Subsystem Technologies and Network Applications for Optical Code Division Multiple Acces Systems
Speaker: Yanhua Deng
Series: Final Public Orals
Location: Engineering Quadrangle J401
Date/Time: Friday, April 22, 2011, 9:00 a.m. - 11:00 a.m.
As local area networks and access networks are becoming more dynamic with higher demand for capacity and speed, an optical network platform that can support heterogeneous data rates, quality of service, and capacity is needed. Optical code division multiple access (optical CDMA) technology is a promising alternative that offers high scalability, flexible on-demand capacity, and asynchronous transmission capability. It is also robust, simple to implement, and compatible with existing optical networks.
Novel subsystem technologies for incoherent optical CDMA networks that implement wavelength-hopping time-spreading codes are presented. Each of them shows the advantages offered by optical CDMA. A robust optical source using an electro-absorption modulator as a pulse carver is investigated. This source has small footprint and low chirp, is polarization insensitive, and can be integrated with a semiconductor laser array to generate multi-wavelength pulses with picosecond pulse width. A compact optical CDMA coder using fiber Bragg grating arrays is also implemented. The coder has small foot-print, low loss, high precision, low birefringence, and low polarization sensitivity. Lastly, to overcome the two major types of noise in the optical CDMA systems, a nonlinear optical loop mirror is implemented at the receiver that suppresses the noise asynchronously and enhances system performance.
Based on these improved subsystems, an optical CDMA ring network is demonstrated. This network implements nonlinear optical loop mirror-based add/drop multiplexers that provide truly asynchronous adding and dropping operations and self-healing protection monitoring circuits that ensure service availability during link failure. The architecture is expanded further to an all-optical hybrid network composed of optical CDMA rings interconnecting through a reconfigurable WDM metro area ring. The network retains the advantages of both optical CDMA and WDM schemes, including asynchronous access and differentiated quality of service, while removing the hard limit on the number of subscribers and increasing network flexibility. Practical applications of interfacing Gigabit Ethernet networks and distributed sensor networks with optical CDMA networks are also investigated. The scalability of the network with realistic traffic in packet transmission is also analyzed. With the new subsystem technologies, optical CDMA networks are becoming a more viable alternative for diverse applications.