Single Mode Semiconductor Ring Laser with 20 cm–1 Continuous Tuning at 6.8 μm

Broadband mid infrared spectroscopy enables simultaneous probing of multiple molecules but requires light sources capable of tuning over a broad range. Single mode tunable ring lasers are highly attractive for spectroscopic sensing, as they combine compactness with the ability to smoothly tune over spectral bandwidths exceeding those of distributed feedback lasers. In this work, we demonstrate a single unidirectional ring laser that achieves continuous single mode tuning over 20.43 cm–1 (93 nm) in continuous-wave operation at room temperature. This performance is enabled by the cavity shape that increases the T0 of the material by more than 80 K, thereby extending the accessible thermal tuning range. The resulting operating regime is fully compatible with wavelength modulation spectroscopy, a widely adopted technique that offers high sensitivity and robustness for trace-gas detection and other spectroscopic applications. The substantial increase in the tuning range of a single ring represents a key step towards scalable ring-array architectures, in which multiple rings could be combined to cover the majority of the available gain bandwidth and enable broadband, high-resolution on-chip spectroscopy.