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Whispering gallery mode (WGM) resonators provide an important platform for fine measurement thanks to their small size, high sensitivity, and fast response time. Nevertheless, traditional methods focus on tracking single-mode changes for measurement, and a great deal of information from other resonances is ignored and wasted. Here, we demonstrate that the proposed multimode sensing contains more Fisher information than single mode tracking and has great potential to achieve better performance. Based on a microbubble resonator, a temperature detection system has been built to systematically investigate the proposed multimode sensing method. After the multimode spectral signals are collected by the automated experimental setup, a machine learning algorithm is used to predict the unknown temperature by taking full advantage of multiple resonances. The results show the average error of 3.8 × 10−3°C within the range from 25.00°C to 40.00°C by employing a generalized regression neural network (GRNN). In addition, we have also discussed the influence of the consumed data resource on its predicted performance, such as the amount of training data and the case of different temperate ranges between the training and test data. With high accuracy and large dynamic range, this work paves the way for WGM resonator-based intelligent optical sensing.

Current induced spin–orbit torque (SOT) switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications. In this work, we systematically investigated the effect of Ta thickness on the magnetic properties, field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer with perpendicular magnetic anisotropy. We found that both the anisotropy field and coercivity increase with increasing Ta thickness from 0.15 nm to 0.4 nm. With further increase of Ta thickness to 0.5 nm, two-step switching is observed, indicating that the two magnetic layers are magnetically decoupled. Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness. Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for the β DL decrease as the Ta spacer thickness increases. The studied structure with the incorporation of a CoFeB layer is able to realize field-free switching in the strong ferromagnetic coupling region, which may contribute to the further development of magnetic tunnel junctions for better memory applications.

A high-sensitivity optical fiber sensor for low refractive index (RI) measurement is proposed and experimentally demonstrated. It is fabricated by fused splicing a section of multimode fiber (MMF) between two single-mode fibers (SMFs) with a slight offset at two splicing joints, then the MMF is tapered using fused tapering technology. The offset splicing between SMF and MMF can effectively excite more high-order modes. The tapered multimode fiber (TMMF) can enhance the strength of the evanescent field and promote the interplay between the high-order modes and the surrounding medium. The experimental results indicate that the offset value and the waist diameter of the TMMF are two determinants for RI sensitivity enhancement. The RI sensitivity up to 12145 nm/RIU is achieved over the low RI range of 1.3345-1.339. This proposed high-sensitivity fiber-optic RI sensor may provide a low-cost and effective approach for low RI measurement in many chemical and biological applications.

Tunable coupled resonator induced transparency (CRIT) is observed based on two asymmetrical self-interference ring resonators (SIRRs). The phase shift of the left feedback arm will regulate the output CRIT lineshape, whereas the right FA does not influence the output lineshape. The transmission spectra of the left SIRR will be greatly reshaped with different cross-coupling coefficients, this characteristic is of great use both for optical sensing and designing output lineshape. Instead of adding ring resonators or tuning the uncontrolled multimodes of the whisper gallery resonator, we realize two transparency windows via changing the cross-coupling coefficients of couplers, which provides a convenient and controllable approach for the multichannel filter in optical devices. Moreover, the number of transparency window can be extended via adding more resonators. The proposed structure provides a potential application in the optical filter, optical sensing, slow light, and optical storage.

A sensitive DC magnetic field sensor is constructed by measuring the signal-to-noise ratio of an AC-modulated magnetic field at a particular frequency from an optical whispering gallery mode microcapillary resonator. The sensing element consists of an optical whispering gallery mode microcapillary resonator bonded to a magnetostrictive material that enables it to respond to external magnetic fields. A DC magnetic field sensitivity of 0.1703dB/Oe and a linear detection range from 4.8Oe to 65.7Oe are realized under an AC modulation field of 168.1kHz in the unshielded environment at room temperature. To our best knowledge, this sensitivity is about 2.3 times of the maximum sensitivity of other DC magnetic field sensors based on magnetic fluid or magnetostrictive material integrated fiber systems that use the dissipative sensing scheme. Furthermore, the sensor can operate at a stable temperature in the range of [-11∼45]°C, as long as the modulation frequency of the AC-modulation field is adjusted according to the ambient temperature. This sensor provides us with a novel DC magnetic field sensing scheme, which may play a role in industrial fields related to current and position detection in the future.

Using textual analysis for a large sample of analyst reports, we find that analysts are more likely to use a DCF model and to discuss more cash flow and discount rate information for firms with more uncertainty, especially under heightened aggregate economic uncertainty and bearish market sentiment. The market reactions to target price changes based on a DCF model are stronger, particularly when the analysts present more cash flow and discount rate discussions. These results indicate that analyst valuation process reflects investors’ information demand under uncertainty, and has a bearing on the informativeness of analyst research.

The nonlinear optical properties of 2,9,16,23-phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phenoxy-phthalocyanine-zinc (Pc2) in solution were investigated under excitation with nanosecond laser pulses at 532 nm. Based on five-level model, the nonlinear absorption in nanosecond regime was theoretically analyzed. The A-OS and OL behavior of Pc1 and Pc2 were further investigated with the pump–probe technique and transmission measurement technique. The results show that the A-OS response time is determined by the lifetime of the first triplet excited state of molecule, and Pc1 and Pc2 exhibit strong optical limiting effect at nanosecond laser pulses. These studies make the samples a promising possibility for device realization.

The high efficiency single-longitudinal-mode (SLM) Tm, Ho:YAP laser with ring cavity is proposed. The Tm, Ho:YAP ring laser was run on unidirectional operation using a Faraday rotator and a half-wave plate. A 0.2-mm F-P etalon was employed for wavelength tuning. SLM power could reach 231 mW with the slope efficiency of 23%, M2 factor of 1.12, and wavelength tuning range of 2053.62 to 2058.0 nm. This is the first report on the SLM Tm, Ho:YAP laser based on Faraday effect with high efficiency and tunability.

We investigated nonlinear optical properties of 1,1-ferrocenedicarbaldehyde (FePz) with a nanosecond Nd:YAG laser pulse at 532 nm. The nonlinear absorption coefficient and nonlinear refractive index were measured using standard Z-scan technique. The experimental results show that the values of the nonlinear absorption coefficient and nonlinear refractive index were 43.32 cm/GW and −1.65 × 10−10 esu, respectively. Moreover, the transmission measurement technique was used to study the optical limiting of FePz. These molecules exhibit an interesting optical limiting performance with nanosecond laser pulses. With good excellent nonlinear optical coefficient, the samples were expected to be the potential applications in optical devices.

The pump–probe technique and transmission measurement technique were used to study the all-optical switching (A-OS) and optical limiting (OL) behavior of 2, 9, 16, 23-phenoxy-phthalocyanine (Pc1) and 2, 9, 16, 23-phenoxy-phthalocyanine-zinc (Pc2) in predominantly the monomeric solution form. The results show that the A-OS response time of Pc2 is longer than that of Pc1, and switch-off and -on times of A-OS for Pc2 are 1.2 and 11.6 μs and for Pc1 are 2.3 and 7.8 μs at the same intensity. Moreover, the results of OL experiments reveal that Pc1 and Pc2 exhibit strong OL effect at nanosecond laser pulses. These studies make the samples a promising possibility for device realization.

We compare the temperature sensitivity between the nested fiber ring resonator (NFRR) and the nested fiber ring resonator coupled Mach-Zehnder interferometer (NFRRCMZI). Theoretical results indicate that the temperature sensitivity of the NFRR is almost twelve times higher than that of NFRRCMZI with same parameters, hence complex MZI system can be removed and the whole sensing system will be more compatible without sacrificing the sensitivity. Taking feedback waveguide part as the sensing element in NFRR structure, the limitation of optical quality factor on sensitivity will be broken and arbitrary sensitivity can be acquired by easily setting different feedback waveguide length.

We theoretically analyze the electromagnetically induced transparency (EIT)-like spectrum in the Eye-like resonator configuration. The EIT-like spectrum results from the interference between the inner ring and the outer ring. In this paper, we obtain a tunable group delay and bandwidth of the transparency window through changing the coupling coefficients and the attenuation factors of the inner and the outer ring. The tunable group delay and the bandwidth will have potential application in optical switching or tunable delay lines and tunable bandwidth filter.

We theoretically investigate the series-coupled fiber double-ring resonator is not exactly the same perimeter, that is, when the double-ring resonator cannot be completely in resonance state, the output characteristics and dispersion characteristics of spectrum and its manifestations. In this paper, we introduce light exhibits different spectral output characteristics through double-ring resonator, when the two rings’ length ratios are δ=1,1.1,1.5, 2. Among them, δ=2 is particularly representative. When the second resonator has the same parameters, the group refractive index of the double-ring resonator whose length ratio is 2 higher than the single ring resonator two or three orders, these results indicate that we could improve the sensitivity of the double-ring resonator because sensitivity is directly related to the group refractive.

We theoretically investigate an all-fiber interleaver consisting of a two-stage cascaded Mach-Zehnder interferometer (MZI). The simulation results of the all-fiber interleaver presented symmetrical and asymmetrical output spectra and a uniform flat-top spectral response by changing the coupling coefficient of the couplers. In addition, the interleaver proposed can realize arbitrary passband width ratio between the two output ports by adjusting the coupling coefficient of the couplers involved. A near box-shaped spectral response can be generated through setting suitable parameters, at the same time, the passband and stopband of optical interleaver are improved significantly. This interleaver proposed should be useful to realize the deployment of flat-top all-fiber asymmetric interleaver in dense wavelength division multiplexing (DWDM) networks of high spectral efficiency.

The filtering characteristic of double-waveguide parallel-coupled microring resonators is theoretically investigated in this paper. Transfer matrix of the structure consisting of arbitrary number of rings is deduced. Number of very narrow symmetrical transparent channels within each stop-band can increase to any integer by extending rings of the structure, and any one or more channels can be continuously tuned and switched on/off selectively by adjusting the additional phase shift between adjacent rings. The structure is compact, reliable, flexible and tunable, and has potential vital applications for optical switches in dense wave division multiplexing (DWDM) systems.

The interaction between plasmonic resonances, sharp modes, and light in nanoscale plasmonic systems often leads to Fano interference effects. This occurs because the plasmonic excitations are usually spectrally broad and the characteristic narrow asymmetric Fano line-shape results upon interaction with spectrally sharper modes. We investigate a plasmonic waveguide system using the finite-difference time-domain (FDTD) method, which consists of a metal-insulator-metal waveguide coupled with a rectangle and a ring cavity. Numerical simulations results show that the sharp and asymmetric Fano-line shapes can be created in the waveguide. Fano resonance strongly depends on the structural parameters. This has important applications in highly sensitive and multiparameter sensing in the complicated environments.

We demonstrate a centimeter-scale optomechanical magnetometer based on a crystalline whispering-gallery-mode resonator. The large size of the resonator, with a magnetic-field integration volume of 0.45 cm3, allows high magnetic-field sensitivity to be achieved in the hertz-to-kilohertz frequency range. A peak sensitivity of 131 pT Hz-1/2 is reported, in a magnetically unshielded noncryogenic environment using optical power levels beneath 100 μW. Femtotesla-range sensitivity may be possible in future devices with the further optimization of laser noise and the physical structure of the resonator, allowing applications in high-performance magnetometry.

We theoretically investigate the series-coupled double micro-ring resonator as tunable optical delay line. Tunable optical delay line can be achieved by tunable self-coupling coefficient and attenuation factor of micro-ring waveguide. Through choosing suitable parameters of structure, the series-coupled double micro-ring resonator can obtain flat delay line that mitigates the deleterious effects of group delay dispersion.

We demonstrate the electromagnetically induced transparency like spectrum in the nested fiber ring resonator with the transfer matrix theory; the system consists of two rings and two waveguides which are connected by four couplers. The simulation results show that the tunable group delay can be realized by changing the coupling coefficients. At transmission window, the transmittance can achieve approximately 97.2% with the 0.05ns group delay. Through tuning the coupling coefficients, the group delay can vary from 0.05ns to -21.23ns and the bandwidth of the transparency window can vary from 37MHz to 15MHz.The ability for realizing such transparency resonance and for controlling the group delay or the bandwidth of such resonance is important for applications such as optical switching, as well as tunable bandwidth filter applications.

An Mach-Zehnder (M-Z) interferometer coupled with the nested fiber ring resonator is theoretically demonstrated. The results show that the dispersion sensitivity of the interferometer is significantly enhanced by the strong dispersive response of the resonator. The sensitivity of the temperature sensor based on the nested fiber ring resonator coupled M-Z interferometer can achieve 320rad/°C, about ten times of that in traditional M-Z interferometer.

We theoretically study a single-ring-resonator-based add/drop interferometer to achieve tunable Fano resonance. The Fano resonance results from the interference of two resonant beams propagating in the ring resonator. The line shapes of the Fano resonance are tunable by controlling the coupling coefficients between the waveguide and ring resonator. The spectra of the drop port and through port of the add/drop interferometer are horizontally mirror-symmetric. A box-like spectral response can be produced with the proper coupling coefficient owing to the double resonances. When the phase difference between the two light inputs to the add/drop interferometer is compensated, a doubled free spectral range can be obtained.

We present our experimental results on the measurements of excited state dynamics in 2, 9, 16, 23-phenoxy-phthalocyanine (Pc1) and 2, 9, 16, 23-phenoxy-phthalocyanine-zinc (Pc2) using the pump-probe experiment. The results show that the lifetime of the first triplet excited state of the Pc2 longer than Pc1. The lifetimes of the triplet excited state for Pc2 and Pc1 are 12.8 μs and 10.1 μs at the same intensity, respectively. Moreover, analysis of modulation characteristics of all-optical switching (A-OS) shows that the stronger the light intensity of the pump light is, the smaller the normalized transmittance is, and the lower the A-OS response time is. The consequences of such short lifetimes are also discussed in view of the strong A-OS properties of these molecules.

Theoretical investigation in a single resonator based add/drop on interferometer was made to achieve Fano resonance. The results show Fano resonance is tunable by controlling the coupling coefficients between the waveguide and ring resonator.

We numerically investigate the properties of the nested fiber ring resonator coupled Mach-Zehnder interferometer as a sensor. By introducing the phase bias of 0.5π in the reference arm, the two output intensities exhibit sharp asymmetric line shapes around the resonance wavelength. Utilizing the intensity interrogation, we analyze the effect of parameters on the sensitivity and the detection limit. For the 30 dB signal-noise system, the sensitivity and the detection limit can achieve 4.0866/°C and 7.341×10(-3)°C, respectively; the results indicate that this structure is suitable for high-sensitivity measurements.

A highly sensitive Mach-Zehnder(M-Z) interferometer coupled with nested fiber ring resonators is theoretically demonstrated. The experimental results show that the sensitivity of the interferometer is significantly enhanced by strong dispersive response of resonators and reach its maximum value at resonance, which agree well with theoretical predictions.

We experimentally demonstrate that the spectral resolution of Fourier transform interferometer could be greatly enhanced by utilizing the dispersive property of semiconductor GaAs in the near infrared region and it is inversely proportional to the maximum group delay time that can be achieved in the system. The spectral resolution could be increased 6 times approximately by using GaAs contrast with conventional FT interferometer under the same conditions.

We propose a single-ring-resonator-based add/drop interferometer and theoretically investigate the transmission characteristics. Due to coherent interference of two resonant pathways, an electromagnetically induced-transparency (EIT)-like spectrum is produced and the line shapes of the transmission spectra are tunable by controlling the coupling coefficients between the waveguide and ring resonator. We observe the EIT-like behavior in a fiber system which agrees well with the theoretical analysis. The proposed configuration has potential applications in tunable delay lines.

We use the add-drop ring resonator (ADRR) to produce the normal and anomalous dispersion simultaneously and apply these two dispersion responses to enhance the sensitivity of the Mach–Zehnder interferometer (MZI). To estimate the sensing ability of the ADRR assisted MZI, the dispersion sensitivity of the structure is theoretically and experimentally demonstrated. For two equal amplitude coupling coefficients, a 19.2-fold increase in the dispersion sensitivity is experimentally achieved, a little lower than 19.5-fold predicted in theory. This value can be futher increased by minimizing the attenuation or by choosing different amplitude coupling coefficient settings at different coupling regions. To acquire better dispersion sensitivity, only output port one should be utilized at the over-coupling region, and two output ports should be adopted at the under-coupling region.

We theoretically proposed a cost-effective refractometer sensor, which includes an unbalanced two-ring Mach–Zehnder interferometer and can exhibit sharp asymmetric Fano lineshape. Our calculated results show this device has high sensitivity and can measure refractive index change in one of the resonators down to 10−9 refractive index units, which is two orders of magnitude higher than previous Fano lineshape based sensors.