WO1998056186A1

WO1998056186A1 - Device for modulating the intensity of a light bundle, method for producing the device, method for modulating the intensity of a light bundle and use of said device

Info

Publication number: WO1998056186A1
Application number: PCT/EP1998/000824
Authority: WO
Inventors: Christhard Deter; Jörg WUNDERLICH
Original assignee: Ldt Gmbh & Co. Laser-Display-Technologie Kg
Priority date: 1997-06-03
Filing date: 1998-02-13
Publication date: 1998-12-10
Also published as: JPH11514109A; DE19723208A1; EP0916228A1; IL127413A0

Abstract

The invention relates to a device (14) for modulating the intensity of a light bundle (12) which is incident in the entrance of a modulator (50). Said modulator can be regulated between two states by means of a control signal (54). In the first state, a minimum proportion of the light bundle (12) leaves an exit of the modulator and in the second state a maximum proportion of the light bundle leaves said modulator. According to the invention, the device (14) has two or more modulators (50, 50', 50'') arranged in a series, so that each light bundle leaving one of the modulators (50, 50') is guided into the entrance of one of the next modulators arranged in the direction of light propagation. After the intensity of the light bundle (16) has been modulated by the device, said light bundle can be removed from the last of the series of modulators (50) arranged in this way in such a manner that the extinction of the device (14) in relation to each of the individual modulators (50) is improved.

Description

DEVICE FOR INTENSITY MODULATING A BUNCH OF LIGHT, A MANUFACTURING METHOD FOR THIS, A METHOD FOR INTENSITY MODULATING A BUNCH OF LIGHT, AND

USE OF THE DEVICE

The invention relates to a device for intensity modulation of a beam, which falls into the input of a modulator, which can be controlled with a control signal between two states, in which in the first state only a minimal part of the bundle and in the second state a maximum part of the bundle fail from an output of the modulator. Furthermore, the invention relates to a production method for a device for intensity modulating a UchtbQbels with a modulator, in the input of which the light beam is incident, wherein this modulator can be controlled with a control signal between two states, in which in the first state only a minimal portion of the light bundle and in the second state, a maximum proportion of the UchtbQ bundle fail from an output of the modulator. In addition, the invention relates to a method for intensity modulating a UchtbQ bundle with a modulator, the input of which is introduced into the latter, the modulator being controlled with a control signal between two states, in which a minimal proportion of the Uchtbündi is present in the first state and one in the second state maximum portion of the UchtbQ bundle fail from an output of the modulator.

Weather the invention relates to uses of this device.

Intensity modulators for UchtbQndel are generally known. An overview is given, for example, in the book by Werner Hülsbusch, "The Laser in the Printing Industry", Vertag Werner Hülsbusch, Konstanz, 1990, pages 91 ff. Accordingly, electro-optical, acousto-optical, thermo-optical, magneto-optical, opto-optical or photothermal modulation can be used. There are also modulators Strip waveguides are known from DE 19503931 A1, in which modulation is achieved by changing the effective refractive index by means of injection or depletion of free charge carriers in semiconductor materials. The effectiveness of the modulation can in general be increased by a structure in the manner of Fabry-Perot interferometers.

Furthermore, electro-optical, acousto-optical, thermo-optical, magneto-optical, opto-optical and photothermal cut-off modulations are known in practice, it also being possible to use a variation of the effective refractive index by injection or depletion of free charge carriers in semiconductor materials.

In addition, a controllable waveguide gain, a controllable polarization rotation, a waveguide mode conversion or electro absorption modulation can be used for the intensity modulation of Ucht bundles.

Of these options, intensity modulators, which the Pockels-

Use the effect in a rod-shaped solid to emphasize. With this effect, the intensity modulation is based on a polarization modulation by means of a controllable external electric field in connection with a downstream analyzer for the polarization, viewed in the right direction. Due to the Pockels effect, the plane of vibration of an incident linear polarized wave is rotated depending on the applied field strength.

The Pockels effect is particularly advantageous because of the electrical controllability with the aid of voltages, due to which a short switching time is also achieved. However, the voltages required for such modulators are due to the ones to be achieved

Field strength very high, so that the drive voltage can only be generated with a certain outlay. That is why other polarizers are often used in practice

Such modulators operate in a limited spectral range. For this reason, the Ucht bundle mentioned at the beginning always relates to a wavelength range within the spectral limit specified by the modulators.

In particular when generating video images using lasers, modulation with high frequencies is required. This video technology has been known for a long time, for example it was described in an article by E. Baker. "Laser display technology" in IEEE spectrum,

December 1968, pp. 47-49, shown Here, a laser beam is scanned on a screen to generate a video image. The necessary deflection is carried out analogously for image display in the Femse tube, however, no magnetic deflection coils or electrostatic deflection plates are used here as with an electron beam, but the laser beam used here is scanned by rapid mechanical changes in the angle of mirrors or by acousto-optical deflection. As a result, all pixels of the video image are sequentially illuminated on a screen analogously to the known television picture. The intensity of the Ucht bundle is controlled for each pixel in the Uch propagation direction before rasterization, for example with one of the modulators mentioned, according to the intensity required for displaying the video image.

However, such modulators have a major disadvantage for the image display, because in the dark state a small part of U ^' cht is still let through, which can be disruptive for particularly dark video images, because even a low residual brightness of the pixels is still perceptible to the eye of an observer , since it essentially has a logarithmic characteristic. This disadvantage is particularly noticeable in planetarium applications in which very bright stars are to be displayed on a night-black sky.

Regarding the suppression of advances, progress has been made since the first publications on laser video technology in that, for example, the polarizing material in polarization modulators and their dimensioning, as well as the polarizing components such as polarizing foils and polarizing prisms, have been optimized. In addition, the Pockels cells were also improved so that the modulation voltage required for the intensity modulation was reduced. The polarization filters used in this case could themselves be improved to such an extent that they are only very narrow

Allow direction of vibration.

However, tests have shown that after an adjustment of polarizers and analyzers a weakening of the incoming laser power depending on the quality of the polarizers and analyzers, for example when using glan

Thompson prisms, still at a fairly high value of 125,000 for video applications. This ratio is further increased by using an electro-optical polarization modulator between the polarizer and analyzer. The deterioration is due, on the one hand, to the poor quality of the modulator material, especially due to the appearance of crystal defects, and on the other hand, other factors are also decisive, which are essentially due to scattered light and a slight mismatch in the position of the polarization plane of the polarizers with respect to the electro-optically acting material are due. Despite intensive development, electro-optical polarization modulators in conjunction with polarizing components for intensity modulation only achieve an extinction value, i.e. the ratio between the minimum transmitted intensity to the maximum transmitted intensity, of the order of 1: 500. This contrast ratio is achieved with the above

Video projection devices, especially for simulation purposes, such as in flight simulators and planetariums, are insufficient.

For example, the intensity modulator must be able to dampen the intensity of the UchtbQbels at the planetarium so much, despite a laser source operating at high nominal power, that complete darkness prevails in the projection room. Until now this has only been achieved satisfactorily with mechanically working apertures, which are used for video images

Frequencies of a few megahertz and above are generally too slow.

Non-mechanical, field-controlled intensity modulators, such as liquid crystal matrices, cannot be used either, because they leave the light blocking

Condition still so much through that the projection surface does not appear completely dark.

The object of the invention is a method for modulating the intensity of a Ucht bundle, an apparatus for carrying out the method and a production method for the same

To create a device in which a significant improvement in the intensity ratio dark / light and especially for frequencies of several megahertz is possible.

The object is achieved according to a generic concept in that the device has two or more modulators in an arrangement in which a bundle of failures falling out of one of the modulators enters the input one at a time

Uch propagation direction arranged following modulator is introduced, wherein the Uchtb Bundle intensity-modulated by means of the device can be removed from the last of the modulators in the row thus formed, so that the extinction of the device is improved compared to that of each individual modulator in a manufacturing process for the

The device is arranged behind the modulator known from the prior art, at least one further modulator in which the one that falls out of the first modulator

Uchtbündel is introduced into the input of the further modulator, so that the absorbance of the device for the removed intensity-modulated Uchtbündels is improved compared to that of each individual modulator. With the device, a method according to the invention for intensity modulation of a Ucht bundle can be carried out, in which two or more modulators for intensity modulation are arranged in series in the Ucht propagation direction, a Ucht bundle emerging from a modulator being introduced into the input of a further modulator arranged in the Ucht propagation direction and the Uchtb Bundle intensity-modulated by means of the device is taken from the last of these modulators in the row thus created, so that the absorbance of the device is improved compared to that of each individual modulator

One would have expected that a solution to the problem would be brought about from a professional point of view by the fact that the individual components had been improved by known modulators, or that a corresponding selection had been made from the various known modulators, which would have resulted in a significant improvement in the extinction ratio Possibly more exact optical components or newer arrangements are required, with which, for example, scattered light can be damped. However, one would expect much more effort for such solutions, in particular due to the required quality of the components, than with known modulators.

On the other hand, a completely different way is described here to solve the problem, in which one can also use very simple modulators, for example with a low extinction value, which are then arranged one behind the other in the direction of propagation. In principle, due to the series connection according to the invention, the residual light of a modulator can be further attenuated with the following modulator, i.e. by means of appropriate control signals, a very high extinction value can be set, which is known as

Product from the individual extinctions of the modulators connected in series yields this approximation, however, assumes that the spectral range of all modulators connected in series is the same.With different modulators with different spectral passband, which is however matched to the wavelength spectrum of the one beam, this product rule is according to the spectral one

Modify the pass band of the individual modulators.

Based on these considerations, it would be expected that a complicated control for the individual control signals for driving these modulators would result, namely when controlling the maximum transmitted intensity to a state of minimal

Real intensity all modulators are set for the passage of the maximum real proportion and then the individual modulators in the control to reduce the Intensity can be darkened one after the other. Unexpectedly, however, it has been shown that a device according to the invention can also be operated with a high extinction value if all modulators are moved from the state of maximum output power to a state of minimum output power by simultaneously changing the control signals.

In addition to the advantage of a good absorbance value, there is another advantage for Pockels cells. As already explained above, a major disadvantage of these Pockels cells is that they have to be operated at high voltages. Due to the improvement in extinction achievable according to the invention, the

Control Pockels cells also with sufficiently good extinction by means of significantly smaller control voltages for lower extinction of each individual cell, whereby, for example, Pockels cells connected in series are arranged in such a way that a maximum light component is coupled out when the control signal is zero and the light is turned on by increasing the control signal a minimum proportion is darkened. This darkening then takes place essentially with a power of the voltage given by the number of Pockels cells, so that much lower voltages are required to achieve a low extinction than in the case of a single Pockels cell. With a series connection of, for example, 17 Pockels cells and control with approximately half the voltage at half the intensity, an extinction value of over 1: 100,000 is achieved, i.e. even with a reduced control voltage, a significantly lower extinction value than with the modulators known from the prior art, whereby inexpensive low-quality materials can also be used for the individual Pockels cells in the row. An arrangement in which the extinction of the nth modulator is 1: 2 "would also allow digital modulation, which would make the modulation extremely immune to interference.

As explained above using the example of the Pockels cell, some advantages result from the fact that the complete intensity at zero signal strength of the control signal is passed through. In an advantageous development of the invention, however, it is required that the first state for all modulators at zero signal strength

Control signal is set.

This gives the main advantage that noise, ripple voltages and similar disturbances on the signal are reduced, which would worsen the achievable extinction value. Such signal disturbances could also be electronically filtered out, but in general the frequency dependence of the control voltages would also be undesirably influenced. The following training relates to modulators that work due to changes in polarization. The first of these advantageous developments of the invention is characterized in that each modulator has a device which can be controlled by the control signal and which divides the Uchtbündel into two depending on the control signal

Splits intensity components with mutually different, mutually orthogonal polarization states, and has a filter at the output of the modulator, which only allows the component of the Uchtb Bundle with one of these orthogonal polarization states to pass through and that this device and the filter from one of the modulators in the row in the first state for the Passage of light beams is aligned in a polarization state which is orthogonal to the polarization state given by the device and filter of the subsequent modulator

This has the particular advantage that the polarization filters of the individual modulators are always adjusted against one another when the first state in which no light is transmitted is set, so that there is a particularly low dark value at the output of the device without the maximum value of the intensity the Uchtbündel is significantly affected. This arrangement will be described in more detail below with the aid of an exemplary embodiment, which illustrates the advantages given thereby even more clearly.

In particular to achieve the high frequency mentioned in the task, it is particularly advantageous if the device is a Pockels cell in accordance with a further preferred development of the invention.

However, the invention can also be used using acousto-optical modulators. In this regard, a preferred development of the invention is characterized in that each modulator has a signal-controllable device for diffraction of Ucht for the control signal-dependent division of the Ucht bundle into intensity components of two different diffraction orders and an aperture on

Output of the modulator, which only allows a portion of the Uchtb Bundle in one of the diffraction orders, and that an aperture of a modulator at control signal zero covers an aperture of the following modulator to prevent vision

Because of the diaphragms arranged one behind the other in the Uchtweg

Further training, the stray light which may arise at each aperture or the bent lens is effectively blocked due to the prevention of vision, so that also thereby an especially good extinction value is advantageously achieved due to the reduction of stray light components. When using the strip waveguides known from DE 19503931 A1 or other integrated modulators, the entire device can be implemented on a substrate as integrated optics with several modulators connected in series. Accordingly, one looks preferable

A further development of the invention provides that the device is designed in an integrated-optical manner by connecting a plurality of integrated-optical modulators in series on the same substrate.

The following developments of the invention relate to simplifying the control of all optically connected modulators, in which the control signal can be the same for all modulators. Accordingly, an advantageous development of the invention, in which the control signals of all modulators are electrical voltages, is characterized in that all leads for the control signals for supplying a single control voltage to the device are shaded in parallel. In the case of modulators which operate, for example, due to the Faraday rotation of the direction of polarization and which are therefore magnetically controlled, the control signals are usually electrical currents with which magnetic coils are applied. With regard to such modulators used for the invention, it is provided in an advantageous development of the invention that the control signals are electrical currents and the controls of all

Modulators are connected in series.

Because of the high extinction values that can be achieved, such devices are particularly suitable for a video projection system in which the modulated light beam is deflected in line and image fashion and is directed at a screen for displaying a video image, the control signal for the device being a video signal with the resting deflection is synchronized

In particular, this application is particularly advantageous when this video projection system is a planetarium, because then all the stars are on night black

Background can be represented with little effort. However, in addition to this example, with the extreme values for light and dark required there, there are also significant advantages for flight simulators in which both the night sky and illuminated cities have to be realistically displayed in relation to daylight. The invention is explained in more detail below in principle on the basis of exemplary embodiments with reference to the drawing. Show it:

1 shows a video system in which the invention is advantageously used.

2 shows a schematic representation to explain the principle of the invention;

3 shows a schematic illustration of the mode of operation of an acousto-optical modulator;

4 shows an embodiment of a device according to the invention based on acousto-optical modulation;

5 shows a basic illustration of the mode of action of a Pockels cell;

6 shows another advantageous exemplary embodiment using Pockels cells as modulators;

In Fig. 1, a laser projection device is shown as it can be used, for example, to display color video images in video devices, planetariums or flight simulators. In all of these applications, it is expedient and, in some applications, even required to create a very large contrast between light and dark, since, for example, all the stars in a planetarium are to be displayed on a night-black sky. A device according to the invention is therefore particularly advantageous when used in a projection device according to FIG. 1

The projection device according to FIG. 1 is oriented towards a colored image representation. For the mixing of three primary colors, three lasers 10, 20, 30, from which three Ucht bundles 12, 22, 32 emanate, are provided, the Ucht having a suitable wavelength for generating

Send out pixels of a video image. In the exemplary embodiment of FIG. 1, the lasers 10, 20, 30 were statically operated gas lasers, the three bundles of beams 12, 22, 32 of which were subsequently modulated with suitable devices 14, 24, 34. With these devices 14, 24, 34, the intensity of the individual Uchtbündels 16, 26, 36 and thus the brightness and color of the pixels are controlled, that is, the aforementioned good extinction is to be realized here, as follows with reference to FIGS. 2 to Fig 6 is explained in detail. After leaving the devices 14, 24, 34, the light bundles 16, 26, 36 are combined into a total light bundle 40 by means of a mirror system 38, which propagates through the further system as a total light bundle 40.

In the exemplary embodiment, the total light bundle 40 was deflected line-by-image and image-wise onto a screen 43 by a deflection device consisting of a polygon mirror 41 and a swivel mirror 42 in order to sequentially illuminate individual pixels of the video image to be generated there. This screen 43 can be flat for the display of normal video images, but in the case of planetariums and flight simulators it is preferable to make it curved.

The screen technology used in such laser projectors is known from television with picture tubes. The technique used here differs from this in that a total light beam 40 instead of an electron beam for generating

Pixels of the video image used wind and the magnetic deflection usual in picture tubes is replaced by mechanical rasterization by means of polygon mirror 41 and swivel mirror 42. The rasterization is, however, not limited to the mechanical aids shown. For example, it can also be carried out acousto-optically.

The intensity of the light bundles 16, 26, 36 and thus also the brightness or, in the case of the color video system, also the color tone of the individual rastered image points on the screen 43 are determined by modulating the light bundles 12, 22, 32 by means of the devices 14, 24, 34 according to the invention via a control device 44 controlled as a function of the video signal introduced on the input side and synchronization signals generated by the deflection device.

The desired low extinction between dark switching and light shade is achieved by a device 14 according to FIG. 2, the internal structure of which is shown in principle as an example for one of the devices 14, 24 or 34 shown in FIG. 1. The Ucht bundle 12 is introduced into an input and the modulated Ucht bundle is removed as an Ucht bundle 16 from an output. The modulation is carried out by a plurality of modulators 50 and 50 'which are arranged one behind the other in the direction of propagation, that is to say connected in series, of which two, the first and the last, are shown by way of example in the exemplary embodiment in FIG. 2. With a correspondingly low value of the individual absorbance

It is generally sufficient for modulators 50, only two modulators to be connected in series, ie then to insert the bundle 52 that fails from the modulator 50 directly into the input of a subsequent modulator 50 *.

The respective modulators 50 and 50 'are acted upon by signals provided for this purpose by control inputs 54 and 54' in order to control the intensity of the real beam 16. If the first modulator 50 is in the dark state, the Ucht bundle 52 can nevertheless have a relatively high Ucht intensity, which is caused, for example, by material imperfections of the modulator 50 or scattered light in this modulator 50. The subsequent modulator 50 ', if it is switched to the dark state, further attenuates the intensity of the light beam 52, so that the light beam 16 can achieve a much better extinction by further reducing the light content of the light beam 52 than if only a single modulator 50 would be provided. The control signals of the individual modulators 50 and 50 'could be chosen quite differently, for example, the first modulator 50 can be switched dark at its input 54 when the control signal is zero, while the last modulator 50', for example, at its input 54 'at maximum signal strength in the dark state is.

This must of course be taken into account when driving the modulators 50 and 50 ". However, it has proven to be the most convenient for practical operation if the signals for all modulators for setting the dark state have the same values, since then a simple parallel connection for the control signals ^'is never shown 56, is possible if the modulators are all the same type. in particular, has further shown that the signals should be selected on the control signals 54 so that the modulators 50 and 50' by the broken U then let through the least amount Ucht when the control signals at inputs 54 and 54 'are in the zero state.

This results in the advantage that, as experience has shown, ripple or noise voltages are also the lowest at signal zero, that the components Ucht that are let through due to these interference voltages are reduced as much as possible and thus the greatest possible extinction without additional filter expenditure for the control signals for generating the Ucht bundle 16 from the Uchtbündel 12 becomes possible.

The previous explanations were directed to a voltage control of the modulators 50 and 50 '. In contrast, wind uses a current to control the modulators 50 and 50', for example to generate a magnetic field for a Faraday rotation of the polarization direction, should the control coils of the modulators 50 and 50 ' accordingly are connected in series, ie all modulators are controlled by the same current light and dark, analogous to the above statements of The dark state of the modulators 50 and 50 'is set due to the structure and arrangement at zero current. How such modulators working on the basis of different polarizations can be constructed and arranged will become clearer in the following using an example explained in more detail in FIG. 6.

The modulators shown in the example in FIG. 2 can be implemented integrated optically. The device according to FIG. 2 can be produced in a particularly reproducible and cost-effective manner if all modulators 50, 50 'and any further ones are integrated on a single substrate.

With the aid of FIGS. 3 and 4, however, it will now be shown how this modulation can be implemented using the acousto-optical principle. 3 shows an example of a modulator 50 which contains a so-called Bragg cell. This consists of a transparent material 60 suitable for the acousto-optical effect, in which acoustic waves are coupled in with the aid of, for example, a piezoelectric voltage-pressure converter 62. The acoustic waves are destroyed on an opposite sound absorber 63. These acoustic waves lead locally to changes in the refractive index in the material 60, which is why in the material 60 there is a diffraction of the real beam 12 incident at the Bragg angle Θ _B. A coating 64 with an anti-reflective coating is in each case on the surfaces for the entry and exit of material 60

Properties provided.

At a suitable frequency, for example from a sound wave, the Ucht bundle 12 not only passes through the transparent material 60 as a beam of neutral order 53, but also a second beam 52 is deflected in a higher diffraction order. The intensity of this beam 52 of the higher diffraction order essentially depends on of the modulation voltage of the piezoelectric transducer 62, while the angle of the deflection is determined by the frequency. The higher the amplitude of the acousto-optical wave generated by this transducer 62, the greater the proportion of light in the beam 52. As can also be seen from FIG. 3, one must generally also with scattered light from the incident beam 12 or the diffracted beam 52. for example by reflection at the sound absorber 63, so that one cannot necessarily expect the intensity zero in the direction of the diffracted beam 52 in the beam 52 with a voltage of 0 V present at the input 54.

To improve the extinction ratio, such acousto-optical modulators according to FIG. 2 are connected in series. In Fig. 4 that is closer in Fig. 2 illustrated principle in the form of a device 14 based on acousto-optical modulation. The device consists of material 60 which is suitable for acousto-optical modulators 50, 50 * and 50 ".

In the arrangement according to FIG. 4, the emerging beam 16 in the uncontrolled state of the modulators 50, 50 'and 50 "is much darker than in the exemplary embodiment in FIG. 3 and the extinction ratio is significantly improved, which is partly due to the fact that the shown diaphragms 67, 67 ', 67 "are offset from each other and so the direct passage of Ucht is greatly reduced.

An intensity modulation working on the basis of different polarization directions is shown in more detail in FIG. 5 on the basis of the principle of a Pockels cell. Modulators based on a change in polarization have the advantage over acousto-optical modulators that almost the entire intensity of the incident beam is reproduced in the outgoing beam, in contrast to the acousto-optical principle, in which an intensity component in other diffraction arrangements must always be taken into account.

5 shows different polarization directions with circles and lines. The light bundle 12 originating from the light source 10 is used to set a defined one

Direction of polarization first passed through a polarizer 71 This polarizer can be dispensed with, however, if the Ucht bundle 12 emerging from the laser 10 shown in FIG. 1 is itself polarized. Although this also applied to the example of FIG. 1, a Glan-Thompson prism was nevertheless used as the polarization filter 71 in the exemplary embodiment in order to achieve the best possible polarization of the optical bundle 13 when it falls into the end face 72 of an electro-optically active material 73.

Electrodes 74 and 75 are arranged in a known manner on the surface of the material 73. In the material 73, due to the electric field applied between the electrodes 74 and 75, a phase modulation of the incident Ucht bundle takes place in such a way that Ucht with different circular polarization states passes through the electro-optical material 73 at different speeds. Due to the different phase velocities of these partial light bundles with different polarization states, a real bundle 77 falls out of the end face 76, the polarization direction of which is changed when the voltage at the electrodes 75 and 76 differs from zero. Behind the electro-optically active material 73, a further polarization filter 79 is arranged in the modulator 50 as a polarizer, which was also a Glan-Thompson prism in the exemplary embodiment. This analyzer filters out only a single polarization direction, so that, depending on the voltage applied to the electrodes 74 and 75, the real bundle 16 emerging from the modulator 50 has different intensities. The two polarization filters 71 and 79, on the other hand, are arranged to act in a direction perpendicular to one another, so that at zero voltage at the electrodes 74 and 75 only a minimum of real intensity is contained in the real bundle 16. Even if the polarizers 71 and 79 are optimally aligned with the electro-optically active material 73, however, it can be determined on the basis of imperfections in the material 73 and / or the polarizers 71 and 79 that the real bundle 16 still has a low real intensity. Comparatively high-quality systems are required to achieve absorbance values of 500. In particular, scattered light will also contribute to the light component in the Ucht bundle 13, a component that the greater the divergence of the incident Ucht bundle 12, the greater the wind.

6 now shows an exemplary embodiment in which two such Pockels cells are connected in series according to the principle explained in more detail in FIG. 2. The same reference numerals thus refer to the same elements as in FIG. 5. In the second modulator 50, however, the corresponding reference numerals wound for better

Make a distinction with an apostrophe.

It can be clearly seen from the example of FIG. 6 that here two modulators 50 and 50 'were not simply connected in series, but the different polarization directions of the outgoing versus the incoming beam were used. This makes it possible to arrange only a single Glan-Thompson prism 79 between the two modulators 50 and 50 '. Further, the direction of polarization of the electro-optical material 73 'is perpendicular to that of the material 73 of the first modulator 50, i.e. at zero voltage at the inputs 74, 75, 74 ', 75', 54 and 54 ', all the components 73, 79, 80, 73' and 79 therefore counteract a direct improvement to the output of the device 14, so that with the aid of a small one Number of components only an extremely low intensity in the Uchtbündel 16 is to be expected.

The maximum intensity is achieved by applying the respective voltage for maximum transmission to each of the two modulators 50, 50 '. Intermediate values can be set by varying one or both of the voltages applied to the polarization modulators. For the arrangement of FIG. 6, measured values for the device implemented in the exemplary embodiment of FIG. 1 are given in the attached tables I and II. The respective output power of the Uchtbündels 16 is shown depending on the voltages between the electrodes 74 and 75 and between the electrodes 74 ^* and 75 '. For the

Measured values according to Table I, the voltage between the electrodes 74 'and 75' was kept at 0 V, while the voltage between electrodes 74 and 75 for the measured values in Table II was set to the value (250 V) for which according to Table I a maximum output power for the Uchtbündel 16 could turn. From the difference between measured values at voltage 0 V and 250 V at electrodes 74 and

75, an extinction of 1: 1,380 of the modulator 50 can be read from Table I. Table II shows an extinction of 1,380: 448,000, that is an extinction of 1: 325, for the second modulator 50 '. The different extinctions of the modulators 50 and 50 'are due, among other things, to the fact that, firstly, each modulator has specific properties, secondly, when there is a voltage variation on the first modulator 50 and on the second modulator

50 'a different number of polarization filters comes into effect and thirdly the influence of stray light due to different light paths in the modulators 50, 50' is different. Above all, it is clear from Table I and Table II that an unprecedented total absorbance of 1: 448,000 is possible. Furthermore, the voltages for maximum intensity at the electrodes 74 and 75 as well as 74 'and 75' are the same, which allows the two voltages at the electro-optically active materials 73 and 73 'to be connected in parallel in the device 14 shown in FIG.

The extinction of 1: 448,000 achieved here has not previously been achieved with conventional modulators 50. In this regard, it should be noted in particular that extremely good extinctions, even if smaller than in this example, can be achieved with an arrangement according to FIG. 6 if the intermediate elements 71, 80 and 79 are of lower quality than in the exemplary embodiment of FIG. 6.

Another modulator can be added for further extinction improvement. This means that components of lower quality can also be used for a good extinction, which, with suitable optimization overall, greatly reduces the costs for a device for modulating real bundles, despite a possible additional modulator. Table I

Table II

Claims

Expectations

1. A device (14) for modulating the intensity of a Ucht bundle (12) which falls into the input of a modulator (50) which can be controlled between two states with a control signal (54), in which in the first state a minimal proportion of the Ucht bundle

(12) and, in the second state, a maximum proportion of the Ucht bundle fail from an output of the modulator, characterized in that the device (14) has two or more modulators (50, 50 ', 50 ") in an arrangement in which one of one of the modulators (50, 50 ', 50 ") failing Ucht bundle is introduced into the input of each following modulator (50, 50', 50") arranged in the Ucht propagation direction, the intensity bundle (16) from the last of which being intensity-modulated by means of the device Modulators (50) in the row formed in this way can be removed so that the absorbance of the device (14) is improved compared to that of each individual modulator (50).

2. Vomchtung (14) according to claim 1, characterized in that the first state for all modulators (50, 50 *. 50 ") is set at zero signal strength of the control signal.

3. Device (14) according to claim 1 or 2, characterized in that each modulator (50, 50 ^* ) by the control signal controllable device (73, 73 *) which the Uchtbündel (12) depending on the control signal in two intensity components divides mutually different, mutually orthogonal polarization states, and has a filter (79, 79 *) at the output of the modulator (50) which only allows the portion of the Uchtb Bundle with one of these orthogonal polarization states to pass and that this device (73) and the filter (79) is aligned by one of the modulators in the row in the first state for the transmission of real bundles in a polarization state which is orthogonal to the polarization state given by the device (73) and filter (79, 79 *) of the subsequent modulator (50 ^* ).

4. Vomchtung according to claim 3, characterized in that the device (73, 73 ") is a Pockels cell.

5. device according to one of claims 1 or 2, characterized in that each modulator (50, 50 ', 50 ") a device controllable by the signal (60, 60 *. 60") for bending Ucht for the control signal-dependent division of the Ucht bundle ( 12, 52, 52 in intensity components (52; 53; 52 '; 53'; 52 "; 53") of two different diffraction orders as well as an aperture (67, 67 ', 67 ") at the output of the modulator (50, 50', 50 ") has only the portion (52, 52 ', 52") of the Ucht bundle (12, 52 52 ") in one of the

Diffraction orders and that an aperture (67) of a modulator (50) at control signal zero covers an aperture (67 ^* ) of the following modulator (50 *) so that it is not visible.

6. The device according to claim 1, characterized in that the device is integrated-optically by connecting a plurality of integrated-optical modulators (50, 50 ') on the same substrate.

7. Device according to one of claims 1 to 6, characterized in that the control signals of all modulators (50) are electrical voltages and all leads (54) for the control signals for supplying a single control voltage of the device (14) are shaded in parallel.

8. Vomchtung according to one of claims 1 to 7, characterized in that the control signals are electrical currents and the controls of all modulators (50)

Device (14) are connected in series.

9. Manufacturing method for a device (14) for intensity modulating a Uchtbündel (12) with a modulator (50), in the input of which the Uchtbündel (12) occurs, this modulator (50) being controllable with a control signal between two states, in which in the first state, a minimum proportion of the Ucht bundle (12) and in the second state, a maximum proportion of the Ucht bundle (12) fail from an output of the modulator, characterized in that at least one further modulator (ßO ⁹ ) is arranged behind this modulator (50) , into the input of which the cht bundle (52) dropping out of the first modulator (50) is introduced, so that the extinction of the device (14) for the intensity-modulated cht bundle (16) removed is improved compared to that of each individual modulator (50).

10. Method for intensity modulating a Ucht bundle (12) with a modulator (50), into the input of which a modulator (50) is introduced, the modulator (50) being controlled with a control signal between two states, in which in the first state a minimal proportion of the Ucht bundle ( 12) and in the second state a maximum proportion of the

UchtbQndels (12) precipitate from an output of the modulator, characterized in that two or more modulators (50, 50 ") itätsmodulation to ^Intens' are arranged in Uchtausbreitungsrichtung in series, a failing of a modulator (50) Uchtbündel (52) in the input of a further modulator (50 *) arranged in the direction of propagation was introduced and the intensity modulated in this way

Uchtbündel (16) in the row thus created is removed from the last of these modulators (50, 50 *, 50 "), so that the extinction of the device (14) is improved compared to that of each individual modulator (50).

11. Use of a device according to claims 1 to 8 in one

Video projection system, in which the modulated Uchtbündel (16) is deflected in a line and image-wise scanning manner onto a screen (43) for displaying a video image, the control signal for the device (14) being a video signal which is synchronized with the dithering deflection.

12. Use according to claim 11, characterized in that the video projection system is a flight simulator or a planetarium.