Patent Publication Number: US-2023151939-A1

Title: Lighting system

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to a lighting system, and more particularly relates to a lighting system including an optical fiber. 
     BACKGROUND ART 
     A lighting fixture including a case, a projection lens, and a light source device has been proposed in the art (see, for example, Patent Literature 1). The light source device disclosed in Patent Literature 1 includes a solid-state light source and a light transmission fiber. The light transmission fiber has a first end face and a second end face, and excitation light emitted from the solid-state light source is introduced into the fiber through the first end face thereof. The light transmission fiber includes a wavelength-converting core, a light-guiding core, and a clad. The wavelength-converting core contains a wavelength-converting material that produces a population inversion state of electrons by absorbing the excitation light and that lets wavelength-converted light, falling within the visible radiation range, emerge therefrom. The light-guiding core covers the peripheral surface of the wavelength-converting core and transmits the wavelength-converted light in a direction from the first end face toward the second end face. The clad covers the peripheral surface of the light-guiding core. 
     The light transmission fiber is configured to have a stimulated emission produced by the wavelength-converted light propagating through the light-guiding core and to let not only the excitation light, emitted from the solid-state light source, but also the wavelength-converted light, amplified by the stimulated emission, emerge from the second end face. 
     It is difficult for the lighting fixture of Patent Literature 1 to increase the intensity of the wavelength-converted light. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2018-195627 A 
       
    
     SUMMARY OF INVENTION 
     It is therefore an object of the present disclosure to provide a lighting system with the ability to increase the intensity of light having a different wavelength from excitation light. 
     A lighting system according to an aspect of the present disclosure includes an optical fiber, a first light source unit, a second light source unit, and a lighting unit. The optical fiber includes a light incident portion, a light emerging portion, and a wavelength-converting portion. The wavelength-converting portion is provided between the light incident portion and the light emerging portion. The wavelength-converting portion contains a wavelength-converting element. The wavelength-converting element is excited by excitation light and amplifies a spontaneous emission of light, having a longer wavelength than the excitation light, with an amplified spontaneous emission of light. The first light source unit makes the excitation light incident on the light incident portion. The second light source unit makes seed light incident on the light incident portion. The seed light causes the wavelength-converting element that has been excited by the excitation light and the amplified spontaneous emission of light to produce a stimulated emission of light. The lighting unit projects, into an external space, light emerging from the light emerging portion of the optical fiber. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    illustrates a configuration for a lighting system according to a first embodiment; 
         FIG.  2 A  is a cross-sectional view of a first end of an optical fiber in the lighting system; 
         FIG.  2 B  is a cross-sectional view of a second end of an optical fiber in the lighting system; 
         FIGS.  3 A- 3 C  illustrate an operating principle of the lighting system; 
         FIG.  4    illustrates a configuration for a lighting system according to a variation of the first embodiment; 
         FIG.  5    illustrates a configuration for a lighting system according to a second embodiment; 
         FIG.  6    illustrates a configuration for a lighting system according to a third embodiment; 
         FIG.  7    illustrates a configuration for a lighting system according to a fourth embodiment; 
         FIG.  8    illustrates a configuration for a lighting system according to a fifth embodiment; 
         FIG.  9    illustrates a configuration for a lighting system according to a sixth embodiment; 
         FIG.  10    is a block diagram of the lighting system; 
         FIG.  11 A  illustrates a configuration for a lighting unit included in the lighting system; 
         FIG.  11 B  is a bottom view of a frame member of the lighting unit included in the lighting system; 
         FIGS.  12 A and  12 B  illustrate how the lighting system operates; 
         FIGS.  13 A and  13 B  illustrate how the lighting system operates; 
         FIGS.  14 A and  14 B  illustrate a lighting unit included in a lighting system according to a first variation of the sixth embodiment; and 
         FIG.  15    illustrates a lighting unit included in a lighting system according to a second variation of the sixth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The drawings to be referred to in the following description of first to sixth embodiments are all schematic representations. That is to say, the ratio of the dimensions (including thicknesses) of respective constituent elements illustrated on the drawings does not always reflect their actual dimensional ratio. 
     First Embodiment 
     A lighting system  1  according to a first embodiment will be described with reference to  FIGS.  1 - 3 C . 
     (1) Overview 
     The lighting system  1  makes excitation light P 1  and seed light P 2  incident on an optical fiber  2  to which a wavelength-converting element (chemical element) is added as shown in  FIGS.  1  and  2 A . The excitation light P 1  excites the wavelength-converting element. The seed light P 2  causes the wavelength-converting element that has been excited by the excitation light P 1  to produce a stimulated emission of light P 3  (see  FIG.  3 C ). As shown in  FIGS.  1  and  2 B , from the optical fiber  2 , light P 4  including the excitation light P 1  and the stimulated emission of light P 3  emerges.  FIGS.  3 A- 3 C  illustrate the principle of operation of the lighting system  1 . In  FIGS.  3 A,  3 B, and  3 C , the ordinate represents the energy of electrons. The upward arrow shown in  FIG.  3 A  indicates absorption of the excitation light P 1 . The downward arrow shown in  FIG.  3 C  indicates transition about a spontaneous emission of light or a stimulated emission of light P 3 . In the lighting system  1 , an electron e −  in a ground state E 0  (including a plurality of energy levels) of the wavelength-converting element is excited to an excitation level E 2  by the excitation light P 1  that has been incident on the optical fiber  2 . Then, the electron e −  at the excitation level E 2  makes a transition to a metastable level E 1 , which is an energy level lower than the excitation level E 2 . Thereafter, the stimulated emission of light P 3  (P 32 ) is produced when the electron e −  at the metastable level E 1  is caused to make a transition to one of the highest ones of the plurality of energy levels (hereinafter referred to as a “second energy level”) of the ground state E 0  by the seed light P 2  (P 22 ), of which the wavelength corresponds to the difference in energy between the metastable level E 1  and the second energy level, for example. In addition, a stimulated emission of light P 3  (P 31 ) is also produced when the electron e −  at the metastable level E 1  is caused to make a transition to another energy level (hereinafter referred to as a “first energy level”), lower than the second energy level out of the plurality of energy levels of the ground state E 0 , by the seed light P 2  (P 21 ), of which the wavelength corresponds to the difference in energy between the metastable level E 1  and the first energy level. 
     The lighting system  1  may be used as a down light, for example. However, this is only an example and should not be construed as limiting. The lighting system  1  may be applied to a facility or a moving vehicle, whichever is appropriate. Examples of facilities to which the lighting system  1  is applicable include tennis courts, athletic stadiums, airports, single-family dwelling houses, multi-family dwelling houses, office buildings, stores, art museums, hotels, and factories. Examples of moving vehicles to which the lighting system  1  is applicable include automobiles, bicycles, railway trains, aircrafts, watercrafts, and drones. 
     (2) Configuration for Lighting System 
     The lighting system  1  includes the optical fiber  2 , a first light source unit  11 , a second light source unit  12 , and a lighting unit  6  as shown in  FIG.  1   . The first light source unit  11  makes the excitation light P 1  incident on a light incident portion  21 . The second light source unit  12  makes the seed light P 2 , which causes the wavelength-converting element excited by the excitation light P 1  to produce the stimulated emission of light P 3  (hereinafter referred to as “external seed light P 2 ”), incident on the light incident portion  21 . 
     (2.1) Optical Fiber 
     The optical fiber  2  includes a core  3 , a clad  4 , and a coating portion  5  as shown in  FIGS.  2 A and  2 B . The clad  4  covers the outer peripheral surface of the core  3 . The coating portion  5  covers the outer peripheral surface of the clad  4 . A cross section, taken along a plane perpendicular to the optical axis, of the core  3  has a circular shape. The clad  4  is disposed coaxially with the core  3 . 
     The core  3  has a first end face  31  (see  FIG.  2 A ) and a second end face  32  (see  FIG.  2 B ), which is located at the opposite longitudinal end of the core  3  from the first end face  31 . The core  3  includes a first core portion  3 A and a second core portion  3 B. The first core portion  3 A and the second core portion  3 B are each shorter in length than the core  3 . The length of the core  3  is the sum of the length of the first core portion  3 A and the length of the second core portion  3 B. The first core portion  3 A includes the first end face  31  but does not include the second end face  32 . The second core portion  3 B includes the second end face  32  but does not include the first end face  31 . The first core portion  3 A contains a light-transmitting material and the wavelength-converting element. The second core portion  3 B contains the light-transmitting material but does not contain the wavelength-converting element. The concentration of the wavelength-converting element in the first core portion  3 A may or may not be uniform along the entire length of the first core portion  3 A. The refractive index of the core  3  may be substantially equal to the refractive index of the light-transmitting material that is a main component of the core  3 . 
     The light-transmitting material may be, for example, a fluoride, an oxide, or a nitride. The fluoride may be glass fluoride, for example. The oxide may be a silicon oxide or quartz, for example. 
     The wavelength-converting element is a rare earth element. In this embodiment, the wavelength-converting element includes an element selected from the group consisting of, for example, Pr, Tb, Ho, Dy, Er, Eu, Nd, and Mn. The wavelength-converting element is contained as an ion of a rare earth element in the core  3 , e.g., contained as an ion of Pr (Pr 3+ ) or an ion of Tb (Tb 3+ ) in the core  3 . In this case, the wavelength-converting element may be excited by either the excitation light P 1  or an amplified spontaneous emission (ASE) of light. The amplified spontaneous emission (ASE) of light is produced by amplifying the spontaneous emission of light, emitted from a different wavelength-converting element other than the wavelength-converting elements itself, as internal seed light. Through such excitation, the wavelength-converting element emits not only an ASE unique to the element of the wavelength-converting element but also a stimulated emission of light having the same wavelength as the external seed light P 2 , thus emitting them as the stimulated emission of light P 3 . The wavelengths of the ASE and the external seed light P 2  are longer than the wavelength of the excitation light P 1  (which may fall within the range from 440 nm to 450 nm, for example). The wavelength of the seed light P 2  will be described later in the “(2.3) Second light source unit” section. 
     Pr 3+  is a wavelength-converting element that may emit either an ASE or amplified seed light in the cyan to red range. The intensity of the stimulated emission of light depends on the respective intensities of the internal seed light (the spontaneous emission of light) and the external seed light. If the core  3  contains Pr 3+  and Tb 3+ , then Tb 3+  is excited by absorbing an ASE from Pr 3+  and may produce an ASE having a wavelength unique to Tb 3+ . 
     The refractive index of the clad  4  is less than the refractive index of the core  3 . The clad  4  does not contain the wavelength-converting element contained in the (first core portion  3 A of the) core  3 . 
     The material of the coating portion  5  may be a resin, for example. 
     The optical fiber  2  includes the light incident portion  21 , a light emerging portion  22 , and a wavelength-converting portion  23 . 
     The light incident portion  21  is a portion on which the excitation light P 1  is incident and may include the first end face  31  of the core  3 , for example. The light emerging portion  22  includes the second end face  32  of the core  3 , through which light P 4  including the excitation light P 1  and the stimulated emission of light P 3  such as an ASE emerges. 
     The light incident portion  21  may include a reflection reducing portion for reducing the reflection of the excitation light P 1  incident on the light incident portion  21  from outside of the optical fiber  2 . The reflection reducing portion may be, for example, an anti-reflection coating that covers the first end face  31  of the core  3 . 
     The light emerging portion  22  may include a reflection reducing portion for reducing reflection of the excitation light P 1  and the stimulated emission of light P 3  including an ASE. The reflection reducing portion is preferably made of a transparent material, of which the refractive index is substantially equal to that of the core  3 , for example. The reflection reducing portion includes an end cap, for example. Providing the reflection reducing portion for the light emerging portion  22  allows the optical fiber  2  to reduce an increase in the electric field strength due to reflection from the second end face  32  of the core  3  and also protect the second end face  32  of the core  3  from damage. In the optical fiber  2 , if the second end face  32  of the core  3  is in contact with the air, a Fresnel reflection of a few % could be caused at the second end face  32 , thus possibly causing parasitic oscillation that makes it difficult to control the optical output. To reduce the Fresnel reflection, the optical fiber  2  preferably includes the reflection reducing portion bonded to the second end face  32  of the core  3 . The material for the reflection reducing portion may also be glass fluoride, silicon oxide, or quartz, for example. The light emerging portion  22  may have a tilted surface which is tilted by a predetermined angle (of 8 degrees, for example) with respect to a plane intersecting at right angles with the optical axis of the optical fiber  2 . This enables, even if there is a refractive index difference between the reflection reducing portion and the core  3 , the optical fiber  2  to reduce components of light reflected back from the boundary between the second end face  32  and the reflection reducing portion to the first end face  31  (i.e., back reflected components), thus causing an increase in the efficiency of the light emerging from the light emerging portion  22 . The predetermined angle does not have to be 8 degrees. When measured along the optical axis of the optical fiber  2 , the length of the end cap may fall within the range from 100 μm to 3 mm, for example. In this embodiment, the end cap is disposed over both the core  3  and the clad  4 . However, this is only an example and should not be construed as limiting. Rather, the end cap only needs to be disposed on the second end face  32  of the core  3 . The reflection reducing portion does not have to be the end cap but may also be, for example, a microscopic surface unevenness (on the order of 200 nm or less) formed on the second end face  32  of the core  3 . In that case, the end cap may or may not be provided from the viewpoint of reflection reduction. 
     The wavelength-converting portion  23  is provided between the light incident portion  21  and the light emerging portion  22 . The wavelength-converting portion  23  contains a wavelength-converting element which is excited by the excitation light P 1  to emit light having a longer wavelength than the excitation light P 1 . The wavelength-converting element is an element that may absorb the excitation light P 1  and amplify, by stimulated emission, either the spontaneous emission of light or seed light having a longer wavelength than the excitation light P 1 . The wavelength-converting portion  23  includes: the first core portion  3 A of the core  3 ; a part, corresponding to the first core portion  3 A, of the clad  4  (i.e., its part covering the outer peripheral surface of the first core portion  3 A); and a part, corresponding to the first core portion  3 A, of the covering portion  5 . In  FIG.  1   , the wavelength-converting portion  23  of the optical fiber  2  and the rest  24  of the optical fiber  2  other than the wavelength-converting portion  23  may be distinguished from each other by dotted hatching. Specifically, in  FIG.  1   , the wavelength-converting portion  23  of the optical fiber  2  is indicated by dotted hatching and the rest  24  of the optical fiber  2  other than the wavelength-converting portion  23  is not shared by dotted hatching. The light-transmitting material of the first core portion  3 A is preferably the same as the light-transmitting material of the second core portion  3 B. The refractive index of the first core portion  3 A is preferably equal to the refractive index of the second core portion  3 B. 
     The core  3  may have a diameter falling within the range from 25 μm to 500 μm, for example. The optical fiber  2  may have a length falling within the range from 3 m to 10 m, for example. As for the length of the wavelength-converting portion  23 , the lower the concentration of the wavelength-converting element in the wavelength-converting portion  23  is, the greater the length of the wavelength-converting portion  23  preferably is. The optical fiber  2  may have a numerical aperture of 0.22, for example. The concentration of the wavelength-converting element in the wavelength-converting portion  23  is the concentration of the wavelength-converting element in the first core portion  3 A. 
     (2.2) First Light Source Unit 
     The first light source unit  11  emits the excitation light P 1  to excite the wavelength-converting element contained in the wavelength-converting portion  23  of the optical fiber  2 . The excitation light P 1  emitted from the first light source unit  11  is incident on the light incident portion  21  of the optical fiber  2 . 
     The first light source unit  11  may include a laser light source, for example. The laser light source emits a laser beam. The excitation light P 1  emitted from the first light source unit  11  (i.e., the laser beam emitted from the laser light source) is incident on the light incident portion  21 . The laser light source may be, for example, a semiconductor laser diode that emits a blue laser beam. In that case, the excitation light P 1  may have a wavelength falling within the range from 440 nm to 450 nm, for example. 
     (2.3) Second Light Source Unit 
     The second light source unit  12  emits the seed light P 2 . The seed light P 2  emitted from the second light source unit  12  is incident on the light incident portion  21  of the optical fiber  2 . 
     The lighting system  1  includes a plurality of (e.g., two) second light source units  12 , each of which emits, for example, seed light P 2  having a single wavelength. The seed light P 2  emitted from one of these two second light source units  12  has a different wavelength from the seed light P 2  emitted from the other of these two second light source units  12 . In the following description, one of the two second light source units  12  will be hereinafter referred to as a “second light source unit  121 ” and the other second light source unit  12  will be hereinafter referred to as a “second light source unit  122 ” for convenience sake. The second light source unit  121  may be a semiconductor laser diode that emits a green light ray, for example. The second light source unit  122  may be a semiconductor laser diode that emits a red light ray, for example. If the wavelength-converting element of the wavelength-converting portion  23  includes Pr 3+ , then the wavelength of the green seed light ray P 21  is preferably about 520 nm, for example, and the wavelength of the red seed light ray P 22  is preferably about 640 nm, for example. These second light source units  12  are light sources, each of which emits quasi-monochromatic light. As used herein, the “quasi-monochromatic light” refers to light falling within a narrow wavelength range (with a width of 10 nm, for example). The number of the second light source units  12  included in the lighting system  1  does not have to be two but may also be three or more or even one. If the lighting system  1  includes three second light source units  12 , then the lighting system  1  may include, as the three second light source units  12 , a semiconductor laser diode that emits a green light ray, a semiconductor laser diode that emits a red light ray, and a semiconductor laser diode that emits an orange light ray. The orange seed light ray preferably has a wavelength of about 600 nm, for example. 
     The light emitted from the second light source unit  121  is incident as a seed light ray P 2  (P 21 ) on the light incident portion  21  of the optical fiber  2 . The light emitted from the second light source unit  122  is incident as a seed light ray P 2  (P 22 ) on the light incident portion  21  of the optical fiber  2 . 
     (2.4) Lighting Unit 
     The lighting unit  6  projects, into the external space S 1 , the light emerging from the light emerging portion  22  of the optical fiber  2 . The lighting unit  6  holds the light emerging portion  22  of the optical fiber  2  thereon. The lighting unit  6  may include an optical member for controlling the distribution of the light emerging from the light emerging portion  22  of the optical fiber  2 . The optical member may be, for example, a lens or a reflector. If the lighting system  1  is used as a down light, then the lighting unit  6  may be fitted into a through hole  102  of the ceiling  101  of a building  100 , for example. In that case, part of the optical fiber  2  will be hidden behind the ceiling  101  and a wall  103  of the building  100 , which form a structure for holding the lighting unit  6 . In other words, part of the optical fiber  2  is installed on the back of the ceiling and the wall. The lighting unit  6  may be mounted to the ceiling  101  with, for example, a flange protruding outward from the bottom of the lighting unit  6  and a plurality of leaf springs to clamp the ceiling  101  between the flange and themselves. Alternatively, the lighting unit  6  may also be mounted onto the ceiling  101  with, for example, a mounting bracket and a plurality of mounting springs. 
     (2.5) Other Constituent Elements 
     The lighting system  1  includes a housing  15  to house the first light source unit  11  and the plurality of second light source units  12  therein. The housing  15  may be installed, for example, on the floor  104  of the building  100  and behind the wall  103 . 
     The lighting system  1  further includes an adjustment unit  10 . The adjustment unit  10  adjusts the intensity of the seed light P 2  having at least one wavelength. In the lighting system  1  according to the first embodiment, the adjustment unit  10  adjusts the intensity of the excitation light P 1  and the respective intensities of seed light rays P 21 , P 22 . The adjustment unit  10  includes: a first driver circuit for driving the first light source unit  11 ; a plurality of second driver circuits, which are provided one to one for the plurality of second light source units  12  and each of which drives a corresponding one of the second light source units  12 ; and a control circuit for controlling the first driver circuit and the plurality of second driver circuits on an individual basis. In the adjustment unit  10 , the control circuit controls the first driver circuit and the plurality of second driver circuits on an individual basis, thus making the chromaticity of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2  adjustable. In short, the lighting system  1  includes the adjustment unit  10 , thus enabling controlling the color of the emerging light. In this embodiment, the adjustment unit  10  is housed in the housing  15 . However, this is only an example and the adjustment unit  10  does not have to be housed in the housing  15 . The first driver circuit and the plurality of second driver circuits are supplied with supply voltage from a first power supply circuit, for example. Meanwhile, the control circuit is supplied with supply voltage from a second power supply circuit, for example. In this embodiment, the first power supply circuit and the second power supply circuit are not counted among the constituent elements of the lighting system  1 . However, this is only an example and should not be construed as limiting. Alternatively, the first power supply circuit and the second power supply circuit may be counted among constituent elements of the lighting system  1 . 
     The lighting system  1  further includes a photocoupler  16  to make the excitation light P 1  and the respective seed light rays P 2  incident on the light incident portion  21  of the optical fiber  2 . The photocoupler  16  is disposed at an opening  151  of the housing  15 . The photocoupler  16  may be, but does not have to be, a waveguide coupler. Alternatively, the photocoupler  16  may also be an optical fiber coupler, or any other multi-wavelength combiner. A material for the waveguide coupler, the optical fiber coupler, and the multi-wavelength combiner may be, but does not have to be, quartz, for example. Optionally, in this lighting system  1 , the photocoupler  16  may include a lens and the lens of the photocoupler  16 , which is arranged to receive the excitation light P 1 , may also receive the seed light P 2 . If the first light source unit  11  and the second light source unit  12  are each configured to let the excitation light P 1  and the seed light P 2  emerge through the optical fiber, then the respective optical fibers may be arranged such that the light emerging from each of the optical fibers is introduced into the photocoupler  16 . Optionally, the light (including the excitation light P 1  and the respective seed light rays P 2 ) incident on the light incident portion  21  of the optical fiber  2  may be adjusted by using a lens, a mirror, a prism, an optical member with a slit that passes light, and other optical members. Adjustments using these optical members may be combined as appropriate even when the first light source unit  11  or the second light source unit  12  lets the light emerge through the optical fiber. Optionally, part of the photocoupler  16 , through which the excitation light P 1  or the seed light P 2  is introduced, may include a reflection reducing portion. The reflection reducing portion may be, for example, an anti-reflection coating. 
     (3) Operation of Lighting System 
     The lighting system  1  makes the first light source unit  11  emit the excitation light P 1  and also makes the plurality of second light source units  12  emit the seed light rays P 21 , P 22 , respectively. Thus, the lighting system  1  allows the excitation light P 1  and the seed light P 2  to be incident on the light incident portion  21  of the optical fiber  2 . Part of the excitation light P 1  incident on the light incident portion  21  emerges from the light emerging portion  22 . In the lighting system  1 , the light P 4  emerging from the light emerging portion  22  of the optical fiber  2  is mixed light in which the excitation light P 1 , an ASE with a wavelength of about 480 nm and produced from the wavelength-converting element, and the light produced by amplifying the seed light P 2  are mixed together. Two types of stimulated emissions of light P 31 , P 32  corresponding one to one to the multiple seed light rays P 21 , P 22  and having mutually different wavelengths may be, for example, a green ray and a red ray, respectively. In that case, the mixed light may be white light, for example. In  FIG.  3 C , the lower stimulated emission of light P 3  (P 31 ) is the green ray and the upper stimulated emission of light P 3  (P 32 ) is the red ray. 
     In the optical fiber  2 , stimulated emission is produced by the spontaneous emission of light and the seed light P 2 , and therefore, the excitation light P 1  incident on the light incident portion  21  and the stimulated emission of light P 3  amplified by stimulated emission emerge from the light emerging portion  22 . The stimulated emission of light P 3  having the same wavelength as the seed light ray P 21  of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2  has a higher intensity than the seed light ray P 21  incident from the second light source unit  121  onto the light incident portion  21 . Also, the stimulated emission of light P 3  having the same wavelength as the seed light ray P 22  of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2  has a higher intensity than the seed light ray P 22  incident from the second light source unit  122  onto the light incident portion  21 . The mixed light emerging from the light emerging portion  22  of the optical fiber  2  is incoherent light. In the lighting system  1 , the chromaticity, color temperature, color rendering index, and other parameters of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2  are determined by the respective wavelengths of the ASE and the seed light P 2 . Note that the operation of the lighting system  1  is different from the operation of a fiber laser that produces laser oscillation. 
     In the lighting system  1 , the wavelength-converting element that serves as a heat source is distributed in the core  3  of the optical fiber  2 , and therefore, an increase in temperature may be reduced while the lighting system  1  is being used. 
     Also, in the lighting system  1 , the adjustment unit  10  adjusts the intensity of the excitation light P 1  and the respective intensities of the multiple seed light rays P 2 . However, this is only an example and should not be construed as limiting. Alternatively, the adjustment unit  10  may also be configured to adjust the intensity of the seed light P 2  having at least one wavelength. 
     (4) Recapitulation 
     A lighting system  1  according to the first embodiment includes an optical fiber  2 , a first light source unit  11 , a second light source unit  12 , and a lighting unit  6 . The optical fiber  2  includes a light incident portion  21 , a light emerging portion  22 , and a wavelength-converting portion  23 . The wavelength-converting portion  23  is provided between the light incident portion  21  and the light emerging portion  22 . The wavelength-converting portion  23  contains a wavelength-converting element, which is excited by excitation light P 1  and amplifies a spontaneous emission of light, having a longer wavelength than the excitation light P 1 , with an amplified spontaneous emission of light (i.e., a stimulated emission). The first light source unit  11  makes the excitation light P 1  incident on the light incident portion  21 . The second light source unit  12  makes seed light P 2  incident on the light incident portion  21 . The seed light P 2  causes the wavelength-converting element that has been excited by the excitation light P 1  and the amplified spontaneous emission of light to produce a stimulated emission of light P 3 . The lighting unit  6  projects, into an external space S 1 , light P 4  emerging from the light emerging portion  22  of the optical fiber  2 . 
     The lighting system  1  according to the first embodiment enables increasing the intensity of light (i.e., the stimulated emission of light P 3 ) having a different wavelength from the excitation light P 1 . 
     In addition, in the lighting system  1  according to the first embodiment, the wavelength-converting portion  23  is provided between the light incident portion  21  and the light emerging portion  22  of the optical fiber  2 . This enables reducing an increase in the temperature of the wavelength-converting portion  23  by increasing the length of the wavelength-converting portion  23 . 
     Furthermore, in the lighting system  1  according to the first embodiment, there are no heat generation sources such as the first light source unit  11 , the second light source unit  12 , and the wavelength-converting portion  23  in the lighting unit  6 . This eliminates the need to provide any heat dissipating member for the lighting unit  6 , thus contributing to reducing the size and weight of the lighting unit  6 . Consequently, this makes it easier to install the lighting unit  6  on the ceiling  101 , for example. 
     Furthermore, the lighting system  1  according to the first embodiment further includes an adjustment unit  10  for adjusting the respective intensities of multiple seed light rays P 2  having multiple different wavelengths, thus making the chromaticity of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2  adjustable. 
     In addition, in the lighting system  1  according to the first embodiment, the wavelength-converting portion  23  contains Pr 3+  as the wavelength-converting element. The wavelength-converting element not only emits an ASE in cyan but also increases the respective intensities of stimulated emissions in green and red, because a plurality of seed light rays P 2  with mutually different wavelengths are incident onto the light incident portion  21 . This allows the lighting system  1  according to the first embodiment to improve the color rendering index of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2 . Furthermore, in the lighting system  1  according to the first embodiment, the wavelength-converting portion  23  contains Pr 3+  and Tb 3+  as two types of wavelength-converting elements, thus enabling further improving the color rendering index of the light P 4  emerging from the light emerging portion  22  of the optical fiber  2 . 
     Variation of First Embodiment 
     Next, a lighting system  1   a  according to a variation of the first embodiment will be described with reference to  FIG.  4   . In the following description, any constituent element of the lighting system  1   a  according to this variation, having the same function as a counterpart of the lighting system  1  according to the first embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. 
     In the lighting system  1   a  according to this variation, the first light source unit  11  and the two second light source units  12  are arranged differently from in the lighting system  1  according to the first embodiment and a cross dichroic prism  14  is further provided, which are differences from the lighting system  1  according to the first embodiment. 
     The cross dichroic prism  14  is arranged to make the excitation light P 1  coming from the first light source unit  11  and the two seed light rays P 21 , P 22  respectively coming from the two second light source units  12  incident on the light incident portion  21  of the optical fiber  2 . 
     The cross dichroic prism  14  includes: a first film  141  which transmits the seed light ray P 21  (e.g., a green light ray in this example) coming from the second light source unit  121  and the seed light ray P 22  (e.g., a red light ray in this example) coming from the second light source unit  122  and reflects the excitation light P 1  (e.g., a blur light ray in this example); and a second film  142  which transmits the excitation light P 1  coming from the first light source unit  11  and the seed light ray P 21  coming from the second light source unit  121  and reflects the seed light ray P 22  coming from the second light source unit  122 . The first film  141  and the second film  142  are arranged to intersect with each other at right angles. In this lighting system  1   a , the second light source unit  121  faces the light incident portion  21  of the optical fiber  2  and the cross dichroic prism  14  is arranged on the optical axis of the second light source unit  121  to be located between the second light source unit  121  and the light incident portion  21  of the optical fiber  2 . In addition, the first light source unit  11 , the cross dichroic prism  14 , and the second light source unit  122  are arranged side by side in a direction intersecting at right angles with the optical axis of the second light source unit  121  and intersecting with the first film  141  and the second film  142 . 
     The lighting system  1   a  according to this variation enables, as well as the lighting system  1  according to the first embodiment, increasing the intensity of light (stimulated emission of light P 3 ) having a different wavelength from the excitation light P 1 . 
     Second Embodiment 
     Next, a lighting system  1   b  according to a second embodiment will be described with reference to  FIG.  5   . In the following description, any constituent element of the lighting system  1   b  according to this second embodiment, having the same function as a counterpart of the lighting system  1  according to the first embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. 
     The lighting system  1   b  according to the second embodiment further includes a protective cover  7 , which is a difference from the lighting system  1  according to the first embodiment. The protective cover  7  covers the wavelength-converting portion  23  partially. In the lighting system  1   b  according to the second embodiment, a space  8  is left between the protective cover  7  and the wavelength-converting portion  23 . The protective cover  7  has, along the longitudinal axis of the protective cover  7 , a first end  71  and a second end  72  opposite from the first end  71 . The protective cover  7  has a tubular shape and has a first opening at the first end  71  and a second opening at the second end  72 . More specifically, the protective cover  7  has a circular tubular shape and has a circular first opening at the first end  71  and a circular second opening at the second end  72 . The inside diameter of the first opening and the inside diameter of the second opening are greater than the outside diameter of the optical fiber  2 . The space  8  communicates with the external space via the first opening and also communicates with the external space via the second opening. Note that the protective cover  7  does not have to have a circular tubular shape but may also have any other shape as long as a space  8  may be left between the inner peripheral surface of the protective cover  7  and the outer peripheral surface of the optical fiber  2 . In that case, the first opening and the second opening may also have an elliptical or square shape, for example. 
     Providing the protective cover  7  for the lighting system  1   b  according to the second embodiment enables protecting at least a part of the wavelength-converting portion  23 . In addition, the lighting system  1   b  according to the second embodiment has a space  8  between the protective cover  7  and the wavelength-converting portion  23 , thus making it easier to dissipate the heat generated by the wavelength-converting portion  23 . 
     In addition, in the lighting system  1   b  according to the second embodiment, a gap  9  is also left between the protective cover  7  and the first light source unit  11  and the second light source unit  12 . More specifically, the lighting system  1   b  according to the second embodiment has the gap  9  between the first end  71  of the protective cover  7  and the photocoupler  16  and the gap  9  exposes one end, adjacent to the photocoupler  16 , of the wavelength-converting portion  23 . This makes it easier for the lighting system  1   b  according to the second embodiment to dissipate the heat generated by the wavelength-converting portion  23 . 
     Furthermore, in the lighting system  1   b  according to the second embodiment, the protective cover  7  has flexibility. Thus, the lighting system  1   b  according to the second embodiment allows the optical fiber  2  and the protective cover  7  to be installed with an increased degree of freedom. 
     In the lighting system  1   b  according to this second embodiment, as well as the lighting system  1  according to the first embodiment, the wavelength-converting portion  23  also contains a wavelength-converting element, which is excited by excitation light P 1  and amplifies a spontaneous emission of light, having a longer wavelength than the excitation light P 1 , with an amplified spontaneous emission of light (i.e., a stimulated emission). The first light source unit  11  makes the excitation light P 1  incident on the light incident portion  21 . The second light source unit  12  makes seed light P 2  incident on the light incident portion  21 . The seed light P 2  causes the wavelength-converting element that has been excited by the excitation light P 1  and the amplified spontaneous emission of light to produce a stimulated emission of light P 3 . The lighting unit  6  projects, into an external space S 1 , the light P 4  (see  FIG.  2 B ) emerging from the light emerging portion  22  of the optical fiber  2 . 
     Thus, the lighting system  1   b  according to the second embodiment enables increasing the intensity of light (i.e., the stimulated emission of light P 3 ) having a different wavelength from the excitation light P 1 . 
     Third Embodiment 
     Next, a lighting system  1   c  according to a third embodiment will be described with reference to  FIG.  6   . In the following description, any constituent element of the lighting system  1   c  according to this third embodiment, having the same function as a counterpart of the lighting system  1   b  according to the second embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. 
     In the lighting system  1   c  according to the third embodiment, the protective cover  7  is longer than the wavelength-converting portion  23  and covers the wavelength-converting portion  23  along the entire length thereof, which is a difference from the lighting system  1   b  according to the second embodiment. 
     The lighting system  1   c  according to this third embodiment allows the protective cover  7  to protect the wavelength-converting portion  23  in its entirety. 
     In addition, the lighting system  1   c  according to the third embodiment further includes a blower  17 . The blower  17  is disposed inside the housing  15 . The lighting system  1   c  according to the third embodiment includes the blower  17 , and therefore, may cool the air inside the housing  15 , thus enabling reducing an increase in the temperature of the first light source unit  11  and the plurality of second light source units  12 . Also, if part of the air blown by the blower  17  is allowed to pass through the space  8  between the protective cover  7  and the wavelength-converting portion  23 , then an increase in the temperature of the wavelength-converting portion  23  may be further reduced. 
     In the lighting system  1   c  according to this third embodiment, as well as the lighting system  1   b  according to the second embodiment, the wavelength-converting portion  23  also contains a wavelength-converting element, which is excited by excitation light P 1  and amplifies a spontaneous emission of light, having a longer wavelength than the excitation light P 1 , with an amplified spontaneous emission of light (i.e., a stimulated emission). The first light source unit  11  makes the excitation light P 1  incident on the light incident portion  21 . The second light source unit  12  makes seed light P 2  incident on the light incident portion  21 . The seed light P 2  causes the wavelength-converting element that has been excited by the excitation light P 1  and the amplified spontaneous emission of light to produce a stimulated emission of light P 3 . The lighting unit  6  projects, into an external space S 1 , light P 4  (see  FIG.  2 B ) emerging from the light emerging portion  22  of the optical fiber  2 . 
     Thus, the lighting system  1   c  according to the third embodiment enables increasing the intensity of light (i.e., the stimulated emission of light P 3 ) having a different wavelength from the excitation light P 1 . 
     Fourth Embodiment 
     Next, a lighting system  1   d  according to a fourth embodiment will be described with reference to  FIG.  7   . In the following description, any constituent element of the lighting system  1   d  according to this fourth embodiment, having the same function as a counterpart of the lighting system  1   b  according to the second embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. 
     In the lighting system  1   d  according to the fourth embodiment, the protective cover  7  has a plurality of through holes  73 , which is a difference from the lighting system  1   b  according to the second embodiment. The plurality of through holes  73  communicate with the space  8  between the protective cover  7  and the wavelength-converting portion  23 . 
     In the lighting system  1   d  according to the fourth embodiment, the protective cover  7  has the plurality of through holes  73 , thus making it easier to dissipate the heat generated by the wavelength-converting portion  23  than in the lighting system  1   b  according to the second embodiment. The protective cover  7  may be, but does not have to be, made of a metal. 
     Fifth Embodiment 
     Next, a lighting system  1   e  according to a fifth embodiment will be described with reference to  FIG.  8   . In the following description, any constituent element of the lighting system  1   e  according to this fifth embodiment, having the same function as a counterpart of the lighting system  1  according to the first embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. Note that in  FIG.  8   , illustration of the wavelength-converting portion  23 , the first light source unit  11 , the plurality of second light source units  12 , and other members of the lighting system  1  according to the first embodiment is omitted. 
     The lighting system  1   e  according to this fifth embodiment is used as lighting for a tennis court, which is a difference from the lighting system  1  according to the first embodiment. 
     A lighting unit  6  included in the lighting system  1   e  according to the fifth embodiment is supported by a hollow pole provided to stand upright from the ground around the tennis court. The pole is a structure for supporting the lighting unit  6 . 
     In the lighting system  1   e  according to the fifth embodiment, part of the optical fiber  2  is inserted into the pole. Thus, the wavelength-converting portion  23  is hidden behind the pole. 
     The lighting system  1   e  includes a plurality of (e.g., four in the example illustrated in  FIG.  8   ) optical fibers  2 . Two out of the plurality of (e.g., four in the example illustrated in  FIG.  8   ) optical fibers  2  are bundled together and another two optical fibers  2  are also bundled together to form two bundles of optical fibers  2  that are held by the lighting unit  6 . This allows the lighting system  1   e  to increase the quantity of light emerging from the lighting unit  6  while reducing an increase in the overall size of the lighting unit  6 . Each bundle, out of the two or more bundles of optical fibers  2 , is partially inserted into the pole. 
     In this lighting system  1   e , the lighting unit  6  includes a lighting unit body  61  that holds the optical fibers  2  and reflectors  62 . Each of the reflectors  62  reflects at least a part of the light P 4  emerging from the respective light emerging portions  22  of its associated bundle of optical fibers  2  toward the external space S 1 . This allows the lighting system  1   e  to make the reflectors  62  control the distribution of the light. In this lighting system  1   e , one reflector  62  is provided for one bundle of two optical fibers  2  and another reflector  62  is provided for another bundle of two optical fibers  2 . 
     The number of the optical fibers  2  provided is not limited to any particular number as long as a plurality of optical fibers  2  are provided. For example, only two optical fibers  2  may be provided. In that case, the two optical fibers  2  only need to be bundled together and the lighting unit  6  may include only one reflector  62 . 
     Sixth Embodiment 
     Next, a lighting system  1   f  according to a sixth embodiment will be described with reference to  FIGS.  9 - 13 B . In the following description, any constituent element of the lighting system  1   f  according to this sixth embodiment, having the same function as a counterpart of the lighting system  1  according to the first embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. 
     As shown in  FIG.  9   , the lighting system if according to the sixth embodiment includes a supporting member  160  for supporting the lighting unit body  61  of each lighting unit  6 . The supporting member  160  includes: a fixed portion  165  to be fixed onto the ceiling  101 ; a hollow arm  166  having a first end coupled to the fixed portion  165  and a second end; and a coupler  167  that couples the second end of the arm  166  to the lighting unit body  61  of the lighting unit  6 . The fixed portion  165  is fixed onto the ceiling  101  with a part of the fixed portion  165  embedded in a mounting hole  111  provided through the ceiling  101 . The fixed portion  165 , the arm  166 , and the coupler  167  have a space to pass the optical fiber  2  and a power cable  300  (to be described later) therethrough. The power cable  300  is connected to a power supply device  155  disposed in the housing  15 . In this lighting system  1   f , part of the optical fiber  2  and part of the power cable  300  are inserted into the fixed portion  165 , the arm  166 , and the coupler  167 . Thus, the part of the optical fiber  2  and the part of the power cable  300  are hidden behind the fixed portion  165 , the arm  166 , and the coupler  167 . The coupler  167  is a hinge device (rotary mechanism) for coupling the lighting unit  6  to the arm  166  to allow the lighting unit  6  to turn from a first position to a second position, or vice versa, around one rotational axis which intersects at right angles with the axis of the arm  166 . More specifically, the coupler  167  is a hinge device that couples the lighting unit  6  to the arm  166  to allow the lighting unit  6  to rotate clockwise and counterclockwise in front view shown in  FIG.  9   . This lighting system if includes the coupler  167  serving as such a hinge device, and therefore, may adjust the irradiation direction of the light P 4  emerging from the lighting unit  6 . 
     As shown in  FIG.  10   , the lighting system if further includes an information acquisition unit  69 , a first driving unit  66 , a second driving unit  67 , and a control unit  68 . The information acquisition unit  69  acquires control related information about the irradiation direction of the light P 4  allowed to project from the lighting unit  6  into the external space S 1 . The first driving unit  66  and the second driving unit  67  drive the lighting unit  6 . The control unit  68  changes, in accordance with the control related information acquired by the information acquisition unit  69 , the irradiation direction of the light P 4  emerging from the lighting unit  6 . The control unit  68  changes the irradiation direction of the light P 4  by having the lighting unit  6  driven by at least one of the first driving unit  66  or the second driving unit  67 . This allows the lighting system  1  to change the lighting area A 1  formed by the light P 4  projected from the lighting unit  6  toward the external space S 1 . Changing the irradiation direction includes changing the irradiation range (light beam angle). 
     The functions of the information acquisition unit  69  and the control unit  68  may be performed by a computer system. The computer system may include, for example, one or more input/output interfaces, one or more memories, and one or more processors (microprocessors). That is to say, the one or more processors may perform the functions of the information acquisition unit  69  and the control unit  68  by executing one or more programs (applications) stored in the one or more memories. In this embodiment, the program is stored in advance in the memory of the control unit  68 . Alternatively, the program may also be downloaded via a telecommunications line such as the Internet or distributed after having been recorded in a non-transitory storage medium such as a memory card. Note that the input/output interface is an interface for inputting and outputting information to/from the control unit  68  and includes a communications interface. The computer system performing the functions of the information acquisition unit  69  and the control unit  68  may be disposed in, for example, the lighting unit  6 . 
     The control related information includes location information, detected by a sensor, about the location of a human being H 10  who is present as a target to irradiate in the external space S 1 . The sensor is an imaging sensor  161  for detecting the human being H 10  present in the external space S 1 . The imaging sensor  161  may be mounted, for example, on the ceiling  101  that faces the external space S 1 . The imaging sensor  161  may be, for example, a thermal imaging sensor including a plurality of pixels, each of which includes an infrared detector implemented as a thermopile. The imaging sensor  161  may generate, based on the thermal image, location information about the location of the human being H 10  in the external space S 1 . Depending on a facility, a plurality of imaging sensors  161  may be provided for a single external space S 1 . In that case, identification information (address) is set on an individual basis for each imaging sensor  161 . Note that the imaging sensor  161  does not have to be a thermal imaging sensor but may also be an imaging sensor including a camera to shoot the external space S 1 . The image sensor included in the camera may be, for example, a complementary metal-oxide semiconductor (CMOS) image sensor. However, the image sensor does not have to be a CMOS image sensor but may also be, for example, a charge-coupled device (CCD) image sensor or an infrared image sensor, for example. 
     The control unit  68  may store, in accordance with the location information of the lighting unit  6 , the location information of the imaging sensor  161 , and the detection area of the imaging sensor  161 , and other pieces of information, the location information of the lighting unit  6  and location information of a plurality of small detection areas corresponding one to one to the plurality of pixels of the imaging sensor  161  in association with each other in a memory of the control unit  68 . 
     Also, in this lighting system  1   f , the control related information also includes device location information, transmitted from a transmitter device  162  in the external space S 1 , about the location of the transmitter device  162 . The transmitter device  162  may be, for example, a remote controller or a smartphone. The control unit  68  controls the first driving unit  66  to change the irradiation direction of the light P 4  in accordance with the device location information transmitted from the transmitter device  162 . The transmitter device  162  transmits a wireless signal including the device location information when operated, for example, by the human being H 10  present in the external space S 1 . The information acquisition unit  69  includes a reception unit to receive the wireless signal transmitted from the transmitter device  162  and acquires the device location information via the reception unit. 
     In the lighting system if according to the sixth embodiment, the control unit  68  changes the irradiation direction of the light P 4  emerging from the lighting unit  6  in accordance with the control related information acquired by the information acquisition unit  69 , thus enabling changing the lighting area A 1 . 
     Optionally, the lighting system if may also be configured to make the information acquisition unit  69  acquire identification information of the human being H 10  as another piece of the control related information and to make the control unit  68  control the adjustment unit  10  based on the identification information and the location information to irradiate the human being H 10  with light, of which the chromaticity is adjusted to his or her preference. The adjustment unit  10  gives control signals to the driver circuits for the first light source unit  11  and the second light source units  12  (i.e., the first and second driver circuits), thereby adjusting the output powers of respective laser light sources of the first light source unit  11  and the second light source units  12 . This allows the lighting system if to irradiate the human being H 10  with the light P 4 , of which the chromaticity is adjusted to his or her preference. 
     As shown in  FIG.  11   , the lighting unit  6  includes a lighting unit body  61  having the shape of a bottomed cylinder and a light projection unit  60  which is arranged in the lighting unit body  61  to project, toward the external space, the light P 4  emerging from the light emerging portion  22  of the optical fiber  2 . The light projection unit  60  includes: a ferrule  27  covering an end portion, including the light emerging portion  22 , of the optical fiber  2 ; a lens  63  facing the light emerging portion  22  of the optical fiber  2 ; a protective member  65  housing the lens  63  and the ferrule  27  therein; a ringlike frame member  690  arranged in the lighting unit body  61  to surround the protective member  65 ; and a flange portion  660  protruding outward from a tip portion of the protective member  65 . The lens  63  may be a biconvex lens, for example. The lens  63  is arranged on the optical axis of the light emerging portion  22  of the optical fiber  2  to be out of contact with the light emerging portion  22 . The lens  63  has a first lens surface  631  facing the light emerging portion  22  of the optical fiber  2  and a second lens surface  632  opposite from the first lens surface  631 . In the light projection unit  60 , the second lens surface  632  of the lens  63  is exposed. The light projection unit  60  is movable inside the lighting unit body  61 . The frame member  690  is fixed to the lighting unit body  61 . 
     In this lighting system  1   f , the first driving unit  66  serves as a driving unit for driving the (light projection unit  60  of the) lighting unit  6  to change the irradiation direction of the light P 4 . Also, in this lighting system  1   f , the second driving unit  67  serves as a driving unit for driving the (light projection unit  60  of the) lighting unit  6  to change the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63 . 
     The first driving unit  66  includes a first actuator  661  and a second actuator  662 . 
     The first actuator  661  includes a first motor M 1 , a first feed screw SC 1 , a first nut N 1 , and a first spring SP 1 . In the first actuator  661 , one end portion of the first feed screw SC 1  is coupled to the rotary shaft of the first motor M 1  and the other end portion of the first feed screw SC 1  is fitted into the first nut N 1 . The first nut N 1  is in contact with the flange portion  660  of the light projection unit  60 . The first spring SP 1  is interposed between the frame member  690  and the flange portion  660  and is stretchable and shrinkable in the direction aligned with the axis of the first feed screw SC 1 . The first feed screw SC 1  is fitted into a first screw hole  691  of the frame member  690  between the first motor M 1  and the flange portion  660 . In the first driving unit  66 , the first motor M 1  is movable, when rotating, along the axis of the first feed screw SC 1 . The axis of the first feed screw SC 1  is substantially parallel to the axis of the lighting unit body  61 . 
     The second actuator  662  includes a second motor M 2 , a second feed screw SC 2 , a second nut N 2 , and a second spring SP 2 . In the second actuator  662 , one end portion of the second feed screw SC 2  is coupled to the rotary shaft of the second motor M 2  and the other end portion of the second feed screw SC 2  is fitted into the second nut N 2 . The second nut N 2  is in contact with the flange portion  660  of the light projection unit  60 . The second spring SP 2  is interposed between the frame member  690  and the flange portion  660  and is stretchable and shrinkable in the direction aligned with the axis of the second feed screw SC 2 . The second feed screw SC 2  is fitted into a second screw hole  692  of the frame member  690  between the second motor M 2  and the flange portion  660 . In the first driving unit  66 , the second motor M 2  is movable, when rotating, along the axis of the second feed screw SC 2 . The axis of the second feed screw SC 2  is substantially parallel to the axis of the lighting unit body  61 . 
     In this lighting system  1   f , the control unit  68  controls the first motor M 1  and second motor M 2  of the first driving unit  66 . In the lighting system  1   f , as the first feed screw SC 1  is driven downward from the state shown in  FIG.  12 A , for example, by rotating the first motor M 1  in a first rotational direction, the flange portion  660  is driven downward so as to tilt around the point of contact between the flange portion  660  and the second nut N 2  as a fulcrum and thereby cause the optical axis of the light emerging portion  22  of the optical fiber  2  to tilt with respect to the axis of the first feed screw SC 1  and the longitudinal axis of the lighting unit body  61 . As a result, the irradiation direction of the light P 4  changes. In addition, the lighting system if may recover the state shown in  FIG.  12 A  by rotating, in the state shown in  FIG.  12 B , the first motor M 1  in a second rotational direction opposite from the first rotational direction. Furthermore, in the lighting system  1   f , as the second feed screw SC 2  is driven downward from the state shown in  FIG.  12 A , for example, by rotating the second motor M 2  in the first rotational direction, the flange portion  660  is driven downward so as to tilt around the point of contact between the flange portion  660  and the first nut N 1  as a fulcrum and thereby cause the optical axis of the light emerging portion  22  of the optical fiber  2  to tilt with respect to the axis of the second feed screw SC 2  and the longitudinal axis of the lighting unit body  61 . As a result, the irradiation direction of the light P 4  also changes. 
     As shown in  FIGS.  13 A and  13 B , the second driving unit  67  includes a third actuator  671 . The third actuator  671  includes a third motor M 3 , a third feed screw SC 3 , a third nut N 3 , and a third spring SP 3 . In the lighting unit  6 , the light projection unit  60  includes a fixed frame member  601  and a moving frame member  602  which are arranged in the protective member  65 . The fixed frame member  601  is fixed to the protective member  65 . The moving frame member  602  is spaced from the fixed frame member  601  in the direction aligned with the optical axis of the optical fiber  2  and is movable to change the distance from the fixed frame member  601 . The optical fiber  2  is not fixed to the fixed frame member  601  but is fixed to the moving frame member  602 . This allows the optical fiber  2  to move along with the moving frame member  602 . In this lighting system  1   f , the fixed frame member  601 , the moving frame member  602 , the light emerging portion  22 , and the lens  63  are arranged in this order in the direction aligned with the optical axis of the optical fiber  2 . In the third actuator  671 , one end portion of the third feed screw SC 3  is coupled to the rotary shaft of the third motor M 3  and the other end portion of the third feed screw SC 3  is fitted into the third nut N 3 . The third nut N 3  is in contact with the moving frame member  602 . The third spring SP 3  is interposed between the fixed frame member  601  and the moving frame member  602  and is stretchable and shrinkable in the direction aligned with the axis of the third feed screw SC 3 . The fixed frame member  601  further includes a screw  613  into which the third feed screw SC 3  is fitted. The lighting unit  6  further includes a supporting pin  603  protruding from the fixed frame member  601  toward the moving frame member  602 . The moving frame member  602  has a first principal surface  621  facing the lens  63  and a second principal surface  622  facing the fixed frame member  601 . The second principal surface  622  has a recess  623  into which the supporting pin  603  is fitted. 
     In the lighting system if according to the sixth embodiment, the control unit  68  controls the third motor M 3  of the second driving unit  67 . In this lighting system  1   f , as the third feed screw SC 3  is driven downward as shown in  FIG.  13 B  by rotating the third motor M 3  in the first direction from the state shown in  FIG.  13 A , for example, the moving frame member  602  is driven downward to change the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63 . Also, the lighting system if may recover the state shown in  FIG.  13 A  by rotating, in the state shown in  FIG.  13 B , the third motor M 3  in a second rotational direction opposite from the first rotational direction. 
     In the lighting system if according to the sixth embodiment, the control unit  68  changes, in accordance with the control related information, the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63 . Also, in this lighting system  1   f , the control unit  68  control the second driving unit  67  to change the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63  as shown in  FIGS.  13 A and  13 B . This allows the lighting system  1   f  to change the light beam angle of the light P 4  emerging from the lighting unit  6  to irradiate the external space S 1 . That is to say, the lighting system if enables changing the spread of the lighting area A 1  by changing the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63 . 
     In the lighting system if according to a first variation of the sixth embodiment, the lens  63  of the lighting unit  6  may also be a plano-convex lens as shown in  FIGS.  14 A and  14 B . In the lens  63 , the planar surface of the plano-convex lens constitutes a first lens surface  631  of the first lens  63  and the convex curved surface of the plano-convex lens constitutes a second lens surface  632  of the first lens  63 . The lighting system if according to the first variation of the sixth embodiment enables changing the spread of the lighting area A 1  by changing the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63 .  FIG.  14 A  illustrates the relative arrangement of the optical fiber  2  and the lens  63  and the distribution of the light P 4  in a situation where the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63  is equal to the focal length of the lens  63 .  FIG.  14 B  illustrates the relative arrangement of the optical fiber  2  and the lens  63  and the distribution of the light P 4  in a situation where the distance between the light emerging portion  22  of the optical fiber  2  and the lens  63  is shorter than the focal length of the lens  63 . 
     In the lighting system if according to a second variation of the sixth embodiment, the lighting unit  6  may further include a second lens  64 , which is disposed inside the lighting unit body  61  and located opposite from the light emerging portion  22  with respect to the lens  63  (hereinafter referred to as a “first lens  63 ”) as shown in  FIG.  15   . The second lens  64  is arranged on the optical axis of the light emerging portion  22  to be out of contact with the first lens  63 . The distance between the light emerging portion  22  of the optical fiber  2  and the second lens  64  is longer than the distance between the light emerging portion  22  and the first lens  63 . 
     The first lens  63  has the first lens surface  631  facing the light emerging portion  22  of the optical fiber  2  and the second lens surface  632  opposite from the first lens surface  631 . The first lens  63  may be, for example, a plano-convex lens that performs a condensing function. In the first lens  63 , the planar surface of the plano-convex lens constitutes the first lens surface  631  of the first lens  63  and the convex curved surface of the plano-convex lens constitutes the second lens surface  632  of the first lens  63 . On the other hand, the second lens  64  is a plano-concave lens with the capability of reducing an axial chromatic aberration, for example. The second lens  64  has a first lens surface  641  facing the first lens  63  and a second lens surface  642  opposite from the first lens surface  641 . In the second lens  64 , the concave curved surface of the plano-concave lens constitutes the first lens surface  641  of the second lens  64  and the planar surface of the plano-concave lens constitutes the second lens surface  642  of the second lens  64 . The lighting unit  6  does not have to include both the first lens  63  and the second lens  64 . Alternatively, the lighting unit  6  may also include at least one of the first lens  63  or the second lens  64 . Still alternatively, the lighting unit  6  may include neither the first lens  63  nor the second lens  64 . 
     Furthermore, in the lighting system if according to a third variation of the sixth embodiment, the coupler  167  may include a motor for turning the lighting unit  6  from a first position to a second position, or vice versa, around a single rotational axis that intersects at right angles with the axis of the arm  166 . The motor controls the angle of rotation of the lighting unit  6  around the rotational axis. The motor is driven by a third driving unit. In the lighting system if according to the third variation, the third driving unit may be arranged in the fixed portion  165  and connected to the motor via an electric wire. The lighting system if according to the third variation may also adjust the irradiation direction of the light P 4  emerging from the lighting unit  6  by making the control unit  68  control the third driving unit. 
     Other Variations 
     Note that the first to sixth embodiments described above are only exemplary ones of various embodiments of the present disclosure and should not be construed as limiting. Rather, the first to sixth exemplary embodiments may be readily modified in various manners depending on a design choice or any other factor without departing from the scope of the present disclosure. 
     For example, in the optical fiber  2 , the number of the wavelength-converting portion(s)  23  provided between the light incident portion  21  and the light emerging portion  22  does not have to be one but may also be multiple, for example. In the latter case, the plurality of wavelength-converting portions  23  are arranged side by side along the optical axis of the core  3 . 
     In the embodiments described above, the core  3  includes the first core portion  3 A and the second core portion  3 B. However, the core  3  needs to include at least the first core portion  3 A. In other words, the wavelength-converting portion  23  does not have to be provided for only a part of the length of the optical fiber  2  but may be provided for the entire length of the optical fiber  2  as well. 
     The laser light source included in the first light source unit  11  does not have to be a semiconductor laser diode that emits a blue laser beam but may also be, for example, a semiconductor laser diode that emits a violet laser beam. Furthermore, the first light source unit  11  does not have to include the semiconductor laser diode but may have a configuration including, for example, a light-emitting diode (LED) light source and an optical system. 
     The second light source unit  121  does not have to be a semiconductor laser diode that emits a green laser beam but may also be an LED that emits a green light ray. The second light source unit  122  does not have to be a semiconductor laser diode that emits a red laser beam but may also be an LED that emits a red light ray. 
     Furthermore, the lighting systems  1 ,  1   a ,  1   b ,  1   c ,  1   d ,  1   e , if each include a plurality of second light source units  12 . However, this is only an example and should not be construed as limiting. Rather, the lighting system  1 ,  1   a ,  1   b ,  1   c ,  1   d ,  1   e , if only needs to include at least one second light source unit  12 . 
     If the protective cover  7  has flexibility, the protective cover  7  may be flexible along the entire length thereof but may also be flexible in at least a part of its length. The protective cover  7  may be configured to have flexibility using a bellows structure, for example. Alternatively, the protective cover  7  may also be configured to have flexibility using a woven structure. 
     The adjustment unit  10  only needs to adjust the intensity of seed light P 2  having at least one wavelength among the plurality of seed light rays P 2 . The adjustment unit  10  may be, for example, a liquid crystal filter which is disposed on an optical path of the seed light P 2  between the second light source unit  12  and the light incident portion  21  of the optical fiber  2  and which may adjust the transmittance of the seed light P 2 . 
     Furthermore, the target to irradiate does not have to be a human being H 10  but may also be an animal, an artwork, a plant, a piece of furniture, or a structure, for example. 
     (Aspects) 
     The first to sixth embodiments and their variations described above may be specific implementations of the following aspects of the present disclosure. 
     Alighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a first aspect includes an optical fiber ( 2 ), a first light source unit ( 11 ), a second light source unit ( 12 ), and a lighting unit ( 6 ). The optical fiber ( 2 ) includes a light incident portion ( 21 ), a light emerging portion ( 22 ), and a wavelength-converting portion ( 23 ). The wavelength-converting portion ( 23 ) is provided between the light incident portion ( 21 ) and the light emerging portion ( 22 ). The wavelength-converting portion ( 23 ) contains a wavelength-converting element, which is excited by excitation light (P 1 ) and amplifies a spontaneous emission of light, having a longer wavelength than the excitation light (P 1 ), with an amplified spontaneous emission of light. The first light source unit ( 11 ) makes the excitation light (P 1 ) incident on the light incident portion ( 21 ). The second light source unit ( 12 ) makes seed light (P 2 ) incident on the light incident portion ( 21 ). The seed light (P 2 ) causes the wavelength-converting element excited by the excitation light (P 1 ) and the amplified spontaneous emission of light to produce a stimulated emission of light (P 3 ). The lighting unit ( 6 ) projects, into an external space (S 1 ), light emerging from the light emerging portion ( 22 ) of the optical fiber ( 2 ). 
     The lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the first aspect enables increasing the intensity of light (stimulated emission of light P 3 ) having a different wavelength from the excitation light (P 1 ). Note that the optical fiber ( 2 ) includes a wavelength-converting portion ( 23 ) containing a wavelength-converting element as described above. The wavelength-converting element may be excited by excitation light (P 1 ) to produce a spontaneous emission of light having a longer wavelength than the excitation light (P 1 ) and may also be excited by an amplified spontaneous emission of light. The first light source unit ( 11 ) makes the excitation light (P 1 ) incident on the optical fiber ( 2 ). The second light source unit ( 12 ) makes seed light (P 2 ) incident on the optical fiber ( 2 ). The seed light (P 2 ) causes the wavelength-converting element excited by either the excitation light (P 1 ) or the amplified spontaneous emission of light to produce a stimulated emission of light (P 3 ). 
     In a lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a second aspect, which may be implemented in conjunction with the first aspect, the first light source unit ( 11 ) includes a laser light source. 
     The lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the second aspect enables increasing the intensity of the excitation light (P 1 ). 
     A lighting system ( 1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a third aspect, which may be implemented in conjunction with the first or second aspect, further includes a protective cover ( 7 ). The protective cover ( 7 ) covers the wavelength-converting portion ( 23 ) at least partially. 
     The lighting system ( 1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the third aspect allows the protective cover ( 7 ) to protect the wavelength-converting portion ( 23 ) at least partially. 
     In a lighting system ( 1   b ;  1   c ;  1   d ;  1   e ; f) according to a fourth aspect, which may be implemented in conjunction with the third aspect, a space ( 8 ) is left between the protective cover ( 7 ) and the wavelength-converting portion ( 23 ). 
     The lighting system ( 1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the fourth aspect makes it easier to dissipate the heat generated by the wavelength-converting portion ( 23 ). 
     In a lighting system ( 1   b ;  1   d ;  1   f ) according to a fifth aspect, which may be implemented in conjunction with the third or fourth aspect, a gap ( 9 ) is left between the protective cover ( 7 ) and the first light source unit ( 11 ) and the second light source unit ( 12 ). 
     The lighting system ( 1   b ;  1   d ;  1   f ) according to the fifth aspect makes it easier to dissipate the heat generated by the wavelength-converting portion ( 23 ). 
     In a lighting system ( 1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a sixth aspect, which may be implemented in conjunction with any one of the third to fifth aspects, at least a part of the protective cover ( 7 ) has flexibility. 
     The lighting system ( 1   b ;  1   c ;  1   d ;  1   e ;  1   f ) allows the optical fiber ( 2 ) and the protective cover ( 7 ) to be installed with an increased degree of freedom. 
     In a lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a seventh aspect, which may be implemented in conjunction with any one of the first to sixth aspects, part of the optical fiber ( 2 ) is hidden behind a structure (e.g., a ceiling  101 ) that holds the lighting unit ( 6 ). 
     The lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) may make the optical fiber ( 2 ) invisible from the external space (S 1 ). 
     A lighting system ( 1   e ;  1   f ) according to an eighth aspect, which may be implemented in conjunction with any one of the first to seventh aspects, includes a plurality of the optical fibers ( 2 ). At least two optical fibers ( 2 ), out of the plurality of the optical fibers ( 2 ), are bundled together and held by the lighting unit ( 6 ). 
     The lighting system ( 1   e ;  1   f ) may increase the quantity of the light emerging from the lighting unit ( 6 ) while reducing an increase in the overall size of the lighting unit ( 6 ). 
     A lighting system ( 1   f ) according to a ninth aspect, which may be implemented in conjunction with any one of the first to eighth aspects, further includes an information acquisition unit ( 69 ), a driving unit (first driving unit  66 ), and a control unit ( 68 ). The information acquisition unit ( 69 ) acquires control related information about an irradiation direction of the light (P 4 ) to project from the lighting unit ( 6 ) into the external space (S 1 ). The driving unit (first driving unit  66 ) drives the lighting unit ( 6 ). The control unit ( 68 ) changes, in accordance with the control related information acquired by the information acquisition unit ( 69 ), an irradiation direction of light (P 4 ) emerging from the lighting unit ( 6 ). 
     The lighting unit ( 1   f ) according to the ninth aspect may change the lighting area (A 1 ) by changing the irradiation direction of the light (P 4 ) emerging from the lighting unit ( 6 ). 
     In a lighting system ( 1   f ) according to a tenth aspect, which may be implemented in conjunction with the ninth aspect, the control related information includes location information detected by a sensor (such as an imaging sensor  161 ) about a location of a target to irradiate (e.g., a human being H 10 ) in the external space (S 1 ). 
     The lighting system ( 1   f ) according to the tenth aspect enables changing the irradiation direction of the light (P 4 ) emerging from the lighting unit ( 6 ) in accordance with the location information of the target to irradiate (e.g., a human being H 10 ). 
     In a lighting system ( 1   f ) according to an eleventh aspect, which may be implemented in conjunction with the tenth aspect, the target to irradiate is a human being (H 10 ). The sensor is an imaging sensor ( 161 ) that detects the human being (H 10 ) present in the external space (S 1 ). 
     The lighting system ( 1   f ) according to the eleventh aspect enables changing the irradiation direction of the light (P 4 ) emerging from the lighting unit ( 6 ) according to the location of the human being (H 10 ) present in the external space (S 1 ). 
     In a lighting system ( 1   f ) according to a twelfth aspect, which may be implemented in conjunction with any one of the ninth to eleventh aspects, the control related information includes device location information transmitted from a transmitter device ( 162 ) in the external space (S 1 ) about a location of the transmitter device ( 162 ). The control unit ( 68 ) controls the lighting unit ( 6 ) to change the irradiation direction of the light (P 4 ) in accordance with the device location information. 
     The lighting system ( 1   f ) according to the twelfth aspect enables changing the irradiation direction of the light (P 4 ) emerging from the lighting unit ( 6 ) according to the location of the transmitter device ( 162 ). 
     In a lighting system ( 1   f ) according to a thirteenth aspect, which may be implemented in conjunction with any one of the ninth to twelfth aspects, the control unit ( 68 ) changes the irradiation direction of the light (P 4 ) by having the lighting unit ( 6 ) driven by the driving unit (first driving unit  66 ). 
     The lighting system ( 1   f ) according to the thirteenth aspect enables changing the irradiation direction of the light (P 4 ) by making the control unit ( 68 ) control the driving unit (first driving unit  66 ). 
     In a lighting system ( 1   f ) according to a fourteenth aspect, which may be implemented in conjunction with any one of the ninth to thirteenth aspects, the lighting unit ( 6 ) includes: a lighting unit body ( 61 ) holding the optical fiber ( 2 ); and a lens ( 63 ) arranged in the lighting unit body ( 61 ) to control distribution of the light (P 4 ) emerging from the light emerging portion ( 22 ). The lens ( 63 ) is arranged on the optical axis of the light emerging portion ( 22 ) of the optical fiber ( 2 ) to be out of contact with the light emerging portion ( 22 ) and controls the distribution of the light (P 4 ) emerging from the light emerging portion ( 22 ). The control unit ( 68 ) changes, in accordance with the control related information, a distance between the light emerging portion ( 22 ) and the lens ( 63 ). 
     The lighting system ( 1   f ) according to the fourteenth aspect enables changing the light beam angle of the light (P 4 ) emerging from the lighting unit ( 6 ) to irradiate the external space (S 1 ). 
     In a lighting system ( 1   f ) according to a fifteenth aspect, which may be implemented in conjunction with any one of the ninth to thirteenth aspects, the lighting unit ( 6 ) includes: a lighting unit body ( 61 ) holding the optical fiber ( 2 ); a first lens ( 63 ) arranged in the lighting unit body ( 61 ) to face the light emerging portion ( 22 ); and a second lens ( 64 ) arranged in the lighting unit body ( 61 ) to be located opposite from the light emerging portion ( 22 ) with respect to the first lens ( 63 ). 
     The lighting system ( 10  according to the fifteenth aspect allows the first lens ( 63 ) and the second lens ( 64 ) to respectively perform two different functions, e.g., enables making the first lens ( 63 ) perform a condensing function and the second lens ( 64 ) perform the function of reducing the axial chromatic aberration. 
     In a lighting system ( 1   e ) according to a sixteenth aspect, which may be implemented in conjunction with any one of the first to fifteenth aspects, the lighting unit ( 6 ) further includes: a lighting unit body ( 61 ) holding the optical fiber ( 2 ); and a reflector ( 62 ) arranged in the lighting unit body ( 61 ) to reflect, toward the external space (S 1 ), at least a part of the light (P 4 ) emerging from the light emerging portion ( 22 ) of the optical fiber ( 2 ). 
     The lighting system ( 1   e ) according to the sixteenth aspect enables controlling the distribution of the light using the reflector ( 62 ). 
     In a lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a seventeenth aspect, which may be implemented in conjunction with any one of the first to sixteenth aspects, the wavelength-converting element includes an element selected from the group consisting of Pr, Tb, Ho, Dy, Er, Eu, Nd, and Mn. 
     The lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the seventeenth aspect enables, when the wavelength-converting element includes two or more elements, for example, excitation caused by the amplified spontaneous emission of light from at least one element to produce an amplified spontaneous emission of light from another element at a different wavelength. 
     Alighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to an eighteenth aspect, which may be implemented in conjunction with any one of the first to seventeenth aspects, includes a plurality of the second light source units ( 12 ). The plurality of the second light source units ( 12 ) respectively emit multiple rays of the seed light (P 21 , P 22 ). The multiple rays of the seed light (P 21 , P 22 ) respectively emitted from the plurality of the second light source units ( 12 ) have mutually different wavelengths. 
     The lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the eighteenth aspect allows light (P 4 ), including multiple stimulated emissions of light (P 3 ) corresponding one to one to the multiple rays of the seed light (P 21 , P 22 ), to emerge from the light emerging portion ( 22 ). 
     Alighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to a nineteenth aspect, which may be implemented in conjunction with any one of the first to eighteenth aspects, further includes an adjustment unit ( 10 ) that adjusts intensity of the seed light (P 2 ). 
     The lighting system ( 1 ;  1   a ;  1   b ;  1   c ;  1   d ;  1   e ;  1   f ) according to the nineteenth aspect enables adjusting the chromaticity of the light (P 4 ) emerging from the light emerging portion ( 22 ) of the optical fiber ( 2 ). 
     REFERENCE SIGNS LIST 
     
         
           1 ,  1   a ,  1   b ,  1   c ,  1   d ,  1   e , if Lighting System 
           2  Optical Fiber 
           21  Light Incident Portion 
           22  Light Emerging Portion 
           23  Wavelength-Converting Portion 
           6  Lighting unit 
           61  Lighting unit body 
           62  Reflector 
           63  Lens (First Lens) 
           64  Second Lens 
           66  First Driving Unit (Driving Unit) 
           67  Second Driving Unit 
           68  Control Unit 
           69  Information Acquisition Unit 
           7  Protective Cover 
           8  Space 
           9  Gap 
           10  Adjustment Unit 
           11  First Light Source Unit 
           12  Second Light Source Unit 
           121  Second Light Source Unit 
           122  Second Light Source Unit 
           101  Ceiling (Structure) 
           161  Imaging Sensor 
           162  Transmitter Device 
         H 10  Human Being 
         P 1  Excitation Light 
         P 2  Seed Light 
         P 21  Seed Light Ray 
         P 22  Seed Light Ray 
         P 3  Stimulated Emission of Light 
         P 4  Light 
         S 1  External Space