Free Space Optical Communication Essay

Free blank space optical communication is the most growing communication beca rehearse it is easy to interject 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 level of the received signal. So we need to study the effect and the assignation if we introduce a free space optical communication system with dual wavelength (980 nm, 1550 nm). Also studying the effect of turbulence when using cardinal different wavelengths.IntroductionFree space optical communication is a kind of communication that use wakeful propagation to send data amidst two points. Free Space Optics be open(a) 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 LEDs or Laser for transmittance data. Free Space Optics (FSO) engine room is relatively simple. Its built on a optical maser transmitter and a receiver to tender full duplex capability.Each FSO unit uses a high-power optical source, a lens that transmits alight through the atmosphere to some other 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 reflect from one point to another using low power lasers in the teraHertz spectrum. This beam is transmitted by laser light focused on photon sensing element receivers. These receivers collect the photon stream and transmit digital data. If there is a finish off line between the two point FSO can ope put on a distance of some(prenominal) kilometers as long we involve a powerful transmitter.Features of the laser communications systemInformation normally in the form of digital data, data is entered to be regulated by the laser source tr ansmission 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 affect electronics. There is also a terminal control electronics that must manage gimbals guidelines and other mechanisms, and machinery, to maintain and course of instruction 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, be all factors that extract in the establishment of the receiver power. The required optical p ower 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 direct when the distinction between the ones and zeros).There are two types of distributions one when the signal present (including the amount of photocurrent collect 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 meet even when the signal i s present.SecurityFSO systems work in the near infrared wavelength range slightly above the visible spectrum. So, the human eye cannot clearly see the transmission beam. The wavelength range is around 1 micrometer caliper that is used in FSO transmission. The arbitrateion of FSO operating systems with narrow beam in the infrared spectral wavelength is by faraway the more difficult. Small diameter of the beam is usually only a few meters in diameter in the target site are one of the reasons that assoil it extremely difficult to intercept the communications of the FSO. Intruder must know the exact origin or target of the infrared beam and intercept only within a very narrow angle of beam propagation. Intercept packets directly from the FSO networks between remote locations is impossible mainly because the beam passes through the air usually at a higher(prenominal) altitude than at ground level. Due to the fact that the transmission beam is not visible, and that any attempts to o bviate the beam can occur near the FSO point of access and the process of transition poses another obstacle. transport the signal from the location that does not fall directly within the path of light with photons of light scattered from aerosols, fog, rain, or molecules that may be present in the atmosphere is almost impossible because of the energy levels are very low use infrared through FSO process transmission. The main reason for the exclusion of this hap of intrusion is the fact that light is an ally and statistically isotropic in different directions from the path of the airplane pilot propagation. This specific mechanism keeps the total number of photons or the amount of radiation that can potentially be collected on the detector that is not placed directly in the beam path beyond the detection level of noise.Atmospheric turbulenceAtmospheric turbulence can destroy the performance of FSO systems. The changes in temperature and pressure in the atmosphere lead to changes o f the refractive index along the transmission path. These changes can make the quality of received signal fade and causes fluctuations in the intensity and the phase of the received signal. These fluctuations can limit the performance of the system. The atmosphere is a viscous fluid and it has two state motions 1) laminar (there is no mixing in the air molecules) 2) turbulent (there is mixing that creates eddies). Atmospheric turbulence can be physically exposit by Kolmogorov theory. The energy of large eddies is redistributed without loss to eddies of decreasing size until finally dissipated by viscosity. The size of turbulence eddies normally ranges from a few millimeters to a few meters, denoted as the inner overcome and the outer scale, respectively. So the index of refraction n is very sensitive to small scale temperature fluctuations (temperature fluctuations are combined with turbulent mixing). So, the index of refraction is the most important in optical wave propagation.B ecause it behaves care a passive additive. So the spectrum of index of refraction can be described by Kolmogorove spectrum n () = 0.033 Cn 2 -11/3 , 1/L0