Patent Publication Number: US-2009238524-A1

Title: Apparatus for Thermal Connection of Optical Fibers, and Method for Thermal Connection of Optical Fibers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/EP2007/062347, filed Nov. 14, 2007, which claims priority to German Application No. 102006056398.0, filed Nov. 29, 2006, both applications being incorporated herein by reference. 
    
    
     FIELD 
     The disclosure relates to an apparatus for thermal connection of at least two optical fibers. The disclosure also relates to a method for thermal connection of respective ends of at least two optical fibers. 
     TECHNICAL BACKGROUND 
     Apparatuses for connection of optical fibers by means of heat influence are referred to as splicers. In splicers, the fiber ends of the optical fibers to be connected are heated, as a result of which they are fused to one another. The fusion process is also referred to as splicing. Different attenuations can occur within the connection, depending on the position of the two optical fibers with respect to one another and further parameters such as the splicing temperature or splicing time that is used. It is, of course, desirable for the resultant attenuation after a splicing process to be as low as possible, in order to avoid unnecessarily reducing the signal quality. 
     In order to improve the quality of a spliced connection such as this, it is known for the ends of the optical fibers to be spliced to be aligned accurately with respect to one another. By way of example, an arc, a corona discharge, a laser beam or some other form of a heat source is then used to melt the fiber ends before joining them together. 
     Electromechanical motors or piezoelectric elements, inter alia, can be used for the alignment or positioning of the two fiber ends with respect to one another. Each of the respectively used positioning types has its own positioning accuracy. For example, stepping motors and the associated step-down conversion are available at low cost, but the positioning accuracy of this mechanism is less than that of piezoelectric elements. 
     Splicers have recently been required which can be produced at low cost and are intended to be as reliable as possible during use, simple to operate, and to require little maintenance. The splicers are generally designed to be portable and are frequently used for installation of optical fibers in buildings. Portable splicers frequently have no complex and accurate positioning mechanism, for cost reasons. Other splicers, for example as known from U.S. Pat. No. 6,230,522, use a complex recording and alignment electronics in order to ensure that the optical fibers are aligned as accurately and reproducibly as possible with respect to one another at the start of a splicing process. To this end, the actual splicing process is then carried out using a fixed splicing current, and for a fixed splicing time. 
     Irrespective of the splicer that is used, the increasingly stringent requirements for signal quality make it necessary to further reduce the attenuation caused by the splicing process between different optical fibers. It is therefore desirable to provide an apparatus of the type mentioned initially, by means of which the quality of a thermal connection of two optical fibers can be improved further. At the same time, it should still be possible to operate the apparatus easily. A further aim is provide a method which offers a better splice quality. 
     SUMMARY 
     One embodiment of the present application provides for two positioning units to be provided in an apparatus for thermal connection of at least two optical fibers, with one optical fiber being associated with each of these positioning units. The positioning units are designed such that the ends of the two optical fibers can be moved relative to one another to a position which allows thermal connection. A device having a first component and a second component is provided for the heating which is required for the thermal connection of the ends of the first and second optical fibers. The two components are arranged along one axis. 
     In order to improve the quality of a thermal connection of the two optical fibers, an observation device is provided, by means of which the distance of the end of at least one of the at least two optical fibers from at least one of the components of the device for heating can be determined. Alternatively, it is possible to determine the distance from the axis along which the components of the device are arranged. The observation device is coupled to a control apparatus, which is designed for adjustment of at least one control parameter for the device for thermal connection, as a function of the distance. 
     The position of the ends of the two fibers relative to a heat source is recorded for the process of thermal connection. This allows the distance of the two ends of the optical fibers from the heating source to be determined accurately. The distance is taken into account in the adjustment of control parameters which are important for the splicing process. Furthermore, it is possible to use the existing positioning units together with the observation device to additionally determine the two ends of the optical fibers relative to one another. This further improves the quality of the spliced connection. 
     In one embodiment, a memory is provided in the control device, in which memory values are stored which represent a predetermined relationship between a possible distance and the at least one control parameter. Alternatively, the control apparatus or the memory may have an appropriate calculation rule which provides a relationship between values of possible distances and the at least one control parameter. This makes it possible to select from a multiplicity of possible settings of a control parameter those parameters which are optimum for the respective distance. Further control parameters may now be selected, by means of which the heat source is then operated for the actual process of connecting the two optical fibers. Alternatively, when an already known calculation rule is used, it is possible to determine the optimum value of one or more control parameters directly from the determined distance. 
     In one embodiment, the at least one control parameter is linked, for example, to a supply current of the heat source or to an amount of heat produced by the heat source. It is likewise possible to adjust the time duration during which the fiber ends are heated, as a function of the determined distance. In addition, different temperature ranges can be selected as a function of the determined distance for the process of connecting the fiber ends. Further options are to adjust a pre-splicing current for the heating of the fiber ends, and/or the time duration for heating of the fiber ends, before the actual connection process, with the aid of the at least one control parameter. 
     In one embodiment, the positioning units can be fixed in position with respect to one another by evaluation of the distance of the two optical fibers from the heat source or from an axis along which the heat source or components of the heat source is or are arranged. The proposed apparatus can therefore also be used in simple appliances without complicated positioning elements. 
     In another embodiment, the heat source comprises a pair of electrodes which are arranged along the axis. In another embodiment, again, the heat source contains a laser device which produces a laser light beam along the axis. It is likewise possible for a resistance wire or heating wire to be provided as the heat source. This is arranged along the axis. 
     In another embodiment, a heat source is provided which has two components arranged along one axis. The two optical fibers to be connected are positioned relative to one another such that they can be connected by heat influence with the aid of the heat source. An image of the ends of the at least two optical fibers with respect to the axis is then recorded. This image is used to determine the distance of at least one end of the two optical fibers from the axis. A value is produced from this, which indicates a dependency between a possible distance and a control parameter which influences the heat produced by the heat source. The heat source is then operated as a function of the control parameter, in order to connect the ends of the at least two optical fibers to one another. The splicing process is controlled individually for each connection by operating the heat source with the aid of the control parameter from the determined distance. By way of example, this makes it possible to correct the different positions of the optical fibers with respect to the axis, thus producing a splice result which is independent of the distance. 
     The concepts will be explained in more detail in the following text with reference to a plurality of exemplary embodiments which are illustrated in the drawings. Components which have the same effect or the same function are provided with the same reference symbols in the various figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  shows an outline circuit diagram with essential elements of a splicer according to a first embodiment; 
         FIG. 2  shows an outline circuit diagram of a splicer according to a second embodiment; 
         FIG. 3  shows a view of a detail of the area of the splicer, in which the process of splicing the ends of the optical fibers is taking place; 
         FIG. 4  shows a view of a detail of a splicer according to a further embodiment; 
         FIG. 5  shows a view of a detail of a further embodiment; 
         FIG. 6  shows one exemplary embodiment for the procedure for one embodiment of a method for thermal connection. 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows a splicer for thermal connection of ends of two optical fibers  10 ,  11 . The two optical fibers  10 ,  11  are arranged opposite one another and fixed on positioning tables  30 ,  31 . The positioning table  31  can be moved along the y direction, for example with the aid of piezoelectric elements or electrical stepping motors, which are not illustrated here. Movement with the aid of an electrically operated stepping motor and a spindle, or some other step-up transmission, currently provides relatively high positioning accuracy. However, this is less than the positioning accuracy which can be achieved by piezo-ceramics, which is in the order of magnitude of about 0.06 μm to 0.01 μm. The stepping motor mechanism provides a positioning accuracy in the lowest case of 1 μm, and typically from 5 μm to 6 μm. The positioning table  30  can be moved in a corresponding manner along the x-direction. Furthermore, a plate  34  is provided for the positioning table  30 , with the aid of which the positioning table  30  and the optical fiber  10  fixed on it can be moved along the z-direction. 
     A heat source having the two components  40  and  41  is provided in order to produce the heat required for thermal connection of the two ends of the optical fibers  10  and  11 . The two components  40 ,  41  represent electrodes whose electrode tips are arranged specifically with respect to one another along an axis  43 . The two optical fibers  10 ,  11  are positioned between them and essentially at right angles to the axis. The electrodes are connected to an electrical power source  91  in order to operate the two electrodes  40 ,  41  and to supply them with the supply current which is required for production of an arc. 
     According to the embodiment shown in  FIG. 1 , the splicer has two cameras  50 ,  60  in order to accurately determine the distance of the optical fibers  11 ,  10 , from the axis  43  and to determine a relative position with respect to one another. In this case, the camera  50  is arranged along the x-direction and the camera  60  is arranged along the y-direction, such that they can record images from the area of the axis  43  of the heat source as well as the ends of the two optical fibers  10 ,  11  within the splicing area. To this end, light sources  51  and  61  are additionally provided opposite the cameras, for better illumination and in order to improve the contrast. The imaging cameras  50  and  60  are, for example, in the form of charge coupled devices (CCD). These cameras provide an image, resolved into pixels, in digital form for the evaluation control unit  63 . The control apparatus  64  is provided in order to operate the two imaging cameras  50  and  60  and the light sources  51  and  61 . 
     The images produced by the cameras  50  and  60  are passed on to the microprocessor  63 , where they are evaluated. The microprocessor sets the position of the optical fibers  10 ,  11  in conjunction with the position of the fixed-mounted cameras. The position of the fibers  10 ,  11  relative to one another and the distance of the two fibers from the axis  43  of the heat source can be determined accurately, taking account of the recording parameters of the position image. 
     During operation of the splicer, the positioning of the fibers  11 ,  10  with respect to one another, for example, is recorded for the splicing process such that the relative offset is reduced as much as possible. The fiber  10  is then moved along the z-direction, such that both fiber ends are now arranged symmetrically about the axis  43  of the heat source. 
     The distance of the fiber ends from the axis  43  is determined in order to improve the actual splicing process and therefore to reduce the attenuation losses after the two fiber ends have been connected. The microprocessor  63  passes this distance to a control apparatus  82  in which, in the present embodiment, a calculation rule is stored. The control apparatus  82  uses the calculation rule to produce a plurality of control parameters, in order to control the splicing process as a function of the determined distance of the two fiber ends from the axis  43 . By way of example, these control parameters include the time duration for a pre-splicing current in the two electrodes  40  and  41  for heating of the two optical fiber ends. Before being melted, the ends are heated for a certain time with the aid of the pre-splicing current, and are therefore prepared for the splicing process. 
     This makes it possible to take account of greater or lesser distances of the two fiber ends from the axis  43  during the heating of the two fiber ends which precedes the actual splicing process. Furthermore, the amount of heat and the splicing time for the splicing process that is then carried out are controlled as a function of the distance of the two fiber ends from the axis  43 . In addition, the offset of the two fiber ends, which is recorded by the cameras and is evaluated in the microprocessor  63 , with respect to one another is taken into account for the splicing process. 
       FIG. 2  shows an outline circuit diagram of a further embodiment of a splicer. In this splicer, the two positioning units  30  and  31  are fixed firmly in their position with respect to one another. Furthermore, they have two grooves  32  whose circumferences correspond to the external circumference of the two optical fibers  10  and  11 . The fibers are placed in the respective grooves  32  in the positioning units, and are fixed there. By way of example, the grooves  32  can be ground in ceramic or else can be etched in silicon, and are therefore accurate to small fractions of a micrometer, by virtue of the production technique. 
     In the present embodiment, the positioning units  30  and  31 , and therefore the grooves  32 , are arranged in exact positions with respect to one another. The positioning accuracy of the optical fibers  11 ,  10  which have been placed in the grooves is governed directly by the position of the fibers  10 ,  11  in the grooves  32 . The position of the optical fibers  10  and  11  can be changed manually. 
     In this case, the optical fibers are in the form of glass fibers with one or more light-carrying cores. Those ends of the optical fibers which are arranged in the splicing area originate from an optical waveguide  200 . The latter in each case comprises its jacket  100  or  110 , which is at a distance from the optical fibers  10  or  11 , outside the splicing area. The actual glass fiber is therefore exposed in the splicing area. All known types of optical waveguides are suitable as optical fibers, but in particular single-mode fibers or NZD fibers (non-zero-dispersion-shifted fibers). 
     The optical fiber  10  can be moved along its z-direction with the aid of a sliding table  34 , which likewise has a V-shaped groove. In addition, cameras  50  and  60  are arranged in the x-direction and z-direction, respectively. Lighting elements  51  and  61  are used for illumination, are associated with the imaging cameras  50  and  60  and illuminate the splicing zone  42 . 
     During operation, once the two optical fibers  10  and  11  have been fixed and positioned in the grooves  32  in the positioning units, the two cameras  50  and  62  produce a respective position image  52  and  62 . The two position images, which are supplied to a microprocessor  80  for further evaluation, can be used to determine the distance of the end of the optical fiber  11  from the two tips of the electrodes  40  and  41 . For a uniform splicing process of both ends, the position of the optical fibers  10  is now changed in the z-direction with the aid of the positioning unit  34 . The ends of the two optical fibers are arranged as far as possible at the same distance around the tips of the two electrodes  40  and  41  and at the same distance from the electrode tips. This results in the two fiber ends being heated uniformly. 
     Control parameters are selected from the memory  81  in the microprocessor  80 , as a function of the determined distance of the two fiber ends from the axis of the electrode tips. The pre-splicing current, the pre-splicing time duration, the splicing current or the time duration for the splicing process are now set for the subsequent splicing process with the aid of the control parameters. The splicing parameters are therefore controlled as a function of the distance of the fiber ends from the tips of the splicing electrodes, thus resulting in a splicing result which is independent of this distance. 
     There are several possible ways to determine the distance of the respective glass fibers or optical fibers from the heat source.  FIG. 3  shows one example, in which the arc which exists between two electrodes is used as a reference for determining the distance. The optical fibers  10  and  11  illustrated here are coated with a coating  100  and  200 , respectively. Furthermore, they each have a core  12 , whose refractive index is different from that of the glass jacket that surrounds them. The cores of the two optical fibers  10  and  11  are now aligned as exactly as possible with respect to one another. An arc is then briefly produced with the aid of the two electrodes  40  and  41 . This arc has a light intensity whose maximum should be located on a connecting axis between the tips  44  of the two electrodes  40 ,  41 . While the arc is being produced, an image is recorded with the aid of the two cameras. The distance of the ends of the optical fibers from the connecting axis between the tips of the two electrodes  40  and  41  can be determined from the intensity distribution and from the information about the ends of the two optical fibers  10  and  11 . 
       FIG. 4  shows a perspective view in the splicing area of a further exemplary embodiment. A heating wire  43   a  runs on the connecting axis between the tips  44  of the two elements  40  and  41 . This heating wire  43   a  is heated by current flowing through it, and thus forms the heat source. The heating current is supplied via the tips  44 . 
     The optical fiber  11 , with its core  12 , is arranged in a groove, which is not illustrated, in a positioning element, at a fixed distance d from the heating wire  43   a.  The cameras record an image of the position of the end of the optical fiber  11  from the tips  44  of the two electrodes and from the heating wire  43   a.  The distance d can be deduced from the recorded images. The optical fiber  10  is then moved along its z-direction until its distance d′ from the heating wire  43   a  corresponds to the distance d. The two ends of the optical fibers  10  and  11  are arranged at the end of the positioning process at the same distance around the wire  43   a.  The appropriate control parameters for the subsequent splicing process are calculated as a function of the distance d, and the thermal connection is thus produced. 
     By way of example, it may be expedient to provide a greater splicing current or longer splicing times if the distances are relatively great. Pre-splicing currents and/or pre-splicing times may also possibly be changed. In one alternative embodiment, for example, a pre-splicing time can also be used to determine the distance d and d′ of the optical fibers from the wire  43   a.  It is therefore possible to determine control parameters, by means of which the subsequent splicing process will be controlled, during the time period in which the two optical fibers are heated. 
       FIG. 5  shows a further perspective view of the splicing area in another embodiment of an apparatus. In this refinement, an auxiliary void  430  is additionally provided. This is arranged on the same plane as the connecting axes between the tips  44  of the two electrodes  40  and  41  and is essentially at right angles to the longitudinal direction of the optical fibers  10  and  11 . As illustrated here, the two optical fibers  10  and  11  are physically offset with respect to one another. This offset can be determined and reduced as much as possible during a positioning phase prior to the splicing process. Furthermore, the self-centering effect which occurs during the splicing process corrects any minor offset between the two ends of the optical fibers, thus resulting in a desired resultant attenuation of the light propagation. 
     In another embodiment, a laser beam is provided as the heat source. In this embodiment, the laser beam can be activated with as low an intensity as possible prior to the splicing process, for positioning and determining the distance of the two fiber ends from the laser beam. The image of the laser beam and the ends of the two optical waveguides with respect to one another can be recorded with the aid of a camera with accurate positioning thus being carried out. 
     Finally,  FIG. 6  shows a flowchart for one embodiment of a method for thermal connection of optical fibers. Once the optical fibers have been positioned and fixed in the positioning units, they are moved with respect to one another in step S 1 , and the ends of the two optical fibers are arranged roughly with respect to one another. In step S 2 , the imaging cameras record an image of the two ends of the fibers with respect to one another, and the position with respect to a heat source for the subsequent connection process. The recorded image is evaluated, in order to determine the position of the fiber elements in three-dimensional space. 
     A decision is then made in step S 3  as to whether the position of the fiber ends with respect to one another is below a predetermined threshold value. If this is not the case, a readjustment process must therefore be carried out, and the method is continued with a further iteration in step S 1 . If, in contrast, the predetermined limit value is undershot in step S 3 , the positioning of the fiber ends with respect to one another has been completed. The rest of the splicing process can then be continued in step S 4 . 
     There, another image of the fiber ends is now recorded with respect to an axis associated with the heat source. The distance of the two fiber ends from the heat source is determined with the aid of these records. 
     The determined distance is made to coincide in step S 5  with control parameters which are used for the subsequent splicing process. The splicing time or else the heat developed by the heat source is controlled with the aid of the control parameters. The process is then carried out in step S 6 , as a function of the distance and the positioning of the fibers with respect to one another. 
     The recording of another image in step S 4  after positioning of the fiber ends with respect to one another may also be omitted if the recording of an image of the fiber ends in step S 2  likewise includes the recording of the image of the fiber ends with respect to an axis which is associated with the heat source. The most recently recorded image of the splicing area before completion of the positioning steps is then used to determine the distance. In step S 5 , the control parameters are determined from the distance that has been determined in this way. 
     It is likewise possible, at least in some cases, to carry out the individual method steps during a pre-splicing process. In particular, it is possible to record an image of the fiber ends during a pre-splicing process in step S 4 . When an arc is produced or a laser beam is used during the pre-splicing process, the distance between the axis associated with the heat source and the fiber ends can thus be determined from the light intensity distribution and the fiber ends. An image can also be recorded particularly easily when using a heating wire as the heat source. 
     The arrangement and the corresponding method allow uniform heating of the two fiber ends in the heating source. This is achieved by using a camera system in a splicing system, by means of which camera system the position of the fiber ends of the optical fibers relative to the heating source can be recorded. The image recorded by the observation device is then evaluated. Splicing parameters such as the splicing current, the time during which the fibers are heated or else different temperature levels which are passed through during the splicing process can then be set as a function of the actual position of the fiber ends with respect to the heating source. These splicing parameters can be stored as a parameter matrix in a memory. It is likewise possible to determine these splicing parameters from a known relationship rule, taking account of the determined distance. The splicing procedure is therefore not carried out with constant splicing parameters, but with the splicing parameters being adapted as a function of the actually determined position of the fibers with respect to the heating source. The position of the fiber ends with respect to the heating source can advantageously be measured by means of electrodes within the recorded image, an auxiliary void, an averaged intensity distribution of an arc, or of a laser beam, by means of the camera image. 
     Many modifications and other embodiments of the present invention, within the scope of the appended claims, will become apparent to the skilled artisan. Therefore, it is to be understood that the invention is not limited to the specific embodiments disclosed herein and that modifications and other embodiments may be made within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.