Whispering Gallery Mode Microresonators for Lasing and Single Nanoparticle Detection

Whispering gallery mode: WGM) microresonators have attracted great interests due to the significantly enhanced light-matter interactions originating from their high quality factors and small mode volumes. They are suitable for a wide range of applications including sensing, lasing, nonlinear optics, and so forth. However, temperature fluctuations as one of the most common environmental noises disturb the cavity resonances and thus degrade the device stability and sensitivity. We introduce a wetting technique to coat the silica resonator with a thin layer of polymer which has the negative thermo-optic coefficient to compensate for the thermal effect in silica, and demonstrate complete thermal compensation. WGM microresonators have shown great promise for ultra-sensitive and label-free chemical and biological sensing by probing the surroundings with evanescent waves leaking out of the resonator. Sensing is achieved by monitoring the shift or splitting of a resonant frequency. The detection limit is determined by the linewidth of the resonant mode which is ultimately limited by material absorption induced loss. To surpass the limit of passive resonators, we report real-time single nanoparticle detection using on-chip WGM microcavity lasers. The ultra-low threshold microlasers are prepared by doping WGM resonators with rare-earth ions through the sol-gel method, and their linewidths are much narrower than the passive counterparts. The detection approach relies on measuring changes in the heterodyne beat note of two split modes originating from splitting of a narrow emission line in the microlaser induced by nanoscale objects. We demonstrate detection of polystyrene and gold nanoparticles as small as 15 nm and 10 nm in radius, respectively, and Influenza A virions by monitoring changes in the beat note of the split lasing modes. The self-heterodyne interferometric method achieved in the on-chip microlaser provides a self-referencing scheme with extraordinary sensitivity, and paves the way for detection and spectroscopy of nano-scale objects using micro/nano lasers

Scatterer induced mode splitting in poly(dimethylsiloxane) coated microresonators

We investigate scatterer induced mode splitting in a composite microtoroidal resonator (Q ~ 10^6) fabricated by coating a silica microtoroid (Q ~ 10^7) with a thin poly(dimethylsiloxane) layer. We show that the two split modes in both coated and uncoated silica microtoroids respond in the same way to the changes in the environmental temperature. This provides a self-referencing scheme which is robust to temperature perturbations. Together with the versatile functionalities of polymer materials, mode splitting in polymer and polymer coated microresonators offers an attractive sensing platform that is robust to thermal noise.Comment: 9 pages, 3 figures, 15 reference

Realization of Analog Wavelet Filter using Hybrid Genetic Algorithm for On-line Epileptic Event Detection

© 2020 The Author(s). This open access work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/.As the evolution of traditional electroencephalogram (EEG) monitoring unit for epilepsy diagnosis, wearable ambulatory EEG (WAEEG) system transmits EEG data wirelessly, and can be made miniaturized, discrete and social acceptable. To prolong the battery lifetime, analog wavelet filter is used for epileptic event detection in WAEEG system to achieve on-line data reduction. For mapping continuous wavelet transform to analog filter implementation with low-power consumption and high approximation accuracy, this paper proposes a novel approximation method to construct the wavelet base in analog domain, in which the approximation process in frequency domain is considered as an optimization problem by building a mathematical model with only one term in the numerator. The hybrid genetic algorithm consisting of genetic algorithm and quasi-Newton method is employed to find the globally optimum solution, taking required stability into account. Experiment results show that the proposed method can give a stable analog wavelet base with simple structure and higher approximation accuracy compared with existing method, leading to a better spike detection accuracy. The fourth-order Marr wavelet filter is designed as an example using Gm-C filter structure based on LC ladder simulation, whose power consumption is only 33.4 pW at 2.1Hz. Simulation results show that the design method can be used to facilitate low power and small volume implementation of on-line epileptic event detector.Peer reviewe

Design of Gm-C wavelet filter for on-line epileptic EEG detection

Copyright © 2019 The Institute of Electronics, Information and Communication EngineersAnalog filter implementation of continuous wavelet transform is considered as a promising technique for on-line spike detection applied in wearable electroencephalogram system. This Letter proposes a novel method to construct analog wavelet base for analog wavelet filter design, in which the mathematical approximation model in frequency domain is built as an optimization problem and the genetic algorithm is used to find the global optimum resolution. Also, the Gm-C filter structure based on LC ladder simulation is employed to synthesize the obtained analog wavelet base. The Marr wavelet filter is designed as an example using SMIC 1V 0.35μm CMOS technology. Simulation results show that the proposed method can give a stable analog wavelet filter with higher approximation accuracy and excellent circuit performance, which is well suited for the design of low-frequency low-power spike detector.Peer reviewe

Women Consciousness Exploration in Jane Austen and Her Works

Jane Austen is one of the greatest realistic novelists in the English literaturein19th century. Austen is contrary to consciousness of man centrism and traditional values of masculine writers before her time. All her 6 novels concerns with love and marriage，they truthfully reflect women life of her age, reveals her feminine consciousness and profound implication

Estimation of Purcell factor from mode-splitting spectra in an optical microcavity

We investigate scattering process in an ultra-high-Q optical microcavity coupled to subwavelength scatterers by introducing "splitting quality" Qsp, a dimensionless parameter defined as the ratio of the scatterer-induced mode splitting to the total loss of the coupled system. A simple relation is introduced to directly estimate the Purcell factor from single-shot measurement of transmission spectrum of scatterer-coupled cavity. Experiments with polystyrene (PS) and gold (Au) nanoparticles, Erbium ions and Influenza A virions show that Purcell-factor-enhanced preferential funneling of scattering into the cavity mode takes place regardless of the scatterer type. Experimentally determined highest Qsp for single PS and Au nanoparticles are 9.4 and 16.19 corresponding to Purcell factors with lower bounds of 353 and 1049, respectively. The highest observed Qsp was 31.2 for an ensemble of Au particles. These values are the highest Qsp and Purcell factors reported up to date.Comment: 5 Pages, 4 Figures, 12 Reference