|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:
Figure 1: Schematic of an optical planar waveguide on a chip and the evanescent tail (cross-section). The waveguide consists of a bottom cladding (SiO2) on a silicon substrate (wafer), a relatively thin waveguiding film (Si3N4 core, 30 – 300 nm) and cover (SiO2 as upper cladding). Confinement of the light is a result of the higher refractive index of the core (nf >ns~nc), whereas the evanescent tail in the window interacts with the gas/liquid environment.
|Geert Besselink, LioniX|