Abstract-In free space optical (FSO) communication links, atmospheric turbulence has a significant impact on the quality of a laser beam propagating through the atmosphere. Turbulence results in intensity scintillation, which can severely impair the operation of target designation and FSO communications systems. Two important parameters for describing quality of FSO communications systems are the signal-to-noise ratio (SNR) and the bit error rate (BER). In this paper, using a modified model we analyze the effect of atmospheric turbulence on the SNR and BER for an FSO system in both weak and strong turbulence conditions.
I.INTRODUCTION FSO systems or optical wireless communication have many advantages when compared with the free space radio frequency based systems such as: high bandwidth, fast deployment, license-free, light weight and reduced size. Unfortunately, free space channel where light propagates is not ideal, thus leading to and suffers from a number of affects including absorption, scattering or displacement depending on the atmospheric condition. However, in clear atmosphere, with a typical attenuation coefficient of 0.43 dB/km, a major challenge facing FSO systems is the effect of turbulence induced irradiance fluctuation on the system performance especially for a link range exceeding 1 km. Atmospheric turbulence is caused by both spatial and temporal random fluctuations of refractive index due to temperature, pressure, and wind variations along the optical propagation path through the channel [1][2][3][4][5][6][7][8]. In this paper we investigate the turbulence effect on performance of an FSO link. We show that BER performance deteriorates with the index of refraction structure parameter (C
A full-vectorial finite-difference-based optical mode solver is presented to analyze travelling wave electroabsorption modulator (TWEAM). The discontinuities of the normal components of the electric field across abrupt dielectric interfaces are considered in this analysis which in contrast is the limitations of scalar and semivectorial approximation method. The optical field distributions in a ridge-type traveling-wave coplanar waveguide (CPW) electroabsorption modulator for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. Then, the effects of microwave and optical properties of waveguides on modulation response of TWEAMs are analyzed.
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