Direct Modulation at 56 and 50 Gb/s of 1.3- $\mu $ m InGaAlAs Ridge-Shaped-BH DFB Lasers

Direct modulation at 56 and 50 Gb/s of 1.3- $\mu $ m InGaAlAs ridge-shaped-buried heterostructure (RS-BH) asymmetric corrugation-pitch-modulation (ACPM) distributed feedback lasers is experimentally demonstrated. The fabricated lasers have a low threshold current (5.6 mA at 85 °C), high temperature characteristics (71 K), high slope relaxation frequency (3.2 GHz/mA $^{\mathrm {\mathbf {1/2}}}$ at 85 °C), and wide bandwidth (22.1 GHz at 85 °C). These superior properties enable the lasers to run at 56 Gb/s and 55 °C and 50 Gb/s at up to 80 °C for back-to-back operation with clear eye openings. This is achieved by the combination of a low-leakage RS-BH and an ACPM grating. Moreover, successful transmission of 56- and 50-Gb/s modulated signals over a 10-km standard single-mode fiber is achieved. These results confirm the suitability of this type of laser for use as a cost-effective light source in 400 GbE and OTU5 applications.