Accuracy Improvement of Blood Glucose Measurement System Using Quantum Cascade Lasers

Abstract

For non-invasive measurement of blood glucose levels, a measurement system based on mid-infrared, attenuated-total-reflection spectroscopy equipped with hollow optical fibers, a trapezoidal multi-reflection prism, and two fixed-wavelength quantum cascade lasers emitting different wavelengths is proposed. From the absorption spectra of lip mucosa measured by Fourier-transform infrared spectrometry, two wavelengths, 1152 cm −1 for absorption by glucose and 1186 cm −1 for the background, were chosen. To reduce measurement errors, the power distribution on the prism surface was investigated , and it was found that some high-intensity spots appear on the prism surface due to the coherency of the laser beam. This inhomogeneous power distribution causes measurement errors for slight movements of the lip mu-cosa. To homogenize the intensity distribution on the prism, a lens to excite higher modes in the fiber was introduced, and the incident angle was changed to suppress interference due to back-reflected light. These improvements increased the measurement stability, and in-vivo experiments demonstrated that the measured optical absorption correlates well with blood glucose levels.