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Significance statement
The sub-millimeter size resonator shown in the Figure is made from lithium niobate by mechanical polishing. It has the quality factor approaching 100 million, which facilitates unusually strong nonlinear interaction between optical fields. This interaction enables various frequency conversion processes as well as other nonlinear-dynamical behaviors that can be used e.g. for implementation of an optical transistor at very low powers or pulse energies. All such processes require the phase matching of coupled optical modes. Phase matching conditions in rotation-symmetric WGM resonators are different from those in bulk crystals or linear resonators. In particular, phase matching in WGM resonators allows for a larger selection of coupled wavelengths. In this paper we study the phase matching for sum-frequency generation (780 nm + 1560 nm to 520 nm) in WGM resonators and demonstrate this process at sub-milliwatt optical powers. This research has allowed us to achieve modulation of light by light and hence demonstrate the optical transistor functionality at 10-100 pJ optical pulse powers, which has been reported in the follow-on publication [“Progress towards interaction-free all-optical devices”, D.V. Strekalov, A.S. Kowligy, Y.-P. Huang, and P. Kumar, Phys. Rev. A 89, 063820 (2014)].
New J. Phys. 16 053025, 2014.
Dmitry V Strekalov1, Abijith S Kowligy2, Yu-Ping Huang2 and Prem Kumar2
1 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, 91109-8099 California, USA .
2 Center for Photonic Communication and Computing, EECS Department, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3118, USA.
ABSTRACT
We demonstrate sum-frequency generation between a telecom wavelength and the Rb D2 line, achieved through natural phase matching in a nonlinear whispering gallery mode resonator. Due to the strong optical field confinement and ultra high Q of the cavity, the process saturates already at sub-mW pump peak power, at least two orders of magnitude lower than in existing waveguide-based devices. The experimental data are in agreement with the nonlinear dynamics and phase matching theory based on spherical geometry. Our experimental and theoretical results point toward a new platform for manipulating the color and quantum states of light waves for applications such as atomic memory based quantum networking and logic operations with optical signals.
