Dual-Comb Functional Near-Infrared Spectroscopy for Perturbation Localization in Dispersive Media

Functional Near-Infrared Spectroscopy (fNIRS) is a significant technology for assessing changes in tissue hemoglobin concentrations [1]. It offers a cost-effective, portable alternative to fMRI for monitoring brain activity and hemodynamics [1], [2]. Current fNIRS techniques include continuous wave (CW), frequency-domain (FD) and time-domain (TD), each with limitations in penetration depth or complexity [3], [4]. This study introduces a novel dual-comb fNIRS (DC-fNIRS) technique, which uses two optical frequency combs generated from a single laser source [5]. This approach allows for the measurement of the tissue's frequency response, including the diffuse time of flight (DTOF), by sampling its amplitude and phase [4], [5]. The method has been demonstrated to retrieve the impulse response of the medium in transmission, enabling the measurement of absolute optical properties [5].