JP6631848B2 - Mode multiplexer / demultiplexer and mode multiplex transmission system - Google Patents

Description

  The present disclosure relates to a mode multiplexer and a mode demultiplexer necessary for mode multiplex transmission, which is a multiplexing method using a propagation mode as a carrier in an optical fiber cable having three or more propagation modes.

  In an optical fiber communication system, a non-linear effect or a fiber fuse generated in an optical fiber becomes a problem, and an increase in transmission capacity is limited. In order to alleviate these limitations, it is necessary to reduce the density of light guided to the optical fiber, and a large-core fiber is being studied as described in Non-Patent Document 1.

  However, there is a trade-off relationship between the reduction of the bending loss, the expansion of the single-mode operation region, and the expansion of the effective area, and there is a problem that the amount of expansion of the effective area under predetermined conditions is limited. Therefore, a mode multiplexing transmission system that uses a multimode fiber as a transmission fiber and performs parallel transmission using a plurality of propagating modes has been studied as a technology for achieving a dramatic increase in capacity (for example, see Non-Patent Documents). 2).

  In a mode multiplex transmission system, a mode multiplexer / demultiplexer has been proposed to propagate a plurality of signals emitted from a transmitter as separate modes in an optical fiber. Until now, various types of mode multiplexer / demultiplexers such as a spatial optical system and a fiber type have been proposed. However, a PLC (Planar lightwave circuit) type mode multiplexer / demultiplexer has low loss and wide band. It is characterized by excellent mass productivity (for example, see Non-Patent Documents 3 and 4).

T. Matsui, et al. , "Applicability of Photonic Crystal Fiber Fiber With Uniform Air-Hole Structure to High-Speed and Wide-Band Transmission Overseas Commendation Convention Comm. Lightwave Technology. 27, 5410-5416, 2009. N. Hanzawa et al. , “Demonstration of mode-division multiplexing transmission over 10 km two-mode fiber with mode coupler”, OFC2011, paper OWA4 (2011) N. Hanzawa et al. , "Asymmetric Parallel Waveguide with Mode Conversion for Mode and Wavelength Division Multiplexing Transmission", OFC2012, OTul. 4. N. Hanzawa et al, “Mode multi / demultiplexing with parallel waveguide for mode division multiple transmission”, Opt. Express vol. 22 pp. 29321-29330 (2014) K. Saitoh et al. , “PLC-based LP11 mode rotator for mode-division multiplexing transmission”, Opt. Express, vol. 22 pp. 19117-19130 (2014). T. Ohara et al. , "Over-1000-Channel Ultradense WDM Transmission With Supercontinuum Multicarrier Source", IEEE J. Phys. Lightw. Technol. , Vol. 24, pp. 2311-2317 (2006) N. Hanzawa et al. , “Demonstration of PLC-based six-mode multiple for mode division multiplexing transmission”, ECOC2015, paper ID 0145 (2015) R. Ryf et al. , "Mode-division multiplexing over 96 km of four-mode fiber using coherent 6x6 MIMO processing", J. Mol. Lightw. Technol. , Vol. 30, pp. 521-531 (2012).

  However, in a transmission path through which a plurality of modes propagate, optical characteristics such as transmission loss, chromatic dispersion, and polarization dispersion differ among the modes. For this reason, in a mode multiplex transmission system in which a plurality of signals emitted from a transmitter are propagated in an optical fiber as separate modes, a transmission quality difference between transmission signals becomes large, and a transmission capacity and a transmission distance of a communication system are limited. Problem.

  Therefore, an object of the present invention is to provide a mode multiplexer / demultiplexer and a mode multiplex transmission system in which the transmission capacity and the transmission distance of the communication system are hardly restricted even in mode multiplex transmission. .

  The inventor of the present application was able to find a structure of a mode multiplexer / demultiplexer capable of dispersing signal light input to any port into all modes that can be transmitted on a transmission path.

A first mode multiplexer / demultiplexer according to the present invention multiplexes light from port 1, port 2 and port 3 on the demultiplexing side to port 4 on the multiplexing side, and transmits light from port 4 to the port. 1. A planar optical circuit type mode multiplexer / demultiplexer for splitting light into the port 2 and the port 3,
Board and
A three-mode waveguide formed on the substrate and having one end connected to the port 4;
The other end of the three-mode waveguide is connected to the port 1 and the port 2 by single-mode waveguides respectively formed on the substrate, and the LP01 mode and the three-mode waveguide of each of the single-mode waveguides are connected. A first multiplexing / demultiplexing unit for converting between the LP01 mode and the LP11a mode of the wave path;
The three-mode waveguide formed on the substrate and connected between the one end and the other end and the port 3 are connected by a single-mode waveguide, and the LP01 mode and the three-mode of the single-mode waveguide are connected. A second multiplexing / demultiplexing unit that converts between the LP01 mode and the LP11a mode of the waveguide;
A first mode rotator formed in the three-mode waveguide between the first multiplexing / demultiplexing unit and the second multiplexing / demultiplexing unit and exchanging all power between the LP11a mode and the LP11b mode;
A second mode rotator formed in the three-mode waveguide between the second multiplexing / demultiplexing unit and the port 4 and exchanging half of power between the LP11a mode and the LP11b mode;
It is characterized by having.

The second mode multiplexer / demultiplexer according to the present invention multiplexes light from port 1, port 2, port 3 and port 4 on the demultiplexing side to port 5 on the multiplexing side, and To a port 1, the port 2, the port 3, and the port 4, a planar optical circuit type mode multiplexer / demultiplexer,
Board and
A first three-mode waveguide formed on the substrate, having a mode rotator between one end and the other end for exchanging all power between the LP11a mode and the LP11b mode, and formed on the substrate; The other end of the first three-mode waveguide is connected to the port 1 and the port 2 by single-mode waveguides, respectively, and the LP01 mode of each of the single-mode waveguides and the first three-mode waveguide are connected. A first arm having a first multiplexing / demultiplexing unit that converts between an LP01 mode and an LP11a mode of a wave path;
A second three-mode waveguide formed on the substrate and having a mode rotator between one end and the other end for exchanging all power between LP11a mode and LP11b mode, and formed on the substrate; And the other end of the second three-mode waveguide is connected to the port 3 and the port 4 by single-mode waveguides, respectively, and the LP01 mode of the single-mode waveguide and the second three-mode waveguide are connected. A second arm having a second multiplexing / demultiplexing unit that converts between the LP01 mode and the LP11a mode of the wave path;
A four-mode waveguide formed on the substrate and having one end connected to the port 5;
The other end of the four-mode waveguide formed on the substrate is connected to one end of the first three-mode waveguide of the first arm and one end of the second three-mode waveguide of the second arm. And converting the LP01 mode of the first three-mode waveguide and the second three-mode waveguide to the LP01 mode and the LP11a mode of the four-mode waveguide, and converting the first three-mode waveguide and the second A third multiplexing / demultiplexing unit that converts the LP11b mode of the two-mode waveguide into the LP11b mode and the LP21a mode of the four-mode waveguide;
It is characterized by having.

A third mode multiplexer / demultiplexer according to the present invention includes:
Two first mode multiplexers / demultiplexers;
Formed on the substrate, one end is connected to the port 5 on the multiplex side, and the square cross section at one end is converted into a non-square cross section at the other end, and the modes of LP21b and LP02 and E13 and E31 modes A 6-mode waveguide having a tapered portion that converts
Connecting the other end of the six-mode waveguide to the port 4 of each of the first mode multiplexers / demultiplexers, forming the LP01 mode of the three-mode waveguide and the six-mode waveguide on the substrate; LP11a mode, LP11a mode, and LP21b mode of the three-mode waveguide, and LP11a mode of the three-mode waveguide and LP01 mode, LP11a mode, E13 mode, and E31 mode of the six-mode waveguide are converted. A fourth multiplexing / demultiplexing unit for converting the LP11b mode of the 6-mode waveguide into the LP11b mode and the LP21a mode of the 6-mode waveguide;
It is characterized by having.

A fourth mode multiplexer / demultiplexer according to the present invention includes:
N (n is an integer of 3 or more) single-mode waveguides on the demultiplexing side formed on the substrate;
A multiplexing-side n-mode waveguide formed on the substrate;
Dividing the single-mode waveguide into groups of m (m is an integer of 2 or more), arranging the single-mode waveguide in the group in a horizontal direction with respect to the substrate, and forming the single-mode waveguide; A different wavelength from the substrate for each group, stacked without gaps, a multiplexing / demultiplexing unit connected to the n-mode waveguide,
Is provided.
Here, the fourth mode multiplexer / demultiplexer is characterized in that the combination (n, m) of n and m is (3, 2) or (6, 2).

  In order to reduce the difference between the ports of the input signal light, the first to fourth mode multiplexers / demultiplexers according to the present invention are configured such that the single-mode signal light incident from the splitter side is It is characterized by coupling to all waveguide modes at -25 dB or more.

Mode multiplex transmission system according to the present invention,
Two first to fourth mode multiplexers / demultiplexers having their respective multiplexing ports connected by a multimode fiber;
A plurality of transceivers connected to each port on the demultiplexing side of the mode multiplexer / demultiplexer,
Is provided.

  The present invention can provide a mode multiplexer / demultiplexer and a mode multiplex transmission system in which the transmission capacity and the transmission distance of the communication system are hardly limited even in the mode multiplex transmission.

FIG. 3 is a diagram illustrating a first mode multiplexer / demultiplexer according to the present invention. FIG. 4 is a diagram for explaining a mode electric field distribution in a waveguide. It is a figure explaining the structure of a mode rotator. 5 is an example of design parameters of a first mode multiplexer / demultiplexer according to the present invention. 4 is a definition of design parameters of a first mode multiplexer / demultiplexer according to the present invention. FIG. 3 is a diagram illustrating loss characteristics of a first mode multiplexer / demultiplexer according to the present invention. FIG. 4 is a diagram illustrating wavelength dependence of loss characteristics of the first mode multiplexer / demultiplexer according to the present invention. FIG. 4 is a diagram illustrating the wavelength dependence of the power ratio of the first mode multiplexer / demultiplexer according to the present invention. FIG. 4 is a diagram illustrating a second mode multiplexer / demultiplexer according to the present invention. 6 is an example of design parameters of a second mode multiplexer / demultiplexer according to the present invention. FIG. 9 is a diagram illustrating an output mode power ratio when light enters from each port of the second mode multiplexer / demultiplexer according to the present invention. FIG. 9 is a diagram illustrating a third mode multiplexer / demultiplexer according to the present invention. It is an example of the design parameter of the 3rd mode multiplexer / demultiplexer concerning this invention. FIG. 11 is a diagram illustrating an output mode power ratio when light is incident from each port of the third mode multiplexer / demultiplexer according to the present invention. It is a figure explaining the 4th mode multiplexer / demultiplexer concerning the present invention. 9 is a definition of design parameters of a fourth mode multiplexer / demultiplexer according to the present invention. It is an example of the design parameter of the 4th mode multiplexer / demultiplexer concerning this invention. FIG. 14 is a diagram illustrating an output mode power ratio when light enters from each port of the fourth mode multiplexer / demultiplexer according to the present invention. FIG. 1 is a diagram illustrating a mode multiplex transmission system according to the present invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the present invention, and the present invention is not limited to the following embodiment. In the specification and the drawings, components having the same reference numerals indicate the same components.

(Embodiment 1)
FIG. 1A is a diagram illustrating a first mode multiplexer / demultiplexer 301. The mode multiplexer / demultiplexer 301 is a three-mode multiplexer / demultiplexer. The mode multiplexer / demultiplexer 301 multiplexes light from the port P1, port P2, and port P3 on the demultiplexing side to the port P4 on the multiplexing side, and transmits light from the port P4 to the port P1, port P2, and port P3. A planar optical circuit type mode multiplexer / demultiplexer for demultiplexing,
A substrate 10;
A three-mode waveguide 11 formed on the substrate 10 and having one end connected to the port P4;
The other end of the three-mode waveguide 11 and the port P1 and the port P2 are formed on the substrate 10 and connected by the single-mode waveguide 12, respectively, and the LP01 mode and the three-mode waveguide of each of the single-mode waveguides 12 are connected. A first multiplexing / demultiplexing unit 13 that converts between the LP11 mode and the LP11a mode of the first multiplexing unit 11;
The three-mode waveguide 11 formed on the substrate 10 and connected between the one end and the other end and the port P3 are connected by a single-mode waveguide 12, and the LP01 mode and the three-mode of the single-mode waveguide 12 are connected. A second multiplexing / demultiplexing unit 15 for converting between the LP01 mode and the LP11a mode of the waveguide 11,
A first mode rotator formed in the three-mode waveguide 11 between the first multiplexing / demultiplexing unit 13 and the second multiplexing / demultiplexing unit 15 and exchanging all power between the LP11a mode and the LP11b mode; ,
A second mode rotator 16 formed in the three-mode waveguide 11 between the second multiplexing / demultiplexing unit 15 and the port P4, and exchanging half power between the LP11a mode and the LP11b mode;
It is characterized by having.

  The first multiplexing / demultiplexing unit 13 is a Y-shaped convergence unit in which two single-mode waveguides 12 merge to form a three-mode waveguide 11. The second multiplexing / demultiplexing section 15 is a Y-shaped convergence section where one single-mode waveguide 12 further merges with the three-mode waveguide 11. At the subsequent stage of the first multiplexing / demultiplexing unit 13 and the second multiplexing / demultiplexing unit 15, there are mode rotators (14, 16) for exchanging between LP11a and LP11b modes, respectively.

  The first multiplexing / demultiplexing unit 13 is designed to have substantially the same input waveguide structure. The LP01 mode propagating through each single-mode waveguide 12 is split into the LP01 and LP11a modes of the three-mode waveguide 11 and multiplexed. At this time, since only the horizontal structure of the waveguide structure of the Y-shaped junction changes, the first multiplexing / demultiplexing unit 13 does not couple from the LP01 mode to the LP11b mode. This is because the mode coupled from the LP01 mode is the LP11a mode having two peaks in the horizontal direction of the waveguide, and the LP11b mode having two peaks in the vertical direction is not coupled to any mode (for example, See Patent Document 4.). FIG. 2 shows electric field distributions in various modes.

  All the power of the LP11a mode that has passed through the first multiplexing / demultiplexing unit 13 is converted to the LP11b mode by the mode rotator 14. This is for the following reason. In the second multiplexing / demultiplexing unit 15, the light of the LP01 mode input from the port P3 is combined into the three-mode waveguide 11 as the LP01 and LP11a modes. For this reason, in the second multiplexing / demultiplexing unit 15, a total of three types of incident light, that is, the LP01 and LP11a modes transmitted from the first multiplexing / demultiplexing unit 13 and the LP01 mode transmitted from the port P3 through the single-mode waveguide 12 are used. After merging with the pattern, it can be coupled only to a total of two modes, LP01 and LP11a modes. This causes a loss in the second multiplexer / demultiplexer 15.

  Therefore, the LP11a mode propagated from the first multiplexer / demultiplexer 13 is converted into the LP11b mode by the mode rotator 14. In the second multiplexing / demultiplexing unit 15, since the structures of the input three-mode waveguide 11 and the output three-mode waveguide 11 are substantially equal, the LP01 mode and the LP11b mode propagated from the three-mode waveguide 11 are not mode-converted. To the second multiplexing / demultiplexing unit 15. On the other hand, the LP01 mode propagating through the single mode waveguide 12 from the port P3 is split and multiplexed in the second multiplexing / demultiplexing unit 15 into the LP01 mode and the LP11a mode.

  Lastly, the mode rotator 16 installed after the second multiplexing / demultiplexing unit 15 and converting half of the power of the LP11a mode and the LP11b mode reduces the power of the signal incident from each port to the LP01, LP11a, LP11b mode. And are multiplexed. That is, as shown in FIG. 1B, the light of the LP01 mode incident from the ports P1 and P2 is distributed to all the propagation modes (LP01, LP11a, LP11b), and is transmitted to the port P4 of the three-mode waveguide 11. They will be multiplexed. Similarly, the second multiplexing / demultiplexing unit 15 also distributes the LP01-mode light incident from P3 to all the propagation modes (LP01, LP11a, LP11b) and multiplexes the light into the port P4 of the three-mode waveguide 11. Will be.

  FIG. 3 shows the structure of the mode rotator (14, 16). The mode rotator is a waveguide having a waveguide width w and height h, and includes a trench layer provided with a groove in at least a part of the cross section. FIG. 3 shows an example in which there is a trench having a depth ht and a width wt at the upper end of the waveguide, but the position and shape of the groove are arbitrary.

At this time, when the propagation constants of the LP11a and LP11b modes in the mode rotator are βa and βb, the length L of the mode rotator is (βa−βb) L = π (Equation 1)
Then, the LP11a or LP11b mode input to the mode exchanger is converted to LP11b or LP11a at the output end (for example, see Non-Patent Document 5).

Also, the length L of the mode rotator is (βa−βb) L = π / 2 (Equation 2)
, Half the power of the LP11a or LP11b mode is converted to the other mode.

  FIG. 4 is a diagram illustrating an example of design parameters of the mode multiplexer / demultiplexer 301. The definitions of the various structural parameters-variables are given in FIG. FIG. 5A is a view of the mode multiplexer / demultiplexer 301 as viewed from above, and FIG. 5B is a cross-sectional view of the mode rotators (14, 16). FIG. 6 is a diagram illustrating a calculation result of the insertion loss of the mode multiplexer / demultiplexer 301. It can be seen that the light incident from any port is distributed into three modes. Loss is less than 0.2 dB at all ports. The mode power ratio has the lowest LP01 mode power of the light incident from the port P3 and is about 10%.

  FIG. 7 shows a calculation result of the wavelength dependence of loss in the mode multiplexer / demultiplexer 301. The mode multiplexer / demultiplexer 301 has a very wide low-loss operation band as compared with the PLC type mode multiplexer / demultiplexer using the parallel waveguide of the related art. FIG. 8 shows the mode power ratio of each wavelength band in the mode multiplexer / demultiplexer 301. Even when the wavelength changes, the light incident from each port is distributed to all modes, and it can be seen that the mode distribution ratio does not change significantly with respect to the wavelength.

  When a mode-multiplexed signal is input from the port P4, it is split into the ports P1 to P3, and the mode multiplexer / demultiplexer 301 can be used as a mode splitter. The loss characteristics and the wavelength characteristics at this time are the same as those in FIGS.

By the way, in order to reduce the power penalty to 1 dB or less in an optical communication system, the crosstalk between signals must be -26 dB or less as described in Non-Patent Document 6.
However, in the present embodiment, since the mode distribution in the mode multiplexer / demultiplexer can be compensated by the MIMO signal processing on the receiving side, the crosstalk between the signals does not need to be −26 dB or less. Rather, a mode distribution ratio of -26 dB or less cannot reduce the quality difference between signals. Therefore, it is considered that the minimum distribution ratio of the significant mode for reducing the signal quality difference is -25 dB or more. In the mode multiplexer / demultiplexer according to the present embodiment, in order to reduce the quality difference between signals, it is necessary to design each parameter so that the mode distribution ratio is -25 dB or more.

(Embodiment 2)
FIG. 9A is a diagram illustrating the second mode multiplexer / demultiplexer 302. The mode multiplexer / demultiplexer 302 is a four-mode multiplexer / demultiplexer. The mode multiplexer / demultiplexer 302 multiplexes the light from the port P1, port P2, port P3, and port P4 on the demultiplexing side to the port P5 on the multiplexing side, and transmits the light from the port P5 to the port P1, port P2, A planar optical circuit type mode multiplexer / demultiplexer for splitting light into ports P3 and P4,
A substrate 10;
A first three-mode waveguide 21a formed on the substrate 10 and having a mode rotator 22a between one end and the other end for exchanging all power between the LP11a mode and the LP11b mode; The other end of the first three-mode waveguide 21a is connected to the port P1 and the port P2 by the single-mode waveguide 12, respectively, and the LP01 mode and the first three-mode of the single-mode waveguide 12 are respectively connected. A first arm 100a having a first multiplexing / demultiplexing unit 23a that converts between the LP01 mode and the LP11a mode of the waveguide 21a;
A second three-mode waveguide 21b having a mode rotator 22b formed between the one end and the other end and exchanging all power between the LP11a mode and the LP11b mode, and The other end of the second three-mode waveguide 21b is connected to the port P3 and the port P4 by the single-mode waveguide 12, respectively, and the LP01 mode and the second three-mode of the single-mode waveguide 12 are connected. A second arm 100b having a second multiplexing / demultiplexing unit 23b that converts between the LP01 mode and the LP11a mode of the waveguide 21b;
A four-mode waveguide 25 formed on the substrate 10 and having one end connected to the port P5;
The other end of the four-mode waveguide 25 formed on the substrate 10 is connected to one end of the first three-mode waveguide 21a of the first arm 100a and one end of the second three-mode waveguide 21b of the second arm 100b. Then, the first three-mode waveguide 21a and the second three-mode waveguide 21b are converted into the LP01 mode and the LP01 mode and the LP11 mode of the four-mode waveguide 25, and the first three-mode waveguide 21a and the second A third multiplexer / demultiplexer 26 that converts the LP11b mode of the three-mode waveguide 21b into the LP11b mode and the LP21a mode of the four-mode waveguide 25;
It is characterized by having.

  The mode multiplexer / demultiplexer 302 includes a mode multiplexer / demultiplexer (first arm 100a and second arm 100a) including the first multiplexer / demultiplexer 13 and the mode rotator 14 of the mode multiplexer / demultiplexer 301 shown in FIG. 100b). Then, the third multiplexing / demultiplexing unit 26 combines the two-mode outputs of the first arm 100a and the second arm 100b at the Y-shaped convergence unit, and couples the output to the four-mode waveguide 25.

  As described in the first embodiment, the LP01 mode incident from each port is divided into LP01 and LP11a modes by the first multiplexing / demultiplexing unit 23a and the second multiplexing / demultiplexing unit 23b, and the three-mode waveguide (21a, 21b). The LP11a mode that has passed through the first multiplexing / demultiplexing unit 23a and the second multiplexing / demultiplexing unit 23b is then converted into the LP11b mode by the mode rotators (22a, 22b).

  Since the third multiplexing / demultiplexing unit 26 has two input waveguide structures that are substantially equal, the LP01 mode is distributed to the LP01 mode and the LP11a mode, similarly to the first multiplexing / demultiplexing unit 23a and the second multiplexing / demultiplexing unit 23b. . The LP11b mode is divided into the LP11b and LP21a modes because the mode that can be coupled is the LP21a mode (for example, see Non-Patent Document 4).

  As a result, as shown in FIG. 9B, the light of the LP01 mode incident from the ports P1 to P4 is distributed to all the propagation modes (LP01, LP11a, LP11b, LP21a), and the port P5 of the four-mode waveguide 25. Will be multiplexed.

  FIG. 10 is a diagram illustrating an example of design parameters of the mode multiplexer / demultiplexer 302. FIG. 11 is a diagram illustrating the calculation result of the insertion loss of the mode multiplexer / demultiplexer 302. In this structure, since all the Y junctions are target structures, the same loss characteristics can be obtained for light incident from any port. As a result, the power is almost equally distributed to all four modes, and the loss that is not coupled to any of the four modes is as low as 0.5 dB.

  When a 4-mode multiplexed signal is input from the port P5, it is split into the ports P1 to P4, and the mode multiplexer / demultiplexer 302 can be used as a mode splitter. The loss characteristics and wavelength characteristics at this time are the same as in FIG.

(Embodiment 3)
FIG. 12A is a diagram illustrating the third mode multiplexer / demultiplexer 303. The mode multiplexer / demultiplexer 303 is a 6-mode multiplexer / demultiplexer. The mode multiplexer / demultiplexer 303
Two mode multiplexers / demultiplexers 301;
Formed on the substrate 10, one end is connected to the multiplexing side port P5, and the square cross section at one end is converted into a non-square cross section at the other end, and the modes of LP21b and LP02 and the E13 and E31 modes A 6-mode waveguide 31 having a tapered portion 32 that converts
The other end of the 6-mode waveguide 31 is connected to the port P4 of each mode multiplexer / demultiplexer 301 and formed on the substrate 10, and the LP01 mode of the 3-mode waveguide 11 and the LP01 mode of the 6-mode waveguide 31 are connected. LP11a mode and LP21b mode are converted, LP11a mode of three-mode waveguide 11 and LP01 mode, LP11a mode, E13 mode and E31 mode of six-mode waveguide 31 are converted, and LP11b mode of three-mode waveguide 11 is converted. A fourth multiplexing / demultiplexing unit 33 that converts between the LP11b mode and the LP21a mode of the 6-mode waveguide 31,
Is provided.

The mode multiplexer / demultiplexer 303 includes the two mode multiplexers / demultiplexers 301 shown in FIG. 1, and is a fourth multiplexer / demultiplexer of a Y-shaped junction where the output of each port 4 is merged with the 6-mode waveguide 31. It has a part 33.
The LP01 mode output from the port 4 of the mode multiplexer / demultiplexer 301 is coupled to LP01, LP11a or LP21b in the fourth multiplexer / demultiplexer 33.
The LP11a mode output from the port 4 of the mode multiplexer / demultiplexer 301 is combined with the LP01, E13 or E31 mode in the fourth multiplexer / demultiplexer 33.
The LP11b mode output from the port 4 of the mode multiplexer / demultiplexer 301 is coupled to the LP11b or LP21a in the fourth multiplexer / demultiplexer 33.
The relationship between the coupling modes is as described in Non-Patent Document 7.

  As described in Non-Patent Document 7, in the non-square waveguide, the waveguide modes corresponding to the LP21b and LP02 modes are E13 and E31 modes, and the last of the 6-mode waveguide 31 (the front stage of the port P5). The LP21b and LP02 modes can be obtained by providing the tapered portion 32 for converting the non-square waveguide into a square shape.

  As a result, as shown in FIG. 12B, the light of the LP01 mode incident from the ports P1 to P6 is distributed to all the propagation modes (LP01, LP11a, LP11b, LP21a, LP21b, LP02) and the 6-mode waveguide It will be multiplexed to 31 port P5.

  FIG. 13 is a diagram illustrating an example of design parameters of the mode multiplexer / demultiplexer 303. FIG. 14 is a view for explaining the calculation result of the insertion loss of the mode multiplexer / demultiplexer 303 (on the side of one mode multiplexer / demultiplexer 301). In this structure, since the fourth multiplexing / demultiplexing unit 33 is entirely a target structure, the same loss characteristics can be obtained even when light enters from the ports P1 to P3 on the other mode multiplexing / demultiplexing unit 301 side. 14, the mode multiplexer / demultiplexer 303 distributes the light input from the ports P1 to P3 to all six modes at a power of 5% or more. The mode multiplexer / demultiplexer 303 has a very low loss of 1.35 dB at the maximum when the input light is not coupled to any of the six modes.

(Embodiment 4)
FIG. 15 is a diagram illustrating the fourth mode multiplexer / demultiplexer 304. The mode multiplexer / demultiplexer 304 is an n (n is an integer of 3 or more) mode multiplexer / demultiplexer. The mode multiplexer / demultiplexer 304 includes:
N (where n is an integer of 3 or more) single-mode waveguides 12 on the demultiplexing side formed on the substrate 10;
A multiplexing-side n-mode waveguide 41 formed on the substrate 10;
The single-mode waveguides 12 are divided into groups of m (m is an integer of 2 or more), and the single-mode waveguides 12 are arranged in parallel with the substrate 10 in the group without gaps in the horizontal direction. A multiplexing / demultiplexing unit 43, which is stacked without gaps at different heights from the substrate 10 for each group, and connected to the n-mode waveguide 41;
Is provided.

In particular, the mode multiplexer / demultiplexer 304 includes:
the thickness of the n-mode waveguide 41 in the direction perpendicular to the substrate 10 is m times (m is an integer of 2 or more) times the thickness of the single-mode waveguide 12 in the direction perpendicular to the substrate 10;
the width of the n-mode waveguide 41 in the direction horizontal to the substrate 10 is n / m times the width of the single-mode waveguide 12 in the direction horizontal to the substrate 10;
The single-mode waveguides 12 are divided into m groups each having n / m lines, are arranged in parallel with the substrate 10 in the group without any gap, and have different heights from the substrate 10 for each group. It is preferable that the layers are stacked without being connected to the n-mode waveguide 41.

  The mode multiplexer / demultiplexer 304 has a Y-shaped multiplexing / demultiplexing portion 43 in which n single-mode waveguides 12 merge into one n-mode waveguide 41. In the multiplexing / demultiplexing unit 43, the n single-mode waveguides 12 are divided into m (m is 2 or more) groups having the same position in the height direction of the planar waveguide. In FIG. 15, n is 6 and m is 2 which is a 6-mode multiplexer / demultiplexer.

  FIG. 16 is a diagram for explaining the definition of the design parameters of the mode multiplexer / demultiplexer 304. FIG. 17 is a diagram illustrating an example of design parameters of the mode multiplexer / demultiplexer 304. Since the width and height of each single-mode waveguide 12 are the same and m = 2, the height of each single-mode waveguide 12 is half the value of the six-mode waveguide 41.

  FIG. 18 is a diagram illustrating a calculation result of the insertion loss of the mode multiplexer / demultiplexer 304. It can be seen that the light incident from any port is distributed into six modes. Loss is less than 0.2 dB at all ports. From the results, it can be seen that the power of any single mode waveguide 12 is distributed to all six modes of the six mode waveguide 41. The loss that does not couple to any of the six modes is a very low loss of 1.3 dB at the maximum. Also, regardless of which port is incident, power of -20 dB or more is distributed to any mode.

  The combination of n and m of the mode multiplexer / demultiplexer 304 can be freely set. In addition to the combinations of n = 6 and m = 2 in FIG. 15, for example, n = 3, m = 2, n = 10, m = 2, or m = 3 are also conceivable. In the present embodiment, an example in which all the single-mode waveguides 12 are uniformly connected to the 6-mode waveguide 41 at the multiplexing unit 43 has been described. However, n = 3, m = 2, n = 10, m = 2 or m = 3, each single-mode waveguide 12 is not always connected to the n-mode waveguide 41 at the multiplexing section 43 evenly.

(Embodiment 5)
FIG. 19 is a diagram illustrating the mode multiplex transmission system 401 of the present embodiment. The mode multiplex transmission system 401 includes:
Two mode multiplexers / demultiplexers 310 in which ports on the respective multiplexing sides are connected by a multimode fiber 50;
A plurality of transceivers (55, 56) connected to each port on the demultiplexing side of the mode multiplexer / demultiplexer 310;
Is provided.

  The mode multiplexer / demultiplexer 310 is any of the mode multiplexers / demultiplexers 301 to 304 described in the first to fourth embodiments. The multimode fiber 50 has a number of propagation modes equal to or greater than the number of modes that the mode multiplexer / demultiplexers 301 to 304 can multiplex / demultiplex. The transceiver 55 and the transceiver 56 form a group for each wavelength to be transmitted and received. That is, the mode multiplex transmission system 401 is also a wavelength multiplex communication system.

  Since the mode multiplexer / demultiplexer 310 distributes the signal to all modes and propagates the signal, the transceivers 55 and 56 include a MIMO signal processing unit for compensating for crosstalk between signals after receiving the signal. The MIMO signal processing unit includes a plurality of FIR filters. For example, a MIMO equalizer using digital signal processing described in Non-Patent Document 8 can be used.

(Other embodiments)
In the present specification, the embodiment relating to the planar lightwave circuit using the SiO 2 -based material (quartz-based material) is described, but the material may of course be other materials. For example, even with a planar lightwave circuit using a semiconductor such as a Si-based or InGaAsP or an organic substance such as a polymer, the same effects as those of the embodiment described in this specification can be obtained.

  Further, the wavelength band to be used is about 1.5 to 1.6 μm in the examples described in this specification, but may be a mid-infrared region (2 μm or more) having a longer wavelength or a visible light band. Absent.

(The invention's effect)
The mode multiplexer / demultiplexer according to the present invention can reduce a signal quality difference in a mode multiplex system.
The mode multiplexer / demultiplexer of the present invention is of a PLC type and has low loss characteristics.

  The present invention can be applied to the information and communication industry.

10: substrate 11: three-mode waveguide 12: single-mode waveguide 12
13: first multiplexer / demultiplexer 14: first mode rotator 15: second multiplexer / demultiplexer 16: second mode rotators 21a and 21b: three-mode waveguides 22a and 22b: mode rotator 23a: first multiplex Demultiplexing part 23b: second multiplexing / demultiplexing part 25: four-mode waveguide 26: third multiplexing / demultiplexing part 31: six-mode waveguide 32: taper part 33: fourth multiplexing / demultiplexing part 41: n-mode waveguide 43 : Multiplexer / demultiplexer 55, 56: transceiver 100a: first arm 100b: second arm 301-304, 310: mode multiplexer / demultiplexer 401: mode multiplex transmission system

Claims (7)

A plane that multiplexes light from port 1, port 2 and port 3 on the demultiplexing side to port 4 on the multiplexing side, and demultiplexes light from port 4 to port 1, port 2 and port 3 An optical circuit type mode multiplexer / demultiplexer,
Board and
A three-mode waveguide formed on the substrate and having one end connected to the port 4;
The other end of the three-mode waveguide is connected to the port 1 and the port 2 by a single-mode waveguide, respectively, and the LP01 mode and the three-mode waveguide of the single-mode waveguide are respectively formed on the substrate. A first multiplexing / demultiplexing unit for converting between the LP01 mode and the LP11a mode of the wave path;
The three-mode waveguide formed on the substrate and connected between the one end and the other end and the port 3 are connected by a single-mode waveguide, and the LP01 mode and the three-mode of the single-mode waveguide are connected. A second multiplexing / demultiplexing unit that converts between the LP01 mode and the LP11a mode of the waveguide;
A first mode rotator formed in the three-mode waveguide between the first multiplexing / demultiplexing unit and the second multiplexing / demultiplexing unit and exchanging all power between the LP11a mode and the LP11b mode;
A second mode rotator formed in the three-mode waveguide between the second multiplexing / demultiplexing unit and the port 4 and exchanging half of power between the LP11a mode and the LP11b mode;
A mode multiplexer / demultiplexer comprising: The light from the port 1, port 2, port 3 and port 4 on the demultiplexing side is multiplexed to the port 5 on the multiplexing side, and the light from the port 5 is transmitted to the port 1, the port 2, the port 3 and the port 3. A planar optical circuit type mode multiplexer / demultiplexer for demultiplexing to port 4,
Board and
A first three-mode waveguide formed on the substrate, having a mode rotator between one end and the other end for exchanging all power between the LP11a mode and the LP11b mode, and formed on the substrate; The other end of the first three-mode waveguide is connected to the port 1 and the port 2 by single-mode waveguides, respectively, and the LP01 mode of each of the single-mode waveguides and the first three-mode waveguide are connected. A first arm having a first multiplexing / demultiplexing unit that converts between an LP01 mode and an LP11a mode of a wave path;
A second three-mode waveguide formed on the substrate and having a mode rotator between one end and the other end for exchanging all power between LP11a mode and LP11b mode, and formed on the substrate; And the other end of the second three-mode waveguide is connected to the port 3 and the port 4 by single-mode waveguides, respectively, and the LP01 mode of the single-mode waveguide and the second three-mode waveguide are connected. A second arm having a second multiplexing / demultiplexing unit that converts between the LP01 mode and the LP11a mode of the wave path;
A four-mode waveguide formed on the substrate and having one end connected to the port 5;
The other end of the four-mode waveguide formed on the substrate is connected to one end of the first three-mode waveguide of the first arm and one end of the second three-mode waveguide of the second arm. And converting the LP01 mode of the first three-mode waveguide and the second three-mode waveguide to the LP01 mode and the LP11a mode of the four-mode waveguide, and converting the first three-mode waveguide and the second A third multiplexing / demultiplexing unit that converts the LP11b mode of the two-mode waveguide into the LP11b mode and the LP21a mode of the four-mode waveguide;
A mode multiplexer / demultiplexer comprising: Two mode multiplexers / demultiplexers according to claim 1;
Formed on the substrate, one end is connected to the port 5 on the multiplexing side, the square cross section on one end is converted into a non-square cross section on the other end, and the modes of LP21b and LP02 and E13 and E31 modes A 6-mode waveguide having a tapered portion that converts
2. The other end of the 6-mode waveguide formed on the substrate and the port 4 of each of the mode multiplexers / demultiplexers according to claim 1, being connected to the LP01 mode of the 3-mode waveguide and the 6-mode waveguide. LP01 mode, LP11a mode and LP21b mode of the mode waveguide are converted, and LP11a mode of the three-mode waveguide and LP01 mode, LP11a mode, E13 mode and E31 mode of the six-mode waveguide are converted. A fourth multiplexing / demultiplexing unit that converts the LP11b mode of the mode waveguide and the LP11b mode and the LP21a mode of the 6-mode waveguide,
A mode multiplexer / demultiplexer comprising: N (n is an integer of 3 or more) single-mode waveguides on the demultiplexing side formed on the substrate;
A multiplexing-side n-mode waveguide formed on the substrate;
Dividing the single-mode waveguide into groups of m (m is an integer of 2 or more), arranging the single-mode waveguide in the group in a horizontal direction with respect to the substrate, and forming the single-mode waveguide; A different wavelength from the substrate for each group, stacked without gaps, a multiplexing / demultiplexing unit connected to the n-mode waveguide,
A planar optical circuit type mode multiplexer / demultiplexer comprising:   The mode multiplexer / demultiplexer according to claim 4, wherein a combination (n, m) of n and m is (3, 2) or (6, 2).   6. The mode coupling / demultiplexing device according to claim 1, wherein the single-mode signal light incident from the demultiplexing side is coupled to all the waveguide modes on the multiplexing side at −25 dB or more. 7. Corrugator. A mode multiplexer / demultiplexer according to any one of claims 1 to 6, wherein ports on the multiplexing side of each other are connected by a multimode fiber;
A plurality of transceivers connected to each port on the demultiplexing side of the mode multiplexer / demultiplexer,
Mode multiplex transmission system comprising: