Optical waveguide

Abstract

The present invention relates to an optical waveguide (10; 110; 210; 310) comprising: an inner tube (12; 112; 212; 312) having a central longitudinal axis and having a surface (18; 118; 218; 318), the inner tube (12; 112; 212; 312) being made of a first transparent material having an index of refraction n1; an outer region (14; 114; 214; 314) made of a second transparent substance having an index of refraction n2, the outer region surrounding the inner tube (12; 112; 212; 312), and the index of refraction n1 of the first transparent material being greater than the index of refraction n2 of the second transparent substance; and a light-emitting means (16; 116; 216; 316) in the inner tube (12; 112; 212; 312), wherein: the inner tube (12; 112; 212; 312) has, in the interior, a first region (B1) and a second region (B2) surrounding the first region (B1); the central longitudinal axis is located in the first region (B1), and the second region (B2) is at a distance from the central longitudinal axis of the inner tube (12; 112; 212; 312); and the light-emitting means (16; 116; 216; 316) is located in the second region (B2), and the first region (B1) is free of light-emitting means (12; 112; 212; 312). The present invention also relates to a measuring device comprising an optical waveguide (10; 110; 210; 310) of this type.

Description

[0001] Optical fiber

[0002] Description

[0003] Technical area:

[0004] The present invention relates to an optical waveguide and a measuring device with an optical waveguide according to the preamble of claim 1.

[0005] State of the art:

[0006] Optical fibers have been known for a long time and are used in a wide variety of applications to collect and transport light and light signals over long distances. Optical fibers are based on the physical principle of total internal reflection, in which light is reflected at the boundary between two media with different refractive indices, n2, and a reflectance of 100% when the angle of incidence of the light into the waveguide exceeds the critical angle 0. C with exceeds.

[0007] Typically, optical fibers used to transmit light signals over long distances comprise a transparent inner tube surrounded by a transparent cladding. The refractive index of the inner tube is higher than the refractive index n2 of the cladding.

[0008] In these optical fibers, the light is usually coupled into the end face of the fiber to utilize the effect of total internal reflection. This is based on the physical fact that a light beam striking the fiber from the side, i.e., the outer surface of the fiber, passes through the fiber without any radiation being captured.

[0009] In a special type of optical waveguide, which is primarily used in metrology, a wavelength-shifting or scintillating agent is located inside the optical waveguide. With the help of a wavelength-shifting agent or a scintillating agent, it is possible to capture and guide radiation incident laterally on an optical waveguide inside the optical waveguide. Figures 1 and 2 show such special optical waveguides 800. As shown in Figures 1 and 2, the optical waveguide 800 comprises an inner tube 810 surrounded by a transparent cladding 820. The refractive index n1 of the inner tube 810 is greater than the refractive index n2 of the cladding. Homogenously distributed wavelength-shifting agents 830 (Figure 1) and scintillating agents 840 (Figure 2) are located within the inner tube 810.

[0010] When light waves strike the optical waveguide 800, as shown in Figure 1, they pass through the sheath 820 and the inner tube 810 until they encounter a wavelength-shifting means 830 (Figure 1). When the light wave (Figure 1) strikes the wavelength-shifting means 830, it is absorbed and re-emitted at a longer wavelength.

[0011] Figure 2 shows the situation when a charged particle, for example, in the form of electrons from beta radiation, strikes the optical waveguide 800. Analogously, the charged particle in Figure 2 is absorbed when it strikes the scintillating agent 840. In this case, however, it is not the charged particle that is emitted, but a light wave. Thus, light is emitted in both cases.

[0012] The wavelength shifting means 830 of Figure 1 and the scintillating means 840 of Figure 2 emit light isotropically into space.

[0013] For example, if the incident light wave strikes a wavelength-shifting means 830 located on the longitudinal axis passing through the center of the inner tube, a portion of the emitted light, namely the portion that falls around the cylinder axis in a cone with an aperture angle TT / 2 - θc (where θc is the critical angle), is retained inside the inner tube 810 (see arrow a), while light emitted at a larger angle (see arrow b) is lost. The cylinder axis of the cone corresponds to the longitudinal axis of the wavelength-shifting means 830 (Figure 1).

[0014] When a charged particle, for example in the form of β-radiation, strikes a scintillating agent 840, optical light is generated. Here, too, the light emitted by the scintillating agent 840 is distributed isotropically in space. If the scintillating agent 840 is located on the longitudinal axis passing through the center of the inner tube, a portion of the emitted light, namely the portion that falls around the cylinder axis in a cone with an aperture angle ΔT / 2 - Δc (where Δc is the critical angle), is retained inside the inner tube 810 (see arrow a), in a manner analogous to that described above. Light emitted at a larger angle (see arrow b) is lost when the scintillating agent is located on the longitudinal axis passing through the center of the inner tube.

[0015] In a measuring device that uses such optical waveguides 800, it is provided that the optical radiation or radiation from charged particles to be detected strikes the surface, in particular the lateral surface, of the optical waveguide 800. According to the relationships shown in Figures 1 and 2, the optical waveguide 800 captures the radiation and transports it along the longitudinal axis of the optical waveguide 800. Photosensors that detect the captured radiation are located on one or both end faces of the optical waveguide.

[0016] The maximum detection efficiency, where the detection efficiency indicates the proportion of the emitted light that is guided inside the optical fiber due to total reflection, is for such an optical fiber that emits the light in the center of the inner tube of the optical fiber: emax = (1 - cos TT / 2 - 0c)

[0017] For optical fibers known to date, the maximum detection efficiency is approximately 7% to 11%.

[0018] However, especially with low-intensity radiation, it is crucial that as little emitted light as possible is lost, thus ensuring high detection efficiency so that even low-intensity events can be detected by the photosensors located at the end faces of the 800 optical fibers. In addition, losses must be expected during the transport of light within the optical fiber. Therefore, detecting low-intensity radiation is difficult with current optical fibers.

[0019] Since the maximum detection efficiency of the known optical fibers is not very high, a large number of parallel optical fibers are often required to obtain a sufficiently high measurement signal at the photosensors.

[0020] Description of the invention:

[0021] It is an object of the present invention to provide an optical waveguide and a measuring device with such an optical waveguide, by means of which it is possible, for example, to reliably detect rare radiation events with little technical effort.

[0022] The invention is based on the approach of increasing the proportion of emitted radiation that can be guided through the optical fiber by total internal reflection, for example, to photosensors, compared to previously known optical fibers. In particular, the object of the present invention is to increase the maximum detection efficiency of an optical fiber.

[0023] According to the invention, the object is achieved by an optical waveguide comprising an inner tube with a central longitudinal axis and with a surface, wherein the inner tube is made of a first transparent material with a refractive index n1, an outer region made of a second transparent material with a refractive index n2, which surrounds the inner tube, wherein the refractive index n1 of the first transparent material is greater than the refractive index n2 of the second transparent material, and a light-emitting means in the inner tube, wherein the inner tube has a first region and a second region surrounding the first region, wherein the central longitudinal axis is located in the first region and the second region is provided at a distance from the central longitudinal axis of the inner tube, wherein the light-emitting means is located in the second region and wherein the first region is free of light-emitting means.

[0024] For the purposes of the invention, a transparent material is a material that is transparent both to the range of light waves visible to humans and to electromagnetic waves with wavelengths that are no longer visible to the human eye.

[0025] The light-emitting agent is preferably distributed uniformly in the second region and comprises, for example, one or more material layers and / or a plurality of particles or molecules.

[0026] As mentioned at the beginning, the light-emitting means ensures that radiation, for example in the form of charged particles or light, which strikes the light-emitting means is absorbed and then emitted in the form of light by the light-emitting means. The light emitted by the light-emitting means is emitted isotropically into the room. When electromagnetic radiation such as light is absorbed, a shift in wavelength generally occurs, so that the emitted light has a different, in particular higher, wavelength than the absorbed light. The invention is based on the finding that the angle of incidence at which the light emitted or radiated isotropically by the light-emitting means strikes the surface of the inner tube changes when the light-emitting means is shifted from the center of the optical waveguide towards the surface of the optical waveguide.

[0027] Furthermore, the following relationship was recognized: The closer the light-emitting means is to the surface of the inner tube of an optical fiber, the smaller the angular range in which radiation is lost. It was recognized that it is particularly advantageous for the light-emitting means to be arranged at a short distance from the surface of the inner tube.

[0028] In the extreme case, where the light-emitting medium is located almost at the surface of the inner tube, only the light emitted into the region of a cone with an aperture angle of 0c is lost. Note that, for reasons of symmetry, the radiation emitted into the cone extending in the opposite direction is also lost. In this case, the maximum detection efficiency is: emax = cos(0c)

[0029] The detection efficiency can be increased by a factor of 5 to 10 compared to known optical fibers.

[0030] According to the invention, the second region is thus adjacent to the surface of the inner tube, since it has been found that the quantity / intensity of the light held in the inner tube by means of total reflection and thus the maximum detection efficiency is particularly high here.

[0031] It has therefore proven particularly advantageous for the distance between the central longitudinal axis and the second region to be greater than 0.5 times the distance between the central longitudinal axis and the surface of the inner tube, in particular greater than 0.6 times the distance between the central longitudinal axis and the surface of the inner tube, preferably greater than 0.9 times the distance between the central longitudinal axis and the surface of the inner tube. The greater the distance between the central longitudinal axis and the second region, the greater the amount of light that can be captured in the inner tube by total internal reflection. In other words, the yield can be increased by shifting the second region towards the top of the inner tube.

[0032] When viewing the optical fibers from the end face, the second region preferably has a smaller radial width than the first region. Additionally or alternatively, the concentration of light-emitting agents in the second region increases toward the surface of the inner tube.

[0033] It was determined that the particles, molecules, or material layers of the light-emitting agent located directly on the surface of the inner tube do not contribute to the total reflection of the light wave. Furthermore, it was recognized that this can be prevented, and all particles, molecules, or material layers of the light-emitting agent can contribute to total reflection, if an intermediate region free of light-emitting agents is provided in the second region between the surface and the light-emitting agents.

[0034] In order to ensure that the radiation striking the inner tube has a sufficient penetration depth into the inner tube so that the emitted light can be totally reflected, it is provided that the distance of the light-emitting means located in the second region from the surface of the inner tube is at least one wavelength of the light emitted by the light-emitting means.

[0035] Preferably, the width of the intermediate region is at least one wavelength to at most 5 wavelengths, preferably at most 2 wavelengths of the light emitted by the light-emitting means.

[0036] For clarification, if the waveguide is symmetrical around the center and the second region is arranged concentrically around the first region, it does not matter whether the width of a region is determined across the entire width of the optical waveguide or only between the central longitudinal axis and the surface. For non-symmetrical optical waveguides, the term "width" refers to the area between the central longitudinal axis and the surface of the optical waveguide.

[0037] In a particularly advantageous embodiment, the second region adjoins the surface of the inner tube, wherein the distance of the second region from the central longitudinal axis is at least 0.9 times the distance between the longitudinal axis and the surface of the inner tube, and wherein the light-emitting means is arranged in the second region such that the distance of the light-emitting means from the surface of the inner tube is at least one wavelength of the emitted light.

[0038] In this embodiment, the second region with the light-emitting means contained therein forms a thin layer around the first region, wherein the light-emitting means are preferably distributed homogeneously in the second region or the concentration of the light-emitting means in the second region increases towards the surface of the inner tube.

[0039] Within the scope of the invention, a third region surrounding the second region may be provided.

[0040] In one embodiment, this third region is free of light-emitting means. Both the second region and the third region have a width in the radial direction of the inner tube. Preferably, the width of the second region in the radial direction is in the range of less than 0.1 times the distance between the longitudinal axis and the surface of the inner tube. In particular, the width of the second region is on the order of several wavelengths, in particular the width of the second region is less than 100 pm. The third region can be made of a different material than the second region and serve, for example, as a protective layer. It is advantageous if the material of the third region has the same refractive index as the material of the second region.

[0041] The material of the second region and, if present, the material of the third region are suitable for coupling charged particles or electromagnetic waves, for example in the form of light, laterally, ie transversely to the longitudinal axis of the optical waveguide, so that at least a section of the lateral surface of the optical waveguide can serve for coupling charged particles or electromagnetic waves, in particular as a sensor surface.

[0042] For reasons of symmetry, it is advantageous for the second region to be arranged concentrically around the central longitudinal axis of the inner tube. This applies to inner tubes with a circular cross-section as well as with a square cross-section. Although the inner tube can have any cross-sectional shape, it is preferred that the inner tube is a cylindrical tube, as this is particularly well suited for guiding light inside the inner tube. Particularly in metrology devices in which radiation strikes a surface section of the optical fiber, it is preferred that the first region and the second region extend in the longitudinal direction of the inner tube. This increases the probability of actually detecting incident radiation. It goes without saying that, if present, the third region can also extend in the longitudinal direction of the inner tube.

[0043] It was further recognized that the maximum detection efficiency can be increased when the ratio of the refractive indices n2 / n1 is < 0.9. In particular, it was recognized that the distance of the light-emitting means from the surface of the inner tube can be increased while maintaining optimal maximum detection efficiency when the difference between the refractive index n1 of the inner tube and the refractive index n2 of the outer layer is comparatively large. In a preferred embodiment, the distance of the light-emitting means from the surface of the inner tube is several wavelengths of the light emitted by the light-emitting means when the ratio of the refractive indices n2 / n1 is < 0.9, preferably the ratio of the refractive indices n2 / n1 is < 0.7.

[0044] It is advantageous for the inner tube to be made of a plastic, particularly polystyrene or PMMA. It has proven advantageous for the inner tube to be solid.

[0045] Within the scope of the invention, the second transparent substance can be a gas, in particular the surrounding air, a transparent liquid or a transparent solid.

[0046] Particularly when the second transparent material is a transparent solid, it is advantageous for the outer region to be formed as an outer layer. For example, the outer layer can be made of a plastic such as PMMA.

[0047] The light-emitting agent preferably comprises wavelength-shifting or scintillating agents. For example, these light-emitting agents can be or contain fluorescent agents. If the light-emitting agent comprises or consists of wavelength-shifting agents, it is suitable for absorbing light of a given wavelength and emitting light of a different, usually higher, wavelength.

[0048] Alternatively, the light-emitting agent is designed to absorb charged particles, such as beta radiation, and emit them in the form of light waves. Here, the light-emitting agent comprises scintillating agents, for example, scintillating agents in the form of scintillation crystals.

[0049] In both cases, the light-emitting agent can consist of or comprise, for example, organic molecules.

[0050] The present invention also relates to a measuring device comprising an optical waveguide according to one of the preceding claims, wherein an optical sensor is attached to at least one end of the optical waveguide.

[0051] Particularly when using the measuring device to detect rare events, such as high-energy radiation in astrophysics, it is advantageous for the optical fiber to have a sensor surface for light and / or charged particles, which is provided on the optical fiber and aligned parallel to the longitudinal axis of the optical fiber. This makes it relatively easy to provide sensor surfaces of the desired size.

[0052] For the sake of simplicity, the term light was chosen, whereby the term light refers to electromagnetic waves in the visible range as well as the wavelength range adjacent to the visible range, in particular the wavelength range with shorter wavelengths.

[0053] In a preferred embodiment, the optical waveguide has a surface, and at least a portion of the surface forms the sensor surface for light waves and / or charged particles. For an optical waveguide with a round cross-section, the surface has a cylindrical shape, for example. This allows for the provision of a simply constructed measuring device that can be used in a variety of different media. For example, at least the portions of the optical waveguide provided with the sensor surface can, if required by the measurement conditions, be introduced directly into a liquid or, as is customary, inserted into holders surrounded by air.

[0054] If, in a preferred further development, the entire lateral surface of the optical waveguide is designed as a sensor surface, a very large sensor surface can also be provided.

[0055] Brief description of the drawings: Preferred embodiments are explained in more detail with reference to the attached drawings, in which:

[0056] Figure 1 shows a known optical waveguide in an incident light application,

[0057] Figure 2 shows a known optical waveguide for the detection of charged particles,

[0058] Figure 3 shows a cross section through a first embodiment of an optical waveguide,

[0059] Figure 4 shows a cross section through a second embodiment of an optical waveguide,

[0060] Figure 5 shows a cross section through a third embodiment of an optical waveguide,

[0061] Figure 6 shows a cross section through a fourth embodiment of an optical waveguide,

[0062] Figure 7 shows the optical waveguide shown in Figure 6 in a side view, and

[0063] Figure 8 is a graphical representation of the measured efficiency as a function of the position of the light-emitting means.

[0064] Best mode for carrying out the invention and industrial applicability:

[0065] Figure 3 shows a cross-section through a first embodiment of a cylindrical optical waveguide 10 with a central longitudinal axis through the center M of the optical waveguide 10. The optical waveguide 10 comprises a transparent solid inner tube 12 with a surface 13 and a transparent outer region 14.

[0066] In this embodiment, the inner tube 12 is made of polystyrene with a refractive index of n1 = 1.6. The transparent outer layer is formed from the ambient air (n2 = 1), so that the ratio of the refractive indices n2 / n1 here is approximately 0.625.

[0067] The inner tube is divided into three regions B1, B2, and B3. The second region B2 concentrically surrounds the first region B1, and the third region B3, in turn, concentrically surrounds the second region B2. The central longitudinal axis passing through the center point M of the inner tube 12 is located in the first region B1. All three regions B1, B2, and B3 are made of the same transparent material, so that they have the same refractive index. While regions B1 and B3 are free of additives, light-emitting means 16 are provided in the second region B2 and are evenly distributed in the second region B2.

[0068] Viewed from the end face of the optical waveguide 10, a ring with light-emitting means 16 is located inside the inner tube 10, which is arranged concentrically around the longitudinal axis of the inner tube 10. The light-emitting means 16 extends at least partially along the longitudinal axis of the inner tube 10.

[0069] The light-emitting agent 16 comprises a wavelength-shifting substance that absorbs light of a predetermined wavelength and then emits it isotropically at a longer wavelength. For example, the light-emitting agent may consist of or comprise organic molecules.

[0070] Instead of the wavelength-shifting substance, a scintillating substance can also be used, which absorbs charged particles, such as beta radiation, and then emits them as light. In principle, it is also possible to use a light-emitting substance that does not shift the wavelength, as long as the light is emitted isotropically.

[0071] The distance between the central longitudinal axis and the second region B2 is greater than 0.5 times the distance between the central longitudinal axis and the surface 13 of the inner tube 12. In particular, the distance between the central longitudinal axis and the second region B2 is greater than 0.6 times the distance between the central longitudinal axis and the surface 13 of the inner tube 12. In other words, the regions B1, B2 and B3 each have a width w1, w2 and w3 in the radial direction of the inner tube 12, wherein the width w1 of the first region B1 is greater than the width w2 of the second region B2. In the embodiment shown in Figure 3, the width w3 of the region B3 is greater than the width w2 of the region B2. Advantageously, the width w2 of the region is in the range of less than 100 pm.

[0072] Figure 4 shows a cross-section through a second embodiment of an optical waveguide 110, which differs from the embodiment shown in Figure 3 in that an outer layer 118 made of PMMA is provided as the outer region 114. The outer layer 118 is firmly connected to the inner tube 112 and arranged concentrically around the inner tube 112. The ratio of the refractive indices n2 / n1 in this case is approximately 0.89-0.93. It is understood that other transparent materials can also be used, as long as the ratio of the refractive indices n2 / n1 is < 1.

[0073] Figure 5 shows a third embodiment of an optical waveguide 210. As in the embodiment shown in Figure 3, the optical waveguide 210 comprises a transparent solid inner tube 212 with a surface 213 and a transparent outer region 214. In this embodiment, the inner tube 212 is also made of polystyrene with a refractive index of n1 = 1.6. The transparent outer region is formed from the ambient air (n2 = 1).

[0074] The inner tube 212 is divided into two regions B1, B2. The second region B2 concentrically surrounds the first region B1 and borders the surface 213. The central longitudinal axis passing through the center point M of the inner tube 212 is located in the first region B1. Both regions B1 and B2 are made of the same transparent material, so they have the same refractive index. While region B1 is free of additives, light-emitting means 216 are provided in the second region B2 and are evenly distributed throughout the second region B2.

[0075] The distance between the central longitudinal axis and the second region B2 is very large here and amounts to more than 0.9 times the distance between the central longitudinal axis and surface 213 of the inner tube 212.

[0076] Although not shown, the light-emitting means 216 are positioned at a distance of at least one wavelength of the emitted light from the surface 213 so that the light penetrating the waveguide 210 can be absorbed by a light-emitting means 216.

[0077] Figure 6 shows an embodiment of an optical waveguide 310 that is a modification of the embodiment of an optical waveguide 210 shown in Figure 5. As in the embodiment shown in Figure 5, the optical waveguide 310 of Figure 6 comprises a transparent, solid inner tube 312 with a surface 313 and a transparent outer region 314, wherein the outer region is formed as an outer layer 318 made of plastic, in particular PMMA. Figure 7 shows a schematic side view of the optical waveguide 210 shown in Figure 5, in which the light-emitting means 216 are arranged at a short distance from the surface 213 of the inner tube 212.

[0078] If radiation, for example in the form of light (photons or electromagnetic waves) or charged particles, such as beta radiation, strikes the optical waveguide 210 from the side, it penetrates the outer surface of the inner tube 212 until it encounters a light-emitting medium 216. There, the radiation is absorbed and emitted isotropically in the form of light.

[0079] In the extreme case, where the light-emitting means 216 is located almost at the surface of the inner tube 210, only the emitted light emitted into the region of the cone with an aperture angle 0c is lost. Note that, for reasons of symmetry, the radiation emitted into the cone extending in the opposite direction is also lost.

[0080] Overall, for the case where the light-emitting means is located on the surface of the inner tube, the following maximum detection efficiency results: emax = cos( 0c) where 0c is the critical angle of total reflection.

[0081] To ensure that the light penetrating the inner tube 212 is actually guided further in the light guide 210 due to total internal reflection, it is necessary for the light-emitting means 216 to be located within the inner tube 212 itself at a short distance from the surface 213. For this purpose, one wavelength of the emitted light is sufficient.

[0082] It should be noted that the mode of operation shown in Figure 7 also applies to the embodiments shown in Figures 3, 4 and 6.

[0083] Figure 6 shows how the detection efficiency depends on the relative radius x = r / R, where r corresponds to the distance of the second region B2 from the surface 213 of the inner tube 212 and R to the radius of the inner tube 212 or the distance between the central longitudinal axis and the surface 213 of the inner tube 212. The width w2 of the second region B2 lies in the range of several wavelengths of the emitted light up to approximately 100 m. In relation to the embodiments of an optical waveguide 10; 110; 210; 310 shown in Figures 3 to 6, this means the following:

[0084] The closer the light-emitting means 16; 116; 216; 316 is to the surface 13; 113; 213;

[0085] 313 of the inner tube 12; 112; 212; 312 of the optical waveguide 10; 110; 210; 310, the smaller the angular range in which radiation is lost. This in turn means that the maximum detection efficiency can be increased if the light-emitting means 216; 316 is located as close as possible to the surface 213; 313 of the inner tube 212; 312 of the optical waveguide 210; 310. A particularly high maximum detection efficiency can be achieved if the distance between the central longitudinal axis and the second region B2 is very large and is preferably more than 0.9 times the distance between the central longitudinal axis and the surface of the inner tube and the second region B2 is adjacent to the surface 213; 313 of the inner tube 212; 312 of the optical waveguide 210; 310 borders.It is assumed that the distance of the light-emitting means 216; 316 from the surface 213; 313 of the inner tube 212; 312 is at least the wavelength of the light emitted by the light-emitting means 216; 316.

[0086] It has further been recognized that the distance of the light-emitting means 16; 116; 216; 316 from the surface 13; 113; 213; 313 of the inner tube 12; 112; 212; 312 of the optical waveguide 10; 110; 210; 310 can be increased while maintaining a given detection efficiency if the difference between the refractive index n1 of the inner tube 12; 112; 212; 312 and the refractive index n2 of the outer layer 14; 114; 214;

[0087] 314 is enlarged.

[0088] The difference between the refractive indices n2 and n1 is significantly greater in the embodiments illustrated in connection with Figures 3 and 5 than in the embodiments illustrated in Figures 4 and 6. Thus, in the embodiment 10; 210 illustrated in Figures 3 and 5, the distance of the light-emitting means 16; 216 from the surface 13; 213 of the inner tube 12; 212 can be greater than the wavelength of the light emitted by the light-emitting means 16; 216 in order to achieve the same detection efficiency as in the embodiments illustrated in Figures 4 and 6.

[0089] The inner tube 10; 110; 210; 310 of the optical waveguides 10; 110; 210; 310 shown in Figures 3 to 6 can be manufactured, for example, by applying a layer of the first material together with wavelength-shifting or scintillating substances to a transparent cylindrical inner tube element made of a first material with a refractive index n1 and a diameter smaller than the inner tube 12; 112; 212; 312. The cylindrical inner tube element made of the first material forms the first region B1, and the layer of the first material together with the wavelength-shifting or scintillating substances forms the second region B2.

[0090] If a third region B3 is provided, as in Figures 3 and 4, an additional layer of the first material can be applied to the resulting inner tube element. A prerequisite for this method for producing an optical fiber is that all regions B1, B2, and, if applicable, B3 have the same refractive index.

[0091] Alternatively, wavelength-shifting or scintillating substances can be applied to the surface of a transparent inner tube element, wherein the inner tube element consists of a transparent material. A preferably thin layer of the transparent material can then be applied to the coated inner tube element.

[0092] Alternatively, to form the inner tube 212; 312, light-emitting agents, in particular wavelength-shifting or scintillating molecules, can be introduced into the finished inner tube 12, 112 by diffusion and deposited in the inner tube 12, 112 on the surface 18; 118. Inner tubes made of a plastic that are softened using a solvent are suitable for this purpose.

[0093] If an outer layer 118; 318 is desired as in the embodiments shown in Figures 4 and 6, this can be applied to the inner tube 112; 312 after the inner tube 112; 312 has been produced, for example by means of known coating technologies.

[0094] Although not shown, the optical waveguides 10; 110; 210; 310 are used in optical measuring devices in which a photosensor is located on at least one end face of the optical waveguide 10; 110; 210; 310. The signal strength detected by the photosensors depends on the detection efficiency of the optical waveguide 10; 110; 210; 310.

[0095] Such optical measuring devices are suitable, for example, for use in measuring devices for detecting high-energy radiation (UV light to gamma radiation) or for detecting particle radiation in the form of beta radiation. The optical fibers shown in Figures 3 and 5 can be placed directly into transparent liquids and gases in these measuring devices, so that the transparent liquids and gases act as the outer region. The cylindrical surfaces of the optical fibers 10; 110; 210; 310 act as a sensor surface through which rare events in the form of light waves or charged particles are coupled into the optical fibers 10; 110; 210; 310.

[0096] For the optical fibers shown, an outer area formed as a layer is therefore not absolutely necessary.

[0097] The present invention also encompasses embodiments not shown, in which individual features of the illustrated embodiments are omitted or individual features of the illustrated embodiments are combined with one another.

Claims

Patent claims:

1. An optical waveguide (10; 110; 210; 310) comprising an inner tube (12; 112; 212; 312) with a central longitudinal axis and with a surface (18; 118; 218; 318), wherein the inner tube (12; 112; 212; 312) is made of a first transparent material with a refractive index n2, an outer region (14; 114; 214; 314) made of a second transparent material with a refractive index n2, which surrounds the inner tube (12; 112; 212; 312), wherein the refractive index of the first transparent material is greater than the refractive index n2 of the second transparent material, and a light-emitting means (16; 116; 216; 316) in the inner tube (12; 112; 212; 312), wherein the inner tube (12; 112; 212; 312) has a first region (B1) and a second region (B2) surrounding the first region (B1), wherein the central longitudinal axis is located in the first region (B1) and the second region (B2) is spaced apart from the central longitudinal axis of the inner tube (12; 112; 212; 312) is provided, wherein the light-emitting means (16; 116; 216; 316) is located in the second region (B2) and the first region (B1) is free of light-emitting means (12; 112; 212; 312), characterized in that the second region (B2) adjoins the surface (218; 318) of the inner tube (212; 312) and that the distance of the light-emitting means (216; 316) located in the second region (B2) from the surface (218; 318) of the inner tube (212; 312) is at least one wavelength of the light emitted by the light-emitting means (216; 316) emitted light.

2. Optical waveguide according to claim 1, characterized in that the distance between the central longitudinal axis and the second region (B2) is greater than 0.5 times the distance between the central longitudinal axis and the surface (18; 118; 218; 318) of the inner tube (12; 112; 212; 312), in particular greater than 0.6 times the distance between the central longitudinal axis and the surface (18; 118; 218; 318) of the inner tube.

3. Optical waveguide according to claim 1, characterized in that the distance between the central longitudinal axis and the second region (B2) is greater than 0.9 times the distance between the central longitudinal axis and the surface (18; 118; 218; 318) of the inner tube (12; 112; 212; 312).

4. Optical waveguide according to one of the preceding claims, characterized in that a third region (B3) is provided which surrounds the second region (B2), wherein the third region (B3) is preferably free of light-emitting means (12; 112; 212; 312).

5. Optical waveguide according to one of the preceding claims, characterized in that the second region is arranged concentrically around the central longitudinal axis of the inner tube (12; 112; 212; 312).

6. Optical waveguide according to one of the preceding claims, characterized in that the inner tube (12; 112; 212; 312) is cylindrical.

7. Optical waveguide according to one of the preceding claims, characterized in that the first region (B1) and the second region (B2) extend in the longitudinal direction of the inner tube (12; 112; 212; 312).

8. Optical waveguide according to one of the preceding claims, characterized in that the ratio of the refractive indices nz / m is < 0.

9.

9. Optical waveguide according to one of the preceding claims, characterized in that the inner tube (12; 112; 212; 312) is made of a plastic, in particular of polystyrene or PMMA.

10. Optical waveguide according to one of the preceding claims, characterized in that the second transparent substance is a gas, in particular the ambient air, or a transparent liquid or a transparent solid.

11. Optical waveguide according to one of the preceding claims, characterized in that the outer region (114; 314) is formed as an outer layer (118; 318).

12. Optical waveguide according to one of the preceding claims, characterized in that the light-emitting means (16; 116; 216; 316) comprises or consists of wavelength-shifting or scintillating means.

13. Measuring device comprising an optical waveguide according to one of claims 1 to 12, characterized in that an optical sensor and / or a photosensor is attached to at least one end of the optical waveguide (10; 110; 210; 310).

14. Measuring device according to claim 13, characterized in that the optical waveguide (10; 110; 210; 310) has a sensor surface for light waves and / or charged particles, which is provided on the optical waveguide (10; 110; 210; 310) and is aligned parallel to the longitudinal axis of the optical waveguide (10; 110; 210; 310).

15. Measuring device according to claim 14, characterized in that the optical waveguide (10; 110; 210; 310) has a surface and at least a portion of the surface forms the sensor surface for light waves and / or charged particles.

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