Free Space Optical Communication

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Florida Institute of technology|
FSO Report|
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Rami nahas|
4/29/2011|

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Free space optical communication is the most growing communication because it is easy to install and has a high speed because the signal is transmitted in the air. So that will introduce the atmospheric affect in the optical wave propagation. Atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal. So we need to study the effect and the limitation if we introduce a free space optical communication system with dual wavelength (980 nm, 1550 nm). Also studying the effect of turbulence when using two different wavelengths. Introduction

Free space optical communication is a kind of communication that use light propagation to send data between two points. Free Space Optics are capable of up to 2.5 Gbps of data, voice and video communications through the air, allowing optical connectivity without requiring fiber-optic cable or securing spectrum licenses. So we can use LED’s or Laser for transmission data. Free Space Optics (FSO) technology is relatively simple. It's built on a laser transmitter and a receiver to provide full duplex capability. Each FSO unit uses a high-power optical source, a lens that transmits light through the atmosphere to another lens receiving the information. The receiving lens connects to a high-sensitivity receiver via optical fiber. Because the transmission in occurred in air it is easily upgradable. FSO send a light beam from one point to another using low power lasers in the teraHertz spectrum. This beam is transmitted by laser light focused on photon detector receivers. These receivers collect the photon stream and transmit digital data. If there is a clear line between the two point FSO can operate on a distance of several kilometers as long we have a powerful transmitter.

Features of the laser communications system
Information usually in the form of digital data, data is entered to be regulated by the laser source transmitting electronics. Coding techniques can be used directly or indirectly depending on the type of laser used. Output source passes through the optical system in the channel. The visual system usually involves the transfer, beam shaping, and the telescope optics. Beam receiver comes in through the optical system and passed to the detection and signal processing electronics. There is also a terminal control electronics that must manage gimbals guidelines and other mechanisms, and machinery, to maintain and track the acquisition of the operating system designed in the mass of the process. In order to communicate, you must have received enough energy by the detector to distinguish signal from noise. Laser power, optical transmission system losses, pointing out shortcomings of the system, transmitter and receiver antenna gains and losses, receiver, receiver and loss tracking, are all factors that force in the establishment of the receiver power. The required optical power is determined by data rate, detector sensitivity, configuration modes, noise, and detection methods. When the receiver is to detect the signals, it is in fact the decision-making regarding the nature of the signal (digital signal is sent when the distinction between the ones and zeros). There are two types of distributions: one when the signal present (including the amount of photocurrent due to the background and the current detector in the dark), and one when there is no signal present (including sources of no signal current only). A threshold must be developed to increase the success rate and reduces the error rate. Even when there is no signal present, the fluctuation sources of no signal lead periodically to the threshold to be exceeded. This is an error stating that the signal exists when there is no signal present. Distribution of signal may also fall on the other side of the threshold, so any errors stating that the signal is going to happen even when the...
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