Photonic Crystals: Shaping the Flow of Thermal Radiation
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1162-J01-02
Photonic Crystals: Shaping the Flow of Thermal Radiation Ivan Čelanović, Michael Ghebrebrhan, Yi Xiang Yeng, John Kassakian, Marin Soljačić, John Joannopoulos Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
ABSTRACT In this paper we explore theory, design, and fabrication of photonic crystal (PhC) based selective thermal emitters. In particular, we focus on tailoring spectral and spatial properties by means of resonant enhancement in PhC’s. Firstly, we explore narrow-band resonant thermal emission in photonic crystals exhibiting strong spectral and directional selectivity. We demonstrate two interesting designs based on resonant Q-matching: a vertical cavity enhanced resonant thermal emitter and 2D silicon PhC slab Fano-resonance based thermal emitter. Secondly, we examine the design of 2D tungsten PhC as a broad-band selective emitter. Indeed, based on the resonant cavity coupled resonant modes we demonstrate a highly selective, highlyspectrally efficient thermal emitter. We show that an emitter with a photonic cut-off anywhere from 1.8 mm to 2.5 mm can be designed.
INTRODUCTION The ability of photonic crystals to modify spontaneous emission and as a consequence, their ability to tailor thermal radiation has received significant attention in recent years [1,2]. It was shown that photonic crystals offer unparalleled possibilities for designing thermal radiation sources with properties that are often non-intuitive and deviate significantly from those of typical grey-body sources [3-10]. There are two general research areas being pursued with regard to shaping thermal radiation using photonic crystals. On the one hand, photonic crystals are used to design highly selective narrow-band thermal emitters, exhibiting wavelength, directional and polarization selectivity. These structures show promise for applications in IR sensors and a variety of IR sources[3-7]. On the other hand, PhC’s are explored to design wide-band, selective thermal emitters exhibiting near blackbody thermal emission within a given wavelength range and largely attenuated emission outside the given range [8-10]. Applications such as thermophotovoltaic energy conversion, solar-thermophotovoltaic conversion, and solar absorbers/reflectors are considered as main drivers behind advances in broad-band selective thermal emitters. In the following sections we will explore the opportunities that electromagnetic resonances in PhC’s present for tailoring thermal radiation properties. We will start our exploration with a simple one-dimensional (1D) PhC structure that can be designed to exhibit narrow-band emittance. In addition, we will examine how almost totally transparent thin silicon PhC slab can be designed to exhibit narrow-band resonant thermal emission. Lastly, we will address how a broad-band thermal emitter can be designed based on multiple electromagnetic resonances.
NARROWBAND RESONANT THERMAL EMISSION Bulk thermal emission sources are commonly perceived as isotropic, broad-band and incoherent elec
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