Altered Laser Property: Polarization/Amplitude
Effect on the Laser Light: Polarisation / Amplitude Modulation
Electro-optic amplitude modulators (AM) are essentially Pockels cells consisting of a single or multiple electro-optic crystals with zero or compensated natural birefringence. Applying an electric field to the crystal induces a change in both the ordinary and extraordinary indices of refraction giving rise to an electric field dependent birefringence which leads to a change in the polarisation state of the transmitted optical beam. In this way the electro-optic crystal acts as a variable waveplate with retardance linearly dependent on the applied electric field. By placing a linear polariser after the modulator, the beam intensity through the polariser varies quasi sinusoidally with linear change in applied voltage. The voltage required to produce a retardance of π radians is called the halfwave voltage or simply Vπ.