The influence of material absorption on the quality factor of photonic crystal cavities

Tao Xu,J Stewart Aitchison,Mohammad Mojahedi,Mark S Wheeler,Harry E Ruda

doi:10.1364/oe.17.008343

Abstract

Accounting for material absorption is very important for developing high quality factor (Q) photonic crystal cavities. However, to our knowledge, there have been very few systematic experimental investigations of its role in such cavities. In this paper, we present detailed experiments to reveal the relationship between Q, material absorption coefficient and field pattern. Modes with different field patterns and materials with different absorption coefficients were tested. We have developed a simple formula to describe the relationship, which can be used to replace time-consuming numerical calculations. The experimental and numerical data agree well with this formula.

Highlights

The quality factor (Q) measures the energy leakage rate of the mode confined inside an optical cavity
In a ultrahigh Q (> 1 million) photonic crystal (PhC) cavity, the material absorption loss is comparable to the radiation loss even when a small amount of lossy materials such as one atomic layer of water molecules is adsorbed on the surface of the cavity [3]
For the same cavity and mode, each time when the material absorption coefficient changes or the lossy materials relocate to different places inside or on the surface of the cavity, recalculation is needed

Summary

Introduction

The quality factor (Q) measures the energy leakage rate of the mode confined inside an optical cavity. The 3D FDTD method with the inclusion of material absorption by adding an imaginary part to the refractive index of lossy materials can generate a quite accurate estimation of total energy loss (total Q). For the same cavity and mode, each time when the material absorption coefficient changes or the lossy materials relocate to different places inside or on the surface of the cavity, recalculation is needed. The formula needs as input the mode field distribution, lossy material distribution and the absorption coefficient. The prediction from the formula agree well with both the numerical and experimental data

Background theory

Modes and experimental setup

Numerical and experimental results

21.5 Ez Sim

Conclusion