Time-resolved (TR) near-infrared spectroscopy (NIRS) offers non-invasive clinical applications in monitoring the blood oxygenation, where absolute values of oxygenated and deoxygenated hemoglobin, and absorption and scattering coefficient, can be obtained. Various detectors have been utilized to realize a TR-NIRS system, such as PMT, SiPM, and SPAD. This paper proposed a prototype NIRS device implemented using a 128 x 128 lock-in pixel CMOS image sensor (CIS) based on the lateral electric field-charge modulator (LEFM) to achieve high time resolution. Preliminary experiments based on the reflectance of an agar phantom with varying absorption coefficient have been conducted and the ability to detect the changes in the absorption coefficient has been demonstrated. The reflectance of the agar phantom is directly observed by the image sensor, which was operated at a time-window of 900 ps with a sensor detection area of 2.9mm2 . The results suggest that a NIRS device using CIS is feasible, which opens the potential of a miniature wearable time-resolved NIRS device.
A CMOS image sensor using high-speed lock-in pixels for stimulated Raman scattering (SRS) spectroscopy is presented in this paper. The effective SRS signal from the stimulated emission of SRS mechanism is very small in contrast to the offset of a probing laser source, which is in the ratio of 10-4 to 10-5. In order to extract this signal, the common offset component is removed, and the small difference component is sampled using switched-capacitor integrator with a fully differential amplifier. The sampling is performed over many integration cycles to achieve appropriate amplification. The lock-in pixels utilizes high-speed lateral electric field charge modulator (LEFM) to demodulate the SRS signal which is modulated at high-frequency of 20MHz. A prototype chip is implemented using 0.11μm CMOS image sensor technology.