SU1216757A1 - Method of modulating optical radiation - Google Patents

Description

The invention relates to the modulation of optical radiation using the diffraction of light by acoustic waves and can be used in information transmission, encoding and demodulation systems.

The purpose of the invention is to reduce the loss of optical radiation during the modulation process and to ensure that the phase modulation is independent of the amplitude (Fig. 2, where the upper part of the optical radiation graphs.

Figure 1 shows the dependence of the phase of optical radiation on the amplitude of the acoustic wave; Fig. 2 is a graph for the case of simultaneous modulation of the amplitude and phase of optical radiation.

In the range of the amplitude A of the acoustic wave from zero to point a, the derivative of the transmitted phase of the radiation varies slightly (Fig. 1). At point q, a sharp change in the phase of this radiation by an amount li is observed.

With a further increase in the amplitude A in the interval from rchka a to point b, in which the derivative

d3 ". Oh, the phase change of the past

radiation is negligible. Thus, by changing the amplitude of the acoustic wave from the values in

About about 3 g

interval

Where

dA

before

values in the range

(B where

J3n

dP

 Oh, and back, you can

receive phase modulation of optical radiation.

In those cases when it is necessary to carry out only phase modulation, it is advisable that when the control voltage pulse is turned on, the phase of the transmitted optical radiation changes to IT and the intensity does not change. This is achieved by applying to the piezoelectric transducer a control of the cadmium pulse with an amplitude at which the intensity of the transmitted beam is maximum (point c, Fig. 1), while the amplitude of the acoustic wave jumps to 215757

Coincidentally varies from zero to the value corresponding to point b

The method also allows for the simultaneous modulation of phase 5 and the intensity of the transmitted radiation, thereby transmitting more information using a single beam of light. This embodiment of the implementation of the method 1 is explained using

ka shows the dependence of 3 „/ Ld (A), while the bottom shows the change in the magnitude of A over time t.

At times t, and t, the amplitude A of the acoustic wave is changed within the limits of OQ, where the derivative is rjr 0. This leads to a change in

dft

J

the intensity of the intensity of the radiation passing through the medium (points 1 and 2 on the upper part of the graph), while its phase remains unchanged. At time i 3, the amplitude of the acoustic wave abruptly changes from a value corresponding to a point to a value corresponding to

J

ke

point

at which intensity

The intensity of the transmitted radiation does not change to the sinks 2 and 2 correspond to the same values of the radiation intensity). Since the amplitude of the acoustic wave corresponding to point e is in the range of values where the derivative is J3,

the phase of the transmitted radiation

d A

at time i

3

changes to

IT relative to the initial one in accordance with the dependence liCf (Al, shown in Fig. 1. The amplitude of the acoustic wave is kept constant for a period of time, determined by the desired phase modulation law, and at time iy is changed to a value point J. At the same time, the intensity of the transmitted radiation remains constant, and the phase is changed to the original value. In this way, the transmitted amplitude and phase are simultaneously modulated (the radiation is independent of one another.

i. hail

360+.

a 4 Thebes. one

in b af from, gd

Claims (2)

1. METHOD OF MODULATION OF OPTICAL RADIATION, including passing it through a transparent medium, the refractive index of which is changed by exciting an acoustic wave in it at a Bragg angle to the propagation direction of the specified radiation, and changing the amplitude of the acoustic wave, characterized in that, in order to reduce the loss of optical radiation in the process of modulation and ensuring the independence of the phase modulation from the amplitude of the optical radiation, the amplitude of the acoustic wave is changed stepwise in the integral, including chenie ^on 'X ^ ~ · in which derivatives where 3 "- the intensity of the optical radiation passing through a transparent medium; And the amplitude of the acoustic wave is from a given value to a value at which the intensity of the transmitted radiation is equal to its initial intensity. 2. The method of Pop. 1, with the exception that the amplitude of the acoustic wave is changed from zero to a value corresponding to the maximum value of the intensity of transmitted radiation. © 5 M SP m