Liquid crystal dynamics in a photonic crystal cavity created by selective microfluidic infiltration

A Casas Bedoya,B J Eggleton,E.C Mägi,C Monat,R W Van Der Heijden,S Tomljenovic-Hanic,P Domachuk,C Grillet,S Mahmoodian

doi:10.1364/oe.18.027280

Abstract

A microfluidic double heterostructure cavity is created in a silicon planar photonic crystal waveguide by selective infiltration of a liquid crystal. The spectral evolution of the cavity resonances probed by evanescent coupling reveals that the liquid crystal evaporates, even at room temperature, despite its relatively low vapor pressure of 5 × 10(-3) Pa. We explore the infiltration and evaporation dynamics of the liquid crystal within the cavity using a Fabry-Perot model that accounts for the joint effects of liquid volume reduction and cavity length variation due to liquid evaporation. While discussing how the pattern of the infiltrated liquid can be optimized to restrict evaporation, we find that the experimental behavior is consistent with basic microfluidic relations considering the small volumes of liquids and large surface areas present in our structure.

Highlights

The inherently mobile fluid phase is naturally suited for dynamic infiltration or withdrawal in nm or micron scale photonic structures [1]
Our results demonstrate that the liquid crystals (LCs) evaporates, even at 20°C temperature, despite its relatively low vapor pressure (5 × 10 3 Pa) and that even modest evaporation rates (10% liquid volume reduction in ~35min) greatly affect the spectral signature of our cavity
By measuring the time evolution of the associated spectra, we investigated the LC dynamics in our system below and above the phase transition and explored its stability due to liquid transport and evaporation

Summary

Introduction

The inherently mobile fluid phase is naturally suited for dynamic infiltration or withdrawal in nm or micron scale photonic structures [1] This flourishing field of optofluidics [1,2], the combination of microfluidics and photonics, has been successfully applied to tuning the optical properties of photonic crystal (PhC) devices [3]. An approach for creating high Q double heterostructure PhC cavities by selectively infiltrating a PhC waveguide with liquids was proposed [6] and demonstrated in chalcogenide glass [12] and Si membranes [3,13] These cavities relied on the infiltration of immersion oil, whose thermal properties were subsequently exploited to induce a temperature-insensitive cavity [14]

Results

Discussion

Conclusion