Time Domain NIRS Optode based on Null/Small Source-Detector Distance for Wearable Applications

Abstract

We present the designs of novel optode based probes integrating light detection and light-pulsing electronics in a single CMOS chip with functional blocks such as a fast pulse-laser driver and synchronized single-photon detection circuit, while exploiting the null/small source-detector distance (ns-SDD) configuration which features the highest sensitivity to deep tissue. With the perspective of simplifying the output, photon counts are accumulated in a counter on-chip and transmitted as an analog signal mimicking the signal one would get from normal linear analog photodetectors. Development of a single optode, incorporating source and detectors very close to each other within the assembly, eliminates the use of optical fibers and could yield a completely novel near infrared system (NIRS) architecture where time-domain photon-counting approach is utilized to quantify changes in the number of photons scattering back to nearly where they came from.