Three-dimensional Full-vectorial Beam Propagation Research Articles

Design of an InGaAsP/InP compact integrated optical depolarizer

In this paper, we propose and demonstrate two integrated optics InGaAsP/InP depolarizer circuits. The first one is based on the Lyot depolarizer configuration, while the second one is based on the Mach-Zehnder configuration. Detailed simulation, using three-dimensional full vectorial beam propagation method, shows that a high-index contrast material allows the design of a compact polarization insensitive depolarizer. For the first design, an output degree of polarization (DOP) less than 0.1 is obtained for light sources with spectral widths larger than 25nm, while for the second one, output DOP less than 0.06 is obtained for light sources with spectral widths larger than 40nm.

Design of a compact polarization splitter composed of a multiple-slotted waveguide and a silicon nanowire

A polarization splitter (PS) based on a directional coupler (DC) composed of a vertical multiple-slotted waveguide (MSW) and a silicon nanowire is proposed and designed by using a modified three-dimensional full-vectorial beam propagation method (BPM). By utilizing the unique modal properties of the slotted waveguide, the coupling of the DC in quasi-TE modes can be almost neglected, and only that in quasi-TM modes is considered, leading to a compact PS. Moreover, the MSW has the advantages of both strong field confinement and high birefringence, which improve the performance of the device. The numerical results show that a PS with a length of 20.5 μm in the coupling region is achieved with a bandwidth of up to 22 nm (ranging from 1.540 to 1.562 μm) with the crosstalk lower than −20 dB. In addition, the fabrication tolerances for the structural parameters are investigated in detail. The evolution of the injected field along the propagation distance through the PS is also demonstrated.

Design of polarization-independent optical couplers composed of three parallel slot waveguides

The characteristics of directional couplers and power splitters based on three-guide optical couplers in slot waveguide structures are analyzed in detail by a three-dimensional full-vectorial beam propagation method. The numerical results show the achievement of a compact three-guide directional coupler operating as polarization independent with a length of 58.0 microm and having almost evenly spaced propagation constants of the three lowest order modes for quasi-TE and quasi-TM modes. Thus, a high coupling efficiency from one outside waveguide to the other outside waveguide is demonstrated and is over 99.5% for both polarization states. For a three-guide power splitter, multiple sets of waveguide parameters for achieving polarization-independent operation are presented. Tolerances to operating wavelength and structural parameters are also analyzed, and the evolution of the injected field along the propagation distance through the proposed devices is demonstrated.

Design of a Compact Polarization Splitter in Horizontal Multiple-Slotted Waveguide Structures

A compact polarization splitter based on the directional coupler in horizontal multiple-slotted waveguide (HMSW) structures is proposed and designed by using a modified three-dimensional full-vectorial beam propagation method with perfectly matched layer absorbing boundary conditions. The results show that the birefringence of the HMSW is stronger than that of the single-slotted waveguide, leading to a reduction in length for the present device. Moreover, the HMSW can also enhance the optical confinement inside the slot regions. The coupling length of the directional coupler composed of two-parallel HMSWs as functions of the waveguide parameters are analyzed, and a compact device of 238.0 µm in length is achieved with the crosstalks of -27.9 and -35.6 dB for quasi-transverse-electric and quasi-transverse-magnetic modes, respectively. In addition, the evolution of the injected field along the propagation distance through the polarization splitter is also demonstrated.

An improved three-dimensional full-vectorial finite-difference imaginary-distance beam propagation method

A modified alternating direction implicit approach is proposed to discretize the three-dimensional full-vectorial beam propagation method (3D-FV-BPM) formulation along the longitudinal direction. The cross-coupling terms (CCTs) are neglected at the first sub-step, and then double used at the second substep. The order of two substeps is reversed for each transverse electric field component so that the CCTs are always expressed in an implicit form, thus the calculation is efficient and stable. Based on the multinomial inter-polation, a universal finite difference scheme with a high accuracy is developed to ap-proximate the 3D-FV-BPM formulation along the transverse directions, in which the dis-continuities of the normal components of the electric field across the abrupt dielectric in-terfaces are taken into account and can be applied to both uniform and non-uniform grids. The corresponding imaginary-distance procedure is first applied to a buried rectangular and a GaAs-based deeply-etched rib waveguide. The field patterns and the normalized propagation constants of the fundamental and the first order modes are presented and the hybrid nature of the full-vectorial guided-modes is demonstrated, which shows the validity and utility of the present approach. Then the modal characteristics of the deeply- and shallow-etched rib waveguides based on the InGaAsp/InGaAsP strained multiple quantum wells in InP substrate are investigated in detail. The results are necessary for modeling and the design of the planar lightwave circuits or photonic integrated circuits based on these waveguides.

Fast-Fourier-based three-dimensional full-vectorial beam propagation method

An accurate and highly efficient fast-Fourier-based full-vectorial beam propagation method (BPM) with perfectly matched layer absorbing boundary conditions is presented. Full vectorial results obtained for highly guiding z-variant structures, such as a spot size converter and a Y-branch in rib technology, show that accurate results can be obtained with reduced computational effort, thus making this technique an interesting alternative to other existing BPM strategies.

Singlemode and polarisation free conditions for small silicon-on-insulator waveguides

An analysis based on simulation of polarisation depedence and the singlemode condition for small and deeply etched silicon-on-insulator waveguide dimensions is presented. Examples of designs that satisfy both requirements simultaneously have been evaluated using the three-dimensional full vectorial beam propagation method.

A three-dimensional full vectorial beam propagation method for z-dependent structures

A full vector beam propagation method based on the split-operator approach is developed for 3-D z-dependent structures. The inherent coupling of the three electric field components found in the vector wave equation, which stems from the variation of the refractive index along the axial z/spl circ/ direction, is fully taken into consideration. Three distinct procedures are proposed for the numerical implementation based on the FFT, Pade approximation, and alternating direction implicit (ADI), respectively. Typical integrated optics applications are considered in order to verify and assess the applicability of the method.