Power Absorption Efficiency in Superconducting Fiber Optical Waveguides

By using an analytical model and a finite element method, we investigate a new, very sensitive, superconducting traveling wave photodetector made by a fiber waveguide, which includes two high index layers and an active superconducting layer. A comparison with the corresponding superconducting box shaped waveguide shows that a larger width of the superconducting layer can be used to obtain single degenerate hybrid mode HE ₁₁. The real part of the propagation constants in the fiber is smaller in comparison with that of the box-shaped waveguide with similar dimensions but the imaginary part of the propagation constant and the power absorption efficiency in superconducting layer are comparable with those of the corresponding box-shaped waveguide. The confinement regimes of the light and the power absorption efficiency in superconducting layer can be optimized by only acting on the fiber geometry.     

Sensitivity of Traveling Wave Photodetectors in Superconducting Box-Shaped Plasmon-Polariton Optical Waveguides

A very sensitive superconducting traveling wave photodetector made of a modified box-shaped waveguide, which includes two high index layers and an active superconducting layer, is studied. The optical propagation constants and the power absorption efficiency for guided modes are determined using the finite element method; the results show that by acting only on the waveguide geometry, different confinement regimes of the light in the absorption superconducting layer can be achieved and optimized.     

Efficiency of Traveling-Wave Photodetectors in Superconducting Box-Shaped Metamaterial Optical Waveguides

Using finite element simulations we investigate a new, very sensitive, superconducting traveling-wave photodetector made from a modified box-shaped waveguide, which includes a high-index layer, a metamaterial layer and an active superconducting layer. The maximum of the electric field is shifted from the middle of the waveguide towards an interface which includes the active YBCO layer for an optimum imaginary part of the refractive index of the metamaterial. For some values of the refractive index of metamaterial and an optimized geometry of the waveguide, the power absorption efficiency in superconducting layer is comparable with or better than that of the plasmon–polariton optical waveguide.     

Sensitivity of Traveling Wave Photodetectors in Superconducting Fiber Plasmon–Polariton Optical Waveguides

By using an analytical model and a finite element method, we investigate a new, very sensitive, superconducting traveling wave photodetector made by a fiber waveguide, which includes a high index layer, a metallic layer, and an active superconducting layer. A comparison with the corresponding superconducting box shaped waveguide shows that a larger number of modes (HE₁₁, TM₀₁ and HE₁₂) are obtained in optical fiber due to the surface plasmon–polariton modes at the interfaces between gold and air layers or between gold and YBCO layers. The radial component of the electric field is perpendicular to the metal surface and has sign changes at the gold boundaries as in the simple case of surface plasmon polaritons on metal cylinder with dielectric core. In a structure of the fiber with six layers, the imaginary parts of the TM₀₁, HE₁₂ modes, and the power absorption efficiency in superconducting layer are larger in comparison with that of the fiber with five layers. The confinement regimes of the light and the power absorption efficiency in superconducting layer can be optimized by only acting on the fiber geometry.     

Absorption Efficiency of Traveling Wave Photodetectors in Superconducting Fiber Plasmon–Polariton Optical Waveguides

By using an analytical model and a finite element method, we investigate a new, very sensitive, superconducting traveling wave photodetector made by an optical fiber, which includes a high index layer (LaAlO₃) with small losses, a metallic (gold) layer, and two active superconducting layers (YBCO). While the fundamental guided degenerate mode HE₁₁ is highly confined in the interior YBCO layer, the plasmon non-degenerate mode TM₀₁ and plasmon degenerate mode HE₁₂ are tightly confined in the exterior superconducting layer. In our structure of the fiber with five layers (without a buffer layer), the imaginary parts of the HE₁₁, TM₀₁, HE₁₂ modes and the power absorption efficiency in superconducting layers are larger in comparison with that of a fundamental mode from a LaAlO₃?CYBCO?CAu planar waveguide. The confinement regimes of the light and the power absorption efficiency in superconducting layers can be optimized by only acting on the fiber geometry.     

Very High Absorption of Traveling Wave Photodetectors in Superconducting Fiber Plasmon–Polariton Optical Waveguides

By using a finite element method, we investigate a new, very sensitive, superconducting traveling wave photodetector made by an optical fiber, which includes a high index layer (LaAlO₃) with small losses, a number of metallic (gold) cylinders, and a single active superconducting layer (YBCO). Although in our structure of the fiber with 32 smaller gold cylinders, the number of the modes is large (3 nondegenerate modes and 16 twofold degenerate modes), the imaginary parts of the HE₁₁, TM₀₁, HE₁₂, and higher order plasmon modes and also the power absorption (0.93 for HE₁₁,0.91 for HE₁₂,0.95 for TM₀₁ and larger than 0.93 for all higher order plasmon modes) in the active superconducting layer are larger in comparison with that of a fundamental mode from a LaAlO₃–YBCO–Au planar waveguide or with that of the HE₁₁, TM₀₁, HE₁₂ modes from a model previously published where the gold cylinders are replaced with a single gold layer. The nondegenerate HE₁₁ mode and the highest nondegenerate plasmon mode are highly confined in the YBCO layer in the space between the neighboring gold cylinders. Also, the plasmon mode TM₀₁ is highly confined in the YBCO layer but on the exterior surface of the gold cylinders. The HE₁₂ and the higher plasmon modes are highly confined in the YBCO layer in the space between the neighboring gold cylinders or very close to their exterior surface. The confinement regimes of the light and the power absorption efficiency in the superconducting layer can be optimized by only acting on the fiber geometry.     

Efficient Sub-wavelength Plasmonic Superconducting Photodetectors in Ultra-Thin Planar Waveguides and in Optical Fibers

By using a finite-element method we investigate the efficiency of sub-wavelength plasmonic superconducting photodetectors in ultra-thin planar waveguides (the incident wave is P-polarized) and in optical fibers (a traveling wave). The unit cell of a periodic sub-wavelength planar waveguide is made by a gold strip that is encapsulated in an YBCO layer and further enclosed above by an air layer and beyond by a thick gold plate substrate. For a planar structure with a single unit cell, the power absorption in YBCO layer is very large (between 0.929 and 0.975) for a fixed wavelength λ=1.55 μm when the distance between the strips and gold substrate is varied between 17 nm and 32 nm. When the wavelength is varied between 1.1 μm and 1.9 μm, the power absorption in YBCO layer is between 0.944 and 0.965 with a maximum of 0.976 at λ=1.40 μm. The superconducting traveling wave photodetector is made by an optical fiber, which includes a gold core surrounded by a number of smaller gold cylinders at a small distance from the central gold region and that are encapsulated in an active YBCO layer and further enclosed by an air layer. In our structure of the fiber with 18 smaller gold cylinders, the imaginary parts of the effective index of plasmon modes (two nondegenerate modes and eight twofold degenerate modes) and the power absorption (between 0.904 and 0.976) in active YBCO layer are very large. The first nine modes are highly confined in the YBCO layer in the space between the neighboring gold cylinders and the other nine modes are highly confined in the YBCO layer but in the space between the small gold cylinders and the gold core. Although in our structure, the thickness of the YBCO layer is 10 times smaller in comparison with that of a recently published model with 32 small gold cylinders, the losses in active YBCO layer are also very large.     

Analysis of planar superconducting waveguides in DC magnetic field

A theoretical analysis of microwave properties of planar superconducting waveguides of finite thickness in the presence of an external dc magnetic field is presented in this article. Some analytical formulas are derived for determining the attenuation and dispersion properties of the superconducting waveguide, which may account for the effects of the dc magnetic field, the electrodynamic properties of type-II superconductors, the thickness of superconducting films, and the dielectric loss in the waveguide. Numerical results are then given to show quantitatively how the dc magnetic field influences the propagation properties of the planar superconducting waveguide. Some analysis are also given to study the effect of dc magnetic field on the quality factorQ and the resonant frequency of planar superconducting waveguide resonators.     

Modelling of anisotropic superconducting waveguide as equivalent transmission line

This article presents a method of linking full-wave field analysis to distributed-circuit analysis by modelling anisotropic superconducting waveguides, consisting of two or more parallel superconductors, as equivalent transmission lines. As an application of this method, a full-wave solution is first found for an anisotropic superconducting planar waveguide by solving Maxwell's equations and London's equations modified to account for the effect of both anisotropy and normal electron conduction in anisotropic superconductors. Based on the full-wave solution, a complete set of equivalent transmission line parameters is then derived analytically to model the anisotropic superconducting planar waveguide. Numerical results are given to show quantitatively how the effect of anisotropy influences the transmission properties of the anisotropic superconducting planar waveguide at high frequencies. The results are compared with those for an isotropic superconducting planar waveguide as well as with some well-known results from a quasi-static approximation. It is shown that the full set of equivalent transmission line parameters based on the full-wave analysis is desired to model properly some strongly anisotropic superconducting waveguides at millimeter-wave frequencies.     

多自由度波导抑振器平面阵列的吸声性能研究

多自由度波导抑振器具有吸收低频入射声波的功能。研究了由波导抑振器阵列等效成的单极子-偶极子共振器复合阵列的声学散射问题,研究表明当共振器具有特定的阻尼值时,该多自由度波导抑振器阵列可以成为一个有效的声吸收器。根据布列霍夫斯基赫分层介质中波的相关理论,把波导抑振器阵列层等效成某个特性阻抗的均匀介质层,并数值分析了波导抑振器敷设在水下结构物表面后的吸声性能,得到了吸声性能和共振器阻尼系数,抑振器分布周期的关系。     

光波导显微技术测量微小厚度变化

在表面等离子波显微技术(SPM)的基础上,提出了一种新的反射型波导显微理论,并且进行了实验研究.这种显微技术采用棱镜波导耦合结构,在棱镜下底面依次镀有金属膜-波导层-样品层.利用导模共振吸收峰对样品层厚度敏感的特性,通过反射光强的测量来确定样品层厚度的变化值.和表面等离子波显微技术相比,光波导显微技术所采用的波导结构能够有效地削弱金属的吸收特性造成的影响,减小衰减全反射曲线的半峰全宽,进而提高波导显微对厚度变化的灵敏度.实验表明,光波导显微技术对厚度变化有很高的灵敏度.     

Optical waveguide absorption sensor using a single coupling prism

We propose an optical waveguide sensor that uses a leaky guided mode for measuring absorption of liquid samples. The sensor is composed of a single coupling prism on which a cladding layer and a waveguide layer are deposited. The guided mode generates dips in the reflectance spectrum; the depths of the dips depend on the extinction coefficient of a sample facing the layer. The sensitivity of the sensor is controlled by the thickness of the cladding layer. A simple theoretical model has been developed to analyze the behaviors of the sensor. In experiments we obtained sensitivity 17 times higher than that obtained by the conventional attenuated total reflection method.     

Orientation of methyl red dye molecules in a polymer matrix

We have studied the optical anisotropy of waveguide layers formed upon introduction of Methyl Red azo dye molecules into a polycarbonate matrix. The observed anisotropy of absorption in the dyed layers is related to ordering of the azo dye molecules in the course of waveguide layer formation. The order parameter is estimated and the possible mechanism of orientation is proposed.     

Tunable Wave Propagation in Superconducting Microstrip Line Based on Ferroelectric Thin Films

The microwave propagation characteristics in superconducting microstrip line supported by ferroelectric layer are theoretically investigated. The control of propagation constant and attenuation coefficient of the waveguide with biasing electric field is analyzed using the spectral domain method. The dependence of propagation characteristics on thickness of ferroelectric thin film as well as operating frequency for different applied electric fields is studied. The variation of propagation constant with temperature is also investigated. This method of analysis can be easily implemented in the design of tunable microwave devices.     

Strong Light Absorption of Traveling Wave Photodetectors in Superconducting Plasmon Optical Fiber

By using an analytical model and a finite element method, we investigate a new, very sensitive, superconducting traveling wave photodetector made by an optical fiber, which includes a gold core and another thin gold layer in between two active superconducting (yttrium barium copper oxide, YBCO) layers. It is possible to tune the geometrical parameters of the fiber such as only two guided modes (fundamental degenerate HE₁₁ and plasmon nondegenerate TM₀) are highly confined in the interior YBCO layer. For a particular fiber structure, a single degenerate HE₁₁ mode can be obtained if the gold core layer is replaced with a LaAlO₃ layer. One advantage of our optical fiber with a gold core is that the power fraction of the HE₁₁ and TM₀ modes is mainly absorbed (above 94 %) in the interior superconducting layer. Our optical fiber can be used in miniaturizing plasmonic superconducting photodetectors due to sub-wavelength dimensions and very efficient absorption.     

Matrix method for two-dimensional waveguide mode solution

In this paper, we show that the transfer matrix theory of multilayer optics can be used to solve the modes of any two-dimensional (2D) waveguide for their effective indices and field distributions. A 2D waveguide, even composed of numerous layers, is essentially a multilayer stack and the transmission through the stack can be analysed using the transfer matrix theory. The result is a transfer matrix with four complex value elements, namely A, B, C and D. The effective index of a guided mode satisfies two conditions: (1) evanescent waves exist simultaneously in the first (cladding) layer and last (substrate) layer, and (2) the complex element D vanishes. For a given mode, the field distribution in the waveguide is the result of a ‘folded’ plane wave. In each layer, there is only propagation and absorption; at each boundary, only reflection and refraction occur, which can be calculated according to the Fresnel equations. As examples, we show that this method can be used to solve modes supported by the multilayer step-index dielectric waveguide, slot waveguide, gradient-index waveguide and various plasmonic waveguides. The results indicate the transfer matrix method is effective for 2D waveguide mode solution in general.     

InGaAs/InAlAs quantum-well electroabsorption waveguide modulators with large-core waveguide structure: design and characterization

The design and the systematic characterization of the waveguide and the material properties of a modulator based on InGaAs/InAlAs quantum-well material for 1.5-μm operation are described. Following our previously developed theoretical design algorithm for optimizing the total performance of waveguide electroabsorption modulators [IEEE J. Quantum Electron, 29, 2476 (1993)], we designed an unconventional waveguide structure with a large passive core to yield better coupling efficiency for standard optical fibers and a thin active layer that yields a small optical-confinement factor. To evaluate the performance of this waveguide modulator, experimental methods for measuring the coupling efficiency, the optical-filling factor, and the absorption coefficient of the waveguide modulator and for characterizing the material properties were developed. The limitations of the material and the waveguide design, and the generalization of the limited set of experimental results based on a specific modulator to the design of more-general waveguide modulators are discussed.     

Superconducting and Structural Properties of Nb/PdNi/Nb Trilayers

The superconducting and structural properties of S/F/S (Superconductor/Ferromagnet/Superconductor) heterostructures have been studied by means of microwave measurements (1–20 GHz) and x-ray absorption fine structure (XAFS) spectroscopy. Nb/PdNi/Nb trilayers have been studied as a function of F layer thickness. With respect to pure Nb, XAFS analysis shows that the heterostructures exhibit larger structural disorder in the S layers. Microwave measurements show evidence for a progressively weaker vortex pinning with increasing F thickness. However, no clear correlation is found with the local disorder in Nb: the weakest pinning is not in the most disordered trilayer. Therefore, the structural disorder in the superconducting material cannot explain on its own the changes in vortex pinning. We argue that the F layer acts on the superconducting state itself. We propose possible explanations for the observed behavior.     

Eigenvalue equation and core-mode cutoff of weakly guiding tapered fiber as three layer optical waveguide and used as biochemical sensor

The core-mode cutoff plays a major role in evanescent field absorption based sensors. A method has been proposed to calculate the core-mode cutoff by solving the eigenvalue equations of a weakly guiding three layer optical waveguide graphically. The variation of normalized waveguide parameter (V) is also calculated with different wavelengths at core-mode cutoff. At the first step, theoretical analysis of tapered fiber parameters has been performed for core-mode cutoff. The taper angle of an adiabatic tapered fiber is also analyzed using the length-scale criterion. Secondly, single-mode tapered fiber has been developed to make a precision sensor element suitable for chemical detection. Finally, the sensor element has been used to detect absorption peak of ethylenediamine. Results are presented in which an absorption peak at 1540 nm is observed.     

Capillary waveguide optrodes: an approach to optical sensing in medical diagnostics

Glass capillaries with a chemically sensitive coating on the inner surface are used as optical sensors for medical diagnostics. A capillary simultaneously serves as a sample compartment, a sensor element, and an inhomogeneous optical waveguide. Various detection schemes based on absorption, fluorescence intensity, or fluorescence lifetime are described. In absorption-based capillary waveguide optrodes the absorption in the sensor layer is analyte dependent; hence light transmission along the inhomogeneous waveguiding structure formed by the capillary wall and the sensing layer is a function of the analyte concentration. Similarly, in fluorescence-based capillary optrodes the fluorescence intensity or the fluorescence lifetime of an indicator dye fixed in the sensing layer is analyte dependent; thus the specific property of fluorescent light excited in the sensing layer and thereafter guided along the inhomogeneous waveguiding structure is a function of the analyte concentration. Both schemes are experimentally demonstrated, one with carbon dioxide as the analyte and the other one with oxygen. The device combines optical sensors with the standard glass capillaries usually applied to gather blood drops from fingertips, to yield a versatile diagnostic instrument, integrating the sample compartment, the optical sensor, and the light-collecting optics into a single piece. This ensures enhanced sensor performance as well as improved handling compared with other sensors.