Multi-wavelength light source for dense wavelength division multiplexing optical communications system

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The dense wavelength division multiplexing (DWDM) optical communication system is a promising technology for the next generation massive communication. The DWDM optical communication system, however, has to suppress the fluctuation of the wavelength spacing between any neighboring carriers within 0.01nm. In the conventional method, more than 100 laser diodes (LD's) are used and all of them must be controlled for precise wavelength stabilization, which leads to cost problems and technical difficulties.This study developed and evaluated a low-cost and stable multi-wavelength light source for DWDM optical communication system. It consists of an optical frequency comb generator, a device producing flattop multi-wavelength spectra. The principle is generation of multiple sidebands by overdriving series-connected optical modulators. This method keeps all the channel spacing equal to the driving frequency of the comb generator. By stabilizing only the wavelength of a seed LD, all the wavelengths for the carrier in each channel are stabilized. We successfully generated more than 20 carriers with 50-GHz spacing by using this optical comb generator and a stabilized seed LD. It was also confirmed that our comb generator is independent of the wavelength of the seed LD and can cover approximately hundred channels of entire C-band with 8 seed LD's. The transmission experiments over 100 km achieved bit error rate of 10-12 for 10 Gbps NRZ signal, which is sufficient for a practical massive communication system.