WO2015176906A1 - Interféromètre à guide d'ondes optique pour mesurer une information spectrale - Google Patents

Interféromètre à guide d'ondes optique pour mesurer une information spectrale Download PDF

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Publication number
WO2015176906A1
WO2015176906A1 PCT/EP2015/058746 EP2015058746W WO2015176906A1 WO 2015176906 A1 WO2015176906 A1 WO 2015176906A1 EP 2015058746 W EP2015058746 W EP 2015058746W WO 2015176906 A1 WO2015176906 A1 WO 2015176906A1
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Prior art keywords
optical
signal
interferometer
coupler
waveguide
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PCT/EP2015/058746
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German (de)
English (en)
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Max Ralf RÖSSNER
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Technische Universität München
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35303—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using a reference fibre, e.g. interferometric devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G01J3/0218—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using optical fibers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/45—Interferometric spectrometry
    • G01J3/453—Interferometric spectrometry by correlation of the amplitudes
    • G01J3/4531—Devices without moving parts
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K5/00—Measuring temperature based on the expansion or contraction of a material
    • G01K5/48—Measuring temperature based on the expansion or contraction of a material the material being a solid
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
    • G02B6/29382—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM including at least adding or dropping a signal, i.e. passing the majority of signals
    • G02B6/29383—Adding and dropping
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02062—Active error reduction, i.e. varying with time
    • G01B9/02064—Active error reduction, i.e. varying with time by particular adjustment of coherence gate, i.e. adjusting position of zero path difference in low coherence interferometry
    • G01B9/02065—Active error reduction, i.e. varying with time by particular adjustment of coherence gate, i.e. adjusting position of zero path difference in low coherence interferometry using a second interferometer before or after measuring interferometer

Definitions

  • the present invention is in the field of optical measurement systems and relates to a waveguide interferometer for measuring spectral information.
  • Waveguide interferometers such as fiber interferometers, are used in the art for measuring spectral information, such as the Bragg wavelength of a fiber Bragg grating (FBG) grating sensor
  • FBG fiber Bragg grating
  • Fiber interferometer for measuring the Bragg wavelength of an FBG sensor is described in the article "Passive, light intensity-independent interferometric method for flat Bragg grating interrogation", MD Todd et al., ELECTRONICS LETTERS, 1999, Vol. 22, p. 1970.
  • the fiber interferometer described therein comprises a 2x2 fiber coupler and a 3x3 fiber coupler interconnected by two optical fiber interferometer arms.
  • FIG. 1 shows a schematic structure of an FBG sensor 10, which contains a Bragg grating 12 with a specific grating constant ⁇ .
  • a narrow-band optical signal 16 to be measured is reflected, which has a spectral maximum at the Bragg wavelength ⁇ .
  • the optical signal 16 may also be a broadband signal transmitted by the FBG sensor 10, which has a narrowband spectral minimum at the Bragg wavelength ⁇ .
  • the Bragg wavelength ⁇ is approximately proportional to the lattice constant ⁇ and to the effective refractive index ne ff , which change in accordance with the stress state or an elongation or a temperature change of the FBG sensor 10.
  • strain sensitivity By determining the wavelength of the intensity maximum of the optical signal 16, known interaction (hereinafter referred to as "strain sensitivity") between the Change of an external influencing variable, z. As the temperature or the mechanical force, and the change of the Bragg wavelength ⁇ the external influence variable in the vicinity of the FBG sensor 10 can be determined.
  • the optical signal 16 can be supplied to the above-mentioned fiber interferometer, wherein the optical signal 16 is split by means of said 2x2 fiber coupler into two sub-signals which are respectively supplied to one of the two interferometer arms.
  • the two sub-signals pass through a different optical path length and interfere with each other at said 3x3 fiber coupler.
  • From the 3x3 fiber coupler ler three interference signals run on different fibers and are detected with associated optical detectors.
  • the Bragg wavelength ⁇ and thus the strain state of the FGB sensor 10 or its temperature can be determined.
  • known strain sensitivity or temperature sensitivity can be determined by measuring the change in the Bragg wavelength ⁇ an associated temperature change.
  • the absolute temperature in the vicinity of the FBG sensor 10 can also be determined via the measurement of the Bragg wavelength ⁇ .
  • the measurement method described has the disadvantage that the measurement can be falsified when the ambient conditions of the interferometer change. For example, a temperature change in the vicinity of the interferometer may result in a change in the path length difference of the interferometer arms. Due to the resulting changes in the interference signals, a temperature change in the environment of the sensor would be erroneously detected.
  • a stabilized fiber interferometer which avoids the above drawback is disclosed in the article "Stabiised 3x3 Coupler-based Interferometer for the Demodulation of Fiber Bragg Grating Sensors", Yi Jiang, Optica! Engineering, 2008, Vol. 47 (1).
  • This interferometer includes a 2x2 fiber coupler and a 3x3 fiber coupler interconnected by two interferometer arms, and a piezoelectric driven phase shifter is provided in an interferometer arm which can stabilize the interferometer by means of feedback and control circuitry.
  • FIG. 6 Another example of a fiber interferometer device capable of measuring the signals of multiple FBG sensors and multiple reference FBG sensors is disclosed in US 6,674,928 B2.
  • the device comprises a tunable filter, the two Interferometerarmen is connected upstream and in response to a control signal allows a serial detection of the signals and the reference signals using three common optical Detelctoren.
  • another optical detector is provided for generating a sample signal for an analog-to-digital conversion.
  • This object is achieved by a waveguide interferometer according to claim 1 and a method according to claim 29.
  • the waveguide interferometer according to the invention is used to measure a spectral information of an optical signal and comprises: an optical signal input for the optical signal, a at least two optical interferometer arms, which have a different optical path length and can each be traversed by a portion of the optical signal, a first NxM Waveguide coupler, where N> 2 and M> 3, which is waveguide-optically connected to the interferometer arms and adapted to
  • a first and a second optical detector for detecting in each case one of the two outgoing partial signals or a signal derived from the respective partial signal, an optical reference input for an optical reference signal, which is so waveguide-optically connected to the first coupler or with an additionally provided second KxL waveguide coupler, wherein K> 2 and L> 3, that
  • the optical interferometer can each be traversed by a proportion of the reference signal
  • At least two portions of the reference optical signal each enter the first coupler or the second coupler from an associated one of the two interferometer arms and interfere with each other in the first and second couplers, respectively, with at least a portion of the intensity of said first and second couplers, respectively incoming reference signal components is divided into at least two outgoing reference sub-signals, and a first and a second optical reference detector for detecting each one of the two outgoing reference sub-signals or a signal derived from the respective reference sub-signal.
  • the present invention is not limited to the optical fibers described above as a waveguide, but may alternatively or additionally be performed with other waveguides.
  • An example is waveguides which are incorporated in substrates or in optical layers applied thereto, for example by means of a lithographic process.
  • a “waveguide-optical connection” in the sense of the present description refers to the connection between different sections of the same optical waveguide or a connection between waveguide sections of different optical waveguides, the connection having a partial or complete transition of optical intensity from one of the connected waveguide sections to the other
  • An example of a waveguide optical connection is a fiber optic connection.
  • a signal input or reference input and associated optical detectors or reference detectors are provided.
  • these different signals can be fed to the waveguide interferometer simultaneously and continuously and they can also be simultaneously and continuously detelcted.
  • the interferometer arms are simultaneously and continuously traversed by the optical signal and the reference signal.
  • no interruption of the measurement and no active switching is necessary, but it can be done simultaneously for detection and continuously.
  • the waveguide interferometer according to the invention therefore allows a comparatively high measuring bandwidth, which indicates the frequency up to which temporal signal changes can still be measured.
  • the first waveguide coupler has at least three outputs on the side facing away from the interferometer arms, it is possible for energy conservation reasons that the spectral transmission profiles resulting from the interference for the at least two outgoing component signals at the coupler outputs are also of the same size maximum transmission have a spectral offset of less than half a period or interference period.
  • the spectral position of a narrow-band optical signal can be unambiguously determined even with the aid of two optical detectors, even if the spectral position shifts over one or more interference periods of the spectral transmission profiles at the coupler outputs.
  • the information of the spectral position of the signal would pass through the minima and maxima of the resulting from the interference spectral transmission profiles, because - starting from a local minimum or maximum - based on a It can not be detected if the change in intensity is based on a shift to a larger or a smaller wavelength.
  • the derivatives of the spectral transmission profiles on the wavelength for the at least two outgoing partial signals at any spectral position are simultaneously zero.
  • the spectral position of the signal or reference signal can furthermore be unambiguously determined.
  • the possible measurement range or the dynamic range of the interferometer due to the first NxM waveguide coupler, with N> 2 and M> 3 is not limited to an interference period, but is independent of this and can be many times, for example, 10 or 100 -Fold up to 1000 times, be bigger.
  • the dynamic range indicates the ratio between the largest and the smallest measurable value and the measuring range that measurement range within which the measurement deviations lie within predetermined predetermined limits.
  • the spectral length of an interference period depends on the path length difference and can be adjusted via this.
  • a short period length leads to a comparatively sensitive detection of a wavelength change, whereas a large period length leads to a comparatively large measuring range in which wavelength changes can be detected. Note that the range of measurement given here should not be confused with the wavelength range given by the product of the period length and the maximum number of counts or cycles counted.
  • the waveguide interferometer further comprises a third optical detector and / or a third optical reference detector for detecting in each case a further signal which is based on the optical signal or on the optical reference signal.
  • a third optical detector and / or a third optical reference detector for detecting in each case a further signal which is based on the optical signal or on the optical reference signal.
  • the further detector and / or reference detector can be connected so that it detects an outgoing partial intensity that has not interfered and therefore independent from its spectral position and independent of the path length difference in the interferometer at least approximately proportional to the intensity of the light source behaves.
  • the intensity of the light source can be determined solely by means of this additional detector or reference detector. If the light source intensity is detected on the basis of the expiring partial intensities after the interfering, then a detector is necessary at each coupler output on which a partial intensity expires, ie at least three.
  • the waveguide interferometer according to the invention is preferably set up to measure the Bragg wavelength of an FBG sensor, wherein the waveguide interferometer is preferably connected to the FBG sensor in a waveguide-optical manner.
  • the waveguide interferometer according to the invention can also be set up for an operation in which the reference signal is the signal of an athermal reference FBG sensor or the signal is a wavelength-stable reference source.
  • the waveguide interferometer according to the invention may also be adapted for an operation in which both the optical signal and the optical reference signal are the signals of an FBG sensor, wherein a ratio between two Bragg wavelengths of the respective FBG sensors is measured.
  • this measurement distortion results for both measurements in the same or approximately the same degree. If only one ratio, for example a temperature ratio, is measured, then the two measurement distortions compensate each other so that the measured ratio corresponds to the actual ratio between the respective spectral information or temperatures.
  • the signal input and the reference input can be formed by the same optical waveguide or formed by different optical waveguides.
  • the optical signal to be measured and the optical reference signal can be supplied to the waveguide interferometer through the same waveguide or through different waveguides at different positions.
  • the optical paths between the signal input and the detectors and / or between the reference input and the reference detectors can be at least 70%, preferably at least 90%, particularly preferably completely waveguide integrated run. Such a structure is less susceptible to interference and stable.
  • the first NxM waveguide coupler is at least one 3x3 waveguide coupler (N> 3 and M> 3).
  • a third optical interferometer is further provided, wherein all three interferometer have a different Liehe optical path length. This results in the output of the coupler interferometric spectral transmission profiles each having a first spectral period and a second spectral period, wherein the first spectral period is greater than the second spectral period. Due to the course according to the first period, a spectral position can first be determined roughly and globally. Subsequently, the position can be accurately determined on the basis of the course according to the second period.
  • an optical switch for interrupting the optical connection may also be provided in one of the three interferometer arms. With three interferometer arms it may happen that the minima and maxima of transmission profiles of different outputs coincide in some places. Due to the switch, after the first coarse determination of the spectral position, an interferometer arm can be interrupted so that new transmission profiles result at the outputs of the coupler without coincident minima and maxima. A tracking of the spelctral position by means of a counting of the passed periods is thus readily possible again.
  • the waveguide interferometer according to the invention may further comprise in at least one interferometer arm a compensating means, in particular an optically integrated phase modulator, a fiber stretcher or a delay line, in order to change the optical path length of at least one interferometer arm.
  • a compensating means in particular an optically integrated phase modulator, a fiber stretcher or a delay line, in order to change the optical path length of at least one interferometer arm.
  • the measurement of the reference optical signal may be used to compensate for the effects on the measurement with a change in optical path length.
  • optical detectors and / or the optical reference detectors may, for example, be photodiodes. This allows a simple and inexpensive construction of the waveguide interferometer.
  • the first and the second waveguide coupler are in each case arranged opposite one another. lying ends of the interferometer arms waveguide optically connected to these.
  • This structure corresponds to the structure of a Mach-Zehnder interferometer, in which the signal splitting and the interferometric Caribbean Stirlirung done in different waveguide couplers.
  • both the signal input and the reference input can be connected to the second coupler so that both the stated components of the signal and the stated components of the reference signal from the second coupler run into the respectively associated interferometer arms and in each case in the first Couplers interfere with each other.
  • the signal input to the second coupler and the reference input to the first coupler may be connected, so that the optical signal enters the second coupler and enter said portions of the signal from the second coupler in the respectively associated interferometer arms and interfere with each other in the first coupler , And so that the optical reference signal enters the first coupler and said portions of the reference signal from the first coupler enter the respectively associated interferometer arms and interfere with each other in the second coupler.
  • the optical signal and the optical reference signal pass through the interferometer in opposite directions.
  • reflectors are provided at the ends of the interferometer arms, and both the components of the signal and the components of the reference signal pass from the first coupler into the respectively associated interferometer arms, are each reflected by an associated reflector, then run out of their associated interferometer arms in the first coupler and interfere in the first coupler.
  • the structure of this embodiment corresponds to the construction of a Michelson interferometer.
  • the three detectors may be connected to respective outputs of the first coupler which are respectively opposed to the interferometer arms.
  • the signal input may be connected to the second or first coupler, wherein one of the three detectors may be connected to an output of the second and first couplers, respectively, which opposes and resides on the signal input Coupler side as the interferometer is located.
  • the three reference detectors may, for example, be connected to associated outputs of the first or second coupler, the outputs being opposite to the interferometer arms, respectively.
  • the incoming into the first and second coupler intensity of the components of the optical reference signal is divided into three reference sub-signals, which leak on an associated output from the first and the second coupler and run to an associated reference detector.
  • the reference input may be connected to the second or to the first coupler, wherein one of the three reference detectors is connected to an output of the second and the first coupler, wherein the output is opposite the reference input and the output is on the same coupler side as the interferometer arms.
  • the signal input together with a detector or a reference detector may be connected to an output of the first or second coupler so that one of the partial signals or reference partial signals to be detected leaves the first or second coupler through the same output the optical signal enters the first and second coupler.
  • the reference input can be connected together with a detector or a reference detector to an output of the first or the second coupler, so that one of the partial signals or reference partial signals to be detected leaves the first or second coupler through the same output, through which the optical reference signal in the enters first and second coupler.
  • a detector and a reference detector may be connected in common via a WDM (Wavelength Division Multiplexing) coupler, preferably a WDM waveguide coupler, to an associated output of the first coupler. If the optical signal and the optical reference signal have a different wavelength, the associated outgoing partial signals or reference partial signals can be separated by means of the WDM coupler and fed to the associated detectors or reference detectors.
  • WDM Widelength Division Multiplexing
  • the waveguide interferometer according to the invention can furthermore be used for Fourier transform (FT) triangulation, the optical path length being measured on an interferometer arm by means of an actuating means, in particular an optically-integrated phase modulator or preferably a fiber-stretcher or a "delay line" is variable over a predetermined Wegdorfnunter Kunststoff.
  • said reflectors may be Faraday reflectors.
  • the resulting spectral transmission profile at the outputs of the waveguide coupler may deviate from the desired "striped" interference profile, in particular the desired "slice visibility" in the spectral transmission profile may be impaired.
  • the return polarization reflected by the Faraday reflector can be rotated by 90 degrees to the polarization before reflection, thereby compensating for an impairing polarization change that can take place on the way to the Faraday reflector on the return path. It can thereby be ensured that the interfering signal components have a polarization in which the strip visibility is maximum.
  • polarization-maintaining waveguide connections and couplers are provided. This ensures that the polarization of the optical signal and of the optical re- signal does not rotate uncontrolled in the waveguide interferometer and high fringe visibility is present in the spectral transmission profile.
  • the spectral offset between the transmission profiles of the first and / or the second coupler preferably being ⁇ P / 2, more preferably ⁇ 7P / 16, especially ⁇ 6P / 16.
  • the derivative (according to the wavelength) of transmission profiles staggered in this way is simultaneously zero at no spectral position, so that the spectral position remains determinable even with a change over an interference minimum and / or maximum.
  • the present invention further comprises a method for measuring a spectral information of an optical signal by means of a waveguide interferometer according to one of the aforementioned embodiments, the method comprising the following steps:
  • the signal and / or the reference signal may, for example, be unpolarized optical signals. This can prevent the deterioration of the striped visibility, which can occur when using differently polarized signals.
  • the optical signal and the reference signal are preferably fed to the waveguide interferometer at the same time and the outgoing partial signals are detected simultaneously with the outgoing reference partial signals.
  • the optical signal and the reference signal may have a different wavelength.
  • the optical signal and the reference signal can leave the waveguide interferometer through the same inputs and outputs, whereby due to the different wavelengths after the leak, a separation can be made, for example by means of a WDM oppler.
  • the method can furthermore comprise a pulsed and simultaneous illumination of a plurality of FBG sensors, wherein the optical signal is a pulsed signal, and at least some of the pulses originate from different FBG sensors.
  • This embodiment furthermore comprises an assignment of the partial signal pulses detected with the detectors to their associated FBG sensors, wherein the assignment takes place on the basis of different detection times. This embodiment thus allows using temporal multiplexing to measure the signals of multiple FBG sensors.
  • a plurality of spectral information of a plurality of optical signals is measured by means of a plurality of waveguide interferometers according to one of the aforementioned embodiments, the optical waveguide interferometers being supplied with associated optical reference signals originating from the same reference signal source.
  • This embodiment may be used, for example, in the context of spatial multiplexing of the optical signal and / or the reference optical signal using multiple waveguide interferometers. Because the waveguide interferometers can be comparatively inexpensive due to their simple construction, only a small additional expenditure is incurred when using a comparatively cost-intensive optical source. With the help of spatial multiplexing, several optical sensors can be read out efficiently and inexpensively.
  • a change in the wavelength of the reference signal and / or the optical signal may further include a counting in of the interference periods, the interference periods in the said wavelength change being in the intensity detected by the detectors and / or the reference detectors result.
  • the determination of a wavelength can also take place on the basis of the assignment of the detected intensity to a specific interference period.
  • the wavelength determination can also be determined solely on the basis of the counting in which the accuracy of the wavelength determination corresponds to one third of the length of an interference period. By adjusting the optical path length difference, the length of an interference period can be reduced and the measurement resolution can be increased. Due to the wavelength determination via counting, the measurement of the spectral position can be carried out purely digitally - without a quantitative intensity determination.
  • the method further comprises first measuring spectral information, wherein the first measurement is based on the interference of three signal components, each having passed through different interferometer arms with different optical path lengths, and a second measurement of spectral information, the second one Measuring based on the interference of two signal components, which have each passed through different interferometer arms with different optical path lengths.
  • the path length difference of the waveguide interferometer and the wavelength of the optical signal can each be unambiguously determined and ambiguities due to periodic interference behavior can be avoided. This makes it possible to unambiguously and absolutely determine a spectral position of a wavelength to be measured, which can change.
  • FIG. 1 shows a schematic view of an FBG sensor, for providing an optical signal which can be measured with a waveguide interferometer according to the invention
  • FIG. 2 shows a schematic structure of a waveguide interferometer according to the invention according to a first embodiment
  • FIG. 8 shows the spectral transmission for three outputs of a waveguide coupler of the waveguide interferometer according to the fifth embodiment of FIG. 7, FIG. 8 shows the schematic structure of a waveguide interferometer according to the invention.
  • Figures 9 to 12 according to the invention waveguide interferometer according to a sixth, seventh, eighth and ninth embodiment, each of which is suitable for a Fourier transform (FT) -Spektrometrieflop, and
  • FT Fourier transform
  • Figure 13 shows various functional relationships that result in the determination of the spectrum of an optical signal using FT spectrometry.
  • FIG. 2 shows a fiber interferometer 18 according to a first embodiment of the invention.
  • the fiber interferometer 18 comprises a first fiber coupler 20 and a second fiber coupler 22, each of which is 2x3 fiber couplers and which are fiber optically interconnected via first and second interferometer arms 24 and 26, respectively.
  • the optical path length difference between the first and second interferometer arms 24 and 26 is ⁇ 1.
  • the first coupler 20 On a side opposite to the interferometer arms 24, 26, the first coupler 20 has three fiber outputs which are each fiber optically connected to first, second and third optical detectors 28, 30 and 32, respectively.
  • the second coupler 22 on one side, which faces the interferometer arms 24, 26, has three outputs which are each fiber optically connected to a first, a second and a third optical reference detector 34, 36 and 38, respectively.
  • the fiber interferometer 18 further comprises a signal input 40 and a reference signal input 42, wherein the signal input 40 is fiber-optically connected to an output of the second coupler 22 via a first optical circulator 44 and the reference signal input 42 via a second optical circulator 46 to an output of the first Fiber coupler 20 is fiber optically connected.
  • 3x3 fiber couplers may also be used. All in all, however, the 3x3 fiber couplers only need five outlets. In principle, it is possible to use a 3x3 coupler in each embodiment of the present invention instead of a 2x3 coupler.
  • the signal input 40 is supplied with an optical signal 16.
  • the optical signal 16 may be, for example, the narrow-band signal of an FBG sensor 10 shown in FIG. 1 with an intensity maximum at the Bragg wavelength ⁇ .
  • the optical signal 16 enters the second coupler 22 via the first circulator 44.
  • the fiber optic coupler output on which the optical signal 16 enters and the opposing fiber optic coupler outputs which form the inputs of the two interferometer arms 24 and 26 are connected or coupled by a fiber optic coupling connection.
  • the optical fiber of an interferometer arm input is identical to one of the two optical fibers of said opposing coupler outputs. Accordingly, the coupling of the three fiber optic outputs of the second coupler 22 (ie, the incoming optical signal output 16 and the two opposing outputs to the interferometer arms 24 and 26) is coupled by a coupler internal connection of two or three different optical fibers. Due to the coupling, part of the incoming intensity of the optical signal 16 passes into or is coupled into at least one other optical fiber.
  • the two signal components respectively pass through the associated one of the interferometer arms 24 and 26 and enter the first coupler 20.
  • the signal components entering the first coupler 20 have traveled through different path lengths and are therefore phase-shifted relative to one another by a corresponding phase difference ⁇ .
  • the phase-shifted signal components are brought together so that they can interact with each other or interfere.
  • the first coupler 20 is also inserted into the first coupler 20. fende optical intensity of the incoming phase-shifted signal components divided into three opposite outputs, but with the difference that not one signal but two signal components arrive and run out not two but three signal components.
  • the expiring from the first coupler 20 sub-signals are each detected by an associated one of the optical detectors 28, 30 and 32, wherein the partial signal detected by the third optical detector 32 previously passes through the second circulator 46, to which the reference input 42 is connected.
  • the optical detectors 28, 30 and 32 are preferably - as with the optical reference detectors 34, 36 and 38 - photodiodes which output an electrical signal which is proportional or at least approximately proportional to the incident on the detector optical intensity.
  • FIG. 3 shows the profiles T 1, T 2 and T 3 of the spectral transmission for the outputs of the first fiber coupler 20. According to the spectral transmission profiles T 1, T 2 and T 3, the optical intensity from the first coupler 20 enters or is fed into the associated outputs.
  • the course of the spectral transmission profiles Tl, T2 and T3 shown results from the path length difference ⁇ 1 between the interferometer arms 24 and 26, which determines the period P, with which each of the transmission profiles Tl, T2 and T3 along the spectral wavelength axis and spectral offsets caused by the coupler 20.
  • the spectral offsets between the spectral transmission profiles Tl, T2 and T3 occur for reasons of energy conservation during the transition of the optical intensity in the outputs of the first fiber coupler 20. If, as is preferably the case with the first fiber coupler 20, exactly three partial signals can exit from the first coupler 20 and the maximum values of the associated spectral transmission profiles T1, T2 and T3 are equal, then the spectral offset between the respective spectral Transmission profiles Tl, T2 and T3 - as shown in Figure 3 - a third of the period P. In a 2x2 coupler, however, the spectral offset would be at half a period P.
  • the spectral offset can be less than half a period P, namely, when a part of the intensity is transferred to another coupled optical fiber.
  • the intensity that expires in this fiber or in this output does not necessarily have to be detected.
  • FIG. 3 further shows the spectral intensity or power density profile of an exemplary optical signal 16 which corresponds to the signal of an FBG sensor having a Bragg wavelength ⁇ of 1.55 ⁇ .
  • the optical detectors 28, 30 and 32 each detect the intensity on an associated output of the coupler 20.
  • the associated spectral transmission profiles or transmission profiles T1, T2 and T3 are shown in FIG. It can be seen from FIG. 3 that in the narrow-band optical signal 16 with the Bragg wavelength of 1.55 ⁇ , the intensity detected by the first and third detectors 28 and 32 is approximately the same and that detected by the second detector 30 Intensity is minimal. If the Bragg wavelength ⁇ shifts to the spectral position of the wavelength ⁇ shown in FIG. 3, for example due to a temperature change in the surroundings of the FBG sensor 10, then that of the second and third detectors 30 and 32, respectively detected intensity about the same size and detected by the first detector 28 intensity minimal.
  • the intensities detected by the detectors 28, 30, and 32 are repeated after each pass of one period.
  • FIG. 3 it can be seen that due to the spectral offset of one third of a period P there are no spectral positions at which two or three transmission profiles T1, T2 and T3 simultaneously have a local extremum (local minimum or maximum) or at which the first derivative (in terms of wavelength) of two or three transmittances T1, T2 and T3 is zero at the same time.
  • the optical path length difference ⁇ 1 in the interferometer can be increased.
  • the period P of the transmission profiles Tl, T2 and T3 decreases and a spectral wandering of the Bragg wavelength ⁇ to be detected causes a faster change in the intensities at the detectors 28, 30 and 32.
  • the determination of a spectral position can also be based on the assignment to a specific wavelength or period interval, which is for example between local minima and / or maxima of the same or different transmission characteristics Tl, T2 and T3, with the accuracy of a period P or a fraction of a period.
  • the determination of the wavelength position is thus purely digital possible. Since the period P is dependent on the path length difference ⁇ 1, the accuracy or resolution of the measurement can be improved by changing ⁇ 1. Starting from a known initial counter reading, the actual spectral position of an optical signal 16 can therefore be determined absolutely by counting the period cycles.
  • the following describes how the initial count and the initial spectral position can be determined, for example, after switching on the measuring system.
  • the signals at the detectors of the interferometer are at least approximately proportional to ⁇ 1 + cos ( ⁇ - ⁇ 1 + ⁇ p) j, where ⁇ 1 is the path length difference between the interferometer arms, ⁇ is the wavelength of the input signal and ⁇ is a constant phase shift.
  • the detected intensities can each be I 28 , I30 and Z, which are the following Relationships with the intensity I 0 of the incoming optical signal 16 may be related:
  • the determination of the wavelength / path length difference can be from the value of cos- terms with knowledge of the path length difference / the wavelength can not be made unambiguously, if the ratio ⁇ is not known. So there is an ambiguity because different values for the ratio ⁇ ⁇ lead to the same value of the cos term.
  • two optical reference signals with different and respectively known wavelength for example, with the Bragg wavelengths ⁇ ⁇ 1 and ⁇ ⁇ 2 .
  • two athermal fiber Bragg gratings may be used as reference FBGs or other stable wavelength reference sources.
  • One of these reference FBGs may also be provided for providing the reference optical signal 48 described below, and may be connected to the reference signal input 42 for this purpose.
  • the other reference FBG can be connected to the signal input 40 and can later be replaced by a measuring FBG.
  • the difference between the two wavelengths ⁇ ⁇ can be chosen or set so small that ensures that both wavelengths ⁇ ⁇ 1 and ⁇ ⁇ 2 less than half period are spaced.
  • the phase difference ⁇ is smaller than the phase difference ⁇ can be represented by the following equation (1):
  • the path length difference ⁇ 1 of the interferometer can be uniquely determined by the following equation (2):
  • equation (2) can unambiguously determine the path length difference ⁇ 1 of the interferometer.
  • an unknown wavelength ⁇ of an optical signal can also be determined unambiguously.
  • the path length difference ⁇ 1 of the interferometer can be slightly adjusted and the optical signal detected for two different path length differences Ali and ⁇ 1 2 .
  • ⁇ ⁇ 4 - ⁇ 3 can be determined unambiguously from such values for ⁇ 3 and ⁇ 4 , which can be uniquely determined, for example, from one of the following intervals: [0; ⁇ ], [ ⁇ ; 2 ⁇ ], [ 2TT; 3TT], ..., [ ⁇ ; ( ⁇ + 1) ⁇ ].
  • This procedure in which an initial count by means of a separate and unique determination of ⁇ 0 and ⁇ 1 or ⁇ 1 1; ⁇ 1 2 can be made, for example, as an initialization procedure once after switching on the measuring system. Subsequently, it is possible to change to an operating mode for one or more measurements. With this approach, it is possible to capture absolute temperatures, not just temperature changes.
  • an optical reference signal 48 can be supplied to the fiber interferometer 18 at the reference signal input 42.
  • the optical reference signal 48 which is the interferometer 18 in the opposite direction to the optical one Signal 16 passes, be measured accordingly by means of the optical reference detectors 34, 36 and 38.
  • the optical signal 48 can be, for example, the signal of an athermal reference FBG or a narrowband intensity signal of a wavelength-stable optical source.
  • the wavelength of the reference signal 48 is known. If the interferometer 18 is disturbed by external influences, for example due to a change in temperature, then the optical path length ⁇ 1 within the interferometer 18 may change, resulting in changed spectral transmission profiles T1, T2 and T3 at the outputs of the coupler 20. In consequence, an apparent change of the spectral position of the Bragg wavelength ⁇ is determined by means of the detectors 28, 30 and 32, which is not really based on a change of the optical signal 16 to be measured, but on an altered interferometer 18.
  • the measurement correction using the reference measurements can be done in two steps as follows:
  • the detectors 34, 36 and 38 of Figures 2, 5, 1, 9, 11 (but not the detectors 38 of Figures 4, 6, 10, 12) provide signals approximately proportional to the term
  • the actual path length difference ⁇ 1 can be determined from the measured detector signal.
  • detectors 28, 30 and 32 of Figures 2, 5, 7, 9, 11 (but not the detectors 32 of Figures 4, 6, 10, 12) provide signals approximately proportional to the term
  • the wavelength ⁇ to be measured can be determined from the measured detector signal.
  • the remaining over-determination can also be used to reduce remaining statistical measurement errors by averaging.
  • the algorithm described above can not determine in which interferometer period the optical signal or the optical reference signal lies. However, this is accomplished as described by counting over multiple periods of interference.
  • This correction has the advantage that it can be carried out in a simple manner following the detection with the detectors 28, 30 and 32 and the reference detectors 34, 36 and 38.
  • the optical signal can be measured continuously and without interference, without any active optical elements, e.g. corrector corresponding switch to be required in the interferometer 18.
  • Active optical elements are in particular those elements which change an optical property in response to an electrical input. An interruption for the purpose of a correction is likewise not necessary.
  • Another possibility of measurement correction in the event of interference of the interferometer is to use the electrical detection signals of the reference detectors 34, 36 and 38 for feedback.
  • a compensating means (not shown) provided in at least one interferometer arm 24, 26 can be controlled.
  • the compensation means may be formed for example by an optically integrated phase modulator, a fiber stretcher or a delay line.
  • the delay line is particularly advantageous since it can be used to implement comparatively long path length differences.
  • the optical path length difference ⁇ 1 of the interferometer arms 24 and 26 can be adjusted in response to a disturbance such that the detected reference wavelength remains constant or nearly constant even in the event of a disturbance.
  • the interference effect on the reference measurement can be compensated. Because the couplers 20, 22 and the interferometer arms 24, 26 are shared for the reference measurement and the measurement of the optical signal 16, the compensation of the reference measurement compensates for the measurement of the optical signal 16 at the same time. Although this variant requires active compensation, it avoids any subsequent compensation or correction after the detection, which can continue to take place continuously.
  • FIG. 4 shows a fiber interferometer 118 according to a second embodiment of the invention, in which the third optical detector 32 and the third optical reference detector 38 are respectively connected to an output of the second fiber coupler 122 and the first fiber coupler 120, respectively each located on the side of the interferometer arms 24 and 26.
  • the third optical detector 32 and the third optical reference detector 38 are respectively connected to an output of the second fiber coupler 122 and the first fiber coupler 120, respectively each located on the side of the interferometer arms 24 and 26.
  • six outputs of the first fiber coupler 120 and the second fiber coupler 122 are used in the fiber interferometer 118 according to the second embodiment.
  • the first fiber coupler 120 and the second fiber coupler 122 of the second embodiment 118 of the fiber interferometer are 3x3 fiber couplers.
  • the fiber interferometer 118 does not require the optical circulators 44 and 46 of the fiber interferometer 18 of the first embodiment, because the signal input 40 and the reference signal input 42 are each not used to supply an expiring signal component to a detector or reference detector.
  • the third detector 32 and the third reference detector 38 in the fiber interferometer 118 do not detect an interference signal but a signal whose intensity is independent of the path length difference ⁇ 1 of the interferometer arms 24, 26 and which is at least approximately proportional to the intensity of the optical signal 16 and the reference optical signal 48, respectively is.
  • the intensity of the optical signal 16 or that of the optical reference signal 48 can be determined in the case of the fiber interferometer 118, in contrast to the fiber interferometer 18, solely with the detector 32 and solely with the reference detector 38.
  • the fiber interferometer 18 at least two (ideally - ie with knowledge of the exact intensity and phase relationship of the respective coupler outputs) or three (based on the sum of the three measured intensities) of the detectors 28, 30, 32 or at least two or all three of the reference detectors 34, 36, 38 are needed.
  • the sum of that intensity that leaks into the reference signal input 42 and is not detected and those intensities detected by the detectors 28, 30, as well as the intensity measured at the detector 32, is at least approximately proportional to the intensity
  • the un-made measurement of said Intensity that expires through the reference signal input 42 are reconstructed.
  • This reconstructed measurement corresponds to the measurement at the detector 32 of the fiber interferometer 18. The same applies to the fiber interferometer 118 also for the reference measurements.
  • the fiber interferometer 118 also provides the measurement at the detector 32 and at the reference detector 38 a third independent measurement in addition to the two independent measurements at the detectors 28 and 30 and at the reference detectors 34 and 36th
  • the attenuation in the two interferometer arms 24 and 26 is unequal. This can happen, for example, if 24 and 26 splice or connectors of different quality are in the Interferometerarmen. Such an unequal attenuation is noticeable by the fact that no more complete destructive interference takes place and an underground intensity is detected over the entire wavelength range. If this unequal damping always remains the same, the effect can be equalized by appropriate calibration of the measuring system.
  • This measurement correction can be performed in two steps using the reference measurements as follows: 1.
  • the reference detectors 34, 36 and 38 of Figures 2, 5, 1, 9, 11 (but not the detectors 12) provide signals approximately proportional to that
  • the detectors 28, 30 and 32 of Figures 2, 5, 1, 9, 11 (but not the detectors 32 of Figures 4, 6, 10, 12) provide signals approximately proportional to the term.
  • the tatlab is v ⁇
  • the measured wavelength ⁇ can be determined from the measured detector signals. Also information about the terms (from) and from falls.
  • the spectral transmission profiles for the signal components of the optical signal 16 and of the reference signal 48 which terminate from the first fiber coupler 120 or from the second fiber coupler 122 on the side remote from the interferometer in that, as in the case of the fiber interferometer 18 (in each case three sub-signals), preferably offset by one third of a period from one another, so that the described "counting" of the traversed interference periods can also be performed with the fiber interferometer 118.
  • FIG. 5 shows a fiber interferometer 218 according to a third embodiment, in which only a first 3 2 fiber coupler is provided and in which a reflector 50, in particular a Faraday reflector, is provided at each end of an interferometer arm 24, 26.
  • This fiber interferometer 218 thus has the structure of a Michelson interferometer.
  • the signal input 40 and the reference signal input 42 are formed by the same optical fiber, which is fiber-optically connected to an output of the first fiber coupler 20 via an optical circulator 44.
  • the terminals of a fiber coupler may be referred to as "outputs" even if they serve to supply a signal to the coupler.
  • first, second, and third WDM couplers 52, 54, and 56 each fiber optically coupled to an associated output of the fiber coupler 20 that faces the interferometer arms 24 and 26.
  • the WDM couplers 52, 54 and 56 each have two outputs for different wavelengths, with one output connected to an associated optical detector 28, 30 and 32 and the other output connected to an associated optical one Reference detector 34, 36 and 38 is connected.
  • the first WDM coupler 52 is fiber-optically connected to the first coupler 20 via said circulator 44.
  • the optical signal 16 and the reference optical signal 48 have a different wavelength and may be supplied to the fiber interferometer 218 simultaneously and continuously through said common input 40 and 42, respectively.
  • the optical signal 16 and the reference signal 48 enter the first coupler 20 and are split into the interferometer arms 24 and 26.
  • Each of the interferometer arms 24 and 26 is traversed by a portion of the optical signal 16 and by a portion of the optical reference signal 48 and passed through a second time after reflection of the signal components at the reflectors 50.
  • the reflected partial signals of the optical signal 16 and of the optical reference signal 48 entering the first coupler 20 interfere with one another and are respectively divided into three outgoing component signals, the associated transmission profiles being offset by one third of one period.
  • a partial signal of the optical signal 16 and a partial signal of the optical reference signal 48 together enter into one of the associated WDM couplers 52, 54 and 56 and are separated in this due to their different wavelength, so that the sub-signals of the optical signal 16 each one of the associated optical detectors 28, 30 and 32, respectively. are guided and the sub-signals of the optical reference signal 48 are each supplied to an associated one of the optical reference detectors 34, 36 and 38, respectively.
  • the measurement and compensation of the measurement can be carried out as previously described with reference to FIGS. 2 and 3.
  • FIG. 6 shows a fiber interferometer 318 according to a fourth embodiment, which is a modification of the aforementioned third embodiment 218.
  • the first fiber coupler 120 is a 3x3 fiber coupler
  • the third WDM coupler 56, third detector 32 and third reference detector 38 are coupled to an output of the fiber coupler 120, which is the other outputs for the first and second outputs second detectors 28, 30 and reference detectors 34, 36 is opposite.
  • FIG. 7 shows a fiber interferometer 418 according to a fifth embodiment, which is a modification of the first embodiment 18.
  • a further, third interferometer arm 58 is provided which is connected in each case to a connection of the second fiber coupler 122 and to a connection of the first fiber coupler 120 in a fiber optic manner.
  • the first, the second and the third interferometer arm 24, 26 and 58 each have a different optical path length, so that between the first and second Interferometerarm 24 and 26, a first optical path length difference ⁇ and between the first and third Interferometerarm 24 and 58, a second optical path length difference ⁇ 1 2 exists.
  • the three outputs of the first fiber coupler 120 for the outgoing partial signals of the optical signal 16 each have a spectral transmission TU, T22 and T33, as shown in Figure 8.
  • the spectral transmissions T33, T1 and T22 fluctuate both with a change in the spectral position a comparatively long period PI as well as with a comparatively large period P2.
  • an optical switch can be provided in one of the interferometer arms 24, 26 or 58, with which the optical connection can be separated, so that a measuring arrangement results, which the interferometer 18 of Figure 2 with the curves Tl, T2 and T2 of Figure 3 corresponds.
  • the interferometer 418 having a first measuring arrangement, in which arise at the three Deteldor- and reference detector outputs of the first and second couplers 122 and 120, the spectral transmissions TU, T22 and T33, and with a second measuring arrangement in which the spectral transmissions Tl, T2 and T3 result, are measured.
  • a rough determination of a spectral position can be made by taking advantage of the "slow” periodic change with the period P2, after which the spectral position in the second measuring arrangement can be adjusted by means of the "faster” periodic change of the period P from FIG be determined more precisely.
  • 9, 10, 11 and 12 respectively show a fiber interferometer according to the present invention according to a sixth embodiment 518, a seventh embodiment 618, an eighth embodiment 718 and a ninth embodiment 818 which can be used as Fourier transform (FT) spectrometers ,
  • FT Fourier transform
  • embodiments 518, 618, 718, 818 are similar to those of Figures 2, 4, 5 and 6.
  • the embodiments 518, 618, 718, 818 of Figures 9 to 12 further include a Adjustment means 60 in at least one of the interferometer arms 24 and 26, with which the optical path length of the interferometer terarm concerned over a predetermined range can be changed.
  • the illustrated interferometers 518, 618, 718 and 818 can be used not only for determining the wavelength or the spectral position of a narrowband optical signal 16, but also as an FT spectrometer for determining a spectral intensity distribution of a broadband optical signal 16 ,
  • the adjusting means 60 may be, for example, a piezoelectric fiber stretcher, an optical delay line or an optically integrated phase modulator. Unlike previously described for the measurement correction using a compensation means, the actuator 60 is not used to compensate for a disturbance, but as a measuring element. With the adjusting means, the measuring arrangement is deliberately changed, so that different intensities for the same input spectrum of the optical signal 16 at the detectors 28, 30, 32 are deliberately generated for different path length differences ⁇ 1 (which are also referred to as "retardation") and with the Compared with the optically integrated phase modulator, the fiber stretcher and, in particular, the delay line are preferably used in the FT spectrometer application due to a usually higher achievable retardation.
  • a stable narrow-band signal having a known wavelength ⁇ is preferably used, so that the current path length difference ⁇ 1, which is the current spectral transmission profiles T 1, T 2, T 3 for the outgoing interference components the signal 16 and the reference signal 48 can be determined at any time with the reference measurement.
  • the input spectrum S (v) of an optical signal 16 can be determined from measurements of ⁇ ( ⁇ 1) and ⁇ 1 using the following formula:
  • D (v) a window function which, for example, has a value of 1 in the operating bandwidth of the interferometer and is otherwise zero,
  • the optical path length difference ⁇ 1 is thus varied over a predetermined range with the aid of the adjusting means 16, thereby measuring ⁇ ( ⁇ 1) and the associated ⁇ 1.
  • ⁇ 1 can also be unambiguously determined by means of a count-in, eg of the minima and / or maxima passed, because the spectral offset between each two of the spectral transmission profiles T1, T2, T3 is less than 180 ° is.
  • the fiber interferometers according to the invention offer the advantage that the determination of the path length differences ⁇ 1 can be carried out quite simply and simply by counting.
  • the FT spectrometer according to the invention offers the further advantage that it can be constructed entirely or at least largely without free-beam elements. As a result, for example, an impairment caused by contamination can be prevented.
  • FIG. 13 shows the result of a simulation of the previously described method for determining a spectrum of an optical signal 16.
  • FIG. 13 five processing steps are shown from top to bottom.
  • a simulated or randomly generated input field S (X) or S (v) of an optical signal 16 is shown, the uppermost diagram showing the spectral intensity 8 ( ⁇ ) as a function of the wavelength ⁇ and the second diagram from above shows the spectral intensity S (v) as a function of the wave number v.
  • the middle diagram shows, depending on the path length difference or the retardation rank ⁇ 1, the interferogram ⁇ ( ⁇ 1) of the input spectrum S (v), which is related to the spectrum S (v) via the following Fourier transformation, in / ( ⁇ 1 ) the interferogram, but without already subtracted subsurface intensity:
  • the first term after the second equal sign indicates the above constant background intensity, which does not change with ⁇ 1 when detected.

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  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

La présente invention concerne un interféromètre à guide d'ondes (18,…, 818), destiné à mesurer une information spectrale d'un signal optique (16), qui comporte une entrée de signal optique (40) destiné au signal optique (16) et une entrée de référence optique (42) destiné à un signal de référence optique (48). L'interféromètre à guide d'ondes (18,…, 818) comprend en outre au moins deux interféromètres optiques (24, 26, 58), qui ont des longueurs de trajet optiques différentes qui peuvent chacune être parcourues par une partie du signal optique (16) et du signal de référence (48). L'interféromètre à guide d'ondes (18,…, 818) selon l'invention comprend en outre au moins un premier coupleur de guide d'onde NxM (20, 120), avec N ≥ 2 et M ≥ 3, au moins deux détecteurs optiques (28, 30) servant à détecter des parties du signal optique (16) et au moins deux détecteurs de référence optiques (34, 36) servant à détecter des parties du signal de référence optique (48).
PCT/EP2015/058746 2014-05-20 2015-04-23 Interféromètre à guide d'ondes optique pour mesurer une information spectrale WO2015176906A1 (fr)

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