Widely-Tunable Ring-Resonator Semiconductor Lasers

Chip-scale widely-tunable lasers are important for both communication and sensing applications. They have a number of advantages, such as size, weight, and cost compared to mechanically tuned counterparts. Furthermore, they allow for integration in more complex integrated photonic chips to realize added functionality. Here we give an extensive overview of such lasers realized by utilizing ring resonators inside the laser cavity. Use of ring resonators for tuning allows for wide-tunability by exploiting the Vernier effect, and at the same time improves the laser linewidth, as effective cavity length is increased at ring resonance. In this review, we briefly introduce basic concepts of laser tuning using ring resonators. Then, we study a number of laser cavity configurations that utilize two ring resonators, and compare their tuning performance. We introduce a third ring resonator to the laser cavity, study three different cavity configurations utilizing three ring resonators, and select the optimal one, for which we show that laser tuning is straightforward, provided there are monitor photodetectors on-chip. Finally, we give a literature overview showing superior linewidth performance of ring-based widely-tunable lasers.