Compact spectroscopic sensor using an arrayed waveguide grating

We propose a new compact planar spectroscopic sensor using an arrayed waveguide grating (AWG) to meet the conditions for both miniaturization and high wavelength resolution of sub-nanometer order. In a preliminary experiment, the concentration of sodium acetate solute was determined with an average deviation of 0.25 wt%. Following this, we designed and fabricated a compact spectroscopic sensor using a visible AWG with an insertion loss of 4 dB. To improve the sensitivity of the visible AWG spectroscopic sensor, the optimum design of multiple grooves for the liquid sample was carried out using the refractive index and transmittance of chlorophylls a and b as various environmental indicators. We also obtained a transmittance difference of 1.4 dB, which is two times higher than that in the conventional scheme (0.7 dB) by an absorbency change of 1.0 (optical path: 1.0 mm). Additionally, we applied a parabola-shaped sample injection waveguide to our proposed visible arrayed waveguide grating spectroscopic sensor for the improvement of the sensitivity, and demonstrated experiments for discriminating chlorophylls a and b as an environmental indicator. We confirmed that a compact AWG-based spectroscopic sensor is effective in environmental measurement and other application fields.