The mode of operation and theoretical concept behind a type of near-infrared spectrometer is discussed, which is used to measure concentrations of glucose, ethanol, CaCl 2 , and KCl solutions in water, respectively. The main features of the instrument are its potential for short time-to-measurement resolution on the order of tens of milliseconds, its broad spectral bandwidth from 1.0 to 2.4 μm, and its ruggedness. These features allow the device to operate remotely in field applications and to utilize a wide variety of optical interfaces based on state-of-the-art fiber optic technology. Also, they provide a straightforward path to miniaturization with the concomitant enhancement in time resolution and applicability of the instrument and the technique.
The use of a silicon-germanium platform for the development of optically active devices will be discussed in this paper, from the perspective of Raman and Brillouin scattering phenomena. Silicon-Germanium is becoming a prevalent technology for the development of high speed CMOS transistors, with advances in several key
parameters as high carrier mobility, low cost, and reduced manufacturing logistics. Traditionally, Si-Ge structures have been used in the optoelectronics arena as photodetectors, due to the enhanced absorption of Ge in the telecommunications band. Recent developments in Raman-based nonlinearities for devices based on a silicon-on-insulator platform have shed light on the possibility of using these effects in Si-Ge architectures. Lasing and amplification have been demonstrated using a SiGe alloy structure, and Brillouin/Raman activity from acoustic phonon modes in SiGe superlattices has been predicted. Moreover, new Raman-active branches and inhomogeneously broadened spectra result from optical phonon modes, offering new
perspectives for optical device applications. The possibilities for an electrically-pumped Raman laser will be outlined, and the potential for design and development of silicon-based, Tera-Hertz wave emitters and/or receivers.
We demonstrated conversion of optical signals from 1550nm band to the 1300nm band in silicon waveguides. The conversion is based on parametric Stokes to anti-Stokes coupling using the Raman susceptibility of silicon. Achieving high conversion efficiency requires phase matching in the waveguides as well as means to reduce
waveguide losses including the free carrier loss due to two photon absorption.
Silicon-On-Insulator integrated optics boasts low loss waveguides and tight optical confinement necessary for the design of nanophotonic devices. In addition, the processing is fully compatible with capabilities of standard silicon foundries. Because of crystal symmetry, silicon does not possess 2nd order nonlinear optical effects. However, the combination of nanoscale geometries with the high refractive index contrast creates high optical intensities where 3rd order effects may become important, and in fact, may be exploited. In this context, we study the two main nonlinear processes that can occur in silicon waveguides, namely Stimulated Raman Scattering (SRS) from zone-center optical phonons and Two-Photon Absorption (TPA). Because of the single crystal structure, the Raman gain coefficient in silicon is several orders of magnitude larger than that in the (amorphous) glass fiber while its bandwidth is limited to approximately 100GHz. To achieve Raman gain in the 1550nm region requires the pump to be centered at around 1427nm. We discuss the Raman selection rules in a silicon waveguide and present the design of an SOI Raman amplifier. We show that by causing pump depletion, TPA can limit the amount of achievable Raman gain. TPA also limits the maximum optical SNR of the silicon amplifier.
We present a technique to perform noninvasive, spatially- resolved measurements on low pressure, subsonic, laminar gas flows using Raman spectroscopy. From the Raman signal, the density and temperature conditions of the flow can be extracted directly, with reasonably low integration times. The use of a high power laser diode adds to the simplicity of the measurement, plus it makes it a very attractive low cost, efficient technique. Temperature regimes studied are from 290 K - 725 K, spatial resolution obtained is approximately 2.5 X 1.5 mm2 in the flow cross section, and 10-30 micrometers in the flow direction, within a flow profile of diameter approximately 1.5 cm. The flow was generated by a conical double nozzle system with CO2 at the center and Ar as sheath gas. The goal of the measurements is to study the gas dynamical focusing obtained, which will be used for future experiments on highly nonvolatile compounds.