Quasi-continuous single-mode tuning of a circularly polarized microcavity laser via the reflection phase

Tunable lasers have garnered significant attention due to their pivotal roles in various fields, such as biomedical imaging, quantum optics, and spectroscopy. Laser tuning has been demonstrated either discretely based on mode-hopping or continuously on the resonator length and refractive index. By taking cholesteric liquid crystals (CLCs) as an example, we demonstrate quasi-continuous wavelength tuning of a circularly polarized microcavity laser, which is a sandwiched structure comprising two CLC layers and an isotropic polymer layer. Its lasing threshold is 1.02 μJ, and full-width at half maximum is 0.15 nm. The tuning range of the emission wavelength is about 7.8 nm for a temperature change of 12 ℃, with a tuning step less than 1.5 nm. The tuning mechanism is clarified by considering the reflection phase properties of the CLC, and the numerical results from the proposed structure comply well with those obtained using the Berreman 4 × 4 matrix method. Our work provides a novel approach for designing tunable microcavity mode lasers, which have promising applications in radar technology, sensing, display technology, and other photonics fields.