Tzong Jer Yang

Differential microstrip lines with reduced crosstalk and common mode effect based on spoof surface plasmon polaritons

We apply the concept of spoof surface plasmon polaritons (SPPs) to the design of differential microstrip lines by introducing periodic subwavelength corrugations on their edges. The dispersion relation and field distribution of those lines are analyzed numerically. And then through designing practical coupling circuits, we found that compared with conventional differential microstrip lines, the electromagnetic field can be strongly confined inside the grooves of the corrugated microstrip lines, so the crosstalk between the differential pair and the adjacent microstrip lines is greatly reduced, and the conversion from the differential signal to the common mode signal can also be effectively suppressed. The propagation length of those lines is also very long in a wide band. Moreover, the experimental results in time domain demonstrate those lines perform very well in high-speed circuit. Therefore, those novel kinds of spoof SPPs based differential microstrip lines can be widely utilized in high-density microwave circuits and guarantee signal integrity in high-speed systems.

Subwavelength Microwave Guiding by a Periodically Corrugated Metal Wire

The guiding properties of a periodically corrugated metal wire at microwave frequencies are studied theoretically. The outer radius of the corrugated wire is of subwavelength size, and it seems difficult for spoof surface plasmon polaritons (SPPs) in the wire to be confined highly, even if the set of the geometric parameters of the wire structure is optimized. However, if the grooves of the corrugated wire are filled with a dielectric with high permittivity, the strong field confinement of spoof SPPs can be achieved even at frequencies smaller than the asymptotic frequency, for which the SPP losses are quite low. It is also shown that for this type of wire structure, the subwavelength microwave guiding is available for a certain frequency range.

Magnetic-Field Dependence of Effective Plasma Frequency for a Plasma Photonic Crystal

The effective plasma frequency in a photonic crystal (PC) is defined as the lowest frequency at which electromagnetic wave can start to propagate through the PC. In this paper, we theoretically investigate the effective plasma frequency fp, eff for a magnetized 1-D plasma PC (PPC). The PPC is made of two constituents, i.e., the plasma and the dielectric material like quartz. The effective plasma frequency in a PPC is obtained based on the calculated photonic band structure (PBS). It is found that fp, eff can be controlled by the externally applied static magnetic field, namely, fp, eff decreases significantly as the static magnetic field increases. This suggests that the plasma layer in a PPC shows a dielectric-like behavior when the magnetic field is applied. In addition, in the presence of static magnetic field, fp, eff will be increased as a function of electron density and thickness of the plasma layer. In the angular dependence of effective plasma frequency, we find that fp, eff is a decreasing function of angle of incidence in the absence of the static magnetic field. However, it becomes an increasing function of angle of incidence when the static magnetic field is applied. Finally, the effect of filling factor of the plasma layer is also illustrated.

Analysis of Wave Properties in Photonic Crystal Narrowband Filters with Left-Handed Defect

Optical wave properties for a photonic crystal narrowband filter with a left-handed defect are theoretically investigated. The filter is made of a defect layer together with two quarter-wave dielectric photonic crystals in a symmetric manner. It is found that a narrowband transmission filter can be achieved with the value of negative refractive index in defect being an even integer when the defect thickness equals the quarter wavelength. It also can be implemented when the value of negative refractive index is equal to an integer if the defect thickness is taken to be the half wavelength. As for the asymmetric one, there is only one selection rule for the quarter wavelength defect. Additionally, the effects of losses coming from the left-handed defect are also examined. The results establish guiding rules for the choice of the negative refractive index that are of technical use in designing such a filter with a left-handed defect.

Analysis of effective plasma frequency in a superconducting photonic crystal

In this work, a theoretical analysis on the effective plasma frequency (EPF) for a one-dimensional superconductor dielectric photonic crystal is made. First, the EPF is extracted from the first photonic band calculated within the framework of transfer matrix method together with Bloch theorem in a periodic multilayer structure. We investigate the EPF as a function of the filling factor and the permittivity of the dielectric layer, and the operating temperature as well. Then, the EPF is comparatively studied by the analytical expression derived from the effective medium theory. It is found that both results are in fairly good agreement.

Backward Guiding of Terahertz Radiation in Periodic Dielectric Waveguides

The guiding properties of periodic dielectric waveguides (PDWGs) are investigated theoretically at terahertz frequencies for both two- and three-dimensional model systems. It is shown that in a PDWG there may exist several bound modes, and among them often occur backward modes with antiparallel phase velocity and energy flow. The backward guiding behavior of the PDWG is demonstrated by its contra-directional coupling with a conventional dielectric waveguide (CDWG). For the coupler formed by a PDWG and a CDWG, the coupling direction of energy flow is selectable, since the PDWG supports either a forward or a backward mode at different frequencies.

Propagation of Low-Frequency Spoof Surface Plasmon Polaritons in a Bilateral Cross-Metal Diaphragm Channel Waveguide in the Absence of Bandgap

In this work, spoof surface plasmon polaritons in a novel subwavelength periodic bilateral cross-metal diaphragm channel waveguide are theoretically and experimentally investigated. It is found that the propagation frequency range can be broadened due to the absence of the bandgap between the fundamental band and the second guiding band by tuning the geometric parameters. In addition, the dispersion curve of the second band can pass through the light line and then enter into the radiation region, leading to a frequency-based beam steering radiation. We also find that, below the light line, there exists an anomalous linear dispersion such that the guiding mode propagation length can be extended up to around 200λ. Good agreement has been achieved between experimental and numerical results.

ANALYSIS OF TRANSMISSION PROPERTIES IN A PHOTONIC QUANTUM WELL CONTAINING SUPERCONDUCTING MATERIALS

Properties of wave transmission in a photonic quantum well (PQW) structure containing superconducting materials are theoretically investigated. We consider two possible PQW structures, (AB) P (CD) Q (AB) P -asymmetric and (AB) P (CD) Q (BA) P -symmetric, where the host photonic crystal (PC) (AB) P is made of dielectrics, A = SrTiO3, B = Al2O3, and the PQW (CD) Q contains C = A and superconducting layer D = YBa2Cu3O7ix, a typical high-temperature superconducting thin fllm. Multiple transmission peaks can be seen within the photonic band gap (PBG) of (AB) P and the number of peaks is directly determined by the stack number of PQW, i.e., it equals Q-1. Additionally, the results show that symmetric PQW structure is preferable to the design of a multichannel transmission fllter. The efiect of stack number of photonic barrier is also illustrated. Such a fllter operating at terahertz with feature of multiple channels is of technical use in superconducting optoelectronic applications.

Experimental Verification of Circuit Analog of Three- and Four-Level Electromagnetically Induced Transparency

Since a two-level resonant atomic system can be simulated by a simple circuit, three- and four-level electromagnetically induced transparency (EIT) that occur due to light-atom interaction can find its classical counterpart in circuit analog. As the optical response of an EIT atomic medium (including atomic vapors and semiconductor-quantum-dot dielectrics) can be controlled via tunable quantum interference induced by applied external control fields, in the scheme of circuit analog, such a controllable manipulation is achieved via capacitor coupling, where two loops are coupled by a capacitor that can represent the applied control fields in atomic EIT. Both numerical simulation and experimental demonstration of three- and four-level EIT were performed based on such a scenario of circuit analog. The classical “coherence” relevant to quantum interference among transitions pathways driven by both probe and control fields in EIT atomic systems has been manifested in the present circuit analog of EIT.

Frequency-Sensitive Optical Response via Tunable Band Structure in an EIT-Based Layered Medium

The optical response of an atomic vapor can be controlled by using tunable quantum interference induced by external control field. A periodic layered medium whose unit cells consist of dielectric (e.g., GaAs) and EIT (electromagnetically induced transparency) atomic vapor is suggested. It is demonstrated that such an EIT-based periodic layered medium shows more flexible optical response (sensitive to frequency) than a conventional photonic crystal does. The controllable band structure that depends on the external control field can be applicable to designs of new devices such as photonic switches and photonic logic gates, where one laser field can be controlled by the other one, and would have potential applications in the field of integrated optical circuits and other related areas, e.g., the all-optical technique.