The Use of Light as a Communication Media: China Great Wall

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The use of light as a communication media used in China Great Wall distance more than 7300 km with in 1 hour to sent signal from one tower to another. In the late 20th century optical communication took back in to the seat for its advantages over coaxial transport and other electrical communication system. In 1966, Kaw and Hockman proposed the idea of using optical fiber light wave communication and their prediction was data loss 20dB/km [12]. In late 1980s to 1990s, coherent detection communication systems were introduced to enhance the transmission system. However, optical system needs still regeneration over long distance. By early 1990s, the system channel capacity boosted and reached to 10Gb/s but in 2003 it reached up to 40Gb/s via support WDM system. Recently, some experiments have done to transmit data 21.7 Tb/s though crossing the 10Tb/s per fiber barrier and it is new challenges for optical communication to innovate novel schemes of optical amplification, modulation technique or Fiber channel design.

2.2 Coherent Optical OFDM

The application of OFDM to optical communications used surprisingly late and relatively compared with RF complement, although the first paper on optical OFDM in the open literature was created by Pan and Green in 1996 and also in this year’s some research was happen. However, the fundamental advantages of OFDM against optical channel dispersion was not recognized in optical communication until 2001, when OFDM to combat model model dispersion in multimode fiber (MMF). A clear understanding of the unique optical channel or optical system make possible the most efficient design of the CO-OFDM system. Coherent optical OFDM (CO-OFDM) represents the ultimate performance in receiver performance, sp...

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... of dispersion management in optical transmission, which are Direct Detection optical OFDM (DDO-OFDM) and Coherent Optical OFDM (CO-OFDM). According to the performance in spectral efficiency, receiver sensitivity and polarization dispersion, CO-OFDM is better performance but more complexes to implement then DDO-OFDM. CO-OFDM has emerged for 100 GB/s transmission over 1000km SSMF. However , at this data rates, the signal quality is significantly interrupted mainly due to the impact of PMD, CD and intra channel nonlinearity effect but using Coded OFDM and efficient modulation technique we will try to improve error free data rata and intra channel nonlinearity of fiber. The choice of different digital modulation method directly affect to OSNR, [7] Optical fiber dispersion, nonlinear effect, bandwidth efficiency and BER which can effect as a whole system performance.

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