DE102012100733B4 - Method for compensating parasitic reflections and measuring device - Google Patents

Abstract

A method of compensating parasitic reflections in an optical waveguide, comprising: coupling optical radiation into the optical waveguide having at least one integrated sensor, wherein the coupled optical radiation is modified by the integrated sensor in a first wavelength range and is not modified in at least a second wavelength range ; Decoupling at least a portion of the modified and at least a portion of the unmodified optical radiation; Comparing the decoupled modified optical radiation with the decoupled unmodified optical radiation; and compensating the parasitic reflections based on the comparison.

Description

TECHNICAL AREA

The present application relates generally to a measuring device for detecting physical quantities, in particular mechanical quantities, by means of sensors integrated in optical waveguides, and more particularly relates to a measuring device with compensation of parasitic reflections in the optical waveguide which contains at least one integrated sensor. Furthermore, the present application relates to a compensation method for compensating parasitic reflections in an optical waveguide.

STATE OF THE ART

In optical metrology, optical fiber-based or fiber-based measurement methods are becoming increasingly important. As a rule, such measuring methods have one or more sensors integrated in an optical waveguide or in an optical fiber, which are read out by means of optical radiation. The sensors can be designed, for example, as fiber Bragg grating sensors. Such integrated sensors are illuminated with light of a predeterminable wavelength or of a predefinable wavelength spectrum, wherein, depending on the design of the sensor and the physical variable to be measured, a portion of the incident light is reflected by the sensor and can be examined in an evaluation and analysis unit ,

The document FR 2 934 365 B1 describes a sensor for measuring a physical quantity, wherein the sensor comprises a measuring light guide with a Bragg grating, and an optical means arranged, a first pumping shaft having a first optical frequency and a second so-called probe shaft having a second optical Injecting frequency into the fiber, wherein the second optical frequency is different from the first frequency. The Bragg grating is adapted to reflect the first and second optical waves. The document WO 2003/065619 A2 describes a method for detecting a parameter to be measured. The method includes inserting optical radiation into an optical fiber, and producing an electrical output signal in response to the optical radiation that is backscattered from the optical fiber.

Intensity and / or wavelength range of light reflected by the sensor allow, for example, a statement about which mechanical forces act on the sensor integrated in the optical waveguide or which temperatures prevail. Such optical waveguide-based measuring devices find various applications in the monitoring of mechanical structures, for the measurement of mechanical stresses in structures, in the remote diagnosis of loads on components, for temperature measurement, etc.

For optically interrogating sensors integrated into the optical waveguide, a light source is provided which irradiates the sensor structure in a defined wavelength range, wherein a detector detects back-reflected light. Measuring devices based on fiber-based design have a variety of components such as connectors, fiber couplers, fiber end faces, and so forth. Reflections of light introduced into the sensor structure, which is reflected at such impurities or terminations, are superimposed on the measuring light, which results from the structure of the integrated sensor, on the detector. Such so-called parasitic reflections on other components of the fiber optic measuring device outside the actual sensor area contribute to an interference signal and thus to a deterioration of the signal quality. This leads disadvantageously to a reduction of the measurement accuracy.

SUMMARY OF THE INVENTION

The present invention provides a compensation method for compensating parasitic reflections in an optical waveguide including an integrated sensor according to claim 1. Furthermore, the present invention provides a compensating device for compensation of parasitic reflections in an optical waveguide with at least one integrated sensor having the features of independent claim 5.

According to one embodiment, the present invention provides a method for compensating parasitic reflections in an optical waveguide, which comprises coupling optical radiation into the optical waveguide, which has at least one integrated sensor, wherein the coupled-in optical waveguide Radiation is modified by the integrated sensor in a first wavelength range and is not modified in at least a second wavelength range, coupling out at least a portion of the modified and at least a portion of the unmodified optical radiation, comparing the coupled-out modified optical radiation with the decoupled one -modified optical radiation, and compensating for the parasitic reflections based on the comparison.

According to a further embodiment, the present invention provides a device for compensation of parasitic reflections in an optical waveguide with at least one integrated sensor, wherein the sensor modifies optical radiation in a first wavelength range and does not modify it in at least a second wavelength range, the device comprising a light source arrangement, which is configured to emit optical radiation having a variable wavelength spectrum including at least the first wavelength range and the second wavelength range, at least one device, for example a fiber coupler or a fiber coupler-containing device, configured to couple the optical emitted from the light source device Radiation in the optical waveguide and for decoupling at least a portion of the modified and at least a portion of the unmodified optical radiation, at least one an array-related detector configured to detect the modified and unmodified optical radiation and includes a detector connected to the detector configured to determine the compensation or compensation value of the parasitic reflections based on a detector Comparison of the decoupled modified optical radiation with the decoupled unmodified optical radiation.

According to yet another embodiment, the present invention provides an apparatus for compensating for parasitic reflections in an optical waveguide having at least one integrated sensor, wherein the sensor modifies optical radiation in a first wavelength range and does not modify it in at least a second wavelength range, wherein the device comprises a first A light source adapted to emit optical radiation in the first wavelength range, at least one second light source configured to emit optical radiation in the second wavelength range, at least one device, for example a fiber coupler or a fiber coupler-containing device, designed is for coupling the optical radiation emitted by the first and the second light source into the optical waveguide and for decoupling at least part of the modified and at least part of the unmodified optical radiation, at least one detector associated with the array or fiber coupler and configured to detect the modified and unmodified optical radiation and includes a detector connected to the detector configured to determine the compensation of the parasitic Reflections based on a comparison of the decoupled modified optical radiation with the decoupled unmodified optical radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated in the drawings and explained in more detail in the following description. In the drawings show:

1 a sensor fiber which includes an integrated sensor element for measuring fiber strain formed as a fiber Bragg grating;

2 a sensor reflection response caused by an in 1 illustrated integrated sensor element within the fiber;

3 a schematic block diagram of a fiber optic measuring device with light source, fiber coupler and detection device, according to an embodiment;

4 an optical compensation device with a light source and a detector module, according to a further embodiment;

5 an optical compensation device with a light source having a variable emission spectrum, according to a further embodiment; and

6 a flowchart illustrating a method for compensating parasitic reflections in an optical waveguide.

In the drawings, like reference characters designate like or functionally identical components or steps.

WAYS FOR CARRYING OUT THE INVENTION

In the following, more detailed reference will be made to various embodiments of the invention, one or more examples of which are illustrated in the drawings.

Embodiments of the present invention described herein relate inter alia to an apparatus for compensating for parasitic reflections in an optical waveguide having at least one integrated sensor, the sensor modifying optical radiation in a first wavelength range and not or hardly modifying it in at least one second wavelength range. The compensation device includes a light source assembly configured to emit optical radiation having a variable wavelength spectrum including at least the first wavelength range and the second wavelength range.

According to another embodiment described below, the light source assembly may include a first light source configured to emit optical radiation in the first wavelength range and at least one second light source configured to emit optical radiation in the second wavelength range , Typically, the first wavelength range differs from the second wavelength range such that there is an overlap in at most 50% of the wavelength ranges, there is no overlap of the wavelength ranges, or the intensity weighted average wavelengths of the respective wavelength range have a wavelength spacing that is within a range of 10 nm to 200 nm, typically in a range of 20 nm to 100 nm, and more typically at least 30 nm or at least 50 nm. The compensation device furthermore has at least one arrangement or device which is designed to couple the optical radiation emitted by the light source arrangement into the waveguide and to decouple at least part of the modified and at least one part of the unmodified optical radiation. The arrangement or device may be a fiber coupler or include a fiber coupler. It may include alternative or additional, including a lens system or other means for coupling light to the fiber, according to other embodiments that may be combined with the embodiments described herein. With z. B. the fiber coupler is an optical detector in communication, which is designed to detect the modified and the unmodified optical radiation. A determination unit connected to the detector is designed to determine the compensation or a compensation value of the parasitic reflections on the basis of a comparison of the coupled-out modified optical radiation with the coupled-out unmodified optical radiation. An influence of parasitic reflections occurring at different reflection points in the optical waveguide can thus be eliminated or at least reduced. Thus, background light that contains no measurement information, the measurement or only slightly disturbing. It should be noted that the term "unmodified optical radiation" refers to optical radiation transmitted through the at least one integrated sensor 303 typically at least 80%, more typically at least 90% in its wavelength-dependent intensity profile is not modified.

1 illustrates a sensor integrated into an optical waveguide or a sensor unit 303 which is a fiber Bragg grating 306 having. Although in 1 only a single fiber Bragg grating 306 1, it is to be understood that the present invention is not limited to data acquisition from a single fiber Bragg grating 306 is limited, but that along a transmission fiber or a sensor fiber 304 a variety of fiber Bragg gratings 306 can be arranged. 1 thus shows only a portion of an optical waveguide, which as a sensor fiber 304 is formed, this sensor fiber 304 sensitive to fiber elongation 308 is.

It should be noted that the term "optical" or "light" is intended to indicate a wavelength range in the electromagnetic spectrum, which may extend from the ultraviolet spectral range over the visible spectral range to the infrared spectral range.

A center wavelength of the fiber Bragg grating 306 , that is, a so-called Bragg wavelength λ _B , is obtained by the following equation: λ _B = 2 × n _k × Λ. Here, n _{k is} the effective refractive index of the fundamental mode of the core of the sensor fiber 306 and A is the spatial grating period (modulation period) of the fiber Bragg grating 306 ,

A spectral width, which is given by a half width of the reflection response, depends on the extent of the fiber Bragg grating 306 along the sensor fiber 304 from. The light propagation within the sensor fiber 304 is thus due to the effect of the fiber Bragg grating 306 depending on physical variables such. As forces, moments and mechanical stresses and temperatures at which the sensor fiber 304 and in particular the sensor element 306 within the sensor fiber 304 be charged.

As in 1 shown, measuring light occurs 204 from the left into the sensor fiber 304 one, being part of the measuring light 204 as a transmitted light 206 with one compared to the measuring light 204 changed wavelength course emerges. An irradiated wavelength range provided by the integrated sensor 303 is changed, is hereinafter referred to as a first wavelength range. Further, it is possible to reflect reflected light 205 at the input end of the fiber (ie at the end, at which also the measuring light 204 is irradiated), the reflected light 205 also a modified wavelength distribution, such as in 2 is shown (sensor reflection response).

In a case where the measuring light 204 is irradiated in a wide spectral range, results in the transmitted light 206 at the location of the Bragg wavelength, an absorption minimum (compared to the in 2 course shown inverted course). In the reflected light results at this point a reflection maximum, which below with reference to 2 is explained.

2 schematically represents a sensor reflection response 400 which is received when broadband measuring light 204 is irradiated, and when the center wavelength of the fiber Bragg grating 306 ( 1 ), ie the Bragg wavelength λ _B , the dashed line 403 equivalent.

The sensor reflection response 400 may be one with respect to the center wavelength 403 have symmetrical course, the course of a half-width 404 (FWHM, Full Width at Half Maximum), ie has a spectral width at half the maximum intensity. At the in 3 shown application example is this sensor reflection response 400 spectrally sampled according to a preferred embodiment of the present invention.

Schematically are in 2 here sampling points 405 (Circles). By the evaluation of the with the detector unit 104 recorded modified secondary light, it is now possible, the in 2 shown course, ie the sensor reflection response 400 as a function of wavelength λ. In 2 is thus an intensity distribution I (λ), ie that of the sensor element 304 reflected intensity as a function of the wavelength λ. In the case of spectral resolution, the spectrum may be quasi-continuous or as in 2 be determined by interpolation between or regression of a curve at the sampling points. According to some embodiments that may be combined with embodiments described herein, alternative a measurement system without spectral resolution may be used.

A wavelength distribution to be detected by the measuring device results from a wavelength response range 406 by the double arrow in 2 is shown. Modified secondary light has wavelength components in this region when the fiber Bragg grating 304 is measured. The modified secondary light then corresponds to the in 2 shown sensor reflection response 400 , that is, a reflection intensity 402 is considered as a function of wavelength 401 added.

3 illustrates a block diagram of a fiber optic measuring device according to an embodiment. As in 3 shown is a light source 101 provided to a fiber coupler 301 via a transmission fiber, ie a transmission optical fiber, is coupled. In the example shown here is the fiber coupler 301 is designed as a light coupling device which divides an incident light intensity in the ratio 50:50 onto corresponding output channels. Thus, via the sensor fiber 304 Light intensity to the sensor integrated in the sensor fiber 303 in which the incident light, as above with reference to 1 and 2 is explained, modified.

That of the integrated sensor 303 in turn, reflected light is transmitted through the fiber coupler 301 and another fiber coupler 301 ' in order to be split into two detection beam paths, wherein a first detection beam path is a first detector unit 105 and a first filter unit 107 contains, and wherein a second detection beam path, a second detector unit 106 and a second filter unit 108 contains.

The first and second detector units 105 . 106 have associated optical detectors which convert incident light intensity into an electrical signal. Furthermore, the first and second detector units 105 . 106 have associated amplifier units which amplify the output from the optical detectors electrical signal and convert into corresponding electrical detector output signals (not shown).

The sensor reflection response 400 thus becomes two different filter units 107 . 108 fed, which have, for example, opposing filter edges. By such an arrangement, an intensity fluctuation, for. As a jitter or the like, in the output signal of the integrated sensor 303 ie in the sensor reflection response 400 be compensated. It should be noted here that in the in 3 shown measuring system used light source 101 one in comparison to the half width 404 the sensor reflection response 400 (please refer 2 ) has broad spectral response.

Reflection sites, which lead to disturbing light reflections (parasitic reflections) that do not contribute to the measurement signal, for example, by a reference numeral 102 marked positions occur. Other reflection sites that 3 not shown may result from soiled fiber connectors, faulty splices, soiled fiber terminations, faulty terminated fiber terminations, etc.

According to an embodiment of the present invention, which will be described below with reference to FIGS 4 and 5 be explained in more detail, such parasitic reflections by a wavelength-dependent intensity comparison of optical radiation in different wavelength ranges can be detected and thus compensated.

wobei I(λ) die Leistungsdichte der Lichtquelle bezeichnet, R(λ) das Reflexionsspektrum des beispielsweise als Faser-Bragg-Gitter ausgebildeten integrierten Sensors 303 darstellt, und T_s(λ) bzw. T_p(λ) die spektrale Transmission des Filters für beide Hauptpolarisationsrichtungen darstellt. Ein zeitlich mittlerer Anteil der Intensität von linear polaristiertem Licht des Polarisationsgrads P an der Gesamtintensität Iges ist damit gegeben durch die folgende Gleichung:

This in 3 shown measuring system based on the use of the broadband light source 101 based, provides, depending on the load condition, on the integrated sensor 303 reflected light spectrum. That of the sensor 303 After two signal splitting, the reflected light is reflected by the two spectrally opposing filter edges of the first and second filter units 107 . 108 to the photodetectors (optical detectors) 105 . 106 led with downstream photo amplifiers. The photodetectors 105 . 106 are dimensioned so that their electronic bandwidth is greater than the expected bandwidth of the load signal. An intensity of the light propagating across the filter edge, for example linearly polarized light, in the ith measurement channel is given by the following equation (1):

where I (λ) denotes the power density of the light source, R (λ) the reflection spectrum of the built-in, for example as a fiber Bragg grating integrated sensor 303 and T _s (λ) and T _p (λ) represent the spectral transmission of the filter for both main polarization directions. A time-average proportion of the intensity of linearly polarized light of the degree of polarization P on the total intensity Iges is thus given by the following equation:

Assuming a constant power density I (λ) of the light source 101 in the range of the Bragg wavelength λ _B and assuming a spectrally narrow-band sensor, the light intensity at the photodiode can be approximated according to the following equation (3). Φ _i ≈ ((1 - α) · T _{s, i} (λ _B) + α · T _{p, i} (λ _B)) · I (λ _B) · R (λ _B) Δλ (3) where Δλ is a spectral width, ie a half width 404 ( 2 ) of the integrated sensor 303 (Fiber Bragg Grating). From the wavelength-dependent intensities Φ ₁ and Φ _{2, it is} possible to determine via a clear inverse mapping according to the following equation (4). (λ _B , I (λ _B )) = ρ ^-1 (Φ ₁ , Φ ₂ ) (4) the Bragg wavelength λ _{B of} the sensor can be determined. For such a measurement, a unique pre-calibration according to the following equation (5) (Φ ₁ , Φ ₂ ) = ρ (λ _B , I (λ _B )) (5) to be provided.

The at the reflection points described above 102 occurring parasitic reflections lead to an optical background light in the reflection spectrum of the reflected light from the integrated sensor, ie in the sensor reflection response 400 ( 2 ). In this case, deviations in the evaluation of the sensor wavelength can occur. For example, optical backlight may be due to a finite reflection background of the integrated sensor 303 , due to a faulty fiber termination (see 3 ) and / or contaminated fiber connectors. An error caused by such backlight may be approximated by the following equation (6):

An evaluation function of the system can be provided by the relationship (λ _B , I (λ _B )) = ρ ^-1 (Φ ₁ , Φ ₂ ) where ΔΦ _{i is} the background light in the ith measurement channel. Such errors by generally unknown reflection points 102 in the sensor fiber 304 or on other optical components in the fiber optic sensing system are eliminated by the optical compensator according to one or more of the embodiments described herein. Reflections in the fiber can be caused, for example, by soiled fiber plugs, faulty splices, soiled fiber ends, faulty fiber terminations, etc.

In order to avoid measurement errors due to parasitic reflections in a measuring string, an optical compensation device is used, as described below with reference to FIGS 4 and 5 described.

4 shows a block diagram of an optical compensation device 100 according to an embodiment. The optical compensation device is based on the irradiation of light by a first light source 101 and a second light source 101b provided and via appropriate transmission fibers 302 a fiber coupler 301 is supplied. At the output of the fiber coupler 301 is a sensor fiber 304 connected to the integrated sensor 303 contains. Along the optical waveguide arrangement are denoted by reference numerals 102 Reflecting points characterized, which can lead to parasitic reflections. Such reflection sites 102 may be caused by, for example, soiled plugs, faulty fiber termination, and the like.

From the fiber coupler 301 Thus, an optical radiation which outputs the useful signal, ie the sensor reflection response, is decoupled 400 , and contains parasitic reflections. Both signals, ie the useful signal 400 and the interfering signal caused by the parasitic reflections becomes a detector module 104 fed. In the detector module 104 a wavelength spectrum included in the received signal is evaluated. For evaluation of the wavelength contains the detector module 104 a second filter unit 108 , which has a transmission path T variable over the wavelength λ.

Thus, one gets to the second filter unit 108 connected second detector unit 106 a signal which has a center wavelength 403 ( 2 ) of the sensor reflection response 400 reflects. To a sensor reflection response 400 can be obtained as described above with reference to the 1 and 2 described, the emission spectrum of the first light wave 101 (Sensor excitation light source) has a spectral width equal to or greater than the spectral width of the sensor reflection response 400 exhibit. That is, in the optical waveguide (in the sensor fiber) 304 becomes the radiation of the first light wave 101 coupled, wherein the coupled optical radiation through the integrated sensor 303 is modified in a first wavelength range.

The first light source 101 is thus designed to emit optical radiation in the first wavelength range. Furthermore, as in 4 shown the second light source 101b provided which is designed for the emission of optical radiation in the second wavelength range in which the integrated sensor 303 the irradiated optical radiation is not modified or hardly modified.

The fiber coupler 301 is designed for coupling of the first light source 101 and from the second light source 101b emitted optical radiation in the optical waveguide 304 and for decoupling at least a portion of the modified and at least a portion of the unmodified optical radiation. The detector module associated with the fiber coupler 104 is designed to detect both the modified and unmodified optical radiation.

It should be noted here that the second wavelength range is chosen such that it does not match the sensor reflection response 400 ie optical radiation in the second wavelength range is only at the reflection points 102 in the optical measuring system, while optical radiation in the first wavelength range is reflected both by the integrated sensor 303 as well as through the reflection points 102 is modified. Thus, in one of the detector module 104 connected determination unit 109 a comparison can be made between the coupled-out part of the modified optical radiation and the decoupled part of the unmodified optical radiation such that the parasitic reflections can be determined and / or compensated therefrom.

That is, the compensation method according to one of the embodiments described herein is based on that the optical radiation in the first wavelength range and the optical radiation in the second wavelength range are influenced, ie modified, by the impurities in approximately the same way. To further improve the measurement accuracy, it is also possible that of the first light source 101 and / or the second light source 101b emitted optical radiation by means of a reference photodetector 110 to monitor.

In addition, it is possible to modulate the optical radiation prior to coupling in terms of their intensity, for example, to use a lock-in technique. Such intensity modulation may be by a (in 4 not shown) modulation unit at the output of the first light source 101 and / or the second light source 101b to be provided.

As in 4 shown, the detector module 104 Further, a first detector unit 105 comprise the light via a first filter unit 107 receives. The first filter unit 107 has a constant transmission over the wavelength λ and T serves to detect an intensity variation of the detector signal due to parasitic reflections. The for the determination of parasitic reflections 102 used second light source 101b For example, it may be provided as a laser light source which emits optical radiation in a wavelength range of 1310 nm. This wavelength is included in the second wavelength range according to the embodiment described here.

It should be noted here that the second light source 101b optical radiation narrowband or broadband in the sensor fiber 304 can couple. The light propagates through all coupling points as well as over one or more into the sensor fiber 304 integrated sensors 303 to the fiber end (reflection point) 102 , The in the sensor fiber 304 integrated sensor 303 is for that of the second light source 101b emitted light transparent (T ≈ 1). At the impurities (reflection points) 102 reflected light can be guided via passive or active fiber optic elements to an evaluation unit. There, the light in the optical evaluation component is converted into electrical signal. In this case, a fiber Bragg grating evaluation unit as well as a separate evaluation unit, for example connected via a WDM coupler, can be provided.

The photodetectors used are designed so that they have sufficient sensitivity at the wavelength of the light source. In particular, it is possible to use the second light source 101b as a laser, an LED (light emitting diode), an SLD (Superluminlic Diode) or a SOA (Semiconductor Optical Amplifier) parallel to the first light source 101 For example, provided as an ASE (Amplified Spontaneous Emission) light source.

Furthermore, it is possible to use the second light source 101b serial to the first light source 101 to provide, that is, from the second light source 101b emitted radiation is transmitted through the first light source 101 is transmitted, provided that the medium of the designed as a broadband light source first light source 101 sufficiently transparent is sufficient for the light emitted by the additional light source or for the light emitted by the additional light source sufficient amplifying effect.

The light of the additional light source can be in the sensor fiber 304 be coupled. The emitted light power of the additional light source can be detected by means of a reference detector 110 be monitored for example by a monitor photodiode. The additional light source may be during operation of the first light source 101 be switched on.

Alternatively, the additional light source can be operated separately. In one embodiment, it is possible to use the additional second light source 101b to modulate. From a signal measured at the photodetectors and the emitted light output of the light source, the reflection at the fiber end 102 (Reflection point) or at other reference points 102 (Reflection sites) are determined by means of a suitable algorithm. This can be done for all modes of operation (modulated / non-modulated, parallel to the broadband light source, operation without broadband light source). The reflection measured in this way in the measuring strand (in the sensor fiber 304 ) can thus in the calculation of the wavelength or the load state on the integrated sensor 303 be taken into account.

5 shows a block diagram of an optical compensation device 100 according to a further embodiment. It should be noted that components and steps with reference to previous 1 to 4 are not again detailed to avoid a redundant description. Unlike the in 4 shown optical compensation device 100 has the in 5 shown optical compensation device 100 a single light source as a light source arrangement 103 which provides a variable emission spectrum. As in the module 103 displayed, the wavelength-dependent intensity I ₁ or I ₂ can be set, that is, different intensity gradients S1, S2 can be generated over the wavelength λ. This can for example be realized by a variation of the current with which the light source as a light source arrangement 103 is operated. Thus, it is possible to perform a method of compensating for parasitic reflections in the optical waveguide with a single light source.

The light source arrangement 103 is thus adapted to emit optical radiation having a variable wavelength spectrum including at least the first wavelength range and the second wavelength range. The fiber coupler 301 is in turn designed to couple the optical radiation emitted by the light source arrangement into the optical waveguide 304 and for decoupling at least a portion of the modified and at least a portion of the unmodified optical radiation.

In this case, the integrated sensor modifies the coupled-in optical radiation in a first wavelength range, the optical radiation coupled in in the second wavelength range passing through the sensor 303 not or hardly modified. The with the fiber coupler 301 related detector module 104 is designed to detect the modified and unmodified optical radiation. The to the detector module 104 connected determination unit 109 is designed to determine the compensation of the parasitic reflections based on a comparison of the coupled-out modified optical radiation with the decoupled unmodified optical radiation. By in the in 5 shown embodiment provided light source as a light source assembly 103 Thus, it is possible to modify the optical radiation prior to coupling in its wavelength spectrum. This has opposite the in 4 illustrated optical compensation device has the advantage that only a single light source as a light source arrangement 103 must be provided for compensating parasitic reflections at the input of the optical waveguide.

In the detector module 104 is at least one optical filter unit 107 . 108 which is designed for the spectral resolution of the part of the optical radiation modified by the integrated sensor. Furthermore, it is possible to use a reference detector 110 for example, which may be configured as a monitor photodiode. The reference detector 110 is configured to detect a reference signal based on the light source arrangement 103 emitted optical radiation with variable wavelength spectrum.

Thus, a determination of parasitic reflections z. B. at the fiber end and at other locations in the optical fiber can be made by varying the spectral characteristics of the sensor light source. The light source couples broadband light with a spectrum S1 into the measuring fiber. The light propagates over all coupling points as well as over the sensor element integrated in the measuring fiber 303 (one or more) to the fiber end. The sensor element 303 This can be done by the light source as a light source arrangement 103 reflect emitted light narrowband. At the with a reference number 102 in the 5 characterized places parasitic reflections may occur due to the incident light. Subsequently, the measuring fiber is made using the same light source as the light source array 103 Broadband irradiated with a second spectrum S2. Assuming a nearly ideal measuring fiber, a characteristic wavelength dependent relationship is given by the following equation (7):

In a real measuring fiber occurring parasitic reflections can be considered by the following equation (8):

Depending on the emitted spectrum of the light source 103 and the parasitic reflections at the reflection sites 102 in the measuring fiber, the components denoted by a and b in the above equation vary. In the filter-based measuring system, therefore, the Bragg wavelength λ _{B of} the integrated sensor 303 determined from the above ratio according to equation (8) by means of a linearization or a look-up function. Variations in the parameters a and b contained in the above equation thus lead to a variation in the wavelength determination or to a deviation in the obtained wavelength λ _B.

With a controlled change of the light source from the light source arrangement 103 emitted light source spectrum can thus from a measured variation by means of a suitable algorithm an estimate of the parasitic reflections at the reflection sites 102 be determined. From this estimate can be compensation values for the at the two photodetectors 105 . 106 detected signals are detected. By applying these compensation values to the signals measured in both light source spectrums, such an error can be minimized.

A variation of the emission spectrum of the light source as a light source arrangement 103 can be realized in a broadband ASE (Amplified Spontaneous Emission) light source, for example, by changing the pump power. Further realizations for ASE light sources can be provided by using fiber optic switches, switchable filters (long period FBG) or thin film filters.

Instead of a second generated signal spectrum, for example, the temporal change of the light source spectrum during turn-off / turn-on, for example, in an ASE light source, are used. Similarly, other broadband light sources, such as super-light emitting diodes, can be used which alter their emission behavior by varying the pumping current or by changing the temperature.

6 FIG. 10 is a flowchart illustrating a method for compensating parasitic reflections in an optical waveguide. FIG. In a block 501 the procedure is started. Coupling of optical radiation into the optical waveguide takes place in one block 502 , The optical waveguide has at least one integrated sensor 303 in which the coupled-in optical radiation is modified by the integrated sensor in a first wavelength range and is not or hardly modified in at least one second wavelength range. In another block 503 At least a portion of the modified and at least a portion of the unmodified optical radiation is coupled out. Finally, the decoupled modified optical radiation is compared with the decoupled unmodified optical radiation (block 504 ). Herein, according to typical embodiments that may be combined with the embodiments described herein, the "sensor light" and the "AFTC light" (automated fiber termination compensation), that is not or hardly modified by the sensor Light, be injected simultaneously or sequentially.

By the one in the block 504 carried out comparison, it is then possible to detect the parasitic reflections at different reflection sites 102 in the fiber-based optical measuring system may occur to compensate. The procedure ends in a block 506 ,

Although the present invention has been described above by means of typical embodiments, it is not limited thereto, but modifiable in many ways. Also, the invention is not limited to the applications mentioned.

Claims (10)

A method for compensating parasitic reflections in an optical waveguide, comprising: Coupling optical radiation into the optical waveguide, which has at least one integrated sensor, wherein the coupled optical radiation is modified by the integrated sensor in a first wavelength range and is not modified in at least a second wavelength range; Decoupling at least a portion of the modified and at least a portion of the unmodified optical radiation; Comparing the decoupled modified optical radiation with the decoupled unmodified optical radiation; and Compensating the parasitic reflections based on the comparison. The method of claim 1 wherein the step of comparing the extracted modified optical radiation with the extracted unmodified optical radiation comprises one of the group consisting of wavelength comparison, intensity comparison, spectral history comparison, polarization state comparison, and any combination thereof , A method according to claim 1 or 2, wherein the optical radiation is modified prior to coupling in its wavelength spectrum. Method according to at least one of claims 1 to 3, wherein the optical radiation is intensity-modulated prior to coupling. A device for compensating parasitic reflections in an optical waveguide with at least one integrated sensor, wherein the sensor modifies optical radiation in a first wavelength range and does not modify it in at least a second wavelength range, the device comprising: a light source assembly configured to emit optical radiation having a variable wavelength spectrum comprising at least the first wavelength range and the second wavelength range; at least one arrangement that is designed to couple the optical radiation emitted by the light source arrangement into the optical waveguide and to decouple at least part of the modified and at least part of the unmodified optical radiation; at least one detector associated with the array and configured to detect the modified and unmodified optical radiation; and a determination unit connected to the detector, which is designed to determine the compensation of the parasitic reflections on the basis of a comparison of the coupled-out modified optical radiation with the decoupled unmodified optical radiation. The apparatus of claim 5, wherein the at least one array comprises a fiber coupler and / or wherein the device further comprises at least one optical filter unit configured to spectrally filter the portion of the optical radiation modified by the integrated sensor. Apparatus according to claim 5 or 6, further comprising a modulation unit adapted to modulate the optical radiation emitted by the light source assembly. An apparatus according to any of claims 5 to 7, further comprising a reference detector configured to detect a reference signal based on the variable wavelength spectrum optical radiation emitted by the light source array. The apparatus of claim 5, wherein the light source assembly comprises a first light source configured to emit optical radiation in the first wavelength range and at least one second light source configured to emit optical radiation in the second wavelength range; wherein the at least one arrangement is designed for coupling the optical radiation emitted by the first and the second light source into the optical waveguide, and / or wherein the at least one arrangement comprises a fiber coupler; and / or wherein the at least one arrangement comprises a fiber coupler and the detector is in communication with the fiber coupler. The apparatus of claim 6, further comprising at least one optical filter unit configured to spectrally filter the portion of the optical radiation modified by the integrated sensor.

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