Bandwidth Tunable Optical Bandpass Filter Based on Parity-Time Symmetry

A chip-scale tunable optical filter is indispensable to meeting the demand for reconfigurability in wavelength division multiplexing systems, channel routing, and switching, etc. Here, we propose a new scheme of bandwidth tunable band-pass filters based on a parity-time (PT) symmetric coupled microresonator system. Large bandwidth tunability is realized on the basis of the tuning of the relative resonant frequency between coupled rings and by making use of the concept of the exception point (EP) in the PT symmetric systems. Theoretical investigations show that the bandwidth tuning range depends on the intrinsic loss of the microresonators, as well as on the loss contrast between the two cavities. Our proof-of-concept device confirms the tunability and shows a bandwidth tuning range from 21 GHz to 49 GHz, with an extinction ratio larger than 15 dB. The discrepancy between theory and experiment is due to the non-optimized design of the coupling coefficients, as well as to fabrication errors. Our design based on PT symmetry shows a distinct route towards the realization of tunable band-pass filters, providing new ways to explore non-Hermitian light manipulation in conventional integrated devices.

Composite pulses for high fidelity population transfer in three-level systems

In this work, we propose a composite pulses scheme by modulating phases to achieve high fidelity population transfer in three-level systems. To circumvent the obstacle that not enough variables are exploited to eliminate the systematic errors in the transition probability, we put forward a cost function to find the optimal value. The cost function is independently constructed either in ensuring an accurate population of the target state, or in suppressing the population of the leakage state, or both of them. The results demonstrate that population transfer is implemented with high fidelity even when existing the deviations in the coupling coefficients. Furthermore, our composite pulses scheme can be extensible to arbitrarily long pulse sequences. As an example, we employ the composite pulses sequence for achieving the three-atom singlet state in an atom-cavity system with ultrahigh fidelity. The final singlet state shows robustness against deviations and is not seriously affected by waveform distortions. Also, the singlet state maintains a high fidelity under the decoherence environment.

Design Procedure Based on Maximum Efficiency for Wireless Power Transfer Battery Chargers with Lightweight Vehicle Assembly

This paper analyzes two different design procedures for a series-parallel compensated WPT battery charger, based on different definitions of the operating resonant frequency in the condition of maximum link efficiency. The behaviour of the voltage gain magnitude and the input impedance angle of the resulting WPT links is studied for different loads and coupling coefficients. The design algorithms are supported by analytical formulas derived from an exact circuit analysis of the WPT link, avoiding approximations as far as possible. To support the theoretical approach a case study is proposed, in which both design procedures are implemented considering specifications in line with the actual automotive standards. To conclude, a characterization of the efficiency in both cases is derived.

Systematic identification of crosstalk and bandwidth upper limit in highly cascaded Mach-Zehnder lattice optical filters

Crosstalk among channels in wavelength division multiplexing (WDM) filters must be suppressed to enhance receiver sensitivity in direct-detection-based optical communication systems. We present a systematic method to identify the maximum crosstalk and upper limit of the transmission spectrum bandwidth of a highly multi-staged Mach-Zehnder interference (MZI) lattice optical filter with a number of cascade N (N=1,2,…,∞). The scattering matrix including the wafer-level-measurement-based coupling coefficients of directional couplers is used to calculate the transmittance from the input to each output channel and the result is exactly extrapolated to infinite N. This method can be used to design, characterize, and evaluate $N$-cascaded MZI lattice optical filters that must meet strict WDM specifications.

Higher-order synchronization on the sphere

We construct a system of $N$ interacting particles on the unit sphere $S^{d-1}$ in $d$-dimensional space, which has $d$-body interactions only. The equations have a gradient formulation derived from a rotationally-invariant potential of a determinantal form summed over all nodes, with antisymmetric coefficients. For $d=3$, for example, all trajectories lie on the $2$-sphere and the potential is constructed from the triple scalar product summed over all oriented $2$-simplices. We investigate the cases $d=3,4,5$ in detail, and find that the system synchronizes from generic initial values, for both positive and negative coupling coefficients, to a static final configuration in which the particles lie equally spaced on $S^{d-1}$. Completely synchronized configurations also exist, but are unstable under the $d$-body interactions. We compare the relative effect of $2$-body and $d$-body forces by adding the well-studied $2$-body interactions to the potential, and find that higher-order interactions enhance the synchronization of the system, specifically, synchronization to a final configuration consisting of equally spaced particles occurs for all $d$-body and $2$-body coupling constants of any sign, unless the attractive $2$-body forces are sufficiently strong relative to the $d$-body forces. In this case the system completely synchronizes as the $2$-body coupling constant increases through a positive critical value, with either a continuous transition for $d=3$, or discontinuously for $d=5$. Synchronization also occurs if the nodes have distributed natural frequencies of oscillation, provided that the frequencies are not too large in amplitude, even in the presence of repulsive 2-body interactions which by themselves would result in asynchronous behaviour.

Guided waves in a functionally graded 1-D hexagonal quasi-crystal plate with piezoelectric effect

For the purpose of design and optimization for piezoelectric quasi-crystal transducers, guided waves in a functionally graded 1-D hexagonal piezoelectric quasi-crystal plate are investigated. In this paper, a model combined with the Bak’s and elastohydrodynamic models is utilized to derive governing equations of wave motion, and real, pure imaginary, and complex roots of governing equations are calculated by using the modified Legendre polynomial method. Subsequently, dispersion curves and displacements of phonon and phason modes are illustrated. Then, guided waves in functionally graded 1-D hexagonal piezoelectric quasi-crystal plates with different quasi-periodic directions are studied. And the phonon-phason coupling effect on Lamb and SH waves are analyzed. Accordingly, some interesting results are obtained: The phonon-phason coupling just affects Lamb waves in the x- and z-direction quasi-crystal plates, and SH waves in the y-direction quasi-crystal plate. Besides, frequencies of propagative phason modes decrease as phonon-phason coupling coefficients Ri increase. Furthermore, a variation in the polarization has a more significant influence on phonon modes, and a variation in the quasi-periodic direction has a more significant influence on phason modes.

Computation of optical waveguide interaction for quantum gates implementation

The system of two coupled optical dual-mode waveguides is considered. The coupling of the system is studied to find a circuit for building a control switch for two qubit gates. The classical coupled mode theory is applied and the exact expressions for coupling coefficients are derived. The parameters of the system for performing the desired operations are numerically computed and analysed. The system describing the influence of intermodal interactions is solved numerically. The distortions are analysed.

On the Magnetoelectric Performance of Multiferroic Particulate Composite Materials

In the current work, quantitative analysis of magnetoelectric particulate composite material system explicated the main mechanisms responsible for the below-optimal performance of this class of materials. We considered compliant particulate composite materials, with constituents relevant to technological and scientific interest, leading to 0-3 Terfenol-D/PVDF-TrFE composite samples. To this objective, thick Terfenol-D/PVDF-TrFE films (10-15 µm) were fabricated and analyzed for chemical, mechanical, and magnetic properties to demonstrate their suitability for energy applications in harsh environmental conditions. The vigorous experimental characterization of the composite exemplified the multifunctional properties, quantifying the interrelationship between the composition and performance. We observed that the addition of magnetic particles to the electroactive copolymer matrix resulted in improvement in the mechanical and electrical properties since the particles acted as pinning sites, hindering the deformation of the chains and enhancing polarization. The effective modulus model was amended to account for the crystallization-induced change in material stiffness. We also measured and computed the magnetic particles motion to explicate the detrimental effect of mobility and migration on the overall magnetoelectric coupling performance of the composite. Thereby, we derived an analytical model based on the magnetic force due to the co-presence of alternating and constant magnetic fields, and the viscous drag force due to the viscoelastic properties of the electroactive copolymer matrix. We demonstrated that the mobility of the particles plays a crucial role in the short and long term performance of magnetoelectric coupling in multiferroic particulate composites, uncovering the underpinnings of the dichotomy in performance between experimentally measured and analytically predicted coupling coefficients., thus, allowing for the proposal of new approaches to realize the scientific potential of magnetoelectric particulate composites in energy applications.

Analysis of Wavelength Sensitivity of Coupling Coefficients and Inter-core Crosstalk in a 9 core Multi-core Fiber

Wavelength dependence of coupling coefficients and inter-core crosstalk in a 9-core homogeneous multi-core optical fiber (MCF) are investigated analytically. The analysis is further extended to evaluate the mean crosstalk power at the output of any core with light launched into other core of the MCF. Propagation length dependence of mean crosstalk power is investigated using both coupled mode theory (CMT) and coupled power theory (CPT). CPT based results show that mean crosstalk power linearly dependent on propagation distance, and it is higher for higher values of coupling coefficient. On the other hand, the mean crosstalk power is found to oscillate with the propagation distance in case of CMT. It is also observed that the mean crosstalk power (dB) is more prominent at a lower wavelength for a given propagation distance. The behavour of relative crosstalk power is also investigated analytically where it is noticed that the relative crosstalk power increases almost linearly with core pitch and with wavelength. It is also seen that the relative crosstalk power (dB) is more in an MCF with lower number of cores when it is varied with respect to wavelength. This is due to the increase of core pitch under the same cladding diameter and cladding thickness limitations.