8 research outputs found
Birefringence of GaN/AlGaN optical waveguides
This is the published version. Copyright © 2003 American Institute of PhysicsWe have experimentally studied the birefringence of wurtzite GaNgrown on a sapphire substrate. The measurements were done with single-mode GaN/AlGaN planar optical waveguides on c-plane grownheterostructure films. The refractive indices were found to be different for signal optical field perpendicular or parallel to the crystal c axis (n⊥≠n∥). More importantly, we found an approximately 10% change in index difference Δn=n∥−n⊥ with variation of the waveguide orientation in the a–b plane, and a 60° periodicity was clearly observed. This is attributed to the hexagonal structure of nitride materials
An Anchor-Point Based Image-Model for Room Impulse Response Simulation with Directional Source Radiation and Sensor Directivity Patterns
The image model method has been widely used to simulate room impulse
responses and the endeavor to adapt this method to different applications has
also piqued great interest over the last few decades. This paper attempts to
extend the image model method and develops an anchor-point-image-model (APIM)
approach as a solution for simulating impulse responses by including both the
source radiation and sensor directivity patterns. To determine the orientations
of all the virtual sources, anchor points are introduced to real sources, which
subsequently lead to the determination of the orientations of the virtual
sources. An algorithm is developed to generate room impulse responses with APIM
by taking into account the directional pattern functions, factional time
delays, as well as the computational complexity. The developed model and
algorithms can be used in various acoustic problems to simulate room acoustics
and improve and evaluate processing algorithms.Comment: 19 pages, 8 figure
GaN-based waveguide devices for long-wavelength optical communications
This is the published version. Copyright © 2003 American Institute of PhysicsRefractive indices of AlxGa1−xN with different Al concentrations have been measured in infrared wavelength regions. Single-mode ridged optical waveguidedevices using GaN/AlGaN heterostructures have been designed, fabricated, and characterized for operation in 1550 nm wavelength window. The feasibility of developing photonic integrated circuits based on III-nitride wide-band-gap semiconductors for fiber-optical communications has been discussed
Efficient Pyramid Channel Attention Network for Pathological Myopia Detection
Pathological myopia (PM) is the leading ocular disease for impaired vision
and blindness worldwide. The key to detecting PM as early as possible is to
detect informative features in global and local lesion regions, such as fundus
tessellation, atrophy and maculopathy. However, applying classical
convolutional neural networks (CNNs) to efficiently highlight global and local
lesion context information in feature maps is quite challenging. To tackle this
issue, we aim to fully leverage the potential of global and local lesion
information with attention module design. Based on this, we propose an
efficient pyramid channel attention (EPCA) module, which dynamically explores
the relative importance of global and local lesion context information in
feature maps. Then we combine the EPCA module with the backbone network to
construct EPCA-Net for automatic PM detection based on fundus images. In
addition, we construct a PM dataset termed PM-fundus by collecting fundus
images of PM from publicly available datasets (e.g., the PALM dataset and ODIR
dataset). The comprehensive experiments are conducted on three datasets,
demonstrating that our EPCA-Net outperforms state-of-the-art methods in
detecting PM. Furthermore, motivated by the recent pretraining-and-finetuning
paradigm, we attempt to adapt pre-trained natural image models for PM detection
by freezing them and treating the EPCA module and other attention modules as
the adapters. The results show that our method with the
pretraining-and-finetuning paradigm achieves competitive performance through
comparisons to part of methods with traditional fine-tuning methods with fewer
tunable parameters.Comment: 12 page