Continuously and widely tunable semiconductor ring lasers

Tunable semiconductor lasers are indispensable for applications ranging from spectroscopy to telecommunications, yet achieving continuous, mode-hop-free tuning across broad frequency ranges in a compact, robust device remains challenging. Here, we present a ring-array quantum cascade laser (QCL) architecture that combines the single-mode, smooth tuning of distributed feedback lasers with an extended tuning range greater than 10cm\textminus1, all within a compact chip-scale format. Our ring-array laser employs multiple small, independently addressable ring QCLs. These rings, coupled to a shared bus waveguide, have different radii, resulting in distinct lasing frequencies. This configuration enables multi-ring spectral sweeps with stable emission facilitated by unidirectional lasing. In contrast to traditional tunable lasers, our device achieves mode-hop-free tuning over broad bandwidths, is resilient under high levels of optical feedback, and supports beam combining for broadband spectral coverage, resulting in a combined tuning range of 33cm\textminus1 from three different rings. This versatile platform offers a pathway for scalable, compact spectroscopic sources, with potential applications across the mid-infrared and beyond.