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We clarified experimentally that an EA-DFB laser in which the EAM and DFB parts are coupled with a passive waveguide provides a large bandwidth, even when a large reverse bias is applied to the EAM. This allows the chip to operate in a negative-chirp condition. We fabricated an EA-DFB module terminated with a 50 Omega resistor through a dc-block capacitor to suppress the increase in dc current as the reverse bias increases. A module equipped with our new EA-DFB chip successfully transmitted data over a distance of 3 km at a rate of 40 Gbit/s and at a driving voltage as low as 2 V.