High density wavelength division multiplexing (WDM), where the channels are 100 GHz to 200 GHz separated, is one of the approaches for increasing the fiber optic network capacity to meet the demand of transmitting the ever increased volume of multimedia information. To avoid crosstalk between adjacent channels, the precision of wavelength as well as the wavelength stability of the light sources need to be obtained and maintained throughout the system's service lifetime. Many techniques have been studied in recent years to improve the wavelength stability of semiconductor lasers for the applications in dense WDM systems. In this paper, approaches in achieving wavelength stability by wavelength referencing and locking are discussed. Concerns on depending on wavelength stability of the free running DFB lasers at the stage of mass deployment of multiple wavelength dense WDM systems also are presented.
K. D. Chik, K. D. Chik,
"Precision wavelength light sources for dense WDM system", Proc. SPIE 3038, High-Speed Semiconductor Lasers for Communication, (10 April 1997); doi: 10.1117/12.271466; https://doi.org/10.1117/12.271466