Patent Publication Number: US-2023163862-A1

Title: Power sourcing equipment of power-over-fiber system and power-over-fiber system

Description:
RELATED APPLICATIONS 
     The present application is a National Phase of International Application No. PCT/JP2020/047830 filed Dec. 22, 2020, which claims priority to Japanese Application No. 2020-044891, filed Mar. 16, 2020. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to optical power supply. 
     BACKGROUND ART 
     Recently, an optical power supply system has been studied 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. 
     PTL 1 discloses an optical communication device including an optical transmitter, an optical fiber, and an optical receiver. The optical transmitter transmits signal light modulated based on an electric signal and feed light for supplying electric power. The optical fiber includes a core, a first cladding surrounding the core, and a second cladding surrounding the first cladding. The core transmits the signal light. The first cladding has a refractive index lower than that of the core and transmits the feed light. The second cladding has a refractive index lower than that of the first cladding. The optical receiver 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 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2010-135989 
     SUMMARY OF INVENTION 
     Technical Problem 
     When an optical fiber ( 250 A) is used as a power supply medium and light ( 112 ) output by a laser ( 111 ) is used as an electric power supply source (see  FIGS.  11  and  12   ), the arrival time of the light varies because of the modal dispersion (see  FIG.  12   ). 
     Thus, a light intensity distribution varies at an output end ( 202 A) of the optical fiber. Consequently, a photoelectric conversion efficiency decreases at a photoelectric conversion element ( 311 ). 
     Solution to Problem 
     In one aspect of the present disclosure, power sourcing equipment of a power-over-fiber system includes a first laser, a second laser, a light input/output part. The first laser oscillates with electric power to output feed light. The second laser oscillates with electric power to output feed light. The light input/output part inputs first feed light output by the first laser and second feed light output by the second laser to a single channel of an optical fiber. A light intensity distribution of the first feed light at an output end face of the channel differs from a light intensity distribution of the second feed light at the output end face of the channel. The first feed light and the second feed light are simultaneously input to the channel to reduce non-uniformity of a light intensity distribution at the output end face. 
     Advantageous Effects of Invention 
     In the one aspect of the present disclosure, the power sourcing equipment of the power-over-fiber system reduces the non-uniformity of the light intensity distribution at the feed light output end face of the optical fiber and increases the photoelectric conversion efficiency at the photoelectric conversion element. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating a configuration of a power-over-fiber system according to a first embodiment of the present disclosure. 
         FIG.  2    is a diagram illustrating a configuration of a power-over-fiber system according to a second embodiment of the present disclosure. 
         FIG.  3    is a diagram illustrating the configuration of the power-over-fiber system according to the second embodiment of the present disclosure, and illustrates optical connectors, etc. 
         FIG.  4    is a diagram illustrating a configuration of a power-over-fiber system according to another embodiment of the present disclosure. 
         FIG.  5    is a diagram illustrating a configuration of a power-over-fiber system in which two lasers serve as feed light sources. 
         FIG.  6    is a diagram illustrating an optical path of feed light in the case of  FIG.  5   . 
         FIG.  7    is a cross-section illustrating cross-sections of a channel of  FIG.  6   . 
         FIG.  8    is a diagram illustrating a configuration of a power-over-fiber system in which two lasers serve as feed light sources. 
         FIG.  9    is a diagram illustrating an optical path of feed light in the case of  FIG.  8   . 
         FIG.  10    is a cross-section illustrating cross-sections of a channel of  FIG.  9   . 
         FIG.  11    is a diagram illustrating a configuration of a power-over-fiber system in which one laser serves as a feed light source. 
         FIG.  12    is a diagram illustrating an optical path of feed light in the case of  FIG.  11    and variances of arrival time at respective cross-sections. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Some embodiments of the present disclosure are described below with reference to the drawings. 
     (1) Overview of System 
     First Embodiment 
     As illustrated in  FIG.  1   , a power-over-fiber (PoF) system  1 A according to the present embodiment includes power sourcing equipment (PSE)  110 , an optical fiber cable  200 A, and a powered device (PD)  310 . 
     In the present disclosure, the power sourcing equipment  110  is equipment that converts electric power into optical energy and supplies the optical energy, and the powered device  310  is a device that receives 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 channel of feed light. 
     The powered device  310  includes a photoelectric conversion element  311 . 
     The power sourcing equipment  110  is connected to a power source, which electrically drives the semiconductor laser  111  for power supply and so on. 
     The semiconductor laser  111  for power supply oscillates with electric power supplied from the power source to output feed light  112 . 
     The optical fiber cable  200 A has one end  201 A connectable to the power sourcing equipment  110  and an other end  202 A connectable to the powered device  310 , and transmits 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. The feed light  112  propagates through the optical fiber  250 A and is output from the other end  202 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 photoelectric conversion element  311  through the conversion is used as driving electric power needed in the powered device  310 . The powered device  310  is capable of outputting, for an external device, the electric power obtained by the photoelectric conversion element  311  through the conversion. 
     Semiconductor materials of semiconductor regions that exhibit a light-electricity conversion effect of the semiconductor laser  111  for power supply and the photoelectric conversion element  311  are semiconductors having a short laser wavelength of 500 nm or shorter. 
     Semiconductors having a short laser wavelength have a large band gap and a high photoelectric conversion efficiency. Thus, the photoelectric conversion efficiency on the power-supplying side and the powered side of optical power supply increases, and consequently the optical power supply efficiency increases. 
     Therefore, the semiconductor materials to be used may be, for example, semiconductor materials that are laser media having a laser wavelength (fundamental wave) of 200 to 500 nm such as diamond, gallium oxide, aluminum nitride, and gallium nitride. 
     The semiconductor materials to be used may be semiconductors having a band gap of 2.4 eV or greater. 
     For example, semiconductor materials that are laser media having a band gap of 2.4 to 6.2 eV such as diamond, gallium oxide, aluminum nitride, and gallium nitride may be used. 
     Laser light having a longer wavelength tends to have a higher transmission efficiency. Laser light having a shorter wavelength tends to have a higher photoelectric conversion efficiency. Thus, in the case of long-distance transmission, a semiconductor material that is a laser medium having a laser wavelength (fundamental wave) longer than 500 nm may be used. When the photoelectric conversion efficiency is prioritized, a semiconductor material that is a laser medium having a laser wavelength (fundamental wave) shorter than 200 nm may be used. 
     These semiconductor materials may be used in either the semiconductor laser  111  for power supply or the photoelectric conversion element  311 . The photoelectric conversion efficiency increases on the power-sourcing side or the powered side, and consequently the optical power supply efficiency increases. 
     Second Embodiment 
     As illustrated in  FIG.  2   , a power-over-fiber (PoF) system  1  according to the present embodiment is a system including a power supply system and an optical communication system with an optical fiber. Specifically, the power-over-fiber system  1  includes a first data communication device  100  including 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  that perform data communication. The first data communication device  100  corresponds to 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  and a cladding  220 . The core  210  forms a channel of signal light. The cladding  220  is arranged to surround the core  210  and forms a channel 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  is a unit that processes a received signal. The second data communication device  300  is a node in a communication network. Alternatively, 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, which electrically drives the semiconductor laser  111  for power supply, the semiconductor laser  121  for signals, the modulator  122 , the photodiode  131  for signals, and so on. The first data communication device  100  is a node in the communication network. Alternatively, the first data communication device  100  may be a node that communicates with another node. 
     The semiconductor laser  111  for power supply oscillates with electric power supplied from the power source to output 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 photoelectric conversion element  311  through the conversion is used as driving electric power for the transmitter  320 , the receiver  330 , and the data processing unit  340  and as other driving electric power needed in the second data communication device  300 . The second data communication device  300  may be capable of outputting, for an external device, the electric power obtained by the photoelectric conversion element  311  through the conversion. 
     On the other hand, the modulator  122  of the transmitter  120  modulates laser light  123  output from the semiconductor laser  121  for signals into signal light  125  on the basis of transmission data  124 , and outputs the signal light  125 . 
     The photodiode  331  for signals of the receiver  330  demodulates the signal light  125  transmitted through the optical fiber cable  200  into an electric signal, and outputs the electric signal to the data processing unit  340 . The data processing unit  340  transmits data based on the electric signal to a node. The data processing unit  340  also receives data from the node, and outputs, as transmission data  324 , the data to the modulator  322 . 
     The modulator  322  of the transmitter  320  modulates laser light  323  output from the semiconductor laser  321  for signals into signal light  325  on the basis of the transmission data  324 , and outputs the signal light  325 . 
     The photodiode  131  for signals of the receiver  130  demodulates the signal light  325  transmitted through the optical fiber cable  200  into an electric signal, and outputs the electric signal. Data based on the electric signal is transmitted to a node. On the other hand, data from the node is treated as the transmission data  124 . 
     The feed light  112  and the signal light  125  output from the first data communication device  100  are input to one end  201  of the optical fiber cable  200 . The feed light  112  and the signal light  125  propagate through the cladding  220  and the core  210 , respectively, and are output from an other end  202  of the optical fiber cable  200  to the second data communication device  300 . 
     The signal light  325  output 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 illustrated 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 . 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  at the one end  201  of the optical fiber cable  200  is connected to the optical connector  141 . An optical connector  240  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 , and transmits the feed light  112 . In the present embodiment, the optical fiber cable  200  transmits the signal light  125  and the signal light  325  bidirectionally. 
     As semiconductor materials of semiconductor regions that exhibit a light-electricity conversion effect of the semiconductor laser  111  for power supply and the photoelectric conversion element  311 , same and/or similar materials as those mentioned in the first embodiment may be used, so that a high optical power supply efficiency is implemented. 
     As in an optical fiber cable  200 B of a power-over-fiber system  1 B illustrated in  FIG.  4   , an optical fiber  260  that transmits signal light and an optical fiber  270  that transmits feed light may be provided separately. The optical fiber cable  200 B may include a plurality of optical fiber cables. 
     (2) Reduction of Non-Uniformity of Light Intensity Distribution 
     In contrast to the power-over-fiber system  1 A described above, a power-over-fiber system  1 C is implemented in which a first semiconductor laser  111   a  and a second semiconductor laser  111   b  simultaneously input feed light to a single channel  2501  as illustrated in  FIGS.  5  and  6   . The channel  2501  is a core and is surrounded by a cladding  2502 . The configuration above may be implemented in the optical power supply system in the power-over-fiber system  1  or  1 B. The implementation can be made in the same and/or similar manner when the channel is the cladding  220  as in the case of  FIG.  2   . 
     Power sourcing equipment  110 A illustrated in  FIG.  5    includes the first semiconductor laser  111   a  and the second semiconductor laser  111   b . The first semiconductor laser  111   a  serves as a first laser that oscillates with electric power to output feed light. The second semiconductor laser  111   b  serves as a second laser that oscillates with electric power to output feed light. 
     The power sourcing equipment  110  further includes an optical multiplexer  140 A as a light input/output part. 
     The optical multiplexer  140 A inputs first feed light  112   a  output by the first semiconductor laser  111   a  and second feed light  112   b  output by the second semiconductor laser  111   b  to the same channel  2501  of the optical fiber  250 A. 
     Let α 1  denote an incident angle of the first feed light  112   a  to an input end face PO of the channel  2501 , and let α 2  denote an incident angle of the second feed light  112   b  to the input end face PO of the channel  2501 . The power-over-fiber system  1 C illustrated in  FIGS.  5  and  6    corresponds to the case of α 1 =α 2 . 
     For example, in the powered device  310 A, feed light  112   c , feed light  112   d , and feed light  112   e  are respectively distributed to three photoelectric conversion elements  311   a ,  311   b , and  311   c  through an optical demultiplexer  350 A. 
     As illustrated in an upper portion of  FIG.  7   , each of the first feed light  112   a  and the second feed light  112   b  locally concentrates at the input end face P 0 . Thus, the non-uniformity of the light intensity distribution is high. 
     The non-uniformity reduces because of the modal dispersion as the first feed light  112   a  and the second feed light  112   b  travel through the channel  2501 . Since more light propagation modes are present than in the case of the first feed light  112   a  alone or in the case of the second feed light  112   b  alone, the modal dispersion becomes intense. 
     As illustrated in a middle portion of  FIG.  7   , the non-uniformity of the light intensity distribution reduces to some extent at a cross-section P 1  at a short distance. If the cross-section P 1  were an output end face of the channel  2501 , the light intensity distribution of each of the feed light  112   c , the feed light  112   d , and the feed light  112   e  respectively input to the photoelectric conversion elements  311   a ,  311   b , and  311   c  also varies. Thus, the photoelectric conversion efficiency reduces at each of the photoelectric conversion elements  311   a ,  311   b , and  311   c . The energies of the feed light  112   c , the feed light  112   d , and the feed light  112   e  are different from one another. Thus, electric powers output by the respective photoelectric conversion elements  311   a ,  311   b , and  311   c  through conversion are different from one another. Thus, the efficiency reduces as a whole. 
     As illustrated in a lower portion of  FIG.  7   , the non-uniformity of the light intensity distribution further reduces at a cross-section P 2  at a long distance. If the cross-section P 2  were the output end face of the channel  2501 , the uniformity of the light intensity distribution of each of the feed light  112   c , the feed light  112   d , and the feed light  112   e  respectively input to the photoelectric conversion elements  311   a ,  311   b , and  311   c  increases. Thus, the photoelectric conversion efficiency increases at each of the photoelectric conversion elements  311   a ,  311   b , and  311   c . The differences among the energies of the feed light  112   c , the feed light  112   d , and the feed light  112   e  also reduce. Thus, the differences among the electric powers output by the respective photoelectric conversion elements  311   a ,  311   b , and  311   c  through conversion also reduce. Thus, the efficiency increases as a whole. 
     A light intensity distribution obtained at the cross-section P 1  at the short distance when the first feed light  112   a  alone is input and a light intensity distribution obtained at the cross-section P 1  at the short distance when the second feed light  112   b  alone is input are considered. 
     The former light intensity distribution differs from the latter light intensity distribution. The former and latter light intensity distributions have a relationship in which a low intensity region of one of the light intensity distributions is compensated by a high intensity region of the other light intensity distribution. The former and latter light intensity distributions may be distributions that are approximate to each other rotationally symmetrically. 
     Thus, when the first feed light  112   a  and the second feed light  112   b  are simultaneously input to the channel  2501 , the non-uniformity of the light intensity distribution at the cross-section P 1  at the short distance is reduced, that is, the uniformity increases as compared with the case where the first feed light  112   a  alone is input and the case where the second feed light  112   b  alone is input. 
     A light intensity distribution obtained at the cross-section P 2  at the long distance when the first feed light  112   a  alone is input and a light intensity distribution obtained at the cross-section P 2  at the long distance when the second feed light  112   b  alone is input are considered. 
     The former light intensity distribution differs from the latter light intensity distribution. The former and latter light intensity distributions have a relationship in which a low intensity region of one of the light intensity distributions is compensated by a high intensity region of the other light intensity distribution. The former and latter light intensity distributions may be distributions that are approximate to each other rotationally symmetrically. 
     Thus, when the first feed light  112   a  and the second feed light  112   b  are simultaneously input to the channel  2501 , the non-uniformity of the light intensity distribution at the cross-section P 2  at the long distance is reduced, that is, the uniformity increases as compared with the case where the first feed light  112   a  alone is input and the case where the second feed light  112   b  alone is input. 
     Thus, in the power-over-fiber system  1 C illustrated in  FIGS.  5  and  6   , the non-uniformity of the light intensity distribution at the output end face reduces irrespectively of the transmission distance as a result of simultaneous input of the first feed light  112   a  and the second feed light  112   b  to the channel  2501 . 
     In the power-over-fiber system  1 C, the non-uniformity of the light intensity distribution reduces at the output end face of the optical fiber  250 A, and consequently the photoelectric conversion efficiency increases at the photoelectric conversion elements  311   a ,  311   b , and  311   c.    
     A power-over-fiber system  1 D illustrated in  FIGS.  8  and  9    corresponds to the case of α 1 ≠α 2 , except for which, the power-over-fiber system  1 D has a configuration that is same as and/or similar to the configuration of the system  1 C. In  FIGS.  8  and  9   , α 1 &lt;α 2  holds. 
     In this case, as illustrated in an upper portion of  FIG.  10   , each of the first feed light  112   a  and the second feed light  112   b  also locally concentrates at the input end face P 0 . Thus, the non-uniformity of the light intensity distribution is high. 
     The non-uniformity reduces because of the modal dispersion as the first feed light  112   a  and the second feed light  112   b  travel through the channel  2501 . Since more light propagation modes are present than in the case of the first feed light  112   a  alone or in the case of the second feed light  112   b  alone, the modal dispersion becomes intense. Because α 1 ≠α 2  is set, the modal dispersion becomes more intense. 
     As illustrated in a lower portion of  FIG.  10   , the non-uniformity of the light intensity distribution reduces also at the cross-section P 1  at the short distance. Since the modal dispersion becomes more intense because α 1 ≠α 2  is set, the uniformity of the light intensity distribution is higher than the uniformity of the light intensity distribution at the cross-section P 1  in the case of α 1 =α 2  in  FIG.  7   . Thus, the uniformity of the light intensity distribution of the feed line  112   c , the feed light  112   d , and the feed light  112   e  respectively input to the photoelectric conversion elements  311   a ,  311   b , and  311   c  also increases, and the photoelectric conversion efficiency increases at each of the photoelectric conversion elements  311   a ,  311   b , and  311   c . The differences among the energies of the feed light  112   c , the feed light  112   d , and the feed light  112   e  reduce, and values of the electric powers output by the respective photoelectric conversion elements  311   a ,  311   b , and  311   c  through conversion become closer to one another. Thus, the efficiency increases as a whole. 
     Thus, the photoelectric conversion efficiency at the photoelectric conversion elements of the power-over-fiber system  1 D in which α 1 ≠α 2  is set further increases as compared with that of the power-over-fiber system  1 C in which α 1 =α 2  is set. 
     Let β1(t) denote a phase of the first feed light  112   a  at the input end face P 0 , and let β2(t) denote a phase of the second feed light  112   b  at the input end face P 0 . 
     In the power-over-fiber system  1 D illustrated in  FIGS.  8  and  9   , α 1 ≠α 2  is set. The same and/or similar advantageous effect can be obtained by setting β1(t)≠β2(t) instead of setting α 1 ≠α 2 . 
     When β1(t)≠β2(t) is set, the first feed light  112   a  and the second feed light  112   b  are from laser light sources of the same kind and have the same wavelength, and conversion wavelengths of the photoelectric conversion elements  311  ( 311   a ,  311   b , and  311   c ) correspond to this wavelength. Such a configuration can be efficient since the laser light sources of one kind and the photoelectric conversion elements of one kind are used. The conversion efficiency does not vary at the photoelectric conversion elements  311   a ,  311   b , and  311   c  because the received feed light has the same wavelength but different phases. 
     By setting α 1 ≠α 2  and setting β1(t)≠β2(t), the equivalent or better advantageous effect can be obtained. 
     In the case of signal communication using light, to suppress an influence of a fluctuation of the arrival time caused by the modal dispersion, a GI mode optical fiber is used. However, in the case of optical power supply transmission, transmission using a non-GI-mode fiber is also possible since the optical power supply transmission is not intended for signal extraction. In any case, the incident angles α 1  and α 2  are set to allow total reflection at a critical angle or less. 
     While the embodiments of the present disclosure have been described above, these embodiments are merely presented as examples and can be carried out in various other forms. Each component may be omitted, replaced, or modified within a range not departing from the gist of the invention. 
     The powered device  310 A may include only a single photoelectric conversion element. Even if the powered device  310 A includes a single photoelectric conversion element, the uniformity of the light intensity distribution increases at a light-receiving surface of the photoelectric conversion element. Thus, the same and/or similar advantageous effect can be obtained. 
     In the power sourcing equipment  110 A, the feed light may be input to the same channel from three or more lasers. In such a case, the three or more lasers may include at least one laser with a different incident angle. Further, all the incident angles may be set to be different from one another. 
     Industrial Applicability 
     The present invention can be used for optical power supply.