Optical satellite communications with Erbium doped fiber amplifiers

For implementing an optical free-space transmission system at data rates up to 10 Gbit/s, commercially available devices developed for terrestrial fiber optic applications may be employed to advantage. We designed, set up and tested a breadboard consisting of an NRZ/RZ transmitter with a booster amplifier of 1 Watt optical output power and an optically preamplified direct detection receiver. The main objective was to determine the receiver sensitivity and assess critical components. With the breadboard parameters optimized, the required average number of photons per bit at the receiver input was 55 for a bit error probability of BEP = 10 in case of NRZ coding. We further demonstrated a sensitivity improvement of about 1 dB by applying RZ coding. The measurements yielded excellent agreement with simulations performed with a tool especially designed for this purpose.