Abstract:
A unit includes: a module configured to convert an electric signal into an optical signal and transmit the optical signal, or receive an optical signal and convert the received optical signal into an electric signal; and a connector connected to the module and configured to hold an end portion of an optical fiber transmitting the optical signal. The connector includes a ferrule configured to hold the optical fiber, and a flange portion provided at one end of the ferrule. The module includes an element configured to convert the electric signal into an optical signal or the optical signal into an electric signal, and a metal case configured to store the element. A connector side screw portion is provided on the ferrule, and a module side screw portion screwed with the connector side screw portion is provided in a sleeve of the metal case into which the ferrule is inserted.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT international application Ser. No. PCT/JP2015/062564 filed on Apr. 24, 2015 which designates the United States, incorporated herein by reference, and which claims the benefit of priority from Japanese Patent Applications No. 2014-191851, filed on Sep. 19, 2014, incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to an optical transmitter unit, a method of connecting an optical transmitter module and a transmitter side optical connector, and an endoscope system. 
         [0003]    In the related art, an endoscope system is used in the medical field when an organ of a subject such as a patient is observed. The endoscope system includes, for example, an endoscope and a processing device. The endoscope includes an insertion portion formed in a flexible elongated shape, a distal end of which is provided with an imaging sensor. The insertion portion is inserted into a body cavity of the subject. The processing device is coupled to the insertion portion via a cable and a connector to perform an image process on an in-vivo image captured by the imaging sensor. The processing device causes a display device to display the in-vivo image. 
         [0004]    In recent years, an imaging sensor with a large number of pixels which enables a clearer image observation has been developed, and the use of the imaging sensor with a large number of pixels for the endoscope has been considered. In addition, the insertion portion is required to be reduced in diameter in consideration of easiness of introduction into the subject. Furthermore, in order to transmit a large volume of signals between the imaging sensor and the processing device at high speed while realizing the reduction in the diameter of the insertion portion, an optical transmission system that transmits a signal using laser light is employed in the endoscope system. 
         [0005]    In the optical transmission system with the use of the laser light or the like, it is important to perform the transmission without reducing the light quantity of an optical signal emitted from a light emitting element such as a laser diode. As an example of such a technique, an optical connector and an aligning method have been disclosed in which a plurality of fitting portions and cutouts having different lengths in an axial direction are provided on an outer peripheral surface of a base fixed to a ferrule, the ferrule is rotated at an interval (90 degrees) of the provided fitting portions to adjust eccentricity (aligning), and fixation and coupling are performed (for example, refer to JP H11-38276 A). 
         [0006]    There is a need for an object thereof is to provide an optical transmitter unit, a method of connecting an optical transmitter module and a transmitter side optical connector, and an endoscope system which reduce a light loss in optical transmission. 
       SUMMARY 
       [0007]    A unit according to one aspect of the present disclosure includes: a module configured to convert an electric signal into an optical signal and transmit the optical signal, or receive an optical signal and convert the received optical signal into an electric signal; and a connector connected to the module and configured to hold an end portion of an optical fiber transmitting the optical signal, wherein the connector includes a ferrule configured to hold the optical fiber, and a flange portion provided at one end of the ferrule, the module includes an element configured to convert the electric signal into an optical signal or the optical signal into an electric signal, and a metal case configured to store the element, a connector side screw portion is provided on the ferrule, and a module side screw portion configured to be screwed with the connector side screw portion is provided in a sleeve of the metal case into which the ferrule is inserted, and the module side screw portion is elastically deformed or moved by pressing force of a fixing member when the connector and the module are pressed and fixed by the fixing member. 
         [0008]    The above and other objects, features, advantages and technical and industrial significance of this disclosure will be better understood by reading the following detailed description of presently preferred embodiments of the disclosure, when considered in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic view illustrating an overview configuration of an endoscope system according to a first embodiment of the present disclosure; 
           [0010]      FIG. 2  is a view separately illustrating an optical transmitter module and a transmitter side optical connector that constitute an optical transmitter unit used in the endoscope system illustrated in  FIG. 1 ; 
           [0011]      FIG. 3  is a side view of the optical transmitter unit illustrated in  FIG. 2 ; 
           [0012]      FIG. 4  is a flowchart explaining a method of connecting the optical transmitter module and the transmitter side optical connector; 
           [0013]      FIG. 5A  and  FIG. 5B  are diagrams explaining an adjustment of eccentricity between the optical transmitter module and the transmitter side optical connector; 
           [0014]      FIG. 6A  is a view explaining the method of connecting the optical transmitter module and the transmitter side optical connector; 
           [0015]      FIG. 6B  is a view explaining the method of connecting the optical transmitter module and the transmitter side optical connector; 
           [0016]      FIG. 7  is a view explaining a method of connecting an optical transmitter module and a transmitter side optical connector according to a first modification of the first embodiment of the present disclosure; 
           [0017]      FIG. 8  is a view explaining a method of connecting an optical transmitter module and a transmitter side optical connector in an optical transmitter unit according to a second modification of the first embodiment of the present disclosure; 
           [0018]      FIG. 9  is a side view of an optical transmitter unit according to a third modification of the first embodiment of the present disclosure; 
           [0019]      FIG. 10  is a view separately illustrating an optical transmitter module and a transmitter side optical connector in an optical transmitter unit according to a second embodiment of the present disclosure; 
           [0020]      FIG. 11  is a view explaining a method of connecting an optical transmitter module and a transmitter side optical connector in an optical transmitter unit according to a first modification of the second embodiment of the present disclosure; 
           [0021]      FIG. 12  is a schematic view illustrating an overview configuration of an optical transmission unit according to a third embodiment of the present disclosure; 
           [0022]      FIG. 13A  to  FIG. 13C  are views explaining a groove provided on a flange portion of a transmitter side optical connector according to the third embodiment of the present disclosure; and 
           [0023]      FIG. 14  A to  FIG. 14C  are views explaining a groove provided on a flange portion of a transmitter side optical connector according to a modification of the third embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    In the following description, as an embodiment for practicing the present disclosure (hereinafter referred to as the “embodiment”), an endoscope system will be described. The present disclosure is not limited by the embodiments. In the drawings, identical elements are provided with the same reference signs. 
       First Embodiment 
       [0025]      FIG. 1  is a schematic view illustrating an overview configuration of an endoscope system according to a first embodiment of the present disclosure. As illustrated in  FIG. 1 , an endoscope system  1  according to the present embodiment includes an endoscope  2 , a processing device  3 , a light source device  4 , and a display device  5 . The endoscope  2  is introduced into a subject and captures the inside of a body of the subject to generate an image signal of the inside of the subject. The processing device  3  performs a predetermined image process on the image signal captured by the endoscope  2 , and controls each part of the endoscope system  1 . The light source device  4  generates illumination light of the endoscope  2 . The display device  5  displays an image of the image signal subjected to the image process by the processing device  3 . 
         [0026]    The endoscope  2  includes an insertion portion  6 , an operating unit  7 , and a flexible universal code  8 . The insertion portion  6  is inserted into the subject. The operating unit  7  is located on a proximal end portion side of the insertion portion  6  and gripped by an operator. The universal code  8  extends from the operating unit  7 . 
         [0027]    The insertion portion  6  is realized with the use of an illumination fiber (light guide cable), an electric cable, and an optical fiber or the like. The insertion portion  6  includes a distal end portion  6   a , a curve portion  6   b , and a flexible pipe portion  6   c . The distal end portion  6   a  includes an imaging unit in which an imaging sensor that captures the inside of the subject is incorporated. The curve portion  6   b  includes a plurality of curve pieces so as to be freely curved. The flexible pipe portion  6   c  is provided on a proximal end portion side of the curve portion  6   b  and has flexibility. The distal end portion  6   a  is provided with an illumination unit, an observation unit, an opening portion  6   d , and an air/water supply nozzle (not illustrated). The illumination unit illuminates the inside of the subject through an illumination lens. The observation unit captures the inside of the subject. The opening portion  6   d  communicates with a treatment tool channel. 
         [0028]    The operating unit  7  includes a curve knob  7   a , a treatment tool insertion portion  7   b , and a plurality of switch units  7   c . The curve knob  7   a  curves the curve portion  6   b  in an up-down direction and a left-right direction. A treatment tool such as living body forceps and a laser scalpel is inserted into a body cavity of the subject through the treatment tool insertion portion  7   b . A peripheral device such as the processing device  3 , the light source device  4 , an air supply device, a water supply device, and a gas supply device is operated through the plurality of switch units  7   c . The treatment tool inserted through the treatment tool insertion portion  7   b  passes through a treatment tool channel provided inside and comes out of the opening portion  6   d  at the distal end of the insertion portion  6 . 
         [0029]    The universal code  8  is configured with the use of an illumination fiber, an electric cable, and an optical fiber or the like. The universal code  8  branches at a proximal end thereof. An end portion of one of the branches is a connector  8   a , and an end portion of the other is a connector  8   b . The connector  8   a  is detachably attached to a connector  3   a  of the processing device  3 . The connector  8   b  is detachably attached to the light source device  4 . The universal code  8  propagates the illumination light emitted from the light source device  4  to the distal end portion  6   a  through the connector  8   b , the operating unit  7 , and the flexible pipe portion  6   c . The universal code  8  transmits the image signal captured by the imaging unit provided in the distal end portion  6   a  to the processing device  3  by means of an optical transmitter unit to be described later. 
         [0030]    The processing device  3  performs the predetermined image process on the image signal of the inside of the subject captured by the imaging unit of the distal end portion  6   a  of the endoscope  2 . The processing device  3  controls each part of the endoscope system  1  based on various instruction signals transmitted from the switch units  7   c  of the operating unit  7  of the endoscope  2  through the universal code  8 . 
         [0031]    The light source device  4  is configured with the use of a light source that emits light and a condenser lens or the like. Under the control of the processing device  3 , the light source device  4  emits the light from the light source and supplies, to the endoscope  2  coupled via the connector  8   b  and the illumination fiber of the universal code  8 , the light as the illumination light for the inside of the subject that serves as an object. 
         [0032]    The display device  5  is configured with the use of a display or the like in which liquid crystal or organic electro luminescence (EL) is used. The display device  5  displays, through a video cable  5   a , various types of information including the image subjected to the predetermined image process by the processing device  3 . Consequently, the operator may observe a desired position in the subject and determine the condition of the desired position by operating the endoscope  2  while watching the image (in-vivo image) displayed by the display device  5 . 
         [0033]    Next, in the endoscope  2  described in  FIG. 1 , the optical transmitter unit that transmits the image signal captured by the imaging unit to the processing device will be described.  FIG. 2  is a view separately illustrating an optical transmitter module and a transmitter side optical connector that constitute the optical transmitter unit used in the endoscope system illustrated in  FIG. 1 . In  FIG. 2 , for an easy understanding, an optical transmitter module  30  is illustrated in a cross-sectional view, a transmitter side optical connector  20  is illustrated in a side view, and a fixing member is not illustrated.  FIG. 3  is a side view of an optical transmitter unit  10  illustrated in  FIG. 2 . 
         [0034]    The optical transmitter unit  10  is configured in such a manner that the transmitter side optical connector  20  and the optical transmitter module  30  are coupled by a fixing member  50  as illustrated in  FIGS. 2 and 3 . The optical transmitter unit  10  is arranged at the operating unit  7  or the insertion portion  6  of the endoscope  2 . 
         [0035]    The transmitter side optical connector  20  includes a ferrule  22  and a flange portion  23 . The ferrule  22  holds an optical fiber  21 . The flange portion  23  is provided at one end of the ferrule  22 . In the ferrule  22  having a substantially columnar shape, a micro hole (not illustrated) that passes through a center of the columnar shape in an axial direction is provided. The optical fiber  21  is inserted into the micro hole, whereby the transmitter side optical connector  20  holds the optical fiber  21 . The optical fiber  21  is inserted into the micro hole and exposed at an end surface (hereinafter referred to as a “distal end portion”) of the ferrule  22  that is inserted into a sleeve  35 . An end surface of the optical fiber  21  is polished in order to reduce a loss of the light quantity at an optical connection portion. A connector side screw portion  24  is formed on an outer peripheral portion of the ferrule  22  located on an insertion portion side. The flange portion  23  having a columnar shape that is concentric with the ferrule  22  is provided on an outer peripheral portion of the ferrule  22  located opposite to the distal end portion (hereinafter referred to as a “proximal end portion”). 
         [0036]    The optical transmitter module  30  includes a light emitting element  32  and a metal case  34 . The metal case  34  stores and optically connects the light emitting element  32  and the ferrule  22 . The light emitting element  32  is coupled to a flexible substrate  40  via a lead  39 . The image signal captured by the imaging unit is transmitted to the light emitting element  32  through the flexible substrate  40 , subjected to a photoelectric conversion, and emitted from a light emitting unit  31  as an optical signal. The optical signal emitted from the light emitting unit  31  is collected by a condenser lens  33  and a transparent glass body  36 . The metal case  34  includes the sleeve  35  into which the ferrule  22  is inserted. A module side screw portion  37  that is screwed with the connector side screw portion  24  is provided in the vicinity of the transparent glass body  36  in the sleeve  35 . The module side screw portion  37  is formed of an elastic deformable material such as rubber. 
         [0037]    The ferrule  22  is inserted into the sleeve  35  of the optical transmitter module  30 , the connector side screw portion  24  and the module side screw portion  37  are screwed with each other, and eccentricity is adjusted. After that, as illustrated in  FIG. 3 , the optical transmitter module  30  is fixed by the fixing member  50  that presses the ferrule  22  in the sleeve  35  of the metal case  34 . The fixing member  50  is made of a metal material, and includes U-shaped holding portions  51  and  52  at both ends thereof. The holding portions  51  and  52  are fit with the optical transmitter unit  10  in an opening direction of the U shape, and fixed. The holding portion  51  is fit with a recessed portion  38  of the metal case  34 , and the holding portion  52  is fit with a proximal end side of the flange portion  23  of the transmitter side optical connector  20 . The length between the holding portion  51  and the holding portion  52  is designed to be shorter than the length from the recessed portion  38  to the proximal end portion of the flange portion  23 . Therefore, when the fixing member  50  is fit with the optical transmitter unit  10 , the fixing member  50  performs the fixation while pressing the ferrule  22  in the sleeve  35 . 
         [0038]    Next, a connecting method for the optical transmitter unit  10  will be described.  FIG. 4  is a flowchart explaining a method of connecting the optical transmitter module  30  and the transmitter side optical connector  20 . 
         [0039]    First, the flange portion  23  of the transmitter side optical connector  20  is directly gripped, or the transmitter side optical connector  20  is gripped using a jig attached to the flange portion  23 , and the ferrule  22  is inserted into the sleeve  35  of the optical transmitter module  30  (step S 1 ). 
         [0040]    After the ferrule  22  is inserted into the sleeve  35 , the transmitter side optical connector  20  is rotated, and the connector side screw portion  24  is screwed with the module side screw portion  37 . At this time, the light is emitted from the light emitting unit  31 , and the light quantity transmitted by the optical fiber  21  is measured on a proximal end side of the optical fiber  21  (step S 2 ). 
         [0041]    In the transmitter side optical connector  20 , the eccentricity might occur between an outer diameter center of the ferrule  22  and a core center of the optical fiber  21  inserted into the micro hole during the manufacturing process. Similarly, the eccentricity might also occur between a center of the light emitting unit  31  and a center of the sleeve  35  in the optical transmitter module  30 . 
         [0042]      FIG. 5A  and  FIG. 5B  are diagrams explaining the adjustment of the eccentricity between the optical transmitter module  30  and the transmitter side optical connector  20 .  FIG. 5A  is a state before the adjustment of the eccentricity, and  FIG. 5B  is a state after the adjustment of the eccentricity. In  FIGS. 5A and 5B , the eccentricity is illustrated on a large scale for an easy understanding. 
         [0043]    In a case where the eccentric transmitter side optical connector  20  and the eccentric optical transmitter module  30  are optically connected, no problem occurs when a direction of the eccentricity of the transmitter side optical connector  20  is the same as that of the optical transmitter module  30 . However, in a case where the directions are different from each other as illustrated in  FIG. 5A , the transmission light quantity is significantly reduced if the transmitter side optical connector  20  and the optical transmitter module  30  are connected as they are. In a case where the transmitter side optical connector  20  and the optical transmitter module  30  that are eccentric in the different directions are connected, for example, the transmitter side optical connector  20  is rotated as illustrated by an arrow in  FIG. 5A , whereby the direction of the eccentricity between the transmitter side optical connector  20  and the optical transmitter module  30  may be adjusted as illustrated in  FIG. 5B , and the light loss may be reduced. In the first embodiment, since the connector side screw portion  24  and the module side screw portion  37  are screwed with each other to adjust the eccentricity, the transmission light quantity may be sequentially detected, and a position where the maximum light quantity is obtainable may be detected. 
         [0044]    After the transmitter side optical connector  20  is rotated, and the connector side screw portion  24  is screwed with the module side screw portion  37 , the transmitter side optical connector  20  is rotated in an opposite direction until the transmitter side optical connector  20  reaches a position for the maximum light quantity, whereby the eccentricity between the transmitter side optical connector  20  and the optical transmitter module  30  is adjusted (step S 3 ). 
         [0045]    After the eccentricity between the transmitter side optical connector  20  and the optical transmitter module  30  is adjusted, the transmitter side optical connector  20  and the optical transmitter module  30  are fixed by the fixing member  50  (step S 4 ). 
         [0046]    In a case where the light quantity is measured in step S 2 , and the maximum light quantity is obtained when the distal end portion of the ferrule  22  is located at the rearmost end of the module side screw portion  37  as illustrated in  FIG. 6A , the adjustment of the eccentricity is finished at the position in  FIG. 6A . However, the light loss occurs since a space exists between the transparent glass body  36  and the distal end portion of the ferrule  22 . In the first embodiment, the module side screw portion  37  is formed of the elastic member. Therefore, when the fixing member  50  is fit with the optical transmitter unit  10  in  FIG. 6A  subjected to the adjustment of the eccentricity, pressing force is exerted in a direction illustrated by an arrow in  FIG. 6A , and the module side screw portion  37  is elastically deformed as illustrated in  FIG. 6B . Consequently, the transparent glass body  36  and the distal end portion of the ferrule  22  may be brought into contact with each other and connected, and the light loss may be reduced. 
         [0047]    Alternatively, the module side screw portion may move through the inside of the sleeve  35  instead of being elastically deformed by the pressing force caused by the fixing member  50 .  FIG. 7  is a view explaining a method of connecting an optical transmitter module and a transmitter side optical connector according to a first modification of the first embodiment of the present disclosure. In the first modification, a module side screw portion  37 A is formed at a position apart from the transparent glass body  36  in the same way as that of the first embodiment illustrated in  FIG. 6A . However, the module side screw portion  37 A is pressed by the fixing member  50  and moves in a direction toward the transparent glass body  36  together with the ferrule  22 . In the first modification, the pressing force of the fixing member  50  only needs to be set to be larger than frictional force between the sleeve  35  and the module side screw portion  37 A. Consequently, the transparent glass body  36  and the distal end portion of the ferrule may be brought into contact with each other and connected, and the light loss may be reduced. 
         [0048]    In addition, a similar effect may be obtained in the optical transmitter module that uses a stub  41  in place of the transparent glass body  36 .  FIG. 8  is a view explaining a method of connecting an optical transmitter module  30 B and the transmitter side optical connector  20  according to a second modification of the first embodiment of the present disclosure. In the second modification, the optical transmitter module  30 B and the transmitter side optical connector  20  are optically connected using the stub  41 . A groove portion  41   a  is formed on an outer peripheral side of the stub  41  that is in contact with the sleeve  35 . In the same way as the module side screw portion  37 A of the first modification, a module side screw portion  37 B may move in a direction toward the stub  41  together with the ferrule  22  when pressed by the fixing member  50 , and go into the groove portion  41   a . Even in a case where the maximum light quantity is obtained when the distal end portion of the ferrule  22  is located before the rearmost end of the module side screw portion  37 B, since the groove portion  41   a  is formed on the stub  41 , the distal end portion of the ferrule  22  and the stub  41  may be brought into contact with each other and connected, and the light loss may be reduced. 
         [0049]    In the first embodiment, the adjustment of the eccentricity between the optical transmitter module and the transmitter side optical connector is performed by causing the screw portions provided in the sleeve and on the surface of the ferrule to be fit with each other. Alternatively, the adjustment of the eccentricity may be easily performed by providing a positioning marker on each of an outer peripheral portion of the sleeve and an outer peripheral portion of the flange portion.  FIG. 9  is a side view of an optical transmitter unit according to a third modification of the first embodiment of the present disclosure. In the optical transmitter unit  10 E according to the third modification, a marker  35   e  and a marker  25  are provided on the outer peripheral portion of the sleeve and the outer peripheral portion of a flange portion  23 E, respectively. The adjustment of the eccentricity is facilitated by providing the marker  25  and the marker  35   e.    
       Second Embodiment 
       [0050]      FIG. 10  is a view separately illustrating an optical transmitter module and a transmitter side optical connector in an optical transmitter unit according to a second embodiment of the present disclosure. In an optical transmitter unit  10 C according to the second embodiment of the present disclosure, a module side screw portion  37 C is provided on an insertion opening side of the sleeve  35  for the ferrule  22 , and a connector side screw portion  24 C is provided on a side of the ferrule  22  located close to the flange portion  23 . 
         [0051]    In the second embodiment as well, the ferrule  22  is inserted into the sleeve  35 , a transmitter side optical connector  20 C is rotated, and the connector side screw portion  24 C is screwed with the module side screw portion  37 C, whereby the transmitter side optical connector  20 C is adjusted to reach a position for the maximum light quantity. After that, an optical transmitter module  30 C and the transmitter side optical connector  20 C are pressed and fixed by the fixing member, and the transparent glass body  36  and the distal end portion of the ferrule  22  are brought into contact with each other and connected, whereby the light loss may be reduced. In the same way as the module side screw portion  37  of the first embodiment, the module side screw portion  37 C may be an elastic member, and the transparent glass body  36  and the distal end portion of the ferrule  22  may be connected in contact with each other by means of the elastic deformation of the module side screw portion  37 C. Alternatively, in the same way as the module side screw portion  37 A of the first modification of the first embodiment, the module side screw portion  37 C may be configured to move through the inside of the sleeve  35  by means of the pressing force. A similar effect may be obtained when the transparent glass body  36  is replaced by the stub  41 . 
         [0052]    In addition, the module side screw portion provided on the insertion opening side of the sleeve  35  for the ferrule  22  may be provided on the outer peripheral portion of the sleeve  35 , not in the sleeve  35 .  FIG. 11  is a cross-sectional view explaining a method of connecting an optical transmitter module  30 D and a transmitter side optical connector  20 D according to a first modification of the second embodiment of the present disclosure. In an optical transmitter unit  10 D according to the first modification of the second embodiment, a flange portion  23 D is formed to be thicker in diameter than the sleeve  35 , and provided with, at a distal end side of the ferrule  22 , an insertion portion  26  into which the sleeve  35  of the metal case  34  is inserted. A connector side screw portion  24 D is provided in the insertion portion  26 . In the first modification of the second embodiment as well, the eccentricity may be adjusted to obtain the maximum light quantity, and the light loss may be reduced. In the same way as the module side screw portion  37  of the first embodiment, a module side screw portion  37 D may be an elastic member, and the transparent glass body  36  and the distal end portion of the ferrule  22  may be connected in contact with each other by means of the elastic deformation of the module side screw portion  37 D. Alternatively, in the same way as the module side screw portion  37 A of the first modification of the first embodiment, the module side screw portion  37 D may be configured to move on the surface of the sleeve  35  by means of the pressing force. 
       Third Embodiment 
       [0053]    In an endoscope of a third embodiment, the transmission of the image signal is performed using a plurality of optical transmission units.  FIG. 12  is a schematic view illustrating an overview configuration of the optical transmission unit according to the third embodiment of the present disclosure. 
         [0054]    An optical transmission unit  100  includes an optical transmitter unit  10 F, the optical fiber  21 , and an optical receiving unit  80 . The optical transmitter unit  10 F is installed at the operating unit or the insertion portion of the endoscope, and the optical receiving unit  80  is installed in the processing device. The optical transmitter unit  10 F is configured in such a manner that the optical transmitter module  30  and a transmitter side optical connector  20 F illustrated in  FIG. 12  are coupled and fixed by the fixing member. The optical transmitter module  30  has a configuration similar to that of the optical transmitter module  30  of the first embodiment. The transmitter side optical connector  20 F includes a flange portion  23 F in place of the flange portion  23  of the transmitter side optical connector  20  of the first embodiment. The flange portion  23 F includes a groove  27  on an outer peripheral portion thereof. Since the flange portion  23 F serves as a grip portion, a corner portion that constitutes the groove  27  is preferably rounded. The groove  27  may be provided over the entire periphery of the flange portion  23 F, or may be partially provided. 
         [0055]    The optical receiving unit  80  is configured in such a manner that an optical receiving module  60  and a receiving side optical connector  70  illustrated in  FIG. 12  are coupled and fixed by a fixing member. The optical receiving module  60  performs a photoelectric conversion on the optical signal transmitted by the optical fiber  21 . Although the optical receiving module  60  includes a sleeve into which a ferrule  72  of the receiving side optical connector  70  to be described later is inserted, a module side screw portion is not formed in the sleeve. The receiving side optical connector  70  includes the ferrule  72  and a flange portion  73 . The ferrule  72  holds the optical fiber  21 . The flange portion  73  includes a groove  27  and is provided at one end of the ferrule  72 . In the third embodiment, the flange portion  73  has the same shape as the flange portion  23 F of the transmitter side optical connector  20 F. However, the ferrule  72  is different from the ferrule  22  in that a distal end portion of the ferrule  72  does not include a connector side screw portion. Alternatively, in order to perform the adjustment in the optical receiving unit  80  so that the light quantity received at the optical receiving module  60  is equal to or more than the lowest receiving sensitivity, a connector side screw portion and a module side screw portion similar to those of the optical transmitter unit  10 C may be respectively provided on the ferrule  72  and inside a metal case of the optical receiving module, and may be fit with each other. 
         [0056]    In a case where the image signal is transmitted using the plurality of optical transmission units, an insertion error might occur since the optical transmission units cannot be identified. In the third embodiment, therefore, different types of grooves are provided on the respective optical transmission units in order to identify the plurality of optical transmission units. For example, in a case where three types of optical transmission units are used, the optical transmission units may be identified by changing the number of grooves formed on the flange portions of each optical transmission unit as illustrated in  FIGS. 13A to 13C and 14A to 14C . In  FIG. 12 , the transmitter side optical connector  20 F having the one groove  27  and the receiving side optical connector  70  having the one groove  27  constitute the optical transmission unit  100 . In an optical transmission unit that uses a transmitter side optical connector  20 G having two grooves  27 G illustrated in  FIG. 13B , a receiving side optical connector having two grooves  27 G is used, and in an optical transmission unit that uses a transmitter side optical connector  20 H having three grooves  27 H illustrated in  FIG. 13C , a receiving side optical connector having three grooves  27 H is used, whereby the optical transmission units may be identified. The same applies to a case where transmitter side optical connectors having grooves  27 ,  27 J, and  27 K shaped as illustrated in  FIGS. 14A to 14C  are used. The shapes of the grooves are not limited to those illustrated in  FIGS. 13A to 13C and 14A to 14C . 
         [0057]    According to the present disclosure, screw portions are provided on a ferrule or a flange portion and in a sleeve into which the ferrule is inserted, and a transmitter side optical connector and an optical transmitter module may be placed at a position for the maximum light quantity while the screw portions are rotated so as to be screwed with each other. The transmitter side optical connector and the optical transmitter module may also be brought into close contact with each other. Therefore, a light loss at the time of transmission may be reduced. 
         [0058]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.