Band Gaps In One-dimensional Photonic Crystals Research Articles

Tunable wide-angle high-efficiency polarization selectivity based on a one-dimensional photonic crystal containing elliptical metamaterials

Recently, researchers achieved wide-angle high-efficiency polarization selectivity based on polarization-sensitive photonic bandgaps in one-dimensional photonic crystals containing elliptical metamaterials. However, wide-angle high-efficiency polarization selectivity can only operate at fixed wavelengths (around band edges), which intensively limits the practical applications. To overcome this limitation, we construct a one-dimensional photonic crystal containing phase-change-material-based elliptical metamaterials. The position of the polarization-sensitive photonic bandgap can be flexibly controlled by the crystallization rate of the phase change material. Empowered by the wavelength-tunable polarization-sensitive photonic bandgap, we achieve wavelength-tunable wide-angle high-efficiency polarization selectivity. As the crystallization rate increases from 0 % to 100 %, the operating wavelength of polarization selectivity can be flexibly tuned from 1440 to 1796 nm. Meanwhile, the operating angular width remains larger than 50° and the optimal polarization extinction ratio remains on the order of 104. Our work provides a viable route to designing tunable high-performance polarizers.

Mechanical Control of the Optical Bandgap in One-Dimensional Photonic Crystals.

Over the last several years, two-photon polymerization has been a popular fabrication approach for photonic crystals due to its high spatial resolution. One-dimensional photonic crystals with photonic bandgap reflectivities over 90% have been demonstrated for the infrared spectral range. With the success of these structures, methods which can provide tunability of the photonic bandgap are being explored. In this study, we demonstrate the use of mechanical flexures in the design of one-dimensional photonic crystals fabricated by two-photon polymerization for the first time. Experimental results show that these photonic crystals provide active mechanically induced spectral control of the photonic bandgap. An analysis of the mechanical behavior of the photonic crystal is presented and elastic behavior is observed. These results suggest that one-dimensional photonic crystals with mechanical flexures can successfully function as opto-mechanical structures.

Terahertz angle-independent photonic bandgap in a one-dimensional photonic crystal containing InSb-based hyperbolic metamaterials.

According to the Bragg scattering theory, terahertz (THz) photonic bandgaps (PBGs) in all-dielectric one-dimensional (1-D) photonic crystals (PhCs) are strongly dependent on the incident angle. Such a strongly angle-dependent property of the PBGs not only limits the widths of omnidirectional PBGs, but also causes the strongly angle-dependent property of defect modes and optical Tamm states in multilayer structures containing all-dielectric 1-D PhCs. Until now, ways to achieve a THz angle-independent PBG have been an open problem. Herein, according to the existing phase-variation compensation theory, we achieve a THz angle-independent PBG in a 1-D PhC containing indium antimonide (InSb)-based hyperbolic metamaterials for transverse magnetic polarization. Different from conventional strongly angle-dependent PBGs, the angle-independent PBG remains almost unshifted as the incident angle changes. The relative frequency shifts of the upper and the bottom edges of the angle-independent PBG are only 1.4% and 0.4%, respectively. Besides, the angle-independent property of the PBG is robust against the disturbance of the layer thickness. The proposed 1-D PhC composes only two frequently used materials: silicon (Si) and InSb. Such a Si/InSb multilayer can be fabricated by the current ion-assisted electron beam coating or spin coating techniques. This THz angle-independent PBG would be utilized to design THz omnidirectional filters or absorbers.

Omnidirectional nonreciprocal absorber realized by the magneto-optical hypercrystal.

Photonic bandgap design is one of the most basic ways to effectively control the interaction between light and matter. However, the traditional photonic bandgap is always dispersive (blueshift with the increase of the incident angle), which is disadvantageous to the construction of wide-angle optical devices. Hypercrystal, the photonic crystal with layered hyperbolic metamaterials (HMMs), can strongly modify the bandgap properties based on the anomalous wavevector dispersion of the HMM. Here, based on phase variation competition between HMM and isotropic dielectric layers, we propose for the first time to design nonreciprocal and flexible photonic bandgaps in one-dimensional photonic crystals containing magneto-optical HMMs. Especially the zero-shift cavity mode and the blueshift cavity mode are designed for the forward and backward propagations, respectively. Our results show maximum absorption about 0.99 (0.25) in an angle range of 20-75 degrees for the forward (backward) incident light at the wavelength of 367 nm. The nonreciprocal omnidirectional cavity mode not only facilitates the design of perfect unidirectional optical absorbers working in a wide-angle range, but also possesses significant applications for all-angle reflectors and filters.

Omnidirectional photonic bandgap in one-dimensional photonic crystals containing hyperbolic metamaterials.

We theoretically and experimentally investigate the angle-dependent omnidirectional photonic bandgap (PBG) in one-dimensional photonic crystals (PCs) comprising hyperbolic metamaterials (HMMs) for TM polarization, which is different from blue-shifted PBG in conventional all-dielectric photonic crystals. The frequency range of PBG increases when the incident angles increase, owing to the red-shift and blue-shift of the long-wavelength and short-wavelength band edges, respectively. The red-shifted band edge originates from the phase-variation compensation mechanism between the HMMs and dielectric material. The experimental values are in good agreement with the simulation results. These nanostructures are ideal for fabricating photonic devices such as omnidirectional reflectors.

Angle-insensitive mid-infrared photonic bandgap in one-dimensional photonic crystal containing single-material semiconductor hyperbolic metamaterial layers

Angle-insensitive mid-infrared photonic bandgap in one-dimensional photonic crystal containing single-material semiconductor hyperbolic metamaterial layers

Temperature Dependent Tuning of Defect Mode inside Photonic Bandgap for Cwdm Applications

A theoretical study of temperature dependent tuning of defect mode inside photonic bandgap of one-dimensional photonic crystal with binary defect for optical communication applications based on coarse wavelength division multiplexing (CWDM) is presented. The transmission properties of the proposed structure are investigated through the transfer matrix method (TMM) at normal incidence. The proposed contraption is capable of selecting and switching any one wavelength channel at a time centered at particular wavelength out of 12 CWDM channels as per the international telecommunication union (ITU) grid G.694.2. It is very useful for narrowband wavelength selective switching (NWSS) applications based on CWDM. This study also provides some insight to design new kind of thermally tunable optical filters which can be used effectively in remote sensing and thermal imaging applications.

Tunable photonic band-gaps in one-dimensional photonic crystals containing linear graded index material

We have demonstrated control of the photonic band gaps (PBGs) in 1-D photonic crystals using linear graded index material. The analysis of PBG has been done in THz region by considering photonic crystals in the form of ten periods of second, third and fourth generation of the Fibonacci sequence as unit cell. The unit cells are constituted of two kinds of layers; one is taken of linear graded index material and other of normal dielectric material. For this investigation, we used a theoretical model based on transfer matrix method. We have obtained a large number of PBGs and their bandwidths can be tuned by changing the grading profile and thicknesses of linear graded index layers. The number of PBGs increases with increase in the thicknesses of layers and their bandwidths can be controlled by the contrast of initial and final refractive index of the graded layers. In this way, we provide more design freedom for photonic devices such as reflectors, filters, optical sensors, couplers, etc.

High-order bandgaps in one-dimensional photonic crystals

Bandgaps, including high-order ones, of one-dimensional photonic crystals are analysed.Accurate analytical expressions for band edges for both s and p polarized light are derived.As a consequence, the conditions for bandgap closing are obtained in a simple analyticalform. The derivation is based on a perturbative expansion of the dispersion equation using anew parameter which remains small around the band edges of all physically feasibleone-dimensional photonic crystals.

Robustness of one-dimensional photonic band gaps under random variations of geometrical parameters

The supercell method is used to study the variation of the photonic bandgaps in one-dimensional photonic crystals under random perturbations to thicknesses of the layers. The results of both plane wave and analytical band structure and density of states calculations are presented along with the transmission cofficient as the level of randomness and the supercell size is increased. It is found that higher bandgaps disappear first as the randomness is gradually increased. The lowest bandgap is found to persist up to a randomness level of 55 percent.