Abstract:
A prism  11  is formed which has a first face  11   a  opposing an end face of an optical fiber  21  and receiving a light-to-be-received from the optical fiber, second and third faces  11   b  and  11   c  adjoining opposite ends of the first face  11   a  at right angles and opposing each other, a fourth face  11   d  for reflecting the light-to-be-received from the face  11   a  toward the face  11   b , and a fifth face  11   e  reflecting a light-to-be-transmitted as projected from a light source through the face  11   c  toward the face  11   a . First and second light-to-be-received converging lenses  12  and  13  are disposed on the faces  11   a  and  11   b  of the prism  11  and first and second light-to-be-transmitted converging lenses  14  and  15  are disposed on the faces  11   a  and  11   c . The tilt angles β 1  and β 2  of the faces  11   d  and  11   e  with respect to the optical fiber axis  21   a  are less than 45°. With this configuration, if the light-to-be-received enters the light-receiving element  22  and the light-emitting element  23  and is reflected by these elements, such reflected light is prevented from returning back into the optical fiber whereby occurrence of far-end crosstalk can be suppressed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an optical component for use in two-way optical communication in which transmission and reception of light are effected through a single optical fiber, and an optical transmitter-receiver constructed by the use of the optical component. 
     2. Description of the Related Art 
       FIGS. 6A and 6B  illustrate a previous optical component (which will be referred to as previous device hereinafter) of the type concerned which has been devised in the factory facilities of the assignee of the present patent application, although not publicly known and from which the present invention originated, and an optical transmitter-receiver constructed by incorporating the component therein together with an optical fiber and light-receiving and light-emitting elements. This previous device will be described below as an example of comparison merely for facilitating of the understanding of the present invention. 
     In the previous device illustrated, the optical component  10  is constructed by using a prism  11  of pentagular shape (five-sided polygon) in cross-section having first to fifth operative faces  11   a - 11   e  which take part in optical transmission and reception. These first to fifth operative faces  11   a - 11   e  are all formed perpendicular to the plane of the drawing of  FIG. 6A  and have respective opposite ends perpendicular to the plane of the drawing. It should be noted, of course, that the prism has end faces  11   g  and  11   h  parallel to the plane of the drawing (see  FIG. 6B ). 
     One end of the first face  11   a  of the prism  11  and one end of the second face  11   b  adjoin each other at a corner Pab such these faces  11   a  and  11   b  form a right angle and similarly the other end of the first face  11   a  and one end of the third face  11   c  adjoin each other at a corner Pac such these faces  11   a  and  11   c  form a right angle. It is thus to be understood that the second face  11   b  and the third face  11   c  oppose each other in parallelism. 
     The other end of the second face  11   b  of the prism  11  and one end of the fourth face  11   d  adjoin each other at a corner Pbd, and the other end of the third face  11   c  and one end of the fifth face  11   e  adjoin each other at a corner Pce. 
     Further, the other end of the fourth face  11   d  and the other end of the fifth face  11   e  adjoin each other at a corner P, and the fourth face  11   d  and the fifth face  11   e  are recessed inwardly from the corners Pbd and Pce toward the first face  11   a  and form a V-shape as viewed in  FIG. 6A . That is, the corner P at which the fourth face  11   d  and the fifth face le adjoin each other is located adjacent the first face  11   a  closer than the corners Pbd and Pce are. 
     The first face  11   a  and the second face  11   b  of the prism  11  are formed integrally with first and second condensing lens  12  and  13 , respectively for light-to-be-received, and further the first face  11   a  and the third face  11   c  are formed integrally with first and second condensing lens  14  and  15 , respectively for light-to-be-transmitted. In addition, it is to be noted that the first light-to-be-received condensing lens  12  and the first light-to-be-transmitted condensing lens  14  provided on the first face  11   a  are partially cut away at planes perpendicular to the plane of the drawing such that the cut surfaces of those lens are joined together. 
     An optical fiber  21  has an end face  21   b  at its one end located adjacent and in opposition to the lens  12  and  14  formed on the face  11   a  and has its axis  21   a  coincide at a point of intersection between a first plane X (shown in a one-dotted chain line in  FIG. 6B ) passing through the coupled end surfaces (interface) between the first light-to-be-received condensing lens  12  and the first light-to-be-transmitted condensing lens  14  and the corner P and perpendicular to the plane of the drawing of  FIG. 6A  on one hand and a second plane Y (shown in a one-dotted chain line in  FIG. 6B ) passing through the centers of the lens  12 ,  13 ,  14  and  15  parallel to the plane of the drawing of  FIG. 6A  and orthogonal to the first plane X on the other hand. 
     With this arrangement, the upper half portion of the prism  11  located above the first plane X constitutes a receiving path while the lower half portion of the prism  11  located below the first plane X constitutes a transmitting path. 
     A light-receiving element  22  is positioned in opposition to the lens  13  on the face  11   b  with its center A 22  aligned with the central axis A 13  of the lens  13  while a light-emitting element  23  is positioned in opposition to the lens  15  on the face  11   c  with its center A 23  aligned with the central axis A 15  of the lens  15 . It is also to be noted that the light-receiving element  22  and the light-emitting element  23  are oppositely positioned in parallel. 
     In this example, the light-receiving element  22  and the light-emitting element  23  are both mounted on a reed frame  24  and resin-encapsulated in transparent resin. In the drawing,  24  indicates the reed frame and  25  an encapsulating resin. This encapsulating resin has a lens portion  25   a . The light-emitting element  23  may be a laser diode (LD) or a light-emitting diode (LED), for example, and the light-receiving element  22  may be a photodiode (PD), for example. 
     As shown in  FIG. 6A , a light  31  to be received which has been emitted from the end face  21   b  of the optical fiber  21  is condensed through the light-to-be-received condensing lens  12  prior to entering the prism  11  through the face  11   a  and is then reflected by the face  11   d  to be directed at the face  11   b , followed by being condensed through the light-to-be-received condensing lens  13  before entering the light-receiving element  22 . In this regard, the lens portion  25   a  of encapsulating resin aids the light-receiving element in condensing the light. 
     On the other hand, a light  32  to be transmitted which has been emitted from the light-emitting element  23  is condensed by the light-to-be-transmitted condensing lens  15  prior to entering the prism  11  through the face  11   c  and is then reflected by the face le to be directed at the face  11   a , followed by being condensed through the light-to-be-transmitted condensing lens  14  before entering the end face  21   b  of the optical fiber  21 . 
     It is thus to be appreciated that in the illustrated example the arrangement is such that transmission and reception of light is effected through a single optical component  10 . 
     It should be here appreciated that in this type of optical component in charge of both transmission and reception of light, crosstalk is a great concern with respect to its performance and that it is a significant problem to suppress the crosstalk. 
     Crosstalk in the optical component of the type concerned means that light being transmitted leaks into the receiving side in this side station and enters a light-receiving element in this side station. Particularly, crosstalk ascribable to reflection at an optical interface in the parting area between the receiving path and the transmitting path in this side station or at a proximal end face of the optical fiber is called near-end crosstalk. 
     In contrast, crosstalk ascribable to reflection at an optical interface in the parting area between the receiving path and the transmitting path in the other side (opponent&#39;s) station or at a distal end face of the optical fiber or at the faces of a light-receiving element and light-emitting element in the other side station is called far-end crosstalk. The optical component  10  shown in  FIGS. 6A and 6B  and the optical transmitter-receiver constructed by combining the optical component  10  with the light-receiving element  22  and the light-emitting element  23  in the illustrated arrangement has been found to have the construction apt to cause especially far-end crosstalk. That is, the previous device described above cannot avoid causing crosstalk. More specifically, it has been found as a result of researching into the cause of such crosstalk that as shown in  FIG. 7 , since the tilt angles α 1  and α 2  of the faces (reflective faces)  11   d  and  11   e , respectively relative to the plane X passing through the corner P and the axis  21   a  of the optical fiber  21  and perpendicular to the plane of the drawing are both set to be relatively large, say at 45°, the light  31  to be received may enter the respective faces  22   a  and  23   a  of the light-receiving element  22  and the light-emitting element  23  and the light reflected by these element faces may again follow the path along which it has entered before back into the optical fiber  21  so that it is apt to cause far-end crosstalk in the other side station. 
     In addition, since the light-receiving element  22  and the light-emitting element  23  are both positioned in direct opposition to the lens  13  and  15 , respectively and the centers A 22  and A 23  of those elements are aligned with the central axes  13   a  and  15   a  of the lens  13  and  15 , respectively, the previous device are constructed in this respect as well such that the light reflected by these element faces may again follow the path along which it has entered before back into the optical fiber  21 , tending to cause far-end crosstalk in the other side station. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing situation, it is an object of this invention to provide an optical component for two-way optical communication which is configured to significantly reduce far-end crosstalk, and an optical transmitter-receiver having such optical component incorporated therein. 
     In accordance with a first aspect of the present invention, an optical component for use in two-way optical communication in which transmission and reception of light are effected through a single optical fiber is provided, the component comprising an optical prism: first and second light-to-be-received condensing lens; and first and second first light-to-be-transmitted condensing lens; the optical prism having a first face opposing an end face of an optical fiber; second and third faces each adjoining the first face at substantially right angles and opposing each other in parallel; a fourth face adjoining the second face and adapted to reflect a light to be received which has entered through the first face and direct it toward the second face; and a fifth face adjoining the third face and adapted to reflect a light to be transmitted which has entered through the third face and direct it toward the first face; the fourth and fifth faces adjoining each other and the junction therebetween being positioned closer to the first face than the junction where the fourth face adjoins the second face and the junction where the fifth face adjoins the third face are. The first and second light-to-be-received condensing lens are formed integrally with the first and second faces, respectively and the first and second light-to-be-transmitted condensing lens are formed integrally with the first and third faces, respectively. In addition, tilt angles of the fourth and fifth faces relative to the axial direction of the optical fiber are selected to be less than 45°. 
     In accordance with another aspect of the present invention, the tilt angles are selected to be in the range of 30° to 40°. 
     In accordance with yet another aspect of the present invention, the joint of the fourth face with the first face and the joint of the fifth face with the first face are offset from each other in the axial direction and the two joints are interconnected by a sixth face extending parallel to the axial direction. 
     In accordance with still another aspect of the present invention, an optical transmitter-receiver for two-way optical communication is provided which comprises: the aforesaid optical component for two-way optical communication; a light-receiving element positioned at a position offset from the center of the frontal face of the second light-to-be-received condensing lens on the second face in the axial direction away from the first face and having a receiving face oriented parallel to the axial direction so as to receive the light to be received which is emitted from the lens on the second face; and a light-emitting element positioned at a position offset from the center of the frontal face of the second light-to-be-transmitted condensing lens on the third face in the axial direction away from the first face and having an emitting face oriented parallel to the axial direction so as to have the light to be transmitted enter the third face. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1  illustrate one embodiment of the optical component according to this invention and the optical transmitter-receiver utilizing the component, wherein  FIG. 1A  is a side view looking in the direction A in  FIG. 1B ; and  FIG. 1B  is a front view looking in the direction B in  FIG. 1A ; 
         FIGS. 2A-2E  illustrate a modified form of the optical component shown in  FIGS. 1A-1B  and the optical transmitter-receiver utilizing the same, wherein  FIG. 2A  illustrates the manner in which light is received through this modified form of the optical component;  FIG. 2B  is a side view of this modified form of the optical component;  FIG. 2C  is a front view thereof; and  FIG. 2D  is a bottom view, and  FIG. 2E  illustrates the manner in which light is transmitted through this modified form of the optical component; 
         FIG. 3A  illustrates the manner in which light being received is reflected at the operative faces of the light-receiving and light-emitting elements in the configuration shown in  FIGS. 2A-2E ; 
         FIG. 3B  illustrates the manner in which light to be transmitted reaches the element face of the light-receiving element in the configuration shown in  FIGS. 2A-2E  to thereby cause near-end crosstalk; 
         FIGS. 4A and 4B  are side views of another embodiment of the optical component according to this invention; 
         FIG. 5  is a bottom view illustrating the optical component shown in  FIGS. 2A-2D  being incorporated in an optical connector; 
         FIGS. 6A and 6B  illustrate a previous optical component according to the technology closest to the present invention and how light is transmitted and received through the component, wherein  FIG. 6A  is a side view and  FIG. 6B  is a front view; and 
         FIG. 7  illustrates the manner in which light to be received is reflected at the element faces of the light-receiving and light-emitting elements in the configuration shown in  FIGS. 6A and 6B  to thereby cause far-end crosstalk. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of this invention will now be described by way of example with reference to the accompanying drawings, in which the parts which correspond to those shown in  FIGS. 6A-6B  are designated by like reference numerals and will not be discussed again in detail. 
       FIGS. 1A-1B  illustrate one embodiment of the optical component  40  for two-way optical communication according to this invention and the optical transmitter-receiver constructed by combining the optical component  40  with a light-receiving element  22  and a light-emitting element  23 . In this example, the optical component  40  comprises a prism  11  having a pentagular shape in cross-section generally similar to that of the prism  11  of the optical component  10  shown in  FIGS. 6A-6B  and having lens  12 - 15  formed integrally on the faces. In  FIG. 1A , the one-dotted chain line indicates an axis  21 A of an optical fiber  21  positioned in conjunction with the optical component  40 . 
     The prism  11  of this embodiment differs from that of the previous device in that the tilt angles β 1  and β 2  which the face  11   d  constituting a reflective face on the receiving side and the face  11   e  constituting a reflective face on the transmitting side form with respect to the plane X containing the optical fiber axis  21   a , passing through the joint surface between the cut-away surfaces  12   a  and  14   a  of the lens  12  and  14 , respectively as well as the corner P and perpendicular to the plane of the drawing are both less than those (α 1  and α 2 ) of the previous device, that is, set at an angle less than 45°, preferably selected to be in the range of 30° to 40°. 
     In the embodiment of  FIG. 1 , the axis  21   a  of the optical fiber  21  positioned adjacent and in opposition to the lens  12  and  14  on the face  11   a  of the prism  11  is aligned with a point of intersection between the plane X (shown in a one-dotted chain line in  FIG. 1B ) passing through the joint (interface) between the lens  12  and  14  and the corner P and perpendicular to the plane of the drawing of  FIG. 1A  on one hand and the plane Y (shown in a one-dotted chain line in  FIG. 1B ) passing through the centers of the lens  12 ,  13 ,  14  and  15  parallel to the plane of the drawing of  FIG. 1A  on the other hand, as shown in  FIG. 1A  and as in the previous device shown in  FIG. 6B . 
       FIGS. 1A-1B  illustrate the optical transmitter-receiver constructed by combining the optical component  40  with the light-receiving element  22  and the light-emitting element  23  and the manner in which this optical transmitter-receiver is used to carry out transmission and reception of light. 
       FIGS. 2A-2E  illustrate a modified form  40 ′ of the optical component  40  and an optical transmitter-receiver by combining the optical component  40 ′ with a light-receiving element  22  and a light-emitting element  23  and the manner in which this optical transmitter-receiver is used to carry out transmission and reception of light. 
     In this modified embodiment, the axis  21   a  of the optical fiber  21  positioned adjacent and in opposition to the lens  12  and  14  on the face  11   a  of the prism  11  is aligned with a point offset by a distance d toward the lens  12  from the plane X (shown in a one-dotted chain line in  FIG. 2B ) passing through the joint (interface) between the cut-away surfaces of the lens  12  and  14  as well as the corner P and perpendicular to the plane of the drawing of  FIG. 2A  as shown in  FIG. 2B , instead of being aligned with the plane X. 
     While in the previous device the central vertical axis A 22  of the light-receiving element  22  is positioned so as to be in alignment with the central axis A 13  of the lens  13 , it is to be noted in both of the embodiment of  FIG. 1  and the modified embodiment of  FIG. 2  that the light-receiving element  22  is positioned such that the center A 22  of the light-receiving element  22  is offset with respect to the center of the frontal face of the lens  13 , that is, the axis A 13  of the lens  13  by a distance dl in the direction of the axis  21   a  in the plane Y away from the face  11   a  of the prism  11 , rather than being aligned with the center of the frontal face of the lens  13 . 
     Similarly, the light-emitting element  23  is also positioned such that the center A 23  of the light-emitting element  23  is offset with respect to the axis A 15  of the lens  15  by a distance d 2  in the direction of the axis  21   a  in the plane Y away from the face  11   a  of the prism  11 , rather than being aligned with the center of the frontal face of the lens  15 . 
     Further, it should be noted that the light-receiving element  22  and the light-emitting element  23  have their element faces  22   a  and  23   a , respectively both oriented parallel to the axis  21   a.    
     In operation, as shown in  FIGS. 1A and 2A , a light  31  to be received which has been emitted from the end face  21   b  of the optical fiber  21  is collected through the lens  12  prior to entering the prism  11  and is then reflected at the face  11   d  to be directed at the face  11   b , followed by being condensed through the lens  13  before entering the light-receiving element  22 . In this regard, since in the present invention the angles β 1  and β 2  which the reflective faces  11   d  and  11   e , respectively of the prism  11  form with respect to the plane X containing the central axis  21   a  of the optical fiber  21  are selected to be less than 45°, the light  31  to be received as introduced parallel to the central fiber axis  21   a  is caused to obliquely enter the element face  22   a  of the light-receiving element  22 , as shown in  FIG. 2A . 
     Similarly, a light  32  to be transmitted which has been emitted from the light-emitting element  23  obliquely enters the lens  15  and is condensed by the lens  15  prior to entering the prism  11  and is then reflected at the face  11   e  to be directed at the face  11   a , followed by being condensed through the lens  14  and finally entering the end face  21   b  of the optical fiber  21 . 
     It will be appreciated that the optical component  40  or  40 ′ constructed as described above and the optical transmitter-receiver having such optical component incorporated therein and arranged in association with the light-receiving element  22  and the light-emitting element  23  as described above allow for significantly reducing far-end crosstalk which was a problem with the prior art. 
     Specifically, since the tilt angles β 1  and β 2  of the faces (reflective faces)  11   d  and  11   e  are set to be less than 45°, and more gentle than those (α 1 =45°, α 2 =45°) of the previous device, the light  31  to be received as reflected by these reflective faces  11   d  and  11   e  will travel rearwardly of the lens  13  and  15  (in a direction away from the face  11   a ) to obliquely enter the respective faces  22   a  and  23   a  of the light-receiving element  22  and the light-emitting element  23  which are located rearward of the lens  13  and  15 , as shown in  FIG. 3A , so that the light reflected by these element faces  22   a  and  23   a  will travel further rearwardly, as shown in  FIG. 3A . 
     Consequently, the path along which the light travels after being reflected at the element faces  22   a  and  23   a  is parted from rather than close to the path along which the light has initially entered the prism. That is, the configuration according to this invention prevents the reflected light from again following the path along which it has entered before back into the optical fiber  21  as is the case with the previous device, which otherwise would lead to occurrence of far-end crosstalk. It is thus to be appreciated that this invention provides for significantly reducing far-end crosstalk. 
     In addition, it should be noted that in the embodiment shown in  FIGS. 2A-2E  and described above, the configuration is such that the axis  21   a  of the optical fiber  21  is positioned on the side of the lens  12  and that the area of the opening of the light-receiving path is made larger than the area of the opening of the light-transmitting path so that a greater amount of light  31  to be received may enter the light-receiving element  22 . This is an optical arrangement favorable for reception of light. 
     In this regard, if the light-receiving element  22  and the light-emitting element  23  are changed in position with each other in  FIGS. 2A-2E , an optical system favorable for transmission of light may be provided. It may be determined which of the two alternative arrangements should be selected appropriately, taking into account the performance of the light-receiving element  22  and the light-emitting element  23 , for example. 
     While the embodiment and its modified example described above are capable of suppressing far-end crosstalk as compared with the previous device owing to the tilt angles β 1  and β 2  of the faces  11   d  and  11   e  being set to be less than 45°, another embodiment of the optical component which is configured to allow for reducing near-end crosstalk as well as far-end crosstalk will be described with reference to  FIGS. 4A and 4B . 
     Before proceeding with describing the another embodiment, it will be explained with reference to  FIG. 3B  how near-end crosstalk may occur in the prism  40 ′ in the modified example described above. 
       FIG. 3B  includes a duplicate of  FIG. 2E . If we define an effective transmitting path through which such a portion of the light-to-be-transmitted as emitted from the light-emitting element  23 , is reflected at the reflective face  11   e  and thereafter enters through the face  11   a  into the optical fiber  21  in  FIG. 3B , what is shown as the light-to-be-transmitted  32  in  FIG. 2E  exactly corresponds to the light passing through that defined effective transmitting path. There is, however, another portion of the light-to-be-transmitted as emitted from the light-emitting element  23  which has missed being collected by the second light-to-be-transmitted converging lens  15  deviates from the effective transmitting path, goes beyond the corner P, interferes directly into the receiving path, and is reflected back by the face  11   a  and the front side interface of the first light-to-be-received converging lens  12  as a leakage light  33  (shown in dotted lines) which may possibly be received directly into the light-receiving element  22  without either engaging the reflective face  11   d  or passing through the first light-to-be-received converging lens  13  on the receiving side. This is a cause of near-end crosstalk. 
     In this regard, an optical component  50  illustrated in  FIG. 4A  is still another embodiment further improved according to this invention. This optical component  50  is configured such that a face  11   d  which is a reflective face on the receiving side and a face  11   e  which is a reflective face on the transmitting side does not define a V-shape therebetween, that is, they do not adjoin each other at a corner P, but instead are offset in the direction of the optical fiber axis  21   a . Specifically, in this example, a joint P 2  of the face  11   e  with the face  11   a  is located at a position spaced apart from a joint P 1  of the face  11   d  with the face  11   a  in the direction of the optical fiber axis  21   a  away from the face  11   a  and the two joints P 1  and P 2  are interconnected by a sixth face  11   f  extending parallel to the direction of the optical fiber axis  21   a.    
     With the optical component  50 , as will be appreciated if one considers the operation of a device incorporating therein the optical component  50  in substitution for the optical component  40 ′ in  FIG. 3B , that portion of the receiving path shaded as viewed from the light-emitting element  23  positioned on the lens  15  side is increased by the provision of the face  11   f . Consequently, a portion of the leakage light  33  is prevented from interfering into the receiving path by the corner P 1 , whereby occurrence of near-end crosstalk and stray light may be correspondingly much more suppressed than the optical components  40  and  40 ′. 
     As is opposed to the configuration illustrated in  FIG. 4A ,  FIG. 4B  illustrates an optical component  60  configured such that a joint P 2  of the face  11   e  with the face  11   a  is located at a position closer to the face  11   a  than a joint P 1  of the face  11   d  with the face  11   a  in the direction of the optical fiber axis  21   a  and the two joints P 1  and P 2  are interconnected by a sixth face  11   f  extending parallel to the direction of the optical fiber axis  21   a.    
     With this optical component  60 , since the light-emitting element is located away from the leakage light  33  which goes beyond the corner P and interferes directly into the effective transmitting path, near-end crosstalk and reception of stray light may be correspondingly suppressed, as is the case with the optical component  50  shown in  FIG. 4A . 
       FIG. 5  illustrates an example of a single-core optical connector  70  having incorporated therein an optical transmitter-receiver comprising the optical component  40 ′, the light-receiving element  22  and the light-emitting element  23 . In  FIG. 5 , the reference numeral  71  indicates a sleeve having an optical fiber plug inserted therein. 
     As is appreciated form the foregoing description, the optical component for two-way optical communication according to this invention allows for significantly reducing far-end crosstalk, and thereby enhancing reliability. 
     Further, the present invention provides for reducing near-end crosstalk in addition to far-end crosstalk, thereby providing an optical component for two-way optical communication having higher reliability.