High density wavelength division multiplexing technology for optical communication networks

In our department, work is underway on dense wavelength division multiplexing (WDM) technology, using the techniques of multi-beam modulation and subcarrier multiplexing (MBM-SCM). The proposed system can provide 250 channels, with each channel transmitting a 1 Gb/s digital signal. The dense WDM technology can potentially use the optical bandwidth of hundreds of THz, by coupling a large number of channels into one single mode fiber. In the MBM-SCM techniques, high frequency subcarriers are automatically created by low speed laser diodes and separated by microwave filters.;In this dissertation work, a two-channel MBM-SCM fiber data link has been demonstrated. Both a 600MHz analog signal and a 600 Mb/s signal were transmitted and demodulated. The highest subcarrier (21GHz) has been stabilized. Automatically stabilizing and switching the laser frequency was the first step guaranteeing that the MBM-SCM would fulfill its potential. In the two-channel MBM-SCM experimental setup, laser wavelengths were stabilized with the frequency locking loop and the temperature control loop. Hysteresis phenomena of F-P lasers in wavelength stabilizing and switching was investigated and explained. Fast channel stabilization and selection were accomplished by computer real time control. A C program was developed for data acquisition. Because semiconductor lasers have a certain linewidth which has a big influence on the system bit error rate, signal-to-noise analysis has been done to get the quantitative relation between the laser linewidth and the bit error rate. From the analysis, the better result of system bit error rate would be obtained with a large frequency deviation. The testing of system bit error rate was done and the experiment results supported the analyses. The dense channel optical frequencies were calculated to avoid the interference and to get maximum using of optical bandwidth. Discussion about absolute frequency references using the optogalvanic effect and design consideration of Fabry-Perot frequency standard were presented. An experiment involving division selecting using acoustic optical tunable filters was done and an introduction of optical fiber amplifiers was also presented. The applications of the MBM-SCM scheme in all-optical networks were briefly discussed.