We review recent demonstration of stimulated Brillouin scattering in a chalcogenide photonic chip and its application to
optical and microwave signal processing tasks. The interaction between light and sound via stimulated Brillouin scattering
(SBS) was exploited in chalcogenide photonic circuits to achieve on-chip SBS slow and fast light, microwave photonic
filters, and dynamic gratings using travelling-wave geometry. Using a ring-resonator geometry, photonic-chip based
Brillouin laser was demonstrated.
The ability to control the speed of light on an optical chip is fundamental to the development of nanophotonic components for alloptical
signal processing and sensing [1-7]. However this is a significant challenge, because chip-scale waveguides require very large
changes in group index (Δn<sub>g</sub>) to achieve appreciable pulse delays. Here, we use Stimulated Brillouin Scattering (SBS) to report the
demonstration of on-chip slow, fast and negative group velocities with Δn<sub>g</sub> ranging from −44 to +130, and delays of up to 23ns at a
pump power of ~300mW and propagation length of 7cm. These results are obtained using a highly-nonlinear chalocogenide (As<sub>2</sub>S<sub>3</sub>)
rib waveguide, in which the confinement of both photons and phonons results in strong interaction. SBS can be used to achieve
controllable pulse delays at room temperature over a large wavelength and signal-bandwidth . These results open up a new set of
photonic applications ranging from microwave photonics  to spectrometry .
We report the first demonstration of on-chip stimulated Brillouin scattering (SBS). SBS is characterized in a
chalcogenide (As<sub>2</sub>S<sub>3</sub>) photonic chip where the measured Brillouin shift and full-width at half-maximum (FWHM)
linewidth are 7.7 GHz and 34 MHz respectively. The measured Brillouin gain coefficient (g<sub>B</sub>) is 0.715 x 10<sup>-9</sup> m/W, consistent with the theoretical estimate.
On-chip, all-optical quantization based on pulse spectral broadening in a 6 cm long chalcogenide waveguide and
subsequent filtering is analyzed. Transfer function is obtained for an 8-level quantizer using 2 nm bandwidth filters.
Matrix transformation is used to encode the quantized data into a gray-code. An all-optical implementation of the matrix
transformation encoder is proposed based on all-optical Exclusive-OR (XOR) gate. Broad bandwidth supercontinuum
generation in a chalcogenide waveguide and optical XOR gate based encoder paves the way for ultra-high bandwidth,
high-resolution all-optical analog-to-digital conversion chip.
We present the methodology for designing the optimal gain profiles
for slow-light systems under the given system constraints. Optimal
system designs for the multiple Lorentzian gain lines make the gain
spectrum uniform over larger bandwidth compared to the single-line
gain system. The design procedure for the multiple-line gain systems
is modified to make the gain spectrum uniform over arbitrarily broad
bandwidth and applied to the design of the gain-only and
gain+absorption slow-light media. The optimization of the
triple-line gain system improves the delay-bandwidth product 1.7
times the delay-bandwidth product for the single-line gain system.
For the broadband slow-light system, the optimal gain + absorption
design and the optimal gain-only design improve the fractional delay
performance by factors of 1.8 and 1.4, respectively, compared to the
Gaussian noise pump broadened (GNPB) system.