Abstract:
A light guide for a lighting device, wherein the light guide extends along a longitudinal axis and has a coupling-out area which runs over the longitudinal axis and from which light can be emitted along the longitudinal axis, and wherein the light guide has, in its longitudinal extent, an end region which is provided with a cover in order to suppress high-intensity light emission in the end region. The cover is formed by laser-machining the light guide material in the end region of the light guide. The invention further relates to a method for forming a cover in the end region of the light guide.

Description:
[0001]    This nonprovisional application is a continuation of International Application No. PCT/EP2016/056919, which was filed on Mar. 30, 2016, and which claims priority to German Patent Application No. 10 2015 105 168.0, which was filed in Germany on Apr. 2, 2015, and which are both herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a light guide for a lighting device, wherein the light guide extends along a longitudinal axis and has a coupling-out area extending about the longitudinal axis from which light can be emitted along the longitudinal axis, and wherein the light guide in its longitudinal extension has an end region, which is provided with a cover in order to prevent light emission of higher intensity. 
       Description of the Background Art 
       [0003]    Light guides are used for the transmission of light coupled into the light guide, and light guides are known, which have over their longitudinal extension a prismatic structure in order to decouple the light, which was coupled-in, back out as evenly as possible over the length of the light guide. This creates line beams, which serve in particular to fulfill a signaling function of a lighting device for a vehicle. The continuation of the light along the light guide is made by way of total reflection at the interfaces of the light guide, which guide is typically made of a plastic body, for example, polycarbonate. Light which has been guided in the light guide up to the end region exits in an increased manner in the end region because there is an enhanced coupling-out of light through an end face provided in the end region. The enhanced coupling-out of light through the end face is due to exceeding a total reflection angle, since the light is incident on the end face, which is inclined with respect to the longitudinal axis and essentially completely decouples from the latter. Disadvantageously, a decoupling of increased intensity ensues, wherein the intensity is higher than the intensity of the coupled-out light above the coupling-out area, which runs, for example, along or parallel the longitudinal axis of the light guide and to the line emission of the light. 
         [0004]    An example of an intentional coupling-out through an end face of a light guide is shown in DE 44 27 606 A1. Light is coupled into a light guide via a light emitting diode, and the light is guided along the light guide to a desired output location. In the end region of the light guide, the latter is defined by an end face, and the end face has a larger angle to the longitudinal axis of the light guide. This angle is dimensioned such that the light is reflected inside the end face, and is finally coupled out via the opposite boundary surface of the light guide. 
         [0005]    In order not to visibly carry out a coupling-out via the end face of a light guide when viewed from an outer side of the lighting device, DE 10 2012 108 553 A1 shows a cover in the end region of a light guide, so that light coupled out through the end face is not transmitted and thus remains invisible from the outside of the lighting device. However, such a cover requires a further part, for example, as a component of the light guide receiver, which is not generally available as a function of the installation position of a light guide. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the invention to provide a light guide with an improved cover on one end face of the light guide, in order to prevent light emission of higher intensity in the end region. 
         [0007]    In an exemplary embodiment the invention provides that the cover is formed by laser machining the light guide material in an end region of the light guide. 
         [0008]    Laser machining of the light guide can cause optical density of the light guide material, through which incoming light is absorbed in the machined area so that it does not reflect. A coupling-out of the light from the light guide is thereby partly or completely prevented. The particular advantage of a laser machined region of the light guide is that for forming the cover, no further part is required, in particular, no further component and also no coating, foil or the like needs to be applied from the outer side to the end region of the light guide. In particular, a component which forms the cover can be omitted. 
         [0009]    The laser machining of the light guide material takes place with a laser beam and forms an anti-reflection area. The anti-reflection area is preferably located in the end region of the light guide. 
         [0010]    According to an embodiment, the anti-reflection area is formed on one end face in the end region of the light guide. The laser radiation is focused from the outside on the end face, and by a corresponding parameterization of the laser radiation, optical density of the end face can be achieved. 
         [0011]    According to an embodiment of the invention, the anti-reflection area is located inside the material of the light guide, in particular adjacent to the end region. By focusing the laser radiation in the material of the light guide, the material can be influenced such with appropriate parameterization of the laser radiation that an anti-reflection area is generated inside the light guide. The particular advantage lies in the specific resistance of the anti-reflection area, especially since further oxidation processes cannot take place. 
         [0012]    Advantageously, the anti-reflection area is generated by an oxide layer on or in the material of the light guide. For example, the light guide has a polycarbonate, and an interaction with laser radiation leads to carbonization of the material, which results in optical density. This optical density causes the formation of an anti-reflection area since the light radiation guided in the light guide is absorbed in the area of the carbonization. 
         [0013]    When machining material with laser radiation, different approaches can be provided. For example, the end face of the light guide or an internal area in the light guide can be machined over the entire surface or in an inner layer over the entire cross-sectional area with laser radiation, for example, by scanning the laser beam. A scanned laser beam can also act on a surface of the light guide in lines or on dots so that a line structure or, for example, a dot pattern is generated. It can also be provided that a portion of the end face is darkened over the entire surface; another part of the end face is, for example, unmachined. Through targeted machining of an end face with laser radiation, the intensity of light coupled out can also be affected such that said intensity adapts to the intensity of the light that is coupled out over the coupling-out area. This can also prevent light emission of higher intensity in the end region of the light guide. 
         [0014]    The invention is further directed to a method of forming a cover of a light guide for a lighting device, which cover is provided in an end region of the light guide in order to prevent light emission of higher intensity in the end region, and wherein the method provides that first, a light guide is provided; further, a laser beam is provided and laser machining of the light guide material takes place in the end region of the light guide in order to create the cover. 
         [0015]    The method provides that an anti-reflection area is formed by the laser beam in that an interaction of the laser beam with the light guide material is created. 
         [0016]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0018]      FIG. 1  is a partial view of a light guide with an end face, which is darkened over its entire area; 
           [0019]      FIG. 2  illustrates the light guide according to  FIG. 1 , wherein the end face is darkened in lines; and 
           [0020]      FIG. 3  illustrates the light guide according to  FIG. 1 , wherein the end face is darkened in a dot pattern. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIGS. 1, 2 and 3  respectively show a light guide  1  with a different embodiment of a cover  13  formed according to the invention in the end region  12  of the light guide  1 . The light guide  1  extends along a longitudinal axis  10  and over the longitudinal axis  10 , the light guide  1  has a coupling-out area  11  via which light  21  is coupled out having a substantially constant intensity. By way of example, an intensity profile  22  is shown which substantially has an equal intensity over the longitudinal extension of the light guide  1  along the longitudinal axis  10 . In the end region  13  of the light guide  1 , an end face  16  closes off the light guide  1  so that the intensity of the intensity profile  22  changes along the longitudinal axis  10  when it reaches the end face  16 . 
         [0022]    For coupling out the coupled-in light  21  via the coupling-out area  11  there is a prism structure  20  which is provided opposite the coupling-out area  11 . According to the principle of total reflection, the light  21  is guided through the light guide  1  at the interfaces of the light guide  1  along the longitudinal axis  10 , wherein upon impingement of the light on the prism structure  21 , a critical angle for total reflection on the opposite coupling-out area  11  is not reached, so that the light finally decouples via this surface. The principle of the direct coupling-out across an interface also takes place via the end face  16  so that via the inclined surface transverse to the longitudinal extension of the light guide  1 , a higher output intensity of the coupled-out light  21  is created. To avoid this, according to the invention, various forms of anti-reflection areas  15  are shown by way of example on the end face  16 . 
         [0023]    To this end,  FIG. 1  shows an anti-reflection area  15 , which is produced over the entire surface of the end face  16 . The darkening with the laser beam  14 , which is provided by the laser beam source  19  shown schematically, is performed completely and over the entire area so that at the threshold of the end face  16  and upon reaching the end face  16 , the intensity profile  22  falls to zero from a continuous, constant value over the extent of the coupling-out area  11 . The anti-reflection area  15  is formed by an oxidation process by means of an interaction between the laser radiation  14  and the material of the light guide  1 , for example, made of polycarbonate. 
         [0024]      FIG. 2  shows an exemplary embodiment of the anti-reflection area  15  on the end face  16  of the light guide  1 , which are arranged in the form of lines. This creates a line structure  17 , and parts of the coupled-in light  21  are absorbed by the darkened lines of the line structure  17  and between the lines, the light can be coupled out via the end face  16  without alteration. This makes possible a partial permeability of coupled-in light  21  for coupling out via the end face  16 . 
         [0025]      FIG. 3  shows an exemplary embodiment of the light guide  1  with an anti-reflection area  15  on the end face  16 , which comprises a dot pattern  18 . The dots form darkened areas, which lead to an anti-reflection effect of the coupled-in light  21  so that the proportion of light which is incident on the dots of the dot pattern  18  is absorbed, and the proportion of light which occurs in the intermediate areas between the dots of the dot pattern  18  is reflected. This results in a slow decrease of the intensity in the intensity profile  22  over the end face  16 . 
         [0026]    The exemplary embodiments shown in respect of the formation of the cover  13  by an anti-reflection area  15  generated by laser radiation  14  are based on a full-area or partial darkening of the shown end face  16  of the light guide  1 . It is also conceivable to generate the shown anti-reflection area  15  on the inside in the material of the light guide  1 , i.e., preferably in the end region  12  of the light guide  1 . 
         [0027]    The end region  12  forms the so-called cold, not fired end of the light guide  1 , and in order to avoid uncontrollable reflexes resulting from partial total reflection on the end face  16 , according to the invention, the cover  13  is formed by a surface blackened by laser radiation. The inventive design of the cover  13  by an anti-reflection area  15  formed with laser radiation  14  causes, in addition to preventing cover in the form of individual parts, that the light guide  1  is harnessed over its entire length. The end region  12  of the light guide  1  does not have to be guided behind a cover so that the end region  12  is no longer visible from outside the lighting device. With its free, cold, non-fired end, the light guide  1  may terminate in an area which is visible from the outside of the lighting device. 
         [0028]    Besides being able to machine an end face  16  of the light guide  1  with laser radiation  14 , other areas of the light guide can also be machined with laser radiation  14  to bring about darkening. These areas may be, for example, bending areas or transition areas of the light guide  1 ; that is, generally areas of coupled out light can be equipped with increased intensity with the anti-reflection area  15  of the invention. 
         [0029]    The examples of the linear structure  17  and the dot pattern  18  only show the ability to also vary the degree of darkness; for example, through appropriate parameterization of the laser beam source  19 , a uniform degree of darkening can be produced over the surface, which ranges between 0% to 100%. This way, an inherently homogeneous partial darkening can be achieved that, similar to the line structure or the dot pattern, partially or proportionately permits a partial reflection. 
         [0030]    Additional components, for example, materials for covering the inhomogeneously illuminated light guide, which possibly reflect and/or are coated in a reflex dampening manner, can thereby be omitted. 
         [0031]    An additional coating of the outer surface of the light guide near the end is not necessary, that is, for example, shielding by partial darkening or a light exit surface of the light guide or by a reflective layer, can be omitted. Refractive index transitions that result in an incomplete reflection reduction are prevented. A reflection reducing effect can also be achieved continuously in the interior of the light guide volume. 
         [0032]    The invention is not limited in its embodiment to the above-described preferred exemplary embodiment. Rather, a number of variants are conceivable, which make use of the described solution even for fundamentally different embodiments. All features and/or advantages arising from the claims, the description or the drawings, including design details, spatial arrangements and process steps, can be essential to the invention both individually and in various combinations.