Og-6 Voice Communication Using a Laser Beam (The Faraday Effect)
Published: Wednesday 15 March 2006 - Updated: Monday 28 March 2011
To demonstrate the transmission of sound via the modulation of a laser beam using the Faraday effect.
- 10 mW Laser
- Faraday cell modulator -A
- Amplifier and speaker
Click on pictures to enlarge.
The Faraday modulator cell A consists of a crystal surrounded by a coil. The crystal has a large Verdet constant of 0.05 minutes of arc per magnetic field cm. The polarised laser beam has its plane of polarisation rotated by an amount proportional to the magnetic field strength in the coil. The coil is modulated directly from the output of a radio receiver. The laser beam strikes a photocell B which has a polaroid filter which may be rotated to maximise the signal.