JP2015114548A - Optical multiplexer/demultiplexer and optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical multiplexer/demultiplexer which is capable of multiplexing input light to a multi-core multimode optical fiber with a plurality of cores for transmission in a plurality of modes or demultiplexing output light from a multi-core multimode optical fiber with a plurality of cores for transmission in a plurality of modes.SOLUTION: The optical multiplexer/demultiplexer includes: a mode conversion waveguide array formed on a substrate, in which N mode conversion waveguides (N is an integer satisfying N≥2) for converting M inputs (M is an integer satisfying M≥2) to m kinds of modes and outputting them (m is an integer satisfying 2≤m≤M) are arranged; multi-core space position conversion means which brings output ends of cores of N or more optical fibers including cores of N multimode optical fibers for propagation of the m kinds of modes, close to each other to make them into one bundle; and optical coupling means which optically couples N outputs of the mode conversion waveguide array and input ends of N multimode cores out of the cores of the plurality of optical fibers of the multi-core space position conversion means.

Description

  The present invention relates to an optical multiplexer / demultiplexer and an optical communication system.

  With the rapid development of broadband services accompanying the spread of optical fiber communication in recent years, the communication capacity continues to increase year by year. Up to now, the increase in capacity of optical networks corresponding to the rapid increase in communication capacity has been realized by increasing the capacity of optical communication systems without changing the structure of optical fibers. The optical fiber that forms the basis of the current large-capacity optical network has a single core as a path for optical signals in one optical fiber, and transmits an optical network of 1 terabit per second over a long distance. Has been put to practical use. However, due to the recent increase in communication capacity, further increase in communication capacity has been an issue.

  Under such circumstances, research and development of space division multiplexing optical communication technology using an optical fiber having a new spatial structure including a multi-core optical fiber having a plurality of cores in one optical fiber has been proposed (non- Patent Document 1). By having a plurality of cores, the capacity that can be transmitted by one optical fiber is increased by the number of cores. Realization of this space division multiplexing optical communication requires a multi-core optical fiber and an input / output device for connecting a conventional optical fiber to each core of the multi-core optical fiber, and research and development have been advanced. In the latest technology, transmission capacity (transmission distance: 10 km) of 305 terabits per second (transmission distance: 10 km) by using one multi-core optical fiber having 19 cores (12), 12 By using one multi-core optical fiber having a core of 1 mm, long-distance large-capacity optical transmission of 1 petabit per second (transmission distance: 50 km) was realized with one optical fiber, which is the current world record (non- Patent Document 3).

  As another technique for increasing the communication capacity, attention is paid to a mode division multiplexing optical communication technique in which a plurality of modes are transmitted to one core. By using a plurality of modes, the capacity that can be transmitted by one optical fiber is increased by the number of modes. In order to realize this mode division multiplexing optical communication, a multimode optical fiber that propagates a plurality of modes (a few-mode optical fiber and fumode light that selectively propagates only a few low-order modes that are easy to control the propagation mode) (Including fiber) and mode multiplexer / demultiplexers that can multiplex and demultiplex modes are important components. In a recent optical transmission test, mode division by a mode multiplexer / demultiplexer using a number mode optical fiber designed to propagate three modes, LP01 and LP11 (degenerate to LP11a and LP11b), and a phase plate and a spatial optical system. Multiplex transmission was shown (Non-Patent Documents 4 and 5).

  Also, mode-division multiplex transmission using a few-mode optical fiber and a spot-type mode multiplexer / demultiplexer (Non-Patent Document 6), a mode using a strongly-coupled number-mode optical fiber having three cores close to each other and three collimators Division multiplexing transmission (Non-patent Document 7) has been reported. Furthermore, a transmission (non-patent document 8) has been reported in which a single core propagates up to six modes using a mode multiplexer / demultiplexer in which six waveguides are placed close to each other. . As other mode multiplexer / demultiplexers other than the above transmission, a quartz planar lightwave circuit type mode multiplexer / demultiplexer (Non-Patent Document 9), a vertical grating type mode multiplexer / demultiplexer (Non-Patent Document 10), a bulk A multimode single mode converter for optical wavelength blockers (Non-patent Document 11) has also been reported.

T. Morioka, OECC2009, FT4. J. Sakaguchi et al., OFC2012, PDP5C.1. H. Takara et al., ECOC2012, Th.3.C.1. R. Ryf et al., OFC2011, PDPB10. E. Ip et al., OFC2013, PDP5A.2. R. Ryf et al., OFC2012, PDP5B.5. R. Ryf et al., OFC2012, PDP5C.2. R. Ryf et al., OFC2013, PDP5A.1. H. Kubota et al., IEICE ELEX, Vol. 10, No. 12, pp. 1-6, June 2013. A. M. J. Koonen et al., IEEE Photonics Technology Letters, Vol. 24, No. 21, pp. 1961-1964, Nov. 2012. N. K. Fontaine et al., OFC2013, OTh1B.1.

  In the prior art, the communication capacity can be expanded by increasing the number of cores in one optical fiber. However, the clad diameter of the optical fiber that can maintain the strength is up to about several hundred μm, and if the core is too close, the crosstalk from the adjacent core increases, so there is a limit to the number of cores that can be increased in one optical fiber. Yes, at present, the 12-core optical fiber disclosed in Non-Patent Document 3 and the 19-core optical fiber disclosed in Non-Patent Document 2 are the maximum number of cores suitable for long-distance transmission.

  In the prior art, the communication capacity can be increased by increasing the number of modes that propagate through the core in one optical fiber. However, the number of modes suitable for transmission is up to about 3 to 6, and the higher the mode, the more rapidly the propagation loss and dispersion increase, so there is a limit to the number of modes that can be used. The three modes shown in Documents 4 and 5 and the 6 modes shown in Non-Patent Document 8 are the maximum number of modes suitable for long-distance transmission.

  Therefore, in order to further increase the communication capacity, it is conceivable to increase the number of cores in one optical fiber and increase the number of modes that propagate through each core. If it can do in this way, the capacity which can be transmitted with one optical fiber will increase by the number of cores x the number of modes.

  However, in the conventional technology, input light is multiplexed into a multicore multimode optical fiber having a plurality of cores that propagate a plurality of modes, or from a multicore multimode optical fiber having a plurality of cores that transmit a plurality of modes. There was no optical multiplexer / demultiplexer that could demultiplex the output light. If the conventional mode multiplexer / demultiplexer described in Non-Patent Document 4 or the like is used, mode multiplexers / demultiplexers using a phase plate and a spatial optical system are required for the number of cores, and the size is large and enormous. There is a problem that it is expensive, and there is a problem that it is difficult to realize.

  The present invention has been made in view of such circumstances, and a core that multiplexes input light into a multi-core multi-mode optical fiber that has a plurality of cores that transmit a plurality of modes, or that transmits a plurality of modes. It is an object of the present invention to provide an optical multiplexer / demultiplexer that can demultiplex output light from a plurality of multicore / multimode optical fibers and an optical communication system using the optical multiplexer / demultiplexer.

  The present invention is a mode conversion waveguide that is formed on a substrate and converts M (M is an integer of M ≧ 2) inputs into m (m is an integer of 2 ≦ m ≦ M) types of modes and outputs them. N (N is an integer greater than or equal to N ≧ 2) arranged mode conversion waveguide arrays and N multimode optical fiber cores that propagate the m types of modes, and a plurality of N or more light beams A multi-core spatial position conversion means for bringing the output ends of the fiber cores close together and bundled together; N outputs of the mode conversion waveguide array; and a plurality of optical fiber cores of the multi-core spatial position conversion means And optical coupling means for optically coupling input terminals of N multimode cores.

  The present invention is characterized in that each of the N sets of optical coupling means includes one or a plurality of lenses.

  In the present invention, one or more of the N sets of optical coupling means are arranged in a casing, and one lens side surface of the casing constitutes the multi-core spatial position converting means. The other lens-side surface of the housing is placed on the substrate end surface or the substrate upper surface where the N outputs of the mode conversion waveguide array are arranged at the input ends of the cores of the plurality of optical fibers, and are optically coupled. It is characterized by that.

  According to the present invention, the input ends of a plurality of optical fiber cores constituting the multi-core spatial position conversion means are optically connected by butt-joining the substrate end surface or the substrate upper surface where N outputs of the mode conversion waveguide array are arranged. It couple | bonds with.

  In the present invention, the optical path length of the mode conversion waveguide is set so that the optical path lengths of the M sets of optical paths from M inputs to one output of the mode conversion waveguide are equal. It is characterized by that.

  According to the present invention, M × N from the M × N inputs of the mode conversion waveguide array to the output end of the optical fiber core bundled together in the vicinity of the multi-core spatial position conversion means. The optical optical path length of the mode conversion waveguide and the optical optical path length of the core of the optical fiber constituting the multi-core spatial position converting means are set so that the optical optical path lengths of the pair of optical paths are equal. And

  The present invention is characterized in that the number of optical fiber cores constituting the multi-core spatial position converting means is larger than a mode type m propagating through the multi-mode optical fiber core.

  The present invention is a mode conversion waveguide that is formed on a substrate and converts M (M is an integer of M ≧ 2) inputs into m (m is an integer of 2 ≦ m ≦ M) types of modes and outputs them. N (N is an integer of N ≧ 2) arrayed M × N inputs of a mode conversion waveguide array, each of which is connected to a single mode fiber and propagates the m modes. The multi-core spatial position conversion means for bundling together the output ends of a plurality of N or more optical fiber cores including the mode optical fiber cores. 8. An N-core / m-mode optical fiber comprising N cores each propagating m types of modes or N core groups each propagating m types of modes is connected to the output end. The optical multiplexer / demultiplexer according to any one of An optical signal is input to M × N inputs of the mode conversion waveguide array of the optical multiplexer / demultiplexer, and the optical signal is multiplexed by the optical multiplexer / demultiplexer, or An optical signal is input from a core of optical fibers bundled close together in the multi-core spatial position converting means of the optical multiplexer / demultiplexer, and the optical signal is demultiplexed by the optical multiplexer / demultiplexer. .

  According to the present invention, input light is multiplexed into a multicore multimode optical fiber having a plurality of cores transmitting a plurality of modes, or from a multicore multimode optical fiber having a plurality of cores transmitting a plurality of modes. The effect that the output light can be demultiplexed is obtained.

It is the schematic which shows the basic concept of the optical multiplexer / demultiplexer of this invention. It is a figure which shows the structural example of the mode conversion waveguide in 1st Embodiment. 1A is a perspective view, FIG. 1B is a cross-sectional view of a chip end surface on a single mode side, and FIG. 2C is a cross-sectional view of a chip end surface on a multi-mode side. It is a figure which shows the example of three types of modes used by 1st Embodiment. (A) LP01 mode, (b) LP11a mode, (c) LP11b mode. 1A is a cross-sectional view of an output end of a multi-core spatial position conversion unit in the first embodiment, and FIG. 2B is a cross-sectional view of an N-core / m-mode multi-core / multi-mode optical fiber. It is a figure which shows an example of the optical coupling of the output of a mode conversion waveguide, and the input end of the multimode optical fiber which comprises a multi-core space position conversion means. The block diagram of the optical multiplexer / demultiplexer produced in 1st Embodiment is shown. It is a figure which shows sectional drawing of the chip | tip end surface of the mode conversion waveguide array in 1st Embodiment. (A) Cross-sectional view of chip end surface on single mode side, (b) Cross-sectional view of chip end surface on multi-mode side. The block diagram of the optical multiplexer / demultiplexer produced in 2nd Embodiment is shown. It is a figure which shows sectional drawing of the chip | tip end surface of the mode conversion waveguide in 2nd Embodiment. (A) Cross-sectional view of chip end surface on single mode side, (b) Cross-sectional view of chip end surface on multi-mode side. (A) Sectional drawing of the output end of a multi-core space position conversion means in 2nd Embodiment, (b) Sectional drawing of a multi-core multimode optical fiber is shown. It is a figure which shows an example of the mode crosstalk of LP11 mode with respect to LP01 mode by position shift between the cores of an optical fiber and a waveguide. The block diagram of the optical multiplexer / demultiplexer produced in 3rd Embodiment is shown. It is a figure which shows the structural example of the mode conversion waveguide in 3rd Embodiment. (A) First-layer waveguide (first and third waveguides drawn with dark lines), (b) Second-layer waveguide (second waveguide drawn with dark lines) . It is a figure which shows the structural example of the mode conversion waveguide in 3rd Embodiment. 1A is a top view, FIG. 1B is a sectional view of a chip end surface on a single mode side, and FIG. 2C is a sectional view of a chip end surface on a multimode side. It is a figure which shows sectional drawing of the chip | tip end surface of the mode conversion waveguide array in 3rd Embodiment. (A) Cross-sectional view of chip end surface on single mode side, (b) Cross-sectional view of chip end surface on multi-mode side. (A) Sectional drawing of the output end of a multi-core space position conversion means in 3rd Embodiment, (b) Sectional drawing of the N-core m-mode multi-core multi-mode optical fiber is shown. The block diagram of the optical multiplexer / demultiplexer produced in 4th Embodiment is shown. It is a figure which shows the structural example of the mode conversion waveguide in 4th Embodiment. 1A is a top view, FIG. 1B is a sectional view of a chip end surface on a single mode side, and FIG. 2C is a sectional view of a chip end surface on a multimode side. It is a figure which shows the example of three types of modes used in 4th Embodiment. (A) 1st mode, (b) 2nd mode, (c) 3rd mode. It is a figure which shows the structural example of the optical coupling means in 4th Embodiment. (A) Sectional drawing of output end of multi-core space position conversion means in 4th Embodiment, (b) Sectional drawing of multi-core multimode optical fiber of N core and m mode is shown. The top view of the structural example of the mode conversion waveguide array in 5th Embodiment is shown. It is the figure which showed a mode that the 45-degree mirror was formed in a waveguide and the optical path of light was changed to the perpendicular direction. It is a figure which shows an example of the optical coupling in the output light of the mode conversion waveguide array in 5th Embodiment, the lens of an optical coupling means, and the core of the optical fiber of a multi-core space position conversion means. It is a figure which shows the structural example of the mode conversion waveguide in 6th Embodiment. (A) First-layer waveguide (first and third waveguides drawn with dark lines), (b) Second-layer waveguide (second waveguide drawn with dark lines) . It is a figure which shows sectional drawing of the chip | tip end surface of the mode conversion waveguide in 6th Embodiment. (A) Cross-sectional view of chip end surface on single mode side, (b) Cross-sectional view of chip end surface on multi-mode side. The block diagram of the optical multiplexer / demultiplexer module produced in 6th Embodiment is shown. The block diagram of the optical multiplexer / demultiplexer module produced in 7th Embodiment is shown. It is a figure which shows the structural example of the mode conversion waveguide in 8th Embodiment. (A) First-layer waveguide (second and third waveguides drawn with dark lines), (b) Second-layer waveguide (first waveguide drawn with dark lines) . The block diagram of the optical multiplexer / demultiplexer module produced in 8th Embodiment is shown. The internal block diagram of the optical multiplexer / demultiplexer module produced in 9th Embodiment is shown. It is a figure which shows the external appearance of the optical multiplexer / demultiplexer module produced in 9th Embodiment. (A) Sectional drawing of output end of multi-core spatial position conversion means in 9th Embodiment, (b) Sectional drawing of multi-core multimode optical fiber of N core and m mode is shown. The block diagram of the optical multiplexer / demultiplexer produced in 10th Embodiment is shown. It is a figure which shows an example of the optical communication system using the optical multiplexer / demultiplexer of this invention. It is a figure which shows an example of the optical communication system using the optical multiplexer / demultiplexer of this invention.

  Hereinafter, an optical multiplexer / demultiplexer according to an embodiment of the present invention and an optical communication system using the optical multiplexer / demultiplexer will be described in detail with reference to the drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Note that in this specification and the drawings, the same reference numerals are given to components having the same functions, and repeated description thereof is omitted. Each embodiment can be combined as much as possible.

(First embodiment)
FIG. 1 is a schematic diagram showing the basic concept of an optical multiplexer / demultiplexer according to the present invention. The optical multiplexer / demultiplexer of the present invention includes a mode conversion waveguide that is formed on a substrate and converts M (an integer of M ≧ 2) input into m (2 ≦ m ≦ M) types of modes and outputs the mode. A plurality of N or more optical fiber cores including N (an integer of N ≧ 2) arranged mode conversion waveguide arrays 101 and N multimode optical fiber cores that propagate m types of modes. Multi-core spatial position conversion means 103 that brings output ends close together and bundles them together, N outputs of mode conversion waveguide array 101, and N of the plurality of optical fiber cores of multi-core spatial position conversion means 103 The optical coupling means 102 optically couples the input ends of the multimode core.

  A configuration example of the optical multiplexer / demultiplexer in the present embodiment will be described in more detail. First, a configuration example of the mode conversion waveguide is shown. As shown in FIG. 2A, the mode conversion waveguide of this embodiment is composed of first to third M (M = 3) waveguides 241, 242, and 243 formed on a substrate. The other end is formed so that the core interval of the waveguide is separated, and the other end is formed so as to be close to the core interval of the waveguide. FIG. 2B is a cross-sectional view of the chip end surface where the core interval of the first to third waveguides is separated, and FIG. 2C is made the core interval of the first to third waveguides closer. Sectional drawing of the other chip | tip end surface is shown. Here, suppose that FIG. 2B is referred to as a single mode side and FIG. 2C is referred to as a multimode side.

  When light is input to each of the first to third waveguides on the single mode side of the mode conversion waveguide, the cores of M (M = 3) waveguides gradually approach as they propagate through the mode conversion waveguide. Optical coupling with the adjacent waveguide occurs. From the multi-mode side, light coupled to each other in a pseudo multi-mode is output. The mode to be generated can be changed by the combination of the intensity and phase of light input from the single mode side. In the present embodiment, single mode light input from M (M = 3) ports on the single mode side is simulated to m (m = 3) in the LP01 mode, LP11a mode, and LP11b mode (see FIG. 3). The mode was converted into various modes, and these m types of modes were output from one port on the multi-mode side. The polarization multiplexed light was used as the input light, and the TE01 (s-polarized) LP01 mode, LP11a mode, and LP11b mode and the TM-polarized (p-polarized) LP01 mode, LP11a mode, and LP11b mode were output.

  In this embodiment, each of the degenerated modes (LP11a mode and LP11b mode) is counted as one mode. However, since polarization multiplexing is considered separately from mode multiplexing, the mode multiplexing numbers in the above example are LP01 mode, LP11a. M = 3 types of mode and LP11b mode). This operation is for use as a mode multiplexer. On the other hand, when used as a mode demultiplexer, by inputting light mixed with m (m = 3) types of modes from one port on the multimode side, the mode conversion is performed by this mode conversion waveguide, Light is demultiplexed and output from M (M = 3) ports on the mode side. The mode conversion waveguide array 101 was formed by arranging N (N = 7) mode conversion waveguides having such a configuration.

  Next, a configuration example of the multi-core space position conversion unit will be described. In this embodiment, N multimode optical fibers that propagate m (m = 3) types of modes are used as the multi-core spatial position conversion means, and one end thereof is brought close to each other and bundled together. Here, the end of the fiber bundle that is bundled close together is called an output end, and the other end is called an input end. FIG. 4A shows a cross-sectional view (in the case of N = 7) of the output end of the multi-core space position converting means of the present embodiment. When this output end is connected to the N-core / m-mode multi-core / multi-mode optical fiber having the cross-sectional structure shown in FIG. 4 (b), the multi-mode cores 671-1 of the multi-core / multi-mode optical fiber are connected. N multi-mode optical fiber cores 401 to 407 of the multi-core spatial position converting means are arranged and bundled so as to match the position 677.

  Finally, a configuration example of the optical coupling means will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of optical coupling. In this embodiment, two lenses 501 are used as optical coupling means. The outputs of the respective mode conversion waveguides 211 and multi-core spatial position conversion means are configured, and the input ends of the multi-mode optical fiber 301 having the multi-mode core 401 are optically coupled.

  FIG. 6 is a diagram showing a specific configuration of the manufactured optical multiplexer / demultiplexer. The mode conversion waveguide array 101 is formed of a silicon waveguide formed on a silicon substrate. The mode conversion waveguides 211 to 217 that convert M = 3 input into m = 3 types of modes and output them are output as N = 7. They were made side by side. In order to easily connect an optical fiber block in which a plurality of optical fibers are arranged on a V-groove substrate to the input of the mode conversion waveguide array 101, 21 on the input side of the mode conversion waveguide array 101 (= mode conversion waveguide) The number of input ports M × number of mode conversion waveguides N) is formed so as to have the same pitch on the substrate layer on which the mode conversion waveguide array 101 is formed (FIG. 7 ( a)). Further, 7 (= the number N of mode conversion waveguides) outputs of the mode conversion waveguide array 101 are also formed to have the same pitch on the substrate layer on which the mode conversion waveguide array 101 is formed. (See FIG. 7B).

  The position of the core on the input side was the position of the center of one core, while the position of the core on the output side was the position of the center of three cores (see FIG. 7). Further, the pitch of the core on the input side of the mode conversion waveguide array 101 was set to p, and the pitch of the core on the output side was set to q = M × p. Thus, by arranging the input / output positions of the N mode conversion waveguides 211 to 217 on a straight line, it becomes easy to connect the optical fiber blocks, and further, the pitches are equal on the line connecting the input / output positions. By arranging in this way, a general-purpose optical fiber block can be used, which leads to cost reduction of members.

  The multi-core spatial position conversion means 103 was manufactured using N = 7 optical fibers 301 to 307. N = 7 optical fibers were designed to propagate a step index type refractive index profile, a core diameter of 12 μm, and at least m = 3 types of modes (step index type number mode optical fiber). In addition, the cladding diameter of these N = 7 optical fibers is 125 μm, the core diameter remains constant, the cladding diameter gradually decreases from the input end to the output end, and the cladding diameter at the output end is reduced to 80 μm. Diameter was increased. Then, the output ends of the cores of N = 7 optical fibers were brought close to each other, bundled so that the cross section had the core arrangement shown in FIG. 4A, and covered with a coating.

  As the optical coupling means 102, N = 7 sets of two microlenses are used, and seven sets of microlenses 501 to 507 are arranged in an array so as to match N = 7 output positions of the mode conversion waveguide arrays 211 to 217. Subsequently, N = 7 optical fibers 301 to 307 on the input end side of the multi-core spatial position conversion means 103 were arranged. Then, each set of microlenses 501 to 507 and the multi-core spatial position conversion are performed so that the optical axes of the optical paths from the output of the mode conversion waveguide arrays 211 to 217 to the input of the multi-core spatial position conversion means 103 through the optical coupling means 102 are aligned. The position of the core of the optical fibers 301 to 307 at the input end of the means 103 was finely adjusted.

  When single mode light is input from M = 3 inputs of the mode conversion waveguide 211 of the manufactured optical multiplexer / demultiplexer, light is condensed on one output of the mode conversion waveguide 211, and m = 3 types of modes are combined. A demultiplexed pseudo multimode light was obtained. The multimode light is optically coupled to the input end of the first optical fiber 301 of the multi-core spatial position conversion means 103 through the optical coupling means 501, and from the first core 401 at the output end of the multi-core spatial position conversion means 103. Was output. The mode to be generated is set by the combination of the amplitude and phase of the three single-mode input lights.

  Similarly, when single mode light is inputted from M = 3 inputs of the mode conversion waveguide 212 of the optical multiplexer / demultiplexer, the multimode light generated by the mode conversion waveguide 212 is passed through the optical coupling means 502 to the multi-core spatial position conversion means 103. When the single mode light is input from the three inputs of the mode conversion waveguide 217 of the optical multiplexer / demultiplexer, the multimode light generated by the mode conversion waveguide 217 is optical coupling means. 507 is output from the seventh (= N) core 407 at the output end of the multi-core spatial position conversion means 103. As a result, it was confirmed that the fabricated optical multiplexer / demultiplexer operates as a multiplexer in spatial multiplexing and mode multiplexing transmission. Conversely, when spatially multiplexed and mode multiplexed light is input from the output end of the multi-core spatial position conversion means 103, the demultiplexed light is output from the respective input ports of the mode conversion waveguide array, and is used as a demultiplexer. Also confirmed to work.

  The optical multiplexer / demultiplexer of the present embodiment has a spatial multiplexing number of 21 (= core number × mode number = N × m), and realizes a larger spatial multiplexing number than the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 7) of the cores of the number mode optical fiber to be performed is set to be larger than the mode type m (= 3) propagating through the number mode optical fiber.

  In this embodiment, the multi-core spatial position conversion means 103 is formed by bundling N number mode optical fibers, but other means can be used. For example, FIG. 2 (b) uses a waveguide in which the core is drawn on the substrate by a laser, and the output ends of the cores of N multimode optical fibers each propagating m types of modes are gradually approached. The bundled waveguides may be formed on the substrate by a laser and used as the multi-core spatial position conversion means 103 shown in FIG.

  As described above, according to the present embodiment, an optical multiplexer / demultiplexer capable of multiplexing / demultiplexing spatially multiplexed and mode multiplexed light has been realized, and the number of spatial multiplexing has been increased as compared with the prior art.

(Second Embodiment)
In the first embodiment, the multi-core spatial position conversion means 103 is formed by bringing one end of N multimode optical fibers propagating m types of modes close to each other and bundling them together. The multi-core spatial position conversion means 103 can be formed by mixing different types of optical fibers. As a result, for example, as shown in FIG. 10B, a multi-core with a core arrangement that improves crosstalk by using a plurality of cores having different core diameters (propagation constants) and separating core intervals of the same core diameter. An optical multiplexer / demultiplexer applicable to a multimode optical fiber can be realized.

  FIG. 8 is a diagram illustrating the overall configuration of the optical multiplexer / demultiplexer according to the second embodiment. The optical multiplexer / demultiplexer of the present embodiment is formed on a substrate and converts M (M is an integer of M ≧ 2) inputs to m (m is an integer of 2 ≦ m ≦ M) types of modes. A mode conversion waveguide array 101 in which N (N is an integer of N ≧ 2, N = 3 in the example shown in FIG. 8) output mode conversion waveguides 211 to 213 and N number of modes that propagate m kinds of modes are output. Multi-core spatial position conversion means 103 that bundles the output ends of N or more optical fiber cores including the cores of multi-mode optical fibers 301 to 303 close to each other, and N of mode-converting waveguide arrays 101 And optical coupling means 102 for optically coupling the input ends of N multi-mode cores among the plurality of optical fiber cores of the multi-core spatial position conversion means 103.

  The mode conversion waveguides 211 to 213 are formed of first to sixth M (M = 6) waveguides formed on the substrate, and one end of the mode conversion waveguides 211 to 213 is spaced apart from the core of the waveguide. Is formed so that the core interval of the waveguide is reduced. 9A is a cross-sectional view of the chip end surface where the core interval of the first to sixth waveguides is separated, and the core interval of the first to sixth waveguides is made closer to FIG. 9B. Sectional drawing of the other chip | tip end surface is shown. Here, suppose that FIG. 9A is referred to as a single mode side and FIG. 9B is referred to as a multi-mode side.

  When light is input to each of the first to sixth waveguides on the single mode side of the mode conversion waveguides 211 to 213, the cores of M (M = 6) waveguides gradually move along the mode conversion waveguide. Approaches and optical coupling occurs with the adjacent waveguide. From the multi-mode side, light coupled to each other in a pseudo multi-mode is output. The mode to be generated can be changed by the combination of the intensity and phase of light input from the single mode side. For example, in this embodiment, single mode light input from M (M = 6) ports on the single mode side is converted into m (m = 6) types of modes, and these m types of modes are converted to the multimode side. Output from one port. This operation is for use as a mode multiplexer.

  On the other hand, when used as a mode demultiplexer, by inputting light mixed with m (m = 6) types of modes from one port on the multi-mode side, the mode conversion is performed by this mode conversion waveguide. Light is demultiplexed and output from M (M = 6) ports on the mode side. The mode conversion waveguide array 101 was formed by arranging N (N = 3) mode conversion waveguides having such a configuration.

  As the multi-core spatial position conversion means 103, N (N = 3) multi-mode optical fibers 301 to 303 that propagate m (m = 6) types of modes and four single-mode optical fibers 321 that propagate the fundamental mode. Using ~ 324, one end of them was brought close together and bundled together. Here, the end of the fiber bundle that is bundled close together is called an output end, and the other end is called an input end. As shown in FIG. 8, the input ends are arranged such that the inputs of N fibers 301 to 303 among the plurality of optical fibers of the multi-core spatial position conversion means 103 are arranged in one fiber block 331, and N pieces of the mode conversion waveguide array are arranged. The fiber block 331 has a substrate end face on which the mode conversion waveguide array 101 is formed so that the output of the optical fiber and the inputs of N optical fibers 301 to 303 among the plurality of optical fibers of the multi-core spatial position conversion means are optically coupled. It is connected to the.

  FIG. 10A shows a cross-sectional view of the output end of the multi-core spatial position conversion means 103 of the present embodiment. When this output end is connected to the multi-core / multi-mode optical fiber having the cross-sectional structure shown in FIG. 10 (b), the type of each core of the multi-core / multi-mode optical fiber and the position of the core are matched. N = 3 multimode optical fiber cores 401 to 403 and four single mode optical fiber cores 421 to 424 of the multicore space position converting means 103 are arranged and bundled.

  N = 3 sets of one lens were used as the optical coupling means. Then, the outputs of the mode conversion waveguides 211 to 213 and the input ends of the N = 3 multimode optical fibers 301 to 303 among the optical fibers constituting the multicore spatial position conversion means are connected via the lenses 501 to 503. Optically coupled.

  A specific example of manufacturing the optical multiplexer / demultiplexer of this embodiment will be described. The mode conversion waveguide array 101 is formed on a substrate with a pulse laser, and N = 3 mode conversion waveguides that convert M = 6 inputs into m = 6 modes and output them. The center positions of 18 cores on the input side of the mode conversion waveguide array 101 (= number of input ports of the mode conversion waveguide M × number of mode conversion waveguides N) are equal pitch p on the planar substrate, and the layers of the substrate The center positions of the output cores of the same height and the output side 3 (= number of mode conversion waveguides N) sets (center positions of the six cores) are equal pitch q = M × p on the flat substrate, It was made to have the same height on the layer of the substrate.

  However, when the mode conversion waveguide array 101 was manufactured, in actuality, a position error occurred on the plane substrate due to a manufacturing error, and an error of 1 μm at the maximum occurred. In optical connection in multimode, mode conversion occurs with coupling loss due to misalignment of the connecting portion. For example, in the mode conversion waveguide of the present embodiment, as shown in FIG. 11, the mode crosstalk of the LP11 mode with respect to the LP01 mode becomes −17 dB due to the positional deviation of 1 μm, and the signal quality is deteriorated. Of course, it may be compensated by signal processing, but since mode conversion occurs for each connection portion of the transmission path, it is desirable to minimize the displacement of the connection portion in order to reduce the load of signal processing.

  Therefore, in this embodiment, the formation positions on the planar substrate of the 18 cores on the input side of the manufactured mode conversion waveguide array are measured, and V grooves are formed on the V groove substrate in accordance with the positions where the cores are formed. Then, an optical fiber block was fabricated by arranging optical fibers in the V-groove. Further, the positions of the three sets of outputs on the output side of the mode conversion waveguide array on the plane substrate are measured, V grooves are formed on the V groove substrate in accordance with the output positions, and the optical fibers are arranged in the V grooves. An optical fiber block 331 was produced. In the present embodiment, the positional deviation of the connecting portion is suppressed to 0.4 μm or less and the mode crosstalk is reduced to −25 dB or less by the highly precise formation technique of the V groove. As described above, by manufacturing the optical fiber block according to the position where the input / output of the mode conversion waveguide array 101 is formed, the input / output of the mode conversion waveguide array 101 and the optical fiber can be connected with high accuracy. In addition to reducing splice loss and minimizing mode conversion, which is particularly problematic in multimode, a high-performance optical multiplexer / demultiplexer has been realized.

  The multi-core spatial position conversion means 103 was manufactured using N = 3 optical fibers 301 to 303 and four single mode optical fibers 321 to 324. N = 3 optical fibers were designed to propagate a step index type refractive index profile, a core diameter of 15 μm, and at least m = 6 types of modes (step index type number mode optical fiber). In addition, the clad diameter of these seven optical fibers is 125 μm, the core diameter remains constant, the clad diameter gradually decreases from the input end to the output end, and the clad diameter at the output end is reduced to 75 μm. Diameter was increased. Then, the output ends of the cores of these seven optical fibers were brought close to each other, bundled so that the cross section had the core arrangement shown in FIG. 10A, and covered with a coating.

  As the optical coupling means 102, N = 3 sets of one microlens were used, and three sets of microlenses were arranged in an array so as to match N = 3 output positions of the mode conversion waveguide array 101. Subsequently, N = 3 multi-mode optical fibers on the input end side of the multi-core spatial position conversion means 103 are arranged on a V-groove substrate manufactured according to the position where the output of the mode conversion waveguide array 101 is formed. A mode optical fiber block 331 was formed. Each pair of microlenses 501 to 503 and the multimode optical fiber block 331 are aligned so that the optical axes of the optical paths from the output of the mode conversion waveguide array 101 to the input of the multicore spatial position conversion means 103 through the optical coupling means 102 are matched. The position of was finely adjusted.

  The optical multiplexer / demultiplexer according to the present embodiment has a spatial multiplexing number of 22 (= N × m + 4), and realizes a larger spatial multiplexing number than the prior art. Note that the combination of the number of cores and the number of modes is arbitrary, but it is easier to obtain good transmission characteristics when the number of cores is increased than when the number of modes is increased. The number N + 4 (= 7) of cores of the optical fiber to be configured is set to be larger than the mode type m (= 6) propagating through the number mode optical fiber.

  In this embodiment, the multi-core spatial position conversion means 103 is formed by bundling N number mode optical fibers, but other means can be used. For example, FIG. The core as described in 2 (b) uses a waveguide in which a core is drawn on a substrate by a laser, and each of N multimode optical fiber cores that propagate m types of modes and four singles A waveguide in which the output ends of the cores of the mode optical fibers are gradually brought close together and bundled together may be formed on the substrate by a laser and used as the multi-core spatial position conversion means 103.

  As described above, according to the present embodiment, an optical multiplexer / demultiplexer capable of multiplexing / demultiplexing spatially multiplexed and mode multiplexed light has been realized, and the number of spatial multiplexing has been increased as compared with the prior art. In addition, adjacent crosstalk in multi-core and multi-mode optical fibers has been greatly improved by using different types of cores. Furthermore, the input / output position of the mode conversion waveguide array was measured, and an optical fiber block to be connected according to the positional deviation was produced, thereby suppressing mode crosstalk and connection loss.

(Third embodiment)
In the first embodiment, the multi-core spatial position conversion means 103 is formed by bringing one end of N multimode optical fibers that propagate m types of modes close to each other and bundling them together, but does not propagate an optical signal. The multi-core spatial position conversion means 103 can be formed by mixing spare optical fibers. Thus, for example, as shown in FIG. 16 (b), the optical multi / demultiplexing that can be applied to a multi-core multi-mode optical fiber having a core arrangement that increases the crosstalk by separating the adjacent distances between the multi-mode cores that propagate. Can be realized. In this embodiment, the mode conversion waveguide array can be easily manufactured by forming the waveguide on a substrate composed of a plurality of layers.

  FIG. 12 is a diagram illustrating an overall configuration of an optical multiplexer / demultiplexer according to the third embodiment. The basic configuration is the same as in the first embodiment. 13 and 14 show configuration examples of the mode conversion waveguide 101 in the present embodiment. The mode conversion waveguide array of this embodiment is formed of two layers of waveguides on a substrate. Specifically, the first-layer waveguide was formed on the substrate, the clad was deposited, and the second-layer waveguide was formed thereon. FIG. 13 shows a top view. The first and third waveguides 241 and 243 drawn with a solid line shown in FIG. 13A are on the first layer, and the second waveguide 242 drawn with a solid line shown in FIG. It is formed in the second layer. As shown in FIG. 14A, one end is formed so that the core interval of the waveguide is separated, and the other end is formed so as to be close to the core interval of the waveguide. FIG. 14B is a cross-sectional view of the chip end surface where the core interval of the first to third waveguides is separated, and FIG. 14C is made to bring the core interval of the first to third waveguides closer. Sectional drawing of the other chip | tip end surface is shown.

  A major difference from the configuration of the first embodiment shown in FIG. 2 is that the core 248 of the second waveguide shown in FIG. 14B is formed in the second layer. Waveguides can be formed on the same plane more easily and accurately than when the core height is changed (for example, FIG. 2A). Therefore, a plurality of waveguides can be formed as in this embodiment. A high-performance mode conversion waveguide array 101 can be obtained by forming each waveguide in the same layer on a substrate having a plurality of waveguide layers.

  The mode conversion waveguide array 101 is formed of a polymer waveguide formed on a substrate, and N = 13 mode conversion waveguides 211 to 223 that convert M = 3 inputs into m = 3 types of modes and output them. Made side by side. In order to easily connect an optical fiber block in which a plurality of optical fibers are arranged on a V-groove substrate to the input of the mode conversion waveguide array 101, 39 (= mode conversion waveguide) on the input side of the mode conversion waveguide array 101 is used. Number of input ports M × number of mode conversion waveguides N) cores are formed to have the same pitch p and the same height on the two waveguide layers of the substrate on which the mode conversion waveguide array 101 is formed. (FIG. 15A). Further, 13 (= number N of mode conversion waveguides) outputs of the mode conversion waveguide array 101 have the same pitch q = M × p and the same height on the substrate layer on which the mode conversion waveguide array is formed. (FIG. 15B). The position of the core on the input side is the center position of one core, while the position of the core on the output side is the position of the center of the three cores (see FIG. 15B).

  In this way, the input / output height positions of the N mode conversion waveguides 101 are on the same number of lines as the number of waveguide layers (in this embodiment, two layers as shown in FIG. 15A). Or an optical fiber block connected to the mode conversion waveguide array of the optical multiplexer / demultiplexer of the present invention becomes easy. Furthermore, by arranging the input / output positions so as to have a constant pitch on the connecting lines, the optical fiber block can be shared, leading to cost reduction of the members.

  The multi-core spatial position conversion means 103 has N (N = 13) multi-mode optical fibers 301 to 313 that propagate m (m = 3) types of modes, and the same outer diameter as these multi-mode optical fibers. Six spare multimode optical fibers 414 to 419 that do not propagate an optical signal and spacers 471 to 482 were used (FIG. 16A), and one end thereof was brought close to each other and bundled together. Here, the end of the fiber bundle that is bundled close together is called an output end, and the other end is called an input end. The optical fibers at the input end were arranged at a constant pitch q = M × p to form a multimode optical fiber block 331. FIG. 16A shows a cross-sectional view of the output end of the multi-core spatial position conversion means 103 of the present embodiment. When this output end is connected to the multi-core / multi-mode optical fiber having the cross-sectional structure shown in FIG. 16B, the multi-core space is aligned with the respective cores 671 to 683 of the multi-core / multi-mode optical fiber. N = 13 multi-mode cores 401 to 413 of the position converting means 103 are arranged, and together with six spare multi-mode cores 414 to 419 and twelve spacers 471 to 482, the cylindrical tube 492 It is bundled inside.

  By inserting a spare multi-mode optical fiber or spacer in the multi-core spatial position conversion means 103, the positions of the cores 401 to 413 of the multi-mode optical fiber used for transmission are more firmly fixed. The connection accuracy with the core has been improved. Six spare multi-mode cores 414 to 419 may also be used for transmission, but in this embodiment, the interval between the cores is increased by not allowing light to pass, and crosstalk between the cores is improved. To obtain good signal quality.

  The N = 13 optical fibers 301 to 313 and the six spare optical fibers 314 to 319 used for the multi-core spatial position conversion means 103 have a step index type refractive index distribution, a core diameter of 13 μm, and at least m = 3 types. Each core is provided with a ring-shaped trench structure having a diameter of 50 μm and a width of 10 μm, which is designed to propagate the mode and further has a lower refractive index than the surrounding cladding so as to reduce crosstalk from the adjacent core ( Step index type number mode optical fiber having a trench structure). The cladding diameter of these optical fibers was 125 μm, the core diameter was kept constant, the cladding diameter was gradually decreased from the input end to the output end, and the cladding diameter at the output end was reduced to 85 μm.

  As the optical coupling means 102, a connection mechanism by the butt joint method, that is, the substrate end face of the output of the mode conversion waveguide array 101 is polished, and the input of the multimode optical fiber constituting the multi-core spatial position conversion means 103 is mirror-polished, A low-loss connection was realized by bringing the polished substrate end face and optical fiber end face into physical contact with each other. In addition, the connection part may be fixed by containing an adhesive in the butt joint connection part, or the coupling efficiency may be improved by containing a refractive index matching agent. Adhesives and refractive index matching agents can also be considered as components of the optical coupling means.

  The optical multiplexer / demultiplexer of this embodiment has a spatial multiplexing number of 39 (= N × m), and realizes a spatial multiplexing number larger than that of the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 13) of optical fiber cores to be transmitted is set to be larger than the mode type m (= 3) propagating through the number mode optical fiber.

  As described above, according to the present embodiment, an optical multiplexer / demultiplexer capable of multiplexing / demultiplexing spatially multiplexed and mode multiplexed light has been realized, and the number of spatial multiplexing has been increased as compared with the prior art. Further, the mode conversion waveguide array is formed in a plurality of layers, and the waveguides are formed on the same layer, thereby improving the mode conversion waveguide performance. Furthermore, the position accuracy of the core has been improved by incorporating spare optical fibers and spacers into the multi-core spatial position conversion means.

(Fourth embodiment)
In the third embodiment, the waveguide of the mode conversion waveguide array 101 is formed in a plurality of layers, and a plurality of cores are arranged close to each other at the chip end surface on the multimode side of the mode conversion waveguide. In the embodiment, the mode conversion waveguide array 101 is formed only on a single layer, and the number of cores on the chip end surface on the multimode side of the mode conversion waveguide 101 is one. By realizing the mode conversion waveguide array 101 with only one layer, the mode conversion waveguide array 101 can be manufactured by a general-purpose waveguide manufacturing technique, which is more than the mode conversion waveguide array 101 of the third embodiment. Made it even easier. In the first and second embodiments, one or a plurality of lens sets are used as the optical coupling means 102. However, in this embodiment, one or a plurality of lens sets are arranged in an array, Encased and hermetically sealed. Thereby, the optical coupling means 102 made of a lens can be made into a general-purpose component, and N sets can be optically connected in a lump without arranging lenses one by one, thereby improving the reliability of optical connection. This led to cost reduction and simplification.

  FIG. 17 is a diagram illustrating an overall configuration of an optical multiplexer / demultiplexer according to the fourth embodiment. A mode conversion waveguide array 101 including N = 7 mode conversion waveguides 211 to 217 formed on a flat substrate and a lens array including N = 7 sets of microlenses 501 to 507 housed in a casing ( An optical coupling means 102) and a multi-core spatial position conversion means 103 comprising N optical fibers 301 to 307 are constituted.

  FIG. 18 shows a configuration example of the mode conversion waveguides 211 to 217 in the fourth embodiment. FIG. 18A shows a top view of the mode conversion waveguide. It has three single mode input ports and one multimode output port, and the circuit is configured to convert one or more input single mode light into m = 3 modes and output them. ing. The second waveguide 242 is composed of a combination of a tapered waveguide whose waveguide width is gradually changed and a plurality of linear waveguides having different waveguide widths. The first waveguide 241 and the third waveguide 243 include The input light is brought close to the straight waveguide of the second waveguide and optically coupled.

  FIG. 18B is a cross-sectional view of the single-mode chip end surface, and FIG. 18C is a cross-sectional view of the multi-mode chip end surface. A major difference from the configuration described in the first to third embodiments is that the waveguide core is formed in only one layer, as shown in FIGS. 18B and 18C. In general, it is much easier to produce a waveguide on the same plane than the case where the waveguide is produced by changing the position in the height direction of the core or when it is produced over a plurality of layers, and the accuracy is high. Since it can be manufactured, a high-performance mode conversion waveguide array can be obtained by forming a waveguide on a substrate having a single waveguide layer as in this embodiment.

  FIG. 19 shows m = 3 types of modes output from the multimode side port of the mode conversion waveguide of this embodiment as an example. FIG. 20 shows a configuration example of the optical coupling means 102 in the present embodiment. Two sets of lenses 501 to 507 were arranged in N = 7 sets inside the housing 521 and hermetically sealed. The surface of the housing in contact with the lens was a glass window. In the present embodiment, the number of arrays of lenses is the same as the number of arrays of mode conversion waveguides 211 to 217, but the number of both may be different.

  FIG. 21A shows a cross-sectional view of the output end of the multi-core spatial position converting means of this embodiment. When this output end is connected to an N-core / m-mode multi-core / multi-mode optical fiber having a cross-sectional structure shown in FIG. N = 7 multi-mode cores 401 to 407 of the multi-core spatial position converting means are arranged and bundled so as to be aligned with 677. In the present embodiment, the shape of the core is rectangular so that the mode spreading in the horizontal direction can be transmitted with high quality. In the present embodiment, as shown in FIG. 21, the N = 7 pieces are arranged in the same direction so that the long sides of the rectangular core are horizontal, but the directions of the respective cores may be different.

  A specific example of manufacturing the optical multiplexer / demultiplexer of this embodiment will be described. The mode conversion waveguide array 101 was produced by a quartz planar lightwave circuit technique. In order to easily connect an optical fiber block in which a plurality of optical fibers are arranged on a V-groove substrate to a single mode input of the mode conversion waveguide array 101, 21 (= mode) on the input side of the mode conversion waveguide array 101 is used. The number of input ports of the conversion waveguide M × the number of mode conversion waveguides N) The center positions of the cores were formed to have the same pitch p on the flat substrate and the same height on the substrate layer. In this way, the input positions of the N mode conversion waveguides are arranged in a straight line, so that the connection of the optical fiber blocks is facilitated, and the arrangement is made so that the pitches are equal on the line connecting the input positions. The optical fiber block can be used, leading to cost reduction of members.

  Further, in order to make it easy to connect the lens array shown in FIG. 20 to the multimode output of the mode conversion waveguide array 101, 7 (= number N of mode conversion waveguides) sets on the output side of the mode conversion waveguide array 101 The center positions of the output cores were made so as to have the same pitch q = M × p on the flat substrate and the same height on the substrate layer. As with the input side, the lens array can be easily connected, and the cost can be reduced by sharing the members.

  The multi-core spatial position conversion means 103 was manufactured using N = 7 optical fibers. N = 7 optical fibers have a rectangular core type refractive index profile, and are designed to propagate a core diameter of 10 × 20 μm and m = 3 types of modes. These seven optical fibers were thin fibers having a cladding diameter of 70 μm. Then, the output ends of the cores of these seven optical fibers were brought close to each other, bundled so that the cross section had the core arrangement shown in FIG.

  In the present embodiment, when the input pitch of the mode conversion waveguide array 101 is p, the N groups of lenses in the housing 521 of the lens array and the N cores of the multimode optical fiber block 331 have a pitch q = M × p are arranged at an equal pitch so that the height is constant. Such an array arrangement facilitates connection between members, and the common use of members leads to cost reduction.

The optical multiplexer / demultiplexer of this embodiment has a spatial multiplexing number of 21 (= N × m), and realizes a spatial multiplexing number larger than that of the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 7) of optical fiber cores to be transmitted is made larger than the mode type m (= 3) propagating through the number mode optical fiber.
As described above, according to the present embodiment, an optical multiplexer / demultiplexer capable of multiplexing / demultiplexing spatially multiplexed and mode multiplexed light has been realized, and the number of spatial multiplexing has been increased as compared with the prior art.

(Fifth embodiment)
In the mode conversion waveguides of the first to third embodiments, the multimode-side output port composed of a plurality of adjacent cores is formed on the end face of the substrate. It was formed on the upper surface of the substrate. By adopting such a configuration, as in the fourth embodiment, the mode conversion waveguide can be formed on a single-layer planar substrate, and an advantage that it is easy to manufacture can be obtained. Furthermore, in the mode conversion waveguides of the first to third embodiments, since the light exit end is on the substrate end face, precise height direction control is necessary to emit a mode with good symmetry. However, by using the light emitting end as the upper surface of the substrate as in this embodiment, good positional accuracy can be obtained even with a standard flat substrate manufacturing technique.

  FIG. 22 is a top view of a configuration example of the mode conversion waveguide array 101 in the fifth embodiment. Each mode conversion waveguide includes three single-mode input ports input from the end face of the substrate, a tapered waveguide, and two-dimensional waveguide gratings 251 to 259. The electric field of light input from the single mode input port is adiabatically converted by the tapered waveguide, the optical path is converted in the vertical direction by the two-dimensional grating, and output from the upper surface of the substrate. The positions of the plurality of two-dimensional gratings can be set arbitrarily. For example, by arranging three two-dimensional waveguide gratings symmetrically three times, it is possible to output multimode light with good symmetry from the upper surface of the substrate.

  In this embodiment, the grating is used as means for converting the optical path of light propagating in the horizontal direction with respect to the substrate into the vertical direction, but other means can be used. For example, as shown in FIG. 23, by forming a 45-degree mirror 260 in the waveguide on the substrate 201, the horizontal optical path can be converted into the vertical optical path.

  A specific example of manufacturing the optical multiplexer / demultiplexer of this embodiment will be described. The mode conversion waveguide array 101 is made of a silicon waveguide on the substrate 201. In order to easily connect an optical fiber block in which a plurality of optical fibers are arranged on a V-groove substrate to a single mode input of the mode conversion waveguide array 101, 21 (= mode) on the input side of the mode conversion waveguide array 101 is used. The number of input ports of the conversion waveguide M × the number of mode conversion waveguides N) The center positions of the cores were formed to have the same pitch p on the flat substrate and the same height on the substrate layer. In this way, the input positions of the N mode conversion waveguides are arranged in a straight line, so that the connection of the optical fiber blocks is facilitated, and the arrangement is made so that the pitches are equal on the line connecting the input positions. The optical fiber block can be used, leading to cost reduction of members.

  In order to suppress reflection of input light, the substrate end face of the mode conversion waveguide array 101 was polished at an angle of 8 °, and a 21-core single mode optical fiber block was connected. As for the multimode output of the mode conversion waveguide array 101, in order to make it easy to connect the lens array, 7 (= number of mode conversion waveguides) sets of waveguide gratings on the output side of the mode conversion waveguide array 101 are used. The center position of the output end is made to be equal pitch q = M × p on the flat substrate. The center position of the output end is the center position of the three light exit ends.

  The multi-core spatial position conversion means 103 was manufactured using N = 7 optical fibers. N = 7 optical fibers have a multi-step index (staircase) type refractive index distribution, and the core diameters of the cores of the first refractive index and the second refractive index are changed in two steps of 12 μm and 15 μm, respectively. = Designed to propagate three types of modes. These seven optical fibers were thin fibers having a cladding diameter of 90 μm. The output ends of the cores of these seven optical fibers were brought close to each other, bundled so that the cross section was the same as that shown in FIG. 4A, and covered with a coating.

  As the optical coupling means 102, a single lens array of N = 7 is used, and the multimode light emitted from the upper surface of the mode conversion waveguide array 101 by the waveguide grating is converted into an optical fiber of the multicore spatial position conversion means 103. Bonded to the core.

  FIG. 24 shows the state of optical coupling in the output light of the mode conversion waveguide array 101, the lens 501 of the optical coupling means 102, and the core 401 of the optical fiber 301 of the multi-core spatial position conversion means 103 in this embodiment. In this configuration example, only the multimode side is output from the upper surface (including the oblique upper surface) of the substrate, but the single mode input port is configured to input / output from the upper surface (including the oblique upper surface). May be.

  The optical multiplexer / demultiplexer of this embodiment has a spatial multiplexing number of 21 (= N × m), and realizes a spatial multiplexing number larger than that of the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 7) of optical fiber cores to be transmitted is made larger than the mode type m (= 3) propagating through the number mode optical fiber.

  As described above, according to the present embodiment, an optical multiplexer / demultiplexer capable of multiplexing / demultiplexing spatially multiplexed and mode multiplexed light has been realized, and the number of spatial multiplexing has been increased as compared with the prior art.

(Sixth embodiment)
In the first to fifth embodiments, an example in which a waveguide circuit including a plurality of waveguides is used as means for realizing the mode conversion waveguide array 101 has been described. The length of these multiple waveguides is arbitrary, but by making the optical path lengths from the input to the output equal, it is possible to reduce the burden of signal processing when transmitting optical signals. Better transmission performance can be obtained.

  A specific configuration example will be described in more detail. As shown in FIG. 25, the mode conversion waveguide of the present embodiment is configured by first to third M (M = 3) waveguides formed of a straight waveguide and a bent waveguide on a substrate. Has been. The waveguide is formed in two layers, and the first and third waveguides drawn with a solid line shown in FIG. 25A are drawn with a solid line shown in FIG. 25B on the first layer. A second waveguide is formed on the second layer above the first layer.

  The first waveguide constituting the mode conversion waveguide is composed of a straight waveguide 261 having a length s1 and two bending waveguides 271 and 272 having a central angle θ1, and is formed in the first layer on the substrate. . The second waveguide constituting the mode conversion waveguide includes two straight waveguides 263 and 264 having a length s2a and a length s2b (s2a + s2b = s2), and two bending waveguides 275 having a central angle θ2a. 276 and two bending waveguides 277 and 278 having a central angle θ2b, which are formed in the second layer on the substrate. The third waveguide constituting the mode conversion waveguide is composed of a straight waveguide 262 having a length s3 and two bending waveguides 273 and 274 having a central angle θ3, and is formed in the first layer on the substrate. . Then, the length of the straight waveguide and the central angle of the bending waveguide are set so that the optical path lengths of the first to third waveguides are equal.

  An example of setting the length of the straight waveguide and the center angle of the bending waveguide of the waveguide constituting the mode conversion waveguide is shown. The pitch at the input end of the mode conversion waveguide is p, the gap between the waveguides at the output end of the mode conversion waveguide is g, the width of the mode conversion waveguide is w, the radius of curvature of the bending waveguide is R, and the mode conversion waveguide The length in the longitudinal direction is D, the thickness of the core of the mode conversion waveguide is t, and the distance between the first layer and the second layer is d (see FIGS. 25 and 26).

  When the origin is a position where the input position of the second waveguide on the plane is projected onto the first layer, the input position of the first waveguide is (0, p, t) on the first layer on the substrate. / 2), the output position is (D, (w + g) / 2, t / 2), and θ1 = acos (1− (p− (w + g) / 2) / (2 · R)), s1 = D-2 · R · sin θ1. In the first layer on the substrate, the input position of the third waveguide is (0, −p, t / 2), and the output position is (D, − (w + g) / 2, t / 2). And θ3 = θ1 and s3 = s1. Further, in the second layer on the substrate, the input position of the second waveguide is (0, 0, t / 2 + (t + d)), and the output position is (D, 0, t / 2 + (t + d). )), Θ2a = θ2b, s1 + 2 · R · θ1 = (D-4 · R · sinθ2) + 4 · R · θ2 is set to satisfy, and s2 = D-4 · R · sinθ2 is set. did.

  Specific numerical examples are shown. p = 127 μm, g = 3 μm, w = 5 μm, R = 1000 μm, D = 1500 μm, t = 5 μm, d = 3 μm, θ1 = θ3 = 0.3525 radians, s1 = s3 = 809.4 μm, θ2a = θ2b = It was set to 0.2796 radians and s2 = 396.1 μm. The optical path lengths of the first to third waveguides are all equal and 1514.5 μm.

  In this way, by setting the optical path length of the mode conversion waveguide so that the optical path lengths of the M sets of optical paths from the M inputs to one output of the mode conversion waveguide are equal, The burden of signal processing in transmission can be reduced. In the present embodiment, a design example in which the mode conversion waveguide used in the first embodiment and the third embodiment is made equal in length has been shown. However, as in the second embodiment, the mode conversion waveguide is configured. The number of waveguides may be other than three, and even if it is a planar waveguide type mode conversion waveguide as in the fourth embodiment or a grating type mode conversion waveguide as in the fifth embodiment, the length is equalized. The design is applicable.

  An optical multiplexer / demultiplexer was manufactured using the mode conversion waveguide. FIG. 27 shows a schematic diagram of the manufactured optical multiplexer / demultiplexer. A mode conversion waveguide array 231 in which N = 7 mode conversion waveguides described above are arranged is formed of a two-layer quartz waveguide, and N = 7 multimode outputs of the mode conversion waveguide can be stored in a housing. Further, optically coupled to the multimode optical fibers 301 to 307 of the N = 7-core multimode optical fiber block 331 constituting the multicore spatial position conversion means via the N = 7 sets of two lens arrays 531. . The pitch between the lens array 531 and the fiber block 331 was set to q = M × p. Further, in order to facilitate use in an actual system, a 21-core single-mode optical fiber block 601 is connected to the single-mode side input port of the mode conversion waveguide array 231, and the multi-core spatial position conversion means 103 is connected from this optical fiber block. The members up to the multimode optical fiber block 331 were housed in the housing 611. In this way, by placing a part (or all) of the components of the optical multiplexer / demultiplexer in the housing, the optical multiplexer / demultiplexer is protected and easy to handle when used.

  In the above manufacturing example, only the mode conversion waveguide array has the same length, but the M × N inputs of the mode conversion waveguide array are close together and bundled together by the multi-core spatial position conversion means. By making the optical path lengths of the entire M × N optical paths up to the output end of the core equal, the burden of signal processing in transmission can be further reduced. The optical path length of the mode conversion waveguide, the optical path length of the optical path passing through the optical coupling means, and the optical optical path length of the core of the optical fiber constituting the multi-core spatial position conversion means may be equal to each other. The optical path lengths of the cores of the optical fibers constituting the mode conversion waveguide, the optical path passing through the optical coupling means, or the multi-core spatial position conversion means are set so that the total length is constant in the M × N optical paths. May be. Further, not only inside the optical multiplexer / demultiplexer but also a member connected to the optical multiplexer / demultiplexer (for example, a single mode optical fiber connected to the mode conversion waveguide array, or an output end of the multi-core spatial position conversion means) By making the cores of multi-core and multi-mode optical fibers, etc., the same length, the burden of signal processing on the entire transmission line can be reduced.

(Seventh embodiment)
In the sixth embodiment, the optical path length of the optical path from the input to the output of the plurality of waveguides constituting each mode conversion waveguide of the mode conversion waveguide array is made constant. Due to manufacturing deviations, errors may occur in the optical path length. Therefore, in this embodiment, the manufacturing error is corrected by providing the optical multiplexer / demultiplexer with means for adjusting the optical path length. In the present embodiment, a thin film heater is used as means for adjusting the optical path length of the waveguides of the mode conversion waveguide array. The thin film heater is a technique generally used as an optical path length adjusting means. A thin film heater is formed on the upper surface of the core of the waveguide, and the refractive index is changed by the thermo-optic effect to change the optical path length of the waveguide. Can be controlled.

  Further, M × N sets of optical paths from the M × N inputs of the mode conversion waveguide array to the output ends of the optical fiber cores bundled close together of the multi-core spatial position conversion means. When the optical path length is made equal, for example, the optical path length adjusting means may be provided in the multi-core spatial position converting means. As an example, after the optical multiplexer / demultiplexer is manufactured, N sets of optical paths from the output of the mode conversion waveguide array to the output end of the core of the optical fiber of the multi-core spatial position conversion means through the optical coupling means. By measuring the length and adjusting the length of the optical fiber constituting the multi-core spatial position converting means, the long optical path can be corrected for the optical path length error.

  FIG. 28 is a diagram showing an outline of the produced optical multiplexer / demultiplexer. N = 7 mode conversion waveguides of equal length described in the sixth embodiment are arranged on the substrate, and thin film heaters 291 to 299 are provided on the respective waveguides constituting these N = 7 mode conversion waveguides. Formed. Although not shown, each thin film heater 291 to 299 is connected to an electrode terminal 613 in the vicinity of the substrate end face by electric wiring, and each thin film heater is electrically connected from the outside via an electric connector 615 on the electrode substrate 614. Power can be supplied.

  Further, in the mode conversion waveguide array of this embodiment, waveguides 281 to 283 for alignment are also formed on the substrate in addition to the mode conversion waveguide. Multimode light is more difficult to align than single mode light, and connection errors are likely to occur between the core of the input optical fiber and the core of the mode conversion waveguide. Therefore, in this embodiment, the cores of the single-mode waveguides 281 to 283 and the cores of the optical fibers of the single-mode optical fiber block 601 corresponding to the positions of these cores are aligned and connected. did.

  A single lens array 531 of N = 7 channels arranged at an equal pitch q = M × p on the output end face of the manufactured mode conversion waveguide array, and N = 7 optical fibers 301 to multi-core spatial position conversion means. A multimode optical fiber block 331 in which the core of 307 is blocked at an equal pitch q = M × p is connected, and a member and an electrode substrate are connected from the single mode optical fiber block 601 to the multimode optical fiber block 331. It was housed in a housing 611. In this way, by placing a part (or all) of the components of the optical multiplexer / demultiplexer in the housing, the optical multiplexer / demultiplexer is protected and easy to handle when used.

  After fabricating the optical multiplexer / demultiplexer, the thin film heater was driven so that the optical path lengths of the respective mode conversion waveguides were equal. Subsequently, the lengths of the N sets of optical paths from the output of the mode conversion waveguide to the output end of the core of the optical fiber of the multi-core spatial position conversion means were measured. Since the optical path passing through the other multimode optical fibers 301 to 306 was longer than the optical path passing through the multimode optical fiber 307, the long optical fiber was cut off halfway. FIG. 28 shows fused portions 341 and 342 after unnecessary lengths of the multi-mode optical fibers 301 and 302 are cut and their lengths are adjusted.

  As described above, in the present embodiment, the example in which the thin film heater is used as the optical path length adjusting means has been described, but other means such as laser irradiation and stress application may be used. In addition, as a means for adjusting the length of the optical fiber, a method of cutting off an unnecessary optical fiber was used. However, as with the mode conversion waveguide, other means such as heating, laser irradiation, and stress application may be used. Good.

(Eighth embodiment)
In the present embodiment, as in the sixth embodiment, the optical lengths of the mode conversion waveguides are equalized so that the optical path lengths of the M sets of optical paths from the M inputs to one output of the mode conversion waveguide are equal. An example of setting the target optical path length is shown. With such a design, the burden of signal processing when transmitting an optical signal can be reduced, and more excellent transmission performance can be obtained.

  A specific configuration example will be described in more detail. As shown in FIG. 29, the mode conversion waveguide of the present embodiment is configured by first to third M (M = 3) waveguides formed of a straight waveguide and a bent waveguide on a substrate. Has been. The waveguide is formed in two layers, and the second and third waveguides drawn with a solid line shown in FIG. 29A are drawn on the first layer with a solid line shown in FIG. 29B. A first waveguide is formed on the second layer above the first layer.

  The first waveguide constituting the mode conversion waveguide includes two straight waveguides 263 and 264 having a length s1a and a length s1b (s1a + s1b = s1), and two bending waveguides 277 having a central angle θ1. 278, and formed in the second layer on the substrate. The second waveguide constituting the mode conversion waveguide is a straight waveguide 261 having a length s2, two bending waveguides 271 and 272 having a central angle θ2a, and two bending waveguides 273 and 274 having a central angle θ2b. And formed in the first layer on the substrate. The third waveguide constituting the mode conversion waveguide is composed of a straight waveguide 262 having a length s3 and two bending waveguides 275 and 276 having a central angle θ3, and is formed in the first layer on the substrate. . Then, the length of the straight waveguide and the central angle of the bending waveguide are set so that the optical path lengths of the first to third waveguides are equal.

  An example of setting the length of the straight waveguide and the center angle of the bending waveguide of the waveguide constituting the mode conversion waveguide is shown. The pitch at the input end of the mode conversion waveguide is p, the gap between the waveguides at the output end of the mode conversion waveguide is g, the width of the mode conversion waveguide is w, the radius of curvature of the bending waveguide is R, and the mode conversion waveguide The length in the longitudinal direction is D, the thickness of the core of the mode conversion waveguide is t, and the distance between the first layer and the second layer is d. When the input position of the second waveguide on the plane is the origin O, the input position of the first waveguide is (0, p, t + d) and the output position is (0, p) in the second layer on the substrate. D, (w + g) / 4, t + d), and θ1 = acos (1− (p− (w + g) / 4) / (2 · R)), s1 = D−2 · R · sin θ1 Set to.

  In the first layer on the substrate, the input position of the third waveguide is (0, −p, 0), the output position is (D, − (w + g) / 4, 0), and θ3 = θ1, s3 = s1 were set. Further, in the first layer on the substrate, the input position of the second waveguide is (0, 0, 0), the output position is (D, 3 (w + g) / 4, 0), and D− 2 · R · (sin θ2a + sin (acos (3 · (w + g) / (8 · R) + cos θ2a))) = s1 + 2 · R · θ1-2 · R · (θ2a + acos (3 · (w + g) / (8 .Theta.2a is set so as to satisfy R) + cos .theta.2a)), and .theta.2b = acos (3. (w + g) / (8.R) + cos .theta.2a) and s2 = D-2.R. (Sin .theta.2a + sin .theta.2b) are set.

  Examples of specific numerical values are shown. p = 127 μm, g = 2 μm, w = 4 μm, R = 750 μm, D = 1000 μm, t = 4 μm, d = 2 μm, θ1 = 0.512 radian, s1a = 199.4 μm, s1b = 200 μm, θ2a = 0. 3312 radians, θ2b = 0.219 radians, s2 = 37.6 μm, θ3 = 0.512 radians, and s3 = 399.4 μm were set. The optical path lengths of the first to third waveguides are all equal and 1017.3 μm.

  An optical multiplexer / demultiplexer was manufactured using the mode conversion waveguide. FIG. 30 is a diagram showing an outline of the produced optical multiplexer / demultiplexer. A set of six mode conversion waveguides arranged at regular intervals is taken as one set, and two sets of these six mode conversion waveguides are arranged on the substrate, and a total of N = 12 mode conversion waveguide arrays 231 are arranged in two layers The quartz waveguide was formed. While the optical path lengths of the three waveguides constituting each mode conversion waveguide are kept constant, 36 on the input side of the mode conversion waveguide array (= number of input ports of the mode conversion waveguide M × mode conversion guide) The number of waveguides (N) was pitch-converted using an S-shaped waveguide so that the cores had an equal pitch p on the substrate end face.

  Of the plurality of optical fibers of the multi-core spatial position conversion means, N inputs 301 to 312 are arranged in a plurality of fiber blocks 331 and 332 at an equal pitch q = M × p, respectively. 1 of 6 channels arranged at equal pitch q = M × p so that N outputs and N inputs 301 to 312 of the plurality of optical fibers of the multi-core spatial position conversion means are optically coupled. Multimode optical fiber blocks 331 and 332 are connected to the end face of the substrate on which the mode conversion waveguide array 231 is formed via the single lens array 531 and 532.

  The N = 12 optical fibers 301 to 312 used for the multi-core spatial position conversion means are designed to propagate at least m = 3 types of modes with a multi-step index type refractive index profile having a trench structure. A 36-core single-mode optical fiber block 601 is connected to the input end face of the mode conversion waveguide array 231, and an N-core / m-mode optical fiber 621 is connected to the output end of the multi-core spatial position conversion means via a holder. . The members were housed in the housing 611 from the single mode optical fiber block 601 to the N core / m mode optical fiber 621. Thus, by storing the entire optical multiplexer / demultiplexer in the casing, the optical multiplexer / demultiplexer is protected and is easy to handle when used.

  The optical multiplexer / demultiplexer of the present embodiment has a spatial multiplexing number of 36 (= N × m), and realizes a spatial multiplexing number larger than that of the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 12) of optical fiber cores to be transmitted is made larger than the mode type m (= 3) propagating through the number mode optical fiber.

  In this embodiment, instead of using a 12-channel lens array or a 12-core multimode optical fiber block, a configuration using a plurality of 6-channel lens arrays or 6-core multimode optical fiber blocks is used. This is because the larger the number of channels, the worse the yield and the difficulty of producing the member. The yield is improved by dividing into a small number of sets, and the same member can be used when manufacturing an optical multiplexer / demultiplexer having a different N, leading to cost reduction.

(Ninth embodiment)
The present embodiment has a configuration of an optical multiplexer / demultiplexer similar to that of the eighth embodiment, but is characterized in that the mode conversion waveguide array has a multi-chip configuration. By dividing the mode conversion waveguide array into a plurality of chips, not limited to the lens array and the multimode optical fiber block, the yield can be improved, and the cost can be reduced by sharing the members.

  FIG. 31 is a diagram illustrating an internal configuration of the manufactured optical multiplexer / demultiplexer. The mode conversion waveguide array 231 is composed of nine mode conversion waveguides used in the eighth embodiment and alignment waveguides 281 and 282 on both sides of the chip. Produced. As the lens array 531, an 11-channel single lens array arranged at an equal pitch q = M × p was used, two at both ends were used for alignment, and the remaining nine were used as optical coupling means. The multimode optical fiber block 331 is composed of the cores of nine optical fibers 301 to 309 out of N = 18 of the multi-core spatial position conversion means, and single mode optical fibers for alignment on both sides. The cores of the nine optical fibers 301 to 309 are arranged at an equal pitch q = M × p on the fiber block. The optical fiber block 601 was composed of a 27-core single-mode optical fiber and single-mode optical fibers for alignment on both sides. These optical components were connected as shown in FIG. 31 using an alignment port.

  The mode conversion waveguide array 232, the lens array 532, the multimode optical fiber block 332, and the optical fiber block 602 have the same configuration, and these optical components are also connected as shown in FIG. 31 using the alignment port. The N = 18 optical fibers 301 to 318 used for the multi-core spatial position converting means are designed to propagate a graded index type refractive index profile and a core diameter of 18 μm and at least m = 3 types of modes. The clad diameter of these optical fibers was 80 μm. The output end of the multi-core space position converting means is routed inside the housing and taken out from the outside of the housing.

  FIG. 32 is a diagram illustrating the appearance of the housing. 54 optical connectors connected to 54 single-mode ports of the mode conversion waveguide arrays 231 and 232 and one optical connector connected to the multi-core multi-mode ports are provided on the front surface of the housing. With such a configuration, the patch cord of the optical fiber can be easily inserted and removed from the outside of the housing, and the optical multiplexer / demultiplexer of the present invention can be easily used.

  33A is a cross-sectional view of the output end of the multi-core spatial position conversion means, and FIG. 33B is a cross-sectional view of an N-core / m-mode multi-core / multi-mode optical fiber used in this embodiment. . The optical multiplexer / demultiplexer of the present embodiment has a spatial multiplexing number of 54 (= N × m), and realizes a spatial multiplexing number larger than that of the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 18) of optical fiber cores to be transmitted is set to be larger than the mode type m (= 3) propagating through the number mode optical fiber.

  In the present embodiment, the alignment waveguide is formed as a circuit other than the mode conversion waveguide on the substrate on which the mode conversion waveguide array 231 is formed. As described above, the mode conversion waveguide array according to the present invention has an advantage that an optical circuit can be easily formed on a flat substrate. In addition to the alignment waveguide, the mode conversion waveguide array has an optical circuit such as a monitor waveguide and a splitter. Any optical circuit other than the conversion waveguide may be formed on the substrate.

(10th Embodiment)
The present embodiment has an optical multiplexer / demultiplexer configuration similar to that of the ninth embodiment, but is characterized in that the optical multiplexer / demultiplexer has a multi-module configuration. By dividing the optical multiplexer / demultiplexer into a plurality of optical multiplexers / demultiplexers, not limited to lens arrays, multimode optical fiber blocks, and mode conversion waveguide arrays, the yield can be improved and the cost can be reduced by sharing the members.

  FIG. 34 is a diagram showing the internal configuration of the manufactured optical multiplexer / demultiplexer. The mode conversion waveguide array 231 is composed of six mode conversion waveguides used in the eighth embodiment and alignment waveguides 281 and 282 on both sides of the chip, and is made of a two-layer silicon laminated waveguide. . As the lens array 531, a single lens array of 6 channels arranged at an equal pitch q = M × p was used. The multi-mode optical fiber block 331 is composed of the cores of six optical fibers 301 to 306 among N = 12 multi-mode optical fibers of the multi-core spatial position converting means. Note that the cores of the six optical fibers 301 to 306 are arranged at an equal pitch q = M × p on the fiber block. The optical fiber block 601 is composed of single-mode optical fibers 631 to 650 with a 20-core optical connector (including single-mode optical fibers for alignment on both sides).

  After the optical fiber block 601 was connected to the mode conversion waveguide array 231 using the alignment port, the lens array 531 and the multimode optical fiber block 331 were connected, and these members were housed in the housing 611. Similarly, the mode conversion waveguide array 232 includes the six mode conversion waveguides used in the eighth embodiment and the alignment waveguides 283 and 284 on both sides of the chip, and is a two-layer silicon laminated waveguide. It was made with. A single lens array of 6 channels was used as the lens array 532. The multi-mode optical fiber block 332 is constituted by the cores of six optical fibers 307 to 312 among N = 12 multi-mode optical fibers of the multi-core spatial position converting means. The optical fiber block 602 is composed of single-mode optical fibers 651 to 670 with 20-core optical connectors (including single-mode optical fibers for alignment on both sides). After the optical fiber block 602 was connected to the mode conversion waveguide array 232 using the alignment port, the lens array 532 and the multimode optical fiber block 332 were connected, and these members were housed in the housing 612.

  As multi-core spatial position converting means, N (N = 12) multi-mode optical fibers 301 to 312 propagating m (m = 3) types of modes, and propagating fundamental modes as in the second embodiment 7 The single mode optical fibers 321 to 327 were mixed, and one end thereof was brought close to each other and bundled together. N = 12 optical fibers 301 to 312 were designed to have a graded index type refractive index distribution having a trench structure. An N = 12 core / m = 3 mode optical fiber 621 having seven single mode cores was connected to the output end of the multi-core spatial position conversion means via a holder.

  The optical multiplexer / demultiplexer of the present embodiment has a spatial multiplexing number of 43 (= N × m + 7), and realizes a spatial multiplexing number larger than that of the prior art. Although the combination of the number of cores and the number of modes is arbitrary, it is easier to obtain better transmission characteristics by increasing the number of cores than by increasing the number of modes. The number N (= 12) of optical fiber cores to be transmitted is made larger than the mode type m (= 3) propagating through the number mode optical fiber.

  The two housings 611 and 612 of the present embodiment may be used in the same direction at the same time, or one of them can be used as a spare, and usually only one of them is used and replaced with a spare in the event of a failure. . Further, for example, the transmission direction can be changed for each case, such as the case 611 is up and the case 612 is down. Further, in the core arrangement of the multi-core spatial position conversion means, the core arrangement as shown in FIG. 33 is used, the inner seven cores are single mode cores of this embodiment, and the outer twelve cores are multimode cores of this embodiment. It is good. Then, the multimode optical fiber cores connected to the casings 611 and 612 are alternately arranged so that the transmission directions of the adjacent multimode cores are opposite to each other, thereby crossing the multimode adjacent cores. Talk can be greatly suppressed.

  Alternatively, the core diameter (propagation constant) of the multimode optical fiber connected to the housing 611 and the core diameter (propagation constant) of the multimode optical fiber connected to the housing 612 are different, and the multimode optical fiber connected to the housings 611 and 612 is different. By alternately arranging the cores of the mode optical fiber and using multiple cores with different core diameters (propagation constants) and separating the core intervals of the same core diameter, crosstalk between adjacent cores of the multimode is greatly suppressed. be able to. A single mode core may be used as a transmission line like a conventional multicore fiber, or only a multimode core is used as a transmission line, and a single mode core is used for other purposes such as signal quality monitoring. It can also be used.

(Eleventh embodiment)
In this embodiment, an example of an optical communication system using the optical multiplexer / demultiplexer disclosed in the first to tenth embodiments is shown. In the optical communication system of the present embodiment, single mode fibers are connected to M × N inputs of the mode conversion waveguide array, respectively, and the multi-core spatial position conversion means of the optical fibers bundled together in close proximity are combined. In an optical multiplexer / demultiplexer in which a multicore / multimode optical fiber is connected to an output end of a core, an optical signal is input to M × N inputs of a mode conversion waveguide array of the optical multiplexer / demultiplexer. The optical signal is multiplexed by the optical fiber core, or the optical signal is input from the core of the optical fiber bundled close together of the multi-core spatial position converting means of the optical multiplexer / demultiplexer, and the optical signal is output by the optical multiplexer / demultiplexer Was demultiplexed.

  FIG. 35 is a diagram illustrating an example of an optical communication system using the optical multiplexer / demultiplexer according to each of the above-described embodiments. This optical communication system includes an optical transmitter 701, an optical multiplexer / demultiplexer 731 of the present invention (functioning as a mode multiplexer), an optical transmission line 721, and an optical multiplexer / demultiplexer 732 of the present invention (as a mode demultiplexer). Function) and an optical receiver 711. As the optical transmission line 721, an N-core / m-mode optical fiber 621 or the like can be used.

  FIG. 36 is a diagram illustrating an example of an optical communication system using the optical multiplexer / demultiplexer according to each embodiment described above. This optical communication system includes an optical transmitter 701, an optical receiver 712, an optical multiplexer / demultiplexer 731 (functioning as a mode multiplexer / demultiplexer) of the present invention, an optical transmission line 721, and an optical multiplexer / demultiplexer of the present invention. It is composed of a wave 732 (functioning as a mode multiplexer / demultiplexer), an optical receiver 711, and an optical transmitter 702. As the optical transmission line 721, an N-core / m-mode optical fiber 621 or the like can be used.

  As described above, the optical multiplexer / demultiplexer of the present invention is applied to a point-to-point optical communication system as the simplest example, but it is of course useful for more complicated optical communication systems such as ROADM nodes. .

  The aspect described above shows one aspect of the present invention, and the present invention is not limited to the above-described embodiment, and has the configuration of the present invention and can achieve the objects and effects. It goes without saying that modifications and improvements within the scope are included in the content of the present invention. Further, the specific structure, shape, and the like in carrying out the present invention are not problematic as other structures, shapes, and the like as long as the objects and effects of the present invention can be achieved. The present invention is not limited to the above-described embodiments, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

  As described above, in each embodiment, the example (M = m) in which the number M of input ports of the mode conversion waveguide is equal to the type m of the mode to be used has been described. Of course, M and m may be different. For example, in a mode conversion waveguide having M = 6 input ports, m = 3 types of modes may be combined / demultiplexed. For example, FIG. When the mode multiplexer / demultiplexer shown in FIG. 3 is used as a component of the mode conversion waveguide of the present invention, the number of input ports is M = 6, and the number of modes is m = 3 (LP01, LP11a, LP11b).

  Further, although the mode conversion waveguide array in the above-described embodiment is mainly formed using a silicon, polymer, or quartz material, the waveguide material may be polyimide, a semiconductor, LiNbO2, or the like, or a substrate. The material may be quartz or silicon.

  Furthermore, in the output end of the multi-core spatial position conversion means shown in FIG. 4, FIG. 11, FIG. 16, FIG. 21, FIG. 33, and the multi-core / multi-mode optical fiber, N cores that propagate multi-mode light are In any case, m types of modes are propagated by one core, but m types of modes may be propagated by a plurality of cores. For example, when the design is such that m = 3 types of modes propagate in an optical fiber having a strongly coupled core composed of three adjacent cores, this will be referred to as one core group. Therefore, for example, a multi-core multimode optical fiber composed of N cores that propagate m types of modes shown in FIG. 4B of the first embodiment is used as a group of N cores that propagate m types of modes. The same function as an optical multiplexer / demultiplexer can be obtained by replacing the multi-core / multi-mode optical fiber. A multicore / multimode optical fiber having an arbitrary structure, the number of cores, and the number of modes can be used depending on the required transmission characteristics.

  As described above, in an optical multiplexer / demultiplexer for spatial mode division multiplex communication, input light is multiplexed into a multi-core multimode optical fiber having a plurality of cores that transmit a plurality of modes, or a plurality of modes are transmitted. Output light from a multi-core multi-mode optical fiber having a plurality of cores to be demultiplexed.

  With this configuration, input light is multiplexed into a multicore multimode optical fiber having a plurality of cores that transmit a plurality of modes, or output light from a multicore multimode optical fiber having a plurality of cores that transmit a plurality of modes. It is possible to provide an optical multiplexer / demultiplexer that can demultiplex.

  Input light is multiplexed into a multi-core multimode optical fiber having multiple cores that transmit multiple modes, or output light from a multi-core multimode optical fiber that has multiple cores that transmit multiple modes is demultiplexed Can be applied to indispensable uses.

  DESCRIPTION OF SYMBOLS 101 ... Mode conversion waveguide array, 102 ... Optical coupling means, 103 ... Multi-core spatial position conversion means, 201 ... Substrate, 202 ... Single mode side substrate end surface, 203 ... Multi mode Side substrate end face, 211 to 223, mode conversion waveguide, 231 to 232, mode conversion waveguide array, 241, first waveguide, 242, second waveguide, 243,. Third waveguide, 247... First waveguide core, 248... Second waveguide core, 249... Third waveguide core, 251 to 259. Waveguide grating, 260 ... 45 degree mirror, 261 to 264 ... linear waveguide, 271 to 278 ... bending waveguide, 281 to 284 ... waveguide for alignment, 291 to 299 ... optical path Length adjustment means, 301 to 319 Multimode optical fiber, 321 to 327 ... single mode optical fiber, 331 to 332 ... multimode optical fiber block, 341 to 342 ... fusion point, 401 to 419 ... multimode core, 421-424 ... single mode core, 431-437 ... clad, 471-482 ... spacer, 491 ... coating, 492 ... cylinder, 501-507 ... lens, 521 ... Lens housing, 531 to 532 ... lens array, 541 to 553 ... adhesive, 601 to 602 ... optical fiber block, 611 to 612 ... housing, 613 ... electrode terminal, 614 ... Electrode substrate, 615 ... Electric connector, 621 ... N core / m mode optical fiber, 631-670 ... Single with optical connector Optical fiber, 671 to 689... Multi-mode core of N core / m mode optical fiber, 691 to 694... Single mode core of N core / m mode optical fiber, 701 to 702. Transmitter, 711-712 ... optical receiver, 721 ... optical transmission line, 731-732 ... optical multiplexer / demultiplexer

Claims (8)

A mode conversion waveguide is formed on the substrate and converts M (M is an integer of M ≧ 2) inputs into m (m is an integer of 2 ≦ m ≦ M) types of modes and outputs N (N Is an integer of N ≧ 2) arranged mode conversion waveguide arrays;
Multi-core spatial position conversion means for bringing the output ends of N or more optical fiber cores including N multi-mode optical fiber cores propagating the m types of modes close to each other and bundling them together;
N outputs of the mode conversion waveguide array, and optical coupling means for optically coupling input terminals of N multimode cores among a plurality of optical fiber cores of the multi-core spatial position conversion means. An optical multiplexer / demultiplexer comprising:   The optical multiplexer / demultiplexer according to claim 1, wherein each of the N sets of optical coupling means includes one or a plurality of lenses.   One set or a plurality of sets of lenses of the N sets of optical coupling means are arranged in a casing, and a surface on one lens side of the casing is a plurality of optical fibers constituting the multi-core space position converting means The other lens side surface of the casing is placed on the substrate end surface or the top surface of the mode conversion waveguide array where the N outputs of the mode conversion waveguide array are arranged, and is optically coupled to the input end of the core. The optical multiplexer / demultiplexer according to claim 2.   Optically coupling the input ends of a plurality of optical fiber cores constituting the multi-core spatial position converting means by butt-joining the substrate end surface or the substrate upper surface where N outputs of the mode conversion waveguide array are arranged. The optical multiplexer / demultiplexer according to claim 1.   The optical path length of the mode conversion waveguide is set so that the optical path lengths of the M sets of optical paths from M inputs to one output of the mode conversion waveguide are equal. The optical multiplexer / demultiplexer according to any one of claims 1 to 4.   M × N sets of optical paths from the M × N inputs of the mode conversion waveguide array to the output ends of the optical fiber cores bundled together in the vicinity of the multi-core spatial position conversion means. The optical path length of the mode conversion waveguide and the optical path length of the core of the optical fiber constituting the multi-core spatial position conversion means are set so that the optical path lengths are equal. 5. The optical multiplexer / demultiplexer according to any one of 1 to 4.   The number of cores of the optical fiber constituting the multi-core spatial position converting means is larger than a mode type m propagating through the core of the multi-mode optical fiber. An optical multiplexer / demultiplexer as described in 1. A mode conversion waveguide is formed on the substrate and converts M (M is an integer of M ≧ 2) inputs into m (m is an integer of 2 ≦ m ≦ M) types of modes and outputs N (N Is an integer of N ≧ 2) single mode fibers are respectively connected to M × N inputs of the arranged mode conversion waveguide arrays.
The output ends of a plurality of N or more optical fiber cores including the N multimode optical fiber cores propagating the m types of modes are brought close to each other, and the multi-core spatial position conversion means bundled together are brought close to each other. N core / m mode consisting of N cores each propagating m types of modes, or N core groups each propagating m types of modes, at the output end of optical fiber cores bundled together An optical communication system comprising the optical multiplexer / demultiplexer according to any one of claims 1 to 7, to which an optical fiber is connected.
An optical signal is input to M × N inputs of the mode conversion waveguide array of the optical multiplexer / demultiplexer, and the optical signal is multiplexed by the optical multiplexer / demultiplexer, or the multi-core spatial position of the optical multiplexer / demultiplexer An optical communication system, wherein an optical signal is input from a core of optical fibers bundled close together in a conversion means, and the optical signal is demultiplexed by the optical multiplexer / demultiplexer.

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