2.4 km free-space optical communication 1550 nm transmission link operating at 2.5 Gb/s : experimental results

We describe a terrestrial free-space optical data link operating @ 2.5 Gb/s using currently available 1.5 μm telecommunications electro-optic transmission components. The 2.4 km free-space optical data-link is characterized by bit-error-rate (BER) system performance. The optical link utilizes a 1.5 μm DFB laser device which is directly modulated and operating within the erbium amplification band. An erbium doped optical amplifier (EDFA) is used to provide up to +27 dBm of optical launch power to a specially designed transmitting telescope and reflected by a remote mirror located 1.2 km away. The reflected signal is then coupled into a receiving telescope in close proximity to the transmitting telescope. The received optical signal is focused onto the core of a 62.5 μm multi-mode (MM) optical fiber using coupling optics within the receive telescope. The coupled optical signal is interfaced to a 2.5 Gb/s APD receiver. The BER and optical stability measurements are presented to quantify and demonstrate link quality for a 2.4 km span. Both results are presented and compared to baseline BER and a short free-space indoor link. BER and received optical coupled power data is presented to illustrate atmospheric effects associated with typical link performance. The number of transmitting apertures is varied to illustrate the impact upon scintillation effects as well as BER performance.