Finite element approach for the modal analysis of open-boundarywaveguides

A general finite element approach to computing the modes of open-boundary waveguides is presented. This efficient and robust scheme applies equally to situations with real and complex propagation constants. By using a localised boundary impedance condition, the approach preserves the sparsity of the global matrices. A comparison with the well established infinite element technique and the analysis of a 2-D leaky optical structure are given as examples     

Magnetless Optical Circulator Based on an Iron Garnet with Reduced Magnetization Saturation

A three-port circulator for optical communication systems comprising a photonic crystal slab made of a magneto-optical material in which an magnetizing element is not required to keep its magnetic domains aligned is suggested for the first time. By maximizing the incorporation of europium to its molecular formula, the magneto-optical material can remain in the saturated magnetic state even in the absence of an external DC magnetic field. Two- and three-dimensional simulations of the device performed with full-wave electromagnetic solvers based on the finite element method demonstrate that, at the 1550 nm wavelength, the insertion loss, isolation, and reflection levels are equal to or better than −1 dB, −14 dB, and −20 dB, respectively. Since its operation does not require an electromagnet or a permanent magnet, the suggested circulator is much more compact, being able to reach footprints in the range of three orders of magnitude smaller, when compared to other circulator designs referred to in the literature and the presented results can be useful for the design of other nonreciprocal devices with reduced dimensions for optical communication systems.     

Improved all-optical switching in a three-slab nonlineardirectional coupler with gain

We propose and study numerically with a split-step finite-element method, an all-optical switching device made of three nonlinear active optical planar waveguides. Solving directly the nonlinear partial differential equations for the transverse electric polarised fields, the method can analyze real slab structures, where the gain is introduced by doping the guiding region with high erbium concentration. The effect of different amount of gain and loss on the switching performance is investigated. The introduction of suitable gain overcomes the problem of performance degradation due to losses, decreases the switching power and allows the input power to be successfully switched, by a simple power control, among all the three output ports     

Simple nonparaxial beam-propagation method for integrated optics

A simple beam-propagation method for solving the scalar TE nonparaxial or Helmoltz equation is presented. This versatile algorithm, based on a two-step finite-difference scheme for solving the propagation coordinate, is amenable to be easily extended to solve vector wave equations, which could take into account nonlinear effects. In addition, a general procedure to check its stability is given in detail. The applicability of the present method and its distinction from paraxial or Fresnel solutions are demonstrated through several examples, including very strongly guided structures of variable transverse section     

Broadband cascaded four-wave mixing by using a three-pump technique in optical fibers

We present an optimized technique to generate frequency combs by four-wave mixing in highly nonlinear low-dispersion fibers. Three-pumps with unequally spaced frequencies (separation of 100 and 200 GHz) were used. The pumps were located relatively close to the zero-dispersion wavelength of the fiber. Using this three-pump technique we obtained a total of 275 FWM products experimentally, with a 100 GHz spacing and a spanning of over 220 nm.     

Novel FEM Approach for the Analysis of Cylindrically Symmetric Photonic Devices

A novel scheme based on a 2-D finite element method (2-D-FEM) for the frequency domain, in cylindrical coordinates in conjunction with the perfectly matched layers (PML), is proposed and validated here. This scheme permits the analysis and simulation of photonic devices, including discontinuities along the propagation direction. Also, the present approach takes into account the dispersive nature of metals at optical wavelengths.     

Time-domain full-band method using orthogonal edge basis functions

A new time-domain numerical approach for two-dimensional vectorial wave equation solutions based on slow wave variation is presented. The algorithm incorporates finite-element discretization and uses orthogonal edge basis functions to describe pulse propagation in optical waveguides.     

Broadband single-polarization guidance in hybrid photonic crystal fibers

We present hybrid photonic crystal fibers that provide broadband single-polarization guidance based on two different propagation mechanisms, namely, total internal reflection and the photonic bandgap effect. Experimental results demonstrate polarization dependent loss as high as 26.7 dB and the bandwidth of single-polarization behavior over 225 nm.     

Nonlinear interaction between two different photonic bandgaps of a hybrid photonic crystal fiber

Nonlinear interaction between spectral components in two different photonic bandgaps is experimentally demonstrated by launching femtosecond pulses near a zero-dispersion wavelength of a hybrid photonic crystal fiber, which guides by a combination of total internal reflection and bandgap effects. It is demonstrated that the initial pulse becomes spectrally broadened, and narrowband resonant radiation is generated in a different bandgap from the one responsible for guiding at the pump wavelength. The spectral intensity of the resonant radiation peaks at 2.7 dB below that of the broadened pulse in the pump-guiding bandgap.     

Genetic algorithm and finite-element design of short single-section passive polarization converter

A very short passive polarization rotator is proposed, consisting of a single-section asymmetric waveguide. The use of a genetic algorithm together with the finite-element method was crucial to achieve a structure with 99% polarization conversion and a length of 90 /spl mu/m. This optimum structure exhibits a low total insertion loss: 1.16 dB.