Low Confinement Loss Research Articles

Proposal for Supercontinuum Generation by Optofluidic Infiltrated Photonic Crystal Fibers

We propose a technique based on optofluidic infiltration to design a photonic crystal fiber (PCF) to control chromatic dispersion for supercontinuum generation. Selectively infiltrating the PCF air-holes with an optical fluid having an appropriate refractive index, we have achieved a PCF with low confinement loss and ultra-flattened near zero dispersion centered about λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ZD</sub> ~ 1325 nm, without a need for nano-scale geometrical tuning. Numerical simulations show that femto-second pulses, with center wavelengths within the range of 1250 nm ≤ λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ≤ 1625 nm, can generate relatively flat supercontinuum spectra as wide as 640 to 1180 nm, passing through a 250-mm long PCF whose dispersion profile is engineered via selective optofluidic infiltration. Simulations also show that optical fluid with refractive index of n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> = 1.32 for input signals having the aforementioned range of wavelengths result in the widest flat supercontinua. This is attributed to the smallest corresponding effective mode area as well as the smallest and flat corresponding dispersion both of which enhance the PCF nonlinearities.

Proposal for highly residual dispersion compensating defected core decagonal photonic crystal fiber over S+C+L+U wavelength bands

A defected core decagonal photonic crystal fiber is designed and numerically optimized to obtain its residual chromatic dispersion compensation in the wavelength range of 1460 to 1675 nm i.e., over S+C+L+U wavelength bands having an average dispersion of about −390 ps/(nm km) with a dispersion variation of 7 ps/(nm km). The designed fiber, with a flattened dispersion profile, has four rings of holes in the cladding region, which results in low confinement loss and small effective mode area at wavelength 1550 nm. For residual chromatic dispersion compensation, the proposed fiber can be used in wavelength division multiplexing optical fiber data communication systems.

A highly nonlinear photonic quasi-crystal fiber with low confinement loss and flattened dispersion

We proposed a novel photonic quasi-crystal fiber with near-zero flattened dispersion, highly nonlinear coefficient, and low confinement loss by using the dual concentric core structure. By optimizing the structure parameter, the proposed photonic quasi-crystal fiber can achieve a nonlinear coefficient larger than 33W−1km−1 and near-zero flatten dispersion of 0±3.4ps/nm/km with a near-zero dispersion slope of 8.5×10−3ps/nm2/km at the wavelength of 1550nm. Near-zero flattened dispersion and low confinement loss in the ultralow order of 10−7dB/m are simultaneously obtained in the wavelength range from 1373 to 1627nm. Furthermore, two zero dispersion wavelengths can be achieved in a wide wavelength ranger from 1373 to 1725nm. From the point of view of practical fabrication, the influence of deviation of each air hole diameter within 3% of imperfections on dispersion, nonlinearity, and is discussed to verify the robustness of our design.

Analysis of supermode and structural characteristics of octagonal multicore photonic crystal fiber with large effective mode area and low confinement loss

An octagonal multicore photonic crystal fiber is proposed. The supermode and its far field distribution have been analyzed by using the full-vector finite element method. In the condition of in-phase supermode, the influences of different wavelengths, air filling fraction, and air hole diameter between cores on normalized intensity of cores are studied. The equal intensity distribution of cores in the output plane is realized. Finally, the effects of changing the air hole diameter between different cores on the effective mode area and confinement loss are investigated. The results show that the effective way to change the relative intensity between cores is to resize the air holes between different cores. If this parameter is changed, a better intensity distribution with large effective mode area and low confinement loss for propagation is obtained.

Highly nonlinear with low confinement losses square photonic crystal fiber based on a four-hole unit

A novel simple structure of a highly nonlinear square photonic crystal fiber with low confinement losses is proposed. The simulation results show that a nonlinear coefficient of 83.3W−1km−1 and a low confinement loss of less than 10−9dB/m at the wavelength of 1.55μm, and the corresponding effective mode area is about 1.46μm2 by introducing the unique four-hole unit structure in the cladding region. The proposed PCF is expected to be useful for super-continuum generation, nonlinear optics and optical communication systems.

Optimum values of air-filling fraction for photonic crystal fibers with different configurations and fixed number of air rings

In this study, a Gaussian amp function related to the Gaussian family is employed to approximate the output intensity profile of various arrangements of air holes in photonic crystal fibers (PCFs) with a fixed number of air rings (N=4). It is shown that d/Λ=0.5 can be the best minimum value of air-filling fraction for all of the studied PCFs when λ=1.35 μm, whereas, for λ=1.55 and 1.65 μm, d/Λ=0.6 is suitable for achieving the maximum output intensity with very low confinement loss.

Characteristics analysis of large solid-core square-lattice photonic crystal fibers with hybrid cladding

A photonic crystal fiber (PCF) with low confinement loss and nearly zero ultraflattened chromatic dispersion over ultra-broad wavelength is proposed. Some important PCF design parameters, such as the influences of the diameter of air holes and hole pitch on the confinement loss, chromatic dispersion has been thoroughly investigated by employing the full vectorial finite element method with anisotropic perfectly matched layers. The simulation results show that the dispersion coefficient is <0.6 ps/(km⋅nm) and is larger than −0.5 ps/(km⋅nm) from 1.32 to 1.64 μm, and the confinement losses are <10 −7 dB/m in the same wavelength range by introducing extra air holes in the same ring.

Low Confinement Loss Photonic Crystal Fiber (PCF) With Flat Dispersion over C-Band

A new structure of low confinement loss with flat dispersion PCF over C-band is proposed and analysed by full vector finite element method. A solid core PCF has been designed with circular air-holes of different diameters and the background index are calculated from Sellmeier equation. From the results it is confirmed that the proposed design finds application in communication with its extremely low confinement loss and flat dispersion over the Cband. Within the wavelength band 1. 5 μm to 1. 6 μm the fast axis mode vanishes leaving single polarization.

“Hexagonal Lattice Photonic Crystal Fiber with Low Confinement Loss and Low Chromatic Dispersion”

In this paper, We design a novel Hexagonal Lattice photonic crystal fiber (PCF) made of soft glass achieving low confinement loss and low chromatic dispersion through the optimization of the arrangement and diameter of circular air holes. The motivation behind this is to optimize the design parameter of PCF to gain low-flattened chromatic dispersion and low confinement loss at wide wavelength range. This new design of PCF having low-flattened chromatic dispersion and low confinement loss in wide wavelength range is demonstrated by carefully adjusting the air holes in each rings, air holes dimensions and spacing between air holes or pitch. 2- D finite difference time domain (FDTD) method is used for the analysis of this PCF Keywords: Photonic crystal fibre (PCF), FDTD method, dispersion, confinement loss I. INTRODUCTION Optical Fibers have brought a great revolution in the field of Communication as they have provided better quality and good properties of the signal. But they also had limitations with respect to losses, dispersion and non linearity. Photonic-crystal fiber (PCF) is a new class of optical fiber based on the properties of photonic crystals. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber. Photonic crystal fibers (PCFs) were first demonstrated in 1996 and have attracted much attention in recent years regarding new optical fiber applications (4). The most important property of PCF are that they can possess dispersion properties that are significantly different from those of conventional optical fibres, because their cladding portion consist of micrometer size air holes that run parallel along the length of the fibrer. PCFs provide confinement and guidance of light in a defect region around the centre as they are single- material fibers with an arrangement of air holes running along the length of the fiber. For the light confinement mechanism, index guiding PCFs rely on total internal reflection to confine light in the region of a missing air hole forming a central core. PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. Photonic crystal fibers may be considered a subgroup of a more general class of microstructured optical fibers, where light is guided by structural modifications, and not only by refractive index differences. Several methods are used for the analysis of PCFs each having its own advantages and disadvantages. In this work, the FDTD method is used to find characteristics of PCFs. Confinement loss (CL), including cladding material losses, is comprehensively evaluated for TE and TM modes of photonic crystal fibers. However, confinement loss can significantly degrade the performance of devices based on such small core fibers. We also identify a range of fiber designs that result in high fiber nonlinearity and low confinement loss. In this paper we have tried to study confinement loss by proposing the four rings of circular shape of holes having the radius of 0.8um with lattice pitch of 2.3um and simultaneously we have also tried to study the dispersion characteristics and tried to confine it to nearly zero dispersion. PCFs can have a significantly larger numerical aperture than conventional fiber types because the cladding region can be mostly comprised of air. When this is combined with a wavelength-scale core, PCFs can provide tight mode confinement (i.e., small values of the effective mode

Investigation of a novel all-solid large-mode-area photonic quasi-crystal fiber

Large-mode-area single-mode fibers play an important role in the field of high power lasers, high power delivery, and high sensitivity sensor. A novel all-solid large-mode-area single-mode photonic quasi-crystal fiber with extremely low loss is proposed. This kind of fiber contains a hexagonal quasi-crystal array of slightly fluorine-doped silica rods in a silica background. Its structure and properties are simulated numerically in virtue of finite element method. Effects of variation of d/Λ, or Λ on fiber loss and effective mode-area properties are investigated. Numerical results demonstrate that an effective mode-area of 5197 μm2, low confinement loss of 10-5 dB/km for fundamental mode and high confinement loss of 100 dB/km of second-order mode at a wavelength of 1064 nm. Numerical simulations show that this fiber can operate effectively in single-mode and remove the conflict between large-mode-area and low loss. Moreover, the bending loss for a bending radius of 10 cm is as low as 0.01 dB/m. This fiber can increase the thermal damage threshold of the PQF, decrease the coupling loss and simplify the fabrication process. The design of new fibers is highly meaningful for the development of high power delivery, fiber lasers, and fiber amplifiers.

Dispersion-ultra-flattened square-lattice photonic crystal fiber with small effective mode area and low confinement loss

Proposed in this paper is a simple square-lattice photonic crystal fiber (PCF) with nearly zero flattened dispersion (NZFD) over a wide wavelength span. We make a trade-off between the coupling efficiency and the effective mode area in order to obtain relatively low confinement loss and high nonlinearity. Via full-vector finite element method with hybrid edge/node elements, over 1137–1710nm, the dispersion coefficient is 0.3±0.3ps/(kmnm), the confinement loss is relatively low, in level of 10−7–10−4dB/km and the effective mode area remains 5.88–6.59μm2.

High sensitivity evanescent-field gas sensor based on modified photonic crystal fiber for gas condensate and air pollution monitoring

Flammable and/or toxic gas sensors can be used as safety measuring in gas production facilities, especially in oil rigs. The gas sensors detect gas leaks capable of causing fire, explosion, and toxic exposure. Here we proposed an index-guiding photonic crystal fiber for gas sensing that have a broad spectral transmission band and so is capable to detect more gas condensate components. The dependence of relative sensitivity and confinement loss on the fiber parameters is numerically investigated by finite element method (FEM). Introducing a hollow high index ring with an air hole in the center of fiber simultaneously enhances the relative sensitivity and achieves low confinement loss. In addition, we prove that increasing the diameter of holes located in the inner rings, improve the relative sensitivity and increasing the ring diameter holes located in the outer rings, greatly reduces the confinement loss. Placing hexagonal holes instead of circular holes in the innermost ring, the relative sensitivity is effectively enhanced. The relative sensitivity at wavelength of λ=1.33μm that is in the Methane absorption line is enhanced to value of 13.23%. The confinement loss is also improved to 3.77×10−6.

Endlessly single-polarization single-mode holey fibers with low confinement loss

We present a novel structure for holey fibers (HFs) with endlessly single-polarization single-mode characteristics, which is realized by introducing four elliptical airholes arranged in a hexagonal matrix in the core region. The validation of the design is done by use of a full-vectorial finite element method. We exhibit one typical design that can deliver a single-polarization single-mode region of more than 2400 nm with a confinement loss level lower than 0.01 dB/km. We have also shown that the persevered polarization state possesses a wide wavelength band of flat dispersion behavior. As a consequence, such HFs are useful in high-speed communication systems or optical-fiber sensors since they are free of polarization mode dispersion and simultaneously immune to cross-talk effect.

Highly birefringent microstructured polymer fibers optimized for a preform drilling fabrication method

We propose two designs of birefringent microstructured fibers assuring high geometrical birefringence in the visible range and low confinement losses. An increased birefringence level in the visible range is achieved by breaking the hexagonal symmetry of the structure and shifting selected holes with respect to the nodes of the hexagonal lattice. Such geometry of the microstructured cladding is feasible for polymer fibers fabricated using a preform drilling method. In the first optimized design, two large air-holes adjacent to the core are shifted towards each other to increase modal birefringence. In the second design, high birefringence is achieved by approaching two regions with large holes separated by a row of smaller holes. The simulation results show that in the first fiber with a pitch distance of 3.0 μm, it is possible to obtain a phase birefringence of the fundamental mode greater than 1 × 10−4, while the confinement losses do not exceed 0.06 dB m−1 in the visible range. In the second fiber with the same pitch distance, the confinement losses are smaller than 0.3 dB m−1 in the spectral range of 500–1100 nm, while the phase modal birefringence exceeds 1 × 10−4 in the visible range and reaches 4.0 × 10−4 at 633 nm. We also present the fiber fabricated according to the second design and compare the calculated and the measured spectral dependence of birefringence.

Design of highly birefringent holey fibers with near-zero ultra-flattened chromatic dispersion and ultralow confinement loss

We present a holey fiber (HF) with elliptical air-holes located in the center core area that ensures high birefringence, near-zero ultra-flattened chromatic dispersion and very low confinement losses in a wide wavelength range. The finite element method with perfectly matched boundary layer is used to investigate the guiding properties. It is demonstrated that it is possible to design a low-loss dispersion-flattened HF with a high birefringence of 0.0033 at a 1.55 µm wavelength. According to simulation, near-zero ultra-flattened dispersion of 0 ± 0.5 ps/nm/km is obtained in a 1.25 to 1.65 µm wavelength range with low confinement losses of 0.0008 dB/km in the entire band of interest.

Analysis on photonic crystal fibers with circular air holes in elliptical configuration

In this paper, two novel structures of photonic crystal fibers (PCFs) containing elliptical rings of circular air holes are presented. The circular air holes in both structures are arranged in seven elliptical rings, but the number of holes in each ring is different for these structures. Moreover, air hole diameter and hole-to-hole pitch are altered along the distance from the center of the fiber’s cross section. Properties, such as birefringence and confinement loss, of these structures with different numbers of air hole rings are numerically analyzed by using the multipole method. Numerical results show that a high birefringence of 1.626×10−3can be reached at the wavelength of 1.55μm, and a low confinement loss on the order of 10−8dB/m can be achieved at the same wavelength. Furthermore, it is also found that elliptic ratio obviously affects birefringence and confinement loss, but the number of air hole rings has little impact on birefringence.

Photonic crystal fiber with high birefringence and low confinement loss

In this paper, a highly birefringent index-guiding photonic crystal fiber with low confinement loss is proposed by enlarging the central row of air holes in the structure. By employing the multipole method, properties of this structure, including the effective index, birefringence and confinement loss, are investigated. Simulation results indicate that high birefringence of 1.65×10−3 can be reached at the wavelength of 1.55μm, and a low confinement loss on the order of 10−6dB/km can be achieved at the same wavelength. Moreover, the impacts of air hole sizes on birefringence and confinement loss are also analyzed in detail.

Numerical Analysis on Birefringence of Photonic Crystal Fiber by Tuning Patterns and Infiltrating Materials of Innermost Air Holes

In this paper, we give a numerical analysis of a novel high-birefringence and low-confinement loss index-guiding photonic crystal fiber (PCF) using the finite element method by tuning patterns and filling the medium of innermost air holes. This PCF is composed of a solid silica core surrounded by six elliptical air holes and a cladding that consists of binary unit cells. The novelty of the proposed PCF structures is that the large elliptical air holes closest to the core have been rotated in different ways. Results show that the asymmetry in PCF cladding and the area of the PCF core are the key factors for determining the localization extent of the transverse mode. Modal birefringence values and confinement loss at the excitation wavelength of λ=1.55 µm can be easily achieved at a magnitude of the order of 10-2 and at less than 0.39 dB/km, respectively. From the viewpoint of numerical analysis, the effects of a material [with a refractive index <1 (i.e., a metamaterial)] on birefringence infiltrating into small (100–280 nm) innermost air holes, which are reported for the first time here, are also considered.

Highly nonlinear layered spiral microstructured optical fiber

A layered spiral microstructured optical fiber (LS-MOF) is presented, which offers the possibility of a good control of both the dispersion and the nonlinear properties. The proposed design is analyzed using a finite element method considering silica and air as the materials. Zero dispersion, low confinement loss, and a record value of γ=70.0W−1/km for the LS-MOF nonlinear parameter are simultaneously obtained at 1.55μm, whereas a higher value γ=169.4W−1/km can be achieved at 1.06μm. Our results demonstrate the great potential of the LS-MOF for several nonlinear applications, namely for an efficient generation of the supercontinuum.

Highly birefringent photonic crystal fibers with flattened dispersion and low confinement loss

A highly birefringent index-guiding photonic crystal fiber (PCF) with flattened dispersion and low confinement loss is proposed by introducing two small air holes with the same diameter in the core area. The fundamental mode field, birefringence, confinement loss, effective mode area and dispersion characteristic of the fibers are studied by the full-vector finite element method (FEM). Simulation results show that a high birefringence with the order of 10−3 and a low confinement loss of 0.001 dB/km are obtained at 1550 nm. Furthermore, flattened chromatic dispersion from 1450 nm to 1590 nm is obtained.