Laser Communications Demonstration

by the ECE senior design class of '01, Matt Brooks '02, and Brian Holt '03

printed circuit board

We designed and built a display for the Science Museum of Western Virginia to intuitively demonstrate how an audio signal may be transmitted by light, which is at the heart of today's fiber-optic telephone and internet communications systems. This design project won third place in VMI's 2002 Undergraduate Research Symposium.

An analog signal from a CD player is first sampled at 128kHz (128,000 times a second) and at each sample the magnitude of the audio intensity is represented by a number from 0-255, or in binary, 00000000 to 11111111. Each of the eight binary digits then drives a corresponding laser (the lipstick-shaped elements arranged vertically in the photo above). The signal is received by phototransistors on the right, decoded into a continuous voltage waveform by a digital to analog converter, and then amplified and played. The lasers are visible through a protective plexiglass enclosure, and museum visitors may interact with the demonstration by moving a sliding bar that selectively blocks the laser beams and causes a degradation in signal quality.

This project was jointly completed by the ECE senior class of 2001 supervised by COL Dan Barr and by Matt Brooks ('02) and Brian Holt ('03) supervised by MAJ Jim Squire.