Patent Publication Number: US-2022236498-A1

Title: Optical element and optical transmission system

Description:
TECHNICAL FIELD 
     The present disclosure relates to an optical element and an optical transmission system. 
     BACKGROUND ART 
     There is disclosed in Patent Literature 1 an optical multiplexer/demultiplexer that separates light of a plurality of wavelengths transmitted through an optical fiber. In the optical multiplexer/demultiplexer of Patent Literature 1, in the middle of an optical path, an optical filter allows light of a first wavelength and light of a second wavelength to pass through and reflects light of a third wavelength, thereby transmitting light of a plurality of wavelengths to a plurality of cores. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2013-225010 A 
     SUMMARY OF INVENTION 
     Problem to Solve 
     If light is transmitted through an optical fiber, it is desired that the light can be transmitted efficiently. 
     Solution to Problem 
     An optical element of the present disclosure includes: 
     a first condensing lens; and 
     a plurality of second condensing lenses, 
     wherein the optical element is disposed so as to face an end of an optical fiber including a core, a first cladding located around the core, and a second cladding located around the first cladding, 
     wherein the first condensing lens is disposed at a position corresponding to the core, and 
     wherein the second condensing lenses are disposed around the first condensing lens at positions corresponding to the first cladding. 
     An optical transmission system of the present disclosure includes: 
     an optical fiber including a core, a first cladding located around the core, and a second cladding located around the first cladding, signal light and feed light being transmitted through the optical fiber; and 
     the above optical element facing an output end of the optical fiber. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a power over fiber system of an embodiment(s). 
         FIG. 2  is a front view of an optical element shown in  FIG. 1 . 
         FIG. 3  shows the optical element shown in  FIG. 1  and its surroundings. 
         FIG. 4  shows a modification of the optical element. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present disclosure will be described in detail with reference to the drawings.  FIG. 1  is a block diagram of a power over fiber system of an embodiment(s). 
     As shown in  FIG. 1 , a power over fiber (PoF) system  1  of this embodiment is an optical transmission system that performs power supply and optical communication through an optical fiber  250 . The power over fiber system  1  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 over fiber system  1  further includes an optical element  360 . The optical element  360  may be included in the second data communication device  300 . 
     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 the optical fiber  250 . The optical fiber  250  includes: a core  210  that forms a transmission path of signal light; a cladding  220  (corresponding to a first cladding) that is arranged around the core  210  and forms a transmission path of feed light; and an outer cladding  225  (corresponding to a second cladding) that is arranged around the cladding  220 . 
     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 . 
     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. 
     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 . 
     &lt;Optical Element&gt; 
       FIG. 2  is a front view of the optical element shown in  FIG. 1 .  FIG. 3  shows the optical element shown in  FIG. 1  and its surroundings. The optical element  360  faces an output end face of the optical fiber  250  and separates the signal light  125  and the feed light  112  output from the optical fiber  250 . The optical element  360  includes: a tabular base  361  that allows light to pass through; and a lens assembly  365  including a first condensing lens  362  and a plurality of second condensing lenses  363 . 
     The first condensing lens  362  and the second condensing lenses  363  are each a planoconvex lens having a convex surface on one side and a plane surface that may be united to the base  361 . The diameter L 2  of each second condensing lens  363  is smaller than the diameter L 1  of the first condensing lens  362 . The second condensing lenses  363  may all have the diameter L 2 , or some may have a diameter different therefrom. 
     The first condensing lens  362  is disposed at a position corresponding to the core  210  of the optical fiber  250 . The second condensing lenses  363  are disposed at positions corresponding to the cladding  220 . The position corresponding to the core  210  corresponds to a position through which the laser light output from the core  210  propagates. The positions corresponding to the cladding  220  correspond to positions through which the laser light output from the cladding  220  propagates. 
     The second condensing lenses  363  are closely aligned. For example, the second condensing lenses  363  are arranged in a honeycomb array. The second condensing lenses  363  may each be circular as viewed in the axial direction of the first condensing lens  362 . A honeycomb array of circles means an array of circles that are inscribed circles of regular hexagons, assuming that a honeycomb is composed of regular hexagons. This arrangement achieves a configuration in which the second condensing lenses  363  are closely aligned in the radial direction and the circumferential direction with the first condensing lens  362  at the center. 
     As shown in  FIG. 3 , the photodiode  331  is disposed at a position in the axial direction of the first condensing lens  362 , the position onto which the first condensing lens  362  focuses the signal light  125 . The photoelectric conversion element  311  of the powered device  310  is disposed at a position onto which the second condensing lenses  363  focus the feed light  112 . There may be a plurality of photoelectric conversion elements  311  dispersedly disposed around the photodiode  331 . The axial directions of the respective second condensing lenses  363  may be different from one another depending on their respective positions in the radial direction and the circumferential direction such that the second condensing lenses  363  focus the feed light  112  onto the photoelectric conversion elements  311  that are dispersedly disposed. 
     A configuration may be adopted in which the signal light  125  separated by the optical element  360  is led to the photodiode  331  through a second optical fiber different from the optical fiber  250 . In this case, at the position of the photodiode  331  shown in  FIG. 3 , an input face of the second optical fiber may be disposed. Similarly, a configuration may be adopted in which the feed light  112  separated by the optical element  360  is led to the photoelectric conversion element(s)  311  through a third optical fiber different from the optical fiber  250 . In this case, at the position(s) of the photoelectric conversion element(s)  311  shown in  FIG. 3 , an input face of the third optical fiber may be disposed. 
     The first condensing lens  362  and the second condensing lenses  363  can be formed by using, for example, nanoimprint technology. The nanoimprint technology is a technology of pressing a mold formed by inverting protrusions/recesses of a target shape against resin as a molding/forming material, thereby transferring the target shape thereto. The first condensing lens  362  and the second condensing lenses  363  of the optical element  360  may be formed by using various other technologies. Examples thereof include MEMS (Micro Electro Mechanical Systems) processing techniques and metallic molding. 
     &lt;Actions and Effects of Optical Element&gt; 
     The feed light  112  and the signal light  125  input from the first data communication device  100  have different wavelengths and propagate through the cladding  220  and the core  210  of the optical fiber  250 , respectively. The signal light  125  output from the core  210  of the optical fiber  250  at the other end  202  passes through the first condensing lens  362  of the optical element  360  to be focused onto the photodiode  331 . Much of the feed light  112  output from the cladding  220  passes through the second condensing lenses  363  to be focused onto the photoelectric conversion element(s)  311 . Part of the feed light  112  passing through gaps between the second condensing lenses  363  is not input to the photoelectric conversion element(s)  311 . However, the ratio of the area of the gaps between the second condensing lenses  363  to the area of an end face of the cladding  220  is small. Hence, the ratio of the feed light  112  not to be input to the photoelectric conversion element(s)  311  to the feed light  112  output from the cladding  220  is small. This effectuates highly-efficient optical transmission and highly-efficient photoelectric conversion. 
     The signal light  325  output from the second data communication device  300  passes through the first condensing lens  362  to be transmitted to the core  210  of the optical fiber  250 . 
     As described above, according to the optical element  360  of this embodiment, the optical element  360  includes the first condensing lens  362  disposed at a position corresponding to the core  210  and the second condensing lenses  363  disposed at positions corresponding to the cladding  220 . The first condensing lens  362  and the second condensing lenses  363  can separate the feed light  112  and the signal light  125  with a small loss. 
     Further, according to the optical element  360  of this embodiment, the diameter of each second condensing lens  363  is smaller than the diameter of the first condensing lens  362 . This enables dense arrangement of the second condensing lenses  363  and can further reduce the loss of the feed light  112 . 
     Further, according to the optical element  360  of this embodiment, the second condensing lenses  363  are more densely disposed, for example, in a honeycomb array. This further reduces the loss of the feed light  112 . 
     Further, according to the optical element  360  of this embodiment, the optical element  360  includes the lens assembly  365  including: the base  361 ; and the first condensing lens  362  and the second condensing lenses  363  united to the base  361 . This improves ease of handling of the optical element  360 . 
     According to the power over fiber system  1  of this embodiment, the optical element  360  providing the above-described effects faces the output end face of the optical fiber  250 . This can effectuate highly-efficient transmission of the signal light  125  and the feed light  112 . 
     (Modification) 
       FIG. 4  shows a modification of the optical element. The optical element  360  may include the lens assembly  365  and an optical-fiber-side optical element  367  disposed at a side of the lens assembly  365  closer to the optical fiber  250 . 
     The optical-fiber-side optical element  367  has functions of a refractive index adjustment part, an anti-reflection part or both. The function as the refractive index adjustment part may be achieved, for example, by a biconvex lens, a planoconvex lens, a Fournel lens, an aspheric lens, a plane lens or the like that adjusts the spread angle of the laser light that is output from the output end face of the optical fiber  250 . The function as the anti-reflection part may be achieved by an anti-reflection coating. Alternatively, the function as the anti-reflection part may be achieved by the input end face of the optical-fiber-side optical element  367  and the output end face of the optical fiber  250  with inclinations in the same direction formed. 
     In  FIG. 4 , the optical-fiber-side optical element  367  and the lens assembly  365  are separate components, but may be integrated. 
     As described above, according to the optical element  360  of this modification, the optical-fiber-side optical element  367  having the function as the refractive index adjustment part, the function as the anti-reflection part or both can further improve the transmission efficiency of the signal light  125  and the feed light  112 . 
     Although one or more embodiments of the present disclosure have been described above, the present invention is not limited to these embodiments. For example, in the above embodiment(s), the first condensing lens and the second condensing lenses are planoconvex lenses, but may be various other lenses that provide the focusing effect. Examples thereof include biconvex lenses and meniscus lenses. The second condensing lenses are not limited to being circular as viewed in their axial directions, but may have another shape. For example, they may be hexagonal. Further, in the above embodiment(s), the first condensing lens and the second condensing lenses are united to the tabular base, but various other support structures may be applied. Examples thereof include a structure in which the edges of the first condensing lens and the second condensing lenses are bonded so that they support one another and are fixed to one another. The details described in the embodiment(s) may be appropriately modified within a range not departing from the scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to an optical element and an optical transmission system. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Power over Fiber System (Optical Transmission System) 
               100  First Data Communication Device 
               110  Power Sourcing Equipment 
               111  Semiconductor Laser for Power Supply 
               112  Feed Light 
               120  Transmitter 
               125  Signal Light 
               130  Receiver 
               200  Optical Fiber Cable 
               210  Core 
               220  Cladding (First Cladding) 
               225  Outer Cladding (Second Cladding) 
               250  Optical Fiber 
               300  Second Data Communication Device 
               310  Powered Device 
               311  Photoelectric Conversion Element 
               320  Transmitter 
               325  Signal Light 
               330  Receiver 
               331  Photodiode for Signals 
               360  Optical Element 
               361  Base 
               362  First Condensing Lens 
               363  Second Condensing Lens 
               365  Lens Assembly 
               367  Optical-fiber-side Optical Element (Refractive Index Adjustment Part, Anti-reflection Part)