High-performance free-space optical modem hardware

This paper describes key aspects of modem hardware designed to operate in free space optical (FSO) links of up to 200 km. The hardware serves as a bridge between 10 gigabit Ethernet client data systems and FSO terminals. The modem hardware alters the client data rate and format for optimal transmission and reception over the FSO link by applying forward error correction (FEC) processing and differential phase shift keying (DPSK) modulation. Optical automatic gain control (OAGC) is also used. The result of these features provide sensitivities approaching -48 dBm with 60 dB of error-free dynamic range while in the presence of turbulent optical conditions to deal with large dynamic range optical power fades.