Communication system

Abstract

To provide a communication system that achieves an expansion of communication band and an extension of transmission distance by optical fibers.SOLUTION: A communication system includes an optical fiber FB, a first device 10 installed at one end side of the optical fiber FB and inputting a first transmission light R1 and a second transmission light R2 into the optical fiber FB, and a second device 20 installed at the other end side of the optical fiber FB and receiving the first transmission light R1 and the second transmission light R2 propagated through the optical fiber FB. The wavelength of the first transmission light R1 is shorter than the wavelength of the second transmission light R2 and is set in a band in which the absorption due to the Raman response of the optical fiber FB is 2 dB or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to communication systems. [Background technology]

[0002] Non-Patent Document 1 discloses a technique for amplifying light transmitted through an optical fiber by Raman amplification in order to extend the transmission distance through the optical fiber.

[0003] Non-Patent Document 2 discloses an optical fiber power supply technology that realizes power supply in remote locations by generating electricity using high-intensity light transmitted through an optical fiber and a photoelectric converter in a remote location. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] MN Islam, "Raman amplifiers for telecommunications," IEEE Journal of Selected Topics in Quantum Electronics, vol. 8, no. 3, pp. 548-559 (2002) [Non-patent document 2] K. Kurokawa et al., "Stimulated Raman Scattering and Power-over-Fiber Property of Multi-core Fiber," in Optical Fiber Communication Conference (OFC) 2022, paper Tu3F.3 (2022). Summary of the Invention [Problem to be solved by the invention]

[0005] In the Raman amplification used in the technology described in Non-Patent Document 1, high-intensity light with a frequency about 10 to 15 THz higher than the band to be amplified is used as pump light. On the other hand, when a band with a higher frequency than the high-intensity light is used as the communication band, the effect of the high-intensity light on communication quality is unknown, which causes a problem that the expansion of the communication band and the extension of the transmission distance by optical fiber are limited.

[0006] The present disclosure has been made in view of the above problems, and has as its object to provide a communication system that can realize an expansion of the communication band and an extension of the transmission distance using optical fiber. [Means for solving the problem]

[0007] In order to solve the above-described problems, a communication system according to one aspect of the present disclosure includes an optical fiber, a first device installed at one end of the optical fiber and inputting first and second transmission lights into the optical fiber, and a second device installed at the other end of the optical fiber and receiving the first and second transmission lights propagated through the optical fiber. The wavelength of the first transmission light is shorter than the wavelength of the second transmission light and is set to a band in which absorption due to Raman response of the optical fiber is 2 dB or less. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a communication system that can realize an expansion of the communication band and an extension of the transmission distance using optical fibers. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating a configuration of a communication system according to the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an example of Raman response characteristics of an optical fiber. [Figure 3] FIG. 10 is a diagram illustrating an example of the relationship between the Raman gain coefficient and the amount of absorption. [Figure 4] FIG. 10 is a diagram illustrating an example of a Raman response spectrum. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description, the same components are designated by the same reference numerals and redundant description will be omitted.

[0011] [Communication system configuration] 1 is a schematic diagram showing the configuration of a communication system according to the present disclosure. The communication system includes an optical fiber FB, a first device 10, and a second device 20.

[0012] The first device 10 is installed at one end of the optical fiber FB and inputs the first transmission light R1 and the second transmission light R2 into the optical fiber FB. For example, the first device 10 includes a transmitter circuit 11 that transmits the first transmission light R1 and a transmitter circuit 12 that transmits the second transmission light R2. The transmitted first transmission light R1 and second transmission light R2 are introduced into the optical fiber FB via a wavelength multiplexer CP1.

[0013] Here, the wavelength of the first transmission light R1 is set to be shorter than the wavelength of the second transmission light R2. The wavelength of the first transmission light R1 is set to be in a band in which the absorption due to the Raman response of the optical fiber FB is 2 dB or less. The wavelength range of the first transmission light R1 that is set will be described later.

[0014] The transmitter circuits 11 and 12 are equipped with a light source for optical power supply or communication. For example, the light source may be an LED (light emitting diode), a VCSEL (vertical emitting semiconductor laser), a DPL (double pulse laser), or the like. LEDs are low cost and highly durable, while VCSELs have high output and high accuracy, and are therefore used for applications such as data transmission. DPLs are highly efficient and high output, and are used for high-speed data transmission and high-accuracy distance measurement. Alternatively, the light source may be a fiber laser, or may be one in which light from the above-mentioned light sources is amplified and output by an amplifier.

[0015] The optical fiber FB propagates the first transmission light R1 and the second transmission light R2 from one end to the other. The first transmission light R1 and the second transmission light R2 propagate within the same core of the optical fiber FB. Note that the wavelengths of the light transmitted using the optical fiber FB are not limited to the wavelengths of the first transmission light R1 and the second transmission light R2. The wavelengths of the light transmitted using the optical fiber FB may be two or more.

[0016] The second device 20 is installed at the other end of the optical fiber FB and receives the first transmission light R1 and the second transmission light R2 propagated through the optical fiber FB. For example, the second device 20 includes a receiving circuit 21 and a receiving circuit 22. The first transmission light R1 and the second transmission light R2 output from the optical fiber FB are separated by a wavelength demultiplexer CP2, and the first transmission light R1 is introduced into the receiving circuit 21, and the second transmission light R2 is introduced into the receiving circuit 22.

[0017] Here, the receiving circuit 22 may be an opto-electrical converter that converts the second transmission light R2 into electric power. The converted electric power is output to the outside of the receiving circuit 22.

[0018] The receiving circuit 21 may receive the first transmission light R1 and output the signal transmitted by the first transmission light R1 via the optical fiber FB. The receiving circuit 21 may be driven by power output from the receiving circuit 22, which is an opto-electrical converter.

[0019] By driving the receiving circuit 21 with the power output from the receiving circuit 22, the second device 20 does not need to be supplied with power from an external power source.

[0020] For example, the second device 20 may be an IoT device or a communication device. Power may be supplied from the receiving circuit 22 to a sensor, a camera, or the like installed outdoors. Even when the second device 20 is installed indoors, there is no need to connect the second device 20 to an external power source with a power cable, which reduces installation costs. Furthermore, restrictions on the installation location of the second device 20 can be reduced.

[0021] [Raman response characteristics of optical fibers] Next, we will explain the Raman response characteristics of optical fibers. When setting the wavelength of the first transmission light R1, it is necessary to consider the influence of the second transmission light R2, which propagates through the same core as the first transmission light R1 within the optical fiber FB. For example, when the optical intensity of the second transmission light R2 exceeds 20 dBm, the first transmission light R1 will be affected by stimulated Raman scattering due to the second transmission light R2, depending on the length of the optical fiber FB.

[0022] Generally, stimulated Raman scattering is used for Raman amplification using an optical fiber FB as the amplification medium. The amplification characteristics are determined by the relationship between the frequencies of the first and second transmission lights R1 and R2 to be amplified.

[0023] Until now, Raman amplification has used high-intensity light with a frequency about 10 to 15 THz higher than the band to be amplified as pump light. In other words, the first transmission light R1 has been amplified using the second transmission light R2, which has a higher frequency than the frequency of the first transmission light R1. The reason for this is that a high gain can be obtained due to the shape of the Raman response spectrum of the optical fiber.

[0024] In response to this, the inventors have obtained new knowledge regarding the setting of the wavelength of the first transmission light R1 by investigating the effect on the first transmission light R1 when the first transmission light R1 and the second transmission light R2 are multiplexed. In particular, new knowledge regarding the absorption characteristics of the first transmission light R1 has been obtained by using the second transmission light R2, which has a lower frequency than the frequency of the first transmission light R1.

[0025] Fig. 2 is a diagram showing an example of the Raman response characteristics of an optical fiber. In Fig. 2, the horizontal axis represents the wavelength of the first transmission light R1, and the vertical axis represents the difference in intensity of the first transmission light R1 at the second device 20 before and after the second transmission light R2 is incident. When measuring the Raman response characteristics, the wavelength of the second transmission light R2 was set to 1550 nm, and the intensity power of the second transmission light R2 was set to 2 W.

[0026] The intensity difference of the first transmission light R1, shown on the vertical axis of Figure 2, is calculated by subtracting the intensity of the first transmission light R1 when the second transmission light R2 is not incident from the intensity of the first transmission light R1 when the second transmission light R2 is incident. Therefore, referring to the graph shown by the solid line, when a point on the graph exceeds the line of intensity difference 0 dB, it indicates that the intensity of the first transmission light R1 is increased by the incidence of the second transmission light R2. On the other hand, when a point on the graph falls below the line of intensity difference 0 dB, it indicates that the intensity of the first transmission light R1 is decreased by the incidence of the second transmission light R2.

[0027] The wavelength of the second transmission light R2, 1550 nm, is the boundary between the region where the intensity of the first transmission light R1 increases and the region where the intensity decreases. However, referring to Figure 2, it can be seen that the intensity of the first transmission light R1 increases in the region above 1520 nm. This is because the wavelength demultiplexer CP2 is not able to completely remove the wavelength spread of the second transmission light R2.

[0028] 2, it can be seen that the intensity of the first transmitted light R1 is slightly reduced in the wavelength range of 1300 nm to 1370 nm, and that the intensity of the first transmitted light R1 is significantly reduced in the wavelength range of 1370 nm to 1520 nm.

[0029] As described above, in the long-wavelength region of the first transmission light R1, where the wavelength of the first transmission light R1 is 1520 nm or more, the intensity of the first transmission light R1 increases due to Raman amplification. On the other hand, in the short-wavelength region of the first transmission light R1, where the wavelength of the first transmission light R1 is 1370 nm to 1520 nm, the intensity of the first transmission light R1 decreases. In other words, it can be seen that absorption due to Raman response occurs in the short-wavelength region.

[0030] 1, when the first transmission light R1 and the second transmission light R2 are simultaneously transmitted through the optical fiber FB, the intensity of the first transmission light R1 increases or decreases depending on the relationship between the wavelengths of the first transmission light R1 and the second transmission light R2. When a signal is propagated through the first transmission light R1, if the intensity of the first transmission light R1 decreases significantly, it will lead to a deterioration in communication quality.

[0031] When measuring the Raman response characteristics shown in Figure 1, a 14.1 km long single-mode optical fiber conforming to ITU-T G.652 was used as the optical fiber FB. In the measurement results, a solid line was not drawn in the range of 1400 to 1420 nm because the loss was too large due to the characteristics of the wavelength multiplexer CP1 and wavelength demultiplexer CP2 to properly evaluate the results. Furthermore, a solid line was not drawn for the 1550 nm light, as this is the wavelength of the second transmission light R2 and was excluded from the results.

[0032] [Relationship between Raman gain coefficient and absorption] Next, we calculated the absorption characteristics when the optical fiber FB is a single-mode optical fiber (SMF) conforming to ITU-T G.652. Assuming an optical access network, the length L of the optical fiber FB is 10 km, and the effective cross-sectional area A eff is 80 μm 2 , Raman gain efficiency at wavelength 1550 nm g r is 6.6 x 10 -14 The wavelength of 1550 nm is the wavelength of the second transmission light R2 used when measuring the Raman response characteristics shown in FIG.

[0033] Stimulated Brillouin scattering and stimulated Raman scattering are known to limit the input power to the optical fiber FB. When the linewidth of the second transmission light R2 used as the feed light is approximately 1 nm or more, the threshold value of stimulated Brillouin scattering becomes very large. Therefore, the input power to the optical fiber FB is essentially limited by the threshold value of stimulated Raman scattering.

[0034] where the threshold of stimulated Raman scattering, P this expressed by the following equation (1). P th =(16×A eff ) / (g r ×L eff ) ···(1)

[0035] For single-mode optical fiber (SMF), the threshold for stimulated Raman scattering, P th This is approximately 2.3W.

[0036] "L" that appears in equation (1) eff " is the effective length, and is given by the following equation (2). L eff ={1-exp(-αL)} / α (2)

[0037] Here, the input intensity of the second transmission light R2 is set to 2.3 W, but the intensity may be any value as long as it is 2.3 W or less.

[0038] The amount of absorption of the first transmission light R1 when the second transmission light R2 having a wavelength of 1550 nm is incident using the above-mentioned optical fiber FB will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the relationship between the Raman gain coefficient and the amount of absorption. Fig. 3 particularly shows the relationship between the Raman gain coefficient and the amount of absorption when the wavelength of the first transmission light R1 is set below the wavelength at which absorption due to Raman response occurs.

[0039] The amount of absorption affects the power penalty of the first transmission light R1 that propagates the signal. The power penalty tolerance of a communication system is specified as 2 dB (JT-G959.1). In other words, a "power penalty tolerance of 2 dB" guarantees that communication can be maintained even if the intensity of the first transmission light R1 that passes through the optical fiber FB drops by 2 dB.

[0040] When the amount of absorption corresponding to the decrease in the intensity of the first transmitted light R1 is 2 dB, the Raman gain coefficient is approximately −0.2×10 -14 As shown in the shaded area in Figure 3, to keep the absorption in the range of 0 to 2 dB, the Raman gain coefficient must be between 0 m / W and -0.2 × 10 -14It is sufficient if the value is between m / W.

[0041] [Relationship between frequency shift and Raman gain coefficient] Next, the relationship between the amount of frequency shift and the Raman gain coefficient will be explained using Fig. 4. Fig. 4 is a diagram showing an example of a Raman response spectrum, showing the amount of shift on the low frequency side relative to the input light. In Fig. 4, the horizontal axis represents the amount of frequency shift, and the vertical axis represents the Raman gain coefficient (absolute value). The Raman gain coefficient has a spectral shape that is symmetrical from left to right and up to down about the input light (second transmission light R2), with a negative Raman gain spectral shape on the high frequency side relative to the input light and a positive Raman gain spectral shape on the low frequency side relative to the input light.

[0042] The horizontal axis represents the amount of frequency shift, which can be converted into wavelength. The wavelength becomes longer as the frequency shifts lower than the input light, and shorter as the frequency shifts higher than the input light.

[0043] Based on Figure 4, the Raman gain coefficient ranges from 0 m / W to -0.2 × 10 -14 By finding the amount of frequency shift when the frequency is between 1 / 2 m / W, it is possible to find the band that can be used as the frequency of the first transmission light R1.

[0044] In Fig. 4, the absolute value of the Raman gain coefficient is 0.2 × 10 -14 The frequency shift amount at which the absorption is 0 to 2 dB is calculated from the Raman gain coefficient from 0 m / W to -0.2 × 10 -14 m / W. Based on Fig. 4, the range in which the absorption amount is 0 to 2 dB corresponds to the range in which the frequency shift amount is 27 THz or more.

[0045] When the wavelength of the second transmission light R2, which is the input light, is 1550 nm, the wavelength of the light that results in a frequency shift of 27 THz is calculated to be 1360 nm. When the wavelength of the first transmission light R1 is 1360 nm, the absorption level of the first transmission light R1 is 2 dB. In order to keep the absorption level of the first transmission light R1 within the range of 0 to 2 dB, the wavelength of the first transmission light R1 is set to 1360 nm or less.

[0046] The shape of the Raman response spectrum does not change significantly depending on the ions doped into the optical fiber, so the above discussion can be applied equally to any doped optical fiber.

[0047] [Specified wavelength range of the first transmission light] To summarize the above discussion, in the configuration of Figure 1, when the second transmission light R2 is input from the transmitter circuit 12 to the optical fiber FB, this affects the first transmission light R1 input from the transmitter circuit 11 to the optical fiber FB. More specifically, the intensity of the first transmission light R1 decreases.

[0048] However, by setting the wavelength of the first transmission light R1 to be shorter than the wavelength of the second transmission light R2 and further setting the wavelength of the first transmission light R1 to a band in which the absorption due to the Raman response of the optical fiber FB is 2 dB or less, it is possible to maintain communication between the transmitting circuit 11 and the receiving circuit 21.

[0049] For example, if the wavelength of the second transmission light R2 is 1550 nm and the wavelength of the first transmission light R1 is 1360 nm, the frequency shift amount is 27 THz. Therefore, the absorption amount of the first transmission light R1 can be set to 2 dB. By setting the wavelength of the first transmission light R1 to 1360 nm or less, the frequency shift amount can be set to 27 THz or more. As a result, the absorption amount of the first transmission light R1 becomes 2 dB or less. This makes it possible to more reliably maintain communication between the transmitting circuit 11 and the receiving circuit 21.

[0050] [Variations] Although the optical fiber FB is described as being a single-mode optical fiber (SMF) in FIG. 1, the present disclosure is not limited thereto.

[0051] For example, the optical fiber FB may be a single-core optical fiber or a multi-core optical fiber. The optical fiber FB may be a single-mode optical fiber or a multi-mode optical fiber. Alternatively, the optical fiber FB may be a photonic crystal optical fiber.

[0052] If the optical fiber FB has multiple cores, a first device 10 and a second device 20 may be provided for each core. That is, each core is configured to propagate a first transmission light R1 and a second transmission light R2. For each core, the wavelength of the first transmission light R1 may be shorter than the wavelength of the second transmission light R2 and may be set in a band in which absorption due to the Raman response of the optical fiber is 2 dB or less.

[0053] Additionally, the second device 20 may include a transmitting circuit that inputs the third transmission light to the optical fiber FB. The transmitting circuit included in the second device 20 may be driven by power output from the receiving circuit 22, which is an opto-electrical converter.

[0054] The first transmission light R1, the second transmission light R2, and the third transmission light may propagate within the same core of the optical fiber FB. In this case, the wavelength of the third transmission light may be shorter than the wavelength of the second transmission light R2 and may be set in a band in which the absorption due to the Raman response of the optical fiber is 2 dB or less.

[0055] [Effects of the embodiment] As described above in detail, the communication system according to this embodiment includes an optical fiber, a first device installed at one end of the optical fiber and inputting first and second transmission lights into the optical fiber, and a second device installed at the other end of the optical fiber and receiving the first and second transmission lights R1 and R2 propagated through the optical fiber. The wavelength of the first transmission light R1 is shorter than the wavelength of the second transmission light, and is set in a band in which the absorption due to the Raman response of the optical fiber is 2 dB or less.

[0056] This makes it possible to provide a communication system that can expand the communication band and extend the transmission distance using optical fibers. In particular, even when a band having a higher frequency than the high-intensity light is used as the communication band, it is possible to suppress the effect of the high-intensity light on the light in the communication band and to suppress deterioration of communication quality. As a result, it is possible to expand the communication band and extend the transmission distance using optical fibers.

[0057] Furthermore, in the communication system according to this embodiment, the second device may include an opto-electric converter that converts the second transmission light and outputs the resulting power. This allows optical power feeding to be performed using the second transmission light to the second device located in a remote location via an optical fiber. This eliminates the need for power supply from an external power source to the second device. In particular, since there is no need to connect the second device to the external power source using a power cable or the like, restrictions on the installation location of the second device can be reduced.

[0058] Furthermore, in the communication system according to this embodiment, the second device may include a receiving circuit that receives the first transmission light and outputs a signal transmitted through the optical fiber, and the receiving circuit may be driven by power output from the photoelectric converter. This eliminates the need for power supply from an external power source to the second device. As a result, the cost and workload of installing the second device can be reduced.

[0059] In the communication system according to the present embodiment, the second device may include a transmitter circuit that inputs the third transmission light into the optical fiber, and the transmitter circuit may be driven by power output from the photoelectric converter. This allows bidirectional communication between the first device and the second device. For example, data acquired by a sensor connected to the second device and images acquired by a camera can be transmitted to the first device in real time.

[0060] For example, even if the power supply in the area where the second device is installed is cut off due to a disaster such as an earthquake, energy can be supplied through the optical fiber. Then, the disaster situation can be acquired using a sensor or the like, and information about the situation can be obtained. In addition, the presence or absence of a break in the optical fiber can be determined based on the presence or absence of information transmitted from the transmission circuit provided in the second device.

[0061] Furthermore, in the communication system according to this embodiment, the optical fiber may have multiple cores, with a first device and a second device provided for each core. This allows a large amount of information to be transmitted using an optical fiber having multiple cores, instead of arranging multiple single-mode optical fibers. As a result, the cost and workload associated with installing the optical fiber can be reduced. Another advantage is that the reduction in the number of optical fibers to be installed simplifies the maintenance and management of the communication system.

[0062] Furthermore, even when many sensors are installed in remote locations, the connection with the sensors can be ensured by installing an optical fiber with a number of cores equal to or greater than the number of sensors, thereby reducing the cost and workload associated with installing the sensors and optical fibers.

[0063] Although the contents of the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these descriptions, and various modifications and improvements are possible, which will be apparent to those skilled in the art. The descriptions and drawings that form part of this disclosure should not be understood as limiting the present disclosure. Various alternative embodiments, examples, and operating techniques will be apparent to those skilled in the art from this disclosure.

[0064] Of course, the present disclosure includes various embodiments not described herein. Therefore, the technical scope of the present disclosure is defined only by the invention-specifying matters according to the scope of the claims that are appropriate from the above description. [Explanation of symbols]

[0065] 10 1st device 11,12 Transmitting circuit 12 Transmitting circuit 20 Second device 21,22 Receiver circuit CP1 wavelength multiplexer CP2 wavelength demultiplexer FB optical fiber R1 First transmission light R2 Second transmission light

Claims

1. An optical fiber; a first device that is installed on one end side of the optical fiber and that inputs a first transmission light and a second transmission light into the optical fiber; a second device that is installed on the other end side of the optical fiber and that receives the first transmission light and the second transmission light propagated through the optical fiber; Equipped with a wavelength of the first transmission light is shorter than a wavelength of the second transmission light, and is set to a band in which absorption due to Raman response of the optical fiber is 2 dB or less.

2. The communication system according to claim 1 , wherein the second device includes an optical-to-electrical converter that converts the second transmission light and outputs the resulting electric power.

3. the second device includes a receiving circuit that receives the first transmitted light and outputs a signal transmitted through the optical fiber; the receiving circuit is driven by power output from the photoelectric converter; The communication system according to claim 2 .

4. the second device includes a transmitting circuit that inputs a third transmission light into the optical fiber; the transmission circuit is driven by power output from the photoelectric converter; The communication system according to claim 2 .

5. the optical fiber has a plurality of cores, The first device and the second device are provided for each of the cores. A communication system according to any one of claims 1 to 4.

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