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Herein, the lasing action of fabricated bulged CH3NH3PbBr3 microwires is demonstrated with features of a low threshold, narrow linewidth, single‐mode operation, and high intensity. Benefiting from the bulged end facets, the CH3NH3PbBr3 microwires are feasible for constructing a high‐brightness, whispering‐gallery‐mode(WGM)‐type, and single‐mode laser while suppressing Fabry–Pérot‐type multi‐mode lasing. Numerical simulation unveils that the bulged end facets result in the significantly reduced reflectivity of fundamental waveguided modes. The obtained microlasers require neither complex structures (such as distributed Bragg reflector) nor careful pumping adjustment, suggesting the practical feasibility of a higher single‐mode lasing intensity than conventional WGM perovskite microlasers. The results provide new routes to realize high‐performance perovskite microlasers and their potential application in sensing refractive index. [ABSTRACT FROM AUTHOR]

Herein, the lasing action of fabricated bulged CH3NH3PbBr3 microwires is demonstrated with features of a low threshold, narrow linewidth, single‐mode operation, and high intensity. Benefiting from the bulged end facets, the CH3NH3PbBr3 microwires are feasible for constructing a high‐brightness, whispering‐gallery‐mode(WGM)‐type, and single‐mode laser while suppressing Fabry–Pérot‐type multi‐mode lasing. Numerical simulation unveils that the bulged end facets result in the significantly reduced reflectivity of fundamental waveguided modes. The obtained microlasers require neither complex structures (such as distributed Bragg reflector) nor careful pumping adjustment, suggesting the practical feasibility of a higher single‐mode lasing intensity than conventional WGM perovskite microlasers. The results provide new routes to realize high‐performance perovskite microlasers and their potential application in sensing refractive index.

In recent years, high quality factor echo wall mode optical microcavities have developed rapidly and become a hot research topic in the fields of optics and physics. Optical microcavity is a kind of micro optical element. Due to its small size and high-quality factor, it can enhance the interaction between light and matter, enabling long-time light stays. Echo wall mode resonators are one of the typical representatives of optical microcavities, with advantages of small size, high sensitivity, and long life. Currently, applications based on echo wall mode resonators are mainly concentrated in various fields such as sensors, lasers, filters, and so on. However, current research on echo wall mode resonators has not yet achieved large-scale production, and is only in the laboratory research stage. Industrial production still has shortcomings such as high cost and manufacturing process difficulties. This article focuses on the research progress of echo wall mode resonators, expounds the impact of echo wall materials on Q values, and discusses the applications of echo wall mode resonators in the fields of sensors, lasers, and filters in recent years. It also proposes the challenges and further research directions of echo wall mode resonators in the future, which may realize all-optical networks. For further research directions, we believe that it is necessary to reduce costs, shorten time, and improve the accuracy and efficiency of the preparation process. It is also necessary to solve the coupling problem between the microcavity and the optical device, improving the coupling efficiency and the anti-interference ability. It should also address the sensitivity of the cavity to the environment to ensure that the microcavity has good stability when preparing devices such as filters.

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Optical microcavities are known for their strongly enhanced light–matter interactions. Whispering gallery mode (WGM) microresonators have important applications in nonlinear optics, single-mode output, and biosensing. However, there are few studies on resonance modes in the ultraviolet spectrum because most materials with high absorption properties are in the ultraviolet band. In this study, the performance of a microdisk cavity based on boron nitride (BN) was simulated by using the Finite-difference time-domain (FDTD) method. The WGM characteristics of a single BN microdisk with different sizes were obtained, wherein the resonance modes could be regulated from 270 nm to 350 nm; additionally, a single-mode at 301.5 nm is achieved by cascading multiple BN microdisk cavities. Moreover, we found that a BN microdisk with a diameter of 2 μm has a position-independent precise sensitivity for the nanoparticle of 140 nm. This study provides new ideas for optical microcavities to achieve single-mode management and novel coronavirus size screening, such as SARS-CoV-2, in the ultraviolet region. [ABSTRACT FROM AUTHOR]

A novel multi-optofluidic microbubble resonator (OMBR) sensitivity equalization method is presented that equalizes the sensing signal from different OMBRs. The method relies on the fact that the ratio of the wavelength shifts to the bulk refractive index sensitivity (BRIS) does not depend on the physical dimensions of the OMBR. The proof of concept is experimentally validated and the sensing signals from individual OMBRs can be directly compared. Furthermore, a wide dynamic range of sensing with favorable consistency and repeatability is achieved by piecing together signals from 20 OMBRs for HIV-1 p24 antigen detection from 50 fg/mL to 100 ng/mL (2.1 fM to 4.2 nM), indicating significant potential for practical applications, such as in drug screening and disease diagnosis. [ABSTRACT FROM AUTHOR]

Whispering gallery mode (WGM) microcavities have attracted wide attention due to their small mode volume, ultra-high Q value, and low threshold. However, in rotationally symmetric WGM microcavities, multiple longitudinal mode laser radiation can be generated, and the directionality of the radiation is poor, which limits its practical applications. Finding effective methods to achieve single-mode radiation of WGM lasers is a key issue for microcavity lasers to move toward practical applications. This review focuses on several methods of single-mode modulation of WGM lasing in recent years, including reducing cavity size, adding mode selection structure, based on the vernier effect, parity-time symmetry breaking, deformed microcavity, etc. This review aims to provide a reference for researchers in related fields and deepen their understanding of the physical mechanism of single-mode modulation of WGM lasing. [ABSTRACT FROM AUTHOR]

Chalcogenide glasses (ChGs) are technologically superior materials, and their properties underpin the demands of whispering gallery mode–based integrated photonic devices. The prime focus of this review is to showcase the recent advances in the field of ChG high Q cavities. The review also covers the theoretical research aspects and brief on the research challenges and limitations involved in the topic. [ABSTRACT FROM AUTHOR]

A novel multi-optofluidic microbubble resonator (OMBR) sensitivity equalization method is presented that equalizes the sensing signal from different OMBRs. The method relies on the fact that the ratio of the wavelength shifts to the bulk refractive index sensitivity (BRIS) does not depend on the physical dimensions of the OMBR. The proof of concept is experimentally validated and the sensing signals from individual OMBRs can be directly compared. Furthermore, a wide dynamic range of sensing with favorable consistency and repeatability is achieved by piecing together signals from 20 OMBRs for HIV-1 p24 antigen detection from 50 fg/mL to 100 ng/mL (2.1 fM to 4.2 nM), indicating significant potential for practical applications, such as in drug screening and disease diagnosis.

• We propose a packaging that couples light from a tapered fiber to a whispering gallery mode resonator. • The device is designed with a special flexible structure that can realize the three-dimensional precision adjustment of the relative position of the resonator and the tapered fiber, thereby adjusting the coupling state. • This package is suitable for various types of millimeter sized resonators. It has the advantages of high stability, small size, low cost, and high portability. In this study, we proposed a packaging that couples light from a tapered fiber to a whispering gallery mode resonator. The packaging is suitable for a wide range of resonators, such as quartz rods and crystal microdisks. The device uses a self-designed brass base with a special flexible structure to realize the three-dimensional precision adjustment of the relative position of the resonator and the tapered fiber. This structural is different from the packaging proposed in previous studies. It can adjust the coupling state of the resonator by adjusting the relative position between the resonator and the tapered fiber. We demonstrated the coupling process using a crystal resonator as an example and demonstrated three typical coupling states of the WGM system. The packaging also has the advantages of high stability, small size, low cost, and high portability. In addition, we tested the long-term robustness of the packaging and verified the application of the packaging for magnetic field sensing and temperature tuning. [ABSTRACT FROM AUTHOR]

Microlasers hold great promise for the development of photonics and optoelectronics. At present, tunable microcavity lasers, especially regarding in situ dynamic tuning, are still the focus of research. In this study, we combined a 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) piezoelectric crystal with a Poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) microring cavity to realize a high-quality, electrically tunable, whispering-gallery-mode (WGM) laser. The dependence of the laser properties on the diameter of the microrings, including the laser spectrum and quality (Q) value, was investigated. It was found that with an increase in microring diameter, the laser emission redshifted, and the Q value increased. In addition, the device effectively achieved a blueshift under an applied electric field, and the wavelength tuning range was 0.71 nm. This work provides a method for in situ dynamic spectral modulation of microcavity lasers, and is expected to provide inspiration for the application of integrated photonics technology. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate the effects of supplementation of tuna hydrolysate (TH), squid hydrolysate (SH) and mixture of both hydrolysates in wheat gluten meal (WGM)‐based diets on the growth, haemato‐biochemical, immunological parameters and antioxidant indicators of GIFT tilapia. Experimental fish were fed different diets, namely a control diet containing fishmeal (FM) without WGM and hydrolysate; a WGM diet without FM and hydrolysate (WGM); a WGM diet without FM and 5 g/kg TH (WGM‐TH); a WGM diet without FM and 5 g/kg SH (WGM‐SH); and a WGM diet without FM and mixture of 5 g/kg of TH and SH (WGM‐Mix). A total of 450 fish (9.83 ± 0.01 g) were fed on the five experimental diets in triplicate groups for 8 weeks. The growth performance and feed utilization indices of the fish were found to be significantly higher in WGM supplemented with TH diet followed by WGM‐SH, WGM‐Mix and WGM diets. There was no significant impact in blood and serum biochemical parameters among the treatments. The immunological and antioxidant indicators were not significantly different between hydrolysate‐supplemented diets; however, they were significantly greater than hydrolysate‐unsupplemented diets (control and WGM diets). Based on the results, it is suggested that FM can be replaced by WGM for better growth performance even without the supplementation of hydrolysates, whereas hydrolysates are considered important for better immunological responses and antioxidant status of GIFT tilapia. [ABSTRACT FROM AUTHOR]

A whispering-gallery-mode (WGM) resonator with an L-shaped microcavity for humidity sensing is proposed and demonstrated. The L-shaped microcavity is fabricated by using femtosecond laser micromachining, fusion discharge and chemical etching methods. By placing two microspheres in the microcavity, of which one is used as the whispering gallery mode resonant cavity, and the other plays the role of changing the optical path to help activating whispering gallery mode resonance. The device has a linear response to humidity with the linearity of 99.1% and the sensitivity of −0.23 dB/%RH, within the relative humidity range of 30%–70%, under the room temperature of 25 °C. The response time for the humidity increasing is as short as 240 ms, and the recovery time is 453 ms. The device is simple in fabrication, robust and has good operation stability. [ABSTRACT FROM AUTHOR]

The development of innovative bio-chemical sensors is of great importance to make new devices available to the market. In the current paper, we review recent trends on optical resonant sensors that may involve plasmonic or geometrical resonances. In all cases, resonance is activated by excitation with electromagnetic light of proper wavelength. Plasmonic hot electrons, obtained by shining light on metal nanoparticle decorated metal oxides, can bring new effects in physicochemical processes, affecting electrical and optical properties (absorption/transmission, Surface Enhanced Raman Spectroscopy SERS). Geometrical resonances are involved in Mie and Whispering Gallery Modes (WGM) based sensing, including metasurfaces for optical detection of molecules and nonlinear effects in metamaterials. [ABSTRACT FROM AUTHOR]

We have fabricated a tubular whispering gallery mode laser based on InGaN/GaN quantum wells and transferred it onto a flexible substrate. Compared with those without the transferring processes, the threshold energy density was reduced by 60%, at about 25.55 µJ/cm2, while a high-quality factor of >15,000 was obtained. Finite-difference time-domain simulation demonstrated that such a low threshold energy density can be attributed to the decreased mode volume, from 1.32 × 10−3 μm3 to 6.92 × 10−4 μm3. The wavelength dependences on strain were found to be 5.83 nm, 1.38 nm, and 2.39 nm per stretching unit ε in the X, Y, and Z directions, respectively. Such strain sensitivity was attributed to the deformation of the GaN microtube and the change in the refractive index of the PDMS.

WGM resonators can be used for studies of condensed matter, especially for the study of the dielectric liquids properties. However, the electromagnetic properties of the real resonator structures are not well understood. The microwave response of quasioptical radially-two-layered dielectric resonator in the form of a cylindrical ring sandwiched between two flat conducting endplates is studied. Usually real resonator has an additional layer between the leucosapphire ring and a conducting surface, that eliminates a possibility of the rigorous solution for the corresponding electromagnetic problem. The leucosapphire resonator is studied with numerical modeling methods and experimental measurements in the Ka-band. A good agreement between the experimentally measured and calculated values of frequencies and Q-factors is achieved. It is shown that the resonator allows the measurement of the complex permittivity of solutions with an error of about 3 %.

The radiation power from active area into the planar waveguide has been studied theoretically in order to model VCSEL characteristics. Exact and simple quantitative connection between modal gain and spontaneous emission into planar waveguide has been established. The possibility of the in-plane lasing in the conventional VCSEL with gain area laterally limited by gain aperture has been examined and condition required for this has been found. [ABSTRACT FROM AUTHOR]

During the last two decades, there has been a public health concern of severe invasive infections caused by Group A Streptococcus (GAS) of the emm1 genotype. This study investigated the dynamics of emm1 GAS during 1994–2013 in Belgium. emm1 GAS isolated from blood, tissue, and wounds of patients with invasive infections (n  = 23, S1–S23), and from patients with uncomplicated pharyngitis (n  = 15, NS1–NS15) were subjected to whole-genome mapping (WGM; kpn) (Opgen). Whole-genome sequencing was performed on 25 strains (WGS; S1–S23 and NS6–NS7) (Illumina Inc.). Belgian GAS belonged to the M1T1 clone typified by the 36-kb chromosomal region encoding extracellular toxins, NAD+-glycohydrolase and streptolysin O. Strains from 1994–1999 clustered together with published strains (MGAS5005 and M1476). From 2001 onward, invasive GAS showed higher genomic divergence in the accessory genome and harbored on average 7% prophage content. Low evolutionary rate (2.49E-008; P  > 0.05) was observed in this study, indicating a highly stable genome. The studied invasive and pharyngitis isolates were no genetically distinct populations based on the WGM and core genome phylogeny analyses. Two copies of the speJ superantigen were present in the 1999 and 2010 study strains (n  = 3), one being chromosomal and one being truncated and associated with phage remnants. This study showed that emm1 GAS in Belgium, compared with Canada and UK M1 strains, were highly conserved by harboring a remarkable genome stability over a 19-year period with variations observed in the accessory genome. [ABSTRACT FROM AUTHOR]

We measure low-temperature micro-photoluminescence spectra along a MoS 2 nanotube, which exhibit the peaks of the optical whispering gallery modes below the exciton resonance. The energy fluctuation and width of these peaks are determined by the changes of the nanotube wall thickness and propagation of the optical modes along the nanotube axis, respectively. We demonstrate the potential of the high-quality nanotubes for realization of the strong coupling between exciton and optical modes when the Rabi splitting can reach 400 meV. We show how the formation of exciton-polaritons in such structures will be manifested in the micro-photoluminescence spectra and analyze the conditions needed to realize that.

Optical microcavities have been widely employed for sensing and detection, because of their ultrasensitive responsiveness to surrounding environment. Here we report an active diskshaped whispering gallery mode (WGM) microcavity fabricated from a water-sensitive material of dye-doped PEG-DA hydrogel through two-photon polymerization. We demonstrate that as the environment humidity changes the microcavity can homogenously expand or shrink to keep the disk-shaped structure, producing stable WGM lasing emissions.We further show that the WGM wavelength of the microlaser shifts linearly as the humidity increases from 25% to 65%, resulting in a wavelength variation of about 1.72 nm, which indicates that the stretchable microlaser can be acted as a humidity sensor. Due to the "smart" response of humidity and biocompatibility of PEG-DA hydrogel material, our results provide a way to the design and fabrication of flexible PEG-DA hydrogel biochips for biomedical applications. [ABSTRACT FROM AUTHOR]

• A self-assembled whispering gallery mode microbottle resonator was fabricated. • The proposed microbottle resonator can be used for acetone gas sensing. • The sensor has merits of small size, low cost, and simple manufacture using non-toxic materials. In this paper, an acetone gas sensor based on a polyvinyl alcohol (PVA) self-assembled whispering gallery mode (WGM) microbottle resonator coated with polydimethylsiloxane (PDMS) is proposed and demonstrated. The preparation of the PVA self-assembled microresonator and the coating of PDMS are all finished by employing a dip coater. Compared with the PVA microresonator and the PDMS microresonator, the PVA microresonator coated with PDMS shows the highest acetone gas sensitivity, which is up to −6.34 pm/ppm. Besides, it can effectively reduce the effects of humidity on the detection of acetone gas compared to the PVA microresonator. Since the concentration of acetone in breathing gas is an indicator of diabetes, the proposed sensor with the benefits of small size, low cost, and simple manufacture using non-toxic materials presents promising applications for painless and non-invasive diagnosis of diabetes. [ABSTRACT FROM AUTHOR]

A robust, easy-to-fabricate, and sensitive liquid refractometric sensor utilizing optical fiber resonators (OFRs) obtained by simple stripping and cleaning of conventional optical fibers is presented. The sensing scheme is based on recording the spectral changes of the whispering gallery modes (WGMs) observed in the transmission spectrum of an OFR excited with a tunable laser coupled to the OFR through an independent tapered optical fiber. The demonstrated sensor device is tested and fully characterized with water solutions of ethanol and ethylene glycol (EG). Good agreements are obtained with theoretical predictions for both ethanol and EG cases when TE and TM polarized WGMs are considered. The limit of detection of the demonstrated sensor is determined to be between 2.7 and 4.7 × 10 −5 refractive index unit (RIU) comparable to the state-of-the-art when precise temperature control of the sample chamber is missing. [ABSTRACT FROM AUTHOR]

This study analyzes the capabilities of a LiNbO3 whispering gallery mode microdisc resonator as a potential bolometer detector in the THz range. The resonator is theoretically characterized in the stationary regime by its thermo-optic and thermal coefficients. Considering a Q-factor of 107, a minimum detectable power of 20 µW was evaluated, three orders of magnitude above its noise equivalent power. This value opens up the feasibility of exploiting LiNbO3 disc resonators as sensitive room-temperature detectors in the THz range. [ABSTRACT FROM AUTHOR]

We demonstrate a microfluidic flowmeter based on a polymer whispering gallery mode (WGM) resonant microcavity. The microcavity is fabricated by coating the dye-doped polymer on the capillary tube. The flowmeter measures the flow velocity based on the temperature variation by the thermo-optic effect. The refractive index of the microcavity changes when the temperature decreases, which is caused by air flow cooling down the microcavity. Therefore, the flow of the fluid can be estimated through calculating the wavelength shift of the resonant microcavity. We achieve a sensitivity of 17 p.m./sccm, and the dynamic range up to 50 sccm. This work will provide a platform for microfluidic flowmeter and miniaturized lasers sensing. The flowmeter measures the flow velocity based on the temperature variation by the thermo-optic effect. The refractive index of the microcavity changes when the temperature decreases, which is caused by air flow cooling down the microcavity. Therefore, the flow of the fluid can be estimated through calculating the wavelength shift of the resonant microcavity. [Display omitted] • The flowmeter measures the flow velocity based on the thermo-optic effect. • The changes of fluid flow can be read out optically using a microfluidic flowmeter through calculating the wavelength shift in the resonant microcavity. [ABSTRACT FROM AUTHOR]

Money management, also known as asset allocation, is constantly at the forefront of research in the trading and investing fields. Since Markowitz established the current portfolio theory in 1952, it has drawn many experts to this intriguing topic. The Kelly criteria are one of the brightest stars among these new techniques. It provides an elegant solution for players and investors to get the best bidding fraction and maximize their logarithm worth over time. However, it ignores the fact that each investor has a different risk tolerance, and the proportion was calculated using the Kelly criterion without taking into account the downside risk. This paper attempts to develop a risk prediction model using a probability-based method and adjust the reward function of deep reinforcement learning to account for the downside risk. To summarize, rather than a naive reward function that solely optimizes the return, the improved deep reinforcement learning may consider an investor's risk tolerance. Finally, we solely analyze the scenario of a single asset and employ DXY, GBP/USD, and EUR/USD as the underlying training and validation data sets. The outcome demonstrates that the adjustment to the reward mechanism produces an interesting performance. When the required MDD (Maximum draw-down) is greater than 3%, the likelihood is on average greater than 70%. • We propose a probability-based approach to capture the downside risk, i.e. P r o b. (MDD < α) > β. This function uses MDD as the metric to measure the risk in a financial market, which is more practical to the discipline of money management. • A revised reward function is used to make our agent have risk awareness. Compared to the past studies which mostly focus on the reward instead of risk, our revised reward function makes the reinforcement learning agent more like a real investor who not only considers return but also downside risk. • G A R C H (1 , 1) , a widely used econometric model is used in the experiment. As a result, make the result of our simulation is more resilient and closer to the real world, because G A R C H (1 , 1) introduces randomness into deviation. Specifically, the volatility of a time series is influenced by its historical data. [ABSTRACT FROM AUTHOR]

Optical microcavities with whispering-gallery modes (WGMs) have large potential and, in particular, those with a tubular geometry have attracted increasing attention due to their special geometry and interesting properties such as trimmed resonant modes, simplicity as fluidic channels, three-dimensionally (3D) mode confinement, unique evanescent wave, and so on. Optical microcavities with the tubular geometry meet the challenge of assembly of conductive, semiconductive and insulating materials into a tubular geometry, thus spurring multifunctional applications to optofluidic devices, optical microdevices like microlasers, and bio/chemical sensors. Fabrication methods such as the fiber-drawing method, rolled-up nanotechnology, electrospin technique, and template-assistant method have been developed to address the various requirements. These tubular optical microcavities enable researchers to explore and construct novel optical microdevices for a wide range of potential applications. This review describes the tubular optical microcavities from the perspectives of theoretical consideration, optical characterization, and potential applications. [ABSTRACT FROM AUTHOR]

Whispering gallery modes (WGMs) in circular resonators are investigated. Conformal transformation is used to transform circular resonators to more simplified structures. The principle of transverse resonance is utilized to calculate the resonant frequencies. Transmission line theory is applied to calculate the fields of electromagnetic waves. The resonant frequencies and field distributions in different high-Q resonators, including small resonators of several micrometers and large resonators of several millimeters in diameters, are investigated. The method provides a more efficient way to analyze the devices incorporating circular resonators. [ABSTRACT FROM PUBLISHER]

We analyze the transport of 25 nm polystyrene nanoparticles through a microfluidic geometry housing a microtoroidal whispering gallery mode (WGM) sensor, taking into account diffusion, convection and optical forces. In particular, we look at the effects of tightly confining the flow of nanoparticles near the microtoroid’s equatorial rim, and calculate the average nanoparticle detection time as well as the total yield for passage of a 1 L sample. Compared to purely diffusive transport, flow rates on the order of 2 nL mingive yield enhancements of up to 15, with nanoparticles being detected every 12 s. Even shorter detection times (1.2 s) can be achieved, but at the expense of lower yield. The sensor’s transport properties are further improved due to gradient optical forces exerted on the nanoparticles. [ABSTRACT FROM PUBLISHER]

Whispering gallery mode (WGM) optical microresonators have attracted intense interests in the past decades. The combination of high quality factors ( Q) and small mode volumes of modes in WGM resonators significantly enhances the light-matter interactions, making them excellent cavities for achieving low threshold and narrow linewidth lasers. In this Review, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed. Label-free detection using WGM resonators has emerged as highly sensitive detection schemes. However, the resolution is mainly limited by the cavity Q factor which determines the mode linewidth. Microcavity lasers, due to their narrow laser spectral width, could greatly improve the detection resolution. Some recent developments in sensing using microcavity lasers are discussed. [ABSTRACT FROM AUTHOR]

Abstract: An optical temperature sensor has been presented based on Whispering Gallery Mode (WGM) dielectric microresonator. The effect of Transverse Electric (TE) wave propagation in dielectric micro-spheres presented has been for optical resonances based on WGM. TE waves are characterized both theoretically and experimentally for large size parameter of the micro-spheres. A theoretical model has been developed based on asymptotic approach. The theoretical development is mathematically robust and significantly less complicated than existing approaches presented in the literature. The quality factor of experimental resonance spectra observed in the laboratory is calculated approximately in the order of 104 which is sensitive enough to detect micro or nano level temperature changes in the surrounding medium. The sensitivity of the Morphology Dependent Resonance (MDR) temperature sensor is wavelength change of 10−9 m for one degree centigrade change in temperature. This sensor could potentially be used for nano technology, Micro-Electro-Mechanical Systems (MEMS) devices, and biomedical applications. [Copyright &y& Elsevier]

Abstract: Optical resonances for Transverse Magnetic (TM) wave based on Whispering Gallery Modes (WGM) have been presented with comprehensive mathematical formulations. The present study is characterized both theoretically and experimentally by considering the fact that the size parameter of the dielectric microspheres is very large at optical wavelengths. An asymptotic expression has been developed based on electromagnetic theory for large size parameter. The developed expressions for optical resonance condition of TM wave are very simple and can accurately characterize resonances in dielectric microspheres. The theoretical development is mathematically robust and significantly less complicated than existing approaches based on quantum physics presented in the literatures. The theoretical result of size parameter for consecutive morphology dependent resonance (MDR) peaks is validated by experimental data. The comparisons are shown to be very accurate for large size parameters. [Copyright &y& Elsevier]

• The effect of roughness on Q-factors of WGM resonator is studied by FDTD method. • The mm-size LN WGM resonator is annealed for the first time. • The Q-factor of WGM resonator is increased by more than 2 orders of magnitude. We demonstrated a monolithic optical whispering-gallery-mode (WGM) resonator made of lithium niobate (LN) single crystal. The effect of WGM resonator side roughness on the quality factor (Q-factor) of resonator was simulated by finite-difference time-domain (FDTD) method. WGM resonators were annealed at high temperature(1050 °C) to improve the Q-factor, and measured the side roughness of the WGM resonator before and after annealing with a white light interference microscope. It found that Q-factor of WGM resonator can be increased by more than 2 orders of magnitude by thermal treatment at 1050 °C. [ABSTRACT FROM AUTHOR]

Abstract: Single particle fluorescence of Eu3+-doped TiO2 hydrate microsphere formed in sol–gel process has been studied, where TiO2 hydrate spheres are characterized by the relatively high refractive index of 1.8. Observed fluorescence spectra display a structure that consists of narrow peaks of varying height superimposed on the familiar broadband emission from europium ions. Such emission peaks result from spherical cavity resonances, and resonance mode positions were assigned from Lorenz–Mie theory calculation. We have also directly measured the lifetime of the MDR peaks of the fluorescence spectra from 8-μm diameter Eu3+ doped TiO2 hydrate microsphere. [Copyright &y& Elsevier]

Abstract: We have developed a novel optical sensor for mercuric ion Hg(II) detection in an aqueous environment by utilizing a fused silica microsphere ring resonator. Due to the high Q-factor associated with the whispering gallery modes (WGM) (>105) at the surface of the microsphere, the light interaction with the analytes on the sphere surface is significantly increased, resulting in enhanced sensitivity. The spectral position of the WGM of a microsphere shifts in response to the binding of Hg(II) to the surface of the microsphere, which is activated by the thiol group. Our experimental results show that the Hg(II) detection limit of the microsphere sensor is approximately 50ppb (w/w) and that mercuric ions bind to thiol groups with 1:3 stoichiometry. Control experiments with zinc ions and 2-mercaptobenzothiazole (2-MBT) were also performed to ensure that Hg(II) binds selectively to thiol groups. [Copyright &y& Elsevier]

• An 'in-fiber' tunable single mode diode laser is presented. • The laser is locked to different Whispering Gallery Modes of a silica microsphere. • Tunability of ~ 15 nm is demonstrated. • Very high power efficiency of more than 90% is obtained. • The WGMs to which the diode laser is locked are calculated and identified. • The conditions required in order to achieve a microsphere-locked tunable laser are found. We present spectral narrowing of a multi-longitudinal-mode diode laser by locking the diode to a Whispering Gallery Mode (WGM) microresonator. By controlling both the temperature and polarization of the diode laser, locking may occur to different TE and TM modes of the microresonator. Fine tuning the laser diode's temperature from 15 °C to 35 °C, makes it possible to lock the laser to 19 different WGMs, resulting in a single longitudinal mode, 2 mW laser, with spectral tunability of 15 nm, and power loss of less than 10%. The WGMs to which the diode laser is locked are calculated and identified. This reported 'in-fiber' system can be packaged to form a simple, cheap, and compact tunable single mode laser device. [ABSTRACT FROM AUTHOR]

We have fabricated a tubular whispering gallery mode laser based on InGaN/GaN quantum wells and transferred it onto a flexible substrate. Compared with those without the transferring processes, the threshold energy density was reduced by 60%, at about 25.55 µJ/cm2, while a high-quality factor of >15,000 was obtained. Finite-difference time-domain simulation demonstrated that such a low threshold energy density can be attributed to the decreased mode volume, from 1.32 × 10−3 μm3 to 6.92 × 10−4 μm3. The wavelength dependences on strain were found to be 5.83 nm, 1.38 nm, and 2.39 nm per stretching unit ε in the X, Y, and Z directions, respectively. Such strain sensitivity was attributed to the deformation of the GaN microtube and the change in the refractive index of the PDMS. [ABSTRACT FROM AUTHOR]

This paper proposes a magnetic field sensor based on side-polished fiber and microspheres. We use side-polished fiber and SiO 2 microspheres to form fiber microsphere cavity, and then package the fiber microspheres in a capillary filled with magnetic fluid form magnetic field sensor. By adding optical fiber microspheres, light propagates through the near-field coupling to the microspheres and directly arouse the whispering gallery modes. The WGM resonance formed in the microcavity will cause a resonance peak with an ultra-narrow spectral line-width in the transmission spectrum, which will improve the quality factor (Q) and figure of merit (FOM) of the sensor. The paper uses finite element analysis to simulation the mode transmission characteristics of side-polished fiber microspheres and the magnetic field sensing performance. The simulation results show that the magnetic field sensor has a strength sensitivity of up to 0.75 dB/Oe and the quality factor up to 2.5 × 10 4 , which has a refractive index sensitivity of 125 nm/RIU, and a maximum FOM of 2.5 × 103. The paper effectively improves the quality factor of the sensor, by adding a microsphere, which provides an alternative research platform for the development of new magnetic field sensors compatible with high-sensitivity sensing and high-precision detection. • A magnetic field sensor based on side-polished fiber and microsphere is proposed. • The proposed sensor has a simple structure, low production cost, high Q-factor and high FOM. • The simulation results show that the magnetic field sensor has a strength sensitivity of up to 0.75 dB/Oe and the quality factor up to 2.5 × 104, which has a refractive index sensitivity of 125 nm/RIU, and a maximum FOM of 2.5 × 103. • It has potential application prospects in developing magnetic field sensors compatible with high-sensitivity sensing and high-precision detection. [ABSTRACT FROM AUTHOR]

In this study, Cr doped hexagonal CuGaO 2 (CGO) nanoplates (NPs) are fabricated successfully. It is worth noting that an emission band located at approximately 700 nm has been found in the photoluminescence (PL) spectrum of CuGa 1−x Cr x O 2 NPs, which can be ascribed to the deep levels emission caused by the Cr 3d and 4s states. Moreover, six resonance peaks also appear in the PL spectrum, which prove that resonance is formed in CGO NPs cavity. The resonant process and resonance mode were investigated in experiment and theory. As the consequence, mode spacing is approximately 8.5 nm and the mode numbers are 60, 59, 58, 57, 56 and 55 corresponding to the peaks of 691 nm, 699 nm, 707 nm, 715 nm, 723 nm and 731 nm in the PL spectrum. The finite difference time domain (FDTD) solution is also used to study resonance mechanism of CGO NPs. These results reveal that the mode calculations and FDTD simulations well agree with the experimental data. The present work further improves the potential applications of CuGa 1−x Cr x O 2 NPs in the field of optoelectronic devices. • Cr doping can improve the conductivity of CGO NPs. • PL emission of Cr doped CGO NPs is found due to deep level. • Resonance actions is discovered and match well with WGM resonance. [ABSTRACT FROM AUTHOR]

We measure low-temperature micro-photoluminescence spectra along a MoS 2 nanotube, which exhibit the peaks of the optical whispering gallery modes below the exciton resonance. The energy fluctuation and width of these peaks are determined by the changes of the nanotube wall thickness and propagation of the optical modes along the nanotube axis, respectively. We demonstrate the potential of the high-quality nanotubes for realization of the strong coupling between exciton and optical modes when the Rabi splitting can reach 400 meV. We show how the formation of exciton-polaritons in such structures will be manifested in the micro-photoluminescence spectra and analyze the conditions needed to realize that. [ABSTRACT FROM AUTHOR]