Free-Space Optical (FSO) communication holds the potential for data communications at high bandwidths security while minimizing size, weight, and power (SWAP). However, the effects of atmospheric turbulence on an optical beam during propagation limits and degrades communication performance and bit-error-rate. Although degradation of beam quality occurs due to many factors, typically unwanted aberrations due to fluctuations in the refractive index n along beam path causing scattering, absorption, and beam wander is the main cause. Randomly distributed cells called eddies are formed in the propagating medium giving rise to turbulence as well. In this paper, we report experimental results from a 3-meter FSO data link. An intensity modulated 10 Gbps beam in the next phase will be analyzed and correlated to real time weather. We study scintillations and deviation of the beam from its original path (beam wander and spread). A phosphor-coated silicon CCD is used to record and study the beam’s intensity profile.
Free-space optical communication (FSOC) holds unmatched potential for high bandwidth and secure communications while minimizing size, weight, and power (SWAP). However, the effects of atmospheric scintillations on high bandwidth signals limits data link performance by degrading OSNR (Optical signal-to-noise ratio) and Q-factor. A critical component due to which a communication signal quality deteriorates is timing jitter. Jitter may be due to timing of the data signal or it may be due to the amplitude variations in the data bit stream as it propagates through free-space. As the data bandwidth increases, these effects become more significant. A small-time deviation in a lower data rate signal which would be tolerable or be above a receiver sensitivity, turns into an intolerable signal at higher data rates as jitter increases. The total jitter (TJ) can be further broken down to deterministic jitter (DJ) and random jitter (RJ). These may help understand signal behavior and the root cause of degradation in a FSOC or any data communication link. Thus, for a system to achieve desired BER (bit-error-rate and bit-error-ratio), an in-depth analysis of jitter by investigating each of the subclass of both timing jitters, DJ and RJ, would be extremely helpful and enhance the robustness of the link. In this paper, we report in-depth jitter analysis from a FSOC data link at 10 Gbps propagating at 1550 nm.
KEYWORDS: Free space optics, Data communications, Signal attenuation, Scintillation, Turbulence, Eye, Free space optical communications, Atmospheric turbulence, Atmospheric propagation, Receivers
Free-space optical communication (FSOC) holds an unmatched potential for data communications with high bandwidth and security while minimizing size, weight, and power (SWAP). However, the effects of atmospheric turbulence on an optical wave during propagation limits and degrades communication performance. Although this degradation of beam quality occurs due to many factors, but unwanted aberrations due to scattering and absorption of the propagating electromagnetic wave is typically the primary cause. In this paper, we report experimental results from a free space optical FSO communication data link. Bandwidth up to 10 Gbps at 1550 nm is correlated to 𝑐𝑛2 (refractive index structure parameter), transmission wavelength, transmit and receive parameters. For further random and data dependent analysis, the communication link's transmission and receive data eye with amplitude and time jitter decomposition is performed using multiple NRZ PRBS patterns. Additionally, with the aim of reducing SWAP and cost, the experiment is built and designed mostly using off-the-shelf long-range single mode, small factor pluggable devices.
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