Mode-Locked DBR and DFB Lasers With Multiple Phase-Shifted Gratings for THz Generation

We propose mode-locked distributed Bragg reflector (DBR) and distributed feedback (DFB) lasers based on multiple phase-shift gratings (MPSGs) for terahertz (THz) signal generation, with the latter incorporating an equivalent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula>-phase shift. By integrating optimized MPSGs, we achieve multi-channel lasing with uniform reflectivity and dense channel spacing. Modelocked DBR lasers operating at THz frequencies of 150 GHz, 400 GHz, 800 GHz, and 1.2 THz have been demonstrated, as confirmed by second harmonic generation measurements. Additionally, a 200 GHz mode-locked DFB laser was realized. Amplified by an erbium-doped fiber amplifier (EDFA), the modelocked DFB laser output was injected into a photoconductive antenna (PCA) to generate THz signals, with the measured power reaching 19.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>W. These results highlight the potential of MPSGbased mode-locked lasers for compact and efficient THz generation systems.