42 research outputs found
Experimental characterization of a 400  Gbit/s orbital angular momentum multiplexed free-space optical link over 120 m
We experimentally demonstrate and characterize the
performance of a 400-Gbit/s orbital angular momentum
(OAM) multiplexed free-space optical link over 120-
meters on the roof of a building. Four OAM beams, each
carrying a 100-Gbit/s QPSK channel are multiplexed and
transmitted. We investigate the influence of channel
impairments on the received power, inter-modal
crosstalk among channels, and system power penalties.
Without laser tracking and compensation systems, the
measured received power and crosstalk among OAM
channels fluctuate by 4.5 dB and 5 dB, respectively, over
180 seconds. For a beam displacement of 2 mm that
corresponds to a pointing error less than 16.7 μrad, the
link bit-error-rates are below the forward error
correction threshold of 3.8×10-3 for all channels. Both
experimental and simulation results show that power
penalties increase rapidly when the displacement
increases
Mode division multiplexing in radio-over-free-space-optical system incorporating orthogonal frequency division multiplexing and photonic crystal fiber equalization
Radio over free space optics (Ro-FSO) is a revolutionary technology for seamlessly integrating radio and optical networks without expensive optical fiber cabling. RoFSO
technology plays a crucial role in supporting broadband connectivity in rural and remote areas where current broadband infrastructure is not feasible due to geographical and economic inconvenience. Although the capacity of Ro-FSO can be increased by mode division multiplexing (MDM), the transmission distance and capacity is still limited by multipath fading and mode coupling losses due to atmospheric turbulences such as light fog, thin fog and heavy fog. The main intention of this thesis is to design MDM system for Ro-FSO for long and short haul
communication. Orthogonal frequency division multiplexing (OFDM) is proposed for long haul communication to mitigate multipath fading and Photonic Crystal Fiber (PCF) is proposed for short haul communication to reduce mode coupling
losses. The reported results of the proposed scheme for long haul communication show a significant 47% power improvement in deep fades from multipath propagation with the use of OFDM in MDM-Ro-FSO systems as compared to without OFDM. The results of the proposed scheme for short haul communication show 90.6% improvement in power in the dominant mode with the use of PCF in MDM-Ro-FSO as compared to without PCF. The reported results in the thesis show
significant improvement in Ro-FSO systems as compared to previous systems in terms of capacity and transmission distance under clear weather conditions as well as under varying levels of fog. The contributions of this thesis are expected to provide seamless broadband services in remote areas
Introduction to free space optical (FSO) communications
The demand for high bandwidth and secure communication is increasing. Free space optical (FSO) wireless communications technology could be one possible alternative option to the RF technologies that can be adopted in certain applications to unlock the bandwidth bottleneck issue, specifically in the last mile access networks, between mobile base stations in RF cellular wireless networks, and for radio over fiber; and over the last decade, we have seen growing research and development activities in FSO communications in the field of high data rate wireless technology applications as well as the emergence of commercial systems