array 80. Fig. 6B is a bottom view of MEMS tilt mirror 85. As can be seen from Figs. 6A and 6B, MEMS tilt mirror 85 has one reflective surface 851 formed on the front surface of main body 850, and a plurality of electrode pads 859 for power supply formed on the back surface.

[0041] 7, the MEMS tilt mirror 85 is surface-mounted on the substrate 81 by soldering with the electrode pads 859 facing the substrate 81. In FIG. 7, the rear row of MEMS tilt mirrors 85 is not shown.

[0042] The MEMS tilt mirror 85 is configured so that the reflecting surface 851 can be rotated around two rotation axes Cx and Cy parallel to the surface of the substrate 81 based on power supplied from electrode pads 859 through the substrate 81. The two rotation axes Cx and Cy are perpendicular to each other.

[0043] A controller 90 is connected to the substrate 81 so as to be able to supply power to the plurality of MEMS tilt mirrors 85. Each MEMS tilt mirror 85 receives power supply from the controller 90 via an electrode pad 859, and drives the reflective surface 851 to rotate.

[0044] Controller 90 is connected to reflective mirror array 80 so as to be able to individually control the voltage applied to each of the multiple MEMS tilt mirrors 85. The rotation of reflective surface 851 and the tilt angle of reflective surface 851 are controlled by controlling the applied voltage by controller 90. Hereinafter, the tilt angle of reflective surface 851 will also be referred to as the tilt angle of MEMS tilt mirror 85.

[0045] The tilt angles of the multiple MEMS tilt mirrors 85 included in the reflective mirror array 80 are individually controlled by a controller 90 to tilt angles corresponding to the output cores. The output cores referred to here refer to the cores 21 of the output MCFs to which the reflected light is to be optically coupled. The output cores correspond to the output destinations of the reflected light.

[0046] Each MEMS tilt mirror 85 reflects input light from a corresponding one of the cores 21 at a tilt angle controlled by the controller 90. Depending on the tilt angle, the reflected light propagates to one of the multiple cores 21 included in the output MCF, that is, the output core, selected by the controller 90, and is output from the core 21 to the outside of the core selection switch 10 as output light.

[0047] In the core selection switch 10 configured as described above, input light from each core 21 of the input MCF passes through the corresponding microlens 41 and condenser lens 50. The input light that has passed through the condenser lens 50 is incident on the corresponding MEMS tilt mirror 85.

[0048] Light incident on MEMS tilt mirror 85 is reflected by its reflecting surface 851 in a direction according to the tilt angle of MEMS tilt mirror 85. The reflected light is optically coupled to an output core, which is one core 21 of an output MCF selected by controller 90 through control of the tilt angle of the corresponding MEMS tilt mirror 85.

[0049] The reflected light is incident on the output core from the reflecting surface 851 of the MEMS tilt mirror 85, through the condenser lens 50 and the corresponding microlens 41. The light incident on the output core propagates to the outside of the core selection switch 10 through the output core.

[0050] According to the core selection switch 10 described above, the reflective mirror array 80 can receive input light from the multicore fiber 20 in an enlarged geometric pattern and pitch and reflect each of these input light beams toward an output core. The MEMS tilt mirror 85 serving as the reflective mirror in the reflective mirror array 80 has low optical loss and a wide bandwidth, and can operate with low power consumption.

[0051] Furthermore, in MEMS tilt mirror 85 of this embodiment, electrode pad 859 is provided on the back surface of main body 850, opposite to the front surface on which reflective surface 851 is provided. With this configuration, it is possible to provide reflective surface 851 with a larger area on the front surface of main body 850, compared to when electrode pad 859 is provided on the front surface of main body 850. Therefore, it is possible to suppress insertion loss caused by light incident on MEMS tilt mirror 85 going beyond reflective surface 851.

[0052] In the core selection switch 10, insertion loss can occur due to vignetting of input light at the reflecting mirror array 80. The vignetting occurs when a part of the input light protrudes beyond the reflecting surface 851 of the MEMS tilt mirror 85 due to the beam diameter of the input light incident thereon being larger than that of the reflecting surface 851. The part of the input light protruding beyond the reflecting surface 851 causes insertion loss.

[0053] The insertion loss caused by vignetting varies depending on the ratio between the mirror diameter D2 of the MEMS tilt mirror 85 and the mirror pitch D1, which is the distance D1 between adjacent MEMS tilt mirrors 85. The ratio of the mirror diameter D2 to the mirror pitch D1, D2 / D1, is also called the fill factor.

[0054] The smaller the fill factor, the larger the resulting insertion loss. When attempting to suppress the insertion loss due to vignetting to less than a certain percentage, the higher the core density of the multi-core fiber 20, the higher the fill factor required.

[0055] In this embodiment, as described above, the electrode pad 859 is provided on the back surface of the main body 850, and therefore the mirror diameter D2 of the reflecting surface 851 provided on the surface can be made larger than when the electrode pad 859 is provided on the surface of the main body 850.

[0056] The fill factor can be improved if the mirror diameter D2 can be increased relative to the size of the main body 850. Therefore, according to this embodiment, it is possible to reduce the insertion loss due to vignetting.

[0057] The above-described MEMS tilt mirror 85 may be replaced with the MEMS tilt mirror 100 shown in Figures 8A and 8B. Alternatively, the above-described MEMS tilt mirror 85 may be configured as the MEMS tilt mirror 100 shown in Figures 8A and 8B.

[0058] The MEMS tilt mirror 100 shown in Figures 8A and 8B includes a lower structure 110 as a first structure, and an upper structure 150 as a second structure. The lower structure 110 includes a main body 111, a frame 113, and a plate 115. The lower structure 110 is configured to be able to rotate the plate 115 around two rotation axes Cx and Cy. In Figure 8A, the components of the upper structure 150 are shown in a transparent manner. These components are represented by dashed lines in the figure.

[0059] The plate 115 is a rectangular plate 115 and is connected to the frame 113 so as to be rotatable about the rotation axis Cx. The plate 115 has comb-shaped electrodes 115A on two sides parallel to the rotation axis Cx. The comb-shaped electrodes 115A are provided to rotate the plate 115 about the rotation axis Cx by electrostatic force.

[0060] The frame 113 is rectangular and defines an internal space capable of accommodating the plate 115. The plate 115 is connected to the frame 113 so as to be rotatable about a rotation axis Cx in the internal space. The frame 113 surrounds the periphery of the plate 115 in a state in which the frame 113 is connected to the plate 115.

[0061] The frame 113 has comb electrodes 113A having a shape complementary to the comb electrodes 115A provided on the plate 115 at positions opposite the comb electrodes 115A provided on the plate 115, i.e., on two inner sides parallel to the rotation axis Cx.

[0062] The plate 115 is connected to the frame 113 so that a comb electrode 115A provided on the plate 115 and a comb electrode 113A provided on the inner side of the frame 113 are interdigitated with a small gap between them. The electrostatic force generated between the comb electrodes 115A and 113A causes the plate 115 to rotate around the rotation axis Cx relative to the frame 113.

[0063] The frame 113 has comb electrodes 113B on two outer sides parallel to the rotation axis Cy. The comb electrodes 113B are provided to rotate the frame 113 around the rotation axis Cy by electrostatic force.

[0064] The main body 111 is a rectangular box-shaped structure having a bottom, and has an opening 111A capable of accommodating the frame 113. The frame 113 is connected to the main body 111 so as to be rotatable about a rotation axis Cy at the opening 111A. When connected to the frame 113, the main body 111 surrounds the frame 113 with its inner surface facing the outer surface of the frame 113.

[0065] The main body 111 has comb electrodes 111B having a shape complementary to the comb electrodes 113B provided on the frame 113 at positions opposite the comb electrodes 113B provided on the outer sides of the frame 113, i.e., on two inner sides parallel to the rotation axis Cy.

[0066] The frame 113 is connected to the main body 111 so that the comb electrode 113B provided on the outer edge of the frame 113 and the comb electrode 111B provided on the inner edge of the main body 111 are interdigitated with a small gap between them. The electrostatic force generated between the comb electrode 113B and the comb electrode 111B causes the frame 113 to rotate around the rotation axis Cy relative to the main body 111.

[0067] Similar to MEMS tilt mirror 85, electrode pads 119 for power supply are provided on the rear surface of main body 111. Similar to MEMS tilt mirror 85, modified MEMS tilt mirror 100 is also surface-mounted on substrate 81 of reflective mirror array 80.

[0068] The MEMS tilt mirror 100 receives a voltage application from the controller 90 through the substrate 81 and the electrode pads 119. The plate 115 of the MEMS tilt mirror 100 is driven to rotate around two rotation axes Cx and Cy through electrostatic forces generated by the voltage application.

[0069] The upper structure 150 of the MEMS tilt mirror 100 is fixed to the plate 115 that is driven to rotate in this manner. The upper structure 150 includes support columns 151, a support plate 155, and a reflecting surface 159. As described above, the support columns 151, the support plate 155, and the reflecting surface 159 that are components of the upper structure 150 are shown in perspective in FIG. 8A .

[0070] The support pillar 151 is fixed at its lower end to the plate 115 so as to stand in the normal direction of the plate 115. Specifically, the support pillar 151 is erected at the center of the plate 115. The support plate 155 is connected at its rear surface, i.e., the lower surface, to the upper end of the support pillar 151 and is fixed to the support pillar 151.

[0071] The support plate 155 is disposed parallel to the plate 115 of the lower structure 110, with a gap therebetween in the normal direction of the plate 115 by the height of the support columns 151. As a result, the support plate 155 is disposed on the lower structure 110 so as to overlap with the lower structure 110 in the normal direction, and extends in a direction perpendicular to the normal direction.

[0072] Specifically, the support plate 155 has a size larger than the plate 115 of the lower structure 110. The support plate 155 is disposed so as to completely cover the plate 115 of the lower structure 110 from above.

[0073] The surface, i.e., the upper surface, of support plate 155 has a larger area than the surface of plate 115. A reflective surface 159 is formed on this larger surface of support plate 155. This reflective surface 159 has a larger area than the reflective surface that can be formed on the surface of plate 115.

[0074] That is, in the modified MEMS tilt mirror 100, a support plate 155 having a large area is provided so as to overlap the plate 115 of the lower structure 110, and a reflecting surface 159 having a large area is provided thereon.

[0075] Therefore, according to the modified MEMS tilt mirror 100 , it is possible to effectively suppress the insertion loss caused by the light input to the reflecting mirror array 80 going beyond the reflecting surface 159 .

[0076] [Other Embodiments] The present disclosure is not limited to the above-described embodiment and can adopt various aspects. For example, the number of multi-core fibers 20 and the number of cores thereof shown in the figures are merely examples. The present disclosure can be applied to an optical switch including one or more any number of multi-core fibers 20.

[0077] The function of one component in the above embodiments may be distributed among multiple components. The functions of multiple components may be integrated into one component. Some of the configurations of the above embodiments may be omitted. All aspects included in the technical idea specified by the wording of the claims are embodiments of the present disclosure.

Claims

1. An optical switch comprising: a connection section to which one or more multicore fibers are connected; a lens arranged to pass input light from the one or more multicore fibers connected to the connection section; and a reflective mirror array configured to reflect the input light incident through the lens toward an output destination, wherein each of the one or more multicore fibers has a plurality of cores arranged two-dimensionally at a predetermined pitch so as to form a predetermined geometric pattern, the lens is arranged such that the input light passing through the lens is incident on the reflective mirror array in an enlarged geometric pattern and pitch, the reflective mirror array comprising a plurality of reflective mirrors arranged two-dimensionally with the enlarged geometric pattern and pitch, and each of the plurality of reflective mirrors is configured to be capable of rotating a reflective surface around two rotation axes.

2. The optical switch of claim 1, wherein said plurality of reflective mirrors includes a plurality of MEMS tilt mirrors.

3. An optical switch as claimed in claim 1 or 2, wherein each of the plurality of reflecting mirrors comprises a body having the reflecting surface on its surface and an electrode pad for power supply, the electrode pad being provided on the rear surface of the body.

4. The optical switch according to claim 3, wherein said reflecting mirror array comprises a substrate, and said plurality of reflecting mirrors are surface-mounted on said substrate via said electrode pads.

5. An optical switch according to any one of claims 1 to 4, wherein the reflective mirror array comprises, as the plurality of reflective mirrors, a plurality of MEMS devices configured as MEMS tilt mirrors, each having one reflective surface.

6. An optical switch as described in any one of claims 1 to 5, wherein the reflective mirror comprises: a first structure that is driven to rotate about the two rotation axes; and a second structure having a front and a back surface and connected to the first structure at the back surface, wherein the front surface of the second structure extends in a direction perpendicular to the normal direction so as to overlap the first structure in the normal direction, and the reflective surface is provided on the front surface of the second structure.

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