Wavelength Uniformity in λ/4-Shifted DFB Laser Array WDM Transmitters

Wavelength division multiplexed (WDM) optical transmission requires laser sources with wavelengths closely aligned to the pass-bands of demultiplexing optical filters at the receiving end. A common and simple strategy to meet this demand is the use of wavelength-stabilized discrete sources and passive demultiplexing filters without active tracking, i.e., both the source and the demultiplexing filter being independently responsible for maintaining the wavelength channel assignment within a prescribed accuracy. Properly engineered distributed feedback (DFB) laser resonators are well-known in their ability to offer exceptionally robust longitudinal mode stability, both in their long-term resistance to mode jumps with environmental and operating condition changes, and in basic side-mode suppression characteristics. Temperature-stabilized DFB lasers have been shown to have very low (0.1nm-level) wavelength drift with aging over system life[1,2].