| Optical code division multiple access (OCDMA) is a sort of spread spectrum communication technique. It takes full advantage of available fiber bandwidth resources and overcomes the bottleneck of optic/electric transformation in order to allow more users to share fiber channel. The address codes which have excellent performance are the basis for enhancing OCDMA system performance, even for realizing the technique. In this dissertation, the codes which frequently used are analyzed and a 3D code which has better performance on capability and bit error rate (BER) is brought forward.First, the codes which frequently used are analyzed, including prime code, correlative improved codes, optical orthogonal code (OOC) and various of time/wavelength two-dimension codes. Their code length, code weight, auto-correlation, cross-correlation and complexity of constructing the codes, which are also important evaluation factors. The analysis shows that with the complexity of construction and the dimension increasing, the performance of address codes gets much improved.Second, on the basis of understanding the structure and characteristics of OCDMA system, combining the codes we have studied, several encoders/decoders are analyzed on their structure and characteristics, including time-domain encoder/decoder based on fiber delay line and time/wavelength encoder/decoder based on fibber bragg gratting (FBG). The main components of encoder/decoder are also analyzed, including source, fiber etc. In order to introduce the structure of encoder/decoder, a code which has better performance is constructed.Last, general multiple wavelength prime code (GMWPC) is analyzed, which can apply to MWOCDMA system. And based on the 2D code, combining 3D code theory, 3D GMWPC is constructed, in which we spread code on time, wavelength and space synchronously. Simulation results show that the performance of 3D code is much better than 2D GMWPC, including capability, bit error rate and bandwidth efficiency. Combining the construction method of 3D code, current encoder/decoder for 3D code is analyzed and improved encoder/decoder using array wave-guide gratting (AWG) is constructed. It can prove that the performance of improved encoder/decoder is much better, and it can carry into execution quite easier than current encoder/decoder. |
