Ultra-wide bandwidth laser communications: Part II—An operating laboratory system

A description is presented of the system configuration, principal components, and preliminary system test results of a laboratory laser communication link for high-fidelity transmission of base-band analog signals with bandwidths up to 0.4 GHz. An experimental system is described in which the information signal first is frequency modulated onto a 1.5-GHz microwave subcarrier. This FM subcarrier is then intensity modulated onto the laser beam by means of a gigahertz-bandwidth electrooptic modulator. The FM/IM signal on the beam is demodulated in the optical receiver by means of a fast-response photodetector and a gigahertz-bandwidth frequency discriminator. Results of initial measurements of linearity and frequency-response characteristics of the signal-handling components of the system are given, as well as overall system characteristics. A single-frequency argon laser is used as the source of the optical carrier.