Current-Tuned Tunable In-Series DFB Laser Array Assisted With Thin Film Heater

In this letter, we propose and demonstrate a tunable in-series distributed feedback (DFB) laser array, and the wavelength is continuously tuned with the assistance of the monolithically integrated thin-film heater. Compared with an in-parallel laser array with an optical combiner, the proposed in-series DFB laser array avoids significant power loss resulting from the optical combiner. The three-section structure is utilized to suppress the grating crosstalk among the in-series laser array and guarantees single-mode stabilities. Besides, the reconstruction-equivalent-chirp technique is utilized to simplify grating fabrication and enhance the precise control of the grating phase. Four lasers with wavelength spacings of 2.4 nm are integrated into the in-series laser array and the Ti/Pt thin film heaters are monolithically integrated near the waveguides of each laser unit. The wavelength of the proposed structure is coarsely tuned by selecting the working laser and finely tuned by adjusting the injection current to the laser unit and the thin-film heaters. 9.6 nm continuous wavelength tuning range and fast wavelength tuning are obtained for the proposed in-series laser array without adjusting the temperature of the thermal-electric cooler (TEC). The proposed structure provides a solution for the wavelength tunable laser, which is promised to be used in the dense wavelength division multiplexing (DWDM) systems.