SU991349A1 - Electrooptical modulator - Google Patents

Description

(5) ELECTROOPTICAL MODULATOR

one

The invention relates to communications, in particular to a transmitting part of optical communication systems with high demands on the linearity of the modulation characteristic of a modulator.

An optical amplitude modulator is known based on the rotation of the polarization plane til.

Its disadvantages are the low linearity of the modulation characteristic.

The closest in technical essence and the achieved result is an electro-optical module of the mountains of light containing a successively installed polarizer, an electro-optical crystal with electrodes, an analyzer and a control unit with two outputs, the first output of which is connected to the electrodes of an electro-optical crystal | 2.

Its disadvantages also include the low linearity of the modulation characteristic.

The purpose of the invention is to increase the linearity of the modulation characteristic.

 This is achieved by adding a second electro-optical crystal with electrodes to an electro-optical modulator containing a successively installed polarizer, an electro-optical crystal with electrodes, an analyzer, and a two-output control unit, the first output of which is connected to the electrodes of an electro-optical crystal. installed between the polarizer and the first electro-optical crystal 15 or the first electro-optical crystal and the analyzer, the optical axis of the second crystal being Em angle oLoT - 4,5 with the polarization plane of the polarizer

20 and its electrodes are connected to the second output of the control unit.

Claims (2)

FIG. 1 shows a diagram of the proposed electro-optical module. a in FIG. 2 is a family of modulation characteristics; in FIG. 3 curves, showing the winning, obtained in the modulation loop for different oi. The electro-optical modulator contains a polarizer 1, a second additional electro-optical crystal 2 with electrodes 3 and 4, a first electro-optical crystal 5 with electrodes 6 and 7..J analyzer 8, and a control unit 9 with outputs 10 and 11. The device works as follows the polarizer 1 is then to the input of the electro-optical crystal 2, from its output to the input of the electro-optical crystal 5, and then to the analyzer 8, the modulating signal from the outputs 10 and 11 of the control unit 9 is applied to the electrodes 3t and 6, 7 of the electro-optical crystals. The optical axes of the first electro-optic crystal 5 are set, as usual, at an angle of 45 to the planar. stabilize radiation to achieve maximum modulation depth. The analyzer can be installed either coordinated or crossed to the polarizer. The second crystal serves to distort the field of the light wave entering the first (main) crystal. The nature of the predistortion depends on the level of the voltage applied to the crystal and on the orientation of the crystal axes. With the same crystals (first and additional), the voltage applied to the additional crystal should be 2 times the voltage applied to the first crystal. The ° С angle between one of the crystal axes and the plane of polarization of the beam is chosen based on the desired modulation characteristic. . The family of modulation characteristics for DIFFERENT o (. Is shown in FIG. 2, and is described by the expression S.V V -siw4JLsivi4V w 2.VcSin 5U -S tMciiM O-EVc sin IcLJ, where. - coefficient of scale and dimension ,, modulator transfer coefficient. The linearity of the modulation characteristic increases with ei from, S to f, however, as can be seen from FIG. 3 (where the value indicating how many times the modulation depth m of the pre-Lagged modulator is greater than the modulation depth of the known modulator with the nonlinear distortion coefficient allowed in the communication line), to obtain the maximum gain with different requirements j of the nonlinear distortion coefficient choose the appropriate value cc angle The greatest gain in the depth of modulation with high requirements for linearity is achieved at oL "2 ,. With ot7t.S, the nonlinear distortion will be large for any modulation depth. This is due to the occurrence of a significant overcorrection (curve ct 5, fig. 2). The proposed device allows to increase the linearity of the modulation characteristic and the modulation depth of the transmitted signal. The invention includes an electro-optical modulator containing a sequentially installed polarizer, an electro-optical crystal with electrodes, an analyzer, as well as a two-output control unit, the first output of which is connected to electrodes of an electro-optical crystal, in order to increase the linearity of the modulation characteristic, it is additionally introduced a second electro-optical crystal with electrodes, installed between the polarizer and the first electro-optical crystal or the first electro-optical skim crystal and the analyzer, wherein the optical axis of the second crystal coc Tavlya an angle oiot -4,5 .Z to the plane of polarization of the polarizer and its electrodes are connected to the second output of the control unit. Sources of information taken into account in the examination 1.Katys G, Modulation and variation of optical radiation. M., Science, 1967, p. 37. 2, Mystel E.R. et al. Methods of modulating and scanning light. M ,, auka, 1970. with. 28