WO2004043542A1 - Electroluminescent textile structure, in particular for medical use - Google Patents

Abstract

The inventive electroluminescent textile structure used, in particular for medical purposes comprises a flat support (2) and a plurality of electroluminescent elements (4) fixed thereto. Each electroluminescent element comprises an optical fibre (6) for light guiding and is accurately associated to each corresponding optical fibre (6). Said element comprises at least one output point formed by the local curvature of the optical fibre. Said local curvature is selected in such a way that light laterally exits from the optical fibre because of the absence of a total reflection.

Description

LIGHT-EMITTING TEXTILE, IN PARTICULAR FOR MEDICAL APPLICATIONS

Technical field 5 The invention relates to a light-emitting textile structure according to the preamble of claim 1 and a use thereof.

State of the art

A generic textile structure is specified in EP 0 359 450 A2. The

The textile structure described there is designed as a light-emitting panel, on one side of which a multiplicity of woven optical fibers are arranged, which are provided with bends at discrete locations along the length of the fibers. These bends mean that light guided inside the fibers at the bend points due to the lack of total reflection laterally from the optically

15 see fibers is emitted. Possible applications of the light-emitting panel include photo-therapeutic treatments, for example photo-therapy of jaundice in newborns.

The known light-emitting textile structure is designed in the manner of a fabric in which the light-conducting fibers are arranged as warp threads, the bends acting as lighting elements being located at the intersection points of the warp threads with weft threads running transversely thereto. Accordingly, a large number of luminous elements arranged in a row like pearls is assigned to each light-conducting fiber. A serious disadvantage with this type of arrangement results from the fact that the luminous intensity of the individual luminous elements decreases along the fiber. If, for example, a certain fraction of the light located there in the fiber is emitted laterally on each light-emitting element, the light intensity along the fiber will decrease substantially exponentially. In order to achieve an approximately homogeneous light distribution over the entire structure, care must be taken to ensure that the fraction of the light emerging from the individual light elements gradually increases along the light-conducting fiber. Alternatively, an attempt can be made to gradually reduce the distance between the lighting elements along the light-conducting fiber, in order to compensate for the decreasing intensity per lighting element by a higher density of lighting elements. However, this is complex and, moreover, is difficult to implement, particularly in the case of a fabric-like textile structure which is generally periodically constructed. For all these reasons, it is hardly possible to achieve a homogeneous light distribution in the light-emitting textile structure described in EP 0 359 450 A2. However, this runs counter to the requirements of a very large number of applications, in particular also some medical applications, which require the most uniform possible illumination of an area to be irradiated with light.

However, the pearl cord-like arrangement of the lighting elements according to EP 0 359 450 A2 is also not suitable for applications in which inhomogeneous illumination of a specified type is specifically required. Again, the series connection of the lighting elements proves to be a considerable restriction, since the intensity distribution along a chain of lighting elements is essentially predetermined, i. H. it is only possible to arbitrarily vary the intensity in the transverse direction with respect to the optical fibers by selectively supplying the individual fibers with light of different intensities. In contrast, in the longitudinal direction - with a given arrangement of the tissue - no variation of the intensity is possible.

A further light-emitting structure is described in GB 2 305 848 A, which contains optical fibers in textile structures of different types, ie knitted and braided structures are mentioned there in addition to fabrics. It is essential that the lateral light emission is not necessarily brought about by wavy optical fibers. Rather, the fibers are provided with local injuries to the lateral surface, which act as light exit points of the fiber, before they are processed into the structure. As Examples of such injuries are notches, grooves, dents and other irregularities in the surface. However, the problem of the intensity decreasing along each optical fiber is not addressed in GB 2 305 848 A.

No. 4,234,907 describes a light-emitting fabric which has optical fibers as warp threads and other fibers as weft threads. Again, lateral light emission from the optical fibers is caused by local injuries, especially scratches. In order to compensate for the drop in intensity along the individual fibers, the points of injury are arranged closer and closer as the distance from the light source increases. Although an almost homogeneous light distribution over the entire light-emitting fabric can be achieved with this solution, there is no possibility of subsequently producing a distribution of the desired shape which is inhomogeneous in the warp direction in the finished fabric. It is therefore not possible, for example, to produce a lighter-colored strip of any given direction, but this would be desirable for some applications.

The US 4,727,603 describes a garment that is embroidered with light-conducting fibers. Again, these are optical fibers, the surface of which is provided with a large number of small injuries. The garment is to be equipped with bright ornaments, which represent, for example, floral or leaf motifs. These motifs are each made up of a plurality of line-like light fibers. The problem of the drop in intensity along the fibers is not addressed; however, the provision of a homogeneously luminous textile structure is precisely not the goal sought in US Pat. No. 4,727,603. On the other hand, the non-homogeneous light distribution is fixed by the embroidery pattern and cannot be changed afterwards or only to a very limited extent. Representation of the invention

The object of the invention is to provide an improved light-emitting textile structure with which the disadvantages mentioned above are avoided. In particular, this textile structure should be suitable for general lighting purposes but also for human and veterinary applications.

This object is achieved by the textile structure defined in claim 1. This comprises a flat carrier and a multiplicity of light elements fastened thereon, each light element having a light-feeding optical fiber. Because each optical fiber is assigned exactly one light-emitting element, which is accordingly individually addressable, the light intensity of each light-emitting element can be set individually by coupling light of suitable intensity into the associated fiber. In this way, an extremely homogeneous as well as a deliberately inhomogeneous light distribution of any shape can be set on the textile structure. In addition, the light distribution can be changed without intervention on the textile structure by changing the intensity of the light coupled into the individual fibers. The individual light-emitting elements are formed from one or, preferably, a plurality of coupling points formed by local curvature of the optical fiber, the local curvature being selected such that, due to the lack of total reflection, light emerges from the side of the fiber, that is to say from its outer surface. The individual light-emitting elements can thus be made very compact, which ultimately allows a high number of light-emitting elements per unit area and accordingly enables good control of the light distribution of the textile structure. Because the individual light-emitting elements represent units that are independent of one another, a light-emitting textile structure with very high flexibility can be produced with a correspondingly designed carrier. The light-emitting textile structure according to the invention can thus be used not only for illuminating flat objects, but in particular also for illuminating structured objects. For example, in medical treatment lungs can be used like a conventional textile structure on the skin and in other internal and external organs of the body.

The light-emitting textile structure according to the invention can be produced very inexpensively under suitable production conditions and is therefore also suitable for single use.

The most important applications of the textile structure according to the invention are photodynamic diagnostics and the photodynamic therapy of malignant tumors of all kinds (for example solid tumors such as carcinomas and sarcomas) and their metastases and the preliminary stages. In addition, applications in pathological cell proliferation (e.g. endometriosis) are planned. Other applications include wound healing for various chronic diseases (e.g. diabetes or skin diseases), biostimulation and the fight against viral and bacterial infections, which is also advantageous in dentistry, among other things. In addition, the textile structure according to the invention can generally be used to eliminate microorganisms on surfaces of all kinds.

A special use of the textile structure is defined in claim 15. In this case, at least one decoupling point of an optical fiber is used as a light collector in order to dissipate light incident on the textile structure through the optical fiber. For example, the fluorescence intensity of an irradiated object, in particular an irradiated tissue region, can be determined continuously or at intervals. This enables photodynamic diagnostics to be carried out in situ, which offers great advantages over conventional methods.

Advantageous embodiments of the invention are defined in the dependent claims. In principle, the light-emitting elements can be arranged on the carrier in various ways, both regular and irregular arrangements being possible. In the embodiment according to claim 2, the lighting elements form a pixel-like arrangement in the manner of a regular grid. On the one hand, this enables a homogeneous light distribution to be achieved in that essentially each light element is supplied with the same light intensity. On the other hand, the pixel-like arrangement is also well suited for the generation of predetermined inhomogeneous light distributions. It proves to be advantageous that the lighting elements are distributed homogeneously on the carrier and each lighting element can thus be uniquely characterized by a row and column number. A desired light distribution can thus be achieved by expressing it as a function of two coordinates, which essentially correspond to the said row or column number and then applying the light intensities corresponding to the optical fibers assigned to the individual light elements.

In principle, there are various options for attaching the lighting elements to the carrier. Advantageously, the lighting elements are embroidered on the carrier according to claim 3. This means that at the same time a displacement-free arrangement of each lighting element at the intended position of the support, but also a very loose arrangement of the feeding optical fibers, can be realized. The result is a light-emitting textile structure with great flexibility.

The individual optical fibers can be designed essentially in a straight line, one or more loops only having to be provided in the area of the assigned lighting element. According to claim 4, however, the individual optical fibers are arranged in a U-shape with a near-apex lighting element. This has the advantage that two legs of the associated fiber are assigned to each lighting element, both of which can be used to supply light to the lighting element. In particular, the two can belong together. end of the leg can be combined into a single light entry point.

In the embodiment according to claim 5, the decoupling point is formed by a loop of the optical fiber. The curvature of the loop is to be selected so that at least at certain points in the loop a lateral light emission is possible due to the lack of total reflection.

A further embodiment of the decoupling point is defined in claim 6, according to which the decoupling point is formed by a local injury or deformation of the optical fiber. The said injury or deformation point acts as a scattering center for the light guided in the fiber, which enables light to emerge from the side. In particular, in the embroidered embodiment according to claim 2, the local injury or deformation points can be caused by the action of fixing stitches. This means that the decoupling points are only formed in the course of the embroidery process and, consequently, expensive pretreatment of the optical fibers can be omitted.

It is possible to form the individual optical fibers according to claims 5 and 6, i.e. to be provided both with loop-shaped and with coupling points formed by local injuries or deformations.

The material of the carrier expediently depends on the intended application. For example, the carrier can be formed from a textile material or from a film. According to the embodiment defined in claim 9, the carrier can be removed before the textile structure is put into use. In particular, the textile structure, together with the carrier, can be attached to a desired location, for example on the skin or in the body of a patient, and then the carrier can be attached be removed before exposure to light. If required, removability can be achieved by using a soluble carrier material.

The textile structure according to claim 10 has a light-reflecting back, with which an increased light radiation is achieved in the opposite front direction. A particularly homogeneous light distribution results in the textile structure according to claim 11, which is provided with an optically effective layer arranged on the front. In the present context, an optically active layer is to be understood to mean any type of material layer which has a desired influence on the radiation characteristics of the textile structure. In particular, said layer can act as a diffuser. The textile structure is advantageously provided both with a light-reflecting rear side and with an optically active layer arranged on the front side.

The embodiment defined in claim 12 is designed for medical applications, in particular for photodynamic therapy. The textile structure is covered with a photosensitive substance (photosensitizer) or a precursor thereof and is designed in the manner of a plaster. Accordingly, with a single access to a part of the body in need of treatment, the photosensitizer or its preliminary stage can be attached and then - if necessary after waiting until the preliminary stage is converted - the photodynamic treatment can be carried out.

In the textile structure according to claim 13, the optical fibers are combined at the end to form at least one fiber bundle. The textile structure can thus be connected to existing light sources in a manner known per se. A further embodiment is defined in claim 14, according to which the textile structure is provided with light coupling means by means of which the light supply of the individual optical fibers can be adjusted. Brief description of the drawings

Exemplary embodiments of the invention are described in more detail below with reference to the drawings, in which:

Figure 1 shows a detail of a light-emitting textile structure, in a schematic representation.

2 shows three lighting elements of the textile structure of FIG. 1, in a schematic illustration, and a section of one of the lighting elements, in an enlarged illustration;

3 shows an optical fiber held by two fixing stitches, with a loop provided, in a schematic illustration;

Figure 4 shows the fiber of Figure 2 with the loop drawn together;

5 shows a light-emitting textile structure with a pixel-like arrangement of the lighting elements, in a schematic illustration;

6 shows a light-emitting structure with three different types of alignment of elongated lighting elements, in a schematic representation;

7 shows the light-emitting textile structure of FIG. 6, in the operating state, in a photographic illustration;

8 shows a light-emitting textile structure suitable for medical applications, in a schematic illustration;

9 two lighting elements fastened to a flat support and a matchstick for size comparison, in a photographic illustration; 10 several lighting elements fastened to a flat support and a matchstick for size comparison, in a photographic illustration.

Ways of Carrying Out the Invention

General remarks

In the medical field, textiles are mainly used as plasters or wound dressings, but also as implants, whereas until recently they had no light-guiding functions.

Recently photosensitive substances (photosensitizers) are available on the market that specifically accumulate in pathological cells. Owing to their photophysical and photochemical properties, photosensitizers enriched in such cells under irradiation with non-ionizing electromagnetic radiation can be used on the one hand to identify or localize the diseased cells on the basis of the emitted fluorescence (photodynamic diagnostics) and on the other hand to destroy these cells as a result of photochemical reactions ( Photodynamic therapy). In connection with these photosensitizers, light is required for the area-like, homogeneous lighting, which enables the targeted treatment of skin areas, in particular skin folds and in structured cavities of organs. So far, intensive instruments such as balloon catheters have been available for use in the body, the use of which is hampered by the inaccessibility of certain areas of the skin and the insufficiently controllable dosimetry. For the most part, lighting devices are currently used, which mostly consist of a fiber-optic light supply in which a surface can be homogeneously illuminated by means of expansion optics. While this form of application shows good results on smooth, mostly outer skin areas, it is usually unsatisfactory with regard to structured surfaces. embodiments

The section of a light-emitting textile structure shown in FIG. 1 comprises a flat carrier 2 and a light-emitting element 4 fastened thereon with a light-feeding optical fiber 6. The light-emitting element 4 comprises a number of loops 8, 8a, 8b, etc., the curvature of which is selected in this way is that due to the lack of total reflection, light can emerge from the side of the optical fiber 6. Accordingly, said loops act as decoupling points. It should be pointed out that the luminous element shown in FIG. 1 is formed from a single optical fiber, only the parts of the fiber 6 that protrude from the plane of the drawing are shown for reasons of drawing. Depending on the application of the textile structure, the lighting elements can be attached to a single or to both sides of the carrier 2.

In its entirety, the light-emitting textile structure has a multiplicity of lighting elements with associated optical fibers, with exactly one lighting element being assigned to each optical fiber. This can be seen schematically in FIG. 2, in which three lighting elements 4, 4a, 4b with individually assigned optical fibers 6, 6a, 6b are shown. The enlarged section of FIG. 2 shows part of the lighting element 4 with a number of loops 8, 8a, 8b, etc. In this example, the lighting elements are fixed by means of fixing stitches 10 to the support (not shown in more detail).

The formation of local areas of curvature of the optical fiber required for the functioning of the lighting elements is shown schematically in FIGS. 3 and 4. First, an optical fiber 6 is laid out on a carrier, not shown, to form a loop 8. The fiber is then embroidered onto the carrier by means of two fixing stitches 10, 10a in such a way that the loop area 8 is located between the two fixing stitches. Finally, the fiber is pulled in the longitudinal direction L, whereby the loop 8 is increasingly drawn together. On the one hand, the contraction The radius of the loop is greatly reduced and, on the other hand, the fiber is twisted in the loop area. If the radius of curvature falls below a critical value at a point 12 of the loop, the condition for total reflection of the light guided in the optical fiber is no longer fulfilled at this point. As a result, light emerges from the side of the fiber. The conditions for total reflection depend on various factors such as light wavelength, refractive index, etc., the relationships of which are known per se.

Strongly curved local areas, which act as light decoupling points, are also created when the fixation stitches are attached or subsequently through their effect. On the one hand, an injury to the lateral surface of the optical fiber can be formed when the fixing stitch is attached. On the other hand, as indicated in FIG. 4, a local kink 13 can form in the area of a fixing stitch 10a under tensile loading of the optical fiber 6. In contrast to the example shown in FIG. 4, injuries or deformations acting as decoupling points can also be generated without the formation of loops under the action of fixing stitches.

The individual optical fibers are advantageously arranged in a U-shape, as shown in the enlarged section of FIG. 2, the associated lighting element being located in the apex area. This gives the advantage that two legs of the associated fiber are assigned to each lighting element, both of which can be used to supply light to the lighting element. However, it is also possible to arrange the lighting element at the end of the associated optical fiber, as shown in FIG. 1.

5 shows a pixel-like arrangement of the lighting elements using the example of a section with six lighting elements 4 (j, k), with row index j = 1, 2.3 and column index k = 1, 2. Further arrangement options can be seen in FIG. 6, which shows a textile structure with elongated lighting elements 4, which have three different types of alignment A, B, C. It is here on it pointed out that the optical fibers and the lighting elements are in an unambiguous relationship to one another, ie exactly one lighting element is assigned to each optical fiber and vice versa. The fact that this is not recognizable with the type of alignment C in FIG. 6 has only drawing reasons.

FIG. 7 shows a photograph of a light-emitting textile structure according to FIG. 6 in the operating state, i.e. when red light is coupled into the optical fibers, but without a light-scattering layer arranged on the front. The textile structure has a width of approximately 80 mm and a length of approximately 100 mm and is provided with approximately 300 lighting elements.

As a rule, these optical fibers consist of a light-guiding core, which is provided with a sheath. In principle, optical fibers made of glass or plastic can be used as optical fibers. The optical fibers made of polymethyl methacrylate (PMMA) known from data transmission technology are particularly suitable for medical use. Other suitable fiber materials are polycarbonate (PC) and polystyrene (PS) or other amorphous plastics such as polyamides (PA). For the optical fibers, monofilaments or multifiles can be used, which can be used in different titers, treated or untreated, and coated or uncoated. It is also expedient to use twisted and wound threads. In the examples shown, a twisted optical monofilament fiber made of PMMA with a diameter of 125 micrometers and a titer of 370 dtex (corresponding to 370 grams per 10000 m thread length) was used. A stick fixing thread made of textured polyester with 113 dtex was used to embroider the optical fibers onto the flat carrier. Among other things, a polyester fabric with a weight per square meter of 80 grams / m ^{2 was} used as the carrier material.

The sheet-like support structure can be formed from various structures such as textiles or foils and is preferably flexible and drapable. designed. The optical fibers are attached to the support using embroidery technology, which gives great freedom of design with regard to the arrangement of the lighting elements. Usually you embroider in the two-thread system in which the front thread is a light-conducting thread and the rear thread is a support thread. The reversal of this principle or other combinations with two or more threads is also possible. Both thread systems are connected on the support structure and together form the embroidery pattern.

At least initially, a support structure is required for the manufacture of a light-conducting textile using embroidery technology. In order to save weight and improve the drapability of the light-emitting textile structure, however, the carrier structure can be removed again after the embroidery process, for example by dissolving it in a suitable solvent such as water. However, so that the structure does not fall apart, the individual optical fibers must be equipped with suitable connection structures before the carrier is removed. These connection structures are advantageously formed in the course of the embroidery process.

FIG. 8 shows a light-emitting textile structure that can be used for human and veterinary applications. This has a flexible flat carrier 2 made of a textile material and a plurality of lighting elements 4 attached to it, of which only a small number is shown in the figure. Each lighting element is located in the apex area of a U-shaped optical fiber 6, so that each fiber 6 has a pair of legs 14a, 14b. The plurality of pairs of legs 14a, 14b is combined at the end to form a first fiber bundle 16, which is surrounded by an annular sleeve 18. The example shown is a metallic sleeve with a nominal width of 5 mm. The light entry point 20 formed in this way is intended to be connected to a conventional incoherent light source, ie a lamp or a light-emitting diode (LED), or else to a coherent laser light source. If desired, the combined fiber bundle can be Desired distance to be designed as an optical cable. The intensity and spectral distribution of the light fed in in the entry direction E and possibly also its polarization depend on the particular application and can be adjusted in a manner known per se.

The textile structure shown in FIG. 8 further comprises a light-reflecting layer 22 attached to the back of the carrier 2, by means of which increased light radiation in the opposite front direction of the textile structure can be achieved. In this sense, it is also possible to manufacture the carrier itself from a light-reflecting material, for example from a light-reflecting film. Furthermore, the light-emitting textile structure is provided with a light-scattering layer 24 arranged on the front, by means of which a particularly homogeneous light distribution can be achieved. 8 shows the light-scattering effect of layer 24 due to a blurred appearance of the components lying behind it.

As can further be seen from FIG. 8, the textile structure is equipped with a number of light collectors 26, by means of which light incident on the textile structure can be detected. In the example shown, the light collectors 26 are identical to the lighting elements 4, the associated legs 28a and 28b of the optical fibers 30 being combined to form a second fiber bundle 32. This is led to a light exit point 34, from which the collected light is guided in the detection direction D to an optical detection device. The principle of operation of the arrangement described is based on a reversal of the principle of the lighting elements 4, ie the lack of total reflection at the decoupling points of the optical fibers not only allows light to exit the fiber, but also allows light to enter the fiber. As an alternative to this configuration, the textile structure can be provided with suitable photoelectric light detectors. By detecting the light incident on the textile structure, the characteristic of the light emitted by an irradiated tissue region can be determined. This characteristic is determined both by the light reflected directly from the tissue and by the fluorescent radiation of the tissue, it being possible to separate the corresponding portions on the basis of their different spectral distribution with the aid of optical filters or other suitable optical elements. Alternatively or in addition to this, the irradiation carried out with light of a first wavelength which is optimal for photodynamic therapy can be briefly interrupted in order to detect the fluorescence intensity while irradiating light of a second wavelength which is optimal for photodynamic diagnosis. Accordingly, the increasing fading of a previously attached or administered photosensitizer can be tracked by continuously or at intervals determining the fluorescence intensity of an irradiated tissue region. In addition, photodynamic diagnostics can also be carried out in situ.

A wavelength in the range of 635 nm is preferably used for photodynamic therapy with 5-aminolevulinic acid, while a wavelength around 400 nm is required for photodynamic diagnostics with protoporphyrin IX.

While most homogeneous light distribution is desirable for most medical applications, there are also areas of application for which a deliberately inhomogeneous light distribution is sought. This can be achieved thanks to the individual addressability of the individual lighting elements. For this purpose, in the example of FIG. 8, it would have to be ensured that each leg pair 14a, 14b is supplied with a predetermined light intensity, for which purpose suitable light coupling means are to be provided. As can be seen from FIG. 9 on the basis of a size comparison with a matchstick, the individual lighting elements can be produced, for example, with a width of approximately 1 mm and a length of approximately 6 mm.

While the lighting elements shown in FIG. 9 comprise clearly pronounced loops, the lighting elements shown in FIG. 10 have non-looped U-shaped end sections which are each fastened to the flat carrier by a number of fixing stitches. It has been shown that with these lighting elements, the light emission occurs primarily in the vicinity of the fixing stitches.

Claims

claims 1. Light-emitting textile structure, in particular for medical applications, with a flat carrier (2) and a plurality of light elements (4, 4a, 4b) attached thereto, each light element having a light-feeding optical fiber (6, 6a, 6b), characterized in that that each optical fiber (6, 6a, 6b) is assigned exactly one lighting element (4, 4a, 4b) which has at least one coupling point (8, 8a, 8b) formed by a local curvature (12, 13) of the optical fiber , where the local curvature is chosen such that, due to the lack of total reflection, light emerges from the side of the optical fiber. 2. Textile structure according to claim 1, characterized in that the lighting elements have a pixel-like arrangement (4 (1, 1), 4 (1, 2), 4 (2,1), 4 (2,2), 4 (3 , 1), 4 (3,2)). 3. Textile structure according to claim 1 or 2, characterized in that the lighting elements (4, 4a, 4b) are embroidered on the carrier (2). 4. Textile structure according to one of claims 1 to 3, characterized in that the individual optical fibers (6) are arranged in a U-shape with a lighting element (4) lying close to the apex. 5. Textile structure according to one of claims 1 to 4, characterized in that the decoupling point is formed by a loop (8, 12) of the optical fiber. 6. Textile structure according to one of claims 1 to 4, characterized in that the decoupling point is formed by a local injury or deformation (13) of the optical fiber. 7. Textile structure according to claims 3 and 6, characterized in that the local injury or deformation (13) is caused by a fixing stitch (10a). 8. Textile structure according to one of claims 1 to 7, characterized in that the carrier (2) is formed from a textile material or a film. 9. Textile structure according to one of claims 1 to 8, characterized in that the carrier (2) is removable before use. 10. Textile structure according to one of claims 1 to 9, characterized in that it has a light-reflecting back (22). 11. Textile structure according to one of claims 1 to 10, characterized in that it is provided with an optically active layer (24) arranged on the front. 12. Textile structure according to one of claims 1 to 11, characterized in that it is coated with a photosensitive substance or a precursor thereof. 13. Textile structure according to one of claims 1 to 12, characterized in that the optical fibers are combined to form at least one fiber bundle (16, 32). 14. Textile structure according to one of claims 1 to 13, characterized in that it has light coupling means, by means of which the light supply of the individual optical fibers is adjustable. 15. Use of the textile structure according to one of claims 1 to 14, wherein at least one decoupling point of an optical fiber is used as a light collector (26) in order to dissipate light incident on the textile structure through the optical fiber (30).