Free Space Optical Communications — Theory and Practices

Abstract

FSO is a line-of-sight technology that uses lasers to provide optical bandwidth connections or FSO is an optical communication technique that propagate the light in free space means air, outer space, vacuum, or something similar to wirelessly transmit data for telecommunication and computer networking. Currently, FSO is capable of up to 2.5 Gbps [1] of data, voice and video communications through the air, allowing optical connectivity without requiring fiberoptic cable or securing spectrum licenses. Operate between the 780-1600 nm wavelengths bands and use O/E and E/O converters. FSO requires light, which can be focused by using either light emitting diodes (LEDs) or lasers (light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiberoptic cables; the only difference is the transmission media. Light travels through air faster than it does through glass, so it is fair to classify FSO as optical communications at the speed of the light. FSO communication is considered as an alternative to radio relay link line-of sight (LOS) communication systems. This chapter is concentrate on ground-to-ground free-space laser communications. FSO components are contain three stages: transmitter to send of optical radiation through the atmosphere obeys the Beer-Lamberts`s law, free space transmission channel where exist the turbulent eddies (cloud, rain, smoke, gases, temperature variations, fog and aerosol) and receiver to process the received signal. Typical links are between 300 m and 5 km, although longer distances can be deployed such as 8-11 km are possible depending

On Divergence-Angle Efficiency of a Laser Beam in Free-Space Optical Communications for High-Speed Trains

“…SNR as a function of the received power when a direct detection receiver with an APD is employed. The variance of the noise is calculated according to (13), (14), and (15). The visibility is 500 m, which corresponds to the presence of moderate fog.…”

“…The visibility is 500 m, which corresponds to the presence of moderate fog. total noise used to calculate (16) follows (13), (14), and (15), and the parameters given in Table I. The solid blue line in Figure 8 indicates the received power values and the corresponding SNR that provide a BER of 10 −9 or lower.…”

“…However, 5G is not yet deployed and requires spectrum licensing. Free-space optical communications (FSOC), which is also known as optical wireless communications (OWC), is a line-of-sight (LOS) technology that propagates modulated light to transmit data between stations in stationary or mobile conditions [14]. Recently, FSOC technology has attracted considerable attention because it has the potential to provide transmissions at very-high data rates between two terminals separated over a distance that varies from a few meters to thousands of kilometers.…”

“…In this way, the receiver aperture may only collect a fraction of the incident beam. The remaining uncollected light results in a loss called divergence or geometric loss [14]. The geometric loss decreases the received power if the other communication parameters, such as the communication distance, transmission power, and the diameter of the transmitting and receiving apertures remain constant.…”

Analysis of the effect of BER and Q-factor on free space optical communication system using diverse wavelength technique

“…When a laser beam transmits via the atmosphere, it experiences power loss caused by multiple known factors. One of them is absorption and scattering loss as mentioned in Beer's Law [9]. The photon of the beam bouncing with haze particles in the mid-air caused a condition called as the absorption.…”