Large Effective Mode Area Research Articles

Comprehensive Analysis of Dual Core Photonic Crystal Fibers for Optimizing Optical Properties Towards Highly Coherent Supercontinuum Generation

A systematic study implementing numerical analysis has been presented in this work in order to design a hexagonal lattice dual core photonic crystal fiber (DC-PCF) which will be simple to fabricate but possesses very good values of optical properties for supercontinuum generation (SCG). By utilizing a full vectoral finite element method with perfectly matched boundary conditions, important propagation properties are numerically evaluated and tuned to desired value through the optimization of structural parameters. Finally, it is found that the optimized PCF structure exhibits very low confinement loss, high birefringence, large effective mode area while maintaining negative chromatic dispersion of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 8.3138 ps/km.nm pumping at 1060 nm wavelength. The fiber when excited by a hyperbolic secant pulse having a full-width at half-maximum (FWHM) of 50 fs and a relatively low energy of 4 nJ generates a SC spectrum spanning 600 nm to 1600 nm. The effect of altering the pump power and other parameters on the generated spectra is also explored. Furthermore, the input noise effects on generated SCs have been analyzed through the inclusion of different types of noise. It is found that the generated SC demonstrates excellent coherence property over the entire band extended from visible to the near-IR region and thus it may find applications in lasing, biological imaging, and telecommunication.

Non-Zero Dispersion-Shifted Ring-Core Fiber Supporting 60 OAM Modes

Orbital angular momentum (OAM) modes have becoming more promising to further achieve higher spectral efficiency and data capacity in space-division-multiplexing (SDM) fiber communication systems. In this work, we design and optimize a graded-index non-zero dispersion-shifted ring-core fiber (GI-NZDSRF) to support OAM modes in fiber-based transmission system. A record high number of 60 OAM modes in the C band with <10 ps/nm/km chromatic dispersion (CD) is obtained. A low differential mode delay (DMD) (<5.11 ps/m) and a large effective mode area (>1418 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of OAM modes are achieved by the designed fiber. Furthermore, the effects of fiber parameters on OAM modes are also investigated, including the index shape, doping concentration, central location, and half width of the high index region.

A large effective mode area photonic crystal fiber supporting 134 OAM modes

A large effective mode area photonic crystal fiber supporting 134 OAM modes

Highly Sensitive Bilirubin Biosensor Based on Photonic Crystal Fiber in Terahertz Region

An unstable bilirubin level in the human blood causes many dangerous health problems, such as jaundice, coronary artery disease, ulcerative colitis, and brain lesions. Therefore, the accurate and early detection of bilirubin concentrations in the blood is mandatory. In this work, a highly sensitive biosensor based on photonic crystal fiber (PCF) for monitoring bilirubin levels is proposed and analyzed. The sensor parameters, including relative sensitivity, effective mode area, confinement loss, and effective material loss, are calculated. The geometrical parameters are studied, and a modal analysis of the suggested sensor is carried out using the full-vectorial finite element method (FEM). The fabrication tolerance of the geometrical parameters is also studied to ensure the fabrication feasibility of the reported design. High sensitivities of 95% and 98% are obtained for the x-polarized and y-polarized modes, respectively. Furthermore, a small material loss of 0.00193 cm−1, a small confinement loss of 2.03 × 10−14 dB/cm, and a large effective mode area of 0.046 mm2 are achieved for the y-polarized mode. It is believed that the presented sensor will be helpful in health care and in the early detection of bilirubin levels in the blood.

Terahertz Women Reproductive Hormones Sensor Using Photonic Crystal Fiber With Behavior Prediction Using Machine Learning

In this article, we propose a rectangular hollow core Photonic Crystal Fiber (PCF) sensor for high detection of women’s reproductive hormones (progesterone and estradiol) in the blood sample at THz regime (0.8 THz to 1.7 THz). The numerical sensing performances are evaluated by the full vector finite element method (FVFEM). We have achieved improved relative sensitivity with minimal loss for sensing progesterone concentrations and estradiol concentrations by optimizing structural parameters. The obtained maximum relative sensitivity is 99.87% for 10 n mol/L (progesterone) and 99.88% for 3 n mol/L (Estradiol) at 1.35 THz. Further, we have obtained low effective material loss (EML) and a large effective mode area. The primary takeaway from this research is that it’s critical to monitor estradiol and progesterone levels in order to ensure that a woman’s reproductive system is functioning in a balanced manner and in general health systems. Also, this biosensor can be fabricated by current fabrication technologies. Moreover, the prediction carried out with the help of Locally Weighted Linear Regression, and hyperparameter tuning, we can conclude that for weighting hyperparameter value of 0.02. We have achieved the maximum prediction accuracy with the unity R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> score and this model can be employed for the prediction of relative sensitivity for various parameters.

A novel few-mode multi-core fiber with large effective mode area and low inter-core crosstalk

This paper proposes a novel 7-core 5-mode fiber with large mode area and low inter-core crosstalk(XT). The proposed optical fiber, by adopting a combination of air-trench structure and high-index ring, realizes large mode area and low XT. The numerical analyses reveal that the proposed fiber can stably transmit 5 LP modes in the C+L band; the effective mode area of each of the 5 LP modes is larger than 110 µm2; the XT of in each of the 5 LP modes is smaller than −79 dB/km; each mode has an effective refractive index difference bigger than 1.1 × 10−3. Therefore, a low XT result can still be achieved when the mode area is large. The proposed optical fiber may be well utilized to construct a high-capacity fiber optic transmission system.

(INVITED)Dispersion-shifted tellurite fibers for nonlinear frequency conversion

We report a detailed numerical investigation of step-index tellurite fiber properties based on the careful experimental characterization of refractive indices for two tellurite-glass systems employed in fiber manufacturing. More specifically, our study focuses on two typical step-index configurations, namely weak and strong index differences between core and cladding glasses. We reveal that a wide range of dispersion-shifted features for tellurite fibers can be obtained in the 2–3 μm range combined with small or large effective mode areas. Our work also outlines the potential application of such dispersion-engineered fibers for nonlinear wavelength converters between near- and mid-infrared regions.

An all-optical fiber mode converters based on 5-LP mode fiber of weakly coupling and large effective mode area

In this work, an all-optical fiber-based mode converter was created by mating a self-made 5-mode fiber (5MF) with a single mode fiber (SMF) using the fused tapering approach. The 5MF was characterized by weakly coupling and large effective mode area with the attenuation of 0.277 dB/km. By controlling the core size during the pre-tapering process, mode conversions of high efficiency were successfully realized between the fundamental mode in the SMF with the five modes (LP01, LP11, LP21, LP02 and LP31) in the 5MF. At the wavelength of 1550 nm, the reality normalized coupling efficiencies of the five conversion processes were 0.952, 0.930, 0.990, 0.923 and 0.998, respectively. Moreover, a 5-mode-division multiplexer was produced by cascading the five mode converters in terms of descending order (LP01, LP11, LP21, LP02, LP31). The 5MF, mode converters and multiplexers provide a convenient and effective option for constructing the high-capacity mode division multiplexing communication systems.

A Bend-resistant Photonic Crystal Fiber with Large Effective Mode Area

A photonic crystal fiber (PCF) with excellent bend-resistant performance and large mode field area is proposed and analyzed by the finite element method in this paper. The bending loss and mode field area characteristics in the operating wavelengths that most commonly used are studied in detail. Under the premise of reducing the difficulty of fabricating the fiber, the structural parameters of the optical fiber is optimized. The calculation results demonstrate that the single mode operation bending radius ranges at the wavelength of 1.064 μm, 1.31 μm and 1.55 μm can reach to 7.73 cm, 6.53 cm and 5.91 cm respectively. Meanwhile, a large effective mode area which exceeds 1300 μm2 is obtained. The proposed PCF has potential applications in the fields of high-power laser systems and optical fiber sensing.

Design of ultra-dispersion flattened M-type few-mode fiber for weakly-coupled mode division multiplexing transmission

In this work, we present an ultra-dispersion flattened few-mode (UDF-FMF) fiber design that can support ten linearly polarized modes in the C-band. The proposed fiber has an M-type refractive index profile with 13.5% GeO2 doped original core, and fused silica cladding. A high-index ring is inserted in the cladding, to increase the number of modes with low mode coupling. A trench in the cladding and a depression in the original core are added to manage the chromatic dispersion parameter and to reduce the bending loss. The fiber exhibits non-zero dispersion at 1.55 µm for the fundamental LP01 mode to satisfy the ITU-G.655 standard and yields a minimum dispersion flatness of ~0.18 ps/nm/km over the C-band for the first time according to our knowledge. The modal characteristics of the UDF M-type FMF have been systematically analyzed through the finite element method-based COMSOL software. The fiber parameters and the dopants concentration are systematically chosen through simulations to guide ten LP modes with large mode separation (max∆neff≅5×10−3), optical loss in the range of 10-10 to 10-12, minimum differential mode delay of 0.09ps/m, nonlinear coefficient lower than 2 × 10-3 km−1 W−1, and large effective mode-area of 385 µm2 across the C-band. We believe the proposed fiber design can be a potential contender for new-generation optical communication using mode-division multiplexing.

Ultra-low loss polymer-based photonic crystal fiber supporting 242 OAM modes with high bending tolerance for multimode THz communication

A novel polymer-based ring-core circular photonic crystal fiber (C-PCF) is proposed and investigated. The solid core C-PCF structure is composed of Topas as background material, a high refractive index (RI) Kapton polymer as a ring material and four layers of air hole patterns. Numerical simulation is used to optimize the PCF geometry to support maximum stable modes with minimum losses. The proposed C-PCF supports 242 stable OAM modes near 1.9 THz with mode purity >0.9. The fiber exhibit low confinement loss (CL) ∼10-9 dB/cm, large effective mode area ∼ 10-2 mm2, low dispersion <1 ps/THz/cm and high effective mode index difference (Δneff) >10-3 in the range 1.5 THz to 3.5 THz. Attenuation, mode stability, material dispersion and fiber bending tolerance of PCF are analyzed to increase the transmission capacity. The detailed experimental feasibility and design sensitivity are theoretically addressed. The proposed PCF supports stable modes and works at a wider spectrum then the previously reported studies. The fiber has the potential to be employed for next-generation THz multimode communication systems.

Multicore raised cosine fibers for next generation space division multiplexing systems

Space division multiplexing (SDM) is a promising solution for improving the transmission capacity and increasing the spectral efficiency. SDM over few mode multicore fibers (FM-MCFs) is an attractive approach that observes increasing interest. In this work, after reviewing the basic guidelines for FM-MCFs design, we address, for the first time, the Raised Cosine (RC) profile to multicore fibers context. We optimize the single core RC profile in order to support exactly 6 linearly polarized (LP) modes with large effective mode area (min Aeff = 96 μm2), with low differential mode delay (DMD) (max DMD = 33 ps⧹km) and high intermodal separation (⩾2×10−4). Once achieved, we investigate the induced crosstalk between twin RC cores and twin trenched RC (TRC) cores. We then propose four 6 modes 7 cores RC⧹TRC fibers. Their crosstalk and their relative core multiplicity are analysed and compared with those reported in recently graded index-FM-MCFs. The selected designs could be promising candidates for short and medium haul interconnects.

Design of 18-mode hole-assisted elliptical-core polarization-maintaining few-mode fiber

We present a novel hole-assisted elliptical-core polarization-maintaining few-mode fiber (EC-PM-FMF) composed of three layers of air holes. The proposed fiber breaks degeneracy of modes by introducing geometry asymmetry. Through optimizing the parameters, the designed fiber could support 18 separate polarization-maintaining modes with the minimum effective refractive index difference (Δneff) between adjacent modes larger than 1.21 × 10−4 over the whole C + L band. Moreover, the designed fiber exhibits good mode and propagation properties including large effective mode area, low nonlinear coefficient, small and flat chromatic dispersion, low confinement loss and bending loss. Thus, the fiber can be used in mode division multiplexing (MDM) system without multi-input multi-output (MIMO) digital signal processing (DSP) technology to improve channel utilization.

KW-level monolithic single-mode narrow-linewidth all-solid photonic bandgap fiber amplifier.

Further power scaling of narrow-linewidth fiber lasers is critical for beam combining. Using all-solid photonic bandgap fibers with large effective mode areas and strong higher-order-mode suppression is an interesting approach. Previously, we demonstrated ∼400W single-frequency single-mode power at 1064 nm from a 50/400 photonic bandgap fiber amplifier, limited only by transverse mode instability (TMI). In this work, we demonstrate a TMI-limited single-mode power of 1.37 kW from a monolithic fiber amplifier with a 25/400 photonic bandgap fiber, the highest output power from a photonic bandgap fiber demonstrated to date, to the best of our knowledge. The spectral linewidth is broadened to ∼8GHz to suppress stimulated Brillouin scattering.

Epsilon negative-based, broadband single-polarization single-mode hollow core anti-resonant photonic crystal fiber.

A broadband single-polarization single-mode (SPSM) hollow core anti-resonant photonic crystal fiber (HC-ARPCF) is proposed and analyzed by the finite element method in this paper. The HC-ARPCF design consisted of outer semicircular cladding tubes and inner circular cladding tubes. The SPSM behavior is achieved through controlling the effective material absorption loss (EML) by loading epsilon negative (ENG) material in the selected semicircular cladding tubes. Optimization of the configuration parameters is conducted to yield a large loss difference (LD) between one of the two orthogonally polarized fundamental modes and all the other unwanted modes. Therefore, only one desired mode will exist after a proper propagation distance, i.e., SPSM guidance. Specially, the optimal design provides a 288 nm (from 1408 nm to 1676 nm and from 1680 nm to 1700 nm) bandwidth in terms of 40 dB/m minimum LD (MLD) and 168 nm (from 1452 nm to 1620 nm) bandwidth in terms of 100 dB/m MLD. Furthermore, this fiber also exhibits a large effective mode area and near-zero dispersion properties over the entire operation bandwidth. The proposed HC-ARPCF may find its applications in polarization maintaining and high-power laser systems.

Amplification characteristics in active tapered segmented cladding fiber with large mode area

Abstract A kind of tapered segmented cladding fiber (T-SCF) with large mode area (LMA) is proposed, and the mode and amplification characteristics of T-SCFs with concave, linear, and convex tapered structures are investigated based on finite-element method (FEM) and few-mode steady-state rate equation. Simulation results indicate that the concave tapered structure can introduce high loss for high-order modes (HOMs) that is advantageous to achieve single-mode operation, whereas the convex tapered structure provides large effective mode area that can help to mitigate nonlinear effects. Meanwhile, the small-to-large amplification scheme shows further advantages on stripping off HOMs, and the large-to-small amplification scheme decreases the heat load density induced by the high-power pump. Moreover, single-mode propagation performance, effective mode area, and heat load density of the T-SCF are superior to those of tapered step index fiber (T-SIF). These theoretical model and numerical results can provide instructive suggestions for designing high-power fiber lasers and amplifiers.

Modelling and simulation of novel liquid‐infiltrated PCF biosensor in Terahertz frequencies

The liquid-infiltrated photonic crystal fibre (LI-PCF) is proposed for guiding terahertz radiation. Geometrical asymmetry is achieved by introducing a large ellipse in the core. By filling the ellipse with liquid cocaine, the optical properties of the photonic crystal fibre (PCF) are theoretically examined using finite element method-based COMSOL multiphysics software. At an operating frequency of 1 THz, the proposed LI-PCF demonstrates a sensitivity of 87.02% and confinement loss in the order of 10 −4 cm −1 . The PCF also demonstrates extremely low effective material loss <0.01 cm −1 , a birefringence of 0.018, large effective mode area of 1.11 × 10 5 µm 2 , a high numerical aperture of 0.45 and near-zero ultra-flattened chromatic dispersion of 1.4351 ± 0.5883 ps/THz/cm. The design simplicity and high sensitivity, strong confinement factor, low material losses and high birefringence of the fibre suggest that the proposed fibre may be convenient for PCF-based cocaine sensing, for application in the security and defence industries.

Ultra-low NA step-index large mode area Yb-doped fiber with a germanium doped cladding for high power pulse amplification.

High concentration rare earth doped, large mode area (LMA) step-index fibers, which feature a very high cladding absorption per unit length at the pump wavelength, high efficiency, and excellent beam quality, are ideal for high power pulsed fiber lasers/amplifiers where large effective mode areas and short device lengths are crucial in order to reduce detrimental nonlinear effects associated with high peak power operation. In this Letter, we realize low numerical aperture (NA) high absorption fibers, simply by employing a germanium (Ge)-doped cladding rather than a pure silica cladding to offset the high refractive index associated with using a high concentration of ytterbium (Yb) in the core. This approach allows us to separate the two inter-linked fiber design parameters of pump absorption and NA in a step-index fiber. Using a conventional modified chemical vapor deposition process combined with solution doping, a low NA (0.04), LMA (475µm2) silica fiber is fabricated with a cladding absorption value of >20dB/m, which is the highest value among LMA step-index fibers with NA<0.06 so far reported to the best of our knowledge. The fabricated Yb-doped fiber was tested in a high-power picosecond amplifier system and enabled the generation of 190 ps laser pulses with a 101 µJ pulse energy and 0.5 MW peak power at an average power of 150 W.

Design of Highly Sensitive Photonic Crystal Fiber for Sensing Harmful Chemicals

Highly sensitive Photonic Crystal Fiber (PCF) has been designed and investigated for sensing the most harmful chemicals that exist in the world. The proposed structure of PCF consists of a solid circular core in which the samples of the chemicals are to be filled, surrounded by a hexagonal air-hole ring. The outermost cladding region comprises circular air-holes arranged in a helical (spiral) manner. Moreover, the sensitivity ratio of the liquid samples is investigated with respect to the wavelength. Sensitivity is monitored by checking for different wavelengths that range from 0.4μm to 1.85μm. With this proposed structure, the relative sensitivity of the chemicals such as paraffin liquid (n=1.48), pyridine (n=1.51), and bromobenzene (n=1.56) are found to be 78.49%, 82.99%, and 89.34% respectively. The proposed PCF structure is used to detect chemicals and any liquids due to its high sensitivity, large effective mode area, and low confinement loss.

Sensing of Illegal Drugs by Using Photonic Crystal Fiber in Terahertz Regime

Abstract Stimulant abuse enhances dopamine release, thereby causing increased excitation. Any extent of stimulant abuse can considerably harm the user. Thus, methods of detecting stimulants must be precise, accurate, and reliable. A novel terahertz (THz) photonic crystal fiber with a Topas substrate is designed and rigorously investigated for detecting liquid amphetamine, cocaine, and ketamine. The fiber structure has a pentagonal shape and comprises circular air holes in the core and cladding spatial extents. As shown in finite element simulation, the proposed fiber yields a high relative sensitivity of approximately 80 % when any of the liquid stimulants is infiltrated in the core air holes. At 1 THz operating frequency, the proposed fiber produces a large effective mode area, negligible confinement loss, and extremely low bending and effective material losses. Other THz waveguiding properties, such as core power fraction and total loss, are also studied. Lastly, a positive and negative 2 % fabrication tolerance is set to ensure seamless potential practical realization of the fiber.