Cascaded energy transfer for efficient broad-band pumping of high-quality, micro-lasers.

require high-fi nesse, high-quality factor (highQ ) micro-lasers. Such lasers must be exceptionally transparent at their emission wavelength. But if highQ micro lasers exhibit correspondingly weak absorption at the pump wavelengths, they are challenging to excite. Here, we demonstrate micro-ring lasers that exhibit Q > 5.2 × 10 6 and a fi nesse of > 1.8 × 10 4 with a direct-illumination, non-resonant pump. The micro-rings are coated with a combination of three organic dyes. This cascaded combination of near and ultimately far fi eld energy transfer reduces materiallosses by a factor of more than 10 4 , transforming incoherent light to coherent light with high quantum-effi ciency. The operating principle established here is general and can enable fully integrated on-chip, high fi nesse micro lasers without the complications of coupled pump and emitter resonators. The quality factor of a lasing cavity is the ratio between the stored power and the power dissipated by the cavity. [ 9 ] HighQ lasers exhibit quality factors of > 10 6 , equivalent to photon cavity propagation lengths beyond one meter. Thus, in microresonators, a high Q -factor implies many photon cycles in the cavity and a high fi nesse. Such a laser must be based on a low-loss resonator, such as an on-chip toroidal resonator with nearly atomically-perfect surfaces. [ 10 ] Silica-based highQ resonators are particularly attractive, because they are constructed on silicon chips. But there is presently no cost effective way to integrate the optical gain element for a highQ source within the silica-on-silicon based architecture. To date, highQ optical sources have required highly absorptive, lowQ gain media