Optical conversion apparatus and optical transmission system

Abstract

To reduce crosstalk between a plurality of optical signals generated in an optical transmission system including a multi-mode fiber.SOLUTION: In an optical transmission system S, a receiving side optical conversion apparatus 200 comprises: a mode converter 4 that inputs each of a plurality of optical input signals corresponding to a plurality of modes transmitted by a multi-mode fiber F3, which transmits an optical signal in a plurality of modes from a transmitting side optical conversion apparatus 100, into a plurality of cores of a multi-core fiber F4, and has a piezoelectric element 41 for changing a state of the multi-mode fiber F3; a fiber converter 5 that inputs a plurality of optical output signals outputted from the plurality of cores to a plurality of single-core fibers F5; a measurement unit 8 that measures a signal quality of a plurality of optical output signals outputted from the plurality of single-core fibers F5; and a state control unit 9 that changes the state of the multi-mode fiber F3 by controlling the piezoelectric element 41 based on the signal quality measured by the measurement unit 8.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical conversion device and an optical transmission system. [Background technology]

[0002] There is known a technique for multiplexing a plurality of optical signals using a multimode fiber that can transmit optical signals in a plurality of modes over a single physical transmission path. Patent Documents 1 and 2 disclose a MIMO (Multi-Input Multi-Output) equalization processing technique for suppressing crosstalk occurring between a plurality of optical signals corresponding to a plurality of modes transmitted by the multimode fiber. Patent Document 1 discloses a configuration in which a MIMO equalization processing is performed after a plurality of optical signals corresponding to a plurality of modes transmitted by the multimode fiber are input into a multicore fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 5878985 [Patent Document 2] Patent No. 7290172 Summary of the Invention [Problem to be solved by the invention]

[0004] In a configuration in which multiple optical signals corresponding to multiple modes transmitted through a multimode fiber are output from a multicore fiber, there was a problem in that crosstalk could not be sufficiently suppressed even when MIMO equalization processing was performed.

[0005] The present invention has been made in view of these points, and has as its object to reduce crosstalk between a plurality of optical signals that occurs in an optical transmission system including a multimode fiber. [Means for solving the problem]

[0006] An optical conversion device of a first aspect of the present invention is a mode converter that inputs each of a plurality of optical input signals corresponding to a plurality of modes transmitted by a multimode fiber that transmits optical signals in a plurality of modes into a plurality of cores of a multicore fiber, and includes: a mode converter having a piezoelectric element that changes the state of the multimode fiber; a fiber converter that inputs a plurality of first optical output signals output from the plurality of cores into a plurality of single-core fibers; a measurement unit that measures signal qualities of a plurality of second optical output signals output from the plurality of single-core fibers; and a state control unit that changes the state of the multimode fiber by controlling the piezoelectric element based on the signal quality measured by the measurement unit.

[0007] The multimode fiber may be wrapped around a side surface of the piezoelectric element, and the state control unit may apply a voltage based on the signal quality to the piezoelectric element to deform the piezoelectric element, thereby compressing or stretching the multimode fiber and changing the mode state of the multimode fiber.

[0008] The multimode fiber is coupled to the piezoelectric element such that a relative position between the multimode fiber and the multicore fiber changes due to deformation of the piezoelectric element, and the state control unit may change the relative position between the multimode fiber and the multicore fiber as the state of the multimode fiber by applying a voltage based on the signal quality to the piezoelectric element to deform the piezoelectric element.

[0009] The measuring unit may measure the signal quality of the second optical output signal based on the magnitude of the second optical output signal output from the single-core fiber corresponding to a mode in which the optical input signal is not input.

[0010] The measurement unit may measure an amount of crosstalk between two of the plurality of second optical output signals as the signal quality, and the state control unit may change the state so as to reduce an amount of crosstalk between the two second optical output signals whose measured amount of crosstalk is equal to or greater than a threshold.

[0011] The measurement unit may measure, as the signal quality, an amount of crosstalk of two second optical output signals corresponding to a combination in which the corresponding cores are adjacent, among a plurality of combinations of two second optical output signals in the plurality of second optical output signals.

[0012] The measurement unit may measure the S / N ratio of each of the plurality of optical output signals as the signal quality.

[0013] The measurement section may measure the signal qualities of the plurality of second optical output signals while the mode converter is receiving the plurality of optical input signals based on a predetermined training signal.

[0014] The measurement unit may repeat an operation of measuring the signal quality until the signal quality satisfies a predetermined condition after the state control unit changes the state based on the signal quality.

[0015] The measuring unit may measure the signal quality of the plurality of optical output signals over a predetermined period of time, and the state control unit may change the state over the predetermined period of time and control the piezoelectric element so that, when the predetermined period has elapsed, the piezoelectric element is in the state that resulted in the best signal quality during the predetermined period of time.

[0016] The optical fiber may further include a MIMO equalizer for suppressing crosstalk between two second optical output signals corresponding to two adjacent modes among the plurality of second optical output signals corresponding to the plurality of modes transmitted in the multimode fiber.

[0017] an input multi-core fiber; a first mode converter that converts the optical signals output from the first cores into a plurality of optical signals corresponding to a plurality of modes input to a multi-mode fiber that transmits in a plurality of modes; a second mode converter that inputs each of the optical input signals corresponding to the plurality of modes transmitted by the multi-mode fiber to a plurality of second cores of a second multi-core fiber, the second mode converter having a piezoelectric element that changes a state of the multi-mode fiber; a second fiber converter that inputs the first optical output signals output from the second cores into a plurality of second single-core fibers; a measurement unit that measures signal qualities of the second optical output signals output from the second single-core fibers; and a state control unit that changes the state of the multi-mode fiber by controlling the piezoelectric element based on the signal quality measured by the measurement unit. [Effects of the Invention]

[0018] The present invention provides an advantage in that it is possible to reduce crosstalk between a plurality of optical signals that occurs in an optical transmission system including a multimode fiber. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram for explaining an overview of an optical transmission system S. [Figure 2] FIG. 1 is a diagram for explaining a plurality of types of optical fibers. [Figure 3] 10 is a diagram for explaining the relationship between the multi-core fiber F2 and the multi-core fiber F4 and the multi-mode fiber F3. FIG. [Figure 4] FIG. 2 is a diagram illustrating an example of the configuration of a MIMO equalizer 7. [Figure 5] 10A and 10B are diagrams illustrating an example of the operation of the piezoelectric element 41. [Figure 6]10A and 10B are diagrams illustrating another example of the operation of the piezoelectric element 41. [Figure 7] FIG. 10 is a diagram showing the configuration of an optical transmission system S1 which is a modified example of the optical transmission system S. [Figure 8] 1 is a diagram showing the configuration of a MIMO equalizer 10 which is a modified example of the MIMO equalizer 7. FIG. [Figure 9] FIG. 10 is a diagram illustrating an example of the configuration of a second fiber converter 5, an optical receiver 6, and a MIMO equalizer 7 when the number of input and output signals is four. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Outline of Optical Transmission System S] Fig. 1 is a diagram for explaining an overview of an optical transmission system S. The optical transmission system S is a system for transmitting a plurality of signals via optical fiber. The optical transmission system S includes an optical converting device 100 on the transmitting side and an optical converting device 200 on the receiving side. In Fig. 1, two signals, a signal x1 and a signal x2, are shown as signals to be transmitted, but more signals may be transmitted in the optical transmission system S.

[0021] The optical transmission system S includes an optical transmitter 1 (optical transmitter 1-1, optical transmitter 1-2), a first fiber converter 2, a first mode converter 3, a second mode converter 4, a second fiber converter 5, an optical receiver 6 (optical receiver 6-1, optical receiver 6-2), a MIMO equalizer 7, a measurement unit 8, and a state control unit 9. At least one of the MIMO equalizer 7, the measurement unit 8, and the state control unit 9 is realized by, for example, a processor executing a program.

[0022] The optical transmitter 1 and the first fiber converter 2 are connected by a single-core fiber F1. The first fiber converter 2 and the first mode converter 3 are connected by a multi-core fiber F2. The first mode converter 3 and the second mode converter 4 are connected by a multi-mode fiber F3. The second mode converter 4 and the second fiber converter 5 are connected by a multi-core fiber F4. The second fiber converter 5 and the optical receiver 6 are connected by a single-core fiber F5.

[0023] FIG. 2 is a diagram for explaining several types of optical fibers. FIG. 2(a) shows cross-sectional views of a single-core fiber F1 and a single-core fiber F5. The white part in the center is the core, and the shaded part around it is the cladding. FIG. 2(b) shows cross-sectional views of a multi-core fiber F2 and a multi-core fiber F4. The multi-core fiber F2 and the multi-core fiber F4 shown in FIG. 2(b) have seven cores. FIG. 2(c) shows a cross-sectional view of a multi-mode fiber F3. The multi-mode fiber F3 shown in FIG. 2(c) has a core with a larger cross-sectional area than the cores of the single-core fiber F1 and the single-core fiber F5 shown in FIG. 2(a). The core of the multi-mode fiber F3 has several light transmission paths.

[0024] Multicore fiber has multiple transmission paths in a single fiber, which allows for high communication capacity, but it has the problem of high cost. Multimode fiber can transmit optical signals of multiple propagation modes over a single physical transmission path by changing polarization, etc., and can achieve both high communication capacity and low cost. However, multimode fiber generally requires MIMO equalization processing because crosstalk occurs.

[0025] Fig. 3 is a diagram for explaining the relationship between the multicore fibers F2 and F4 and the multimode fiber F3. In the example shown in Fig. 3, the multimode fiber F3 can transmit optical signals in six modes, namely, LP01, LP11a, LP11b, LP21a, LP21b, and LP02, and in the second mode converter 4, the optical signals transmitted in each mode are input to any of the multiple cores of the multicore fiber F4.

[0026] Returning to FIG. 1, the configuration and operation of each unit of the optical transmission system S will be described. The optical transmitter 1 receives an input of a signal to be transmitted by the optical transmission system S, and inputs an optical signal based on the input signal to the single-core fiber F1. The optical transmitter 1 has, for example, a device that converts an electrical signal into an optical signal. The optical transmitter 1 may receive an input of an electrical signal, and input an optical signal generated after attenuating or amplifying the input electrical signal to the single-core fiber F1.

[0027] The first fiber converter 2 outputs optical signals input to the plurality of first single-core fibers F1 to the plurality of first cores of the input multi-core fiber F2. The first fiber converter 2 inputs, to each of the plurality of cores of the multi-core fiber F2, an optical signal received from a single-core fiber F1 associated in advance among the plurality of single-core fibers F1.

[0028] The first mode converter 3 converts the multiple optical signals output from the multiple first cores into multiple optical signals corresponding to the multiple modes that can be transmitted through the multimode fiber F3. In the first mode converter 3, the multicore fiber F2 and the multimode fiber F3 are arranged to face each other, and the multiple optical signals corresponding to the multiple modes generated by the first mode converter 3 are input to the multimode fiber F3.

[0029] The second mode converter 4 divides each of the optical signals corresponding to the modes transmitted by the multimode fiber F3, and inputs the divided optical input signals to the second cores of the second multicore fiber F4. The second mode converter 4 has a piezoelectric element 41 that deforms the multimode fiber F3 or changes the position of the multimode fiber F3. The piezoelectric element 41 is, for example, a piezoelectric vibration actuator.

[0030] The second fiber converter 5 inputs the plurality of first optical output signals output from the plurality of second cores of the multi-core fiber F4 to the plurality of second single-core fibers F5.

[0031] The optical receiver 6 receives the optical signal (first optical output signal) output by the single-core fiber F5 and converts the received first optical output signal into an electrical signal. The optical receiver 6 outputs the generated electrical signal to the MIMO equalizer 7 and the measurement unit 8. In the example shown in FIG. 1, the optical receiver 6-1 outputs an electrical signal y1, and the optical receiver 6-2 outputs an electrical signal y2.

[0032] The MIMO equalizer 7 restores the multiple signals input to the optical transmitter 1 based on the multiple electrical signals input from the multiple optical receivers 6. Specifically, the MIMO equalizer 7 generates an output signal x1' corresponding to the signal x1 input to the optical transmitter 1-1 based on the electrical signal y1, and generates an output signal x2' corresponding to the signal x2 input to the optical transmitter 1-2 based on the electrical signal y2. The MIMO equalizer 7 suppresses crosstalk between two second optical output signals corresponding to two adjacent modes out of the multiple second optical output signals corresponding to the multiple modes transmitted in the multimode fiber.

[0033] 4 is a diagram showing an example configuration of the MIMO equalizer 7. The MIMO equalizer 7 has attenuators 71, 72, 73, 74, operational amplifiers 75, and 76. The attenuation factor of the attenuator 71 is h11, the attenuation factor of the attenuator 72 is h12, the attenuation factor of the attenuator 73 is h21, and the attenuation factor of the attenuator 74 is h22.

[0034] Electrical signal y1 is input to attenuator 71 and attenuator 73. Electrical signal y2 is input to attenuator 72 and attenuator 74. The signal attenuated in attenuator 71 and the signal attenuated in attenuator 72 are input to operational amplifier 75. The signal attenuated in attenuator 73 and the signal attenuated in attenuator 74 are input to operational amplifier 76. Operational amplifier 75 generates output signal x1' based on the difference between the two input signals. Operational amplifier 75 generates output signal x2' based on the difference between the two input signals.

[0035] Returning to Fig. 1, the measurement unit 8 measures the signal quality of the plurality of optical signals (second optical output signals) output from the plurality of second single-core fibers F5. The measurement unit 8 measures the signal quality of the plurality of second optical output signals, for example, by analyzing the plurality of electrical signals output from the optical receiver 6. Specifically, the measurement unit 8 measures the amount of crosstalk between two of the plurality of second optical output signals output from the second fiber converter 5 as the signal quality.

[0036] The measurement unit 8 measures the signal quality of the second optical output signal based on the magnitude of the second optical output signal output from the single-core fiber F5 corresponding to the mode in which no optical input signal is input. Specifically, the measurement unit 8 measures the magnitude of the electrical signal converted by the optical receiver 6 from the second optical output signal output from the single-core fiber F5 corresponding to the mode in which no optical input signal is input as the amount of crosstalk, thereby measuring the signal quality of the second optical output signal.

[0037] When crosstalk does not occur, the second optical output signal output from the single-core fiber F5 corresponding to the mode in which no optical input signal is input is zero, whereas when crosstalk occurs, the second optical output signal is not zero. Therefore, the measurement unit 8 determines that the signal quality of the second optical output signal is poor when the second optical output signal output from the single-core fiber F5 corresponding to the mode in which no optical input signal is input is equal to or greater than a threshold. The measurement unit 8 may output a score indicating the signal quality on a multi-level scale based on the magnitude of the second optical output signal.

[0038] In order to measure the amount of crosstalk, it is desirable that the measuring unit 8 recognizes the pattern of the transmitted signal. Therefore, the measuring unit 8 may measure the signal qualities of the plurality of second optical output signals output by the second fiber converter 5 while the mode converter is receiving the plurality of optical input signals based on a predetermined training signal.

[0039] As an example, the measuring unit 8 measures the amount of crosstalk by measuring the amount of a training signal included in an electrical signal output from the optical receiver 6-2 while a predetermined training signal (e.g., a sine wave) is input to the optical transmitter 1-1 and no signal is input to the optical transmitter 1-2. This allows the measuring unit 8 to measure the amount of crosstalk with a simple configuration and high accuracy.

[0040] The measuring unit 8 may convert the electrical signals y1 and y2 output by the optical receivers 6-1 and 6-2 in response to the transmission of the signals x1 and x2, which have different frequencies, into signals in the frequency domain, and measure the amount of crosstalk based on the magnitude of the frequency component of the signal x2 contained in the electrical signal y1 and the magnitude of the frequency component of the signal x1 contained in the electrical signal y2.

[0041] Crosstalk is likely to occur when cores are adjacent to each other. Therefore, the measuring unit 8 may measure, as signal quality, the amount of crosstalk of two second optical output signals corresponding to combinations of adjacent corresponding cores, among multiple combinations of two second optical output signals in the multiple second optical output signals output by the second fiber converter 5. This can shorten the time required for the measuring unit 8 to measure the signal quality.

[0042] The measuring unit 8 may measure, as the signal quality, the S / N ratio of each of the plurality of optical output signals output from the second fiber converter 5. The measuring unit 8 may, for example, identify the S / N ratio of each of the plurality of optical output signals based on the S / N ratios of the plurality of electrical signals output from the optical receiver 6 based on the plurality of optical output signals.

[0043] The state control unit 9 changes the state of the multimode fiber F3 by controlling the piezoelectric element 41 based on the signal quality measured by the measurement unit 8. The state control unit 9 changes the state of the multimode fiber F3, for example, to reduce the amount of crosstalk between two second optical output signals whose crosstalk amount measured by the measurement unit 8 is equal to or greater than a threshold value. The threshold value is a value stored in advance in memory.

[0044] The state control unit 9 changes the mode state of the multimode fiber F3 by, for example, applying a voltage based on the signal quality to the piezoelectric element 41 to deform the piezoelectric element 41, thereby compressing or elongating the multimode fiber F3 coupled to the piezoelectric element 41. The state control unit 9 may change the relative position of the multimode fiber F3 and the multicore fiber F4 by applying a voltage based on the signal quality to the piezoelectric element 41 to deform the piezoelectric element 41.

[0045] 5A and 5B are diagrams illustrating an example of the operation of the piezoelectric element 41. The piezoelectric element 41 has a positive electrode 411, a negative electrode 412, and a piezoelectric element 413. FIG. 5A is a top view of the piezoelectric element 41 (viewed from the direction in which the piezoelectric element 41 deforms). FIGS. 5B and 5C are cross-sectional views of the piezoelectric element 41 (viewed from a direction perpendicular to the direction in which the piezoelectric element 41 deforms). As shown in FIGS. 5B and 5C, a multimode fiber F3 is wound around the side of the piezoelectric element 413.

[0046] The state control unit 9 applies a voltage based on the signal quality between the positive electrode 411 and the negative electrode 412, thereby deforming the piezoelectric element 413. The voltage applied to the positive electrode 411 differs between the state shown in FIG. 5(b) and the state shown in FIG. 5(c), and the voltage applied to the piezoelectric element 413 in FIG. 5(c) is larger than the piezoelectric element 413 in FIG. 5(b). As a result, in the state shown in FIG. 5(c), the multimode fiber F3 is elongated more than in the state shown in FIG. 5(b). This changes the mode state of the multimode fiber F3, thereby changing the state of crosstalk.

[0047] Fig. 6 is a diagram showing another example of the operation of the piezoelectric element 41. In the example shown in Fig. 6, the multimode fiber F3 is coupled to the piezoelectric element 41 via a coupling member 414 such that the relative position between the multimode fiber F3 and the multicore fiber F4 changes due to deformation of the piezoelectric element 41. Fig. 6(a) and Fig. 6(b) respectively show states in which the state control unit 9 applies different voltages to the piezoelectric element 41. The piezoelectric element 413 deforms in accordance with the voltage applied to the piezoelectric element 41 by the state control unit 9, changing the position of the multimode fiber F3, thereby changing the relative position between the multimode fiber F3 and the multiple cores of the multicore fiber F4.

[0048] As described above, the state control unit 9 controls the piezoelectric element 41 to deform the piezoelectric element 41, thereby changing the state of the multimode fiber F3, which can change the state of crosstalk and improve signal quality. However, the signal quality may not be improved to the desired level just by changing the state of the multimode fiber F3 once by the state control unit 9. Therefore, after the state control unit 9 changes the state based on the signal quality, the measurement unit 8 may repeatedly measure the signal quality until the signal quality satisfies a predetermined condition, and the state control unit 9 may again change the state of the multimode fiber F3 based on the measured signal quality.

[0049] Furthermore, there may be cases where signal quality deteriorates due to the state control unit 9 changing the relative position. Therefore, the measurement unit 8 may measure the signal quality of a plurality of optical output signals over a predetermined period, and the state control unit 9 may change the state of the multimode fiber F3 over the predetermined period, and when the predetermined period has elapsed, control the piezoelectric element 41 so that the state attains the best signal quality during the predetermined period. The predetermined period may be, for example, a period during which a predetermined training signal is input to the optical transmitter 1.

[0050] Specifically, the state control unit 9 stores the voltage in memory each time the state control unit 9 changes the voltage applied to the piezoelectric element 41 during a predetermined period. The measurement unit 8 measures the signal quality each time the state control unit 9 changes the voltage applied to the piezoelectric element 41 during a predetermined period, and stores a value indicating the measured signal quality in memory in association with the voltage stored by the state control unit 9. After the predetermined period has elapsed, the state control unit 9 identifies the best value among the multiple signal quality values ​​stored in memory, and identifies the voltage stored in association with the identified value. Thereafter, the state control unit 9 applies the identified voltage to the piezoelectric element 41, thereby achieving the best signal quality.

[0051] As described above, the optical converting device 200 can improve signal quality by including the measuring unit 8 that measures the signal quality of a plurality of optical output signals output from a plurality of single-core fibers F5, and the state control unit 9 that changes the state of the multimode fiber F3 by controlling the piezoelectric element 41 based on the signal quality measured by the measuring unit 8. Furthermore, since the signal quality is improved by changing the state of the multimode fiber F3, it is possible to simplify the implementation configuration for MIMO equalization processing.

[0052] [First Modification] 7 is a diagram showing the configuration of an optical transmission system S1, which is a modified example of the optical transmission system S. The measuring unit 8 in the optical transmission system S1 differs from that in the optical transmission system S in that it measures signal quality based on the output signals x1' and x2' output by the MIMO equalizer 7, but is otherwise the same. With the optical transmission system S1 configured in this way, the state of the multimode fiber F3 can be changed to suit the performance of the MIMO equalizer 7, making it possible to improve signal quality regardless of the performance of the MIMO equalizer 7.

[0053] [Second Modification] 8 is a diagram showing the configuration of a MIMO equalizer 10 which is a modified example of the MIMO equalizer 7. The MIMO equalizer 10 has an optical fiber branching unit 11, an optical fiber coupler 12, and a balanced photodiode 13.

[0054] The optical fiber branching unit 11 inputs the signal y1 to a first terminal of the optical fiber coupler 12-1 and a first terminal of the optical fiber coupler 12-2, and inputs the signal y2 to a second terminal of the optical fiber coupler 12-1 and a second terminal of the optical fiber coupler 12-2. The optical fiber coupler 12-1 has a branching ratio of h11:h21, and the optical fiber coupler 12-2 has a branching ratio of h12:h22.

[0055] The signal output from the optical fiber coupler 12-1 is input to both ends of the balanced photodiode 13-1, and an output signal x1' is output from the junction of the multiple diodes of the balanced photodiode 13-1. The signal output from the optical fiber coupler 12-2 is input to both ends of the balanced photodiode 13-2, and an output signal x2' is output from the junction of the multiple diodes of the balanced photodiode 13-2. In the optical conversion device 200, the state of the multimode fiber F3 changes and the signal quality improves, so equalization processing can also be performed by such a MIMO equalizer 10.

[0056] [Third Modification] 1 illustrates an example in which the number of input and output signals is two, but the number of input and output signals may be greater. Fig. 9 is a diagram showing an example of the configuration of the second fiber converter 5, optical receiver 6, and MIMO equalizer 7 in which the number of input and output signals is four.

[0057] In the example shown in FIG. 1, all transmitted signals are input to the MIMO equalizer 7. However, if the number of input and output signals increases, performing equalization processing based on all signals will complicate the equalization processing. Therefore, the MIMO equalizer 7 shown in FIG. 9 performs equalization processing to suppress crosstalk between two first optical signals corresponding to two adjacent modes among multiple optical signals of multiple modes transmitted through the multimode fiber F3. In the optical conversion device 200, the state of the multimode fiber F3 changes, improving signal quality, so that it is possible to reduce the number of optical signals to be subjected to equalization processing. This simplifies the configuration of the MIMO equalizer 7 and shortens the time required for equalization processing.

[0058] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0059] 1 Optical transmitter 2. First fiber converter 3 First mode converter 4 Second mode converter 5. Second fiber converter 6 Optical receiver 7 Equalizer 8. Measurement section 9 State control section 10 Equalizer 11 Optical fiber branching section 12 Optical Fiber Coupler 13 Balanced Photodiode 41 Piezoelectric element 71 Attenuator 72 Attenuator 73 Attenuator 74 Attenuator 75 Operational Amplifier 76 Operational Amplifier 100 Photoconversion device 200 Photoconversion device 411 Positive electrode 412 Negative electrode 413 Piezoelectric element 414 Connecting members

Claims

1. a mode converter that inputs a plurality of optical input signals corresponding to a plurality of modes transmitted by a multimode fiber that transmits optical signals in a plurality of modes into a plurality of cores of the multicore fiber, the mode converter having a piezoelectric element that changes the state of the multimode fiber; a fiber converter that inputs a plurality of first optical output signals output from the plurality of cores into a plurality of single-core fibers; a measurement unit that measures signal qualities of a plurality of second optical output signals output from the plurality of single-core fibers; a state control unit that changes a state of the multimode fiber by controlling the piezoelectric element based on the signal quality measured by the measurement unit; A light conversion device having:

2. the multimode fiber is wound around a side surface of the piezoelectric element; the state control unit applies a voltage based on the signal quality to the piezoelectric element to deform the piezoelectric element, thereby compressing or expanding the multimode fiber and changing the mode state of the multimode fiber; 2. The optical conversion device of claim 1.

3. the multimode fiber is coupled to the piezoelectric element such that a relative position between the multimode fiber and the multicore fiber changes due to deformation of the piezoelectric element; the state control unit applies a voltage based on the signal quality to the piezoelectric element to deform the piezoelectric element, thereby changing the relative position of the multimode fiber and the multicore fiber as the state of the multimode fiber. The optical conversion device of claim 1 .

4. the measuring unit measures the signal quality of the second optical output signal based on a magnitude of the second optical output signal output from the single-core fiber corresponding to a mode in which the optical input signal is not input. The optical conversion device of claim 1 .

5. the measurement unit measures an amount of crosstalk between two of the plurality of second optical output signals as the signal quality; the state control unit changes the state so as to reduce the amount of crosstalk between the two second optical output signals whose measured crosstalk amount is equal to or greater than a threshold. The optical conversion device of claim 1 .

6. the measurement unit measures, as the signal quality, an amount of crosstalk of two second optical output signals corresponding to a combination in which the corresponding cores are adjacent to each other, among a plurality of combinations of two second optical output signals in the plurality of second optical output signals; The optical conversion device of claim 5 .

7. the measurement unit measures the S / N ratio of each of the plurality of optical output signals as the signal quality. The optical conversion device of claim 1 .

8. the measurement unit measures the signal qualities of the plurality of second optical output signals while the mode converter is receiving the plurality of optical input signals based on a predetermined training signal; The optical conversion device of claim 1 .

9. the measuring unit repeats an operation of measuring the signal quality until the signal quality satisfies a predetermined condition after the state control unit changes the state based on the signal quality; The optical conversion device of claim 1 .

10. the measurement unit measures the signal qualities of the plurality of optical output signals over a predetermined period of time; the state control unit changes the state over the predetermined period, and when the predetermined period has elapsed, controls the piezoelectric element so that the state is the state when the signal quality was best during the predetermined period. The optical conversion device of claim 1 .

11. the optical fiber further includes a MIMO equalizer for suppressing crosstalk between two second optical output signals corresponding to two adjacent modes among the plurality of second optical output signals corresponding to the plurality of modes transmitted in the multimode fiber.

11. A light conversion device according to any one of claims 1 to 10.

12. a plurality of first single-core fibers; a first fiber converter that outputs optical signals input to the plurality of first single-core fibers to a plurality of first cores of an input multi-core fiber; a first mode converter that converts the plurality of optical signals output from the plurality of first cores into a plurality of optical signals corresponding to a plurality of modes input to a multimode fiber that transmits in a plurality of modes; a second mode converter that inputs a plurality of optical input signals corresponding to a plurality of modes transmitted by the multimode fiber into a plurality of second cores of a second multicore fiber, the second mode converter having a piezoelectric element that changes a state of the multimode fiber; a second fiber converter that inputs the plurality of first optical output signals output from the plurality of second cores into a plurality of second single-core fibers; a measurement unit that measures signal qualities of a plurality of second optical output signals output from the plurality of second single-core fibers; a state control unit that changes a state of the multimode fiber by controlling the piezoelectric element based on the signal quality measured by the measurement unit; An optical transmission system having:

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