Type Of Photonic Crystal Fiber Research Articles

Structural dependence of transmission characteristics for photonic crystal fiber with circularly distributed air-holes

Abstract In this study, design and transmission characteristics of a special type of photonic crystal fiber (PCF) geometry namely, circular-lattice photonic crystal fiber (C-PCF) structure are presented. The cladding of the structure consists by a cylindrically symmetrical distribution of air-holes in the silica background and the core is created by omitting one air-hole at the center. The structure provides high degree of flexibility in the fiber design and hence tailorable modal properties. Structural dependence of transmission characteristics of the geometry is numerically investigated by using finite difference mode convergence algorithm. The wavelength responses of fiber parameters, such as effective refractive index, chromatic dispersion, mode-effective area, and nonlinear coefficient of the structure are systematically investigated. Besides, effective V-parameter and single-mode operation of the fiber are also evaluated and discussed. The simulation results show the possibility of large negative dispersion and dispersion flattened nature of the geometry.

Topological photonic crystal fiber with honeycomb structure.

We analyze a new type of photonic crystal fiber which consists of the core and cladding that distinct in topology by tuning the position of air holes in each hexagonal unit cell where the C6v symmetry is respected. The p-d band inversion between the core and cladding leads to topological interface modes inside the band gap, which can propagate along the fiber with a nonzero momentum in perpendicular to the corss section of a fiber. The helical topological interface modes possess the pseudospin-momentum locking effect inherited from the corresonding two-dimensional photonic crystal characterized by the Z2 topology. The wave functions for the topological interface modes are analytically studied and compared successfully to the numerical results, enlighting a novel way to use photonic crystal fiber to transfer information.

Double-parameter sensing of voltage and magnetic field based on photonic crystal fiber

In this paper, a new type of photonic crystal fiber (PCF) sensor is proposed for detecting the voltage and magnetic field simultaneously. In the PCF, an air hole of the cladding is coated with gold film and filled with the liquid crystal, thus the surface plasmon resonance (SPR) channel is formed to detect the voltage. While another air hole of the cladding is filled with magnetic fluids, the directional coupling channel is formed to detect the magnetic field. The SPR sensing channel and directional coupling channel are relatively independent. A finite element method (FEM) has been used for the optimization of the structure parameters, transmission characteristics of different modes, and analysis of the sensing characteristics. Numerical results reveal that the voltage sensitivity is 2.11 nm/V in the range of 5–35 V and the magnetic field sensitivity is 0.86 nm/Oe in the range of 90–210 Oe.

Modeling and analysis of D–shaped plasmonic refractive index and temperature sensor using photonic crystal fiber

In this study, a D–type photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor is proposed for measurement of both refractive index (RI) and temperature. The RI sensing part is constructed by deposition of a silver layer on the plane of the D–type structure, and the temperature sensing part is formed by filling the silver nanowire and the liquid analyte into an elliptical hole in the PCF. The proposed design then can be used for temperature and analyte RI sensing through the coupling between the core guided modes and the surface plasmon modes around the nano silver rod and layer. We study the coupling characteristic and sensing performance of the sensor. The numerical results show that the maximal sensitivity in terms of RI units (RIU) is 6.9 μm/RIU in the range of 1.33–1.38, and the maximal temperature sensitivity is 3 nm /°C in the range of 27–67 °C.

Temperature-based dispersion compensating ability of a photonic crystal fiber

The effects of temperature on the dispersion properties of a square lattice photonic crystal fiber (PCF) have been studied. Holes in the cladding part of PCF are packed with a semiconducting material, InSb, whose characteristics depend upon temperature in the terahertz optical frequency. The effective index of PCF is calculated with the help of a semivectorial finite difference technique. Using the effective index values, computation of chromatic dispersion parameters is done, which are plotted against wavelength. Four temperatures have been considered in our work from 290 to 335 K in equal steps. The results depict that as the temperature rises, the values of effective indexes of PCF decrease while dispersion of the fiber increases. In places where temperature is not constant and keeps varying, this type of PCF can be installed for multiple optical channel dispersion compensating applications. It has also been observed that with the change in surrounding temperatures, mode carrying capacity of the fiber remains unaffected, which makes this fiber suitable for special applications, such as distributed perimeter sensing of chemical plants.

Design of a novel star type photonic crystal fiber for mid-infrared supercontinuum generation

In this work, we have designed two simple photonic crystal fibers (PCFs) with the highly nonlinear chalcogenide material of Ge11.5As24Se64.5 for broadband mid-infrared supercontinuum generation. The hexagonal lattice of air holes in a star type arrangement has been considered in the designs, where only two different air hole sizes and a constant pitch are employed. The study shows that the diameter of the air hole has significant influence on both the dispersion and the nonlinearity parameters of the PCFs. The numerical solutions of the generalized nonlinear Schrödinger equation (GNLSE) for a secant hyperbolic input pulse at different pumping wavelengths at mid-infrared region are investigated by varying input pulse power and fiber lengths. About 3000 nm wide supercontinuum can be generated at pumping wavelength of 2400 nm and input pulse power of 3000W with the designs. Thus, the designs of the PCF can be employed for generating supercontinuum to be useful for medical imaging, bio-sensing, spectroscopy, wave division multiplexing (WDM) systems, and optical communication systems.

Optical Waveguides and Terahertz Signal by Finite Element Method: A Survey

This paper examines the use of the Finite Element Method (FEM) in the field of optical waveguides and terahertz signals, with the main goal of explaining how this method aids in recent advances in this field. The basics of FEM are briefly reviewed, and the technique's application to waveguide discontinuity analysis is observed. Second-order and higher-order derivatives result from optical waveguide modeling, which is significant for information exchange and many other nonlinear phenomena. The use of FEM in the improvised design of hexagonal sort air hole porous core microstructure fibers, which produces hexagonal structure cladding and rectangular-shaped air holes in the fiber core for excellent terahertz signal transmission, was also observed. These modifications were intended to improve the fiber's properties in comparison to other structures. This approach verifies that the fiber has high birefringence, low material loss, a high-power fraction, and minimal dispersion varia-tion. The features of square-type microstructure fiber are investigated. A folded-shaped po-rous cladding design is recognized for sensing applications. This type of photonic crystal fiber is also known as FP-PCF since it features circular air holes. The most approximate findings of this application are obtained using FEM. In comparison to many other approach-es for various applications, it is evident that FEM is a powerful and numerically efficient tool. This work does a survey of optical waveguides and terahertz signals using the Finite Element Method. Terahertz signals can be used in conjunction with electromagnetic waves to identify viruses. Thus, Terahertz signals are employed in real-world applications such as fuel adulteration, liquid metal synthesis, and virus detection.

Low dispersion and confinement loss photonic crystal fiber for orbital angular momentum mode transmission

In this paper, we design a novel type of photonic crystal fiber (PCF) with a kind of typical micro-structure in its innermost cladding area, which can totally transmit 26 orbital angular momentum modes (OAMs). Over a bandwidth of 300 nm from 1.5 to 1.8 μm, this new type PCF shows a great improvement in dispersion property when it is compared with the total internal reflection PCF for reference. Moreover, other mode properties are also calculated and listed in curves, including effective indices, confinement loss and nonlinear coefficient. And basing on the test results, we further ameliorate the micro-structure and cladding of previous PCF structure and propose two effective ways to reduce the dispersion and confinement loss respectively. One is to insert typical type of micro-structure; the other is to change the arrangement and size of air holes in the cladding area. We finally propose an optimized structure which can support 30 OAM modes with the application of the two ways. Results show the optimized structure performs very well and achieves great progress in terms of dispersion and confinement loss.

A novel gold-coated PCF polarization filter based on surface plasmon resonance

In this study, a novel photonic crystal fiber (PCF) polarization filter has been designed. To resonate the surface plasma mode with the core mode, gold is selectively filled in the air holes. Using numerical simulations based on the finite element method, the influence of structural parameters on the filter is analyzed, and a set of rules for designing the PCF polarization filter is determined. The numerical simulation shows that the peak loss in the y-polarization direction at 1.31 μm reaches 1209.57 dB/cm, whereas the peak loss in the x-polarization is close to zero. Working at 1310 nm in the communication band, a new type of PCF is designed using these characteristics.

High birefringence, low loss, and flattened dispersion photonic crystal fiber for terahertz application**Project supported by the National Natural Science Foundation of China (Grant No. 11604260) and the Outstanding Youth Science Fund of Xi’an University of Science and Technology, China (Grant No. 2019YQ3-10).

A type of photonic crystal fiber based on Kagome lattice cladding and slot air holes in a rectangular core is investigated. Full vector finite element method is used to evaluate the modal and propagation properties of the designed fiber. High birefringence of 0.089 and low effective material loss of 0.055 cm−1 are obtained at 1 THz. The y-polarized fundamental mode of the designed fiber shows a flattened and near-zero dispersion of 0 ± 0.45 ps · THz−1 · cm−1 within a broad frequency range (0.5 THz–1.5 THz). Our results provide the theory basis for applications of the designed fiber in terahertz polarization maintaining systems.

Design of graded index type photonic crystal fiber having α-power air hole diameter distribution with α < 1 for fiber collimator application

A graded-index type photonic crystal fiber (GI-PCF) that has α-power air hole diameter distribution in radial direction has a characteristic that the beam diameter varies periodically along the propagation direction in the Gaussian beam excited GI-PCF, and it is similar to a GI type multimode fiber (GI-MMF). Since GI-MMFs are used as fiber collimators, it is considered that GI-PCFs are also possible to apply for fiber collimators. However, it is difficult to draw fiber with air hole diameter control in considering higher coupling efficiency at $$1 \le \alpha \le 2$$ . In this paper, we theoretically analyzed light propagation characteristics in Gaussian beam excited GI-PCF having α-power air hole diameter distribution with α < 1 and investigated the coupling efficiency with conventional PCF and its wavelength characteristics. It was found that the coupling efficiency became larger as the air hole diameter d was smaller at α < 1. In particular, a better tolerance for fiber length error and wavelength characteristics were obtained at α = 1/2. From these results and the difficulty of GI-PCF drawing, we designed the suitable structure of GI-PCF for fiber collimator application.

Optical coupling characteristics of graded-index type photonic crystal fiber collimator depending on air hole diameter ratio to pitch

A graded-index type photonic crystal fiber (GI-PCF) has a graded effective index distribution that can be realized by an α-power air hole diameter distribution in radial direction. Since a beam diameter varies periodically along the propagation direction in the GI-PCF with Gaussian beam excitation, an appropriate length of GI-PCF should be spliced to a single-mode PCF for collimator application. It is desired that GI-PCF structures to obtain high optical coupling efficiency and good tolerance for fiber length error are designed. In this paper, we theoretically studied coupling characteristics of GI-PCF collimator for conventional single-mode PCF depending on air hole diameter ratio to pitch, where the GI-PCF had parabolic air hole diameter distribution in radial direction, and had the air hole pitch that was equal to that in the conventional single-mode PCF. It was found that the optical coupling efficiency could be higher for larger air hole diameter ratio to pitch, where the coupling efficiency almost equal to that in conventional GI-type multimode fiber (GI-MMF) collimator could be obtained. On the other hand, it was clarified that GI-PCF collimators were more tolerant for fiber length error compared with GI-MMF collimator and that the GI-PCF with smaller air hole diameter ratio to pitch exhibited a better tolerance in fiber length error. We clarified that the GI-PCF collimator had an ability to obtain better wavelength characteristics with fiber length error compared with the GI-MMF collimator.

Transmission characteristics of vortex beams in a sixfold photonic quasi-crystal fiber

In an optical fiber communication system, vortex beams have aroused great interest in the last several decades. Vortex beams possess many intriguing properties. For example, they have the ability to carry orbital angular momentum (OAM) which is mutually orthogonal. The OAM is a fundamental physical quantity of light which can be used as information carriers for transmission channel of optical fiber. Combined with the existing multiplexing techniques such as wavelength division multiplexing technique, advanced multilevel amplitude modulation formats, etc., the vortex beams provide an alternative to the increase of the transmission capacity and spectral efficiency of the optical fiber transmission system. Recently, long-length transmission of vortex-beam in optical fiber has been realized and there have also occurred some new designs of optical fiber on vortex beams, such as air-core ring shaped fiber, graded index vortex fiber, multi-ring fiber, and supermode fiber. Photonic crystal fiber (PCF) is flexible in design. Therefore, it is easy to regulate the transmission performance of PCF by adjusting the radius and the pitch of the air holes and so on. In this paper, we propose a newly designed sixfold photonic quasi-crystal fiber (SPQCF) to transmit vortex beams stably. Transmission characteristics of this newly designed fiber are simulated and calculated by using COMSOL multiphysics software. When the wavelength of the incident light is 1550 nm, the effective index difference between the vortex modes in a group is more than 10&lt;sup&gt;–4&lt;/sup&gt; which is large enough to preclude the LP modes from being formed, and to transmit 7 vector modes (10 OAM modes). Changing the radius and pitch of the air holes, we can regulate the dispersion characteristic and confinement loss of the SPQCF flexibly. At 1550 nm, the confinement loss of the SPQCF maintains 10&lt;sup&gt;–8&lt;/sup&gt;−10&lt;sup&gt;–7&lt;/sup&gt; which is low enough to confine the vortex beams in the fiber core. When the incident light wavelength of HE&lt;sub&gt;21&lt;/sub&gt; ranges from 1500 nm to 1800 nm (&lt;i&gt;r&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt; = 1.9 μm), the dispersion coefficient of the SPQCF is between 63.51−65.42 ps·nm&lt;sup&gt;–1&lt;/sup&gt;·km&lt;sup&gt;–1&lt;/sup&gt; which tends to be flat. By changing &lt;i&gt;r&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt;, the flat trend is adjusted to different wavelength range. This dispersion characteristic possesses great potential for the transmission of optical solitons. The effective mode area (HE&lt;sub&gt;21&lt;/sub&gt;) is about 40 μm&lt;sup&gt;2&lt;/sup&gt; and the nonlinear coefficient (HE&lt;sub&gt;21&lt;/sub&gt;) is maintained on the order of 10&lt;sup&gt;–3&lt;/sup&gt; between 1500−1600 nm. These features suppress the generation of nonlinear effect in the fiber and benefit the transmission of vortex beams. The stable transmission distance is longer than 1 km. In summary, we design a new type of PCF featuring quasi-crystal structure which has a ring shaped fiber core and supports the transmission of vortex beams stably.

Ultrahigh birefringent dual-slot silica photonic crystal fiber with ultralow nonlinearity

We proposed a new type of photonic crystal fiber (PCF) using two nano-scale elliptical air holes in the core region to control the property of birefringence and reduce the performance of nonlinearity simultaneously. Benefiting from the slot effect induced sub-wavelength mode confinement, the nonlinear coefficients of quasi-TE mode and quasi-TM mode at 1.55 μm are as low as 0.0143 W−1 m−1 and 0.02 W−1 m−1, respectively. More importantly, ultrahigh birefringence of 0.0293 is obtained at the wavelength of 1.55 μm thanks to the asymmetry of the fiber design. Owing to these excellent optical characteristics, the proposed dual-slot silica PCF will have great potential for high-speed telecom applications.

Connection loss reduction in variable optical delay line by using graded‐index type photonic crystal fiber

A low‐loss butt‐joint connection method between photonic crystal fibers (PCFs) by using a graded‐index type photonic crystal fiber (GI‐PCF) is proposed. The GI‐PCF, in which the diameter of the air holes is chosen in a parabolic distribution in the effective refractive index, is analyzed numerically by a beam propagation method. It is found that the mode extent in the GI‐PCF varies periodically along the propagation direction when the LP01 mode of the PCF is launched into the GI‐PCF. This characteristic is successfully applied to reduce the butt‐joint connection loss between the PCFs by 1.6 dB with a 20.6‐mm GI‐PCF under 200 µm air gap. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Characterization of Erbium Doped Photonic Crystal Fiber

Photonic crystal fibers (PCFs) which exhibit unique and tremendous optical properties have been undergoing quick growth in recent years. Studies on the characteristics of various types of PCFs have been reported. However, characterization on erbium-doped PCF has not previously been investigated. Therefore, in this paper, an erbium-doped core PCF having 7 rings of hexagonal air holes has been modeled. A perfectly matched layer (PML) is modeled within the PCF structure and simulated using Finite Element Method (FEM) using COMSOL software. The PML is optimized by varying the radius and thickness of the layer. Modal properties of the PCF have been investigated in terms of its effective index of the supported fundamental mode, confinement loss and thickness of the perfectly matched layer. This erbium-doped PCF has a confinement loss of 1.0E-6 at 1500 nm and a maximum effective refractive index of 1.476. This paper gathers useful data, which could be used for studying the characteristics of a PCF.

Combinatorial Study of Supercontinuum Generation Dynamics in Photonic Crystal Fibers Pumped by Ultrafast Fiber Lasers

We numerically study the dynamics of supercontinuum generation (SCG) for a variety of possible combinations of photonic crystal fibers (PCFs) and ultrafast fiber laser pulses that the current technologies offer. Three types of PCFs typically used in SCG and four representative types of ultrafast fiber laser pulses are considered for this combinatorial study. We numerically model and qualitatively discuss the nonlinear evolution of the pulses for their whole 12 combinatorial cases. We also quantitatively analyze their output spectra and organize a performance chart for them in terms of spectral bandwidth, flatness, and degree of spectral coherence. Finally, we suggest the most viable combinations among the given PCFs and ultrafast fiber laser pulses in order for generating a target supercontinuum spectrum for various specific cases.

Studies of the modal properties of circularly photonic crystal fiber (C-PCF) for high power applications

The guiding properties of a new type of photonic crystal fibers where air-holes are arranged in a circular pattern (C-PCF) with a silica matrix have been investigated. The dispersion properties of the fiber with different spacing of circle and air-hole diameter have been studied in detail. It is shown that C-PCFs with smaller values of radius and higher air-filling fraction can be used as dispersion compensating fiber. A comparison between fibers with circular and triangular lattice has also been performed, taking into account the dispersion properties and the effective area in the wavelength range between 1200nm and 1600nm. C-PCF can better compensate the inline dispersion for both single wavelength and broadband wavelength applications which is a unique property not observed by regular triangular-lattice or square-lattice PCFs. The fiber provides higher effective area, making it a better candidate for high power accumulations in the core of the fiber. The fiber also shows red-shifting of the first zero dispersion wavelength (ZDW), flatter dispersion slope and lower Group Velocity Dispersion (GVD) in the normal dispersion region thereby making it a better candidate for high power nonlinear applications like super-continuum generation, soliton pulse propagation etc. With the above advantages, we have considered a series study of these circular-lattice structures for various geometrical parameters and temporal pulses in order to explore the characteristics of broadband supercontinuum generation. This design study for high power supercontinuum generation will be very helpful for potential application of new sources in various fields like astronomy, climatology, spectroscopy optical tomography and sensing etc. to name a few.

Tunable parametric amplifier for mid-IR application based on highly nonlinear chalcogenide material

A novel dispersion controlling technique towards attaining tunable parametric amplification based on highly nonlinear photonic crystal fibers has been investigated. Selective infiltration of the liquid into the air-holes leads to alter the zero dispersion wavelength towards a broader parametric gain in the mid-IR spectrum by only changing the temperature of the system externally. The dispersion profile specially the zero dispersion wavelengths can be well tuned around the pumping wavelength, thereby generating several hundred nanometer parametric bandwidth in near-IR to mid-IR region. The tunability of the photonic crystal fibers (PCFs) can also be useful for generating new frequencies in both the red- and blue-shifted regions far from the pumping wavelength. Our numerical calculations reveal that we could achieve very wide band fiber optic parametric amplifier both in the communication wavelength and in the IR region. Also two different types of PCFs can be used to achieve same broadband wavelength spectra however with a tradeoff between the fiber lengths and pump power.

Fiber guiding at the Dirac frequency beyond photonic bandgaps

AbstractLight trapping within waveguides is a key practice of modern optics, both scientifically and technologically. Photonic crystal fibers traditionally rely on total internal reflection (index-guiding fibers) or a photonic bandgap (photonic-bandgap fibers) to achieve field confinement. Here, we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures. Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers. What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation. We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps. This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps, thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding. The result presented here demonstrates the discovery of a new type of photonic crystal fibers, with unique characteristics that could lead to new applications in fiber sensors and lasers. The Dirac equation is a special symbol of relativistic quantum mechanics. Because of the similarity between band structures of a solid and a photonic crystal, the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons, phonons, and electrons.