Abstract:
A scanning endoscope includes: an optical fiber that emits an illuminating light from a distal end; an actuator that causes a distal end of the optical fiber to oscillate; a fixing block that fixes the optical fiber; and a propagation portion that is provided in close contact with an outer circumferential face of a cladding of the optical fiber at a position on the distal end side relative to the fixing block, and on which, among the illuminating light, light that reaches the outer circumferential face of the cladding is incident and is propagated or absorbed inside the propagation portion.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of PCT/JP2015/073867 filed on Aug. 25, 2015 and claims benefit of Japanese Application No. 2014-239158 filed in Japan on Nov. 26, 2014, the entire contents of which are incorporated herein by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a scanning endoscope that detects and images return light of illuminating light irradiating an object while scanning an illumination fiber. 
         [0004]    2. Description of the Related Art 
         [0005]    An electronic endoscope is known that photoelectrically converts an object image by means of an image pickup apparatus having a solid-state image pickup device such as a CCD or a CMOS, and displays an image of the object on a monitor. Further, an optical scanning endoscope apparatus is known as an apparatus that displays an image of an object without using the technology of a solid-state image pickup device. An optical scanning endoscope picks up an image of an observation target region by continuously receiving reflected light while scanning light that is irradiating a minute point on the observation target region. 
         [0006]    In Japanese Patent Application Laid-Open Publication No. 2008-165236, an endoscope and an optical fiber system are described which include a scanning optical fiber having an optical fiber that has a core that transmits an illuminating light and at least one cladding that covers the core and transmits reflected light from an object, and at least one photo sensor that detects reflected light. 
       SUMMARY OF THE INVENTION 
       [0007]    A scanning endoscope according to one aspect of the present invention includes: an optical fiber that propagates an illuminating light radiated from a light source portion and, from a distal end, emits the illuminating light that is propagated; an actuator that causes the distal end of the optical fiber to oscillate in order to scan the illuminating light on an observation target; a fixing portion that fixes the optical fiber to cause the distal end of the optical fiber to be oscillated by the actuator; and a propagation portion that is provided in close contact with an outer circumferential face of a cladding of the optical fiber at a position on a distal end side relative to the fixing portion, and on which, among the illuminating light, light that reaches the outer circumferential face of the cladding is incident and is propagated or absorbed inside the propagation portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a view for describing a scanning endoscope apparatus; 
           [0009]      FIG. 2  is a view for describing the configuration of a distal end portion of an insertion portion and a light scanning unit of the scanning endoscope; 
           [0010]      FIG. 3  is a cross-sectional view along a line indicated by arrows Y 3 -Y 3  in  FIG. 2 ; 
           [0011]      FIG. 4  is a cross-sectional view along a line indicated by arrows Y 4 -Y 4  in  FIG. 3 ; 
           [0012]      FIG. 5  is a view for describing a configuration example in which a hole for a medium is provided which has a tapered face whose inner diameter continuously changes to a smaller diameter in a proximal end direction from a distal end opening side; 
           [0013]      FIG. 6A  is a view for describing a light scanning unit in which an annular member that blocks a distal end opening of a hole for a medium is provided; and 
           [0014]      FIG. 6B  is a view for describing a light scanning unit in which an annular member that blocks a distal end opening of a hole for a medium is provided. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    Hereunder, an embodiment of the present invention is described with reference to the attached drawings. 
         [0016]    Note that the respective drawings used for the following description are drawings that schematically illustrate the present invention, and with respect to the dimensional relation and contraction scale and the like of the respective members, the contraction scale is varied for each component so as to be shown in a size that is recognizable in the drawings. Further, the present invention is not limited only to the quantity of components, the shapes of components, the ratios between the sizes of components, and the relative positional relationship between the respective components illustrated in the drawings. 
         [0017]    As shown in  FIG. 1 , a scanning endoscope apparatus  1  includes a scanning endoscope (hereunder, referred to simply as “endoscope”)  2 , a main body apparatus  3  to which the endoscope  2  is connected, and a monitor  4 . 
         [0018]    The endoscope  2  radiates an illuminating light at a subject while scanning the illuminating light, and obtains return light from the subject. A subject image that is generated by the main body apparatus  3  is displayed on the monitor  4 . 
         [0019]    The endoscope  2  has an elongated insertion portion  11  that is inserted through the inside of a living organism. The insertion portion  11  is configured mainly with a tube body having predetermined flexibility. A distal end portion  12  is provided on the distal end side of the insertion portion  11 . 
         [0020]    A connector and the like which are not shown in the drawing are provided on the proximal end side of the insertion portion  11 . The endoscope  2  is configured to be detachably connectable to the main body apparatus  3  via the connector and the like. 
         [0021]    A distal end illumination lens  13   a  that is an optical member which is included in an illuminating optical system  13 , and a condenser lens  16   a  that is an optical member which is included in a detection optical system  16  are provided at a distal end face  12   a  of the distal end portion  12 . 
         [0022]    Reference character  13   b  denotes a second illumination lens that is one of the optical members constituting the illuminating optical system  13 . The second illumination lens  13   b  is constituted by one or a plurality of optical lenses. The detection optical system  16  has the condenser lens  16   a  and a detection fiber  17 . 
         [0023]    Inside the insertion portion  11  are provided the illuminating optical system  13 , an illumination fiber  14  and an actuator  15  which constitute a light scanning unit  40 , the detection fiber  17 , an endoscope memory  18  and the like. 
         [0024]    Various kinds of information relating to the endoscope  2  are stored in the endoscope memory  18 . When the endoscope  2  is connected to the main body apparatus  3 , the endoscope memory  18  is connected to a controller  23 , described later, via an unshown signal wire. 
         [0025]    A configuration is adopted so that, in the connected state described above, the various kinds of information stored in the endoscope memory  18  are read by the controller  23 . 
         [0026]    The illumination fiber  14  propagates an illuminating light that is emitted from a light source unit  24  serving as a light source portion that is provided in the main body apparatus  3 , and emits the propagated illuminating light from a distal end face. The illuminating light emitted from the distal end face of the fiber passes through the illuminating optical system  13  and travels in the direction of an object that is an observation target. 
         [0027]    The detection fiber  17  is inserted through the insertion portion  11 , along an inner circumference. The detection fiber  17  transmits return light from the observation target which is received by the condenser lens  16   a  to a detection unit  26  that is described later. That is, the condenser lens  16   a  is arranged at a distal end of the detection fiber  17 . 
         [0028]    Note that the detection fiber  17  is a fiber bundle which includes at least two fibers. When the endoscope  2  is connected to the main body apparatus  3 , the detection fiber  17  is connected to a demultiplexer  36  that is described later. 
         [0029]    As shown in  FIG. 2  to  FIG. 4 , a covering  14   c  is peeled off at the distal end side of the illumination fiber  14  to expose a cladding  14   b.  Reference character  14   a  denotes a core. The cladding  14   b  is provided around the core  14   a,  along a central axis of the core  14   a.  As is known, the refractive index of the cladding  14   b  is set so as to be lower than the refractive index of the core  14   a.    
         [0030]    Note that a distal end face of the covering  14   c  is disposed so as to be separated by a predetermined distance from a proximal end side  44   a  of a fixing block  44 . In the following description, the exposed cladding  14   b  including the core  14   a  from which the covering  14   c  of the illumination fiber  14  is peeled off is referred to as “optical fiber  14 F.” 
         [0031]    The optical fiber  14 F is inserted and disposed inside a ferrule  41  as a fiber holding portion, and is held by the ferrule  41 . 
         [0032]    Note that the ferrule  41  is formed of a material such as zirconia or nickel on which hole machining that corresponds to an external diameter (for example, 125 μm) of the illumination fiber  14  can be performed easily and with high accuracy (for example, ±1 μm). 
         [0033]    In the present embodiment, the ferrule  41  is a non-conductive material such as zirconia, and for example is a quadrangular prism. The ferrule  41  has side faces  42   a  and  42   c  that are perpendicular to an X-axis direction, and side faces  42   b  and  42   d  that are perpendicular to a Y-axis direction. 
         [0034]    Note that, a longitudinal axis direction of the insertion portion  11  is defined as a Z-axis direction, and the two directions which are orthogonal to the Z-axis direction and are orthogonal to each other are defined as the X-axis direction and the Y-axis direction. 
         [0035]    A stepped through-hole  41   h  is formed along the central axis in the ferrule  41 . A hole for a fiber  41   h   1  as a first hole, and a hole for a medium  41   h   2  as a second hole are provided in the stepped through-hole  41   h.  The hole for a medium  41   h   2  is located on a distal end side of the ferrule  41 , and has a larger diameter than the first hole. 
         [0036]    The inner diameter of the hole for a fiber  41   h   1  is formed to be slightly larger than the external diameter of the optical fiber  14 F. A predetermined clearance is set between the hole for a fiber  41   h   1  and the optical fiber  14 F. 
         [0037]    After being inserted through the inside of the hole for a fiber  41   h   1  from a proximal end opening  41   m   1  of the stepped through-hole  41   h,  the optical fiber  14 F passes through the hole for a fiber  41   h   1  and the hole for a medium  41   h   2  and is extended by a predetermined distance from a distal end opening  41   m   2  of the through-hole  41   h.    
         [0038]    An inner diameter d of the hole for a medium  41   h   2  is formed to be larger by a predetermined dimension than an external diameter D of the cladding  14   b  constituting the optical fiber  14 F. An adhesive  19  having a low conductivity of a level such that light that leaks from the fiber does not specularly reflect and which can serve as a high refractive index medium having a refractive index that is greater than the refractive index of the cladding  14   b  is filled in a gap between the hole for a medium  41   h   2  and the optical fiber  14 F. 
         [0039]    As a result of the adhesive  19  setting, a distal end side portion of the optical fiber  14 F that is extended from the distal end opening  41   m   2  is fixedly supported in a cantilevered state by the ferrule  41 . 
         [0040]    The adhesive  19  is a propagation member and is a transparent adhesive such as a heat setting adhesive or ultraviolet setting adhesive, and is filled into the gap between the hole for a medium  41   h   2  and the optical fiber  14 F in the state of a liquid having a predetermined viscosity and then sets to function as a propagation portion. The set adhesive  19  closely contacts the outer circumferential face of the optical fiber  14 F and the inner circumferential face of the hole for a medium  41   h   2  and enters a fixed state. Further, the refractive index of the set adhesive  19  is greater than the refractive index of the cladding  14   b.    
         [0041]    The fixing block  44  is a fixing portion at which the proximal end side of the ferrule  41  is fixedly installed. The fixing block  44  is a circular disc shape that has a predetermined thickness. A lead wire insertion hole  44   h   1  and a ferrule mounting hole  44   h   2  are formed in the fixing block  44 . 
         [0042]    A plurality of lead wires  45  are inserted through and disposed in the lead wire insertion hole  44   h   1 . The proximal end portion of the ferrule  41  is fitted into and disposed in the ferrule mounting hole  44   h   2 , and is integrally fixed to the ferrule mounting hole  44   h   2  by, for example, adhesion. 
         [0043]    In this fixed state, a boundary between the hole for a fiber  41   h   1  and the hole for a medium  41   h   2  is configured so as to be positioned further on the distal end side than a proximal end side  44   r  of the fixing block  44 . 
         [0044]    The fixing block  44  to which the ferrule  41  is fixed is integrally fixed by adhesion or the like at a predetermined position on a proximal end side of a frame body  43 . In the integrally fixed state, a central axis of the fixing block  44  and a central axis of the frame body  43  coincide. 
         [0045]    Note that, in the present embodiment, a configuration is adopted so that, by placing the proximal end side of the ferrule  41  and the proximal end side  44   r  of the fixing block  44  in a flush state, the distal end face of the optical fiber  14 F in the cantilevered state is disposed at a predetermined position in the longitudinal direction of the frame body  43 . 
         [0046]    The actuator  15  is, for example, a piezoelectric element. In the present embodiment, the actuator  15  is constituted by four actuators  15   a,    15   b,    15   c  and  15   d . The respective actuators  15   a,    15   b,    15   c  and  15   d  are provided at predetermined positions on the distal end side of the illumination fiber  14 . The respective actuators  15   a,    15   b,    15   c  and  15   d  are provided at positions that are adjacent to the respective side faces  42   a,    42   b,    42   c  and  42   d  of the ferrule  41 , and are respectively point symmetrical at 90°. 
         [0047]    That is, the ferrule  41  is arranged between the actuator  15  and the illumination fiber  14 . 
         [0048]    The actuators  15   a,    15   b,    15   c  and  15   d  have a configuration in which electrodes are provided on two separated surfaces of a piezoelectric element (a piezo element), and expand and contract in response to a drive signal from a driver unit  25  that is described later. 
         [0049]    The respective actuators  15   a,    15   b,    15   c  and  15   d  apply a vibration to the ferrule  41  to cause the distal end of the illumination fiber  14  to oscillate and scan the distal end of the illumination fiber  14  in an elliptic spiral shape. 
         [0050]    The illumination fiber  14 , the ferrule  41  and the actuator  15  constitute the light scanning unit  40  that is a scanning portion. 
         [0051]    Note that, a resonance frequency that causes the illumination fiber  14  to oscillate significantly is determined by the diameter of the illumination fiber  14  and a length of the free end that is a protruding length from the distal end face of the ferrule  41 . 
         [0052]    The respective actuators  15   a,    15   b,    15   c  and  15   d  are not limited to piezoelectric transducers that are each constituted by a piezoelectric element having a pair of electrodes, and may be, for example, coil-type transducers that are electromagnetically driven. 
         [0053]    As a GND electrode for the respective actuators  15   a,    15   b,    15   c  and  15   d,  when the ferrule  41  is a nonconductive material, the surface of the ferrule  41  is subjected to conductive film formation and is used as the GND electrode. In contrast, when a conductive material such as nickel is used for the ferrule  41 , the ferrule  41  itself is used as the GND electrode. 
         [0054]    Further, in the above description the ferrule  41  is described as a quadrangular prism. However, the shape of the ferrule  41  is not limited to a quadrangular prism, and for example the ferrule may be a cylindrical shape or may have a prismatic shape of any kind. 
         [0055]    As shown in  FIG. 1 , a power source  21 , a main body memory  22 , the controller  23 , the light source unit  24 , the driver unit  25 , the detection unit  26  and the like are provided in the main body apparatus  3 . 
         [0056]    The light source unit  24  includes three light sources  31   a ,  31   b  and  31   c , and a multiplexer  32 . 
         [0057]    The driver unit  25  includes a signal generator  33 , digital/analog (hereunder, referred to as “D/A”) converters  34   a  and  34   b,  and an amplifier  35 . 
         [0058]    The detection unit  26  includes the demultiplexer  36 , detectors  37   a,    37   b  and  37   c,  and analog/digital (hereunder, referred to as “A/D”) converters  38   a,    38   b  and  38   c.    
         [0059]    The power source  21  supplies power to the controller  23  in accordance with operation of an unshown power source switch or the like. 
         [0060]    The main body memory  22  stores a control program and the like for performing overall control of the main body apparatus  3 . 
         [0061]    When the supply of power from the power source  21  is started, the controller  23  reads the control program from the main body memory  22  and performs control of the light source unit  24 , the driver unit  25  and the detection unit  27 . 
         [0062]    Based on control of the controller  23 , the light sources  31   a,    31   b  and  31   c  of the light source unit  24  emit light of respectively different wavelength bands, for example, light of the wavelength bands of R (red), G (green) and B (blue) to the multiplexer  32 . The multiplexer  32  multiplexes the lights of the wavelength bands of R, G and B that are emitted from the light sources  31   a,    31   b  and  31   c,  and emits the resultant light towards the illumination fiber  14 . 
         [0063]    The signal generator  33  of the driver unit  25  outputs a drive signal for causing the distal end of the illumination fiber  14  to scan in a desired direction, for example, in an elliptic spiral shape, based on the control of the controller  23 . 
         [0064]    The signal generator  33  outputs a drive signal for driving the distal end of the illumination fiber  14  in a lateral direction (X-axis direction) with respect to the longitudinal axis of the insertion portion  11  to the first D/A converter  34   a,  and outputs a drive signal for driving the distal end of the illumination fiber  14  in a vertical direction (Y-axis direction) with respect to the insertion axis of the insertion portion  11  to the second D/A converter  34   b.    
         [0065]    The D/A converters  34   a  and  34   b  convert the respectively inputted drive signals from digital signals to analog signals, and output the analog signals to the amplifier  35 . The amplifier  35  amplifies the inputted drive signals and outputs the amplified drive signals to the actuator  15 . 
         [0066]    In the present embodiment, the two actuators  15   a  and  15   c  as a first driving portion drive in accordance with a drive signal from the D/A converter  34   a,  and the other two actuators  15   b  and  15   d  as a second driving portion drive in accordance with a drive signal from the D/A converter  34   b  to cause the distal end that is the free end of the illumination fiber  14  to oscillate and scan in an elliptic spiral shape. 
         [0067]    Thus, the light emitted from the light source unit  24  to the illumination fiber  14  is sequentially emitted in an elliptic spiral shape to the subject that is the observation target. 
         [0068]    After the light is emitted to the subject, a return light that is reflected on a surface region of the subject is guided to the demultiplexer  36  of the detection unit  26  by the detection fiber  17 . The demultiplexer  36  is, for example, a dichroic mirror, and demultiplexes the return light in predetermined wavelength bands. 
         [0069]    The demultiplexer  36  demultiplexes the return light that is guided by the detection fiber  17  into return lights of the wavelength bands of R, G and B, and outputs the return lights to the detectors  37   a,    37   b  and  37   c,  respectively. 
         [0070]    The detectors  37   a,    37   b  and  37   c  detect the light intensities of the return lights of the R, G and B wavelength bands, respectively. Signals of the light intensities detected by the detectors  37   a,    37   b  and  37   c  are outputted to the A/D converters  38   a ,  38   b  and  38   c,  respectively. The A/D converters  38   a,    38   b  and  38   c  convert the signals of the light intensities respectively outputted from the detectors  37   a,    37   b  and  37   c  from analog signals to digital signals, and output the digital signals to the controller  23 . 
         [0071]    The controller  23  performs predetermined image processing on the digital signals from the A/D converters  38   a,    38   b  and  38   c  to generate an object image, and displays the object image on the monitor  4 . 
         [0072]    The operation of the light scanning unit  40  provided inside the distal end portion  12  of the insertion portion  11  will now be described. 
         [0073]    By the optical fiber  14 F being inserted and disposed in the hole for a fiber  41   h   1  formed in the ferrule  41 , stress is liable to be applied to the optical fiber  14 F disposed in the vicinity of the proximal end side  44   r  of the fixing block  44 . In a case where stress is applied to the optical fiber  14 F and the optical fiber  14 F is deformed, unnecessary mode light is generated, and the base mode light is propagated through the inside of the core  14   a,  and the unnecessary mode light is propagated through the inside of the cladding  14   b  and travels towards the distal end face of the optical fiber  14 F. 
         [0074]    In the present embodiment, the adhesive  19  that is set and whose refractive index is greater than the refractive index of the cladding  14   b  is provided in a closely contacting state on the outer circumferential face of the optical fiber  14 F that is inserted through the hole for a medium  41   h   2  of the ferrule  41 . 
         [0075]    Accordingly, the unnecessary mode light that is propagated through the inside of the cladding  14   b  enters the adhesive  19  from the interface between the cladding  14   b  and the adhesive  19  and is thus removed from inside the cladding  14   b.  As a result, the base mode light that propagates through inside the core  14   a  can be mainly emitted from the distal end face of the optical fiber  14 F. 
         [0076]    Therefore, in a scanning state in which the optical fiber  14 F that is supported in a cantilevered state is caused to oscillate, illuminating light having a small spot size and a light intensity distribution that is a Gaussian distribution is sequentially emitted in an elliptic spiral shape to the subject that is the observation target from the distal end face of the optical fiber  14 F, and a favorable observed image of the observation target that has a high resolution can be obtained. 
         [0077]    Note that, in the above described embodiment, a configuration is adopted in which the adhesive  19  having a low conductivity of a level such that light that leaks from the fiber does not specularly reflect and which has a refractive index that is greater than the refractive index of the cladding  14   b  is filled in a gap between the hole for a medium  41   h   2  and the optical fiber  14 F. However, the following configurations may also be adopted. 
         [0078]    A filler that absorbs unnecessary mode light is mixed into the adhesive  19 . As a result, unnecessary mode light that entered the adhesive  19  from the cladding  14   b  is absorbed by the filler, and thus the unnecessary mode light propagating through the inside of the adhesive  19  decreases. Note that, instead of mixing filler that absorbs unnecessary mode light into the adhesive  19 , a configuration may be adopted so as to obtain a similar action and effect by blackening the inner face of the hole for a medium  41   h   2  so as to absorb unnecessary mode light. 
         [0079]    Further, as shown in  FIG. 5 , the inner face of a hole for a medium  41   h   3  is configured as a tapered face having an inner diameter that continuously changes to a smaller diameter from the distal end opening  41   m   2  side in a proximal end direction of the central axis. The adhesive  19  is provided by being filled in a gap between the hole for a medium  41   h   3  and the optical fiber  14 F, and the adhesive  19  sets. 
         [0080]    According to this configuration, unnecessary mode light that enters from the interface between the cladding  14   b  and the adhesive  19  is reflected at the inclined interface between the adhesive  19  and the inner face of the hole for a medium  41   h   3 , and the angle of reflection is changed each time as the unnecessary mode light is repeatedly reflected. As a result, re-entry of the unnecessary mode light into the cladding  14   b  can be prevented. 
         [0081]    Further, a configuration may also be adopted so as to absorb unnecessary mode light by mixing the above described filler into the adhesive  19  or blackening the inner face of the hole for a medium  41   h   3 . 
         [0082]    Furthermore, as shown in  FIG. 6A  and  FIG. 6B , an annular member  20  is provided that blocks the distal end opening  41   m   2  of the hole for a medium  41   h   2  or  41   h   3  formed in ferrule  41 , to prevent the leakage of light. The annular member  20  is a light absorbing portion that absorbs unnecessary mode light or is a light reflecting portion that reflects unnecessary mode light, and is integrally bonded and fixed to the adhesive  19 . 
         [0083]    According to this configuration, unnecessary mode light that enters the adhesive  19  and is propagated through the inside of the adhesive  19  can be prevented from being emitted to outside from the distal end face of the adhesive. 
         [0084]    Note that, in  FIG. 6A  and  FIG. 6B , a predetermined gap is provided between the inner circumferential face of the annular member  20  and the outer circumferential face of the optical fiber  14 F to prevent interference with respect to oscillation of the optical fiber  14 F. 
         [0085]    Note that, a configuration may also be adopted in which the adhesive  19  is applied onto the outer circumferential face of the optical fiber  14 F that is extended from the ferrule  41  and set, so that unnecessary mode light that is propagated through inside the cladding  14   b  is caused to enter the adhesive  19  from the interface between the cladding  14   b  and the adhesive  19  and to be removed from the cladding  14   b.    
         [0086]    According to the present invention, a scanning endoscope can be realized that, while removing unnecessary mode light, emits base mode light from a distal end face of an optical fiber for illuminating light that has a configuration that is supported in a cantilevered state by a fiber holding portion, and obtains an observation target image that has a favorable resolution. 
         [0087]    The invention described in the foregoing embodiment is not limited to the embodiment and modifications described above, and various modifications can be implemented within a range that does not depart from the spirit and scope of the present invention in the implementing stage.