الفهرس | Only 14 pages are availabe for public view |
Abstract The main challenges of today’s telecommunication networks are to provide more and cheaper bandwidth in data communication motivates the development of high-speed and low-cost optical links. Dense wavelength division multiplexing (DWDM) was originally designed for long-haul transmission emerges as a technology to alleviate this problem. Only DWDM technology is able to cope with terabit levels of demand at reasonable costs. DWDM, providing routing at the wavelength level and increasing the capacity of the current fiber, these abilities allow accommodating more and more users at lower costs, as opposed to legacy technologies for which costs saturate at some minimum levels. Sub-Carrier Multiplexing (SCM) provides high capacity transmissions at lower costs and enables fiber based wireless access. It uses optical components for high performance but limitations of electronic components cause electronic bottleneck which leads to limit the bit rate, number of users and the overall system performance. New type of laser called Vertical-cavity surface-emitting laser (VCSEL) over conventional lasers like lower threshold currents, better Wavelength stability, lower manufacturing cost and high temperature operation up to 80°C. Using various dispersion compensation techniques namely FBG (Fiber Bragg Grating), OPC (Optical Phase Conjugation) and DCF (Dispersion compensating Fiber) lead to compensate the dispersion and enhance bit rate up to 20Gbps through SMF. EDFA (Erbium-doped fiber amplifier) used to amplify signals. The Return to Zero (RZ) pulse just occupies a part of the bit slot therefore it has wide spectrum and a duty cycle smaller than 1. A relatively wide optical spectrum is a major characteristic of RZ modulated signals so it has a minimized the tolerance of dispersion and reduced a spectral efficiency. NRZ modulation format has many advantages as it requires a relatively low electrical bandwidth for transmitters and receivers compared with RZ, it is not sensitive to laser phase noise, the cost is low and the configuration of transmitter and receiver is simple so it is used in most commercial systems. Unfortunately, for high bit rate and long distances, NRZ modulation format is not appropriate. In case of the channels number is large, NRZ modulation is the best. Abstract vii For future wireless networks, radio over free space optics (Ro-FSO) is a promising technology. FSO communication is an optical communication technology where optical data wirelessly transmitted from one place to another. The major advantages of FSO are free spectrum license, high security and faster installation. The performance of FSO technique is affected by the conditions of the atmosphere such as etc. To minimize the impacts of the atmospheric disturbances by utilizing some techniques such as spatial diversity and Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) with dual polarization, the performance enhancement of FSO system using DWDM OFDM technique under haze, snow and fog conditions. |