We experimentally demonstrate the use of high contrast, CMOS-compatible integrated photonic waveguides for Raman spectroscopy. We also derive the dependence of collected Raman power with the waveguide parameters and experimentally verify the derived relations. Isopropyl alcohol (IPA) is evanescently excited and detected using single-mode silicon-nitride strip waveguides. We analyze the measured signal strength of pure IPA corresponding to 819 cm -1 Raman peak due to inphase C-C-O stretch vibration for several waveguide lengths, and deduce a pump power to Raman signal conversion efficiency on the waveguide to be at least 10 -11 per cm.
Abstract-The high index contrast silicon-on-insulator platform is the dominant CMOS 1 compatible platform for photonic integration. The successful use of silicon photonic chips in optical communication applications has now paved the way for new areas where photonic chips can be applied. It is already emerging as a competing technology for sensing and spectroscopic applications. This increasing range of applications for silicon photonics instigates an interest in exploring new materials, as silicon-oninsulator has some drawbacks for these emerging applications, e.g. silicon is not transparent in the visible wavelength range. Silicon nitride is an alternate material platform. It has moderately high index contrast, and like silicon-on-insulator, it uses CMOS processes to manufacture photonic integrated circuits. In this paper, the advantages and challenges associated with these two material platforms are discussed. The case of dispersive spectrometers, which are widely used in various silicon photonic applications, is presented for these two material platforms.
PECVD silicon nitride photonic wire waveguides have been fabricated in a CMOS pilot line. Both clad and unclad single mode wire waveguides were measured at ¼ 532, 780, and 900 nm, respectively. The dependence of loss on wire width, wavelength, and cladding is discussed in detail. Cladded multimode and singlemode waveguides show a loss well below 1 dB/cm in the 532-900 nm wavelength range. For singlemode unclad waveguides, losses G 1 dB/cm were achieved at ¼ 900 nm, whereas losses were measured in the range of 1-3 dB/cm for ¼ 780 and 532 nm, respectively.
There is a rapidly growing demand to use silicon and silicon nitride (Si 3 N 4 ) integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS technology, complex miniaturized circuits can be easily realized on a large scale and at a low cost covering visible to mid-IR wavelengths. In this paper we present our recent work on the development of silicon and Si 3 N 4 -based photonic integrated circuits for various spectroscopic sensing applications. We report our findings on waveguide-based absorption, and Raman and surface enhanced Raman spectroscopy. Finally we report on-chip spectrometers and on-chip broadband light sources covering very near-IR to mid-IR wavelengths to realize fully integrated spectroscopic systems on a chip.
Abstract:We develop and experimentally verify a theoretical model for the total efficiency η 0 of evanescent excitation and subsequent collection of spontaneous Raman signals by the fundamental quasi-TE and quasi-TM modes of a generic photonic channel waveguide. Single-mode silicon nitride (Si 3 N 4 ) slot and strip waveguides of different dimensions are used in the experimental study. Our theoretical model is validated by the correspondence between the experimental and theoretical absolute values within the experimental errors. We extend our theoretical model to siliconon-insulator (SOI) and titanium dioxide (TiO 2 ) channel waveguides and study η 0 as a function of index contrast, polarization of the mode and the geometry of the waveguides. We report nearly 2.5 (4 and 5) times larger η 0 for the fundamental quasi-TM mode when compared to η 0 for the fundamental quasi-TE mode of a typical Si 3 N 4 (TiO 2 and SOI) strip waveguide. η 0 for the fundamental quasi-TE mode of a typical Si 3 N 4, (TiO 2 and SOI) slot waveguide is about 7 (22 and 90) times larger when compared to η 0 for the fundamental quasi-TE mode of a strip waveguide of the similar dimensions. We attribute the observed enhancement to the higher electric field discontinuity present in high index contrast waveguides.
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