Optical repeater and optical access network

Abstract

An optical repeater comprising: a synthesizing / branching device that branches downlink signal light outputted from a base station into individual downlink signal light outputted to each of a plurality of user terminals, and that synthesizes individual uplink signal light outputted from each of the plurality of user terminals and outputs the synthesized uplink signal light to the base station as uplink signal light; a first optical fiber that transmits power supply light outputted from the base station; and an optical amplification circuit that amplifies any of the uplink signal light, the individual downlink signal light, and the individual uplink signal light by power obtained by photoelectrically converting the power supply light.

Description

Optical repeater and optical access network

[0001] The present disclosure relates to an optical repeater and an optical access network.

[0002] An optical access network called a Passive Optical Network (PON) is known. For optical access networks, a number of standards with different transmission speeds and signal wavelength bands have been standardized, as shown in Non-Patent Document 1, for example.

[0003] ITU-T G.989.1 40-Gigabit-capable passive optical networks (NG-PON2): General requirements

[0004] In an optical access network, it is required to amplify the optical intensity of an upstream signal transmitted from a user terminal to a base station or a downstream signal transmitted from a base station to a user terminal.

[0005] The present disclosure provides a technique for amplifying the optical intensity of an upstream signal light transmitted from a user terminal to a base station or a downstream signal light transmitted from a base station to a user terminal, using power obtained by photoelectric conversion of a power supply light.

[0006] In one aspect of the present disclosure, an optical repeater is provided that includes a multiplexer / splitter that branches downlink signal light output from a base station into individual downlink signal light that is output to each of a plurality of user terminals, and combines the individual uplink signal light output from each of the plurality of user terminals and outputs the combined signal light to the base station as an uplink signal light, a first optical fiber that transmits power supply light output from the base station, and an optical amplifier circuit that amplifies any of the uplink signal light, the individual downlink signal light, and the individual uplink signal light using power obtained by photoelectric conversion of the power supply light.

[0007] According to the optical repeater of the present disclosure, the optical intensity of the upstream signal light transmitted from the user terminal to the base station or the downstream signal light transmitted from the base station to the user terminal can be amplified by the power obtained by photoelectric conversion of the power supply light.

[0008] FIG. 1 is a diagram illustrating an outline of an optical access network according to a first embodiment. FIG. 2 is a diagram illustrating an outline of an optical access network according to a second embodiment. FIG. 3 is a diagram illustrating an outline of an optical access network according to a third embodiment. FIG. 4 is a diagram illustrating an outline of an optical access network according to a fourth embodiment. FIG. 5 is a diagram illustrating an outline of an optical access network according to a fifth embodiment. FIG. 6 is a diagram illustrating an outline of a modification of the optical access network according to the fifth embodiment. FIG. 7 is a diagram illustrating an outline of a first example of a user terminal in the optical access network according to this embodiment. FIG. 8 is a diagram illustrating an outline of a second example of a user terminal in the optical access network according to this embodiment. FIG. 9 is a diagram illustrating an outline of a third example of a user terminal in the optical access network according to this embodiment. FIG. 10 is a diagram illustrating an outline of a fourth example of a user terminal in the optical access network according to this embodiment. FIG. 11 is a diagram illustrating an outline of an optical access network according to a sixth embodiment. FIG. 12 is a diagram illustrating an outline of an optical access network according to a seventh embodiment. FIG. 13 is a diagram illustrating an outline of an optical access network according to an eighth embodiment. FIG. 14 is a diagram illustrating an outline of an optical access network of a reference example.

[0009] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0010] In addition, with regard to the description of the specification and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be designated by the same or corresponding reference numerals to avoid redundant explanation. In addition, the scale of each part in the drawings may differ from the actual scale to facilitate understanding.

[0011] First, a description will be given of the configuration that is roughly common to various standards. Fig. 14 is a diagram showing an outline of an optical access network 9 of a reference example.

[0012] The optical access network 9 includes a base station 901, a multiplexer / splitter 902, and a plurality of user terminals 903. An optical fiber 904 connects the base station 901 and the multiplexer / splitter 902. An optical fiber 905 connects the multiplexer / splitter 902 and each of the plurality of user terminals 903.

[0013] In the optical access network 9, the optical fiber 904 is shared by many users, thereby reducing the cost of the entire network.

[0014] Conventionally, user terminals 903 have been installed in offices or private homes and used for telephone and internet connections. In the future, it is expected that so-called IoT (Internet of Things) devices, including sensing devices and service devices, will be connected, so there is a demand for an increase in the number of users that can be accommodated.

[0015] In order to increase the number of users that can be accommodated, it is necessary to increase the optical intensity of the downstream signal light DSL (Downstream Signal Light) from the base station 901 and to increase the sensitivity of the receiving circuit in the user terminal 903. Note that the signal light transmitted from the base station 901 to the user terminal 903 is referred to as the downstream signal light DSL, and the signal light transmitted from the user terminal 903 to the base station 901 is referred to as the upstream signal light USL (Upstream Signal Light).

[0016] However, increasing the optical intensity of the downstream signal light DSL causes degradation of the optical signal due to the optical nonlinear effect in the optical fiber 904. Also, while it is conceivable to use a coherent transmission method to increase sensitivity, adopting a coherent transmission method increases the cost of the equipment.

[0017] For example, a conventional technology related to the present disclosure is an optical power feeding technology using optical fiber. As an example of the conventional technology, for example, Fiber Labs Co., Ltd. sells a system construction device using multimode fiber. Tamagawa Electronics Co., Ltd. sells an optically powered RoF transmitter system using standard single-mode fiber. Furthermore, Nippon Telegraph and Telephone Corporation has reported on a research on a system that combines optical power feeding and transmission using a multicore fiber.

[0018] However, multimode fiber cannot increase the signal transmission speed. Furthermore, standard single-mode fiber cannot increase the optical power of the optical feed. Multicore fiber can increase the power of the optical feed by the number of cores, but only by a factor of 10 at most. Furthermore, these optical power feeding technologies do not address the need to install and drive optical amplifier circuits in optical access networks.

[0019] The optical access network of the present disclosure transmits a power feed light to an optical repeater and amplifies an upstream signal light or a downstream signal light with power obtained by photoelectric conversion of the power feed light. According to the optical access network of the present disclosure, by amplifying the upstream signal light or the downstream signal light with power obtained by photoelectric conversion of the power feed light, the number of users can be increased without requiring an external power source.

[0020] First Embodiment An optical access network according to a first embodiment will be described below. Fig. 1 is a diagram showing an outline of an optical access network 1, which is an example of an optical access network according to the first embodiment.

[0021] <Optical Access Network 1> The optical access network 1 includes a base station 101, an optical repeater 111, and a user terminal 103. The optical access network 1 includes multiple user terminals 103. Note that the number of user terminals 103 in the optical access network 1 is not limited to multiple, and may be one.

[0022] In the optical access network 1, the distance in Section A (SA) between the base station 101 and the optical repeater 111 is, for example, 10 kilometers. Also, in the optical access network 1, the distance in Section B (SB) between the optical repeater 111 and the user terminal 103 is, for example, 10 kilometers. Note that the distances in Section SA and Section SB may be any distance in the range of, for example, 0.01 kilometers to 40 kilometers, depending on the area where the optical access network 1 is installed.

[0023] [Base Station 101] The base station 101 transmits downstream signal optical DSL containing signals to be transmitted to each of the multiple user terminals 103. The base station 101 also receives upstream signal optical USL containing signals transmitted from each of the multiple user terminals 103. Furthermore, the base station 101 supplies power supply light PSL (Power Supply Light) to the optical repeater 111 to generate power in the optical repeater 111.

[0024] The base station 101 includes a receiving circuit 101r, a transmitting circuit 101t, and a light source 101s. The receiving circuit 101r is a circuit for receiving upstream signal light USL. The transmitting circuit 101t is a circuit for transmitting downstream signal light DSL. The light source 101s is a light source for generating power supply light PSL. The light source 101s generates power supply light PSL that is stronger than the downstream signal light DSL in order to supply power for power generation.

[0025] The downstream signal light DSL transmitted from the base station 101 passes through the optical fiber 104 and is input to the optical repeater 111. Similarly to the downstream signal light DSL, the power supply light PSL transmitted from the base station 101 passes through the optical fiber 104 and is input to the optical repeater 111. The base station 101 multiplexes the downstream signal light DSL and the power supply light PSL and inputs the multiplexed signal to the optical fiber 104.

[0026] The upstream signal light USL output from the optical repeater 111 passes through the optical fiber 106 and is input to the base station 101 .

[0027] The wavelengths of the upstream signal light USL and downstream signal light DSL transmitted and received at the base station 101 are, for example, 1550 nanometers. Note that the wavelengths of the upstream signal light USL and downstream signal light DSL transmitted and received at the base station 101 are not limited to 1550 nanometers and may be changed as appropriate.

[0028] The wavelength of the power supply light PSL transmitted and received in the base station 101 is different from the wavelengths of the upstream signal light USL and the downstream signal light DSL. The wavelength of the power supply light PSL transmitted and received in the base station 101 is, for example, 1450 nanometers.

[0029] [User Terminal 103] The user terminal 103 is installed in an office or a private home. The user terminal 103 is used for telephone calls, internet connections, etc. The user terminal 103 is also connected to, for example, IoT devices.

[0030] The user terminal 103 transmits and receives individual downstream signal light DSLi and individual upstream signal light USLi via an optical fiber 105 .

[0031] [Optical repeater 111] The optical repeater 111 includes a multiplexer / splitter 102, a wavelength demultiplexer 107, an opto-electric converter 108, a power supply circuit 109, and an optical amplifier circuit 110. The optical repeater 111 also includes an optical fiber 104 connected to the multiplexer / splitter 102 and provided between the base station 101 and the multiplexer / splitter 102. The optical repeater 111 also includes an optical fiber 105 connected to the multiplexer / splitter 102 and provided between the multiplexer / splitter 102 and each of the multiple user terminals 103. The optical repeater 111 also includes an optical fiber 106 connected to the multiplexer / splitter 102 and provided between the base station 101 and the multiplexer / splitter 102.

[0032] Each of the components of the optical repeater 111 will now be described in detail.

[0033] (Split / Splitter 102) The splitter 102 splits the downstream signal light DSL transmitted from the base station 101 and transmits the split signal light to each of the multiple user terminals 103. The splitter 102 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103 and transmits the upstream signal light USL to the base station 101.

[0034] The multiplexer / splitter 102 has, for example, N (N is an integer equal to or greater than 2) optical input / output terminals on the base station 101 side and M (M is an integer equal to or greater than 2) optical input / output terminals on the user terminal 103 side. In the example of FIG. 1, N is 2.

[0035] The multiplexer / splitter 102 is, for example, an N:N star coupler (N is an integer equal to or greater than 2). For example, when a star coupler is used as the multiplexer / splitter 102, it operates as a 2:N multiplexer / splitter by using two of the optical input / output terminals on the base station 101 side.

[0036] An optical fiber 104 and an optical fiber 106 are connected to optical input / output terminals on the base station 101 side of the multiplexer / splitter 102. Furthermore, a plurality of optical fibers 105 are connected to optical input / output terminals on the user terminal 103 side of the multiplexer / splitter 102, respectively.

[0037] (Wavelength demultiplexer 107) The wavelength demultiplexer 107 separates the downstream signal light DSL and the power supply light PSL transmitted to the optical fiber 104 by wavelength. In other words, the wavelength demultiplexer 107 demultiplexes the downstream signal light DSL and the power supply light PSL transmitted to the optical fiber 104. Then, the wavelength demultiplexer 107 outputs the downstream signal light DSL to the multiplexer / branch 102. In addition, the wavelength demultiplexer 107 outputs the power supply light PSL to the photoelectric converter 108.

[0038] The wavelength demultiplexer 107 is provided in the optical fiber 104. The wavelength demultiplexer 107 is, for example, a dichroic optical fiber coupler.

[0039] (Optoelectric Converter 108) The optoelectric converter 108 converts the power supply light PSL input from the wavelength demultiplexer 107 into electric power. The optoelectric converter 108 outputs the electric power obtained by converting the power supply light PSL to the power supply circuit 109.

[0040] The photoelectric converter 108 includes a power generating element such as a solar cell, a photodiode, etc. The power generating element included in the photoelectric converter 108 is preferably a power generating element optimized for the wavelength of the power supply light PSL.

[0041] (Power Supply Circuit 109) The power supply circuit 109 converts the power supplied from the photoelectric converter 108 into power for driving the optical amplifier circuit 110. For example, the power supply circuit 109 smoothes the power output from the photoelectric converter 108. The power supply circuit 109 also adjusts the power output from the photoelectric converter 108 to a predetermined voltage. Then, the power supply circuit 109 supplies power to the optical amplifier circuit 110.

[0042] (Optical Amplification Circuit 110) The optical amplification circuit 110 amplifies the optical intensity of the upstream signal light USL passing through the optical fiber 106. The optical amplification circuit 110 may be, for example, a rare-earth element-doped optical fiber amplifier. More specifically, the optical amplification circuit 110 may be, for example, an erbium-doped optical fiber amplifier. For example, the optical amplification circuit 110 uses power obtained by converting the feed light PSL by the opto-electrical converter 108 as power for a light source that generates pump light to be supplied to the erbium-doped fiber.

[0043] (Optical fiber 104) The optical fiber 104 transmits downstream signal light DSL and power supply light PSL transmitted from the base station 101 to the optical repeater 111. The optical fiber 104 connects the base station 101 and the optical repeater 111. The optical fiber 104 is composed of a hole-core fiber.

[0044] The optical fiber 104 is not limited to a single optical fiber, but may be configured by connecting a plurality of optical fibers in series, for example.

[0045] (Optical fiber 105) The optical fiber 105 transmits an individual downstream signal light DSLi from the optical repeater 111 to the user terminal 103. The optical fiber 105 also transmits an individual upstream signal light USLi from each of the multiple user terminals to the optical repeater 111.

[0046] The optical fiber 105 connects the optical repeater 111 and the user terminal 103. The optical fiber 105 is not limited to a single optical fiber, and may be configured by connecting a plurality of optical fibers in series, for example.

[0047] (Optical Fiber 106) The optical fiber 106 transmits upstream signal light USL from the optical repeater 111 to the base station 101.

[0048] The optical fiber 106 connects the base station 101 and the optical repeater 111. The optical fiber 106 is not limited to a single optical fiber, and may be configured by connecting a plurality of optical fibers in series, for example.

[0049] <Operation of Optical Access Network 1> The operation of the optical access network according to the first embodiment will be described using the optical access network 1, which is an example of the optical access network according to the first embodiment. It should be noted that the distance between each of sections SA and SB is 10 kilometers.

[0050] The downstream signal light DSL and the power supply light PSL are multiplexed from the base station 101 and supplied to the optical fiber 104. The power supply light PSL has a different wavelength from that of the downstream signal light DSL. The wavelength demultiplexer 107 demultiplexes the downstream signal light DSL from the power supply light PSL. The downstream signal light DSL is transmitted from the wavelength demultiplexer 107 to the multiplexer / splitter 102. The power supply light PSL is transmitted from the wavelength demultiplexer 107 to the photoelectric converter 108.

[0051] The optical fiber 104 is, for example, a hole-core fiber. The hole-core fiber is not damaged even when light having an intensity 1000 times greater than the intensity allowable in a standard optical fiber specified in, for example, ITU-T G. 652 is input. Furthermore, the hole-core fiber can transmit light over long distances without waveform degradation even when light having an intensity 1000 times greater than the intensity allowable in a standard optical fiber is input.

[0052] The downstream signal light DSL is branched by the branching / multiplexing device 102. The individual downstream signal light DSLi branched by the branching / multiplexing device 102 is transmitted to an optical fiber 105 arranged in the section SB up to the user terminal 103.

[0053] For example, if a hole-core fiber with a loss per unit distance of 1 dB / km (decibels per kilometer) is used, the loss of the transmission line in section SA is 10 dB. If the loss of optical fiber 105 in section SB is 0.2 dB / km and the excess loss other than the branching loss in coupler 102 is 2 dB, the total loss from base station 101 to user terminal 103, excluding the branching loss in coupler 102, is 14 dB.

[0054] If the downstream signal light DSL is an intensity-modulated optical signal of 10 gigabits per second, the receiving sensitivity at the user terminal 103 is about -18 dBm. The holey-core fiber used in the optical fiber 104 can transmit downstream signals with an optical intensity (+35 dBm) 1000 times that of a standard optical fiber without waveform degradation. Therefore, a loss of 53 dB is allowed between the base station 101 and the user terminal 103.

[0055] A loss of 53 dB is allowed between the base station 101 and the user terminal 103, and the total loss from the base station 101 to the user terminal 103 excluding the branching loss at the branching coupler 102 is 14 dB, so a branching loss of 39 dB is allowable.

[0056] If a branching loss of up to 39 dB is allowed, the maximum number of branches in the branching / multiplexing device 102 is approximately 7900. In an optical access network using standard fiber, the maximum number of branches is approximately 64, so the optical access network according to the first embodiment can accommodate a 100-fold or greater increase in the number of users that can be accommodated.

[0057] The maximum intensity of the feed light PSL that can be input from the base station 101 is limited by a damage threshold. When the optical fiber 104 is a holey-core fiber, the maximum intensity of the feed light PSL is +63 dBm. The optical intensity of the feed light PSL after transmission through the section SA is +53 dBm. If the conversion efficiency of the photoelectric converter 108 is -5 dB, the power obtained in the photoelectric converter 108 is +48 dBm. The power obtained in the photoelectric converter 108 is supplied to the power supply circuit 109 to drive the optical amplifier circuit 110. For example, if the amplification efficiency of the optical amplifier circuit 110 is -10 dB, the optical amplifier circuit 110 can achieve optical amplification with a saturated output of +38 dBm.

[0058] Furthermore, when the optical fiber 104 is a standard optical fiber, the maximum intensity of the feed light PSL is +33 dBm. The optical intensity of the feed light PSL after transmission through the section SA is approximately +31 dBm. If the conversion efficiency of the photoelectric converter 108 is -5 dB, the power obtained from the photoelectric converter 108 is +26 dBm. If the amplification efficiency of the optical amplifier circuit 110 is -10 dB, the optical amplifier circuit 110 can achieve optical amplification with a saturated output of +16 dBm.

[0059] If an erbium-doped optical fiber amplifier is used in the optical amplifier circuit 110, the small signal gain can be increased to 30 dB or more.

[0060] When the modulation speed is 10 Gbps, similar to the downstream signal light DSL, the intensity of the individual upstream signal light USLi output from the user terminal 103 is set to +5 dBm so as not to degrade the waveform in the section SB of the optical fiber 105. If the loss in the section SB is 2 dB, the loss excluding the branching loss in the branching / multiplexing device 102 is 2 dB, and the branching loss in the branching / multiplexing device 102 is 37 dB, the upstream signal intensity output from the branching / multiplexing device 102 is −36 dBm.

[0061] The signal intensity of the upstream signal light USL becomes -6 dBm when amplified in the optical amplifier circuit 110. When a loss of 2 dB occurs in the optical fiber 106, the optical intensity of the upstream signal light USL at the base station 101 becomes -8 dBm.

[0062] The S / N ratio is degraded by noise in the optical amplifier circuit 110. On the other hand, since the optical intensity of the upstream signal light USL in the optical amplifier circuit 110 is sufficient, the noise figure of the optical amplifier circuit 110 is 5 dB or less, and therefore reception at the base station 101 with a low error rate is possible.

[0063] According to the optical access network of the first embodiment, the upstream signal transmitted from the user terminal to the base station can be amplified by amplifying the upstream signal light using power generated by the power feed light. Also, according to the optical access network of the first embodiment, by amplifying the upstream signal transmitted from the user terminal to the base station, the signal-to-noise ratio of the upstream signal can be increased even when the number of users increases, and the upstream line speed can also be increased. Furthermore, according to the optical access network of the first embodiment, since optical power is fed using the power feed light, an external power source is not required, and the upstream signal can be amplified even in places where an external power source cannot be secured.

[0064] According to the optical access network of the first embodiment, the optical intensity of the feed light can be increased by using a holey-core fiber as the first optical fiber. According to the optical access network of the first embodiment, by increasing the optical intensity of the feed light, it is possible to supply sufficient power required for the optical amplifier circuit.

[0065] The optical fiber 104 is an example of a first optical fiber, and the optical fiber 106 is an example of a second optical fiber.

[0066] Second Embodiment An optical access network according to a second embodiment will now be described. Fig. 2 is a diagram showing an outline of an optical access network 2, which is an example of an optical access network according to the second embodiment.

[0067] The optical access network according to the second embodiment enables upstream signal light USL to be transmitted to a plurality of base stations in the optical access network according to the first embodiment.

[0068] The optical access network 2 includes a base station 101 and a base station 101 a, an optical repeater 211 , and a plurality of user terminals 103 .

[0069] [Optical Repeater 211] The optical repeater 211 includes a multiplexer / demultiplexer 202, a wavelength demultiplexer 107, an opto-electric converter 108, a power supply circuit 209, an optical amplifier circuit 110, and an optical amplifier circuit 110a.

[0070] Regarding the configuration of the optical repeater 211 that is common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0071] The multiplexer / splitter 202 splits the downstream signal light DSL transmitted from the base station 101 and transmits it to each of the multiple user terminals 103. The multiplexer / splitter 202 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103, further splits it, and transmits it to each of the base stations 101 and 101a.

[0072] The multiplexer / splitter 202 has, for example, N (N is an integer equal to or greater than 2) optical input / output terminals on the base station 101 side and M (M is an integer equal to or greater than 2) optical input / output terminals on the user terminal 103 side. In the example of FIG. 2, N is 3.

[0073] The optical fiber 104, the optical fiber 106, and the optical fiber 106a are connected to optical input / output terminals on the base station 101 side of the multiplexer / brancher 202. Furthermore, a plurality of optical fibers 105 are connected to optical input / output terminals on the user terminal 103 side of the multiplexer / brancher 202.

[0074] The power supply circuit 209 converts the power supplied from the photoelectric converter 108 into power for driving the optical amplifier circuit 110 and the optical amplifier circuit 110a, and then supplies power to each of the optical amplifier circuit 110 and the optical amplifier circuit 110a.

[0075] The optical repeater 211 further includes an optical amplifier circuit 110a provided in the optical fiber 106a in addition to the optical repeater 111. By including the optical amplifier circuit 110a, the optical repeater 211 can transmit the upstream signal light USLa to a base station 101a other than the base station 101. The basic operation is the same as that of the optical repeater 111 in the optical access network 1.

[0076] The optical repeater 211 includes an optical amplifier circuit 110 and an optical amplifier circuit 110a, but the number of optical amplifier circuits may be two or more as long as the power supply circuit 209 can supply power to the optical amplifier circuits. In other words, the optical repeater 211 includes multiple optical amplifier circuits. Since the power supply optical PSL can supply sufficient power, optical amplification up to +33 dBm is possible in each of the multiple optical amplifier circuits.

[0077] According to the optical access network of the second embodiment, in addition to the optical access network of the first embodiment, it is connected to a plurality of base stations, so that a redundant and robust network can be configured.

[0078] For example, if two optical fibers 105 are looped back together, communication between the base station 101 and the base station 101a is also possible.

[0079] Note that the optical fiber 104 is an example of a first optical fiber, the optical fiber 106 is an example of a second optical fiber, the upstream signal light USLa is an example of a second upstream signal light, the optical fiber 106a is an example of a third optical fiber, and the optical amplifier circuit 110a is an example of a second optical amplifier circuit.

[0080] Third Embodiment An optical access network according to a third embodiment will now be described. Fig. 3 is a diagram showing an outline of an optical access network 3, which is an example of an optical access network according to the third embodiment.

[0081] The optical access network according to the third embodiment transmits upstream signal light USL, downstream signal light DSL, and power supply light PSL over a single optical fiber.

[0082] The optical access network 3 includes a base station 101 , an optical repeater 311 , and a plurality of user terminals 103 .

[0083] [Optical Repeater 311 ] The optical repeater 311 includes a multiplexer / brancher 302 , a wavelength demultiplexer 107 , an opto-electric converter 108 , a power supply circuit 109 , an optical amplifier circuit 110 , an optical circulator 312 and an optical circulator 313 .

[0084] Regarding the configuration of the optical repeater 311 that is common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0085] The multiplexer / splitter 302 splits the downstream signal light DSL transmitted from the base station 101 and transmits it to each of the multiple user terminals 103. The multiplexer / splitter 302 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103 and transmits it to the base station 101.

[0086] The optical repeater 311 includes an optical circulator 312 and an optical circulator 313 on the optical fiber 104. The optical repeater 311 also includes a bypass optical fiber 314 that bypasses and connects the optical circulator 312 and the optical circulator 313.

[0087] Between the optical circulator 312 and the optical circulator 313, the downstream signal light DSL passes through the optical fiber 104. On the other hand, between the optical circulator 312 and the optical circulator 313, the upstream signal light USL passes through the bypass optical fiber 314. The optical repeater 311 includes an optical amplifier circuit 110 in the bypass optical fiber 314 that amplifies the upstream signal light USL. In order to amplify the upstream signal light USL, the optical repeater 311 bypasses the upstream signal light USL through the optical circulator 312, the optical circulator 313, and the bypass optical fiber 314.

[0088] The optical circulator 312 outputs the downstream DSL signal light input from the base station 101 via the wavelength demultiplexer 107 to the optical circulator 313. The optical circulator 313 outputs the downstream DSL signal light input from the optical circulator 312 to the multiplexer / splitter 302.

[0089] Furthermore, the optical circulator 313 outputs the upstream signal light USL input from the multiplexer / splitter 302 to the optical amplifier circuit 110 via the bypass optical fiber 314. The optical circulator 313 outputs the upstream signal light USL input from the optical amplifier circuit 110 via the bypass optical fiber 314 to the base station 101.

[0090] According to the optical access network of the third embodiment, in the optical access network of the first embodiment, the configuration can be further simplified by transmitting the upstream signal light USL and the downstream signal light DSL from the base station through the same optical fiber.

[0091] The optical circulator 313 is an example of a first optical circulator, the optical circulator 312 is an example of a second optical circulator, and the bypass optical fiber 314 is an example of a first bypass optical fiber.

[0092] Fourth Embodiment An optical access network according to a fourth embodiment will now be described. Fig. 4 is a diagram showing an outline of an optical access network 4, which is an example of an optical access network according to the fourth embodiment.

[0093] The optical access network according to the fourth embodiment transmits downstream signal light DSL and power supply light PSL by a fiber bundle or a multi-core fiber.

[0094] The optical access network 4 includes a base station 101, an optical repeater 411, and a plurality of user terminals 103. Downstream signal light DSL and power supply light PSL are transmitted from the base station 101 to the optical repeater 411 via a fiber bundle 404. The fiber bundle 404 includes an optical fiber 404a and an optical fiber 404b.

[0095] [Optical Repeater 411] The optical repeater 411 includes a multiplexer / splitter 402, an optical / electrical converter 108, a power supply circuit 409, an optical amplifier circuit 110, and an optical amplifier circuit 410b.

[0096] In the optical repeater 411, for the configuration common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0097] The multiplexer / splitter 402 splits the downstream signal light DSL transmitted from the base station 101 via the optical fiber 404a included in the fiber bundle 404, and transmits the split signal light to each of the multiple user terminals 103. The multiplexer / splitter 402 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103, and transmits the combined signal light to the base station 101 via the optical fiber 106.

[0098] The optical fiber 404b transmits the feed light PSL output from the base station 101. The optical fiber 404b is a multi-core fiber. The optical access network 4 uses the optical fiber 404b as a multi-core fiber and transmits the feed light PSL using multiple cores, thereby increasing the intensity of the transmittable feed light PSL. The optical access network 4 can increase the power generated in the opto-electrical converter 108 by transmitting high-intensity feed light PSL. The optical access network 4 can increase the power supplied to the optical amplifier circuit 110 and the optical amplifier circuit 410b by increasing the power generated in the opto-electrical converter 108.

[0099] The optical access network 4 can use a multi-core fiber having multiple cores similar to a standard optical fiber, instead of a hole-core fiber, as the optical fiber for transmitting the power supply light PSL. Although the power that can be supplied is lower than when a hole-core fiber is used, the optical access network 4 can be configured as a network using a relatively low-cost multi-core fiber.

[0100] The photoelectric converter 108 photoelectrically converts the power supply light PSL transmitted via the optical fiber 404 b into electric power, and supplies the power supply circuit 409 with the electric power obtained by photoelectrically converting the power supply light PSL.

[0101] The power supply circuit 409 supplies power to the optical amplifier circuit 110 and the optical amplifier circuit 410b to drive the optical amplifier circuit 110 and the optical amplifier circuit 410b.

[0102] The optical amplifier circuit 410b amplifies the downstream signal light DSL transmitted through the optical fiber 404a.

[0103] For example, in optical fiber 404b, which is a multi-core fiber, if it is possible to drive an optical amplifier circuit with a saturated output of up to +16 dBm by power supply from one core, then it is possible to drive two optical amplifier circuits with a saturated output of up to +16 dBm by power supply from two cores.

[0104] The optical amplifier circuit 410b is disposed near the multiplexer / splitter 402 and amplifies the downstream DSL signal light. By amplifying the downstream DSL signal light, the number of branches in the multiplexer / splitter 402 can be increased. When a +16 dBm downstream DSL signal light is output from the base station 101 as the downstream DSL signal light, the loss due to the multiplexer / splitter 402 and the optical fiber 105 is 4 dB, and if the receiving sensitivity at the user terminal 103 is -18 dBm, an excess loss of up to 30 dB can be tolerated. Therefore, the number of branches in the multiplexer / splitter 402 can be increased to approximately 1,000.

[0105] In the above example, a multi-core fiber is used as the optical fiber 404b, but instead of the optical fiber 404b which is a multi-core fiber, a bundle of multiple optical fibers may be used. In other words, a fiber bundle may be used instead of the optical fiber 404b.

[0106] According to the optical access network of the fourth embodiment, in the optical access network of the first embodiment, it is possible to reduce costs and increase the number of divisions in the multiplexer / divider.

[0107] The optical fiber 404b is an example of a first optical fiber, the optical fiber 106 is an example of a fourth optical fiber, the optical fiber 404a is an example of a fifth optical fiber, and the optical amplifier circuit 410b is an example of a third optical amplifier circuit.

[0108] Fifth Embodiment An optical access network according to a fifth embodiment will now be described. Fig. 5 is a diagram showing an outline of an optical access network 5, which is an example of an optical access network according to the fifth embodiment.

[0109] The optical access network according to the fifth embodiment amplifies the individual downstream signal light DSLi after branching by power generated by the power supply light PSL. Also, the optical access network according to the fifth embodiment amplifies the individual upstream signal light USLi before combining by power generated by the power supply light PSL.

[0110] The optical access network 5 includes a base station 101, an optical repeater 511, and a plurality of user terminals 103. From the base station 101, upstream signal light USL, downstream signal light DSL, and power supply light PSL are transmitted to the optical repeater 511 via optical fibers 104.

[0111] [Optical Repeater 511] The optical repeater 511 includes a multiplexer / demultiplexer 502, a wavelength demultiplexer 107, an opto-electric converter 108, a power supply circuit 509, an optical amplifier circuit 510c, and an optical amplifier circuit 510d.

[0112] Regarding the configuration of the optical repeater 511 that is common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0113] The multiplexer / splitter 502 splits the downstream signal light DSL transmitted from the base station 101 via the optical fiber 104 and transmits the split signal light to each of the multiple user terminals 103. The multiplexer / splitter 502 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103 and transmits the resulting upstream signal light USL to the base station 101 via the optical fiber 104.

[0114] The optical repeater 511 includes an optical fiber 505, which is one of the optical fibers connecting the user terminal 103 and the multiplexer / splitter 502, and includes an optical circulator 512 and an optical circulator 513. The optical fiber 505 is, for example, an optical fiber for extension. The optical fiber 505 is longer than the optical fiber 105, for example, having a length of 10 kilometers or more. The optical repeater 511 also includes a bypass optical fiber 514 that bypasses and connects the optical circulator 512 and the optical circulator 513.

[0115] Between the optical circulator 512 and the optical circulator 513, the individual downstream signal light DSLi passes through the optical fiber 505. The optical repeater 511 includes an optical amplifier circuit 510c in the bypass optical fiber 514 between the optical circulator 512 and the optical circulator 513, which amplifies the individual downstream signal light DSLi. On the other hand, between the optical circulator 512 and the optical circulator 513, the individual upstream signal light USLi passes through the bypass optical fiber 514. The optical repeater 511 includes an optical amplifier circuit 510d in the bypass optical fiber 514, which amplifies the individual upstream signal light USLi. In order to amplify the individual upstream signal light USLi passing through the optical fiber 505, the optical repeater 511 bypasses the individual upstream signal light USLi passing through the optical fiber 505 using the optical circulator 512, the optical circulator 513, and the bypass optical fiber 514.

[0116] The optical circulator 512 outputs the individual downstream signal light DSLi input from the multiplexer / brancher 102 to the optical amplifier circuit 510c. The optical amplifier circuit 510c amplifies the input individual downstream signal light DSLi and outputs it to the optical circulator 513. The optical circulator 513 outputs the individual downstream signal light DSLi input from the optical amplifier circuit 510c to the user terminal 103.

[0117] Furthermore, the optical circulator 513 outputs the individual upstream signal light USLi input from the user terminal 103 to the optical amplifier circuit 510d via the bypass optical fiber 514. The optical amplifier circuit 510d amplifies the individual upstream signal light USLi input from the optical circulator 513 and outputs it to the optical circulator 512. The optical circulator 512 outputs the individual upstream signal light USLi input from the optical amplifier circuit 510d via the bypass optical fiber 514 to the multiplexer / branch 102.

[0118] The power supply circuit 509 supplies power to each of the optical amplifier circuits 510c and 510d for driving the optical amplifier circuits 510c and 510d.

[0119] The optical amplifier circuit 510c amplifies the individual downstream signal light DSLi transmitted through the optical fiber 505. The optical amplifier circuit 510d amplifies the individual upstream signal light USLi bypassed by the bypass optical fiber 514.

[0120] According to the optical access network of the fifth embodiment, in the optical access network of the first embodiment, the transmission distance from the optical repeater to the user terminal can be further extended, making it possible to communicate with user terminals in remote locations.

[0121] In the example of the optical access network 5, a pair of optical amplifier circuits is provided, but multiple pairs of optical amplifier circuits may be provided as long as sufficient power can be supplied from the power supply circuit 509. In other words, the number of user terminals to be extended is not limited to two, but may be three or more.

[0122] Furthermore, in the above example, the individual upstream signal light USLi is transmitted through the bypass optical fiber 514, but the individual downstream signal light DSLi may also be transmitted through the bypass optical fiber 514. In other words, between the optical circulator 512 and the optical circulator 513, one of the individual downstream signal light DSLi and the individual upstream signal light USLi may be transmitted through the bypass optical fiber 514, and the other may be transmitted through the optical fiber 505.

[0123] Furthermore, only one of the optical amplifier circuit 510c and the optical amplifier circuit 510d may be provided.

[0124] Furthermore, in the optical access networks according to the first to fourth embodiments, an optical amplifier circuit may be provided on the user terminal side, as in the optical access network according to the fifth embodiment.

[0125] Next, a modification will be described. Fig. 6 is a diagram showing an outline of an optical access network 5a which is a modification of the optical access network according to the fifth embodiment. The optical fiber 505 may be provided with a multiplexer / splitter 516 instead of the user terminal 103. The multiplexer / splitter 516 may be provided with a plurality of user terminals 103. By further providing the multiplexer / splitter 516, the number of splitters can be further increased. By increasing the number of splitters, the number of users can be further increased.

[0126] The optical fiber 104 is an example of a first optical fiber, the optical fiber 505 is an example of a sixth optical fiber, the optical amplifier circuit 510d is an example of a fourth optical amplifier circuit, the multiplexer / splitter 516 is an example of a second multiplexer / splitter, the optical circulator 512 and the optical circulator 513 are examples of a third optical circulator or a fourth optical circulator, and the bypass optical fiber 514 is an example of a second bypass optical fiber.

[0127] <User terminal in optical access network according to the present embodiment> A user terminal used in the optical access network according to each embodiment of the present disclosure will be described. As the user terminal 103, which is an example of a user terminal in the optical access network according to the present embodiment, the following example user terminal may be used.

[0128] 7 is a diagram showing an outline of a user terminal 103A, which is a first example of a user terminal in the optical access network according to this embodiment. The user terminal 103A is assumed to be connected to an optical fiber 105, which is, for example, a single-core fiber.

[0129] The user terminal 103A includes a transmitting circuit 103t, a receiving circuit 103r, and an optical circulator 103c. The individual downstream signal light DSLi transmitted through the optical fiber 105 is transmitted to the receiving circuit 103r by the optical circulator 103c. The individual upstream signal light USLi transmitted from the transmitting circuit 103t is transmitted to the optical fiber 105 by the optical circulator 103c.

[0130] The receiving circuit 103r converts the individual downstream signal light DSLi into an electrical signal, and the transmitting circuit 103t converts the electrical signal into the individual upstream signal light USLi.

[0131] 8 is a diagram showing an outline of a user terminal 103B, which is a second example of a user terminal in the optical access network according to this embodiment. The user terminal 103B is assumed to be connected to an optical fiber 105, which is, for example, a single-core fiber.

[0132] The user terminal 103B includes a transmitting circuit 103t, a receiving circuit 103r, and an optical coupler 103p. The optical coupler 103p is, for example, a 1:2 optical coupler. The individual downstream signal light DSLi transmitted through the optical fiber 105 is transmitted to the receiving circuit 103r by the optical coupler 103p. The individual upstream signal light USLi transmitted from the transmitting circuit 103t is transmitted to the optical fiber 105 by the optical coupler 103p.

[0133] By using the optical coupler 103p, the optical power is reduced, but the cost can be reduced.

[0134] 9 is a diagram showing an outline of a user terminal 103C, which is a third example of a user terminal in the optical access network according to this embodiment. The user terminal 103C is connected to, for example, an optical fiber 105, which is a single-core fiber. Furthermore, the wavelength of the individual upstream signal light USLi is assumed to be different from the wavelength of the individual downstream signal light DSLi.

[0135] The user terminal 103C includes a transmission circuit 103t, a reception circuit 103r, and a wavelength multiplexer / demultiplexer 103w. The wavelength multiplexer / demultiplexer 103w switches the optical propagation path based on the wavelength. The individual downstream signal light DSLi transmitted through the optical fiber 105 is transmitted to the reception circuit 103r by the wavelength multiplexer / demultiplexer 103w. The individual upstream signal light USLi transmitted from the transmission circuit 103t is transmitted to the optical fiber 105 by the wavelength multiplexer / demultiplexer 103w.

[0136] 10 is a diagram showing an outline of a user terminal 103D, which is a fourth example of a user terminal in the optical access network according to this embodiment. The user terminal 103D is assumed to be connected to an optical fiber 105A, which is a multi-core fiber, for example.

[0137] The user terminal 103D includes a transmission circuit 103t and a reception circuit 103r. The individual downstream signal light DSLi transmitted through a predetermined core of the optical fiber 105A is transmitted to the reception circuit 103r. The individual upstream signal light USLi transmitted from the transmission circuit 103t is transmitted to a core of the optical fiber 105A different from the core through which the individual downstream signal light DSLi was transmitted.

[0138] Sixth Embodiment An optical access network according to a sixth embodiment will now be described. Fig. 11 is a diagram showing an outline of an optical access network 6, which is an example of an optical access network according to the sixth embodiment.

[0139] The optical access network according to the sixth embodiment includes wavelength multiplexers / demultiplexers instead of the optical circulators in the optical access network according to the third embodiment.

[0140] The optical access network 6 includes a base station 101 , an optical repeater 611 , and a plurality of user terminals 103 .

[0141] [Optical Repeater 611 ] The optical repeater 611 includes a multiplexer / demultiplexer 602 , a wavelength demultiplexer 107 , an opto-electric converter 108 , a power supply circuit 109 , an optical amplifier circuit 610 , a wavelength multiplexer / demultiplexer 612 and a wavelength multiplexer / demultiplexer 613 .

[0142] In the optical repeater 611, for the configuration common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0143] The multiplexer / splitter 602 splits the downstream signal light DSL transmitted from the base station 101 and transmits it to each of the multiple user terminals 103. The multiplexer / splitter 602 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103 and transmits it to the base station 101. In the optical access network 6, the wavelength of the upstream signal light USLi is assumed to be different from the wavelength of the downstream signal light DSL.

[0144] The optical repeater 611 includes a wavelength multiplexer / demultiplexer 612 and a wavelength multiplexer / demultiplexer 613 on the optical fiber 104. The optical repeater 611 also includes a bypass optical fiber 614 that bypasses and connects the wavelength multiplexer / demultiplexer 612 and the wavelength multiplexer / demultiplexer 613.

[0145] Between the wavelength multiplexer / demultiplexer 612 and the wavelength multiplexer / demultiplexer 613, the downstream signal light DSL passes through the optical fiber 104. On the other hand, between the wavelength multiplexer / demultiplexer 612 and the wavelength multiplexer / demultiplexer 613, the upstream signal light USL passes through the bypass optical fiber 614. The optical repeater 611 includes an optical amplifier circuit 610 in the bypass optical fiber 614 that amplifies the upstream signal light USL. In order to amplify the upstream signal light USL, the optical repeater 611 bypasses the upstream signal light USL through the wavelength multiplexer / demultiplexer 612, the wavelength multiplexer / demultiplexer 613, and the bypass optical fiber 614.

[0146] The wavelength multiplexer / demultiplexer 612 outputs the downstream DSL signal light input from the base station 101 via the wavelength demultiplexer 107 to the wavelength multiplexer / demultiplexer 613. The wavelength multiplexer / demultiplexer 613 outputs the downstream DSL signal light input from the wavelength multiplexer / demultiplexer 612 to the multiplexer / demultiplexer 602.

[0147] Furthermore, the wavelength multiplexer / demultiplexer 613 outputs the upstream signal light USL input from the multiplexer / demultiplexer 602 to the optical amplifier circuit 110 via the bypass optical fiber 314. The wavelength multiplexer / demultiplexer 613 outputs the upstream signal light USL input from the optical amplifier circuit 610 via the bypass optical fiber 614 to the base station 101.

[0148] According to the optical access network of the sixth embodiment, in the optical access network of the first embodiment, the configuration can be further simplified by transmitting the upstream signal light USL and the downstream signal light DSL from the base station through the same optical fiber.

[0149] The wavelength multiplexer / demultiplexer 612 and the wavelength multiplexer / demultiplexer 613 are an example of a first wavelength multiplexer / demultiplexer or a second wavelength multiplexer / demultiplexer, and the bypass optical fiber 614 is an example of a third bypass optical fiber.

[0150] Seventh Embodiment An optical access network according to a seventh embodiment will now be described. Fig. 12 is a diagram showing an outline of an optical access network 7, which is an example of an optical access network according to the seventh embodiment.

[0151] The optical access network according to the seventh embodiment includes a wavelength multiplexer / demultiplexer instead of the optical circulator in the optical access network according to the fifth embodiment.

[0152] The optical access network according to the seventh embodiment amplifies the individual downstream signal light DSLi after branching by power generated by the power supply light PSL. Also, the optical access network according to the seventh embodiment amplifies the individual upstream signal light USLi before combining by power generated by the power supply light PSL.

[0153] The optical access network 7 includes a base station 101, an optical repeater 711, and a plurality of user terminals 103. From the base station 101, upstream signal light USL, downstream signal light DSL, and power supply light PSL are transmitted to the optical repeater 711 via optical fibers 104.

[0154] [Optical Repeater 711] The optical repeater 711 includes a multiplexer / demultiplexer 702, a wavelength demultiplexer 107, an opto-electric converter 108, a power supply circuit 709, an optical amplifier circuit 710c, and an optical amplifier circuit 710d.

[0155] Regarding the configuration of the optical repeater 711 that is common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0156] The multiplexer / splitter 702 splits the downstream signal light DSL transmitted from the base station 101 via the optical fiber 104 and transmits the split light to each of the multiple user terminals 103. The multiplexer / splitter 702 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103 and transmits the upstream signal light USL to the base station 101 via the optical fiber 104. In the optical access network 6, the wavelength of the upstream signal light USL is assumed to be different from the wavelength of the downstream signal light DSL.

[0157] The optical repeater 711 includes a wavelength multiplexer / demultiplexer 712 and a wavelength multiplexer / demultiplexer 713 in an optical fiber 115, which is one of the optical fibers connecting the user terminal 103 and the multiplexer / demultiplexer 702. The optical fiber 115 is, for example, an optical fiber for extension. The optical fiber 115 is longer than the optical fiber 105, for example, having a length of 10 kilometers or more. The optical repeater 711 also includes a bypass optical fiber 714 that bypasses and connects the wavelength multiplexer / demultiplexer 712 and the wavelength multiplexer / demultiplexer 713.

[0158] Between the wavelength multiplexer / demultiplexer 712 and the wavelength multiplexer / demultiplexer 713, the individual downstream signal light DSLi passes through the optical fiber 115. The optical repeater 711 includes an optical amplifier circuit 710c in the bypass optical fiber 714 between the wavelength multiplexer / demultiplexer 712 and the wavelength multiplexer / demultiplexer 713, which amplifies the individual downstream signal light DSLi. On the other hand, between the wavelength multiplexer / demultiplexer 712 and the wavelength multiplexer / demultiplexer 713, the individual upstream signal light USLi passes through the bypass optical fiber 714. The optical repeater 711 includes an optical amplifier circuit 710d in the bypass optical fiber 714, which amplifies the individual upstream signal light USLi. In order to amplify the individual upstream signal light USLi passing through the optical fiber 115, the optical repeater 711 bypasses the individual upstream signal light USLi passing through the optical fiber 115 by the wavelength multiplexer / demultiplexer 712, the wavelength multiplexer / demultiplexer 713, and the bypass optical fiber 714.

[0159] The wavelength multiplexer / demultiplexer 712 outputs the individual downstream signal light DSLi input from the multiplexer / demultiplexer 102 to the optical amplifier circuit 710c. The optical amplifier circuit 710c amplifies the input individual downstream signal light DSLi and outputs it to the wavelength multiplexer / demultiplexer 713. The wavelength multiplexer / demultiplexer 713 outputs the individual downstream signal light DSLi input from the optical amplifier circuit 710c to the user terminal 103.

[0160] Furthermore, the wavelength multiplexer / demultiplexer 713 outputs the individual upstream signal light USLi input from the user terminal 103 to the optical amplifier circuit 710d via the bypass optical fiber 714. The optical amplifier circuit 710d amplifies the individual upstream signal light USLi input from the wavelength multiplexer / demultiplexer 713 and outputs it to the wavelength multiplexer / demultiplexer 712. The wavelength multiplexer / demultiplexer 712 outputs the individual upstream signal light USLi input from the optical amplifier circuit 710d via the bypass optical fiber 714 to the multiplexer / demultiplexer 102.

[0161] The power supply circuit 709 supplies power to each of the optical amplifier circuits 710c and 710d for driving the optical amplifier circuits 710c and 710d.

[0162] The optical amplifier circuit 710c amplifies the individual downstream signal light DSLi transmitted through the optical fiber 115. The optical amplifier circuit 710d amplifies the individual upstream signal light USLi bypassed by the bypass optical fiber 714.

[0163] According to the optical access network of the seventh embodiment, in the optical access network of the first embodiment, the transmission distance from the optical repeater to the user terminal can be further extended, making it possible to communicate with user terminals in remote locations.

[0164] The optical fiber 115 is an example of a sixth optical fiber, the optical amplifier circuit 710d is an example of a fifth optical amplifier, the wavelength multiplexer / demultiplexer 712 and the wavelength multiplexer / demultiplexer 713 are examples of a third wavelength multiplexer / demultiplexer or a fourth wavelength multiplexer / demultiplexer, and the bypass optical fiber 714 is an example of a fourth bypass optical fiber.

[0165] Eighth Embodiment An optical access network according to an eighth embodiment will now be described. Fig. 13 is a diagram showing an outline of an optical access network 8, which is an example of an optical access network according to the eighth embodiment.

[0166] The optical access network according to the eighth embodiment includes a core splitting / coupling device instead of the optical circulator in the optical access network according to the fifth embodiment.

[0167] The optical access network according to the eighth embodiment amplifies the individual downstream signal light DSLi after branching by power generated by the power supply light PSL. Also, the optical access network according to the eighth embodiment amplifies the individual upstream signal light USLi before combining by power generated by the power supply light PSL.

[0168] The optical access network 8 includes a base station 101, an optical repeater 811, and a plurality of user terminals 103. From the base station 101, upstream signal light USL, downstream signal light DSL, and power supply light PSL are transmitted to the optical repeater 811 via optical fibers 104.

[0169] [Optical Repeater 811] The optical repeater 811 includes a multiplexer / demultiplexer 802, a wavelength demultiplexer 107, an opto-electric converter 108, a power supply circuit 809, an optical amplifier circuit 810c, and an optical amplifier circuit 810d.

[0170] In the optical repeater 811, for the configuration common to the optical repeater 111, the description of the optical repeater 111 should be referred to, and detailed description thereof will be omitted here.

[0171] The multiplexer / splitter 802 splits the downstream signal light DSL transmitted from the base station 101 via the optical fiber 104 and transmits the split signal light to each of the multiple user terminals 103. The multiplexer / splitter 802 also combines the individual upstream signal light USLi transmitted from each of the multiple user terminals 103 and transmits the resulting upstream signal light USL to the base station 101 via the optical fiber 104.

[0172] The optical repeater 811 includes a core-splitting coupler 812 and a core-splitting coupler 813 in an optical fiber 115A, which is one of the optical fibers connecting the user terminal 103 and the multiplexer / splitter 802. The optical fiber 115A is, for example, an optical fiber for extension. The optical fiber 115A is assumed to be a multi-core fiber. In the optical fiber 115A, the individual downstream signal light DSLi and the individual upstream signal light USLi are assumed to transmit through different cores. The optical fiber 115A is longer than the optical fiber 105, for example, having a length of 10 kilometers or more. The optical repeater 811 also includes a bypass optical fiber 814 that bypasses and connects the core-splitting coupler 812 and the core-splitting coupler 813. Each of the core-splitting coupler 812 and the core-splitting coupler 813 changes the path along which light propagates based on its core.

[0173] Between the core-splitting coupler 812 and the core-splitting coupler 813, the individual downstream signal light DSLi passes through the optical fiber 115A. The optical repeater 811 includes an optical amplifier circuit 810c in the bypass optical fiber 814 between the core-splitting coupler 812 and the core-splitting coupler 813, which amplifies the individual downstream signal light DSLi. On the other hand, between the core-splitting coupler 812 and the core-splitting coupler 813, the individual upstream signal light USLi passes through the bypass optical fiber 814. The optical repeater 811 includes an optical amplifier circuit 810d in the bypass optical fiber 814, which amplifies the individual upstream signal light USLi. In order to amplify the individual upstream signal light USLi passing through the optical fiber 115A, the optical repeater 811 bypasses the individual upstream signal light USLi passing through the optical fiber 115A using the core-splitting coupler 812, the core-splitting coupler 813, and the bypass optical fiber 814.

[0174] The fiber splitting coupler 812 outputs the individual downstream signal light DSLi input from the multiplexer / splitter 802 to the optical amplifier circuit 810c. The optical amplifier circuit 810c amplifies the input individual downstream signal light DSLi and outputs it to the fiber splitting coupler 813. The fiber splitting coupler 813 outputs the individual downstream signal light DSLi input from the optical amplifier circuit 810c to the user terminal 103.

[0175] Furthermore, the fiber splitting coupler 813 outputs the individual upstream signal light USLi input from the user terminal 103 to the optical amplifier circuit 810d via the bypass optical fiber 814. The optical amplifier circuit 810d amplifies the individual upstream signal light USLi input from the fiber splitting coupler 813 and outputs it to the fiber splitting coupler 812. The fiber splitting coupler 812 outputs the individual upstream signal light USLi input from the optical amplifier circuit 810d via the bypass optical fiber 814 to the multiplexer / splitter 802.

[0176] The power supply circuit 809 supplies power to each of the optical amplifier circuits 810c and 810d for driving the optical amplifier circuits 810c and 810d.

[0177] The optical amplifier circuit 810c amplifies the individual downstream signal light DSLi transmitted through the optical fiber 115A. The optical amplifier circuit 810d amplifies the individual upstream signal light USLi bypassed by the bypass optical fiber 814.

[0178] According to the optical access network of the eighth embodiment, in the optical access network of the first embodiment, the transmission distance from the optical repeater to the user terminal can be further extended, making it possible to communicate with user terminals in remote locations.

[0179] The optical fiber 115A is an example of a sixth optical fiber, the optical amplifier circuit 810d is an example of a sixth optical amplifier circuit, the core splitting coupler 812 and the core splitting coupler 813 are examples of a first core splitting coupler or a second core splitting coupler, and the bypass optical fiber 814 is an example of a fifth bypass optical fiber.

[0180] The optical access network according to the present embodiment can accommodate a greater number of user stations than conventional optical access networks. The optical access network according to the present embodiment can utilize optical fibers in the optical access network, eliminating the need for external power sources other than optical power feeds. Furthermore, the optical access network according to the present embodiment can drive optical amplifier circuits located near multiplexers / splitters using optical power feeds to amplify upstream signal light and suppress degradation of the signal-to-noise ratio. Furthermore, the optical access network according to the present embodiment can amplify individual downstream signal light split by an optical multiplexer / splitter to extend the transmission distance, or can further increase the number of user stations by adding additional optical multiplexers / splitters. Furthermore, the optical access network according to the present embodiment can split and amplify upstream signal light, and transmit the upstream signal to another base station, thereby increasing network redundancy and enabling stable network use.

[0181] Although the optical access network has been described above using the embodiments, the present invention is not limited to the above-described embodiments. Various modifications and improvements, such as combinations and substitutions with part or all of other embodiments, are possible within the scope of the present invention.

[0182] This application claims priority from basic patent application No. 2024-001989, filed with the Japan Patent Office on January 10, 2024, the entire contents of which are incorporated herein by reference.

[0183] 1, 2, 3, 4, 5, 5a, 6, 7, 8 Optical access network 101, 101a Base station 102, 202, 302, 402, 502, 602, 702, 802 Multiplexer / Divider 103, 103A, 103B, 103C, 103D User terminal 104, 105, 106, 106a, 505, 115, 115A Optical fiber 107 Wavelength demultiplexer 108 Photoelectric converter 109, 209, 409, 509 Power supply circuit 110, 110a, 410b, 510c, 510d Optical amplifier circuit 111, 211, 311, 411, 511 Optical repeater 312, 313, 512, 513 Optical circulator 612, 613, 712, 713 Wavelength multiplexer / demultiplexer 812, 813 Core separation coupler 314, 514, 714, 814 Bypass optical fiber 404 Fiber bundle 404a, 404b Optical fiber 516 Multiplier / demultiplexer

Claims

1. An optical repeater comprising: a multiplexer / demultiplexer that branches the downlink signal light output from a base station into individual downlink signal lights output to respective ones of a plurality of user terminals, and combines the individual uplink signal lights output from respective ones of the plurality of user terminals and outputs the combined signal as an uplink signal light to the base station; a first optical fiber that transmits the power supply light output from the base station; and an optical amplification circuit that amplifies any one of the uplink signal light, the individual downlink signal lights, and the individual uplink signal lights with the power obtained by photoelectrically converting the power supply light.

2. The optical repeater according to claim 1, further comprising: the first optical fiber that transmits the downlink signal light and the power supply light; a wavelength demultiplexer provided in the first optical fiber that demultiplexes the downlink signal light and the power supply light according to wavelength; a photoelectric converter that photoelectrically converts the power supply light output from the wavelength demultiplexer; and a power supply circuit that supplies the power obtained by photoelectrically converting the power supply light by the photoelectric converter to the optical amplification circuit.

3. The optical repeater according to claim 2, wherein the first optical fiber transmits the uplink signal light, the downlink signal light, and the power supply light, and the wavelength demultiplexer demultiplexes the uplink signal light and the downlink signal light from the power supply light.

4. The optical repeater according to claim 3, further comprising: a first optical circulator and a second optical circulator provided in the first optical fiber; and a first bypass optical fiber that connects the first optical circulator and the second optical circulator and transmits the uplink signal light from the first optical circulator to the second optical circulator, wherein the optical amplification circuit amplifies the uplink signal light in the first bypass optical fiber.

5. The optical repeater according to claim 1, further comprising: a second optical fiber connected to the multiplexer / demultiplexer that transmits the uplink signal light, wherein the optical amplification circuit amplifies the uplink signal light in the second optical fiber.

6. The optical repeater according to claim 5, further comprising: a third optical fiber connected to the multiplexer / demultiplexer that transmits a second uplink signal light different from the uplink signal light; and a second optical amplification circuit that amplifies the second uplink signal light in the third optical fiber with the power obtained by photoelectrically converting the power supply light.

7. The optical repeater according to claim 1, further comprising: a fourth optical fiber connected to the multiplexer / demultiplexer that transmits the uplink signal light, wherein the optical amplification circuit amplifies the uplink signal light in the fourth optical fiber.

8. A fifth optical fiber connected to the multiplexer / demultiplexer and transmitting the downstream signal light, and a third optical amplifier circuit that amplifies the downstream signal light in the fifth optical fiber by the power obtained by photoelectrically converting the power supply light. The optical repeater according to claim 7, further comprising the above.

9. The optical repeater according to claim 1, further comprising a sixth optical fiber connecting any one of the plurality of user terminals and the multiplexer / demultiplexer, wherein the optical amplifier circuit amplifies either the individual downstream signal light or the individual upstream signal light in the sixth optical fiber.

10. A third optical circulator and a fourth optical circulator provided in the sixth optical fiber, a second bypass optical fiber connecting the third optical circulator and the fourth optical circulator and transmitting either the individual downstream signal light or the individual upstream signal light from the third optical circulator to the fourth optical circulator through the sixth optical fiber, and a fourth optical amplifier circuit that amplifies either the individual downstream signal light or the individual upstream signal light in the second bypass optical fiber. The optical amplifier circuit amplifies the other of the individual downstream signal light and the individual upstream signal light between the third optical circulator and the fourth optical circulator in the sixth optical fiber. The optical repeater according to claim 9, further comprising the above.

11. The optical repeater according to claim 9, further comprising a second multiplexer / demultiplexer connected to the sixth optical fiber.

12. A first wavelength multiplexer / demultiplexer and a second wavelength multiplexer / demultiplexer provided in the first optical fiber, and a third bypass optical fiber connecting the first wavelength multiplexer / demultiplexer and the second wavelength multiplexer / demultiplexer and transmitting the upstream signal light from the first wavelength multiplexer / demultiplexer to the second wavelength multiplexer / demultiplexer. The optical amplifier circuit amplifies the upstream signal light in the third bypass optical fiber. The optical repeater according to claim 3, further comprising the above.

13. A third wavelength multiplexer / demultiplexer and a fourth wavelength multiplexer / demultiplexer provided in the sixth optical fiber, a fourth bypass optical fiber connecting the third wavelength multiplexer / demultiplexer and the fourth wavelength multiplexer / demultiplexer and transmitting either the individual downlink signal light or the individual uplink signal light transmitted from the third wavelength multiplexer / demultiplexer to the fourth wavelength multiplexer / demultiplexer through the sixth optical fiber, and a fifth optical amplification circuit amplifying either the individual downlink signal light or the individual uplink signal light in the fourth bypass optical fiber. The optical amplification circuit amplifies the other of the individual downlink signal light and the individual uplink signal light between the third wavelength multiplexer / demultiplexer and the fourth wavelength multiplexer / demultiplexer of the sixth optical fiber. The optical repeater according to claim 9.

14. A first core separation coupler and a second core separation coupler provided in the sixth optical fiber, a fifth bypass optical fiber connecting the first core separation coupler and the second core separation coupler and transmitting either the individual downlink signal light or the individual uplink signal light transmitted from the first core separation coupler to the second core separation coupler through the sixth optical fiber, and a sixth optical amplification circuit amplifying either the individual downlink signal light or the individual uplink signal light in the fifth bypass optical fiber. The optical amplification circuit amplifies the other of the individual downlink signal light and the individual uplink signal light between the first core separation coupler and the second core separation coupler of the sixth optical fiber. The optical repeater according to claim 9.

15. The first optical fiber is a holey core fiber. The optical repeater according to any one of claims 1 to 14.

16. The first optical fiber is a multi-core fiber. The optical repeater according to any one of claims 1 to 14.

17. An optical access network comprising the optical repeater according to any one of claims 1 to 14, the base station, and the plurality of user terminals.

18. The base station includes a light source that generates the power supply light. The optical access network according to claim 17.

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