Finite Element-based Beam Propagation Research Articles

Asymmetric Si-Slot Coupler With Nonreciprocal Response Based on Graphene Saturable Absorption

We present the study of a proof-of-concept integrated device that can be used as a nonlinear broadband isolator. The device is based on the asymmetric loading of a highly-confining silicon-slot photonic coupler with graphene layers, whose ultrafast and low-threshold saturable absorption can be exploited for nonreciprocal transmission between the cross-ports of the coupler. The structure is essentially a non-Hermitian system, whose exceptional points are briefly discussed. The nonlinear device is modeled with a coupled Schrodinger equation system whose validity is checked by full-vector finite element-based beam-propagation method simulations in CW. The numerically computed performance reveals a nonreciprocal intensity range (NRIR) in the vicinity of 100 mW peak power with a bandwidth spanning tens of nanometers, from CW down to ps-long pulses. Finally, the combination of saturable absorption and self-phase modulation (Kerr effect) in graphene is studied, indicating the existence of two NRIR with opposite directionality.

Efficient Scalar Bidirectional Beam Propagation Analysis for Photonic Devices With Circular Symmetry

In this letter, a scalar non-iterative bi-directional finite element based beam propagation method (NI-BiBPM) is proposed for the analysis of light propagation in photonic devices with circular symmetry. We adopt the Blocked Schur algorithm (BSA) for calculating the square root of the characteristic matrix in order to achieve fast and stable results and to avoid the complications and limitations of other computational modeling techniques such as Taylor or Pade approximations. The suggested NI-BiBPM approach does not only offer reduction in execution time and memory requirements but also guarantees the numerical stability.

Design and Characterization of Biophotonics Devices

In this paper we study the design and characterization of optical biosensors based on the integrated optics technology. The finite element based perturbation technique has been used to characterize the surface plasmon waveguide. The finite element based beam propagation method has been used to characterize the ring resonators. Some of the novel biosensor structures will be characterized and modal loss and sensitivity and selectivity of these biosensors are studied

Accurate finite element modal solution of photonic crystal fibres

The imaginary distance full vectorial finite element based beam propagation method (IDVFEBPM) is applied to perform an accurate modal solution to photonic crystal fibres (PCFs). The robust perfectly matched layer (PML) boundary condition is employed at the edges of the computational window in order to account for the leakage property of the modes. The effects of the number of holes and the geometrical parameters of the PCF on the effective index, the confinement losses, the effective mode area and the dispersion of the fundamental mode have been thoroughly studied.

Characterisation of low-loss waveguide bends with offset-optimisation for compact photonic integrated circuits

Use of a semivectorial finite element-based beam propagation method is benchmarked with the results available by using alternative numerical methods to analyse compact optical bends in photonic integrated circuits. It is also shown that the incorporation of the perfectly matched layers boundary condition is a superior approach for the treatment of high radiation loss from compact bends to the more common use of the absorbing boundary conditions. The least squares boundary residual method is employed to calculate the lateral offset necessary to maximise the transmission and simultaneously to minimise the reflection coefficients at the straight-to-bend waveguide interfaces. Using these efficient numerical techniques, the radiation loss, transition loss and the required waveguide offset to maximise the transmission and reduce the reflection are calculated.