Comparison between two detection systems for fiber-optic chemical sensor applications

Two optical detection system designs are compared for fiber-optic chemical sensor applications. A single grating spectrograph with fiber-optic input and photodiodes at three different wavelengths is compared to 1 × 3 fiber-optic splitters and photodiode detectors with integrated interference filters. The splitters are used to direct the optical power to the filter-photodiodes. Three types of 1 × 3 commercially available splitters were tested: a 400 μm fused glass fiber-optic coupler, a 1000 μm fused plastic fiber-optic coupler, and a 1000 μm glass fiber-optic bundle. This study-finds that the fiber-splitter-based detection systems have similar stray light, signal-to-noise ratio, and long-term absorbance stability compared to the spectrograph detection system with a modest improvement in spectral resolution (from ∼12 nm to ∼6 nm). It is also much smaller in size and lower in cost. Applications of the two systems in a colorimetric CO ₂ partial pressure sensor are compared and similar accuracy and precision are achieved.