LIGHT RAYS THAT CARRY INFORMATION,
FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSON AFB OHIO
Pagination or Media Count:
The ever-expanding need for exchange of information has crowded the radio frequency spectrum. A qualitatively new solution to the problem of channel capacity is offered by the recently created sources of monochromatic coherent light. These so-called masers and lasers operate at extremely high frequencies, and, since the quantity of information theoretically able to be transmitted on a communications channel is directly proportional to the frequency, their theoretical information capacity is tremendous. The capacity of a laser communications channel is at least 1000 times greater than the capacity of all radio channels used up to now, including microwave. The primary problem hindering laser communications now is modulation of the laser beam. Theoretically, any of the four standard parameters of a laser beam can be modulated to place information of the beam frequency, amplitude, phase and polarization. Actually, two primary methods can be used to modulate the light beam exiting from a laser internal and external methods. In the first case, the light beam is acted upon as it is being formed, i.e., within the actual laser. In the second case, the modulation is performed after the beam has been created. Internal methods include regeneration modulation, modulation using the Stark effect and modulation using the Seeman effect. Scientists at present are giving preference to the external modulation methods, which include modulation of the pumping, mechanical modulation, modulation using the Faraday effect, modulation using the Kerr effect and modulation using the optical birefringence effect in piezoelectric crystals.
- Lasers and Masers
- Non-Radio Communications