EP1470434A2

EP1470434A2 - Imaging device for recording depth

Info

Publication number: EP1470434A2
Application number: EP03706242A
Authority: EP
Inventors: Gerhard Bonnet
Original assignee: Spheron VR AG
Current assignee: Spheron VR AG
Priority date: 2002-01-19
Filing date: 2003-01-20
Publication date: 2004-10-27
Also published as: WO2003061084A1; JP2005515416A; AU2003235653A1; US20050117160A1; US7800738B2; AU2003208268A8; AU2003208268A1; US20050078296A1; WO2003060426A3; US7684019B2; EP1470621A1; WO2003060426A2; JP2005515642A

Abstract

The invention relates to a device for determining the distance of an object in local resolution mode, using a frequency-shifted feedback radiation source for irradiating the object with radiation that can be used to determine distance and using a position-sensitive object recording sensor. According to the invention, the frequency-shifted feedback laser for irradiating the object is equipped with an element for increasing the beat intensity of the emission frequency component and the position-sensitive object recording sensor is configured to record the beat intensity of the object and not the incoming radiation from the object.

Description

Title: Depth-Imaging Device

description

The present invention relates to the preamble and thus deals with the measurement of the distance of objects using frequency-shifted feedback radiation sources.

It has long been known to measure distances optically. In addition to echo sounder-like measurements, in which short light pulses are emitted and the time until the reception of backscattered or reflected pulses is measured, interferometric methods are also known.

In interferometric methods, a light beam is split into a reference light beam and an object light beam. The object light beam is irradiated onto an object and received back by it. The reference and object light beams are then superimposed on a light receiver and it is then concluded from the superimposition signal how far the object is. Depending on the arrangement, this procedure allows highly precise measurements; however, depth measurement on extended objects is difficult at various points.

It is also known to carry out distance measurements with frequency shift feedback lasers or frequency shifted feedback lasers (frequency shifted feedback lasers, FSF lasers). Examples of the FSF laser can be found in

- l - the essays by FV Kowalski, PD Haie and SJ Shattil "Broadband continuous-wave lasers", Opt. Lett. 13, 622 (1988) and PD Haie and FV Kowalski "Output characteristics of a frequency shifted feedback laser: theory and experiment" IEE J. Quantum Electron. 26, 1845 (1990) and by K. NAKAMURA, T. MIYAHARA, M. YOSHIDA, T. HARA and H. ITO "A new technique of optical ranging by a frequency-shifted feedback laser", IEEE Photonics Technology Letters, Volume 10, 1998, pages 1772 ff. An example of the use of such lasers for distance measurement is described in detail in the article "Observation of a highly phase-correlated chirped frequency comb output from a frequency-shifted. Feedback laser" by K. NAKAMURA, T. MIYAHARA and H. ITO, Applied Physics Letters, Volume 72, No. 21, pages 2631 ff. And in the article "Spectral Characteristics of an All Solid-State Frequency-Shifted Feedback Laser" by K. NAKAMURA, F. ABE , K. KASA-HARA, T. HARA, M. SATO and H. ITO in IEEE-JOURNAL OF QUANTUM ELECTRONICS, volume 33, pages 103 ff. It should also be noted that ICM Littler, S. Balle and K. Bergmann “The cw model laser: spectral control, performance data and build-up dynamics "Opt. Commun. 88, 514 (1992) and S. Balle, FV Kowalski and K. Bergmann "Frequency shifted feedback dye laser operating at small frequency shift" Opt. Commun. 102, 166

(1993) and G. Bonnet, S. Balle, Th. Kraft and K. Bergmann "Dynamics and self-modelocking of a Titanium-Sapphire laser with intracvacity frequency shift" Opt. Commun. 123, 790

(1996). The last three documents further characterize FSF lasers according to the prior art. These documents, like DE 100 45 535, are fully incorporated by reference for disclosure purposes. An arrangement in which an FSF laser is used for the spatially resolved distance measurement is in DE 100 45 535.2 and PCT / EP 01/10416.

The principle of distance measurement with an FSF laser, which contains an acousto-optic modulator in addition to the amplification medium in its resonator, can be briefly illustrated as follows: Light amplification of light waves entering the amplification medium only takes place for those frequencies at which the amplification is greater than 1 is. At all other frequencies, the light is attenuated as usual. Similar to a vibrating string, the optical resonator now has preferred frequencies, so-called resonator modes. Each resonator mode has a certain frequency, which means that it corresponds to light of a precisely defined wavelength. Those resonator modes in which the amplification of the amplifying medium is greater than 1 are now preferably emitted.

In principle, this is the behavior of a laser without an acousto-optic modulator. If the acousto-optic modulator is now excited, the material vibration creates a moving grid of different densities; the light circulating in the resonator is diffracted at this density grating, an interaction of the light photons with the phonons characterizing the density oscillation of the acousto-optic modulator, which shifts the frequency of the diffracted light by the excitation frequency of the acousto-optic modulator. This means that the laser modes shift slightly in frequency with time, that is, the frequency of a mode changes with time; if there is more than one mode, this applies to all modes that vibrate in the resonator. It goes without saying that, depending on how far above the reinforcement 1 the reinforcement profile runs, the intensities of the individual vibrating modes differ. are different and that the mode intensity changes with frequency. It is also clear that the frequencies change for all modes in the same way over time. In other words, light that is emitted at different times will have different frequencies.

If light rays arrive at a location such as a detector and are radiated in via optical paths of different lengths, that is to say were also emitted from the laser at different times, there must be a frequency difference between the two. This frequency difference can be detected as a beat frequency on a photosensitive element. The path length can be inferred from the beat frequency.

The known measuring arrangement is described in more detail in the documents referred to above.

In practice it has now been shown that the signals at the measuring receiver are very noisy. If the distance to be determined is fixed, a single sharp line would be recognizable without noise in the beat frequency spectrum. In reality, however, it is shown that instead a very broad structure instead of a sharp line is obtained with FSF lasers, which massively affects the quality of the measurement obtained.

It is desirable to change the known arrangements and methods so that the usability can be increased. The object of this invention is to provide something new for commercial use.

The solution to this problem is claimed in an independent form.

According to a first essential aspect of the present invention, a device for spatially resolved object distance determination with a frequency-shifted feedback radiation source for object irradiation with radiation that can be used for distance determination and a position-sensitive object detection sensor is proposed, the frequency-shifted feedback radiation source for object irradiation with a means for increasing the emission frequency component and the position detection sensitivity for the object intensity Detection of the beat intensity is formed by the object and not by the incoming radiation.

It was therefore not only recognized that the assumption prevailing in the interpretation of the prior art that the beat components originating from individual modes of the frequency-shifted laser would add up does not apply; rather they extinguish themselves. Surprisingly, the signal achievable in the prior art with FSF lasers is based on the fact that noise occurs during operation of the known lasers, that is to say fluctuation in intensity and / or phase, which prevents a complete - which is theoretically actually to be expected with more precise analysis Extinction of the mutually coherent frequency components, as would otherwise occur, occurs. Noise caused by measurements with state-of-the-art FSF lasers therefore does not appear to be a consequence of the noise of the laser, but rather the actual measurement signals themselves that are caused only by the noise of the laser, that is to say its inherent fluctuations. On the basis of this knowledge, it is now not only proposed that means for increasing the intensity of the beat of frequency components of the emitted radiation are provided at the radiation source, but it is also given how this knowledge can be used for better spatially resolved object distance determination.

In a preferred variant it can be provided that the means for increasing the emission frequency component beat intensity are designed as means for increasing the non-stochastic emission frequency component beat intensity; they will therefore require an increase in intensity above that which is caused by spontaneous emission, particularly in the gain medium.

Typically, an injection light source will be provided, which injects light into the radiation source, that is to say provides a seed radiation field there. As an alternative to this, it would also be possible to disrupt a complete extinction of frequency components beyond what is caused by spontaneous emission in the stationary operating state, for example by modulating the pump light, which is typically less preferred due to the level lifetimes, etc., or rapid loss mechanisms in the amplifier medium to effect yourself. However, the provision of an injection light source is particularly advantageous because it represents a structurally simple possibility by means of which a large number of advantageous designs can be implemented. In a particularly preferred variant, the injection light source is an injection laser. Its radiation can be guided into the resonator, in particular and / or onto the gain medium of the frequency-shifted feedback radiation source.

It is preferred if the injection light source emits light at a wavelength which is close to that at which the gain of the gain medium of the frequency-shifted feedback radiation source is 1; it can optionally be radiated near the upper and / or lower threshold wavelength. The frequency of the injected light radiation will typically be within the range in which the gain G is greater than 1 and not outside. In the case of seed radiation injected very close to the threshold and in particular modulation thereof, however, this threshold can in particular be temporarily exceeded. However, it would always be preferred to select the irradiation frequency in such a way that amplification takes place after a few resonator revolutions.

It is preferred if the injection light source emits radiation in a narrow band, narrow band being related to the gain bandwidth of the gain medium of the frequency-shifted feedback radiation source. A narrow band can have a width of not more than 5%, preferably not more than 1%, of the gain bandwidth. In a particularly preferred variant, a single-mode injection laser with an exactly defined, modulable frequency and / or amplitude is used for the injection. The injection light radiation is preferably varied with regard to the intensity and / or the phase. This variation can take place, for example, by means of regular modulation, that is to say modulation of intensity and / or phase that obeys prescribed laws or is subject to restrictions, although this does not necessarily have to be even.

It is particularly preferred if the modulation is not constant, but if the intensity and / or the phase of the modulation of the injection light radiation varies with time, which is done particularly advantageously in a periodic manner. It is particularly preferred if the frequency of the intensity modulation is changed linearly within certain intervals, because a linear variation of the modulation frequency of the injection light radiation significantly simplifies an evaluation of beat signals obtained, in particular for determining the distance.

If a modulation of the radiation emitted from the injection light source is carried out with respect to phase and / or intensity, it is preferred if the frequency of this modulation is close to that which results from the so-called chirp rate and the distance which is currently determined with the radiation source , The chirate rate is given by the frequency of the acousto-optical or other modulator within the frequency-shifted feedback radiation source, based on the round trip time of the radiation in the resonator of this source.

It should be mentioned that the radiation source will typically be a frequency-shifted feedback laser. This can in particular in infrared, in particular in eye-safe areas. The wavelength ranges which can be used particularly inexpensively for telecommunication devices and are well developed in terms of technology can also be used for the purposes of the present invention, which opens up the possibility of using inexpensive elements in the construction of arrangements and devices.

A device is preferred in which the frequency-shifted feedback radiation source is formed by a laser and the means for increasing the emission frequency component beat intensity is a frequency-modulated seed laser that radiates seed light into the first laser, the device further comprising a means for adapt the frequency of the seed laser frequency modulation to the distances to be determined. In other words, it is proposed that the device for spatially resolved object distance determination comprises a tunable seed laser and the beat signal is determined as a function of the seed laser scan.

It is particularly preferred if the seed frequency is changed gradually in order to provide sufficient time for setting a stable beat and determining it on the sensor. The seed frequency can accordingly be changed in stages and kept constant for a certain measuring time. Alternatively, it is possible to sweep the seed frequency in each case by a certain value, which avoids that frequency jumps in the seed frequency tuning lie in such a way that certain distances are not recorded and therefore no and / or only inaccurate distances can be determined for individual objects or object subareas. The seed frequency can also be systematically changed in different runs be changed, with different levels and the like, it being clear that the object distance is then determined taking into account the signals from several passes.

It is particularly advantageous if the beat intensity-related object detection sensor signals detected with the object detection sensor are filtered. A filter can be specially designed to filter out only the AC signal components. It is particularly advantageous that a relevant signal will only occur in the area of the seed frequency and can therefore be narrow-band filtered to this seed frequency, the filter being able to run with the seed frequency and / or having a certain narrow-band nature. It should be pointed out that artifacts can lead to sharp frequency components with a high proportion being present in the conditioned object detection sensor signal, whereby these frequency components can differ from the seed frequency. Such interference signals can be filtered out particularly well with narrow-band filters.

The object detection sensor signal conditioning will typically include signal amplification, it being particularly preferred to provide the amplification behind the filter stage because a very large amplification is possible there, which allows even very weak beat signals to be evaluated per se. It will be appreciated that the regulated and / or controlled signal conditioning, in particular with regard to the regulated and / or otherwise set gain, is particularly preferred in order to be able to measure even at large intervals. In particular, it is possible to make a dependence of the respective gain on the current seed frequency. in order to take into account that a given seed frequency corresponds to a certain distance and accordingly a distance-proportional gain with eg 1 / r ² - or 1 / r ⁴ - dependence can be useful.

The signature of the object detection sensor signal is typically detected as a function of the seed frequency tuning. It can be provided that the maximum value of the object detection sensor signal is determined during the seed frequency tuning, whereby, as mentioned above, the seed frequency tuning can be carried out step by step, or that an effective value is determined which is amplified as a real effective value after rectification and low-pass filtering of the preferably bandpass-filtered Object detection sensor signal is obtained and / or the effective value can be determined in a specific frequency window for determining the distance.

It is possible to use derivatives of the object detection sensor signal with the change in seed frequency, or, if this takes place over time, the variation of the object detection sensor signal with time to determine the distance. Since noise can cause rapid signal fluctuations and thus large derivatives, a noise influence can be reduced by simultaneous consideration of a signal comparator output, which ensures that changes in the derivatives are only taken into account if the possibly conditioned object detection sensor signal is sufficiently large, because in such Cases can be assumed that there is no exclusive noise influence. The evaluation can be a distance measurement value with regard to the time between a predetermined characteristic, such as reaching a maximum in the object. Determine the version sensor signal since the start of a seed frequency sweep or a successive frequency change. That this can be done using analog circuits, in particular with which the respective maximum is held and a “maximum reached signal” is generated as soon as an object detection sensor signal does not rise further, by means of this “maximum reached signal” for writing Allowing a seed frequency-related or sweep time duration signal counter value in a digital register is mentioned.

A particularly preferred variant consists in using an infrared-emitting FSF laser with frequency-shifted feedback as the radiation source. On the one hand, this gives inherent eye-safe operation in the corresponding infrared ranges and, on the other hand, irradiation of an object which is preferably simultaneously recorded in visible light is possible without changing the colors seen there. It should be mentioned that it is possible to first determine the beat intensity in close succession with one and the same object detection sensor and then to detect natural light from the object. In such a case, obviously different signal conditioning for signals from one and the same pixel is preferably provided. It is a further possibility to carry out an object detection with a multipixel chip such as a CMOS or CCD array, which in particular, as is known per se, can be designed for multi-color detection, with a “color” being the preferred, but not mandatory, infrared radiation can be detected by the object or its superimposition on the chip with a radiation component irradiated via a reference path if separate sensor element fields for different colors or IR and visible light are used. Det are, per se known position matching can be brought about by image position correction levels.

The invention will now be described in the following only by way of example with reference to the drawing. In this shows:

1 shows a schematic structure of a frequency-shifted feedback radiation source for a device according to the invention;

2 shows the frequency variation of a single laser mode with linear chirp over time;

3 shows the synchronous variation of all components (modes) of a radiation light source with frequency-shifted feedback;

4 shows the frequency spectrum of an FSF laser with a given amplification curve (top in the picture);

5 shows a schematic structure for a distance measurement with an arrangement according to the present invention;

6 shows a gray-scale representation of a beat frequency spectrum, as can be obtained from the prior art, with position-independent artifact structures and a weak measurement signal structure which can be recognized as strips running obliquely through the image; 7 shows an example of a beat frequency signal as a function of a seed radiation frequency modulation.

Fig. 8 shows an example of a structure of a device according to the invention.

According to FIG. 1, a frequency-shifted feedback radiation source 1, generally designated 1, comprises a means 2 for increasing the emission frequency component beat intensity.

The frequency-shifted feedback radiation source 1 is a ring laser with frequency-shifted feedback in the present example. The ring resonator of the ring laser 1 is formed by two highly reflecting mirrors la, lb and an acousto-optical modulator lc, to which a piezo element lcl as actuator and input and output prisms lc2, lc3 are assigned and which is arranged in the resonator ring in such a way that the zeroth diffraction order is shown can be coupled out as a beam 3, while the first diffraction order guides the light circulating in the resonator. The acousto-optical modulator lc is selected such that diffraction coefficients of more than 90% result for the first diffraction order, which is frequency-shifted in a known manner by the acousto-optical modulation. The geometry is further selected so that the primers lc2, lc3 assigned to the acousto-optical modulator lc are compensated for in terms of their dispersion and a compact structure is nevertheless possible.

A fiber medium ld is arranged between the two highly reflecting mirrors la and lb, and the fiber is coupled in and out. Optics 1dl and ld2 are assigned. Energy is radiated into the fiber from a point laser designed here as a diode laser (not shown), so that it can be used as a gain medium. The coupling takes place on a fiber switch le. The fiber shown is a conventional ytterbium fiber with a large usable gain bandwidth of here, for example, at least 70 nm in the spectral range around 1.2 μm; Such elements are readily available from the field of optical telecommunications, just as other arrangements that can also be used, for example fiber lasers based on YAG at 1.06 μm with a few nm bandwidth or approximately erbium at 1.5 μm, could be used.

The arrangement of the FSF laser as described so far is essentially conventional. Means for increasing the emission frequency of component beat intensity are now provided. For this purpose, a fiber switch 2a is provided, via which injection light, indicated at 2b, can be coupled into the fiber via a coupling optic 2c. The injection light 2b comes from an injection laser (not shown), which in turn can be modulated in a time-varying manner with regard to its amplitude and the phase of the optical carrier. The injection or seed laser emits radiation, the wavelength of which is close to the lower one here for the up-chirp point G = 1 of the gain profile of the FSF ring laser 1 or the fiber 1d, see FIG. 4, where in the upper part of the Image of the gain profile is drawn as a solid line, together with the gain threshold 1, which is shown horizontally and the optical carrier frequency of the seed laser is entered as a vertical, dash-dotted line. It should also be mentioned that instead of and / or in addition to a coupling via a fiber switch 2a, it would also be possible to couple an injection light beam through one of the highly reflecting mirrors, as indicated by beam 2b2 in the case of the mirror la, and / or a coupling could take place into the into the acousto-optic modulator, as indicated by arrow 2b3. For the sake of completeness, it should also be indicated here that the pump light, which differs from the injection light here, can not only be coupled into the reinforcing fiber ld from the pump light beam lel via a fiber switch, but also, for example, via the highly reflecting mirrors, a pump light coupling is, as indicated by ray le2 near the mirror lb.

The arrangement is operated as follows:

Pump light is irradiated onto the fiber 1d, so that an inversion which enables laser operation results. Then the piezo driver 11 of the acousto-optic modulator is set in vibration, so that the ring of the frequency-shifted feedback laser is closed. Light that is now emitted from the fiber can now pass through the mirror la, through the prism lc2 and the acousto-optical modulator lel and the prima lc3. The majority of this light is directed towards the mirror lbl in accordance with the high diffraction efficiency of the acousto-optical modulator and is radiated into the fiber ld.

Passing through the acousto-optical modulator lc also changes the frequency of the light. The light that is directed towards the mirror la with a predetermined frequency the acousto-optical modulator has run, will therefore arrive at the other highly reflecting mirror 1b with a shifted frequency or wavelength. This light with a shifted frequency is amplified in the fiber ld, in turn passes over the mirror la with further frequency shift by the acousto-optical modulator lc to the mirror lb, etc. This leads to the frequency shifting with each pass. The speed at which the frequency changes depends on the time it takes for the light to circulate and how strong the frequency shift is in the acousto-optic modulator. The shift is carried out in the same way for all components or modes that can be amplified in the resonator, so that the frequency comb, which the modes of the FSF laser represent, are gradually shifted in a synchronous manner. There is a so-called "chirp". This is shown in FIG. 3, while FIG. 2 shows the variation of the frequency for a given linear chirp.

This light is now used for distance measurement. In principle, this is first discussed for an interferometer arrangement that is not yet spatially resolved, as shown in FIG. 5, in which the light source 1 according to the invention, a beam splitter element 4 in the outcoupling beam 3 of the light source 1, a reference path 6 to a reference surface 6 ^Λ and a measuring path 7 a measurement object 7 ^Λ are shown, the beams from the reference object β ^λ and from the measurement object 7 ^Λ to a detector

5 are performed.

The situation that arises in such an arrangement before the seed source is put into operation on the detector can be seen in Figure

6 can be seen. There it is in a grayscale display Beat frequency spectrum for a laser arrangement shown as a function of the path difference ΔL of the arms 6 and 7 of the measuring arrangement. The gray scale display initially shows position-independent lines, i.e. lines that do not vary with the path difference ΔL and thus run horizontally in the picture, which are caused by a standing wave component in the acousto-optic modulator and are repeated after the resonator orbit time. Furthermore, the actual measurement signal can be seen with a lot of noise, which runs diagonally through the image as a dark stripe.

Now the injection light source is put into operation, specifically at a carrier frequency close to the lower region of the amplification curve, that is to say just within the region in which the amplification is greater than 1. The optical carrier frequency, which is shown in dashed vertical lines, is modulated, namely in the present example amplitude-modulated, the modulation itself also not being constant, but varying with a frequency which is approximately determined from the so-called chirate rate α, that is to say the frequency shift per The resonator revolution divided by the resonator revolution time and further determined by the light transit time along the path difference ΔL between the measuring beam path and the reference beam path in the construction of FIG. 5. The modulation frequency of the injection light is therefore not kept constant, but is varied by this so-called signature value, that is, by that value, which results from the chirp rate and ΔL from the formula

where c is the speed of light. The modulation frequency is changed around this signature frequency, preferably in a linear sawtooth shape. An intensity at the detector then results, as shown in FIG. 7. It is shown that a very clearly pronounced, sharp intensity peak of the beat signal can be obtained, that is to say that the signal has very little noise and in particular has less noise and thus a more precise measurement than was previously possible in the prior art. It is essential that the injection radiation modulation and the beat frequency intensity are closely connected to one another and that a beat frequency intensity maximum is reached when the injection modulation frequency corresponds to the frequency expected for a given path difference, taking into account the chirp rate.

This is currently justified as follows: by injecting the radiation of the injection laser at the edge of the amplification area, modes are shifted in steps Δv _A0M over the entire amplification range in the resonator, so that the laser cannot move into a stationary, practically noise-free equilibrium, which he would otherwise tend to. It therefore appears to be the case that the conventional picture about the occurrence of the beat spectrum is incorrect and the intensity of a beat would actually vanish in a noise-free case.

It can now be determined that the structure width of the signal structure obtained is determined by the amplification bandwidth, that is to say a high bandwidth of the radiation light source with frequency-shifted feedback, that is to say of the FSF laser, which leads to good spatial resolution. Since over Since the range measurement accuracy is essentially determined by the chirp size, it is desirable to choose a large frequency shift by the acousto-optical modulator and a small laser resonator length of the FSF laser resonator.

It can be ascertained that with a distance measurement and, if necessary with successive distance measurements at a certain time interval, also with speed and / or acceleration measurements, very high accuracies can be achieved which essentially depend only on the driver frequency constancy of the acousto-optic modulator, as well as the laser resonator length stabilities during the measurement period. In addition, only quantities such as the accuracy of the beat frequency determination have to be taken into account. It is clear that systematic resolutions and accuracies around 10 ^"6 - 10 ^{~ 8 can be} achieved. Due to the significantly improved signal-to-noise ratio, it is also possible to carry out measurements with very low power, since only a high-frequency component in the detected signal has to be detected as a beat and this at known or approximately known frequencies.

8, a device for location-resolved object distance determination 100, generally designated 100, comprises a frequency-shifted feedback radiation source 101 for irradiating an object 102 with distance-usable radiation 103 and a position-sensitive object detection sensor 104, the frequency-shifted feedback radiation source 101, which in the present case is formed as an infrared frequency-shifted feedback sensor 101 is associated with a seed laser 105 that is modulated and incrementally variable-frequency seed light feeds into the gain medium of the FSF laser 101. The object detection sensor 104 on the one hand receives the radiation 103 from the object, on the other hand via a beam splitter unit 106 reference light over a reference path of known length from the FSF laser 101 and visible light from the object 102, as indicated by rays 107. It should be noted that for directing the FSF light from the radiation source 101 onto the object 102 and for collecting light or radiation that can be used for determining the distance from the object 108 on the object detection sensor 104, for beam splitting, imaging, etc., conventional optical elements are used as in 109 indicated can be provided. They can be constructed in accordance with conventional rules of the prior art, taking into account the respective wavelengths, desired imaging properties and so on. It should be pointed out that an embodiment is possible in such a way that all-round monitoring and detection is possible, but the objects form a sphere or partial sphere around the device, for example through a suitable mechanical rotary and / or pivot bearing of all or part of the device Device components is possible.

As can be understood from the general principle of the FSF laser under seed injection explained above, there will be a beat signal on the sensor 104 due to the superimposition of the reference light and the light 108 received by the irradiated object 102. This signal becomes maximum when the seed frequency with which the seed laser 105 is modulated results from the chirp rate of the radiation of the frequency-shifted feedback radiation source 101 and that additionally traveled by the object beam 108-103 Path according to the formula above. An evaluation arrangement 110 is now assigned to each pixel of the sensor 104 designed here as a CMOS array, with which the electrical signal from each pixel of the object detection sensor 104 is narrow-band filtered and conditioned by suitable amplification and then fed to a maximum holding circuit provided in the evaluation arrangement 110 which, at any point in time, compares an instantaneous value of the conditioned signal with the previously observed maximum and outputs a stop signal if such a maximum is undershot, which is indicated by a signal drop. The stop signal is sent to a counter, which begins to count across several, gradually changing seed signal frequencies at the start of a seed frequency signal sweep. The stop value stored for each pixel thus corresponds to a frequency at which the object detection sensor signal signature has its maximum. By using the known chirp rate, the geometric relationships, in particular with regard to the reference beam path length and the temporal seed frequency signal behavior, a corresponding distance value of the object area mapped onto this pixel can be determined. In parallel to the determination of the distance of the object, as described above, the two-dimensional, conventional image can be captured in a digital manner and then, for example, a superimposition of the images can be achieved by means of a suitable electronic circuit. In this way, the depth values can be determined for a point in a recorded two-dimensional surface image and a spatial image can be obtained. It should be pointed out that with such an arrangement, lighting fields can be determined particularly well, which relies particularly on the theses taken from the shape of the surroundings, which then serve as objects.

Claims

claims

1. A device for spatially resolved object distance determination with a frequency-shifted feedback radiation source for object irradiation with distance-usable radiation and a position-sensitive object detection sensor, characterized in that the frequency-shifted feedback radiation source for object irradiation with a means for increasing the emission frequency component beat intensity and the position-sensitive object detection and non-detection of object detection sensor incoming radiation is formed.

2. Device according to the preceding claim, characterized in that the means for increasing the emission frequency component beat intensity is designed as a means for increasing the non-stochastic emission frequency component beat intensity and / or comprises an injection light source, in particular an injection laser, preferably in particular light being injected into a resonator with which the frequency-shifted feedback radiation source is formed, with radiation in particular preferably being emitted onto the amplification medium thereof, and wherein the injection light source is preferably designed to emit radiation of a radiation frequency close to the upper or lower amplification threshold (G = 1) and / or the injection light source is for radiation Injection light is narrow-band based on the amplification bandwidth of the frequency-shifted feedback radiation source, in particular has a width of less than 5%, preferably less than 1% of the bandwidth of the amplification of the frequency-shifted feedback radiation source and / or the injection light source for irradiation of those modulated with respect to intensity and / or phase of the optical carrier Light is designed, in particular for the regular modulation of the intensity and / or phase of the injection light and / or is designed to carry out a modulation of the intensity and / or phase that changes over time, in particular periodically, in particular the injection light source is designed such that at least temporarily a linear modulation frequency variation takes place, the injection light source preferably being designed to determine a modulation, the frequency of which is of the order of magnitude and / or close to that determined by the radiation source e distance and the chirate rate obtained from the frequency-shifted feedback radiation source lies, preferably also the frequency-shifted feedback radiation light source is a laser and in particular a resonator-internal optical fiber is provided as the amplification medium thereof.

3. Device according to one of the preceding claims, wherein the frequency-shifted feedback radiation source is a laser and the means for increasing the emission frequency component beat intensity is a seed light that radiates frequency-modulated seed laser into the first laser, a means being provided, to adapt the frequency of the seed laser frequency modulation to the distances to be determined.

4. Device according to the preceding claim, characterized in that a means is provided to gradually change the seed frequency in particular step by step, preferably the means is designed to keep the seed frequency constant for a certain measuring time T and / or by an average to wobble around a respective seed frequency value, in particular with a stroke sufficient to avoid distance gaps and / or to vary the seed frequency change in repeated passes, in particular by systematically reducing the frequency resolution in repeated passes.

5. Device according to the preceding claim, characterized in that a filter is provided for filtering the beat intensity-related object detection sensor signals determined on the object detection sensor.

6. Device according to the preceding claim, characterized in that the filtering for filtering out alternating signal components, in particular those on and / or narrow-band around the seed frequency.

7. Device according to one of the preceding claims, wherein a signal amplification is provided for conditioning the object detection sensor signals, in particular an amplification stage is provided behind the filter stage in the embodiment according to one of the two preceding claims, in particular at least one regulating and / or control circuit is provided for setting a specific signal conditioning, in particular a specific amplification.

8. Device according to one of the preceding claims, characterized in that a stage for determining the distance on the basis of the object detection sensor signal is provided as a function of the seed frequencies.

9. Device according to one of the preceding claims, characterized in that the stage for determining the distance on the basis of the object detection sensor signal is designed as a function of the seed frequencies for determining the distance in response to the reaching of a maximum value of the object detection sensor signal which has been processed as required when the seed frequency changes and / or in response to an effective value, in particular a real effective value, in particular as obtained by rectification and low-pass filtering, of the object detection sensor signal processed as required when the seed frequency changes and / or in response to an effective value, in particular in a frequency window around the seed frequency and / or in response to the strength of a seed frequency component in the object detection sensor signal.

10. Device according to one of the preceding claims, characterized in that a stage for changing the seed frequency is provided over time and an object detection sensor signal evaluation stage as a distance-related measured value determines a value representative of a time until a predetermined object signal signature is reached, in particular by measuring the Time until a threshold and / or maximum value is reached, for which purpose in particular an analog maximum hold circuit for recording the temporal signal curve with an assigned digital register for writing in a value, in particular a seed frequency-related value, in particular a sweep time and / or counter value particularly preferably with a circuit for determining the value to be written in as a function of reaching an analog threshold and / or maximum value

is provided and / or

for which purpose, in particular, a derivation stage is provided for deriving the frequency-dependent object detection sensor signal signature, in particular under simultaneous consideration of a signal comparator output, which reduces the influence of noise.

11. Device according to one of the preceding claims, characterized in that the position-sensitive object detection sensor for simultaneous and / or temporal reception and / or evaluation of radiation from the return reception of the object radiation on the one hand and other light from the object on the other hand is carried out in a closely sequential manner, in particular the radiation source, which is frequency-shifted, is designed for emission in the infrared and / or the position-sensitive object detection sensor is furthermore particularly designed for receiving visible light is formed as other light from the object, in particular an evaluation of the object detection sensor signals for received radiation and other light can take place after different signal conditioning.

12. Device according to one of the preceding claims, characterized in that the position-sensitive object detection sensor is designed for pixel-by-pixel detection of radiation from the return of the object radiation and / or other light from the object, wherein the position-sensitive object detection sensor comprises in particular a multipixel chip for multi-color detection with a color filter pattern and / or separate multipixel elements, in particular illuminated by means of a beam splitter in an object imaging beam path, are provided for light and / or radiation in different wavelength ranges, wherein in particular an image position correction stage is provided to bring about an image position match.

13. Device according to one of the preceding claims, characterized in that the position-sensitive ob- object detection sensor for pixel-by-pixel detection of radiation from the return of the object radiation and / or other light from the object, a plurality of evaluation units, in particular one per pixel, in particular for increasing the evaluation and / or refresh rate are provided.

14. A method for spatially resolved object distance determination with a frequency-shifted feedback radiation source for object irradiation with distance-usable radiation and a position-sensitive object detection sensor, characterized in that the emission frequency component beat intensity at the frequency-shifted feedback radiation source for object radiation is increased by the stochastic fluctuations in the radiation source and the fluctuations in the frequency source radiation from the object and not from the object is determined as a distance-indicative signal.