37 research outputs found
Self-imaging silicon Raman amplifier
We propose a new type of waveguide optical amplifier. The device consists of
collinearly propagating pump and amplified Stokes beams with periodic imaging
of the Stokes beam due to the Talbot effect. The application of this device as
an Image preamplifier for Mid Wave Infrared (MWIR) remote sensing is discussed
and its performance is described. Silicon is the preferred material for this
application in MWIR due to its excellent transmission properties, high thermal
conductivity, high damage threshold and the mature fabrication technology. In
these devices, the Raman amplification process also includes four-wave-mixing
between various spatial modes of pump and Stokes signals. This phenomenon is
unique to nonlinear interactions in multimode waveguides and places a limit on
the maximum achievable gain, beyond which the image begins to distort. Another
source of image distortion is the preferential amplification of Stokes modes
that have the highest overlap with the pump. These effects introduce a tradeoff
between the gain and image quality. We show that a possible solution to this
trade-off is to restrict the pump into a single higher order waveguide mode.Comment: 11 pages, 5 figures and 5 sections. Submitted to Optics Expres
Strong Single- and Two-Photon Luminescence Enhancement by Nonradiative Energy Transfer across Layered Heterostructure
The strong light-matter interaction in monolayer transition metal
dichalcogenides (TMDs) is promising for nanoscale optoelectronics with their
direct band gap nature and the ultra-fast radiative decay of the strongly bound
excitons these materials host. However, the impeded amount of light absorption
imposed by the ultra-thin nature of the monolayers impairs their viability in
photonic applications. Using a layered heterostructure of a monolayer TMD
stacked on top of strongly absorbing, non-luminescent, multi-layer SnSe2, we
show that both single-photon and two-photon luminescence from the TMD monolayer
can be enhanced by a factor of 14 and 7.5, respectively. This is enabled
through inter-layer dipole-dipole coupling induced non-radiative Forster
resonance energy transfer (FRET) from SnSe2 underneath which acts as a
scavenger of the light unabsorbed by the monolayer TMD. The design strategy
exploits the near-resonance between the direct energy gap of SnSe2 and the
excitonic gap of monolayer TMD, the smallest possible separation between donor
and acceptor facilitated by van der Waals heterojunction, and the in-plane
orientation of dipoles in these layered materials. The FRET driven uniform
single- and twophoton luminescence enhancement over the entire junction area is
advantageous over the local enhancement in quantum dot or plasmonic structure
integrated 2D layers, and is promising for improving quantum efficiency in
imaging, optoelectronic, and photonic applications
Harmonic to anharmonic tuning of moir\'e potential leading to unconventional Stark effect and giant dipolar repulsion in WS/WSe heterobilayer
Excitonic states trapped in harmonic moir\'e wells of twisted heterobilayers
is an intriguing testbed. However, the moir\'e potential is primarily governed
by the twist angle, and its dynamic tuning remains a challenge. Here we
demonstrate anharmonic tuning of moir\'e potential in a WS/WSe
heterobilayer through gate voltage and optical power. A gate voltage can result
in a local in-plane perturbing field with odd parity around the high-symmetry
points. This allows us to simultaneously observe the first (linear) and second
(parabolic) order Stark shift for the ground state and first excited state,
respectively, of the moir\'e trapped exciton - an effect opposite to
conventional quantum-confined Stark shift. Depending on the degree of
confinement, these excitons exhibit up to twenty-fold gate-tunability in the
lifetime ( to ns). Also, exciton localization dependent dipolar
repulsion leads to an optical power-induced blueshift of 1 meV/W - a
five-fold enhancement over previous reports.Comment: Accepted in Nature Communication
Mapping Molecular Orientation with Phase Sensitive Vibrationally Resonant Sum-Frequency Generation Microscopy
We demonstrate a phase sensitive, vibrationally resonant sum-frequency generation (PSVR-SFG) microscope that combines high resolution, fast image acquisition speed, chemical selectivity, and phase sensitivity. Using the PSVR-SFG microscope, we generate amplitude and phase images of the second-order susceptibility of collagen I fibers in rat tail tendon tissue on resonance with the methylene vibrations of the protein. We find that the phase of the second-order susceptibility shows dependence on the effective polarity of the fibril bundles, revealing fibrous collagen domains of opposite orientations within the tissue. The presence of collagen microdomains in tendon tissue may have implications for the interpretation of the mechanical properties of the tissue. [Image: see text
Single and Multi-dimensional Integrated optic Photon sources for Quantum communication
We present an on-chip nonlinear optics based correlated and higher dimensional state photon source using silicon hybrid materials. The four-wave mixing process occurring in a ring resonator is used to generate a frequency comb of signal and idler wavelengths corresponding to different resonant wavelengths around the pump resonance. The frequency comb based four-wave mixing process is used to generate higher-dimensional entangled photon pairs. The individual comb lines, into which the correlated photon pairs could be generated leads to higher dimensional entanglement. The ability to generate higher dimensional photon states is advantageous to pack more information for high data rate quantum communication and information processing applications