Geert Besselink - Medische Elektronica

Integrated Optical Waveguides Based on TriPleX technology for Spectroscopy and Sensing Applications
	Planar waveguide evanescent field sensing enables the measurement of absorption, fluorescence and refractive index changes in the region immediately above the waveguide surface. This kind of probing occurs via the so-called evanescent tail of the mode that propagates through the integrated optical (IO) waveguide. Thanks to the freedom in choice of materials, high contrast-ratio waveguides can be built on (silicon) chips, featuring large evanescent field sensitivity in combination with low bending losses. As a consequence, long interaction lengths with e.g. spirals on small-sized chip are feasible, provided the waveguide attenuation (loss) is small enough. Exploiting TriPleX waveguides (one of the three commercially available IO platforms in the world), being formed out of a combination of SiO₂ and Si₃N₄-layers, all these criteria are met. The interaction with the media environment occurs through a photolithographically defined window in the waveguide, i.e. the absence of the upper SiO₂ cladding (Figure 1). TriPleX based waveguide technology is implemented in different sensing and detection formats such as absorption spectrometry, fluorescence spectrometry, optical micro cavity sensing and interferometry and can be embodied in optofluidic chips for detection of solutes and gases. The unique features of such an optical chip sensor are: small, compact, in-situ/in-line capability potentially cheap remote signal and data processing enabled by fiber interconnects applicable in harsh environmental conditions: In the current presentation, different examples of commercialized optofluidic gas/liquid sensor devices will be shown exemplifying the applicability of Triplex based waveguide technology.
Figure 1: Schematic of an optical planar waveguide on a chip and the evanescent tail (cross-section). The waveguide consists of a bottom cladding (S_iO₂) on a silicon substrate (wafer), a relatively thin waveguiding film (S_i3N₄ core, 30 – 300 nm) and cover (S_iO₂ as upper cladding). Confinement of the light is a result of the higher refractive index of the core (n_f >n_s~n_c), whereas the evanescent tail in the window interacts with the gas/liquid environment.
	Geert Besselink, LioniX