WO1999050650A1

WO1999050650A1 - Fibre-optic sensor

Info

Publication number: WO1999050650A1
Application number: PCT/DE1999/000047
Authority: WO
Inventors: Joachim Schneider; Anton Pfefferseder; Andreas Hensel; Ulrich Oppelt
Original assignee: Robert Bosch Gmbh
Priority date: 1998-04-01
Filing date: 1999-01-14
Publication date: 1999-10-07
Also published as: DE19814575A1

Abstract

The invention relates to an optical sensor to determine at least one physical and/or chemical parameter relating to a sample. The inventive device comprises at least one optical transmitter, at least one optical receiver and at least one sensitive element, especially a gas-sensitive element, which is arranged in an optical path between the at least one optical transmitter and the at least one optical receiver and which can be exposed to the sample in addition to being able to modify its absorption and/or refractive index for electromagnetic radiation of a specific wavelength when the parameters of the sample are modified. Optionally, an evaluation unit, arranged downstream from the at least one optical receiver, is also provided. The at least one optical transmitter (2) and the at least one optical receiver (4) are coupled to at least two interspaced sensitive elements by at least one optical fibre (10).

Description

FIBER OPTICAL SENSOR

The invention relates to an optical sensor with the features mentioned in the preamble of claim 1 and its use.

State of the art

Various types of sensors for detecting samples and substances are known, for example gas sensors for early fire detection and fire detection. Thus, in the older German patent application 197 41 335.8, optically working gas sensors are described which are based on the principle of measuring an interaction of certain gases with a layer which is transparent to light, an absorption level of light of a certain wavelength being dependent on the gas concentration. A disadvantage of the known optical gas sensors are, among other things, the relatively complex and voluminous measurement setups, since in addition to an optical transmitter and an optical receiver, an arrangement of a gas-sensitive layer within a beam path between these two components is necessary. In particular, are measurements in which concentrations of certain gases differ from the optical ones Components that are further away in space and that are to be detected, for example, at measurement sites that are subject to high temperatures and / or vibrations, are only possible with difficulty.

Advantages of the invention

The optical sensor according to the invention with the features mentioned in claim 1 has the advantage that the spatial separation of the at least one optical transmitter and the at least one optical receiver and at least two interacting with a sample, for example a gas or gas mixture, means the transmission very sensitive and inexpensive integrated components can be produced for sensitive layers that change light of a specific wavelength. When an integrated module, which preferably consists of an optical transmitter and an optical receiver, is coupled to the sensitive layers that can be used at any remote location via at least one optical waveguide, the complete spatial separation of these structural units from one another and thus positioning of the gas-sensitive layers is also possible at locations where, owing to the space and / or the thermal and / or mechanical conditions, no sensitive optical and / or electronic components can be used and installed.

Through the use of a material that is largely transparent to electromagnetic radiation and its absorption properties upon contact with a gas or a gas mixture. Shafts and / or its refractive index for gas-sensitive layer or membrane which changes electromagnetic radiation, hereinafter also referred to as optode, as a sensitive element, it is easy to produce very compact and miniaturizable gas sensors. In the context of the present invention, an optode is understood in particular to mean polymer layers which, owing to the indicator substances embedded therein, show a dependence of the light transmission on the concentration of a specific gas in the atmosphere surrounding the optode. Optodes used according to the invention react selectively and reversibly to the concentration of a certain gas. The interaction of the indicator substance present in the optode leads, for example, to an at least local maximum of the absorption for electromagnetic radiation, for example light. The location of the absorption maximum, that is to say the wavelength range, is typically for each specific gas and / or gas mixture at different wavelength values of the electromagnetic radiation, the height of the absorption maximum also being correlated with the concentration of the interacting gas and / or gas mixture. By measuring the absorption properties of the indicator substance exposed to the gas and interacting with it, which is present in the gas-sensitive layer or membrane, very low gas concentrations can be measured and detected with relatively simple optical devices. Preferably, the one present in the gas-sensitive layer, preferably in a polymer material, speaks trix stored, indicator substance only on a certain gas, so that gas-specific acting sensors can be represented with different indicator substances.

In an advantageous embodiment of the optical sensor, at least one source for electromagnetic radiation, preferably an optical transmitter, and at least one detector for electromagnetic radiation, preferably an optical receiver, are interposed - in the beam path - of at least two spaced apart optodes, which, depending on physical and / or chemical interaction with a certain gas change the transmission or absorption properties for the electromagnetic radiation. The at least two optodes are coupled to the transmitter and receiver via at least one optical waveguide. The source for electromagnetic radiation can be, for example, a light-emitting diode as an optical transmitter, which emits light in a selectable wavelength range. It is also possible to use a laser light source as the source for electromagnetic radiation, which has the advantage of being able to adjust the wavelength of the emitted electromagnetic waves very precisely to the position of an absorption maximum of the optodes. Accordingly, a photodiode as an optical receiver with a frequency range matched to the emitted wavelength of the light-emitting diode or laser light source can be used for the detection of the electromagnetic radiation. Such a structure can be rather be realized with very inexpensive individual parts. The optodes arranged in the beam path between the optical transmitter and the optical receiver are preferably calibrated or calibrated quantitatively according to their absorption properties at certain light wavelengths, so that different light wavelengths with differently reacting indicator substances can detect different gases.

In an advantageous embodiment of the invention, the at least two optodes coupled via at least one optical waveguide to the at least one optical transmitter and the at least one optical receiver are connected in series. As a result, two or more optodes, which are also expediently spaced from one another, can be used at locations which are almost arbitrarily distant. The almost lossless transmission of electromagnetic radiation, preferably in the light range, within the optical waveguide enables the spatial separation of optical transmitters and receivers from the optodes. This makes it easy to use the optodes in locations that are unsuitable for use with sensitive optical and electronic components due to their temperature load, for example. The optodes can be coupled to the optical transmitter and the optical receiver both via a series and a parallel connection or also in a combination of series and parallel connection. The design of the connection or coupling of the at least one optical waveguide with The optodes can advantageously be designed in such a way that a sheath surrounding a core of the optical waveguide along its entire length is interrupted at individual points and is covered at each of these points with a gas-sensitive layer forming the optodes. These sections, at which the cladding is interrupted, can either be designed as oval windows, for example, or as sections at which the core is freed from the cladding on its entire circumference and instead is covered with the gas-sensitive layer representing the optode. The core, which conducts the light signals almost without attenuation, consists, for example, of quartz glass in conventional optical fibers.

In an advantageous embodiment, the refractive index (n ₂ ) for light from the core of the optical waveguide is selected such that it is significantly above the refractive index (n ₃ ) for light from the cladding. In this way it is achieved that light guided in the core of the optical waveguide is deflected at an interface between the core and the sheath with total reflection and thus does not leave the core, which also ensures loss-free light guidance. By suitable selection of a material for the gas-sensitive layer with a refractive index (n ₃ ) for light of the optode with approximately the same value as the refractive index (n ₂ ) for light of the core, it can be achieved in an advantageous manner that light guided in the core is a Core-optode interface can be overcome almost without loss without reflection, but deflected back at an optode-air interface under total reflection and penetrates back into the core. An interaction of the optode with a surrounding gas and / or gas mixture changes the transmission behavior for light of the optode. A light beam passing through the optode is thereby weakened. This weakening of the light can be detected and analyzed by means of the evaluation unit connected downstream of the optical receiver. By selecting the appropriate sensitivity, very precise values for different gas concentrations can be determined and displayed. In an advantageous embodiment of the invention, an optical waveguide is provided with a plurality of spaced apart optodes which react sensitively to the same gas and / or gas mixture in each case. In this way, the gas and / or the gas mixture can be detected at any location in very low concentrations in a simple manner with appropriate laying of the optical waveguide.

In a further advantageous embodiment of the invention, the length of the at least one optical waveguide is provided with a plurality of optodes spaced apart from one another, which are sensitive to different gases in each case. By suitable modulation of the light emitted by the optical transmitter and corresponding evaluation and signal assignment by means of the evaluation unit downstream of the optical receiver, the gas concentration at each individual optode can be determined with high accuracy. For this purpose it is useful to analyze the duration of the impulses and in this way the different ones Assign signals precisely to the different optodes, for which purpose the signal reflected at the optodes acting as defects in the light guide is evaluated. The at least one optical waveguide can advantageously be designed in a ring shape, which enables simple concealed laying even within larger areas and unambiguous assignment of the signals arriving at the optical receiver to the individual optodes.

In a further advantageous embodiment of the invention, provision is made for more than one ring-shaped optical waveguide to be provided. For example, two or more ring-shaped optical waveguides can be used, each with optodes sensitive to different gases and / or gas mixtures. These multiple optical waveguides can advantageously be bundled and laid in parallel, which enables reliable detection of different gases and / or gas mixtures at defined, even distant, locations. It is also advantageous to provide a common optical transmitter for the at least two optical waveguides used, which among other things reduces the construction effort. Expediently, however, each of the plurality of optical waveguides is coupled to a separate optical receiver in order to enable reliable signal evaluation. In order to achieve compact and operationally reliable units, it can be advantageous to combine optical transmitters and receivers in a monolithic combination, for example by casting with plastic, to connect to the end faces of the optical fibers. Optionally, the optical transmitter and receiver can also be spatially combined in a common assembly or integrated in a common component, which has considerable advantages in terms of easier assembly.

The optical sensor according to the invention can furthermore advantageously be used for monitoring air quality in rooms, for example for controlling ventilation flaps in air conditioning systems. Likewise, optical sensors according to the invention can be used for ventilation and climate control in interiors and / or in tunnels. Of course, such optical sensors are also suitable for smoke and / or fire detectors, the detection and reporting time being greatly reduced compared to known devices and the false alarm security being significantly increased by determining fire control gases by means of individual optical sensors or a combination of several sensors can. In the manner described above, very simple, maintenance-free and reliable optical fire detectors can be implemented by laying optical fibers provided with appropriate optodes over a wide area. The extremely low power consumption of the semiconductor components which are preferably used as optical transmitters and receivers, for example in the form of LEDs, means that battery detectors can advantageously be used to implement fire detectors which are independent of the power supply system. Another advantageous application is the detection of hydrocarbons. 10

Further advantageous embodiments of the invention result from the other features mentioned in the subclaims.

drawings

The invention is explained in more detail in an exemplary embodiment with reference to the accompanying drawings. Show it:

Figure 1 is a schematic representation of a first variant of an individual optical sensor;

Figure 2 is a schematic representation of a variant of an optical sensor with a plurality of optical fibers;

FIG. 3 shows a diagram of a further variant of an optical sensor;

Figure 4 is a schematic representation of an optical fiber provided with an optode and

5 shows a schematic diagram of the reflection processes in the optical waveguide and at the optode.

Description of the embodiments

Figure 1 shows a measuring arrangement for an optical sensor, consisting of a source of electromagnetic radiation as an optical transmitter 2, here for example a light emitting diode, a detector for 11

electromagnetic radiation as an optical receiver 4, for example a photodiode, which are coupled via an optical waveguide 10 to a plurality of spaced-apart sensitive elements, hereinafter referred to as optodes 12. However, a laser light source can, for example, just as well be used as the source for electromagnetic radiation.

In many applications it is desirable to spatially separate the gas-sensitive layers or the optodes 12 from the optical transmitter 2 and optical receiver 4, for example in the case of fire detectors or sensors which are intended to interact with very hot gases. The two semiconductor components can be attached, for example, as so-called SMD (Surface Mounted Device) components on a common circuit board in a housing (not shown here), whereas the optodes 12 are preferably attached at locations that are more easily accessible for the gas to be detected, that is, outside the housing are. According to the invention, the use of at least one optical waveguide 10 is provided for optically coupling the optodes 12 to the optical transmitter 2 and the optical receiver 4. The light emitted by the optical transmitter 2 is coupled vertically at a preferably straight end face 36 into the optical waveguide 10, which at its other end, facing the optical receiver 4, also has a straight end face 37 which is perpendicular to the longitudinal direction of the optical waveguide 10 12

is arranged. In this way, a spatial separation of electronics and optodes 12 is possible.

Optical transmitters 2 and receivers 4 can be used which work with infrared or ultraviolet light or which work with light in the visible wavelength range, preferably in each case in a narrow wavelength range. Decisive for the function of the measuring arrangement is the coordination between the wavelength of the light emitted by the optical transmitter 2 and the absorbed wavelength of the gas-sensitive layers or optodes 12 described below.

The gas-sensitive layers or optodes 12 each consist of a chemically largely inert carrier material, preferably a polymer material, and an indicator substance embedded therein or applied thereon. When in contact with certain samples, for example a certain gas and / or gas mixture, the indicator substance shows an interaction in the form of a change in transmission for electromagnetic radiation of a certain wavelength. At a certain gas concentration, there is a fixed correlation to the degree of absorption of transmitted light. The effectiveness of the gas-sensitive layers has so far been proven for a large number of different gases and gas mixtures, with the smallest gas concentrations thus far detectable being in the range of a few ppb. 13

Each of the optodes 12 arranged on the optical waveguide 10 in the exemplary embodiment shown contains an indicator substance sensitive to a specific gas and / or gas mixture and is calibrated by means of previous measurements before installation. As soon as the gas to be detected enters the area between the optical transmitter 2 and the optical receiver 4, i.e. reaches at least one of the optodes 12 and interacts with its indicator substance, the indicator substance contained in the optode 12 changes its absorption for certain wavelength ranges of the electromagnetic ones interacting with it Radiation. Since this wavelength corresponds to a local absorption maximum of the indicator substance, the optical receiver 4 registers a changed amplitude of the received light signal. The height of the absorption maximum in the previously known optodes 12 is proportional to the concentration of the gas. The received light signal can be detected by means of an evaluation unit (not shown here) and forwarded to a signal transmitter, for example.

In the exemplary embodiment shown, the optodes 12 connected in series are each calibrated to the same substance, so that with a sufficiently long optical waveguide 10 and optodes 12 mounted thereon and spaced apart from one another, detection of a specific gas and / or gas mixture over long distances or within a wide range Area is possible. For example, with such an optical sensor with only very few components and with only one line, 14

namely, the optical waveguide 10, with a correspondingly selected sensitivity of the optodes 12, a highly sensitive fire detector can be realized. By feeding in suitably modulated light signals through the optical transmitter 2 (here a laser) and a suitable evaluation with regard to the transit times, it is also possible to detect the interaction of each individual optode 12 with the gas and / or gas mixture. This makes it possible to record and display the exact location of the interaction and thus the location, for example, of a fire with high accuracy.

FIG. 2 shows a schematic of a variant of an optical sensor in which a plurality of optical fibers 10 are each provided with a plurality of optodes 12, 13, 14. The same parts as in Figure 1 are provided with the same reference numerals and not explained again. In the exemplary embodiment shown, three ring-shaped optical waveguides 10 are fed by a common optical transmitter 2. However, it is also possible to provide a separate optical transmitter 2 for each individual optical waveguide, these multiple optical transmitters 2 each being able to transmit electromagnetic radiation either in the same or in different wavelength ranges. It is also possible to provide a large number of optical waveguides 10 instead of just three.

A separate optical receiver 4, 6 and 8 is provided for each of the three optical fibers 10, so that 15

an analysis of the optodes 12, 13, 14 interacting with different gases and / or gas mixtures is possible. The optodes 12, 13, 14 connected to the optical fibers 10 are expediently calibrated and tuned such that the optodes 12 of the first optical fiber 10 are sensitive to a specific gas and / or gas mixture, that the optodes 13 of the second optical fiber 10 to another gas and / or gas mixture are sensitive and that the optodes 14 of the third optical waveguide 10 are in turn sensitive to a different gas and / or gas mixture. Such an arrangement can be expanded almost as desired by additional optical fibers with individually calibrated optodes attached to it.

In the exemplary embodiment shown, it is provided to provide optodes 12, 13, 14 of the same type, that is to say sensitive to the same substance, for one optical waveguide 10 each. As in the manner described in FIG. 1, these can be spaced closer or further apart, so that, if necessary, substances can be detected over long distances and within wide areas. The optodes 12, 13, 14 can, for example, be calibrated in such a way that they are sensitive to different combustion gases, which enables more reliable fire detection and avoidance than when using only one combustion gas sensitive optodes 12. In each case in the desired areas To detect all desired substances, it is expedient to lay the three optical fibers 10 in parallel. The usage 16

of an individual optical receiver 2, 4 and 6 for each individual optical fiber 10 used facilitates the evaluation with regard to different gases and / or gas mixtures to be detected. If, as already described for FIG. 1, the exact locations of the interactions of an optode 12, 13, 14 with a gas and / or gas mixture are to be recorded and analyzed, the signal processing in a downstream of the optical receivers 4, 6, 8 Evaluation unit when using three optical receivers 4, 6 and 8 is less complex than when using only one.

FIG. 3 shows a further variant of an optical sensor in a schematic illustration. The same parts as in the previous figures are provided with the same reference numerals and are not explained again. Only one optical waveguide 10 is provided here with a plurality of optodes 12, 13 and 14 which are sensitive to different substances or gases and / or gas mixtures. The optical transmitter 2 at one end of the optical waveguide 10 emits electromagnetic radiation in the wavelength range in which the optodes 12, 13 and 14 show a change in transmission upon interaction with a specific gas and / or gas mixture. The optical receiver 4 at the other end of the optical waveguide routes the received signals to an evaluation unit (not shown here), which is able to compare the received signal with respect to the amplitudes at the relevant frequencies with the signal emitted by the optical transmitter 2 and from this 17

gene about the detected substances and their exact location. To enable the latter, however, it is necessary to modulate the signal emitted by the optical transmitter 2 in a suitable manner and to evaluate the reflected signal obtained at an optical receiver at the optical fiber input with regard to the impulse responses.

For example, it is possible to sequentially position several groups of three different optodes 12, 13 and 14 placed close to each other at a distance from each other on the optical waveguide, so that three different substances, for example three different gases and / or gas mixtures, are present in this way a large number of different locations can be detected, the displays being able to be assigned exactly to the different defined locations. If, for example, a fire detector is to be implemented with the aid of the optical sensor, the locations of a fire development can be determined precisely in large areas on the basis of the combustion gases released there and registered by the optodes 12, 13, 14.

FIG. 4 shows a section of a structure of an optical waveguide 10 arranged in the beam path between the optical transmitter 2 and the optical receiver 4 with an optode 12, 13, 14 applied thereon. The same parts as in the previous figures are provided with the same reference symbols and are not explained again. A core 20 of the optical waveguide 10 can be seen, which is encased by a jacket 22 over its entire length. 18th

is enveloped. The refractive index for light of the core 20 (n ₂ ) typically has a significantly higher value than that of the cladding 22 (n _x ). If, for example, quartz glass is used as the material for the optical waveguide, this has a refractive index of n ₂ = 1.46. For air, the value of the refractive index is n = 1. The value of the refractive index of the cladding 22 is therefore expediently within these two values, for example at n _λ = 1.2. This ensures that light guided in the core 20 is reflected almost completely without attenuation and completely at an interface 21 core-shell. In the exemplary embodiment shown, a section 24 or a window 25 is provided in which the core 20 is exposed, that is to say freed from the enveloping jacket 22 and covered or encased with a gas-sensitive layer or an optode 12, 13, 14. The material of the optode 12, 13, 14 expediently has a value for the refractive index (n ₃ ) which is approximately that of the core

20 corresponds. When using quartz glass as the material for the core 20 of the optical waveguide 10, the appropriate values for the refractive indices n ₂ = n ₃ = 1.46 result. It is thereby achieved that a light beam can pass through an interface 27 core optode, but is completely reflected at an interface 23 optode-air due to the significantly different refractive indices.

FIG. 5 shows the reflection processes in the optical waveguide 10 in a schematic detailed view. The same parts as in the previous figures are included 19

provided the same reference numerals and not explained again. The core 20 with the enveloping jacket 22, which is interrupted at an exemplary section 24, can again be seen. An optode 12, 13, 14 is located there. A light beam 30 shown by way of example is reflected at the interface 21 core-cladding due to the different refractive indices and thus remains in the core 20. A further light beam 32 can be seen from the interface 27 almost identical refractive indices penetrate unhindered, i.e. almost loss-free, and is then reflected at the interface 23 optode-air, which is due to the significantly lower value of the refractive index in air (n = 1) than the value for the refractive index of the optode (n ₃ ) . The light beam 32 thus also remains in the core 20, but is significantly weakened as it passes through the optode 12, 13, 14 depending on the interaction with a specific substance. With a suitable control of the optical transmitter 2 with a modulated signal and the optical receiver 4 and the downstream evaluation unit, this signal weakening can be evaluated as the detection of a substance.

Claims

20 patent claims

1. Optical sensor for determining at least one physical and / or chemical parameter of a sample, with at least one optical transmitter and at least one optical receiver and one in a beam path between the at least one optical transmitter and the at least one optical receiver and the sample a sensitive element, in particular a gas-sensitive element, which can change its absorption and / or its refractive index for electromagnetic radiation of a certain wavelength, and optionally with an evaluation unit connected downstream of the at least one optical receiver, characterized in that the at least one optical transmitter (2) and the at least one optical receiver (4, 6, 8) is coupled to at least two spaced-apart sensitive elements via at least one optical fiber (10).

2. Optical sensor according to claim 1, characterized in that the sensitive elements for electromagnetic radiation are largely permeable optodes (12, 13, 14) which change their absorption properties and / or their refractive index for electromagnetic radiation upon contact with the sample. 21

3. Optical sensor according to claim 2, characterized in that the sample is a gas and / or a gas mixture.

4. Optical sensor according to claim 3, characterized in that the optodes (12, 13, 14) each have an indicator substance which is chemically or physically reversible with the gas with at least indirect contact with at least one specific gas and / or specific gas mixture or gas mixture interacts.

5. Optical sensor according to claim 4, characterized in that the interaction leads to the occurrence of an at least local absorption maximum for electromagnetic radiation.

6. Optical sensor according to claim 5, characterized in that the position of the absorption maximum for each specific gas and / or gas mixture is at different wavelength values of the electromagnetic radiation.

7. Optical sensor according to one of the preceding claims, characterized in that the height of the absorption maximum is correlated with the concentration of the interacting gas and / or gas mixture.

8. Optical sensor according to one of claims 2 to 7, characterized in that the at least one

Optical waveguide (10) with the at least one optical transmitter (2) and the at least one optical transmitter 22

Receivers (4, 6, 8) coupled at least two optodes (12, 13, 14) are connected in series.

9. Optical sensor according to one of claims 2 to 7, characterized in that via at least one optical waveguide (10) with the at least one optical transmitter (2) and the at least one optical receiver (4, 6, 8) coupled at least two optodes (12, 13, 14) are connected in parallel.

10. Optical sensor according to one of the preceding claims, characterized in that the at least one optical transmitter (2) with the at least one optical receiver (4, 6, 8) coupling light waveguide (10) a light signals almost without attenuation leading core ( 20) and a sheath (22) enveloping the core (20) over the entire length of the optical waveguide (10), the sheath (22) having at least one section (24) a window (25) in which the core ( 20) is completely covered with an optode (12, 13, 14).

11. Optical sensor according to one of claims 2 to 9, characterized in that the at least one optical transmitter (2) with the at least one optical receiver (4, 6, 8) coupling optical waveguide (10) carry a light signal almost without attenuation Core (20) and a sheath (22) enveloping the core (20) over the entire length of the optical waveguide (10), the sheath (22) being interrupted at at least one section (24) and 23

the core (20) at this section (24) is completely encased by an optode (12, 13, 14).

12. Optical sensor according to one of claims 10 to 11, characterized in that the refractive indices (n ₂ , n ₃ ) for light of the core (20) or the optode (12, 13, 14) have significantly higher values than the refractive index ( n _x ) for light of the cladding (22).

13. Optical sensor according to claim 11, characterized in that the refractive index (n ₂ ) of the core (20) and the refractive index (n ₃ ) of the optode (12, 13, 14) have approximately equal values.

14. Optical sensor according to claim 13, characterized in that the optical waveguide (10) along its length a plurality of spaced sections

(24) with optodes (12, 13, 14) sensitive to the same gases and / or gas mixture.

15. Optical sensor according to claim 13, characterized in that the optical waveguide (10) has a plurality of spaced apart sections (24) along its length with sensitive to different gases and / or gas mixtures optodes (12, 13, 14).

16. Optical sensor according to one of the preceding claims, characterized in that the optical transmitter (2) is a source of electromagnetic radiation, in particular a light emitting diode (LED), the so 24

is chosen so that its emission spectrum matches the gas-sensitive absorption of the optode.

17. Optical sensor according to one of claims 1 to 15, characterized in that the optical transmitter

(2) a source of electromagnetic radiation, especially a laser light source, a discrete one

Wavelength is.

18. Optical sensor according to one of the preceding claims, characterized in that the optical receiver (4, 6, 8) is a photodiode.

19. Optical sensor according to one of claims 14 to 18, characterized in that the at least one

Optical waveguide (10) is annular.

20. Optical sensor according to claim 19, characterized in that at least two ring-shaped optical waveguides (10) are used, each with optodes sensitive to different gases and / or gas mixtures (12, 13, 14).

21. Optical sensor according to claim 20, characterized in that the at least two used

Optical fibers (10) are provided with a common optical transmitter (2).

22. Optical sensor according to claim 21, characterized in that each of the at least two optical fibers (10) used is each provided with an optical receiver (4, 6, 8). 25th

23. Optical sensor according to claim 22, characterized in that the at least two optical fibers used (10) with the at least one optical transmitter (2) and the at least one optical receiver (4, 6, 8) are each cast in a common housing.

24. Optical sensor according to claim 23, characterized in that the at least two optical fibers used (10) with the at least one optical transmitter (2) and the at least one optical receiver (4, 6, 8) are each cast with plastic.

25. Optical sensor according to claim 24, characterized in that the at least one optical transmitter (2) and the at least one optical receiver (4, 6, 8) are combined spatially and / or structurally.

26. Optical sensor according to claim 25, characterized in that the at least one optical transmitter (2) and the at least one optical receiver (4, 6, 8) are integrated in a common component.

27. Optical sensor according to one of the preceding claims, characterized in that the optodes (12, 13, 14) preferably interact with gaseous combustion products.

28. Optical sensor according to one of the preceding claims, characterized in that in the evaluation unit the at least two different opto- 26

the (12, 13, 14) detected signals are detectable with regard to their specific transit times.

29. Optical sensor according to claim 28, characterized in that different transit times of the signals supplied by different optodes (12, 13, 14) can be evaluated to obtain location information.

30. Optical sensor according to claim 29, characterized in that a plurality of ring-shaped optical waveguides (10) detect fires in large areas and that the signals supplied can be evaluated in the evaluation unit with regard to the location of the fire.

31. Use of at least one of the optical sensors according to claim 1 to 30 in fire detectors.

32. Use of at least one of the optical sensors according to claims 1 to 29 for determining and monitoring an air quality in rooms.

33. Use according to claim 32, characterized in that devices for air and climate control in indoor spaces are regulated with the measured values obtained.

34. Use according to claim 32, characterized in that the concentration of CO and / or C0 _{2 is} detected. 27

35. Use according to claim 32, characterized in that ventilation systems in tunnels are controlled with the measured values obtained.