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This work proposes a sensitive low-temperature sensor based on the refractive index (RI) method. It uses a one-dimensional (1D) photonic crystal (PC) structure. The proposed sensor design consists of a bilayer stack of dielectric and superconductor materials. YaBa₂Cu₃O₇ is the superconductor utilized in this case, and we consider air to be the dielectric material. The RI of air doesn’t change much with the temperature, especially compared to the superconductor material. YaBa₂Cu₃O₇ is a superconductor that is ideal for temperature sensing applications because of its temperature-dependent RI. The sensing temperature range for the proposed sensor is 35–70K. The crucial structural factors have been precisely adjusted to increase sensing performance. Based on our knowledge, this is done to increase the sensor’s efficiency to levels that are higher than anything previously reported in the literature. Results show that the designed structure achieves an impressive RI sensitivity of 821.53nm/RIU and a temperature sensitivity of 3nm/K. This sensor could be very useful for medical applications for the detection of low temperatures.

Using the equifrequency surfaces (EFS) to describe negative refractions in left-handed materials (LHMs) and photonic crystals (PCs), negative phase and negative group refractive indexes in LHMs were compared with positive phase and negative group refractive indexes in PCs. The refractive indexes in PCs were dependent on frequencies and incident angles of electromagnetic wave, while indexes in LHMs were constant in the left-handed region. Furthermore, the phase compensating effect resulting from the negative phase refractive index was addressed to distinguish the perfect lens made of LHMs from the superlens realized in the all angle negative refraction (AANR) region of PCs.

The size influence of silica microspheres on the photonic band gap (PBG) of three-dimensional face-centered-cubic (fcc) photonic crystals (PCs) is studied by means of colloidal photonic crystals, which are self-assembled by the vertical deposition technique. Monodispersed SiO₂ microspheres with a diameter of 220–320 nm are synthesized using tetraethylorthosilicate (TEOS) as a precursor material. We find that the PBG of the PCs shifts from 450 nm to 680 nm with silica spheres increasing from 220 to 320 nm. In addition, the PBG moves to higher photon energy when the samples are annealed in a temperature range of 200–700°C. The large shift results from the decrease in refraction index of silica due to moisture evaporation.

Two-dimensional photonic crystals (2D-PCs) with Ge₂Sb₂Te₅ (GST) nanohole arrays were prepared by the nanosphere lithography (NSL) process. A primary factor of PCs is that the refractive index (n) and the n-modulation can be realized by using the GST films, which exhibit a reversible phase transformation between amorphous and crystalline states by laser illumination. The polystyrene (PS) spheres with a diameter of 500 nm were spin-coated on Si substrate and subsequently reduced by O₂-plasma treatment. The reduced spheres were utilized as a lift-off mask of the NSL process and their size and separation could be precisely controlled. Amorphous GST films were thermally evaporated and then the reduced PS spheres were removed. The fabricated GST nanohole arrays were observed by SEM and AFM. The nanohole diameters are nearly linearly reduced with increasing plasma-treatment time (t). The reduction rate (δ) for the conditions of this work was evaluated to be ~ 0.92 nm/s. The period (Λ) and filling factor (η) of PCs are structure parameters that determine their photonic bandgaps (PBGs). η-modulation can be easily achieved via a control of t and the Λ can be also modulated by the use of PS spheres with specific diameter. In addition, the PBGs for the fabricated GST 2D PC were calculated by considering the amorphous and crystalline states of GST.

The 90° waveguide bend is an important component of optical circuit applications. We propose several models for such a bend, some of them assisted by a two-dimensional photonic crystal with a bandgap in the desired range of operating frequencies. We show that a photonic crystal assisted bend reduces bending loss by several orders of magnitude for transverse electric modes.

We suggest that exotic sphere fibrations can be mapped to band topologies in condensed matter systems. These fibrations can correspond to geometric phases of two double bands or state vector bases with second Chern numbers m+n and -n, respectively. They can be related to topological insulators, magnetoelectric effects, and photonic crystals with special edge states. We also consider time-reversal symmetry breaking perturbations of topological insulator, and heterostructures of topological insulators with normal insulators and with superconductors. We consider periodic TI/NI/TI/NI′ heterostructures, and periodic TI/SC/TI/SC′ heterostructures. They also give rise to models of Weyl semimetals which have thermal and electrical transports.

The condition for the formation of Dirac cones at arbitrary points in the Brillouin zone by the accidental degeneracy of two photonic bands was examined by the degenerate perturbation theory and group theory based on the spatial symmetry of two modes. The analysis was applied to a two-dimensional square-lattice photonic crystal with C_4v symmetry and the dispersion relation in the vicinity of the M point was examined. Exact agreement between the analytical and numerical calculation was obtained.

We present a multiple-scattering method in conjunction with supercell calculations to study the electromagnetic surface states in three-dimensional photonic crystal (PC) slab. Using our technique, we obtain the first prediction of Dirac-cone photonic surface state in some three-dimensional PC slabs. Such a state can be used to investigate some extremal transmission phenomena of electromagnetic waves near the Dirac point on the surface of the crystal, which is similar to the case of electron on the surface of topological insulators.

In this paper, we propose a structure with cascaded two photonic crystal line-defect waveguides to reduce group velocity dispersion (GVD) of slow light. The width of the line-defect waveguides is tuned to obtain the two matched dispersion relations, where one of the dispersion relations has a maximum point with zero group velocity and large positive GVD; the other has a minimum point with zero group velocity and large negative GVD. The waveguides have ultra slow light with the group velocity 0.0012c. Finite-difference time-domain simulation demonstrates that the spreading of the slow light pulse in the first waveguide can be recovered by the dispersion compensation of the second waveguide with positive GVD.

In order to obtain tunable surface modes of photonic crystal, we add a magnetic material layer on the truncated surface of a two-dimensional photonic crystal. Through calculations of photonic band, we obtain the surface defect modes in the first and second gaps. Through the modulation of applied magnetic field, we can control the frequency, the group velocity and the exciting incidence direction of the surface defect mode. In particular, in the frequency range of surface defect modes, we can tune the group velocity to zero.

Phoxonic crystal (PXC) is a promising artificial periodic material for optomechanical systems and acousto-optical devices. The multi-objective topology optimization of dual phononic and photonic max relative bandgaps in a kind of two-dimensional (2D) PXC is investigated to find the regular pattern of topological configurations. In order to improve the efficiency, a multi-level substructure scheme is proposed to analyze phononic and photonic band structures, which is stable, efficient and less memory-consuming. The efficient and reliable numerical algorithm provides a powerful tool to optimize and design crystal devices. The results show that with the reduction of the relative phononic bandgap (PTBG), the central dielectric scatterer becomes smaller and the dielectric veins of cross-connections between different dielectric scatterers turn into the horizontal and vertical shape gradually. These characteristics can be of great value to the design and synthesis of new materials with different topological configurations for applications of the PXC.

We propose a design of narrow-band multi-channel optical filter using multiple stacks of unit cell consisting of trilayer of Doubly positive medium (DPS)–Doubly negative medium (DNG)–Epsilon negative medium (ENG). Finite Difference Time Domain (FDTD) technique is used to numerically simulate the effect of optical thickness of DPS, DNG and ENG media on tunability of the transmission spectrum of such a medium. We also demonstrate the control on the number of channels at different frequencies that can be transmitted through such medium.

A tunable transverse electric (TE) and transverse magnetic (TM) wave splitter using one-dimensional plasma dielectric photonic crystal which consists of plasma arranged periodically in a host dielectric medium is proposed. We performed a detailed study to explore the phenomena of reflection and transmission that occurs on obliquely incident electromagnetic wave propagating in the proposed plasma dielectric photonic crystal. We exactly calculated the transmittance based on the transfer matrix method. We find that if the parameters are selected appropriately, in the TE-stop or TM-stop frequency region, the other polarized component TM or TE wave is totally transmitted. The results also show that the dielectric constant, plasma thickness, incident angle and the applied magnetic field have significantly changed the properties of the TE/TM wave splitter. Moreover, the external magnetic field can be used as a kind of tunable method once the splitter is fabricated. Parameter dependence of the effects for the TE/TM wave splitter is calculated and discussed.

In this work, the transfer matrix method (TMM) is used to calculate the transmission of superconductor-dielectric 1D photonic crystal with central defect of semiconductor material (GaAs) at high superconductor critical temperature ($T_c)$. It is noticed that there is a red shift to high wavelength region by increasing the thickness of constituent materials. Also we study the effect of changing the incident angle, the doping density of GaAs and the applied pressure. The results show that the sense and change of photonic bandgap and transmittance peaks based on the thickness, incident angle, doping density of GaAs and hydrostatic pressure. In the case of change the thickness and hydrostatic pressure, the PBG and peak of transmittance shifted to higher wavelengths (red shift), while in the case of changing the incident angle and doping density, the PBG and peak of transmittance shifted to shorter wavelengths (blue shift).

By using the transfer matrix method (TMM), we theoretically explore the transmittance properties and cutoff frequency of one-dimensional photonic crystal (1DPCs) within the terahertz frequency region. The present structure consists of high-temperature superconductor and semiconductor layers. The results of the calculations represent the effects of various parameters on the cutoff frequency. We have used the two-fluid model as well as the Drude model to describe the permittivity of superconductor and semiconductor. Further, we consider that the permittivity of both the materials is depending on the hydrostatic pressure. The present results show that with the increasing of different parameters as the operating temperature, the thickness of semiconductor, and the filling factor of semiconductor, then the cutoff frequency shift to lower frequencies regions. By the increasing of superconductor thickness, hydrostatic pressure, doping concentration and filling factor of the superconductor, we found the cutoff frequency shifts to higher frequency regions. These results indicate that cutoff frequency can be modified through these different parameters. Finally, the present design could be useful for many optical systems as the optical filter, reflector and photoelectronic applications in the Terahertz regime.

In this paper, we consider the influence of magnetic pump field on the propagation of three-dimensional ultrashort optical pulse with Airy cross-section in a medium of a photonic crystal made of carbon nanotubes (CNTs). It is shown, that the pulse remains localized in a limited region of space and propagates quasi-stable. The possibility of efficient generation of high harmonics under the influence of an external magnetic field that were initially absent is observed.

Photonic crystal is a dielectric structure arranged according to certain rules, and its excellent electromagnetic wave characteristics can be used to manufacture a lot of kinds of photonic crystal devices. In this paper, a defect is introduced into the photonic crystal, and the transfer matrix method is used to study the relationship between the liquid concentration and the peak value of the liquid transmission at the electromagnetic wave length when the defect is a mixture of ethanol and glycol. The results show that by observing and measuring the position of the peak transmittance of the mixed liquid, the substance content of the liquid mixture, that is, the concentration, can be inferred. The accuracy of this method is compared with the experimental results, which shows that this method has high accuracy. This method is simple and easy to operate. This result opens up a new direction for the application of photonic crystals.

In this paper, we propose an active photonic-crystal microcavity waveguide with two-level atom-doped-dielectric slab as background material, and derive the model for signal gain calculation and analyze its gain characteristics. The analytical results show that the structure can generate high gain in a short length because of the efficient utilization of pump power in the microcavity. The proposed waveguide will be promising for the development of an active integrated photonic system.

One-dimensional defective binary photonic crystal is considered with the structure (AB)${}^N$D(AB)${}^N$, where A (TiO${}_2)$ and B (SiO${}_2)$ are the layers constituting the photonic crystal and D is the defect layer. The temperature dependence of the defect mode is investigated by considering both thermo-optic and thermal expansion effects. As the refractive indices and thicknesses of the photonic crystal layers are varied by temperature, the properties of the photonic crystal, such as bandgap and defect mode, are modified. Thus, we propose a tunable transmission filter operating in the visible region of the spectrum. It is found that the transmittance peak shift of the defect mode can be enhanced with the increase of both thermo-optic and the thermal expansion coefficients of the defect mode. As an example, we consider a photonic crystal with the structure (TiO₂–SiO${}_2{)}^6$/SiOC/(TiO₂–SiO${}_2{)}^6$ and a transmittance peak shift of the defect mode of 1.51 nm is obtained for a temperature increase of $100^{\circ }$C.

We investigate the photonic spin Hall effect (PSHE) of a Gaussian beam passing through a one-dimensional photonic crystal with a graphene defect film. We show that an epsilon singularity point and an epsilon-near-zero point of graphene emerge by varying its chemical potential. We find that the chemical potential of graphene significantly alters the transverse shifts of PSHE, while the temperature of graphene has a slight impact on the transverse shifts of PSHE. Moreover, we find that the behavior of PSHE near the singularity point considerably differs from that near the epsilon-near-zero point. Additionally, we further explore the different wavelengths of the incident Gaussian beam on the tunability of PSHE. We show that the considerable transverse shifts can be obtained simultaneously depending on the incident wavelength of the Gaussian beam and the chemical potential of graphene.