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A Narrowband Photo-Thermoelectric Detector Using Photonic Crystal
摘要： Here, a wavelength-specific photo-thermoelectric (PTE) device is reported that achieves narrowband optical absorption and thermoelectric conversion functions using a stack of thin films on a grating-patterned substrate. Conventional PTE devices are broadband with the absorption of electromagnetic radiation from ultraviolet to terahertz. There are demands for PTE devices that can exhibit narrowband response at a desired wavelength. Here, the narrowband PTE device consists of a photonic crystal (PC) filter with metal cladding and a thin-film thermocouple. The PC-PTE design is investigated numerically to illustrate the underlying energy conversion mechanism. The device is fabricated using nanoreplica molding followed by coating of thin films. The fabricated metal-cladding PC resonator exhibits a narrowband optical absorption with a resonant absorption coefficient of 85.4% and full-width-half-maximum of 14.8 nm in the visible wavelength range. The PTE measurements show that the thermoelectric output is sensitive to the coupling of incident light and guided-mode resonance modes. Illuminated under the resonant condition, the PTE device exhibits a responsivity and noise equivalent power of 0.26 V W?1 and 7.5 nW Hz?1/2, respectively. This PC-PTE technology has the unique attributes of narrowband detection, large surface area, and low cost for the potential application in sensors, optical spectroscopy, and imaging.
关键词： photo-thermoelectric effect,photonic crystals,guided-mode resonance,narrowband filters
更新于2025-09-10 09:29:36
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Phototunable <i>Morpho</i> Butterfly Microstructures Modified by Liquid Crystal Polymers
摘要： The unique hierarchical microstructures of the Morpho butterfly wing (MBW) exhibit angle independent blue iridescence. Biomimicking these microstructures and turning them into functional photonic crystals (PhCs) have fascinated scientists yet remain challenging. Here, a phototunable PhC is fabricated by depositing the azobenzene-containing linear liquid crystal polymer (LLCP) onto the MBW template. Thanks to the excellent mechanical properties and deformability of LLCP, the generated 3D bilayer microstructures demonstrate hierarchical deformation upon UV light irradiation, leading to a blueshift of the reflection peak (70 nm) and a remarkable change of reflectance (40%). This phototunable PhC may have potential applications in pigments, cosmetics, and sensors.
关键词： electrospinning,liquid crystal polymers,Morpho butterfly wings,photonic crystals,photoresponsiveness
更新于2025-09-10 09:29:36
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Separation-cooperated assembly of liquid photonic crystals from polydisperse particles
摘要： Easy and cost-e?ective production of high-quality photonic crystals (PCs) remains challenging but attractive, not just because they are a type of gemstone but more for their scientific applications (e.g., serving as lossless waveguides, visual sensors, novel pigments and novel separation media). Herein presented is a separation-cooperated assembly (SCA) strategy able to organize cheap polydisperse particles into PCs. Its feasibility was validated through sink-induced SCA of poorly disperse (size variation up to 56%) particles into iridescent liquid PCs in 3 days or more. Strikingly, with a sharp photonic band gap down to 10 nm (ca. 1/7 of the reported 66 nm), the liquid PCs are able to cyclically recover their iridescent color in ca 20 s after agitation, and keep their structural order after dryness, making them practicable to write and paint directly. Also significant is that SCA yielded uniform particles with size variation down to 0.7%. It is thus an easy way to isolate homogeneous particles from disperse ones.
关键词： photonic crystals,liquid PCs,polydisperse particles,separation-cooperated assembly,iridescent color
更新于2025-09-10 09:29:36
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Polarization-independent and super broadband flat lens composed of graded index annular photonic crystals
摘要： In this paper, we propose two types of all-dielectric polarization-independent graded index annular flat lens with a wide operating frequency range. The lenses are composed of two-dimensional triangular and square lattice photonic crystals with circular silica (SiO2) rods in the air. We assume in both square and triangular structures, the lenses are obtained by making air holes within each dielectric rod and we consider that the outer radius of the created annular rods are maintained constant while the size of the inner air holes varies along the transverse direction whose the air holes variation follow linear and parabolic function. The graded structures are made in such a way that the modulus of the refractive index is biggest at the center and decreases toward the edges. The optical properties and the physical background of the polarization-independent focusing mechanism are studied in frequency and spatial domains, using plane wave expansion and finite-difference time-domain methods. Our numerical results show that, through an appropriate set of design, the deigned lenses are able to focus the light regardless of polarization for a wide frequency range into approximately same focal length in which difference between focal distance of TE and TM polarization modes stays below λ/4. Compared to previously polarization-independent designed photonic crystal based lenses, our proposed structures work under much wider frequency range. Also, in contrast with most of the graded structures, our graded lens are made without altering the lattice constant along optical axis or transverse to optical axis. Moreover, the design approach is restricted to use of silica and non-use of more complicate materials such as liquid crystals, plasma, and the like. Thus, the designed systems can be constructed easier relative to the previously designed lenses.
关键词： Graded index annular photonic crystals,Optical beam focusing,broadband frequency lens,Polarization-independent lens
更新于2025-09-10 09:29:36
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Kinetic bandgap analysis of plasma photonic crystals
摘要： The dispersion relation of plasma and plasma-dielectric photonic multilayer structures is approached in terms of a one-dimensional Particle-in-Cell simulation. For several plasma-dielectric configurations, the system response is obtained using a pulsed excitation and a subsequent two-dimensional frequency analysis. It is first shown that the dispersion relation of a single, homogeneous plasma slab is well described by the cold-plasma model even at a low pressure of 1 Pa. The study is extended to the simulation of plasma photonic crystals with a variety of configurations based on the work of Hojo and Mase [J. Plasma Fusion Res. 80, 89 (2004)]. Considering a one-dimensional plasma photonic crystal made from alternating layers of dielectric and homogeneous plasma slabs, it is shown that the assumption of a cold-plasma description is well justified also in this case. Moreover, in this work, the results are reformatted and analyzed in a band diagram representation, in particular, based on the lattice constant a. Based on these considerations, a scaling invariant representation is presented, utilizing a generalized set of parameters. The study is completed with an exemplary comparison of three plasma-dielectric photonic crystal configurations and their corresponding band diagrams.
关键词： band diagram,Particle-in-Cell simulation,cold-plasma model,dispersion relation,plasma photonic crystals
更新于2025-09-10 09:29:36
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Band Gap Optimization Design of Photonic Crystals Material
摘要： The photonic crystal has a fundamental characteristic - photonic band gap, which can prevent light to spread in the crystals. This paper studies the width variation of band gaps of two-dimension square lattice photonic crystals by changing the geometrical shape of the unit cells' inner medium column. Using the finite element method, we conduct numerical experiments on MATLAB 2012a and COMSOL 3.5. By shortening the radius in vertical axis and rotating the medium column, we design a new unit cell, with a 0.3*3.85e-7 vertical radius and a 15 degree deviation to the horizontal axis. The new cell has a gap 1.51 percent wider than the circle medium structure in TE gap and creates a 0.0124 wide TM gap. Besides, the experiment shows the first TM gap is partially overlapped by the second TE gap in gap pictures. This is helpful to format the absolute photonic band gaps and provides favorable theoretical basis for designing photonic communication material.
关键词： band gap,photonic crystals,finite element method,MATLAB,COMSOL
更新于2025-09-10 09:29:36
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EFFECT OF TEMPERATURE ON NANOCOMPOSITE OF METAL NANOPARTICLES IN PHOTONIC CRYSTALS
摘要： We theoretically investigate the photonic band gaps in one-dimensional photonic crystals based on nanocomposite of silver nanoparticles. The dielectric permittivity is calculated in accordance with temperature dependence of plasma frequency of silver nanoparticle. The effect of temperature on these structures by incorporating the volume expansion coefficient of nanoparticle is analysed. The behaviors of photonic band gaps with variation of filling factor, radii of nanoparticle and temperature are observed. The evolution of these results leads to designing the desired photonic crystals.
关键词： photonic crystals,nanocomposite,photonic band gaps,temperature dependence,silver nanoparticles
更新于2025-09-09 09:28:46
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Optically active inverse opal photonic crystals
摘要： Chiral photonic crystals have been a widely investigated topic in chemistry, physics and biology. Till now, the researches about chiral photonic crystals are conducted on the objects of helical structures, while the chiral photonic crystals made of periodic chiral media remain unexplored experimentally. In this work, we have successfully constructed three-dimensional chiral polymer inverse opal photonic crystals (3D CPIOPCs) by a template-based method. Impressively, the 3D CPIOPCs exhibit emerging circular dichroism responses near the photonic band gaps. The experiments and calculations clearly elucidate the contribution of photonic structures and chiral media to this characteristic optical activity.
关键词： chiral media,circular dichroism,chiral photonic crystals,photonic band gaps,inverse opal
更新于2025-09-09 09:28:46
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A new method for glucose detection using the one dimensional defective photonic crystals
摘要： In order to enhance the sensing and measuring process of glucose, a sensitive tool surrounding environment. Therefore, we have studied the effects of many physical parameters on the position of the transmitted resonant peak. We have deduced that the glucose properties. Glucose is an important biomaterial can be affected by the should be developed to stimulate glucose properties. In the present paper, we propose intensity is formed within the photonic band gap which is directly related to the insertion of the glucose solution inside the defect layer. A resonant peak with a sharp theoretically the one dimensional photonic crystals that contain a defect layer to act as basics of the characteristic matrix method. Our proposed idea is mainly based on the a sensor for glucose detection. The theoretical modeling is essentially based on the defective photonic crystals.
关键词： Defect mode,Photonic band gaps,Glucose detection,Photonic crystals
更新于2025-09-09 09:28:46
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Dual-Bandgap Effect of Photonic Crystals on TiO2 Photocatalytic Activity in Ultraviolet and Visible Light Regions
摘要： Photonic crystals (PCs) have promising characteristic to raise the light harvest of materials. PCs with one photonic band gap (PBG) were usually used to enhance the light harvest of materials. In this research work, we used PCs with dual PBGs to increase the light harvest. SiO2 PCs with dual PBGs were constructed through depositing a SiO2 PCs layer on another SiO2 PCs layer by vertical deposition method. Then the bi-layer structured SiO2 PCs were composited with nanocrystalline TiO2 film which was sensitized by CdS quantum dots (QDs) (Q-T), to produce photocatalyst for photodegradation of gaseous acetaldehyde. By adjusting the PBGs of the bi-layer SiO2 PCs, namely one PBG matching with the absorption edge of TiO2 and another PBG matching with the absorbing range of CdS QDs, the photocatalytic activity of the composite film under white light irradiation was increased to 2.11 times of that of the control photocatalyst (the Q-T film coated on a disordered porous SiO2 film). When Q-T film was coupled with a monolayer SiO2 PCs, which has single PBG centered at TiO2’s electronic band gap (EBG) of 380 nm, its photocatalytic activity was increased by 1.34 times. When coupled with a monolayer SiO2 PC with the PBG centering at the EBG of CdS QDs (465 nm), the photo-catalytic activity of the Q-T film was increased by 1.54 times. Because the SiO2 PCs with dual-PBGs can simultaneously enhance the light harvest in ultraviolet and visible light region, the Q-T film coupled with dual-PBGs SiO2 PCs showed the highest activity.
关键词： Photocatalyst,SiO2 Opal,Dual photonic band gaps,TiO2,Photonic crystals
更新于2025-09-09 09:28:46