Calculating photonic Green's functions using a non-orthogonal finite difference time domain method

TL;DR

This paper introduces a non-orthogonal finite difference time domain method for calculating photonic Green's functions, enabling efficient analysis of complex photonic structures with accurate stability and conservation properties.

Contribution

It extends the FDTD method to non-orthogonal coordinates, providing a simple, rigorous derivation and implementation for photonic Green's functions in complex structures.

Findings

Successfully calculated local densities of states in dielectric multilayers and defect structures.

Demonstrated suppression of state density due to photonic band gaps.

Showed potential for designing photonic crystal-based laser cavities.

Abstract

In this paper we shall propose a simple scheme for calculating Green's functions for photons propagating in complex structured dielectrics or other photonic systems. The method is based on an extension of the finite difference time domain (FDTD) method, originally proposed by Yee, also known as the Order-N method, which has recently become a popular way of calculating photonic band structures. We give a new, transparent derivation of the Order-N method which, in turn, enables us to give a simple yet rigorous derivation of the criterion for numerical stability as well as statements of charge and energy conservation which are exact even on the discrete lattice. We implement this using a general, non-orthogonal co-ordinate system without incurring the computational overheads normally associated with non-orthogonal FDTD. We present results for local densities of states calculated using this method for a number of systems. Firstly, we consider a simple one dimensional dielectric multilayer, identifying the suppression in the state density caused by the photonic band gap and then observing the effect of introducing a defect layer into the periodic structure. Secondly, we tackle a more realistic example by treating a defect in a crystal of dielectric spheres on a diamond lattice. This could have application to the design of super-efficient laser devices utilising defects in photonic crystals as laser cavities.