Study of cascaded tunable DFB semiconductor laser with wide tuning range and high single mode yield based on equivalent phase shift technique

The tunable distributed feedback (DFB) semiconductor lasers with cascaded configuration were designed and fabricated using equivalent phase shift (EPS) technique. 32-wavelength division multiplexing (WDM) channels with 50-GHz and 100-GHz wavelength spacing were experimentally demonstrated. In such a tunable laser, single mode operation can be ensured by introducing EPS and the wavelength tuning can be realized by cascaded sections with specific sampling periods combining with chip heating. The proposed approach has some advantages such as good single mode property, low fabrication cost and feasibility of monolithic integration. The experimental results show that the tuning range can be nearly up to 25 nm and the side mode suppression ratios (SMSRs) of most channels are above 40 dB. The proposed laser should be promising for cost-effective applications in WDM systems.