This work presents results of mode analysis and dispersion spectral characteristic computation, performed for recently presented successfully fabricated silica few-mode microstructured optical fiber (MOF) with hollow-GeO2-doped-ring core (HRC). Here, we utilized manufactured HRC MOF end face photo image to get averaged parameters for input data. Therefore, following simplified model HRC MOF was simulated and researched: it has outer diameter 67 µm; inner diameter of hollow ring-core is 10 µm, wall thickness 4 µm and refractive index difference Δn = 0.030 (percent of GeO2 dopant is about 20.5 mol%); 90 air holes, placed over typical hexagonal geometry in the periphery region with averaged diameter 1.85 µm and pitch 3.9 µm. According to simulation results (mode analysis, performed by rigorous finite element method via commercially available software COMSOL Multiphysics® 6.1), modeled HRC MOF provides two guided LP-modes (fundamental LP01 and the first higher-order LP11) or 4 HE/EH odd and even eigenmodes – HE11/EH11 and HE21/EH21, respectively: therefore, two orbital angular momentum (OAM) modes (OAM11 and OAM21) are localized and supported by the researched and simulated HRC MOF design. In this work we present results of spectral characteristics, computed for mode effective refractive indexes as well as for mode group delays and chromatic dispersion parameters, calculated both for eigen and OAM modes.
This work intends to present various Photonic Crystal fibers (PCF) for the propagation of orbital angular momentum(OAM) modes. Hexagonal, spiral and octagonal-shaped fibers are designed for the observation of OAM modes. The proposed fiber designs have shown high purity of nearly 90% and has proved that the hexagonal design has the highest mode confinement. The finite element method is employed to obtain 12 OAM modes at the operating wavelength of 1.55 μm.
Earlier on we introduced model of piece-wise regular fiber optic link, operating in a few-mode regime: laser-based data transmission over large core optical fiber. Presented model is based on piecewise regular representation with general approach of split-step method application. It allows to take into account laser-excited optical signal launching conditions, differential mode delay, differential mode attenuation, higher-order mode chromatic dispersion and mode mixing / power diffusion, occurring due to optical fiber irregularity and fiber optic cable bends / twisting / stress / tension. While optical fiber irregularity can be directly set by protocols of optical fiber outer diameter monitoring system of drawing tower, cable external mechanical influences are simulated via equivalent angular misalignment at the splices of regular spans. Therefore, this work is concerned with issues of selection of this equivalent angular misalignment (EAM). We performed a computational test series under various values of mentioned above EAM under following comparison with experimentally measurements of few-mode optical pulse responses at the output of multimode optical fibers with strong differential mode delay effect.
This work reports results of laser beam profile measurements, performed for earlier on designed and successfully fabricated silica few-mode microstructured optical fiber (MOF) with hollow-GeO2-doped-ring core (HRC). We compared two drawn from the same preform HRC MOF samples without and with induced during the drawing process twisting of 790 revolutions per meter. Researched silica HRC MOF with outer diameter 65 µm contains hollow ring-core inner diameter of 30.5 µm with wall thickness of 1.7 µm and refractive index difference Δn = 0.03; 90 air holes, placed over typical hexagonal geometry in the periphery domain from the outside HRC at the distance 14 µm, with hole averaged diameter 2.5 µm and pitch 7.5 µm. According to simulation results (mode analysis, performed by rigorous finite element method via commercially available software COMSOL Multiphysics®), it supports two guided LP-modes (fundamental LP01 and the first higher-order LP11) or 4 HE/EH odd and even eigenmodes – HE11/EH11 and HE21/EH21, respectively. We present some results of laser beam profile measurements, performed under various launching conditions (different laser sources as well as excited optical fibers (both commercially available single-mode optical fiber of ITU-T Rec. G.652 and multimode optical fiber 50/125 of ISO/IEC Cat. OM2+/OM3)) at the output ends of researched HRC MOF twisted and untwisted samples as well as at the output end of large core multimode optical fiber 100/125, aligned with excited HRC MOF.
This work reports comparative results of mode analysis, performed for earlier on designed silica microstructured optical fiber with ideal equiangular spiral six-ray geometry (ESSR-MOF) and for its real fabricated sample, differing from the model by weak asymmetry and deformed air holes. We discuss issues of input data preparation to specify analyzed complicated non-ideal fiber optic structure for computation by using rigorous finite-element method. Some results of the comparison between mode field patterns as well as guided mode effective refractive index spectral characteristics are represented. It is demonstrated, that potential deviations from the desired MOF geometry, occurring due to features of silica MOF fabrication technological process, should be taken into account during the design to predict real values of mode parameters for manufactured MOF.
All-optical computing has drawn increased interest from researchers in recent years to meet the need for fast optical signal processing. This paper demonstrates the design of an all-optical CNOT logic gate using a silicon nitride (Si3N4) based optical ring resonator (ORR). Two optical ring resonators have been employed to design the CNOT logic gate. The simulation results obtained from MATLAB using the mathematical equations of the ring resonator validates the proposed CNOT logic gate. The proposed CNOT logic gate is compact and elementary.
The current work proposes an optimized design for 2-bit synchronous up counter using silicon nitride on insulator optical microring resonators (MRRs). The research involves exploring the existing designs of up counter structures based on MRRs, and then minimizing the number of rings being used in the proposed model. The proposed design uses four MRRs for Synchronous up counter operation and the model has been validated through the MATLAB simulation result. The main component of the design is the MRR which can act as a switch depending upon the output at the drop port or the through port according to the MRR being in an on-resonance or off-resonance state respectively. The principle of the MRR is that on applying a vertical pump signal over the ring, the non-linear refractive index of the ring undergoes a temporary blue shift resulting due to π- phase shift in the ring, changing the resonant frequency of operation of the ring. The average pump power required for the blue shift can be obtained from the phase shift vs. the average pump power graph simulated in MATLAB. This shift in resonance frequency is employed to switching action for the signal to be output at the drop port or the through port of the MRR and based on the drive signal inputs of the present state and the clock to the rings in the resonator structure which act as pump signal over the ring, the next state of the counter is determined.
This work presents results of test series, performed for earlier on designed and successfully fabricated twisted silica fewmode microstructured optical fibers (MOF) with six GeO2-doped cores. While Part I introduces results of differential mode delay map measurements, Part II is focused on researches of spectral responses, measured for fiber Bragg gratings, recorded in these multi-core MOFs with core graded refractive index profiles and induced twisting 100 revolutions per meter. Specially setup for spectral response measurement for described complicated fiber optic element was developed, that provides selected alignment of matching singlemode optical fiber with particular single core of MOF via free space and reducing of reflection by precision 8 angle cleaving. Comparing analysis of measured spectral responses confirmed written FBGs in 2 of 6 cores, and demonstrated potentiality of fabricated complicated structure, containing multi-core MOF with FBG, for applications in multichannel fiber optic sensors with spatial division multiplexing technique.
In this paper, we present the results of numerical simulations of Octagonal Photonic Crystal Fiber (O-PCF). The fiber has a ring core made up of Germanium doped silica and cladding is made up of silica glass with aire-holes arranged in octagonal lattice. The O-PCF is capable of propagating 6 OAM modes with highest mode quality-OAM purity equal to 92% at 1.55µm. Other parameters investigated are OAM purity, Neff, Effective Area, Dispersion, Confinement loss and non-linearity. Finite Element Method (FEM) is used for analysis of O-PCF characteristics using COMSOL Multiphysics. High mode purity, flat dispersion and low confinement loss makes the proposed O-PCF a potential candidate for telecom applications such as high-speed, high-capacity, transmission, Space Division Multiplexing (SDM), 6G applications as well as for non-telecom applications such as Supercontinuum Generation (SCG).
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