Free Space Optical (FSO) systems are being actively considered as viable options for seamless integration between backhaul optical fiber links and RF or copper links used for last mile connectivity. However, adverse atmospheric conditions can affect the performance and distance over which the link can operate reliably. Propagation of optical waves through the atmosphere is affected by atmospheric turbulence, scattering of aerosols and atmospheric absorption. Atmospheric turbulence is a result of localized variations of temperature, humidity, and pressure in the atmosphere. Turbulence is by nature a random process, and as such may be described using statistical quantities. Atmospheric turbulence induced fading is one of the main impairments affecting Free Space Optics (FSO). FSO systems can suffer outages in the presence of heavy fog, smog and haze. Many places in India see very heavy rainfall. We have studied the effects of rainfall on propagation characteristics in Dakshina Kannada district, Karnataka, India where Surathkal is located which is affected by heavy rainfall for about four to six months in a year. We observe that the attenuation during heavy rainfall is quite high and leads to extremely low levels of the received signal or complete erasure of the transmitted data. With the validation through simulation in this paper, on the use of Digital Fountain codes in FSO links, we suggest that if such codes are used in areas prone to rainfall, it would help in the recovery of dropped packets and would also improve the BER performance.
Optical fibres provide the best solutions for transmitting high speed, large amounts of data with good power efficiency. However such transmission would also need amplification for transmission over large distances. Erbium Doped Fibre Amplifiers(EDFAs) are currently being used for optical amplification. But good amplification is achievable with multiple stages and considerable length of EDFA fibres. In this paper we compare the use of Silver Split Ring Resonators(SRRs) , Gold Nano Rods and Silver Fishnet structures which give metamaterial properties to be used in optical fibres to give better amplification than EDFA based fibres.
Metamaterials belong to a new class of materials with negative values for permittivity and permeability. Such materials would exhibit negative refractive index leading to these materials being called as left handed media.If such left handed media have an internal structure made of dimensions much smaller than the wavelength but sufficiently thick to exhibit bulk properties, using other optical domains such as plasmonics, it is possible to control light interactions and propagation. Artificial structures smaller than the wavelength of light can be used to enhance electric and magnetic fields.
Surface plasmons can be excited on a metal and this can enhance the electric field at the surface. Our paper proposes the use of this phenomenon of achieving gain at optical frequencies by using SRRs, Fishnet structures , Nano Rods. We compare the performance of these structures and observe that they provide gain which is much more than that provided by EDFAs.