Topological nanorainbow laser

Multiwavelength (or multifrequency) coherent light sources with spatial isolation are essential for diverse applications. Nevertheless, regulating the multiple emission wavelengths in an ultracompact scale is challenging. In this work, we realize a topological nanorainbow laser by exploiting synthetic dimensions in parameter space as a freedom to manipulate the optical resonances in a photonic crystal gain system. The system has spectrally isolated and spatially dispersed topological synthetic modes with near-diffraction-limited mode volumes and appropriately designed high-quality factors. We achieve high-performance nanorainbow lasing with low threshold, broadband spectrum, large spontaneous emission factor (β), and milliwatt output power, simultaneously. These emission features are predetermined by the ultrasmall mode volumes and appropriately designed high-quality factors of the spectrally and spatially isolated topological synthetic modes. This work enables high-performance, spatially multiplexed multiwavelength emission for on-chip photonics, facilitating advances in broadband signal processing, optical computing, and beyond.