Loss-reduced highly birefringent selectively liquid-filled photonic crystal fibers

We have theoretically investigated the birefringence and loss properties of the selectively liquid-filled photonic crystal fibers with the liquid asymmetrically infiltrated into one-line air holes along x-axis. A high birefringence value B = 1.74 × 10⁻³ can be achieved at λ = 1.55 μm. By varying the index of the infiltrating liquid, the birefringence values are shown to be well tuned. In addition, the confinement losses can be efficiently reduced by diminishing the number of liquid holes, which is quite useful for optical devices.     

Design of high-Q cavities in 2D photonic crystals air holes filled with polymer

We design novel photonic crystal heterostructure, substituting the air in the holes with materials of refractive index higher than n = 1. This can be achieved by infiltrating the photonic crystal (PC) with polymer. We theoretically investigate the L₂ cavity with two missing holes in the center, where the six holes surrounding the cavity are locally filled with polymer. We show that cavity modes can be differently tuned depending on the size and the position of the first hole adjacent to the cavity. A photonic microcavity with a high Q factor of 5.5 × 10⁶ and a modal volume V of 0.1919 is demonstrated. We demonstrate that the calculated Q factor for the designed cavity increases by a factor of 22 relative to that for a cavity without displaced and reduced air holes, while the modal volume remains almost constant.     

Demonstration of temperature resilient properties of 2D silicon carbide photonic crystal structures and cavity modes

In this paper, photonic crystal (PhC) based on two dimensional (2D) square and hexagonal lattice periodic arrays of Silicon Carbide (SiC) rods in air structure have been investigated using plane wave expansion (PWE) method. The PhC designs have been optimized for telecommunication wavelength (λ = 1.55 μm) by varying the radius of the rods and lattice constant. The result obtained shows that a photonic band gap (PBG) exists for TE-mode propagation. First, the effect of temperature on the width of the photonic band gap in the 2D SiC PhC structure has been investigated and compared with Silicon (Si) PhC. Further, a cavity has been created in the proposed SiC PhC and carried out temperature resiliency study of the defect modes. The dispersion relation for the TE mode of a point defect A1 cavity for both SiC and Si PhC has been plotted. Quality factor (Q) for both these structures have been calculated using finite difference time domain (FDTD) method and found a maximum Q value of 224 for SiC and 213 for Si PhC cavity structures. These analyses are important for fabricating novel PhC cavity designs that may find application in temperature resilient devices.     

Measurement of glycerol concentration in B–H–G solution using 3D photonic crystal structure

A novel technique is used to measure the concentration of glycerol in blood-hemoglobin-glycerol (B–H–G) solution using 3D photonic crystal structure is presented in this paper. Glycerol concentration is estimated accurately by measuring the intensities of transmitted light. Here, reflection as well as absorption losses is considered to measure the transmitted intensity of light having wavelength 540 nm. The principle of measurement is based on the linear variation of photonic band gap with respect to glycerol concentration. Simulations for photonic band gap are made using plane wave expansion (PWE) method. An experimental set up is theoretically designed to measure the concentration of glycerol at different hemoglobin concentration.     

Analysis and design of optically transparent antenna on photonic band gap structures

An optically transparent microstrip patch antenna is designed on photonic bandgap structures and its radiation characteristics are computed and analyzed in the visible spectrum region. The proposed antenna consists of indium tin oxide, a transparent conducting material used both as a radiating patch and a ground plane separated by the 5 μm thin glass substrate. The introduction of periodic cylindrical air cavity structures in the glass substrate leads to the formation of photonic band gap. The patch thickness is carefully selected based on the analysis of the optical transmission coefficient with respect to patch thickness. The effective dielectric constant of the photonic band gap loaded glass substrate is computed using the effective medium approach. The refractive index of the proposed antenna is presented and discussed. The radiation efficiency of the antenna is shown to improve significantly due to insertion of proposed photonic band gap structures. The proposed design has yielded a bandwidth of 2–2.3 THz for a return loss (S₁₁) of less than −15dB and achieved a peak gain of 4.97dB at 2.27 THz.     

Analysis of a highly birefringent photonic crystal fiber with ellipse–rhombus air core

A novel highly birefringent photonic crystal fiber with small effective mode area is proposed. Four elliptical air-holes are designed in the internal layer of the fiber to cause the anisotropy, and the fiber has the property of highly birefringence and small effective mode area. The influences of elliptical air-holes on effective index, birefringence, effective mode area and nonlinear coefficient are analyzed by using full-vector finite element method (FEM). Simulation results show the birefringence can achieve the magnitude of 10⁻³ under the condition of d > 2.3 μm and a > 1.4 μm, which d and a are the distance and semimajor axis of elliptical air holes. By adjusting the parameters d and a, different effective mode area and nonlinear coefficient can be obtained, which demonstrates the flexibility of the proposed photonic crystal fiber.     

Ultra-wideband single-polarization single-mode, high nonlinearity photonic crystal fiber

We report a novel design of photonic crystal fiber (PCF) with a rectangular array of four closely-spaced, highly elliptical air holes in the core region and a circular-air-hole cladding. The proposed PCF is able to support ultra-wideband single-polarization single-mode (SPSM) transmission from the visible band to the near infrared band. With the aid of the inner cladding formed by the central air holes, one polarization of the fundamental mode can be cut off at very short wavelengths and ultra-wideband SPSM propagation can be achieved. The inner cladding also suppresses the higher order modes and allows large air filling fraction in the outer cladding while the proposed fiber remains SPSM, which significantly reduces the mode effective area and the confinement loss. Our simulation results indicate that the proposed PCF has a 1540 nm SMSP range with <0.25 dB/km confinement loss and an effective area of 2.2 μm². Moreover, the group velocity dispersion (GVD) of the proposed PCF can also be tuned to be flat and near zero at the near infrared band (∼800 nm) by optimizing the outer cladding structure, potentially enabling many nonlinear applications.     

Research on terahertz photonic crystal fiber characteristics with high birefringence

A new high birefringence photonic crystal fiber is proposed within the terahertz frequency region. It has two types of claddings, the inner is composed of six ellipse air holes arranged in a honeycomb array and the outer surrounded by circle holes. By using the full vector finite element method with anisotropic perfectly matched layers absorption boundary condition, the birefringence, chromatic dispersion and confinement loss of the fundamental mode are evaluated. The results show that the birefringence can achieve 10⁻³ when the wavelength increases from 600 μm to 900 μm. This structure will provide some reference value for the designing of high birefringence terahertz photonic crystal fiber.     

Tuning of full band gap in anisotropic photonic crystal slabs using a liquid crystal

We analyze the tunability of full band gap in photonic crystal slabs created by square and triangular lattices of air holes in anisotropic tellurium background, considering that the regions above and below the slab are occupied by SiO₂ and the holes are infiltrated with liquid crystals. Using the supercell method based on plane wave expansion, we study the variation of full band gap by changing the optical axis orientation of liquid crystal. Our results demonstrate the existence and remarkable tunability of full band gap in both square and triangular lattices, largest band gap and tunability being obtained for the triangular lattice.     

Nonlinear performance in silicon nitride slow light photonic crystal waveguides with elliptical holes

We propose a slow-light photonic crystal waveguide, which uses a combination of circular and elliptical air holes arranged in a hexagonal lattice with the background material of silicon nitride (refractive index n = 2.06). Large value of normalized delay bandwidth product (NDBP = 0.3708) is obtained. We have analyzed nonlinear performance of the structure. With our proposed geometry strong SPM is observed at moderate peak power levels. Proposed photonic crystal waveguide has slow light applications such as reduction in length and power consumption of all-optical and electro-optic switches at optical frequency.