**6. References**


FSO system can spread as a reliable solution for high bandwidth and short distance. There are some factors which must be taken into consideration during the design of FSO system as controllable and uncontrollable factors. Controllable factors include wavelength, transmission range, beam divergence, loss occurred between transmitter and receiver and detector sensitivity. Uncontrollable factors include visibility, rainfall rate, raindrop radius,

Atmospheric attenuation may be absorption or scattering. Absorption lines at the visible and IR wavelengths are narrow and separated. So, we can ignore absorption effect at the wavelength identified as atmospheric windows. Wavelength at FSO system must be eye safe and able to transmit a sufficient power during the bad weather condition. Mie scattering represents the main affects on FSO systems. The main cause of Mie scattering is fog and hazy. Attenuation caused by fog in Yemen is so important for Taiz as the low visibility range can less than 0.05 km during the extensive fog according to the data taken from metrology authority. Transmission in this city may be cut off, so the distance between the transmitter and receiver must be reduced. However, Sana'a and Aden cities the weather is clear during the whole year in comparison with Taiz city. Rayleigh scattering we can ignore it at the visible and infrared wavelength as its effect on the ultraviolet wavelengths is huge. This scattering occurs when the molecules size is less than the wave length of the laser

Non-selective scattering independent on wavelength and occurs when the molecules size is bigger than wavelength and it occurs due to the rainfall. Generally, FSO system is so adequate in Yemeni environment according to the previous results. The performance of wavelength 1550 nm is better at the bad weather conditions in comparison with wavelengths 850 nm and 780 nm. Furthermore, the wavelength 1550 nm allows a high power may reach to over 50 times in comparison with the wavelengths 850 nm & 780 nm. By analyzing results obtained at chapter four, we conclude that we are able to improve the performance of transmission of FSO system at the bad weather conditions by using the

[1] Weichel H., "Laser Beam Propagation in the Atmosphere", SPIE, Optical Engineering

[2] A. K. Majumdar, J. C. Ricklin, "Free Space Laser Communications Principles and

[3] H. Hemmati, "Near-Earth Laser Communications", California, Taylor & Francis Group,

[4] H. Willebrand and B. S. Ghuman, "Free-Space Optics Enabling Optical Connectivity in

[5] B. Olivieret, et al., "Free-Space Optics, Propagation and Communication", Book, ISTE,

wavelength 1550 nm and short distance between transmitter and receiver.

Advances", Springer ISBN 978-0-387-28652-5, 2008.

Today's Networks", SAMS, 0-672-32248-x, 2002.

**5. General conclusion of this chapter** 

atmospheric attenuation and scintillation.

beam.

**6. References** 

Press, Vol. TT-3, 1990.

Book, LLC, 2008.

2006.


**3** 

**Full-Field Detection with** 

Jian Zhao and Andrew D. Ellis

*University College Cork* 

 *Ireland* 

**Electronic Signal Processing** 

*Photonic Systems Group, Tyndall National Institute & Department of Physics,* 

The rapid growth in broadband services is increasing the demand for high-speed optical communication systems. However, as the data rate increases, transmission impairments such as chromatic dispersion (CD) become prominent and require careful compensation. In addition, it is proposed that the next-generation optical networks will be intelligent and adaptive with impairment compensation that can be software-defined and re-programmed to adapt to changes in network conditions. This flexibility should allow dynamic resource reallocation, provide greater network efficiency, and reduce the operation and maintenance cost. Conventional dispersion compensating fiber (DCF) is bulky and requires careful design for each fiber link as well as associated amplifiers and monitoring. Recently, the advance of high-speed microelectronics, for example 30 GSamples/s analogue to digital converters (ADC) (Ellermeyer et al., 2008), has enabled the applications of electronic dispersion compensation (EDC) (Iwashita & Takachio, 1988; Winters & Gitlin, 1990) in optical communication systems at 10 Gbaud and beyond. The maturity in electronic buffering, computation, and large scale integration enables EDC to be more cost-effective, adaptive, and easier to integrate into transmitters or receivers for extending the reach of legacy multimode optical fiber links (Weem et al., 2005; Schube & Mazzini, 2007) as well as metro and long-haul optical transmission systems (Bülow & Thielecke, 2001; Haunstein & Urbansky, 2004; Xia & Rosenkranz, 2006, Bosco & Poggiolini, 2006; Chandrasekhar et al., 2006; Zhao & Chen, 2007; Bulow et al., 2008). Transmitter-side EDC (McNicol et al., 2005; McGhan et al., 2005 & 2006) exhibits high performance but its adaptation speed is limited by the round-trip delay. Receiver-side EDC can adapt quickly to changes in link conditions and is of particular value for future transparent optical networks where the reconfiguration of the add- and drop-nodes will cause the transmission paths to vary frequently. Direct-detection maximum likelihood sequence estimation (DD MLSE) receivers are commercially available and have been demonstrated in various transmission experiments (Farbert et al., 2004; Gene et al., 2007; Alfiad et al., 2008). However, the performance of conventional EDC using direct detection (DD) is limited due to the loss of the signal phase information (Franceschini et al., 2007). In addition, the transformation of linear optical impairments arising from CD into nonlinear impairments after square-law detection significantly increases the operational complexity of the DD EDC. For example, DD MLSE was numerically predicted to achieve 700km single mode fiber (SMF) transmission at 10 Gbit/s but required 8192 Viterbi processor states (Bosco & Poggiolini, 2006).

**1. Introduction** 

