Misalignment distortion penalty in moderate-speed directly modulated WDM systems and its reduction using fiber Bragg grating lasers

Experimental studies show that dc and dynamic chirps in directly modulated distributed-feedback (DFB) lasers cause even larger distortion penalties in lower speed (155-622 Mb/s) wavelength-division multiplexed (WDM) fiber transmission systems than in high speed (2.5 Gb/s) when the passband edges of the wavelength-selective components act as frequency discriminators and result in FM-to-AM conversion. Such penalties impose laser-to-filter wavelength alignment accuracy requirements on the order of 0.1 nm for 1-dB penalty. Low-chirp lasers such as directly modulated fiber Bragg grating lasers are shown to reduce penalties to less than 0.5 dB for 0.2-nm detuning.