DE102014004697B4 - System and method for distance measurement - Google Patents

Abstract

A system (500) for distance measurement, comprising - a multi-wavelength holographic module (100) for capturing a holographic measurement data set for at least one measurement point based on at least one synthetic wavelength, the multi-wavelength holography module (100) comprising: - at least two holographic light sources (110, 112, 114, 116 at least one beam splitter (124, 160) for splitting each holographic light beam into an object light beam (155) and a reference light beam (135), and - at least one diffractive element (134, 138) for dispersive Tilting the reference light beams (135), wherein the at least one diffractive element (134, 138) is arranged and arranged to determine an associated estimate for each wavelength of the at least two holographic light beams, and wherein the system further comprises: - a referencing module (300) for besti ming the at least one synthetic wavelength on the basis of the associated estimated values, and - an evaluation module for determining the distance of the at least one measuring point.

Description

The present invention relates to a system and method for distance measurement. In particular, the present invention relates to a system and a method for coordinate measurement and / or for the measurement of 3D objects.

In geometric metrology, higher and higher absolute measurement accuracies are aimed for. In this case, punctiform measuring optical distance sensors are often used. These determine the distance between a reference point (eg a point in the gauge) to a point on the surface of an object. The pursuit of ever higher measuring accuracies is technically in competition with the demand for the largest possible measuring ranges. For the measurement of large objects or volumes, the aim is to measure distances from meters to micrometers or even more accurately.

According to the state of the art so-called time-of-flight methods are common for the measurement of long distances. Both pulse transit time and phase transit time methods are used. Both methods have in common that a light source, usually a laser, is time modulated. In the case of the pulse transit time method, individual laser pulses are emitted and detected again after reflection and / or scattering on an object surface. The time t between emission of the pulse and detection is a measure of the distance d between the measuring device and the illuminated object point: d = ct / 2 (1).

The quantity c denotes the speed of light in the medium between the measuring device and the measuring point. In the case of the phase delay method, the amplitude of the light source is periodically modulated, e.g. B. rectangular or sinusoidal. The phase angle φ between emitted and detected modulation is here a measure of the distance d between measuring device and measuring point: d = 1/2 φ · c / 2π · f (2).

The quantity f denotes the modulation frequency of the light source. The unique measuring range is given by the halfway the light travels during a period of modulation. In order to ensure large measuring ranges with good depth resolution, measurements with different modulation frequencies are carried out simultaneously or successively. Measuring ranges of a few meters at resolutions in the range of millimeters are realized in this way. The modulation frequency can, however, for technical reasons, in particular due to limitations of the bandwidth of the detector, z. As pin diode, and / or the electronics, not be increased arbitrarily. The achievable measurement resolutions are therefore limited.

Another method of distance measurement is interferometry, which is used primarily for highest resolutions. Particularly in coordinate metrology and in the testing of optical functional surfaces, interferometric methods with only one wavelength are used. The unique measuring range is limited upwards by half the wavelength of the light source used, typically a laser. In order to increase the measuring range, a larger measuring distance can be traversed and the resulting interference minima and interference maxima can be counted. Alternatively, the measurement may be repeated with two slightly different wavelengths λ ₁ and λ ₂ . The distance to the measuring point results in:

The third fraction in this equation is called synthetic wavelengths Λ _Synth :

Large measuring ranges with high measuring resolutions can also be achieved here by using different synthetic wavelengths. The maximum achievable measuring range of the Mehrwellenlängeninterferometrie or Mehrwellenlängenholographie is limited in technical implementations by the stability of the single wavelengths λ ₁ and λ ₂ . Because for large synthetic wavelengths small differences between λ ₁ and λ _{2 are} necessary, so that small deviations of the wavelengths of their setpoint, due z. B. by temperature change, lead to large errors.

The publication US 4 295 741 A discloses a two-wavelength phase control system for generating synthetic error signals to reduce 2πN ambiguity resulting from an initial optical path length difference. The system includes an oscillator for generating an input beam having different lines, an interferometer, first and second detectors, and a phase controller. The detectors detect incident input signal beams and generate first and second electrical output signals. The phase controller, based on the electrical output signals generated by the detectors, generates error signals which comprise an actuator with one within the interferometer Control level control, so as to adjust the optical path length difference.

The publication US Pat. No. 6,078,392 discloses a digital holography measuring system wherein holograms are picked up in an Offaxis arrangement.

Frisco Schlottau et al .: "Demonstration of a continuous scanner and time-integrating correlator using spatial-spectral holography", Journal of Luminescence, Vol. 107, No. 1-4, May 2004, pages 90-102, ISSN 0022-2313 discloses a "spatial-spectral holographic scanner (SSHS)".

Jonas Kühn et al .: "Real-time dual wavelength digital holographic microscopy with a single hologram acquisition", OPTICS EXPRESS, Vol. 15, No. 12 (2007), pages 7231-7242, discloses a multi-wavelength digital holographic microscope , with which a multi-wavelength holography with spatial phase shifting can be performed. For different wavelengths, different tiltings are introduced by guiding the respective reference beams over different spatially separated mirrors with different tiltings.

Harald Wölfeschneider et al .: "Fast Distance Measurement for Laser Scanners", tm - Technical Measuring, Volume 72, Issue 7-8 (2009), pages 455-467, ISSN 0171-8096, discloses the use of phase delay measurements for distance determination.

Daniel Karl et al. "Multiwavelength digital holography with autocalibration of phase shifts and artificial wavelengths", Applied Optics 48, H1-H8 (2009), discloses an approach to multi-wavelength interferometry.

It is an object of the present invention to provide a system and method that enables a simpler, more stable, more reliable and / or more accurate distance measurement than conventional systems and methods. In particular, it is an object of the present invention to provide a system and a method for distance measurement, which enable a high resolution with a large measuring range.

This object is achieved by the subject matters of the independent claims. Advantageous embodiments are subject of the dependent claims.

• – ein Mehrwellenlängenholographiemodul zum Erfassen eines ersten Holographiemessdatensatzes für zumindest einen Messpunkt auf Basis von zumindest einer synthetischen Wellenlänge, wobei das Mehrwellenlängenholographiemodul aufweist:
• – zumindest zwei Holographielichtquellen zum Erzeugen von zumindest zwei kohärenten Holographielichtstrahlen mit unterschiedlichen Wellenlängen,
• – zumindest einen Strahlteiler zum Aufteilen jedes Holographielichtstrahls in einen Objekt- und Referenzlichtstrahl, und
• – zumindest ein Beugungselement zum dispersiven Verkippen der Referenzlichtstrahlen, und wobei das System ferner umfasst:
• – ein Referenzierungsmodul zum Bestimmen der zumindest einen synthetischen Wellenlänge auf Basis der zugehörigen Schätzwerte, und
• – ein Auswertemodul zum Bestimmen der Distanz des zumindest einen Messpunkts.

A first aspect for achieving the object relates to a system for distance measurement, comprising

• A multi-wavelength holography module for capturing a first holographic measurement data set for at least one measurement point based on at least one synthetic wavelength, wherein the multi-wavelength holography module comprises:
• At least two holographic light sources for generating at least two coherent holographic light beams having different wavelengths,
• At least one beam splitter for splitting each holographic light beam into an object and reference light beam, and
• At least one diffractive element for dispersively tilting the reference light beams, and wherein the system further comprises:
• A referencing module for determining the at least one synthetic wavelength on the basis of the associated estimated values, and
• An evaluation module for determining the distance of the at least one measuring point.

The "multi-wavelength holography module" may also be referred to as a multi-wavelength interferometer.

The "holography measurement data set" can also be referred to as the first distance measurement data set. For the purposes of the present description, a "distance measurement data set" is to be understood in general as meaning a set of measured values which can be used to determine a distance. A ranging data set may include one or more, i. H. include a variety of measurements. Measured values may be, for example: intensity of a light beam, phase or phase difference of one or more light beams, phase shift, wavelength, frequency, time, in particular transit time of a light beam, interference or interference pattern, etc .. The holographic measurement data set comprises one or more measured values of a interferometric distance determination, in particular one or more interference images.

For the purposes of this description, a "measuring point" is understood to mean a point, an area and / or a section of an object or a surface of the object. Preferably, a measuring point has an extension in the range of 10 μm ² to 100 μm ² , more preferably in the range of 10 μm ² to 50 μm ² , even more preferably in the range of 10 μm ² to 30 μm ² . The extension of a measuring point can also be lower or higher than the values given above. An object can be a two- or three-dimensional object, for example a wind turbine or a turbine blade, whose distance or its shape, in particular three-dimensional shape, is to be measured. It is understood that the term "distance" is always related to the measuring system. Unless otherwise is therefore always understood as the distance in the sense of this description, the distance of the measuring point from the measuring system, in particular a sensor of the measuring system.

A "synthetic wavelength" Λ _Synth can be composed or generated from a plurality of wavelengths, in particular from two wavelengths λ ₁ and λ ₂ , wherein Λ _{Synth is} defined according to formula (4). The measurement with multiple wavelengths or with a synthetic wavelength has the advantage that the uniqueness range, ie the measuring range for a unique measurement can be increased, in particular if the difference of the wavelengths used is much smaller than the wavelength itself. The basic principle of interferometry This is because a laser beam reflected back from the test object is coherently superimposed with a reference beam. This coherent superposition requires that the wavefront of the backscattered light be deformed by significantly less than one wavelength λ. Accordingly, the roughness R of the illuminated surface must be significantly below λ, in the case of visible light R << 600 nm. For many technical surfaces, this is generally not the case, which is why interferometric measurements with only one wavelength are generally eliminated. However, by generating a comparatively large synthetic wavelength Λ _Synth from two closely spaced wavelengths, interferometric measurements are possible even on rough surfaces. By using a number of different synthetic wavelengths, the unique measuring range can be extended up to a few millimeters. When four holographic light beams are used, a synthetic wavelength Λ _12.34 can be generated from the synthetic wavelengths Λ ₁₂ and Λ ₃₄ , which is calculated as:

If Λ ₁₂ and Λ _{34 are} similarly large, the synthetic wavelength Λ _12,34 becomes correspondingly large, even if the individual synthetic wavelengths Λ ₁₂ and Λ _{34 are} relatively small. For the wavelength differences of the individual wavelengths, this means that the distance between λ ₁ and λ ₂ can be selected to be similar to the distance between λ ₃ and λ ₄ .

The multi-wavelength holography module comprises at least two holographic light sources, in particular holography lasers. In particular, the multi-wavelength holographic module comprises two, three, four, etc. holographic light sources. Preferably, the holographic light sources are lasers, for example diode lasers. The holographic light sources are designed to generate and emit coherent holographic light beams. Advantageously, the wavelength of the holographic light sources can be adjusted within a predetermined range.

The multi-wavelength holography module comprises one or more beam splitters, in particular polarizing beam splitters or beam splitter cubes, for dividing the holographic light beams into an object and reference beam path or an object and reference light beam. With the object light beam, the measurement object is illuminated, which reflects and / or scatters at least a part of the object light beam. The reference light beam is not reflected or scattered by the measurement object. Alternatively, the holographic light beams can be divided into an object, reference and zero beam path by the at least one beam splitter. The zero-point beam path advantageously makes it possible to compensate for a drift of a predetermined zero point and / or a drift of the object or reference light beam-in particular thermally induced-and thus the drift of the phase position between the object and reference light beams. When using a pure Michelson interferometer, the Mehrwellenlängenholographiemodul z. B. include exactly one beam splitter. In particular, the multi-wavelength holography module comprises at least two, preferably at least three, more preferably at least four, and most preferably five beam splitters.

The multi-wavelength holography module may comprise at least one, in particular two, rotatable half-wave plates, with which the division ratio into the two or three optical paths, that is to say two or three. H. Object light beam, reference light beam and optional zero beam can be adjusted.

The multi-wavelength holographic module preferably comprises a multi-wavelength holographic detector which may comprise a plurality of photosensitive elements, in particular a CCD camera, CMOS camera or a photodiode array. The elements, d. H. the pixels of the photodiode array can be arranged one or two-dimensionally, that is, as a line or area camera. The multi-wavelength holographic detector is preferably arranged such that it detects both the object light beam reflected and / or scattered by the measurement object and also the reference light beam and optionally the zero point light beam. In particular, the multi-wavelength holographic detector is arranged such that the object light beam reflected and / or scattered by the measurement object and the reference light beam on the multi-wavelength holographic detector interfere with each other, so that an interference image is formed on the multi-wavelength holographic detector or the camera.

The multi-wavelength holography module further comprises at least one diffractive element for dispersively tilting the holographic light beams. The term "dispersive" in the sense of this description means wavelength-dependent. The diffraction element is thus designed to tilt the light beams incident on the diffraction element in a wavelength-dependent manner. In other words, light beams of different wavelengths are tilted or deflected differently by the diffraction element. The multi-wavelength holographic module may include only one diffractive element. However, the multi-wavelength holography module may also comprise two or more diffraction elements. The at least one diffraction element is preferably designed such that it acts not only tilting to a predetermined wavelength, but to all wavelengths of the holographic light beams.

The at least one diffraction element can advantageously ensure that, for a later evaluation, the reference beams of the holography light sources strike a camera at slightly different angles. Preferably, the angular dispersion of the diffractive element is in the range of 1 mrad to 30 mrad, more preferably in the range of 2 mrad to 25 mrad, even more preferably in the range of 3 mrad to 20 mrad, between the smallest and the largest wavelength of the holographic light beams, in particular reference light beams. For a given wavelength, the angles can scale with the pixel size of the camera. In particular, for a given wavelength, the angles reciprocally scale with the pixel size of the camera, i. H. decreasing the pixel size will increase the angles. If the diffraction element is a diffraction grating, the diffraction grating is preferably designed and / or arranged such that only the + 1-th or -1-th diffraction order, in particular by an optic following the diffraction grating, reaches the detector, but not the 0 -te or the + 1th and -1st order simultaneously. Otherwise, the desired effect does not occur, in particular, otherwise the wavelength can not be determined unambiguously by means of the diffraction grating.

Preferably, the multi-wavelength holography module comprises two diffraction elements. The diffraction elements can be reduced by means of reduction lenses imaged on the detection camera. In particular, the first diffraction element can be imaged onto the second diffraction element with the aid of first reduction lenses, and the second diffraction element in turn can be imaged sharply by means of second reduction lenses onto the multi-wavelength holographic detector or the camera. This advantageously ensures that all holographic light beams illuminate the same area on the camera, but that the angles of incidence are different due to the dispersion of the at least one diffraction element. The effects of the two diffraction elements add up. In addition, the image of the second diffraction element can be made to decrease in size, preferably with a magnification in the range of -0.2 to -0.8, more preferably in the range of -0.3 to -0.7, even more preferably in the range of -0, 4 to -0.6, in particular of about -0.5 - act, which also increases the angle of incidence of the individual holographic light beams. However, the diffraction elements can also be imaged by means of lenses in a 1: 1 imaging ratio or enlarged by means of magnifying lenses on the detection camera.

The diffraction element advantageously ensures a tilting of the beam paths of different wavelengths, without requiring a complicated adjustment, as would be necessary, for example, in the case of mirrors. The tilting of the wavelengths to each other is fixed by the dispersive properties of the diffraction element and not dependent on a precise adjustment. The system according to the invention is thus easier to operate than conventional systems. In addition, the system of the invention is less error prone and provides more reliable and more accurate results.

The at least one diffraction element is designed and arranged to determine an associated estimated value for each wavelength of the at least two holographic light beams. Furthermore, the system comprises a referencing module for determining the at least one synthetic wavelength on the basis of the associated estimated values.

Advantageously, the at least one diffraction element not only serves for tilting the reference light beams, but is also designed to measure or determine the wavelengths of the holographic light beams and thus the estimated values as output data for the referencing module. The at least one diffraction element is therefore advantageously used as a spectrometer. In other words, the diffraction element is used both for tilting the reference light beams and for determining estimated values, ie the wavelengths of the holographic light beams, which are required for determining the at least one synthetic wavelength by means of the referencing module. The wavelength is determined by means of the diffraction element as a spectrometer, ie by measuring and evaluating intensity minima or intensity maxima of the diffracted by the diffraction element rays or reference beams. Preferably, the intensity minima and intensity maxima can be determined with the aid of a holography detector, for example a camera, be detected and evaluated. Preferably, the evaluation can be carried out on the basis of the holographic measurement data set, in particular on the basis of one or more interference images, which were preferably recorded by the holography detector. Advantageously, the at least one diffraction element or diffraction grating has a blaze. In other words, the diffraction element is preferably a blazed grating or echelette grating. Thus, advantageously, a high efficiency can be achieved. In addition, the at least one diffraction element or diffraction grating is preferably designed and / or arranged such that large diffraction angles occur. In particular, the at least one diffraction element or diffraction grating is designed and / or arranged such that only one diffraction order, ie a diffraction order without the remaining orders, is imaged onto the holography detector. This can be achieved by arranging the at least one diffraction element or diffraction grating, in which correspondingly large diffraction angles occur.

The measurement accuracy of the Mehrwellenlängeninterferometrie is given by the accuracy of the phase measurement and by well-known as possible synthetic wavelengths, which result from the distances of the wavelengths of the holographic light beams. With the aid of the referencing module, advantageously an interferometric measurement can be made evaluable independently of frequency drifts of the holographic light sources. The referencing module determines the frequency differences of the holographic light beams. Since the frequency differences can be several hundred GHz, they are not accessible to direct measurement by conventional means. The referencing module determines the frequency differences by means of a phase modulation. For this purpose, part of the optical power is branched off from each holographic light source with optical couplers, preferably fiber couplers, and modulated in electro-optical phase modulators with precisely defined electrical frequencies. The phase modulation produces higher-order side lines which bridge the large frequency spans between every two holographic light beams. The modulation frequencies can advantageously be derived from a common frequency standard. For detection, the modulated signals are superimposed on a referencing detector, which preferably comprises a photodiode. The resulting low-frequency beat signals in the range of a few hundred MHz can be converted analog-to-digital and digitally processed with a computer. Higher frequencies can be filtered with a low pass filter. The frequencies of the beats can be accurately determined by Fourier analysis. From the measured beat frequencies, the predetermined modulation frequencies and the knowledge of the number of side lines lying between the holographic light sources, the frequency spacing of two holographic light sources and thus the associated synthetic wavelength can be determined. The number of side lines lying between the holographic light sources results from the wavelengths of the individual holographic light beams, which can be measured with the aid of the at least one diffraction element. The wavelengths measured with the at least one diffraction element are referred to as estimated values in the context of this description. The measurement of the estimated values preferably takes place simultaneously with the distance measurement. Thus, for each distance measurement, the wavelengths of the holographic light beams present at the time of the distance measurement can be used for the exact determination of the at least one synthetic wavelength. Consequently, errors due to frequency drift of the holographic light sources can be reduced or even avoided.

In a further preferred embodiment of the system for distance measurement, the at least one diffraction element is an optical grating, in particular a surface grating. The at least one diffraction element or surface grating may be a reflection grating or a transmission grating.

In a further preferred embodiment, the system for distance measurement furthermore comprises a phase transit time measuring module for detecting a phase transit time data record or a second distance measuring data record of the at least one measuring point on the basis of a modulated, in particular frequency-modulated, phase transit time light beam.

The phase delay data record comprises one or more measured values of a time-of-flight distance determination. In particular, the phase delay data record comprises one or more terms of the phase delay light beam.

Advantageously, the holographic light beams and the phase delay light beam have different wavelengths. The reflected and / or scattered light at the measuring point is partially reflected back into the system for distance measurement. There, the light can be formed, for example, by optical components and divided into at least two light-sensitive sensors or detectors, in particular the multi-wavelength holographic detector and a phase delay detector of the phase delay measuring module. The division can z. B. by dichroic filters, diffraction gratings and / or other color-selective optical elements - diffractive and / or refractive - done, but also simple beam splitters and mirror assemblies and separation according to polarization - polarizing Beam splitter and / or beam combiner - are possible. The two sensors or detectors with downstream evaluation electronics initially record the associated measurement signals separately from one another. The phase delay detector of the phase delay measuring module may comprise, for example, a photodiode as the photosensitive element.

In a further preferred embodiment of the system for distance measurement, the phase transit time measuring module has a phase transit time light source, in particular a phase transit time laser, for emitting at least one phase transit time light beam.

Preferably, the at least one phase delay light source and the at least two holographic light sources are arranged such that the at least one phase delay light beam and the at least two holographic light beams are directed to the same measuring point or hit the same measuring point. This can be z. B. coaxially happen in that the light beams are passed through fiber optic beam splitter and / or beam combiner in a common optical waveguide, the outlet then can serve as a nearly point-like, well collimated beam source for the measurement. Alternatively or additionally, however, the superposition may also be free-space-optically.

In a further preferred embodiment, the evaluation module is designed to determine the distance of the at least one measurement point on the basis of the holographic measurement data set and the phase delay measurement data set.

The evaluation module can have an optical interface which comprises, for example, FC / APC fiber plugs with polarization-maintaining fibers. The transmission of the wavelength or frequency distances of the holographic light sources measured by the referencing module for the exact and traceable determination of the synthetic wavelengths can take place via a local network, in particular LAN, between computers of the referencing module and the phase delay module and / or the multi-wavelength holography module. In particular, a TCP / IP protocol can be used for this purpose.

• – Bereitstellen eines erfindungsgemäßen Systems;
• – Erfassen des Holographiemessdatensatzes für den zumindest einen Messpunkt mittels des Mehrwellenlängenholographiemoduls;
• – für jede Wellenlänge der zumindest zwei Holographielichtstrahlen, Bestimmen des zugehörigen Schätzwertes mittels des zumindest einen Beugungselements;
• – Bestimmen der zumindest einen synthetischen Wellenlänge auf Basis der zugehörigen Schätzwerte mittels des Referenzierungsmoduls; und
• – Bestimmen der Distanz des zumindest einen Messpunkts mittels des Auswertemoduls.

Another aspect of the present invention relates to a method for distance measurement, comprising the steps

• - Providing a system according to the invention;
• - Detecting the Holographiemessdatensets for the at least one measuring point by means of the multi-wavelength holography module;
• For each wavelength of the at least two holographic light beams, determining the associated estimated value by means of the at least one diffraction element;
• Determining the at least one synthetic wavelength on the basis of the associated estimated values by means of the referencing module; and
• - Determining the distance of the at least one measuring point by means of the evaluation module.

For evaluating the holographic measurement data set or an interference image, a phase shift method, in particular a temporal or a spatial phase shift method, can be used. In the temporal phase shift method, a plurality of interference images are successively taken, while between the images, the optical path length traveled by the reference light beam and / or the object light beam is slightly changed. In the spatial phase shift method, the reference or reference light beam does not impinge perpendicularly on the holographic detector but at a predetermined angle to the normal of the detector or camera. The tilt causes a stripe pattern to be generated on the camera. The fringe pattern is initially sinusoidal and can be interpreted as a carrier signal for the actual measurement information, namely the phase position of object to reference wave. By Fourier transformation - one-dimensional or two-dimensional - of the interference image, the measurement information of background data - in particular DC component and / or background light - are separated.

Advantageously, the reference light beams of the different holographic light sources for the different wavelengths λ _i are tilted differently. After the Fourier transformation, several peaks then arise in the frequency spectrum, which represent the measurement signals of the individual wavelengths. The different tilting can be done by mechanically separated reference paths for each wavelength and a separate adjustment of the tilting. Preferably, however, the tiltings are realized by the dispersive element or the diffraction element-such as a grating, a lens with a large chromatic aberration and / or a prism. The dispersive element is ideally imaged optically, possibly also out of focus, on the holography detector, so that the individual reference light beams are superimposed with one another but have different tiltings. The tilt can be adjusted by changing the magnification: For example, a reduced image of the diffraction element provides larger tilting.

In order to compensate for a drift within the holography detector, such as an optical path length change of the reference path, the inventive system or the Multi-wavelength holography module comprise a Driftausgleichsmessstrecke known length. Thus, the distance measurement to the measurement point can not be made absolutely but as a difference to a predetermined point, which is preferably located within the system.

In a preferred embodiment, detecting the first distance measurement data set for the at least one measurement point by means of the multi-wavelength holography module comprises generating side lines-in the optical spectrum-by means of a phase modulation, in particular an electro-optical phase modulation, of the at least two holographic light beams.

The diffraction element or diffraction grating is preferably used as a spectrometer, so that a determination or estimation of the wavelength can be carried out in a known and simple manner.

In order to make the interferometric measurement traceable independently of frequency drifts of the laser sources traceable to international standards, a referencing method is used, which determines the optical frequency intervals of several hundred GHz simultaneously with the distance measurement. In this case, part of the optical power is branched off from each holographic light source used with optical couplers, preferably fiber couplers, and modulated in electro-optical phase modulators with precisely defined electrical frequencies. The phase modulation generates higher-order side lines which bridge the large frequency ranges between two lasers each. The modulation frequencies are derived from a common frequency standard. For detection, the optical signals are superimposed on a holographic detector. The resulting low-frequency electrical beat signals in the range of a few hundred MHz can be converted analog-to-digital and digitally processed with a computer. Higher frequencies are filtered with a low pass filter. The frequencies of the beats can be accurately determined by Fourier analysis. Thus, the frequency separations of two adjacent side lines, each belonging to two holographic light sources, known. From the measured beating frequencies - in the range of several hundred MHz - the known modulation frequencies and the knowledge of the number of lying between the holographic light beams sidelines, d. H. a rough knowledge of the wavelengths of the holographic light sources, the frequency spacing of two holographic light sources and thus the synthetic wavelength of the interferometric measurement can be determined.

• – Erfassen des Phasenlaufzeitmessdatensatzes für den zumindest einen Messpunkt auf Basis eines modulierten, insbesondere frequenzmodulierten, Phasenlaufzeitlichtstrahls mittels des Phasenlaufzeitmessmoduls.

In a further preferred embodiment, the method according to the invention further comprises the following step:

• - Detecting the phase delay time data record for the at least one measuring point based on a modulated, in particular frequency-modulated, phase transit time light beam by means of the phase transit time measuring module.

Advantageously, in this embodiment, the requirement for high resolution and wide measurement range is solved by the combination of phase delay method and Mehrwellenlängeninterferometrie: In both measurement methods, the measuring range is limited by the fact that the measurement within the wavelength of the light used or the modulation of the light or must be synthetic wavelength, because after exceeding the wavelength or phase 2π repeats the signal and it is not possible to see whether the signal comes from the first, second or a later period, d. H. the signal is not clear. So that the measurement result is unique, it must be within the simple wavelength. In the pulse transit time measurement, the modulation of the light with a comparatively long wavelength - for example, a wavelength between 30 cm and 30 m, preferably between 1 m to 3 m - are selected. However, then the measurement error is also comparatively large. In a second step is now measured with the Mehrwellenlängeninterferometer. This has a smaller measuring range and also a smaller measuring error. If the measurement range of the multi-wavelength interferometer covers the measurement error of the phase delay measurement, then the inaccuracy can be measured by the measurement error of the phase delay measurement with the Mehrwellenlängeninterferometer. Thus, the total error of the measurement can be reduced to the error of the Mehrwellenlängeninterferometrie, wherein the measuring range of the phase delay measurement or the measuring range of the phase transit time measurement module is maintained.

In a further preferred embodiment of the method according to the invention, the phase transit time light beam is modulated with at least one predetermined phase delay modulation frequency, wherein the at least two holographic light beams are respectively modulated with an associated predetermined holographic modulation frequency, and wherein the phase delay modulation frequencies and the holographic modulation frequencies are derived from a common frequency standard.

Deriving the phase delay modulation frequencies and the holographic modulation frequencies from a common frequency standard has the advantage that the two measurement methods can be better connected with each other, since the normalization errors are then no longer independent of each other. In particular, the derivation of the phase transit time modulation frequencies and the holographic modulation frequencies from a common frequency standard has the advantage that errors in the combination of the two measurement signals, ie the measurement signals of the Phasenlaufzeitmessmoduls and the Mehrwellenlängenholographiemoduls, either by Messususchen arise or by the fact that the ratio of the wavelengths assumed wrong can be reduced or even completely avoided. As a common frequency standard can be high-precision, in particular calibrated, quartz or Rubidiumfrequenzstandards, a frequency signal for radio clock -. For example, the radiated DCF77 frequency standard of the Physikalisch-Technische Bundesanstalt - or a frequency signal derived from a GPS signal can be used.

In a further preferred embodiment, the distance of the at least one measuring point is determined on the basis of the holographic measuring data set and the phase delay measuring data set.

Preferably, the coarse distance is first determined with a relatively high inaccuracy of measurement of the measuring point on the basis of the phase delay time data record. Finally, the exact distance of the measurement point is determined by evaluating the holographic measurement data set with low measurement inaccuracy on the basis of the coarse distance of the measurement point already determined on the basis of the phase delay measurement data set. High inaccuracy in the millimeter range, for example, inaccuracy in the range of 100 μm to 5 mm, or higher, is considered as high inaccuracy of measurement. As a low measurement inaccuracy, an inaccuracy in the micrometer range, for example, an inaccuracy in the range of 10 nm to 10 microns, or less is considered.

In a further preferred embodiment of the method according to the invention, the detection of the holographic measurement data set and the detection of the phase transit time measurement data set take place essentially simultaneously. However, the subsequent evaluation of the measurements can be delayed. Preferably, the phase delay time data set is first evaluated and then the holographic measurement data set is evaluated on the basis of the results of the phase delay time measurement or on the basis of the phase delay time data set.

This has the advantage that the evaluation of the distance measurement datasets for distance determination not by a drift of measurement parameters, such. B. the wavelengths of the holographic light sources between the measurements is adversely affected.

By combining the phase delay module according to the invention, the multi-wavelength holography module and the referencing module or the corresponding method, it is possible to realize a measuring range of up to about one or several meters with a measuring accuracy of a few micrometers.

In the following, individual embodiments for solving the problem will be described by way of example with reference to the figures. In this case, the individual embodiments described have in part features that are not absolutely necessary in order to carry out the claimed subject matter, but which provide desired properties in certain applications. Thus, embodiments are also to be regarded as falling under the described technical teaching, which does not have all the features of the embodiments described below. Further, in order to avoid unnecessary repetition, certain features will be mentioned only with respect to each of the embodiments described below. It should be noted that the individual embodiments should therefore be considered not only in isolation but also in a synopsis. Based on this synopsis, those skilled in the art will recognize that individual embodiments may also be modified by incorporating one or more features of other embodiments. It should be understood that a systematic combination of the individual embodiments with single or multiple features described with respect to other embodiments may be desirable and useful, and therefore should be considered and also understood to be encompassed by the description.

Brief description of the drawings

1 shows a schematic sketch of an optical structure according to an embodiment of the system according to the invention for distance measurement;

2 shows a further schematic sketch of an optical structure according to a preferred embodiment of the system according to the invention for distance measurement;

3a shows a camera image of an exemplary interference measurement;

3b shows the Fourier transform of the camera image 3a ;

4 shows a schematic structure of the homing module according to the invention;

5 shows an exemplary frequency spectrum of four holographic laser sources as well as generated 36GHz and 40GHz sidebands;

6 shows a schematic sketch of the phase delay time method used in the phase delay module;

7 shows a schematic sketch for the combination of the phase delay measurement and the holography measurement.

Detailed description of the drawings

1 shows a schematic diagram of an optical structure according to a preferred embodiment of the system according to the invention for distance measurement. The system according to 1 comprises a multi-wavelength holography module 100 and a phase delay measuring module 200 ,

The multi-wavelength holography module 100 comprises four holographic light sources or multi-wavelength holography lasers 110 . 112 . 114 . 116 and a multi-wavelength holographic detector 180 , Coherent light emitted by the multi-wavelength holographic lasers 110 . 112 . 114 . 116 is emitted, is divided into an object and a reference wave, that is, in object light beams and reference light beams. The reference wave or the reference light beams are in a fiber optic 127 guided. The object wave or the object light beams illuminate an object to be measured 50 , The object 50 or a measuring point of the object 50 Backscattered light is transmitted via a dichroic beam splitter 40 , a beam splitter 160 and an imaging optics 170 to the multi-wavelength holographic detector 180 steered and superimposed there with the reference wave. The multi-wavelength holography laser 110 . 112 . 114 . 116 have different wavelengths in the range of 1548 nm to 1554 nm. For the object beam whose light is coaxially superimposed, while slightly different tilted reference waves are used for the reference beam for each of the wavelengths relative to the object beam path. The tilting of the reference waves takes place with the aid of one or more diffraction elements or area gratings (in 1 Not shown). As a result, the interference signals of the individual wavelengths can be separated by means of spatial phase shifting. Each of the interference signals provides a value for the complex amplitude of the wave from the object 50 was scattered back. The phase angle of the complex amplitude can be measured directly on reflecting objects as a measure of the distance between the object to be measured 50 and sensor 180 but initially only with a clear measuring range that is as large as half the wavelength of the laser light used (ie about 775 nm). On rough objects 50 ie objects 50 With one that plays a major role especially for technical applications, the phase shift is superimposed by random interferences, the laser speckles, which make direct use of the phase for distance measurement impossible. The solution for both constraints is the difference between the measured phase values at the different wavelengths. For one thing, the negative influence of random laser speckles disappears. On the other hand, the unambiguous measuring range is extended up to the mm range with a suitable choice of the wavelengths according to the principle of synthetic wavelengths. As a result, an overlap of the measurement ranges of the two methods is achieved, so that the measurement results of the two methods can be combined to form a new measurement signal that combines the large measurement range of the phase delay measurement with the high measurement accuracy of digital holography.

The phase delay module 200 comprises a phase delay light source or a phase delay laser 210 and a phase delay detector 280 , The phase delay laser 210 is periodically modulated. The emitted laser light is detected by means of mirrors 224 and beam splitters 260 distracted and hits the dichroic beam splitter 40 on a surface to be measured or on a measuring point of a test object 50 , At which the laser light is scattered. Part of the stray light reaches the phase transit time detector 280 , The phase relationship between the modulation of the emitted and detected light is a measure of the distance between the phase delay detector 280 and measuring point or object surface. If, for example, a modulation frequency of 128 MHz is used, clear distance measurements up to 1.17 m can be realized. The measurement accuracy that comes with the phase delay module 200 can be achieved and can not be significantly undercut by optical and electronic boundary conditions, is on the order of <5 mm.

2 shows a further schematic sketch of an optical structure according to a preferred embodiment of the system according to the invention for distance measurement. The beam path for the phase delay method is in the lower left part of 2 Shown: The light of a fiber-coupled diode laser 210 with a wavelength of 1470 nm is first through the collimator 212 collimated. Subsequently, the beam is transmitted via a deflection mirror 214 and a dichroic beam splitter 40 on the test object 50 directed. The dichroic has a band edge of 1550 nm, so that only light with wavelengths <1550 nm is reflected. Longer wave light is transmitted. Preferably, the dichroic is Designed to reflect only light with wavelengths between 1480 nm and 1540 nm, ideally only one wavelength in the middle between 1470 nm and 1550 nm, ie about 1510 nm. The beam diameter of the laser beam is about 1 mm, so that a good collimation of the beam over a range of 1 m is given. The diffraction-limited beam divergence is about 0.9 mrad. The laser light, which is backscattered by the measurement object, passes over the dichroic 40 , a tilted deflection mirror 215 and a condenser lens 216 on an avalanche photodiode 220 , This converts the recorded laser light into an electrical signal, which can then be evaluated.

The part of the optical setup that enables the digital-holographic measurements is in 2 through a reference beam path 135 , a zero beam path 145 and an object beam path 155 characterized. For all three beam paths, four highly stable diode lasers are used 110 . 112 . 114 . 116 slightly different and adjustable wavelength (eg, 1547.112 nm, 1548.652 nm, 1550.482 nm, 1552.924 nm) using three polarization-maintaining fiber beam splitters in a common polarization-maintaining optical fiber 118 coupled. After leaving the fiber 118 becomes the light with the help of the collimator 122 collimated. The subdivision into object, reference and zero beam paths is carried out via polarizing beam splitter cubes 124 , With the help of two rotatable half-wave plates 126 the division ratio can be set in the three beam paths.

For the object beam path 155 The collimated laser light passes through another polarizing beam splitter cube 148 and a quarter wave plate 150 , The light then hits the measuring point of the object 50 and is scattered there. Part of the scattered light then passes through the quarter wave plate 150 again to the polarizing beam splitter cube 148 , The quarter wave plate 150 ensures that the polarization of the laser light is rotated by 90 °, since it is traversed twice in total, and thus causes the backscattered light at the polarizing beam splitter 148 at 90 ° in the direction of the multi-wavelength holographic detector or camera 180 is distracted. Because as measuring objects 50 Also, and especially rough surfaces are of high interest, the backscattered light will have laser speckles. For example, the laser speckles in the plane of the camera can be about as large as 3 to 5 camera pixels, ie, about 20 μm to 50 μm. To be able to adjust the size of the laser speckles and only a part of the line scan camera 180 To illuminate the image, there is a slit in the further beam path 146 with adjustable gap size. The light, the slit diaphragm 146 has passed through, then passes on the line camera 180 ,

For the reference beam path 135 Part of the laser light becomes a polarization-maintaining fiber 128 coupled. After leaving the fiber 128 the light is going through a collimator 130 collimated. The following is the light over several lenses 132 and two optical grids 134 . 138 finally passes and interferes with the object steel 155 on the line camera 180 , For the later evaluation of the camera images of the line scan camera 180 It is necessary that the reference beams of the lasers 1 to 4 hit the camera at slightly different angles. The optical grids 134 . 138 make sure of that. The angular dispersion of one of the gratings used for the four laser wavelengths is about 3.2 mrad. Ideally, however, should be up to 20 mrad between the reference waves of the two extreme laser. That's why there are two grids 134 . 138 used, which additionally reduced to the camera 180 be imaged. This is the first grid 134 with the help of the inserted lenses 132 on the second grid 138 pictured and the second grid 138 turn sharp on the camera 180 displayed. This ensures that all laser beams cover the same area on the camera 180 illuminate, the impact angle due to the grid dispersion but are different. The effects of the two lattices 134 . 138 add up. In addition, the second grid is displayed 138 zooming (magnification about -0.5), which also increases the angle of incidence of the individual laser beams. This results in a spread of the wavelengths of the four lasers 110 . 112 . 114 . 116 to an angular range of about 12 mrad, which is sufficient for the later evaluation. In addition, the grids are designed and arranged such that only one of the diffraction orders of the grating passes through the lenses to the camera.

The zero beam path 145 The holographic structure is used to determine the zero point of the interferometric measurement. In interferometry, a critical point is always the compensation of drift of the arbitrary zero point. In the present case, this drift is mainly due to thermal influences on the reference beam path 135 owed. When heated, the optical path length of the reference beam changes. The phase angle between object and reference beam measured in the interferometer follows this change and falsifies the measured distance to the measuring point. To compensate for this, an almost unaffected part of the laser light within the optical structure is formed by means of a polarizing beam splitter 124 decoupled and also through a slit 146 on the line camera 180 directed. The rays from the object beam path 155 and zero beam path 145 meet different areas of the camera, so that both can be evaluated separately. This allows a direct Measurement of the drift in the reference beam path 135 , which can then be compensated in the evaluation.

Another light fiber 120 feeds a portion of the multi-wavelength holography laser beams to a referencing module 300 , which will be described in more detail below.

For the distance measurement based on digital holography, the recording and evaluation of interference images is necessary. In the developed optical setup, an infrared line scan camera is used to record the interference images 180 for use. A typical camera signal is in 3a shown. A brightness base level is generated by the reference wave. The object light and the light from the zero beam hit different areas of the camera line, so that the two signals can be easily separated. The superposition of all signals leads to interference, which is reflected in sinusoidal modulation of the beat signal. Because the reference waves of the four lasers 110 . 112 . 114 . 116 with the help of the at least one diffraction element 134 . 138 At different angles to the camera line, the four superimposed interference signals have different spatial frequencies.

In the Fourier transform of the camera signal, as in 3b Therefore, there are four peaks that represent the interference patterns of the individual lasers 110 . 112 . 114 . 116 correspond. In Fourier space, therefore, the measuring signals of the four lasers 110 . 112 . 114 . 116 be separated from each other by the peaks are cut out respectively. After clipping the peaks and inverse Fourier transform, the amplitude and phase of the object and zero waves of the four different lasers can be determined 110 . 112 . 114 . 116 be determined. The phase position φ _i , which is measured at a wavelength λ _i , is a measure of the traveled optical path length L:

wobei

die synthetische Wellenlänge bezeichnet. Auf diese Art kann der Eindeutigkeitsbereich vergrößert werden, wenn die Differenz der verwendeten Wellenlängen sehr viel kleiner ist als die Wellenlängen selbst. Durch Verwendung einer Reihe verschiedener synthetischer Wellenlängen kann so der eindeutige Messbereich bis in den Bereich einiger Millimeter erweitert werden.The phase position is for both the zero point beam 145 as well as for the object beam 155 measured. From the difference between the two phase values, the actual optical path length traveled in the object beam is calculated according to the above formula 155 measured and the influence of drift in the reference beam 135 minimized. In this way, the optical path length can first be determined only with a uniqueness range of one wavelength, since the measured phase is periodic with λ. In addition, the measured phase position of random interference patterns, in particular laser speckles, superimposed on rough surfaces, which prevent a direct evaluation of the phase position for distance measurement. The roughness R of the illuminated surface must be clearly below the wavelength of the light used, with visible light R << 600 nm, which is not the case for many surfaces. To bypass the speckle problem and to extend the uniqueness range, a multi-wavelength approach is chosen. The difference between the phase values measured at two different wavelengths serves as a measuring signal:

in which

denotes the synthetic wavelength. In this way, the uniqueness range can be increased if the difference in the wavelengths used is much smaller than the wavelengths themselves. By using a number of different synthetic wavelengths so the unique measurement range can be extended to the range of a few millimeters.

The generation of further synthetic wavelengths from previously generated synthetic wavelengths makes it possible to select the frequency spacings between adjacent individual wavelengths to be low, ie a few hundred GHz, and yet to cover a wide range of different wavelengths. Analogous to the above equations, when using four individual wavelengths, a synthetic wavelength Λ _12.34 can be generated from the synthetic wavelengths Λ ₁₂ and Λ ₃₄ , which is calculated as:

If Λ ₁₂ and Λ _{34 are} similar in size, the synthetic wavelength Λ _12,34 that is now generated becomes very large, even though the individual synthetic wavelengths Λ ₁₂ , and Λ _{34 are} rather small. For the wavelength differences of the individual wavelengths, this means that the distance from λ ₁ to λ ₂ can be chosen to be as large as that from λ ₃ to λ ₄ . This ensures that these wavelength differences with the aid of the referencing module to be described below 300 are well measurable.

4 shows a schematic structure of the homing module according to the invention, which is an accurate and traceable determination allows the used for distance measurement synthetic wavelengths. This is a prerequisite for highly accurate distance measurements and allows the feedback of the results to an internationally valid frequency standard. The frequency distances of the four laser lines used are measured. These are in the range of a few hundred gigahertz and thus beyond the possibilities of commercially available high-frequency electronics. For measurement therefore side lines are generated in the optical spectrum by means of electro-optical phase modulation. These side lines bridge the large frequency gaps between the lasers. The modulation frequencies of 36 GHz and 40 GHz are derived from a high-precision frequency standard. The modulation frequencies are chosen so that, in combination with the frequency intervals of the laser adjacent side lines typically with a few hundred MHz frequency spacing arise. The resulting beat frequencies can be detected and evaluated with sub-GHz electronics. From the measured frequencies, the known modulation frequencies and the knowledge of the number of side lines lying between the lasers, ie a rough knowledge of the laser wavelength, the frequency distances of the lasers and from them the synthetic wavelengths result. Since the Referenzierungsmessung takes place simultaneously with the distance measurement, so can the effects of fluctuations in the laser wavelengths -. B. by environmental influences such as temperature or mechanical vibrations - be compensated.

Part of the laser power, for example 50% or even only 1 to 10%, is provided by fiber couplers 120 - please refer 2 - the referencing module 300 made available. The selected wavelengths of the holographic distance measuring method can be referenced with side lines at a distance of 36 GHz or 40 GHz. These sidelines are using electro-optical modulators 312 . 314 generated. The driver frequencies can be from a 10 MHz frequency standard 320 be derived. In order to produce sidebands of higher order, the greatest possible depth of modulation is required, ie a combination of a strong driver signal and a small π-voltage Uπ of the modulators. The π voltage designates the voltage amplitude of the driver signal, in which a phase shift of π in the modulator arms is achieved. Therefore, electrical amplifiers with a high output power, for example 29 dBm, and modulators with a small π voltage, for example Uπ = 3.5 V, are advantageous. The optical signals become after the sideband generation in a fiber coupler 330 combined and with so-called balanced photodiodes 332 . 334 detected. By this type of detection, the DC component disappears in the photocurrent and only the superposition signal generated by closely adjacent side lines of different lasers is detected. The signals are transmitted by means of an analog-to-digital converter 340 recorded and loaded on a computer for digital processing. Due to the exclusive use of polarization-maintaining fiber components, adjusting the polarizations to maximize the interference signal on the photodiode is advantageously not necessary. In principle, the referencing module 300 not spatially to the multi-wavelength holography module 100 or the phase delay module 200 bound, it only requires a connection via fiber optic and a transmission of the measured values, for example via LAN or Internet.

5 shows exemplary optical spectral lines of the four holography laser sources 110 . 112 . 114 . 116 , as well as generated sidebands. Due to the electro-optical phase modulation with 36 GHz or 40 GHz side bands are generated with these frequency intervals from the respective laser line. To simplify the illustration are in 5 only sidebands up to a maximum of 6th order taken into account. Spectral closely spaced side lines produce measurable beat frequencies, here in the range of 413 MHz to 1237 MHz. Other theoretically possible beats between the lines are not detected. The frequencies of these beats are well above the 3 dB bandwidth of the detectors used (800 MHz), so that the detector acts as a low-pass filter. The frequency difference between two lasers then results from the measured beat frequency f _{beat of} the number of the respective side lines n, which is known by a rough knowledge of the wavelengths, and the modulation frequencies f _{mod1,2 of} the two oscillators, which are known from the frequency _standard Δf = n ₁ f _mod1 + n ₂ f _mod2 ± f _beat (9).

The respective sign and the assignment of the measured beat frequencies to the lasers 110 . 112 . 114 . 116 can be determined by a minimum fine adjustment of the laser frequencies. The respective beat frequency also moves to smaller or larger frequencies, so that the sign can be read from it.

6 shows a schematic sketch of the phase delay module 200 used phase transit time method. This is the intensity of the transmitter laser 210 high-frequency modulated. The transmitted light passes on the way to the measured object 50 the distance D, is scattered and / or reflected there, and a portion of the light passes through the distance D again and finally reaches the detector 280 , The modulation signal undergoes a phase shift Δφ in this way. This phase shift between transmit signal and received signal can be measured electronically with reasonable effort very precise. Due to the known relationship between the modulation frequency f _mod or modulation wavelength λ _mod , the speed of light c and the distance traveled, the distance D to the workpiece is obtained from the formula:

The result is unique only in a limited measuring range λ _mod / 2. At a modulation frequency of 128 MHz, the unique measurement range is approximately 1.17 m. The uniqueness range can be realized by additional lower modulation frequencies.

With this phase transit time measuring principle, a coaxial optics construction is possible because no angle between the light source 210 and detector 280 In addition, the method is very robust against background radiation, since not only an optical filtering of the received light takes place but similar to a lock-in amplifier only the light is processed by the electronic signal processing, which contains the modulation frequency of the laser. This corresponds to a very narrow-band filtering of the received signal. In order not to interfere with the interferometric measurement by means of the multi-wavelength holography module 100 It is preferable to generate a laser 210 used with a wavelength of 1470 nm. The fiber-coupled laser 210 is temperature-stabilized and can deliver an average output power of approx. 180 mW. To disturb the receiving electronics by the for the laser 210 necessary to avoid high high-frequency currents, is the complete modulation and control electronics together with the laser 210 housed in a closed metal housing.

As a detector 280 serves an InGaAs avalanche photodiode, which is housed in a completely shielded housing together with a temperature-controlled high-voltage module and a preamplifier. The present task does not require a large measuring range, but the measurement uncertainty should be less than about 2 mm. Therefore, the laser is modulated with a modulation frequency of f _mod = 128 MHz. The associated modulation wavelength λ _mod is 2.322 m. Since the light passes the measuring distance on the way there and back, the corresponding unique measuring range is about 1.17 m.

7 shows a schematic sketch for combining the phase delay measurement and the Mehrwellenlängenholographiemessung. The in 7 The sensor shown corresponds to the multi-wavelength holographic detector, depending on the method used 180 or the phase delay detector 280 , In a first step, a first distance value between the sensor and the object to be measured 50 coarsely determined by means of a time-of-flight (TOF) or a phase delay measurement. In a second step, a second distance value is determined by means of an interferometric measurement from the phase shift Δφ _int modulo of the longest synthetic wavelength measured thereby. In a third step, as many synthetic wavelengths are added to the second distance value until a combined distance value obtained thereby comes to rest within a measurement inaccuracy interval of the first distance value.

LIST OF REFERENCE NUMBERS

40

Dichroic beam splitter / dichroit

50

measurement object

100

Mehrwellenlängenholographiemodul

110

Laser (holography laser / holographic light source)

112

Laser (holography laser / holographic light source)

114

Laser (holography laser / holographic light source)

116

Laser (holography laser / holographic light source)

118

fiber coupler

120

Fiber to the referencing module

122

collimator

124

beamsplitter

126

Half-wave plates

127

Fiber optics for reference beams

128

Polarization maintaining fiber

130

collimator

132

Optical lenses

134

Diffraction element / optical surface grid

135

Reference beam / reference beam path

136

Optical lenses

138

Diffraction element / optical surface grid

140

Optical lens

142

beamsplitter

144

beamsplitter

145

Zero-ray / zero light path

146

slit

150

Quarter-wave plate

155

Object beam / object beam path

160

beamsplitter

170

imaging optics

180

Line scan camera (multi-wavelength holographic detector)

200

Phase delay measurement module

210

Phase delay laser (phase delay light source)

212

collimator

214

deflecting

215

deflecting

216

converging lens

224

deflecting

260

beamsplitter

280

Photodiode (phase delay detector)

300

Referenzierungsmodul

302

RF oscillator

304

RF oscillator

306

amplifier

308

amplifier

312

modulator

314

modulator

320

Frequency standard / frequency standard (10 MHz)

330

fiber coupler

332

Balanced Detector / Balanced Photodiode

334

Balanced Detector / Balanced Photodiode

340

Analog-to-digital converter

350

computer

500

System for distance measurement

Claims (11)

System ( 500 ) for distance measurement, comprising - a multi-wavelength holography module ( 100 ) for capturing a holographic measurement data set for at least one measurement point on the basis of at least one synthetic wavelength, wherein the multi-wavelength holography module ( 100 ): - at least two holographic light sources ( 110 . 112 . 114 . 116 ) for generating at least two coherent holographic light beams having different wavelengths, - at least one beam splitter ( 124 . 160 ) for splitting each holographic light beam into an object light beam ( 155 ) and a reference light beam ( 135 ), and - at least one diffractive element ( 134 . 138 ) for dispersively tilting the reference light beams ( 135 ), wherein the at least one diffraction element ( 134 . 138 ) is arranged and arranged to determine an associated estimate for each wavelength of the at least two holographic light beams, and wherein the system further comprises: a referencing module (10) 300 ) for determining the at least one synthetic wavelength on the basis of the associated estimated values, and an evaluation module for determining the distance of the at least one measuring point. A system according to claim 1, wherein the at least one diffractive element ( 134 . 138 ) is an optical grating. System according to one of the preceding claims, further comprising - a phase delay measuring module ( 200 ) for detecting a phase delay time data set of the at least one measurement point based on a modulated phase delay light beam. The system of claim 3, wherein the phase transit time measurement module ( 200 ) at least one phase delay light source ( 210 ) for emitting at least one phase delay light beam, and wherein the at least one phase delay light source ( 210 ) and the at least two holographic light sources ( 110 . 112 . 114 . 116 ) are arranged such that meet the at least one phase delay light beam and the at least two holographic light beams at the same measuring point. System according to one of the preceding claims, wherein the evaluation module is adapted to determine the distance of the at least one measurement point based on the Holographiemessdatensatzes and the phase delay data record. Method for distance measurement, comprising the steps - providing a system ( 500 ) according to any one of claims 1 to 3; Detecting the holographic measurement data set for the at least one measurement point by means of the multi-wavelength holography module ( 100 ) - for each wavelength of the at least two holographic light beams, determining the associated estimated value by means of the at least one diffraction element ( 134 . 138 ); Determining the at least one synthetic wavelength on the basis of the associated estimated values by means of the referencing module ( 300 ); and - determining the distance of the at least one measuring point by means of the evaluation module. The method of claim 6, wherein detecting the holography measurement data set for the at least one measurement point by means of the multi-wavelength holography module. 100 ) comprises generating side lines by means of a phase modulation of the at least two holographic light beams. Method according to claim 6 or 7, wherein a system ( 500 ) according to one of claims 3 to 5, and wherein the method further comprises the following step: - detecting the phase delay data record for the at least one measuring point on the basis of a modulated phase transit time light beam by means of the phase transit time measuring module ( 200 ). The method of claim 8, wherein the phase transit time light beam is modulated with at least one predetermined phase delay modulation frequency, wherein the at least two holographic light beams are each modulated with an associated predetermined holographic modulation frequency, and wherein the phase delay modulation frequencies and the holographic modulation frequencies from a common frequency standard ( 320 ) be derived. Method according to one of claims 6 to 9, wherein a system ( 500 ) according to claim 5, and wherein the distance of the at least one measurement point is determined on the basis of the holographic measurement data set and the phase delay measurement data set. Method according to one of claims 6 to 10, wherein the detection of the Holographiemessdatensatzes and the detection of the phase delay time data record are carried out substantially simultaneously.

Images