Rabah Attia

Full vector modal analysis of microstructured optical fiber propagation characteristics

Microstructured optical fibers (MOFs) are optical fibers having a periodic air-silica cross-section. The air holes extend along the axis of the fiber for its entire length. The core of the fiber is formed by a missing hole in the periodic structure. Remarkable properties of MOFs have recently been reported. This paper presents new work in the modeling of the propagation characteristics of MOFs using the Finite Element Method (FEM) and the Galerkin Method (GM). This efficient electromagnetic simulation package provides a vectorial description of the electromagnetic fields and of the associated effective index. This information includes accurate determination of the spectral extent of the modes, cutoff properties and mode-field distributions. We show that FEM is well adapted for describing the fields at abrupt transitions of the refractive index while GM has the advantage to accurately analyze MOFs of significant complexity using only modest computational resources. This presentation will focus on the specific techniques required to determine single mode operation, dispersion properties and effective area through careful choice of the geometrical parameters of the fibers. We demonstrate that with suitable geometrical parameters, the zero dispersion wavelength can be shifted. This tool can also provide design criteria for fabricating MOFs and a corresponding map of effective area. This approach is validated by comparison with experimental results and measurements on actual MOFs fabricated at IRCOM and at Alcatel Research and Innovation Center.

Mode scrambler for polymer optical fibers

This paper covers the design and operation of a new mode scrambler for polymer optical fibers. This scrambler enables the rapid achievement of the equilibrium mode distribution without incurring significant insertion loss. Its main other features are small size and a costeffective design, making it very easy to build, configure, and operate. A numerical model based on geometrical optics is developed to understand the behavior of the scrambler, assess its overall performance, and help optimize its configuration. Results obtained through numerical simulation are then validated through experiments.

Behaviour of propagation through one dimension photonic crystal

In this work we present a first result of a 1D-photonic crystals (PC) modelling. Our final aim is the characterization of a multimode waveguide which uses this kind of crystal. In this case the optical propagation properties are strongly modified by the anisotropy of the photonic crystal. The transmission of a plane wave depends on the wavelength and its direction. Also the geometries of the structure must be taken into account. The results are obtained by using numerical tools: finite difference time domain (FDTD) and plane wave method (PWM).

Toward All Optical Interconnections in Chip Multiprocessor (2)

The need to find new strategies and architectures in development of multi processors system on chip (MPSoC) makes necessary to reduce consumption while growing data transfer by increasing number of cores in one chip. This paper proposes a new configuration for an optical router on chip called ROTAR, it will study its different elements, detailing the operation of each component and their physical structure and thus by a study of wave guide losses at crossing, bends and in evanescent coupling based upon the numerical method FDTD. The use of such routers in optical network on chip (OnoC) has several benefits such as a static and simple routing algorithm and more interconnection capacity compared to ?-router [2]. This paper studies active micro resonator optical behavior and propose an algorithm performing a global estimation of all type of losses in this optical network on chip, assuming 1mm2 area and use of 8*8 routers. Fat-H-Tree topology offer in optical domain many advantages, allowing to connect more cores in one chip with the same number of micro resonators compared to the same topology in electrical domain. Silicon wave guides (refraction index = 3,5) surrounded by a layer of silica (1,44) were used to achieve a strong field confinement in the wave guide.

Two-dimensional photonic crystals in lithium niobate (LiNbO3)

We show the feasibility of two-dimensional structures air/LiNbO3 which ensures the achievement of ordered functions such as dynamic filtering. A study by FDTD (Finite Difference Time Domain) simulation shows that a variation of 0.005 of the refractive index in LiNbO3 allows a linear shifting of the Photonic Band Gap of 4.1 nm.

Numerical solution to modal field equation with a finite difference beam propagation method: application to Bragg fiber

The Beam Propagation Method (BPM) is the most widely used tool for the investigation of complex photonic structures. Since the original BPM was introduced, many improvements and extensions have been proposed. We have developed a computer program based on the Finite Difference BPM for modeling propagation in optical waveguides. This method has been successfully applied for several 3D problems such as propagation on Bragg Fiber. The main drawback of this method is its complexity and long computation time using a personal computer. In this paper, a simple efficient numerical solution method, we called double 2D-BPM, is proposed. This technique is based on the decomposition of the 3D field propagation equation onto two 2D equations related to transverse plans. Propagation along the x and y axes is computed separately in two steps. Using a similar technique, a finite difference approximation for each propagation step involves the solution of two equations and the complete problem splits into two independent 2D problems. We performed propagation tests in elementary 3D problems but also on Bragg fiber. The numerical results of 3D-BPM and double 2D-BPM have been compared. The propagation step along the propagation axis has been experimentally determined. Parameters that affect the accuracy and the stability of this method were discussed. Losses induced by propagation on Bragg fiber were also considered. We have established that the global effect of the double 2D-BPM is equivalent to 3D-BPM technique. Comparison with exact results obtained from analytical expressions also shows excellent agreement.

Analysis of the error probability for optical unipolar two-dimensional codes using a serial elimination interferences receiver

The utilization of unipolar optical two-dimensional codes(2D codes) employed in OCDMA systems has given a better system performance and a diminution of multiple access interferences (MAI) relative to optical unipolar codes with one dimension(lD code). In this paper we study the error probability of 2D optical codes namely prime hop system and hybrid codes using a probability distribution approach. We demonstrate in this work that we have a higher performance when we use serials eliminations interferences receiver versus conventional receiver, in other words the error probability is decrease and the system provide an important number of simultaneous users sharing the network.

Modelling dispersion in photonic crystal and its application in reducing chromatic dispersion

In this work we model the dispersive properties of photonic crystal (PC) modelling. Our final aim is making easier the choice of the appropriate direction when correcting waveguides dispersion with a PC material. In this case the optical propagation properties are strongly modified by the anisotropy of the photonic crystal. The transmission of a plane wave will depends on the wavelength and its direction. The results are obtained by using numerical tools: Bandsolve of RSoft [1].

Misalignment loss at hybrid standard-single-mode-fibre/microstructured-optical-fibre connections

We present experimental results on Microstructured Optical Fibre (MOF) coupling with standard Single Mode Fibre (SMF) using a simple and reliable set-up. An electric-arc splicing system is used to demonstrate its effectiveness in splicing SMF with MOFs. The measurements of the additional loss induced by transverse and longitudinal offsets at connections between SMF and MOF are reported and discussed. The influence of mode size mismatch is emphasized.

Modelling microstructured optical fibres

In this paper we present an analysis and design of the microstructured optical fibres using the effective index and the Galerkin models. Some performance of air guiding microstructured fibers is discussed. We establish the effective indexes, field distributions and chromatic dispersion of the guided modes. We demonstrate that the full-vectorial Galerkin method can be efficiently used to obtain the propagation characteristics of microstructured optical fibres. Comparison with previous models and numerical methods is made and excellent agreement is achieved.