Photonic Quasicrystals Research Articles

Topological photonic quasicrystal alloy

Recently, a concept of topological photonic alloy was proposed by mixing magnetized and non-magnetized gyromagnetic rods in a two-dimensional square photonic crystal that supports tunable Chern bandgaps and robust chiral edge states even at a low concentration of magnetized rods. However, whether such a notion can be extended to non-crystalline systems is still an open question. Here, we theoretically demonstrate that topological photonic quasicrystal alloys can also sustain nontrivial Chern bandgaps and nonreciprocal chiral edge states. More interestingly, compared with the conventional topological photonic alloy with a crystalline lattice, we find that the topological photonic quasicrystal alloy with a non-crystalline lattice needs a higher threshold concentration of magnetized rods to open the Chern bandgap. These results not only broaden our understanding of topological photonic alloy but also offer a platform for exploring the unique properties of topological photonic quasicrystals.

Topological states in Penrose-square photonic crystals

Topological edge states (TESs) and topological corner states (TCSs) in photonic crystals (PCs) provide an effective way to control the propagation and localization of light. The topological performance of integrated photonic devices can be improved by introducing the basic structural unit of photonic quasicrystals (PQCs) into PCs. However, the previous works arranged the basic structural unit of Stampfli-type and 12-fold Penrose-type photonic quasicrystals into triangular lattices, which have a complex structure and allow light to only propagate around 60° or 120° corners, limiting their applications. In this paper, a Penrose-square PC is proposed, which realizes both TESs and TCSs, and light successfully propagates around 90° corners. This work may reduce the difficulties encountered in the preparation of topological photonic crystals (TPCs) structured by arranging the basic structural units of PQCs periodically. It also provides a new, to the best of our knowledge, platform for studying TPCs and new ideas for improving the performance of integrated photonic devices.

Transport properties of electromagnetic waves in dielectric photonic quasicrystals

Transport properties of electromagnetic waves in dielectric photonic quasicrystals

Observation of Topological Corner State Arrays in Photonic Quasicrystals (Laser Photonics Rev. 18(7)/2024)

Observation of Topological Corner State Arrays in Photonic Quasicrystals (Laser Photonics Rev. 18(7)/2024)

Non-Hermitian Delocalization in a Two-Dimensional Photonic Quasicrystal.

Theoretical and experimental studies suggest that both Hermitian and non-Hermitian quasicrystals show localization due to the fractal spectrum and to the transition to diffusive bands via exceptional points, respectively. Here, we present an experimental study of a dodecagonal photonic quasicrystal based on electromagnetically induced transparency in a Rb vapor cell. First, we observe the suppression of the wave packet expansion in the Hermitian case. We then discover a new regime, where increasing the non-Hermiticity leads to delocalization, demonstrating that the behavior in non-Hermitian quasicrystals is richer than previously thought.

Observation of photonic chiral edge states in penrose quasicrystals

Photonic chiral edge states with one-way propagation and robust topological protection are hallmark features of photonic Chern insulators. To date, photonic chiral edge states have been observed in two-dimensional (2D) periodic and amorphous gyromagnetic photonic crystals. Recent theoretical studies reveal that photonic chiral edge states can also exist in 2D Penrose quasicrystals with long-range order but lack translational symmetry. Here, we report the first experimental observation of photonic chiral edge states in a 2D Penrose-tiled gyromagnetic photonic quasicrystal. By using microwave measurements, we observe a complete photonic band gap in the Penrose photonic quasicrystal despite the absence of bulk Bloch bands in momentum space. Moreover, we directly observe unidirectional backscattering-immune photonic chiral edge states within the photonic bandgap of the 2D Penrose quasicrystal. These results broaden our understanding of photonic chiral edge states and provide a new platform for exploring the intriguing properties of topological photonic quasicrystals.

Robust Anderson transition in non-Hermitian photonic quasicrystals.

Anderson localization, i.e., the suppression of diffusion in lattices with a random or incommensurate disorder, is a fragile interference phenomenon that is spoiled out in the presence of dephasing effects or a fluctuating disorder. As a consequence, Anderson localization-delocalization phase transitions observed in Hermitian systems, such as in one-dimensional quasicrystals when the amplitude of the incommensurate potential is increased above a threshold, are washed out when dephasing effects are included. Here we consider localization-delocalization spectral phase transitions occurring in non-Hermitian (NH) quasicrystals with local incommensurate gain and loss and show that, contrary to the Hermitian case, the non-Hermitian phase transition is robust against dephasing effects. The results are illustrated by considering synthetic quasicrystals in photonic mesh lattices.

Observation of Topological Corner State Arrays in Photonic Quasicrystals

AbstractRecently, the studies of topological corner states (TCSs) have been extended from crystals to quasicrystals, which are referred to as higher‐order topological quasicrystalline insulators (HOTQIs). However, the TCSs of complete quasi‐periodic structure in photonic systems have yet to be demonstrated. Moreover, there is only one TCS in each corner region in higher‐order topological insulators (HOTIs). Increasing the number of TCS is expected to increase the application potential of TCSs. In this work, HOTQIs in photonic systems are experimentally observed. It is found that HOTQIs possess TCS arrays, and each TCS array contains several TCSs. Furthermore, the universal theoretical framework of the multimer analysis method is improved, and the difference in the average charge density is proposed as a real‐space topological index. These results will open up new ideas for investigating highly integrated, multi‐region localized TCSs and are expected to provide new ways to explore topological phenomena and the applications of photonic quasicrystals.

Observation of localization of light in linear photonic quasicrystals with diverse rotational symmetries

Observation of localization of light in linear photonic quasicrystals with diverse rotational symmetries

Controlling Thermal Radiation in Photonic Quasicrystals Containing Epsilon-Negative Metamaterials

The transfer matrix approach is used to study the optical characteristics of thermal radiation in a one-dimensional photonic crystal (1DPC) with metamaterial. In this method, every layer within the multilayer structure is associated with its specific transfer matrix. Subsequently, it links the incident beam to the next layer from the previous layer. The proposed structure is composed of three types of materials, namely InSb, ZrO2, and Teflon, and one type of epsilon-negative (ENG) metamaterial and is organized in accordance with the laws of sequencing. The semiconductor InSb has the capability to adjust bandgaps by utilizing its thermally responsive permittivity, allowing for tunability with temperature changes, while the metamaterial modifies the bandgaps according to its negative permittivity. Using quasi-periodic shows that, in contrast to employing absolute periodic arrangements, it produces more diverse results in modifying the structure’s band-gaps. Using a new sequence arrangement mixed-quasi-periodic (MQP) structure, which is a combination of two quasi periodic structures, provides more freedom of action for modifying the properties of the medium than periodic arrangements do. The ability to control thermal radiation is crucial in a range of optical applications since it is frequently unpolarized and incoherent in both space and time. These configurations allow for the suppression and emission of thermal radiation in a certain frequency range due to their fundamental nature as photonic band-gaps (PBGs). So, we are able to control the thermal radiation by changing the structure arrangement. Here, the We use an indirect method based on the second Kirchoff law for thermal radiation to investigate the emittance of black bodies based on a well-known transfer matrix technique. We can measure the transmission and reflection coefficients with associated transmittance and reflectance, T and R, respectively. Here, the effects of several parameters, including the input beam’s angle, polarization, and period on tailoring the thermal radiation spectrum of the proposed structure, are studied. The results show that in some frequency bands, thermal radiation exceeded the black body limit. There were also good results in terms of complete stop bands for both TE and TM polarization at different incident angles and frequencies. This study produces encouraging results for the creation of Terahertz (THz) filters and selective thermal emitters. The tunability of our media is a crucial factor that influences the efficiency and function of our desired photonic outcome. Therefore, exploiting MQP sequences or arrangements is a promising strategy, as it allows us to rearrange our media more flexibly than quasi-periodic sequences and thus achieve our optimal result.

Inhibition of non-Hermitian topological phase transitions in sliding photonic quasicrystals.

Non-Hermitian (NH) quasicrystals have been a topic of increasing interest in current research, particularly in the context of NH topological physics and materials science. Recently, it has been suggested and experimentally demonstrated using synthetic photonic lattices that a class of NH quasicrystals can feature topological spectral phase transitions. Here we consider a NH quasicrystal with a uniformly-drifting (sliding) incommensurate potential and show that, owing to violation of Galilean invariance, the topological phase transition is washed out and the quasicrystal is always in the delocalized phase with an entirely real-energy spectrum. The results are illustrated by considering quantum walks in synthetic photonic lattices.

Reentrant delocalization transition in one-dimensional photonic quasicrystals

Reentrant delocalization transition in one-dimensional photonic quasicrystals

Light wave propagation and diffraction inhibition in three-dimensional photonic quasicrystal lattices

We have investigated the linear propagation of light wave in three-dimensional photonic quasicrystal lattices by numerical simulation. The diffraction characteristics of the light waves in the longitudinal non-modulated, in-phase modulated and out-of-phase modulated quasicrystal lattices have been compared and discussed. We have demonstrated the diffraction inhibition of light wave in three-dimensional photonic quasicrystals. Linear transverse light localization has been realized in the longitudinal out-of-phase modulated three-dimensional quasicrystal lattices by adjusting the structural parameters appropriately. Furthermore, the results also show that the longitudinal out-of-phase modulated photonic quasicrystals are easier to produce diffraction inhibition than the longitudinal out-of-phase modulated periodic lattices under low transverse refractive index contrast. Distortionless dot image transmission has numerically demonstrated in out-of-phase modulated photonic quasicrystals array. It provides a new way for distortion-free image transmission, which has promising applications in optical information transmission and all-optical signal processing.

Dual-Band Laser Stealth Based on Quasi Photonic Crystals

A quasi photonic crystal (QPC) dual-band absorber for laser stealth is designed and numerically studied. It consists of a defective two-dimensional photonic crystal on a thick Ni film. The defective photonic crystal is a continuous Ge layer with air holes, but some of the holes are periodically removed. Under a normal incidence that is perpendicular to the plane of the defects, the absorptivity can achieve 92.8% at the 1.064 μm wavelength and 93.2% at the 1.55 μm wavelength. Within large incident angles (<45 degrees), the dual-band absorptivity is still >80%. Additionally, the emissivity is as low as 5.8%~20.0% and 2.8%~5.8% in the 3–5 μm and 8–14 μm atmospheric windows. It is found that the introduced defects can couple the incidence into the structure and lead to spectral peaks (electromagnetic resonances) even without the bottom Ni film. With the help of the high-loss Ni film, the resonances are transformed into magnetic or/and electric modes of different orders. As a result, the QPC generates four absorption peaks. They are superimposed in pairs, resulting in enhanced absorption of the two laser wavelengths.

Polarization singularities in planar electromagnetic resonators with rotation and mirror symmetries

In this work, we apply the group representation theory to systematically study polarization singularities in the in-plane components of the electric fields supported by a planar electromagnetic (EM) resonator with generic rotation and reflection symmetries. We reveal the intrinsic connections between the symmetries and the topological features, i.e., the spatial configuration of the in-plane fields and the associated polarization singularities. The connections are substantiated by a simple relation that links the topological charges of the singularities and the symmetries of the resonator. To verify, a microwave planar resonator with the D8 group symmetries is designed and numerically simulated, which demonstrates the theoretical findings well. Our discussions can be applied to generic EM resonators working in a wide EM spectrum, such as circular antenna arrays, microring resonators, and photonic quasi-crystals, and provide a unique symmetry perspective on many effects in singular optics and topological photonics.

Narrow bandpass filter using Octonacci photonic quasicrystal

Abstract In this paper, we propose structures for tunable narrow bandpass optical filters covering the visible range of 400–800 nm. The transmittance spectra of s-polarized (TE mode) light in one-dimensional photonic crystals are obtained by using a theoretical calculation based on the transfer matrix method. Here, photonic crystals and photonic quasicrystals composed of Si and SiO2 are organized according to some generations of the Octonacci sequence. The number of output channels and their central wavelengths are found to be dependent on the generation number and the angle of incidence. The results show an increase in the quality factor as the angle of incidence increased. Therefore, the proposed structures are believed to be suitable for efficient narrow bandpass filters operating in the visible range.

Chiral photonic topological states in Penrose quasicrystals.

Electromagnetic topological edge states typically are created in photonic systems with crystalline symmetry and these states emerge because of the topological feature of bulk Bloch bands in momentum space according to the bulk-edge correspondence principle. In this work, we demonstrate the existence of chiral topological electromagnetic edge states in Penrose-tiled photonic quasicrystals made of magneto-optical materials, without relying on the concept of bulk Bloch bands in momentum space. Despite the absence of bulk Bloch bands, which naturally defiles the conventional definition of topological invariants in momentum space characterizing these states, such as the Chern number, we show that some bandgaps in these photonic quasicrystals still could host unidirectional topological electromagnetic edge states immune to backscattering in both cylinders-in-air and holes-in-slab configurations. Employing a real-space topological invariant based on the Bott index, our calculations reveal that the bandgaps hosting these chiral topological edge states possess a nontrivial Bott index of ±1, depending on the direction of the external magnetic field. Our work opens the door to the study of topological states in photonic quasicrystals.

Tunable and giant spatial Goos–Hänchen shifts in a parity-time symmetric Cantor photonic crystals incorporated with a centered graphene layer

In this study, we present the spectral features of a one-dimensional parity-time symmetric layered structure was composed of two quasi-photonic crystals which submit to the Cantor sequence and a graphene layer is embedded in the center of the quasi-crystals. Exceptional points, reflection and transmission spectra and the spatial Goos-Hänchen (GH) shifts are investigated at two distinct terahertz regions in the presence and absence of the graphene layer and compared them. The effect of the modification of imaginary part of refractive index of constituting gain and loss media are also examined. Our results show that, the proposed structure display giant enhanced GS shifts which are tunable with the chemical potential of embedded graphene layer, while GH shifts are weak in the absence of graphene layer. Results display different value and sign of GH shifts for the zero and nonzero chemical potentials. Very extreme GH shifts are obtained by judicious choice of chemical potential and imaginary value of the refractive index of constituting materials. Our results display that not only the photonic bandgap edge modes, but also bandgap modes can support giant GH shifts at Terahertz frequencies. Functionally, these types of structures are very desirable for designing optoelectronic devices that can be adjusted by the amount of chemical potential.

Coupling photonic quasicrystals with a one-dimensional critical high-temperature superconducting cavity

The transfer matrix method is used to calculate the transmission spectra in one-dimensional photonic quasicrystal (1D-PQ) coupling via a superconducting cavity. The layers that make up 1D-PQs are barium titanate ferroelectric (BaTiO3) and yttrium dielectric oxide (Y2O3), organized following the Fibonacci sequence. We consider the superconducting cavity to be a critical high-temperature superconductor (YBa2Cu3O7). Based on such proposed heterostructure, a multichannel filter in the near-infrared spectral region is obtained due to the existence of localized modes with an increasing Fibonacci sequence. Such localized modes are found in the null-transmission region named photonic band gaps. We observed that when increasing an incidence angle, the confinement of localized modes augments. Specifically, it is shown that, in 1D-PQs, from ferroelectric and dielectric materials with a Fibonacci sequence arrangement of an order of five (Fb5), two localized modes emerge as part of the PBG localized modes with a quality factor (Q) of Q=155.67 and Q=150.26. In the telecom region, such localized modes are tuned to longer wavelengths as the operating temperatures of the superconducting cavity increase from 10 to 80 K. Finally, we found that an increase in the thickness of the superconducting cavity favors a shift of a localized mode to longer wavelengths. The proposed heterostructure operates in cryogenic temperature environments, and we expect for it to be integrated into the optoelectronic circuit design.

The Multiplexing of Six Vortex Modes in a Multicore Photonic Quasi-Crystal Fiber

We propose a photonic quasi-crystal fiber which has five ring-shaped cores in the cross section. It realizes the multiplexing of 6 vortex modes. The fiber is based on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and has an octuple photonic quasi-crystal structure. It achieves four independent dual-core coupling pairs with the optimization of geometric parameters. By adjusting the thickness of five ring-shaped cores, the fundamental mode (HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) in the small side ring-shaped fiber cores couple to different higher order vector modes (TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> , TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> ) in the large center ring-shaped fiber core, which makes the light field transfer from small side cores to large center core and realizes the multiplexing of 6 vortex modes (TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{OAM}_{ \pm 1,1}^ \pm $</tex-math></inline-formula> , TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{OAM}_{ \pm 2,1}^ \pm $</tex-math></inline-formula> ). The transmission characteristics are analyzed with supermode theory. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta {n}_{\text{eff}}$</tex-math></inline-formula> of adjacent vector modes is larger than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${10}^{ - 4}$</tex-math></inline-formula> due to the thin center ring core. The coupling length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${L}_c$</tex-math></inline-formula> ) keeps in the order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${10}^{ - 2}$</tex-math></inline-formula> m between 1500--1600 nm and the coupling efficiency is larger than 90% in 1550 nm for four dual-core coupling pairs. We believe this design will have great potential in the field of all-fiber vortex mode division multiplexing.