Unidirectional Transmission Behavior Research Articles

Analytical modeling of piezoelectric meta-beams with unidirectional circuit for broadband vibration attenuation

Broadband vibration attenuation is a challenging task in engineering since it is difficult to achieve low-frequency and broadband vibration control simultaneously. To solve this problem, this paper designs a piezoelectric meta-beam with unidirectional electric circuits, exhibiting promising broadband attenuation capabilities. An analytical model in a closed form for achieving the solution of unidirectional vibration transmission of the designed meta-beam is developed based on the state-space transfer function method. The method can analyze the forward and backward vibration transmission of the piezoelectric meta-beam in a unified manner, providing reliable dynamics solutions of the beam. The analytical results indicate that the meta-beam effectively reduces the unidirectional vibration across a broad low-frequency range, which is also verified by the solutions obtained from finite element analyses. The designed meta-beam and the proposed analytical method facilitate a comprehensive investigation into the distinctive unidirectional transmission behavior and superb broadband vibration attenuation performance.

Unidirectional transmission analysis of all-optical routers with asymmetric structured photonic crystals based on FDTD

The unidirectional transmission behavior of photonic crystal (PC) consisting of defect pairs is investigated by the finite-difference time-domain (FDTD) method. By selecting the appropriate size proportion of the constitutional PC defects and changing the power intensity of the incident light, the transmission contrast as well as the maximum transmission can be significantly improved. The simulation results are supported by the coupled-mode theory(CMT). This conclusion provides a reference for the design of an all-optical router with low insertion loss.

Silicon photonic crystal heterojunctions based dual-band unidirectional transmission with high transmissivity

Heterojunctions, which consist of two-dimensional circular- and square- hole silicon photonic crystals (PCs), are presented. Based on the finite-different time-domain simulations, the light transmission spectra and field distributions are obtained. A dual-band efficient unidirectional transmission behavior is realized by exciting higher diffraction orders through the novel interface structure. Owing to the self-collimation effect, high-quality unidirectional beam splitting phenomena are also observed. A heterojunction, which can achieve both dual-band unidirectional transmission with high transmissivity of 86.7% and two high-intensity good-directionality split beams, is constructed.

Ultrahigh Contrast One-Way Optical Transmission Through a Subwavelength Slit

We computationally demonstrate one-way optical transmission characteristics of a subwavelength slit. We comparatively study the effect in single layer and double layer metallic corrugations. We also investigate the effect of a dielectric spacer layer between double corrugations to control the volumetric coupling of plasmon and optical modes. We computationally show unidirectional transmission behavior with an ultrahigh contrast ratio of 53.4 dB at λ = 1.56 μm. Volumetric coupling efficiency through the nanoslit strongly depends on the efficient excitation of both the surface plasmon resonance and metal–insulator–metal waveguide modes. We show that the behavior is tunable in a wide spectral range.

A pipe-like one-way structure of acoustic wave

We proposed a pipe-like structure with linear materials to obtain the acoustic unidirectional transmission. The system consists of a bending pipe and a phononic crystal and designed by extending the idea of frequency selection in nonlinear acoustic diode into the mode selection of a linear acoustic system. The system has a significant transmission efficiency and good rectifying ratio which is designed to work in the air. We also experimentally realized the unidirectional transmission behavior for acoustic waves and the experimental results agree well with the theoretical simulation. This device is expected to have potential applications in ultrasonic devices such as acoustic diodes.

Design of ultrahigh-contrast all-optical diodes based on coupled nonlinear photonic crystal defects

Abstract We design and investigate the unidirectional transmission behavior of coupled photonic crystal defects with instantaneous Kerr nonlinearity. Theoretical analysis based on coupled-mode theory and numerical simulations based on finite-difference time-domain techniques indicate that ultrahigh-contrast all-optical diodes can be achieved by properly misaligning the frequencies of the coupled cavities. The transmission contrasts of such configurations composed of three and four cavities are demonstrated to be as high as 518 and 7015, with 42.8% and 46.3% forward transmissions, respectively.

On-chip optical diode based on silicon photonic crystal heterojunctions

Optical isolation is a long pursued object with fundamental difficulty in integrated photonics. As a step towards this goal, we demonstrate the design, fabrication, and characterization of on-chip wavelength-scale optical diodes that are made from the heterojunction between two different silicon two-dimensional square-lattice photonic crystal slabs with directional bandgap mismatch and different mode transitions. The measured transmission spectra show considerable unidirectional transmission behavior, in good agreement with numerical simulations. The experimental realization of on-chip optical diodes with wavelength-scale size using all-dielectric, passive, and linear silicon photonic crystal structures may help to construct on-chip optical logical devices without nonlinearity or magnetism, and would open up a road towards photonic computers.

One-way mode transmission in one-dimensional phononic crystal plates

We investigate theoretically the band structures of one-dimensional phononic crystal (PC) plates with both antisymmetric and symmetric structures, and show how unidirectional transmission behavior can be obtained for either antisymmetric waves (A modes) or symmetric waves (S modes) by exploiting mode conversion and selection in the linear plate systems. The theoretical approach is illustrated for one PC plate example where unidirectional transmission behavior is obtained in certain frequency bands. Employing harmonic frequency analysis, we numerically demonstrate the one-way mode transmission for the PC plate with finite superlattice by calculating the steady-state displacement fields under A modes source (or S modes source) in forward and backward direction, respectively. The results show that the incident waves from A modes source (or S modes source) are transformed into S modes waves (or A modes waves) after passing through the superlattice in the forward direction and the Lamb wave rejections in the backward direction are striking with a power extinction ratio of more than 1000. The present structure can be easily extended to two-dimensional PC plate and efficiently encourage practical studies of experimental realization which is believed to have much significance for one-way Lamb wave mode transmission.

Design of highly efficient optical diodes based on the dynamics of nonlinear photonic crystal molecules

We investigate the unidirectional transmission behavior of photonic crystal (PC) molecules consisting of defect pairs with Kerr nonlinearity and focus on how to enhance the transmission contrast and maximum transmission of the resulting optical diodes. Theoretical analyses in combination with the numerical simulations based on the finite-difference time-domain technique are employed to evaluate the designed optical diodes. It is found that by intentionally and properly misaligning the resonant frequencies of the constitutional PC atoms, the transmission contrast as well as the maximum transmission of the nonlinear PC molecules can be significantly improved. The figure of merit that characterizes the performance of optical diodes can be enhanced by a factor of 5 as compared with the optical diodes constructed by single asymmetrically confined PC atoms. In addition, the optimum performance of the optical diodes can be achieved only when the operating frequency is properly chosen.

All-optical diodes based on photonic crystal molecules consisting of nonlinear defect pairs

We investigate the unidirectional transmission behavior of photonic crystal (PC) molecules consisting of nonlinear defect pairs by use of the coupled mode theory and the finite-difference time-domain technique. As compared with the all-optical diodes based on single asymmetrically confined PC defects (or PC atoms), a significant enhancement in the transmission contrast is achieved. A qualitative comparison of the dynamical response to external excitation is carried out for nonlinear PC atoms and molecules and the physical origins responsible for the enhancement of transmission contrast are clarified. In addition, the tolerance of the resulting optical diodes against the fabrication error is discussed. Furthermore, it is revealed that the figure of merit, which is defined as the product of the threshold transmission and the transmission contrast, can be greatly improved by dropping the use of air defects. Some abnormal and intriguing transmission behaviors are observed in the PC molecules without using air defects.

Enhancement of unidirectional transmission through the coupling of nonlinear photonic crystal defects

We investigate the unidirectional transmission behavior of coupled photonic crystal defects with nonlinearity by using the coupled mode theory, focusing on how to enhance the transmission contrast. Although the unidirectional transmission originates from the asymmetric configuration and nonlinear property of the structure, it is revealed that the maximum transmission contrast depends mainly on two linear factors. For two coupled defects, they are the highest order of the frequency detuning appearing in the transmission formula and the frequency splitting due to the coupling. Our analyses are supported by the numerical simulations based on the finite-difference time-domain technique. An enhancement of the maximum transmission contrast by an order of magnitude is achieved in the structure consisting of two coupled defects.