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We propose a general variable bandwidth filter of arbitrary even order based on the sum-difference microring filter architecture. The filter bandwidth can be varied by tuning only the resonant frequencies of the microrings and thus do not require additional controls other than those used to tune the filter center frequency. In addition, we show that there exists a bandwidth tuning range over which the filter exhibits no extra insertion loss and no degradation in the filter shape. We demonstrated a $4^{\text {th}}$ -order variable bandwidth filter in Silicon-on-Insulator, achieving a bandwidth tuning range from 0.3 nm to 1.35 nm with a maximum in-band ripple of 3 dB. The proposed variable bandwidth filter could serve as a key element in elastic optical networks which can support variable data bandwidth allocation on demand.

Hopf insulators are topological insulators whose topological behavior arises from the nontrivial mapping from a 3D sphere to a 2D sphere, known as the Hopf map. The Hopf map, typically encountered in the study of spinor and skyrmion systems, is classified topologically by an integer invariant called the Hopf index. Here we show that due to the periodic circulation of light inside each microring, a 2D lattice of microring resonators can emulate an $N$-band photonic Hopf insulator with nontrivial Hopf index. In particular, we show by numerical computation and direct analytical proof that the $N$-band Hopf index of the microring lattice is identical to its winding number. The result shows that the Hopf index is an alternative topological invariant for classifying 2D microring photonic lattices and establishes a correspondence between the Hopf insulator phase and the anomalous Floquet insulator phase of the lattice. More generally, our work shows that 2D microring lattices can provide a versatile nanophotonic platform for studying non-Abelian topological photonic systems., 10 pages, 3 figures

This study aimed to develop the destination consumption-customer attitude model to explain tourist travel satisfaction and revisit intention with the moderating effect of religious involvement. Data were collected using a survey questionnaire. Respondents of 392 tourists who visited four major Buddhist monasteries in Taiwan have been analysed, and research hypotheses were assessed by employing partial linear square structural equation modelling (PLS-SEM). The findings revealed that destination consumption has positive and significant effects on rational attitude and emotional attitude toward revisiting a destination, which further facilitates travel satisfaction and revisit intention. Furthermore, this study supported the moderating role of religious involvement on the influence of national and emotional attitude and travel satisfaction on revisit intention. The results emphasized that symbolic experiential and functional consumption of a certain religious destination will significantly influence the rational and emotional attitudes toward revisiting the same destination. These results suggested that destination marketer should design a tourist’s destination consumption based on not only functional factors but also symbolic factors (such as self-concept, lifestyle, and destination) and experiential factors (such as entertainment, joy, pleasure, escape). Since the issues of destination consumption were still subject to further validation, this study provided an important reference for destination marketing to develop marketing strategies. The results were also valuable to provide as a theoretical base for further empirical validation.

The research was conducted to evaluate the antioxidant activity of carotenoid extract from bacteria strainsisolated in An Giang Province. There by, the strain of bacteria with the best antioxidant capacity was selected. The results of DPPH free radical reduction survey on crude carotenoid extracts of the tested bacterial strains showed that all the crude carotenoid extracts of these strains have good DPPH free radical reductionability. Carotenoid extracts from strains NC4-3, NC8-3, NC1-6, NC3-3 and NC7-4 have IC50 values of 2,88; 3,30; 3,45; 5,15 và 9,05 mg/mL, respectively. This showed that the carotenoid extracts of these clones have lower antioxidant activity than the b-carotene control (IC50 = 2,70 mg/mL). Remarkably, the carotenoid extract of theNC4-3 strain had the best antioxidant activity of the 5 strains examined (IC50 = 2,88 mg/mL), only lower than the antioxidant activity of the control sample bcarotene.

In this research work, an anisotropic photonic crystal fiber (PCF) biosensor working on a refractive index (RI) variation and based on surface plasmon resonance (SPR) is presented. Liquid analytes (LA) having a RI within the range of 1.340 to 1.380 RIU are investigated from the proposed biosensor. Spectroscopy analysis of LA having RI values of 1.340 RIU, 1.360 RIU, and 1.380 RIU is performed from the developed sensing setup for modeling an ultrasensitive biosensor. The numerical analysis of the sensing parameters for the proposed sensor presents a maximum wavelength sensitivity (WS) of 20000 nm/RIU for x- polarization (x − pol.) and 18000 nm/RIU for y- polarization (y − pol.), respectively, using the wavelength interrogation technique. Maximum amplitude sensitivity (AS) of 2158 RIU−1 and 3167 RIU−1 is obtained for x − pol. and y − pol., respectively, using the amplitude interrogation technique. Maximum sensor resolution (SR) of 5.00 × 10−6 RIU and 5.55 × 10−6 RIU is obtained for x − pol. and y − pol., respectively. The linear relationship of the resonant wavelength (RW) with the RI produces R2 = 0.9972 and R2 = 0.9978, corresponding to a degree (2) for x − pol. and y − pol., respectively. The figure of merit (FOM) for x − pol. and y − pol. are 93.45 RIU−1 and 105.88 RIU−1, respectively. The sensing parameters have obtained the maximum value for the LA having a RI value of 1.375 RIU.

The study aims to examine the determinants affecting the adoption of e government services in Vietnam. An extended version of the unified theory of acceptance and use of technology model is employe...

We experimentally investigated methods of enhancing the small-signal responsivity of a silicon pin microring photodetector based on two-photon absorption for detecting small optical signals in the telecommunication wavelength range. Two approaches are demonstrated, the first exploiting the bistability effect in the nonlinear microring resonator while the second employing an optical bias at a different wavelength to increase the differential responsivity. We achieved a small-signal responsivity of 180 mA/W with the first approach and 141 mA/W with the second approach, both of which represent almost 10-fold enhancement over direct detection of small optical signals by the same silicon pin microring detector. Our techniques have potential applications in amplitude demodulation, heterodyne detection, and optical power monitoring in WDM communication channels.

We report a p+pn+ junction silicon microring avalanche photodiode based on linear defect state absorption. The large avalanche photocurrent gives rise to giant thermo-optic nonlinearity in the microring, resulting in a unique linear photocurrent-wavelength response.

We report a 4 th -order Vernier cascaded microring (VCMR) filter on Silicon-on-Insulator that can be continuously tuned over an effective free spectral range of 32 nm using the thermo-optic effect. The filter consists of two cascaded double-microring filter stages with free spectral ranges of 7.8 nm and 6.5 nm. The cascaded architecture allows the two stages to be thermally isolated and individually calibrated, which enables accurate tuning of the VCMR filter without further spectral optimization at each set wavelength. We achieved a wavelength tuning accuracy of ±15 pm over 32 nm and a 3-dB bandwidth variation of ±6.5%, which represent the most accurate tuning performance reported for silicon Vernier microring filters to date. In addition, integrated on-chip thermistors allow for precise tracking of the local temperatures of the microrings, thereby providing a mechanism for monitoring the filter performance.

The phenomenon of bound state in the continuum (BIC) with an infinite quality factor and lifetime has emerged in recent years in photonics as a new tool to manipulate light–matter interactions. However, most of the investigated structures only support BIC resonances at very few discrete points in the ω ∼ k space. Even when the BIC is switched to a quasi-BIC (QBIC) resonance through perturbation, its frequency will still be located within a narrow spectral band close to that of the original BIC, restricting their applications in many fields where random or multiple input frequencies beyond the narrow band are required. In this work, we demonstrate that a new set of QBIC resonances can be supported by using a special binary grating consisting of two alternatingly aligned ridge arrays with the same period and zero-approaching ridge width difference on a slab waveguide. These QBIC resonances are distributed continuously over a broad band along a line in the ω ∼ k space and can thus be considered as 1D QBICs. With the Q factors generally affected by the ridge difference, it is now possible to arbitrarily choose any frequencies on the dispersion line to achieve significantly enhanced light–matter interactions, facilitating many applications where multiple input wavelengths are required; e.g., sum or difference frequency generations in nonlinear optics.

Topological photonic insulators have attracted considerable attention due to their unique ability to transport light via topologically-protected edge states that are immune to defect scattering. Among the various potential applications, this property can be exploited to engineer robust photonic devices that are insensitive to fabrication imperfections. This chapter reviews the key concepts of topological insulator systems in one and two dimensions and their realizations using coupled microring resonator lattices. Particular emphasis will be placed on the treatment of microring lattices as periodically-driven systems and their Floquet topological characteristics. Experimental efforts in realizing Floquet microring lattices and demonstrating anomalous Floquet insulator behaviors will also be reviewed.

We propose a general variable-bandwidth filter for lossless tuning based on the sum-difference microring filter architecture. We demonstrate a 4th-order filter in SOI, achieving ∼5 folds increase in bandwidth without extra insertion loss or degradation in filter shape.

We report a new defect-mode resonance phenomenon in a Floquet topological insulator by tuning the cyclic phase of a Floquet bulk mode. The resonance is cavity-less, tunable and can be formed anywhere in the bulk.

We demonstrate frequency generation by four-wave mixing using novel cavityless Floquet defect mode resonance in 2D silicon microring Floquet topological lattice, achieving a conversion efficiency enhancement of 12.5 dB over the edge mode alone.

We experimentally investigated various topological phases of Floquet topological insulators based on 2D coupled octagonal resonators, verifying that the lattice can behave as normal, Chern, or Anomalous Floquet insulator depending on the lattice coupling strengths. © 2020 The Author(s)

Cochannel interference is one of the inevitable deleterious components in designing and analyzing of a wireless network. The use of multiple antennas at both transmitting and receiving nodes is a promising technique to suppress and/or alleviate the effect of cochannel interference on capacity. In this paper, we assess the effects of both antenna correlation and cochannel interference on the ergodic capacity of multiple-input multiple-output channels with covariance feedback. In particular, we consider a general family of spatial fading correlation model-called unitary-independent-unitary -which encompasses most of zero-mean channels with arbitrary fading profiles including the popular separable correlation channel models. We derive the average minimum mean-square error and signal-to-interference-plus-noise ratio of the parallel spatial streams using Berezin’s supermathematics. We then put forth the structure of optimal input covariance matrix maximizing the mutual information connected with the necessary and sufficient conditions as a generalization of the noise-limited case, which is tested by a simple iterative algorithm. Together with the powerful supermathematical framework, the result in the paper enables us to quantify the multiuser MIMO interference effects on the capacity in terms of spatial correlation and interference power heterogeneity.

We experimentally realized Floquet topological photonic insulators using a square lattice of direct-coupled octagonal resonators. Unlike previously reported topological insulator systems based on microring lattices, the nontrivial topological behaviors of our system arise directly from the periodic evolution of light around each octagon to emulate a periodically driven system. By exploiting asynchronism in the evanescent coupling between adjacent octagonal resonators, we could achieve strong and asymmetric couplings in each unit cell, which are necessary for realizing anomalous Floquet insulator behaviors. Direct imaging of scattered light from fabricated samples confirmed the existence of chiral edge states as predicted by the topological phase map of the lattice. In addition, by exploiting the frequency dispersion of the coupling coefficients, we could also observe topological phase changes of the lattice from a normal insulator to Chern and Floquet insulators. Our lattice thus provides a versatile nanophotonic system for investigating 2D Floquet topological insulators.

Floquet topological photonic insulators characterized by periodically varying Hamiltonians are known to exhibit much richer topological behaviors than static systems. In a Floquet insulator, the phase evolution of the Floquet–Bloch modes plays a crucial role in determining its topological behaviors. Here, we show that by perturbing the driving sequence, it is possible to manipulate the cyclic phase change in the system over each evolution period to induce self-interference of a bulk mode, leading to a resonance effect, which can be regarded as a Floquet counterpart of defect-mode resonance in static lattices. This Floquet Defect Mode Resonance (FDMR) is cavity-less since it does not require physical boundaries; its spatial localization pattern is, instead, determined by the driving sequence and is found to be different in topologically trivial and nontrivial lattices. We demonstrated excitation of FDMRs by edge modes in a Floquet octagon lattice on silicon-on-insulator, achieving extrinsic quality factors greater than 104. Imaging of the scattered light pattern directly revealed the hopping sequence of the Floquet system and confirmed the spatial localization of FDMR in a bulk-mode loop. The new Floquet topological resonator could find various applications in lasers, optical filters and switches, nonlinear cavity optics, and quantum optics.

We report a CMOS-compatible silicon microring-enhanced avalanche photodiode based on linear defect-state absorption in a p + p n + junction, with high responsivities exceeding 1 A/W at telecommunication wavelengths. The large photogenerated currents give rise to giant thermo-optic nonlinearity in the microring resonator, resulting in a linear photocurrent-wavelength response spanning the full free spectral range of the microring. This unique photocurrent spectrum could enable novel applications in wavelength-resolved photodetection, such as compact on-chip spectrometers, linear chirp frequency laser source characterization, and low-cost refractometric sensors without requiring precise wavelength-tunable lasers.

This letter reports our study on the effects of free carrier lifetimes due to surface/interface recombination and Auger recombination on the nonlinear dynamics of light propagation in a silicon waveguide at moderate to high power levels. It is shown that due to the coupling dynamics between the optical intensity and the free carrier density, the effective decay time of the optical intensity in the waveguide is not constant but becomes significantly reduced at high input powers, a result which may have important implications to nonlinear optics applications of silicon waveguides such as all-optical switching and modulation.

Phase errors caused by fabrication variations in silicon photonic integrated circuits are an important problem, which negatively impacts device yield and performance. This paper reports our recent progress in the development of a method for permanent, postfabrication phase error correction of silicon photonic circuits based on femtosecond laser irradiation. Using beam shaping technique, we achieve a 14-fold enhancement in the phase tuning resolution of the method with a Gaussian-shaped beam compared to a top-hat beam. The large improvement in the tuning resolution makes the femtosecond laser method potentially useful for very fine phase trimming of silicon photonic circuits. We also show that femtosecond laser pulses can directly modify silicon photonic devices through a SiO2 cladding layer, making it the only permanent post-fabrication method that can tune silicon photonic circuits protected by an oxide cladding.

This paper presents a new simple method for analyzing the linear response of a single pile with circular cross-section under vertical load in layered soils. The properties of each soil layer are assumed to be constant but can vary from layer to layer. The method is based on energy principles and variational approach with an explicit solution by using the finite element method in pile displacement approximation. Bar elements models the pile and soil column below the pile tip while a series of independent springs distributed along the pile shaft models the surrounding layered soils. Properties of the corresponding soil layer determine the spring stiffness. The iterative solutions provide vertical displacement along the pile, vertical displacement of soil as a function of the radial distance at any depth, and equivalent stiffness of the pile-soil system. Validation of the proposed method is conducted by comparing its results to analytical solutions, three-dimensional finite element analyses, and a field load test.

We report a silicon pin microring photodetector based on two-photon absorption with responsivity enhanced by optical resonance and optical biasing. A small-signal responsivity of 100mA/W was achieved, which is the highest reported TPA-based silicon photodetectors.

Topological photonic insulators (TPIs) have attracted considerable attention due to their unique ability to transport light via topologically-protected edge states that are immune to defect scattering [1]. Among the various possible implementations of TPIs, coupled microring resonator lattices have been shown to be a versatile platform for realizing Floquet topological insulators [2,3]. However, most works to date have focused mainly on the unique properties of the topologically-protected edge states [2,3,4] while very little attention has been paid to exploring the bulk mode properties of these lattices for potential applications. In this paper, we report a new optical resonance phenomenon in which light is trapped and stored in the localized bulk modes of a Floquet TPI microring lattice. We show that this "bulk mode resonance" arises from the topological behaviour of the lattice, does not require a physical cavity and can be excited deep in the bulk through nonlocal interactions.

Microring resonators have been shown to be extremely versatile elements for constructing high-order optical filters [1]. By coupling multiple microring resonators together, high-order optical transfer functions with flat-top passband and sharp skirt roll-offs can be realized. However, most coupled microring optical filters to date are based on the 1D serially-coupled configuration (also known as CROW filters) [1], which can only realize transfer functions with all poles and no transmission zeros. The inability of the 1D configuration to realize transmission zeros limits the rate of skirt roll-off that can be achieved in the filter spectrum. In contrast, the 2D coupling configuration provides multiple pathways of light through the lattice, which can result in complete destructive interference of the transmitted light at certain frequencies [2]. By positioning these transmission nulls near the edge of the passband, filter spectra with very sharp skirt roll-offs can be realized, which are important for applications requiring separation of two closely spaced wavelengths, such as in dense WDM communication systems, fluorescence spectroscopy and nonlinear pump-and-probe experiments.