High-Speed Adaptive Control Technique Based on Steepest Descent Method for Adaptive Chromatic Dispersion Compensation in Optical Communications

The traffic volume of the data transmission is increasing each year with the explosive growth of the Internet. The networking technologies supporting the data transmission are optical fiber transmission technologies. In the physical layer, the networks are classified into three networks, the long-haul network that connects city to city, the metropolitan area network that connects the central station in the city to the neighboring base station, and the access network that connects the base station to the home. In order to adapt to the increase of the data transmission, we need to achieve high-speed transmission and increase the capacity of transmission in each network. In the access network, many kinds of passive optical networks (PON) are studied to offer a high-speed access to the Internet at low cost. In the metropolitan area network, we contemplate the update of the network structure from the conventional peer-to-peer transmission to the ring or mesh structure for the high-capacity and highly reliable networks. In the long-haul network, the study on multilevel modulation such as the differential quadrature phase shift keying (DQPSK) is a recent popular topic for the high-capacity transmission because the multilevel modulation utilizing the phase information offers highspeed transmission without increasing the symbol rate. Other modulation and multiplexing technologies are also studied for the high-capacity networks. The orthogonal frequency division multiplexing (OFDM) is one of the wavelength division multiplexing methods and achieves high spectral efficiency by the use of orthogonal carrier frequencies. The optical code division multiple access (OCDMA) is a multiplexing technique in the code domain. These techniques are developed in the wireless communication and modified for the optical transmission technologies in these days. In the long-haul and the metropolitan area networks whose transmission distance is over 10 km in 40 Gb/s, chromatic dispersion (CD) is one of the main factors which limits the transmission speed and the advances of the network structure. The CD is a physical phenomenon that the group velocity of light in the fiber depends on its wavelength (Agrawal, 2002). The CD causes the degradation of the transmission quality as the optical