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The Control of the gain and loss in microcavities, especially microrings, and discs, plays a crucial role in harnessing the excited modes in these types of microlasers. In multi-microring configurations, the Vernier effect eliminates various excited modes within the system, while simultaneously strengthening and producing many latitudinal modes. The implementation of the spectral Vernier effect involves the utilization of two coupled asymmetric microrings to enhance the effective free spectral range (FSR). By carefully balancing the gain/loss ratio and breaking parity-time symmetry, these latitudinal modes can be extensively suppressed, resulting in the single-mode lasing operation. Here, we have successfully demonstrated that wavelength-selective single-frequency lasing can be achieved in structures consisting of two coupled size-mismatched microrings by simultaneously employing the Vernier effect and broken parity-time (PT) symmetry. By controlling the gain/loss ratio through pump variations, the gain can adapt to changes in single-mode lasing wavelength, while the loss effectively suppresses numerous excited modes, leaving only a dominant mode. Thanks to gap engineering, the single-mode lasing based on broken parity-time symmetry at different wavelengths occurs by changing the air gap between two symmetric microrings. The proposed structures have been thoroughly analyzed both experimentally and numerically. Our findings can contribute to a deeper understanding of the spectral modulation process in coupled microrings lasers, offering valuable insights for future research in this field.

Chalcogenide (As2S3) is a material with promising applications in integrated photonics. This material has the potential for low-threshold, compact, and high-coherence light sources. Our team has developed a chalcogenide-based distributed feedback (DFB) laser using a ridge polymer waveguide structure, incorporating a 500 nm As2S3 grating as the wavelength selective element. With precise engineering of the DFB laser structure, we have achieved single-mode lasing with an 18 nJ lasing threshold and a side mode suppression ratio (SMSR) of 28 dB. Additionally, we have found that the single-mode lasing persists over a wide range of pump power energy. To validate our experimental results, we performed a numerical simulation of the proposed structure, which confirmed experimental results.