Xiao Jinbiao

Semi-vectorial analysis of a compact wavelength demultiplexer based on the tapered multimode interference coupler

Based on a parabolically tapered multimode interference (MMI) coupler with a deep-etched SiO2/SiON rib waveguide, a compact wavelength demultiplexer operating at 1.30 and 1.55µm wavelengths is proposed and analysed by using three-dimensional semi-vectorial finite-difference beam propagation method (3D-SV-FD-BPM). The results show that a MMI section of 330.0µm in length, which is only 76% length of a straight MMI coupler, is achieved with the contrasts of 42.3 and 39.2dB in quasi-TE mode, and 38.4 and 37.8dB in quasi-TM mode at wavelengths 1.30 and 1.55 µm, respectively, and the insertion losses below 0.2dB at both wavelengths and in both polarization states. The alternating direction implicit algorithm with the Crank–Nicholson scheme is applied to the discretization of the 3D-SV-FD-BPM formulation along the longitudinal direction. Moreover, a modified FD scheme is constructed to approximate the resulting equations along the transverse directions, in which the discontinuities of the derivatives of magnetic field components Hy and Hx along the vertical and horizontal interfaces, respectively, are involved.

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 substep, 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 interpolation, a universal finite difference scheme with a high accuracy is developed to approximate the 3D-FV-BPM formulation along the transverse directions, in which the discontinuities of the normal components of the electric field across the abrupt dielectric interfaces 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.

Three-dimensional beam propagation method based on the variable transformed Galerkin’s method

A novel three-dimensional beam propagation method (BPM) based on the variable transformed Galerkin’s method is introduced for simulating optical field propagation in three-dimensional dielectric structures. The infinite Cartesian x-y plane is mapped into a unit square by a tangent-type function transformation. Consequently, the infinite region problem is converted into the finite region problem. Thus, the boundary truncation is eliminated and the calculation accuracy is promoted. The three-dimensional BPM basic equation is reduced to a set of first-order ordinary differential equations through sinusoidal basis function, which fits arbitrary cladding optical waveguide, then direct solution of the resulting equations by means of the Runge-Kutta method. In addition, the calculation is efficient due to the small matrix derived from the present technique. Both z-invariant and z-variant examples are considered to test both the accuracy and utility of this approach.

Cathode life evaluation based on the evolution of heater power and perveance

Reliability of cathodes is critical for the reliability of traveling wave tubes. Accordingly, the reliability test and life prediction of diodes can provide useful information for cathode and TWT reliability evaluation. In this paper, a simple cathode life prediction method considering the evolving of heater power and perveance is presented. The method is applied on the reliability test data for some glass diode samples and several gun samples. The evaluation results show that the cathode life in the electron guns is much longer than those in the diode samples. And the cathode life prediction result for the diodes, based on the evolving of perveance and heater power for a certain anode current and voltage, is close to the final test result.

Full-vectorial analysis of optical waveguides by the finite difference method based on polynomial interpolation

Based on the polynomial interpolation, a new finite difference (FD) method in solving the full-vectorial guided-modes for step-index optical waveguides is proposed. The discontinuities of the normal components of the electric field across abrupt dielectric interfaces are considered in the absence of the limitations of scalar and semivectorial approximation and the present FD scheme can be applied to both uniform and non-uniform mesh grids. The modal propagation constants and field distributions for buried rectangular waveguides and optical rib waveguides are presented. The hybrid nature of the vectorial modes is demonstrated and the singular behaviours of the minor field components in the corners are observed. Moreover, solutions are in good agreement with those published early, which tests the validity of the present approach.

Full-vectorial finite-difference beam propagation method based on the modified alternating direction implicit method

A modified alternating direction implicit algorithm is proposed to solve the full-vectorial finite-difference beam propagation method formulation based on H fields. The cross-coupling terms are neglected in the first sub-step, but evaluated and doubly used in the second sub-step. The order of two sub-steps is reversed for each transverse magnetic field component so that the cross-coupling terms are always expressed in implicit form, thus the calculation is very efficient and stable. Moreover, an improved six-point finite-difference scheme with high accuracy independent of specific structures of waveguide is also constructed to approximate the cross-coupling terms along the transverse directions. The imaginary-distance procedure is used to assess the validity and utility of the present method. The field patterns and the normalized propagation constants of the fundamental mode for a buried rectangular waveguide and a rib waveguide are presented. Solutions are in excellent agreement with the benchmark results from the modal transverse resonance method.

Novel strip EAM with a ring resonator on InP/InGaAsP-MQW

This article describes the three-dimension time domain method employed as simulation instrument to design the strip EAM with a ring resonator on InP/InGaAsP-MQW. The 3D-FDTD arithmetic is applied, and PML (perfectly matched layer) absorption boundary layer is designed in the premise of satisfaction of stability and constringency of the iteration. The main testing equipment is the optical spectral analyzer. PIC is the key chip unit that forms the future optical communication system with high reliability and stability, optical information processing system, optical surveying system.