Application Of Electro-Optic Modulation In Optical Communication


The system uses light waves to transmit sound information. The laser generated by the laser becomes linearly polarized light after the polarizer, and then becomes circularly polarized light after the λ / 4 wave plate, so that the two polarization components (o light and e light) produce π / 2 phase difference before entering the electro-optical crystal, so that the modulator works in the approximate linear region. At the same time as the laser passes through the electro-optic crystal, an external voltage is applied to the electro-optic crystal. This voltage is the sound signal to be transmitted.

When the voltage is added to the electro-optic crystal, the refractive index and other optical properties of the crystal change, change the polarization state of the light wave, so that the circularly polarized light becomes elliptically polarized light, and then becomes linearly polarized light through the polarizer, and the light intensity is modulated. At this time, the light wave contains sound information and propagates in free space. The photodetector is used to receive the modulated optical signal at the receiving place, and then the circuit conversion is carried out to convert the optical signal into electrical signal. The sound signal is restored by demodulator, and finally the optical transmission of the sound signal is completed. The applied voltage is the transmitted sound signal, which can be the output of a radio recorder or a tape drive, and is actually a voltage signal that varies over time.