Abstract:
A simple, effective and inexpensive method produces an optical connection on an optical component. A waveguide section, a sleeve for enclosing the waveguide section and an optical component, which has a receptacle for the waveguide section and the sleeve, are provided. The waveguide section is inserted with the first end face into the receptacle of the component and is only cut to length after insertion, while it is mounted on the component. The front end face of the waveguide section is milled away in a centered, spherical concave form.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a method for producing an arrangement comprising a waveguide section and an optical component in general and for producing an optical connection on an optical component in particular.  
         BACKGROUND OF THE INVENTION  
         [0002]    Optical data transmission is increasingly gaining in significance over electrical data transmission. Therefore, intensive work is in progress on new connecting techniques and standards for optical connectors.  
           [0003]    However, the production of optical connections faces considerably greater difficulties from various aspects than electrical connections. In particular, optical connecting points require small production tolerances.  
           [0004]    An important area of application for optical data transmission is the automotive sector. Work is in progress there on a common standard, the “Media Oriented Systems Transport” (MOST®) to standardize the networking of multimedia applications in automobiles.  
           [0005]    To connect an optical waveguide to an optoelectronic circuit in an optical component, the component is typically provided with a short waveguide section, which is fastened on the component and forms a connecting link between the circuit and the waveguide.  
           [0006]    However, to establish a reliable connection, precise dimensioning tolerances have to be maintained. In particular, the distance of the connection face from a sleeve surrounding the waveguide section and the distance from the component housing are of decisive significance, for example for the loss at the interface between the waveguide and waveguide section.  
           [0007]    According to a known method, the waveguide section is firstly brought to a precise length and subsequently inserted into the sleeve or adhesively fixed on the component.  
           [0008]    One problem with this procedure is that the optical connection face in the component is poorly toleranced and therefore the length of the waveguide section has to be created very precisely. This makes production and machining complex and cost-intensive. Furthermore, the longitudinal positioning of the connection face of the waveguide section is difficult.  
         GENERAL DESCRIPTION OF THE INVENTION  
         [0009]    It is therefore an object of the invention to provide a method for producing an arrangement comprising a waveguide section and an optical component which works in a simple, effective and inexpensive manner.  
           [0010]    A further object of the invention is to provide a method for producing an arrangement comprising a waveguide section and an optical component which maintains predetermined tolerances precisely and reliably and permits a permanent reliable optical connection on the waveguide section.  
           [0011]    Yet another object of the invention is to provide a method for producing an arrangement comprising a waveguide section and a component which avoids or at least reduces the disadvantages of the prior art.  
           [0012]    The object of the invention is already achieved in a surprisingly simple way by the subject-matter of the independent claims. Advantageous developments of the invention are defined in the subclaims.  
           [0013]    The invention proposes a method for producing an assembly comprising an optical waveguide or waveguide section and an optical or electrooptical component, in which the waveguide section is fastened on the component as an optical connection or terminal. The waveguide section preferably comprises a core and a jacket surrounding the core, and has in this case a first and a second end face, respectively for coupling optical signals in and out, the second end face lying opposite from the first end face. The component, or preferably a housing of the component, has a receptacle into which the optical waveguide is inserted with the first end face, in order to permit optical contact with optical circuits in the component, so that signals can be coupled into the component and/or can be coupled out of the component via the first or rear end face.  
           [0014]    The optical waveguide section is preferably relatively short, for example in the range of several tens of millimeters, and has the function of a connecting link between the component and a fiber-optic cable, by means of which the component can in turn be connected to other components for optical signal transmission.  
           [0015]    The waveguide section is enclosed in a sleeve which is, in particular, substantially cylindrical or in an annular holder, known as a ferrule, the enclosure preferably being carried out before the fastening on the component, and this sleeve being fastened on the housing of the component. The sleeve and the waveguide section consequently form a connection pin for connecting a fiber-optic cable or its optical connector.  
           [0016]    It is particularly advantageous within the scope of the method according to the invention firstly to provide a long waveguide with a sleeve, for example to encapsulate it with a plastic sleeve coming from a reel, and subsequently divide it up, for example cut it up, into short pieces, in order to obtain the waveguide sections. The waveguide section can consequently be inserted into the sleeve such that it is flush or even with an overhang.  
           [0017]    In an advantageous way, approximate cutting to length of the connection pin or composite element comprising the waveguide and the sleeve is sufficient at this stage of the method. This is so because, according to the invention, the approximately cut-to-length connection pin is fastened, for example adhesively attached or welded, on the housing of the optical component and only subsequently subjected to finishing work or cut to length in order to obtain the final and precise length.  
           [0018]    The final cutting-to-length of the waveguide section consequently only takes place after the insertion of the waveguide section and the sleeve into the receptacle of the component, i.e. when the latter have together been mounted or fastened on the component and the waveguide section is surrounded by the sleeve.  
           [0019]    During the final cutting to a predetermined length, that is after the mounting of the connection pin and the sleeve on the component or in the mounted state, a precisely predefined positioning of the second end face of the waveguide section is achieved in relation to an end face of the sleeve, or its front edge, surrounding said second end face and/or in relation to the component or its housing. In this respect, a tolerance of less than 50 μm, in particular less than 10 μm, is achieved.  
           [0020]    As an alternative, it is also possible that firstly the sleeve is fastened on the component and after that the waveguide section is inserted into the sleeve. It is also possible for the component housing and the sleeve to be of a one-piece or integral configuration.  
           [0021]    One advantage of the method according to the invention is that it is considerably easier to bring the waveguide section to the final precise length when it is on the ready mounted component and/or inserted in the sleeve than it is to accomplish this before mounting.  
           [0022]    The cutting-to-length of the waveguide section preferably takes place by means of machining the second or front end face of the waveguide section, that is the end face remote from the component. The front end face is preferably machined by material removal or abrasion, in particular milled or ground away by means of a milling or grinding tool.  
           [0023]    A diamond tool is preferably used for this purpose. This has the advantage that, in a single working step, both the length of the waveguide section is exactly defined and the surface of the front end face is already machined with a finish suitable for coupling optical signals in and/or out. There is consequently no need for an additional polishing step.  
           [0024]    In other words, the machining of the surface of the front end face and its exact longitudinal positioning in relation to the sleeve or the component, or the definition of the length of the waveguide section, takes place simultaneously and/or in one working step.  
           [0025]    According to a preferred embodiment of the invention, when it is cut to length, the waveguide section is shortened in such a way that a predetermined depression or a predetermined set-back of the front end face of the waveguide section is created in relation to an end face of the sleeve at the front or enclosing the front end face of the waveguide section. In this case, a predetermined distance is also created between the front end face of the waveguide section and the component is or its housing.  
           [0026]    The set-back of the front end face of the waveguide section in relation to a front edge of the sleeve is preferably between 0 μm and 500 μm, preferably 0 μm to 50 μm, most preferably in the range from 15 μm to 30 μm. It is consequently possible in an advantageous way to comply with the MOST specifications. In particular, the minimum and/or maximum set-back lie within the aforementioned intervals over the entire end face of the waveguide section or the core.  
           [0027]    The milling or grinding cutter preferably rotates transversely in relation to the longitudinal axis or longitudinal line of the waveguide section and is moved parallel onto the waveguide section in order to mill or grind away the waveguide section until the predefined set-back is created. Consequently, the set-back can be created in a simple way.  
           [0028]    The set-back avoids direct contact of the front end face of the waveguide section with a waveguide to be connected to it, since the ferrule acts as a stop, if appropriate in interaction with a counterpiece. By keeping the two waveguides that are to be optically contacted apart, losses at the interfaces are avoided.  
           [0029]    It may also be advantageous to machine the front end face of the sleeve, in particular remove material from it or mill or grind it away, at a point in time at which the waveguide section and the sleeve are fastened on the component and/or in one working step and/or simultaneously with the front end face of the waveguide section. As a result, the distance of the front end face of the sleeve from the component housing is also defined in this working step. The front end face of the sleeve can in this case be machined completely or in certain regions.  
           [0030]    According to a particularly preferred embodiment of the invention, a surface of the front end face that is in particular concave in two dimensions is created by means of the machining of the front end face of the waveguide section. The concave surface preferably has in this case an apex point within the circumference of the waveguide section, in particular a centered apex point.  
           [0031]    The concave surface is created most easily with a milling or grinding cutter with a convex surface.  
           [0032]    To a person skilled in the art, it may appear at first glance to be illogical and disadvantageous to form the connection face of the waveguide section in a concave form, since it is known that non-planar connection faces are liable to create increased diffusion. Therefore, until now it has been endeavored for the most part to polish the surface as flat as possible.  
           [0033]    However, the inventor has surprisingly found that the diffusion, and consequently the insertion loss, is kept within acceptable limits, in particular in the preferred areas of application of the invention, so that the advantages of the invention, that is the simplicity of the method, by far outweigh this apparent disadvantage.  
           [0034]    Particularly preferred is an elliptical, in particular spherical, to be more precise spherical-concave, form of the surface of the front end face, which is created for example by a milling or grinding cutter with a surface which is spherical at least in certain portions.  
           [0035]    The inventor has also found that a milling or grinding cutter with a radius or radius of curvature of 2 mm to 100 mm, preferably 4 mm to 40 mm, particularly preferably 8 mm to 22 mm, produces outstanding results. Consequently, after machining, the surface of the front end face of the waveguide section also has a radius of curvature of 2 mm to 100 mm, preferably 4 mm to 40 mm, particularly preferably 8 mm to 22 mm. The width of the blade, i.e. the portion of the tool that removes material, is preferably 0.1 mm to 10 mm, in particular 0.5 mm to 5 mm, particularly preferably 2 mm ±50%.  
           [0036]    These dimensions have proven to be particularly suitable if, as preferred, a waveguide section made of plastic or a plastic optical fiber (POF) with a core diameter of approximately 1 mm and a jacket diameter of 1.5 mm is used.  
           [0037]    Preferably, at least the entire surface of the front end face, if appropriate including a protective coating surrounding the fiber, is formed in a concave manner. The front end face of the sleeve may either remain completely planar or be provided at least partly or completely with a concave surface.  
           [0038]    According to an exemplary embodiment of the invention, the front end face of the sleeve has an inner ring and an outer ring, which are adjacent or concentric in relation to each other, the inner ring being provided with a concave surface and the outer ring having or retaining a planar surface.  
           [0039]    As an alternative to milling or grinding, the front end face may, however, also be thermally molded. For this purpose, a melt die which is, in particular, convex or spherically convex is moved under force or pressed onto the front end face of the waveguide section until a predetermined set-back is achieved. It is particularly advantageous to use a rotating melt die with a hotter portion and a colder portion. In this case, firstly the hotter portion is pressed onto the front end face to melt and mold it and the die is subsequently turned further until the front end face is cooled again by means of the colder portion. As a result, a surface of good optical quality is achieved.  
           [0040]    Not only during the thermal molding is it preferred to use a sleeve material which has a coefficient of thermal expansion similar to that of the material of the waveguide section. The two coefficients of expansion preferably deviate from each other by at most 20%. As a result, the desired tolerances are maintained over the entire operating temperature range, for example in an automobile from −50° C. to +100° C.  
           [0041]    The invention is explained in more detail below on the basis of exemplary embodiments and with reference to the drawings, identical and similar elements being provided with the same designations and it being possible for features of the various embodiments to be combined with one another.  
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0042]    In the Figures:  
         [0043]    [0043]FIG. 1 shows a perspective view of an optoelectronic component with a connection pin,  
         [0044]    [0044]FIG. 2 shows a schematic representation of an optical data transmission connection,  
         [0045]    [0045]FIG. 3 shows a perspective view of a connection pin,  
         [0046]    [0046]FIG. 4 shows a cross section through the connection pin from FIG. 3,  
         [0047]    [0047]FIG. 5 shows a perspective view of a connection pin according to an embodiment of the invention,  
         [0048]    [0048]FIG. 6 shows a cross section through the connection pin from FIG. 5 in the form of a detail,  
         [0049]    [0049]FIG. 7 shows a perspective view of a connection pin according to a further embodiment of the invention,  
         [0050]    [0050]FIG. 8 shows a cross section through the connection pin from FIG. 7 in the form of a detail,  
         [0051]    [0051]FIG. 9 shows a perspective view of a connection pin according to a further embodiment of the invention,  
         [0052]    [0052]FIG. 10 shows a cross section through the connection pin from FIG. 9 in the form of a detail,  
         [0053]    [0053]FIG. 11 shows a schematic sectional drawing of a milling apparatus according to the invention,  
         [0054]    [0054]FIG. 12 shows a front view of a milling cutter in the form of a detail and  
         [0055]    [0055]FIG. 13 shows a side view of the milling cutter from FIG. 12. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0056]    [0056]FIG. 1 shows an optoelectronic component  10  with a plurality of electrical connections  12  for making contact with a circuit carrier and with an annular receptacle  14 , in which a connection pin  16  is inserted and adhesively fixed.  
         [0057]    The component  10  has a housing  11  with a front side  11   a . The optical connection pin  16  comprises a hollow-cylindrical plastic sleeve or ferrule  20  and an optical waveguide section  30 , which are inserted in the receptacle  14  by in each case a first or rear end face  24  and  34 , respectively (see FIG. 4). The sleeve or annular holder  20  has, for instance in the rear third, or the third toward the component  10 , a groove  21  for fastening a connector (not shown).  
         [0058]    The plastic sleeve  20  has a second or front annular end face  22 , which surrounds or encloses a second or front circular end face  32  of the plastic waveguide section  30 . The front end face  32  of the optical waveguide section  30 , which forms an optical connection face for a waveguide or a fiber-optic cable  18 , is set back from the front end face  22  of the sleeve.  
         [0059]    Referring to FIG. 2, an optoelectronic connection arrangement is represented, with a first and a second electronic component  42 ,  44  to be connected. Connected to the electronic components  42 ,  44  are optoelectronic or electrooptical components, in particular converters  46 ,  48 , which are respectively connected by means of a connection pin  16 ,  16 ′ and the fiber-optic cable  18 .  
         [0060]    Referring to FIGS. 3 and 4, the connection pin  16  from FIG. 1 is represented. It can be seen that the waveguide section  30  comprises a core  50  and a jacket or coating  40 . The plastic jacket  40  surrounds the core  50 . It should be noted, that the waveguide section  30  or plastic optical fiber section further comprises a cladding (not shown separately in the Figures) surrounding the waveguiding inner core. In other words, the core  50  represents the waveguiding inner core and the cladding. The front end face  52  of the core  50  and a front end face  42  of the jacket  40  form a front end face  32  of the waveguide section  30  and are respectively arranged perpendicularly in relation to a longitudinal axis  31  of the waveguide section  32  or connection pin  16 . Furthermore, in this example the front end faces  52  and  42  are arranged such that their surfaces are flush with each other and are formed in a planar manner.  
         [0061]    The front end face  32  of the waveguide section  30  and the front end faces  42  and  52  of the jacket and core have a constant set-back RS=15 μm from the front end face  22  of the sleeve  20 .  
         [0062]    The connection pin  16 , as it is represented in FIGS. 1, 3 and  4 , may have been produced in a conventional way, that is to say that the waveguide section  30  was adhesively cemented into the sleeve with the finish-machined front end face. The connection pin  16  may, however, also be produced by the method according to the invention, the set-back RS of the planar front end face  32  of the waveguide section  30  being created with a cylindrical milling cutter which is moved transversely in relation to its axis of rotation over the end face  32  of the waveguide section  30  once the connection pin  16  has been mounted on the component  10 .  
         [0063]    [0063]FIGS. 5 and 6 show a connection pin  116  with a front end face or connection face  132  of the waveguide section  130  that is milled away in a spherically concave form.  
         [0064]    As can best be seen in FIG. 6, the front end faces  132  and  142  of the waveguide section  130  and of the jacket  140 , respectively, are milled away in a completely concave form. The front end face  122  of the sleeve  120  has an inner, likewise concavely milled-away ring  124  and an outer, planar ring  126 , the inner concave ring adjoining flush with the surface of the front end face  132  of the waveguide section  130 .  
         [0065]    In this case, only a small part of the sleeve  120  is milled away, so that the width of the outer ring  126  is greater than the width of the inner ring  124 . In this example, the width of the inner ring  124  is approximately 50 μm. The front end face  132  of the waveguide section is formed or depressed rotationally symmetrically about the longitudinal axis  131 .  
         [0066]    The radius of curvature R of the spherically concave front surfaces  142  and  152  and also  132  and  124  is 8 mm. This radius has proven to be a good compromise for diameters of the sleeve of D H =2.9 mm, of the jacket of D M =1.5 mm and of the core of D K =1 mm.  
         [0067]    The milling depth or the maximum set-back RS max  between the end face  122  of the sleeve  120  and the apex point  136  of the depression is 40 μm. The difference of the set-back between the apex point  136  and the outer edge  158  of the core  150  is 15.6 μm. This gives a minimum set-back of the core  150 , that is at the outer edge  158  in relation to the surface  129  of the front end face  122 , of 14.4 μm. Consequently, the set-back of the core  150  over its entire front end face  152  lies between 14.4 μm and 40 μm and is consequently within the MOST tolerance of 0 to 50 μm.  
         [0068]    [0068]FIGS. 7 and 8 show a further exemplary embodiment of the invention, in which the sleeve  220  is milled away or out more than the sleeve  120 . The inner, concave ring  224  is approximately 10 times as wide as the outer, planar ring  226  of the end face  222  of the sleeve  220 . The front end faces  252  and  242  of the core  250  and of the jacket  240 , respectively, i.e. the front end face  232  of the waveguide section  230 , are formed in a completely spherically concave manner.  
         [0069]    [0069]FIGS. 9 and 10 show a further exemplary embodiment, in which the front end face  322  of the sleeve  320  has been milled away completely over its entire diameter to its outer edge  328 . In order to achieve a suitable set-back of the end face  332  of the waveguide section  330 , or of the end face  352  of the core  350 , a milling cutter with a radius of approximately 22 mm is used, whereby a set-back RS max  of the apex point  336  in relation to the front edge  329  of the sleeve  320  of approximately 48 μm is created.  
         [0070]    [0070]FIG. 11 shows an apparatus  1  according to the invention for the simultaneous milling away of two connection pins  116 . The apparatus  1  comprises two receptacles  2 , for temporarily fastening a component  110  in each case. Two milling cutters  3  rotate perpendicularly in relation to the longitudinal axes  131  of the connection pins  116  about an axis  4 . For machining parallel to the longitudinal axes  131 , the two milling cutters  3  are lowered in the direction of the arrow  5  onto the connection pins  116 , until the predetermined set-back or a predetermined distance A of the front edge  129  of the sleeve  120  from a front side  111   a  of the component  110 , to be more precise of the component housing  111 , is achieved. It is clear that the concept can be extended from two components to more than two components or a multiplicity of components.  
         [0071]    [0071]FIGS. 12 and 13 show in detail the milling cutter  3  with which the terminal pin  116  in FIGS. 5 and 6 is produced.  
         [0072]    The milling cutter  3  has a cylindrical carrier  6  and a blade section  7  projecting from this carrier and having a blade width of B=1.6 mm. The surface  8  of the blade section  7  is diamond-impregnated. As a result, in the surface-removing operation the surface of the waveguide section is already machined with a finish suitable for permitting low-loss signal coupling in/out without additional polishing. For prototypes, a high-grade steel blade may also be used.  
         [0073]    The radius R F  of the milling cutter is, for example, 8 mm, the blade surface  8  being spherical, i.e. the radius of curvature R K  of the blade surface is 8 mm in both dimensions.  
         [0074]    It is evident to a person skilled in the art that the embodiments described above are to be understood as being given by way of example, and the invention is not restricted to these but can be varied in many ways without departing from the spirit and scope of the invention.