Optical and Nanomechanical Characterization of an Omnidirectional Reflector Encompassing 850 nm Wavelength
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Optical and Nanomechanical Characterization of an Omnidirectional Reflector Encompassing 850 nm Wavelength Manish Deopura, Yoel Fink and Christopher A. Schuh Department of Materials Science and Engineering, Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge, Massachusetts, USA 02139 ABSTRACT We demonstrate that multilayers composed of nineteen alternating layers of tin sulfide and silica can function as omnidirectional reflectors. These materials exhibit omnidirectional reflectivity for a range of frequencies in the near infra-red (NIR) encompassing the 850 nm wavelength. A refractive index contrast of 2.7/1.46 is achieved, one of the highest values demonstrated until now in NIR photonic bad gaps. In addition, new nanoindentation procedures have been developed to measure mechanical properties of these fine laminate materials, and demonstrate that tin sulfide-silica multilayers are mechanically stable for practical applications. INTRODUCTION Optical materials design requires knowledge from several fields including the physics of devices, optical properties of materials, processing methods, and characterization for robustness in applications. These various facets provide many design constraints, and opportunities at the same time. Most optical materials design in the past has been empirical, with researchers in academia and industry focusing on physics of devices and development of materials with low optical loss, since these are key requirements in any optical device. In contrast, systematic procedures for processing these optical materials and corresponding characterization techniques (particularly mechanical characterization) have been developed only to a limited extent. More recently, a new trend in optical materials design has emerged. With the advent of photonic crystals in the last decade [1] and the generalization of some optical device principles, researchers from other fields (i.e., polymer synthesis or materials mechanics) have begun to be actively involved in shaping material design schemes. In photonic crystals, the omnidirectional reflector [2,3], a 1-D photonic band gap structure, has recently been reported for 700 nm wavelengths. When properly shaped in an appropriate geometry, this structure can provide optical performance similar to 2-D and 3-D photonic band gap structures without the associated processing costs and complexity. The purpose of the present paper is to extend the concept of the 700 nm omnidirectional reflector reported in Ref. [3], to develop a 1-D photonic crystal for the 850 nm wavelength. This wavelength is significant for optical data transmission technologies, however until now it has been limited to generally short distance operation. To extend the 850 nm technology to long distance communications, practical limitations exist, most significantly the high attenuation and dispersion of the transmitted signal. Traditional fibers have already reached their attenuation and dispersion limit, and hence new materials systems for use as photonic crystal fibers
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