Enhanced Performance of Wavelength-Tunable EML Based on REC Technique

A wavelength-tunable electroabsorption-modulated DFB laser (EML) with performance enhanced by the integrated thin film heater is proposed and experimentally demonstrated. The reconstruction equivalent chirp (REC) technique is used to simplify the grating fabrication and introduce equivalent phase shifts in the cavity to guarantee single-mode operation. The electroabsorption modulator and the DFB laser share identical active layers to decrease the fabrication complexity. A Ti/Pt thin film heater is monolithically integrated near the DFB waveguide to enable wavelength tuning while keeping the temperature of the EAM almost unchanged. Compared to the wavelength tuning by the thermoelectric cooler, the wavelength tuning by the thin-film heater can obtain low loss for the electroabsorption modulator, uniform output power, and uniform modulation performance. As a result, eight wavelengths with a wavelength spacing of 0.5 nm are tuned by the heater, with a thermal tuning efficiency of 5.7 nm/W. The side mode suppress ratios kept above 45 dB and the output power decreased within 2 dB. The integrated SOA can amplify the output power to 27 mW at a bias current of 120 mA. The 3-dB bandwidth of the electroabsorption modulator is above 22 GHz, and clear eye diagrams for both the 10 Gb/s and 25 Gb/s NRZ modulation are obtained for the tuned wavelength. The proposed wavelength-tunable EML provides a solution for the tunable transmitters used in the DWDM systems.