Dual-wavelength DFB lasers based on continuous-phase-shift gratings for MMW/THz photomixing

We demonstrate five dual-wavelength DFB lasers based on continuous-phase-shift gratings (CPSGs). The CPSG design preserves an effective coupling coefficient comparable to that of uniform Bragg gratings, while enabling deterministic control of the dual-mode spacing via a global phase ramp implemented in a single lithography step. Beat-note spacings ranging from 50 GHz to 1 THz are achieved, with dual‑mode operation exhibiting a side‑mode suppression ratio (SMSR) above 33 dB over a DFB drive current range exceeding 40 mA, albeit with increased threshold and reduced slope efficiency for the smallest 50 GHz spacing. These results establish CPSG-based dual-wavelength DFB lasers as compact optical beat sources for millimeter-wave/THz photomixing and heterodyne systems.