Md. Selim Habib

Low-loss hollow-core silica fibers with adjacent nested anti-resonant tubes

We report on numerical design optimization of hollow-core anti-resonant fibers with the aim of reducing transmission losses. We show that re-arranging the nested anti-resonant tubes in the cladding to be adjacent has the effect of significantly reducing leakage as well as bending losses, and for reaching high loss extinction ratios between the fundamental mode and higher order modes. We investigate two versions of the proposed design, one optimized for the mid-IR and another scaled down version for the near-IR and compare them in detail with previously proposed anti-resonant fiber designs including nested elements. Our proposed design is superior with respect to obtaining the lowest leakage losses and the bend losses are also much lower than for the previous designs. Leakage losses as low as 0.0015 dB/km and bending losses of 0.006 dB/km at 5 cm bending radius are predicted at the ytterbium lasing wavelength 1.06 µm. When optimizing the higher-order-mode extinction ratio, the low leakage loss is sacrificed to get an effective single-mode behavior of the fiber. We show that the higher-order-mode extinction ratio is more than 1500 in the range 1.0-1.1 µm around the ytterbium lasing wavelength, while in the mid-IR it can be over 100 around λ = 2.94 μm. This is higher than the previously considered structures in the literature using nested tubes.

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.

Low-loss single-mode hollow-core fiber with anisotropic anti-resonant elements.

A hollow-core fiber using anisotropic anti-resonant tubes in the cladding is proposed for low loss and effectively single-mode guidance. We show that the loss performance and higher-order mode suppression is significantly improved by using symmetrically distributed anisotropic anti-resonant tubes in the cladding, elongated in the radial direction, when compared to using isotropic, i.e. circular, anti-resonant tubes. The effective single-mode guidance of the proposed fiber is achieved by enhancing the coupling between the cladding modes and higher-order-core modes by suitably engineering the anisotropic anti-resonant elements. With a silica-based fiber design aimed at 1.06 µm, we show that the loss extinction ratio between the higher-order core modes and the fundamental core mode can be more than 1000 in the range 1.0-1.65 µm, while the leakage loss of the fundamental core mode is below 15 dB/km in the same range.

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.

Highly birefringent photonic crystal fiber with ultra-flattened negative dispersion over S + C + L + U bands

We present a new cladding design for photonic crystal fiber (PCF) on a decagonal structure to simultaneously achieve ultra-flattened large negative dispersion and ultrahigh birefringence. Numerical results confirm that the proposed PCF exhibits ultra-flattened large negative dispersion over the S+C+L+U wavelength bands and average dispersion of about -558.96  ps/nm/km with absolute dispersion variation of 9.7  ps/nm/km from 1460 to 1675 nm (215 nm bandwidth). Moreover, ultrahigh birefringence of 0.0299 is also achieved at a 1500 nm wavelength.

A Novel Low Loss, Highly Birefringent Photonic Crystal Fiber in THz Regime

We present a new kind of dual-hole unit-based porous-core hexagonal photonic crystal fiber (H-PCF) with low loss and high birefringence in terahertz regime. The proposed fiber offers simultaneously high birefringence and low effective material loss (EML) in the frequency range of 0.5-0.85 THz with single-mode operation. An air-hole pair is used inside the core instead of elliptical shaped air holes to introduce asymmetry for attaining high birefringence; where the birefringence can be enhanced by rotating the dual-hole unit axis of orientation. The proposed H-PCF provides a birefringence of ~0.033 and an EML of 0.43 dB/cm at an operating frequency of 0.85 THz.

Relative dispersion slope matched dispersion compensating highly birefringent spiral microstructure optical fibers using defected core

Abstract. A highly birefringent dispersion compensating microstructure optical fiber (MOF) based on a modified spiral (MS)-MOF is presented that successfully compensates the dispersion covering the E- to L-communication bands ranging from 1370 to 1640 nm. It is shown theoretically that it can obtain a negative dispersion coefficient of about −221 to −424  ps/(nm·km)) over S to L bands and −327  ps/(nm· km)) at the operating wavelength of 1550 nm. The relative dispersion slope is perfectly matched to that of single-mode fiber of about 0.0036  nm−1. Besides, the proposed MS-MOF offers high birefringence of 1.79×10−2 with a large nonlinear coefficient of about 41.8  W−1 km−1 at the operating wavelength along with two zero dispersion wavelengths at 610 and 1220 nm. Futhermore, the variation of structural parameters is also studied to evaluate the tolerance of the fabrication.

Tailoring polarization maintaining broadband residual dispersion compensating octagonal photonic crystal fibers

Abstract. We present a residual dispersion compensating highly birefringent photonic crystal fiber (PCF) based on an octagonal structure for broadband dispersion compensation in the wavelength range 1460–1625 nm. The finite element method with perfectly matched boundary condition is used as the numerical design tool. It has been shown theoretically that it is possible to obtain a negative dispersion coefficient of about −418 to −775  ps/nm/km over the S-, C-, and L-bands, relative dispersion slope (RDS) close to that of single mode fiber (SMF) of about 0.0036  nm−1 at 1550 nm. According to the simulation, birefringence of 2×10−2 is obtained at 1550-nm wavelength. The variation of structural parameters is also studied to evaluate the tolerance of the fabrication. The proposed octagonal PCF can be a potential candidate for residual dispersion compensation as well as maintaining single polarization in optical fiber transmission system.

Highly nonlinear polarization maintaining dispersion compensating fiber for high-speed transmission system

Abstract. A photonic crystal fiber design is presented, which has simultaneously ultra-high birefringence, high nonlinearity, and high negative dispersion. The relative dispersion slope matches with that of standard single-mode fiber of about 0.0036  nm−1. The finite element method with circular perfectly matched boundary layer is used to investigate the guiding properties. The proposed fiber ensures a large negative dispersion coefficient of about −639.16  ps/(nm km), birefringence of order 3.55×10−2, and nonlinear coefficient of 41  W−1 km−1 at 1550-nm wavelength.