Patent Publication Number: US-2011052126-A1

Title: Optical Receptacle and Optical Module Using the Same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical receptacle and an optical module which are used for optical communication, optical information processing, an optical sensor, and the like. 
     2. Description of the Related Art 
     Conventionally, a receptacle type optical module  104  as shown in  FIG. 17  in which a package  112  accommodating a photon-electron or electron-photon conversion element  102  therein is disposed at one end of an optical receptacle  100  (on the right side in the drawing), and a plug ferrule  103  is connected to the other end of the optical receptacle  100 , to transmit or receive an optical signal, has been provided as an optical module (refer to, for example, JP 2003-075679A). 
     This optical receptacle  100  includes a fiber stub  107  composed of a ferrule  105  and an optical fiber  106  inserted in a hole of the ferrule  105 . The rear end part of the fiber stub  107  is pressed to be fixed into a holder  108 . The front end part of the fiber stub  107  is inserted into an inner hole of a sleeve  109 . 
     The plug ferrule  103  is inserted into the sleeve  109  from the side of the front end part of the optical receptacle  100  configured in this way, and an edge face of the optical fiber  106  in the fiber stub  107  and an edge face of the optical fiber  106  on the side of the plug ferrule  103  are brought into contact with each other, to exchange an optical signal. 
     Meanwhile, the shape of the light-emitting device using the optical module  104  is standardized. However, as a modulation rate of an electrical signal applied to the photon-electron or electron-photon conversion element  102  is speeded up, an electrical circuit required for driving the photon-electron or electron-photon conversion element  102  tends to be larger in size. It is required to shorten the optical receptacle  100  in order to bring the optical module  104  into a given size. 
     However, it is not easy to shorten the optical module  104  using the fiber stub  107 . 
     Then, an optical receptacle in which the fiber stub  107  is omitted, and the photon-electron or electron-photon conversion element  102  and the plug ferrule  103  are optically connected via a light-transmissive plate-like body in place of the fiber stub  107  has been proposed (refer to, for example, JP-2005-242314A). 
     In this optical receptacle, the outer circumferential surface of the plate-like body is made to adhere to the inner side of a through hole formed in the holder  108 , to block the through hole in the holder  108 . Then, the front end of the plug ferrule  103  is contacted with the plate-like body, and the ferrule  103  is placed in the correct position. 
     However, in the case where the plug ferrule  103  is repeatedly inserted and pulled out, or in the case where the optical receptacle is used for a long period in a high-temperature and humid circumstance, the problem that the plate-like body drops off from the holder  108  may occur. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in consideration of the above-described circumstances. An object of the present invention is to provide a short-type optical receptacle and a short-type optical module which are resistant to a mechanical impact, to be capable of obtaining a suitable optical connection. 
     An optical receptacle according to an aspect of the present invention, the optical receptacle to which a plug ferrule for holding an optical fiber is connected, includes a case forming an outer shell, the case having an insertion hole which has a bottom surface at one end thereof and into which the plug ferrule is inserted, and a transparent substrate disposed on the bottom surface. The case has a through hole formed so as to penetrate from the bottom surface of the insertion hole to an end face of the case. The through hole having a diameter smaller than that of the insertion hole and the through hole is communicated with the insertion hole. The transparent substrate is in contact with the bottom surface of the case so as to cover an opening of the through hole which opens in the bottom surface of the case. 
     An optical module according to another aspect of the present invention includes the optical receptacle, an optical element for receiving or emitting a light passing through the through hole, and a cylindrical body joined to the case of the optical receptacle to accommodate the optical element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an optical receptacle according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view showing an optical receptacle and an optical module according to an embodiment of the present invention. 
         FIG. 3A ,  FIG. 3B ,  FIG. 3C  and  FIG. 3D  are plan views showing each shape of a transparent substrate. 
         FIG. 4  is a graph showing changes of the contacting areas between a transparent substrate and a sleeve relative to the diameter of the transparent substrate. 
         FIG. 5A  and  FIG. 5B  are plan views for explaining a method for processing a transparent substrate. 
         FIG. 6  is a schematic view for explaining a method for processing a circular transparent substrate. 
         FIG. 7A  is a cross-sectional view showing an optical receptacle according to an embodiment of the present invention, and  FIG. 7B  is an enlarged sectional view of a part of the  FIG. 7A . 
         FIG. 8A  is a cross-sectional view showing an optical receptacle according to an embodiment of the present invention, and  FIG. 8B  is an enlarged sectional view of a part of the  FIG. 8A . 
         FIG. 9A ,  FIG. 9B  and  FIG. 9C  are perspective views showing an example of the shape of a transparent substrate used in the optical receptacle according to an embodiment of the present invention. 
         FIG. 10A  and  FIG. 10B  are plan views showing an example of the method for producing the transparent substrate. 
         FIG. 11A  and  FIG. 11B  are plan views showing another example of the method for producing the transparent substrate. 
         FIG. 12A  is a plan view showing still another example of the method for producing the transparent substrate, and 
         FIG. 12B  is a sectional view of a part of the  FIG. 12A . 
         FIG. 13  is a cross-sectional view showing an optical receptacle and an optical module according to an embodiment of the present invention. 
         FIG. 14  is a cross-sectional view showing an optical receptacle and an optical module according to an embodiment of the present invention. 
         FIG. 15  is a cross-sectional view showing an optical receptacle and an optical module according to an embodiment of the present invention. 
         FIG. 16  is a cross-sectional view showing an optical receptacle and an optical module according to an embodiment of the present invention. 
         FIG. 17  is a cross-sectional view showing an example of a conventional optical receptacle and an optical module using the same. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An optical receptacle according to the present invention will be described in detail below with reference to the accompanying drawings. However, the following respective examples of the embodiments are merely exemplified as the present invention, and the present invention is not limited thereto. In addition, in the respective drawings, common portions, components, and members are denoted by the same reference numerals, and overlapping descriptions will be omitted. The terms “the left, right, top and bottom” used for the descriptions are merely used for explanation of the positional relationships on the drawings. These do not mean the positional relationships in actual use. 
       FIG. 1  shows an optical receptacle  1  according to an embodiment of the present invention. The optical receptacle  1  is provided with a case  5  having an insertion hole  20  into which a plug ferrule  3  is inserted, and a transparent substrate  15  disposed on a bottom surface  20   a  of the insertion hole  20 . Further, the case  5  has a through hole  19  communicated with the insertion hole  20  from the bottom surface  20   a  of the case  5  to an end face  5   a  of the case  5 . The through hole  19  is smaller in diameter than the insertion hole  20 . The transparent substrate  15  disposed on the bottom surface  20   a  is disposed in contact with the bottom surface  20   a  so as to cover the opening of the through hole  19  which is open in the bottom surface  20   a . Then, in the optical receptacle  1 , the plug ferrule  3  for holding an optical fiber  6  is inserted into the insertion hole  20  so as to contact the transparent substrate  15 . 
     In some cases, a sleeve  9  is disposed inside the insertion hole  20 . In this case, it is preferable that the sleeve  9  is disposed so as to the rear edge face of the sleeve  9  contacts the transparent substrate  15 . The sleeve  9  has a function to keep stop the plug ferrule  3 . In addition, in the case where the sleeve  9  is not disposed, the plug ferrule  3  is inserted into the insertion hole  20 . 
     The insertion hole  20  is blocked on its end face  5   a  side by the bottom surface  20   a . The through hole  19  is provided in the bottom surface  20   a  so as to be communicated with the insertion hole  20 . The other side of the insertion hole  20  is open to the outside of the case  5 . As the hollow insertion hole  20  and the through hole  19  communicated with the insertion hole  20  are arranged to be aligned in the case  5 , the case  5  forms a tubular form as a whole. In addition, light optically connected to the optical fiber  6  held in the plug ferrule  3  is propagated through the through hole  19  provided in the bottom surface  20   a.    
     The transparent substrate  15  is transmissive for light emitted from the optical fiber  6  or light incident from the through hole  19 , and has a function to position the plug ferrule  3  such that the transparent substrate  15  is brought into contact with the front end of the plug ferrule  3  to locate the front end of the plug ferrule  3  at a predetermined position. The transparent substrate  15  is disposed in contact with the bottom surface  20   a  of the insertion hole  20 . The transparent substrate  15  may be fixed at the bottom surface  20   a  of the holder  5  with an adhesive or the like. As shown in  FIG. 1 , a hollow hole may be further processed in the bottom surface  20   a , and the transparent substrate  15  may be disposed so as to be fit into this hollow hole. 
     The transparent substrate  15  is disposed in contact with the bottom surface  20   a  of the insertion hole  20 . Even when the front end of the plug ferrule  3  is inserted into the insertion hole  20  so as to be brought into contact with the transparent substrate  15 , and the plug ferrule  3  applies force to the transparent substrate  15 , the transparent substrate  15  does not easily drop off, since the transparent substrate  15  is supported by the bottom surface  20   a . Further, since the transparent substrate  15  is supported by the bottom surface  20   a , positional deviation of the transparent substrate  15  is hardly caused, which makes it possible to maintain the optical characteristics. 
     In addition, the inside of the through hole  19  may be filled with a refractive index matching agent  21 . The refractive index matching agent  21  is disposed so as to contact the transparent substrate  15 , and has a refractive index comparable with the refractive index of the transparent substrate  15 . When the refractive index of the transparent substrate  15  and the refractive index of the refractive index matching agent  21  are matched to be comparable with each other, it is possible to inhibit refraction and reflection of light between the transparent substrate  15  and the refractive index matching agent  21 . It is preferable that the edge face  21   a  of the refractive index matching agent  21  on the side of the end face  5   a  is inclined to a plane perpendicular to the axial direction of the through hole  19 . With the inclined surface, it is possible to reduce light reflected on the edge face of the refractive index matching agent  21  to return in the reverse direction. 
       FIG. 2  is a cross-sectional view showing the optical receptacle  1  and an optical module  4  including the optical receptacle  1  according to another embodiment of the present invention. 
     In the optical receptacle  1  according to the present embodiment, the case  5  is composed of a holder  8  and a shell  10 . Then, the insertion hole  20  is composed of a hole passing through the shell  10  and a hole  17  provided in the holder  8 . Further, the through hole  19  passing from the bottom surface  20   a  of the insertion hole  20  to the surface on the opposite side of the bottom surface  20   a  is provided so as to be communicated with the insertion hole  20 . The transparent substrate  15  is disposed on the bottom surface  20   a  so as to be brought into contact with the bottom surface  20   a  to cover the through hole  19 . 
     The holder  8  has a tubular form as a whole, with the through hole  19  with a diameter smaller than the diameter of the hole  17  partially forming the insertion hole  20 . In addition, the through hole  19  is provided for optical connection between the photon-electron or electron-phton conversion element  2  in the package  12  and the optical fiber  6  held by the plug ferrule  3 , and for passing through a signal light through the through hole  19 . 
     The tubular sleeve  9  is held inside the shell  10 . The plug ferrule  3  for holding the optical fiber  6  is inserted into the sleeve  9 . Then, the transparent substrate  15  is disposed so as to be held between the bottom surface  20   a  of the insertion hole  20  and a rear edge face  9   a  of the sleeve  9 . Accordingly the transparent substrate  15  is held inside the optical receptacle  1 , and the transparent substrate  15  hardly drops off. 
     That is, in the optical receptacle  1  of the present embodiment, the transparent substrate  15  is pressed against the bottom surface  20   a  of the through hole  20  by inserting the plug ferrule  3  into the optical receptacle  1 . And the front end position of the plug ferrule  3  brought into contact with the transparent substrate  15  is usually disposed at a constant position. Accordingly, the front end position of the optical fiber  6  is always kept at a constant position even when the plug ferrule  3  is repeatedly inserted and pulled out. In addition, the transparent substrate  15  is held between the bottom surface  20   a  and the rear edge face  9   a  of the sleeve  9 , thereby the transparent substrate  15  hardly drops off from the holder  8 . In the case where an adhesive is not used for fixation of the transparent substrate  15 , even in the case where the optical receptacle is used for a long period in a high-temperature and humid environment, there is no positional deviation of the transparent substrate  15  due to an adhesive expanding or contracting by a temperature change or an adhesive absorbing moisture to have swelling. 
     When the plug ferrule  3  is inserted, the transparent substrate  15  is pressed against the bottom surface  20   a  of the insertion hole  20 . Accordingly, when the bottom surface  20   a  is set perpendicular to the insertion direction of the plug ferrule  3 , it is easy to set the transparent substrate  15  perpendicular to the insertion direction of the plug ferrule  3 . Thereby, it is possible to make a good physical contact between the optical fiber  6  and the transparent substrate  15 , which makes it possible to reduce deterioration of a signal light. 
     In addition, the front end of the plug ferrule  3  inserted into the optical receptacle  1  is mirror polished so as to have a curved surface with a radius of curvature of 5 to 30 mm in order to facilitate the physical contact, and the edge face of the optical fiber  6  disposed in the center of the plug ferrule  3  is disposed in the vicinity of the foremost end part of the plug ferrule  3 . The edge face of the optical fiber  6  physically contacts the transparent substrate  15  by inserting the plug ferrule  3  into the optical receptacle  1 . It is desirable that the transparent substrate  15  is a parallel plate in order to get the optical fiber  6  in the plug ferrule  3  in good contact with the transparent substrate  15 . 
     It is preferable that the transparent substrate  15  has different shape from a generally used tetragonal shape, such as a hexagonal shape shown in  FIG. 3B  or an octagonal shape sown in  FIG. 3C , or a discoid shape shown in  FIG. 3D . In addition, among the transparent substrates  15  shown in the respective drawings of  FIGS. 3B ,  3 C, and  3 D, it is preferable that, in the case where the transparent substrate  15  has a polygonal shape such as a hexagonal shape or an octagonal shape, its diagonal line length  15   a  and the diameter of the hole  17  are set to be substantially equal. Further, it is preferable that, in the case where the transparent substrate  15  is a circular shape, its diameter  15   a  and the diameter of the hole  17  are substantially equal. In this way, the transparent substrate  15  is disposed so as to internally touch the inside of the hole  17 , thereby making the transparent substrate  15  hardly move in the radial direction in the hole  17 . 
     Moreover, the diameter of the inscribing circle of the transparent substrate  15  is set to be longer than the diameter of the through hole  19  and the inside diameter of the sleeve  19 . In the case where the transparent substrate  15  is a circular shape, the diameter of the transparent substrate  15  is set to be longer than the diameter of the through hole  19  and the inside diameter of the sleeve  19 . 
     In the case where a vibration or an impact is applied to the optical receptacle  1 , the transparent substrate  15  is hit against the bottom surface  20   a  of the holder  8  and the rear edge face  9   a  of the sleeve  9 , which may cause defects such as cracks or chips. The corner portions of the transparent substrate  15  on the side of the sleeve  9  tends to be easily defective. 
     The hatchings of the transparent substrates  15  in  FIGS. 3A ,  3 B,  3 C, and  3 D indicate the portions on which the surface of the transparent substrate  15  and the rear edge face of the sleeve  9  are in contact with each other. Herein, in the case where the transparent substrate  15  is formed into a conventional tetragonal shape as shown in  FIG. 3A , the area in contact with the sleeve  9  is narrower, as the number of corners is less. Therefore, stress is concentrated on the corners of the transparent substrate  15 . In contrast thereto, the transparent substrate  15  of the present embodiment shown in  FIGS. 3B ,  3 C, and  3 D has a hexagonal shape, an octagonal shape, or a circular shape, and the numbers of the corners are many, and those corners are provided with obtuse angles greater than the right angle, and the contacting areas with the rear edge face  9   a  of the sleeve  9  is possibly greater. Therefore, stress applied on the transparent substrate  15  is dispersed, which makes it hardly crack or chip. 
       FIG. 4  is a graph showing changes of the contacting areas between the transparent substrate  15  and the sleeve  9 . In  FIG. 4 , the diameters of the transparent substrate  15 , or, the ratios that the diagonal line lengths  15   a  or the diameters  15   a  of the transparent substrates  15  are divided by the inside diameter of the sleeve  9  are plotted on the abscissa axis, and the contacting areas between the transparent substrate  15  and the sleeve  9  are plotted on the ordinate axis. In addition, the diameters of the transparent substrate  15  are normalized with respect to the inside diameter of the sleeve  9 . For example, when the normalized value is  1 , the diameter of the transparent substrate  15  is meant to be equal to the inside diameter of the sleeve  9 . Further, it is assumed that the respective shapes of the transparent substrate  15  have all regular polygonal shapes. 
     As shown in  FIG. 4 , it is shown that, in the case where the transparent substrate  15  has a tetragonal shape, the level of stress concentration is higher, because its contacting area is smaller than those of the other shapes. In contrast thereto, in the cases where the transparent substrates  15  have a hexagonal shape, an octagonal shape, and a circular shape, their contacting areas are increased, and the levels of stress concentration are lowered accordingly. In addition, even in the case where the transparent substrate  15  is formed into a tetragonal shape, by making the transparent substrate  15  larger in size, its contacting area with the sleeve  9  is increased accordingly, which relieves the stress concentration. However, in this case, the diagonal line length  15   a  of the transparent substrate  15  would be too large. Consequently, it is necessary to increase the diameter of the hole  17  into which the transparent substrate  15  is inserted according to the increase of the diagonal line length  15   a . However, since the optical receptacle  1  is required to be further downsized, it is not easy to enlarge the diameter of the hole  17 . 
     When the diameter of the circle circumscribing the transparent substrate  15  (i.e., the inside diameter of the hole  17 ) is set sufficiently longer than the inside diameter of the sleeve  9 , the contacting portion between the transparent substrate  15  and the sleeve  9  forms a ring shape with a substantially constant width which is seamless in its circumferential direction. In the case where the entire outer circumference of the transparent substrate  15  contacts the ring shape, stress is not concentrated on the corner portions of the transparent substrate  15  in any case, which does not cause cracks or chips. In addition, in the case where the transparent substrate  15  has a polygonal shape such as a hexagonal shape or an octagonal shape, the diameter of the inscribing circle of the transparent substrates  15  is substantially equal to the distance between the distance of the opposite sides thereof, and as the extreme case where the transparent substrate  15  is a circular shape, the diameter of the inscribing circle of the transparent substrates  15  becomes equal to the diameter of the circular shape. As explained herein, in the case where the shape of the transparent substrate  15  having a hexagonal shape, an octagonal shape, or a circular shape, the contacting portion between the transparent substrate  15  and the sleeve  9  forms a ring shape which is seamless in its entire circumference and the transparent substrate  15  does not have to be large in size. 
     This will be again described with reference to  FIG. 4 . Places at which the rates of increase of the contacting areas is changed in the respective shapes of the transparent substrates  15  are shown in  FIG. 4  (the place is indicated by the rhombuses in the graph). The shape of the contacting portion between the transparent substrate  15  and the sleeve  9  will form a seamless ring shape, when the transparent substrate is larger than the places. When the shape of the transparent substrate  15  is a circular shape, the contacting portion between the transparent substrate  15  and the sleeve  9  is naturally a ring shape which is always seamless, and therefore no rhombuses mark is shown. As shown herein, in the case when the transparent substrate  15  is a tetragonal shape, the contacting portion forms a seamless ring shape only after the diameter of the hole  17  provided in the holder  8  becomes 1.4 times as long as the inside diameter of the sleeve  9 . In contrast thereto, in the cases where the transparent substrates  15  having a hexagonal shape, an octagonal shape, and a circular shape, their shape of contacting portions that form seamless ring shapes are before the diameter of the hole  17  formed in the holder  8  becomes 1.2 times as long as the inside diameter of the sleeve  9 . 
     The transparent substrate  15  which has a polygonal shape may be obtained by segmentalizing a large-sized parallel planar substrate with a thickness equal to that of the transparent substrate  15  by a cutting work such as dicing or the like.  FIG. 5A  shows a dicing pattern for obtaining a hexagonal-shaped transparent substrate  15 , and  FIG. 5B  shows a dicing pattern for obtaining an octagonal-shaped transparent substrate  15 . In the case where the transparent substrate  15  has a hexagonal shape, a large-sized parallel planar substrate is segmentalized by cutting in three directions at an angle of 60 degrees to each other shown by A, B, and C in  FIG. 5A . In the case where the transparent substrate  15  has an octagonal shape, a large-sized parallel planar substrate is segmentalized by cutting in four directions at an angle of 45 degrees to each other shown by D, E, F, and G in  FIG. 5B . As described here, when the transparent substrate  15  is formed into an even-ordered polygonal shape such as a hexagonal shape or an octagonal shape, the processing is easier as the opposed sides facing each other (opposite sides) are respectively parallel to each other. 
     The circular transparent substrate  15  is obtained by segmentalizing the substrate by ultrasonic machining using free abrasive grains. The ultrasonic machining is shown in  FIG. 6 . The ultrasonic machining is a technique that a working fluid  22  in which abrasive grains are mixed into a solvent such as oil or water is added between a tool  23  vibrating vertically in ultrasonic frequency and a processing object. The tool  23  is pressed against the processing object with appropriate pressure force, then crushing the object by an impact of the abrasive grains, and the shape of the tool  23  is transcribed onto the processing object. An ultrasonic-vibrator  25  is built into the tool  23  via a joint called a horn  24 . Stainless steel, hard steel, hardened steel, or the like is used for the tool  23  as a material thereof. Further, carborundum, boron carbide, silicon carbide, or the like is used as abrasive grains. 
     As described above, in the case where the transparent substrate  15  has a polygonal shape such as a hexagonal shape or an octagonal shape which has the number of vertex more than five (pentagonal shape) and particularly an even-ordered polygonal shape, or has a circular shape, the contacting area with the sleeve  9  can be sufficiently large enough to lower the level of concentration of stress, even in the case where there is a limit in the size of the transparent substrate  15 . And therefore, this makes it possible to provide the optical receptacle  1  resistant to a vibration or an impact in the optical receptacle  1 . Further, even in the case where the contacting portion with the sleeve  9  is formed into a seamless ring shape in order to prevent damage to the transparent substrate  15 , the transparent substrate  15  can be formed relatively small in size, which may contribute to downsizing of the optical receptacle  1  and the optical module  4 . 
       FIG. 7A  is a cross-sectional view showing the optical receptacle  1  according to another embodiment of the present invention, and  FIG. 7B  is an enlarged sectional view of a part of  FIG. 7A . The optical receptacle  1  has the shell  10  and the transparent substrate  15  formed into a polygonal shape and disposed inside the insertion hole  20  provided in the holder  8 . The optical receptacle  1  according to the present embodiment is the same as the optical receptacle  1  of the embodiment shown in  FIG. 2  except for chamfered portions  31  which are formed onto the corner portions of a contacting surface of the transparent substrate  15 , the contacting surface being in contact with the bottom surface  20   a  of the insertion hole  20 . Because the difference of the present embodiment is at the chamfered portion  31  for the embodiment shown in  FIG. 2 , the descriptions common to the embodiment of  FIG. 2  thereof will be omitted. 
     As shown previously, in the case where a vibration or an impact is applied to the optical receptacle  1 , the transparent substrate  15  may violently crash against the bottom surface  20   a  or the sleeve  9 . As shown in  FIGS. 8A and 8B , in the case where there is a chamfered plane area or rounded plane area  29  on the outer circumferential portion of the bottom surface  20   a  of the insertion hole  20 , the corners of the outer circumferential sides of the transparent substrate  15  may touch the chamfered plane area or rounded plane area  29 , and stress is concentrated on the corner portions of the transparent substrate  15 , that tends to cause defects therein. The chamfered plane area or rounded plane area can be brought about in the holder because the corner portion of a drilling machine or an end mill is not always at a right angle. When the chamfered portions  31  are formed onto the corner portions of the transparent substrate  15 , gaps are provided between the corner portions of the transparent substrate  15  and the inner surface of the insertion hole  20  as shown in  FIGS. 7A and 7B , thus the transparent substrate  15  does not contact the chamfered plane area or rounded plane area  29  created on the outer circumferential portion of the bottom surface  20   a , which avoid concentration of stress, that may cause little cracks or chips. 
     The transparent substrate  15  is pressed against the bottom surface  20   a  of the hole  17  provided in the holder B when the plug ferrule  3  is inserted into the optical receptacle  1 . However, in the case where the transparent substrate  15  is riding on the chamfered plane area or rounded plane area  29  as shown in  FIG. 8B , the transparent substrate  15  may be inclined to the insertion direction of the plug ferrule  3  in some cases Herein, the plug ferrule  3  to be inserted into the optical receptacle  1  is, as described above, subject to mirror polishing on its front edge face to be a curved surface, and the edge face of the optical fiber  6  disposed in the center of the plug ferrule  3  is disposed in the vicinity of the foremost end part of the plug ferrule  3 . 
     When the transparent substrate  15  is inclined to the insertion direction of the plug ferrule  3 , the physical contact (PC) between the transparent substrate  15  and the optical fiber  6  becomes unstable, which may caused by a gap between the transparent substrate  15  and the optical fiber  6 , to bring about a light reflection in some cases. In contrast thereto, when the chamfered portions  31  are formed onto the corner portions of the transparent substrate  15  as shown in  FIGS. 7A and 7B , the transparent substrate  15  does not run on the chamfered plane area or rounded plane area  29  created on the outer circumferential portion of the bottom surface  20  in any case, and is disposed so as to be perpendicular to the insertion direction of the plug ferrule  3 . Therefore, a stable physical contact between the transparent substrate  15  and the optical fiber  6  is possibly obtained. 
     As shapes of the chamfered portions  31  onto the corner portions of the transparent substrate  15 ,  FIG. 9  are perspective views showing the examples of various shapes of the chamfered portions  31 . Herein, the hexagonal shape is shown as a shape of the transparent substrate  15 . However, it is possible to apply the same chamfered portions  31  onto an octagonal shape and other shapes as well. 
     Herein, in  FIG. 9A , the chamfered portions  31  are formed only onto the corner portions of the transparent substrate  15 . In  FIG. 9B , the chamfered portions  31  are formed along the side of the transparent substrate  15  onto one of two adjacent sides so that chamfered sides of the chamfered portions  31  and non-chamfered sides are arranged alternately. Moreover, in  FIG. 9C , the chamfered portions  31  are formed onto an entire circumference of the transparent substrate  15 . 
     The chamfered portions  31  of the transparent substrate  15  shown in  FIG. 9A  are obtained by etching the corner portions of the transparent substrate.  15 . This is shown in  FIG. 10 . First, as shown in  FIG. 10A , a given patterned photoresist is applied onto the large-sized parallel planar substrate  21 . The shaded portions in the drawing are portions coated with the photoresist. Thereafter, the large-sized parallel planar substrate  21  is etched, and then the photoresist is washed out. The shaded portions shown in  FIG. 10B  are the etched portions. Next, as shown by the solid lines in  FIG. 10B , the parallel planar substrate  21  is segmentalized into a plurality of transparent substrates  15 . As a segmentalizing method, a cutting work such as dicing is appropriate. 
     Herein, the pattern of the photoresist shown in FIG.  10 A is designed such that the resist is not applied onto the portions corresponding to the corners of the transparent substrates  15  to be obtained by the process shown in  FIG. 10B , and the chamfered portions  31  are formed onto the corner portions of the transparent substrates  15  by etching. A favorable etching depth is to be comparable with a radius of curvature of the rounded plane area at the bottom surface of the holder  8 , which is desirably about several ten μm. 
     The shapes of the chamfered portions  31  of the transparent substrates  15  shown in  FIGS. 10B and 10C  are obtained by a cutting work such as dicing. By forming the chamfered portions  31  simultaneously with the process of segmentalizing the parallel planar substrate  21  with a cutting work, the chamfered portions  31  can be formed simply and economically. 
       FIG. 11A  shows a process example of the transparent substrates  15  shown in  FIG. 9B .  FIG. 11B  shows a cross-sectional shape of the processed portion. Herein, cutting lines A indicate cutting lines for segmentalizing the large-sized parallel planar substrate  21  into pieces, and cutting lines B shown by dotted lines indicate cutting lines for forming the chamfered portions  31  onto the transparent substrate  15 . The cutting depths of the cutting lines A and B are respectively different. The depth of the cutting lines A are deep enough to the thickness of the parallel planar substrate  21 , then the cutting lines A segmentalize the transparent substrate  15  into pieces. On the other hand, the depth of the cutting lines B is several ten microns from the surface, then the cutting lines B form grooves with shallower depth than the thickness of the parallel planar substrate  21 . The cutting lines B are formed along the cutting lines A so that the cutting lines B are in parallel with the cutting lines A and partially overlap with the cutting lines A in the width direction of the cutting lines A. In the transparent substrate  15  after the segmentalization, the cutting lines B are disposed on one of two adjacent sides and are arranged alternately. Thereby, the chamfered portions  31  are formed onto the corner portions and along the sides of the transparent substrates  15 . 
     The cutting lines A and B may be processed with a same dicing blade, so as to shift a position into which the dicing blade is inserted and change the cutting depth. 
       FIG. 12A  shows a process example of the transparent substrates  15  shown in  FIG. 9C . In the same manner as in  FIG. 11 , the cutting lines A indicate cutting lines for segmentalizing the large-sized parallel planar substrate  21  into pieces, and the cutting lines B indicate cutting lines for forming the chamfered portions  31  onto the transparent substrate. The cutting lines B are formed along the cutting lines A so that the cutting lines B are in parallel with the cutting lines A and partially overlap with the both sides of the cutting lines A, and in the transparent substrates  15  segmentalized into pieces, the cutting lines B which will be the chamfered portions  31  are disposed on its entire circumference. Thereby, the chamfered portions  31  are formed onto the entire circumference of the transparent substrates  15 . 
     A width of the cutting line is almost the same as a width of the processing blade used for cutting. The widths of cutting lines A and B in  FIGS. 10 and 11  are the same, but may be different from each other. In particular,  FIG. 11  shows the cutting lines B formed by two processes. However, the cutting lines B may be formed by one process by use of a blade having a width wider than a width of a blade for the cutting lines A. 
     However, since an additional process of changing the blades during a cutting step such as dicing is needed if the plural blades having the different widths are used, it is easier and desirable to shift the blade which can forma cutting line with a constant width. Further, the shape of transparent substrates  15  shown in  FIG. 9B  is more preferable than the shape shown in  FIG. 9C  in the light of less number of processes for forming the chamfered portions  31  onto the corner portions of the transparent substrate  15 . 
     As described above, in accordance with the optical receptacle  1  according to the one embodiment of the present invention, the chamfered portions  31  are formed onto the corner portions of the transparent substrate  15 , thereby the transparent substrate  15  will not be into contact with the chamfered plane area or rounded plane area  29  even when the chamfered plane area or rounded plane area  29  is created on the outer circumferential portion of the bottom surface  20   a , which makes it possible to provide the transparent substrate  15  which causes little chips by a vibration and an impact, and as a result, to provide the short-type optical receptacle  1  with mechanical endurance. Further, it is possible to bring the transparent substrate  15  into contact on its entire circumference with the bottom surface  20   a , as a result, the transparent substrate  15  is disposed in parallel with the bottom surface  20   a.    
     The example of the above-described embodiment shows the example in which the chamfered portions  31  are formed onto the surface on the side of the transparent substrate  15  contacting the holder  8 . However, the chamfered portions  31  may be formed onto the surface on the side of the transparent substrate  15  contacting the sleeve  9  as well. In this case, it is possible to increase the mechanical endurance to a crash against the sleeve  9 . 
     Other various embodiments relating to the configuration between the transparent substrate  15  and the case  5  (or the holder  8 ) will be hereinafter shown. 
       FIG. 13  shows an example of an embodiment of the optical receptacle  1  in which the bottom surface  20   a  of the insertion hole  20  is inclined to a plane perpendicular to the axis of the insertion hole  20 . Since the bottom surface  20   a  is formed into an inclined surface, the surface of the transparent substrate  15  in contact with the bottom surface  20   a  is formed into an inclined surface to an optical axis parallel to the axis of the insertion hole  20 . Therefore, A light signal emitted from the photon-electron or electron-photon conversion element  2  and reflected by the surface of the transparent substrate  15  will not become an incident light into the photon-electron or electron-photon conversion element  2  as a reflected returning light. 
     In this case, the rear edge face  9   a  of the sleeve  9  is formed into an inclined surface along the angle of inclination of the bottom surface  20   a . Further, the front edge face of the plug ferrule  3  as well is subjected to an angled PC process along the angle of inclination. Thereby, it is possible to have a good contact with the transparent substrate  15 . 
     In this case, it is preferable to provide a marking  18  indicating the direction of inclination of the bottom surface  20   a  on the outer side of the optical receptacle  1  or the optical module  4 . When the angled PC plug ferrule  3  is inserted so as to match the direction of inclination, it is possible to easily make a PC connection between the front end of the optical fiber  6  and the transparent substrate  15 . 
       FIG. 14  shows an example in which a transparent convex portion  15   b  is formed on the one surface of the transparent substrate  15  in place of the refractive index matching agent  21  shown in  FIG. 1 , and the transparent substrate  15  is disposed so as to bring the convex portion  15   b  inserted into the through hole  19 . In such an embodiment, since the through hole  19  is filled with the convex portion  15   b  having the same refractive index as the transparent substrate  15 , it is possible to reduce the reflection of light due to a refractive index difference. Further, when the surface of the convex portion  15   b  is formed into a slope face shape inclined to the plane perpendicular to the axial direction of the through hole  19 , it is possible to restrain light transmitted toward the through hole  19  from the photon-electron or electron-photon conversion element  2 , such as a light-emitting element, being reflected by the surface of the convex portion  15   b , to return to the photon-electron or electron-photon conversion element  2  as a returning light. 
       FIG. 15  shows an example of an embodiment of the optical receptacle  1  in which an elastic member  22  is further provided, so as to be disposed between the transparent substrate  15  and the bottom surface  20   a  of the insertion hole  20  of the case  5 . 
     In this case, the both surfaces of the elastic member  22  are disposed so as to respectively contact the transparent substrate  15  and the bottom surface  20   a  at predetermined pressures, and are disposed so as to be sandwiched by the transparent substrate  15  and the bottom surface  20   a . When the elastic member  22  is disposed between the transparent substrate  15  and the bottom surface  20   a , it is easy to bring the front edge face of the plug ferrule  3 , i.e., the front end of the optical fiber  6  and the transparent substrate  15  into good contact with each other with no influence thereon by a deviation from flatness or the like of the transparent substrate  15 , and therefore, it is possible to prevent reflection or loss of light at the connecting point. 
     The elastic member  22  may be formed of a resin or a spring. For example, a resin plate having elasticity formed of silicone resins, urethane resins, acrylic resins, fluororesins, or the like may be used. Or, a coil spring or a plate spring made of metal or resin, or the like may be used as the elastic member  22 . 
       FIG. 16  is a cross-sectional view showing an example of one embodiment of the optical receptacle  1  in which an optical isolator element  16  is disposed on the one edge face  5   a  on the outer side of the case  5  of the optical receptacle  1 . The optical receptacle  1  is different from the above-described respective optical receptacles  1  in the point that the optical isolator is further provided in the optical receptacle  1 , and the other configurations are the same. 
     The optical isolator is composed of the optical isolator element  16  and a cylindrical magnet surrounding the optical isolator element  16 , that inhibits passage of a reflected returning light returned from the side of the plug ferrule  3 . The optical isolator is disposed such that a Faraday rotator composing the optical isolator element  16  is located inside the cylindrical magnet. 
     The optical isolator element  16  is disposed so as to block the opening of the through hole  19  open in the one edge face  5   a  of the case  5  on the opposite side of the insertion hole  20 . Further, in the optical receptacle  1 , the inside of the through hole  19  is filled with the refractive index matching agent  21 . The refractive index matching agent  21  has a refraction refractive index matched to the refractive index of the transparent substrate  15  and the optical isolator element  16 , which reduces refraction and reflection of light between the transparent substrate  15  and the optical isolator element  16 . 
     It is preferable that, as shown in  FIG. 16 , a counterbore portion  5   b  is provided on the one edge face  5   a  of the case  5 , in which the optical isolator element  16  is disposed. It is possible to accurately dispose the optical isolator element  16  by positioning the optical isolator element  16  in the counterbore portion  5   b . Further, it is preferable that, as shown in  FIG. 16 , the counterbore portion  5   b  is inclined to the plane perpendicular to the optical axis, to incline the optical isolator element  16 . It is preferable that the counterbore portion  5   b  is inclined at, for example, 4 to 11 degrees to the plane perpendicular to the optical axis. 
     The following materials may be used for the respective parts of the optical receptacle  1 . 
     In the respective embodiments of the optical receptacle  1 , in the case where the optical receptacle  1  is used for the optical module  4 , in many cases, the optical receptacle  1  is welded to a case in which the photon-electron or electron-photon conversion element  2  (a light-emitting element or a light-receiving element) which is mounted in the optical module  4  is accommodated. Therefore, a weldable material such as stainless steel, copper, iron, or nickel is preferably used for the case  5  or the holder  8 . Among such materials, stainless steel is desirable from the standpoint of resistance to corrosion and weldability. Further, considering adhesiveness with solder, gold plating or the like may be applied onto the outer surface of the case  5  or the holder  8 . 
     In the case where the through hole  19  formed in the case  5  or the holder  8  need to be sealed in an airtight manner, it is possible to bring the transparent member  15  to adhere to the case  5  or the holder  8  with an organic adhesive such as epoxy resin, low-melting glass, or the like, to hermetically seal them. Since the hermetically-sealing is the purpose, for example, the outer circumferential surface of the transparent member  15  and the inner circumferential surface of the insertion hole  20  may be adhere to one another. 
     As the transparent member  15 , an inorganic material such as glass, quartz, or sapphire, or a resin material such as an acrylic resin, a polymethyl methacrylate (PMMA) resin, a polycarbonate resin, or a polyolefin resin is given as an example. However, any material which is light-transmissive is not limited thereto. In particular, glass is preferable because of inexpensiveness and durability, and even when the plug ferrule  3  is repeatedly brought into contact, it keeps durable. 
     As the sleeve  9 , zirconia ceramics, alumina ceramics, copper, or the like is used. It is preferable that a zirconia ceramic material is used from the standpoint of abrasion resistance. In addition, considering the insertability, it is desirable that the surface roughness of the inside diameter of the sleeve  9  has an arithmetic average roughness Ra=0.2 μm or less. It is desirable that a tolerance between the outside diameter of the plug ferrule  3  and the inside diameter of the sleeve  9  is 1 μm or less. With this configuration, the position of the optical fiber  6  accommodated in the plug ferrule  3  is disposed at a constant position even when the plug ferrule  3  is repeatedly inserted and pulled out, which leads to a stable optical connection. 
     The refractive index matching agent  21  may be any material having a refractive index comparable with that of the transparent substrate  15 . For example, acrylic resins, epoxy resins, vinyl resins, ethylene resins, silicone resins, urethane resins, polyamide resins, fluororesins, polybutadiene resins, polycarbonate resins, or the like may be used. Among these materials, acrylic resins and epoxy resins are preferable from the standpoint of humidity resistance, heat resistance, peeling resistance, and impact resistance. In addition, when a refractive index difference between the refractive index matching agent  21  and the transparent substrate  15  is 0.1 or less, it is possible to sufficiently reduce reflection of light due to a refractive index difference. 
     Next, the optical module  4  according to an embodiment of the present invention has any one of the above-described optical receptacles  1  as shown as typical examples in  FIGS. 2 ,  13 ,  14 ,  15 , and  16 . The optical module  4  is configured such that, for example, the package  12  in which the photon-electron or electron-photon conversion element  2  and a lens  12  are accommodated is joined to the outer side of the rear end part of the holder  8  via spacers  13  and  14 . Then, the optical fiber  6  and the photon-electron or electron-photon conversion element  2  are optically coupled via the transparent member  15  and the through hole  19  by inserting the plug ferrule  3  into the insertion hole  20 . In addition, the lens  11  disposed between the photon-electron or electron-photon conversion element  2  and the transparent substrate  15  is installed so as to focus on the core front end part of the optical fiber  6  brought into contact with the transparent substrate  15 . 
     In many cases, the optical receptacle  1 , the spacers  13  and  14 , and the package  12  are joined together by welding such as YAG laser welding. Therefore, as materials composing the package  12  and the spacers  13  and  14 , the same material as that of the holder  8  is preferable. 
     In the case where the optical module  4  is assembled with an adjustment to get a maximum optical coupling to the optical fiber  6 , an optical signal is focused to a spot size of about 10 μm in the vicinity of the front edge face of the optical fiber  6  after passing through the lens  12 , the optical isolator element  16 , and the like. In this case, its optical output may fluctuate even a slight positional fluctuation of the spot by several μm. Therefore, in some cases, in the optical module  4 , its focal point may be shifted slightly back and forth to enlarge the spot size in the vicinity of the front edge face of the optical fiber  6  on purpose so that about 40% to 60% of the light output from the photon-electron or electron-photon conversion element  2  is optically coupled on the optical fiber  6 . 
     Since a reflected light generated on an optical surface of the transparent member  15  or the optical isolator element  16  on the side of the photon-electron or electron-photon conversion element  2  is returned as a returning light to the photon-electron or electron-photon conversion element  2  via the lens  11 , it is preferable that an anti-reflection coating (not shown) is applied onto the optical surface. 
     In this way, according to the receptacle type optical module  4  of the embodiment of the present invention, the inserted plug ferrule  3  is brought into contact with the transparent substrate  15 , and the inserted ferrule  3  is placed at the constant position in the insertion direction. The transparent substrate  15  is supported by the case  5  or the holder  8 , and the transparent substrate  15  is placed at a constant position by inserting the plug ferrule  3 , which provides the optical module  4  having the excellent optical characteristics. The excellent optical module  4  having good reliability can be provided even in the case where the plug ferrule  3  is repeatedly inserted and pulled out, or in a high-temperature and humidity environment. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 : Optical receptacle 
           2 : Photon-electron or electron-photon conversion element 
           3 : Plug ferrule 
           4 : Optical module 
           5 : Case 
           6 : Optical fiber 
           8 : Holder 
           9 : Sleeve 
           10 : Shell 
           11 : Lens 
           12 : Package 
           13 ,  14 : Spacer 
           15 : Transparent substrate 
           17 : Hole 
           18 : Marking 
           19 : Through hole 
           20 : Insertion hole 
           20   a : Bottom surface 
           31 : Chamfered portions