Patent ID: 8346329

Claim:
A method of noninvasive measuring of a human component with a selectable optical length, the component being of a type that absorbs light at wavelengths within an absorption line range, the method comprising the steps of: driving diode laser sources by laser drivers to provide wavelength modulated light; splitting the wavelength modulated light into measuring light and reference light; irradiating the measuring light to skin of a human body; receiving scattering light from a tissue under the irradiated skin; frequency selectively detecting beat frequency signals between the reference light and the scattering light by using a phase sensitive detector (PSD) circuit; and processing the detected beat frequency signals to determine a concentration of the component in the human body, wherein the scattering light from the human tissue having different optical lengths is simultaneously received and detected, a first scattering light having an optical length which is a zero or near zero sensitivity in compliance with a floating reference principle being selected, and a beat frequency signal between the reference light and the first scattering light being used as a reference value, and a second scattering light having an optical length which is a maximum sensitivity in compliance with the floating reference principle being selected, and a beat frequency signal between the reference light and the second scattering light being used as a measuring value for calculating the concentration of the component in the human body by referring to the reference value.