DE102008009139B4 - Side-emitting step index fibers, fiber bundles and flat structures and their uses as well as preforms and processes for their production - Google Patents

Abstract

Side-emitting step-index fiber, containing a light-conducting core (1) made of inorganic glass with the refractive index n1 and a transparent and / or translucent cladding (2) made of inorganic glass with the refractive index n2, which surrounds the core along the fiber axis (A), with the core and cladding at least one scattering area (3) is located, which is formed from an inorganic glass which essentially has the refractive index n1 and in which scattering particles are embedded, the thermal expansion coefficient of the inorganic core glass being greater than the thermal expansion coefficient of the inorganic cladding glass, characterized in that between the core (1) and the cladding (2) there is at least one discrete scattering area (3) which extends over a partial area of the core circumference along the fiber axis (A).

Description

The invention relates to side-emitting step-index fibers made of inorganic glass, preforms and processes for their production, as well as fiber bundles containing side-emitting step-index fibers and flat structures and their applications.

Step index fibers are understood to be light-guiding fibers, the light guiding in the fiber core taking place by total reflection of the light guided in the core on the cladding surrounding the fiber core along the fiber axis. Total reflection occurs when the cladding has a lower refractive index than the fiber core that guides the light. However, the condition of total reflection is only possible up to a critical angle of the light hitting the cladding, which depends on the refractive indices of the core and cladding. The critical angle β _min , ie the smallest angle at which total reflection still occurs can be calculated as sin (β _Min ) = n ₂ / n ₁ , where β _min is measured from a plane perpendicular to the fiber axis, n _{1 represents} the refractive index of the fiber core and n _{2 represents} the refractive index of the cladding.

In general, the best possible way of guiding the light in the fiber is sought, i.e. as little light as possible should be lost during coupling into the fiber and during transport in the fiber. A side-emitting step index fiber is a step index fiber in which light is intentionally coupled out of the fiber core and out of the fiber. In general, a uniform outcoupling is desired, which in the ideal case allows a side-emitting step-index fiber to appear as a uniformly luminous band or line. This makes them interesting for a variety of applications, especially in lighting technology.

Side-emitting in the sense of the invention means that the fiber is able to emit light from the side, regardless of whether it is in operation, i.e. whether a light source is actually connected and the light is switched on.

As is generally known, the fibers are produced with the aid of fiber drawing processes, at least the preform of the fiber core being heated up to the softening temperature of the material of the preform or the fiber core or beyond and a fiber being drawn out. The principles of the fiber drawing process are for example in the German patents DE 103 44 205 B4 and DE 103 44 207 B3 described in detail.

Various methods for producing the side emission effect are known from the prior art. One known method is to ensure that light is decoupled in the fiber core.

The Japanese Patent Application Laid-Open JP H09-258 028 A discloses side-emitting step index fibers in which the light coupling is to be generated by a non-circular core. The coupling out occurs when light hits the interface between fiber core and cladding at angles that are smaller than the critical angle of total reflection β _min are. As a result of the non-circular core geometries described, for example square, triangular or star shapes, geometric areas are generated in the core in which light otherwise guided by total reflection can be coupled out. The production of side-emitting fibers by such core geometries is, however, associated with the problem that the coupling out of the light is very inefficient in this case. The light is guided in the fiber to the cladding at essentially very flat angles of incidence, and the core geometries described extend along the fiber axis. Accordingly, there are hardly any areas where β _min is fallen below. Furthermore, it is very expensive to use the core geometries disclosed in JP H09-258 028 A for fibers made of glass, because it is very difficult to produce the corresponding preforms required for fiber drawing. In addition, especially in the case of glass fibers, the breaking strength of such fibers with non-circular fiber core diameters is greatly reduced. It is probably for this reason that this document only discloses fibers made of polymers.

Another method of decoupling the light from the fiber core is in the U.S. 4,466,697 A described. Accordingly, light-reflecting and / or scattering particles are mixed in the fiber core. Here it turns out to be difficult to manufacture longer fibers with uniform side-emitting properties, since the light conduction in the core is weakened by absorption by the added particles in the core, since there are no completely scattering particles, but only those that scatter almost all of the incident light. Because the probability is very high with particles evenly distributed in the core that the light guided in the core will strike such particles, the absorption probability is also very high, even if the total number of particles is small. As a result, the decoupling effect is also very difficult to scale, which makes reproducible results in fiber draw extremely complex or almost impossible, at least for fibers over 3 m in length, at least as long as glass fibers are to be produced.

Scalability in the sense of the present disclosure is understood to mean the possibility of specifically setting the side emission effect over the length of the fiber. This is necessary because fiber lengths for different applications can vary very widely, but the most uniform possible intensity of the light should be achieved over the entire fiber length.

As an alternative to decoupling the light directly from the fiber core, side-emitting properties in fibers can also be caused by effects in the interface between fiber core and cladding or in the cladding itself. It is known from the prior art that crystallization reactions between core and cladding glasses are undesirable, since the crystallites in the interface between core and cladding can serve as scattering centers, so that light is coupled out of the fiber and thus reduces its light conductivity. This effect is generally undesirable with optical fibers and glass fibers are used as in the German patent DE 102 45 987 B3 usually specifically designed so that crystallization does not take place between the core and the cladding. However, it is conceivable that the crystallization between the core and the cladding is used specifically to generate side-emitting properties. Crystallization occurs during fiber draw when the core and cladding fuse together and the fiber cools down again. Tests have shown, however, that the crystallization process is difficult to adjust and control during the fiber draw, so that a reproducible and scalable production of side-emitting glass fibers whose side-emitting properties are based on the presence of crystallites in the interface between core and cladding, has not yet been economically successful.

To generate side-emitting properties due to scattering centers in the interface between core and cladding, according to the patent LV 11644 B proposed for quartz glass fibers to apply a coating on the drawn quartz glass fiber which contains scattering particles. The outer protective jacket around the quartz glass fiber can then be applied. As is usual with quartz glass fibers, the coatings of both the scattering layer and the outer jacket are made of plastics. This has the disadvantage that the drawn out fiber core has to be subjected to further coating steps and is unprotected during this time. Dirt particles that settle between the core and the coating lead to possible breakages and / or points with strong light extraction. Quart fibers as such are extremely expensive anyway because of the material, but the complex manufacturing process required in this document makes them even more expensive.

the US 2005/0074216 A1 discloses a side emitting fiber with a transparent core made of plastic, which first has a transparent first cladding and then a second cladding, both also made of plastic. Scatter particles are embedded in the second jacket, which is the outer jacket. This method is only possible for fibers with very large core diameters of 4 mm or more, because the light guided in the fiber core has to be coupled out due to the inhomogeneities that inevitably exist at the very large interface between the core and the first cladding. In this case, the second jacket with the embedded scattering particles is used to homogenize the decoupled light over all solid angles. Fibers with such a large core diameter are, however, not very flexible and can therefore only be laid with difficulty. Such fibers can only be produced from glass as rigid fiber rods and are completely inflexible.

the WO 2006/124548 A1 describes as well as the EP 1105673 B1 a side-emitting fiber made of plastic that has syrup particles embedded in the volume of its jacket.

EP 0800036 A1 Contains plastic fibers made from core rods made of plastic, onto which light-scattering areas are applied, which in turn are surrounded with an index matching oil to avoid unwanted decoupling from the core rod.

the US 2002/0159732 A1 also discloses plastic fibers with side emitting properties. A light-scattering area made of plastic is printed or painted on a light-conducting rod, with scattering particles being dispersed in the plastic of the light-scattering area.

EP 1319636 A2 deals with the implantation of particles into a fiber core during the drawing process of the fiber.

EP 0895104 A1 discloses optical fibers having a core of plastics or liquids. A light extraction is generated by deformation of the core.

the JP 2007-272 070 A describes a side-emitting fiber in which the cladding is doped using CVD methods. A refractive index reduction in cladding areas is to be achieved by diffusion.

A serious disadvantage with all the solutions described which contain plastic is that the plastic sheaths described are all combustible. Hence, such fibers should generally be undesirable. Apart from that, they cannot be approved at least in areas with increased fire protection regulations, for example within aircraft cabins.

As such, glass fibers are not flammable. Side-emitting glass fibers are, however, also already known. The established method for producing glass fibers with side-emitting properties provides for the preform of the fiber core to be roughened by grinding or sandblasting. These machining processes create structures that protrude into the fiber core on the circumferential surface of the fiber core and are intended to couple out the guided light. Here, too, it has been shown that the process for generating the side emission is inefficient and also difficult to scale. In addition, the processing of preforms, especially if they are made of glass, is often expensive and time-consuming. The structures protruding into the fiber core also represent injuries to the fiber core, from which load peaks and, as a result, cracks can arise under bending loads, as a result of which such fibers suffer from a reduced breaking strength. This is another reason why this technology appears to be in need of improvement.

Against this background, it is an object of the invention to provide a side-emitting step-index fiber which can be produced economically, which efficiently couples the light out to the side, the effect should be easily scalable, and which, moreover, is non-flammable. Another object of the invention is to provide a method for producing such side-emitting fibers, as well as fiber bundles containing such side-emitting fibers and their applications.

The task and / or the subtasks are solved by the independent claims. Preferred embodiments emerge from the subclaims.

A side-emitting step index fiber according to the invention contains a light-conducting core made of an inorganic glass with the refractive index n ₁ and a transparent and / or translucent cladding made of an inorganic glass with the refractive index n ₂ that surrounds the core along the fiber axis, with at least one scattering area between the core and the cladding which is formed from an inorganic glass which has essentially the same refractive index n ₁ as the core and in which scattering particles are embedded. A side-emitting step index fiber according to the invention can be flexible or else rigid.

As is usual with fibers, the cladding completely encloses both the core and the scattering area (s) along the fiber axis. The scattering area or areas are accordingly on the surface of the fiber core, protected by the cladding.

In the present invention, the side emission effect is produced by scattering the light guided in the core in an area between core and cladding that is thin in relation to the core diameter. For this purpose, there is a scattering area in which the scattering takes place between the core and the cladding in direct contact between the two. Scatter particles that are embedded in the scatter area are responsible for the scattering. In the context of the invention, scattering particles are all particles, regardless of their shape, material and / or size, that can scatter the guided light. Scattering particles can develop their scattering effect through classic scattering, in particular Rayleigh and / or Mie scattering, as well as through diffraction and / or reflection and multiple processes of these mechanisms with one another. Their only task is to divert incident light individually or as a whole.

The inventors have recognized that the effect of the side emission is best scalable if the scattering takes place mainly on the scattering particles themselves. To do this, the light guided in the core must first be able to reach it. Therefore, the refractive index of the material in which the scattering particles are incorporated is essentially the same as the refractive index n _{1 of} the core. The incorporation of the scattering particles in a matrix made of inorganic glass is therefore necessary in the context of the invention in order to be able to apply them to the core in an economical manner in the first place. A refractive index of the matrix material which deviates significantly from n ₁ would result in the matrix material itself having effects which would influence the light conduction in the core. For example, if the refractive index were significantly smaller than n ₁ , the light guided in the core would be reflected more by the material of the matrix than by the scattering particles, so that there could be little or no scattering on the scattering particles. Such a fiber would only couple out a small amount of light to the side. If, on the other hand, the refractive index of the material of the matrix were significantly greater than n ₁ , the light guided in the core would reach the outside very quickly and the fiber would lose its entire light intensity over a very short length, so that only very short fiber lengths would be possible. If, on the other hand, the refractive index of the matrix material is essentially the same as the refractive index n ₁ of the core, the light guided in the core is at most negligibly disturbed by the matrix material, so that the light guided in the core from the matrix material can strike the scattering particles unhindered. Thus, by choosing the concentration of the scattering particles in the scattering area, an efficient scaling of the lateral emission is possible.

The greatest effect of the side emission can be achieved if there is at least one scattering area between the core and cladding that completely surrounds the core along the fiber axis. This means that the scatter area extends over the entire circumferential surface of the fiber core. In this case, the jacket in turn preferably encloses the entire structure of the core and the scattered area. In this embodiment, the scattering particles can be distributed homogeneously in the scattering area. Such a scattering area is generated during fiber draw by fusing several inlay rods, which consist of the matrix material in which the scattering particles are embedded. The drawing process and the inlay rods are explained in more detail in connection with the description of the preform and the manufacturing process. By using the inlay rods and the resulting formation of a scattering area closed around the core by fusing inlay rods, the use of a tube for producing the preform used for the fiber draw for the scattering area can be dispensed with. This is advantageous because this preform does not have to be produced by a tube of glass in which scattering particles are embedded. This would be disadvantageous because a pipe pulling system would be required exclusively for the production of these preforms provided with scattering particles, since in pipe pulling systems also used for conventional glass pipes, scattering particles would usually be undesirable and their addition would contaminate the entire system. By dispensing with such a tubular preform, such a side-emitting fiber can thus be produced more economically.

A further embodiment provides that there is at least one scattering area between the core and the cladding, which completely surrounds the core in a partial area along the fiber axis. In other words, this means that the scattering particles are only embedded in parts of the matrix glass, these parts ring-like enclosing the core. If the distance between areas in which scatter particles are present and those which do not have scatter particles is sufficiently large, a side-emitting fiber can be produced in a targeted manner, which shows the emission effect in some areas and not in other areas. Such a fiber can be advantageous in order to achieve a corresponding design effect, or else it can first guide the light through the area with as little loss as possible without the side emission effect to the location where the side emission is to take place. This enables the separation of the light source, which is to be coupled into the fiber, and the lighting location. Fibers of this type can be produced if inlay rods are used in which scatter particles are embedded only in partial areas along their axis. When the fiber is drawn, however, the area of the inlay rods not doped with scattering particles also fuses with the fiber core, so that the sum of the core diameter and thickness of the scattering area without embedded scattering particles and with embedded scattering particles remains essentially the same over the entire fiber length.

In one embodiment according to the invention, the side-emitting step index fiber has at least one discrete scattering area between core and cladding, which extends over a partial area of the core circumference along the fiber axis. This means that in this case at least one scattering area extends along the fiber axis or partial areas along the fiber axis, but does not completely surround the fiber. Such scattering areas can be generated if the inlay rods do not or not completely fuse with one another during fiber draw. The generation of such discrete scattering areas can be adjusted by the number and / or the diameter and thus the volume of the inlay rods used. In this embodiment there is accordingly at least one area on the circumferential surface of the core which extends along the fiber axis and which is also not covered with the material in which the scattering particles are otherwise embedded. Of course, however, it is also possible that the discrete scattering area or areas extending along the fiber axis, as described with regard to the previous embodiment, have areas along the fiber axis in which no scattering particles are embedded, so that the fiber according to the invention in this case not over its entire length has the side emission effect, so that, for example, areas with side emission alternate with areas without side emission.

The light decoupling of the side-emitting step index fiber can be scaled excellently by the number of discrete scattering areas extending essentially along the fiber axis. Since efficient lateral decoupling from the fiber is generally desired, a particularly preferred side-emitting step-index fiber according to the invention has several discrete scattering areas between core and cladding, each of which extends over a partial area of the core circumference along the fiber axis. The number of discrete scatter ranges is preferably from 5 to 100, particularly preferably from 10 to 50.

In the case of the side-emitting step-index fiber according to the invention, scattering particles are usually used whose melting temperature is higher than the melting temperature of the glass in which they are embedded. Because the scattering particles in this case at least do not change their scattering properties during the manufacturing process, their selection is made easier and they can accordingly be purchased as raw material.

The scattering particles preferably have a diameter between 10 nm and 5000 nm, particularly preferably between 100 nm and 1200 nm. For non-round scattering particles, their maximum extent is understood as their diameter in the context of the invention.

The scattering particles can be selected from a variety of materials. They preferably consist essentially of SiO ₂ and / or BaO and / or MgO and / or BN and / or AlN and / or SN and / or ZrO ₂ and / or Y ₂ O ₃ and / or Al ₂ O ₃ and / or TiO ₂ and / or Ru and / or Os and / or Rh and / or Ir and / or Ag and / or Au and / or Pd and / or Pt and / or diamond-like carbon and / or glass ceramic particles. Mixtures of scattering particles made of different materials, compounds and / or conglomerates of these or also scattering particles fused and / or sintered with one another are also conceivable and encompassed by the invention as well as the metallic components of the aforementioned oxides and nitrides alone.

The efficiency of the coupling out from the scattering area and thus from the fiber depends not only on the scattering property of the scattering particles as an intrinsic parameter but also on the concentration of the scattering particles in the scattering area. It was found that concentrations of the scattering particles in the scattering range between 10 ppm and 1000 ppm enable efficient coupling-out, the preferred range being between 20 ppm and 100 ppm. The concentration in ppm refers to the proportion of scattering particles in relation to the mass proportions of the constituents of the glass in which the scattering particles are embedded.

The parameters with which the side emission effect can preferably be set and thus scaled are the number of discrete scattering areas along the fiber axis, the scattering properties of the scattering particles used and their concentration. A suitable combination of these parameters makes it possible to produce side-emitting fibers of various lengths that appear largely homogeneous to the human eye, so that a large number of applications are possible in the first place.

In addition to the efficiency and homogeneity of the side emission, the fibers according to the invention must also withstand mechanical loads as well as possible. If the fibers are mechanically too sensitive, fiber breaks easily occur, which can render the fiber unusable. In particular, the fibers according to the invention must be able to be bent repeatedly without breaking. One criterion for assessing the breaking strength of fibers is the so-called loop test. A loop is formed from a fiber, which is then tightened. The smaller the diameter of the loop at which the fiber breaks, the more break-resistant it is.

Adequate breaking strengths can be achieved by using pre-tensioned fibers. For the fibers according to the invention, this means that the coefficient of thermal expansion of the core glass is greater than the coefficient of thermal expansion of the cladding glass. In the manufacturing process of the fiber, the sheath is thus drawn onto the core and / or the scattered area during cooling, so that the sheath exerts a tension on the core and / or the scattered area. Such pre-tensioned fibers are usually considerably more resistant to breakage than non-pre-tensioned fibers. In addition to the thermal prestressing described, other methods of generating the stress are of course also possible. For example, the fiber could also be chemically prestressed during the manufacturing process or afterwards. Known processes for chemical toughening would preferably introduce ions into the jacket, which would be responsible for building up the voltage.

In a preferred side-emitting step index fiber according to the invention, the diameter of the core is from 10 μm to 150 μm, the at least one scattering area has a thickness of 100 nm to 2 μm and the cladding is between 500 nm and 2 μm thick.

Of course, the side-emitting step index fibers according to the invention are used in the rarest of cases as individual fibers, but in fiber bundles together with other side-emitting step index fibers or together with other optical fibers which have no side emission effect. In turn, the fiber bundle is usually surrounded by a protective outer sheath, which in most cases consists of plastic. Compared to a single fiber with the same diameter, fiber bundles have the advantage that they are much more flexible and can be laid in smaller bending radii. For this reason, almost only fiber bundles are used commercially in lighting applications. Due to this fact, fiber bundles which contain the side-emitting step index fiber described above are also the subject of this invention.

The fiber bundle does not necessarily have to be flexible in the sense of the invention; it is also possible for the fiber bundle to be designed as a rigid fiber rod which is brought into its final shape by later reshaping, for example bending and / or pressing.

A fiber bundle according to the invention contains a multiplicity of inorganic glass fibers and an outer jacket which completely encloses this multiplicity of inorganic glass fibers along the fiber bundle axis, the inorganic glass fibers containing a multiplicity of the above-described side-emitting step index fibers according to the invention and the outer jacket at least in partial areas along the fiber bundle axis transparent and / or is translucent. The transparency and / or translucency of the outer jacket is therefore necessary so that the light emitted laterally by the individual fibers can also leave the fiber bundle and thus become visible to the viewer. If a translucent outer sheath is used instead of a transparent outer sheath, it is possible to homogenize the light emitted from the side by the individual fibers.

The fiber bundle according to the invention can typically have from 100 to 10,000 individual fibers.

In order to ensure the highest demands with regard to the fire safety of the fiber bundle according to the invention, the outer jacket of the fiber bundle is preferably made of flame-resistant plastics or a woven fabric of inorganic glass fibers. However, it is also possible that the outer cladding is produced by wrapping the plurality of inorganic glass fibers with one or a plurality of inorganic glass fibers. It is also possible to spin the individual fibers of the bundle with one another, so that a type of rope and / or yarn is created that no longer requires a separate sheath.

The invention makes it possible to provide side-emitting step index fibers with efficient side emission, in which the side emission effect can also be scaled very well according to the requirements and thus the amount of light coupled out can be easily adjusted over the fiber length. This makes it possible to connect the side-emitting step index fibers according to the invention also together with other light guides and / or other side-emitting step index fibers and / or textile fibers to form a flat structure. In the context of the invention, a flat structure is an object which has a large area in relation to its thickness. In this way, on the basis of the side-emitting step index fibers according to the invention, a self-luminous, flat structure can be produced which can emit light homogeneously distributed over the surface. Such a flat structure is preferably designed in such a way that a viewer perceives it as a homogeneously luminous surface when the flat structure is in operation, i.e. when light is coupled into the side-emitting step index fibers of the flat structure.

In a preferred embodiment, the side-emitting step index fibers are arranged essentially parallel to one another in such a flat structure. However, side-emitting step-index fibers arranged differently within the sheet-like structure in accordance with the emission characteristic are of course also possible.

In order to obtain a stable flat structure, the side-emitting step index fibers are preferably fixed on a carrier element. In this way, a composite element is formed from the carrier element and side-emitting step index fibers. The carrier element is preferably also flat, but can have any shape and curvature.

As an alternative to fixing the side-emitting step index fibers on the carrier element, they can also be embedded in the carrier element and in this way form a composite element made from carrier element and side-emitting step index fibers. This can be done by an injection molding process in which preferably transparent plastic encapsulates the optical fibers. Thermoplastic plastics such as polycarbonate, PVC, thermoplastic elastomers or silicones can be used for this purpose.

The side-emitting step index fibers are preferably fixed on the carrier element by sewing and / or weaving. It is also possible to sew the step index fibers to one another and / or to the carrier element. Both textile yarns and, in turn, inorganic glass fibers can be used as sewing thread.

In general, the planar structure can also take place by connecting the side-emitting step index fibers according to the invention to a suitable carrier, for example by gluing, laminating, optionally together with a film and / or other suitable methods.

Particularly preferred is the carrier element of the planar structure according to the invention, on which and / or in which the side-emitting step index fibers are fixed, transparent and / or translucent so that the light emitted by the step index fibers can pass through the carrier element. To achieve color effects, the carrier element can be colored.

To further stabilize the sheet-like structure, it is also provided in a further preferred embodiment according to the invention that the composite element made up of the carrier element and side-emitting step index fibers is connected to a stabilization element.

The stabilization element is particularly preferably arranged such that the side-emitting step index fibers are located between a surface of the carrier element and a surface of the stabilization element. The stabilization element can thus also help protect the step index fibers. It is preferably arranged on the back as a cover layer in the form of a film or a rigid plate.

To increase the light yield, the side of the carrier element and / or the stabilization element facing the side-emitting step index fibers is preferably designed such that it can reflect the light emitted by the side-emitting step index fibers. This means that the side of the carrier element or of the stabilization element facing the step index fibers can be colored white or has a reflective design. This can be achieved particularly easily, for example, if aluminum foil is used as the stabilizing element. In this case, the carrier element preferably consists of a transparent and / or translucent plastic such as, for example, Plexiglas. Of course, it is also possible to connect further stabilizing elements to the composite element.

For light coupling, the optical fibers are grouped together by means of a bundle of light guides, the light guides being combined by means of end sleeves and / or adhesive tapes, usually glued, and the end faces being ground and polished so that optimal light coupling can take place. To increase the luminance of the emitting surface, the optical fibers can also be combined on both sides so that light can be coupled in on both sides.

To operate the planar structure according to the invention, light can be coupled into the optical fibers and thus into the side-emitting step index fibers. Point-shaped light sources are preferably used as the light source which, for optimal light yield, focus the light by means of an auxiliary lens in such a way that the light is irradiated within the acceptance angle specific for the optical fibers. Due to their compact design and comparatively high light yield, LEDs in particular, particularly preferably white light LEDs or RGB LEDs, are proposed for coupling in light.
In order to be able to introduce light into the planar structure according to the invention, it preferably has measures for connecting at least one LED as a light source. A flat structure according to the invention particularly preferably has measures for connecting at least one LED to opposite edges of the flat structure so that the light can couple into the end faces on both sides of the step index fibers.

Because the generation of the scattering area in the side-emitting fiber according to the invention is a serious problem, the preform which is used in the manufacturing process is also an essential part of the invention. The term “preform” is the expert in the field of Fiber draw is well known. It comprises the structure from which the fiber is drawn. A conventional preform, which is used to manufacture glass fibers without side-emitting properties, generally consists of a core rod made of glass, around which a cladding tube made of glass is arranged coaxially. The core rod can be created by pouring the glass into a mold. Post-processing, for example by grinding or fire polishing, is usually necessary. The cladding tube can come from a tube train. Processes for manufacturing glass tubes are well known. When the preform is pulled out to form the fiber, the cladding tube fuses with the core rod, the fiber core being formed from the core rod and the jacket being formed from the cladding tube. The diameter of the fiber is many times smaller than that of the preform, and many kilometers of fiber can be drawn from a single preform in this way.

A preform according to the invention for producing a side-emitting step index fiber according to the invention includes a core rod made of inorganic glass with the refractive index n ₁ and a cladding tube made of an inorganic glass with the refractive index n ₂ , the cladding tube enclosing the core rod along the core rod axis. At least one inlay rod made of an inorganic glass, which essentially has the refractive index n ₁ and in which scattering particles are embedded, is arranged between the core rod and the cladding tube, parallel to the core rod axis. The scattering areas are formed from the inlay rods during the fiber drawing.

A preform according to the invention preferably has 5 to 100 inlay rods between the core rod and the cladding tube, which are arranged parallel to the core rod axis. The inlay rods can be arranged at substantially the same distances from one another. However, the exact positioning of the inlay rods in the preform is not necessarily essential for the later appearance of the fiber bundle described, since inhomogeneities resulting from inaccurate positioning cancel each other out due to the large number of side-emitting fibers present in the fiber bundle.

Inlay rods with a diameter of 0.2 mm to 2 mm are preferably used for the preform.

The diameter of the scattering particles in an inlay rod can preferably be from 10 nm to 2000 nm, particularly preferably between 100 nm and 1200 nm.

The scattering particles that are embedded in the material of the inlay tube preferably contain SiO ₂ and / or SiN and / or BaO and / or MgO and / or ZnO and / or Al ₂ O ₃ and / or AlN and / or TiO ₂ and / or ZrO ₂ and / or Y ₂ O ₃ and / or the metals of these oxides alone and / or BN and / or B ₂ O ₃ and / or Ru and / or Os and / or Rh and / or Ir and / or Ag and / or Au and / or Pd and / or Pt and / or diamond-like carbon and / or glass ceramic particles.

Their concentration in the at least one inlay rod is preferably between 10 ppm and 1000 ppm, particularly preferably between 20 ppm and 100 ppm.

To produce the side-emitting step index fiber according to the invention, at least one preform described above is first produced as an intermediate product. For this purpose, a core rod made of an inorganic glass with the refractive index n _{1 is} provided, around the core rod at least one inlay rod made of an inorganic glass with the refractive index n _{1 is arranged} parallel to the core rod axis. The previously described scattering particles are embedded in the glass of the inlay rod and / or the inlay rods. A cladding tube made of an inorganic glass with the refractive index n _{2 is then} arranged around the core rod and inlay rods, so that the core rod and the inlay rod and / or the inlay rods are located within the cladding tube. However, it is also possible to arrange the inlay rod or rods after the arrangement of the core rod and inlay rod in the space between the core rod and the cladding tube. The preform obtained in this way is then fastened in a heating unit, heated in this and drawn into a glass fiber in a manner known to the person skilled in the art.

During the fiber draw, the core and the respective inlay rod fuse at the interface between the core and inlay rod. The inlay rod is also reshaped, i.e. if it had a round diameter in the preform, it forms a flat, slightly curved area on the circumferential surface of the core after the fiber has been drawn. If the scattering particles are embedded in this area, a scattering area that is extended along the fiber axis is generated. The scattering particles are distributed in this way, so to speak, on certain areas of the core circumferential surface. If several inlay rods fuse with one another, it is possible that the scattered area completely surrounds the core of the fiber, i.e. over its entire circumferential surface.

The temperature at which the fibers are drawn is called the drawing temperature and is above the softening temperature of the glass from which the cladding tube is made. Usually glasses are used for the core which have a lower softening temperature than the glass of the cladding tube, so that a temperature is reached in the core rod during the heating in the heating unit which is above the softening temperature of the glass of the core rod. However, heating methods are also known which enable the softening temperature of the core rod to be above that of the cladding tube. The drawing temperature is preferably also above the softening temperature of the highest melting glass which is used in the preform. Adjusting the drawing temperature influences the viscosity of the glass during fiber drawing in such a way that, in conjunction with the drawing speed, a fiber of the desired thickness can be obtained.

The inlay rods in which the scattering particles are embedded must, as described above, have essentially the same refractive index as the core rod. The easiest way to achieve this is to use the same glass for the core rod and inlay rods. Deviations in the refractive indices of the core rod and inlay rod and thus of the fiber core and matrix glass of the scattering area, which can occur due to variations in the production of the glass, are of course also covered by the invention.

In order to obtain the aforementioned discrete scattering areas extending along the fiber axis but not completely surrounding the core circumferential surface, the method according to the invention provides that at least one inlay rod fuses with the core rod when the preform is pulled out. If more than one inlay rod is used, they are arranged in such a way that they cannot completely fuse with one another. However, it is also possible that the inlay rods are arranged in such a way that some merge with one another, while others do not. In this way, discrete scattering areas of different widths can be generated along the fiber axis.

However, it is also possible that a scatter area is to be generated which completely surrounds the core along the fiber axis. The scatter area then, so to speak, occupies the entire circumferential area of the core. This is achieved by the method when a plurality of inlay rods are used and arranged in the preform in such a way that they fuse both with the core rod and with one another when the preform is pulled out. The thickness of the scatter area can be adjusted by the number and diameter of the inlay rods.

When the fiber is pulled out of the preform, a vacuum is preferably applied to it, i.e. a pressure is generated in the interstices of the preform which is lower than the pressure of the medium surrounding the preform. In this way, during the drawing process, the application of the cladding tube or the jacket to the core rod or the fiber core and / or the inlay rods or the scattered area is supported. This aspect of the method supports the application of the cladding to the scattered area and / or core during fiber draw and thus helps to avoid undesired gaps in the drawn fibers.

In a preferred embodiment of the method according to the invention, a glass is used for the cladding tube, the coefficient of thermal expansion of which is smaller than the coefficient of thermal expansion of the core glass used. The core glass is the glass from which the core rod and thus the fiber core are made. As described above, this ensures that the cladding exerts a tension on the fiber core and / or the scattered area (s), so that the resulting fiber has an increased breaking strength.

The method according to the invention is particularly preferably used in a multi-fiber drawing plant. In a multi-fiber drawing system, a corresponding number of fibers are drawn simultaneously from a plurality of preforms. In this way, fiber bundles can be produced efficiently. A multi-fiber drawing system is for example in the German patents DE 103 44 205 B4 and DE 103 44 207 B3 described in detail. Essentially, several preforms are arranged next to one another in a heating unit of a multi-fiber drawing system and several side-emitting step fibers are drawn out simultaneously in a multi-fiber drawing system, so that a fiber bundle is obtained which contains side-emitting step index fibers.

The fiber bundle obtained in this way can either be further processed or further processed with further fiber bundles with or without side-emitting properties to form a larger fiber bundle. To protect the fiber bundle, a particularly preferred embodiment of the method according to the invention provides that an outer jacket made of a transparent and / or translucent plastic is extruded around the fiber bundle. The plastic used is preferably flame-resistant.

Alternatively, the fiber bundle can be surrounded with glass fibers, which form an outer, non-combustible, transparent and / or translucent jacket around the fiber bundle. This can be done by looping around with other glass fibers or by wrapping a fabric made of glass fibers.

The side-emitting step index fiber according to the invention is preferably used together with other light guides and / or other side-emitting step index fibers in a fiber bundle which, as described above, is surrounded by an outer transparent and / or translucent jacket.

In order to produce rigid fiber bundles, the preforms are not drawn into fibers with diameters of typically 50 μm to 150 μm, as is the case with flexible fiber bundles, but rather into fiber rods with a diameter of approximately 0.5 mm to 1 mm. Then about 200 to 10,000 of these fiber rods are tightly packed in a jacket tube, the diameter of which can be about 10 mm to 60 mm, and drawn out to form a rigid fiber bundle with a diameter of about 0.5 mm to 20 mm. This fiber bundle has essentially the same side-emitting properties as a flexible fiber bundle. This primarily results in possible uses of up to typically around 2 m in length for precisely straight lighting. By thermal deformation, for example bending and / or pressing, two-dimensional or three-dimensional objects can be produced from the straight fiber rods. These can be all of the lighting solutions mentioned below, but also lettering or the like. The production of flat fiber rods or generally non-circular, rigid fiber rods or plates is also possible. Both fiber bundles made of fiber rods and also made of flexible fibers are encompassed by the term fiber bundle for the purposes of the invention.

A fiber bundle according to the invention can be used for the accent lighting of interiors and / or facades in architecture. The fiber bundles are preferably attached along the contours of interior components, for example passages, support elements, outlines of buildings, etc., and are connected to suitable light sources. It is thus possible to simulate the contours of a building or parts of a building using the fiber bundle with side-emitting fibers and to realize a linear light source.

The fiber bundle containing the side-emitting fibers according to the invention is particularly preferably used for the accentuated lighting of interiors of vehicles, in particular automobiles, aircraft, ships and / or trains. The fiber bundle can be attached at any point or inserted into the contours of these interiors. If light is coupled into the fiber bundle, it preferably appears as a luminous band or luminous line along these contours. Because the fiber bundle can be designed in such a way that it only contains flame-retardant substances, it can even meet very strict fire safety regulations. This makes it particularly suitable for use in all types of vehicles. In automobiles, a preferred place of attachment of a fiber bundle according to the invention can be, for example, a door lining, in which the contour of the recesses of the door opener, armrest, the transitions in the lining material, etc. can be emphasized in this way. On airplanes and ships, it can be attached along the ribbon windows, hand luggage compartments, etc. The fiber bundle according to the invention can advantageously be used for marking escape routes in aircraft and ships.

It is also preferred to use the fiber bundle according to the invention as part of furniture, in particular seating furniture, vehicle seats, living spaces and / or kitchens. If the fiber bundle is worked into the seams of seating furniture such as armchairs, sofas, chairs, etc., the contours of this furniture can be accentuated as a luminous band when the fiber bundle is illuminated. When integrating into shelves, cupboards, entire living landscapes can be designed with targeted lighting effects in this way.

In the automotive industry in particular, headlights are also increasingly being used to create a recognition value for the manufacturer through special lighting devices. For this reason, some automobile headlights have parking light rings which surround the low beam and appear as a largely homogeneously glowing ring when the lights are switched on. For example, other manufacturers use a band of LEDs in their headlights. The fiber bundle according to the invention is preferably used in headlights, in particular vehicle headlights of all types, particularly preferably in headlights of automobiles. The fiber bundle according to the invention makes it possible to produce any desired, preferably homogeneously luminous structures in headlights. For various reasons, LEDs are also finding increasing use in automobile headlights. Compared to LEDs arranged in strips, this use according to the invention has the advantage that a few LEDs are sufficient to produce the lighting. In addition, compared to a strip of LEDs, no individual light points are visible, which can also be preferred for design reasons. One or more LEDs can also be installed in the end face of the inventive Fiber bundle are coupled. In terms of the use according to the invention, the function as position light is included within headlights, which in turn include, for example, applications as parking lights and daytime running lights.

Another preferred use of the fiber bundle according to the invention is the contour lighting of vehicles, in particular automobiles, airplanes, ships and / or trains. This contour lighting can, if necessary, replace or supplement the prescribed position lights in the corresponding vehicles and thus contribute to road safety.

The use of the fiber bundle according to the invention for illuminating runways for aircraft, for example aircraft, helicopters, airships, etc., is also preferred. So far, runways have been illuminated by a large number of incandescent lamps arranged in a row. These have a limited lifespan, which is why the failed light bulbs in such a row have to be replaced again and again while the airport is in operation. If the fiber bundle according to the invention is arranged along the runway and / or also in the center thereof, a linear, luminous structure is generated which marks the position of the runway in the dark and / or in poor visibility. The lighting source can couple the light into the fiber bundle at a few central points that do not even have to be in the immediate vicinity of the runway. The fiber bundle according to the invention is largely maintenance-free, so that the maintenance of this runway lighting is limited to the few light sources used. In this way, for example, the runways of airports can be marked, but also those of aircraft carriers, helipads and other aircraft can be marked.

Another preferred application of the planar structure according to the invention is the backlighting of displays. Displays can be display devices of all kinds, but preferably flat screens, for example computer monitors, flat screen televisions and the displays of cell phones and PDAs (Personal Digital Assistants). So far, large-format displays that require backlighting have been illuminated by fluorescent tubes which are arranged on the edge of the display or behind the display surface of the display. The most homogeneous possible illumination of the display surface is desired, which is why there is usually a diffuser plate between the fluorescent tubes and the display surface, which homogenizes the light emitted by the fluorescent tubes. The light can also be coupled in from the side in diffuser plates, for example if the fluorescent tubes are arranged on the edge of the display. The diffuser plate then acts as a light guide. In the case of smaller displays, for example displays of cell phones and / or PDAs, light from LEDs is usually coupled laterally into the diffuser plate. With larger displays, LED lighting has not yet been used to any significant extent, although it would be more cost-effective than lighting with fluorescent tubes, because it has not yet been possible to achieve a sufficiently homogeneously illuminated light surface. The side-emitting fiber bundles according to the invention can provide a remedy. If they are laid in suitable structures behind the display surface, behind or without a diffuser plate as required, LEDs can couple light into the end faces of the fiber bundles so that the fiber bundle or bundles with side-emitting properties provide the background lighting for the display. If the arrangement of the fiber bundle is compared with the intensity profile of the laterally emitted light, a large-area, homogeneous background lighting for displays can also be achieved in a cost-effective manner.

All of the aforementioned applications are also possible with such a flat structure. In particular, such a flat structure can also be designed as part of the seat of seating furniture, but also of clothing and all known uses for textiles.

• 1a: den Längsschnitt entlang der Faserachse einer nicht seitenemittierenden Stufenindexfaser aus dem Stand der Technik.
• 1b: den Querschnitt einer nicht seitenemittierenden Stufenindexfaser aus dem Stand der Technik.
• 2a: den Längsschnitt entlang der Faserachse einer seitenemittierenden Stufenindexfaser mit den Kern vollumfänglich umschließendem Streubereich.
• 2b: den Querschnitt einer seitenemittierenden Stufenindexfaser mit den Kern vollumfänglich umschließendem Streubereich.
• 3a: den Längsschnitt entlang der Faserachse einer seitenemittierenden Stufenindexfaser mit Streubereichen, die den Kern in Teilbereichen entlang der Faserachse vollumfänglich umschließen.
• 3b: den Querschnitt einer seitenemittierenden Stufenindexfaser mit Streubereichen, die den Kern in Teilbereichen entlang der Faserachse vollumfänglich umschließen.
• 4a: den Längsschnitt entlang der Faserachse einer erfindungsgemäßen seitenemittierenden Stufenindexfaser mit diskreten Streubereichen, die sich auf einem Teilbereich des Kernumfangs entlang der Faserachse erstrecken.
• 4b: den Querschnitt einer erfindungsgemäßen seitenemittierenden Stufenindexfaser mit diskreten Streubereichen, die sich auf einem Teilbereich des Kernumfangs entlang der Faserachse erstrecken.
• 5a: den Längsschnitt entlang der Faserachse einer erfindungsgemäßen seitenemittierenden Stufenindexfaser mit diskreten Streubereichen, die sich jeweils auf einem Teilbereich des Kernumfangs auf Teilbereichen entlang der Faserachse erstrecken.
• 5b: den Querschnitt einer erfindungsgemäßen seitenemittierenden Stufenindexfaser mit diskreten Streubereichen, die sich jeweils auf einem Teilbereich des Kernumfangs auf Teilbereichen entlang der Faserachse erstrecken.
• 6a: eine erfindungsgemäße Preform zum Herstellen einer seitenemittierenden Stufenindexfaser.
• 6b: ein Faserbündel beinhaltend seitenemittierenden Stufenindexfasern.
• 7: das Schema einer Vielfaserziehanlage.
• 8: einen Schnitt quer zur Faserachse durch ein erfindungsgemäßes Flächengebilde, bei dem die seitenemittierenden Stufenindexfasern zwischen einem Trägerelement und einem Stabilisierungselement fixiert sind.
• 9: einen Schnitt quer zur Faserachse durch ein alternatives erfindungsgemäßes Flächengebilde, bei dem die seitenemittierenden Stufenindexfasern in einem Trägerelement eingelagert sind.
• 10: einen Schnitt quer zur Faserachse durch ein erfindungsgemäßes Flächengebilde, bei dem die seitenemittierenden Stufenindexfasern als Faserbündel auf einem Trägerelement fixiert sind und das Gebilde in einem Gehäuse gekapselt ist.
• 11: ein Flächengebilde mit Maßnahmen zum Anschließen von Lichtquellen
• 12: den schematischen Schnitt durch ein Display beinhaltend ein erfindungsgemäßes Flächenelement zur Hintergrundbeleuchtung des Displays.
• 13: ein Flächengebilde entsprechend 11, jedoch mit Maßnahmen zum Anschließen von Lichtquellen an beidem Stirnflächen der seitenemittierenden Stufenindexfasern.
• 14: einen Flugzeuginnenraum mit Anwendungen von Faserbündeln mit seitenemittierenden Eigenschaften.
• 15a: einen Automobilscheinwerfer mit Faserbündeln mit seitenemittierenden Eigenschaften.
• Fig, 15b: einen weiteren Automobilscheinwerfer mit Faserbündeln mit seitenemittierenden Eigenschaften.
• 16: ein Gebäude mit einer akzentuiert leuchtenden Spitze.
• 17: die Landebahn eines Flughafens mit leuchtender Landebahnmarkierung.
• 18: Messkurven der Helligkeitsverteilung erfindungsgemäßer seitenemittierender Stufenindexfasern im Vergleich zum Stand der Technik.
• 19: Messkurven der spektralen Transmission erfindungsgemäßer seitenemittierender Stufenindexfasern.

The invention is further explained with reference to the accompanying drawings. They represent:

• 1a : the longitudinal section along the fiber axis of a non-side-emitting step index fiber from the prior art.
• 1b : the cross-section of a non-side-emitting step index fiber from the prior art.
• 2a : the longitudinal section along the fiber axis of a side-emitting step-index fiber with the scattering area completely surrounding the core.
• 2 B : the cross-section of a side-emitting step-index fiber with the scattering area completely surrounding the core.
• 3a : the longitudinal section along the fiber axis of a side-emitting step index fiber with scattering areas that completely surround the core in partial areas along the fiber axis.
• 3b : the cross-section of a side-emitting step index fiber with scattering areas that completely surround the core in partial areas along the fiber axis.
• 4a : the longitudinal section along the fiber axis of a side-emitting step-index fiber according to the invention with discrete scattering areas which extend on a partial area of the core circumference along the fiber axis.
• 4b : the cross-section of a side-emitting step index fiber according to the invention with discrete scattering areas which extend on a partial area of the core circumference along the fiber axis.
• 5a : the longitudinal section along the fiber axis of a side-emitting step-index fiber according to the invention with discrete scattering areas, which each extend on a sub-area of the core circumference on sub-areas along the fiber axis.
• 5b : the cross-section of a side-emitting step index fiber according to the invention with discrete scattering areas, each of which extends on a sub-area of the core circumference on sub-areas along the fiber axis.
• 6a : a preform according to the invention for producing a side-emitting step index fiber.
• 6b : a fiber bundle including side-emitting step-index fibers.
• 7th : the scheme of a multi-fiber drawing machine.
• 8th : a section transverse to the fiber axis through a flat structure according to the invention, in which the side-emitting step index fibers are fixed between a carrier element and a stabilizing element.
• 9 : a section transverse to the fiber axis through an alternative planar structure according to the invention, in which the side-emitting step index fibers are embedded in a carrier element.
• 10 : a section transverse to the fiber axis through a flat structure according to the invention, in which the side-emitting step index fibers are fixed as fiber bundles on a carrier element and the structure is encapsulated in a housing.
• 11 : a flat structure with measures for connecting light sources
• 12th : the schematic section through a display containing a surface element according to the invention for backlighting the display.
• 13th : a flat structure accordingly 11 , but with measures for connecting light sources to both end faces of the side-emitting step-index fibers.
• 14th : an aircraft interior with applications of fiber bundles with side emitting properties.
• 15a : an automobile headlight with fiber bundles with side-emitting properties.
• 15b: a further automobile headlight with fiber bundles with side-emitting properties.
• 16 : a building with an accentuated glowing tip.
• 17th : the runway of an airport with illuminated runway markings.
• 18th : Measurement curves of the brightness distribution of side-emitting step-index fibers according to the invention in comparison with the prior art.
• 19th : Measurement curves of the spectral transmission of side-emitting step-index fibers according to the invention.

All figures are schematic, the diameters of their elements are not to scale and the proportions of all elements to one another can also differ in the real objects from the drawings.

1a shows the longitudinal section along the fiber axis (A) of a step index fiber from the prior art. This step index fiber consists of a core ( 1 ) with the refractive index n ₁ . This is completely covered by the coat ( 2 ) enclosed, which has the refractive index n ₂ . Incident light ( 4th ) is in the core ( 1 ) because due to the smaller refractive index n ₂ total reflection on the cladding ( 2 ) occurs. However, the condition of total reflection is only possible up to a critical angle of the light hitting the cladding, which depends on the values of the refractive indices of the core and cladding. The critical angle β _min can be calculated by sin (β _Min ) = n ₂ / n ₁ , where β _{Min is} measured from a plane perpendicular to the fiber axis.

The refractive indices of the fiber core and the surrounding cladding are also for the acceptance angle α _Max decisive, which, measured from the fiber axis (A), describes the maximum angle of the light hitting the end face of the fiber that can be coupled into the fiber. _{The numerical aperture N A of} the fiber is commonly used as a measure of the fiber's ability to couple light incident at an angle. It is calculated as N _A = n sin (αMax) = (n1 ² - n2 ² ) ^1/2 , where n represents the refractive index of the medium that the light passes through before it is coupled into the fiber.

1 b shows the cross section of the fiber from 1a , ie a section transverse to the fiber axis (A). In the 1a and 1b The fibers shown have no side-emitting properties because they do not contain any scattering range.

2a shows a side-emitting step index fiber in its longitudinal section along the fiber axis (A). This fiber has a scatter area ( 3 ), which is between the core ( 1 ) and coat ( 2 ) of the fiber and the core ( 1 ) completely encloses. Light coupled into the fiber ( 4th ) is in the scatter range ( 3 ) outwards, ie radially coupled out of the fiber, even if the angle β _min is exceeded. Without the scatter range ( 3 ) otherwise the condition of total reflection would be fulfilled and the fiber would essentially absorb the light in the core ( 1 ) conduct. Responsible for decoupling the light ( 4th ) is the scattering of light ( 4th ) to those in the scatter range ( 3 ) stored scattered particles. Because the material of the scattering area ( 3 ), in whose matrix the scattering particles are embedded, essentially the same refractive index n ₁ as the material of the core ( 1 ), the light ( 4th ) reach the scattering particles largely unhindered from the matrix material. Through single or multiple interaction with the scattering particles, it can be deflected by the scattering particles from its original angle of incidence, so that the angle of incidence on the mantle ( 2 ) is reduced so that it is smaller than β _min and can couple the light out of the fiber. Is the angle of incidence on the mantle ( 2 ) greater than β _min , there is a reflection back into the scatter area ( 3 ) or depending on the impact and / or interaction with the scattering particles in the core ( 1 ).

Hits the light ( 4th ) on its way through the scattering area ( 3 ) randomly does not come across any scattering particles, it hits the mantle ( 2 ) and behaves as if there was no spread. In this case, this means that if the angle of passage through the scatter area ( 3 ) and thus the angle of impact on the mantle ( 2 ) greater than β _min is the light from the mantle ( 2 ) back into the scatter range ( 3 ) is reflected back. As in the case previously described, the back-reflected light can in turn meet scattering particles, which can result in beam paths that ultimately lead to the light being coupled out of the fiber or to its conduction in the core ( 1 ) being able to lead.

That the spread ( 3 ) completely encloses the core is based on 2 B clearly visible which the cross-section of the fiber according to 2a shows.

In 3a is are scatter range ( 3 ) of the shown fibers are designed in such a way that they have alternating areas with embedded scattering particles, which extend along the fiber axis (A) and the core ( 1 ) according to the cross-section 3b completely enclose and alternate with areas along the fiber axis (A) which have the matrix material of the scattering area, but in which no scattering particles are embedded. Does that hit the core ( 1 ) guided light ( 4th ) to scatter areas ( 3 ) with embedded scattering particles, the light ( 4th ) are coupled out radially with a certain probability according to the mechanisms described above. Meets in the core ( 1 ) guided light ( 5 ) However, in areas of the scattering area that do not have any scattering particles, it passes through these areas largely unhindered because, as described, they have the same refractive index n ₁ as the core ( 1 ) and can be due to total reflection on the cladding ( 2 ) are guided in the fiber. By specifically setting the interval between the spreading areas ( 3 ) with embedded scattering particles and the areas without embedded scattering particles, the amount of light that is coupled out can be adjusted. As already described, however, other parameters are also responsible for the efficiency of the coupling.

4a shows the longitudinal section of a step index fiber according to the invention along the fiber axis (A), the discrete scattering areas ( 3 ), which extend along the fiber axis (A), but which, as shown in the cross-section, follow 4b can only be seen to extend to partial areas of the core perimeter. In other words, in this case only partial areas of the core circumferential surface with scattered areas ( 3 ) covered. This is why we speak of discrete scatter ranges in this case. As previously described, these discrete scattering areas are created by fusing inlay rods with a core rod. In the 4b The form shown is to be understood purely schematically. The discrete spread ( 3 ) can be shaped however you want. In essence, the merging process determines the actual shape of the discrete scattering area ( 3 ). As with 2a described, light ( 4th ) through the discrete scattering areas ( 3 ) are radially coupled out of the fiber.

Analogous to the embodiment according to 3a it is also in the presence of discrete scatter areas ( 3 ) corresponding 4a possible that the discrete scatter ranges ( 3 ) are only provided with scattering particles on parts of their extension along the fiber axis (A). A longitudinal section along the fiber axis (A) of such a fiber is shown in 5a shown, a cross-section in 5b .

6a shows a preform ( 10 ), which is suitable for producing a side-emitting step-index fiber according to the invention with discrete scattering areas enclosing the core only on partial areas of the core circumference. It is therefore necessary as a preliminary product for the fiber according to the invention. The preform ( 10 ) includes a core rod ( 11 ) around which the inlay rods ( 13th ) are arranged. The core rod ( 11 ) and the inlay rods ( 13th ) are from a cladding tube ( 12th ) surround. In most cases, core rod ( 11 ) and cladding tube ( 12th ) aligned coaxially to each other, i.e. the axis of the core rod ( 11 ) and cladding tube ( 12th ) are essentially on top of each other, and are located between the core rod ( 11 ) and cladding tube ( 12th ) the inlay rods ( 13th ) are located. The axes of the inlay rods ( 13th ) are usually parallel to the axis of the core rod ( 11 ) and cladding tube ( 12th ) aligned.

In 6b is a bundle of fibers ( 23 ), which contains a large number of side-emitting step index fibers ( 22nd ) contains. In the present form it is of an outer coat ( 24 ), which protects the bundle from mechanical loads and which, as described, can consist of plastics and / or glass fibers.

The core rod consists of a glass with the refractive index n ₁ and the cladding tube consists of a glass with the refractive index n ₂ . The inlay rods also consist of a glass with the refractive index n ₁ , in which the scattering particles are embedded. As described, it is preferred if the glass of the inlay rods ( 13th ) largely identical to that of the core rod ( 11 ), as this is the best way to ensure that the refractive indices match and that there is also the least risk of undesirable contact reactions which can occur during fiber draw and which can significantly reduce the fiber quality. In order to maintain a tensioned fiber, the glass of the cladding tube ( 12th ) as described, preferably chosen so that its thermal expansion is smaller than that of the glass of the core rod ( 11 ) is.

When pulling out the preform ( 10 ) becomes from the core rod ( 11 ) the fiber core ( 1 ) and from the duct ( 12th ) the coat ( 2 ). The inlay rods ( 13th ) with the embedded scattering particles merge with the core rod when the fibers are drawn ( 11 ) and the duct ( 12th ) and become the spreading areas ( 3 ). It is also possible that the inlay rods ( 13th ) also merge with each other. If there is a correspondingly strong fusion and / or if there are a sufficient number of inlay rods ( 13th ) in the preform ( 10 ), the inlay rods ( 13th ) a scattering area ( 3 ) which form the fiber core ( 1 ) according to the 2a until 3b fully encloses. Is the fusion of the inlay rods ( 13th ) incomplete with each other, the discrete scattering areas ( 3 ) according to the 4a until 5b .

7th shows the simultaneous fiber drawing of fibers ( 22nd ) from several preforms ( 10 ) in a multi-fiber drawing machine. The preforms ( 10 ) are installed in a heating unit ( 20th ) brought in. At least the lower area of the preforms ( 10 ) drawing temperature is brought. Usually the heating unit ( 20th ) several heating sockets, with each preform ( 10 ) a heating socket is assigned. The heating socket usually contains the means for heating the preform ( 10 ) contain. Multiple fibers ( 22nd ) are pulled at the same time according to the drawing, over a pulley ( 21 ) deflected and wound on a take-up spool. There is a bundle of fibers on the take-up spool ( 23 ), which in this case is not surrounded by an outer jacket. The number of fibers in the fiber bundle corresponds to the number of fibers drawn at the same time ( 22nd ).

8th shows the basic structure of a flat structure according to the invention as a section transverse to the fiber bundle axis (A). The individual side-emitting step index fibers ( 22nd ) are here as a monolayer on a transparent carrier element ( 71 ) glued on and thus fixed with this. The side-emitting step index fibers ( 22nd ) emitted light ( 4th ) passes through the carrier element ( 71 ) and is preferably emitted from there in all possible spatial directions. The surface of the carrier element facing away from the step index fibers ( 71 ) thus acts as a preferably homogeneously luminous radiating surface. On the back there is a stabilizing element ( 72 ) connected to the side-emitting step index fibers so that they are connected to the carrier element ( 71 ) and the stabilizing element ( 72 ) form a sandwich structure. as Stabilizing element ( 72 ) For example, an aluminum foil can be used, which can be fixed in a simple manner by gluing.

In 9 a variant is shown in which the side-emitting step index fibers ( 22nd ) are encapsulated by a transparent plastic, which in this way supports the carrier element ( 71 ) forms. This can be done in sections as an injection molding process or virtually endlessly as an extrusion process. The light emitted by the step index fibers ( 4th ) can preferably radiate from both surfaces of the sheet-like structure. It is also possible, however, for a surface of the sheet-like structure to be provided with a reflective layer so that the light can only be emitted in one direction, but its intensity is increased.

In 10 are the side-emitting step index fibers at least part of spaced-apart fiber bundles ( 23 ), in which a large number of side-emitting step index fibers ( 22nd ) is included. The fiber bundles ( 23 ) on a carrier element ( 71 ) fixed with a reflective cover layer. The whole arrangement encapsulated ( 75 ). That of the fiber bundles ( 23 ) emitted light ( 4th ) passes through the encapsulation ( 75 ). This can consist of a transparent plastic. However, other materials are also possible, so that hermetic encapsulation of the sheet-like structure is made possible. Of course, it is also possible with this encapsulation solution that instead of the fiber bundles ( 23 ) also side-emitting step index fibers ( 22nd ) on the carrier element ( 71 ) are fixed.

11 shows a fabric in which the side-emitting step index fibers ( 22nd ) and / or fiber bundles ( 23 ) containing the side-emitting step index fibers are predominantly arranged in parallel. The step index fibers ( 22nd ) and / or the fiber bundles ( 23 ) be fixed to each other and / or with non-illustrated support elements ( 71 ) and / or stabilizing elements ( 72 ) be connected. A light source ( 81 ) can be inserted into the end face of the step index fibers according to the invention ( 22nd ) and / or the fiber bundles ( 23 ) are coupled. The step index fibers ( 22nd ) and / or the fiber bundles ( 23 ) by means of the light guide bundling ( 83 ) so that the flat arrangement becomes a coupling surface ( 82 ) is transformed. In the coupling area ( 82 ) are the end faces of the step index fibers ( 22nd ) preferably summarized as closely as possible. Is light coming from the light source ( 81 ) via the coupling surface ( 82 ) into the step index fibers ( 22nd ) and / or the fiber bundles ( 23 ) and thus coupled into the fabric, the step index fibers ( 22nd ) and / or fiber bundles ( 23 ) are coupled out laterally and emitted from the surface ( 4th ).

Corresponding 13th the fabric can also have two coupling surfaces ( 81 , 82 ) so that in the fiber bundle ( 23 ) and / or the side-emitting step index fibers ( 22nd ) light can be coupled in from both end faces. Depending on the type of arrangement of the fiber bundles ( 23 ) and / or the side-emitting step index fibers ( 22nd ) but there is also a higher number of coupling surfaces ( 81 , 82 ) possible.

12th represents the schematic section through a display containing a surface element according to the invention for backlighting the display. Here, a display unit ( 91 ) by means of several spaced apart, parallel to each other arranged fiber optic bundles ( 23 ) each with a large number of side-emitting step index fibers ( 22nd ) backlit. The fiber bundle ( 23 ) is on a support element ( 72 ) fixed, which is preferably on the fiber bundle ( 23 ) facing side is mirrored. The display unit ( 91 ) can be, for example, a TFT unit with the two polarization plates and the liquid crystals in between. That from the fiber bundle ( 23 ) emitted light ( 4th ) passes through the TFT unit. In this application example, LEDs are particularly preferred as the light source ( 81 ) used.

In 14th the interior of an aircraft is shown, for example the cabin of a passenger aircraft. Fiber bundles containing the side-emitting fibers according to the invention can find diverse applications in aircraft cabins. If the outer sheaths of the fiber bundles are formed from materials that are flame retardant, the fiber bundles, which otherwise contain glass, meet the licensing requirements of the authorities responsible for licensing passenger aircraft and the applicable manufacturer requirements. In 14th the side-emitting fiber bundles are sometimes shown as broad bands. This representation does not have to be true to scale. Usually, the fiber bundles are used as a narrow fiber strand that appears as a glowing line.

Such a light strip can be used as contour lighting ( 30th ) along windows of the aircraft cabin, the compartments of the hand luggage storage or interior dividers. In general, any form of contour lighting is possible within the aircraft cabin. In the floor of the aircraft cabin is the side-emitting fiber bundle for marking the paths ( 31 ) mounted inside the aircraft. Particularly This waymarking is advantageous ( 31 ) to mark the paths to the emergency exits. It is also possible to use the side-emitting fiber bundles as contour lighting for seats ( 33 ) to use. In addition to the decorative effect, this application has the advantage that the ambient light can be reduced to set night conditions in the cabin, which are used for the passengers to support sleep phases, but the passengers can still find their seats. It has been recognized that, especially on long-haul flights, taking a nap makes the journey less stressful for passengers. That is why more and more importance is attached to suitable night-time equipment for aircraft interiors.

If the side-emitting optical fibers are used in the form of a flat structure, for example by being woven with textile fibers, they can be integrated into the fabric of the seat covers. Then it is not only possible to use the fibers to create contour lighting, but also areas such as parts of the surface of the seats ( 32 ) to make bright.

15a shows an automobile headlight ( 40 ), in which side-emitting fiber bundles take on lighting tasks. In this example they enclose as a ring ( 41 ) Dimmed headlights ( 42 ) and / or high beam ( 42 ). The side-emitting fiber bundles can thus be inside the headlight ( 40 ) can be used as parking lights or daytime running lights.

In 15b is also an automobile headlight ( 40 ) in which the side-emitting fiber bundle ( 45 ) as a strand below the main headlights ( 42 ) is arranged. In this example too, in addition to decorative functions, it can also perform tasks as parking lights and / or daytime running lights.

The application of the fiber bundle according to the invention ( 41 , 45 ) in automobile headlights ( 40 ) is advantageous because the fiber bundle ( 41 , 45 ) consists at least predominantly of glass and is therefore resistant to heat and weathering, which can be intensified by the action of aggressive substances. The fiber bundle according to the invention made of glass is less sensitive to weathering and heat stress than side-emitting fiber bundles made of plastics. In addition, much higher light outputs can be coupled into fiber bundles made of glass than is possible in fiber bundles made of plastic.

Likewise, LEDs in particular are particularly suitable for coupling into side-emitting fiber bundles, since their radiating surface, which is small in comparison to incandescent lamps or gas discharge lamps, enables efficient coupling without a large-volume optics. In this way, costs, weight and space can be saved in an automobile headlight. Compared to the attachment of LEDs arranged in a band, the use of a side-emitting fiber bundle ( 41 , 45 ) in automobile headlights ( 40 ) the advantage that the light is emitted homogeneously, so that the aesthetically unattractive impression of individual light points is not created, other road users are not irritated by a large number of light points, the light effect is largely independent of the angle and the number of LEDs is reduced and thus energy during use the headlight can be saved, which in turn can reduce the fuel consumption of the vehicle.

16 shows the contour lighting ( 51 ) of parts of a building ( 50 ). In the present example, the building is a high-rise, with the outlines of the dome appearing to be luminous to the viewer due to the side-emitting fiber bundles.

Based 17th is the use of the fiber bundles according to the invention with side-emitting properties as marking of runways of aircraft ( 60 ) shown. Both the side marking ( 61 ) as well as a median ( 62 ) can, as described above, advantageously be implemented by means of the side-emitting step-index fibers according to the invention.

In 18th are the measured brightnesses of the side emission of side-emitting step-index fibers according to the invention ( 90 , 91 , 92 ) plotted in against the distance from the end face of the fiber. The curves ( 93 ) and ( 94 ) represent side-emitting step index fibers from the prior art as a comparison. The measurement of the brightness as a function of the distance gives the brightness distribution profile of the side-emitting fiber. The greatest possible brightness over the greatest possible distance is desirable for most applications. The brightness values in the 18th are given in arbitrary units. Curve ( 91 ) shows the brightness distribution profile of a side-emitting step-index fiber according to the invention, which were drawn from a preform with 45 inlay rods, curve ( 92 ) one made from a preform with 93 inlay rods and curve ( 90 ) one from a preform with 15 inlay rods. The scattering particles consisted of Pt in all cases. As you can see, the brightness and thus the coupling efficiency of the side-emitting step index fibers according to the invention ( 90 , 91 , 92 ) significantly larger than those known from the prior art ( 93 , 94 ).

Curve ( 94 ) represents a step index fiber in which a groove has been milled into the preform of the core rod parallel to the core rod axis. The drawn fiber accordingly has a non-circular core with a notch along the fiber axis. As can be seen from the very low brightness values, the coupling-out efficiency of such a fiber is only very low, which is why it only shows a very weak side emission effect. It only shines very dark, so to speak, which is why such a fiber is unusable for most applications.

In the case of the fiber, which by curve ( 93 ), the core of the fiber was doped with scattering particles. As you can see, such a fiber decouples the guided light reasonably well, but no side emissions can be detected within a short distance. As a result, such a fiber can only be used disadvantageously for applications which require longer fiber lengths.

By comparing the curves of the side-emitting step index fibers according to the invention ( 90 , 91 , 92 ) with those from the state of the art ( 93 , 94 ) one sees immediately that the fibers according to the invention have the side emission effect in usable brightness ranges (brightness values above 2) over a longer fiber stretch than the fibers from the prior art. The decoupling efficiency correlates with the number of inlay rods, as shown in particular by comparing the curves ( 91 ) and ( 92 ) can be determined. Such fibers shine very brightly over shorter distances. If longer fiber lengths are required, a more homogeneous brightness distribution is possible by reducing the inlay rods, such as curve ( 90 ) shows. By comparing the curves ( 90 , 91 , 92 ) of the side-emitting step index fibers according to the invention, the scalability of the side emission effect can also be demonstrated very well by the number of inlay rods in the preform.

Further evidence of the scalability of the side emission effect through the number of inlay rods can be 19th in which the transmission of side-emitting step index fibers according to the invention is plotted against the wavelength of the light guided in the fiber. The greater the transmission, the more of the coupled light is guided in the fiber. Since the measured fibers actually had no absorption in the fiber core, the transmission is also a measure of the efficiency of the desired lateral coupling out of the fibers. This means that the greater the transmission, the smaller the effect of the side emission. A fiber that has a higher transmission therefore shines weaker.

Curve ( 95 ) represents a side-emitting step index fiber according to the invention, which was drawn from a preform with 15 inlay rods, the diameter of which was 2.8 mm. In all the curves shown, the scattering particles consisted essentially of nano-fine Pt powder. With curve ( 95 ) a size distribution was chosen so that the diameter of the scattering particles was from 500 nm to 1200 nm. Curve ( 96 ) represents a side-emitting step index fiber according to the invention, which was also drawn from a preform with 15 inlay rods with a diameter of 2.8 mm, the size distribution of the scattering particles being selected so that their diameter was from 150 nm to 450 nm. How to compare the curves ( 95 ) and ( 96 ), smaller scattering particles in the wavelength range up to about 560 nm cause a slightly lower transmission, in the range above about 560 nm a slightly higher transmission.

The curves ( 97 ) and ( 98 ) represent side-emitting step index fibers according to the invention, which were also drawn from a preform with 30 inlay rods with a diameter of 2.8 mm. The scattering particles again consisted essentially of nano-fine Pt powder. With curve ( 97 ) the diameter of the scattering particles was from 150 nm to 450 nm, with curve ( 98 ) from 500 nm to 1200 nm. At a wavelength of up to about 700 nm, the fiber with smaller scattering particles (curve ( 97 )) a higher transmission than the fiber with larger scattering particles (curve ( 98 )), at wavelengths over about 700 nm the ratio is reversed.

The comparison of the transmissions of the fibers drawn from preforms with 15 inlay rods (curves ( 95 ) and ( 96 )), with fibers made from preforms with 30 inlay rods (curves ( 97 ) and ( 98 )) shows that fibers, increasing the number of inlay rods in the preform, reduces the transmission of the resulting fiber and thus increases the efficiency of the lateral coupling out of the fiber. In this way, too, the scalability of the side emission effect can be demonstrated by the choice of the number of inlay rods in the preform.

To produce a preferred embodiment of the side-emitting step index fiber according to the invention, a core rod ( 11 ) with fire-polished surface together with inlay rods ( 13th ) and a cladding tube drawn into a fiber according to the method described. The core rod had a diameter of 30 mm. The cladding tube ( 12th ) had an outer diameter of 35 mm and an inner diameter of 33.5 mm. In the cladding tube that is melted shut at one end ( 12th ) became the core rod ( 11 ) and 1 to 100 inlay rods ( 13th ) from a glass with the same composition as the core rod ( 11 ), to which, however, nano-fine zirconium particles or nano-fine precious metal particles in the concentration range from 1 ppm to 100 ppm were added to the melt. The diameter of the inlay rods was between 0.1 mm and 2 mm. The closed end of the resulting preform ( 10 ) was placed between the core rod ( 11 ) and cladding tube ( 12th ) into the heating unit ( 20th ) of a known drawing machine and heated up to drawing temperature. After softening the end of the preform ( 10 ) this was removed from the heating unit ( 20th ) pulled and thus tapered to a fiber. Through this process the inlay rods ( 13th ) softened so much that they deformed and eventually a scattering area ( 3 ) between core ( 1 ) and coat ( 2 ) the fiber ( 22nd ) formed. By tracking the preform ( 10 ) in the heating unit ( 20th ) a continuous fiber drawing process was possible, the result of which was a side-emitting step index fiber with a diameter of 5 µm to 300 µm and a length of several kilometers.

Advantageously, as materials for the core rod ( 11 ) and thus for the core ( 1 ) Glasses with the compositions mentioned below are used.

Core glass variant 1 with refractive index n ₁ from 1.65 to 1.75, including (in mol% based on oxide) SiO ₂ 25 to 45 Ta ₂ O ₅ 0.1 to 6 B ₂ O ₃ 13 to 25 ZrO ₂ 0.1 to 8 CaO 0 to 16 ZnO 0.1 to 8 SrO 0 to 8 CaO + SrO + BaO + ZnO> 33 BaO 17 to 35 Al ₂ O ₃ 0 to 5 La ₂ O ₃ 2 to 12

Core glass variant 2 with refractive index n ₁ from 1.65 to 1.75, including (in mol% based on oxide) SiO ₂ 54.5 to 65 ZnO 18.5 to 30 Sum of the alkali oxides 8 to 20 La ₂ O ₃ 0 to 3 ZrO ₂ 2 to 5 HfO ₂ 0.02 - 5 ZrO ₂ + HfO ₂ 2.02 to 5 BaO 0.4 to 6 SrO 0 to 6 MgO 0 to 2 CaO 0 to 2 Sum of alkaline earth oxides 0.4 to 6 Li ₂ O 0.5 to 3, but not more than 25 mol% of the sum of the alkali oxides SiO + ZrO ₂ + HfO ₂ > 58.5 Ratio ZnO: total of alkaline earth oxides> 3.5: 1

Core glass variant 3 with refractive index n ₁ from 1.58 to 1.65, including (in mol% based on oxide) SiO ₂ 50 to 60 Nb ₂ O ₅ 0 to 4 B ₂ O ₃ 0 to 15 La ₂ O ₃ + Y ₂ O ₃ + Nb ₂ O ₅ 0 to 4 BaO 10 to 35 Na ₂ O 4.5 to 10 SrO 0 to 18 K ₂ O 0.1 to 1 Sr + Ba 10 to 35 Rb ₂ O 0 to 1.5 ZnO 0 to 15 Cs ₂ O 0 to 1.5 Sr + Ba + Zn 10 to 40 Rb ₂ O + Cs ₂ O 0 to 1.5 B ₂ O ₃ + ZnO 5 to 35 Sum of alkaline earth oxides 4.8 - 11 Al ₂ O ₃ 0.1 to 1.9 MgO 0 to 6 ZrO ₂ 0 to 4 CaO 0 to <5 La ₂ O ₃ 0 to 4 Y ₂ O3 0 to 4

Core glass variant 4 with refractive index containing (in% by weight based on oxide) SiO ₂ 42 to 53 ZnO 30 to 38 Na ₂ O <14 K ₂ O <12 Na ₂ O + K ₂ O ≥ 2 BaO <0.9

Core glass variant 5 with refractive index containing (in% by weight based on oxide) SiO ₂ 30 to 45 B ₂ O ₃ <12 ZnO <10 BaO 25 to 40 Na ₂ O <10 K ₂ O <2 Al ₂ O ₃ <1 La ₂ O ₃ <10

Cladding glass variant 1 (in% by weight based on oxide), including SiO ₂ 70 to 78 MgO 0 to 1 Al ₂ O ₃ 0 to 10 CaO 0 to 2 B ₂ O ₃ 5 to 14 SrO 0 to 1 Na ₂ O 0 to 10 BaO 0 to 1 K ₂ O 0 to 10 F. 0 to 1 and essentially no Li ₂ O.

Cladding glass variant 2 (in% by weight based on oxide), including SiO ₂ 63 to 75 MgO 0 to 5 Al ₂ O ₃ 1 to 7 CaO 1 to 9 B ₂ O ₃ 0 to 3 BaO 0 to 5 Na ₂ O 8 to 20 F. 0 to 1 K ₂ O 0 to 6 and essentially no Li ₂ O.

Cladding glass variant 3 (in% by weight based on oxide), including SiO ₂ 75 to 85 Al ₂ O ₃ 1 to 5 B ₂ O ₃ 10 to 14 Na ₂ O 2 to 8 K ₂ O 0 to 1 and essentially no Li ₂ O and MgO.

Cladding glass variant 4 (in% by weight based on oxide), including SiO ₂ 62 to 70 B ₂ O ₃ > 15 Li ₂ O > 0.1 Na ₂ O 0 to 10 K ₂ O 0 to 10 MgO 0 to 5 CaO 0 to 5 SrO 0 to 5 BaO 0 to 5 ZnO 0 to 5 F. 0 to 1

Cladding glass variant 5 (in% by weight based on oxide), including SiO ₂ 60 to 72 B ₂ O ₃ <20 Al ₂ O ₃ <10 Na ₂ O <18 K ₂ O <15 Li ₂ O <5 F. ≤ 1

Cladding glass variant 6 (in% by weight based on oxide), including SiO ₂ 72-78 B ₂ O ₃ 5 to 15 Al ₂ O ₃ 5 to 10 Na ₂ O <10 K ₂ O <10 Li ₂ O <5 F. ≤ 1

Cladding glass variant 7 (in% by weight based on oxide), including SiO ₂ 70-80 B2O3 <5 Al ₂ O ₃ <10 La ₂ O ₃ <2 Na ₂ O <10 K ₂ O <10 ZrO ₂ <2

As described, all glasses used for the core glasses within the meaning of the invention can also be used for the glass of the inlay rods ( 13th ) can be used and thus as matrix glass for the production of the scattering area ( 3 ) by depositing scattering particles in the glass.

The glass fiber obtained in this way is excellent in breaking strength. Loop tests carried out resulted in the following values in the loop test for side-emitting step fibers which were drawn from the aforementioned glasses at a drawing temperature of 1040 ° C: N _I = 15 N _I = 15 N _I = 30 N _I = 30 FF = 150-450 FF = 500-1200 FF = 150-450 FF = 500-1200 d _Min [mm] 1 1 1 1 dMax [mm] 4th 3 2 4th d _break [mm] 1.84 1.36 1.88 1.64

The scattering particles consisted mainly of Pt. N _I denotes the number of inlay rods used in the preform, FF the form factor, meaning the diameter of the scattering particles. FF = 150-450 symbolizes the presence of scattering particles in a grain size distribution with diameters 150 nm to 450 nm. FF = 500-1200 accordingly scattering particles in a grain size distribution with diameters 500 nm to 1200 nm. For every combination of N _I and FF 25 loop tests were carried out each time. d _Min indicates the smallest diameter of the loop in mm at which the fiber breaks, d _Max the largest diameter of the loop in mm at which a fiber break was observed. d _break is the arithmetic mean of the individual results of the 25 loop tests in mm.

The table shows that the increase in the diameter of the scattering particles appears to lead to a slight improvement in the breaking strength _{because of the decrease in d breakage.} However, an increase in the number of inlay rods seems to reduce the breaking strength slightly. The comparison with a glass fiber without the scatter ranges according to the invention, which has a value of d _break = 1.25 mm, however, shows that the side-emitting step index fibers according to the invention still ensure very good breaking strength. Side-emitting step index fibers with non-circular core diameters, as are known from the prior art, break significantly earlier in the loop tests.

Compared to the side-emitting step index fibers known from the prior art, the side-emitting step index fibers according to the invention also have the advantage that they more efficiently couple the light sideways, that the effect of the side emission through the use of the inlay rods ( 13th ) is very easily scalable for the applications in question and that the side-emitting step index fibers according to the invention are fire-resistant due to the material from which they are made. Therefore, they can be used in areas with increased fire protection regulations. These are areas of application which are particularly closed to fibers made of plastics. With the method according to the invention, fiber bundles containing the side-emitting step index fibers according to the invention can be produced economically by machine.

Claims (48)

Side-emitting step index fiber, comprising a light-conducting core (1) made of inorganic glass with the refractive index n ₁ and a transparent and / or translucent cladding (2) made of inorganic glass with the refractive index n ₂ , which encloses the core along the fiber axis (A) Core and cladding are at least one scattering area (3) which is formed from an inorganic glass which essentially has the refractive index n ₁ and in which scattering particles are embedded, wherein the coefficient of thermal expansion of the inorganic core glass is greater than the coefficient of thermal expansion of the inorganic cladding glass, characterized in that between the core (1) and cladding (2) there is at least one discrete scattering area (3) which is located on a partial area of the core circumference along the fiber axis (A) extends. Side emitting step index fiber according to Claim 1 , characterized in that there are several discrete scattering areas (3) between core (1) and cladding (2), each of which extends on a sub-area of the core circumference on sub-areas along the fiber axis (A). Side emitting step index fiber according to Claim 1 or 2 , characterized in that the melting temperature of the scattering particles is greater than the melting temperature of the inorganic glass in which they are embedded. Side-emitting step index fiber according to one of the preceding claims, characterized in that the scattering particles have a diameter of 10 nm to 5000 nm. Side-emitting step index fiber according to one of the preceding claims, characterized in that the scattering particles SiO ₂ and / or SiN and / or BaO and / or MgO and / or ZnO and / or Al ₂ O ₃ and / or AlN and / or TiO ₂ and / or ZrO ₂ and / or Y ₂ O ₃ and / or the metals of these oxides alone and / or BN and / or B ₂ O ₃ and / or Ru and / or Os and / or Rh and / or Ir and / or Ag and / or Au and / or Pd and / or Pt and / or diamond-like carbon and / or glass ceramic particles. Side-emitting step index fiber according to one of the preceding claims, characterized in that the concentration of the scattering particles is in the scattering range from 10 ppm to 1000 ppm. Side-emitting step index fiber according to one of the preceding claims, characterized in that the diameter of the core (1) is from 10 µm to 150 µm, the at least one scattering area (3) has a thickness of 100 nm to 2 µm and the cladding (2) is from 500 nm to 2 µm thick. A fiber bundle (23) containing a multiplicity of glass fibers and an outer jacket (24) which completely encloses the multiplicity of glass fibers along the fiber bundle axis, characterized in that the fiber bundle (23) contains a multiplicity of side-emitting step index fibers (22) according to one of the preceding claims and the outer jacket (24) is transparent and / or translucent. Flat structure with a plurality of side-emitting step index fibers (22) according to one of the preceding Claims 1 until 7th . Fabrics according to Claim 9 wherein the side-emitting step index fibers (22) are arranged parallel to one another. Flat structure according to one of the Claims 9 until 10 , wherein the side-emitting step index fibers are fixed on a carrier element (71) and thus a composite element is formed from carrier element (71) and side-emitting step index fibers. Flat structure according to one of the Claims 9 until 10 wherein the side-emitting step index fibers are embedded in a carrier element (71) and a composite element is thus formed from carrier element (71) and side-emitting step index fibers. Flat structure according to one of the Claims 9 until 11 , wherein the side-emitting step index fibers are fixed to one another and / or to the carrier element (71) by sewing. Flat structure according to one of the Claims 9 until 11 , wherein the side-emitting step index fibers are glued to one another and / or to the carrier element (71, 72). Flat structure according to one of the Claims 9 until 14th , wherein the carrier element is transparent and / or translucent. Flat structure according to one of the Claims 9 until 15th , wherein the composite element of carrier element (71) and side-emitting step index fibers is connected to a stabilizing element (72). Fabrics according to Claim 16 wherein the stabilization element (72) is arranged such that the side-emitting step index fibers are located between a surface of the stabilization element (72) and a surface of the carrier element (71). Flat structure according to one of the Claims 11 until 17th wherein the side of the carrier element (71) and / or of the stabilizing element (72) facing the side-emitting step index fibers is designed in such a way that it can reflect the light emitted by the side-emitting step index fibers. Flat structure according to one of the Claims 9 until 18th , wherein the flat structure has measures for connecting at least one LED as a light source. Preform (10) for producing a side-emitting step index fiber according to one of the Claims 1 until 7th , comprising a core rod (11) made of an inorganic glass with the refractive index n ₁ and a cladding tube (12) made of an inorganic glass with the refractive index n ₂ , the cladding tube (12) enclosing the core rod (11) along the core rod axis, characterized that between core rod (11) and cladding tube (12) parallel to the core rod axis at least one inlay rod (13) made of an inorganic glass is arranged, which essentially has the refractive index n ₁ and in which scattering particles are embedded. Preform (10) after Claim 20 , characterized in that between the core rod (11) and the cladding tube (12) from 5 to 100 inlay rods (13) are arranged parallel to the core rod axis. Preform (10) according to one of the Claims 20 until 21 , characterized in that the diameter of the inlay rods (13) is from 0.2 mm to 2 mm. Preform (10) according to one of the Claims 20 until 22nd , characterized in that the scattering particles have a diameter of 10 nm to 2000 nm. Preform (10) according to one of the Claims 20 until 23 , characterized in that the scattering particles essentially consist of Al ₂ O ₃ and / or TiO ₂ and / or Ru and / or Os and / or Rh and / or Ir and / or Ag and / or Au and / or Pd and / or Pt consist. Preform (10) according to one of the Claims 20 until 24 , characterized in that the concentration of the scattering particles in the at least one inlay rod (13) from 10 ppm to 1000 ppm. A method of making a side-emitting step index fiber according to any one of Claims 1 until 7th , including the process steps - providing a core rod (11) made of an inorganic glass with the refractive index n ₁ , - arranging a cladding tube (12) made of an inorganic glass with the refractive index n ₂ , so that the core rod (11) is inside the cladding tube ( 12) is located and a perform (10) is obtained, - heating the preform (10), - drawing out the preform (10) to form a glass fiber (22), characterized in that at least one inlay rod (10) is also used to maintain the preform (10). 13) made of an inorganic glass with essentially the refractive index n _{1 is arranged} parallel to the core rod axis, with scattering particles being embedded in the glass of the inlay rod (13). Procedure according to Claim 26 , characterized in that when the preform (10) is pulled out, at least one inlay rod (13) fuses with the core rod (11), so that a discrete scatter area is formed which extends at least on a partial circumference of the fiber core (1) along the fiber axis (A ) extends. Method according to one of the Claims 26 until 27 , characterized in that the preform (10) contains a plurality of inlay rods (13) which, when the preform (10) is pulled out, fuse both with the core rod (11) and with one another, so that at least one discrete scattering area (3) is formed which extends at least on a partial circumference of the fiber core (1) along the fiber axis (A). Procedure according to Claim 26 , characterized in that the preform (10) contains a plurality of inlay rods (13) which, when the preform (10) is pulled out, fuse both with the core rod (11) and with one another, so that a scatter area (3) is formed which completely encloses the fiber core (1) along the fiber axis (A). Method according to one of the Claims 26 until 29 , characterized in that negative pressure is applied to the preform (10) when it is pulled out. Method according to one of the Claims 26 until 30th , characterized in that an inorganic glass is used for the cladding tube (12), the coefficient of thermal expansion of which is smaller than the coefficient of thermal expansion of the glass used for the core rod (11). Method according to one of the Claims 26 until 31 , characterized in that several preforms (10) are arranged side by side in a heating unit (20) of a multi-fiber drawing system and several side-emitting step fibers (22) are drawn out simultaneously in a multi-fiber drawing system, so that a fiber bundle (23) is obtained which contains side-emitting step index fibers. Procedure according to Claim 32 , characterized in that an outer jacket made of a transparent and / or translucent plastic is extruded around the fiber bundle (23). Procedure according to Claim 32 , characterized in that the fiber bundle (23) is surrounded with glass fibers which form an outer, non-combustible, transparent and / or translucent jacket around the fiber bundle. Use of at least one side-emitting step index fiber according to one of the Claims 1 until 7th together with other light guides and / or other side-emitting step index fibers according to one of the Claims 1 until 7th in a fiber bundle which is surrounded by an outer transparent and / or translucent jacket. Use after Claim 35 for accent lighting of interiors and / or facades (51) in architecture. Use after Claim 35 for accent lighting of vehicle interiors (30, 31, 32, 33). Use after Claim 37 as part of interior trim (30) for vehicles. Use after Claim 35 as part of furniture. Use after Claim 35 as part (41, 45) of a headlight (40). Use after Claim 40 in automobile headlights (40), the light from point light sources such as LEDs being coupled out through the fiber bundle (41, 45) containing the side-emitting step index fiber. Use after Claim 35 for the contour lighting of vehicles. Use after Claim 35 for lighting runways (61, 62) for aircraft. Use of at least one side-emitting step index fiber according to one of the Claims 1 until 7th together with other light guides and / or other side-emitting step index fibers according to one of the Claims 1 until 7th in a flat structure. Use of a fabric according to one of the Claims 9 until 19th as a lighting fixture. Use after Claim 45 for backlighting of displays. Use after Claim 45 for ambient lighting in vehicle interiors. Use after Claim 45 for ambient lighting in architecture.

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