Tuning of 2-D Silicon Photonic Crystals
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Tuning of 2-D Silicon Photonic Crystals H. M. van Driel, S.W. Leonard, J. Schilling1 and R.B. Wehrspohn1 Department of Physics, University of Toronto Toronto, Canada, M5S1A7 1 Max Planck Institute für Mikrostrukturphysik Weinberg-2, D-06120 Halle, Germany ABSTRACT We demonstrate two ways in which the optical band-gap of a 2-D macroporous silicon photonic crystal can be tuned. In the first method the temperature dependence of the refractive index of an infiltrated nematic liquid crystal is used to tune the high frequency edge of the photonic band gap by up to 70 nm as the temperature is increased from 35 to 59°C. In a second technique we have optically pumped the silicon backbone using 150 fs, 800 nm pulses, injecting high density electron hole pairs. Through the induced changes to the dielectric constant via the Drude contribution we have observed shifts up to 30 nm of the high frequency edge of a band-gap. INTRODUCTION Photonic crystals are widely regarded as materials that have the potential to mold or inhibit the flow of light by virtue of a spatial periodicity of the dielectric constant [1-3]. Many applications for these novel materials have been discussed, ranging from high efficiency, directional light sources to optical microcircuits. However, one could considerably enlarge the range of applications of the crystals, particularly for active devices, by providing methods to tune their optical properties. Because photonic crystals are normally composites of two different materials, one can tune the optical properties of the crystal by controlling the dielectric constant of one or both the constituent materials. In this paper we outline two techniques that we have recently employed to tune 2-D macroporous silicon photonic crystals consisting of air cylinders embedded in a silicon host or backbone. Such crystals have a complete band gap for optical radiation propagating in the plane of periodicity, although light can escape in the 3rd dimension. In the first method we have infiltrated the air cylinders with a nematic liquid crystal. By varying the temperature of the system we are able to tune the refractive index of the cylinder and induce a shift in the photonic band-gap [4]. In the second method we have optically injected electron-hole pairs into the silicon backbone. By taking advantage of the Drude contribution the carriers make to the dielectric constant [5,6] we are able to shift the band-edge of the photonic crystal by as much as 30 nm [7]. The rise time for this effect is simply related to the pulse width although the turn-off time can be much longer, being related to the carrier recombination time. Techniques such as the two discussed here may find application for switching not only the optical band gaps, but also other properties of photonic crystals (e.g., dispersion curves, group velocity characteristics, etc.) on time scales ranging from millisecond to femtoseconds. L3.1.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 23 Aug 2017 at 15:26:08, subject to the Cambridg
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