Raonaqul Islam

Extremely High-Birefringent Asymmetric Slotted-Core Photonic Crystal Fiber in THz Regime

We present a thorough numerical analysis of a highly birefringent slotted porous-core circular photonic crystal fiber (PCF) for terahertz (THz) wave guidance. The slot shaped air-holes break the symmetry of the porous-core which offers a very high birefringence whereas the compact geometry of the circular cladding confines most of the power in the fiber-core. The fiber structure reported in this letter exhibits simultaneously ultrahigh modal birefringence of 7.5 × 10-2 and a very low effective absorption loss of 0.07 cm-1 for y-polarization mode at an operating frequency of 1 THz. It is highly anticipated that the slotted-core waveguide would be of very much convenience in many polarization maintaining THz appliances.

Novel porous fiber based on dual-asymmetry for low-loss polarization maintaining THz wave guidance.

In this Letter, we suggest a novel kind of porous-core photonic crystal fiber (PCF) (to the best of our knowledge) for efficient transportation of polarization maintaining (PM) terahertz (THz) waves. We introduce an asymmetry in both the porous-core and the porous-cladding of the structure to achieve an ultra-high birefringence. Besides, only circular air holes have been used to represent the structure, which makes the fiber remarkably simple. The transmission characteristics have been numerically examined based on an efficient finite element method (FEM). The numerical results confirm a high birefringence of ∼0.045 and a very low effective absorption loss of 0.08  cm(-1) for optimal design parameters at 1 THz. We have also thoroughly investigated some important modal properties such as bending loss, power fraction, dispersion, and fabrication possibilities to completely analyze the structures usability in a multitude of THz appliances. Moreover, physical insights of the proposed fiber have also been discussed.

A Novel Low-Loss Diamond-Core Porous Fiber for Polarization Maintaining Terahertz Transmission

We report on the numerical design optimization of a new kind of relatively simple porous-core photonic crystal fiber (PCF) for terahertz (THz) waveguiding. A novel twist is introduced in the regular hexagonal PCF by including a diamond-shaped porous-core inside the hexagonal cladding. The numerical results obtained from an efficient finite-element method, which confirms a high birefringence of the order 10-2 and low effective material loss of 0.07 cm-1 at 0.7-THz operating frequency. The proposed PCF is anticipated to be useful in polarization sensitive THz appliances.

Single-mode porous fiber for low-loss polarization maintaining terahertz transmission

Abstract. We report on a polymer-based porous-core photonic crystal fiber for simultaneous high-birefringent and low-loss propagation of narrowband terahertz (THz) electromagnetic waves. The high birefringence is induced by using rotated elliptical air holes inside the porous-core. The fiber is numerically analyzed with an efficient finite-element method. The simulation results exhibit an extremely high birefringence of ∼0.042 and a very low effective material loss of ∼0.07  cm−1 at an operating frequency of 1 THz. Moreover, we have found an optimal rotation angle (θ)=n30  deg (n is an odd integer). Other modal features of the fiber, such as confinement loss, power fraction, effective area, bending loss, and dispersion, also have been analyzed. We anticipate that the proposed fiber would be suitable in polarization maintaining THz wave guidance applications.

Bend-Insensitive and Low-Loss Porous Core Spiral Terahertz Fiber

A novel (to the best of our knowledge) kind of porous-core spiral photonic crystal fiber (PCF) is proposed in this letter. It illustrates a tradeoff managed between material absorption and bending loss for efficient guidance of terahertz (THz) waves using a circular lattice array of smaller air-holes inside the core of an equiangular spiral structure. With maximum porosity and operating frequency of 1 THz, bending loss of 4.16×10-16 cm-1 and effective material loss of 0.1 cm-1 are reported. In addition, other modal characteristics, such as effective area, confinement loss, and fabrication techniques of the proposed fiber have been discussed. The proposed THz waveguide can be potentially used for efficient and convenient transmission of THz waves.

Dispersion flattened, low-loss porous fiber for single-mode terahertz wave guidance

Abstract. A porous-core circular photonic crystal fiber is designed for low-loss terahertz (THz) wave propagation. The circular arrangement of air holes, both in the periodic cladding and the porous core, makes it possible to guide most of the optical power through low-loss air, which is confirmed by the rigorous analysis of modal properties of the fiber while maintaining the single-mode propagation condition. The simulation results, found by using an efficient finite element method, show that a flattened dispersion of ±0.09  ps/THz/cm within 0.9 to 1.3 THz and an ultra-low material loss of 0.053  cm−1 at f=1  THz is obtained for the reported design at optimal parameters. This kind of structure can be fabricated using capillary stacking or a sol–gel technique and is expected to be useful for wideband imaging and telecom applications.

Ultra-high birefringent and dispersion-flattened low loss single-mode terahertz wave guiding

This study proposes a dielectric terahertz (THz) porous core fibre with ultra-high birefringence and near zero dispersion-flattened properties. The finite element method is used to design and analyse properties of the proposed THz fibre. The proposed porous core crystal fibre has a triangular lattice with microstructured circular air holes in the outer cladding and elliptical air holes in the core. The design exhibits a high birefringence of 7 × 10−2 and a low effective material loss of 0.1 cm−1 at the operating frequency of f = 1 THz. It also shows nearly zero flattened dispersion with an absolute dispersion variation of ±0.05 ps/THz/cm in the frequency range of 1.3 to 2.2 THz. Power fraction and confinement loss are also reported in this study. The proposed THz porous fibre is deemed suitable for polarisation-maintaining THz wave guidance.

Appearance and shape based facial recognition system using PCA and HMM

This paper presents an approach to enhance the performance of appearance and shape based feature fusion for face recognition system using Principal Component Analysis and Hidden Markov Model. Though the traditional face recognition system is very sensitive to the face parameter variations, the proposed feature fusion based facial recognition system is found to be stance and performs well for improving the robustness and naturalness of human-computer-interaction. Active Appearance Model and Shape Model have been used to extract the appearance and shape based facial features from the facial images. Feature fusion is performed and combined feature vector is created using these two types of features. To reduce the dimensionality of the feature vector, Principal component Analysis method has been used. Hidden Markov Model has been used for learning and classification purpose. In experimental result, appearance based, shape based and combined appearance and shape based output are reported and shows the superiority of the proposed facial recognition system.

A highly birefringent slotted-core THz fiber

We present a slotted porous-core microstructure polymer fiber for polarization maintaining (PM) guidance of terahertz (THz) waves. The numerical analysis is performed using a full vector finite element method (FEM). Our proposed structure contains a compact hexagonal lattice in the cladding and rectangular slotted air-holes inside the core. Geometries inside the core have been designed to introduce asymmetry which results in a high modal birefringence of ∼0.08. Moreover, majority of the mode power is propagated in air medium to exhibit a very low effective material loss of ∼0.08 cm−1. Some other modal characteristics of the fiber are also discussed rigorously, which include confinement loss, mode power fraction, dispersion properties etc.

Extremely low-loss single-mode photonic crystal fiber in the terahertz regime

This paper presents an updated design and numerical characterization of a rotated porous-core hexagonal photonic crystal fiber (PCF) for single-mode terahertz (THz) wave guidance. The simulation results are found using an efficient finite element method (FEM) which show a better and ultra-low effective absorption loss of 0.045 cm-1 at 1 THz and a more flattened dispersion of 0.74±0.07ps/THz/cm in a wider bandwidth (0.54-1.36 THz) than the previously reported results. Besides, the single-mode region has been extended up to 1.74 THz (previously up to 1.3 THz) which is advantageous for wideband THz applications.