Two Channel Thermally Tunable Band-Stop Filter for Wavelength Selective Switching Applications by Using 1D Ternary Superconductor Photonic Crystal

By studying temperature-dependent dispersion characteristics and group velocity of 1D ternary photonic crystal (TPC) composed of dielectric-superconductor-dielectric materials, a thermally tunable band-stop filter which is capable of stopping unique wavelength channels without causing any interference amongst equally spaced wavelength channels of full width at half maximum of 1 nm each as per the requirement of wavelength division multiplexing standards adopted by the International Telecommunication Union specifying channel spacing in terms of frequency (wavelength) is suggested. The proposed structure can efficiently work as a two-channel wavelength selective switch for wavelength division multiplexing (WDM)-based all-optical networks. This study also gives theoretical insight to design some new kind of optical memories and tunable buffers which holds data temporary and have potential applications in modern communication systems.     

可调缺陷层等离子体光子晶体的滤波特性分析

等离子体光子晶体中引入另一种缺陷等离子体层,构成一种新的等离子体光子晶体滤波器.在不需改变等离子体光子晶体几何外形尺寸的情况下,通过改变缺陷等离子体层的参数,实现缺陷等离子体等效折射率改变,使等离子体光子晶体缺陷层的谐振频率发生偏移,实现了滤波器的可调谐特性.数值模拟中采用时域有限差分算法,计算了电磁波通过等离子体光子晶体的透射谱.结果表明通过调控缺陷层等离子体参数,使缺陷层的谐振频率发生偏移,从而实现等离子体光子晶体可调滤波特性.     

Maximization of Photonic Bandgaps in Two-Dimensional Superconductor Photonic Crystals

In this paper, we investigate the properties of photonic band structures in two-dimensional superconductor photonic crystals (2D-SCPCs) using the frequency dependent plane wave expansion method. We consider two types of 2D-SCPCs, which are composed of superconductor (dielectric) rods embedded into a dielectric (superconductor) background, named type I (type II) SCPCs. We target maximization of the gap-to-mid-gap ratio by varying many parameters, namely, shape of the rods, the operating temperature, the permittivity of the dielectric material, and the threshold frequency of the superconductor. We show that the type II SCPCs have a higher gap-to-mid-gap ratio than the type I SCPCs. In addition, the PBGs can be tuned efficiently by the operating temperature. Moreover, the photonic band structures can be tailored by changing the dielectric constant of the background (rods) in the type I (type II) SCPCs.     

Dielectric and Superconducting Photonic Crystals

We present the transmittance of two types of one-dimensional periodic structures. The first type of structure consists of alternating layers of a dielectric material. The second type of structure consists of alternating layers of a dielectric material and a superconductor whose dielectric properties are described by the two-fluid model. The variance of the intensity and the bandwidth of the transmittance are strongly dependent on the thicknesses, temperature, and frequencies. We have compared the transmittance spectra and present some details about the two types of structure. In the first type, we will make a comparison between the optical properties of the high temperature superconducting photonic crystal (HTScPC) by using the YBa₂Cu₃O₇ as a superconductor layer with SrTiO₃ as a dielectric layer. The second type consists of the dielectric photonic crystals (DPCs) and Al₂O₃ or MgO with SrTiO₃ within the ultra-violet region. The comparison obtained according to the difference of the thickness of SrTiO₃ and the variance of the number of periods. The common result is changed in the number of PBGs within the UV range.     

Investigating the Omnidirectional Photonic Band Gap in One-Dimensional Superconductor–Dielectric Photonic Crystals with a Modified Ternary Fibonacci Quasiperiodic Structure

In this paper, an omnidirectional photonic band gap (OBG) of one-dimensional (1D) superconductor–dielectric photonic crystals (SDPCs) with a modified ternary Fibonacci quasiperiodic structure which originates from Bragg gap is theoretically investigated by the transfer matrix method (TMM) in detail. The SDPCs are composed of superconductor and two kinds of homogeneous, isotropic dielectric. Such OBG is independent of the incidence angle and the polarization of electromagnetic wave (EM wave). From the numerical results, the OBG can be notably enlarged by tuning the thickness of superconductor and dielectric layers but cease to change with increasing the Fibonacci order. The OBG also can be manipulated by the ambient temperature of system. Especially, the ambient temperature of system is close to the critical temperature. However, the damping coefficient of superconductor has no effects on the OBG. The gap/midgap ratio of OBG also is studied by those parameters. It is shown that 1D SDPCs with a modified ternary Fibonacci quasiperiodic structure have a superior feature in the enhancement of OBG compared with the conventional 1D ternary and conventional ternary Fibonacci quasiperiodic SDPCs.     

一维光子晶体的带隙特性研究

一维光子晶体是指介质只在一个方向成周期性排列的材料。利用薄膜光学的特征矩阵法研究了一维光子晶体的禁带特性,分析了填充率变化、厚度的随机扰动对光子带隙的影响。结果表明,随着填充率的变化,各能级的带隙率变化,并且存在一个极大值;厚度的随机扰动对光子带隙也有一定的影响,随机度不同,对光子带隙的影响也不一样。本研究对一维光子晶体的设计与制备有一定的参考价值。     

Fano Resonance by Means of the One-Dimensional Superconductor Photonic Crystals

In the present work, we introduce a study about the reflectance properties of a one-dimensional superconductor photonic crystal in a different manner. Our structure is designed from alternately layers of high-temperature superconducting material (BSCCO) and a conventional superconducting material (Nb) terminated by the dielectric cap layer. The investigated numerical results are essentially based on the basics of the transfer matrix method and the two-fluid model. The numerical results showed the appearance of two sharp peaks, which are referred to Fano and electromagnetic-induced reflectance resonances. Also, we demonstrate the effects of many parameters on the reflectance properties of Fano resonance and the electromagnetic-induced reflectance. The effects of the constituent layer thicknesses, the number of periods, the operating temperature, the angle of incidence, and the refractive index of the dielectric cap layer are all considered. Finally, the effects of hydrostatic pressure on the Fano and EIR resonances are studied and calculated. This structure can play an important role in optical switching devices.     

Tunable Design of Structural Colors Produced by Pseudo‐1D Photonic Crystals of Graphene Oxide

It is broadly observed that graphene oxide (GO) films appear transparent with a thickness of about several nanometers, whereas they appear dark brown or almost black with thickness of more than 1 μm. The basic color mechanism of GO film on a sub‐micrometer scale, however, is not well understood. This study reports on GO pseudo‐1D photonic crystals (p1D‐PhCs) exhibiting tunable structural colors in the visible wavelength range owing to its 1D Bragg nanostructures. Striking structural colors of GO p1D‐PhCs could be tuned by simply changing either the volume or concentration of the aqueous GO dispersion during vacuum filtration. Moreover, the quantitative relationship between thickness and reflection wavelength of GO p1D‐PhCs has been revealed, thereby providing a theoretical basis to rationally design structural colors of GO p1D‐PhCs. The spectral response of GO p1D‐PhCs to humidity is also obtained clearly showing the wavelength shift of GO p1D‐PhCs at differently relative humidity values and thus encouraging the integration of structural color printing and the humidity‐responsive property of GO p1D‐PhCs to develop a visible and fast‐responsive anti‐counterfeiting label. The results pave the way for a variety of potential applications of GO in optics, structural color printing, sensing, and anti‐counterfeiting.     

Tunable Multiple Fano Resonances in One-Dimensional Photonic Crystal Containing Multiple Superconductor

We investigated the optical properties of one-dimensional photonic crystal composed of multiple different superconductor materials altogether theoretically by transfer matrix method. The number of Fano resonances generated in transmittance spectra depends on the number of different superconductor materials incorporated in the structure of photonic crystal. The Fano resonances are very sharp and sensitive to the varying parameters. The line profile of multiple Fano resonances in transmission spectra can be tuned by varying the thickness of the layers, the angle of incidence, and the temperature of superconductor photonic crystal. The tunable characteristic of multiple Fano resonances has potential application in bistable optical devices, switches, and sensors.     

Reversible Image Contrast Manipulation with Thermally Tunable Dielectric Metasurfaces

Increasing demand for higher resolution of miniaturized displays requires techniques achieving high contrast tunability of the images. Employing metasurfaces for image contrast manipulation is a new and rapidly growing field of research aiming to address this need. Here, a new technique to achieve image tuning in a reversible fashion is demonstrated by dielectric metasurfaces composed of subwavelength resonators. It is demonstrated that by controlling the temperature of a metasurface the encoded transmission pattern can be tuned. To this end, two sets of nanoresonators composed of nonconcentric silicon disks with a hole that exhibit spectrally sharp Fano resonances and forming a Yin‐Yang pattern are designed and fabricated. Through exploitation of the thermo‐optical properties of silicon, full control of the contrast of the Yin‐Yang image is demonstrated by altering the metasurface temperature by ΔT ≈ 100 °C. This is the first demonstrated technique to control an image contrast by temperature. Importantly, the turning technique does not require manipulating the external stimulus, such as polarization or angle of the illumination and/or the refractive index of this environment. These results open many opportunities for transparent displays, optical switches, and tunable illumination systems.     

Analysis of Reflectance Properties in 1D Photonic Crystal Containing Metamaterial and High-Temperature Superconductor

In the present work, reflectance properties of one-dimensional photonic crystal (1D PC) containing a metamaterial and high-temperature superconductor have been investigated theoretically and analyzed. The reflectance/transmittance spectrum of the proposed structure is obtained by using the characteristic or transfer-matrix method (TMM). The results show that by increasing the thickness of the metamaterial layer, the width of the second reflection band decreases while the width of the first reflection band remains almost the same though it shifts towards the higher frequency side. In addition to this, a new band gap arises in the lower side of frequency. But, when the thickness of the superconductor layer is increased, the width of both the bands increases and no additional band arises in this case. Moreover, the reflection band is also affected by varying the operating temperature of the superconducting layer and the results show that bands get narrower by increasing the operating temperature. Finally, the effect of incident angle on the reflection band has been discussed for both transverse electric (TE) and transverse magnetic (TM) polarizations.     

Filtering Properties of Photonic Crystal Dual-Channel Tunable Filter Containing Superconducting Defects

In this work, we analyze filtering properties in a photonic crystal (PC) dual-channel tunable filter. The filter structure containing twin superconducting thin films is denoted as (1/2) ^M S₁(2/1) ^N S₂(1/2) ^M . Here, 1 and 2 are dielectrics of SrTiO₃ and Al₂O₃, respectively. S₁ and S₂ are two high-temperature superconducting thin films taken to be the typical system, YBa₂Cu₃O_7?x . The two channel frequencies can be designed to locate within the photonic band gap (PBG) of the original PC (1/2) ^M . Channel frequencies can be significantly changed by changing N, the stack number of the center PC. With the use of superconducting defects, channel frequencies are temperature-dependent, that is, the filter is thermally tunable. The proposed filter structure is of technical use in superconducting photonic applications at terahertz frequency.