Ultrathin solid immersion grating microspectrometer for hyperspectral PPG signal measurement and blood pressure monitoring

Abstract

Optical spectroscopy plays a vital role in non-invasive monitoring for applications such as quality control and clinical diagnosis, but has a trade-off relationship between device volume and spectral resolution due to the low angular dispersion. This paper introduces an ultrathin solid immersion grating microspectrometer (SIG-μSPEC) with high spectral resolution in a broad operational range. Unique configuration of the SIG-μSPEC achieves multispectral focal plane on a CMOS line sensor, addressing the limitations of conventional bulky spectrometers. The device is first successfully applied to non-invasive fruit ripeness prediction, with an accurate prediction level. The SIG-μSPEC is further adapted for blood pressure estimation by measuring hyperspectral PPG signals. Applied to a wearable watch-type module, Hyperspectral PPG data exhibits promising results in estimating blood pressure levels. The high-resolution SIG-μSPEC proves effective in both fruit maturity assessment and blood pressure estimation, highlighting its potential in diverse real-time monitoring applications.