Stimulated Raman scattering (SRS) in ultra-high-Q surface-tension-induced
spherical and chip-based toroid microcavities is considered both theoretically
and experimentally. These microcavities are fabricated from silica, exhibit
small mode volume (typically 1000 μm3) and possess whispering-gallery
type modes with long photon storage times (in the range of 100 ns),
significantly reducing the threshold for stimulated nonlinear optical
phenomena. Oscillation threshold levels of less than 100 μ% -Watts of
launched fiber pump power, in microcavities with quality factors of 100 million
are observed. Using a steady state analysis of the coupled-mode equations for
the pump and Raman whispering-gallery modes, the threshold, efficiencies and
cascading properties of SRS in UHQ devices are derived. The results are
experimentally confirmed in the telecommunication band (1550nm) using tapered
optical fibers as highly efficient waveguide coupling elements for both pumping
and signal extraction. The device performance dependence on coupling, quality
factor and modal volume are measured and found to be in good agreement with
theory. This includes analysis of the threshold and efficiency for cascaded
Raman scattering. The side-by-side study of nonlinear oscillation in both
spherical microcavities and toroid microcavities on-a-chip also allows for
comparison of their properties. In addition to the benefits of a wafer-scale
geometry, including integration with optical, electrical or mechanical
functionality, microtoroids on-a-chip exhibit single mode Raman oscillation
over a wide range of pump powers.Comment: 12 pages, 15 figure