Patent Publication Number: US-11381321-B2

Title: Optical power supply system

Description:
CROSS-REFERECE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/442,628 filed on Sep. 24, 2021, which is a National Phase of International Application No. PCT/JP2020/025129 filed Jun. 26, 2020, and claims priority based on Japanese Application Nos. 2019-134238 filed Jul. 22, 2019, and 2019-134241 filed Jul. 22, 2019, entire contents of which are incorporated here in reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to optical power supply. 
     BACKGROUND ART 
     Recently, there has been studied an optical power supply system that converts electric power into light (called feed light), transmits the feed light, converts the feed light into electric energy, and uses the electric energy as electric power. 
     There is disclosed in Patent Literature 1 an optical communication device that includes: an optical transmitter that transmits signal light modulated with an electric signal and feed light for supplying electric power; an optical fiber including a core that transmits the signal light, a first cladding that is formed around the core, has a refractive index lower than that of the core, and transmits the feed light, and a second cladding that is formed around the first cladding, and has a refractive index lower than that of the first cladding; and an optical receiver that operates with electric power obtained by converting the feed light transmitted through the first cladding of the optical fiber, and converts the signal light transmitted through the core of the optical fiber into the electric signal. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2010-135989 A 
     SUMMARY OF INVENTION 
     Problem to Solve 
     In optical power supply, further improvement of optical power supply efficiency is required. As one way therefor, achievement of efficient power supply according to the electric power load at the power receiving side is required. 
     Solution to Problem 
     An optical power supply system according to an aspect of the present disclosure includes: 
     a power sourcing equipment that outputs feed light; 
     a powered device that converts the feed light into electric power, wherein the feed light is from the power sourcing equipment, and the electric power obtained by the conversion by the powered device is supplied to a communicator; 
     an information obtaining part that obtains communication operation information on an operation status of communication that is performed by the communicator; and 
     a power supply controller that, based on the communication operation information obtained by the information obtaining part, controls output of the feed light from the power sourcing equipment. 
     An optical power supply system according to another aspect of the present disclosure includes: 
     a power sourcing equipment that outputs feed light; 
     an optical branching device to which the feed light from the power sourcing equipment is input and to which a plurality of powered devices that convert the feed light into electric power is connectable; 
     a detector that detects the number of powered devices connected to the optical branching device; and 
     a power supply controller that, based on the number of connected powered devices detected by the detector, controls output of the feed light from the power sourcing equipment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a power over fiber system according to a first embodiment of the present disclosure. 
         FIG. 2  is a block diagram of a power over fiber system according to a second embodiment of the present disclosure. 
         FIG. 3  is a block diagram of the power over fiber system according to the second embodiment of the present disclosure and shows optical connectors and so forth. 
         FIG. 4  is a block diagram of a power over fiber system according to another embodiment of the present disclosure. 
         FIG. 5  is a block diagram of a power over fiber system according to a third embodiment of the present disclosure. 
         FIG. 6  is a block diagram of a modification of the power over fiber system according to the third embodiment of the present disclosure. 
         FIG. 7  is a block diagram of a power over fiber system according to a fourth embodiment of the present disclosure. 
         FIG. 8  is a block diagram of a power over fiber system according to a fifth embodiment of the present disclosure. 
         FIG. 9  is a block diagram of a modification of the power over fiber system according to the fifth embodiment of the present disclosure. 
         FIG. 10  is a block diagram of a power over fiber system according to a sixth embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. 
     (1) Outline of System 
     First Embodiment 
     As shown in  FIG. 1 , a power over fiber (PoF) system  1 A of this embodiment includes a power sourcing equipment (PSE)  110 , an optical fiber cable  200 A and a powered device (PD)  310 . 
     In the present disclosure, a power sourcing equipment converts electric power into optical energy and supplies (sources) the optical energy, and a powered device receives (draws) the supplied optical energy and converts the optical energy into electric power. 
     The power sourcing equipment  110  includes a semiconductor laser  111  for power supply. 
     The optical fiber cable  200 A includes an optical fiber  250 A that forms a transmission path of feed light. 
     The powered device  310  includes a photoelectric conversion element  311 . 
     The power sourcing equipment  110  is connected to a power source, and electrically drives the semiconductor laser  111  and so forth. 
     The semiconductor laser  111  oscillates with the electric power from the power source, thereby outputting feed light  112 . 
     The optical fiber cable  200 A has one end  201 A connectable to the power sourcing equipment  110  and the other end  202 A connectable to the powered device  310  to transmit the feed light  112 . 
     The feed light  112  from the power sourcing equipment  110  is input to the one end  201 A of the optical fiber cable  200 A, propagates through the optical fiber  250 A, and is output from the other end  202 A of the optical fiber cable  200 A to the powered device  310 . 
     The photoelectric conversion element  311  converts the feed light  112  transmitted through the optical fiber cable  200 A into electric power. The electric power obtained by the conversion of the feed light  112  by the photoelectric conversion element  311  is driving power needed in the powered device  310 . The powered device  310  is capable of outputting, for an external device(s), the electric power obtained by the conversion of the feed light  112  by the photoelectric conversion element  311 . 
     Semiconductor materials of semiconductor regions of the semiconductor laser  111  and the photoelectric conversion element  311  are semiconductors having a laser wavelength being a short wavelength of 500 nm or less. The semiconductor regions exhibit light-electricity conversion effect. 
     Semiconductors having a laser wavelength being a short wavelength have a large band gap and a high photoelectric conversion efficiency, and hence improve photoelectric conversion efficiency at the power supplying side and the power receiving side in optical power supply, and improve optical power supply efficiency. 
     Hence, as the semiconductor materials, laser media having a laser wavelength (base wave) of 200 nm to 500 nm may be used. Examples thereof include diamond, gallium oxide, aluminum nitride and gallium nitride. 
     Further, as the semiconductor materials, semiconductors having a band gap of 2.4 eV or greater are used. 
     For example, laser media having a band gap of 2.4 eV to 6.2 eV may be used. Examples thereof include diamond, gallium oxide, aluminum nitride and gallium nitride. 
     Laser light having a longer wavelength tends to have a higher transmission efficiency, whereas laser light having a shorter wavelength tends to have a higher photoelectric conversion efficiency. Hence, when laser light is transmitted for a long distance, laser media having a laser wavelength (base wave) of greater than 500 nm may be used as the semiconductor materials, whereas when the photoelectric conversion efficiency is given priority, laser media having a laser wavelength (base wave) of less than 200 nm may be used as the semiconductor materials. 
     Any of these semiconductor materials may be used in one of the semiconductor laser  111  and the photoelectric conversion element  311 . This improves the photoelectric conversion efficiency at either the power supplying side or the power receiving side, and improves the optical power supply efficiency. 
     Second Embodiment 
     As shown in  FIG. 2 , a power over fiber (PoF) system  1  of this embodiment includes a power supply system through an optical fiber and an optical communication system therethrough, and includes: a first data communication device  100  including a power sourcing equipment (PSE)  110 ; an optical fiber cable  200 ; and a second data communication device  300  including a powered device (PD)  310 . 
     The power sourcing equipment  110  includes a semiconductor laser  111  for power supply. The first data communication device  100  includes, in addition to the power sourcing equipment  110 , a transmitter  120  and a receiver  130  for data communication. The first data communication device  100  corresponds to a data terminal equipment (DTE), a repeater or the like. The transmitter  120  includes a semiconductor laser  121  for signals and a modulator  122 . The receiver  130  includes a photodiode  131  for signals. 
     The optical fiber cable  200  includes an optical fiber  250  including: a core  210  that forms a transmission path of signal light; and a cladding  220  that is arranged so as to surround the core  210  and forms a transmission path of feed light. 
     The powered device  310  includes a photoelectric conversion element  311 . The second data communication device  300  includes, in addition to the powered device  310 , a transmitter  320 , a receiver  330  and a data processing unit  340 . The second data communication device  300  corresponds to a power end station or the like. The transmitter  320  includes a semiconductor laser  321  for signals and a modulator  322 . The receiver  330  includes a photodiode  331  for signals. The data processing unit  340  processes received signals. The second data communication device  300  is a node in a communication network. The second data communication device  300  may be a node that communicates with another node. 
     The first data communication device  100  is connected to a power source, and electrically drives the semiconductor laser  111 , the semiconductor laser  121 , the modulator  122 , the photodiode  131  and so forth. The first data communication device  100  is a node in a communication network. The first data communication device  100  may be a node that communicates with another node. 
     The semiconductor laser  111  oscillates with the electric power from the power source, thereby outputting feed light  112 . 
     The photoelectric conversion element  311  converts the feed light  112  transmitted through the optical fiber cable  200  into electric power. The electric power obtained by the conversion of the feed light  112  by the photoelectric conversion element  311  is driving power needed in the second data communication device  300 , for example, driving power for the transmitter  320 , the receiver  330  and the data processing unit  340 . The second data communication device  300  may be capable of outputting, for an external device(s), the electric power obtained by the conversion of the feed light  112  by the photoelectric conversion element  311 . 
     The modulator  122  of the transmitter  120  modulates laser light  123  output by the semiconductor laser  121  to signal light  125  on the basis of transmission data  124 , and outputs the signal light  125 . 
     The photodiode  331  of the receiver  330  demodulates the signal light  125  transmitted through the optical fiber cable  200  to an electric signal, and outputs the electric signal to the data processing unit  340 . The data processing unit  340  transmits data of the electric signal to a node, and also receives data from the node and outputs the data to the modulator  322  as transmission data  324 . 
     The modulator  322  of the transmitter  320  modulates laser light  323  output by the semiconductor laser  321  to signal light  325  on the basis of the transmission data  324 , and outputs the signal light  325 . 
     The photodiode  131  of the receiver  130  demodulates the signal light  325  transmitted through the optical fiber cable  200  to an electric signal, and outputs the electric signal. Data of the electric signal is transmitted to a node, whereas data from the node is the transmission data  124 . 
     The feed light  112  and the signal light  125  from the first data communication device  100  are input to one end  201  of the optical fiber cable  200 , propagate through the cladding  220  and the core  210 , respectively, and are output from the other end  202  of the optical fiber cable  200  to the second data communication device  300 . 
     The signal light  325  from the second data communication device  300  is input to the other end  202  of the optical fiber cable  200 , propagates through the core  210 , and is output from the one end  201  of the optical fiber cable  200  to the first data communication device  100 . 
     As shown in  FIG. 3 , the first data communication device  100  includes a light input/output part  140  and an optical connector  141  attached to the light input/output part  140 , and the second data communication device  300  includes a light input/output part  350  and an optical connector  351  attached to the light input/output part  350 . An optical connector  230  provided at the one end  201  of the optical fiber cable  200  is connected to the optical connector  141 , and an optical connector  240  provided at the other end  202  of the optical fiber cable  200  is connected to the optical connector  351 . The light input/output part  140  guides the feed light  112  to the cladding  220 , guides the signal light  125  to the core  210 , and guides the signal light  325  to the receiver  130 . The light input/output part  350  guides the feed light  112  to the powered device  310 , guides the signal light  125  to the receiver  330 , and guides the signal light  325  to the core  210 . 
     As described above, the optical fiber cable  200  has the one end  201  connectable to the first data communication device  100  and the other end  202  connectable to the second data communication device  300  to transmit the feed light  112 . In this embodiment, the optical fiber cable  200  transmits the signal light  125 ,  325  bidirectionally. 
     As the semiconductor materials of the semiconductor regions, which exhibit the light-electricity conversion effect, of the semiconductor laser  111  and the photoelectric conversion element  311 , any of those described in the first embodiment can be used, thereby achieving a high optical power supply efficiency. 
     Like an optical fiber cable  200 B of a power over fiber system  1 B shown in  FIG. 4 , an optical fiber  260  that transmits signal light and an optical fiber  270  that transmits feed light may be provided separately. Further, the optical fiber cable  200 B may be composed of a plurality of optical fiber cables. 
     (2) Power Supply Controller 
     Next, a power supply controller that controls a power supply amount will be described. 
     Third Embodiment 
       FIG. 5  is a block diagram of a power over fiber system according to a third embodiment to which a power supply controller is applied. In  FIG. 5 , the same components as those described above are denoted by the same reference signs, and detailed descriptions thereof are omitted. 
     As shown in  FIG. 5 , a power over fiber system  1 C of the third embodiment includes a first data communication device  100 C, an optical fiber cable  200  and a second data communication device  300 C. 
     The second data communication device  300 C includes, in addition to the powered device  310 , the transmitter  320 , the receiver  330  and the data processing unit  340 , a wireless communicator  360  and a communication monitor  370 . The second data communication device  300 C corresponds to a wireless base station, for example. 
     The wireless communicator  360  performs wireless communication to transmit and receive data to and from a plurality of wireless communicators. The wireless communicator  360  transmits, by wireless communication, data received from the data processing unit  340 , and also transmits data received by wireless communication to the data processing unit  340 . The wireless communicator  360  consumes electric power corresponding to its communication load, and is driven by electric power supplied from the powered device  310 . 
     The communication monitor  370  monitors the operation status of the wireless communication that is performed by the wireless communicator  360 , and obtains communication operation information on this operation status. 
     The communication operation information is information on the communication load of the wireless communication. More specifically, the communication operation information includes at least one of measured communication load information, potential communication load information and predicted communication load information. The measured communication load information is information on the communication load actually measured, and includes the number of MIMO (Multiple-Input and Multiple-Output) streams, a using bandwidth and so forth of the wireless communication that is performed by the wireless communicator  360 . The potential communication load information is information on the potential maximum communication load, and includes the number of active users that coverable by the wireless communication that is performed by the wireless communicator  360 . The predicted communication load information is information on the communication load predicted, and includes information in which date-and-time information (at least one of a date, a day of the week, and time) is associated with a communication load that is expected to be at the time, such as the amount of the communication load for a time period (e.g. the communication load is small during nighttime, the communication load is large during daytime, etc.). The predicted communication load information may include information on use of event venues (date and time of use, an expected number of participants, etc.) where the communication load is expected to increase, within the communication range. The communication monitor  370  may record the actual communication load (e.g. communication volume) every day and create or update the predicted communication load information on the basis of this record. 
     The communication monitor  370  transmits the obtained communication operation information to the data processing unit  340 . The data processing unit  340  puts the received communication operation information in the transmission data  324  and outputs the transmission data  324  to the modulator  322  of the transmitter  320 . The modulator  322  modulates the laser light  323  on the basis of the transmission data  324 , thereby outputting the signal light  325  containing the communication operation information to the first data communication device  100 C through the optical fiber cable  200 . 
     The first data communication device  100 C includes, in addition to the power sourcing equipment  110 , the transmitter  120  and the receiver  130 , a power supply controller  150 . 
     The power supply controller  150  obtains the communication operation information from the signal light  325  output from the photodiode  131  of the receiver  130 . Then, on the basis of the obtained communication operation information, the power supply controller  150  controls output of the feed light  112  from the power sourcing equipment  110  (semiconductor laser  111 ). 
     Details thereof are as follows. If the power supply controller  150  obtains the measured communication load information (the number of MIMO streams, a using bandwidth, etc.) as the communication operation information, the power supply controller  150  adjusts the output of the feed light  112  on the basis of the ratio of the measured communication load to the maximum value (the maximum number of streams, the maximum bandwidth, etc.). If the power supply controller  150  obtains the potential communication load information (the number of active users coverable, etc.) as the communication operation information, the power supply controller  150  adjusts the output of the feed light  112  on the basis of the maximum communication volume assumed from the potential communication load information. If the power supply controller  150  obtains the predicted communication load information as the communication operation information, the power supply controller  150  obtains the communication load predicted for the current date and/or time from the predicted communication load information, and adjusts the output of the feed light  112  on the basis of this communication load. These multiple types of the communication operation information may be prioritized in advance to be used for the adjustment of the output (e.g. the measured communication load information is given the highest priority, etc.). 
     Thus, the output of the power sourcing equipment  110  is adjusted so as to correspond to the communication load of the wireless communicator  360 , by extension, to the electric power load of the powered device  310 . That is, in a conventional power supply system, a power sourcing equipment supplies certain (maximum) electric power to a powered device regardless of the electric power load of the powered device, and hence surplus electric power is consumed wastefully when the electric power load of the powered device is low, but in the power over fiber system  1 C of this embodiment, the output of the power sourcing equipment  110  is adjusted so as to correspond to the electric power load of the powered device  310 . Hence, unlike the conventional system, efficient power supply according to the electric power load at the power receiving side can be achieved. 
     The configuration of the third embodiment is applicable to the power over fiber system shown in  FIG. 4 . In this case, the first data communication device  100  and the second data communication device  300  shown in  FIG. 4  are replaced by the first data communication device  100 C and the second data communication device  300 C, respectively. 
     In the power over fiber system  1 C of the third embodiment, as shown in  FIG. 6 , the communication operation information may be transmitted from the communication monitor  370  of the second data communication device  300 C to the power supply controller  150  of the first data communication device  100 C through a transmission path  281  that is different from the optical fiber cable  200 . In this case, the communication monitor  370  may be an external device independent of the second data communication device  300 C. 
     Fourth Embodiment 
       FIG. 7  is a block diagram of a power over fiber system according to a fourth embodiment to which a power supply controller is applied. In  FIG. 7 , the same components as those described above are denoted by the same reference signs, and detailed descriptions thereof are omitted. 
     As shown in  FIG. 7 , a power over fiber system  1 D of the fourth embodiment is different from the power over fiber system  1 C of the third embodiment, mainly in that a communication system is separate from a power supply system. 
     The communication system of the power over fiber system  1 D includes a first communicator  160 , a communication cable  290 , a second communicator  380 , a wireless communicator  360  and a communication monitor  370 . 
     The first communicator  160  and the second communicator  380  perform data communication with one another through the communication cable  290 . The wireless communicator  360  performs wireless communication with a plurality of wireless communicators. 
     The wireless communicator  360  transmits, by wireless communication, data received from the second communicator  380 , and also transmits data received by wireless communication to the second communicator  380 . The wireless communicator  360  consumes electric power corresponding to its communication load, and is driven by electric power supplied from the powered device  310 . 
     The communication monitor  370  monitors the operation status of the wireless communication that is performed by the wireless communicator  360 , and obtains the communication operation information on this operation status. The communication monitor  370  transmits the obtained communication operation information to the second communicator  380 . The second communicator  380  transmits the received communication operation information to the first communicator  160  in the same manner as other transmission data. 
     The power supply system of the power over fiber system  1 D includes a power sourcing equipment  110 , an optical fiber cable  200 A and a powered device  310 , and is configured in the same manner as the power over fiber system  1 A of the first embodiment. The output of the power sourcing equipment  110  is controlled by a power supply controller  150 . 
     The power supply controller  150  obtains, from the first communicator  160 , the communication operation information transmitted from the second communicator  380 . Then, on the basis of the obtained communication operation information, the power supply controller  150  controls output of the feed light  112  from the power sourcing equipment  110  (semiconductor laser  111 ). The communication operation information may be transmitted from the communication monitor  370  to the power supply controller  150  through a transmission path that is different from the communication cable  290 . 
     Thus, as in the third embodiment, the output of the power sourcing equipment  110  is adjusted so as to correspond to the communication load of the wireless communicator  360 , by extension, to the electric power load of the powered device  310 . Hence, unlike the conventional system, in which a power sourcing equipment supplies certain (maximum) electric power to a powered device regardless of the electric power load of the powered device, efficient power supply according to the electric power load at the power receiving side can be achieved. 
     Fifth Embodiment 
       FIG. 8  is a block diagram of a power over fiber system according to a fifth embodiment to which a power supply controller is applied. In  FIG. 8 , the same components as those described above are denoted by the same reference signs, and detailed descriptions thereof are omitted. 
     As shown in  FIG. 8 , a power over fiber system  1 E of the fifth embodiment includes a first data communication device  100 E at the power supplying side, an optical fiber cable  200 , and an optical power supply network  390  at the power receiving side. 
     The optical power supply network  390  can perform optical communication with the first data communication device  100 E at the power supplying side (or within the optical power supply network  390 ) while receiving power supply from the first data communication device  100 E. The optical power supply network  390  corresponds to, for example, an IoT (Internet of Things) system. The optical power supply network  390  of this embodiment includes a plurality of optical splitters (optical branching devices)  391  connected to the optical fiber cable  200  in series. Each optical splitter  391  has at least two connection ports  391   a . To (and from) each connection port  391   a , another optical splitter  391  or a second data communication device  300  is connectable (and disconnectable). Each optical splitter  391  splits, at a certain ratio, the signal light and the feed light transmitted from the first data communication device  100 E through the optical fiber cable  200  for the optical splitter(s)  391  and/or the second data communication device(s)  300  connected thereto. 
     In this embodiment, each second data communication device  300  corresponds to, for example, a network camera or a network sensor. When a second data communication device  300  detects its connection to an optical splitter  391 , the second data communication device  300  can perform data communication by the signal light  125 ,  325  and receive power supply by the feed light  112  (can be driven by the electric power into which the powered device  310  converts the feed light  112 ). The number of second data communication devices  300  (powered devices  310 ) connectable to the optical power supply network  390  is not specifically limited. 
     The optical power supply network  390  is configured such that a plurality of second data communication devices  300  (powered devices  310 ) are connectable to each optical branching device to which the feed light  112  from the power sourcing equipment  110  is input. Hence, for example, a single optical splitter  391  may be capable of splitting the signal light and the feed light for a plurality of second data communication devices  300  directly. Further, optical branching devices other than optical splitters may be used to split the signal light and the feed light. 
     The first data communication device  100 E includes, in addition to the power sourcing equipment  110 , the transmitter  120  and the receiver  130 , a load detector  161  and a power supply controller  151  as a power supply controller. 
     The load detector  161  detects the number of second data communication devices  300  (powered devices  310 ) connected to the optical splitters  391  as the electric power load in the optical power supply network  390  at the power receiving side. 
     More specifically, the load detector  161  transmits signals to addresses that are assigned in advance to respective second data communication devices  300 , and detects whether the second data communication devices  300  are connected to the optical splitters  391  by presence or absence of return signals therefrom. The load detector  161  detects the number of connected second data communication device  300  (powered devices  310 ) as the total number of the detections, and outputs the number thereof to the power supply controller  151 . The signals are transmitted and received as the signal light  125 ,  325  through the oscillator  120  and the receiver  130 . The address of each second data communication device  300  may be a unique address assigned thereto in advance or an address assigned when the second data communication device  300  is connected to the optical power supply network  390 , for example. 
     The load detector  161  performs this detection process at the startup of the system and also regularly while the system is in operation. 
     The load detector  161  may detect connected powered devices  310  on the basis of signals from the power receiving side. 
     More specifically, when a second data communication device  300  is connected to an optical splitter  391 , the second data communication device  300  or the optical splitter  391  detects the connection and outputs a signal for notifying the connection to the power supplying side. When receiving the notifying signal, the load detector  161 , as described above, transmits a signal(s) for detecting the second data communication device  300 , and detects whether the second data communication device  300  is connected to the optical splitter  391  by presence or absence of a return signal therefrom. The connection of the second data communication device  300  and the optical splitter  391  may be detected physically, for example, by a connection connector, or may be detected from a switch operation on a switch or the like that user operates when connecting these, the switch being provided on the second data communication device  300  or the optical splitter  391 . 
     The power supply controller  151  controls output of the feed light  112  from the power sourcing equipment  110  (semiconductor laser  111 ) on the basis of information on the number of connected powered devices  310  input from the load detector  161 . For example, the power supply controller  151  has, in advance, correlation data between the number of connected powered devices  310  and the power supply amount needed for the number thereof, adjusts the output of the power sourcing equipment  110  by using this data. 
     Thus, the output of the power sourcing equipment  110  is adjusted so as to correspond to the electric power load in the optical power supply network  390  at the power receiving side. That is, in a conventional power supply system, a power sourcing equipment supplies certain (maximum) electric power to the power receiving side regardless of the electric power load at the power receiving side, and hence surplus electric power is consumed wastefully when the electric power load at the power receiving side is low, but in the power over fiber system  1 E of this embodiment, the output of the power sourcing equipment  110  is adjusted so as to correspond to the electric power load at the power receiving side. Hence, unlike the conventional system, efficient power supply according to the electric power load at the power receiving side can be achieved. 
     In the power over fiber system  1 E of the fifth embodiment, as shown in  FIG. 9 , the signals for detecting connected powered devices  310  may be transmitted and received through a transmission path  281  that is different from the optical fiber cable  200 . 
     Further, as in the power over fiber system shown in  FIG. 4 , in the power over fiber system  1 E of the fifth embodiment, an optical fiber that transmits signal light and an optical fiber that transmits feed light may be provided separately. 
     Sixth Embodiment 
       FIG. 10  is a block diagram of a power over fiber system according to a sixth embodiment to which a power supply controller is applied. In  FIG. 10 , the same components as those described above are denoted by the same reference signs, and detailed descriptions thereof are omitted. 
     As shown in  FIG. 10 , a power over fiber system  1 F of the sixth embodiment is different from the power over fiber system  1 E of the fifth embodiment, mainly in that an optical power supply network has a power supply system only. However, the power over fiber system  1 F may have a not-shown communication system independent of the power supply system. 
     The power over fiber system  1 F includes a power sourcing equipment  110 , an optical fiber cable  200 A and an optical power supply network  390 F. The optical power supply network  390 F includes a plurality of optical splitters  391  connected to the optical fiber cable  200 A in series. To each optical splitter  391 , a second data communication device(s)  300  (powered device  310 ) is connectable. In the optical power supply network  390 F, to the second data communication devices  300  connected to the optical splitters  391 , optical power is supplied from the power sourcing equipment  110  through the optical fiber cable  200 A. 
     The output of the power sourcing equipment  110  is controlled by a power supply controller  151 . 
     The power supply controller  151  obtains information on the number of connected powered devices  310  from the load detector  161 . The load detector  161  detects the number of connected powered devices  310  on the basis of signals transmitted and received to and from the optical splitters  391  through a transmission path  281 F, and outputs information thereon to the power supply controller  151 . The power supply controller  151  controls output of the feed light  112  from the power sourcing equipment  110  (semiconductor laser  111 ) on the basis of the obtained information on the number of connected powered devices  310 . 
     Thus, as in the fifth embodiment, the output of the power sourcing equipment  110  is adjusted so as to correspond to the electric power load in the optical power supply network  390  at the power receiving side. Hence, unlike the conventional system, in which a power sourcing equipment supplies certain (maximum) electric power to a powered device(s) regardless of the electric power load of the powered device(s), efficient power supply according to the electric power load at the power receiving side can be achieved. 
     Although some embodiments of the present disclosure have been described above, these embodiments are made for purposes of illustration and example only. The present invention can be carried out in various other forms, and each component may be omitted, replaced or modified/changed within a range not departing from the scope of the present invention. 
     For example, in the third and fourth embodiments, the electric power obtained by the conversion by the powered device  310  is supplied to the wireless communicator  360  that performs wireless communication. However, the target to which the electric power is supplied may be any communicator. For example, the target may be a communicator that performs not wireless communication but wired communication. 
     INDUSTRIAL APPLICABILITY 
     As described above, an optical power supply system according to the present invention is useful for achieving efficient power supply according to the electric power load at the power receiving side.