DE4344076A1 - Optical determination of object distance, velocity and image quality - Google Patents

Abstract

An apparatus and method for the optical determination of object distance and velocity or which can alternatively be used to analyse the imaging qualities of an optical system e.g. the human eye employs a laser lightsource (1) to illuminate (2) a point (4) on the object surface (3). The dispersion cone (11) of returned and scattered rays of varying phase and spatial distribution impinges on a double aperture diaphragm (6) and the two emergent beams (14,15) are brought to a focus by the lens (7) to fall together on a photorespective image sensor (8) e.g. a CCD line or matrix camera in the region (9) thereby creating an interference pattern. By examining the type and dimensioning of the pattern the object parameters are derived or corrective ophthalmology undertaken.

Description

The invention relates to a method and an arrangement for optical distance and velocity analysis of surfaces and analysis of the image properties of optical systems by means of laser beams, after which a laser beam either directly or by means of an imaging system on a surface court tet and from the spatial position or displacement of the impact point on this is due to a shift of the surface towards the sensor or a Displacement of the sensor towards the surface or by a change of the Ab bildungsseigenschaften of the optical system from the distance or the Ab state change (differential speed) or the change of the image ratio between surface and sensor is determined.

For the optical distance or distance change analysis is known, running time Measurements or measurements according to the so-called triangulation method perform. Furthermore, laser measuring systems with frequency-modulated La exist fibers. In runtime measurements, a very short laser pulse is usually emitted sends, and then determines the time which the light pulse needed to the Distance between sensor and surface back and forth. With this me It is possible, especially at long distances and when many individual measurements can be averaged statistically, with the necessary appa considerable effort is quite accurate. Such constructions are However, very expensive, sensitive, must be calibrated or adjusted regularly are and are very expensive.

The triangulation method is for small distances and for small distances relatively simple with satisfactory accuracy. For long distances and above all with large distance changes must with this sensor however Always lenses or other optical components are moved to a high level To achieve accuracy. A statistical averaging over many individual events is only conditionally possible.

In frequency-modulated distance measuring systems (FMCW) is a continuous (cw) laser beam whose frequency is linearly ramped changed on the DUT (surface) directed. The time delayed, from the surface re inflected signal is mixed with the transmitted signal, so that an intermediate Frequency signal is generated, which is proportional to the distance, the frequency deviation and  the modulation frequency is. The disadvantage here is the required high coherence Length of the laser and other significant technical effort.

In all methods is also perceived as disadvantageous that they do not read it self-checking or device-internal functional checks and diagnostic steps then make it possible, long before a failure or before Damage seriously affects the readings, this to the user display and thus allow timely maintenance.

The determination of the optical properties of the human eye lying imaging system with respect to the retina is currently empirically iterative carried out. In this case, the optician or optometrist of the optometrist Person a lens mounted trial by eye and by changing this lens during a verbal dialogue between ophthalmologist and patient trying to find the optimal lens.

It is considered disadvantageous that this procedure for the ophthalmologist or optometrist is very time consuming. Furthermore, the entire Ver drive poorly at people who express themselves inadequately verbally can, as is the case with children, for example.

On this basis, the invention has for its object to provide a method develop, which avoids the disadvantages of the aforementioned method and thus enables an insensitive, with a high distance and time dynamic, accurate and yet inexpensive sensor to develop. For the case of determining the imaging properties in the human eye this can be done fully automatically without dialogue with the patient can.

The method has essentially the following features:
It shows extreme insensitivity to all imaginable intensity and intensity distribution fluctuations of the luminous spot generated by the laser beam directed onto the surface and thus avoids one of the essential sources of error of all previous methods. Due to the underlying physical principle, neither calibration nor adjustment is necessary over the entire service life, nor can total failures occur if the option of device-internal self-diagnostics is used. Since only a few, simple and common components are used, results in a ro buster and reliable working sensor, which can be completely dispensed with moving parts. The maximum update rate of the measured values extends into the MHz range. This makes it possible to significantly increase the accuracy of the sensor by means of suitable statistical messages. The lasers used do not have to emit longitudinal monomode light any longer, and thus a wide range of lasers (in particular diode lasers) can be used. The process can be carried out fully automatically in all cases.

All embodiments of the invention are based on the same principle: one of Sensor emitted laser beam generated on the surface of the object whose Distance or changed by an upstream optics appearing Entfer to be measured, a spot of light. This spot will be replaced by a suitably designed optics in the form of two separate light bundles on one light-sensitive sensor (image sensor) shown. Cut both light bundles doing so at an angle that of the geometric design of optics and the distance of the DUT clearly depends. Since that of the DUT backscattered laser light due to the selected geometries out has sufficient coherence properties, the two interfere under one Angle on the image sensor incident light beam with each other, so that on the Image sensor an interference fringe pattern arises. Under ideal conditions this interference fringe pattern consists of spatially periodic light / dark Strip whose distance from the intersection angle of the two incident light bundles and therefore relative to the distance or distance to the measurement object to an optionally upstream optical system depends. The picture sensor together with the downstream processing hardware / software must be designed in such a way that the resulting interference fringe image z. B. analyzed with respect to the strip spacing and in the corresponding Infor mation of the distance or the magnification can be implemented.

The various embodiments of the invention differ on the one hand in the way that returns from the light spot on the object Light scattered the two light bundles that fall on the image sensor, who produces and on the other hand by the nature, design and arrangement of the image sensor.  

A simple method for generating the two falling on the image sensor Light bundle looks like this: At the point of impact of the laser beam on the DUT formed spot is using a lens on the image sensor displayed. In this case, the image sensor should be shaped and arranged so that within the depth of field of the imaged optics the image of Luminous spots on the image sensor comes to rest. This must be for all sorts of things Distances of the DUT, within the desired measuring range of the Entire device, be assured. The two separate light bundles become generated by the fact that shortly before or after the imaging lens with an aperture two openings is attached, so that two suitably selected sections of the from the light spot backscattered light hit the image sensor.

Another embodiment of the invention is that of the light spot emitted light is imaged by means of a lens on a beam splitter, where created by two divergent light bundles. These two light bundles can now again by using a second lens on an image sensor be imaged. Again, an interference fringe pattern, the sen spatial period length clearly from the distance of the test object depends, since the intersection angle of the two light bundles with changing Ent Distance changes.

The invention can also be configured such that the light spot on the light emitted to the test object with the aid of a lens on a screen (Diffuser) is displayed. The depth of field of the imaging lens / aperture can be low. The direction of the center of gravity of the screen Exiting light, typically a club-shaped intensity distribution normally agrees with the light spot as well as the Center of the lens defined axis, coincide. This direction is, if the light tende laser beam is not in the axis of symmetry of said front lens, again depending on the distance of the DUT.

The light emerging from the ground glass then hits a beam splitter so that two separate light beams are created. These are angeord by two diagonally Nete mirror and another lens turn on the image sensor for editing brought so that a, dependent on the distance of the DUT interference stripe pattern arises. The image is advantageously chosen so that the screen would be imaged behind the image sensor, so that  the two light bundles striking the image sensor, with changing delimiters tion to the test object, as little as possible.

In the first two embodiments of the invention, Figure with a lens and double iris as well as the picture on a beam splitter and then on the image sensor, the two intersect, the interference fringe pattern he generating light beams in different places at different distances to the test object. Here, the locus of the intersections in changing Ent distance in a good approximation, a straight line, so that the image sensor as a straight or planar, one- or two-dimensional sensor can be formed.

Another embodiment of the invention serves the purpose or Kompen the magnification of an optical system, as in the art but also for example in the form of the human or animal eye comes. As previously described, a collimated, parallel laser beam, preferably by a diaphragm in cross-section limited laser beam, out sandt. This laser beam now penetrates the lens system of the to be measured optical system and creates on a surface behind it one Spot. Depending on whether this surface is at the focal plane of the lens system agrees or not, results in a more or less sharp Light spot on this surface. Part of the now from the light spot in all Spaces of outgoing light now again passes through the lens system therethrough. The light emerging from the lens system can now be different Directions and collimation states: Is the surface on which the Laser beam generates the spot, in front of the focal plane of the lens system (i.e. closer to the lenses), so the backscattered light after exiting the Lens system divergent and not parallel on average (eg oriented away from the laser) to be entering laser beam. In the event that the surface behind the Focal plane, results in a convergent emerging from the lens system Light bundle, which is also not parallel (now oriented towards the laser) for Laser beam runs. Now the surface lies exactly in the focal plane of the Lin sensystems, this creates the emanating from the now relatively small spot Stray light after passing through the lens system a wide, parallel colli miert light beam parallel to the incoming laser beam. The further procedure way is analogous to the two methods described above with beam splitter. Preferably, a hidden by a diaphragm part of the lens System emerging light is, for example, a beam splitter or a  Matt screen shown. Analogously to the Ver then drive two intersecting light bundles on an image sensor testifies. The distance of the resulting interference fringes is now a measure of the Distance of the illuminated surface relative to the focal length of the lens system. In the case of a technical imaging system is often the Ab stood the lens system to the illuminated surface directly accessible, so that then of course determines the absolute focal length of the lens system can be.

Is the refractive power of the lens system changed by connecting a lens be, as for example, in the human eye by attaching glasses or contact lenses, this can also be done that tentatively various corrective lenses in front of the lens system be attached. For example, a desired image is ideal if that read the lens system including the corrective lens emit light beam parallel to the laser beam, because then the focal plane of the Lens system with the illuminated surface (eg retina in the eye) together menfällt. The distance of the interference fringes is now a measure of whether the turned brought corrective lens too strong or too weak, so this then can be exchanged. Iteratively, that is the best corrective lens determine.

This process can, by rotation of the whole before the imaging system arranged system, be repeated for several levels, for example To detect astigmatism errors of the imaging system. In the case of the Bestim the total refractive power of the eye, it is necessary, because the refractive power of the Lens in the eye is changeable, the eye a certain in a certain Ent Distance lying image, for example, by appropriate reflection on so that the person tries to adjust the lens so that this image is possible as sharp as possible. The colors of the picture offered should not be the Color of the laser beam included. In front of the image sensor can then a color filter be attached so that the image sensor only ultimately generated by the laser Can receive light, but not before the image offered to the eye, outgoing light. The entire light intensity striking the retina should be be as small as possible so that the iris diaphragm opens as far as possible in the eye.  

In all the cases described so far, as the image sensor, a plurality of, in a series or arranged as a matrix, opto-electrical converters used (eg CCD line or matrix camera). The resulting electrical Signals can then be further processed, for example, with electronic computers (eg FFT, Frequency Counting, Correlation).

The image sensor can also be designed in such an advantageous manner in all cases that it is made of an optical double slit, the distance of the column preferably to the expected interference fringe distance of the light through the two bundle is matched to the interference fringe pattern generated on the image sensor, consists. Behind each one of the two columns will be one that comes out of the belonging gap leaking light integrally detecting, photodetector (such as APD Photodiode). Both columns are slightly offset from each other, preferably by the mean distance of the interference fringes. Furthermore, can in all cases in the optical path of one of the two, tref to the image sensor fenden light beam causes a slight frequency shift of the light who the. This frequency shift of the light, for example, by a ro animal lattice or an acousto-optic modulator (eg Bragg cell) be called. Because the two light falling on the corresponding gap bundles now have a slightly different frequency, the interference will be move strip pattern on the gap. The on the behind the respective gap arranged photodetector incident light intensity changes so periodically. The change frequency corresponds to the frequency shift of the light through z. B. the acousto-optic converter. A changed distance to the object works as described, in a change in the angle between the two from the image sensor incident light beams, which in turn in a Än tion of the strip spacing of the, now running, interference fringe pattern reflected. The phase relationship of both, from the two photodetectors seen signals is now so a direct measure of the distance to the counter was standing. The structure of a phase detector can, in a similar manner as in Communications technology be performed. This procedure allows one except usually high repetition rate of individual distance measurements. Both Columns are preferably not arranged spatially close to each other, but so, for example with the help of a beam splitter (semitransparent mirror) that they only visually so appear. The two columns can then be used to increase the Light intensity on the photodetectors, also symmetrical at the location of the Column arranged grid to be replaced.  

Deviations of the wavefronts of the two incident on the image sensor light bundle of the considered as ideal flat wavefront, due to a Fo kussierung on the image sensor or by non-ideal optical properties the arrangement, as well as wavefront deformations, caused by upper surface structures of the illuminated by the laser beam surface, leads to egg An interference fringe pattern whose fringe spacing is no longer constant. Inaccuracies can now, after appropriate detection of the intensity distribution on the image sensor, mathematically, in an analogous manner to the procedure at Interferometers, are detected, so that a more accurate value for the cutting angle of the two light beams falling on the image sensor and thus for the distance to the subject on a mathematical reconstruction of the wavefronts ermit can be telt.

Optically, an improved accuracy of the interference fringe pattern can be achieved on the image sensor. Will that spot on the Object generating laser beam brought to a slight vibration, so The interference fringes on the image sensor also appear vibrating. On The same effect can be achieved if an optical, a vibration verur appropriate, element both in the beam path of the laser, as well as in the Reception beam path is introduced. In the case of one in relation to the vibra tion frequency long integration period of individual photodetectors in the picture sensor, the image on the image sensor looks a bit blurry. This picture however, provides notification of a variety of phase conditions of the Image sensor falling waves, so that one of the surface structure of the illuminated surface gives independent interference fringe pattern.

In all methods, but especially in the previously described Method of the slit image sensor with frequency shift due to high temporal resolution of the measured values, from the difference of successive ones Distance measurements the speed of the DUT are determined (ma thematic: derivation of the distance after the time).

In the following the invention will be explained in more detail with reference to the drawing. Show it

Fig. 1 is a distance measuring device with double slit in front of the receiving optics in a schematic representation;

Fig. 2 is a schematic representation of the present imaging geometry;

Figure 3 is a section of the beam path of Figure 1, Figures 6 and 9 with a part of the image sensor....;

Figures 4a, 4b, 4c, the locus of the image of to be measured on the article produced light spot with a changing distance, the variation of the distance of the image point of the imaging lens dependent on the distance of the object and the variation of the interference fringe spacing with the parameters.:

Maximum distance | 6 m Minimum distance 1 m increment 0.1 m Lens focal length 0.14 m Distance lens laser 0.05 m Half aperture distance 0.005 m wavelength 820 nm DX 0 11.49 μm Offset horizontal ( Fig. 4a) 0 Offset vertical ( Fig. 4a) 0.14 m

Figures 5a, 5b, 5c, the locus of the image of to be measured on the article produced light spot with a changing distance, the variation of the distance of the image point of the imaging lens dependent on the distance of the object and the variation of the interference fringe spacing with the parameters.:

Maximum distance | 50 m Minimum distance 4 m increment 0.2 m Lens focal length 0.3 m Distance lens laser 0.1 m Half aperture distance 0.001 m wavelength 820 nm DX 0 12.31 μm Offset horizontal ( Fig. 4a) 0   Offset vertical ( Fig. 4a) 0.3 m

Fig. 6 is a distance measuring device with beam splitter in a schematic Dar position;

Figure 7 is a section of the beam path of Figure 1, Figure 6 and Figure 9 with an inserted frequenzverschiebendem element....;

Figure 8 is a section of the beam path of Figure 1, Figure 6 and Figure 9 with an additionally inserted second photodetector....;

Fig. 9 is a distance meter with ground glass and beam splitter in cal mathematical representation;

Figure 10 is an expanded arrangement for the analysis of the imaging properties of an optical system.

Figures 11a, 11b and 11c shows a detail of the beam path of Figure 10 in three different situations..;

FIG. 12 shows an enlargement of FIG. 10 about elements which allow an additional image to be reflected in the field of view of an eye.

The method described below and shown in Fig. 1 is used to determine Be the distance of the sensor to the DUT.

The laser beam 2 formed by laser 1 strikes the surface of the object 3 and forms there the light spot 4 . The emitted light from this spot 4 light forms more or less evenly distributed, with the surface structures, the surface velocity and movement-related temporal and spatial fluctuations in intensity, the diffuse lobe 11th The double-slit aperture 6 fades out of the radiation lobe 11 the two partial beams 14 and 15 . These are brought through the lens 7 on the image sensor 8 to the section. In the sectional volume 9 , which is identical to the point of impingement of the beams 14 and 15 on the photosensitive layer of the image sensor 8 , now arises the interference fringe pattern shown in FIG . The interference fringe spacing Δx is essentially determined by the laser wavelength λ and the intersection angle Θ. All geometrical influences thus enter the interference fringe distance via Θ. These are the gap distance of the double-slit diaphragm and the imaging ratio, determined by the respective imaging law (see FIG. 2). Thus applies

where f is the lens focal length, G is the object width, B is the image width and δ is the is half the distance between the two columns of the double-slit diaphragm.

Now moves the sensor (consisting of the components 1, 6, 7, 8) to the surface or moves to the surface of the distance sensor, it results at a later time z. B. the new point of impact 5 with the associated radiation lobe 12th The impact point 5 is now imaged at the location 10 on the image sensor. Of course, there is also an interference fringe pattern in the intersection 10 . However, this now has a different interference fringe spacing due to the different object width G relative to the light spot 4 . The distance to the surface is determined by way of this interval of distance, which changes as a function of the object width G. The main advantage here is the high degree of independence of the strip spacing of intensity and intensity distribution variations in intensity of the laser beam 2 he testified luminous spot. The resulting interference fringe spacing can be evaluated with an accuracy of better than 1 ‰. The temporal change of the so determined interference fringe spacing gives the desired speed information.

Since in this arrangement, simultaneously to the changing interference fringe spacing, the interference fringes still move on the image sensor 8 , and since there is a clear relationship between fringe position and fringe spacing, but these are independently determinable quantities, this fact can be used to misalignments or damage of the sensor (which can then lead to a sensor failure or to incorrect measured values) to recognize early and display before it can lead to incorrect measurements or total failures. This means that within certain limits an internal calibration of the sensor can be made at any time and it can always be changed sensor properties are displayed before it can lead to accuracy changes.

Fig. 2 serves to explain the imaging process. The ver tikal exiting in the drawing laser beam strikes in the object point on the object to be measured. Part of the light scattered in all directions is imaged by the lens 7 onto the pixel. Between the object width G, the image width B and the focal length f of the lens 7 , the following relationship exists:

The angle α is determined by the distance of the laser beam to the center of the lens 7 and the distance of the DUT. If the object point is at infinity, the pixel is imaged at the distance of the lens focal length f to the vertical axis. (This point forms the origin of the coordinates in FIGS. 4a and 5a). If the object point approaches the device, the object becomes wider G smaller, the image width B and the angle α larger. The pixel above crosses a certain path in the drawing plane. This locus of the pixels is plotted in FIGS. 4a and 5a. It can be seen that this is approximately a straight line, so that a linear line sensor can be set. The change of the object width G as a function of the distance of the test object is shown in FIGS. 4b and 5b. It can be seen that the accuracy of the sensor increases with decreasing distance, but also the image sensor must be larger. Determining the angle at which the locus curve of the pixels to the vertical axis and under which the image sensor must be arranged, is the distance of the laser beam to the lens. If this distance is chosen to be very small, the scattered light strikes the image sensor only at a very small angle. Fig. 3 shows the interference fringe pattern formed on the surface of the image sensor. The distance Δx is independent of the angle of incidence α of the entire light beam. The intersection angle of the light beam with the image sensor is determined in practice essentially by the tilt angle of the locus of the pixels, ie the distance laser lens, and only slightly from the angle α, ie the distance of the measured object. Due to this angle between the light beam and the image sensor, the interference fringe pattern appears enlarged on the image sensor (by the factor 1 / sin (intersection angle)). The distance laser lens must therefore be selected according to the required accuracy and the resolution of the image sensor.

Fig. 3 shows in detail the impact of the two lenses generated by the apertures in front of the front light cone 14 and 15 on the image sensor. Both light cones generate by interference the interference fringe pattern 13 , the fringe spacing Δx of which results from the intersection angle 2 Θ (see FIG. 1) of the two light cones 14 and 15 :

Figures 4c and 5c show the distance Δx of the interference fringe pattern over the distance, without regard to the tilt angle of the image sensor. For the case shown in Fig. 4a, 4b and 4c results in an intersection angle between tween the image sensor and the incident light beam of about 18.5 ° at an interference fringe spacing of about 12.5 microns. The image sensor then sees a strip spacing of about 39.4 microns, so that a CCD line sensor with 7 microns pixel spacing would be well suited as an image sensor. Similar numbers result for the case of Figs. 5a, 5b and 5c. The interference fringe spacing Δx can be set almost independently of the other parameters discussed by the distance between the two apertures in front of the receiving lens and thus the angle 2 Θ in FIG .

Figures 4a, 4b and 4c show an example of a distance range of 4 to 50 m. The lens focal length is 0.3 m, the distance of the laser to the center of the lens 0.1 m. The pixels cover a distance of about 2.2 cm ( Figure 4a), so that an image sensor with this length can be arranged at an angle of 18.5 ° to the vertical axis. The change of the image width in depen dence of the distance of the DUT is shown in Fig. 4b. It can be known that the image change in distance at small distances is greater, so that here increases the accuracy of determining the position of the light spot on the image sensor. Fig. 4c shows the change of the interference fringe distance Δx over the distance. Again, there is a larger change in the interference fringe spacing at small distances and thus a higher accuracy. With the very similar signal curve of the output signal of a laser Doppler anemometer (LDA) accuracies of better than 1 ‰ can be achieved, whereby a larger dynamic range than in the present case must be covered. An accuracy of 1 ‰ in the determination of the Interferenzstreifenmu sters leads in the case of Fig. 4c to an accuracy of the determined Ent distance of about 4.5 m at a distance of 40 m and 5 cm at a distance of 4 m Ent from the test object.

The example in FIGS. 5a, 5b and 5c was prepared for a distance range of 1-6 m. In this case, a lens focal length of 0.14 m and a distance to the laser of 0.05 m was selected. Again, a sensor with a length of about 2 cm at an angle of about 20 ° had to be attached. The accuracy is now at 6 m distance about 20 cm, at a distance of 1.1 m about 6 mm.

Another embodiment of a distance sensor according to the invention is shown in FIG . The laser beam 2 formed by laser 1 impinges on the object 3 and forms there the light spot. 4 The part of the light spot 4 from radiated and incident on the opening of the aperture 16 light is imaged by the lens 17 in the form of the beam 18 on the beam splitter 19 . The type of mapping is the same as explained in detail above with reference to the example of FIG . The geometry is again shown in FIG . The image of the light spot 4 thus moves on the beam splitter 19 , while the object 3 is approaching the laser 1 and merges into the image of the light spot 5 at a later time. The two light beams generated by the beam splitter 19 are imaged by the lens 20 in the form of the light beams 14 and 15 on the image sensor 8 and brought there to the section. Again, an interference fringe pattern then forms at point 9 in the case of the light spot 4 . For the Inter distance strip distance, the analog considerations apply as in the above geschilder th embodiment (see Fig. 3).

Another embodiment of the invention is shown in FIG . At the point of impact of the laser, not shown in FIG. 9, on the object 3 , the light spot 4 is imaged on the ground glass 30 , with the aperture 27 being adjustable by means of the lens 28 in the form of the light beam 29 . This is not in all cases a true image in which the image of the light spot 4 is sharply imaged on the ground glass 30 : The distance between the lens 28 and the ground glass 30 is advantageously adjusted so that at an average distance of Object 3 to the lens 28, the image of the light spot 4 falls exactly on the ground glass 30 and there he sharp. At smaller distances of the object 3 , the focus of the light beam 29 is now behind, with larger distances in front of the screen 30th If the opening angle of the light cone 29 , due to a large aperture of the aperture 27 , now large, so may be on the screen 30, a diffuse light spot ent. The intensity distribution of the light beam 44 emerging from the ground glass 30 is club-shaped in a typical ground glass screen. The symmetry axis of this lobe, however, is identical to the axis of symmetry of the disc 30 striking the light 29th In a suitably arranged laser thus changes the exit direction of the light beam 44 from the ground glass 30 in dependence from the distance of the object. 3 The light beam 44 strikes the beam splitter 31 . The two light beams emanating from the beam splitter 31 now appear as if they came from the imaginary points 41 and 43 on the virtual ground glass 42 . At a distance a in front of the virtual ground glass 42 is now the virtual lens 40 , which corresponds to the real lens 28 . The two light bundles entering the lens 32 , which exit as light bundles 37 and 38 , are deflected by the lens 32 onto the surface 45 of the image sensor 35 and intersect to form an interference fringe pattern. The upper surface 45 of the image sensor 35 is preferably at a distance

behind the lens 32 is arranged. In this case, f indicates the focal length of the lens 32 , b the distance of the lens 32 to the virtual ground glass 42 (corresponding to the optical distance to the real focusing screen 30 ) and a the distance of the virtual Matt disc 42 to the virtual lens 40 (corresponding to the distance of the ground glass 30th to the lens 28 ). Advantageously, b = f is chosen.

In order to keep the effort in the adjustment of the device and the cost low, several optical elements can be summarized. The mirrors 33 and 34 as well as the beam splitter 31 can for example be realized very advantageously in the form of a single beam splitter prism.

Fig. 10 shows another example of the embodiment of the invention for analyzing the imaging properties of an optical system. Fig. 10 illustrates this with reference to some parts of the human eye shown. Of course, the same applies to other lens systems used in the art with image receiver or ground glass arranged thereafter. The laser beam 2 formed by laser 1 passes through the lens system consisting of cornea 46 , lens 48 and other elements that possibly influence the light and impinges on retina 50 in the form of converging beam 49 . The ent standing light spot 51 now emits light in virtually all directions. A portion of this radiated light now falls through the lens 48 and the cornea 46 through the aperture 52 , which speaks the aperture 16 in Fig. 6 and the aperture 27 in Fig. 9 ent. The portion of the light passing through the aperture 52 then strikes the lens 54 . The lens 54 corresponds to the lens 17 in Fig. 6 and the lens 28 in Fig. 9. The drawn box 53 thus represents the arrangement of Fig. 6 and Fig. 9, which have already been described. The beam path in the vicinity of the Linsensy stems 46/48 and the retina 50 is shown on the basis of three different cases even times in Fig. 11: Fig. 11a shows the case that the retina is located in Brennweite distance behind the lens system. The laser beam 2 is therefore focused sharply on the retina. The back through the lens system escaping de and partially dimmed by the aperture 52 back scattered light from the mesh now runs parallel to the laser beam 2 and is collimated. Fig. 11b shows the case that the retina is too close behind the lens or the focal length of the lens is too large. The light beam produced by the backscattering light is now divergent and directed differently (oriented downwards). In Fig. 11c reverse conditions arise. The focal length of the lens is too small or the distance between lens and retina was too large. The backscattered light outside the eye is now convergent, pointing upwards. Thus, analogous to Fig. 6 and Fig. 9 changes the direction of the emerging light, so that the visible interference fringes on the image sensor distance varies. This interference fringe distance is a measure of the ratio of the focal length of the lens system in the eye to the distance of this lens system to the retina. By attaching a corrective lens in front of the eye (glasses, contact lens), the imaging properties of the eye can be changed. Such a lens, automatically replaceable or preferably with variable focal length (zoom lens), may also be mounted as part of the arrangement shown in FIG . This ancillary lens can then automatically, as part of a control loop, be fitted so that the exiting the eye backscattering light is parallel to the laser beam 2 . The eye, together with the resulting auxiliary lens, then sharply focusses on the retina objects lying at infinity. In order to detect any astigmatism errors of the imaging elements in the eye, the entire arrangement shown in FIG. 10 can be rotated relative to the eye, so that the refractive power can be measured in several planes.

In the actual measurement of the refractive power of the eye, it is necessary to bring the present in the eye adjustable lens in a certain state. This can be achieved medically by temporary paralysis of the corresponding muscles, or by the fact that the eye is offered a real picture. Fig. 12 sketches a corresponding arrangement. The image existing on the surface 57 , for example a lettering, is faded into the eye with the aid of the lens 56 and the beam splitter or mirror 55 . If the distance d between the lens 56 and the surface 57 is exactly the focal length of the lens 56 , then the image for the eye appears at infinity. This is desired when fitting a pair of glasses. If the eye is to adjust to a shorter distance, the distance d is smaller than the focal length of the lens 56 to choose. The ele ment 55 may be embodied either as a beam splitter or as in the area of the laser beam 2 and the incident on the aperture 52 backscattered light permeable (ge drilled) mirror.

The light emanating from the surface 57 should not contain the color of the emitted laser light. An optical color filter, for example, mounted between the element 55 and the receiving unit 53 , which transmits only the wavelength of the laser light, can then be used to pass only the light originally originating from the laser to the image sensor. The total intensity of the light falling on the retina 50 should be low, so that the iris diaphragm 47 remains as large as possible.

The image sensors used in all the mentioned embodiments can For example, in the form of a CCD (Charge Coupled Device) -Zeil- or Flä be formed chenensors. These sensors are relatively cheap as they are in industrial scale (eg in fax machines). The data a preferably used CCD line sensor become a micro processor or microcontroller transferred. The mostly analog output signal of the sensor must be converted to digital information by means of an analog-to-digital converter; then the microprocessor / controller can handle, be implemented. at low readout speeds can possibly be integrated in the microcontroller The analog-to-digital converter can be used. High readout speeds in Combination with a slow processor / controller may require U. an ex internal AD converter and a FIFO for data buffering.  

The image sensor is illuminated in a certain area by two interfering scattered light beams ( Fig. 3). The light intensity on the image sensor, plotted over the pixel number, is in the form of a "modulated burst". This burst is very similar to the output of a laser Doppler anemometer (LDA). Both the modulation frequency (ie, the spacing of the interference fringes) and, in the case of Fig. 1 and Fig. 6, the place where the burst appear on the image sensor that are a measure of the distance of the measurement object. The processing of this sensor output signal can be performed in a variety of ways, similar to the LDA. Digital filter, Fourier transform (FFT) and correlation methods are possible. After properly performed bandpass filtering is present with the beat frequency of the burst around zero oscillating signal, so that the frequency can be determined by determining the Nulldurch courses and the position by determining the envelope. After an FFT, the spectrum shows a significant peak whose position represents the frequency and whose phase represents the position of the burst. The correlation method leads to good results, in particular when determining the position.

An alternative embodiment of the image sensor is as follows: In all the described embodiments of the optical system (Figures 1, 6 and 9...) May in one of the two, producing the interference fringe pattern on the image sensor, light beams (e.g., 15 in. Fig. 1, 15 in Fig. 6 and 38 in Fig. 9) a frequency-shifting element bendes be inserted. Fig. 7 illustrates this: the frequency of the incident light beam 15 is changed by the element 24 so that the frequency of the emergent light beam 25 is typically different by a few tens of MHz. As a frequency-shifting element is, for example, a ro animal optical grating or an acousto-optic modulator (so-called. Bragg cell) in question. By this frequency shift .DELTA.f one of the two, falling on the image sensor, light beam is now no longer resting the generated interference fringe pattern, but moves in the direction of the normal to the interference fringe (see. Laser Doppler anemometer with frequency shift). The interference fringe pattern now runs just as fast over the image sensor, that at a fixed point on the image sensor light with exactly the beat frequency .DELTA.f is seen, with the previously the frequency of one of the two falling on the image sensor light beam has been changed (z B. Driver frequency of the Bragg cell). The surface of the image sensor 8 or 35 is now realized in the form of the slit diaphragm 21 , wherein the slit diaphragm should be oriented parallel to the interference fringes. The behind the slit 21 (in Fig. 7) arranged photo detector 23 is designed so large that all falling through the slit 21 light falls on it. The light detected in the detector 23 is now also modulated with the frequency .DELTA.f. However, this frequency is independent of the angle 2 Θ between the light beams 25 and 14th Therefore, the arrangement, as sketched in FIG. 8, is supplemented by the beam splitter 22 (semitransparent mirror) and a second image sensor, consisting of the slit diaphragm 26 and the photodetector behind it. This photodetector now also sees light modulated at the frequency Δf. The slit diaphragm 26 should be arranged so that its image, with an axial reflection at the, on the surface of the beam splitter 22 in the plane extending axis, not exactly on the slit 21 is imaged, but the slit aperture 26 in the direction of the normal to the gap moved parallel to the surface of the element. This shift is preferential chosen so that it corresponds to the integer multiple of the interference fringe distance Δx, at a mean assumed angle 2 Θ between the light beams 14 and 25 . If the distance to the object 3 changes, and thus the angle 2 Θ, this leads to a change in the interference fringe spacing Δx. The two, seen by the two photodetectors signals with the frequency .DELTA.f and the phase angle of z. For example, 360 ° will change their phase relationship. This phase relationship is thus a measure of the distance of the object 3 . The phase position can be detected by, for example, in the direction of the conventional technique (see also Fractional triggering method, technical description: Techniques for Improved Time Spectroscopy, company EG). The two gaps in aperture 21 or 26 can, to increase the light intensity on the photodetectors, as a multiple column, ie formed as a grid. The lattice constant should correspond approximately to the average interference strip spacing Δx. Again, the imaginary folding of the grid 26 on the grid 21, the two grids must be slightly shifted from each other.

In all arrangements, the interference pattern appearing on the image sensor may be slightly distorted due to distorted waves of the generating light bundles due to focusing of the light, non-ideal optical properties of the device, as well as existing surface structures of the illuminated surfaces 4 and 50, respectively , ie the individual distances between the interference fringes are not exactly the same. In order to take this into account, two methods can be used: If a data processing system can access the data of the interference fringe distribution on the image sensor (as in the case of the CCD line), the deviation of the wavefronts generating the interference fringe pattern from the The ideal plane wave can be computationally determined (estimated) and from this the true intersection angle 2 Θ between the light bundles can be deduced. However, this compensation of the distortions of the interference fringe spacings can also be optically Runaway leads. In this case, the laser beam 2 plates, for example, by rotating wedge plates, acousto-optic deflectors, rotating polygon prisms or moving mirror as fast as possible, more or less far, preferably in the size order of the light spot 4 and 51 on the surface 3 and 50 , back and forth be moved. This "vibration" of the impact point 4 or 51 on the surface 3 or 50 then leads to a sufficiently large integration period of the image sensors 8 , 23 , 23 ', 35 to an average over a plurality of phase states of the on the image sensor 8 , 23 , 23rd ', 35 falling waves, so that one of the upper surface structure of the illuminated surface 3 , 50 results in independent interference pattern. The same effect can be achieved in Fig. 9 in that the ground glass 30 moves parallel to its surface. Preferably, the ground glass 30 rotates about the rotation axis 30 'sufficiently fast.

Claims (50)

1. A method for optical distance and speed analysis of surfaces and for analyzing the imaging properties of optical systems under exposure of the test object with primary light and analysis of the scattered light, characterized in that from the backscattered from the object or optical system light from at least two light beams are guided, they are preferably brought to the same optical paths to the cut and fall on an image sensor and from the nature and / or position of the resulting interference pattern on the distance, the speed or the imaging properties of the object to be measured or optical system is closed, preferably coherent primary light is used. 2. The method according to claim 1, characterized in that the two Light bundle by hiding two different subregions of the be generated backscattered light to the object or optical system. 3. The method according to claim 1, characterized in that for the production of the two light beams from that of the object or optical system backscattered light a beam splitter is used. 4. The method according to claim 1, characterized in that a part of from the object or optical system backscattered light on a Lens is shown. 5. The method according to claim 4, characterized in that the two Light beam using the emerging from the lens Light and a beam splitter can be generated. 6. The method according to any one of claims 2, 3 or 5, characterized records that the two light bundles through a lens on a picture sensor to be cut. 7. The method according to claim 6, characterized in that the on the Image sensor resulting interference pattern strips and with respect is evaluated on its strip spacing.   8. The method according to any one of claims 2,3 or 5, characterized that the locus of the intersecting light beam is a straight line and the image sensor can be straight or even. 9. The method according to any one of claims 1 to 8, characterized that both the outgoing light from the primary light source and the backscattered light penetrates a lens system being the lens system together with the light-scattering surface as an optical one System is considered. 10. The method according to claim 9, characterized in that it is at the optical system is a human or animal eye. 11. The method according to claim 9 or 10, characterized in that from the interference fringe pattern on the image sensor the ratio of Focal length of the existing lens system in the optical system with respect to the distance of the lens system to the light scattering surface is determined. 12. The method according to claim 9 or 10, characterized in that the optical system a corrective lens system with variable focal length is preceded and its focal length, controlled by the with the picture Sensor detected data of the interference pattern, as long as is changed until the desired imaging properties of the overall system - before hired lens system plus optical system - have set. 13. The method according to claim 11 or 12, characterized in that the Orientation of the light rays with respect to the optical to be measured System is changed so that astigmatism errors as well as lens errors higher order can be determined. 14. The method according to claim 10 and 11 or claim 10 and 12, characterized characterized in that the eye, in addition to measuring the same necessary primary light, an image located at an adjustable distance is mirrored so that the existing in the eye lens in one defined state is located.   15. The method according to claim 14, characterized in that the turned mirrored image does not have the same color content as the primary light and in front of the image sensor, a color filter is attached, so that the image does not mirror the interference pattern in front of the image sensor affected. 16. The method according to any one of claims 1 to 15, characterized that as an image sensor a plurality of, in a row or as a matrix ordered, photodetectors are used, preferably one CCD line or matrix camera used. 17. The method according to claim 16, characterized in that from the Strip spacing of the interference on the image sensor stripe pattern the distance of the primary light applied upper surface is derived. 18. The method according to any one of claims 1 to 15, characterized that in at least one of the two incident on the image sensor light Bundle is introduced an element for frequency shift of the light. 19. The method according to claim 18, characterized in that as an image sensor an optical double slit is used whose gap spacing is preferred corresponds to the expected mean interference fringe spacing, wherein behind each of the two columns, a photodetector is attached. 20. The method according to claim 19, characterized in that the two Column, by using a beam splitter, not spatially close must be attached to each other. 21. The method according to claim 19 or 20, characterized in that on Place two column two symmetrically arranged in their place optical Grid to be used.   22. The method according to any one of claims 19 to 21, characterized that the phase relationship determined by the two photodetectors Captured light intensities and as a measure of the removal of the surface or as a measure of the imaging properties of an optical system ver is used. 23. The method according to any one of claims 1 to 22, characterized that deviations of the wavefronts from the ideal shape of the picture sensor falling light beam calculated from the deformation of the interfe be determined in hindsight. 24. The method according to any one of claims 1 to 22, characterized that errors in the interference fringe pattern on the image sensor thereby kom be pensiert that the primary light or the primary light together is slightly deflected with the backscattered light. 25. The method according to any one of claims 1 to 24, characterized that the speed of a moving surface out of the sequence is calculated from distance measurements. 26. Arrangement for the optical distance and velocity analysis of surfaces and for analyzing the imaging properties of optical systems by exposing the test object to primary light and analyzing the scattered light, characterized in that emitted by the light source ( 1 ), preferably coherent primary light ( 2 ) ent neither directly nor after penetrating a lens system ( 46 , 48 ) on a surface of an object ( 3 , 50 ), there generates a light spot ( 4 , 51 ), from the light ( 11 ) at least two light beams are generated, which then preferably the same optical paths to the section ge introduced, whereby an interference pattern ( 13 ) on an image sensor ( 8 , 35 ) is formed and based on the nature and / or position of this interference pattern, the distance of the object ( 3 ), its speed or the imaging properties of the lens system ( 46 , 48 ) with respect to the surface of the article ( 50 ) t will. 27. Arrangement according to claim 26, characterized in that the two light bundles ( 14 and 15 ) by attaching a diaphragm ( 6 ) openings with two Publ and using a lens ( 7 ) from the scattered light ( 11 ) he testifies. 28. Arrangement according to claim 26, characterized in that for the generation of the two light bundles ( 14 and 15 ), a beam splitter ( 19 ) is used. 29. The arrangement according to claim 28, characterized in that the beam splitter ( 19 ) is arranged so that the light spot ( 4 , 51 ) with varying distance of the object ( 3 ) directly or with varying imaging scale of the lens system ( 46 , 48 ) with respect to the article ( 50 ), after penetrating the lens system ( 46 , 48 ), through which the lens ( 17 ) in the form of a light beam ( 18 ) is sharply imaged onto the beam splitter ( 19 ). 30. An arrangement according to claim 29, characterized in that the light bundles ( 14 and 15 ) from the two of the beam splitter ( 19 ) outgoing light beams using a, behind the beam splitter ( 19 ) angeord Neten lens ( 20 ) emerge. 31. Arrangement according to claim 27 or 30, characterized in that the image sensor ( 8 ) along the locus of the intersection, with varying distance of the object ( 3 ) or with varying Abbildungsmaß stab of the lens system ( 46 , 48 ) with respect to the object ( 50 ). the two light beams ( 14 and 15 ) is arranged. 32. Arrangement according to claim 26, characterized in that a part of the light spot ( 4 , 51 ) outgoing scattered light after penetrating the diaphragm ( 27 ) and the lens ( 28 ) on a lens ( 30 ) falls. 33. Arrangement according to claim 32, characterized in that the light emerging from the lens ( 30 ) on a beam splitter ( 31 ) falls, the light beam emanating therefrom deflected by two arranged behind mirror ( 33 and 34 ) and the attached lens ( 32 ) are and the resulting light beams ( 37 and 38 ) impinge on the image sensor ( 35 ), there overlap and the distance c of the lens ( 32 ) to the image sensor ( 35 ) preferably in accordance with the relationship is chosen, where f is the focal length of the lens ( 32 ), b the optical Ab stood between lens ( 32 ) and lens ( 39 ) and a the optical Ab stood between diffuser ( 30 ) and the lens ( 28 ) means. 34. Arrangement according to one of claims 26 to 33, characterized in that the on the image sensor ( 8 , 35 ) resulting interference pattern has stripes and is evaluated with respect to its strip spacing. 35. Arrangement according to one of claims 26 to 34, characterized in that it is the optical system formed by a lens system ( 46 , 48 ) and a surface of an object ( 50 ) is a human or animal eye, wherein the object ( 50 ) represents the retina (fundus). 36. Arrangement according to one of claims 26 to 35, characterized in that from the present on the image sensor ( 8,35 ) interference fringe pattern ( 13 ), the ratio of the focal length of the lens system present in the optical system ( 46 , 48 ) with respect to the distance of the lens system to the object ( 50 ) is determined. 37. Arrangement according to one of claims 26 to 35, characterized in that the lens system ( 46 , 48 ) is preceded by a correcting lens system with variable focal length, preferably between the beam splitter ( 55 ) and the lens system ( 46 , 48 ), and its Focal length, ge controls by the with the image sensor ( 8 , 35 ) detected data of the interference pattern, as long as changed until the desired properties of the overall system, consisting of the preceding lens system together with the existing lens system ( 46 , 48 ) set. 38. Arrangement according to claim 36 or 37, characterized in that all parts belonging to the measuring system are rotatable to a through the light spot ( 51 ) parallel to the laser beam ( 2 ) extending axis, are arranged. 39. Arrangement according to one of claims 35 to 38, characterized in that the eye in addition to the primary light necessary for the measurement ( 2 ) an additional image is superimposed. 40. Arrangement according to claim 39, characterized in that the image ( 57 ) by a lens ( 56 ) and a mirror or beam splitter ( 55 ) is imaged into the eye, wherein preferably the apparent distance by Va riation of the distance between image ( 57 ) and lens ( 56 ) is adjustable. 41. Arrangement according to claim 39 or 40, characterized in that the superimposed image ( 57 ) does not have the same color content as the primary light ( 2 ) and between the mirror or beam splitter ( 55 ) and the image sensor ( 8 , 35 ) a color filter is attached which transmits only light with the color of the primary light ( 2 ). 42. Arrangement according to one of claims 26 to 41, characterized in that as the image sensor ( 8 , 35 ) a plurality of, arranged in a row or as a matrix, photodetectors, preferably in the form of a CCD line or matrix camera attached , 43. Arrangement according to claim 42, characterized in that from the strip spacing of the resulting on the image sensor interference fringe pattern ( 13 ), the removal of the primary light ( 2 ) acted upon upper surface ( 3 , 50 ) is determined. 44. Arrangement according to one of claims 26 to 41, characterized in that in at least one of the two on the image sensor ( 8 , 35 ) falling light beam ( 14 , 15 or 37 , 38 ) a frequency-shifting element, preferably designed as a rotating grid or Bragg cell is introduced, both resulting light beams ( 14 , 25 ) using a beam splitter ( 22 ) in two light bundles aufgespal be split and the respective pairs on two slit diaphragms ( 21 , 26 ), preferably their column as optical Grids are formed, impinge, behind which integrating detecting photodetectors are attached. 45. Arrangement according to claim 44, characterized in that the two diaphragms ( 21 , 26 ) marginally, preferably by an integer multiple of the average, on the image sensor projected fringe spacing of Inter ference strip ( 13 ), against each other, in the plane of the aperture ( 21 , 26 ), preferably perpendicular to the columns, are arranged displaced. 46. Arrangement according to claim 44 or 45, characterized in that the phase relationship of the two, behind the slit screens or grids ( 21 , 26 ) mounted, photodetectors detected light intensities as a measure of the distance of the object ( 3 ) or as a measure of the imaging properties of the optical system ( 46 , 48 together with 50 ) is used. 47. Arrangement according to one of claims 26 to 46, characterized in that the interference pattern in a symmetrical region about the axis of symmetry ( 36 ) of the two on the image sensor ( 35 ) falling light bundle ( 37 , 38 ) and the axis of symmetry of the light beam ( 14,15 ), defined as its bisector, is evaluated. 48. Arrangement according to one of claims 26 to 47, characterized in that deviations of the wavefronts of the image sensor ( 8 , 35 ) falling light beam ( 14 , 15 , 25 , 37 , 38 ) of the ideal form computationally from the deformation of Interference fringes can be determined afterwards. 49. Arrangement according to one of claims 26 to 47, characterized in that errors in the interference fringe pattern are compensated by the fact that the primary light ( 2 ) or the primary light ( 2 ) together with the backscattered light by introducing an optical element, preferably before a rotating wedge plate, in the beam path of the primary light ( 2 ) or in the beam path of the primary light ( 2 ) and beam path of the backscattered light, are slightly deflected. 50. Arrangement according to one of claims 26 to 47, characterized in that errors in the interference fringe pattern are compensated by the fact that the lens ( 30 ) is preferably rotated about the axis ( 30 ').