Effect of Spatial Modulated Light on Position of Self-Calibration Point

In optical sensing, the differentiation between absorption and scattering poses a challenge when dealing with a physiological medium. We have shown that for extracting absorption-based parameters it is optimal to measure at the iso-path length (IPL) point. The IPL position is dependent on the diameter of the medium. In this paper, we will demonstrate how beam shaping can help match the light pattern, so the IPL point remains in the same position and distance from the light source. Hence, the location of the detector will remain constant for different mediums, such as different fingers. A spatial frequency of 0.4 mm-1, in the case of a 15mm diameter cylindrical phantoms, shifts the IPL point's position by 40 degrees on the phantom's surface. Moreover, the spatial modulation yields an optical signature from different depths, which could improve the extraction of optical properties from tissue depth using our method.