DE102014011041A1 - Optical flow-through hollow fiber, process for its production and its use - Google Patents

Abstract

The invention relates to a hollow fiber, in particular a liquid or gas-conductive optical flow measuring hollow fiber, a process for their preparation and their use. The object of the present invention to provide an optical flow measuring hollow fiber, which liquids / gases can accommodate / guide while allowing a light guide on the principle of total reflection in these liquids or gases, is achieved in that the optical flow measuring hollow fiber has a central hollow core (3) surrounded by a number of air chambers (2), wherein the air chambers (2) surrounded by air chamber walls (21) and are completely separated from each other and the outer shell (1) the air chambers (2) at their, that of the central Hollow core (3) facing away from completely enveloped sides, the hollow core (3) is surrounded by a hollow core wall (31), which communicates with the air chamber walls (21) and at least the hollow core wall (31) and the air chamber walls (21) of an optically transparent Material consist, wherein the cross section of the hollow core (3) is polygonal and that through the hollow core (3) through the same early light and liquids or gases are feasible.

Description

The invention relates to a hollow fiber, in particular a liquid or gas-conductive optical flow measuring hollow fiber, a process for their preparation and their use.

The sensitive (trace) detection of low-concentration analytes in liquids, for example dissolved organic molecules in an aqueous environment, is of great importance in a wide variety of fields. Important areas of application include, for example, environmental analysis, the monitoring of clean drinking water and biomedicine.

In order to be able to analyze the smallest amounts of liquid, for example spectroscopically, a wide variety of miniaturized measuring bodies, such as, for example, measuring cuvettes, are used.

A flow measuring cuvette with flow and light channel is, for example, from WO 2005/047869 A1 , of the EP 0 488 947 A1 or from the GB 2 071 355 A known. The disadvantage of these technical solutions, which are based mostly on the capillary principle in quartz glass, is that the condition of a light guide in the aqueous liquid core can not be met because the refractive index of water (n = 1.33) is smaller than the refractive index of Quartz glass (n = 1.45). A light guide on the principle of total reflection is therefore not possible.

The DE 10 2009 035 578 A1 discloses, for example, a fiber optic surface plasmon resonance sensor for determining refractive indices of fiber-adjacent media according to DE 10 2008 046 320 A1 comprising at least one singlemode fiber used as an optical waveguide, a light source and a detector located in the irradiation and radiation region of the singlemode fiber, wherein a fiber coupler or circulator is spliced between the fiber and the light source / detector and wherein the light is on the input region facing the light source enters the fiber and the fiber has an end region designed opposite the input region, and further functional elements (a long-period Bragg grating, LPG - inscribed in the core region of the optical fiber) for coupling the input core mode into a selected cladding mode, a thin clad metal layer surrounding the surface of the cladding of the fiber, at which the selected cladding mode excites a surface plasmon wave and which is arranged to couple the cladding mode). The disadvantage of this technical solution, which is based on a solid fiber core and evanescent fields, is that the highest intensity of the radiation / laser light is guided in the glass and not in the analyte, which leads to an excessive background signal, so that this technical solution not suitable for Raman spectroscopy.

The sensitivity of optical detection methods (Raman spectroscopy, absorption spectroscopy, fluorescence spectroscopy, etc.) can be significantly increased if the laser / excitation light is guided directly in the analyte medium and interacts efficiently with it for spectroscopy.

Optical hollow fibers can also be considered as optimized cuvettes due to their cavity, since they absorb the liquids in their hollow core and in this liquid core at the same time the (their can, which occurs in optical hollow fibers no diffraction limit, as in classical free-jet cuvettes occurs.

The advantage of such hollow core fibers is that they require only a minimal analyte volume and ensure an optimal light-analyte interaction.

• (i) Teflon-Hohlkapillaren weisen jedoch aufgrund des geringen Brechzahlunterschiedes zu Wasser nur eine sehr kleine numerische Apertur auf (was die Effizienz beschränkt) und besitzen im Vergleich zu Quarzfasern eine raue, nanoporöse Oberfläche, an welcher sich sehr leicht Verunreinigungen festsetzen, so dass sich die optischen Transmissionseigenschaften schnell verschlechtern und permanente, aufwendige Reinigungsschritte durchgeführt werden müssen. Eine Anwendung bspw. für SERS ist somit nicht vielversprechend. Weitere Nachteile der Polymer-Kapillarfasern sind die ungünstige aufbau- und verbindungstechnische Kompatibilität zu quarzfaseroptischen Systemen (kein Spleißen, Tapern möglich).
• (ii) HCPCF weisen ebenfalls eine Reihe von Nachteilen für den praktischen Einsatz auf. Die zentralen Hohlräume von HCPCF (für Vis) besitzen einen Durchmesser von nur wenigen μm, so dass eine Fluidik von Flüssigkeiten nur schwierig und mit aufwendigen Pumpensystemen gewährleistet werden kann. Für eine Anwendung mit Flüssigkeiten müssen überdies auch die in der Regel noch kleineren Cladding-Löcher der Fasern befüllt werden, was einen praktikablen Einsatz (schnelle Befüllung, Entleerung, Reinigung, Reproduzierbarkeit) nahezu unmöglich macht. Des Weiteren sind HCPCF aus mehreren Cladding-Ringen mit einer Vielzahl von Kapillaren aufgebaut, so dass sie nur mit sehr hohem technischem Aufwand herzustellen sind.

At present, there are two possible variants of hollow core fibers, which allow light guidance in the water core at light wavelengths in the visible spectral range (Vis). These are (i) polymer fibers of TeflonAF and (ii) Hollow Core Photonic Crystal Fiber (HCPCF).

• (i) Teflon hollow capillaries, however, have only a very small numerical aperture due to the small difference in refractive index to water (which limits the efficiency) and, in comparison to quartz fibers, have a rough, nanoporous surface on which impurities easily settle, so that deteriorate the optical transmission properties quickly and permanent, expensive cleaning steps must be performed. An application eg. For SERS is therefore not promising. Other disadvantages of the polymer capillary fibers are the unfavorable construction and connection compatibility with quartz fiber optic systems (no splicing, taping possible).
• (ii) HCPCF also has a number of disadvantages for practical use. The central cavities of HCPCF (for Vis) have a diameter of only a few microns, so that fluidics of liquids can be ensured only with difficulty and complex pump systems. In addition, for an application with liquids, the usually even smaller cladding holes of the fibers must be filled, making practicable use (rapid filling, emptying, cleaning, reproducibility) almost impossible. Furthermore are HCPCF composed of several cladding rings with a variety of capillaries, so that they can be produced only with very high technical effort.

In addition to various hollow core fibers in which the hollow core and the surrounding capillaries have a circular cross-section, hollow core fibers are known, the hollow cores and capillaries have a polygonal cross-section.

From the WO 03079077 A1 For example, an "index-guiding" fiber is known whose voids are filled with air, vacuum or inert gas to achieve an index guide in which the radius of the fiber is made large and the effective refractive index of the fiber is small.

It reveals the WO 03079077 A1 also the use of 6 corner structures to make the refractive index more adjustable.

The object of the present invention is to provide an optical flow measuring hollow fiber, a process for their preparation and their use, which avoid the above-mentioned disadvantages of the prior art, in particular create an optically transparent capillary system that can absorb or conduct liquids or gases and a light guide on the principle of total reflection or the antiresonant or the double-antiresonant waveguide / leadership in these liquids or gases allows.

According to the invention this object is achieved by the characterizing features of the 1st, 8th and 10th claim. Further favorable embodiments of the invention are specified in the subordinate claims.

The essence of the invention is that the optical flow measuring hollow fiber based on the principle of total reflection or the anti-resonant waveguide or the double-anti-resonant waveguide, resulting in concrete specifications for the geometric structure of this hollow fiber.

The optical flow measuring hollow fiber comprises an outer shell, air chambers and a hollow core, wherein the air chambers surround the hollow core and are surrounded by air chamber walls, which merge into the wall of the hollow chamber. The air chambers are surrounded by the outer jacket.

The air chamber walls, which advantageously consist of quartz glass, have a precisely defined thickness d and are arranged in the longitudinal course of the optical flow measuring hollow fiber precisely plane-parallel to each other and the fiber longitudinal axis.

Due to the high optical surface quality of the quartz glass walls (roughness, plane parallelism) and the Dickenkonstanz along the fiber results in a resonator with a cross-sectional dimension, which is exclusively transmissive only for selected resonance wavelengths. Non-resonant wavelengths are proportionately reflected back into the core, which allows the light guide.

Furthermore, the outer cavity with respect to the cross-sectional dimension can be matched to the core size, in turn, an antiresonant back reflection of the light takes place in the center of the fiber and the propagation losses of the core guided light can be minimized.

Alternatively, the outer cavity with respect to the cross-sectional dimension resonantly tuned to unwanted core modes, so that, for example, higher modes preferably decouple from the core and thereby practically a single-mode operation of the nominally multimode fiber is made possible.

A proportionate combination of both effects is possible.

The hollow core wall is designed in its cross section as a polygon. In the vertices of this central polygon, which may be, for example, a square (corner point = transition of the air chamber walls into the hollow core wall), there are deliberately no thickenings and junctions. As a result, parasitic light guidance in the glass is prevented. The diameter of the central cavity in the hollow core is comparatively large (for example 20 .mu.m), so that a rapid analyte exchange of liquids or gases is ensured.

For the example of the quadrangular structure, only four starting capillaries are needed for the manufacturing process, which will be described below.

The optical flow measuring hollow fiber has spectrally broadband transmission windows from the NIR to the deep UV range, so that low attenuation light guidance and thus highly efficient optical sensor technology can take place in different wavelength ranges.

A particularly important example of this is the application of the optical flow measuring hollow fiber in Raman spectroscopy. By means of the irradiation of different laser wavelengths in different spectral windows, for example, in Raman spectroscopy a multi-spectral sensor system can take place.

The unique characteristics of the optical flow-through hollow fiber are that, when used as intended, a clean fundamental mode (a distinct maxima, not multiple maxima, no multimode sub-maxima) is formed in all spectral ranges and transmission windows exist from the near infrared to the important UV range.

The double-antiresonant guiding principle, which is realized with the optical flow measuring hollow fiber, also has the characteristic that the mode with the smallest losses can be set in a certain frame by clever choice of the geometry parameters (a, w). Which mode has the smallest guide losses and contributes significantly to the light, is defined by the ratio of the core size to the size of the outer cavities, with a periodic behavior is observed here. In this way it can be decided whether, for example, either the fundamental mode HE11 (a pronounced maximum, not several maxima, no multimode secondary maxima) or the higher mode TE01 (annular) has the best guiding properties. This property applies equally to all wavelengths.

• • Herstellung der symmetrischen oder asymmetrischen Ausgangsrohre
• • Herstellung der Kapillaren durch Strecken der Ausgangsrohre (ggf. nach Reinigung, Dotierung, Ummantelung, Überfangen selbiger)
• • Herstellen der Cane-Packung durch Stapeln der Kapillaren und Umgeben mit einem Mantelrohr (innerer Mantel)
• • Erzeugen des Canes durch definiertes druckbeaufschlagtes Strecken und Versintern der Cane-Packung zur Preform 1
• • Herstellen der Preform 2 durch Einsetzen des Cane in einen äußeren Mantel
• • Druckbeaufschlagtes Verziehen der Preform 2 zur optischen Durchflussmesshohlfaser

The manufacturing process for the optical flow measuring hollow fiber comprises the following steps:

• • manufacture of symmetrical or asymmetrical outlet pipes
• • Production of the capillaries by stretching the outlet pipes (if necessary after cleaning, doping, coating, overpinning the same)
• • Cane packing by stacking the capillaries and surrounding with a jacket tube (inner jacket)
• Generation of the can by defined pressurized stretching and sintering of the cane packing to the preform 1
• • Prepare the preform 2 by inserting the cane into an outer shell
• • Pressurized distortion of the preform 2 to the optical flowmeter hollow fiber

The wall of the polygonal hollow core is made of quartz glass, and is fixed (quasi suspended) in a network consisting of the air chamber walls, wherein the air chamber walls are formed as a defined thin quartz glass connecting webs and the outer jacket, which surrounds the air chambers, from a non-crystalline inert material ( inorganic-nonmetallic, for example quartz glass shell).

Surprisingly, in contrast to previously described production methods for holey microstructure fibers (MOFs), for example photonic crystal fibers (HCPCF), it has been found that a special production step is necessary in order to achieve the desired geometric polygon cross sections and web widths.

MOFs or HCPCFs are typically made from hexagonally-arranged capillary packs in an outer jacket (jacket) by pressurized warping on a fiber draw tower. (see for example. US 20110121474 A1 . US 20070009216 A1 . US 20100266251 A1 and US 7,245,807 B ). Typically, the arrangement of independent, non-interconnected capillaries or rods to a complex arrangement, which are then warped under common and / or separate pressurization of the inner and / or interstices to the microstructure fiber or a related precursor (rod, English ,

In contrast to this known procedure, in the case of production of the optical flow measuring hollow fiber in a first step of the preform production, a number of n capillaries touching each other peripherally are sintered at their respective contact lines.

This is done by defined pressurized stretching of the capillaries in an outer jacket to the so-called cane. The inner capillary overpressure and the temperature, tracking and withdrawal speed are adjusted so that all capillaries sinter tangentially exactly along a cross-sectional line on the fiber longitudinal axis, without the central cavity being substantially reduced by collapsing. A second important point is the exact (n / 2-axis) symmetric sintering of the capillaries with the jacket tube (inner jacket) at their respective contact point. The cross-sections of the sintered overlapping surfaces determine the web geometry (web width and length) of the subsequent fiber decisively.

The sintered cane is then warped to the final polygonal hollow core fiber by homogeneous pressurization and targeted stretching of all capillary walls and sintered cross sections, whereby the cane is introduced into an additional cladding tube (outer cladding).

• (i) Nutzung von Kapillaren mit definiert inhomogener azimutaler Wandstärkenverteilung zur gezielten Einstellung einer homogenen, sehr dünnen Hohlkernwandstärke,
• (ii) Ausbildung dickerer Stützbrücken im nicht-optisch wirksamen Mantel zur Verbesserung der mechanischen Stabilität der Faser.

The geometry of the optical flow-through hollow fiber, which allows double antiresonant guidance, can be further obtained by selecting specific capillaries as follows:

• (i) use of capillaries with defined inhomogeneous azimuthal wall thickness distribution for the purposeful adjustment of a homogeneous, very thin hollow core wall thickness,
• (ii) forming thicker support bridges in the non-optically active cladding to improve the mechanical stability of the fiber.

As a result, a fiber structure with defined variable web wall thickness distribution is achieved.

As explained above, hollow fibers, which can carry aqueous liquids (refractive index about n = 1.33) in the hollow core, are of great importance for spectroscopic sensor technology. While simple glass capillaries have very limited applications as hollow core waveguides for high refractive liquids (with n> 1.45) and Teflon capillaries and HCPCF have significant limitations for practical use, the optical flow measuring hollow fiber meets all the essential practical needs. With this novel fiber structure, a significantly improved interaction between irradiated light and dissolved analyte can be achieved. Thus, the analyte molecules contribute better to the detection signal. The optical flow measuring hollow fiber thus represents an optimized analyte container. Due to the small volume in the cavity of the fiber, only minimal sample quantities are needed. Thus, with the optical flow measuring hollow fiber, an increased analytical sensitivity is achieved with minimized sample requirements. Such a sensor fiber can, for example, replace the conventional cuvettes in laboratory analyzers.

As optical detection methods, for example, Raman spectroscopy, absorption spectroscopy and fluorescence spectroscopy come into question. The principle is generalizable to all optical methods that are based on an interaction between light and analyte.

In addition, in order to achieve a particularly efficient guidance of the light in the fiber cavity, all the cavities except for the central cavity at the end faces of the fiber can be closed. As a result, there is a fiber having only one opening of the central cavity at both end surfaces.

This central cavity can then be selectively filled with liquids, during which the surrounding cavities are further filled with air (or with an inert gas such as argon). By this refractive index difference between n = 1.33 in the central cavity and about n = 1 in the surrounding cavities even better guidance of light in the liquid-filled central hollow core can be achieved. The selective sealing of the outer cavities at the fiber end surfaces can be achieved by splicing or by precise sealing with adhesive. It should be noted here that the affected distance along the fiber is minimized so that the optical waveguide properties of the fiber are disturbed only at a minimum distance.

The hollow core fiber can be integrated into an optical analysis system with the help of a specific adapter. In this case, the light is coupled into the optical flow measuring hollow fiber through an optical window.

The analyte fluids may be filled into the optical flowmeter hollow fiber via fluid ports. By means of a second fluidic connection, the optical flow measuring hollow fiber and the adapter can be quickly filled, emptied, possibly cleaned and refilled.

The optical signal (eg Raman signal) can be decoupled in backscatter by the same adapter.

In backscatter geometry, the transmitted power through the optical flowmeter hollow fiber can be permanently measured on an adapter at the fiber end with a power meter. Thus, all apparatus fluctuations (for example fluctuation of the laser power, etc.) can be corrected and an improved quantifiability can be achieved. Alternatively, the Raman scattering can also be coupled out at the fiber end in forward scattering.

In the process for producing polygonal flow measuring hollow core fibers, a transparent material, in particular quartz glass or another oxidic or non-oxidic optical glass is used.

The individual hollow fibers of the preform 1 of the optical flow measuring hollow fiber are combined by targeted thermal, irreversible, peripheral bonding [fusion] of several capillaries with or without stretching to form a hollow structured compact glass body (Cane) as preform 2.

The thus produced hollow-structured compact glass body (preform 2) is processed in a further process step by enclosing with a cladding tube and pressurized warping to the final hollow fiber.

In this case, n capillaries are combined to give a homogeneous glass body having (2n + 1) cavities, where n = integer and ≥ 3.

The advantage here is that all n capillaries have the same cross section (with respect to their shape). However, it is also within the scope of the invention for all the capillaries to have different cross sections (with respect to shape).

Particularly advantageously, all n capillaries have an oval cross-section, in particular a circular or elliptical, wherein the individual capillaries can each be used with the same or different outer diameters.

In this case, all n capillaries with the same or different wall thicknesses (no rotational symmetry) can be used (that is, the centers of the inner cross-sectional area and the outer cross-sectional area can be different.)

In peripheral connection of the capillaries, the degrees of connection (mechanical connections between the capillaries) are selectively adjusted (punctiform, planar), with a location-accurate connection of the capillaries by targeted adjustment of physical-technological manufacturing parameters, in particular targeted setting of the temperature and pressure parameters (application of differential pressure on capillaries and / or intermediate spaces) during production of the hollow-structured compact glass body, takes place, and it is thereby possible to generate specific structural variations.

The connection of the capillaries described above in combination with or without stretching of the starting components takes place in Ziehofen under application of differential pressure on the capillaries and / or the interstices.

The fiber production from the compact glass body (preform 2) is carried out with again variable parameters (by targeted adjustment of the physical-technological manufacturing parameters).

The material used for the sintered capillaries / preform 2 is glass, preferably quartz glass, which is partially or fully doped, it being possible to use oxides of germanium, phosphorus, fluorine, boron, aluminum, rare earth elements or another application as doping materials.

The OH content in the glass is in concentrations between 0.001 and 1500 Ma ppm, in particular higher values for UV radiation stabilization for UV sensor technology.

The capillaries are produced from the outlet tubes in a defined asymmetric temperature profile, so that the symmetry and geometry of the capillaries can be adjusted in a targeted manner.

The preparation of the symmetrical or asymmetric output tubes can be done by drilling quartz glass rods of any kind, for example. Mechanically by symmetrical or asymmetrical drilling of quartz glass rods or by laser drilling, ultrasonic treatment or by chemical etching of quartz glass rods.

For the production of oval capillaries, the application of defined pressure, in particular negative pressure, is necessary.

The hollow fiber according to the invention is produced from a preform, wherein the cross section of the hollow fiber has webs after its production and is clearly articulated in core and exterior areas.

The cross section of the hollow fiber has node-free connection points after its production.

The number of air chambers [cavities] is (2n + 1), where n = integer and ≥ 3.

The central hollow core is polygonal in cross-section, in particular n-angular, wherein the cross section of the hollow core is advantageously an equilateral or non-equilateral n-corner, and particularly advantageously a rectangle, in particular a square.

The air chamber walls [= connecting webs] between the air chambers [cavities] around the central hollow core have a defined web width of max. 10 μm, advantageously <1.4 μm, particularly advantageously 10 to 500 nm.

The hollow fiber according to the invention can be filled with liquid and gaseous analytes. The hollow fiber simultaneously carries light and analyte in the hollow core. This makes it possible that, compared to conventional cuvettes, a significantly improved interaction of the analytes with the light can take place.

The advantage here is that due to the small volume in the cavity of the hollow core of the optical hollow fiber only minimal amounts of sample are needed. As a result, the hollow fiber achieves an increased analytical sensitivity with minimized sample requirement.

Since the hollow fiber can be filled with liquids in its central cavity, it enables highly sensitive optical analysis of liquids, aqueous solutions, and dissolved analytes in liquids as well as dissolved analytes in aqueous solutions.

Since the hollow fiber can be filled in its central cavity with gaseous analytes, this also allows a highly sensitive optical gas analysis.

In gas and / or liquid analysis, the hollow fiber can be selectively closed at the end faces.

It is also within the scope of the invention that only the central cavity is filled with gas or liquid or else that the air chambers are also filled with gas or liquid in order to be able to carry out an analysis of gases, liquids and aqueous solutions.

As optical detection methods for this analysis using the gas or liquid-conducting optical flow measuring hollow fiber, all methods based on an interaction between light and analyte, such as, for example, Raman spectroscopy, absorption spectroscopy and fluorescence spectroscopy come into question.

The invention will be explained in more detail below with reference to the schematic drawings and the embodiments. Showing:

1 FIG. 2 is a schematic sectional view of a first embodiment of an optical flow measuring hollow fiber according to the invention, FIG.

2 FIG. 2 is a schematic sectional view of a second embodiment of an optical flow measuring hollow fiber according to the invention, FIG.

3 FIG. 2 is a schematic overview of the process for producing a flow-through optical hollow fiber according to FIG 1 and

4 : a schematic representation of a section of the method according to 3 ,

In the 1 illustrated optical flow measuring hollow fiber comprises a central hollow core ( 3 ) for guiding light and filling it with liquids or gases coming from a number of air chambers ( 2 ), the air chambers ( 2 ) of an outer jacket ( 1 ) are sheathed.

This outer coat ( 1 ) encases the air chambers ( 2 ) at her, the central hollow core ( 3 ) facing away completely.

The air chambers ( 2 ) are of air chamber walls ( 21 ) and completely separated from each other.

The hollow core ( 3 ) is of hollow core wall ( 31 ) surrounded by the air chamber walls ( 21 ) [= Connecting webs] and with respect to the outer jacket ( 1 ) is spaced.

It is essential that the cross section of the hollow core ( 3 ) is polygonal, for example. Rectangular, in particular square and a light guide in the hollow core ( 3 ) guided gas or the guided liquid (principle of total reflection, or the antiresonant guide or the double antiresonant guide) allows.

The advantage of the optical flow measuring hollow fiber according to the invention consists u. a. in that it has a comparatively simple structure, enables highly efficient light guidance in the aqueous hollow core, has no background signal and has a large core diameter (about ≥ 20 μm) for practicable filling and a practical analyte change of gases or liquids.

This optical flow measuring hollow fiber utilizes the double-antiresonant guiding principle based on modified tunneling leaky modes for light guidance. The first antiresonance is between the guide wavelength and the thickness of the core border. The second antiresonance is between the effective mode index of the core mode (determined by core size) and the effective mode index of the modes in the outer cavity (determined by cavity size.

The hollow core has an area of 3 μm ² to 10,000 μm ² , preferably 100 μm ² to 1000 μm ² .

The hollow core wall ( 31 ) has in its cross-section the shape of a symmetrical or asymmetrical polygon with n> 2 vertices, these vertices directly with the air chamber walls ( 21 ) of the air chambers ( 2 ) keep in touch. The corner points have no thickening / knots. Instead, the nodes are degenerate to the straight line, so that no parasitic light guidance is possible there.

The hollow core walls ( 31 ) are stretched and have a thickness of 10 nm to 10 microns.

The air chamber walls ( 21 ) are stretched and have a thickness of <2 microns, preferably 10-500 nm, on.

This is clarified in 1 in which the inner cavity with diameter a = 20 μm is bounded by high-precision, plane-parallel quartz walls with thickness d. Around the central cavity of the hollow core ( 3 ) is a second layer of cavities of the air chambers ( 2 ) arranged with longitudinal diameter w.

The ratio w / a is adjusted so that the fundamental mode HE11 or the higher mode TE01 has the smallest guiding losses (advantageously the ratio w / a is between 0.1 and 10).

The inventive optical flow measuring hollow fiber is a highly sensitive optical sensor technology of analytes in aqueous solutions allows.

The optical flow measuring hollow fiber has spectrally broadband transmission windows from the NIR to the deep UV range, so that low attenuation light guidance and thus highly efficient optical sensor technology can take place in different wavelength ranges.

A particularly important example of this is the application of the optical flow measuring hollow fiber in Raman spectroscopy. By means of the irradiation of different laser wavelengths, for example, in Raman spectroscopy a multi-spectral sensor system can take place.

The unique features of optical flow-through hollow fiber are that their intended use forms a fundamental mode (a pronounced central maxima) in all spectral ranges and that transmission windows exist from the near infrared to the important UV range.

The dual-antiresonant guiding principle, which is realized with the optical flow measuring hollow fiber, also has the characteristic that the mode with the smallest losses can be set by skillful choice of the geometry parameters. Which mode has the smallest guide losses and contributes significantly to the light guide is defined by the ratio of the core size to the size of the outer cavity, with a periodic behavior is observed here. In this way it can be decided whether, for example, either the fundamental mode HE11 (a clean central maximum) or the higher mode TE01 (annular) has the best guiding properties. This property applies equally to all wavelengths. Thus, the fiber can also be used specifically for shaping and providing desired modes.

The use of the optical flow measuring hollow fiber as a cuvette enables optical and spectroscopic investigations, wherein the hollow core is filled with liquid or gas and guides the light. In particular, Raman spectroscopy, fluorescence spectroscopy and absorption spectroscopy can be used as spectroscopic examination methods. The latter can be used in the UV / Vis range and in the IR range, wherein a plurality of spectral transmission windows are provided, in particular also into the deep UV range.

Within the scope of the invention is also that the optical flow measuring hollow fiber is used as an optical waveguide for the transmission of UV light.

Due to the presence of multiple spectral transmission windows, different laser wavelengths can be irradiated. Thus, a multispectral sensor can be performed. For example, Raman spectra can be excited and guided simultaneously with several lasers in different spectral ranges. This is of particular interest for resonance Raman spectroscopy.

All features described in the description, the exemplary embodiments and the following claims may be essential to the invention both individually and in any combination with one another.

LIST OF REFERENCE NUMBERS

1

outer coat

2

air chamber

21

Air cell walls

3

central hollow core

31

Hollow core wall

a

Length of the hollow core wall

d

Thickness of the hollow core wall

w

Width of the air chamber

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2005/047869 A1 [0004]
• EP 0488947 A1 [0004]
• GB 2071355 A [0004]
• DE 102009035578 A1 [0005]
• DE 102008046320 A1 [0005]
• WO 03079077 A1 [0011, 0012]
• US 20110121474 A1 [0031]
• US 20070009216 A1 [0031]
• US 20100266251 A1 [0031]
• US 7245807 B [0031]

Claims (10)

Optical flow measuring hollow fiber comprising a central hollow core ( 3 ) of a number of air chambers ( 2 ), the air chambers ( 2 ) of air chamber walls ( 21 ) are surrounded and completely separated by these and the outer shell ( 1 ) the air chambers ( 2 ) at her, the central hollow core ( 3 ) facing away completely coated, the hollow core ( 3 ) of a hollow core wall ( 31 ) surrounded by the air chamber walls ( 21 ) and at least the hollow core wall ( 31 ) and the air chamber walls ( 21 ) consist of an optically transparent material, characterized in that the cross section of the hollow core ( 3 ) is polygonal and that through the hollow core ( 3 ) at the same time light and liquids or gases are feasible, so that a double antiresonante guiding the light is generated. Optical flow measuring hollow fiber according to claim 1, characterized in that the polygonal cross section of the hollow core ( 3 ) is rectangular. Optical flow measuring hollow fiber according to claim 2, characterized in that the rectangular cross-section of the hollow core ( 3 ) is square. Optical flow measuring hollow fiber according to claim 1, 2 or 3, characterized in that the optically transparent material is quartz glass. Optical flow measuring hollow fiber according to claim 4, characterized in that the OH content in the quartz glass in between 0.001 and 1500 Ma-ppm. Optical flow measuring hollow fiber according to claim 1, 2, 3 or 4, characterized in that the cross section of the hollow core ( 3 ) has an area of 3 μm ² to 10,000 μm ² , the hollow core wall ( 31 ) has in its cross-section the shape of a symmetrical or asymmetrical polygon with n> 2 vertices and has these vertices directly to the air chamber walls ( 21 ) of the air chambers ( 2 ), where the vertices do not have any thickening / knots. Optical flow measuring hollow fiber according to claim 6, characterized in that the hollow core walls ( 31 ) are stretched and have a thickness of 10 nm to 10 microns. Method for producing a hollow flow optical waveguide according to one or more of Claims 1 to 7, comprising the following steps: • manufacture of symmetrical or asymmetrical outlet pipes • Production of the capillaries by stretching the outlet tubes • Manufacture of the cane packing by stacking the capillaries and surrounding with a jacket tube as an inner jacket Generation of the can by defined pressurized stretching and sintering of the cane packing to the preform 1 • Prepare the preform 2 by inserting the cane into an outer shell • warping the preform 2 to the optical flow measuring hollow fiber, wherein The manufacture of the symmetrical or asymmetrical outlet tubes is carried out by drilling quartz glass rods mechanically by asymmetric boring of quartz glass rods or by laser drilling, ultrasonic treatment or by chemical etching of quartz glass rods, The capillaries are produced from the outlet tubes in a defined asymmetric temperature profile, - The generation of the cane by sintering a number of n is exactly peripherally touching capillaries at their respective contact lines at defined pressurized stretching of the capillaries takes place in a jacket tube to a cane and - The distortion of the cane in the outer jacket to the optical Durchflußmesshohlfaser by homogeneous pressurization and pulling done. Method for producing a hollow flow optical waveguide according to claim 8, characterized in that for the production of oval capillaries a negative pressure is applied to the capillaries. Use of an optical flow measuring hollow fiber according to one or more of claims 1 to 7 as a cuvette in optical or spectroscopic investigations, wherein the hollow core ( 3 ) is filled simultaneously with liquid or gas and is irradiated by light, or as an optical waveguide for transmitting UV light or of multispectral light, or as a beam-shaping element for providing a fundamental mode or a higher mode.

Images