9 research outputs found
Compute-first optical detection for noise-resilient visual perception
In the context of visual perception, the optical signal from a scene is transferred into the electronic domain by detectors in the form of image data, which are then processed for the extraction of visual information. In noisy and weak-signal environments such as thermal imaging for night vision applications, however, the performance of neural computing tasks faces a significant bottleneck due to the inherent degradation of data quality upon noisy detection. Here, we propose a concept of optical signal processing before detection to address this issue. We demonstrate that spatially redistributing optical signals through a properly designed linear transformer can enhance the detection noise resilience of visual perception tasks, as benchmarked with the MNIST classification. Our idea is supported by a quantitative analysis detailing the relationship between signal concentration and noise robustness, as well as its practical implementation in an incoherent imaging system. This compute-first detection scheme can pave the way for advancing infrared machine vision technologies widely used for industrial and defense applications
Efficiency above the Shockley–Queisser Limit by Using Nanophotonic Effects To Create Multiple Effective Bandgaps With a Single Semiconductor
We present a pure photonic approach
to overcome the Shockley–Queisser
limit. A single material can show different effective bandgap, set
by its absorption spectrum, which depends on its photonic structure.
In a tandem cell configuration constructed from a single material,
one can achieve two different effective bandgaps, thereby exceeding
the Shockley–Queisser limit
Large-Scale Spinning of Silver Nanofibers as Flexible and Reliable Conductors
Conducting
metal nanowires can be assembled into thin films for flexible electronics
and optoelectronics applications including transparent electrodes,
nanocircuits, and electronic skin, however, the junction resistances
and low aspect ratios still limit its performance. Herein we report
high-quality silver nanofibers (AgNFs) synthesized by a gas-assistant
solution spinning method. Compared with traditional Ag nanowires that
usually have lengths below 100 μm, AgNFs are infinitely long
and can be easily assembled into large-scale 2D and 3D flexible conductors
with fused junctions between nanofibers. The AgNF networks showed
high transparency, low sheet resistance (e. g, 6 Ω sq<sup>–1</sup> at ∼97% transparency), and high flexibility as transparent
electrodes, whereas the 3D AgNF sponge could be used as a deformable
and robust 3D conductor
Hybrid Silicon Nanocone–Polymer Solar Cells
Recently, hybrid Si/organic solar cells have been studied
for low-cost
Si photovoltaic devices because the Schottky junction between the
Si and organic material can be formed by solution processes at a low
temperature. In this study, we demonstrate a hybrid solar cell composed
of Si nanocones and conductive polymer. The optimal nanocone structure
with an aspect ratio (height/diameter of a nanocone) less than two
allowed for conformal polymer surface coverage via spin-coating while
also providing both excellent antireflection and light trapping properties.
The uniform heterojunction over the nanocones with enhanced light
absorption resulted in a power conversion efficiency above 11%. Based
on our simulation study, the optimal nanocone structures for a 10
μm thick Si solar cell can achieve a short-circuit current density,
up to 39.1 mA/cm<sup>2</sup>, which is very close to the theoretical
limit. With very thin material and inexpensive processing, hybrid
Si nanocone/polymer solar cells are promising as an economically viable
alternative energy solution
Extraordinary Photoluminescence and Strong Temperature/Angle-Dependent Raman Responses in Few-Layer Phosphorene
Phosphorene is a new family member of two-dimensional materials. We observed strong and highly layer-dependent photoluminescence in few-layer phosphorene (two to five layers). The results confirmed the theoretical prediction that few-layer phosphorene has a direct and layer-sensitive band gap. We also demonstrated that few-layer phosphorene is more sensitive to temperature modulation than graphene and MoS<sub>2</sub> in Raman scattering. The anisotropic Raman response in few-layer phosphorene has enabled us to use an optical method to quickly determine the crystalline orientation without tunneling electron microscopy or scanning tunneling microscopy. Our results provide much needed experimental information about the band structures and exciton nature in few-layer phosphorene
Extreme Light Management in Mesoporous Wood Cellulose Paper for Optoelectronics
Wood fibers possess natural unique
hierarchical and mesoporous
structures that enable a variety of new applications beyond their
traditional use. We dramatically modulate the propagation of light
through random network of wood fibers. A highly transparent and clear
paper with transmittance >90% and haze <1.0% applicable for
high-definition
displays is achieved. By altering the morphology of the same wood
fibers that form the paper, highly transparent and hazy paper targeted
for other applications such as solar cell and antiglare coating with
transmittance >90% and haze >90% is also achieved. A thorough
investigation
of the relation between the mesoporous structure and the optical properties
in transparent paper was conducted, including full-spectrum optical
simulations. We demonstrate commercially competitive multitouch touch
screen with clear paper as a replacement for plastic substrates, which
shows excellent process compatibility and comparable device performance
for commercial applications. Transparent cellulose paper with tunable
optical properties is an emerging photonic material that will realize
a range of much improved flexible electronics, photonics, and optoelectronics
Two-Dimensional Chalcogenide Nanoplates as Tunable Metamaterials via Chemical Intercalation
New
plasmonic materials with tunable properties are in great need
for nanophotonics and metamaterials applications. Here we present
two-dimensional layered, metal chalcogenides as tunable metamaterials
that feature both dielectric photonic and plasmonic modes across a
wide spectral range from the infrared to ultraviolet. The anisotropic
layered structure allows intercalation of organic molecules and metal
atoms at the van der Waals gap of the host chalcogenide, presenting
a chemical route to create heterostructures with molecular and atomic
precision for photonic and plasmonic applications. This marks a departure
from a lithographic method to create metamaterials. Monochromated
electron energy-loss spectroscopy in a scanning transmission electron
microscope was used to first establish the presence of the dielectric
photonic and plasmonic modes in M<sub>2</sub>E<sub>3</sub> (M = Bi,
Sb; E = Se, Te) nanoplates and to observe marked changes in these
modes after chemical intercalation. We show that these modal properties
can also be tuned effectively by more conventional methods such as
thickness control and alloy composition of the nanoplates
Two-Dimensional Chalcogenide Nanoplates as Tunable Metamaterials via Chemical Intercalation
New
plasmonic materials with tunable properties are in great need
for nanophotonics and metamaterials applications. Here we present
two-dimensional layered, metal chalcogenides as tunable metamaterials
that feature both dielectric photonic and plasmonic modes across a
wide spectral range from the infrared to ultraviolet. The anisotropic
layered structure allows intercalation of organic molecules and metal
atoms at the van der Waals gap of the host chalcogenide, presenting
a chemical route to create heterostructures with molecular and atomic
precision for photonic and plasmonic applications. This marks a departure
from a lithographic method to create metamaterials. Monochromated
electron energy-loss spectroscopy in a scanning transmission electron
microscope was used to first establish the presence of the dielectric
photonic and plasmonic modes in M<sub>2</sub>E<sub>3</sub> (M = Bi,
Sb; E = Se, Te) nanoplates and to observe marked changes in these
modes after chemical intercalation. We show that these modal properties
can also be tuned effectively by more conventional methods such as
thickness control and alloy composition of the nanoplates
Enhanced Performance of Ge Photodiodes <i>via</i> Monolithic Antireflection Texturing and α‑Ge Self-Passivation by Inverse Metal-Assisted Chemical Etching
Surface
antireflection micro and nanostructures, normally formed
by conventional reactive ion etching, offer advantages in photovoltaic
and optoelectronic applications, including wider spectral wavelength
ranges and acceptance angles. One challenge in incorporating these
structures into devices is that optimal optical properties do not
always translate into electrical performance due to surface damage,
which significantly increases surface recombination. Here, we present
a simple approach for fabricating antireflection structures, with
self-passivated amorphous Ge (α-Ge) surfaces, on single crystalline
Ge (c-Ge) surface using the inverse metal-assisted chemical etching
technology (I-MacEtch). Vertical Schottky Ge photodiodes fabricated
with surface structures involving arrays of pyramids or periodic nano-indentations
show clear improvements not only in responsivity, due to enhanced
optical absorption, but also in dark current. The dark current reduction
is attributed to the Schottky barrier height increase and self-passivation
effect of the i-MacEtch induced α-Ge layer formed on top of
the c-Ge surface. The results demonstrated in this work show that
MacEtch can be a viable technology for advanced light trapping and
surface engineering in Ge and other semiconductor based optoelectronic
devices