Noise Reduction in Silicon Photomultipliers for Use in Functional Near-Infrared Spectroscopy

Silicon photomultipliers (SiPMs) have been recently proposed for different applications in medical imaging area, inclunding functional near-infrared spectroscopy (fNIRS), due to their single photon sensitivity, fast timing response, low operation bias, compactness, and low cost. Here, we report on the electrooptical performances of an SiPM technology suitably optimized for continuous wave (CW)-fNIRS application through the integration of a near-infrared (NIR) long-pass filter on the detector's package. The use of the filter considerably decreases, especially for large overvoltage (OV) values, the SiPM's dark noise rate, due to the significant reduction of optical cross talk effects (up to 90% of dark current reduction at 50%-OV). Moreover, the filter reduces also the absorption of environmental light of more than 85% in the SiPMs linear operation range above the breakdown, allowing at the same time a good photon detection efficiency in all the NIR range above 700 nm cut-on wavelength. These results open new perspectives for the employment of large area SiPMs operating with improved signal-to-noise ratio in advanced CW-fNIRS systems.