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    • 专利摘要:
    Device and method for detecting an optical pulse (I) in an optical signal (x), having at least two parallel receiving channels (U, V), to each of which a portion (xi, x 2) of the optical signal (x) is supplied and the in each case an optoelectronic receiving element (3, 4) for converting the portion (xi, x 2) into an electrical signal (u, v) in which an optical pulse (I) is deposited as an electrical pulse (Eu, Ev), wherein a optical pulse (I) is detected when at least two electrical signals (u, v) - compensated for any signal propagation time differences (At) between the receiving channels (U, V) - within predetermined tolerance limits (o ~) simultaneously an electrical pulse (Eu, Ev) occurs.
    公开号:AT512154A4
    申请号:T500062011
    申请日:2011-12-14
    公开日:2013-06-15
    发明作者:Andreas Dipl Ing Hofbauer；Martin Dr Pfennigbauer；Andreas Dr Ullrich
    申请人:Riegl Laser Measurement Sys；
    IPC主号:
    专利说明:

    PATENT OFFICER DIPL.-ING. Dr.techn. ANDREAS WEISER EUROPEAN PATENT AND TRADEMARK ATTORNEY A-l 130 VIENNA · KOPFGASSE 7 04369 RIEGL Laser Measurement Systems GmbH A-3580 Horn
    The present invention relates to an apparatus and a method for detecting an optical pulse in an optical signal. For the detection of the smallest optical pulses, increasingly high sensitivity receiver elements are used. Examples of such high sensitivity detectors are photomultiplier tubes and hybrid photon detectors (HPDs). Theoretically, impulses consisting of only a few photons can be converted into usable electrical impulses. In addition to the desired signal photons, photons of unavoidable background light {sun, artificial light sources, hot surfaces, etc.), but also other particles, e.g. X-rays or cosmic background radiation, electrical impulses off. Moreover, in the case of particularly sensitive optoelectronic receiving elements, even without external influence due to quantum mechanical effects, spontaneous generation of electrical impulses in the receiving element itself can occur.
    Although the resulting interference pulses can be somewhat reduced by suitable measures such as spatial, spectral and temporal filtering, but remain just those noise pulses whose amplitude is high and not by the TEL: (+43 1) 879 17 06 FAX: (+431 ) 879 1707 EMAIL MAIL @ PATENTENET WEB: WWW.PATENTE.NET FIRST BANK: 038-56704 BLZ 20111 IRAN: AT102011100003856704 BIO GIBAATWW-VAT: AT U 5383290 ·
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    Intensity of the light received by the receiving element can be explained. For example, in the context of laser range finding, such large electrical glitches would be erroneously associated with a large optical echo pulse and indicate a real non-existent measurement target.
    The object of the invention is to overcome this problem in order to make better use of the high sensitivity of modern optoelectronic receiving elements for optical pulse transit time measuring methods, such as laser range finding.
    This object is achieved in a first aspect of the invention with an apparatus for detecting an optical pulse, comprising: at least two parallel receiving channels, each of which a portion of the optical signal is supplied and each containing an optoelectronic Empfangseiement for converting the portion into an electrical signal in which an optical pulse is reflected as an electrical pulse, and an evaluation circuit connected to the receiving elements, which is designed to de-tektieren an optical pulse when compensated in at least two electrical signals to any signal propagation time differences between the receiving channels - within predetermined Tolerance limits at the same time an electrical impulse occurs.
    In a second aspect of the invention, this object is achieved with a method of detecting an optical pulse in an optical signal, comprising:
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    Dividing the optical signal into at least two parallel receiving channels each having an optoelectronic receiving element which converts the respective portion of the optical signal into an electrical signal in which an optical pulse is reflected as an electrical pulse; and
    Detecting an optical pulse when at least two electrical signals - compensated for any signal delay differences between the receiving channels - within predetermined tolerance limits simultaneously an electrical pulse occurs.
    The invention is based on the approach of splitting the optical signal onto at least two receiving elements and comparing the resulting electrical signals to produce a "false" random signal in a receiving element. Recognize pulses as glitches and suppress in further processing. As a "real" or correct pulses are identified only those pulses which - taking into account any signal propagation time differences of the two receiving channels and within predetermined tolerances - simultaneously (coincident) occur in both receiving channels. As explained below, this can be done either in each channel separately threshold detection and then perform the coincidence comparison ("post-detection correlation"), or the outputs of the receiving elements are linked directly for the coincidence comparison and only then subjected to a common threshold detection ("Pre-detection correlation"). The link can have any complexity, in particular if the receiving elements have significantly different noise characteristics or are of a completely different type.
    The invention thus allows the operation of high-sensitivity receiving elements with a higher "glitch rate". or "false trigger rate", as would be possible with a single evaluation according to the prior art. In modern high-sensitivity receiving elements, the glitch rate is often from the point of operation, e.g. a bias voltage of the receiving element, which in turn defines the sensitivity: With the aid of the invention, e.g. selected a higher bias and thus greater sensitivity can be achieved without the associated higher false trigger rate of the individual receiving elements affects the detection reliability of the pulse detection. As a result, with the aid of the invention, the high sensitivity of modern optoelectronic receiving elements can be better utilized.
    In a simple embodiment of the invention, the evaluation circuit can only output the fact of the occurrence of {signal-time-adjusted) coincident pulses as a detection result on an output. Preferably, however, the evaluation circuit of the device according to the invention and the method of the invention are also designed to determine the occurrence time of the optical pulse from the time of occurrence of at least one of said electric pulses in its signal during detection.
    Preferably, at least one receiving element is highly sensitive, e.g. it contains an avalanche photodiode or a photo multiplier tube, preferably a hybrid photon detector. In a first variant of the invention, all the receiving elements may be of the same high sensitivity type, e.g. Hybrid photon detectors. In a second variant, only one or some of the receiving elements may be highly sensitive, e.g. in the form of a photomultiplier, an avalanche photodiode or a hybrid photon detector, and one or more other receiving elements are low in sensitivity, e.g. "Quot conventional &; Optoelectronic receiving elements such as photodiodes, CCD sensors or the like. This embodiment is based on the assumption that a random interference pulse from the high-sensitivity receiving element is always so large that even a conventional low-sensitivity receiving element would have had to deliver a corresponding signal at this point. Such a mix of high sensitivity and low sensitivity receivers can save costs, albeit at a price reduced overall sensitivity.
    The splitting of the optical signal onto the parallel receiving channels or their receiving elements can be carried out in the simplest case by using the receiving elements e.g. be arranged so close to one another (or staggered) that the optical signal ("light beam") hits all the reception elements with one share at a time. This can also be supported by a corresponding receiving optics. If this is not possible or expedient, an optical beam splitter is preferably used, which provides for the division of the optical signal in the said proportions.
    The optical signal can be distributed symmetrically to all receive channels with such a beam splitter, i. the said proportions are in the ratio of 50:50, 33:33:33, 25:25:25:25, etc., etc. According to a further embodiment of the invention, however, the proportions can also be selected unequally large, e.g. at two receiving channels 40:60, 30:70, 20:80, 10:90, etc., which provides an additional degree of freedom in the design of the apparatus and method of the invention. The division can be optimally adapted to the sensitivity of the receiving elements.
    It is particularly favorable if the larger proportion is supplied to the receiving channel with the highly sensitive receiving element in order to maximize its sensitivity; the other receiving channel with the low-sensitivity Empfangselernent is then used as a kind of auxiliary channel for the coincidence comparison for said suppression of interference signals from the sensitive receiving channel.
    The mentioned evaluation circuit, which (taking into account any signal propagation time differences) the simultaneity or coincidence of electrical impulses in hers
    10 ^ 11/50006 detected signals can be realized in various advantageous ways. In a first embodiment of the invention according to a "pre-detection cor-relation" method, the evaluation circuit has a multiplier connected to the outputs of all the receiving elements, whose output is fed to a threshold value detector. In an alternative embodiment according to a "postdetection correlation" method, the evaluation circuit comprises, for each receiving element, a threshold value detector connected to its output, the outputs of all threshold value detectors being fed to an AND element. In the latter variant, each receiving channel can be analyzed individually with the aid of its own threshold detector, which, as explained later, can also carry out additional analyzes such as an evaluation of the pulse width. By contrast, the first-mentioned "pre-detection correlation" embodiment has the advantage that it only means half the signal processing effort in terms of threshold value detection.
    In order to further increase the detection reliability, the amplitude and / or pulse shape of coincident pulses can be checked in addition to the coincidence (coincidence-corrected) of pulses in the receiving channels. In a first preferred variant of the invention, the evaluation circuit is accordingly designed to detect an optical pulse only when the electrical pulses occurring at a predetermined time interval - possibly compensated for gain differences of the receiving elements and for the ratio of the radiation - Also have approximately the same amplitude. This is based on the realization that a "real" electrical pulse, which was triggered by an optical pulse, in all receiving channels - gain-corrected - must have a similar large amplitude.
    For example, the evaluation circuit may have a comparator connected to the outputs of all the receiving elements, which compares the amplitudes of the signals and, if they are equal within a tolerance window, outputs an output signal, e.g. has this (same) amplitude. Preferably, the comparator is followed by a further threshold detector, which evaluates this same amplitude and detects the optical pulse only at a threshold exceeded. Alternatively or additionally, the comparator can also be preceded by threshold detectors at its inputs which only make use of its amplitude comparison if the signals exceed a minimum amplitude.
    Alternatively (or additionally), the evaluation circuit may also be designed to detect an optical pulse only if the electrical impulses occurring at a predetermined time interval also have approximately the same pulse shapes or those assigned to one another in a database. This is based on the further realization that a "real" electrical pulse, which was triggered by one and the same optical pulse, in all receiving channels either 9 equal pulse shapes (if the receiving elements are similar) or mutually assignable pulse shapes (if the receiving elements are different) causes: Thus, by test series that of different receiving elements generated, attributable to one and the same optical pulse pulse shapes are pre-recorded and assigned to each other in a database; Pulse forms occurring in the later "online" detection mode can then be checked for mutual association in the database and, if assigned to one another, used as an additional criterion for the coincidence of coincidental pulses.
    The device of the invention may be constructed in all its analogous techniques, e.g. by means of analog multipliers and threshold detectors, comparators, subtracters, etc. Alternatively, the outputs of the receiving elements may be passed through analog-to-digital converters and the remainder of the device digitally constructed, exploiting the integrability, flexibility and low cost of mass production of digital signal processing elements.
    In a further aspect, the detection method of the invention comprises the additional steps:
    Removing all threshold crossing electrical pulses other than the electrical pulse of at least one of the signals occurring at the time of the detected optical pulse to generate at least one signal thus cleaned; and
    Using the at least one adjusted signal to more accurately determine the time of occurrence; or the additional steps:
    Extracting a portion of at least one of the signals defined by a time window at the time of occurrence of said electrical pulse therein; and
    Using the at least one extracted section for more accurate determination of the occurrence time.
    It is particularly favorable if such cleaned signals or sections are generated from at least two signals and combined to form a signal set or summed up into a sum signal which is used for a more accurate determination of the occurrence time.
    These embodiments combine the discussed advantages of coincidence detection with the advantages of "pre-detection averaging", i. an averaging of a plurality of received signals before a threshold detection, which improves the signal-to-noise ratio with the root of the number of averaged received signals.
    The aforesaid exact determination may be a new threshold detection, now with an adjusted sum signal with improved signal-to-noise ratio, or a "fit" function. a reference pulse known timing in the 11 detected pulse, from which the time of occurrence can be determined more accurately.
    The invention will be explained in more detail with reference to embodiments illustrated in the accompanying drawings. In the drawings show:
    Fig. 1 is a block diagram of the device of the invention operating according to the method of the invention; Figures 2 and 3 are timing diagrams of optical and electrical signals occurring in the apparatus of Figure 1 and the method of the invention; 4 to 7 different embodiments of the Auswert circuit of the device of Fig. 1;
    8a shows the input and output signals of an exemplary threshold detector in the invention, and FIG. 8b shows the partial coincidence overlap of the samples of real pulse shapes; and FIGS. 9 and 10 are timing diagrams of electrical signals which occur in further embodiments of the method according to the invention.
    In Fig. 1 there is shown an apparatus 1 for detecting optical pulses I (Fig. 2) which may be used as part of an optical signal x (t), e.g. in the form of a laser beam, impinging on the device 1. The term "detect " In this case, a pulse I comprises both the mere recognition of the fact that a pulse I is occurring at all, as well as the recognition 12 of this fact and determination of the time of occurrence ti of the pulse I in the optical signal x (t) on a time scale t. '
    The optical signal x (t) is fed to an optical beam splitter 2, which splits this onto at least two parallel receiving channels U, V, each with an optoelectronic receiving element 3, 4. Each receiving channel U, V or each optoelectronic Empfangseiement 3, 4 thus receives a share xi, X2 of the optical signal x (t). The proportions Xi, X; can sum to 100% of the optical signal x (t) unless there are no leakage losses.
    The beam splitting xi: x2 may preferably be symmetric, i. in the present example, two receiving channels χιίΧ2 = 50:50. Optionally, different division ratios may also be used, e.g. 40:60, 30:70; 20:80, 10:90, etc., especially in connection with differently sensitive receiving channels U, V, as will be explained in more detail later.
    For example, the beam splitter 2 may comprise one or more semitransparent mirror or beam splitter plates 5 and one or more deflecting mirrors 5 ', e.g. also cascaded if more than two receiving elements 3, 4 are to be fed. Any other type of optical beam splitter known in the art is also suitable.
    In a simplified embodiment, the beam splitter 2 can also be omitted if the receiving elements 3, 4 are arranged so close to one another (or also offset one behind the other) that the optical signal x (t) can impinge on both receiving elements 3, 4, each with one component , For example, even a highly focused laser beam after some distance and especially after reflection always undergoes some beam broadening, so that the usual beam diameter of a reflected laser beam forming the optical signal x (t) may be sufficient to cover two or more receiving elements 3, 4 , In addition, by a device upstream of the device 1 (not shown), a corresponding conditioning of the optical signal x (t) take place in order to achieve both receiving elements 3, 4. If the beam splitter 2 is omitted, the different proportion distribution Xi: x2 can be realized, for example, by additional attenuation elements in front of one of the receiving elements 3, 4, if desired.
    The receiving elements 3, 4 respectively convert the optical signal x (t) impinging on them into an electrical signal u (t) or v (t) in which each optical pulse I from the optical signal x (t) is a electric impulse Eu or Ev precipitates (FIG. 2). The signals u (t) and v (t) are output on outputs 6, 7. For the receiving elements 3, 4, all kinds of known in the art opto or photoelectric elements may be used, such as photodetectors, photodiodes, phototransistors, photocells, avalanche photodiodes or CCD or CMOS light sensors, etc. The here presented device 1 and her 14
    Methods are particularly suitable for highly sensitive photoelectric elements such as avalanche photodiodes or APDs (Avalanche Photo Diodes), SPADs (Single Photon Avalanche Diodes), GM APDs (Geiger Mode APDs), Si PMs (Silicon Photomultipliers), MPPCs (Multi -Pixel photon counters), negative feedback avalanche diodes (DADs), discrete amplification photon detectors (DAPDs), hybrid photon detectors (HPDs), photomultiplier tubes (PMTs), and the like, which detect even single photons and as electrical photons Pulses Eu, Ev in their output signals u (t), v (t) can output.
    It is also possible to use differently sensitive optoelectronic components for the receiving elements 3, 4. Thus, for cost reasons, for example, only one or some of the receiving elements 3, 4 can use a highly sensitive optoelectronic component such as a hybrid photon detector, and for the other or some others a "conventional". low-sensitivity optoelectronic component such as a photodiode.
    Differently sensitive receiving elements 3, 4 can also be supplied with different proportions Xi, x2 of the optical signal x (t), either to compensate for the different sensitivities or even to amplify them: Thus, a high-sensitivity receiving element 3, 4 can be even larger Proportion Xi, x2 be supplied in order to make maximum use of its high sensitivity, in which case the other (low-sensitivity) receiving element 3, 4 sam same "auxiliary channel". forms suppression for the further described interference signal.
    To the outputs 6, 7 of the Empfangseiemente 3, 4 is an evaluation circuit 8 is connected / at the same time (coincident) in their input signals u (t), v (t) occurring electrical pulses Eu, Ev detected ("coincidence detection", CID) and in the detection case on an output 9 in an output signal s (t) outputs a pulse (Fig. 2). The output pulse Ei of the evaluation circuit 8 represents the detected optical pulse I and optionally also its time of occurrence t1.
    The time of occurrence ti can be evaluated accordingly. An application example is the pulse duration measurement in a laser rangefinder or laser scanner, from which optical pulses I are emitted, reflected on objects to be measured in the surrounding objects and received in the device 1, wherein the difference between the known transmission time and the measured time of reception ( Occurrence time ti) the optical pulse transit time and thus the distance to an environment object can be determined.
    It goes without saying that the evaluation circuit 8 also determines the time of occurrence ti itself and, for example, on a digital output (not shown) in numerical form. In the simplest case, the time of occurrence ti is not further evaluated, and the fact of the occurrence of a pulse Ei in the signal s (t) at the output 9 simply indicates only the fact of the arrival of an optical pulse I in the device 1 as a detection result.
    Fig. 2 shows the signals x (t), u (t), v (t) and s (t) over time t in detail. Due to the high sensitivity of the receiving elements 3, 4 occur in the output signals u (t) and v (t) as mentioned in addition to the "real". Pulses Eu and Ev and regardless of the receiver noise floor ("noise floor") 10 also occasionally high-amplitude glitches 11 at random times on. Such stochastic glitches 11 have much higher amplitude than the noise floor 10 and may even have greater amplitude than the true Eu and Ev pulses. However, due to their stochastic distribution over time t, it is very unlikely that such glitches 11 occur simultaneously in two or more output signals u (t), v (t).
    The evaluation circuit 8 uses this circumstance and takes into account or detects only those pulses Eu, EV / which occur at the same time tu = tv = ti in the signals u (t) and v (t), and thus suppresses all interference pulses 11. The lowest diagram of FIG. 2 shows the output signal s (t) of the evaluation circuit 8 as a result of this coincidence detection. The noise floor 10 remains, but the stochastic interference pulses 11 of large amplitude are suppressed; the correct momentum Ei at the time of occurrence tj is now clearly recognizable and can be detected, for example, by threshold value detection
    10 2011/50006
    Threshold Si, to distinguish it from the noise floor 10, are detected.
    It is understood that the device 1 may also have more than two receiving elements 3, 4 and accordingly more than two signals u (t), v (t), ... from the evaluation circuit 8 to coincidence of pulses Eu, Ev,. .. can be checked. In the case of such a plurality of signals, a pulse I may be considered detected when all of the three or more signals u (t), v (t), ... show an electrical pulse Eu, Ev, ... at the same time ti , or if the majority of signals show this, or if at least two signals show this. The evaluation circuit 8 can perform corresponding logical operations.
    The device 1 can be implemented entirely in analog technology or as far as possible in digital technology. For the latter purpose, the outputs 6, 7 of the receiving elements 3, 4 via analog / digital converters 12, 13, the inputs of the evaluation circuit 8 are supplied, which then, for. is constructed with the help of one or more signal processors.
    It is understood that the coincidence or the simultaneity detection of the pulses Eu and Ev described with reference to FIGS. 1 and 2, any differences in the signal propagation times, which in the receiving channels U, V, i. in each case from the input of the beam splitter 2 to the outputs 6, 7 of the receiving elements 3, 4 (or any analog / digital converters 12, 13) should take into account. Such signals 18
    Time differences may be due to different path lengths traveled by the optical pulse I in the beam splitter 2 and / or by different receiving elements 3, 4 and analog-to-digital converters 12, 13, e.g. show different responses or have different delay times between their inputs and outputs.
    Fig. 3 shows this in detail. On the other hand, when the signal propagation time difference between the receiving channels U (5-3-6-12) on the one hand and V (5-5 '- 4-7-13) is At, electrical receiving pulses Eu and Ev are "coincident" in the above sense, if they are in a time interval At which is equal to the signal propagation time Δt. The evaluation circuit 8 accordingly detects pulses Eu and Ev as coincident, if they follow one another at a predetermined time interval Δt which corresponds to the signal propagation time difference Δt between the receiving channels, as can be determined once for example by reference measurements and then given to the evaluation circuit 8. When determining the time of occurrence ti on a time scale t, the signal propagation time difference Δt is to be correspondingly taken into account, depending on whether the occurrence time tu of the pulse Eu and / or the occurrence time tt of the pulse Ev in the respective time scale t is used for this purpose.
    FIGS. 4 to 7 show possible implementation forms of the evaluation circuit 8, which can be formed both in analog technology (FIGS. 5 and 7 only partially) and in digital technology (with corresponding analog-to-digital converters 12, 13). It is understood that in the case of digital technology, the illustrated hardware components can also be realized by corresponding software components of a suitably programmed signal processor, microprocessor or computer.
    Fig. 4 shows a first embodiment of the evaluation circuit 8, which implements a "pre-detection correlation" method. The signals u (t), v (t) of the receiving elements 3, 4 are here supplied to a multiplier 14, the product s (t) = u {t) * v (t) (each "offset-adjusted", ie without Equal shares). The output of multiplier 14 is preferably (though not necessarily) passed through a threshold detector 15, which compares the comparison shown in FIG. Threshold si performs. Signal propagation time differences Δt between the reception channels U, V can be e.g. be considered by a corresponding time delay element 16 in a receiving channel, which delays this by the time interval At.
    Fig. 5 shows an alternative embodiment of the evaluation circuit 8 which implements a "post-detection correlation" method. Here, the signals u (t), v (t) are respectively supplied to separate threshold detectors 17, the outputs 18, 19 are connected to the inputs of an AND gate 20, the logical AND operation of the detection signals Ud (t), Vd ( t) of the outputs 18, 19 performs. The time delay element 20 16 may be inserted before or after a threshold detector 17.
    Combinations of the embodiments of Fig. 4 and 5 are possible, for example by the signals u (t), v (t) via separate threshold value detectors 17 are supplied to the multiplier 14 of the evaluation circuit 8 of FIG.
    6 shows a further embodiment of the evaluation circuit 8 on the basis of a comparator 21, to which the signals u (t), v (t) of the receiving elements 3, 4 are applied via optional threshold detectors 22 and to which a further optional threshold value detector 23 can be connected downstream. The comparator 21 compares the amplitudes of the signals u {t), v (t); if these are coincident and approximately equal, taking into account the time interval At in the timer 16; Within a tolerance range or window, he detects this as the occurrence of a pulse I and outputs the detection result as a pulse Ei in the signal s (t) on the output 9, if necessary after Schwel 1 value comparison in the optional threshold detector 23. The embodiment of Fig. 6 is based on the insight that real pulses Eu and Ev always have approximately the same amplitude, eg when the beam splitter is a 50:50 divider and the receiving elements 3, 4 are similar, however, interference pulses 11 random and thus usually different amplitudes and compared to the noise floor 10 always have relatively large amplitudes. The optional threshold detectors 22 can thereby ensure that only pulses Eu and Ev are checked for amplitude equality by the comparator 21 with a minimum amplitude, and the optional threshold detector 23 that only comparison results of a minimum amplitude are evaluated as impulse I. Any gain differences in the receive channels, e.g. different output amplitudes of the receiving elements 3, 4 despite the same optical input amplitudes, and asymmetric beam splitter ratios of Xi: x2 # 50:50 are of course to be considered and compensated in the amplitude comparison in the comparator 21.
    7 shows yet another embodiment in which the evaluation circuit 8 and in particular the comparator 21 in addition to - possibly time-adjusted (see delay 16) - coincidence detection and alternatively or in addition to - possibly gain-compensated amplitude comparison of FIG. 6, a pulse shape comparison between coincident Pulses Eu and Ev performs. For this purpose, 24 tuples Pi, P2, ... of mutually assigned pulse shapes Fu, Fv, ... are stored in a database. The pulse shapes Fu and Fv represent the pulse shapes of electrical reference pulses Eu and Ev, which were obtained in response to a variety of types (amplitudes, pulse widths) of input at the device 1 optical pulses I at the outputs 6, 7 of the various receiving elements 3, 4 and for the same pulse I can be assigned to each other. For received pulses Eu and Ev identified as coincident, the assever circuit 8 compares their pulse shape with the reference pulse shapes Fu and Fv stored in the database 24 and, if they correspond to the pulse shapes associated with one another in a tuple Pi, P2,. the pulses Eu and E "are verified as representing one and the same optical pulse I; This is output as a detection result, optionally together with the time of occurrence ti, at the output 9. In this case too, the same threshold value detectors 22, 23 as in the embodiment of FIG. 6 can additionally be used with the same function.
    Alternatively, instead of a complete pulse width comparison, only single meaningful parameters of the pulse shapes could be compared, e.g. (Half-amplitude) pulse width B, (rising) edge steepness S, etc. In a tuple Pi, P2, .. · the database 24 could therefore only each associated pulse shape parameters (Bu, Bv) or (Su, Sv ) and used in the manner mentioned.
    As shown in Fig. 8a, the term " threshold detector " in the present description generally a comparator, Schmitt trigger or the like. which compares a signal a (t) at its input with a predefinable threshold value Si, detects the exceeding of the threshold value si and outputs a non-zero output signal b (t) only in the case of exceeding it, e.g. a predetermined amplitude value or the input signal a (t) itself. 23
    The threshold value detectors considered here can also take into account additional characteristics of the input signal a (t) in the threshold value comparison, for example the pulse width and / or pulse shape of pulses in the input signal. For example, the threshold value detectors can only respond to those input pulses which, in addition to an amplitude which overcomes the threshold value si, do not exceed a maximum pulse width and / or do not fall below a minimum pulse width and / or whose edge steepness corresponds to specific minimum and / or maximum slopes. All of these embodiments are referred to herein by the term "threshold detector". summarized.
    It is understood that in discrete-time implementations of the device 1 or of the method performed by it, in which all electrical signals are present as sequences of samples, at high sampling rates simultaneity or coincidence is not detected only when pulses Eu and Ev in all their samples temporally cover, but already a temporal coincidence within acceptable tolerances exists, eg a temporal overlap in only a few of its samples. FIG. 8b shows this on the basis of two threshold-detected pulses Eu and Ev, which are time-discretely sampled and digitized by means of analogue-to-digital converters 12, 13, in each case in 7 samples, which themselves - taking into account the propagation time differences At - Overlap temporally 24 only in terms of two samples, but this may be sufficient, for example, to consider them within given tolerance limits as coincident, ie if the time deviation | ε | is smaller than a tolerance limit σ or the time deviation ε is between a lower tolerance limit a ~ and an upper tolerance limit o +.
    In the device 1 of FIGS. 1 to 8, the following process thus proceeds in summary form:
    First, in a first step, the optical signal x (t) is split into two or more receiving elements 3, 4 in order to generate electrical signals u (t), v (t).
    Subsequently, the fact - and optionally also the time of occurrence ti - of an optical pulse I is detected when at least two of the signals u (t), v (t) and so on (time-adjusted) an electrical pulse Eu, Ev etc. occurs simultaneously.
    FIGS. 9 and 10 show applications of the device 1 or of the method which it exercises, in which the detection result s (t) is used as an intermediate result for a more detailed determination of the time ti of the optical pulse I. These embodiments are based on an analysis of the signals u (t) and v (t) over their entire time course or at least a portion thereof and require a corresponding time record of the same. The embodiments of FIGS. 9 and 10 can therefore no longer be realized in pure analog technology or real-time digital processing, but only with the aid of digitized, stored signals u (t) and v (t) in the manner of an "Off". -Evaluation of the same.
    In the following, the addition of the time index t is omitted in the description of all the signals u (t), v (t), s {t), etc., in order to facilitate the description of the method.
    The detection result s and the electrical pulse ΕΣ which is detected therein and which represents the optical pulse I are used in the embodiment of FIG. 9 to clean up the input signals u and v by the glitches 11, respectively. The glitches 11 can be obtained as interference signals us or vs, by the threshold value s2 (FIG. 9a) crossing signals Ud, vd, for example, available at the outputs 18, 19 of the threshold value detectors 17 (FIG. 4), the detected pulses Ei are removed, ie us = Ud - s and vs = Vd - s (Figure 9b).
    The spurious signals us, vd are subsequently subtracted from the received signals u, v (FIG. 9a), resulting in adjusted received signals u * = u - us, v '= v - vs (FIG. 9c).
    The thus adjusted to the glitches 11 received signals u ', v1 can then be used for a variety of signal evaluation methods for more accurate determination of the electrical pulse Er and thus the optical pulse I, for example by renewed threshold detection. However, the cleaned-up signals u ', ν' may also be used only as a "sentence". {u ', ν'} of signals are compiled,
    - 26 - which is evaluated together, e.g. by comparison with a set of reference pulses, as will be explained in more detail later.
    Alternatively, the adjusted receive signals u ', v',. "Are summed (averaged) to produce an adjusted sum signal s' = u '+ ν' +..., See Fig. 9d. In the adjusted sum signal s', the desired electrical pulse Ei can be detected even better by threshold value detection with respect to a threshold value S3. Such summing of input signals before threshold detection ("pre-detection averaging") advantageously increases the signal-to-noise ratio of the threshold detection signal s * by the root of the number of summed signals.
    In addition, both in the individual adjusted received signals u ', v *, ... and in the adjusted sum signal s', the time ti of the pulse Ex or the sum pulse E'1 can be determined even more accurately. 9e shows an enlarged section of the time axis t of FIG. 9d, from which it can be seen that in practice the pulse E'i does not have an ideal dirac or rectangular shape, but edges flattened due to the band limitation of real systems 25, 26 and a vertex 27. The decision as to which exact timing (time of occurrence) ti has such a real momentum E'i can then be made by means of various methods.
    27
    A first variant is the detection of the time ti when one of the flanks 25 or 26 exceeds or falls below a certain threshold value S3 (FIG. 9e) or when the apex 27 is detected.
    A second variant is shown in Fig. 9f. Here, the waveform of the detected pulse E'i is compared with the waveform of a known reference pulse Er / as obtained, for example, from reference running time measurements, i. the pulse E'i is optimally "fitted" into the reference pulse Er " (or the other way around). A reference time of the reference pulse He can then be used as the time of occurrence ti of the pulse E'i.
    Fig. 10 shows a modification of the method of Fig. 9, which does not require the step of subtracting the spurs us, vs, by simply dividing from the signals u, v those temporal sections u ", v " which define a time window just around the time of occurrence tU / tv of the received pulses Eu, Ev detected as coincident (FIG. 10a). Fig. 10b shows the extracted temporal sections u ", v " enlarged in detail: Already in these sections u ", v " For example, the occurrence points tu, tv of the received pulses Eu / Ev can be more accurately determined, e.g. by the threshold detection method of Fig. 9e or the reference pulse fitting method of Fig. 9f. Again, sections uM, v " again as a signal set {u ", v "}, e.g. by comparison with a set of reference pulses {Er}.
    Preferably, the extracted portions are " and v " however, to a sum section s " summed {Fig. 10c), which due to the summation again has an advantageously improved signal / noise ratio and can thus be supplied to an improved threshold detection with respect to the threshold value S3 or an improved reference pulse fit according to FIG. 9f in order to more accurately determine the time of occurrence tj.
    The apparatus 1 and the described methods may also be combined with conventional pre- and post-processing apparatus and methods. For example, conventional signal processing methods for spatially, spectrally and / or temporally filtering the signals x, Xi, X2, u, v and s can also be used in or in front of the receiving channels U, V.
    The invention is not limited to the illustrated embodiments, but includes all variants and modifications that fall within the scope of the appended claims. Thus, everything that has been said so far about only two receiving channels or elements and their two signals can be extended to any number of receiving channels or elements and signals.
    权利要求:
    Claims (28)
    [1]
    1. A device (1) for detecting an optical pulse (I) in an optical signal (x), characterized by at least two parallel receiving channels (U, V), each having a portion (Χχ, X2) of the optical signal ( x) is supplied and each containing an optoelectronic receiving element (3/4) for converting the portion (xif X2) in an electrical signal (u, v), in which an optical pulse (I) as an electrical pulse (Eu, Ev ), and an evaluation circuit (8) connected to the receiving elements (3, 4) and adapted to detect an optical pulse (I) when compensated for any signal propagation time differences in at least two electrical signals (u, v) (At) between the receiving channels (U, V) - within specified tolerance limits (σ) at the same time an electrical pulse (Eu, Ev) occurs.
    [2]
    2. Apparatus according to claim 1, characterized in that the evaluation circuit (8) is further adapted to detect the occurrence time (ti) of the optical pulse (I) from the time of occurrence (tu, tv) at least one of said electrical pulses (Eu , Ev) in its signal (u, v).
    [3]
    3. A device according to claim 1 or 2, characterized in that at least one receiving element (3, 4) contains a law- 30 nenphotodiode or a photomultiplier, preferably a hybrid photon detector,
    [4]
    4. Device according to one of claims 1 to 3, characterized in that at least one Empfangselernent (3, 4) is highly sensitive and at least one other receiving element (3, 4) is slightly sensitive,
    [5]
    5. Device according to one of claims 1 to 4, characterized in that the receiving elements (3, 4) are arranged so close to each other or successively staggered that the optical signal (x) all receiving elements (3, 4), each with one of its shares (χχ, x2) hits.
    [6]
    6. Device according to one of claims 1 to 4, further characterized by an optical beam splitter (2) for dividing the optical signal (x) in said components (xi, x2), which is upstream of the receiving channels (U, V).
    [7]
    7. Device according to one of claims 1 to 6, characterized in that the proportions (χχ, x2) are unequal size.
    [8]
    8. The device according to claim 7, characterized in that the receiving channel {U, V) with the highly sensitive receiving element (3, 4) of the larger proportion (Χχ, x2) is supplied.
    [9]
    9. Device according to one of claims 1 to 8, characterized in that the evaluation circuit (8) has a to the outputs (6, 7) of all the receiving elements (3, 4) connected to the multiplier (14) whose output a threshold value detector (15) is supplied. 31
    [10]
    10. Device according to one of claims 1 to 8, characterized in that the evaluation circuit (8) for each receiving element (3, 4) at its output (6, 7) connected threshold value detector (17), wherein the outputs (18, 19) of all threshold value detectors (17) are fed to an AND gate (20).
    [11]
    11. Device according to one of claims 1 to 8, characterized in that the evaluation circuit (8) is adapted to detect an optical pulse (I) only if the electrical pulses occurring at a predetermined time interval (At) (Eu, Ev) - possibly compensated by gain differences of the receiving elements (3, 4) and by the ratio (xi: x2) of the beam splitting - also have approximately the same amplitude.
    [12]
    12. Device according to one of claims 1 to 8 or 11, characterized in that the evaluation circuit (8) is adapted to detect an optical pulse (I) only if the occurring in a predetermined time interval (At) electrical impulses ( Eu, Ev) also have approximately the same (Ρχ, P2) pulse forms (Fu, Fv) or pulse shape parameters (Bu, Bv, Su, Sv) assigned to one another in a database (24).
    [13]
    13. Device according to one of claims 1 to 12, characterized in that it is constructed in analog technology.
    [14]
    14. Device according to one of claims 1 to 13, characterized in that the outputs (6, 7) of the receiving 32 eleraente (3, 4) via analog / digital converters (12, 13) are guided and the remaining device ( 1) is constructed in digital technology.
    [15]
    15. A method for detecting an optical pulse (I) in an optical signal (x), comprising: splitting the optical signal (x) onto at least two parallel receiving channels (U, V) each having an optoelectronic receiving element (3, 4), which converts the respective portion (Xi, x2) of the optical signal (x) into an electrical signal (u, v) in which an optical pulse (I) precipitates as an electrical pulse (Eu, Ev); and detecting an optical pulse (I) when, in at least two electrical signals (u, v) - compensated for any signal delay time differences (At) between the receiving channels (U, V) - within predetermined tolerance limits (σ) simultaneously an electrical pulse (Eu, Ev) occurs.
    [16]
    16. The method according to claim 15, characterized in that when detecting the time of occurrence (ti) of the optical pulse (I) from the time of occurrence (tu, tv) at least one of said electrical pulses (Eu, Ev) in its signal (u, v ) is determined.
    [17]
    17. The method according to claim 16, characterized in that the time of occurrence (tu, tv, ti) by comparing an electrical pulse (Eu, Ev, Ei) with a reference pulse (Er) known timing is determined. 33
    [18]
    18. The method according to any one of claims 15 to 17, characterized in that the optical signal (x) in two unequal proportions (xi, X2) is divided.
    [19]
    19. The method according to claim 18, characterized in that the larger portion (Xi, X2) a receiving channel (U, V) with a highly sensitive receiving element (3, 4) and the smaller proportion (xi, X2) a receiving channel (U, V ) is supplied with a low-sensitivity receiving element (3, 4).
    [20]
    20. The method according to any one of claims 15 to 19, characterized in that for detecting the signals (u, v) multiplied together (14) and the multiplication result a threshold value detector (15) is supplied.
    [21]
    21. The method according to any one of claims 15 to 19, characterized in that for detecting the signals (u, v) respectively via a threshold value detector (17) out and then AND-linked (20).
    [22]
    22. The method according to any one of claims 15 to 19, characterized in that an optical pulse (I) is detected only when the electrical pulses occurring at a predetermined time interval (At) (Eu, Ev) - optionally compensated for gain differences the reception elements (3, 4) and by the ratio (χχ: χ2) of the beam splitting - also have approximately the same amplitude.
    [23]
    23. The method according to any one of claims 15 to 19 or 22, characterized in that an optical pulse (I) is detected only if the occurring in a predetermined time interval 34 (At) electrical pulses (Eu, Ev) and approximately the same or (Pi, P2) pulse shapes (Fu, Fv) or pulse shape parameters (Bu, Bw; Su, Sv) associated with each other in a database (24).
    [24]
    24. The method according to any one of claims 15 to 23, comprising the further steps of: removing all a threshold (s2) crossing electrical pulses (11) with the exception of the side of the detected optical pulse (I) occurring electrical pulse (Eu, Ev, Ei ) from at least one of said signals (u, v) to produce at least one signal tu ', ν') thus cleaned up; and using the at least one adjusted signal (u ', ν') to more accurately determine the time of occurrence (ti).
    [25]
    25. A method according to any one of claims 15 to 23, comprising the further steps of: extracting a portion (u ", v ") from at least one of the signals (u, v) which is represented by a time window at the time of occurrence (tu, tv, ti ) of said electrical pulse (Eu, Ev, Ei) is defined therein; and using the at least one extracted portion (u ", v ") to more accurately determine the occurrence time (11).
    [26]
    26. The method according to claim 24 or 25, characterized in that cleaned signals (uf, v1) or sections (u ", v, r) from at least two signals (u, v) generated in this manner and to a signal set (tu1 , v1}) or summed into a sum signal (s', s "), which is used to more accurately determine the time of occurrence (ti).
    [27]
    27. The method according to claim 26, characterized in that the time of occurrence (tj) by threshold detection in the sum signal (s1, s ") is determined.
    [28]
    28. Method according to claim 26, characterized in that the time of occurrence (ti) is determined by comparing an electrical pulse (E'i) occurring in the sum signal (s1, s ") with a reference pulse (Er) of known time lags.
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    AT500062011A|AT512154B1|2011-12-14|2011-12-14|DEVICE AND METHOD FOR DETECTING AN OPTICAL IMPULSE|AT500062011A| AT512154B1|2011-12-14|2011-12-14|DEVICE AND METHOD FOR DETECTING AN OPTICAL IMPULSE|
    EP12191028.5A| EP2605034B1|2011-12-14|2012-11-02|Apparatus and method for measuring propagation time of an optical pulse|
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