Requirements for modulator-integrated DFB LD's for penalty-free 2.5-Gb/s transmission

Wavelength chirp of modulator-integrated distributed-feedback laser diodes (DFB LD's) is governed by device parameters such as the modulator facet reflectivity, isolation resistance, grating coupling factor, and differential gain. We determined values of these parameters necessary for ensuring penalty-free 2.5-Gb/s transmission over at least 80-km of standard fiber. The influences of the device parameters on wavelength chirp behavior and 2.5-Gb/s data transmission performance are investigated using a new method of characterizing wavelength chirp. By transmitting light from the LD while modulating the modulator, we can determine the light intensity fluctuation after the transmission caused by wavelength chirp. This intensity fluctuation ratio (/spl Delta/I/I) is used to monitor the wavelength chirp. We use integrated devices which satisfy all these requirements, and which are grown by selective metal-organic vapor phase epitaxy (MOVPE), to demonstrate penalty-free 2.5-Gb/s transmission, even over 120-km of standard fiber.<
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