Radius Of Air Holes Research Articles

HIGHLY BIREFRINGENT FOUR-HOLE FIBER FOR PRESSURE SENSING

A highly birefringent four-hole flber (FHF) with a pair of large air holes and a pair of small air holes are proposed for air/hydrostatic pressure sensing. The birefringence of the FHF can be up to 0.01 due to the rectangle-like flber core surrounded by four air holes. Therefore, a FHF with a length of only several centimeters is required for high-sensitivity pressure sensing based on a Sagnac interferometer. Optical properties of the FHF such as efiective index and birefringence are investigated. Pressure sensor based on the FHF depends on the pressure-induced refractive index change or pressure- induced birefringence. The stress distribution of the FHF subjected to an air/hydrostatic pressure is represented. Simulations show that the principal stress component parallel to the slow axis of the of the FHF under the air/hydrostatic pressure is greatly enhanced due to the existence of two large air holes, which consequently results in a high sensitivity of the FHF-based pressure sensor. Relationships between the pressure-induced bireflrngence and the radius of the large air hole, the external diameter of the FHF, or the ellipticity of the elliptical FHF are investigated. The polarimetric pressure sensitivity of the FHF can be up to 607rad/MPa/m.

Photonic crystal slab waveguide-based infiltrated liquid sensors: design and analysis

Infiltrated liquid sensors based on a 2D photonic crystal waveguide were devised. This waveguide is designed by taking into account lowering of the radius of the central air holes in a single row and the optical resonance shifts due to refractive index change of these holes by selectively filling with different liquids. The transmission spectrum of the infiltrated liquid sensor was obtained with the use of a finite difference time domain method. At the working wavelength of 1550 nm, the waveguide mode gap edge shifts with sensitivity of 200 nm per refractive index unit. The mode gap shifts are consistent with dispersion diagrams.

Improving unrestricted imaging quality of a triangular lattice photonic crystal slab by modifying surface configuration

We propose a photonic crystal (PC) structure only by replacing square lattice [Luo et al. (2002) [12]] with triangular lattice to obtain an unrestricted imaging. Equal-frequency contours (EFCs) analysis shows that this triangular lattice two-dimensional PC exhibits an effective isotropic refractive index n eff=−1 at a normalized frequency ω=0.291×2 πc/ a. Imaging quality of this triangular lattice PC slab involving both power intensity and full-width at half-maximum intensity of the image is studied using the finite-difference time-domain (FDTD) simulation. In order to achieve a high-quality image, an appropriate surface termination is chosen. In addition, by adjusting the surface air-hole radius of the PC slab, the imaging quality can be further improved. Coupled-mode theory analysis shows that the optimized surface termination and the adjusted surface air-hole can excite two kinds of surface modes that can couple with the Bloch wave in the PC. With the help of these surface modes, both the intensity of image and the super-resolution capacity of this triangular lattice PC slab can be improved greatly.

Channel drop filters using photonic crystal Fabry–Perot resonators

We have proposed channel drop filters based on a combination of Fabry–Perot (F–P) resonators in a two-dimensional photonic crystal with a triangular lattice of air holes. By tuning the separation, the radii of air holes between F–P resonators, and the length of two F–P resonators, we can selectively improve filter characteristics and obtain a forward-dropping efficiency of 95% and a backward-dropping efficiency of 90% at desired resonance frequencies. For the case where two F–P resonators are directly connected without separation, it forms a ring behavior and has a backward-dropping efficiency of 75% at resonance. Moreover, we investigate the dependence of optical bistability in one of the optimized resonators on initial frequency detunings. A switching speed of 2ps is obtained. By decreasing the initial frequency detuning, overshoot on the switching-on power can be greatly suppressed.

Investigation of the effects of process-induced disorder location on planar photonic crystal waveguide properties

The effects of process-induced disorder location on planar photonic crystal waveguide properties are numerically investigated using three-dimensional finite difference time domain simulation by introducing random fluctuations of the hole radius, size, position, and shape of air-holes of two-dimensional planar photonic crystal slab. Results reveal that bandgap properties are extremely robust with respect to disorder. It is shown that the very first rows of holes play a major role in the amount of disorder-induced optical loss, and that keeping the first two rows of holes unchanged leads to a blue-shift of slow light waveguide properties.

Design and analysis of a wideband photonic crystal waveguide with low group-velocity and low dispersion

The slow light propagation in a line waveguide in the two-dimensional triangular photonic crystal has been numerically studied, based on which a wideband photonic crystal waveguide with low group-velocity and low dispersion is proposed. The numerical simulation analysis shows that it is possible to maximize the group index and minimize the group-velocity dispersion in wide bandwidth by increasing the radius of the basic air hole and changing the position of the first two rows of air holes in photonic crystal waveguides. Such a photonic crystal waveguide exhibits low group velocity and low group-velocity dispersion over a broad wavelength range. A larger group index-bandwidth product is achieved in this type of waveguide structure. The numerically computed results present the normalized bandwidth as 0.32%, 0.48% and 0.642% corresponding to the group index of 85, 58 and 45, respectively.

Improved photonic crystal directional coupler with short length

We investigate a photonic crystal (PC) waveguide coupler which is formed by two closely spaced linear waveguides in a two-dimensional triangular lattice of air holes. Our study shows that shifting one row of the air holes between the waveguides affects the dispersion curves of the guided modes and if the triangular lattice of air holes between the waveguides is replaced by a rectangular lattice, this modification results in an ultra-short coupling structure with coupling length less than 3 a, where a is the lattice constant. Also, we investigate the effect of changing the radii of air holes that are adjacent to or between the waveguides on the coupling length and show that increasing the radius of air holes between the waveguides decreases the coupling length. We analyze the output spectrum of an ultra-short channel drop filter designed based on this structure.

Photonic Crystal Fibers With a General Bravais Lattice

We present a systematic and comprehensive analysis of photonic crystal fibers with a general Bravais lattice and one hole per unit cell. We show how the lack of a proper separation of lattice shape effects from volume rescaling can lead to an incorrect assessment of the impact of lattice shape. We study and compare the endlessly single-mode, waveguide dispersion, and birefringence properties of the fundamental mode across all lattice shapes. For example, we show that the triangular and square lattice shapes offer the largest critical air-hole radius for the endlessly single-mode operation. We identify a general class of PCFs with large birefringence and show that the total birefringence of the fundamental mode is the result of the competition between two opposing effects: the cladding lattice shape and the asymmetry of the core and can vanish for some PCFs with even very nonsymmetric lattices. We show designs for which the birefringence vanishes even with nonsymmetric lattices and cores.

Analysis of Brillouin frequency shift and acoustic waves in a hollow optical fiber

We propose and demonstrate a new method to manipulate the Brillouin frequency shift in silica optical fiber by introducing a silica hollow optical fiber (HOF) waveguide structure. Propagation characteristics of acoustic waves guided along the HOF were theoretically analyzed, and the corresponding Brillouin frequency shifts were measured by a Brillouin optical-correlation domain-analysis system. We experimentally observed that Brillouin frequency shift v(B) monotonically increases as a function of the central air-hole radius, which showed good agreement with the simulation results. We confirmed that a precise control of Brillouin frequency shift can be obtained by controlling the waveguide parameters of the HOF.

Design, analysis and optimization of silicon-on-insulator photonic crystal dual band wavelength demultiplexer

A highly efficient photonic crystal dual band wavelength demultiplexer (DBWD) using silicon-on-insulator (SOI) substrates is proposed for demultiplexing two optical communication wavelengths, 1.31 μm and 1.55 μm. Demultiplexing of two wavelength channels is obtained by modifying the propagation properties of guided modes in two arms of Y type photonic crystal structure. Propagation characteristics of proposed DBWD are analyzed utilizing 3D finite difference time domain (FDTD) method. Enhancement in spectral response is further obtained by optimizing the Y junction of demultiplexer giving rise to high transmission and extinction ratio for the wavelengths, 1.31 μm and 1.55 μm. Hence it validates the efficiency of proposed optimized DBWD design for separating two optical communication wavelengths, 1.31 μm and 1.55 μm. Tolerance analysis was also performed to check the effect of variation of air hole radius, etch depth and refractive index on the transmission characteristics of the proposed design of SOI based photonic crystal DBWD.

Design of Taper Structure for Highly Efficient Coupling Between 1-D Photonic Crystal Coupled Resonator Optical Waveguide and Straight Waveguide

This paper presents a design method of a taper structure for highly efficient coupling between 1-D photonic crystal coupled resonator optical waveguides (1-D PC-CROWs) and input straight waveguides. We propose a new taper structure where not only air hole radius but also waveguide width are varied linearly in order to adjust the dispersion curves shift. By using the proposed tapered structure, we can connect each waveguide with high transmission over wide bandwidth. Our numerical simulation results show that a transmission of 98% around 1550 nm wavelength in a 6.6 mum long taper can be obtained with a 42 nm bandwidth.

Study of 2-D photon crystal Fano slab filters for biological sensing

A new compact optical Fano filter suitable for biological sensing is proposed, which patterns photon crystal in single crystalline silicon nanomembranes (SiNMs) and transferring onto transparent glass substrates. The effects of air hole size and silicon thickness on the transmission characteristics of new filter are numerically investigated by using three-dimensional finite-difference time-domain (FDTD) technique, the spectral response is also studied by back-filling bio-liquid. The results show that the dip wavelength will shift toward longer wavelength by either reducing air hole radius or filling bioliquid. The number of dips will increase with the increase of silicon thickness. The size of proposed filter can be less than 1 mm2.

Ferroelectric thin film photonic crystal waveguide and its electro-optic properties

The electro-optical properties of a tunable photonic crystal (PhC) thin film waveguide structure are simulated using a 2D finite difference time domain (FDTD) method. For a 2D PhC consisting of a square lattice array, the dependence of the bandgap on the air hole radius, lattice constant and filling factor are calculated. For the simulation ferroelectric barium titanate (BTO) PhC is chosen as the nonlinear medium. The calculated spectral range of the PhC waveguide is 187–207 THz with a bandwidth of 20 THz. A tunable superlattice PhC wide band filter was designed and its properties simulated. The passband center frequency decreases linearly with applied voltage over the frequency range of 187–194 THz. Due to the large electro-optic coefficient of BTO, the calculated tunability dfc/dV is −0.18 THz V−1. Simulation indicates that the proposed PhC superlattice structure has significant advantages over conventional devices including both a much reduced size (24 × 4 µm2) and large tunability of the bandgap required for future medium scale photonic integrated circuits.

Effects of fluctuation in air hole radii and positions on optical characteristics in photonic crystal heterostructure nanocavities

We investigate the influence of the nanometer-scale variations in the radii and positions of air holes on the optical characteristics for photonic crystal heterostructure nanocavities. The change in the quality factor, the resonant wavelength, the near-field image, and the polarization property are examined using three-dimensional finite difference time domain calculation with random fluctuation patterns. The variations with a standard deviation as small as 1 nm have a clear effect on these optical characteristics, whose magnitudes are strongly dependent on the fluctuation patterns. To prevent this deterioration, the accuracy of the 50 air holes nearest to the nanocavity is the most important.

The Influence Of Hole Radius On The Properties Of Photonic Crystal Fiber

The influence of air hole radius on the numerical aperture, total dispersion, effective area, and nonlinear coefficient for the photonic crystal fibers are investigated. This study shows, when the pitch size and the number of rings holes are held constant, the increasing of air hole radius up to 0.8µm gives better coupling efficiency due to the increasing in numerical aperture. The results show that the zero dispersion point is shifted toward the shorter wavelength due to the increasing of air hole radius.

Quantum Hadamard Gate Implementation Using Planar Lightwave Circuit and Photonic Crystal Structures

An all optical method has been proposed for quantum Hadamard gate implementation. This quantum gate was realized by using Y-junction beam splitter. Normal modes in waveguides have been used as quantum bit. This all optical gate can be used in quantum computation and communication. The proposed Hadamard gate has potential of being more compact and easily realized compared to other optical implementations. By using planar lightwave circuit in implementation, the width of Yjunction input waveguide, width of each branch, angle of bend and length of bend were obtained 1 micron, 0.75 micron, 45Âo and 0.75 micron, respectively. By using planar lightwave circuit in implementation, the radius of large air holes and the radius of small holes were obtained 0.2 ands 0.1 micron, respectively. The index of substrate was 1.325. Implementation based on photonic crystal structures and planar lightwave circuit technology was used in integrated optics.

Optimization of photonic crystal cavity for chemical sensing

We optimize photonic crystal cavities for enhancing the sensitivity to environmental changes by finite-difference time-domain method. For the heterostructure cavity created by local modulation of the air hole radius, the resonance shifts due to refractive index change of the background material are investigated. The shifts can be enhanced by reducing the photonic crystal slab thickness or introducing air holes in the cavity. The sensitivity of the thinner slab with central air holes is 310 nm/RIU (refractive index unit). The heterostructure created in the slotted waveguide of thin PhC slab shows better sensitivity of 512 nm/RIU owing to strong confinement of electric field in the low-index region.

Elimination of cross-talk in waveguide intersections of triangular lattice photonic crystals

We design an intersection for crossing waveguides in triangular lattice photonic crystals with cross-talk smaller than 10(-5). The cross-talk to the transverse waveguides is suppressed by symmetry mismatch between the cavity mode and the waveguide mode or by the mode-gap effect induced by air hole radius modulation of the waveguides. The transmission behavior of the crossing waveguides are illustrated by numerical simulations through finite difference time domain method.

Ultrahigh-Q photonic crystal cavity created by modulating air hole radius of a waveguide

We propose an ultrahigh quality factor (Q) photonic crystal slab cavity created by the local modulation of the air hole radius in the waveguide. In the cavity, photons are confined between two mirror regions with larger air holes and the lifetime of photons is greatly enhanced by introducing tapered regions with linearly increasing air hole radii. Q and mode volume are investigated for the cavities with various lengths and air hole size offsets of the tapered region with linearly increasing air hole radii by three-dimensional finite-difference time-domain method. The behaviors are analyzed by the mode patterns in real space and wavevector space. We obtain a numerical Q up to 8.8 x 10(7) for a mode volume of 1.6 (lambda/n)(3). Concerning the waveguide coupling, the cavity shows 80% coupling efficiency while keeping Q higher than 10(6).

A ministop band in a single-defect photonic crystal waveguide based on silicon on insulator

This paper reports that a two-dimensional single-defect photonic crystal waveguide in the Γ-K direction with triangular lattice on a silicon-on-insulator substrate is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. A ministop band (MSB) is observed by the measurement of transmission characteristics. It results from the coupling between the two modes with the same symmetry, which is analysed from the stimulated band diagram by the effective index and the two-dimensional plane wave expansion methods. The parameter working on the MSB is the ratio of the radius of air holes to the lattice constant, r/a. It is obtained that the critical r/a value determining the occurrence or disappearance of MSB is 0.36. When r/a is larger than or equal to 0.36, the MSB occurs. However, when r/a is smaller than 0.36, the MSB disappears.