80 research outputs found
VCSEL with finite-size high-contrast metastructure
© Copyright 2018 Society of PhotoâOptical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited.High-contrast metastructures like one-dimensional high-contrast gratings (HCGs) are promising to improve the performance of conventional VCSELs, also presenting a basis for new applications. Different from the previous studies where HCGs are always modelled being of infinite size, we studied here the finite-size HCGs, which match the real situation. We observe finite-size HCGs behaving very differently from infinite-size HCGs. The reflectivity of a finitesize HCG strongly depends on the HCG size and the source size. At the same time, the simulation results show, that finite-size HCGs can shape the output beam, and a Gaussian-like reflected wave is typically achieved. Most important the normally incident light is partly redirected to the in-plane direction, showing unidirectional transmission. Monolithically integrated HCG-based optical sensors can be based on this novel effect. An integrable HCG reflector was fabricated with GaInP as the sacrificial layer targeting the application of HCG-VCSEL at 980 nm range. The measured reflectivity agrees well with the calculated reflectivity
Active beam steering enabled by photonic crystal surface emitting laser
Emitting light towards on-demand directions is important for various
optoelectronic applications, such as optical communication, displaying, and
ranging. However, almost all existing directional emitters are assemblies of
passive optical antennae and external light sources, which are usually bulky,
fragile, and with unendurable loss of light power. Here we theoretically
propose and experimentally demonstrate a new conceptual design of directional
emitter, by using a single surface-emitting laser source itself to achieve
dynamically controlled beam steering. The laser is built on photonic crystals
that operates near the band edges in the continuum. By shrinking laser sizes
into tens-of-wavelength, the optical modes quantize in three-dimensional
momentum space, and each of them directionally radiates towards the far-field.
Further utilizing the luminescence spectrum shifting effect under current
injection, we consecutively select a sequence of modes into lasing action and
show the laser maintaining in single mode operation with linewidths at a
minimum of MHz and emitting power of ten milliwatts, and we
demonstrate fast beam steering across a range of in
a time scale of nanoseconds. Our work proposes a novel method for on-chip
active beam steering, which could pave the way for the development of
automotive, industrial, and robotic applications.Comment: 23 pages, 5 figure
OrdinalCLIP: Learning Rank Prompts for Language-Guided Ordinal Regression
This paper presents a language-powered paradigm for ordinal regression.
Existing methods usually treat each rank as a category and employ a set of
weights to learn these concepts. These methods are easy to overfit and usually
attain unsatisfactory performance as the learned concepts are mainly derived
from the training set. Recent large pre-trained vision-language models like
CLIP have shown impressive performance on various visual tasks. In this paper,
we propose to learn the rank concepts from the rich semantic CLIP latent space.
Specifically, we reformulate this task as an image-language matching problem
with a contrastive objective, which regards labels as text and obtains a
language prototype from a text encoder for each rank. While prompt engineering
for CLIP is extremely time-consuming, we propose OrdinalCLIP, a differentiable
prompting method for adapting CLIP for ordinal regression. OrdinalCLIP consists
of learnable context tokens and learnable rank embeddings; The learnable rank
embeddings are constructed by explicitly modeling numerical continuity,
resulting in well-ordered, compact language prototypes in the CLIP space. Once
learned, we can only save the language prototypes and discard the huge language
model, resulting in zero additional computational overhead compared with the
linear head counterpart. Experimental results show that our paradigm achieves
competitive performance in general ordinal regression tasks, and gains
improvements in few-shot and distribution shift settings for age estimation.
The code is available at https://github.com/xk-huang/OrdinalCLIP.Comment: Accepted by NeurIPS2022. Code is available at
https://github.com/xk-huang/OrdinalCLI
DiffTalk: Crafting Diffusion Models for Generalized Audio-Driven Portraits Animation
Talking head synthesis is a promising approach for the video production
industry. Recently, a lot of effort has been devoted in this research area to
improve the generation quality or enhance the model generalization. However,
there are few works able to address both issues simultaneously, which is
essential for practical applications. To this end, in this paper, we turn
attention to the emerging powerful Latent Diffusion Models, and model the
Talking head generation as an audio-driven temporally coherent denoising
process (DiffTalk). More specifically, instead of employing audio signals as
the single driving factor, we investigate the control mechanism of the talking
face, and incorporate reference face images and landmarks as conditions for
personality-aware generalized synthesis. In this way, the proposed DiffTalk is
capable of producing high-quality talking head videos in synchronization with
the source audio, and more importantly, it can be naturally generalized across
different identities without any further fine-tuning. Additionally, our
DiffTalk can be gracefully tailored for higher-resolution synthesis with
negligible extra computational cost. Extensive experiments show that the
proposed DiffTalk efficiently synthesizes high-fidelity audio-driven talking
head videos for generalized novel identities. For more video results, please
refer to \url{https://sstzal.github.io/DiffTalk/}.Comment: Project page https://sstzal.github.io/DiffTalk
Surface passivation of random alloy AlGaAsSb avalanche photodiode
AlGaAsSb attracts significant interest for nearâinfrared avalanche photodiodes (APD). The authors report a twoâorder reduction in the dark current and a sixâtime enhancement of gain in random alloy (RA) AlGaAsSb APD that is surface passivated by conformal coating of Al2O3 via atomic layer deposition (ALD). The dark currents of the APDs with 400â”m diameter (dry etched) at 90% breakdown voltage (0.9 Vbr) are (5.5 ± 0.5) Ă 10â5 A, (2.1 ± 0.4) Ă 10â5 A, and (6.2 ± 0.8) Ă 10â7 A for nonâpassivated, Si3N4 passivated, and Al2O3 passivated devices, respectively. The dark current at a gain of 10 for the Al2O3 passivated device is 1 Ă 10â8 A which is comparable to the reported value for 100â”m diameter mesa diodes passivated by SUâ8. Maximum gain values of 6, 12, and 35 were obtained for nonâpassivated, Si3N4 passivated, and Al2O3 passivated devices, respectively. Moreover, punchâthrough capacitance of 8 pF in a spectral response of 450 to 850 nm was obtained. Thus, Al2O3 passivation can be the best solution for antimonide optoelectronic devices
Hardware-algorithm collaborative computing with photonic spiking neuron chip based on integrated Fabry-P\'erot laser with saturable absorber
Photonic neuromorphic computing has emerged as a promising avenue toward
building a low-latency and energy-efficient non-von-Neuman computing system.
Photonic spiking neural network (PSNN) exploits brain-like spatiotemporal
processing to realize high-performance neuromorphic computing. However, the
nonlinear computation of PSNN remains a significant challenging. Here, we
proposed and fabricated a photonic spiking neuron chip based on an integrated
Fabry-P\'erot laser with a saturable absorber (FP-SA) for the first time. The
nonlinear neuron-like dynamics including temporal integration, threshold and
spike generation, refractory period, and cascadability were experimentally
demonstrated, which offers an indispensable fundamental building block to
construct the PSNN hardware. Furthermore, we proposed time-multiplexed spike
encoding to realize functional PSNN far beyond the hardware integration scale
limit. PSNNs with single/cascaded photonic spiking neurons were experimentally
demonstrated to realize hardware-algorithm collaborative computing, showing
capability in performing classification tasks with supervised learning
algorithm, which paves the way for multi-layer PSNN for solving complex tasks.Comment: 10 pages, 8 figure
Integrative epigenome profiling of 47XXY provides insights into whole genomic DNA hypermethylation and active chromatin accessibility
Klinefelter syndrome (KS, 47XXY) is a disorder characterized by sex chromosomal aneuploidy, which may lead to changes in epigenetic regulations of gene expression. To define epigenetic architectures in 47XXY, we annotated DNA methylation in euploid males (46XY) and females (46XX), and 47XXY individuals using whole genome bisulfite sequencing (WGBS) and integrated chromatin accessbilty, and detected abnormal hypermethylation in 47XXY. Furthermore, we detected altered chromatin accessibility in 47XXY, in particular in chromosome X, using Assay for Transposase-Accessible Chromatin sequencing (ATAC-seq) in cultured amniotic cells. Our results construct the whole genome-wide DNA methylation map in 47XXY, and provide new insights into the early epigenomic dysregulation resulting from an extra chromosome X in 47XXY
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