Patent Publication Number: US-2010129033-A1

Title: Plug for a hybrid optical waveguide and electrical conductor arrangement, and method for its production

Description:
This application claims priority of PCT application PCT/CH2008/000211 having a priority date of May 9, 2007, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to a plug for a hybrid optical waveguide and electrical conductor arrangement. Furthermore, the invention relates to a corresponding production method. 
     BACKGROUND OF THE INVENTION 
     For connecting electrical conductors, particularly single mode electrical conductors made of fibers, lens plugs are generally used. These are built up in such a manner that they take over the light at the fiber ends with an exit angle that is typical for the fiber, collimate the beam of light with a ball lens and transmit the beam to the medium. In this manner one ensures that the light beam exiting from the ball lens is parallel. The parallel beam is received with a correspondingly equipped plug and is focused back into the fiber of the second cable by means of a similar ball lens. For receiving the fiber a ferrule is used, i.e. a tube made of ceramic, plastic or metal, and the ball lenses are embedded into a metallic body with correspondingly accurate boreholes. The ferrules align the fibers in centered manner with the ball lens. 
     If now a hybrid plug shall be produced, the prior art from which this invention sets out teaches using commercially available contacts for the electrical connection. 
     This solution has turned out to be disadvantageous. As a matter of fact, the plug consists of numerous highly precise components that need to be assembled preferably by handcraft and need to be measured correspondingly. The three principal materials that are built in (ceramics, glass, metal) have different thermal expansion coefficients. For this reason, the requirements concerning the accuracy of the individual components and of the assembled plug are very high. Moreover, because the light beam changes medium several times, each surface needs to be provided with an antireflection coating for the corresponding optical wavelength. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an improved plug for a hybrid optical waveguide and electrical conductor arrangement. 
     The invention is achieved by a plug for a hybrid optical waveguide and electrical conductor arrangement. A hybrid cable that is provided at the center thereof with a tube in which electrical conductors are arranged preferably coaxially, further comprises a plurality of optical waveguides. With this cable, data can be transmitted by means of the optical waveguides, whereas electrical energy, but of course also data, can be transmitted by means of the electrical conductor. The plug according to the present invention is attached to such a cable. The features of the invention primarily result in providing a simple production of the lens part and, further, an essentially temperature independent behavior with excellent optical transmission values. The temperature dependence (expansion coefficient) will be the same due to the identity of the polymer materials used, although it can differ by up to about 0.1%. In general, the refractive index will not be exactly identical: in case of using a quartz for the fiber (refractive index 1.478) and with the adopted polymer (refractive index 1.500), the difference is about 1.5%. In particular, the provisions of the invention lead to the result that the demanding production of ball lenses from costly and poorly reproducible glass material can be avoided. Moreover, the high precision mechanical processing and the high precision assembling of the individual components can be avoided. The plug of the present invention has good optical characteristics. This also allows the plug contacts to have good electrical properties. 
     It is advantageous if the mounting and centering part is produced from the same base material, preferably by means of injection molding. However, the mounting and centering part does not require the property of being optically transmitting because it does not, by itself, comprise any optical elements. 
     In order to be connectable with a preferably similar mating plug, the lens part further comprises a centering borehole for receiving the centering pin of the mating plug, and such a centering pin is adhesively bonded into a further centering borehole. 
     Because the outer surface of the lens optionally forms a transition to air, it is advantageous that the lenses are optically coated on the sides thereof that are directed away from the ferrules. 
     A fixed plug with optical characteristics that do not change, e.g. upon a temperature change, is obtained if the mounting and centering part is connected to the lens part by means of adhesive bonding. 
     In order to allow for an easy electrical connection, both the lens part and also the mounting and centering part each comprise a central feedthrough for said electrical connection. 
     It is particularly advantageous to provide force elements, preferably springs, by means of which the ferrules arranged in ferrule holders can be pressed against the lenses at the sides thereof adjacent to the mounting and centering part, so that an optical light contact without air crossover is formed. In this way the undesirable air crossovers of the light in the plug are avoided in any case. 
     According to a second aspect of the present invention, a method for producing a plug of the previously mentioned type is proposed. 
     The aforementioned elements to be used according to the invention, as well as those claimed and described in the following exemplary embodiments, are not subject to any particular conditions by way of exclusion in terms of their size, shape, use of material and technical design, with the result that the selection criteria known in the respective field of application can be used unrestrictedly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, advantages and features of the subject of the present invention are obtained from the following description of the corresponding drawings, in which inventive plugs for a hybrid optical waveguide and electrical conductor arrangement are explained by way of example. In the drawings, there is shown in: 
         FIG. 1  a representation of the optical body of a plug, in a plan view; 
         FIG. 2  a sectional view of the optical body of the plug according to  FIG. 1 ; 
         FIG. 3  a star-like cover for the optical body of the plug, in a plan view; 
         FIG. 4  a representation of the lens part of the optical body of the plug according to  FIG. 1 , in a sectional view; 
         FIG. 5  a representation of the electro contacting part of the plug according to  FIG. 1 , in a sectional view; 
         FIG. 6  a ferrule holder for use in the plug according to  FIG. 1 , in a sectional view; and 
         FIG. 7  a plug in a schematic representation with an empty centering borehole and a centering pin and a mating plug. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 1 and 2  a plug according to a preferred exemplary embodiment of the present invention is denoted in its entirety as 2.  FIG. 1  shows, as a plan view from the “open” side of the plug, the lenses  4  of a lens part  10  as well as the centering boreholes  6  and an insertion opening  8  for the insert  20  for the electrical connections. In the present exemplary embodiment, the plug is round and it is configured substantially flat towards the open side thereof. 
     The overall view of the plug in the sectional view of  FIG. 2  shows the three essential elements of the plug according to this exemplary embodiment, namely, the lens part  10  and the mounting and centering part  14 , into which are provided channels  12  for the ferrules  30  that are arranged in the ferrule holders  24 . In the lens part  10 , the channels  12  end directly below the lenses  4  so that the lenses  4  are configured as a transition between the channels  12  and the plug surface. 
     A further element of the plug is the star-like cover  16  ( FIG. 3 ), in which are provided recesses  18  as a passage for the ferrule  30  and the optical waveguides, respectively, and a centering borehole  6  and a recess  19  for the insert  20  for the electrical connections. 
       FIG. 4  shows the lens part  10  as a sectional view in detail. The ferrule  30  in the ferrule holders  24  ( FIG. 6 ) fit exactly into the channels  12 . 
     The electrical connection of the preferred exemplary embodiment is evident from  FIG. 5 . An insertion opening  8  for the insert  20  for the electrical connection extends through the lens part  10 , the mounting and centering part  14  and the star-like cover  16 . Said insert is formed as a conventional electrocontact—in the present example as an “IGUN flat contact” (HSS 120 230 A 3002 M 24 A). The “IGUN” sleeve  22  (KS 113 30 M2) has been shortened to 13 mm. 
     In the present exemplary embodiment it is intended that the entire plug is inserted into a metal sleeve that also serves as a second electrical pole (mass pole) for the electrical connection. This sleeve is not shown here and does not have any peculiarities with regard to the present invention. As shown in  FIG. 7 , the positioning in respect to a corresponding mating plug  34 , which in the present example is formed similarly, is achieved by the coupling of the centering boreholes and the centering pins  28 . 
     In the present exemplary embodiment, the plug is produced by individual injection molding of the lens part  10  from a transparent polymer, which in this case is a material that is commercially available under the trade name Topas® (Cycloolefin Copolymer from Ticona/Celenese), in such a manner that the lenses  4  are formed with the requisite shape upon injection molding. Thereafter, the mounting and centering part  14  is injection molded from the same base material, albeit in an opaque version. Into these two injection molded parts, centering pins  28  are first inserted into the corresponding centering boreholes  6  until the lens part  10  and the mounting and centering part  14  are positioned in an accurately fitting mode with respect to each other. Then, these two parts are glued together. The ferrule holders  24  are inserted into the channels  12  for the ferrules  30 , and, furthermore, the ferrules  30  are inserted into the insertion opening  8  of the electrical insert  20 , and the star-like cover  16  is placed upon and connected with the mounting and centering part  14 , for example by adhesive bonding or by screwing. By means of pressure springs  26  the ferrule holders  24  and correspondingly the ferrules  30 , and, finally, the optical waveguides are pressed against the lower side of the lenses  4 . Thereby, an optical connection without air crossover is formed between the optical waveguide and the lower side of the lens  4 . The surfaces of the lenses  4  are optically coated according to the intended wavelengths of the respective lightwaves that are to be guided through the optical waveguides. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               2  plug 
               4  injection molded lens 
               6  centering borehole 
               8  insertion opening for electrical connections 
               10  lens part 
               12  channel for ferrule 
               14  mounting and centering part 
               16  star-like cover 
               18  recess 
               20  insert for electrical connections 
               22  distance sleeve 
               24  ferrule holder 
               26  pressure spring 
               28  centering pin 
               30  ferrule 
               32  electrocontact element 
               34  mating plug