UFR PhITEMPhysics, Engineering, Earth, Environment, Mechanics

Fiber optic telecommunications.
The amplitude of a polarized HeNe laser beam is modulated by the output voltage of a small radio, using a Pockels cell followed by a polaroid. The modulated beam is then injected into a 500 m long optical fiber (large coil). The light intensity at the fiber's output is captured by a photodiode. The electrical signal is sent to a loudspeaker fitted with a small amplifier. In this way, you can hear the sound of the radio, transported by optical means. Volume can be adjusted by turning the polaroid.

Acousto-optic diffraction A laser beam is diffracted by an acoustic grating in an acousto-optic modulator. Above, in the absence of an acoustic wave (order 0); in the middle, in the presence of an acoustic wave but at normal incidence (different diffraction orders: 0, +/1 and +/-2); below, at Bragg incidence (maximum diffracted intensity in order 1).