Widely Tunable Narrow-Linewidth Monolithically Integrated External-Cavity Semiconductor Lasers

We theoretically analyze, design, and measure the performance of a semiconductor laser with a monolithically integrated external cavity. A ~4 cm long on-chip cavity is made possible by a low-loss silicon waveguide platform. We show tuning in excess of 54 nm in the O-band as well as significant reduction in laser linewidth due to controlled feedback from the external cavity. The measured linewidth in full tuning range is below 100 kHz and the best results are around 50 kHz. Approaches to further improve the performance of such laser architectures are described.