Abstract: A method and apparatus for noninvasive measurement of a human body component, such as glucose, in vivo, include near infrared spectroscopy based laser sources driven at a carrier frequency lying within the characteristic absorption of the component. The apparatus also drives the laser diodes with a modulation frequency to generate a frequency difference between the measuring light and reference beam, and the interference of the two beams results in a beat frequency signal, which frequency is proportional to the optical path difference between the measuring light and the reference beam. The scattering lights from human tissue with different optical lengths are simultaneously detected and selected based on the beat frequency. The method is a convenient embodiment of the floating reference principle, which takes advantage of optical length selection.

Abstract: This specification discloses a method and apparatus for noninvasive measurement of human body component, such as glucose, in vivo. The apparatus includes near infrared spectroscopy based laser sources driven at carrier frequency lying within the absorption line of the component. The apparatus also drive the laser diodes with a modulation frequency to generate frequency difference between the measuring light and reference beam, and the interference of the two beam results in a beat signal, which frequency is proportional to optical path difference between the measuring light and reference beam. We can detect the spectrum of the scattering light, which propagate at specifically single optical path, by select the frequency using a phase sensitive detector (PSD) circuit.