Abstract:
Provided is an optical fiber scanner capable of generating an image with excellent image quality, which displaces an emission end of an optical fiber by means of an optical scanning actuator and scans light emitted from the optical fiber, in which the optical fiber 31 includes a photonic crystal fiber at least in a propagation path of the light leading to the optical scanning actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a Continuing Application based on International Application PCT/JP2015/000562 filed on Feb. 6, 2015, the entire disclosure of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to an optical fiber scanner and a scanning endoscope apparatus including the optical fiber scanner. 
       BACKGROUND 
       [0003]    Some scanning endoscope apparatuses are known to scan an inspection site by irradiating illumination light toward the inspection site from an optical fiber extending through inside a scope while displacing, by an optical scanning actuator, the emission end of the optical fiber, and to detect light reflected from the inspection site, to thereby observe the image (see, for example, PTL 1). 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: JP2008-165236A 
       SUMMARY 
       [0005]    The disclosed optical fiber, having an optical scanning actuator to displace an emission end of an optical fiber and scanning light emitted from the optical fiber, 
         [0006]    in which the optical fiber includes a photonic crystal fiber at least in a propagation path of the light leading to the optical scanning actuator. 
         [0007]    The optical fiber may be formed entirely of the photonic crystal fiber. 
         [0008]    The optical fiber may include a single mode fiber fused to an incident end face of the photonic crystal fiber. 
         [0009]    The optical fiber may include a single mode fiber fused to an emission end face of the photonic crystal fiber, and the emission end of the single mode fiber may be displaced by the optical scanning actuator. 
         [0010]    The single mode fiber fused to the emission end face of the photonic crystal fiber may be smaller in outer diameter than the photonic crystal fiber. 
         [0011]    The optical fiber may include a gradient index lens fused to the incident end face of the fiber. 
         [0012]    The gradient index lens and the optical fiber fused with the gradient index lens may be substantially equal to each other in outer diameter. 
         [0013]    Further, the disclosed scanning endoscope apparatus includes: 
         [0014]    a casing having a light source section; and 
         [0015]    the aforementioned optical fiber scanner, 
         [0016]    in which: 
         [0017]    the light source section includes: a plurality of lasers that emit laser lights of different wavelengths; a coupler that multiplexes laser lights from the plurality of lasers; and a fiber that propagates light emitted from the coupler; and 
         [0018]    the optical fiber scanner is installed in a scope detachably connected to the casing such that, when the scope is connected to the casing, the optical fiber has an incident end face optically coupled to an emission end face of the fiber that propagates light emitted from the coupler. 
         [0019]    Further, the disclosed scanning endoscope apparatus includes: 
         [0020]    a casing having a light source section; and 
         [0021]    an optical fiber scanner that includes a single mode fiber fused to the emission end face of the aforementioned photonic crystal fiber, 
         [0022]    in which: 
         [0023]    the light source section includes: a plurality of lasers that emit laser lights of different wavelengths; a coupler that multiplexes laser lights from the plurality of lasers; and a fiber that propagates light emitted from the coupler; and 
         [0024]    the optical fiber scanner is installed in a scope detachably connected to the casing such that the entire single mode fiber including a part where the single mode fiber is fused to an emission end face of the photonic crystal fiber is positioned inside a hard part of the tip part of the scope, the optical scanning actuator displaces an emission end of the single mode fiber, and an incident end face of the optical fiber is optically coupled to the emission end face of the fiber propagating light emitted from the coupler when the scope is connected to the casing. 
         [0025]    Further, the disclosed scanning endoscope apparatus, includes: 
         [0026]    a casing having a light source section; and. 
         [0027]    the aforementioned optical fiber scanner that has the gradient index lens, 
         [0028]    in which: 
         [0029]    the light source section includes: a plurality of lasers that emit laser lights of different wavelengths; a coupler that multiplexes laser lights from the plurality of lasers; a fiber that propagates light emitted from the coupler; and a gradient index lens fused to an emission end face of the fiber; and 
         [0030]    the optical fiber scanner is installed in a scope detachably connected to the casing, and when the scope is connected to the casing, the gradient index lens fused to an incident end face of the optical fiber is optically coupled to the gradient index lens fused to the emission end face of the fiber propagating light emitted from the coupler. 
         [0031]    The gradient index lens of the light source section, the fiber fused with the gradient index lens, the gradient index lens of the fiber scanner, and the optical fiber fused with the gradient index lens may be substantially equal to one another in outer diameter. 
         [0032]    The optical fiber scanner may further include a detection fiber that propagates signal light from an irradiation object irradiated with light from the optical fiber. 
         [0033]    The detection fiber may be formed of a plurality of multimode fibers, 
         [0034]    The light source section may further include a plurality of fibers that each propagate laser lights from the plurality of lasers; and the coupler may multiplex the laser lights from the plurality of fibers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    In the accompanying drawings: 
           [0036]      FIG. 1  is a block diagram illustrating a schematic configuration of a main part of the disclosed scanning endoscope apparatus according to Embodiment 1; 
           [0037]      FIG. 2  is an overview schematically illustrating the scope of  FIG. 1 ; 
           [0038]      FIG. 3  is an enlarged sectional view of the tip part of the scope of  FIG. 2 ; 
           [0039]      FIG. 4  is a sectional view of the photonic crystal fiber; 
           [0040]      FIG. 5  is a view for illustrating the disclosed scanning endoscope apparatus according to Embodiment 2; 
           [0041]      FIG. 6  is a view for illustrating the disclosed scanning endoscope apparatus according to Embodiment 3; 
           [0042]      FIG. 7  is a view for illustrating the disclosed scanning endoscope apparatus according to Embodiment 4; 
           [0043]      FIG. 8  is an external view illustrating configurations of the disclosed optical connector and adapter not joined to each other, according to Embodiment 4; 
           [0044]      FIG. 9  is a sectional view of the optical connector and the adapter of  FIG. 8  not joined to each other; and 
           [0045]      FIG. 10  is a sectional view of the optical connector and the adapter of  FIG. 8  joined to each other. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    When a scanning endoscope, having a single mode fiber as an optical fiber, is applied with a strong bending (curvature radius and bending angle) within a body cavity, for example, the illumination light leaks out from the bent part, causing illumination light loss. As a result, when the optical fiber is formed of a single mode fiber in particular, illumination light with a long wavelength suffers a larger bent loss, causing changes in color balance or reduction in absolute brightness, which could lead to reduced image quality of the observed image. Such phenomena involved in scanning endoscope apparatuses similarly occurs, for example, in projectors which scan light from an optical fiber to project an image. 
         [0047]    It could therefore be helpful to provide an optical fiber scanner and a scanning endoscope apparatus capable of generating an image of excellent image quality. 
         [0048]    Hereinafter, Embodiments of the present disclosure will be illustrated with reference to the accompanying drawings. 
       Embodiment 1 
       [0049]      FIG. 1  is a block diagram illustrating a schematic configuration of a main part of the disclosed scanning endoscope apparatus according to Embodiment 1. The scanning endoscope apparatus  10  of Embodiment 1 includes: a scope (endoscope)  30 ; a control apparatus body (casing)  50 ; and a display  70 . The control apparatus body  50  is configured by including: a controller  51  controlling the entire scanning endoscope apparatus  10 ; a light source section  53 ; and a drive controller  54 . 
         [0050]    The light source section  53  has lasers  55 R,  55 G,  55 B, first fibers  56 R,  56 G,  56 B, a coupler  57 , and a second fiber  58 . The lasers  55 R,  55 G,  55 B are controlled by the controller  51  so that the lasers  55 R,  55 G,  55 B each emit red laser light, green laser light, and blue laser light, respectively. A diode pumped solid state (DPSS) laser and a laser diode, for example, may be available as the lasers  55 R,  55 G,  55 B. Here, each light has a wavelength of, for example, 440 nm to 460 nm for blue light, 515 nm to 532 nm for green light, and 635 nm to 638 nm for red light. Laser lights emitted from the lasers  55 R,  55 G,  55 B are incident on the coupler  57  via the corresponding one of the first fibers  56 R,  56 G,  56 B, and then caused to incident on an illumination optical fiber  31  via the second fiber  58 . 
         [0051]    The first fibers  56 R,  56 G,  56 B are each formed of, for example, a single mode fiber, and the second fiber  58  is formed of, for example, a wide band single mode fiber. Here, the wide band single mode fiber has a core diameter of, for example, 3.5 μm and NA of 0.12. The coupler  57  is configured by including, for example, a dichroic prism. Here, an optical connector  120   a  may be joined to the emission end of the second fiber  58 . The optical connector  120   a  is detachably connected to an adapter  110  fixed to the control apparatus body  50 . Without being limited to the above configuration, the light source section  53  may use other plurality of light sources. Further, the light source section  53  may be accommodated in a separate casing different from the control apparatus body  50 , the casing being connected via a signal line to the control apparatus body  50 . 
         [0052]    The scope  30  is detachably connected to the control apparatus body  50 . When the light source section  53  is stored in a different casing from the control apparatus body  50 , the illumination optical fiber  31  is detachably connected to the casing having the light source section  53 . The illumination optical fiber  31  extends up to the tip part of the scope  30 . An optical connector  120   b,  for example, may be joined to the incident end of the illumination optical fiber  31 . The optical connector  120   b  is detachably connected to the adapter  110 , and optically coupled to the optical connector  120   a  of the light source section  53  via the adapter  110 . With this configuration, illumination light from the light source section  53  is caused to incident on the illumination optical fiber  31 . 
         [0053]    The emission end of the illumination optical fiber  31  is oscillatably supported by an optical scanning actuator  40  to be described later. Illumination light incident on the illumination optical fiber  31  is guided up to the tip part of the scope  30  and irradiated toward an object (irradiation object)  100 . During the irradiation, the drive controller  54  supplies a predetermined drive signal to the optical scanning actuator  40 , to thereby vibratorily drive the emission end of the illumination optical fiber  31 . As a result, the object  100  is two-dimensionally scanned with illumination light emitted from the illumination optical fiber  31 . Further, signal light such as reflected light, scattered light, fluorescence obtained from the object  100  irradiated with illumination light are incident on the tip end face of a detection fiber bundle  33  formed of a multimode fiber extending through inside the scope  30 , and guided therethrough to the control apparatus body  50 . An optical connector  34  may be joined to the emission end of the detection fiber bundle  33 . 
         [0054]    The control apparatus body  50  further includes a spectrometer  60 , photodetectors (PDs)  61 R,  61 G,  61 B, analog-digital converters (ADCs)  62 R,  62 G,  62 B, and an image processor  63 . The detection fiber bundle  33  is detachably joined to the spectrometer  60  via the optical connector  34 , and guides signal light from the object  100  to the spectrometer  60 . The spectrometer  60  splits signal light guided through the detection fiber bundle  33 , into each color of R, G, B, and causes each color of light to incident into the corresponding one of the photodetectors  61 R,  61 G,  61 B. The photodetectors  61 R,  61 G,  61 B each receive incident signal light and convert the signal light thus received into an electric signal corresponding to the color of the illumination light. The ADCs  62 R,  62 G,  62 B each convert analog electric signals output from the corresponding one of the photodetectors  61 R,  61 G,  61 B, into digital signals, and output the digital signals to the image processor  63 . 
         [0055]    The controller  51  calculates information on the scanning position on the scanning locus of laser illumination light, based on information such as the amplitude and phase of the drive signal supplied from the drive controller  54  to the optical scanning actuator  40 , and supplies the information thus calculated to the image processor  63 . The image processor  63  sequentially stores pixel data (pixel values) of the object  100  based on digital signals output from the ADCs  62 R,  62 G,  62 B and the scanning position information from the controller  51 , performs necessary processing such as interpolation processing thereon after the scan or during the scan to generate an image of the object  100 , and displays the image on the display  70 . 
         [0056]      FIG. 2  is an overview schematically illustrating the scope  30 . The scope  30  includes an operation portion  35  and an insertion portion  36 . The illumination optical fiber  31  and the detection fiber bundle  33  are installed as being extended from the operation portion  35  up to the tip part  36   a  (indicated by the broken line of  FIG. 2 ) of the insertion portion  36 , and detachably connected respectively to the control apparatus body  50 . Further, the scope  30  includes a wiring cable  38  connected to the optical scanning actuator  40  and extending from the insertion portion  36  through the operation portion  35 . The wiring cable  38  is detachably connected to the drive controller  54  via a connection connector  39 , as illustrated in  FIG. 1 . Here, the insertion portion  36  is configured as a flexible part  36   b  that is capable of bending, except for the tip part  36   a  configured as a hard part that do not bend. 
         [0057]      FIG. 3  is art enlarged sectional view of the tip part  36   a  of the scope  30  of  FIG. 2 . The optical scanning actuator  40  and an illumination optical system  45  are installed in the tip part  36   a.    FIG. 3  illustrates a case where the illumination optical system  45  is formed of two projection lenses  45   a,    45   b.  The optical scanning actuator  40  includes a ferrule  41  that supports an emission end  31   a  of the illumination optical fiber  31  passing therethrough. The illumination optical fiber  31  is fixedly adhered to the ferrule  41 . The ferrule  41  is joined to a support  42  at an end opposite to the emission end face  31   b  of the illumination optical fiber  31  so as to be oscillatably cantilevered by the support  42 . The illumination optical fiber  31  extends as penetrating through the support  42 . 
         [0058]    The ferrule  41  is formed of metal such as nickel. The ferrule  41  may be formed in an arbitrary outer shape, such as a rectangular column shape or a cylinder shape. The ferrule  41  has piezoelectric elements  43   x  and  43   y  mounted thereon, the piezoelectric elements  43   x  and  43   y  opposing to each other in the x-direction and in the y-direction, respectively, the x-direction and the y-direction being mutually orthogonal to each other in a plane perpendicular to the z-direction parallel to the optical axis direction of the illumination optical fiber  31 .  FIG. 3  shows only one piezoelectric element  43   x.  The piezoelectric elements  43   x  and  43   y  are each in a rectangular shape elongated in the z-direction. The piezoelectric elements  43   x  and  43   y  each have electrodes formed on both faces in the thickness direction, and are configured to extend and contract in the z-direction when applied with a voltage in the thickness direction via the opposing electrodes. 
         [0059]    The piezoelectric elements  43   x  and  43   y  are each adhered to the ferrule  41  via one electrode surface while having the other electrode surface connected to the corresponding wiring cable  38 . Similarly, the ferrule  41  serving as a common electrode of the piezoelectric elements  43   x  and  43   y  is connected to the corresponding wiring cable  38 . The two opposing piezoelectric elements  43   x  in the x-direction are applied with an alternating voltage of the same phase from the drive controller  54  of  FIG. 1  via the corresponding wiring cable  38 . Similarly, the two opposing piezoelectric elements  43   y  in the y-direction are applied with an alternating voltage of the same phase from the drive controller  54  via the corresponding wiring cable  38 . 
         [0060]    In this manner, one of the two piezoelectric elements  43   x  extends while the other contracts, to generate bending vibration in the x-direction in the ferrule  41 . Similarly, one of the two piezoelectric elements  43   y  extends while the other contracts, to generate bending vibration in the y-direction in the ferrule  41 . As a result, the x-direction vibration and the y-direction vibration of the ferrule  41  are combined, so that the ferrule  41  is deflected integrally with the emission end  31   a  of the illumination optical fiber  31 . Accordingly, when illumination light is caused to incident on the illumination optical fiber  31 , the observation object can be two-dimensionally scanned with the illumination light emitted from the emission end face  31   b.    
         [0061]    The detection fiber bundle  33  passes through the outer periphery of the insertion portion  36  to extend up to the tip of the tip part  36   a.  A detection lens, though not illustrated, may be disposed at the tip part  33   a  of each fiber of the detection fiber bundle  33 . 
         [0062]    The projection lenses  45   a,    45   b  are disposed in the extreme tip of the tip part  36   a.  The projection lenses  45   a,    45   b  are configured to converge, onto a predetermined focal position, laser light emitted from the emission end face  31   b  of the illumination optical fiber  31 . When the detection lens is disposed at the tip part  33   a  of the detection fiber bundle  33 , the detection lens is arranged so as to take in, as signal light, light resulting from laser light irradiated onto the object  100  and reflected, scattered, and refracted by the object  100  (light that has been interacted with the object  100 ) or fluorescence, so as to have the light converged and coupled to the detection fiber bundle  33 . The illumination optical system  45  may be formed of one lens or three or more lenses, without being limited to the two projection lenses  45   a,    45   b.    
         [0063]    In the aforementioned configuration, the illumination optical fiber  31  and the optical scanning actuator  40  installed in the scope  30  form an optical fiber scanner. In Embodiment 1, the illumination optical fiber  31  is formed, in its entirety, of a photonic crystal fiber  310 . The photonic crystal fiber  310  is configured by having voids  310   b  regularly formed around a core  310   a  through which laser light propagates, as illustrated in section of  FIG. 4 . The photonic crystal fiber  310  operates in single mode in a wavelength band used, and has a feature in that it can undergo strong bending without suffering hardly any bending loss. 
         [0064]    According to the scanning endoscope apparatus  10  of Embodiment 1, the illumination optical fiber  31  installed in the scope  30  is formed of the photonic crystal fiber  310 , which means that the insertion portion  36  of the scope  30  suffers hardly any loss of illumination light even when inserted, for example, into a body cavity and applied with a strong bending (of, for example, a curvature radius of 10 mm or less and the bending angle of 110° or larger) within the body cavity, without causing any change in color balance or reduction in absolute brightness of the illumination light, to thereby generate an image of excellent image quality. Here, in the photonic crystal fiber  310 , the voids  310   b  may preferably be sealed at the emission end face in order to prevent intrusion of dust, moisture, and the like, into the voids  310   b.  In this manner, the illumination light spatially output from the core  310   a  can be prevented from suffering chronological change in beam diameter, with the result that the beam spot diameter of illumination light on the object  100 , which otherwise affects resolution, can be prevented from being changed. 
       Embodiment 2 
       [0065]      FIG. 5  is a view for illustrating the disclosed scanning endoscope apparatus according to Embodiment 2. The scanning endoscope apparatus  11  of Embodiment 2 is similar to the scanning endoscope apparatus  10  of Embodiment 1 except in that the illumination optical fiber  31  forming the optical fiber scanner is formed of the photonic crystal fiber  310  and a single mode fiber  311  fused to the emission end face thereof. The entire single mode fiber  311 , including a part fused with the photonic crystal fiber  310 , is positioned inside the tip part  36   a  formed of a hard part of the scope  30 , and the emission end  311   a  of the single mode fiber  311  is displaced by the optical scanning actuator  40 . The rest of the configuration is similar to that of Embodiment 1, and thus the description thereof is omitted. 
         [0066]    According to the scanning endoscope apparatus  11  of Embodiment 2, the single mode fiber  311  is fused to the emission end face of the photonic crystal fiber  310 , to thereby seal the voids  310   b  at the emission end face of the photonic crystal fiber  310 . When directly sealing the voids  310   b  at the emission end face of the photonic crystal fiber  310 , the beam diameter of light spatially output therefrom may vary depending on the sealing state (such as sealing rate and sealing length), making it difficult to control quality. The disclosed scanning endoscope apparatus  11  is capable of stabilizing the beam diameter spatially output from the emission end face  311   b  of the single mode fiber  311 , and thus can stably generate an image with excellent image quality. Further, the photonic crystal fiber  310  and the single mode fiber  311  are fused to each other at a position within the tip part  36   a  formed of a hart part of the scope  30 , which allows for stably maintaining the fused state without being affected by the bending of the insertion portion  36 . In Embodiment 2, the single mode fiber  311  may preferably be smaller in outer diameter. For example, when the photonic crystal fiber  310  has an outer diameter of  125  inn, the single mode fiber  311  with an outer diameter of, for example, 80 μm may be used, which is smaller than 125 μm. This configuration reduces the mass of the single mode fiber  311 , allowing the optical scanning actuator  40  to more largely vibrate the single mode fiber  311 , to thereby optically scan the object  100  across a wider range. 
       Embodiment 3 
       [0067]      FIG. 6  is a view for illustrating the disclosed scanning endoscope apparatus of Embodiment 3. The scanning endoscope apparatus  12  of Embodiment 3 is different from the scanning endoscope apparatus  11  of Embodiment 2, in that the illumination optical fiber  31  forming an optical fiber scanner further includes a single mode fiber  312  fused to the incident end face of the photonic crystal fiber  310 . The single mode fiber  312  is disposed at a position between the light source section  53  and the operation portion  35  so that the photonic crystal fiber  310  is disposed in the flexible part  36   b  of the scope  30 . The single mode fiber  312 , with an optical connector  120   b  joined at the incident end thereof, is detachably joined to an optical connector  120   a  of the light source section  53  via the adapter  110 . The rest of the configuration is similar to that of Embodiment 2, and thus the description thereof is omitted. 
         [0068]    According to the scanning endoscope apparatus  12  of Embodiment 3, the single mode fiber  312  is fused to the incident end face of the photonic crystal fiber  310 , to thereby seal the voids  310   b  at the incident end face of the photonic crystal fiber  310 . Therefore, the beam diameter spatially output from the illumination optical fiber  31  can be stabilized, which allows for generating an image with excellent image quality. In Embodiment 3, the single mode fiber  312  and the second fiber  58  of the light source section  53  may desirably be configured as the same single mode fiber. 
       Embodiment 4 
       [0069]      FIG. 7  is a view for illustrating the disclosed scanning endoscope apparatus according to Embodiment 4. The scanning endoscope apparatus  13  of Embodiment 4 includes, in the scanning endoscope apparatus  12  of Embodiment 3, a gradient index lens (GRIN lens)  59  fused to the emission end face of the second fiber  58  of the light source section  53  and a GRIN lens  32  fused to the incident end face of the single mode fiber  312  of the optical fiber scanner. 
         [0070]      FIGS. 8, 9, and 10  illustrate configurations of the optical connector  120   a,  the adapter  110 , and the optical connector  120   b  each detachably joining the second fiber  58  of the light source section  53  to the single mode fiber  312  of the optical fiber scanner.  FIGS. 8 and 9  each are an external view and a sectional view, respectively, illustrating the optical connectors  120   a  and  110   b  not joined to each other, and  FIG. 10  is a sectional view illustrating the optical connectors  120   a  and  110   b  joined to each other. 
         [0071]    The adapter  110  is fixed to the casing of the control apparatus body  50  or of the light source section  53 , so as to detachably join the optical connector  120   a  joined to the second fiber  58  with the optical connector  120   b  joined to the single mode fiber  312  of the optical fiber scanner, between the casing inside and the casing outside. The adapter  110  includes an adapter housing  111  and a split sleeve  112 . The adapter housing  111  includes an outer cylinder  113   a  having an opening on the casing inside, and an outer cylinder  113   b  having an opening on the casing outside. The outer cylinders  113   a,    113   b  have, on the inside thereof, an inner cylinder  114  having a cavity between the optical connector  120   a  side and the optical connector  120   b  side. A cylindrical split sleeve  112  is disposed inside the cavity of the inner cylinder  114 . The inner cylinder  114  has an inner periphery protruding inward at both ends so as to prevent the split sleeve  112  from being detached. The outer cylinders  113   a,    113   b  have outer screws  115   a,    115   b  formed on the outer circumferential end sides. Groove-shaped key receivers  116   a,    116   b  are formed in part of the inner peripheries of the outer cylinders  113   a,    113   b.  As described above, two connector connection parts opposing to each other are formed on the casing inside and the casing outside of the adapter housing  111 , each having a shape capable of connecting the optical connector  120   a  and the optical connector  120   b  to each other. 
         [0072]    The split sleeve  112  is a hollow tubular member having a slit extending in the longitudinal direction (direction along the center axis when disposed inside the inner cylinder  114 ), and formed of hard ceramics such as zirconium. A dustproof ring  117  (shielding member) is arranged between the inner cylinder  114  and the split sleeve  112  on the optical connector  120   a  side of the casing inside and along the outer circumference of the split sleeve  112 . The dustproof ring  117 , which is made of, for example, a high-elastic rubber, serves to shield the casing inside and the inner cylinder  114  inside the adapter housing  111 . The dustproof ring  117  is designed to be light-shielded by the adapter housing  111  and casings so as not to receive external ultraviolet light. This configuration prevents degradation of the dustproof ring  117 . 
         [0073]    The adapter  110  has a PD built-in spacer  118  including a photodetector (PD), within the split sleeve  112  and at an intermediate between the optical connector  120   a  side and the optical connector  120   b  side. Signals from the photodetector (PD) can be monitored from outside of the adapter  110 . 
         [0074]    The optical connector  120   a  is configured by including a connector housing  121   a,  and a ferrule  123   a  incorporating the tip part of the second fiber  58 . Hereinafter, the tip direction of the second fiber  58  of the optical connector  120   a  is referred to as forward, and the direction opposite thereto is referred to as backward. 
         [0075]    The connector housing  121   a  has a tip portion formed as a cylinder  124   a  having a cylindrical wall, which is shaped to fit into a gap between the inner cylinder  114  and the outer cylinder  113   a  of the adapter  110 . A key  125   a  is protrudingly formed on the outer periphery of the cylinder  124   a.  The key  125   a  is fit into the key receiver  116   a  of the adapter  110  when coupling the adapter  110  to the optical connector  120   a,  so as to perform accurate positioning of the adapter  110  and the optical connector  120   a  in the rotation direction. 
         [0076]    A coupling nut  126   a  is formed on the outer periphery of the connector housing  121   a,  as being rotatable and movable in the fiber optical axis direction within a specific range. The coupling nut  126   a  has an inner screw formed on the inner surface, which is configured to mesh with an outer screw  115   a  of the outer cylinder  113   a  of the adapter housing  111 . 
         [0077]    The ferrule  123   a  is in a cylindrical column shape with a chamfered tip, and has, along the center axis thereof, the emission end of the second fiber  58  inserted therethrough. The GRIN lens  59  is fused to the emission end face of the second fiber  58 . The cylindrical column part of the ferrule  123   a  protrudes forward from the center of the cylinder  124   a  of the connector housing  121   a  and supported via the periphery by the connector housing  121   a  at the back of the cylinder  124   a.  A flange is formed on the backward of the ferrule  123   a,  allowing the ferrule  123   a  to slide against the inner periphery of the adapter housing  111  in the optical axis direction of the second fiber  58  within the adapter housing  111 , while being biased forward by a spring  127   a  disposed inside the adapter housing  111 . 
         [0078]    The optical connector  120   b  is similarly configured as the optical connector  120   a,  and thus the same components are denoted by the same reference numerals with the suffix b, to omit the description thereof. The optical connector  120   a  basically remains in the connected state for a lengthy period, while the optical connector  120   b  is detached and attached more frequently than is the optical connector  120   a.    
         [0079]    When connecting the optical connectors  120   a,    120   b  to the adapter  110 , the tip part of the adapter  110  and the tip parts of the optical connectors  120   a,    120   b  are first aligned such that the both axes coincide with each other, and positioned in the rotation direction such that the keys  125   a,    125   b  of the optical connectors  120   a,    120   b  are fit into the key receivers  116   a,    116   b  of the adapter  110 . Then, the ferrules  123   a,    123   b  are fit into the split sleeve  112 , and the cylinders  124   a,    124   b  of the optical connectors  120   a,    120   b  are fit in between the outer cylinders  113   a,    113   b  and both ends of the inner cylinder  114  of the adapter  110 . 
         [0080]    Next, the coupling nuts  126   a,    126   b  are moved to the adapter  110  side and rotated. As a result, the outer screw  115   a  of the adapter housing  111  and the inner screw of the coupling nut  126   a  mesh with each other, so as to advance the coupling nuts  126   a,    126   b  toward the adapter  110  side. Along therewith, the ferrule  123   a  further slides forward within the split sleeve  112 . 
         [0081]    When the tip ends of the ferrules  123   a,    123   b  abut to the PD spacer  118 , the ferrules  123   a,    123   b  and the PD built-in spacer  118  are pressed against each other by means of the springs  127   a,    127   b  in the optical connectors  120   a,    120   b  with a spring force equal to or smaller than a certain level not to damage the tip ends of the ferrules  123   a,    123   b.  The rotations of the coupling nuts  126   a,    126   b  are regulated by steps  128   a,    128   b  formed on the outer peripheries of the connector housings  121   a,    121   b,  so as not to generate any excessive pressing force on the ferrules  123   a,    123   b  against the PD spacer  118 . 
         [0082]    According to the scanning endoscope apparatus  13  of Embodiment 4, when the optical connectors  120   a  and  120   b  are connected to the adapter  110 , the ferrule  123   a  and the ferrule  123   b  are fixed within the split sleeve  112  across the PD built-in spacer  118  interposed therebetween, as illustrated in  FIG. 10 . In this manner, the GRIN lens  59  fused to the emission end face of the second fiber  58  and the GRIN lens  32  fused to the incident end face of the single mode fiber  312  of the optical fiber scanner coaxially face each other via a gap therebetween. Accordingly, the second fiber  58  and the single mode fiber  312  can be joined to each other with high connection efficiency, to thereby obtain the same effect as that of Embodiment 3. 
         [0083]    Further, in Embodiment 4, the second fiber  58  and the single mode fiber  312  are not brought into physical contact with each other, which can reduce the risk of breaking the fiber tip when connecting the optical connectors  120   a,    120   b.  Accordingly, the optical connectors  120   a,    120   b  may repeatedly be connected while maintaining high connection efficiency, without the need for any special operation (such as end face cleaning) for maintaining connection efficiency. Further, when part of light emitted from the second fiber  58  fails to incident on the core of the single mode fiber  312 , the part of light is incident on the photodetector of the PD built-in spacer  118 . Therefore, the output of the photodetector can be monitored to monitor the connection efficiency between the optical connectors  120   a,    120   b.    
         [0084]    In Embodiment 4, the GRIN lens  59  of the light source section  53 , the second fiber  58  fused with the GRIN lens  59 , the GRIN lens  32  of the optical fiber scanner, and the single mode fiber  312  fused with the GRIN lens  32  may desirably be equal to one another in outer diameter. This configuration allows the second fiber  58  and the GRIN lens  59  to be accurately mounted to the ferrule  123   a  of the optical connector  120   a,  and the single mode fiber  312  and the GRIN lens  32  to be accurately mounted to the ferrule  123   b  of the optical connector  120   b,  which facilitates optical adjustment of the ferrules  123   a,    123   b,  to thereby readily obtain high connection efficiency. 
         [0085]    The present disclosure is not limited to Embodiments above, and may be subjected to a number of modifications and alterations. For example, in Embodiments 1 to 3, the optical connectors  120   a,    120   b  may be configured similarly to the optical connectors  120   a,    120   b  of  FIGS. 8, 10 , and the adapter  110  may be configured without the PD built-in spacer  118  of  FIGS. 9 and 10 . In this case, when the tip end of the ferrule  123   a  of the optical connector  120   a  and the tip end of the ferrule  123   b  of the optical connector  120   b  abut to each other inside the adapter  110 , the emission end face of the second fiber  58  and the incident end face of the illumination optical fiber  31  are pressed against each other with a spring force equal to or smaller than a certain level not to cause any damage thereto, by means of the springs  127   a,    127   b  in the optical connectors  120   a.    
         [0086]    The illumination optical fiber  31  of the optical fiber scanner may have the incident end face thereof directly fused to the emission end face of the second fiber  58  of the light source section  53 . In this case, as in Embodiment 3, when the illumination optical fiber  31  fused to the second fiber  58  is formed of the single mode fiber  312 , the single mode fiber  312  and the second fiber  58  may desirably be formed of the same single mode fiber. With this configuration, high connection efficiency can be obtained. Further, in Embodiment 1, the single mode fiber  312  may be fused to the incident end of the photonic crystal fiber  310  as in Embodiment 3, so as to be joined to the light source section  53  via the single mode fiber  312 . Further, in Embodiment 1, the emission end face of the second fiber  58  and the incident end face of the photonic crystal fiber  310  may each be fused with a GRIN lens, and joined to each other as in Embodiment 4. 
         [0087]    The optical scanning actuator  40  may employ, without being limited to the piezoelectric system, other publicly known drive method such as electromagnetic systems using coils and permanent magnets. Further, the detection fiber is not limited to a multimode fiber or bundle. In Embodiments above, the first fibers  56 R,  56 G,  56 B may be omitted, and the light source section  53  may be configured to spatially multiplex, by the coupler  57 , lasers spatially output from the lasers  55 R,  55 G,  55 B and have the resulting laser incident on the second fiber  58 . Further, the present disclosure is applicable to a scanning microscope or a scanning projector apparatus, without being limited to the scanning endoscope apparatus. 
       REFERENCE SIGNS LIST 
       [0088]      10 ,  11 ,  12 ,  13  scanning endoscope apparatus 
         [0089]      30  scope (endoscope) 
         [0090]      31  illumination optical fiber 
         [0091]      32  gradient index lens (GRIN lens) 
         [0092]      33  detection fiber bundle 
         [0093]      36   a  tip part (hard part) 
         [0094]      40  optical scanning actuator 
         [0095]      50  control apparatus body (casing) 
         [0096]      53  light source section 
         [0097]      55 R,  55 G,  55 B laser 
         [0098]      56 R,  56 G,  56 B first fiber 
         [0099]      57  coupler 
         [0100]      58  second fiber 
         [0101]      59  gradient index lens (GRIN lens) 
         [0102]      110  adapter 
         [0103]      120   a,    120   b  optical connector 
         [0104]      310  photonic crystal fiber 
         [0105]      311 ,  312  single mode fiber