COMBO aims to unveil the opportunity to develop coherent sources in the blue domain by use of whispering-gallery mode resonators. The ambition of the COMBO project is to develop a WGM resonator platform in the blue range (405-480 nm) for the demonstration of compact single frequency laser diodes and blue Kerr frequency combs. The project is divided in three main objectives. The first objective will draw up a panorama of the linear and nonlinear properties of WGMR in the blue range. A particular focus will be done on fluoride crystalline resonators identified as best candidates for the realization of either linear or nonlinear optical functions. Indeed, the second objective consists in the demonstration of WGMR based laser stabilization and narrowing taking advantage of the impressive linear properties of such resonators as a large Q factor in excess to 109 and a Finesse over 105. The third objective involves the study of degenerate four-wave mixing leading to frequency comb generation in high-Q WGMRs.

Two main breakthroughs are targeted: the first demonstration of a Kerr frequency comb in the blue range using a high-Q resonator; and an electrically-pumped sub-kHz linewidth single mode Fabry-Perot (SFP) laser based on resonant optical feedback. Combining these two contributions should yield to the demonstration of a compact blue Kerr frequency comb generator.