WO2005066706A1

WO2005066706A1 - Optical switch

Info

Publication number: WO2005066706A1
Application number: PCT/EP2004/013859
Authority: WO
Inventors: Simon Brattke
Original assignee: Carl Zeiss Ag
Priority date: 2003-12-24
Filing date: 2004-12-01
Publication date: 2005-07-21
Also published as: DE10361943A1

Abstract

The invention relates to an optical switch comprising a polarisation beam splitter (1) which divides an input beam (b1) into a first partial beam (b2) having a first polarisation state and a second partial beam (b3) having a second polarisation state in such a way that the first partial beam (b2) exits the polarisation beam splitter (1) in a first direction and the second partial beam (b3) exits the polarisation beam splitter (1) in a second direction, a diverting optics (3, 5) which is designed and disposed in such a way with respect to the polarisation beam splitter (1) that said optics reorients the partial beam (b2, b4) exiting said polarisation beam splitter (1) in the first direction towards the polarisation beam splitter (1) by the second direction and reorients the partial beam (b3, b5) exiting said polarisation beam splitter (1) in the second direction towards the polarisation beam splitter (1) by the first direction and a switchable polarisation device (7) which has at least two switching states and constructed in such a way that the switching state selection influences the polarisation states of the partial beams (b2, b3). The inventive polarisation beam splitter (1) is constructed and disposed in the optical switch in such a way that said splitter recombines the received partial beam (b4, b5) in the form of a beam (b6) and transmits said beams to an output (A) at an intensity depending on the switching state of the polarisation device (7).

Description

Optical switch

The present invention relates to an optical switch, in particular for unpolarized beams, and to an image-forming device with such an optical switch.

Optical switches are used to enable or block the beam path in optical devices, for example in imaging devices such as microscopes or projectors, as required. Such switches often comprise a liquid crystal cell (LC cell, LC: Liquid Crystal) arranged between two polarizers, the polarizers each linearly polarizing a beam of rays passing through them and serving as polarizer and analyzer. The liquid crystal cells used can be switched from an unswitched state, in which there is no rotation of the polarization direction of a beam passing through them, to a switched state, in which the polarization direction is rotated by 90 °, by applying a suitable voltage. Depending on the type of liquid crystal cell used, the ^" switched ^" state can exist in the case of an electrically de-energized liquid crystal cell or when a voltage is applied to the liquid crystal cell.

The optical switches described typically work according to the following principle: the beam to be switched, that is to say the beam to be blocked or transmitted, is first linearly polarized by the first polarizer. The polarized beam then passes through the liquid crystal cell in which the direction of polarization of the linearly polarized beam remains unchanged or rotated by 90 ° depending on the switching state of the liquid crystals. The beam then passes through a further polarizer, which is designed like the first polarizer, but is rotated through 90 ° in comparison to this. The second polarizer serves as an analyzer. If the direction of polarization of the beam in the liquid crystal cell is not rotated, the beam cannot pass through the second analyzer, the beam path is therefore blocked. If, on the other hand, the direction of polarization of the beam in the liquid crystal cell is rotated by 90 °, the beam can pass through the analyzer and the beam path is therefore released.

In the case of unpolarized beams, the described optical switches have a light loss of 50% in the transparent state of the switch. The reason for this is the linear polarization of the beam at the first polarizer and the associated loss of radiation with the other polarization direction. However, an intensity loss of 50% is not acceptable for many applications.

Another option for switching unpolarized light beams are switches based on polymer LC. Although these do not have the principle-related loss of light of 50% like the switches described above, they only show in the state blocking the beam path a diffusion of the beam of rays that is completely transmitted in terms of their intensity, and thus no complete blocking of the beam path. Switches based on this principle release the beam path when de-energized.

Compared to the described prior art, it is an object of the present invention to provide an improved optical switch, in particular for unpolarized beams, with which the disadvantages mentioned can be avoided in particular. It is a further object of the present invention to provide an imaging optical device with an improved optical switch, particularly for unpolarized light.

The first object is achieved by an optical switch according to claim 1 and the second object by an image-forming optical device according to claim 17. The dependent claims contain advantageous refinements of the invention.

An optical switch according to the invention comprises

a polarization beam splitter which divides an input beam into a first partial beam with a first polarization state and a second partial beam with a second polarization state such that the first partial beam leaves the polarization beam splitter in a first partial beam direction and the second partial beam leaves the polarization beam splitter in a second partial beam direction,

deflecting optics which are designed and arranged relative to the polarization beam splitter such that they return a partial beam bundle leaving the polarization beam splitter in the first partial beam direction to the polarization beam splitter coming from the second partial beam direction and a partial beam bundle leaving the polarization beam splitter in the second partial beam direction from the polarization beam splitter coming in first partial beam direction again, and

a switchable polarization device with at least two switching states, which is designed in such a way that the polarization states of the partial beam bundle can be influenced by the selection of the switching state. The polarization beam splitter is configured and arranged in the optical switch according to the invention in such a way that it combines the partial beam bundles supplied to it again to form a beam bundle and directs them to an output with an intensity that depends on the switching state of the polarization device.

The structure of the optical switch according to the invention makes it possible to switch unpolarized beams without the basic loss of light of 50%. In particular, the optical device according to the invention makes it possible To configure the switch, the polarization beam splitter, the deflecting optics and the polarization device in such a way, that is to match them in such a way that the polarization state of the beam bundle combined from the partial beam bundles corresponds to the polarization state of the input beam bundle.

If, for example, the polarization device can change the polarization state of a partial beam from the first polarization state to the second polarization state, the switch can be switched from a completely transparent state to a completely blocking state and vice versa. In one embodiment of the optical switch according to the invention, the polarization device therefore has at least one switching state in which it changes the polarization state of an incident partial beam from the first polarization state to the second polarization state and vice versa, and a switching state in which it does not change the polarization state of an incident partial beam , The first and the second polarization state can be, for example, linearly polarized states whose polarization directions are perpendicular to one another. In this case, a liquid crystal cell can be used as the switchable polarization device which rotates the polarization state by 90 ° in the switched state.

However, the optical switch according to the invention also makes it possible to manufacture switches which provide different degrees of transmission. For this purpose, the polarization device has at least one further switching state in which it changes the polarization state of an incident partial beam so that it does not correspond to either the first polarization state or the second polarization state. If, for example, the first and second polarization states are linearly polarized states whose directions of polarization are perpendicular to one another, this third switching state can, for example, cause the direction of polarization to rotate by an angle other than 90 °. An optical switch designed in this way enables in addition to a switching state that completely blocks the beam path (intensity at the output of the optical switch: zero) and a switching state that completely releases the beam path (intensity at the output corresponds to the intensity at the input of the optical switch), to provide a switching state in which the optical switch is partially transparent. Of course, there can be more than three switching states, so that different degrees of partial permeability can be realized. In particular, in a further development of this embodiment, the polarization device can be switched in such a way that the polarization state of an incident partial beam is to be converted into a freely selectable other polarization state depending on the switching state. In the case of linearly polarized states, this could mean, for example, that the polarization device is able to rotate the polarization direction by any angle between 0 ° and 90 ° depending on the switching state.

The switchable polarization device can be designed as an independent unit in the optical switch according to the invention or can be integrated into the deflecting optics.

If the switchable polarization device is integrated in the deflecting optics, it can be implemented as one of the light-directing elements of the deflecting optics, for example as a switchable reflector that maintains or changes the polarization state of a reflected beam depending on the switching state. This can go so far that only a single optical element is present as the deflecting optics, which also serves as a polarization device, so that the optical switch according to the invention can be implemented with very few individual parts.

If the switchable polarization device is not part of the deflecting optics, it can instead also be designed as an independent element in the beam path of the optical switch, in particular in the beam path of the deflecting optics, and can, for example, maintain the polarization state of a beam of rays passing through it, depending on the switching state to change. The polarization device is then preferably arranged in a region of the beam path of the optical switch in which the beam direction of the partial beam is opposite. In one configuration, the deflecting optics can comprise, for example, two light-directing elements, which can in particular be designed in such a way that they maintain the polarization state of a directed partial beam, the polarization device being arranged between the two light-directing elements.

Finally, it is also possible to divide the function of the switchable polarization device, so that the change in the polarization state is only achieved by an interaction of the deflection optics with an independent polarization device.

The principle of operation of the optical switch according to the invention can also be reversed without major design changes. The optical switch is then designed such that it blocks the beam path in the unswitched state and releases it in the switched state. For this purpose, a further polarization device, which always changes the first polarization state to the second polarization state and the second polarization state to the first polarization state, is additionally introduced into the beam path of the optical switch according to the invention. An optical switch designed in this way is completely transparent in the switched state and completely impermeable in the unswitched state. The additional polarization device can be an independent unit. However, the same effect can also be achieved if the additional polarization device is not designed as an independent unit, in that at least a part of the deflecting optics is designed such that it changes the first polarization state to the second polarization state and the second polarization state to the first polarization state. For example. If the polarization states are linearly polarized states with mutually perpendicular polarization directions and the deflecting optics comprise two deflecting mirrors, each of the two deflecting mirrors can be designed in such a way that the polarization direction is 45 ° into the same Direction rotates so that the total polarization direction is rotated by 90 ° by the deflecting optics. In this example, the switchable polarization device may have to be adapted to the version which does not have the effect of the additional polarization device, in order to be able to continue to provide partial beams with the first or the second polarization state on the polarization beam splitter. In addition, it is possible to implement an optical switch of this type with a reversed operating principle with other switching states in which it is partially transparent.

Polarization devices for influencing the polarization of reflected or transmitted beams can be implemented, for example, in the form of switchable liquid crystal elements.

Examples of possible light-directing elements are mirrors, prisms and optical fibers (individually or bundled), in particular also mirrors, prisms and optical fibers which maintain the polarization of a beam. Mirrors, prisms and fiber bundles are particularly suitable for switches that are to be used in imaging optical devices. In contrast, individual fibers, for example, for switching laser beams. Of course, a combination of mirrors, prisms and / or optical fibers can also be used as light-directing elements in an optical switch according to the invention.

If the polarization beam splitter, the light-directing elements and the switchable polarization device are arranged symmetrically to one another, the paths between the polarization beam splitter and the switchable polarization device are of equal length, so that the same beam convergences, focusing properties, etc. result for both partial beam paths.

In a further advantageous embodiment of the optical switch according to the invention, the switchable polarization device is flat and has a number of individually switchable regions. With a With such a polarization device, the imaging properties of the optical switch can be manipulated in a targeted manner, depending on the position in the beam path of the overall system for the polarization device.

If the dimensions of the individually switchable regions are small enough in a planar polarization device provided with individually switchable regions, in particular if they are approximately in the order of the wavelength of the input beam, the optical switch can be used as a switchable diffractive light modulator. The arrangement can thus be used, for example, as an adaptive optical element, for example an optical element with an auto focus function. The structuring of the individually switchable areas is preferably adapted to the desired application, for example the auto focus function.

An image-forming optical device according to the invention is equipped with at least one optical switch according to the invention. In particular, the imaging optical device can be equipped with an optical switch, the polarization device of which is flat and has a number of individually switchable regions. In such a device, the polarization device can be used as a display. In particular, such an image-forming optical device can be provided with an imaging optical arrangement, the image plane of which coincides with the plane of expansion of the planar switchable polarization device in order to implement the function as a display. Since the polarization device acts on both partial beam bundles, it is thus possible, for example, to implement a projector based on a liquid crystal display which has a light flux which is increased by a factor of 2 compared to a projector based on a liquid crystal display using conventional technology. Conventional technology is to be understood here as the polarizer-liquid crystal element-analyzer arrangement described at the beginning. In particular, the imaging optical device can comprise two imaging optical arrangements which are arranged symmetrically around the switchable polarization device within the beam path of the optical switch. If the optical switch is located in the parallel beam path of the overall system of the image-forming optical device, the imaging optical arrangements can be arranged such that the planar polarization device comes to lie in the focal plane of both arrangements. The extensive polarization device then serves as a display, which is imaged by the optics into the infinite. Alternatively, the imaging optical arrangements can also be arranged around the polarization device in such a way that the plane of expansion of the planar polarization device is located in the Fourier plane of the two optical arrangements. In such an imaging optical device, the optical switch can be used as a spatial frequency filter (image filter). The optical switch according to the invention permits frequency filtering of the image without a loss of light due to the principle. This can have applications in all areas of imaging optics. Microscopy should be mentioned here in particular, since the spatial frequency filter can be used to achieve a manipulation of the contrast that is easy to manipulate.

The imaging optical device can in particular be designed as a projection device or as an optical observation device, for example as an operating microscope.

Further features, properties and advantages of the present invention result from the following description of exemplary embodiments, with reference to the attached figures.

Fig. 1 shows a first embodiment for the optical switch according to the invention with the polarization device not switched. 2 shows the first exemplary embodiment with the polarization device switched.

FIGS. 3a u. 3b show the beam paths of beams which are incident on the optical switch of the first exemplary embodiment with different angles of incidence with the polarization device not switched.

4 shows a second exemplary embodiment of the optical switch according to the invention with the polarization device not switched.

5 shows the second exemplary embodiment with the polarization device switched.

6 shows a third exemplary embodiment of the optical switch according to the invention.

Fig. 7 shows a third embodiment of the optical switch according to the invention.

8 schematically shows an exemplary use of the optical switch according to the invention in an image projector.

The principle of the switch is shown schematically in Figure 1 and Figure 2. Figure 1 shows the optical switch in the unswitched and Figure 2 in the switched state of the switchable polarization device.

The optical switch according to the invention comprises a polarization beam splitter 1, which generates linearly polarized partial beams in the exemplary embodiment and can be designed, for example, as a birefringent element, two mirrors 3, 5 which maintain the polarization as deflecting optics for deflecting the partial beams and a liquid crystal cell 7 as a switchable one , the polarization state depending on the applied Voltage-maintaining or changing polarization device. In the present exemplary embodiment, the liquid crystal cell 7 is designed such that when a voltage is applied, it rotates the direction of polarization of a linearly polarized beam passing through it by 90 °.

An input beam bundle b1 of unpolarized light coming from the input E of the optical switch is converted by the polarization beam splitter 1 into a first partial beam bundle b2, the light of which is linearly polarized, and a second partial beam bundle b3, the light of which is also linearly polarized and whose direction of polarization is perpendicular to the direction of polarization of the partial beam b2 stands, split.

The first partial beam bundle b2 passes the polarization beam splitter 1 without being deflected from its direction and is then reflected by the second mirror 5 in the direction of the first mirror 3. The liquid crystal cell 7 is arranged between the second mirror 5 and the first mirror 3. A partial beam bundle b2 reflected by the second mirror 5 in the direction of the first mirror 3 must therefore pass through this liquid crystal cell 7 on its way to the first mirror 3. The first partial beam bundle that has passed through the liquid crystal cell 7 is referred to below as b4. The first partial beam b4 is finally reflected by the first mirror 3 in the direction of the polarization beam splitter 1.

The second partial beam bundle b3 is deflected by the polarization beam splitter 1 in the direction of the first polarization-maintaining mirror 3, from which it in turn is deflected in the direction of the second polarization-maintaining mirror 5. Like the first partial beam b2, the second partial beam b3 must also pass through the liquid crystal cell 7 on its way from one polarization-maintaining mirror 3 to the other polarization-maintaining mirror 5. The second partial beam that has passed through the liquid crystal cell 7 is referred to below as b5. The second polarization-maintaining mirror 5 second partial beam b5 finally reflected in the direction of the polarization beam splitter 1.

The liquid crystal cell 7 is designed in such a way that it allows the light of the partial light beams to pass through without changing the polarization direction when no voltage is applied to it. If, however, a voltage is present at the liquid crystal cell 7, the direction of polarization of the light passing through it is rotated by 90 °. In other words, the liquid crystal cell 7, when a suitable voltage is applied to it, represents a λ / 2 element, the fast axis of which forms an angle of 45 ° with the polarization directions of the partial beam bundle. Depending on whether a voltage is applied to the Liquid crystal cell 7 is present or not, the polarization direction of the light of the partial beam bundles b2, b4 or b3, b5 passing through it is therefore rotated by 90 ° or not rotated.

As shown in Figure 1, when the liquid crystal cell 7 is in the unswitched state, i.e. If the partial beam bundles b2, b4 and b3, b5 pass through the liquid crystal cell 7 without changing the polarization direction, the partial beam bundle b4 deflected by the first polarization-maintaining mirror 3 in the direction of the polarization beam splitter 1 occurs without directional deflection by the polarization beam splitter 1 in the direction of the Output of the optical switch A through, since the first beam bundle b4 after passing through the liquid crystal cell 7 has the same polarization direction as the beam bundle b2 before passing through the liquid crystal cell 7 and this polarization direction is the polarization direction that passes the polarization beam splitter 1 without deflecting the beam.

The direction of polarization of the second partial beam b5 reflected by the second polarization-maintaining mirror 5 in the direction of the polarization beam splitter 1 is likewise not changed by the liquid crystal cell 7 in the unswitched state, so that its direction of polarization continues to correspond to that direction of polarization which is determined by the polarization beam splitter 1 is reflected. The polarization beam splitter 1 is arranged such that the reflection of the second partial beam b5 takes place in the direction of the output A. The second sub-beam b5 is superimposed on the first sub-beam b4, so that an output beam b6 is formed, the light of which is unpolarized.

Due to the fact that the light of the input beam b1 is first split into two partial beams b2, b3 with perpendicularly polarized light and then the two partial beams b4, b5 are combined again as an output beam b6, there is no principle-related loss of intensity in the optical switch according to the invention.

FIG. 2 shows the beam path and the direction of polarization of the beams in the optical switch according to the invention when the liquid crystal cell 7 is switched. In the present exemplary embodiment, the liquid crystal cell 7 is in the switched state when a suitable voltage is present. In this case, the direction of polarization of the partial beam bundle b2, b4 or b3, b5 passing through the liquid crystal cell 7 is rotated by 90 °. For the light of the first partial beam b2, b4, this means that its polarization direction after passing through the liquid crystal cell 7 corresponds to the polarization direction which is reflected by the polarization beam splitter 1. Accordingly, the first partial beam b4 is now reflected by the polarization beam splitter 1 in the direction of the input E. The direction of polarization of the second partial beam b3, b5 is also rotated by 90 ° with respect to the direction of polarization before it has passed through the liquid crystal cell 7, so that it now corresponds to the direction of polarization that passes through the polarization beam splitter 1 without directional deflection. Correspondingly, the second partial beam b5 is now let through by the polarization beam splitter 1 in the direction of the input E. The second sub-beam b5 is superimposed on the first sub-beam b4, so that an output beam bδ 'is formed, the light of which is unpolarized. In Direction towards output A of the optical switch is no longer transmitted or reflected in the switched state.

In the unswitched state of the liquid crystal cell 7, the two partial beam bundles b2, b4 and b3, b5 leave the optical switch as the output beam bundle b6 through the output channel A. In contrast, in the switched state of the liquid crystal cell 7 they run back into the input channel E. In any case, the two partial beam bundles b2, b4 and b3, b5 are polarized perpendicular to one another, have, provided the optical switch has a symmetrical structure, pass through the same optical elements and light paths and become an unpolarized output beam bundle bδ (with an unswitched liquid crystal cell) or bδ '(when the liquid crystal cell is switched) combined. In the case of ideal, lossless optical elements, the output beam bδ or bδ 'therefore has the full intensity of the input beam b1. A general attenuation of the usable beam to 50% does not occur since the halves of the intensity of the input beam b1 present in the two branches of the optical switch are combined again in the output channel A or in the input channel E. The optical switch thus acts as an optical element that the unpolarized input beam b1 either transmits completely to the output A or reflects to the input E. The switch shows the same spectral characteristic that a switch according to the conventional scheme with a polarizer liquid crystal cell analyzer arrangement would also show.

In the exemplary embodiment described, the polarization beam splitter 1 is designed such that the partial beams b2, b3 run perpendicular to one another after the first passage through the polarization beam splitter 1 or the first reflection on the polarization beam splitter 1, and that the input beam bundle b1 and the output beam bundle bδ also run perpendicular to one another. In alternative configurations, however, the polarization beam splitter 1 can also be designed such that the partial beam bundles b2, b3 after the first passage through the polarization beam splitter 1 or the first reflection on the polarization beam expensive 1 run at an angle other than 90 ° to each other and / or the input beam b1 and the output beam bδ run at an angle other than 90 ° to each other. Finally, it should also be pointed out that there can be more than two polarization-maintaining mirrors. By using at least one further polarization-maintaining mirror, the angle between the input beam b1 and the output beam bδ can be set as desired. In particular, it can be achieved that the input beam b1 and the output beam bδ run parallel to one another.

The mode of operation of the optical switch as a transmitter or mirror can be reversed if, in addition to the liquid crystal cell 7, there is a λ / 2 element for the corresponding wavelength or the corresponding wavelength range of the input beam b1 in the beam path of the optical switch. The orientation of the λ / 2 element is such that the polarization directions of the partial beam bundle each have an angle of 45 ° with the fast axis of the λ / 2 element, so that the λ / 2 element changes the polarization direction of the partial beam bundle by 90 ° rotates. Since the λ / 2 element causes an additional rotation of the polarization direction of the two partial beam bundles b2, b3 and b4, b5, which is independent of the switching state of the liquid crystal cell 7, the behavior of the two partial beam bundles b4, b5 when compared with the polarizing beam splitter 1 is compared reversed for execution without an additional λ / 2 element, so that an input beam b1 is reflected towards the input when the liquid crystal cell 7 is not switched, whereas it is deflected towards the output A when the liquid crystal cell 7 is switched. The optical switch therefore now transmits when the liquid crystal cell is switched and reflects when the liquid crystal cell is not switched.

By using a liquid crystal cell which is able to rotate the polarization through any angle between 0 ° and 90 °, the switch according to the invention allows a continuous transition between the transmitting and reflecting states. Such a liquid crystal cell can be arranged, for example, rotatably about the optical axis of the beam path. In the switched state, the liquid crystal cell then represents a λ / 2 element in which the angle between the direction of polarization of the partial beam and the fast axis of the λ / 2 element can be adjusted by rotating the liquid crystal cell, so that the angle of rotation by the direction of polarization is rotated.

The optical switch according to the invention is not limited to the fact that an input beam is split into linearly polarized partial beams. Rather, it is also possible to split an unpolarized input beam into two circularly or elliptically polarized partial beams, for example into a partial beam with left circularly polarized light and a partial beam with right-hand circularly polarized light.

Applications for the optical switch according to the invention can be found in many imaging systems, in which the possibility of switching the imaging beam path on and off or the lighting should be given. In the case of surgical microscopes in particular, fast-acting closures, so-called shutter elements, are often desired for closing and releasing a beam path. In addition, the shutter elements should have the highest possible transmission, which is why the conventional shutter elements described above are mostly out of the question. The optical switch according to the invention, on the other hand, enables fast switching with very high transmission in the state releasing the beam path. But also the possibility of using the optical switch according to the invention as a switchable mirror offers interesting application possibilities in many areas of optically imaging systems, in particular in the field of optical observation devices, such as in the medical field for surgical microscopes, endoscopes etc., in which there are different beam paths should be switched here. In addition to the field of imaging optical systems, the optical switch can also be used to switch laser beams with any polarization, provided that the light intensity of the laser beam does not exceed a threshold that leads to damage to the polarization device. In particular if the optical switch is constructed symmetrically, the two partial laser beams optically follow the same paths. The linearly polarized partial beams of the laser are therefore brought together again with the correct phase, so that the original polarization is restored. It must be ensured that the phase jumps occurring due to the reflection in the polarization beam splitter add up to a multiple of 2π.

Furthermore, it is also possible to use a segmented or pixelated liquid crystal cell as the polarization device. The segmented or pixelated liquid crystal cell represents a polarization device with areas (segments or pixels) that can be switched back and forth individually between different switching states, for example between a state that maintains the polarization state and changes the polarization state. The imaging properties of the optical system, in which the optical switch according to the invention is located, can be manipulated in a targeted manner with the aid of the segmented or pixelated liquid crystal cell. The manipulation options depend on the point in the beam path of the overall system where the segmented or pixelated liquid crystal cell is used. A symmetrical arrangement, as shown in Figures 1 and 2, allows a similar flexibility as you have when using a conventional segmented or pixelated liquid crystal cell, since the light paths between the beam splitter and the liquid crystal cell are the same length for both light paths and thus the result in the same beam convergences, focusing properties, etc. for the two paths.

FIGS. 3a and 3b show those partial beam bundles b4 (FIG. 3a) and b5 (FIG. 3b) which together form the output beam bundle bδ and which are suitable for different angles of incidence of the input beam bündeis b1 result in the optical switch. The partial beams b4 and b5 in the output branch of the optical switch do not differ except in their direction of polarization, so that the imaging properties of an imaging optical system are not impaired by the switch according to the invention. The pixelated liquid crystal cell can be used in particular as a display in an optical imaging device. This opens up extensive possibilities in image projection technology.

Figures 4 and 5 show a second embodiment of the optical switch according to the invention in a schematic representation. The second exemplary embodiment differs from the first exemplary embodiment in that a liquid crystal cell 71, which forms part of the deflection device, serves as the polarization device. The liquid crystal cell 71 is designed as a switchable reflector with an unswitched state in which the direction of polarization of a reflected beam remains unchanged and a switched state in which the direction of polarization of a reflected beam is rotated by 90 °. Elements that do not differ from the elements of the first exemplary embodiment are denoted by the same reference symbols as in the first exemplary embodiment. The mode of operation of the optical switch corresponds to that of the first exemplary embodiment.

In the unswitched state of the liquid crystal cell 71 (FIG. 4), the partial beam bundles b2, b4 and b3, b5 have the same polarization direction before and after reflection on the liquid crystal cell 71, so that the partial beam bundle b4 has the polarization beam splitter 1 without directional deflection in the direction of the output A passes and the partial beam b5 is deflected by the polarization beam splitter 1 in the direction of the output A.

In the switched state of the liquid crystal cell 71 (FIG. 5), the direction of polarization of the partial beams b4, b5 after the reflection is opposite to the polarization direction of the partial beams b2 and b3, respectively the reflection is rotated by 90 °, so that the partial beam b5 now passes the polarization beam splitter 1 in the direction of the input E and the partial beam b4 is deflected by the polarization beam splitter 1 in the direction of the input E.

A third exemplary embodiment of the optical switch according to the invention is shown in FIG. 6. In contrast to the second exemplary embodiment, the reflecting liquid crystal cell 75 simultaneously serves to deflect the partial beam b2 in the direction of the mirror 3 and the partial beam b5 in the direction of the polarization beam splitter 1. With this configuration of the optical switch according to the invention, the number of components can be compared to the second exemplary embodiment to reduce.

Instead of reflectors or mirrors, optical fibers can also be used as light-directing elements in the optical switch according to the invention. If the switch is not to be used in any imaging optical device, a single optical fiber per light-directing element is generally sufficient. Such an optical switch with only a single optical fiber per light-directing element can be used, for example, for switching laser beams. If, on the other hand, the optical switch with optical fibers as light-directing elements is to be used in an imaging optical device, a fiber bundle with a multiplicity of fibers can be used as a light-directing element, wherein the individual fibers can each direct one pixel of a pixelated image.

7 shows a fourth exemplary embodiment of the optical switch according to the invention. The switch comprises a polarization beam splitter 1, which divides an input beam b1 incident from input E into a first partial beam and a second partial beam b3, and feeds the two partial beams to different ends 101, 103 of an optical fiber 100, which serves, among other things, as deflecting optics. An optical fiber which only linearly polarizes is used as the optical fiber 101 Transmits radiation. Such fibers transmit linearly polarized radiation only when there is a polarization direction which corresponds to one of two directions perpendicular to one another and to the direction of expansion of the fiber. As it passes through the fiber, the polarization direction of the radiation relative to the coordinate system of the fiber is retained.

The optical switch also has a device with which the two fiber ends 101, 103 can be rotated relative to one another. This device is indicated in FIG. 7 by the arrows on the fiber ends 101, 103.

If the ends 101, 103 of the optical fiber 100 are not twisted relative to one another, the direction of polarization of the partial beam bundles b2, b3 remains unchanged relative to a stationary coordinate system during the passage through the fiber 100. As a consequence, the polarization beam splitter 1 combines the partial beams b4, b5 into an output beam bδ, which it directs in the direction of the output A. The switch thus completely transmits the input beam b1 from the input E to the output A.

If, on the other hand, the ends 101, 103 of the optical fiber 100 are rotated by 90 ° relative to one another, then the direction of polarization of the partial beam bundles b2, b3 is likewise rotated by 90 ° when passing through the fiber 100 relative to a stationary coordinate system. As a consequence, the polarization beam splitter 1 combines the partial beam bundles b4, b5 into a beam bundle, which it directs in the direction of the input E. The switch thus completely blocks the beam path from input E to output A.

If the ends 101, 103 of the optical fiber are rotated less than 90 ° relative to one another, the intensity of the output beam bδ can be attenuated relative to the intensity of the input beam b1. Since the rotation is infinitely possible, an optical switch can be realized, its transmission is to be set continuously between complete transmission of the input beam and complete blockage of the input beam.

In the exemplary embodiments described for the optical switch according to the invention, two or three light-directing elements (mirrors, reflectors, optical fibers) were present in the region of the beam path of the partial beam bundles b2, b3, b4, b5. However, if necessary, further light-directing elements can also be present in the beam path of the partial beam bundles b2, b3, b4, b5.

FIG. 8 shows an example of an optical switch according to the invention as part of an image projection device. A pixelated liquid crystal cell 70 is used as the polarization device, which is arranged symmetrically between the polarization-maintaining mirrors 3, 5 of the optical switch. Within the beam path of the optical switch, two imaging optical arrangements 72, 74 are also arranged symmetrically to the pixelated liquid crystal cell 70, which are shown in simplified form in FIG. 8 as lenses. If an optical switch configured in this way is located within the parallel beam path of the image projection device, then the two imaging optical arrangements 72, 74 in the present exemplary embodiment are configured and placed in the beam path of the optical switch in such a way that the pixelated liquid crystal cell 70 is located in the focal plane of FIG optical arrangements 72, 74 extends. The liquid crystal cell 70 then serves as a display which is imaged to infinity by means of the two imaging optical arrangements 72, 74. Alternatively, there may also be an imaging arrangement arranged outside the beam path of the optical switch, with which an image is projected onto a screen which is also outside the beam path of the optical switch. In this case, the image plane of the imaging optical arrangement lies within the optical switch and coincides with the plane of the pixelated liquid crystal cell. Since the liquid crystal cell acts on both partial beam bundles in the optical switch, a projector with a display based on a liquid crystal cell can be realized, which in comparison with a projector which a conventional liquid crystal display, ie a polarizer display analyzer arrangement, has an increased light flux by a factor of 2.

The described projection devices can be used in many areas. Large projection systems that require very high light fluxes or small projection systems such as head-mounted displays (HMD), head-up displays (HUD), video eyepieces (boom systems), etc. are conceivable.

If a pixelated liquid crystal cell is used as the polarization device, in which the extension of the pixels lies approximately in the range of the wavelength of the beam to be switched, the liquid crystal cell can be used to diffract the beam passing through it and can therefore be used as a switchable diffractive light modulator. For example, adaptive optical elements, e.g. Realize autofocus elements.

If the optical imaging arrangements and the pixelated liquid crystal cell are not arranged so that the liquid crystal cell is in the focal plane of the imaging optical systems but in their Fourier plane, frequency filtering of an image can be carried out without loss of light due to a polarizer - Analyzer arrangement would take place. Such a frequency filter can have applications in all areas of imaging optics. In particular, such a frequency filter can be used in microscopy to specifically manipulate the image contrast by means of a suitable control for the pixelated liquid crystal element, for example to adapt it to specific requirements or to optimize it.

Claims

claims

1. Optical switch with - a polarization beam splitter (1), which divides an input beam (b1) into a first partial beam (b2, b4) with a first polarization state and a second partial beam (b3, b5) with a second polarization state that the first Partial beam bundle (b2, b4) leaves the polarization beam splitter (1) in a first partial beam direction and the second partial beam bundle (b3, b5) leaves the polarization beam splitter (1) in a second partial beam direction, - deflecting optics (3, 5; 71; 75; 100) , which is designed and arranged relative to the polarization beam splitter (1) in such a way that it feeds a partial beam bundle (b2, b3) leaving the polarization beam splitter (1) in the first partial beam direction to the polarization beam splitter (1) coming from the second partial beam direction and a 1) partial beam (b4, b5) leaving the polarization in the second partial beam direction ns beam splitter (1) coming in again from the first partial beam direction, and - a switchable polarization device (7; 70; 71; 75; 100) with at least two switching states, which is designed in such a way that the selection of the switching state influences the polarization states of the partial beam bundle, the polarization beam splitter (1) being designed and arranged in such a way that it supplies the partial beam bundle (b4, b5) again combined to form a beam (bδ, bδ ') and conducts it to an output with an intensity which depends on the switching state of the polarization device (7; 70; 71; 75; 100).

2. Optical switch according to claim 1, in which the polarization beam splitter (1), the deflecting optics (3, 5; 71; 75; 100) and the polarization device (7; 70; 71; 75; 100) are designed in such a way, that the polarization state of the combined beam bundle (b4, b5) (bδ, bδ ') corresponds to the polarization state of the input beam (b1).

3. Optical switch according to claim 1 or 2, in which the polarization device (7; 70; 71; 75; 100) has at least one switching state in which it changes the first polarization state to the second polarization state and the second polarization state to the first polarization state, and one in which it does not change the polarization state of a partial beam (b2, b3, b4, b5).

4. Optical switch according to claim 3, wherein the polarization device (7; 70; 71; 75; 100) has at least a third switching state in which it changes the polarization state of a partial beam (b2, b3) such that it does not match the first polarization state, still corresponds to the second polarization state.

5. Optical switch according to claim 4, wherein the polarization device (7; 70; 71; 75; 100) is to be switched such that it converts the polarization state of a partial beam (b2, b3) depending on the switching state into a freely selectable other polarization state ,

6. Optical switch according to one of claims 1 to 5, wherein the polarization device (71; 75; 100) is part of the deflecting optics (3, 5; 71; 75; 100).

7. Optical switch according to claim 6, wherein the deflecting optics (3, 5; 75) comprises at least a first light-directing element (3) and a second light-directing element (75) and the second light-directing element (75) is simultaneously designed as a switchable polarization device ,

8. Optical switch according to claim 7, wherein the second light-directing element is designed as a switchable reflector (75).

9. Optical switch according to one of claims 1 to 5, in which the polarization device (7, 70) is designed as an independent element and is arranged in the beam path of the optical switch.

10. Optical switch according to claim 9, in which the polarization device (7; 70) is arranged in a region of the beam path of the optical switch in which the beam direction of the partial beam bundle (b2, b3, b4, b5) is opposite.

11. Optical switch according to claim 9 or 10, wherein the polarization device (7; 70) is arranged in the beam path of the deflecting optics (3, 5).

12. Optical switch according to one of claims 9 to 11, wherein the deflecting optics comprises at least two light-directing elements (3, 5) and the polarization device (7; 70) is arranged in the beam path between the two light-directing elements.

13. Optical switch according to claim 13, in which the light-directing elements (3, 5) are designed such that they receive the polarization state of a partial beam.

14. Optical switch according to one of the preceding claims, in which there is additionally a further polarization device in the beam path of the optical switch, which always changes the first polarization state to the second polarization state and the second polarization state to the first polarization state.

15. Optical switch according to one of the preceding claims, in which at least one mirror (3, 5) is present as a light-directing element.

16. Optical switch according to one of the preceding claims, in which at least one optical fiber (100) is present as a light-guiding element.

17. An optical switch according to claim 16, wherein a fiber bundle with a plurality of optical fibers (100) is provided as a light-directing element.

18. Optical switch according to one of claims 15 to 17, in which the at least one light-directing element receives the polarization state of a directed beam.

19. Optical switch according to one of the preceding claims, wherein the switchable polarization device is a liquid crystal cell (7; 70; 71; 75).

20. Optical switch according to one of the preceding claims, in which the polarization beam splitter (1), the light-directing elements (3, 5; 100) and the switchable polarization device (7; 70; 71; 100) are arranged symmetrically to one another.

21. Optical switch according to one of the preceding claims, in which the switchable polarization device (70) is flat and has a number of individually switchable regions.

22. Optical switch according to claim 21, in which the size of the individually switchable regions is in the order of magnitude of the wavelength of the input beam (b1).

23. An image-forming optical device with an optical switch according to one of claims 1 to 22.

24. An image-forming optical device according to claim 23 with an optical switch according to claim 21 or 22 and with an imaging optical arrangement (72, 73), the image plane of which coincides with the plane of expansion of the planar switchable polarization device (70).

25. An image-forming optical device according to claim 23 with an optical switch according to claim 21 or 22 and with two imaging optical arrangements (72, 73) which are arranged symmetrically around the switchable polarization device (70).

26. The imaging optical device according to claim 25, wherein the imaging optical arrangements (72, 73) are arranged within the beam path of the optical switch.

27. An image-forming optical device according to claim 25 or 26, in which the imaging optical arrangements (72, 73) are arranged around the switchable polarization device (70) such that their plane of expansion is in the focal plane of the two optical arrangements (72, 73) located.

28. An image-forming optical device according to claim 25 or 26, in which the imaging optical arrangements (72, 73) are arranged around the switchable polarization device (70) such that their plane of expansion is in the Fourier plane of the two optical arrangements (72, 73) located.

29. An image-forming optical device according to one of claims 23 to 28, which is designed as a projection device.

30. Imaging optical device according to one of claims 23 to 28, which is designed as an optical observation device.

31. An image-forming optical device according to claim 30, which is designed as a surgical microscope.