Title of Invention: Arrangement and method for electrically controlling the intensity of unpolarized light
Abstract: In an arrangement and a method for electrically controlling the intensity of non-polarized light, a polarizing beam splitter is acted upon by the light to be controlled via an input face such that the light is split into two polarized light bundles that are orthogonal with respect to each other. Provision is made that a first reflecting device is configured for the reflection of at least one of the polarized light bundles, so that both polarized light bundles run in parallel. At least one electro-optical element is provided in a path of the parallel running polarized light bundles. The polarization is changed as a function of the supplied control voltage. Also provided is a second reflecting device for reflecting the light bundles in the opposite direction. The light bundles pass through the at least one electro-optical element twice and are directed by the first reflecting device to the polarizing beam splitter, and the controlled light can be extracted from at least one output face of the polarizing beam splitter.
Detailed Description: Part PAR: In the Figures, the same parts are given the same reference numerals. In the Figures, the light bundles are represented as straight lines having arrows pointing in the longitudinal direction, the arrows indicating the direction of propagation of the specific light bundle. Double arrows transverse to the longitudinal direction indicate a polarization in the drawing plane (p), whereas circles having a period represent a polarization perpendicular to drawing plane (s).
Part PAR_2: FIG. 2 represents a known electro-optical switch in a closed position (FIGS. 2 (a) and 2(c) and in an open position (FIGS. 2(b) and 2(d).
Part PAR_3: In FIGS. 2(a) and 2(b), the non-polarized light bundle to be switched is fed to a polarizing beam splitter 1 via an input face 1a. Beam splitter 1 switches the non-polarized collimated light at the input face into its polarized components s and p, which leave the polarizing beam splitter as light bundles 2, 3. Polarized light bundles 2, 3 are directed in the direction of a TN liquid crystal cell 104 by a mirror 102, 103, respectively. The reflected light bundles pass through liquid crystal cell 104 in the opposite direction and are reflected back to the polarizing beam splitter by the respective other mirror 103, 102.
Part PAR_4: If no voltage is applied to the electrodes of the liquid crystal cell, the latter rotates the polarization plane of the light bundles in each case by 90.degree.. This is represented in FIG. 2(a). Light bundle 2, which is initially polarized perpendicular to the drawing plane, thus receives a polarization in the drawing plane and is thus directed via mirror 103 to the polarizing beam splitter. Due to this polarization, this beam bundle is not reflected in the beam splitter, but rather is permitted to pass straight through in the direction of the entrance beam.
Part PAR_5: Light which is initially polarized in the drawing plane is rotated perpendicular to the drawing plane and arrives at beam splitter 1 via mirror 103, where it is reflected in the direction of the light bundle that has been sent. At an output face 1b, no light emerges.
Part PAR_6: In the case represented in FIG. 2(b), liquid crystal cell 104 is acted upon by voltage and does not rotate the polarization plane. Thus polarized light bundles 2,3 arrive at beam splitter 1, in each case, having a polarization that is rotated with respect to the arrow in FIG. 2(a). There, returning light bundle 2 is reflected, and returning light bundle 3 is not reflected, so that both light bundles emerge from output face 1b.
Part PAR_7: FIGS. 2(c) and 2(d) depict an electro-optical switch that operates according to a similar principle, sending light that strikes beam splitter 1 from the various channels E, E' to various outputs A, A'. Since the angle of inclination of liquid crystal cells 104', 104" used is limited given the high switching frequencies, a plurality of cells is necessary in order to make possible a complete rotation of the polarization planes of the light bundles. In the closed position according to FIG. 2(c), the light bundle of channel E is conveyed to channel A via a second beam splitter 1'. The light from channel E' arrives at channel A. In the open position according to FIG. 2(d), on the other hand, the light bundles are switched via a cross, so that channels E and A' as well as E' and A are connected to each other.
Part PAR_8: FIGS. 1(a) and 1(b) show two variants of a first exemplary embodiment, in which the light bundle to be controlled is fed via input face 1a of polarizing beam splitter 1 and is first split into two polarized light bundles 2 and 3 as in the known arrangement according to FIGS. 2(a) and 2(b). In a first reflecting device 4, polarized light bundles 2, 3 are then deflected such that they run in parallel. From there they arrive at a device 5, which contains an electro-optical element 6, which rotates the polarization as a function of a supplied control voltage. A second reflecting device is configured in various ways in FIGS. 1(a) and 1(b), namely such that, in the case of FIG. 1(a), each of parallel-running polarized light bundles 2, 3 is reflected back into itself, whereas, in the case of FIG. 1(b), light bundle 2 is reflected as light bundle 2' opposite to light bundle 3, and light bundle 3 is reflected as light bundle 3' opposite to light bundle 2. Both variants are depicted in the on-state.
Part PAR_9: FIGS. 1(c) through 1(j) show the same arrangement as a changeover switch from an input channel E or E' to two output channels A, A', respectively, in different switching states and having different configurations of schematically represented second reflecting device 7. In this context, the light bundle is introduced somewhat offset from the center of beam splitter 1, so that the beam path no longer runs symmetrically, and controlled light bundles 2' and 3' are sent from beam splitter 1 to the one output A or to the other output A' depending on the polarization direction. The deflection of the beam path in reflecting devices 4, 7 can be realized in the most various ways; the particular ways may be selected for this purpose depending on the concrete requirement. In FIGS. 5 and 6, examples are given. Electro-optical element 6, in the examples, is acted upon by a control voltage via connection terminals 6' and 6".
Part PAR_10: A further application case for the arrangement according to the present invention in accordance with the FIGS. 1(c) through 1(j) is depicted in FIGS. 3(a) through 3(d) in two specific configurations, each in two switching states. The arrangement is used as a cross switch among four channels. In accordance with the switching state, each input E, E' is connected to one output A, A', respectively.
Part PAR_11: In FIG. 4(a), electro-optical element 6 is depicted in somewhat greater detail than liquid crystal cell 8 having a liquid crystal 9 between transparent electrodes 9', 9" and a narrow 8', which designates the slow axis. On the other hand, the exemplary embodiment according to FIG. 4(b) contains a delay plate 10.
Part PAR_12: In the exemplary embodiment depicted in FIG. 4(c), provision is made for a further liquid crystal cell 11 having a liquid crystal 12 and transparent electrodes 12' and 12". By placing behind one another two liquid crystal cells 8, 11, in contrast to the exemplary embodiments in accordance with FIGS. 4(a) and 4(b), only half of the rotation is required for achieving the same intensity differential in the controlled light bundle. As will be explained in detail below, under certain preconditions, an angle of +/-5.625.degree. is sufficient for fully advanced control.
Part PAR_13: FIGS. 4(d) through 4(f) show embodiments of the same arrangement as the cross changeover switch.
Part PAR_14: FIGS. 5(a) through 5(h) show exemplary embodiments having different variants of first reflecting device 4, which is executed in FIG. 5(a) as a mirror. In the exemplary embodiment according to FIG. 5(b), for deflecting the polarized light bundles in parallel directions, two mirrors 14, 15 are used. In the exemplary embodiment according to FIG. 5(c), one polarized light bundle 3 is deflected in the direction of other light bundle 2 with the assistance of a prism 16, whereas, for this purpose, in the exemplary embodiment according to FIG. 5(d), two prisms 17, 18 are used. These prisms in the exemplary embodiment according to FIG. 5(e) are each joined to a partial prism of the polarizing beam splitter to make one body. This has the advantage that no losses can occur through reflections on the border surfaces that otherwise exist between beam splitter 1 and prisms 17, 18. In addition, in the exemplary embodiment according to FIG. 5(e), assembly costs are saved.
Part PAR_15: In the exemplary embodiments according to FIGS. 5(f) through, 5(h), which each depict three views, the supplied light bundle as well as the controlled light bundle each lie in a plane parallel to liquid crystal cell 6 and to second reflecting device 7. Both polarized light bundles emerging from the polarized beam splitter are deflected (FIG. 5(f)) in the direction of electro-optical element 6 with the assistance of mirrors 19, 20. This takes place in the exemplary embodiment according to FIG. 5(g) with the assistance of two prisms 21, 22. In addition, in FIG. 5(g), the angle of rotation of 22.5.degree. between the negative and a positive voltage is depicted with respect to liquid crystal cell 6, which in this case contains a ferroelectric liquid crystal. In the exemplary embodiment according to FIG. 5(h), pentaprisms 23, 24 are used for deflection in polarized light bundles 2, 3.
Part PAR_16: FIGS. 5(i) through 5(n) each depict the beam paths of the same arrangements, if they are acted upon, in each case, by two inputs E, E' and two outputs A, A'. In this configuration, the arrangements can again be used as changeover switches.
Part PAR_17: FIGS. 6(a) through 6(g) depict exemplary embodiments for second reflecting device 7, whereas first reflecting device 4 and electro-optical element 6 are not indicated in greater detail. FIG. 6(a) depicts a mirror 25 as a second reflecting device, whereas second reflecting device in FIG. 6(b) is formed by a hollow triple mirror 26, which is composed of three planar mirrors 27, 28, 29.
Part PAR_18: The exemplary embodiment according to FIG. 6(c) includes two such triple mirrors 30, 31, which are composed of three planar mirrors 32, 33, 34 and 35, 36, 37, respectively. In FIG. 6(c), it is also indicated that in the arrangement according to the present invention is not absolutely necessary to reflect the parallel polarized light bundles in themselves or in the respective other light bundle.
Part PAR_19: The exemplary embodiment according to FIG. 6(d) contains a massive triple mirror as the second reflecting device, and the exemplary embodiment according to FIG. 6(e) contains two massive triple mirrors 39, 40.
Part PAR_20: The exemplary embodiment according to FIG. 6(d) contains a pyramid prism as the second reflecting device; the exemplary embodiment according to FIG. 6(e) contains two pyramid prisms 39, 40.
Part PAR_21: FIG. 6(f) depicts two mirrors 41, 42, which form an angle of 90.degree. and which reflect each of the parallel polarized light bundles into the other one. In the exemplary embodiment according to FIG. 6(g), provision is made for two pairs of mirrors 43, 44, which are composed of two individual mirrors 45, 46 and 47, 48, respectively.
Part PAR_22: FIG. 6(h) depicts an example for measures to obtain the same optical path lengths for polarized light bundles 2, 2', 3, 3'. Supplemental path length 49 of light bundle 3, 3' is compensated for through the fact that mirror pair 44 is arranged so as to be closer to electro-optical element 6 than mirror pair 43. Distance 50 corresponds exactly to path length differential 49.
Part PAR_23: The optical path lengths of both light bundles are the same in the exemplary embodiment according to FIG. 6(i) on account of the symmetrical design. As a second reflecting device, a 90.degree. prism 51 is used. In the otherwise identical design, the exemplary embodiment according to FIG. 6(j) includes two 90.degree. prisms 52, 53 as the second reflecting device.
Part PAR_24: The exemplary embodiment according to FIG. 6(k) contains as the first reflecting device a prism 16, a path length differential 54, in turn, resulting between the two polarized light bundles. This is compensated for by an offset shift 55 of prisms 52, 53 that function as the second reflecting device.
Part PAR_25: In the case of the arrangement according to FIG. 6(l), provision is made for two pentaprisms 56, 57 as the second reflecting device in a symmetrical design of the entire arrangement. In this context, first reflecting device 4, which is only schematically represented in FIG. 6(l), is formed, for example, by two mirrors and prisms corresponding to the exemplary embodiment according to FIGS. 5(b), 5(d), or 5(e).
Part PAR_26: In the exemplary embodiment according to FIG. 6(m), provision is made for two ridge prisms 58, 59 as second reflecting device 7, which for illustrative purposes are depicted a second time in a different view. The exemplary embodiment according to FIG. 6(n) contains two ridge mirror systems 60, 61, which are composed of two individual mirrors 62, 63 and 64, 65, respectively.
Part PAR_27: The corresponding application forms as changeover switches can be found in FIGS. 6(o) through 6(za), the exceptional feature arising in FIGS. 6(p) and 6(r), that mirrors 66, 67 and prism 68 are arranged vertically and, as a result, cause a transverse offset of the light bundles. This can present advantages in the spatial disposition of the device in a concrete application.
Part PAR_28: FIG. 7(a) depicts a three-dimensional representation of an exemplary embodiments in the form of an exploded view. A prism 16 functions as a first reflecting device, a mirror 25 as a second. Angle .alpha. is the angle between slow axis 8' of liquid crystal 9 and the s-polarization of bundle 2. Angle .beta. is the angle between rapid axis 10' of delay plate 10 (on a lambda/4 plate) and the s-polarization of light bundle 2.
Part PAR_29: In the exemplary embodiment of FIG. 7(b) designed so as to otherwise correspond to FIG. 7(a), provision is made for a triple mirror 38 as the second reflecting device. In this way, the polarized light bundles that are reflected so as to run in parallel are reversed with respect to the non-reflected light bundles, so that altogether for both light bundles the same optical path results. This also applies to the exemplary embodiment according to FIG. 7(c), in which a 90.degree. prism 51 is arranged as the second reflecting device.
Part PAR_30: FIG. 7(d) depicts the arrangement according to FIG. 7(c) for the application case as changeover switch.
Part PAR_31: FIGS. 8(a) and 8(b) depict an exemplary embodiment having a 90.degree. prism 16 as a first reflecting device, a liquid crystal cell, and a lambda/4 plate 10 as an electro-optical element 6. In addition, a 90.degree. prism 51 is provided as a second reflecting device. FIG. 8(a) represents the arrangement in the off-state, i.e., closed, whereas FIG. 8(b) depicts the device in the on-state, or open.
Part PAR_32: The exemplary embodiment according to FIGS. 8(a) and (b) contains a nematic liquid crystal cell having a positive dielectrical anisotropy. n is the pneumatic director, which corresponds to switchable optical axis 8'. Light bundles 2" and 3" at this angle have a polarization of 45.degree. and -45.degree. In lambda/4 plate 10, this linear polarization is transformed into a right or left rotating circular polarization, which after the reflection in prism 51 obtains a different direction of rotation.
Part PAR_33: In the repeated passage through lambda/4 plate 10, a linear polarization again arises of -45.degree. regarding light bundle 2'", and of +45.degree. regarding light bundle 3'". This polarization, in the repeated passage through the liquid crystal cell, is rotated by 45.degree., so that light bundle 2' is polarized in the drawing plane, whereas light bundle 3' is polarized perpendicular to the drawing plane. In this polarization, light bundle 2" is permitted to pass directly through polarizing beam splitter 1, whereas light bundle 3" after the deflection in prism 16 is reflected in polarizing beam splitter 1 and emerges through input face 1a. Thus no light arrives through output face 1b, so that in the described voltageless case according to FIG. 8(a), the switch is closed. Through a corresponding transmission of the light from input face 1a or through a corresponding arrangement of sensors, the arrangement according to FIGS. 8(a) and 8(b) can also be used as a changeover switch or, in the case of a gradual transition, as cross-fader.
Part PAR_34: In the case depicted in FIG. 8(b), liquid crystal cell 8 is acted upon by a voltage, so that the nematic liquid crystal is placed into the homeotropic state. The non-polarized light at input face 1a is conveyed to output face 1b. Director 8" of nematic liquid crystal 9 is perpendicular to the surface of the electrodes.
Part PAR_35: FIGS. 8(c) and 8(d) depict an exemplary embodiment having a ferroelectric liquid crystal cell 8 of a thickness of the liquid crystal layer, which effects an optical path differentiation of (3/8) lambda in the blocking state according to FIG. 8(c). Prism 16 is used as a first reflecting device, a 90.degree. prism 51 as a second reflecting device. In order to switch from the off-state in the on-state, the polarity of the voltage at electrodes 9', 9" is reversed. In the off-state (closed), light bundles 2" and 3" emerging from liquid crystal cell 8 are elliptically polarized. Through the reflection in prism 51, the direction of rotation and the angle of the axes of ellipsis are changed. In the off-state in accordance with FIG. 8(d), no rotation of polarization takes place by liquid crystal cell 8.
Part PAR_36: The exemplary embodiment according to FIGS. 8(e) and 8(f) contains a ferroelectric liquid crystal cell, whose liquid crystal layer 9 has a thickness d such that the optical path differential is lambda/2. In addition, a lambda/4 plate 10 is used. In the pass-through state according to FIG. 8(e), slow axis 8' is positioned as the polarization plane of light bundle 3. In the blocking state according to FIG. 8(f), slow axis 8' is offset by 22.5.degree. from the polarization plane of light bundle 3. Prism 16 and prism 51 are employed as a first and second reflecting device is as in the exemplary embodiment according to FIG. 8(c) and 8(d).
Part PAR_37: FIGS. 8(g) through 8(j) depict the beam path of the arrangements, described above, in their use as changeover switches.
Part PAR_38: FIG. 9(a) depicts the temperature dependency of the induced angle of inclination +/-.theta. and of average switching time tau for electroclinic material FLC-392. The thickness of the liquid crystal cell is 1.6 .mu.m, the control voltage is +/-10 V. FIG. 9(b) represents the modulation depth of an arrangement according to FIGS. 7(c) and 8(e/f) as a function of control voltage V. A liquid crystal cell having an electroclinic liquid crystal and a lambda/4 plate is based on the measurement.
Part PAR_39: FIG. 9(c) depicts intensity I of the controlled light arriving at outputs A, A' as a function of control voltage U.sub.s. The curves were included in the arrangement according to FIG. 7(d). In the upper diagram, the light comes from input E and in the lower diagram from input E'. It is clear that a complete switchover between outputs A and A' takes place using liquid crystal cell FLC 392 used here at a voltage differential of roughly 60 volts.
Part PAR_40: Through the type of liquid crystal and its drive, through the thickness of the liquid crystal, through the arrangement of a delay plate and further optical preconditions in the arrangement according to the present invention, a great many different combinations are possible. Some of them are described below.
Part PAR_41: If, for example, in the nematic liquid crystal the transformation is undertaken from planar to homeotropic, then a use in binary switching processes (on/off) is given. For this case, the orientation of slow axis 8' coincides with the director of the long molecular axis. It is to be below 45.degree. with respect to the polarization directions of the polarizing beam splitter. In this context, thickness d of the liquid crystal layer is to satisfy the condition .delta.n.multidot.d=lambda/4+N.multidot.lambda, where N=0, +/-1, +/-2, +/-3, . . . In this context, .delta.n is the birefringence of the layer (.delta.n=n.sub.L -n.sub.S), n.sub.L being the refractive index of the liquid crystal in the slow axis and n.sub.s in the rapid axis. Without an electrical field, the switch is in the off-state. With an electrical field, the liquid crystal is homeotropic and the light enters at face 1b (on-state). Examples for such arrangements are depicted in FIGS. 6(b) through 6(e) and 7(b).
Part PAR_42: In the designs according to FIGS. 6(f) through 6(n), the properties of the liquid crystal are different than in the preceding fields. First of all, thickness d of the liquid crystal cell is such that a delay of .delta.n.multidot.d=(3/8) lambda+N.multidot.lambda results. In addition, the director of the layer of 22.5.degree. is switched over to -22.5.degree. in the electrical field with respect to the p-polarization plane. Without an electrical field, the arrangement is switched off. With an electrical field, a homeotropic orientation begins, the arrangement being switched on.
Part PAR_43: Liquid crystal cells combined with the use of the s-effect in nematic liquid crystals can be used for switches of a high aperture and having switching times in the order of magnitude of ms, i.e., in a frequency range of 0 Hz to 100 Hz, preferably using a lambda/4 plate.
Part PAR_44: The SSFLC-effect (surface stabilized ferroelectric liquid crystals) can be used for two different angles of inclination in chiral, smectic, and ferroelectric phases of the liquid crystal. The FLC material having the angle of inclination 22.50 can be used without a delay plate in the specific embodiments according to FIGS. 6(a) through 6(e). Thickness d of the liquid crystal for both polarities of the voltage applied satisfies the condition .delta.n.multidot.d=lambda/4+N.multidot.lambda. The orientation of the normal of the smectic positions (direction of friction) is to have an angle of +22.5.degree. or -22.5.degree. with respect to the polarization direction of the s- or p-light bundle 2, 3. For the one field polarity, light emerges from the output face, for the other field polarity it does not. For the exemplary embodiments in FIGS. 6(a) and 7(a), the polarity has a reversed sign in comparison to FIGS. 6(b) through 6(e) and 7(b).
Part PAR_45: For the exemplary embodiments according to FIGS. 6(f) through 6(n), 7(c), 8(c/d), and 8(e/f), the optical properties of the liquid crystal are different than in the case described above. The FLC positions are to have a delay of (3/8) lambda+N.multidot.lambda. The value of the switching angle is only 11.25.degree.. The normal for the smectic position of the FLC material is to have the angle+11.25.degree. or -11.25.degree. or+33.75.degree. or-33.75.degree. with respect to the p-polarization direction of light bundle .beta.. The arrangements of this type can be used for switching times between 10 .mu.s and 20 .mu.s and voltages between 20 volts and 30 volts.
Part PAR_46: The electroclinic effect and the DHF effect (deformed helix ferroelectrics) are used in arrangements according to the present invention for the optical modulation using intermediate values.
Part PAR_47: For the exemplary embodiments according to FIGS. 6(a) through 6(e), 7(a), and 7(b), the orientation of the normal of the smectic positions is to form an angle of +45.degree. or -45.degree. with the s- or p-polarization plane. The thickness of the liquid crystal layer is to permit the delay lambda/4+N.multidot.lambda. The light intensity permitted to pass through from face 1a to face 1b of the polarizing beam splitter continually varies from 0% to 100%, if the electrically induced angle of inclination of the slow axis of the indicator varies between 0.degree. and45.degree.. For the case in which the DHF effect is used, the necessary axis tilt is +/-22.5.degree., which can be achieved using a few volts of control voltage. The switching time, in this context, is roughly 100 .mu.s. Appropriate liquid crystal cells are described, for example, in: L. A. Beresnev et al: "Deformed Helical Ferroelectric Liquid Crystal Display: a New Electro-optical Mode in Ferro Electrical Liquid Crystals," Liquid Crystals, Volume 5, p. 1171-1179 (1989) and in L. A. Beresnev et al: "Ferroelectric Liquid Crystal Displays," Swiss Patent 3722/87.
Part PAR_48: In the exemplary embodiments according to FIGS. 6(f) through 6(n), 7(c), 8(c/d), 8(e/f), the angle of inclination of slow axis 8' is only 11.25.degree. in the electrical field. For this purpose, a very rapid electroclinic material having switching times of a few .mu.s is used, as is made known, for example, in U.S. Pat. No. 4,838,663. These exemplary embodiments permit a continual modulation of non-polarized light between 0% and 100% at a control voltage in the range of+/-30 volts.
Part PAR_49: An advantageous arrangement according to the present invention includes a ferroelectric liquid crystal cell and a lambda/4-plate, which is depicted in FIGS. 4(b), 7(a) through 7(c), 8(c/d), and 8(e/f). In this context, there is an abundance of possibilities to for realizing the orientation of slow axis 8' of liquid crystal layer 8 and of the rapid axis 10' of delay plate 10 around the off- and on-state of the arrangement. This is depicted in FIG. 8(e/f).
Part PAR_50: In the on-state, polarization directions of light bundles 2, 3 are oriented parallel or perpendicular to the slow axis of the liquid crystal and of delay plate 10. As a result, the light is not changed with respect to its polarization state either in the liquid crystal cell or in the delay plate. Second reflecting device 7 also does not alter the polarization state, so that the light of both polarization directions reaches output face 1b of polarizing beam splitter 1.
Part PAR_51: In the off-state, the director (indicator orientation) of liquid crystal 9 tilts 22.5.degree. as a result of the effect of the electrical field. Since the delay in the liquid crystal is equal to lambda/2, the liquid crystal cell rotates the polarization direction 2.multidot.22.5.degree.=45.degree.. After lambda/4 plate 10, light that is circularly polarized is obtained, which is reflected by second reflecting device 7 so as to be circularly polarized, the direction of rotation being reversed. After the second passage through lambda/4 plate 10, light is obtained that is polarized in light bundle 2'" or 3'" in a linear fashion, and that is polarized (-45.degree.) after the first passage through the liquid crystal cell so as to be orthogonal with respect to the light of light bundles 2" and 3'. These light bundles are rotated in the second passage through the liquid crystal cell by 2.multidot.(45.degree.+22.5.degree.)=(90.degree.+45.degree.) and thus achieve the respective orthogonal orientation 2', 3' of the polarization. Polarizing beam splitter 1 unites the light bundles in face 1b.
Part PAR_52: In the cases of the electroclinic effect and of the DHF effect, the electrically controlled permeability of the arrangement according to present invention between faces 1a and 1b of polarizing beam splitter 1 for non-polarized light between the values 0% and nearly 100% can continually be changed. Applications include rapid optical limiters or the rapid automatic control of light intensities. In this context, light detectors may be located at the output of the arrangement which exercise a control function on the electrodes of the liquid crystal cell through electrical feedback. Applications, by way of example, are described in Swiss Patent No. 888 102 583 and European Published Patent Application No. 0 335 056, as well as in M. Eve et al: "New Automatic-gain-control System Optical Receivers," Electronics Letter 15, pp. 146-147 (1979).
Part PAR_53: The electrically adjustable angles of inclination can be halved in the arrangement according to the present invention if two liquid crystal cells are arranged behind one another. In the electroclinic effect, the extremely small angle of inclination of +/-5.6250 is required in order to switch light through at switching times of 1 .mu.s and working voltages of +/-10 V. Rapid electroclinic liquid crystal materials having switching times of 1 .mu.s and, among them in low working voltages, are composed of mixtures of a lamellar matrix, for example of a smectic A- or C-phase and chiral doping molecules having an angle of inclination of .THETA.m, and they are known, for example, from German Published Patent Application 196 24 769. Experiments have shown that time constants of 100 ns at control voltage is of 10 volts to 20 volts at room temperatures can be achieved. FIG. 9(c) indicates intensity I of the controlled light arriving at outputs A, A' as a function of the control voltage. The curves were included in an arrangement according to FIG. 7(d). In the upper diagram, the light comes from input E and in the lower diagram from input E'. It is clear that a complete switchover between outputs A and A' takes place using the liquid crystal cell FLC-392 used here at a voltage differential of roughly 60 V.


{'bibliographic_information': "{'Patent Number': '063319101', 'Series Code': '9', 'Application Number': '4631080', 'Application Type': '1', 'Art unit': '283', 'Application Filing Date': '20000119', 'Title of Invention': 'Arrangement and method for electrically controlling the intensity of unpolarized light', 'Issue Date': '20011218', 'Number of Claims': '50', 'Exemplary Claim Number(s)': '1', 'Primary Examiner': 'Ben; Loha', 'Number of Drawing Sheets': '44', 'Number of figures': '82'}", 'source_file': './grant/2001/pftaps20011218_wk51.txt', 'source_data': 'USPTO-Grant'}