Focused ion beam engraved phase-shifted Bragg grating microcavity resonator

A cavity with minimal-volume confinement was created in a microfiber engraving a high-contrast phase-shifted Bragg grating by focused ion beam. While waveguiding by the air/silica boundary provides a diffraction-limited 2D confinement, the grating introduces the third degree of confinement. Theoretical simulations verified the phase-shifted cavity confinement and showed a reasonable agreement with the experimental demonstration. This cavity can find a variety of applications ranging from sensing to quantum dynamic experiments

Fast-response high-temperature microfiber coupler tip thermometer

A compact temperature sensor based on a broadband microfiber coupler tip is demonstrated. The thermometer dynamic range spans from room temperature to 1511°C with a response time of tens of ms. This is the highest temperature measured with a silica optical fiber device. A resolution of 0.66°C was achieved for a coupler tip diameter of ~12.56 µm. Better resolution can be achieved with smaller size microfiber coupler tips

Understanding Convolution for Semantic Segmentation

Recent advances in deep learning, especially deep convolutional neural networks (CNNs), have led to significant improvement over previous semantic segmentation systems. Here we show how to improve pixel-wise semantic segmentation by manipulating convolution-related operations that are of both theoretical and practical value. First, we design dense upsampling convolution (DUC) to generate pixel-level prediction, which is able to capture and decode more detailed information that is generally missing in bilinear upsampling. Second, we propose a hybrid dilated convolution (HDC) framework in the encoding phase. This framework 1) effectively enlarges the receptive fields (RF) of the network to aggregate global information; 2) alleviates what we call the "gridding issue" caused by the standard dilated convolution operation. We evaluate our approaches thoroughly on the Cityscapes dataset, and achieve a state-of-art result of 80.1% mIOU in the test set at the time of submission. We also have achieved state-of-the-art overall on the KITTI road estimation benchmark and the PASCAL VOC2012 segmentation task. Our source code can be found at https://github.com/TuSimple/TuSimple-DUC .Comment: WACV 2018. Updated acknowledgements. Source code: https://github.com/TuSimple/TuSimple-DU

A Fast-Response, High- Temperature Microfiber Coupler Thermometer

A compact temperature sensor based on a broadband microfiber coupler tip is demonstrated. The thermometer dynamic range spans from room temperature to 1511 with a response time of tens of milliseconds. This is the highest temperature measured with a silica optical fiber device. A resolution of 0.66 was achieved for a coupler tip diameter of . Better resolution can be achieved with smaller sized microfiber coupler tips

Single-mode tuneable laser operation of hybrid microcavities based on CdSe/CdS core/shell colloidal nanorods on silica microspheres

Colloidal core/shell semiconductor nanonorystals have generated a great deal of interest as gain media in recent years due to a number of salient properties originating from their small size and the associated quantum confinement [1]. These include low-threshold and temperature-insensitive lasing, reduced trapping of excited carriers, and the possibility to alleviate non-radiative Auger recombination by engineering the wavefunction distributions of the electrons, and holes within their volume. Here, single-mode, tuneable operation of fiber-coupled hybrid lasers based on colloidal CdSe/CdS core/shell nanorods on silica microspheres is reported

Single-mode tunable laser emission in the single-exciton regime from colloidal nanocrystals

Whispering-gallery-mode resonators have been extensively used in conjunction with different materials for the development of a variety of photonic devices. Among the latter, hybrid structures, consisting of dielectric microspheres and colloidal core/shell semiconductor nanocrystals as gain media, have attracted interest for the development of microlasers and studies of cavity quantum electrodynamic effects. Here we demonstrate single-exciton, single-mode, spectrally tuned lasing from ensembles of optical antenna-designed, colloidal core/shell CdSe/CdS quantum rods deposited on silica microspheres. We obtain single-exciton emission by capitalizing on the band structure of the specific core/shell architecture that strongly localizes holes in the core, and the two-dimensional quantum confinement of electrons across the elongated shell. This creates a type-II conduction band alignment driven by coulombic repulsion that eliminates non-radiative multi-exciton Auger recombination processes, thereby inducing a large exciton–bi-exciton energy shift. Their ultra-low thresholds and single-mode, single-exciton emission make these hybrid lasers appealing for various applications, including quantum information processing

Photonic crystal fiber half-taper probe based refractometer

A compact singlemode - photonic crystal fiber - singlemode fiber tip (SPST) refractive index sensor is demonstrated in this paper. A CO2 laser cleaving technique is utilised to provide a clean-cut fiber tip which is then coated by a layer of gold to increase reflection. An average sensitivity of 39.1 nm/RIU and a resolvable index change of 2.56 x 10-4 are obtained experimentally with a ~3.2 µm diameter SPST. The temperature dependence of this fiber optic sensor probe is presented. The proposed SPST refractometer is also significantly less sensitive to temperature and an experimental demonstration of this reduced sensitivity is presented in the paper. Because of its compactness, ease of fabrication, linear response, low temperature dependency, easy connectivity to other fiberized optical components and low cost, this refractometer could find various applications in chemical and biological sensing