WO2012110521A1

WO2012110521A1 - Coupling element for the coupling of led to fibre bundle

Info

Publication number: WO2012110521A1
Application number: PCT/EP2012/052523
Authority: WO
Inventors: Martin Moldenhauer; Helmut Laser; Sebastian Knuth
Original assignee: Xion Gmbh
Priority date: 2011-02-14
Filing date: 2012-02-14
Publication date: 2012-08-23
Also published as: DE102011077382A1; DE112012000800A5

Abstract

Coupling element for the coupling of LED to fibre bundle for endoscopy, as glass bodies having, on the two end faces, identical or different geometry, which are embodied in a circular fashion, in rectangular fashion or in any desired form and are thus adapted to LED coupling surfaces and to fibre bundle coupling surfaces, and wherein the coupling element is constructed from a glass core and a plurality of at least 3 to 10 successive glass claddings and these cladding layers have identical or different thicknesses and each cladding layer consists of glass having a different refractive index, wherein the thicknesses and the refractive indices of the cladding layers are selected according to the calculation and optimum beam guidance of the LED beams to be coupled in and of the required beams to be coupled out for coupling‑out into a fibre bundle or a forwarding optical system.

Description

Coupling element for the coupling of LED to fiber bundles

The present invention relates to a coupling element for the coupling of LEDs of different sizes and embodiments to fiber bundles in endoscopy.

In recent years, light emitting diodes (LEDs) that emit a white light have found entrance into illuminations for endoscopy. The main aim is to couple as much as possible of the light emitted by available LED components into fiber bundles of different diameters. LED components are offered both as a chip LED, as well as attached lens, or with windows and have very different dimensions.

Many solutions have been offered to couple the emitted light of this LED into fiber bundles. This can be done in the classical way by means of lenses, as described for example in DE 10 2007 027 615 and in WO 2010/055971 and shown in many other applications. The hitherto diverse designs of lens systems in patents and in publications have the decisive disadvantage that optical systems have to be constructed from a plurality of lenses (eg collimator systems). The lens systems are also very large and expensive. The diameters of these lens systems are usually a lot when transmitting the usually large beam angle of the LED larger than the LED and the fiber bundles themselves. In order to keep the optical transmission paths of these optics small and to minimize the necessary space, the lenses used must be very short focal length. In some cases, aspheres have to be used to realize the required angular transformation for coupling into fiber bundles. Due to the number of lenses used, a portion of the emitted light of the LED is lost by reflection and scattering on the lens surfaces, which is particularly disadvantageous.

The coupling into fiber bundles is also attempted by means of optical elements made of PMMA (polymethyl methacrylate), which are designed as special three-dimensional beam guiding structures, which are commercially available in large numbers. Here, rotationally symmetric elements are provided which are intended to catch as many as possible of all the rays emitted by the LED in their solid angle and to guide them in a desired direction by means of spherical or aspherical or even partially reflecting surface parts. An example of this is shown in US 2006/0044820, in which some of the very special beam-guiding components are described. A disadvantage of these elements are their dimensions, since due to the required solid angle, these elements are several times larger in diameter than the LED itself. The disadvantage here is also the very high price for these precision turned parts in small quantities. For newly developed endoscopes, an adaptation of these elements is usually only possible through recalculation and customization. This also applies to the LED to be used. For each type of LED, a specific element must be calculated and manufactured.

Similar to the beam guiding elements described, highly specific reflectors for LEDs have also been developed (as described, for example, in WO 2005/062099), which are intended to collect as much as possible all emitted light beams and direct them in one direction. In the case of both beam guidance components, the optical elements and the reflectors, there is the great disadvantage that in the deliberately forced good angular conversion the exit surfaces become very large and thus a large proportion of the radiation can not be coupled into the fiber bundles.

For coupling the light of the LED, it is much better possible than with lens systems to bring the fiber bundles and the LED chip areas into direct contact with one another, as has been described in detail in US Pat. No. 7,229,201 (so-called shock coupling). Here, the best Einkoppelergebnisse have been achieved over all other known methods. The disadvantage of this shock coupling is that the commercial available fiber bundle diameter or the fiber bundle diameter used in the endoscopes are not adapted to all common LED chip sizes or can not be adapted. In the described US patent, the illustrated fiber bundles are shown smaller than the actual LED chip, which generally leads to losses in the corners (inscribed circle). Since the LED chips are typically square or rectangular, it is necessary for full light transmission to use fiber bundle diameters larger than the LED chip area (perimeter) for butt coupling with round fiber bundle surfaces. This would be associated with many LEDs a risk of injury to the bonding wires. US 2003/0219207 also describes a fiber bundle placed on the LED chip surface, which, due to the bonding wires, must be smaller than the entire chip surface. Deviating from all known realized LED, this patent also claims a concave LED chip surface, which is particularly disadvantageous.

Also for the LEDs having a lens glued on the chip, coupling into a fiber bundle is possible by placing the fiber bundle directly on top of the lens or on a window in front of the chip, as e.g. in US 2009/0040783. The removal of the lenses or the grinding of existing lenses on LED components are described in these publications. The disadvantage of a coupling of fiber bundles on lens caps of LED or on windowed LED chips is that the farther away from the LED chip the receiving fiber bundle is arranged, due to the beam divergence of the rays emitted by the LED, the area of the beam cross section becomes larger , In order for the most effective possible transmission of radiation emitted into the solid angle, the diameter of the fiber optic bundle would have to be made larger with increasing distance from the chip, which is not always possible as a rule. It can be seen that due to poor areal matching, methods of butt coupling and coupling to lenses can not provide sufficient coupling efficiency, and not for all, e.g. Built in an endoscope, fiber bundles are suitable.

In order to detect as many emitted light beams as possible in these methods of butt coupling or direct placement on LED chips or lens caps or windows, fiber cones have been used in many cases. As described, for example, in US 2009/0122573, the fiber cone is used for aperture conversion and sizing by placing it with its small diameter on the LED chip and the large diameter of the fiber cone comes into contact with the fiber bundle to be used. The Disadvantages here are also the adaptation of the diameter of the small side of the fiber cone to the LED chip, which must indeed be performed as a perimeter around the LED chip to record as many rays, then possibly bonding wires can be damaged.

Known fiber cones and also known glass cones have different diameters of the coupling and decoupling surfaces. Here, the term aspect ratio is to be understood as the quotient of the smaller (e.g., on) coupling surface to the larger (e.g., off) coupling surface. The use of one of the surfaces as a coupling surface is based on the respective, specific task. When coupling LEDs to fiber optics in endoscopy, it is important to collect as much as possible the total luminous flux of the LED in the solid angle and to feed this into the fiber optics in the usual cables or in endoscopes. Since the solid angles of the LEDs generally have much larger angles than the transmittable apertures of commercially available installed glass fibers, in the majority of the coupling tasks, the smaller cone diameter is used as the coupling surface and the LED is installed too skilfully. In this configuration, the large coupled solid angle will be provided according to the aspect ratio in a small solid angle at the decoupling surface. The following statements assume this configuration.

The embodiments of all known LED chips are square or rectangular, the embodiments of known Lichtleitkabel coupling surfaces are round, so that there is an unmatched surface coupling. If the coupling diameter is chosen to be equal to or greater than the diagonal of a square LED chip (circumference), then portions (circular sections) are present in which no light is transmitted. If the diameter of a e.g. If the light guide cable coupled to the shock coupling is chosen to be smaller or the same as the diameter of the inner circle of a square LED chip (incircle), radiation of the chip coming from the protruding edge regions is likewise lost. This is problematic when LED components are used with lenses. Here, the fiber optic interface to be patched must have a much larger diameter than the LED chip to detect all beams, again at the expense of a best fit aspect ratio.

If, for example, a known, commercially available fiber cone or else a known, commercially available glass cone is used for the coupling, then these mismatches are present due to the circular geometry of the coupling surface. In addition comes For the fiber cone or glass cone, add the angle conversion between the coupling surface and the coupling-out surface as the parameter to be taken into account.

This makes it very difficult to find corresponding fiber cones or glass cones with circular input and output surfaces with given LED components and given bundle diameters of illumination fiber bundles in the endoscopy, which have an adapted aspect ratio (small diameter to large diameter) for a minimal loss.

The commercially available fiber cones have fused fibers at both coupling points, so that a very high packing density of the individual fibers is obtained, which results in a high power transmission. In addition, to ensure a good transmission of the light power in the solid angle, this fiber cone should contain fibers with a high numerical aperture. The numerical aperture of the fibers of a fiber cone (or of a cogia cone) is calculated as:

NA = v (n _k ² -n _m ²⁾ n _k = index of refraction (refractive index) in the core n _m = refractive index (refractive index) in the casing where n _k> n _m

In order to be able to detect and transmit the conventional solid LED spatial angles of 130 ° to 160 °, according to NA = sin (0.5-130 °) = 0.91

Apertures greater than or equal to 0.9 are necessary.

Fiber cones with a high aperture and additionally fused coupling and decoupling surfaces are not available as standard and can only be produced with expensive technology. Likewise, other than round coupling and Auskoppelflächen- geometries are not available. Fiber cones from INCOM, USA are offered with high apertures up to 0.9 with very small fiber diameters. The fiber cones also offered by this company with square or rectangular surface geometries correspond Not the required for an effective coupling between LED and fiber bundles tasks of light coupling, since here a round diameter is brought by grinding of fibers to a rectangular geometry and consequently edge fibers are excluded from the light guide. Due to the very small diameter of the fibers in these offered fiber cones occur in addition to higher losses.

For the coupling of LED to fiber bundles are commercially available and glass cone available, which consist of a glass core and a glass jacket with refractive index ratios that allow a reflection in the interior similar to a single glass fiber. The dimensions of the glass cones move in the range of the diameter of the fiber bundles to be used for light transmission in the endoscopes. Even with the glass cones, there are no commercially available high apertures and no other than round shaped coupling and decoupling surfaces.

In a glass cone having a large coupling-out diameter, there are two ray portions of the transmitted solid angle, once a "direct" portion in the core glass itself, which is transmitted relatively unaffected by the glass body and contains substantially parallel beam portions and a portion due to the reflections In the case of a large coupling-out diameter of the decoupling point, the cone of rays is thus determined very strongly by the average radiation components and the resulting solid angle at the decoupling side is very small Aspect ratio (small diameter divided by large diameter = near 1, 00), so there is an increase in the decoupled solid angle to the maximum transmission aperture at the decoupling point, because the direct shares against the reflected Antei be mitigated. Thus, with glass cones only maximum solid angles can be achieved at the decoupling point, which in the order of magnitude of the core-shell aperture after the o.g. Formula lie. In addition, losses occur in a glass cone in such a way that radiation components which do not remain at the aperture angle are scattered into the cladding and are lost.

It is therefore disadvantageous in the use of fiber cones that arise for an effective coupling high cost of execution with high aperture. In addition, a design of fiber cones with square or rectangular cross section, on which all fibers are light-guiding, not available. In addition, the internal losses are added, which affect the coupling efficiency. When using Giaskegein, it is disadvantageous that the decoupled solid angle is strongly influenced by the aspect ratio and limited by the used core-shell refractive index ratio and the losses are high by the scattering of rays in the absorbent shell.

The present invention aims to provide a coupling element for coupling LED light commercially available LED in the fiber bundles used in endoscopy of endoscopes or optical cables or in the optical components used for other lighting applications, the disadvantages of all described coupling elements described above as possible should be avoided.

The object is achieved in that a, for example, cylindrically shaped coupling element of a core, which preferably consists of glass, and a plurality of transverse to the longitudinal direction, successive cladding layers is constructed with matched different refractive indices. The cladding layers likewise each preferably consist of glass and are therefore also referred to below as cladding glasses or glass sheaths and follow one another in the radial direction in such a way that they encase a further inner sheath layer or the core and extend as far as possible in the longitudinal direction of the coupling element over its entire length , which can be localized by polished sections.

It is thus a coupling element for the coupling of LED fiber bundles or other optical elements, in particular for endoscopy, proposed in which a longitudinal direction of the coupling element from a coupling surface of the coupling element extends to a coupling-out of the coupling element and the coupling element of one, in the longitudinal direction extending, photoconductive core and a plurality, in the radial direction transverse to the longitudinal direction successive light-conducting, the core enclosing cladding layers is constructed with divergent refractive indices, wherein refractive indices and layer thicknesses of the cladding layers are coordinated so that at one by the numerical Gesamtapertur (Θ = arctan n _m / NA) of the coupling element predetermined Einkoppelwinkel from falling out of a cladding layer rays by multiple reflection in at least one other cladding layer a corresponding (propagation) angle obtained, which causes them in another layer be redirected by total reflection. Propagation angle is understood here to mean the angle of a respective light beam with respect to the longitudinal direction of the coupling element. Preferably, the coupling element has a numerical aperture greater than 0.8 and more preferably greater than 0.9 and is designed for coupling to fiber bundles or other optical elements with a diameter greater than 4 mm. Fiber bundles for endoscopy usually have diameters of more than 4 mm or 5 mm.

Preferably, the core and the cladding layers are made of glass so that the core is surrounded by a plurality of glass claddings. In the context of this description, a cladding layer of glass is also referred to as a glass cladding. Alternatively, the coupling element can be produced from a multi-step index plastic preform (MSI-POF).

Very particular preference is a coupling element whose cladding layers each consist of homogeneous glass with a respective defined refractive index, wherein the glasses of the cladding layers are made of commercially available glasses with a corresponding refractive index. With such cladding layers, a high aperture can be achieved via the layering. For example, a suitable combination of glasses is (from core to outer cladding layer):

Core SF6, SF4, SF1, SF2, F8, outer sheath LF8

In addition, an embodiment variant is preferred in which the coupling element has at least 3, preferably 5 to 10 successive cladding layers

The cladding layers of the coupling element preferably form successive glass shells with a respective refractive index, so that the refractive indices decrease in their value from the core to the outer sheath. The refractive indices of the successive glass shells from the core to the outer glass sheath are preferably designed with respect to each other according to a calculated beam guidance.

The layer thicknesses of the successive cladding layers are preferably the same. Alternatively or additionally, the layer thicknesses of the successive glass shells are designed differently according to a calculated beam guidance.

Preferably, the layer thicknesses of the cladding layers are greater than 0.1 mm and preferably between 0.5 mm and 1 mm.

It has been found that the solid angle resulting at the decoupling point can be better adapted (eg widened) compared to a pure glass cone, if a coupling element is used, which consists of several layers of glass whose refractive indices are different and whose layer thickness is different or equal and which also tapers - that can be tapered in the longitudinal direction - executed. This coupling element may have a round, square or rectangular geometry at the coupling surfaces and / or at the decoupling surfaces, so that an areal adaptation to any LED geometries or to any geometrically shaped fiber bundles can take place.

Corresponding results in preferred embodiments in which the coupling element is designed as a straight cylindrical or prismatic body or designed as tapered in the longitudinal direction Taper with divergent input and output coupling surfaces sizes. In this case, the coupling-in surface and / or the coupling-out surface of the coupling element preferably has a rectangular, preferably square shape.

The coupling element may have round or angular cross-sectional shapes and correspondingly, e.g. have a cylindrical or prismatic outer shape, with end faces that serve as a coupling surface or decoupling surface. Conically tapered coupling elements and / or in the longitudinal direction of a shape with a round cross-section on a shape with angular cross section passing Koppelemente are equally within the scope of this invention and allow the respective end face and thus the respective input and output surface in their shape to the LED or to adjust the coupling surface of a respective fiber bundle.

In this sense, coupling elements are preferred whose coupling surface corresponds to the surface of a respectively provided LED component. These are, for example, usually rectangular surfaces with a dimension between 1 mm ² and 10 mm ² . A respective LED component and the coupling element preferably form a structural unit which has a connection for connecting a fiber bundle on the side of the coupling-out surface of the coupling element.

As a coupling surface of the coupling element here the in operation of the LED facing (front) surface is designated, through which the light of the LED enters the coupling element. Accordingly, as a decoupling surface of the coupling element that (front) surface referred to, which faces the optical fiber bundle of the endoscope or another subsequent optical component during operation and by the light of the LED exits the coupling element and enters an entrance surface of the fiber bundle or the other optical component.

The coupling-out surface of the coupling element preferably has a shape and also a surface measure which corresponds to the coupling-in surface of a fiber bundle. The cross-sectional dimension of the decoupling surface - with round outcoupling surfaces whose diameter - is accordingly preferably between 0.5 mm and 5 mm. For coupling into other optical components, e.g. Lens systems, the diameters or corner gauges of the coupling element may be larger, e.g. 8-10mm.

Typically, the end surface of the coupling element serving as a coupling surface and the other end face of the coupling element differing from one another both in terms of their shape and in terms of their surface dimension, but preferably in at least one of these aspects. The Einkoppel- fiäche and the coupling surface of the coupling element are preferably designed as ground and polished end faces of the coupling element. A particularly effective transmission of the light in the coupling element according to the invention is achieved by the individual numerical apertures, which results from the design of the refractive indices of the individual mutually contacting neighboring layers. If some of the beams coupled in at the coupling surface exceed the reflection angle 0 existing in the relevant layer with respect to a neighboring layer, which is given by the numerical aperture (0 = arctan n _m / NA), then these beams leave this layer and go into the inner one next layer or in the farther outward next layer over. The individual layers thus have a light-guiding effect for the beam components whose propagation direction does not exceed the total reflection angle 0 between adjacent layers predetermined by the numerical aperture. It is not trivial to find out when and in which layer the rays that fall out of one layer receive a corresponding angle through multiple reflection in other layers, causing them to be redirected to total reflection in another layer, but for those skilled in the art Knowledge of the invention described here based on his expertise possible. Thus, it can be shown that the rays are guided in a curved shape similar to gradient fiber devices through the coupling element. It has become apparent in ray tracing with different LED beam models that this layered transmission of the rays causes the particular effectiveness of the coupling element according to the invention. A particularly preferred coupling element has, for example, a glass core and 5 cladding layers each having different refractive indices with a refractive index difference of about 0.1 of the layers to one another and uniformly decreasing refractive index from the core to the outermost cladding. This component has a square cross section at the LED input side and a round cross section at the output side.

The individual cladding layers are preferably thicker than 0.1 mm and preferably have a layer thickness between 0.5 mm and 1 mm.

The end faces of this coupling element are ground and polished and provided with a reflection-reducing coating. For such a coupling element, the following parameters result for a calculation of the beam guidance between coupling side and coupling-out side:

Any aspect ratio can be chosen

The number of cladding glasses (cladding layers) can be selected

The thickness of the cladding glasses (cladding layers) can be selected. Glasses can be selected for use in terms of their indices of refraction

It can be selected lens pairings, which cause a certain refractive index profile from the core to the outer shell in the coupling element

The cross-sections of the coupling-in and coupling-out sides can be selected (round, square, rectangular)

The outermost layer can be mirrored on the outside

By choosing appropriate glasses, the transmission of the coupling element can be optimized for different wavelengths

By selecting these parameters, corresponding coupling elements for a desired result can be calculated with the available glasses. Advantageous is that the glasses to be used should approximate in their coefficients of thermal expansion and viscosity to provide a compact fused coupling element.

This coupling element can be produced by various methods. It can be produced as a single component by the glass shells are pushed over each other as prefabricated tubes and the entire component collapses in an oven. But it can also be drawn as a continuous strand in a drawing system from a preform whose glass layers by z. B. customary deposition processes have been prepared. Likewise, chill casting of the various glass shells of the coupling element in corresponding shapes is possible. The nesting of several glass plates in an overlay outer tube with subsequent pulling results in such a coupling element selectable dimensions. The preparation of the tapered shape can also be done by conventional methods. The transformation of one or both ends into a rectangular or square cross-section may, for. B. also be achieved later by pressing a corresponding shape.

The o.g. Modifications have effects on the following transmission properties of the coupling element according to the invention:

On the resulting solid angle on the decoupling side

On the maximum possible coupling angle on the coupling side - On the topological coupling on the coupling side

On the resulting decoupling energy on the decoupling side

On the topological numerical aperture of the layers in the coupling element

In the following, the function and the particular advantages of the coupling element according to the invention will be described with reference to drawings of an embodiment. In the drawings show:

Figure 1: an arrangement of a fiber cone or a glass cone for coupling the

Light radiation of a power LED to a fiber bundle a decoupling diagram on a glass cone according to Figure 1 with a small aspect ratio a decoupling diagram on a glass cone according to Figure 1 with a high aspect ratio a decoupling diagram on a glass cone according to Figure 1 with a commonly used aspect ratio of 0.75

Structure of a cylindrical coupling element according to the invention

Structure of a cylindrical coupling element according to the invention in a tattered design

Structure of a coupling element according to the invention with a square coupling point and tapered design a decoupling diagram on a coupling element according to the invention with a preferred first refractive index distribution a decoupling diagram on a coupling element according to the invention as shown in Figure 5 with a second refractive index distribution a decoupling diagram on a coupling element according to the invention according to Figure 5 with a third refractive index distribution a decoupling diagram on a coupling element according to the invention according to Figure 5 with a different refractive index distribution a decoupling diagram on a coupling element according to the invention as shown in Figure 5 with a change in the thickness of a lying close to the outer cladding glass layer

Figure 13: a coupling element according to the invention in an embodiment as a coupling element or beam splitter coupling out at right angles Figure 14: Application of the coupling element according to the invention for a coupling of 3 LEDs on a coupling-out side

Figure 15 Another embodiment for a coupling of 3 LED on a decoupling side with a coupling element according to the invention Figure 16 Application of the coupling element according to the invention for a coupling of several SMD LED on a decoupling side

For the following examples, a measured radiation lobe of a power LED is used as a starting point, which covers an angle range of 40 °.

Figure 1 shows the coupling of a fiber cone or a glass cone to a commercially available power LED. The LED should in this case be present without an attached lens as an embedded LED, as is shown, for example, in US Pat. in the case of the "Phlatlight-LED" supplied by the company LUMINUS (USA) The fiber cone (2) or the glass cone (6) sits in abutment on the window of the LED (1). 5) uses the smaller diameter side to convert the angle conversion from the larger beam angle of the LED to a smaller coupling angle.

The commercial glass cone (6) consists of a glass core with a first refractive index n _k and a glass cladding with a second refractive index n _m . If n _m <n _k , then a known total reflection of the light takes place. The numerical aperture (NA) of the glass cone and its aspect ratio can be selected via the glasses and the sizes of the coupling and decoupling points (4, 5).

Figure 2 shows the coupling-out diagram of a glass cone (6), which has a low aspect ratio of 0.4, ie a large difference in diameter between the coupling-in side (5) and the coupling-out side (4). The resulting solid angle is relatively limited to the aperture (NA) given by the glasses. The room angle of the LED radiation is only used to 40%. As a result, the transmission efficiency is not good.

A wide coupling angle can only be achieved with a glass cone if very high refractive glasses are used. Commercially available glass cones have a numerical aperture of +/- 30 ⁰ . Figures 3 and 4 also show this fact: With a glass cone with a high aspect ratio, the decoupling angle is kept within the limits of the numerical aperture (NA) given by the glasses, while the middle part of the solid angle is flattened. The transmitted light output decreases with increasing aspect ratio.

It can be shown that the Glaskegei can not transmit even more than 50% of the total power of the LED here. The glass cone used here has an absorbent outer layer. For a mirrored glass cone, the transferable performance may be higher.

Figure 5 shows the structure of a cylindrical coupling element according to the invention. It has a glass core with a refractive index of n _k and cladding glasses concentrically around this core with the different refractive indices n ₃ to n ₇ . The glass layers have the thicknesses D1 to D5, which can be the same size or different sizes. The coupling element has a freely selectable length L and has a ground, polished and coated Einkoppelseite (5) with the diameter D _e and a ground and polished and coated coupling-out side (4) with the diameter D _a .

Figure 6 shows a taper of a coupling element according to the invention. The taper with the selectable length L is identical to the inner structure of the coupling element shown in Figure 5 wherein the diameters of the coupling side (5) and the coupling-out side (4) are different and thus set an aspect ratio.

In Figure 7, a taper of a coupling element according to the invention is shown, which on the coupling side (5) has a different surface shape than on the coupling-out side (4). Here, the surface shape of the coupling-in side is rectangularly adapted to an LED chip having the dimensions a ^■ b, while the coupling-out side is round and may be adapted in diameter, for example, to commercially available fiber bundle diameters.

Figure 8 shows in a decoupling diagram how the decoupling angle of a tapered coupling element according to the invention behaves according to FIG. 6 when the aspect ratio is 0.75. In one embodiment, continuously increasing refractive indices from the cladding to the core are used, the refractive index differences of the individual layers having a size of 0.1 relative to one another. This means an aperture of the individual layers to each other of about 0.5 to 0.6. The absolute aperture of the entire component thus results in> 0.9. The jacket thicknesses are kept the same. It can be seen that even with a multilayer coupling element with the same Mantle thicknesses and uniformly from inside to outside changing refractive index of the glass layers, a coupling angle can be obtained, which is wider than the glass cone compared to Figure 4. The total transmitted light output is about twice as high as the simple glass cone according to Figure 4.

Due to the higher aperture between the layers, the coupled-in beams do not change the individual layers as often. As a result, a larger coupling-out angle results.

Figure 9 shows a decoupling diagram for a second refractive index order of the single refractive indices of the individual glass layers in the direction from the core to the cladding. Here, glasses are used which have a refractive index difference from each other of about 0.02 to 0.05. As a result, the beams in the coupling element change very rapidly and very often the layers, with the result that a narrower coupling-out angle and in the central region a slightly wider plateau is formed.

Figure 10 shows a coupling-out diagram for a third refractive index sequence, which is characterized in that the refractive index differences between the layers is about 0.01 to 0.03. With the resulting very small apertures between the layers a center-emphasized smaller Auskoppelwinkel and only a smaller power transmission is achieved.

If the refractive index sequence according to FIG. 8 is interrupted with the high apertures between the layers by introducing a layer which has a refractive index which differs greatly from the surrounding layers, then a coupling-out diagram according to FIG. 11 with a very broad coupling-out angle results. In the picture, this layer lies near the outer coats. By shifting this low-refractive layer, different decoupling profiles of the spatial angle to be decoupled can be achieved.

If one of the cladding layers is changed in thickness, z. B. widened as z. As shown in Figure 12, it can also be used to create widening of the decoupling angle.

The availability of glasses with appropriate parameters allows a wide range of manipulation of the coupling element according to the invention. It can be seen that in the coupling element according to the invention, the coupled-in beams can be more completely and better converted to the coupling-out side than is possible with a glass cone or even with a fiber cone. In addition, the transmittable light output is higher. With the choice of the layer thicknesses, the refractive indices and the aspect ratio, one is able to develop and produce an effective and inexpensive coupling element very quickly for a large number of coupling tasks.

The coupling surface and the decoupling surface of this coupling element according to the invention are ground and polished and can be provided with a reflection-reducing coating or a wavelength-selective coating.

A specially designed coupling element is formed when the entire component is held in a rectangular cross-section. As Figure 13 shows, z. B. the Auskoppelseite be sanded at an angle. This side can be provided with a mirror layer, which leads to a decoupling of the light at right angles to the coupling side. Since the beam guidance through the mirror layer is approximately perpendicular to the individual cladding glasses, not all rays are deflected into the glass layers, but leave the coupling element on the ground shell side. In the case of a coating of the angularly ground outcoupling side with a divider layer with a selectable divider ratio, a decoupling can take place in two different directions. If the splitter layer is designed as a wavelength-selective layer, light mixing elements can also be constructed with the coupling element according to the invention.

Figure 14 shows a structure of 3 LED, which emit different spectral. First, the light of the LED1 is coupled into the planar coupling surface of the upper first coupling element (G1). The decoupled by 45 ° decoupling surface of the upper first coupling element (G1) is coated with a long-pass layer, which leaves the green light of the LED1 through and blue light reflected. At this tapered surface of the first coupling element (G1), the angled at 45 ° and uncoated surface of the second coupling element (G2) is cemented. The second coupling element (G2) conducts the light of the blue LED2 via the wavelength-selective coating on the first coupling element (G1) and the coupling-out point on the second coupling element (G2) into the third coupling element (G3). This third coupling element (G3) has a wavelength-selective long-pass filter, which transmits blue and green but reflects red. At this third coupling element (G3) is the un coated fourth coupling element (G4) cemented, which conducts the light of a red emitting LED, which is reflected at the mirror layer of the third coupling element (G3).

At the right angle to the coupling side (5) lying outcoupling side (4) of the fourth coupling element (G4) can now be coupled a decoupling fiber bundle, in which a mixture of red, blue and green light components mixed with high efficiency is coupled.

Since the coupling elements according to the invention used for the structure according to Figure 14 are all made the same and are provided only with corresponding wavelength-selective coatings, any combinations can be assembled into a light mixing element.

In Fig. 15, a similar construction is shown, which makes it possible to more easily guide the beams of three LEDs, which emit spectrally different colors, to an output path. For this purpose, a coupling element with two angular bevels at an angle of 45 ° is used in the central area of the structure (G2). The other two coupling elements are provided with a flat surface (coupling surface (5) and decoupling surface (4)) and each with a beveled surface at 45 °. The angled surfaces are provided with a wave-selective coating. The splitter mirror coating (14) on the LED 2 (13) consists of a blue-reflecting layer which allows other wavelengths (here in particular the wavelength (green) emitted by the LED1) to pass through. The partial mirror coating (14) on the LED3 (12) consists of a red-reflecting layer that allows all other wavelengths (in particular the wavelengths emitted by the LED1 and LED3 (green and blue)) to pass through. The coupling element sections used here are of the same square cross-section, which is sized in size so that both the coupling point (5) and in the corresponding planar cladding regions (16), the high-power LED can be coupled directly. At the decoupling point (4) of the entire optical component, e.g. a fiber optic bundle (3) are coupled. It is also possible, following the decoupling point (4) to arrange an arbitrarily constructed optical system of a plurality of lenses or lens groups, which assumes an additional beam shaping of the decoupled beams. Such optics are e.g. needed to focus on a micromechanical tilting mirror element (MEMS) for video beamer.

If, for example, low-power LEDs are used in place of the high-performance LED in this described structure as shown in Figure 15, then together with a following focusing the optics a complete optics system for small and light video projectors are built up. Due to the particular light pipe of the coupling element according to the invention, it can be expected that video beamer constructed in this way have a very high image brightness. For fluorescence imaging in endoscopy, this coupling element can be used in a structure such as in Figure 15, for example, to couple the radiation of a white light LED and an ultraviolet LED or even an additional infrared LED to a common decoupling point. The design according to Figure 15 is not limited in its construction to the use of 3 LEDs. Using the assembly principles outlined in Figures 14 and 15, either only 2 LEDs or 4 or more LEDs can be coupled together.

Figure 16 shows that with the coupling element according to the invention a mixture of the emission of several small LEDs, e.g. SMD LED can be made, in the Biid a square coupling element (G5) with plan ground Einkoppel- and Auskopel- pelseiten shown. On the coupling side (5) a total of 6 pieces SMD LED (1) are cemented. To the decoupling side (4) can now turn again, e.g. a fiber optic cable or a subsequent optical system are coupled. When using LEDs with the same wavelength (eg white light LED), it can be shown that, depending on the design of the coupling element in one of the methods mentioned in the description, about 50% to 80% of the light output is the sum of all the coupling-in LEDs at the output point. Light output is available. With such structures, luminaires for various tasks can be assembled with SMD LEDs, which enable a high light output with low electrical power.

Many other combinations of multiple coupling elements in various embodiments are easy to derive from an engineering point of view.

This coupling element according to the invention can also be advantageously integrated into light guide neck of endoscopes. Since in the endoscopes usually wide-angle optical fibers can be used, here is the possibility to couple a solid angle of about 120 °. This is not possible with the commonly used fiber cones. With the coupling element according to the invention higher light powers with higher solid angles can be coupled into endoscopes for the first time at this point. LIST OF REFERENCES

The following designations are used in the drawings:

(1) An LED

(2) A fiber cone

(3) A light guide cable

(4) The decoupling side

(5) The coupling side

(6) A glass cone

(7) A core glass

(8) A jacket glass

0) cladding glass layers

(10) A divider coupling element

(11) A green LED

(12) A red LED

(13) A blue LED

(14) Splitter mirror coating

(15) decoupling point for partial beams

(16) coupling point on a lateral surface

D1 .... D5 = thicknesses of the glass layers

De = diameter of the coupling side

Da = diameter of the decoupling side

(G1) = coupling element 1

(G2) = coupling element 2

(G3) = coupling element 3

(G4) = coupling element 4 (G5) = coupling element 5

η-ι .... n ₇ = refractive indices of the cladding glass layers

n _k = refractive index of the core glass

n _m = refractive index of the cladding

a = lateral dimension 1 of a rectangular coupling-in side

b = lateral dimension 2 of a rectangular coupling-in side

+ NA / -NA = Predefined limit angle given by the numerical aperture

+ a l -a = By the coupling into the light guide cable (3) predetermined maximum

coupling angle

NL = numerical aperture of the fiber optic cable

Claims

claims

1. Coupling element for the coupling of LED to fiber bundles or other optical elements, in particular for endoscopy, wherein a longitudinal direction of the coupling element extends from a coupling surface of the coupling element to a coupling-out surface of the coupling element, characterized in that the coupling element of a, extending in the longitudinal direction , light-conducting core and a plurality of, in the radial direction transverse to the longitudinal direction successive light-conducting, the core enclosing cladding layers is constructed with divergent refractive indices, wherein refractive indices and layer thicknesses of the cladding layers are coordinated so that at one by the numerical aperture (Θ = arctan n _m / NA) given coupling angle of rays falling out of a cladding layer by multiple reflection in at least one other cladding layer obtained a corresponding angle, which causes them in another layer again by total reflection be forwarded on.

2. Coupling element according to claim 1, characterized in that the coupling element has a numerical aperture greater than 0.8 and is designed for coupling to fiber bundles or other optical elements with a diameter greater than 4 mm.

3. Coupling element according to claim 1 or 2, characterized in that the core and the cladding layers consist of glass.

4. Coupling element according to claim 3, characterized in that the cladding layers each consist of homogeneous glass with a respectively defined refractive index, wherein the glasses of the cladding layers are made of commercially available glasses with a corresponding refractive index.

5. Coupling element according to one of claims 1 to 4, characterized in that the coupling element has at least 3, preferably 5 to 10 consecutive sheath layers

6. Coupling element according to one of claims 1 to 5, characterized in that the successive glass shells each have refractive indices, which are decreasing in value from the core to the outer sheath.

7. Coupling element according to one of claims 1 to 6, characterized in that the successive glass shells each have refractive indices, which are executed by the core to the outer sheath in their value with each other according to a calculated beam guidance.

8. Coupling element according to one of claims 1 to 7, characterized in that the layer thicknesses of the cladding layers are greater than 0.1 mm and preferably between 0.5 mm and 1 mm.

9. Coupling element according to one of claims 1 to 8, characterized in that the coupling element is designed as tapered in the longitudinal direction taper with divergent input and Auskoppelflächengrößen.

10. Coupling element according to one of claims 1 to 9, characterized in that the Koppeielement on the Auskoppeifiäche and / or the coupling surface angled bevel, preferably 45 °.

Coupling element according to one of claims 1 to 10, characterized in that the coupling element on the coupling surface and / or the decoupling surface has a spherical, aspheric or free-form, convex or concave bevel according to a calculated beam guidance.

Assembly with a coupling element according to claim 10, characterized in that the assembly contains a plurality of coupling elements with a plurality of LEDs of different spectral emission whose beam portions are combined using wavelength-selective filter coatings of the surfaces to a common decoupling point.

13. Assembly with a coupling element according to one of claims 1 to 1 1, characterized in that the assembly includes a coupling element with multiple LED rather or different spectral emission at the coupling point whose individual beam components are optically mixed fed to the coupling-out.

14 light guide connecting piece for an endoscope, characterized in that one or more coupling elements according to one of claims 1 to 1 1 are integrated in the light guide connecting piece.

15. Use for light mixing in a video or other color mixing projector in cooperation with a MEMS component and / or a projection optics, characterized by a coupling element according to claims 10 and 11 or a structural unit according to claim 12.