Experimental Demonstration of Directly Modulated DFB Lasers With Negative Chirp Over Wide Temperature Operation

Two-section distributed feedback lasers containing an active section and a modulated reflection section have been demonstrated for direct modulation with negative chirp. The reflection section has the same waveguide core and grating pitch as the active section. The active section of the laser has fixed current injection and the modulation voltage is loaded onto the reflection section when the laser normally works. This modulation method can obtain negative chirp because the carrier density variation in the active section during modulation is contrary to traditional current modulation. The threshold current and side-mode suppression ratio of the fabricated laser are about 10-mA and 60-dB at 20 °C, respectively. A 20-GHz modulation bandwidth at 0.9-V reverse bias of the modulated reflection section has been achieved. The negative chirp generated by the modulation is about 45 GHz. 10 Gb/s transmission over 10-km single-mode fiber with error-free-operation over a wide temperature range has been demonstrated as well. The sensitivity of the 10-km transmission was better than BTB configuration at all temperatures due to the negative chirp characteristic.