Data transmission system

Abstract

To realize a data transmission system, which applies vibration to an optical fiber cable and transmits data to a remote location using light modulated by the vibration, using only a single optical fiber in the optical fiber cable, without constructing a Mach-Zehnder interferometer.SOLUTION: The present disclosure relates to a data transmission system including a transmitting device that modulates transmission data and applies vibrations to an optical fiber with the modulated signal, an optical fiber that propagates light modulated by the vibrations in multiple modes, and a receiving device that demodulates the transmission data using at least one of the multiple modes of light propagated through the optical fiber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a technology related to a sensor network for easily realizing information collection from sensor devices installed in remote locations. [Background technology]

[0002] Non-Patent Document 1 shows a method of transmitting data to a remote location by applying vibration to an optical fiber cable and using light modulated by the vibration. In Non-Patent Document 1, sensor data from various sensors is modulated and vibration is applied from the outer sheath of the optical fiber cable by a vibration speaker. The light modulated by the vibration is received as interference light by a Mach-Zehnder interferometer. It is possible to demodulate the sensor data from various electrical sensors by demodulating the output signal of the optical receiver. So far, two-channel, 3-bps information transmission has been achieved using an experimental system using a Mach-Zehnder interferometer and spread spectrum method.

[0003] It is desirable to make the technology of Non-Patent Document 1 applicable to existing optical fiber networks. However, since Non-Patent Document 1 requires the configuration of a Mach-Zehnder interferometer, the configuration of an existing optical fiber network cannot be used as is. In addition, when using an existing optical fiber network, it is difficult to secure two optical propagation paths as a dedicated line. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Tetsuya Manabe, Ryoga Hashimoto, Hiroki Fujita, Atsushi Nakamura, and Yusuke Koshikiya, “Low-speed Data Transmission using a Modulated Vibration Signal on an Optical Cable's Outer Sheath”, Proceedings of the 27th International Conference on Optical Fiber Sensors, W4.3, (2022). [Non-Patent Document 2] Atsushi Nakamura, Tetsuya Manabe, and Yusuke Koshikiya, “Vibration Sensing Based on Inter-Modal Interference Using Two-Mode Region of Conventional Single-Mode Fibers”, Proceedings of the 27th International Conference on Optical Fiber Sensors, Th4.28, (2022). Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to make it possible to realize a data transmission system that applies vibration to an optical fiber cable and transmits data to a remote location using light modulated by the vibration, using only one optical fiber in the optical fiber cable, without constructing a Mach-Zehnder interferometer. [Means for solving the problem]

[0006] In this disclosure, instead of a Mach-Zehnder interferometer, a two-mode optical fiber vibration sensor described in Non-Patent Document 2 is used. The two-mode optical fiber vibration sensor can generate a phase difference θ due to the optical propagation time difference in a single optical fiber. Therefore, this disclosure can realize a data transmission device using a single optical fiber in an optical fiber cable.

[0007] In addition, in Non-Patent Document 1, the transmission speed during two-channel multiplex transmission is only 3 bps. For applications with high practicality such as image transmission, it is desirable to increase the information transmission speed, and for this purpose, it is effective to increase the carrier frequency of the modulated vibration. In this regard, the higher-order modes propagating through optical fibers are more sensitive to vibration than the fundamental mode. For this reason, by adopting a two-mode optical fiber vibration sensor, it is possible to increase the carrier frequency of the modulated vibration to a higher frequency than in Non-Patent Document 1, making it possible to achieve a higher transmission speed.

[0008] The data transmission system of the present disclosure includes: a transmitter that modulates transmission data and applies vibration to an optical fiber with the modulated signal; an optical fiber that propagates the light modulated by the vibration in a plurality of modes; a receiving device that demodulates the transmission data by using at least one of the light beams of the plurality of modes that have propagated through the optical fiber; Equipped with.

[0009] The data transmission system of the present disclosure executes the data transmission method of the present disclosure. The data transmission method of the present disclosure includes: A transmitter modulates data to be transmitted and applies vibration to an optical fiber with the modulated signal; the optical fiber propagates light modulated by vibrations applied to the optical fiber in a plurality of modes; A receiving device demodulates the transmission data using at least one of the light of the plurality of modes propagated through the optical fiber.

[0010] The transmitting device may perform the modulation using a carrier wave having a predetermined frequency, in which case the receiving device demodulates the transmission data using the same frequency as the carrier wave and a frequency twice that of the carrier wave.

[0011] For example, the demodulation device of the present disclosure A received optical signal having a plurality of modes modulated by the vibration is split, The first reception signal is demodulated at the same frequency as the carrier wave to obtain the first transmission data; The second reception signal is demodulated at a frequency twice that of the carrier wave to obtain the second transmission data. Either the first transmission data or the second transmission data is output.

[0012] The multiple modes may be a first higher-order mode and a fundamental mode. Since the first higher-order mode propagating through the optical fiber is more sensitive to refractive index changes caused by vibration or bending than the fundamental mode, it is possible to realize high-speed information transmission by increasing the frequency of modulated vibration.

[0013] The modulation may be differential phase shift keying. In this case, the receiving device may perform differential phase shift keying demodulation at the same angular frequency as the carrier wave and differential phase shift keying demodulation at an angular frequency twice that of the carrier wave.

[0014] The optical fiber vibration sensor may receive each of the light in the plurality of modes propagated through the optical fiber. In this case, the data transmission system according to the present disclosure may include a plurality of demodulators that receive the light modulated by the vibration in the plurality of modes and demodulate the received signals in the plurality of modes for each mode, and may select one of the plurality of transmission data obtained by the plurality of demodulators.

[0015] The optical fiber may have a single-mode propagation characteristic in a communication wavelength band, in which case the light modulated by the vibration may have a wavelength shorter than the communication wavelength band.

[0016] The above disclosures may be combined to the greatest extent possible. Effect of the Invention

[0017] According to the present disclosure, a data transmission system that applies vibration to an optical fiber cable and transmits data to a remote location using light modulated by the vibration can be realized using only one optical fiber in the optical fiber cable, without configuring a Mach-Zehnder interferometer. In addition, since it is possible to increase the carrier frequency of the modulated vibration to a higher frequency than that of Non-Patent Document 1, it is possible to achieve a higher transmission speed. [Brief description of the drawings]

[0018] [Figure 1] 1 illustrates an embodiment of a data transmission system according to the present disclosure. [Diagram 2] FIG. 2 is an explanatory diagram showing an example of a modulation method in a modulation device. [Diagram 3] FIG. 2 is an explanatory diagram showing an example of a demodulation method in a demodulation device. [Figure 4] 1 illustrates an embodiment of a data transmission system according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0020] (First embodiment) 1 shows an embodiment of a data transmission system according to the present disclosure. The data transmission system according to the present disclosure includes a transmitter 2 and a receiver 1. The transmitter 2 and the receiver 1 are connected by an optical fiber cable 120. The receiver 1 uses an optical fiber 114 included in the optical fiber cable 120 for a two-mode optical fiber vibration sensor 110.

[0021] The optical fiber 114 in this embodiment is a general-purpose single-mode optical fiber. At wavelengths shorter than the cutoff wavelength of the general-purpose single-mode optical fiber, not only the fundamental mode but also higher-order modes can propagate. Therefore, in this disclosure, light with a wavelength shorter than the communication wavelength band of the optical fiber 114 is used. In this embodiment, a wavelength shorter than the cutoff wavelength of the optical fiber 114 general-purpose single-mode optical fiber is propagated in the fundamental mode and the first higher-order mode. In this embodiment, an example will be described in which the wavelength shorter than the cutoff wavelength is in the 1 μm band of 1000 nm.

[0022] 1, a two-mode optical fiber vibration sensor 110 has a 1 μm band mode combining / branching coupler 113 connected to both ends of an optical fiber 114, a 1 μm band light source 111 connected to one end of the mode combining / branching coupler 113, and a fundamental mode photodetector 112 connected to the other end of the mode combining / branching coupler 113. The light source 111 outputs continuous light in the 1 μm band. The 1 μm band mode combining / branching couplers 113#1 and 113#2 combine and branch the 1 μm band light for each mode.

[0023] Fundamental mode light emitted from 1 μm band light source 111 is input to optical fiber 114 by 1 μm band mode multiplexing / branching coupler 113#1, passes through 1 μm band mode light multiplexing / branching coupler 113#2 on the opposite side, and is measured as a fundamental mode interference waveform by fundamental mode photodetector 112.

[0024] The transmitting device 2 modulates the transmission data and applies vibrations to the optical fiber 114 with the modulated signal. The receiving device 1 demodulates the transmission data using a reception signal received by a fundamental mode photodetector 112 from among the light of multiple modes propagated through the optical fiber 114. The receiving device 1 and transmitting device 2 of the present disclosure can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0025] Specifically, the transmitting device 2: A modulator 230 for modulating data acquired at a remote location; a vibration generator driver amplifier 220 for amplifying the modulated signal; a vibration generator 210 that applies vibration to the optical fiber cable 120 using the modulated signal amplified by the vibration generator drive amplifier; Equipped with.

[0026] Specifically, the receiving device 1 A fiber optic cable 120; a dual mode optical fiber vibration sensor 110 for detecting light modulated by vibrations on an optical fiber 114 in an optical fiber cable 120; a DC cutoff filter 130 for removing a DC component from the signal received by the two-mode optical fiber vibration sensor 110; a demodulation device 140 for demodulating transmission data from the received signal from which the DC component has been removed; Equipped with.

[0027] 2 shows an example of the configuration of the modulation device 230. An adder 231 adds transmission data d(t) to transmission data b(tT) one symbol time earlier, T. This generates differential data b(t). A phase modulator 233 phase-modulates the differential data b(t) with a carrier wave c(t) generated by a carrier wave generator 232. This makes it possible to obtain a modulated signal u(t). In this embodiment, the modulation in the modulation device 230 uses a differential phase-shift keying method at 0 radians and 2π / 3 radians. Differential phase shift keying may be abbreviated as DPSK (Differential Phase-Shift Keying).

[0028] 3 shows an example of the configuration of the demodulation device 140. The multiplied cosine wave generator 147 and the multiplied sine wave generator 148 generate the same frequency ω v The double cosine wave generator 149 and the double sine wave generator 150 generate a signal with an angular frequency 2ω that is twice that of the carrier wave generator 232. v In this manner, the demodulator 140 performs DPSK demodulation on the same angular frequency as the vibration applied to the optical fiber cable 120 by the transmitter 2 and on the twice angular frequency.

[0029] Transmission data acquired by various sensors and the like in remote locations is sent to the transmitter 2, which generates vibrations to be applied to the fiber cable 120. The modulator 230 creates a phase-modulated signal based on the transmission data. The modulated signal is amplified by the vibration generator driver amplifier 220 and drives the vibration generator 210 to apply vibrations to the outer sheath of the optical fiber cable 120.

[0030] In the optical fiber 114, light in the fundamental mode and the first higher order mode propagates in the 1 μm band, which is different from the communication wavelength. In addition, crosstalk between modes occurs due to bending of the optical fiber, core misalignment at the connector / fusion splice point, external vibration, etc., and mode conversion occurs from the fundamental mode to the first higher order mode and from the first higher order mode to the fundamental mode. When vibration according to the modulation signal is applied from the vibration generator 210 of the transmitting device 2, the interference waveform of the light in the two modes changes in response to this vibration, and a received signal can be obtained by the fundamental mode photoreceiver 112. After the DC component is removed from the received signal by the DC cutoff filter 130, the transmitted data is demodulated by the demodulator 140.

[0031] Here, the efficiency of conversion from the fundamental mode to the first higher-order mode in the entire optical fiber 114 is α, the efficiency of conversion from the first higher-order mode to the fundamental mode is β, and the electric field of the light incident on the two-mode optical fiber vibration sensor 110 in the fundamental mode is expressed by equation (1). Then, the interference waveform E of the fundamental mode and the first higher-order mode separated by the 1 μm-band mode combining / branching coupler 113#2 is expressed as follows: 01(t) and E 11 (t) is expressed by equation (2) and equation (3), respectively. E(t)=Eexp(i(ωt+φ)) (1) E 01 (t) = {(1-α) 2 +αβ}E(t) (2) E 11 (t) = α{(1-α) + (1-β)}E(t) (3) Here, ω is the angular frequency of the fundamental mode light incident on the optical fiber 114, and φ is the phase.

[0032] When the fundamental mode interference waveform is received by the fundamental mode receiver 112, the received signal is expressed as I 01 (t) The interference waveform of the first higher-order mode separated by the 1 μm band mode-multiplexing coupler 113#2 is I 11 If we set it to (t), we get equations (4) and (5). I 01 (t) = K | E 01 (t)| 2 =K{(1-α) 4 E 2 +α 2 β 2 E 2 +2αβ(1-α) 2 E 2 cos(φ 01a -φ 01b )} (4) I 11 (t) = K | E 11 (t)| 2 =K{α 2 (1-β)E 2 +α 2 (1-α) 2 E 2 +2a 2 (1-α)(1-β)E 2 cos(φ 11a -φ 11b )} (5) where K is the coefficient between the optical input and the electrical output of the fundamental mode optical receiver 112. 01a is the phase of the fundamental mode light, φ01b is the phase of the light converted from the first higher-order mode to the fundamental mode. φ 11a is the phase of the first higher-order mode light, φ 11b is the phase of the light that has been converted from the fundamental mode to the first higher-order mode.

[0033] From here, the fundamental mode interference waveform I 01 Consider the case where (t) is received. The vibration given to the optical fiber cable 120 is expressed by the following formula. u(t)=Acos(ω v t+Φ(t)) (6) Here, A is a constant that represents the relationship between the magnitude of the applied vibration and the phase difference caused by the vibration. v is the angular frequency of the applied vibration, and Φ(t) is the modulation phase that is changed according to the transmission data.

[0034] Here, if the phase difference due to the optical propagation time difference between the fundamental mode and the first higher-order mode at the time when the fundamental mode and the higher-order mode propagating through the two-mode optical fiber vibration sensor 110 reach the mode multiplexer / demultiplexer 113 is θ, the phase difference is expressed by the following equation. φ 01a -φ 01b =Acos(ω v t+Φ(t))-θ (7)

[0035] From equations (4), (6) and (7), the received signal I received by the fundamental mode receiver 112 is 01 (t) is expressed as follows.

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[0036] The received signal y(t) after passing through the DC cut filter 130 is expressed by the following equation.

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[0037] By demodulating the first and second terms of the obtained equation (8), it becomes possible to demodulate the transmitted data even when the value of the phase difference θ due to the optical propagation time difference between the fundamental mode and the first higher mode caused by the refractive index and polarization of the optical fiber 114 of the two-mode optical fiber vibration sensor 110 fluctuates.

[0038] When the modulation in the modulation device 230 is the DPSK modulation method, the k-th transmission data is d k Then, the data b that is actually modulated k is given by the following equation:

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[0039] Next, the data b obtained by equation (9) k Based on this, the phase modulator 233 calculates the phase Φ of the carrier generated by the carrier generator 232 according to the following equation: k Modulate the.

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[0040] When the optical fiber cable 120 is vibrated by the phase modulation of equation (10), the received signal is expressed by the following equation.

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[0041] For this received signal y(t), the angular frequency ω vThe sine wave and cosine wave of the signal z I1 (t), z Q1 (t) is expressed as follows. z I1 (t) = D1 sinθ cos(α + Φ k ) (12) z Q1 (t) = D1 sinθ sin(α + Φ k ) (13) Here, D1 is a constant.

[0042] Here, the signals delayed by one symbol time in delay devices 143-1I and 143-1Q are multiplied by multipliers 144-1I and 144-1Q to obtain the following signal. I1=D1 2 sin 2 θcos(α+Φ k )cos(α+Φ k-1 ) (14) Q1=D1 2 sin 2 θsin(α+Φ k )sin(α+Φ k-1 ) (15)

[0043] By adding I1 and Q1 in equations (14) and (15) by an adder 145-1, the following equation is obtained.

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[0044] Similarly, for the received signal y(t), the angular frequency is 2ω v The sine wave and cosine wave of the signal z after multiplying by multipliers 141-2I and 141-2Q and passing through low-pass filters 142-2I and 142-2Q is I2 (t), z Q2 (t) is expressed as follows. z I2 (t) = D2cosθcos(2α+2Φ k ) (17) z Q2(t) = D2cosθsin(2α+2Φ k ) (18) where D2 is a constant.

[0045] Here, the signals delayed by one symbol time in delay devices 143-2I and 143-2Q are multiplied by multipliers 144-2I and 144-2Q to obtain the following signals. I2=D2 2 cos 2 θcos(2α+2Φ k )cos(2α+2Φ k-1 ) (19) Q2=D2 2 cos 2 θsin(2α+2Φ k )sin(2α+2Φ k-1 ) (20)

[0046] By adding I2 and Q2 in equations (19) and (20) by an adder 145-2, the following equation is obtained.

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[0047] The following two demodulated signals p1 and p2 are obtained from the phase-modulated received signal y(t) given by equation (10).

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[0048] The magnitudes of the obtained demodulated signals p1, p2 vary depending on the state of the phase difference θ due to the optical propagation time difference between the fundamental mode and the first higher mode caused by the influence of the refractive index and polarization of the optical fiber 114 of the two-mode optical fiber vibration sensor 110, so the discrimination of the demodulated transmission data may differ. Therefore, the discriminator 146 discriminates between 0 and 1 of the transmission data obtained by demodulation from the two demodulated signals p1, p2 expressed by equations (22) and (23) according to the following criteria.

[0049] First, the discrimination results R1 and R2 of the transmission data are obtained from the demodulated signals p1 and p2.

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[0050] If there is no difference between the two judgment results R1 and R2, the transmission data d' is calculated using the following formula: k Determine. d' k =R1(=R2) (26)

[0051] If there is a difference between the two judgment results R1 and R2, the judgment result R1 or R2 with the larger absolute value of the demodulated signals p1 and p2 is used to obtain the transmission data d' k Determine.

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[0052] The above modulation and demodulation method makes it possible to reliably demodulate the transmitted data even when the phase difference θ due to the optical propagation time difference between the fundamental mode and the first higher order mode caused by the refractive index and polarization of the optical fiber 114 of the two-mode optical fiber vibration sensor 110 fluctuates. 01 The first higher-order mode interference waveform I 11 The same applies when (t) is received.

[0053] Second embodiment 4 shows an embodiment of the data transmission system of the present disclosure. The present disclosure may include a plurality of demodulation devices 140 that receive light of a plurality of modes propagated through an optical fiber 114 and demodulate the received signals of the plurality of modes for each mode. In this embodiment, an interference waveform of the fundamental mode and an interference waveform of the first higher order mode are simultaneously received.

[0054] Specifically, the two-mode optical fiber vibration sensor 110 comprises an optical fiber cable 120, two mode-combining / branching couplers 113 connected to both ends of the optical fiber cable 120, a light source 111 connected to one end of the mode-combining / branching coupler 113, and a fundamental mode receiver 112 and a first higher mode receiver 115 connected to the other end of the mode-combining / branching coupler 113.

[0055] The receiving device 1 of this embodiment also includes a DC cut filter 130 and a demodulator 140 for each of the fundamental mode receiver 112 and the first higher mode receiver 115. The receiving device 1 of this embodiment also includes a mode diversity determiner 160 to which the transmission data demodulated in the two demodulators 140 is input.

[0056] The fundamental mode and first higher mode interference waveforms separated by the 1 μm band mode combining / branching coupler 113 are received by the fundamental mode photoreceiver 112 and the first higher mode photoreceiver 115. The reception signals received by the fundamental mode photoreceiver 112 and the first higher mode photoreceiver 115 pass through a DC cut filter 130, and are then demodulated by a demodulator 140. A mode diversity determiner 160 compares the transmission data demodulated from the fundamental mode interference waveform with the transmission data demodulated from the first higher mode interference waveform, and if they do not match, outputs the transmission data with the larger amplitude when demodulated by the demodulator 140.

[0057] For example, the transmitted data demodulated from the fundamental mode interference waveform is d' LP01 , the amplitude at demodulation is A LP01 , the transmission data demodulated from the interference waveform of the first higher-order mode is d' LP11 , the amplitude at demodulation is A LP11 In this case, the final transmission data d^ is determined as follows.

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[0058] As described above, by demodulating the two interference waveforms of the fundamental mode and the first higher-order mode obtained from the two-mode optical fiber vibration sensor, it is possible to demodulate the transmitted data even if the state of inter-mode crosstalk changes and one of the interference waveforms can no longer be observed.

[0059] (Effects of the present disclosure) As described above, according to the present invention, in a method in which vibration is applied from the outer sheath of an optical fiber cable, it is possible to realize a data transmission device using only one optical fiber in an optical fiber cable.

[0060] In addition, since the first higher-order mode propagating through the optical fiber is more sensitive to vibration than the fundamental mode, it is possible to increase the carrier frequency of the modulated vibration, thereby enabling an increase in transmission speed.

[0061] In the above embodiment, the fundamental mode and the first higher-order mode are used, but the multiple modes in the present disclosure are not limited to this. In addition, a general-purpose single-mode optical fiber is used for the optical fiber 114, but the present disclosure is not limited to this, and any mode that propagates multiple modes can be adopted. In addition, the transmission data transmitted in the present disclosure is not limited to sensor data of various electric sensors, and any data can be transmitted. [Explanation of symbols]

[0062] 1. Receiving device 2.Transmitting device 110.2 mode optical fiber vibration sensor 111.1μm band light source 112. Basic mode receiver 113.1μm band mode-multiplexing coupler 114. Optical Fiber 115. First higher mode receiver 120. Fiber optic cable 130. DC blocking filter 140. Demodulator 141. Multiplier 142. Low-pass filter 143. Delay Unit 144. Multiplier 145. Adder 146. Classifier 147. Same-times cosine wave generator 148. Multiplied sine wave generator 149.2x cosine wave generator 150.2x sine wave generator 160. Mode diversity determination device 210. Vibration Generator 220. Vibration generator driver amplifier 230. Modulation device 231. Adder 232. Carrier Generator 233. Phase Modulator

Claims

1. a transmitter that modulates transmission data and applies vibration to an optical fiber with the modulated signal; an optical fiber that propagates the light modulated by the vibration in a plurality of modes; a receiving device that demodulates the transmission data by using at least one of the light beams of the plurality of modes that have propagated through the optical fiber; A data transmission system comprising:

2. The transmitting device performs the modulation using a carrier wave having a predetermined frequency; The receiving device demodulates the transmission data using a frequency equal to the carrier wave and a frequency twice that of the carrier wave.

2. The data transmission system according to claim 1, wherein:

3. the modulation is differential phase shift keying; The receiver performs differential phase shift demodulation at the same angular frequency as the carrier wave and differential phase shift demodulation at twice the angular frequency of the carrier wave.

3. The data transmission system according to claim 2, wherein:

4. The plurality of modes are a fundamental mode and a first higher order mode.

2. The data transmission system according to claim 1.

5. the optical fiber has a single-mode propagation characteristic in a communication wavelength band; The light modulated by the vibration has a wavelength shorter than the communication wavelength band.

2. The data transmission system according to claim 1.

6. receiving light modulated by the vibration in the plurality of modes; a plurality of demodulation devices for demodulating the reception signals of the plurality of modes for each mode; Selecting one of the plurality of transmission data obtained by the plurality of demodulation devices.

2. The data transmission system according to claim 1.

7. A transmitter modulates data to be transmitted and applies vibration to an optical fiber with the modulated signal; the optical fiber propagates light modulated by vibrations applied to the optical fiber in a plurality of modes; a receiving device demodulating the transmission data by using at least one of the light beams in the plurality of modes propagated through the optical fiber; Data transmission method.

8. A received optical signal having a plurality of modes modulated by the vibration is split, demodulating the branched first received signal at the same frequency as the carrier wave to obtain first transmission data; The second reception signal is demodulated at a frequency twice that of the carrier wave to obtain second transmission data; outputting either the first transmission data or the second transmission data; Demodulator.

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