Abstract
A generic model is introduced to describe the lasing
characteristics of continuous-wave circular and racetrack-shaped
ring Raman lasers based on micro- and nano-scale silicon waveguides.
This model explicitly takes into account the effective Raman gain
values for forward and backward lasing in the ring resonator, the
presence of a bus waveguide in which the Stokes laser radiation
coupled out from the ring undergoes additional Raman amplification,
and the spatial gain variations for different polarization states in
the ring structure. I show numerically that ring lasers based on
micro-scale waveguides generate unidirectional lasing in either the
forward or backward direction because of an asymmetry in nonlinear
losses, whereas those based on nanowires yield only backward lasing
due to a non-reciprocity in effective gain. Furthermore, the model
indicates that backward lasing can yield a significantly higher
Stokes output at the bus waveguide facets than lasing in the forward
direction. Finally, considering a TE-polarized pump input for a
(100) grown silicon ring Raman laser, I demonstrate numerically that
the polarization state of the Stokes lasing radiation strongly
depends on whether micro-scale or nano-scale waveguides are
used.
© 2011 IEEE
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