We report the first (to our knowledge) demonstration of photonic chip based tunable slow and fast light via stimulated Brillouin scattering. Slow, fast, and negative group velocities were observed in a 7 cm long chalcogenide (As(2)S(3)) rib waveguide with a group index change ranging from ~-44 to +130, which results in a maximum delay of ~23 ns at a relatively low gain of ~23 dB. Demonstration of large tunable delays in a chip scale device opens up applications such as frequency sensing and true-time delay for a phased array antenna, where integration and delays ~10 ns are highly desirable.
[Show abstract][Hide abstract] ABSTRACT: We present the first demonstration of a narrow linewidth, waveguide-based
Brillouin laser which is enabled by large Brillouin gain of a chalcogenide
chip. The waveguides are equipped with vertical tapers for low loss coupling.
Due to optical feedback for the Stokes wave, the lasing threshold is reduced to
360 mW, which is 5 times lower than the calculated single-pass Brillouin
threshold for the same waveguide. The slope efficiency of the laser is found to
be 30% and the linewidth of 100 kHz is measured using a self-heterodyne method.
"We choose a rectangular waveguide with n = 2.37, width 4 μm and height 2 μm, embedded in an infinite matrix material with refractive index n = 1.44 (see Fig. 8a). This waveguide has dimensions and optical properties that are comparable to those used in recent SBS experiments   . The velocity of sound in the core is kept fixed at that of chalcogenide v 1 = 2600ms −1 , and we examine the SBS gain for different cladding materials. "
[Show abstract][Hide abstract] ABSTRACT: We examine the effect of acoustic mode confinement on Stimulated Brillouin
Scattering in optical waveguides that consist of a guiding core embedded in a
solid substrate. We find that SBS can arise due to coupling to acoustic modes
in three different regimes. First, the acoustic modes may be guided by total
internal reflection; in this case the SBS gain depends directly on the degree
of confinement of the acoustic mode in the core, which is in turn determined by
the acoustic V-parameter. Second, the acoustic modes may be leaky, but may
nevertheless have a sufficiently long lifetime to have a large effect on the
SBS gain; the lifetime of acoustic modes in this regime depends not only on the
contrast in acoustic properties between the core and the cladding, but is also
highly dependent on the waveguide dimensions. Finally SBS may occur due to
coupling to free modes, which exist even in the absence of acoustic
confinement; we find that the cumulative effect of coupling to these
non-confined modes results in significant SBS gain. We show how the different
acoustic properties of core and cladding lead to these different regimes, and
discuss the feasibility of SBS experiments using different material systems.
Journal of the Optical Society of America B 08/2013; 30(10). DOI:10.1364/JOSAB.30.002657 · 1.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report the first demonstration of a photonic chip based dynamically reconfigurable, widely tunable, narrow pass-band, high Q microwave photonic filter (MPF). We exploit stimulated Brillouin scattering (SBS) in a 6.5 cm long chalcogenide (As<sub>2</sub>S<sub>3</sub>) photonic chip to demonstrate a MPF that exhibited a high quality factor of ~520 and narrow bandwidth and was dynamically reconfigurable and widely tunable. It maintained a stable 3 dB bandwidth of 23 ± 2MHz and amplitude of 20 ± 2 dB over a large frequency tuning range of 2-12 GHz. By tailoring the pump spectrum, we reconfigured the 3 dB bandwidth of the MPF from ~20 MHz to ~40 MHz and tuned the shape factor from 3.5 to 2 resulting in a nearly flat-topped filter profile. This demonstration represents a significant advance in integrated microwave photonics with potential applications in on-chip microwave signal processing for RADAR and analogue communications.
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