title: Whispering-gallery mode resonators for highly unidirectional laser action.
abstract: Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with a wavelength-size notch at the boundary, which support in-plane highly unidirectional laser emission from WGMs. The notch acts as a small scatterer such that the Q factor of the WGMs is still very high. Using midinfrared (λ ∼ 10 μm) injection quantum cascade lasers as a model system, an in-plane beam divergence as small as 6 deg with a peak optical power of ∼5 mW at room temperature has been demonstrated. The beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of this resonator design. The latter is scalable to the visible and the near infrared, thus opening the door to very low-threshold, highly unidirectional microcavity diode lasers.
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, 9 Oxford Street, Cambridge, MA 02138, USA.
authors.forename: Qi Jie
authors.initials: QJ
authors.lastname: Wang
authors.forename: Changling
authors.initials: C
authors.lastname: Yan
authors.forename: Nanfang
authors.initials: N
authors.lastname: Yu
authors.forename: Julia
authors.initials: J
authors.lastname: Unterhinninghofen
authors.forename: Jan
authors.initials: J
authors.lastname: Wiersig
authors.forename: Christian
authors.initials: C
authors.lastname: Pflügl
authors.forename: Laurent
authors.initials: L
authors.lastname: Diehl
authors.forename: Tadataka
authors.initials: T
authors.lastname: Edamura
authors.forename: Masamichi
authors.initials: M
authors.lastname: Yamanishi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Kan
authors.forename: Federico
authors.initials: F
authors.lastname: Capasso
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D007834:Lasers; D008027:Light; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D055096:Optical Devices; D012031:Refractometry / Q000295:instrumentation*; D012542:Scattering, Radiation