SU377715A1 - METHOD FOR DETERMINING AMPLITUDE-FREQUENCY CHARACTERISTICS OF LIGHT MODULATORS - Google Patents

Description

one

The invention relates to laser technology and can be used in measuring the modulation of radiation of optical quantum continuous generators and determining the frequency characteristics of light modulators.

Known methods for determining the amplitude-frequency characteristics of light modulators using reference electro-optical elements.

The frequency range and measurement accuracy in the implementation of the known methods depend on the frequency characteristics of photodetectors, the power of the control voltage generator, the stability of the operating point on the modulator bleaching characteristic, etc.

In order to improve the measurement accuracy in a wide frequency range, a method has been proposed whereby a beam of light is passed successively through a reference electro-optical element and a modulator under study, at the inputs of which high-frequency control signals are generated, modulated in antiphase of the same low-frequency envelope, to establish equality of phase shifts between the polarized components of the light flux in the reference element and the modulator under study, and then the amplitude of the high-frequency control signal at the coupon element determines the phase shift

between these components. for different fixed frequencies of the high-frequency control signal on the modulator.

FIG. 1 shows a block diagram of one embodiment of a device implementing this method; in fig. 2 - forms of modulating outliers on the electro-optical element of the light modulator under study and on the reference electro-optical element and form

phase shifts between two mutually perpendicular: components of the light beam at the output of the electro-optical element of the light modulator under study.

The device includes an optical

continuous quantum generator 1, reference electro-optical element 2, electro-optical element 3 of the light modulator under study, analyzer 4, light modulator under study 5, photodetector 6, recording device 7, fixed high frequency generator 8, high frequency voltmeter 9, high frequency generator 10, tunable in the studied frequency range, high-frequency voltmeter 11, generator 12 modulating voltages.

FIG. 2 accept the following notation:

{/ 1 - control (modulating) voltage on the electro-optical element of the light modulator under study; L / a is the control voltage on the reference electrooptic element; Df1 - phase shift between two mutually Perpendicular components of the light beam at the output of the electron-optical element of the light modulator under study (obndium case); The af-frequency case of DF1, which occurs when the amplitudes of the phase shifts between two mutually perpendicular components of the light beam in the reference electro-optical element and in the elec- tro-optical element of the light modulator under study are equal.

The device works as follows.

By setting the propagation of the light beam in series, a reference electro-optical element 2 and a light modulator 5 are set, the frequency characteristic of which is determined.

The inputs of both devices are supplied with control high-frequency voltages modulated by a low-frequency envelope (of a meander type).

The frequency of the control voltage C / i applied to the light modulator under study varies over the entire frequency range under consideration. The frequency of the f / 2 control unit applied to the reference electro-optical element is fi xxed.

The dependence of the phase shift between two mutually perpendicular polarized components of the beam of light produced in the HOIM standard of the electro-optical element on the magnitude of the control voltage at the selected fixed frequency should be known with a sufficient degree of accuracy.

At the output of the entire modulating system, a variable luminous flux arises, from which, when operating on a nonlinear part, the modulation characteristic of the modulator can be distinguished using a relatively inertial photodetector 6 low-frequency component of the modulated luminous flux corresponding to the envelope of the control high-frequency voltages.

The amplitude of this low-frequency component is the smaller, the closer the maximum values of the phase shifts of Af1 between two mutually perpendicularly polarized components of the light beam, created in the reference electro-optical element and the electro-optical element 5 of the modulator under study, coincide. When the above-mentioned phase shifts of the DF2, the recording device 7, for example, an oscilloscope, shows the minimum signal.

The high-frequency voltage across the reference electrically optical element, corresponding to the minimum of the low-frequency signal on the recording instrument, ensures that the phase shifts of the two mutually perpendicular lines of the light beam generated in both the electro-optical elements are equal. In this case, the maximum phase shift in the electro-optical element of the light modulator under investigation is: to proceed by determining an equal maximum phase shift in the reference electro-ion element.

Ngo is determined from the measured value of the amplitude of the high-frequency voltage applied to the reference electro-optical element, using the known modulation characteristic of this element.

These operations are repeated for a number of fixed frequencies in the considered range and at the same time maintain the amplitude of the high-frequency voltage on the modulator under study both constant and independent of frequency. This makes it possible to determine the dependence of the phase shift between two mutually perpendicular polarized components of the light beam on the frequency of the control high-frequency voltage.

The resulting dependence, along with the selected operating point on the modulator bleaching characteristic, determines the modulation depth of the modulated light flux as a function of the frequency of the modulating voltage or the amplitude-frequency characteristic of the light modulator.

Measurement accuracy can be significantly improved if a resonant amplifier tuned to

the fundamental harmonic of the low-frequency envelope of the high-frequency control voltages.

Subject invention

The method of determining the amplitude-frequency characteristics of light modulators using reference electro-optical elements, characterized in that, in order to improve the measurement accuracy in a wide frequency range, a beam of light is passed sequentially through the reference electro-optical element and the modulator under study, at the inputs of which high-frequency control signals are formed the signals modulated in antiphase of the same low-frequency envelope establish the equality of phase shifts between polarized components the luminous flux in the reference element and the modulator under study, and then on the amplitude of the high-frequency control signal on the reference element, determine the phase shift of these components for different fixed frequencies of the high-frequency control signal on the modulator.

FIG. 2