Narrow linewidth 894 nm distributed feedback lasers with laterally-coupled ridge-waveguide surface gratings fabricated using nanoimprint lithography

The paper presents the modelling and design particularities of laterally-coupled distributed feedback lasers (LC-DFB), the fabrication process, involving a highly productive and cost-effective UV-nanoimprint lithography technique, and the characteristics obtained up to now for the LC-DFB lasers fabricated for pumping Cesium atomic clocks. 550 µm long LC-DFB lasers, emitting at 894 µm, had 10 mA threshold currents and maintained over 40dB side-mode-suppression-ratio between 10 and 100°C. The measured self-homodyne spectrum indicated a linewidth below 1.3 MHz for AR/HR-coated 1000 µm long LC-DFB lasers and the simulations indicate that the use of phase-shift sections could reduce the linewidth below 250 kHz.