DE631821C - Kerr cell switching device for light control purposes, containing two Kerr cells between the analyzer and the polarizer, one of which serves to compensate for the curvature in the control characteristics of the other - Google Patents

Description

The usual controls

the light intensity, especially for sound film recordings, Image transmission, television, etc., which of the electro-optic birefringence (Kerreffekt) make use, consist essentially of a z. B.

condenser housed in nitrobenzene, a polarizer and an analyzer.

These devices have, for example, the characteristic shown in Fig. 1, the shortcoming of which is that their rectilinear part AB is very short; however, the quality of the recording is impaired by the upper and lower curvature.

The invention aims to replace the lower curved part of the characteristic with a straight part AD extending as an extension of the straight part BA and thereby obtain a greater depth of light modulation on the straight part BD of the characteristic.

For this purpose it is already known, in addition to the usual Kerr cell, an additional cell to provide which, in conjunction with the former, the lower part of the characteristic straightened by placing the two cells in an electrical and optical push-pull circuit arranged and operated.

The invention proposes another way of straightening the curvature of the characteristic of the main cell by means of the auxiliary cell, namely by controlling the second cell according to the invention in such a way that it always acts on the light beam to be controlled whenever and to what extent the working point of the main cell deviates from the straight line BA after the curvature. This inventive concept requires a different arrangement of the Kerr cells to one another and a different circuit of the auxiliary cell than in the known Kerr cell push-pull switching arrangement.

In the figures, the subject matter of the invention is shown and explained schematically, namely shows

Fig. Ι the characteristics of an ordinary Kerr cell of the usual type,

Fig. 2 the arrangement of two Kerr capacitors in a common cuvette, which in itself for other purposes is already known for the circuit arrangement according to the present Invention but can also be used.

Fig. 3 a family of curves showing the characteristics of the present facility with details the change in its course to be achieved, -. - ■ - ", '·? *; ·! $"> Fig. 4 and 5 circuit diagrams of the firca | ^ Kerr cell arrangement, ^ j? '^

Fig. 6 a further embodiment "-α Kerr cell with three electrodes according to the present invention,
ίο Fig. 7 the comparison of the non-linear distortions of the known Kerr cell with those of the present device.

The device for carrying out the present invention consists of an ordinary polarizer P and analyzer A (Fig. 2), between which two Kerr cells / C and T are arranged instead of the usual one. These two cells can either have a common or two separate dielectrics of the same value or different. It is only essential that their electric fields are parallel to one another, and they can be directed in the same direction or in opposite directions. After passing through the polarizer P , the light beam must pass through the two capacitors one after the other regardless of their sequence and exit through the analyzer.

Fig. 3 shows a family of curves for the characteristic; here the values of the voltages / C of the main cell are plotted on the abscissa axis in o / _o , and the light yields are also plotted on the ordinate axis in 0/0. The voltage T at the second cell is selected as the parameter.

The curve labeled I for T = O, - ie for a conventional Kerr cell arrangement with a single capacitor, is the same as that in FIG.

If a voltage T is now applied or increased to the second capacitor, the shape of the curve changes, but its course is not only not improved with regard to the increase in its straight line section, but even worsened (see curves II, III, IV and V of Figure 3).

If, for example, one looks at the curve of this family with the parameter T = 45.6 o / _O), the section UBC of which is shown in Fig. 3 as a broken line, you can see that its section UR runs sufficiently close to a straight line, while its lower part RC would have to be replaced by another route that more closely approximates a straight line.

Fig. 4 shows how this improvement in the characteristic according to the present invention Invention is to be achieved.

Here G denotes the secondary winding

of the output transformer, B the battery supplying the bias voltages Ιζ and T. If e · sin ω t is the alternating voltage generated by the transformer, then a total voltage / C -j- e · sin ω t is supplied to the first capacitor Ιζ. Now, L yj shall further designate a device which must previously meet theoretically certain conditions; It will be explained later that this device would have to be built.

If the preload Γ = 45.6 0/0 (Fig. 3) and R is the operating point, the upper part UR of the characteristic is good, while the lower part RC must be replaced by the part RV . In this way, if the alternating voltage component at the first capacitor K corresponds to the path SN , the voltage at the capacitor T will not be T = 45.6 o / _o , but rather smaller, corresponding to the parameter of the curve which passes through the point .4 and in Fig. 3 corresponds to the value T = 40 o / _{o for the given point.}

If we assume that part of the characteristic RV which satisfies us, “we can set up the curve of the alternating voltage on the second capacitor T corresponding to the voltage / C applied to the first capacitor. Since we are satisfied with the part of the characteristic RU (Fig. 3), with the voltages on the first capacitor greater than Ιζ, the voltage T on the second capacitor must remain constant, namely equal to 45.6 0/0.

On the other hand .muß at voltages across the first capacitor is less than the voltage Ιζ T become smaller at the second capacitor such that the characteristic does not proceed further after the curve RC, but according to one of the straight line close RV.

Thus, the device L would have to meet the following conditions:

During the positive half cycle of the alternating component on the capacitor Ιζ , the alternating component on the second capacitor T must be equal to zero, ie the voltage across the same must remain constant. During the negative half cycle of the alternating component on the capacitor Ιζ , however, the alternating component on the second capacitor T must have a negative value and can be expressed at any moment by the difference between the parameters of the corresponding curves, as can be seen from Fig. 3. Is z. If, for example, the instantaneous value of the alternating component at the capacitor Ιζ is given by the distance SN (Fig. 3) , the instantaneous value of the alternating component at the capacitor is T = 5.6 o / _o . It is thus clear that the operation of the device L required by the present invention is limited to a

rectification effect can be traced back got to.

FIG. 5 shows the circuit diagram of a switching arrangement according to the invention which is suitable for real implementation, with the parts which fulfill the task of the device L. FIG. GO ₁ here designates the output transformer, the secondary winding G ₁ of which is closed via the potentiometer P. The constant component of the voltage across the capacitor K is supplied by the battery B ₁

ίο a part of the potentiometer P supplied, whereby the AC component is superimposed on the DC voltage. The alternating component of the second part of the potentiometer / ³ is fed to the grid filament circles of the tube A through the capacitors C ₁ and C ₂ , the resistor R _g and the battery 5 _3. The voltage of the battery B ₃ is dimensioned such that the tube A works as a rectifier tube.

From the circuit diagram it can be seen that when the voltage at the end b is higher than at the end α of the output winding of the transformer, the voltage on the capacitor / C increases, which corresponds to the positive half cycle of the AC voltage. The negative component will grow on the grid of the tube and consequently the anode current will remain zero if the battery B _{3 is selected accordingly,} there will be no voltage drop across the anode resistor R a and the full voltage of the corresponding part of the battery O ₁ across the capacitor T reach.
If, however, the voltage at the end b is lower than at the end of the output winding of the transformer, the voltage on the capacitor K. becomes smaller, which corresponds to the negative half cycle of the AC voltage. The voltage on the tube grid begins to grow, an anode current is generated, and the voltage across the capacitor T is reduced as a result of the voltage drop across the resistor R _0.

By appropriate selection of the circuit elements according to Fig. 5, the required shape of the curve UV in Fig. 3, which practically approximates a straight line, can be obtained.

It is also possible, by changing the voltage of the battery B _3, to shift the position of the point R on the curve UV as desired, ie to partially compensate for the upper part of the characteristic if necessary.

As Fig. 5 shows, two plates of the capacitors / C and T are connected in parallel. In terms of construction, these two plates can be designed as a common plate, as is shown schematically in Fig. 6.

In Fig. 7 is a comparison of that achieved by the usual and by the present device caused distortions. With the appropriate choice of circuit elements Curves I and II show the amplitude distortions and the degree of asymmetry of the curve branches in a conventional Facility and curves III and IV are the same for any of the combinations of the present Invention. The light modulation depth is stored on the abscissa axis. Fig. 7 shows to what extent the properties of the new furnishings are better than the usual ones.

Claims (3)

Patent claims: 1. Kerrzellens ehalt device for light control purposes, containing between the analyzer and the polarizer in addition to the main control cell, an auxiliary cell which serves to reduce the curvature of the control characteristic of the main cell, characterized in that the auxiliary cell (T) with its electric field parallel to that of the Main cell (/ C) is arranged and apart from a constant bias voltage (T) is influenced by a part, preferably a half-wave, of the control voltages (e ' sin ω t) of the main cell (/ C) (Fig. 4). 2. Device according to claim 1, characterized in that the control voltage (e · sin ω t) of the auxiliary cell (T) are fed via an amplifier tube (^ 4) connected as a rectifier (Fig. 5). . 3. Doppelkerr capacitor for the device according to claim 1 or 2, characterized by three capacitor plates arranged in a common cuvette, one of which has two capacitors (/ C, 7 ") is common (Fig. 6). 1 sheet of drawings