lasercom

Laser communication, or lasercom, is an optical communication method that uses a laser transmitter to send information through free-space or optical fiber. In free-space lasercom, a narrow, highly collimated beam—usually near-infrared—is directed between a transmitter and a telescope-based receiver. The approach aims for high data rates over long distances and is used where radio links are limited, especially in space, aviation, and metropolitan backhaul.

How it works: A laser source is modulated with data and steered toward the receiver with precise pointing, acquisition, and tracking. The receiver converts the optical signal to an electrical one. Wavelengths generally span 850 to 1550 nm; 1550 nm is favored for atmospheric transmission and eye safety, and many systems use telecom-grade lasers.

Key components include a laser diode or fiber laser, a high-speed modulator, beam-steering, a receiving telescope, a photodetector (PIN or avalanche), and processing electronics. Design must address link budget, atmospheric losses, scintillation, pointing accuracy, and eye-safety. Common modulation formats include on-off keying and various coherent or differential schemes, chosen per channel conditions.

Applications and milestones: Lasercom has been demonstrated on ground-to-ground, air-to-ground, and space links. Notable milestones include NASA's Lunar Laser Communication Demonstration and ongoing satellite laser relay experiments. It is studied for inter-satellite links, satellite backhaul, and high-capacity terrestrial backhaul in urban networks.

Advantages include high potential data rates, narrow beams that reduce interference and spectrum use, and improved security. Challenges include weather dependence (clouds, fog), atmospheric turbulence, strict pointing requirements, eye-safety concerns, and higher system costs. Research continues to improve efficiency, pointing, and adaptive optics.