Patent Publication Number: US-11387904-B2

Title: Powered device and power sourcing equipment of optical power supply system, and optical power supply system

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 17/442,618 filed on Sep. 24, 2021, which is a National Phase of International Application Number PCT/JP2020/038944 filed Oct. 15, 2020 and claims priority to Japanese Application Numbers 2019-193121 filed Oct. 24, 2019 and 2019-195210 filed Oct. 28, 2019. The entire contents of which applications are incorporated herein by their reference. 
     TECHNICAL FIELD 
     The present disclosure relates to optical power supply. 
     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, ideally, electric power transmitted from the power supplying side is all consumed at the power receiving side. However, the load is not constant but fluctuates, and hence electric power more than consumed by the load could be transmitted. In this case, electric power is left at the power receiving side, which is inefficient. 
     Solution to Problem 
     An aspect of the present disclosure is an optical power supply system including: 
     a power sourcing equipment including a semiconductor laser that oscillates with electric power, thereby outputting feed light; and 
     a powered device including a photoelectric conversion element that converts the feed light into electric power, the feed light being from the power sourcing equipment, 
     wherein the powered device includes:
         a photoelectric conversion element that converts feed light into electric power, the feed light being from a   power sourcing equipment;       

     a semiconductor laser for feedback that oscillates with a portion of the electric power obtained by the conversion by the photoelectric conversion element, thereby outputting feed light to a power supplying side; and
         a control device that monitors a power supply amount of the electric power to a load, the electric power being obtained by the conversion by the photoelectric conversion element, and according to the power supply amount, controls an electricity-light conversion amount of conversion that is performed by the semiconductor laser, and       

     wherein the power sourcing equipment includes:
         a semiconductor laser that oscillates with electric power, thereby outputting feed light to a powered device; and   a photoelectric conversion element for feedback that converts feed light into electric power, the feed light being from the powered device, and outputs the electric power as driving power for the semiconductor laser.       

     An aspect of the present disclosure is an optical power supply system includes: 
     a power sourcing equipment including a semiconductor laser that oscillates with electric power, thereby outputting feed light; and 
     a powered device including a photoelectric conversion element that converts the feed light into electric power, the feed light being from the power sourcing equipment, 
     wherein the powered device includes:
         a photoelectric conversion element that converts feed light into electric power, the feed light being from a power sourcing equipment;   an optical branching device for feedback that outputs a portion of the feed light to be input to the photoelectric conversion element from the power sourcing equipment, to a power supplying side as feedback feed light; and   a control device that monitors a power supply amount of the electric power to a load, the electric power being obtained by the conversion by the photoelectric conversion element, and according to the power supply amount, controls a feedback amount of feedback that is performed by the optical branching device, and       

     wherein the power sourcing equipment includes:
         a semiconductor laser that oscillates with electric power, thereby outputting feed light to a powered device;   an optical combining device for feedback that combines feedback feed light that is from the powered device and the feed light output by the semiconductor laser into combined feed light, and outputs the combined feed light; and   a control device that controls output of the semiconductor laser such that an energy amount that the optical combining device outputs is constant.       

     Advantageous Effects of Invention 
     An optical power supply system according to an aspect of the present disclosure enables execution of efficient optical power supply with surplus electric power at the power receiving side controlled even if the load fluctuates. 
    
    
     
       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 provided with a function of feedback power supply. 
         FIG. 6  is a graph showing temporal change in electric power demand and supply in a comparative example. 
         FIG. 7  is a graph showing temporal change in electric power demand and supply in the power over fiber system shown in  FIG. 5 . 
         FIG. 8  is a block diagram of a power over fiber system provided with a function of feedback feed light. 
         FIG. 9  is a graph showing temporal change in electric power demand and supply in the power over fiber system shown in  FIG. 8 . 
     
    
    
     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) Control of Feedback Power Supply 
     Next, control of feedback power supply will be described with reference to  FIG. 5 ,  FIG. 6  and  FIG. 7  in addition to  FIG. 1  to  FIG. 4 . 
       FIG. 5  shows a configuration of a power over fiber system  1 A 1  provided with a function of feedback power supply. 
     The power over fiber system  1 A 1  is configured by further having the following components in the powered device  310  and the power sourcing equipment  110  of the power over fiber system  1 A (configured as shown in  FIG. 1 ) described as the first embodiment. 
     The powered device  310  includes a semiconductor laser  311 F for feedback and a control device  312 . The semiconductor laser  311 F oscillates with a portion of the electric power obtained by the conversion by the photoelectric conversion element  311 , thereby outputting feedback feed light  112 F to the power supplying side. The control device  312  monitors the power supply amount (Q 1 ) of the electric power (Q) that is supplied to a load  20 , the electric power (Q) being obtained by the conversion by the photoelectric conversion element  311 , and controls the electricity-light conversion amount of conversion that is performed by the semiconductor laser for feedback, namely a feedback power supply amount (Q 2 ), according to the power supply amount (Q 1 ). 
     The power sourcing equipment  110  includes a photoelectric conversion element  111 F for feedback. The photoelectric conversion element  111 F converts the feedback feed light  112 F into electric power, the feedback feed light  112 F being from the powered device  310 , and outputs the electric power as a portion of driving power for the semiconductor laser  111 . 
     The semiconductor laser  111  outputs the feed light  112  with a constant energy value. This is converted into the electric power Q by the photoelectric conversion element  311  of the powered device  310 . Hence, the electric power Q is also a constant value.  FIG. 6  and  FIG. 7  each show a graph of temporal change in the electric power Q and so forth. 
     The power supply amount Q 1  to the load  20  fluctuates according to the operation status of the load  20 , for example, as shown in  FIG. 6 . 
       FIG. 6  shows a case where 110% electric power Q is prepared, wherein the maximum value of the load  20  is 100%. Since the load  20  fluctuates in the range of up to the maximum value, no electric power shortage occurs, and consequently the system can be prevented from going down. 
     However, in this case, surplus electric power R 1  is wasted, which is inefficient. 
     The control device  312  controls the electricity-light conversion amount of conversion, which is performed by the semiconductor laser  311 F, namely the feedback power supply amount Q 2 , such that the value (Q−Q 2 ) obtained by subtracting the conversion amount Q 2  from the electric power Q obtained by the conversion by the photoelectric conversion element  311  converges to a target value that exceeds the load  20  by a predetermined percentage. 
     In this manner, a portion of the surplus electric power R 1  is transmitted to the power supplying side as the feedback power supply amount Q 2 . 
     The feedback power supply amount Q 2  is input to the photoelectric conversion element  111 F as the feedback feed light  112 F and converted by the photoelectric conversion element  111 F into electric power that serves as the driving power for the semiconductor laser  111 . 
     The driving power for the semiconductor laser  111  is covered by this electric power, which is based on the feedback power supply amount Q 2 , and electric power newly provided from a power source  10 . 
     The lower limit of the predetermined percentage is 0%, and the upper limit thereof is a percentage by which the electric power Q exceeds the maximum value of the load  20 . In this example, the percentage by which the electric power Q exceeds the maximum value of the load  20  is 10%. Hence, the predetermined percentage is set in the range of 0-10%. For example, the target value is set to a value that is 10% higher than the load  20 , which is shown in  FIG. 7 . 
     If the power supply amount Q 1  to the load  20  is the maximum value, 100%, the feedback power supply amount Q 2  is zero and no feedback is performed. As the power supply amount Q 1  to the load  20  decreases from the maximum value, the feedback power supply amount Q 2  is increased to keep surplus electric power R 2  small. 
     Although the semiconductor laser  111  outputs the feed light  112  with a constant energy value, and the feed light  112  is converted into the electric power Q, which is constant, by the photoelectric conversion element  311  of the powered device  310 , since the electric power Q 2 , which is unconsumed by the load  20 , is fed back, the electric power newly provided from the power source  10  is only “Q−Q 2 ” equivalent, which enables execution of efficient optical power supply with the surplus electric power R 2  at the power receiving side controlled even if the load  20  fluctuates. 
     In the above description, loss due to the conversion efficiency, the transmission efficiency and so forth being not 100% is ignored. 
     The load  20  includes an external load (electric power that is output for an external device(s)) in addition to the driving power needed in the powered device  310 , but excludes the feedback power supply amount Q 2 . 
     The power over fiber system  1 A 1  shown in  FIG. 5  is configured by the first embodiment as a base, but may be configured by the power over fiber system  1  or  1 B (configured as shown in  FIG. 2  to  FIG. 4 ), the power over fiber system  1  being described as the second embodiment, as a base with the components ( 111 F,  311 F,  312 ) for achieving the function of feedback power supply added in the same manner, thereby being carried out as a configuration including an optical communication system. 
     In this case, the electric power Q obtained by the conversion by the photoelectric conversion element  311  of the powered device  310  is also used as the driving power for the transmitter  320  and the receiver  330  of the second data communication device  300 . 
     (3) Control of Feedback Feed Light 
     Next, control of feedback feed light will be described with reference to  FIG. 6 ,  FIG. 8  and  FIG. 9  in addition to  FIG. 1  to  FIG. 4 . 
       FIG. 8  shows a configuration of a power over fiber system  1 A 2  provided with a function of feedback feed light. 
     The power over fiber system  1 A 2  is configured by further having the following components in the powered device  310  and the power sourcing equipment  110  of the power over fiber system  1 A (configured as shown in  FIG. 1 ) described as the first embodiment. 
     The powered device  310  includes a switchable mirror  311 E as an optical branching device for feedback and a control device  312 E. 
     The switchable mirror  311 E outputs a portion of the feed light  112  to be input to the photoelectric conversion element  311  from the power sourcing equipment  110 , to the power supplying side as the feedback feed light  112 F. The switchable mirror  311 E is an electronic device that is electrically switchable between the mirror state and the transparent state. Adjustment of the light amount of the feedback feed light  112 F may be performed by variable control of the ratio of reflectance to transmittance, or by variable control of the duty ratio of the period of reflection to the period of transmission that are periodically performed. Instead of the switchable mirror  311 E, a mechanism that mechanically switches reflection and transmission may be used to perform the adjustment. 
     The control device  312 E monitors the power supply amount (Q 1 ) of the electric power (Q) to the load  20 , the electric power (Q) being obtained by the conversion by the photoelectric conversion element  311 , and controls the feedback amount of feedback that is performed by the switchable mirror  311 E, namely the light amount (P 1 ) of the feedback feed light  112 F, according to the power supply amount (Q 1 ). 
     The power sourcing equipment  110  includes a combiner  111 E as an optical combining device for feedback and a control device  114 . The combiner  111 E has an aperture through which feed light  112 G from the semiconductor laser  111  enters, an aperture through which the feedback feed light  112 F enters, and an aperture through which the feed light  112  as combined feed light of the feed light  112 G and the feedback feed light  112 F exits. That is, the combiner  111 E combines the feedback feed light  112 F that is from the powered device  310  and the feed light  112 G output by the semiconductor laser  111  into combined feed light, and outputs the combined feed light. 
     The control device  114  controls output of the semiconductor laser  111  such that the energy amount that the combiner  111 E outputs is constant (P). For that, the control device  114  detects the output (P) of the semiconductor laser  111 . 
     Herein, P represents the electric power equivalent of the feed light  112 , P 1  represents the electric power equivalent of the feedback feed light  112 F, Q represents the electric power obtained by the conversion by the photoelectric conversion element  311 , and Q 1  represents the power supply amount to the load  20 . The electric power equivalent P of the feed light  112  is constant.  FIG. 6  and  FIG. 9  each show a graph of temporal change in P, Q and so forth. 
     The power supply amount Q 1  to the load  20  fluctuates according to the operation status of the load  20 , for example, as shown in  FIG. 6 . 
       FIG. 6  shows the case where 110% electric power Q is prepared, wherein the maximum value of the load  20  is 100%. Since the load  20  fluctuates in the range of up to the maximum value, no electric power shortage occurs, and consequently the system can be prevented from going down. 
     However, in this case, the surplus electric power R 1  is wasted, which is inefficient. 
     The control device  312 E controls the feedback amount of feedback that is performed by the switchable mirror  311 E, namely the electric power equivalent P 1  of the feedback feed light  112 F, such that the electric power Q obtained by the conversion by the photoelectric conversion element  311  converges to a target value that exceeds the load  20  by a predetermined percentage. 
     In this manner, a portion of the surplus electric power R 1  is transmitted to the power supplying side as the feedback feed light  112 F before converted into electric power. 
     The feedback feed light  112 F is input to the combiner  111 E and constitutes part of the feed light  112 . 
     The feed light  112  corresponds to the sum of the feedback feed light  112 F and the feed light  112 G output by the semiconductor laser  111 . 
     The lower limit of the predetermined percentage is 0%, and the upper limit thereof is a percentage by which the electric power Q exceeds the maximum value of the load  20 . In this example, the percentage by which the electric power Q exceeds the maximum value of the load  20  is 10%. Hence, the predetermined percentage is set in the range of 0-10%. For example, the target value is set to a value that is 10% higher than the load  20 , which is shown in  FIG. 9 . 
     If the power supply amount Q 1  to the load  20  is the maximum value, 100%, the feedback feed light  112 F (P 1 ) is zero and no feedback is performed. As the power supply amount Q 1  to the load  20  decreases from the maximum value, the feedback feed light  112 F (P 1 ) is increased to keep the surplus electric power R 2  small. 
     Although the electric power equivalent P of the feed light  112  that is output by the power sourcing equipment  110  is constant, since the electric power that cannot be unconsumed by the load  20  is fed back as the feedback feed light  112 F before converted into electric power, the electric power newly provided from the power source  10  is only “P−P 1 ” equivalent, which enables execution of efficient optical power supply with the surplus electric power R 2  at the power receiving side controlled even if the load  20  fluctuates. 
     In the above description, loss due to the transmission efficiency and so forth being not 100% is ignored. Since the feedback is performed before the conversion into electric power, the feedback can be performed without loss due to the photoelectric conversion, which is efficient. 
     The load  20  includes an external load (electric power that is output for an external device(s)) in addition to the driving power needed in the powered device  310 . 
     The power over fiber system  1 A 2  shown in  FIG. 8  is configured by the first embodiment as a base, but may be configured by the power over fiber system  1  or  1 B (configured as shown in  FIG. 2  to  FIG. 4 ), the power over fiber system  1  being described as the second embodiment, as a base with the components ( 111 E,  311 E,  312 E) for achieving the function of feedback power supply added in the same manner, thereby being carried out as a configuration including an optical communication system. 
     In this case, the electric power Q obtained by the conversion by the photoelectric conversion element  311  of the powered device  310  is also used as the driving power for the transmitter  320  and the receiver  330  of the second data communication device  300 . 
     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. 
     INDUSTRIAL APPLICABILITY 
     The present invention is usable for optical power supply.