DE3528294C2 - - Google Patents

Description

The invention relates to a device for fiber optic Transferring the value of a variable physical quantity with the in the preamble of Claim 1, generic features and one suitable for carrying out such a method nete facility.

Such transmission methods and devices should the properties of the optical fibers used, if possible be independent so as part of a fiber optic Sensor for connecting the sensor and evaluation provided fibers with different lengths, cross cuts, losses, curvatures etc. the evaluation of the spectrally encoded usefulness and intensity impair light signals as little as possible.

Fiber optic transducers are described below Understand arrangements that consist of a sensor and a Evaluation device exist that have one or more light guide  fibers are optically connected. In the sensor a physical quantity to be recorded (e.g. pressure, temp rature, force, position, angle, etc.) in an optical signal converted or "encoded", which via the optical fiber is directed to the evaluation device. The decode takes place there tion, d. that is, the value of the am Effective measured variable determined. This value can then displayed, registered or otherwise in a suitable form be further processed, for example in one Regulator.

More common due to the excellent insulation ability Optical fibers consist of such a fiber optic measurement a complete galvanic isolation between Sensor and display device. You can use it without any special Protective measures are used in high voltage technology (Monitoring of transformers), in medicine (none Risk of electric shock for the patient) as well as in systems of Petrochemicals and mining (no short circuit / ignition hazard) or in motor vehicle construction.

Therefore, a multitude of functional principles became fiber optical sensor proposed and demonstrated, such as B. in the article "Optical Fiber Sensor Technology" by T. G. Giallorenzi et al. in the IEEE Journal of Quantum Electronics, Vol. QE-18 (1982), pp. 626-655. Among these sensors is special constructive simplicity from a subgroup in which the mentioned coding is done by an intensity modulation, for example by means of a light barrier. The one  Light source usually housed in the evaluation device coming and via an optical fiber to the sensor conducted luminous flux becomes more or less strong there weakened, according to the value of the currently effective Measurand. The remaining luminous flux runs over the same or another fiber to a detector in evaluation device. That proportion to the light output arriving there tional detector signal is thus a measure of the value of the Measurand.

An advantage of this functional principle is that the analog intensity modulation used here for coding technically very easy by shifting or twisting of apertures that can be performed in the luminous flux are attached and one depending on their position Let a fraction of it happen. Other important pre parts are in the possibility for these transducers to be able to use inexpensive multimode optical fibers and them with luminescent diodes as reliable, small light to operate sources. Also by appropriate Ausge design of the modulator diaphragms a very high absolute Measurement sensitivity with regard to the aperture position reached will.

Typical for this group of sensors Example can be found in that of W. B. Spillmann and D. H. McMahon described "Schlieren Multimode Fiberoptic Hydrophone" (Applied Physics Letters, Vol. 37, 1980, p. 145 ff.) be seen. With this sensor the Intensity modulation achieved in that the luminous flux one after the other two closely adjacent, parallel lines grids interspersed, which form a kind of "Moir´" modulator.  The shifting of one grid against the other by one Line width (typically: 5 µm) causes this modulator from the state of maximum light transmission to the state mini Painter transmission is controlled. This primarily represents Arrangement thus represents a displacement sensor. In the special case This example uses a hydrophone (underwater sound pressure transducer) from it by placing one of the grids with a elastic membrane is connected to which the to be detected Pressure works and it deflects. The membrane thus functions as a pressure → path converter. In the same way you could the modulator mentioned also for the construction fiber optical thermometer, dynamometer, accelerometer and Use transducers for other sizes by instead of Membrane corresponding other transducers are used for example a bimetallic body (temperature → path), a spring body (force → path), or a test mass on one Spring body (acceleration → force → travel).

Another simple fiber optic transducer, the also to the group with analog intensity modulation one of the working sensors is fiber optic thermo meters after A. J. Rogers (Applied Optics Vol. 21, 1982, Pp. 882-885). In this instrument the fiber is used Luminous flux arriving at the sensor is not by means of a mechanically moving aperture, but by means of a temperature dependent, polarization-optical arrangement in its interior weakened before it becomes fiber optic to the evaluation device is returned and a corresponding to the detector signal Display causes.  

If, as known from GB-PS 15 40 907, various measured variables x ₁, x ₂ and x ₃ spectrally separated wavelength ranges with narrowband spectral distribution by a central wavelength, for. B. the wavelengths λ ₁, λ ₂ and λ ₃ can be assigned individually, so several measured variables can be transmitted via a single optical fiber, the assignment of the individual wavelength ranges to the various measured variables on the sensor side by beam splitter and filter arrangements and the identification of the individual measured variables on the detector side takes place in turn by correspondingly coordinated filter arrangements. Here too, the information about the measured variables is encoded into the intensities of the individual partial luminous fluxes.

The so far explained and further, the state of the Technology-related, fiber-optic transducers from Sub-group with coding by intensity modulation have the fundamental disadvantage that the evaluation device can not distinguish between changes in the detec Tor received luminous flux due to changes in Measured variable on the one hand and changes due to fluctuations the fiber losses on the other hand. The latter can for example occur wisely when the fiber is curved or when in a fiber cable its temperature or its mechanical Voltage vary. Another disadvantage is that this Transducers in general with permanently connected Fixed length fiber lines must work. The stake of fiber connectors is eliminated because they usually cause reproducible losses. Pressing the plug could then be used accordingly Variation or uncertainty of the display result. In the same sense, the installation of Fibers of different lengths or attenuation are problematic affect the calibration of the transducers in this subgroup.

Because of this, fiber optics are improved in some A second transmission channel has been introduced, the one of the measurand not or in opposite directions modulated reference luminous flux. For determination the measured variable in the evaluation device is then no longer used absolute performance, but the ratio of performance of the received luminous fluxes in the signal and in the reference Channel. If the changes in fiber losses mentioned are the same in both channels, so change with the fiber lose the absolute power of the luminous flux,  but their relationship remains unaffected, and the ad is independent of these changes. Such a code tion of the measured variable in the intensity ratio of two light currents is used, for example, in the methods described by H. Dötsch et al. specified fiber optic sensors (IEE Conference Proceedings No. 221, "Optical Fiber Sensors", London 1983, Pp. 67-71). A slidable lens in the probe couples the incoming luminous flux into two outgoing, Optical fibers leading to the evaluation device. The measurand affects the position of the lens and thus couples it Light correspondingly stronger in one or the other two fibers in such a way that the ratio of clearly represent the measured variable in both partial luminous fluxes should.

In fact, this compensation of variable fiber losses is only effective to a limited extent, because the signal and reference channels are guided to the evaluation device via two different optical fibers and are therefore not subject to exactly the same influences. In addition to the complex necessity of the additional reference fiber, the above-mentioned disadvantage of non-reproducible connector losses, which will generally be significantly different in the two channels, stands against a broad practical applicability. This disadvantage precludes the use of plugs in this type of transducers so far practically, but their application possibilities are considerably limited. A solution to this problem which at first appears to be worth considering can be seen in routing the signal and reference luminous flux over the same optical fiber and transmitting these two luminous fluxes at two different optical frequencies, for example in the green and red spectral range. However, such a solution using luminous fluxes with a relatively large spectral spacing cannot be satisfactory in practice since most types of fiber losses depend heavily on the optical frequency (or wavelength), as do the detector sensitivity, which results in additional calibration problems can. A transmission with two spectrally different optical frequencies can thus not be independent of the fiber properties, the term "independent of the fiber properties" should mean that the two light fluxes are subject to all types of fiber losses in their transmission in the same way as possible, that is the absorption and scattering losses, curvature losses and coupling losses of plugs, splices as well as cross-sectional changes in the fiber. For a transmission which is independent of the fiber properties in the sense explained above, it would at least be necessary to choose the two optical frequencies very closely adjacent, that is to say in such a way that their frequency spacing Δν to the mean frequency ν ₀ of the two light fluxes is very small. Furthermore, the spectral line width δν of the two light currents would also have to be small, for example δν ≅ Δν . Correspondingly narrow-band optical filter arrangements are possible and can be used in conjunction with polarization-sensitive beam splitter arrangements, such as. B. known from US-PS 35 01 640, are realized, but require a considerable amount of design and would only let a very small, the filter line width corresponding power share from the continuous emission spectrum of a luminescence, which again causes problems with regard to Detection sensitivity or accuracy can result.

These difficulties can be largely avoided, if, as can be seen from GB-PS 15 40 907, measuring light and Reference light currents with the same spectral distribution, but different pulse coding, temporally one inside the other "nested" in time-multiplexing over the same, transmission formed by a single optical fiber route from the sensor to the detector device will. It is then required, however, of a spectral one Coding of the measuring luminous flux and the reference light current to a - temporal - pulse coding via to go what with additional optoelectronic Circuit effort and with a not inconsiderable Loss of usable measurement time is linked.

The object of the invention is therefore a method of Specify the type mentioned above, which one of the Eigen as far as possible independent transmission characteristic of the measured value optical signals and their simple evaluation, and a facility for performing this method.

With regard to the procedure, this task is performed by the characterizing features of claim 1 solved.

Thereafter, two as spectrally interleaved line spectra generated light fluxes I ₁ and I ₂, in the power ratio of the measured variable is encoded, coupled via a single optical fiber marking the light path from the sensor to the evaluation device into the evaluation device, through which an evaluation of the power ratio in one units of the measured variable. The two luminous fluxes are because they have the same optical fiber and the same connec tion elements between this and the sensor on the one hand and the evaluation device on the other hand, for. B. Fiber-Steckver connections are conducted, so far subject to exactly the same influences of the fiber optic transmission path, which therefore stand out as it were when evaluating by ratio, so to speak, so that optimal conditions for an independent design of the fiber optic transmission path given the measured value information are. Due to the line structure of the two luminous fluxes used according to the invention, which can be described as spectrally interleaved or nested comb spectra, it is achieved in a simple manner that the two luminous fluxes to be compared with one another, at least to a very good approximation, practically the same - medium - Wavelengths, so that the - wavelength-dependent - influences of the fiber-optic transmission path on the light fluxes I ₁ and I ₂ that are propagating in this region is also identical, and thus overall independence of the measured value transmission from the properties of the fiber and its fluctuations is achieved. A possibly required dependency of the detector sensitivities on the wavelength - due to the nested spectral structure of the light currents I 1 and I 2 - cannot have a disruptive effect on the measurement result. In addition, it is also possible with the method according to the invention, depending on the number of lines contained in the individual comb spectra, to produce a relatively large fraction of the power from the continuous spectrum of the light source used in each case, e.g. B. a luminescent diode. The United drive according to the invention is otherwise feasible with simply designed optical filter devices.

In the procedure outlined by the features of claim 2, an optimal approximation to the ideal case of absolute equality of the medium wavelengths of the partial light fluxes I ₁ and I ₂ can be achieved, for example because by that the spectrum of a partial luminous flux comprises only a single line and the spectrum of the other partial light flux two lines, the mean wavelength of which speaks to that of the one line of the first partial light flux ent. Such an approach is e.g. B. possible with the use of laser light sources.

The features of claims 3 and 4 on the one hand and 5 on the other hand, there are alternative types of implementation specified the method according to the invention, in one Implementation type with simultaneous transmission of two offs aisle luminous flux ₁ and ₂ and proof of the same with sepa advise detectors being worked while in the other Implementation type with temporally nested transmission of the Output luminous flux ₁ and ₂ and hereby synchronized Receiving the same with the help of only one detector.

To carry out this alternative procedure ge own facilities are, their basic structure according to the features of claims 6 and 7, by which the basis of the invention Partial task is solved.

The features of claims 8 to 25 are alternative or in a meaningful combination of usable design and functional features in the context of facilities according to use claims 7 and 8 to record the measured variable available, advantageously simply designed measuring sensor, which are designed for use in transmission. Such sensors are then not only useful the evaluation device, but also to the respective light source coupled via an optical fiber.

Due to the features of claim 26 is the principle Structure of a Ver to carry out the invention other suitable equipment specified at which of the sensors used to record the measured variable  is designed as a reflection unit. For optical Coupling the sensor to the light source or a Light supply device on the one hand and to the evaluation device on the other hand, only a single optical fiber is used here necessary as well as a partially transparent mirror over which a Part of the light returned by the optical fiber currents ₁ and ₂ to the verification device of the evaluation device can be deflected.

By the features of claims 27 to 34 are a technical means of realizable designs by Specified sensors that are within the scope of a claim 26 trained facility can be used.

Further details and features of the invention emerge itself from the following description of implementation examples of the method according to the invention and from examples of how to implement suitable inputs directions. It shows

Fig. 1 shows the basic structure of a fiction, modern transducer, optical fiber as means for carrying out a fiction, modern method for transmitting a physical measured variable, in a simplified schematic representation Blockbild-,

Fig. 2 (a) source of a typical spectral distribution of the intensity of a usable in the Meßwertauf participants in FIG. 1 light,

Fig. 2 (b) passage characteristics in the context of measuring wertaufnehmers FIG. 1 usable transmission filter,

Fig. 2 (c) and 2 (d) the spectral composition for detecting the measured variable-utilized portion of the light currents I ₁ and I ₂, for explaining the driving Ver invention,

FIGS. 3 and 4 are simplified block diagram representations of the method according proper sensors of alternative embodiments of fiber optic transducers to illustrate alternative ways of performing using measurement, which are in the transmission mode sets,

Fig. 5 to 8 alternative design options within the scope of transducers of FIG. 3 or 4 deployable probe Fig.

FIGS. 9 and 10 suitable for transmission mode sensor with an interference filter designed filter pairs for determining the spectral composition of the partial light reduction currents I ₁ and I ₂, as well as with movable diaphragm to the intensity modulation of these partial luminous fluxes,

FIGS. 11 and 12 is also usable in transmission probe with polarization-dependent splitting of a primary light flux in the unused for data acquisition and partial luminous fluxes having polarization dependent manner modulation means,

Fig. 13 and 14 are alternative designs according to the invention with fiber optic measuring sensor in the reflection mode can be operated sensors,

Fig. 15 to 17 the basic structure of various usable in reflective mode sensor,

Fig. 18 shows a special design of its basic structure according to the sensor shown in FIG. 17 corresponding sensor with interference filters designed as Bragg reflectors for modulating the partial light fluxes I ₁ and I ₂ and

FIGS. 19 and 20 functionally the sensors shown in FIGS. 11 and 12 corresponding, however, be in reflection drivable probe.

In Figs. 1 and 3 through 20 of the drawing structurally and functionally identical or -Analogue elements are each assigned the same reference numerals.

With respect to theFig. 1 and 2, all of which Details explicitly referred to will follow on the one hand the general construction principle of an overall With100 designated transducer explained, the a device for performing a fiction procedure for the transfer of the Value of a continuously changing physical Measurand"x" represents that more in detail theFig. 2 will be explained. The shows Fig. 1 a fiber optic sensor100, the one with coding of the measured variablex into the intensity ratio (ratio of benefits) of two output luminous flux ₁ and ₂ works. The sensor100  includes a light source14 with continuous emissions spectrum, a sensor11who the coding of the meas sizex in the ratio of the intensities of the two out aisle luminous flux ₁ and ₂ mediates that from a - spectral - split one from the light source14 in the sensor11 coupled primary luminous fluxI. in two (input) partial luminous fluxesI.₁ andI.₂ and measurands proportional intensity modulation of at least one of the two partial luminous fluxesI.₁ and / orI.₂ are generated, as well as a Evaluation level10thwhich is a decoding of the intensity ratio of the two luminous fluxes ₁ and ₂ in one units of the measured variablex conveyed and one for the measuring sizex characteristic signal generated by means of of a display instrument22 in units of meas displayed size or for further processing can be exploited, e.g. B. to activate a Pump that charges an accumulator whose pressure not fall below a lower limit may, in which case the measured variablex the pressure is in this accumulator.  

Light emitted by the light source 14 , for example a luminescent diode, is fed as a primary light current I to the sensor 11 via a first optical fiber 12 . In this probe 11, a first pair of filters 15 is provided as an input stage, the luminous flux of the primary I into the two partial light currents I ₁ and I ₂ disassembled, the device as the input light fluxes of a modulation 17 are fed. . By only schematically indicated in Fig 1 pair of filters 15 to flow from the division of the primary light I resulting partial luminous fluxes is I ₁ and I ₂ a characteristic - different - spectral intensity distribution of each narrow-band-line-shaped structure of the spectral distribution of the light output is impressed, in such a way that a spectral line of a light flux I ₁ lies spectrally between two lines of the other light flux I ₂; thereby a spectral Ver nesting of the two luminous fluxes I ₁ and I ₂ is achieved, the spectral distance of a line of each one luminous flux I ₂ from the spectrally adjacent line of the other luminous flux I ₂ is larger than the line width of these spectral components of the two Light currents I ₁ and I ₂.

The one in theFig. 1 shown, for principle Explanation of the invention selected embodiment of a sensor100 experience the starting Partial luminous fluxI.₁ andI.₂ of the first pair of filters15  a spatial separation from each other and it is im Frame of the sensor11 as a modulation device17th a e.g. B. transverse to the direction of propagation of a light currentI.₁ slidable aperture provided, by means of which the light output of one  from the filter pair15 emerging luminous fluxI.₁ on with the shift of the aperture17th correlated valuesI.₁(x)= ₁ is changeable, whereas in the embodiment according toFig. 1 the light output of the other from which Filter pair15 emerging partial luminous fluxI.₂ through the modulation device17th is not influenced so in this case the relationship ₂ =I.₂ applies. The two partial luminous fluxes are in one as an output stage of the sensor provided union element16  reunited in the sense of an overlay and a second optical fiber13 together the Evaluation device10th forwarded.

In the evaluation device10th is a second about optical fiber13 with the exit of the beam union elements16 optically connected filter pair18th intended, that has the same overall transmission characteristic like that in the context of the sensor11 intended, first Filter pair15. The filter pair18th of the evaluation device10th  thus again mediates a separation of the second optical fiber13 together the evaluation device10th supplied conducted partial luminous fluxes ₁ and ₂, their intensities of two each one of the two luminous fluxes ₁ and ₂ assigned detectors19th respectively.20th be detected, whereby the output signal of a detector, e.g. B. of Detector19thby the modulation device17th  modified intensity ₁ of the input luminous fluxI.₁ and the output of the other detector20th the - unchanged in the illustrated explanatory example - Intensity of the other input luminous fluxI.₂ proportional is. For further evaluation is part of the evaluation device an electronic level21st provided the a  the relationshipR=S₁ /S₂ the signal level of the detector Output signalsS₁ andS₂ corresponding output signal forms that by means of the measuring instrument22 can be displayed. Will be in the probe11 the partial luminous fluxI.₁ for example modulated by the fact that it is articulated by the movable arranged aperture17th from its original performanceI.₁ more or less on an achievement ₁ is weakened this reduces the display of the measuring instrument22  corresponding. The in theFig. 1 fiber shown optical arrangement thus represents a transducer for the measurandx if this measured variable is the position the aperture17th controls and the measuring instrument22 in one units of the measured variablex is calibrated.

In Fig. 2 the method is illustrated, the one of the properties of the optical fibers used 12 and 13 independent transfer for the measured variable characteristic optical signals between the sensor 11 and the evaluation device 10 causes. Here, by the Fig. 2 (a) schematically shows the spectral power density distribution I ₀ (ν) of a light source 24 is shown with a continuous emission background spectrum as a function of optical frequency. The bandwidth of the basic spectrum, measured between the frequency values ν L / 2 imd ν H / 2, at which the power density of the basic spectrum is half of the maximum value I ₀ _max. is denoted by B _ν .

Furthermore, in theFig. 2 (b) spectral trans mission characteristicsT₁(ν) darge represents each of the two filter pairs15 and18th  must own. Each of these two transmission Characteristics corresponds to a line spectrum a typical distanceΔν between neighboring lines the same filter15 respectively.18th and with a typical Line widthδν. There is partial light for one electricityI.₁ or ₁ a transmission characteristicT₁(ν)  effective while for the other partial luminous fluxI.₂ or ₂ the transmission characteristicT₂(ν) is effective. In theFig. 2 (b) are, for simplicity, spectral passband of the filter15 and18th in same spectral distances equal to "broad" and the same shown "high". These likenesses, though before part of the effectiveness of the inventive Ver driving, do not have to be strict across the entire rangeB ν  be fulfilled. Rather, it is sufficient if they are approaches the half-value width over larger sub-areasB ν  of the basic spectrum, for example in the sense that the spectrumT₂(ν) outT₁(ν) through a shift at aboutΔν/ 2 emerges. Above all, it is essential that both spectra and transmission characteristicsT₁(ν) and T₂(ν) are so nested in each other that they overlap as little as possible and that a multitude of lines in the rangeB ν of the basic spectrumI.₀(ν) falls.

The following conditions should therefore apply:

δν < Δν / 2 (1)

Δν « B _n (2)

The one from these filter characteristics and the reason spectrumI.₀(ν) the light source24th resulting spec trenI.₁(ν) andI.₂(ν) of luminous fluxI.₁ orI.₂ are in theFig. 2 (c) and 2 (d). It is him evident that because of the condition (2) and the steady Course of the basic spectrum over the frequency scale both spectral distributionsI.₁(ν) andI.₂(ν) in close proximity same average optical frequencyν₀ and also that same overall widthB _ν  own that by reason spectrumI.₀(ν) are specified. This tells the two Luminous fluxI.₁ andI.₂ or ₁ and ₂ the same through the optical fibers12 and13 conditional losses. This The design of the filter pairs can be of advantage15 and 18th can still be achieved even if the fiber losses as a function of optical frequencyν relative change drastically, such as B. the scattering losses that typically proportional toν² increase. The spectral Line spacingΔν must then be chosen small enough that the loss - related differences of the spectral intensities in two spectrally adjacent Lines become smaller than those for the sensor100  required display accuracy. Because of the continuity of all real loss spectra, this is always possible. The fact that the two in the manner according to the invention spectrally composed luminous fluxesI.₁ andI.₂ or ₁ and ₂ practically the same average frequencyν₀ and bandwidthB _ν   possess, also has an advantageous effect in the detection of these Luminous fluxes, especially in the event that their Power to be measured with the same detector, as is the case in self-balancing evaluation processes is moderate. With the same values ofν₀ andB _ν  for both  Partial luminous flux ₁ and ₂ are the detector sensitivities for both luminous fluxes are the same, even if they both have rapidly changing functions of Frequency should be.

Another important advantage of the invention seen coding is that a relative large fraction of that in the basic emission spectrum of the Light source24th available light output is exploitable. This fraction is roughly given through over the rangeB _ν  averaged spec central transmission characteristicsT₁(ν) andT₂(ν)  of the filter pairs15 and18th. According to the illustration according to the filter transmission characteristicsFig. 2 B) these spectral averages both have approximately the value ₁ = ₂≅δν/Δν. It is assumed that the Peak transmission values of transmission CharacteristicsT₁(ν) andT₂(ν) close to the value 1 lie. The values mentioned ₁ and ₂ can order sizes orders are higher than in cases where part luminous fluxI.₁ andI.₂ or ₁ and ₂ only by off filtering a single line of the spectral widthδν be won.

Finally, the fact that filters 15 and 18 with spectral transmission characteristics, as shown in FIG. 2 (b), can be constructed relatively simply in the form of interference filters, which is discussed in more detail below, is particularly advantageous .

For a more detailed explanation of the conditions that occur practically in the process explained so far, the following is considered the numerical example:
a gallium arsenide luminescence diode with an average optical wave number ν ₀ = 12,000 cm ^-1 , corresponding to a wavelength of 0.83 µm, serves as the light source. The bandwidth B _{ν of} the emission spectrum of this luminescence diode has a typical value of 400 cm ^-1 . Conditions (1) and (2) are certainly met if line spacing Δν of 40 cm ^-1 and line widths δν of 2 cm ^-1 are used. This can be achieved practically with interference filters of order m = 300 and finesse F = 20.

The practical implementation of the so far explained Procedure is possible in different ways, which are now based on theFig. 3 and 4 Darge provided transducers100 respectively.100 ′ explained in more detail will. For the sensors11that at the two reading recorders100 and100 ′ be identical can, it is only assumed here that they that over the optical fibers12 and13 added and removed led light fluxesI. respectively.I.₁ andI.₂ different strengths pass, such that the transmission ratio ₁ / ₂ the current value of the measured variablex represents. When through the sensor100 according toFig. 3 represented by type of management of the method according to the invention aisle luminous fluxI.₁ andI.₂ from a primary luminous fluxI. one Light source14 branched off. This causes fluctuations in the Performance of this light source14 no influence on the type show the measured value.  

As a result of the intimate spectral nesting of the two luminous fluxesI.₁ andI.₂, the execution example according toFig. 3 as spectral components in the Primary luminous fluxI. are subject to this two luminous fluxes very exactly the same coupling conditions in the to the sensor11 leading optical Fiber so that they also have the same optical performances have. The one from the sensor11 about the second optical fiber13 to the evaluation device10thin which the light source14  can be integrated, jointly led output Luminous flux ₁ and ₂, as in connection with theFig. 1 explained in a filter pair18th separated and two separate detectors19th and20th in elec trical signalsS₁ andS₂ converted. The intensity relationship ₁ / ₂ that of the detectors19th and20th after assigned output luminous flux ₁ and ₂ corresponding relationshipS₁ /S₂ of the detector signals is then the same the transmission ratio ₁ / ₂, because the two luminous fluxes had the same power in the fiber12 started and documented by the sensor11  apart from the same losses everywhere and were too with the same sensitivity of the detectors19th and20th  proven.

The through the transducer100 ′ according toFig. 4 ver illustrative implementation of the invention In this respect, the procedure represents a reversal of the above method explained as here the two lights currents ₁ and ₂ with the same performance in one receiver35 of an evaluation device10 ′ arrive for that but with different ones, according to the reciprocal of the transmission ratio explained above ent speaking modified services in the of a  Light supply device14 ′ to the sensor11 leading optical fiber can be coupled. To do this are in the frame of the light supply device14 ′ two separate, but im essentially the same light sources30th and31 intended, their output powers through electronic elements32  and33 are controllable. A pair of filters18ththat here, ver compared with the sensor100 according toFig. 3, in Reverse direction, the light filters currentsI.₁ orI.₂ with the characteristic for these nested spectral distribution of their light outputs from the output luminous fluxes of the sources30th respectively.31 off and combines these luminous fluxes at the same timeI.₁ andI.₂, which in to the sensor11 advanced optical fiber turned on be coupled. The required equality of performance the one over the second optical fiber13 from the sensor11  to the evaluation device10 ′ returned light fluxes ₁ and ₂ at the output end of this optical fiber13 will now causes the light sources30th and31 by one bar giver34 can be switched on and off alternately, whereby the two streams of light ₁ and ₂ from the same detector35  be received. With the same luminous flux output ₁ and ₂ gives this detector35 a constant in time Output signal. In the event that the light outputs of the two luminous fluxes ₁ and ₂ slightly different from each other should give way, the detector generates35 an alternating signal, after amplification and synchronous rectification by means of one like a phase sensitive rectifier acting amplifier36 as a fault signal to a controller37  is forwarded to the electronic controls32  and33 influenced in such a way that on the detector side Optical fiber output13 the required equality the light outputs of the two luminous fluxes ₁ and ₂  sets. The influencing of the Light sources30th and31 can be that their Output light power is affected; It is also possible that within a clock period of the clock34, of the light sources30th and31 alternating in their light emitting states controls the duration be changed within which - within one cycle period - one and the other light source30th  respectively.31 operated with a certain output power becomes. With this type of control of the light sources30th  and31 the required equality of light outputs or intensities of the luminous flux ₁ and ₂ when on the detector35 hit, thus by a variation of the individual light within a clock period sources30th and31 emitted light energy achieved. From the resulting ratio of the light sources30th  and31 with regard to their intensity or their luminosity An electronic stage calculates continuously controlling signals21 ′  again the wanted transmission ratio ₁ / ₂ and causes, if necessary after evaluation with a previously determined Calibration function, also a measured value display with the help of the display instrument22. It should be noted that even with the help of theFig. 4 explained methods ultimately the determination of the value of the measurand the ratio of the luminous flux ₁ and ₂ at the decoupling end of the optical fiber13 done, too if this ratio after the settling of the explained control loop has the value 1.  

The construction in the context of transducers 100 and 100 ' as indicated only schematically in FIGS. 3 and 4 can be carried out essentially according to four different construction principles, which are shown in FIGS. 5 to 8, to the details of which reference is now made in which are schematically shown suitable for a comparison, the sensor 11 shown in FIG. 5 corresponding to that already shown in FIG. 1:
Stream from the incoming via the optical fiber 12. Light I, its spectral composition is determined by the emission characteristics of the light source 14, the two light fluxes by means of the pair of filters 15 separated I ₁ and I ₂, modulated by the measured variable, and in the beam combiner 16 again united and coupled into the optical fiber 13 leading to the evaluation device 10 . It is essential here that the modulation acts on the two light fluxes I ₁ and I ₂ different. In Fig. 5, this is indicated by a ver sliding damping filter 17 with location-dependent transmission, a so-called gray wedge; as an alternative to this, a diaphragm which can be displaced transversely to the direction of light propagation could also be provided or some other known method for weakening a light output could be used. While in the sensor 11 of FIG. 5 shows a luminous flux is only a measured variable modulation of the intended I ₁, it is practically advantageous, and the other light current I ₂, however, to modulate these in opposing senses for modulating the light current I ₁, i.e. such that an decrease in the intensity of the light current I ₁ is accompanied by an increase in the intensity of the light current I ₂. The necessary for such a modulation of both luminous fluxes I ₁ and I ₂ in the sensor 11 separation thereof is indicated schematically in Fig. 5 as a real spatial separation.

However, it goes without saying that other types of separation of two light fluxes can be used, for example a separation with respect to the directions of propagation of the light currents I 1 and I 2 or with respect to different polarization states thereof. In both of the latter cases, it is advantageously possible to let both light fluxes I ₁ and I ₂ flow essentially within the same spatial cross section, which is a particularly good equality of all z. B. guaranteed by aperture edges or scatter reflections caused losses.

As a beam union element16 can numerous, the Arrangements known to those skilled in the art can be used otherwise than with wavefront or amplitude division working radiation guide devices are used, for example fiber optic Y-couplers, partially transparent Mirror or the like. In the event that the to unifying, d. H. into the optical fiber13 to coupling partial luminous fluxes ₁ and ₂ in terms of their Distinguish polarization, a polarization Analyzer as a beam combiner16 serve when he has one between the polarization states of the luminous flux ₁ and ₂ horizontal polarization state can happen.  

In the modification shown in Fig. 4 in the context of a transducer 100 or 100 ' , as shown in Figs. 3 and 4, usable sensor 11 is different from the sensor according to Fig. 5, in which a fixed beam combiner and a modulator 17 arranged separately therefrom is used, a beam combiner 16 controlled by the measured variable x is provided, which here fulfills both functions - modulation and beam combining. Depending on the value of the measured variable x, the modulator coupled 16 of the probe 11 shown in FIG. 6 is a more or less large proportion of the power of the light current I ₁ and a complementary part of the power of the light current I ₂ in the further to the processing unit 10 optical fiber a. This type of beam combination in combination with opposing modulation of the intensities of the light fluxes I ₁ and I ₂ can be realized, for example, by a movably arranged lens or, in the case of different polarizations of the light fluxes I ₁ and I ₂, by a function of the measured variable x adjustable polarization analyzer.

In theFig. 7 and 8 are further advantageous Sensor designs11 shown which the for coding the measured variablex necessary, characteristic different modulations - relative changes - the intensities of the partial luminous fluxesI.₁ andI.₂ or ₁ and ₂ convey. The goes in theFig. 7 shown sensor11 out of that according toFig. 5 simply by swapping the order of the filter couple15 and  of the beam combiner16 regarding the spread direction of the partial luminous fluxes, now the according toFig. 5 element acting as a beam combiner16  as a beam splitting element (Fig. 7) works.

The same applies mutatis mutandis to the design of a further sensor 11 shown in FIG. 8, which results from that according to FIG. 6 by corresponding exchange of the successive optical elements 16 seen in the direction of propagation of the luminous fluxes - measurement-controlled beam splitter and filter pair 15 , where the filter pair 15 in turn acts as a beam combining element.

For a more detailed explanation of applicable modulation the details of theFig. 9 and 10, in which schematically is made, as by moving an aperture51  the two output luminous fluxes ₁ and ₂ in opposite directions their services can be modulated.

According toFig. 9 is that of the optical fiber12 on coming luminous fluxI., for example by means of a Collimation lens54 on a pair of filters15 directed, that from two interference filters52 and53 consists, which are of the type of a Fabry-P´rot interferometer. This interference filter52 and53that ever for a transmission characteristic with in the Frequency scale equidistantly arranged, narrow-band Have passband, filter the luminous fluxI.₁ andI.₂ with the narrow used according to the invention banded-linear spectral structure from that  in the explanatory example according toFig. 9 in two rooms Lich separate areas run side by side. The aperture51 shadows from both luminous fluxesI.₁ and I.₂, as from theFig. 9, depending on their Position more or less large areas of light river cross section. If the cover51 depending on the measured variablex, trans vertical to the direction of propagation of the partial luminous fluxI.₁ andI.₂, the portion let through increases ₁ of the Luminous fluxI.₁, during that of the partial luminous fluxI.₂ further directed share ₂ decreases. It goes without saying that the width of the aperture measured in the plane of the drawing51  this must be chosen appropriately, expediently the same the measured transversely to the direction of propagation "Width" of the light flux cross sections of each of the partial lights currentsI.₁ andI.₂. The reunification of the two prevailed left fractions ₁ and ₂ of partial luminous fluxesI.₁ andI.₂, those through the interference filter52 and53 the changes narrow-band lines nested one inside the other shaped spectral structure is imprinted by a converging lens55 achieved which the two part luminous flux ₁ and ₂ or their aperture51  Unshaded fractions on the sensor side Input end of the to the evaluation device10th further leading optical fiber13 focused and into this coupled. An advantage of this simultaneous, against sensible modulation of the partial luminous fluxI.₁ andI.₂ is that it turns out for evaluation used performance ratio ₁ / ₂ depending on Movement of the aperture51 changes twice as fast as if only one of the two partial luminous fluxes would be modulated.  

Even in the design of a sensor 11 shown in FIG. 10, the basic principle already explained with reference to FIG. 9 of a modulation of spectrally interleaved partial light fluxes I ₁ 'and I ₂' with the aid of a transversely displaceable diaphragm 51 'is used , the spectral composition this partial luminous flux I ₁ 'and I ₂' is in turn determined by interference filters 52 ' and 53' , each of which has the characteristic structure for a Fabry-P´rot interferometer.

Seen in the X direction transverse to the direction of light propagation, in the sensor 11 according to FIG. 10 interference filter 52 ' of one type and interference filter 53' of the second type are arranged side by side in an alternating sequence. Thus, there arises a spatially nested arrangement of the interference filter 52 'and 53', wherein the interference filter 52 'have the same transmission characteristics, respectively, through which reduction the spectral composition of these filters 52' transmitted partial luminous fluxes is determined I ₁ ', and the Filters 53 ' each have the same transmission characteristics by which the spectral composition of the partial light currents I ₂' is determined, which in turn have the same spatial "nested" distribution as the interferential filter 52 ' with respect to the interference filter 53' . As in the embodiment according to FIG. 9, in the embodiment according to FIG. 10 the interference filter 52 ' and 53', which corresponds in effect to a total of a filter pair 15 ', are arranged between a collimation lens 54 and a converging lens 55 , which acts as a beam combining element. The sensor 11 shown in FIG. 10 has the advantage that a possible misalignment of the collimator lens 54 can cause no disruptive inequality in the illumination of the interference filter 52 ' and 53' , the effect of which could not be distinguished from a change in the measured variable. If, as indicated schematically in FIG. 10, the sub-filters 52 ' and 53' have a narrow-striped structure or are sector-shaped and, seen in the direction of the optical axis 41 of the sensor 11 , are nested in the azimuthal direction, such that that always a larger number (in a typical case not less than 5) of partial filters 52 ' or 53' of each type are illuminated, a disruptive influence of possible misalignments is greatly reduced. A particular advantage of the nested arrangement of the partial filters 52 ' and 53' explained with reference to FIG. 10 is the simpler type of setting forth such a filter arrangement 52 ', 53' .

If only two interference filters 52 and 53 , as can be seen in FIG. 9, are used, these must be manufactured in such a way that the transmission maxima of one filter 52 , which define the spectral position of the lines of light flux I 1 , with the transmission minima of other interference filters 53 coincide as shown in Fig. 2 (b). So that these conditions are sufficiently well fulfilled over the entire spectral range B ν of the light source, it is necessary that the interference orders of the partial filters 52 and 53 differ at a mean optical frequency ν ₀ by half an order or an odd multiple of half an inter order of interference . In separate production of such sub-filters 52 and 53 but the A requires attitude this condition, a very precise control of the reflector spacing of the interference filter 52 and 53rd

In contrast, the nested arrangement shown in FIG. 10 of the partial filters 52 ' and 53' can be realized in a simple manner by the filters 52 ' and 53' being formed from two parallel, partially transparent reflectors 42 and 43 , at least one of the two reflectors, according to FIG. 10 the reflector 43 , reflects light with a different reflection phase on strip-shaped regions of its reflecting surface than in the strip-shaped regions lying between them. This can be achieved, for example, in that before the partially transparent reflection layer is applied, which covers the entire reflective surface, e.g. B. the reflector 43 covers, in the reflective layer-bearing surface strips with a depth of λ ₀ / 4 (or an odd multiple thereof) are etched. Here λ ₀ is the wavelength corresponding to the mean optical frequency ν ₀ according to FIG. 2. Another possibility equivalent to this is to cover strip-like areas of the reflector surface with a transparent layer with a thickness of 0.25 λ ₀ / ( n -1) after the application of the reflection layer, where n denotes the refractive index of this layer and the term ( n -1) takes into account the optical delay of the light in the coated strips relative to the uncoated strips between them. These possibilities for modifying the reflection phases, with which light is reflected at the different strip-shaped regions, apply in the event that the substrates carrying the reflection layers are arranged outside the resonance volume of the Fabry-P'rot interference filter, that is to say the reflection layers on the mutually facing inner sides of the reflectors 42 and 43 are arranged. Modifications that are necessary in the event that the reflection layers on the opposite outer sides of a transparent support, for. B. a substrate made of quartz glass, are arranged that the resonance volumes of the individual sub-filters 52 ' and 53' fills are considered to be in the field of professional skill. Are in the probe 11 shown in FIG. 10, the sub-filter 52 'respectively, by the raised drawn strip-shaped regions 44 of a reflector 43, and the formed these oppositely disposed portions of the reflector 42 having a planar reflective layer, while the sub-filter 53' raised by between , strip-shaped regions 44 , recessed strip-shaped regions 46 and the surface regions of the flat reflection layer of the reflector 42 arranged opposite them are formed. The effect of the total combination of the partial filters 52 'of the sensor 11 according to FIG. 10 corresponds to that of the filter 52 according to FIG. 9. The same applies analogously with regard to the combination of the partial filters 53 ' according to FIG. 10 and the filter 53 according to FIG. 9 .

Likewise, the entirety of the partial luminous fluxes I ₁ ', the spectral composition of which is determined by the partial filter 52' , corresponds to the partial luminous flux I ₁ and the entirety of the partial luminous fluxes I ₂ ', the spectral composition of which is determined by the partial filter 53' , the partial luminous flux I ₂ whose spectral composition is determined by the filter 53 of the sensor 11 according to FIG. 9. Corresponding to the stripe-shaped structure of the filter arrangement 52 ', 53' of the sensor 11 according to FIG. 10, a stripe-shaped grating structure with alternately opaque stripes 47 and transparent stripes 48 is also provided for its transversely displaceable aperture 51 ' . The type of modulation of the partial luminous fluxes I ₁ 'and I ₂' as shown in FIG. 10 is particularly suitable for sensors which primarily detect a geometric displacement in the X direction. In a sector-shaped design of the partial filter 52 ' and 53' and azimuthal grouping of the same about the central longitudinal axis axis 41 of the sensor 11 and a corresponding sector-shaped design and arrangement of the opaque and permeable areas of the aperture 51 ' and rotatable arrangement of the same about the longitudinal axis 41 an angle of rotation can be detected with such a sensor. The type of sensor can also be used in a known manner for the acquisition of other physical measured variables. B. in the sensor 11 shown in FIG. 10, the transverse displacement of the diaphragm 51 ' against the restoring force of a linear spring, the sensor 11 shown in FIG. 10 is suitable as a force sensor. If the rotational movement of a sector-shaped diaphragm occurs in a sensor with sector-shaped interference filters against the restoring force of a torsion spring, then such a sensor primarily suitable for detecting an angle of rotation can be used as a torque sensor.

Numerous sensors for other sizes, such as Tempe temperature, pressure, electric or magnetic fields, can be done in a corresponding manner by using Expansion bodies, membranes or of piezo electrical or magnetostrictive bodies, by whose deformation-proportional deformation the aperture Movements are controllable, can be realized.

In Fig. 11, to the details of which reference is now made, the sensor 11 is a functionally the filter pairs 15 explained above with partial filters 52 and 53 or 52 ' and 53' ent speaking filter pair 15 ' with the help of a single structural element realized that is designed as an interference filter in the manner of a Fabry-P'rot interferometer. This interference filter 15 ' is like the interference filter pair 15, 52, 53 according to FIG. 9 and the interference filter combination 52', 53 ' according to FIG. 10 arranged between a collimator lens 54 and a condenser lens 55 . The partially transparent reflectors 63 and 64 delimiting the resonator space 62 have flat reflection surfaces 66 and 67, respectively. The resonator space which extends between these reflection surfaces 66 and 67 is filled with a plate-shaped body made of a transparent, birefringent material. The ge in the light propagation direction 41 see the distance between the reflection surfaces 66 and 67 determining the thickness of the birefringent body is chosen so that for two mutually orthogonal polarization states of a light flux passing through the birefringent body 68 in its one polarization state, a delay of about a quarter wavelength relative to the other of the two polarization states. The birefringent body dimensioned in this way then represents a so-called quarter-wave plate. This has the consequence that an interference filter is formed by this body 68 and the reflection layers 66 and 67 arranged outside, the transmission characteristics of which are for two Differentiate orthogonal polarization states by just half an order, as shown in Fig. 2 (b). It is understood that instead of a birefringent body 68, the sationszuständen between orthogonal Polari a delay of one quarter wavelength conveyed, even a birefringent body 68 can be used which averages a delay ver corresponding to an odd multiple of a quarter wavelength .

The combination of two Fabry-P'rot interference filters explained so far into a single one with orthogonal polarization eigenstates can be achieved with both linear and circular birefringence of the birefringent body 68 which fulfills the resonator space 62 , the eigenstates of these polarizations correspond. The practically particularly simple case of linearly polarized eigenstates can also be achieved without the use of birefringent materials in that at least one of the reflectors 63 and / or 64 of the interference filter 15 'is designed such that the reflection phase with perpendicular light is polarization-dependent. This is possible, for example, in that a dielectric or metallic relief grating is applied to this reflector, the grating period of which is smaller than the light waves used to transmit the measured values. The depth of modulation and the period of such grating must be chosen so that the difference in the reflection phases for light that is polarized parallel or perpendicular to the grating lines is a total of 180 ° by a shift in the effective for the two polarization states Trans mission characteristics to ensure half an interference order. Are both reflectors 63 and 64 of the interference filter 15 'provided with such grating grating, they can be designed so that each of the two grating contributes, for example, 90 ° to the difference in the reflection phases.

To further explain the type of modulation that can be carried out by means of the sensor 11 according to FIG. 11, it is assumed that the interference filter 15 'has two eigenstates of linear polarization, the directions of which are oriented parallel and perpendicular to the plane of the drawing. Accordingly, the partial light currents I 1 and I 2 emanating from this filter 15 ' are linearly polarized and parallel to these directions, but are not spatially separated, but spread in the same spatial area and in the same direction. For - opposing - modulation of these partial light fluxes I ₁ and I ₂ a linear polarization analyzer 60 is provided, which is arranged between the interference filter 15 ' and the converging lens 55 of the sensor 11 . If this polarizer is set to an azimuth α with respect to the plane of the drawing, it allows only the fractions cos² α and sin² α of the two partial luminous fluxes I ₁ and I ₂ to pass and thus encodes its azimuthal angular position in the power ratio of these luminous fluxes. The sensor shown in FIG. 11 is therefore particularly suitable for fiber optic angle measurement. As already stated, the measurement of numerous other physical quantities can be carried out by combination with transducer elements sensitive to measurement quantities.

The sensor shown in FIG. 12, to the details of which reference is now made, is particularly suitable for measuring forces. It differs from the sensor shown in FIG. 11 essentially by the fact that between the interference filter 15 ' and the analyzer 60 a voltage optical element 61 is arranged, which becomes birefringent by the action of a force with a defined direction of attack. The direction of application of the force and the arrangement of this voltage-optical element 61 is expediently chosen so that the main birefringence axes have azimuths of ± 45 ° under the action of the force, the analyzer expediently remaining fixed at the azimuth α = 0. When the elasto-optical body 61 is free from birefringence in the force-free case, it does not affect the two light streams orthogonally polarized, with the result that a part of light current I ₁ can pass as output light current I ₁ unattenuated through the analyzer 60, while the other Luminous flux I ₂ is blocked. If a force P acts in the direction of arrow 69 on the elasto-optical body 61 , the two partial light flows I 1 and I 2 are thereby polarized more and more elliptically, with the result that the analyzer 60 increasingly weakens the one partial light flow I 1 the other partial luminous flux I ₂ but can increasingly happen. If the force reaches such a magnitude that the retardation in the elasto-optical body 61 has the value π , the one partial luminous flux I ₁ is completely blocked and the other partial luminous flux I ₂ is completely let through. The sensor 11 shown in FIG. 12 is thus suitable for encoding a force P in the ratio of the powers of partial light fluxes of different polarization.

In the above based on theFig. 3 and 4 alternative types of sensors100 respectively. 100 ′, within their scope, depending on the purpose of such measurement value sensors based on theFig. 5-12 explained Sensor11 can be used, these sensors are in Transmission operated, which in practice has the consequence that a first optical fiber12 must be provided over  the output luminous flux of a light source14 or one Light supply device18, 30, 31 the sensor11  can be fed, and a second optical fiber13, about what partial luminous flux ₁ and ₂ defines different spectral composition, their intensity ratio ₁ / ₂ contains the measured value information, one for their Evaluation provided in units of the measured variable value level10th respectively.10 ′ are feedable.

As an alternative to such transducers 100 and 100 ' , transducers 110 and 110 ' can also be used as devices for carrying out the method according to the invention, the basic structure of which is shown in FIGS. 13 and 14, to the details of which reference is expressly made are and in the reflection mode operable sensor 111 , which can be realized with from FIGS . 15-20, to the details of which reference is also made, designs and functional properties can be realized.

So far in theFig. 13-20 reference numerals are used that with in theFig. 1-12 reference numerals used table should also mean repetitions to avoid referring to those identified identically Elements ofFig. 1-12 belonging description parts be referenced so that the description of the in theFig. 13 and 14 shown transducers110 respectively.110 ′  as well as that in theFig. 15-20 sensor shown 111 essentially on functional properties of the facilities shown and a comparison of same with the above described, functional analog facilities can be limited. The difference  to those in theFig. 3 and 4 are shown takers100 respectively.100 ′ between the light source14  or the light supply device18, 31, 30 on the one hand and the respective sensor11 on the other hand, an on have coupling interface, which z. B. the sensor side End of the first optical fiber12 up can be grasped, and in which between the respective Sensor11 and the evaluation device10th respectively.10 ′ a further optical ones referred to as decoupling interfaces Interface is provided as which z. B. that end of the sensor located at a distance from the respective sensor second, from the sensor11 to the evaluation device10th respectively.10 ′  leading optical fiber13 can be understood is in the in theFig. 13 and 14 Sensors110 respectively.110 ′ between the light source14  according toFig. 13 or the light supply device18, 30, 31  according toFig. 14 and the respective sensor111 on the one hand un 13228 00070 552 001000280000000200012000285911311700040 0002003528294 00004 13109d between this and the evaluation unit10th respectively.10 ′  on the other hand only one common optical input / Decoupling interface provided by the here by the respective trained as a reflection unit Sensor111 distal end113 one optical fiber112 is formed about both Light in the respective sensor111 can be coupled in as also the intensity reflected from this modulated partial luminous flux ₁ and ₂ to the evaluation device 10th respectively.10 ′ can be coupled out.

For the optical "separation" of those that coincide in this way Coupling and decoupling interfaces are in themselves known arrangement a partially transparent mirror23 before seen through the in the case ofFig. 13 one of the light  source14 outgoing primary luminous fluxI. - partially - pass through and into the optical fiber112 coupled can be, and by means of the fiber end113 from measurement sensor111 partial luminous flux arriving ₁ and ₂, in whose intensity ratio is the measured value information is coded to the evaluation device10th be redirected can.

In the case of the embodiment according toFig. 14 are from the light supply device18, 30, 31 outgoing spectral nested partial light flows through the partially transparent mirror23 to the fiber immediately adjacent to it The End113 redirected and into the optical fiber112 a coupled while from the respective sensor111 out outgoing partial luminous flux ₁ and ₂, in their intensity ratio the measured value information is encoded by the semitransparent mirror23 step through and onto the detector35 of the evaluation device10 ′ can hit.

Thus, apart from special designs of the respective measuring sensors 111 forming reflection units, the structural differences of the transducers 110 and 110 ' according to FIGS. 13 and 14 compared to the functionally analog transducers 100 and 100' according to FIGS. 3 and 4 are exhausted. In particular, the evaluation devices 10 and 10 ' provided in the context of the transducers 110 and 110' can have the same structure as described with reference to FIGS. 3 and 4.

Further explanations can therefore be restricted to the special designs of sensors 111 , as shown in detail in FIGS . 15-20:
In the sensor 111 shown in FIG. 15, a filter pair, designated overall by 15 , serves both for the spectral decomposition of a z. B. from the light source 14 emitted primary light flux I in the two spectrally connected partial light fluxes I ₁ and I ₂ as well as for their reunification after these partial light fluxes I ₁ and I ₂ have been thrown back into themselves at these individually assigned reflectors 114 and 116 and at least one of the two partial luminous fluxes, e.g. B. the partial luminous flux I ₁ one of the measured variable x corresponding modulation of its intensity, z. B. has been subjected to a gray wedge 17 or an aperture. The sensor 111 is largely analogous in its construction and function according to the sensor 11 shown in FIG. 7.

The sensor 111 shown in FIG. 16 is comparable in structure and function with the sensors 11 shown in FIGS . 6 or 8 for transmission operation:
A modulation device 16 controls the division of a primary luminous flux I into partial luminous fluxes I ' and I'' depending on the measured variable x . These each run twice, ie once in the forward and once in the backward direction, a pair of transmission filters 15 , the common arm 117 , in which the partial light fluxes I ₁ and I ₂ propagate with spectrally interleaved composition, is completed by means of a reflector 118 .

In the FIG. 16 "upper" and "lower" to the modulator 16 through return light currents I ₁ and I ₂ are then alternatively defined by the single filter of the pair of filters 15, each other in the frequency scale interleaved spectral compositions. In the modulator 16 , these luminous fluxes I ₁ and I ₂ are combined again according to the division ratio of this modulator and coupled into the optical fiber 112 .

The measuring sensor 111 shown in FIG. 17 corresponds structurally and functionally as far as that according to FIG. 16, although in contrast to this, instead of a filter pair 15 with a common arm 117, individual filters 119 and 121 are provided, which filter the partial light fluxes I which are reflected back to the modulator 16 ₁ and I ₂ imprint the nested spectral compositions mentioned, these individual filters 119 each being individually closed by a reflector 114 ' or 116' integrated in the respective filter.

In Fig. 18, a special design of a measuring sensor 111 is shown, which corresponds to its basic construction on the construction and func tion principle shown in Fig. 17.

A 18 is coupled primary light current I from the optical fiber 112 in the probe 111 shown in Fig. Is collimated by means of the lens 54. A slit or perforated diaphragm 122 which is displaceable as a function of the measured variable x transversely to the optical axis 41 of the sensor 111 conveys, depending on the measured variable x, a sensible variation of the intensities in the "upper" and "lower" regions shown in FIG of the light flux cross-section spreading light flows. A reflection filter 119 or 121 is assigned to each of these partial areas, which reflects the incident luminous flux back into itself. In the special example shown, the reflection filters 119 and 121 are designed as high-order Bragg reflectors. Such a reflector consists of a larger number (at least five, but possibly 20 and more) of weakly reflecting partial reflectors 123 and 124 , which, seen in the direction of propagation of the incident light, are arranged at equal intervals d ₁ and d ₂ one behind the other. Has the distance of these reflectors, for. B. the reflectors 123 the value d ₁ and the refractive index of the medium between these reflectors 123 the value n ₁, the distance is Δν spectrally adjacent reflection maxima (see. Fig. 2)

where Δν is expressed in wave numbers (cm ^-1 ). The required spectral nesting reflected by the reflection filters 119 and 121 of partial luminous fluxes I ₁ and I ₂ is achieved in that - with the same values of the refractive indices between the reflectors 123 and 124 of the reflection filter 119 and 121 arranged Media - d the distances ₁ of Partial reflectors 123 of a reflection filter 119 have a different value than the distances d ₂ of the partial reflectors 124 of the other reflection filter.

It is understood that it is also possible to achieve the desired different reflection characteristics of the two reflection filters 119 and 121 by the fact that at the same reflector distances d ₁ and d ₂ the refractive indices n ₁ and n ₂ between the reflectors 123 and 124 respectively ordered media are different.

Also shown in which in Fig. 19, as a reflection unit acting sensors, a coupled-from the optical fiber 112 primary light current I is converted by a collimating lens 54 into a parallel beam 111, the reflection filter formed by means of a Bragg reflector 126 thrown back into itself becomes. The partial reflectors 127 of this reflection filter are made of a birefringent material, so that light with linear polarization parallel and perpendicular to the plane of the drawing "sees" different refractive indices and thus characterized by different polarization states characterized by the reflection filter 126 reflected partial light fluxes I ₁ and I ₂ have the required spectral composition nested in the frequency scale. Between the reflection filter 126 and the collimation lens 54 , a rotatable polarizer 128 is arranged as a function of the measured variable about the central axis 41 , which determines the transmission ratio of the transmitted portions of different polarization, the azimuthal position of this polarizer 128 being proportional to the measured variable x is changeable.

The function of the sensor 111 is analogous to that of the polarization-optical sensor 11 shown in FIG. 11.

The sensor 111 shown in FIG. 20 differs from that according to FIG. 19 only in that the polarizer 128 has a predetermined azimuthal setting (z. B. 45 ° with respect to the plane of the drawing) and that between the polarizer 128 and the turn As a reflection filter designed as a Bragg reflector, an elasto-optical body 129 is arranged, which unfolds a birefringence proportional to the measured variable and thereby mediates a modulation of the polarization of the light emitted by the polarizer 128 . It goes without saying that with the given orientation of the polarizer 128 , the optical axes of the reflection filter 126 must also run at 45 ° with respect to the plane of the drawing. The sensor 111 according to FIG. 20 is functionally analogous to that according to FIG. 12 and is particularly suitable for detecting a pressure which acts on the elasto-optical body 129 .

It should be mentioned that the methods and equipment variants described can be combined, modified and, if necessary, refined by a person skilled in the art in a variety of ways. For example, the variants explained with reference to FIGS . 9-12 for filtering in the measuring sensor can be used directly for filtering in the evaluation device if, instead of the diaphragms, appropriately arranged beam-deflecting elements such as mirrors or prisms are used or if instead of polarization analysis analyzers 60 in sensors are used shown in FIGS. 11 and 12 Wollaston prisms or other polarizers with two output beams. Instead of the simple interference filter considered by way of example, it may also be expedient to suppress two or more such interference filters one after the other in order to suppress a possibly disturbing crosstalk between the partial light fluxes I 1 and I 2 or to use such interference filters which have two or more partially transparent Reflective layers have coupled resonance volumes. Such filter combinations have relatively broad transmission maxima and lower minima.

Claims (34)

1. Method for fiber optic transmission of the value of a variable physical measurand from one to the Measurement-sensitive sensor to an evaluation device, the display characteristic for the measured variable or for a further processing suitable output signals as Generated useful signals, after which the light output of a first luminous flux, the by means of the sensor one with changes in the measured variable performance module in a monotonous context lation is subjected and the light output of a second, used as reference luminous flux comparison which can be carried out by means of the evaluation device be subjected and from this the mentioned useful signal as one for the ratio of the achievements of the two Luminous flux characteristic signal is generated the two luminous fluxes using a fiber optic Arrangement fed from the sensor to the evaluation device will,characterizedthat two input luminous fluxes(I₁, I.₂) with a different, each narrowband linear structure of the spectral distribution of their Light outputs are generated such that a line of a luminous flux spectrally between two lines of the other luminous flux and is therefore a spectral ver nesting of the two input luminous fluxes(I₁,I.₂) is achieved, the spectral distance of a line  each of a luminous flux from a spectrally adjacent beard line each other is greater luminous flux than the line widthd ν of these spectral components of the two partial luminous fluxes that that of the measured variable affected output luminous flux(₂, ₂) one, the light path from the sensor (11; 111) to the evaluation device (10th) optical fiber (13; 112) into the evaluation device (10th) be coupled in and spectrally from each other be measured separately. 2. The method according to claim 1, characterized in that the one luminous flux is a straight Number of spectral lines and the other luminous flux an odd number of spectral lines, which are noteworthy contribute to the total output of these luminous fluxes, with each a spectral line of a luminous flux spectrally between two lines of the other luminous flux lies. 3. The method according to claim 1 or claim 2, characterized in that the two input light currents (I ₁, I ₂) are generated by filtering a luminous flux (I) emitted by a single light source ( 14 ). 4. The method according to any one of claims 1 to 3, characterized in that the output luminous flux(₁, ₂) in the evaluation device (10th) by spectral filter (18th) Cut and two detectors (19, 20) are supplied and that from the ratio of the output signals of the two detec goals (19, 20) the value of the measured variable is determined.   5. The method according to claim 1 or claim 2, characterized in that the two input light currents(I₁,I.₂) by means of one in a light supplier provided light source (30, 31) and the Light sources individually assigned filters of a filter couple (18th) generated and in one by an optical Fiber (12; 112) formed, the Lichtversorgungsge advises (18, 30, 31) optically with a sensor (11; 111) connecting light path are coupled in that this two light sources (30th and31) alternating in time periodic sequence can be switched on and off that over the optical fiber (13; 112) from the sensor (11; 111) the evaluation device (10th) supplied output light currents(₁, ₂) one in time with the light source switch synchronized receiver (35) are forwarded, whose Output signal is therefore periodic with this clock Alternating signal is when the from the sensor (11; 111) emerging light output(₁, ₂) one under have different performances that of a change voltage output signal of the receiver (35) a mistake signal to control a controller (37) is produced, which outputs control signals by means of which the output performance of the two light sources (30, 31) like this be made that the output of the output light currents of the sensor (11; 111) on minimal difference be adjusted and that the control signals, which is a measure for the intensity ratio of the light sources (30, 31) emitted input luminous fluxes are in units the measured variable can be evaluated.   6. Device for carrying out the method according to a of the preceding claims 1 to 4, characterized in that the sensor (11; 111) a first filter pair (15; 15 ′; 119, 121; 126, 128) having, which is the spectral distribution of light output of light source (14) to be compared with each other, spectrally nested partial luminous fluxes(I₁,I.₂ or ₁, ₂) mediates, and that within the scope of the evaluation device (10th) a second pair of filters (18th) is provided, the ent speaking of the spectral composition of the two Output luminous flux(₁, ₂) of the sensor (11; 111), their spatial division and separate feeding each a detector (19th respectively.20th) conveyed. 7. Device for carrying out the procedure according to Claim 5, characterized by the following features:

• (a) there is a first, between the light sources ( 30, 31 ) and the sensor ( 11; 111 ) arranged filter pair ( 18 ) is provided, the spectral composition of the in the sensor ( 11; 111 ) characteristic of the measurand Modulation subordinate input light currents (I ₁, I ₂) determined;
• (b) the sensor (11; 111) contains a second filter pair (15; 15 ′; 119, 121; 126, 128) the same filter has characteristics like the first pair of filters and both the measurement-characteristic modulation of the input luminous flux(I₁,I.₂) as well as the one coupling of the modulated output luminous flux(₁, ₂) into the sensor (11; 111) with the evaluation device (10th) optically connecting fiber (13; 112) mediates;  
• (c) the light sources ( 30, 31 ) can be switched on and off alternately in a controlled manner by means of a clock generator ( 34 );
• (d) it is one by means of the clock (34) synchroni based, the output signals of the detector (35) receiving, in the manner of a phase sensitive electronic rectifier Step (36) provided with their output signal a controller (37) is controllable, the Light outputs of the two lights sources (30, 31) to minimum intensity difference from the detector (35) received Output luminous flux(₁, ₂) of the sensor (11; 111) sets.

8. Device according to claim 6 or claim 7, characterized in that the filter pair ( 15 ) forms an input stage of a sensor ( 11 ) which separates the input luminous flux into the two partial luminous fluxes I ₁ and I ₂, at least one of which can be thrown under is that the output stage of this sensor ( 11 ) is formed by a beam combiner ( 16 ), which couples the two partial light flows into an optical fiber leading to the evaluation device ( 10 ), and that a modulation device ( 17 ), which is a function of the measured variable the power of at least one of the two partial luminous fluxes (I ₁ and / or I ₂) modulated, seen in the direction of propagation of these partial luminous fluxes, between the filter pair ( 15 ) and the beam combiner ( 16 ) is arranged ( Fig. 5). 9. Device according to claim 8, characterized in that the modulation device modulates both light flows in the sense of opposite intensity changes ( Fig. 6). 10. The device according to claim 6 or claim 7, characterized in that a beam splitter ( 16 ) is provided as the input stage of the measuring sensor ( 11 ), which divides an incoming luminous flux into two partial light streams that as the output stage of this measuring sensor ( 11 ) A pair of filters ( 15 ) is provided, which defines the spectral composition of the two partial light flows forwarded for evaluation ( 10 ) and is also designed as a beam combiner, which couples the two light flows into the optical fiber ( 13 ) leading to the evaluation device. 11. The device according to claim 10, characterized in that a modulation device ( 17 ) which, depending on the measured variable, affects the power of at least one of the two partial luminous fluxes, between the input stage ( 16 ) and the output stage ( 15 ) of the sensor ( 11 ) is arranged. 12. The device according to claim 9, characterized in that the modulation device ( 16 ) changes the division ratio with which the light output of the incoming luminous flux is divided between the two partial luminous fluxes ( Fig. 8). 13. Device according to one of the preceding claims, characterized in that at least one of the filter pairs ( 15 and 18 ) consists of two transmission filters operated in transmission ( 52 and 53 ), the spectral transmission characteristics at an average optical frequency of the light fluxes distinguish approximately by an odd multiple of half an interference order. 14. The device according to claim 13, characterized in that the two interference filters ( 52 ' and 53' ) of at least two mutually parallel, partially transparent reflectors ( 42 and 43 ) are formed and that of the area within the cross-sectional area of the light flux the reflecting surface of one of the reflectors ( 43 ) gives about half a reflection with a reflection phase that differs by an odd multiple of π / 2 from the reflection phase with which the other half of the reflection surface of this reflector ( 43 ) reflected. 15. The device according to claim 14, characterized in that a modification of the reflection phases of the reflector ( 43 ) is achieved by applying at least one thin dielectric layer to one of the two partial areas of the reflector ( 43 ). 16. The device according to claim 14 or claim 15, characterized in that a modulation device provided for power modulation of the luminous flux is designed as a movable mask ( 51; 51 ' ), which depends on the value of the measured variable fractions of the partial luminous flux I ₁ and I ₂ missing areas of the light flow cross-section more or less shaded ( Fig. 9 and 10). 17. The device according to claim 16, characterized in that the reflecting surface of a reflector ( 43 ), which partially reflects with different reflection phases, is divided into strips of the same width, which reflect incident light with the different reflection phases, and that the modulation device Transversely to the stripe longitudinally displaceable stripe mask ( 51 ' ), whose structure determined by alternating light-transmitting and light-impermeable areas corresponds to that of the stripe structure of the reflector with different reflection phase ( 43 ) ( Fig. 10). 18. Device according to claim 13, characterized in that a polarization-dependent interference filter ( 15 ' ) is seen as an interference filter pair, which has a spectral interference filter transmission characteristic for light of a first, defined polarization state and for light of the first-mentioned polarization state orthogonal polarization state also has an interference filter transmission characteristic, which is offset from the first-mentioned pass characteristic by an odd multiple of half an interference order ( Fig. 11 and 12). 19. The device according to claim 18, characterized in that the two polarization eigenstates of the polarization-dependent interference filter ( 15 ' ) are the two orthogonal states of linear polarization ( Fig. 11 and 12). 20. Device according to claim 17 or claim 19, characterized in that the resonance volume ( 62 ) of the polarization-dependent interference filter ( 15 ' ) contains a birefringent medium ( 68 ), the phase delay for the two light fluxes orthogonal polarization with a single light passage (transmission) through the resonance volume is approximately an odd multiple of a quarter of an average light wave length. 21. The device according to claim 18 or claim 19, characterized in that in at least one of the reflectors ( 63 and / or 64 ) of the polarization-dependent interference filter ( 15 ' ), the phase with which the reflection takes place on this, is polarization-dependent, the phase difference , which results overall from the reflection of two orthogonally polarized light fluxes on the reflecting surfaces ( 66 and 67 ) of the interferential filter ( 15 ' ), which corresponds to an odd multiple of π / 2. 22. Device according to claim 21, characterized in that the reflector with polarizations dependent phase a relief acting as a phase grating Contains dashed grids whose grating constant is smaller than the wavelength of the measured value transmission used light.   23. Device according to one of the preceding claims 18 to 22, characterized in that a polarizer ( 60 ) is provided as a modulation device which influences both the luminous fluxes I ₁ and I ₂ used for the transmission of the measured variable in a relation mono-tonal with the measured variable, whose excellent polarization state can be changed depending on the measured variable. 24. The device according to claim 23, characterized in that the polarizer ( 60 ) is a linear polarizer whose azimuthal orientation can be controlled by the measured variable. 25. Device according to one of the preceding claims 18 to 24, characterized in that the modulation device comprises a polarizer ( 60 ) and a birefringent element ( 61 ), whose birefringence can be influenced by the measured variable. 26. Device according to claim 6 or claim 7, characterized in that the sensor (111) as one Reflection unit is formed, which for the Coupling of the light which can be subjected to the modulation and for decoupling the evaluation device (10th) forwarded Luminous flux ₁, ₂ a common optical coupling / decoupling Interface (113) by the sensor (111) distal end of an optical fiber (112) is formed, via the in the sensor (111) Light can be coupled in and out the sensor in the opposite direction again the evaluation  device (10, 10 ′) can be fed, and that between this cut Job (113) and the light supply device or the off value device (10, 10 ′) a partially transparent mirror (23) attached is arranged over which part of the through the optical Fiber (112) returned light fluxes ₁ and ₂ for Detection device of the evaluation device (10th) redirect is cash. 27. The device according to claim 26, characterized in that the sensor ( 111 ) has as input and output stage a pair of filters ( 15 ) which mediates a spatial separation of the two individually or together a modulation dependent on the measured magnitudes I ₁ and I ₂, and that at least one reflector is provided, the light streams reflecting back into the filter pair ( 15 ), and that the modulation device ( 17 ), seen in the direction of propagation of the light fluxes I ₁ and I ₂, between the filter pair ( 15 ) and the reflector is arranged ( Fig. 15). 28. The device according to claim 26, characterized in that a beam splitter ( 16 ) is seen as the input and output stage of the sensor ( 111 ), which branches an incoming luminous flux in a division ratio determined by the measured variable into two luminous fluxes, the one the spectral composition of the filter pair ( 15 ) defining the light streams returning to the interface are fed to at least one reflector ( 118 ) which reflects the light striking it back into itself. 29. The device according to claim 26, characterized in that a beam splitter ( 16 ) is provided as the input stage and from the output stage of the sensor ( 111 ), which branches an incoming luminous flux into two luminous fluxes in a division ratio determined by the measured variable, and that these two luminous currents A reflection filter ( 119 and 121 ) is fed in each, which mediates the spectral distribution of the light in the light fluxes reflected back to the interface ( 113 ) ( FIG. 17). 30. The device according to claim 26, characterized in that the reflection filter ( 29 ) each consist of a sequence, seen in the direction of propagation of the incident light, equidistantly arranged and perpendicular to the direction of propagation partially transparent reflectors ( 123, 124 ), the optical distances are different in the two sequences of reflectors and are selected such that the order of interference of the reflected light in one reflection filter ( 119 ) differs from that in the other reflection filter ( 121 ) approximately by an odd multiple of half an order ( FIG. 18 ). 31. The device according to claim 16, characterized in that the sensor ( 111 ) contains a polarization-dependent reflection filter ( 126 ), each of which has a specific, linear reflection characteristic for two orthogonal polarization states, such that the spectral intensity distributions of each with one of the named Polarization states reflected light fluxes of the spectrally interlaced linear structure, and that between this reflection filter ( 126 ) and the interface ( 113 ) a polarizer ( 128 ) is arranged, depending on the measured variable for different polarization states towards the interface ( 113 ) transmitted light is permeable. 32. Device according to claim 31, characterized in that the polarization-dependent reflection filter ( 126 ) is formed as a sequence of equidistantly arranged, partially reflecting birefringent layers. 33. Device according to claim 26, characterized in that the sensor ( 111 ) contains a polarization-dependent reflection filter ( 126 ), each of which has a specific linear reflection characteristic for two orthogonal polarization states, such that the spectral intensity distributions reflect with one of the said polarization states Tiert luminous fluxes have the spectrally nested, linear structure that a polarizer ( 128 ) is arranged between this filter ( 126 ) and the interface ( 113 ) and that between this polarizer ( 128 ) and the reflection filter ( 126 ) one for the useful light Transparent body ( 129 ) is arranged, which unfolds a birefringence which varies with the measured variable. 34. Device according to claim 33, characterized in that the transparent body ( 129 ) consists of an elasto-optical material, which can be impressed with a varying birefringence by a force acting transversely to the direction of light propagation and varying with the measured variable.