Triangular Lattice Of Air Holes Research Articles

Design and optimization of 1 × 2 and 1 × 4 Y-shaped beam splitters in GaSb-based 2D photonic crystals

In this paper, we investigate the structural design of beam splitters with high total transmission efficiency in the two-dimensional (2D) GaSb (Gallium Antimonide)-based photonic crystals, and several optimal structures for [Formula: see text] and [Formula: see text] Y-shaped beam splitters have been provided. Using our proposed alternating iteration algorithm, by introducing several microstructures in the bend and Y-shaped junction areas to achieve topology optimization, the design of Y-shaped beam splitters with high total transmission efficiency at 1550 nm makes great progress. The splitter structures are designed on 2D GaSb-based photonic crystals with a triangular lattice of air holes immersed in the GaSb. All designs are simulated numerically and analyzed by using the finite element method. The optimized structures of [Formula: see text] Y-shaped beam splitters show that our optimization technique is efficient and simple. And the total transmission efficiencies both over [Formula: see text] at output ports are obtained, which indicates that our method is relatively efficient to other methods in some related reports.

Sandwiched photonic crystal fiber for dispersion compensation over the S + C + L + U wavelength bands.

We numerically investigated a sandwiched photonic crystal fiber (S-PCF) based on triangular lattice air holes that can be used for broadband dispersion compensation. By adjusting two layers of air holes diameter in the cladding, the S-PCF performs a large negative dispersion curve that can compensate for the dispersion of a standard single-mode fiber (SMF). The kappa value of the proposed PCF is also consistent with that of the SMF at the wavelength of 1.55 µm. In addition, the dispersion compensation multiple reaches up to 25.37. We have successfully obtained an effective compensated dispersion with the value of -0.5 to +0.1ps/nm/km in the wavelength of 1.46-1.67 µm, which covers the S+C+L+U wavelength bands. Moreover, we considered the manufacturing tolerance of the dispersion and effective compensated dispersion with ±2% and ±5% variation.

Enhancement of magneto-optical properties in magnetic photonic crystal slab waveguide based on yttrium iron garnet

In this work, a polarization-independent waveguide based on magnetic photonic crystal (MPC) with a triangular lattice of air holes in Yttrium Iron Garnet (YIG) slab grown on alumina (Al2O3) substrate is proposed, where both TE-like and TM-like periodic band gaps overlap. YIG is well known for its attracting magneto-optical (MO) properties and used to produce a coupling between the TE and TM modes. Thus, a nonreciprocal effect can be obtained by applying an external magnetic field parallel to the direction of propagation. At 1550 nm, the complete photonic band gap is simulated and optimized using the three dimensional plane-wave expansion method. The aim of this study is to enhance Faraday rotation (FR) while maintaining a low modal birefringence. A numerical analysis in function of magnetic gyration (g) has been reported, using the BeamProp software. The results reveal a proportional relation between FR, Δn and g, such for g = 0.5, a large FR of 26.11×104 °/cm with Δn = 7×10−6. The results show a real improvement of this MPC structure based on YIG with larger FR, lower modal birefringence and minimal losses. The notable enhancement in the MO behaviour could improve the performance of optical isolators, and makes it suitable for nonreciprocal devices.

Cascaded chirped narrow bandpass filter with flat-top based on two-dimensional photonic crystals.

We propose a structure of a cascaded chirped narrow bandpass filter with a flat-top based on two-dimensional (2D) photonic crystals (PhCs). The filter discussed here consists of three filter units, each with a resonator and two reflectors. Coupled mode theory and transfer matrix method are methodologies applied in the analysis of the features. The calculations show that the bandwidth of the filter can be adjusted by changing the distances between resonators and reflectors, and based on this, a flat-top response can be achieved by chirped-cascading the filter units. According to the theoretical model, we design a narrow bandpass filter based on 2D PhCs with a triangular lattice of air holes, the parameters of which are calculated using the finite element method. The simulation results show that the filter has a center frequency of 193.40THz, an insertion loss of 0.18dB, a flat bandwidth of 40GHz, and ripples of about 0.2dB in the passband. The filter is suitable for dense-wavelength-division-multiplexed optical communication systems with 100GHz channel spacing.

Mode conversion in magneto photonic crystal fibre

The first concept of an integrated isolator was based on nonreciprocal TE–TM mode conversion, the nonreciprocal coupling between these modes is caused by the Faraday rotation if the magnetization is aligned along the z–axis, parallel to mode propagation.We propose to study this magneto-optical phenomenon, by the simulation of magneto photonic crystal fibre (MPCF), it consists of a periodic triangular lattice of air-holes filled with magnetic fluid which consists of magnetic nanoparticles into a BIG (Bismuth Iron Garnet) fibre. We simulated the influence of gyrotropy and the wavelength, and calculated Faraday rotation and modal birefringence. In this fibre the light is guided by internal total reflection, like classical fibres. However it was shown that they could function on a mode conversion much stronger than conventional fibres.

Dirac‐mode guidance in silica‐based hollow‐core photonic crystal fiber with high‐index dielectric rings

Transmission of light in hollow‐core photonic crystal fiber (HC‐PCF) is traditionally based on the out‐of‐plane photonic bandgap of the crystal cladding that usually consists of periodically arranged air holes in silica glass. A new kind of wave guidance relying on a special point (Dirac point) of eigenfrequency dispersion plot in high‐index glass‐based HC‐PCF has been reported recently. Pure silica‐based HC‐PCF is not suitable for this kind of guidance. The existence of the Dirac point in a triangular lattice of air holes surrounded by a germania (GeO2)‐doped high‐index ring in pure silica host has been demonstrated. The addition of the high‐index layer provides a control over the density of states around the Dirac point. The operating wavelength can be tuned precisely by controlling the doping concentration and thickness of the doped glass rings. The structure is very simple and can be fabricated through a conventional stack and draw method.

Design of a DWDM Multi/Demultiplexer Based on 2-D Photonic Crystals

A multiplexer and demultiplexer (MUX/DEMUX) based on 2-D photonic crystals (PhCs) for a dense wavelength division multiplexing (DWDM) system is presented. The designed MUX/DEMUX consists of narrow bandpass filters and magneto-optical circulators based on 2-D PhCs with triangular lattice of air holes, the parameters of which are analyzed by a finite element method. The simulation results show that the frequencies 193.4, 193.3, and 193.2 THz could be multi/demultiplexed with a low insertion loss (<;0.5 dB) and large channel isolation (>18.4 dB). The proposed DWDM MUX/DEMUX could be used to provide transport solution for DWDM optical communication system with 100-GHz spacing.

Design and simulation of photonic crystal based all-optical logic gate and modulator using infiltration

We propose all-optical logic gate and modulator using nonlinear Kerr effect. The hybrid structure based on 2-D photonic crystal slab with triangular air-hole lattice is used for this purpose. The proposed cavity of switch structure is designed by infiltration of air holes with low refractive index and high third-order nonlinear coefficient polystyrene. Using numerical simulation, we present a fast logic gate with maximum on/off ratio of 26.61 dB, and minimum switching time window of 5.66 ps, while the maximum threshold power is 181 mW. We, also, propose a modulator which can operate with the bit rate as high as above 70 Gbps.

Surface structure for efficiently coupling into photonic crystal slab waveguides with a triangular lattice of air holes

Highly efficient coupling outer electromagnetic (EM) waves into photonic crystal (PhC) waveguides (PhCWs) is critical to the applications of PhCs in photonic integrated circuits. We investigate and simulate an efficient way of coupling EM waves into PhCWs of air holes array by using surface dielectric margin based on all-PhCs structure. Good matching of modal field profiles on both sides of the interface is obtained by adjusting the surface dielectric margin along the propagation direction. The coupling efficiency can be highly enhanced by suppressing the surface field propagating along the transverse margin at the interface. The numerical results using finite-difference time-domain simulations show that the bandwidth for coupling efficiency larger than 90% can be as broad as about 100[Formula: see text]nm.

Cladding modes in photonic crystal fiber: characteristics and sensitivity to surrounding refractive index

Characteristics of cladding modes in a photonic crystal fiber (PCF) with triangular air-hole lattice in the cladding are numerically analyzed using a finite element method. The transition for LP 11 cladding mode to core mode with variation of the normalized wavelength has been shown. The transition of the LP 01 cladding mode to the outer silica mode and reorganization of the LP 0 m cladding modes caused by varying the fiber radius has been investigated. By choosing the optimized fiber radius, which is located in the cladding modes’ reorganization region, the sensitivity of the coupled wavelength between the core mode LP 01 and cladding mode LP 03 to surrounding refractive index is increased by a factor of five and reaches to 2660 nm/refractive index unit over the range of 1.40 to 1.42. The sensitivity is competitive with that of long-period grating in PCF in response to changes in refractive indices of the medium contained in the cladding air channels.

Nonreciprocal TE–TM Mode Conversion Based on Photonic Crystal Fiber of Air Holes Filled With Magnetic Fluid Into a Terbium Gallium Garnet Fiber

The nonreciprocal optical effect of Faraday rotation (FR) is widely exploited in optical isolators to suppress back-reflections to protect optical sources and other devices from injection noise, or in optical circulators to route counter-propagating signals in a single physical channel to different ports [1]. The first concept of an integrated isolator was based on nonreciprocal TE-TM mode conversion. However, most proposals of the waveguide type isolators are based on nonreciprocal TE-TM mode conversion [2], the nonreciprocal coupling between these modes is caused by the FR if the magnetization is aligned along the z-axis, parallel to mode propagation. FR effect can be used for magnet sensors, because the Verdet constant of silica fibre is small (∼1.1 rad/(T.m) at 1064 nm) [3]. In this work, we propose to study the nonreciprocal TE-TM mode conversion phenomenon, by the simulation of magneto photonic crystal fibre (MPCF). It consists of a periodic triangular lattice of air-holes filled with magnetic fluids (Fe 3 O 4 ) into a Terbium Gallium Garnet (TGG) fibre which is a kind of synthetic garnet with chemical composition Tb 3 Ga 5 O 12 . This garnet was chosen as a Faraday rotator material which has excellent transparency properties and is very resistant to laser damage. TGG has also a high Verdet constant which results in the FR effect. We simulated the influence of gyrotropy and the wavelength, and calculated the FR and modal birefringence. In this MPCF fibre, the light is guided by internal total reflection, like classical fibres. However, it was shown that they could function on a mode conversion much stronger than conventional fibres.

Proposal for high efficiently 1×4 power splitter based on photonic crystal waveguides

We proposed a new kind of 1×4 optical power splitter composed of one input photonic crystal (PC) waveguide (PCW) and two PC branches with a triangular lattice of air holes. By employing the coupling between a defect region and one input, four output PCWs, the input power can be efficiently split into four output ports. The total transmittance as high as 99.4% at the wavelength 1550 nm is achieved. By modifying two holes at junction area, the input power can be almost evenly split into four parts with a bandwidth larger than 80 nm. It provides a new method and a compact model to split input power into multiple output ports in PCW devices and may find practical applications in future photonic integrated circuits.

Design of all optical logic gates in photonic crystal waveguides

In this paper, we report the design of all optical logic gates based on two-dimensional photonic crystal (PhC) composed of triangular lattice of air holes in silicon (Si). The proposed structure has been simulated using finite difference time domain (FDTD) method and it has been shown that all optical logic operations can be achieved if an appropriate initial phase is introduced between the input beams so that they may interfere constructively or destructively. The optical logic gates designed in the proposed structure have a response period of 1.024ps and can operate at a bit rate of 0.976Tbit/s.

Design of high-sensitive biosensor based on cavity-waveguides coupling in 2D photonic crystal

In this work, we design a new biosensor concept that uses a microcavity in 2D photonic crystal (PhC) to sense small refractive index (RI) changes. The RI sensor is formed by a point-defect resonant cavity in the sandwiched waveguide with triangular lattice of air holes. The properties of the sensor are simulated using the finite-difference time-domain method. The calculation results show that a change in ambient RI is apparent; the sensitivity of the sensor is achieved. We succeeded to obtain a new sensitivity value of 425 nm/RIU with a detection limit of 0.001 RIU, which proves the ability of the structure to produce biosensor PhC.

Low-loss, efficient, wide-angle 1 × 4 power splitter at ∼155 μm wavelengths for four play applications built with a monolithic photonic crystal slab

We exhibit a low-loss, efficient, and wide-angle 1×4 power splitter based on a silicon monolithic photonic crystal slab with triangular lattice air holes. A distinctive power-splitting ratio can be obtained depending on the hole shift in the bending region and the structure adjustment at the junction area with regard to the power splitter designed. Simulation results achieved with a rigorous finite-difference time-domain technique show that the TE-polarized light is designed to ensure single-mode operation and the transmitted power is distributed almost equally, with a total transmission of 93.4% at the 1550nm optical operation wavelength. Furthermore, we demonstrate ultralow-loss output of the optimized power splitter, with a transmittance above 22.5% (-6.48 dB) achieved in the ranges of 1524-1594 and 1610-1620nm, which cover the entire C-band and a large portion of the L-band of optical communication.

High-Transmission-Efficiency 120 &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$^{\circ}$&lt;/tex-math&gt;&lt;/inline-formula&gt; Photonic Crystal Waveguide Bend by Using Flexible Structural Defects

We numerically studied a high-output-transmission-efficiency low-reflection-loss 120° photonic crystal (PhC) waveguide bend based on a PhC slab with triangular-lattice air holes. The desired high output transmission efficiency was achieved by introducing flexible structural defects into the bend region of the waveguide. Simulation results obtained using a 3-D finite-difference time-domain method indicated that normalized output transmission as high as 94.3% and negligible normalized reflection loss of 0.1% were obtained at the 1550-nm optical wavelength. Furthermore, the normalized output transmission was more than 90% within the entire optical C-band. In addition, sensitivity of the design parameters of the structural defect was studied to understand the tolerance in the fabrication error, while maintaining high output transmission efficiency.

Highly efficient 1×3 power splitter at 1550 nm for triple play applications using photonic crystal waveguides

We presented a highly efficient 1 × 3 optical power splitter based on photonic crystal waveguides (PCWs) with a triangular lattice of air holes. By only modifying a single hole in a Y junction area, the input power can be almost evenly split into three ports. The optimal device can operate with a total transmittance higher than 99% simultaneously at 1384, 1490, and 1550 nm, which are within the E-, S-, and C-bands of optical communication spectra, respectively. It provides a new method and a compact model to split the input power into three channels in PCW devices and can find triple play applications in an optical communication system. © 2014

Prediction of propagation characteristics of photonic crystal fibers by a simpler, more complete and versatile formulation of their effective cladding indices

We present a simpler, more complete and versatile formulation for the effective cladding index of a solid-core photonic crystal fiber (PCF) with a triangular lattice of air holes in the cladding region. This index depends on two fundamental geometrical parameters: the air hole diameters and their separation in the endlessly single mode region of the PCF corresponding to a prescribed upper limit of relative air hole size as well as the wavelength of the light used. Our earlier available formulation for the normalized propagation constants of the infinite cladding region of the same PCF and hence its effective cladding index takes care only of the dependence on the relative air hole size and wavelength at a particular hole pitch. Now, the hole pitch dependence is also taken into account to make the formulation complete in all senses. The proposed new formulation is shown to be accurate on the basis of a comparison of our results with those obtained by available techniques. Further, to check its validity in different problems of practical interest, we apply our new formulation to evaluate various propagation characteristics of the PCF. On comparison with the previously available results, our results are seen to agree excellently with them. The formulation should find wide use for simple verification by system designers and users.

Mode conversion in a magnetic photonic crystal waveguide

In this work, we have reported a theoretical study of a magnetic photonic crystal waveguide (also called a magneto photonic crystal waveguide). This structure is formed by a triangular lattice of air holes in a bismuth iron garnet (BIG) film, grown on gallium gadolinium garnet substrates. Nonreciprocal TE–TM mode conversion is caused by the Faraday rotation if the magnetization is aligned along the z-axis, parallel to mode of propagation. The properties of this phenomenon are simulated using the beam propagation method. The conversion output has been simulated, and the Faraday rotation and modal birefringence have been calculated by varying the gyrotropy and the thickness of the BIG film. This magnetic photonic crystal waveguide has the advantage of enhancing Faraday rotation in optical isolators.

Band Gaps of a Triangular Lattice of Air Holes in Dielectric Medium

Band Gaps of a Triangular Lattice of Air Holes in Dielectric Medium