Whispering-gallery mode resonators for highly unidirectional laser action

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 la...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 107; no. 52; pp. 22407 - 22412
Main Authors Wang, Qi Jie, Yan, Changling, Yu, Nanfang, Unterhinninghofen, Julia, Wiersig, Jan, Pflügl, Christian, Diehl, Laurent, Edamura, Tadataka, Yamanishi, Masamichi, Kan, Hirofumi, Capasso, Federico
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 28.12.2010
National Acad Sciences
SeriesFrom the Cover
Subjects
Collimation
Computer-Aided Design
Diodes
Ellipses
Emissions
Equipment Design
Laser beams
Lasers
Light
Microscopy, Electron, Scanning
Models, Theoretical
Optical Devices
Optical properties
Physical Sciences
Pumping
Q factors
Refractometry - instrumentation
Resonance scattering
Resonators
Scattering
Scattering, Radiation
Wavelengths
Whispering gallery waves
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Summary: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.
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3Present address: Changchun University of Science and Technology, Changchun, 130022, China.
Contributed by Federico Capasso, October 21, 2010 (sent for review August 1, 2010)
2Present address: School of Electrical and Electronic Engineering and School Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore.
1Q.J.W. and C.Y. contributed equally to this work.
Author contributions: Q.J.W., C.Y., and N.Y. designed research; Q.J.W., C.Y., N.Y., J.U., J.W., C.P., L.D., T.E., M.Y., and H.K. performed research; Q.J.W., C.Y., N.Y., J.U., J.W., C.P., L.D., and F.C. analyzed data; and Q.J.W., C.Y., N.Y., J.U., J.W., and F.C. wrote the paper.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1015386107