Crucial aspects for the use of silicon photomultiplier devices in continuous wave functional near-infrared spectroscopy

Abstract

In this work, we investigate some major issues for the use of silicon photomultiplier (SiPM) devices in continuous wave functional near-infrared spectroscopy (CW fNIRS). We analyzed the after-pulsing effect, proposing the physical mechanism causing it, and determining its relevance for CW fNIRS. We studied the SiPM transients occurring as the SiPM device goes from the dark (LED in off state) to the illumination (LED in on state) conditions, and vice-versa. Finally, we studied the SiPM SNR in standard CW fNIRS operation.

Keywords: (040.6040) Silicon; (110.0113) Imaging through turbid media; (120.3890) Medical optics instrumentation; (230.5160) Photodetectors; (290.1350) Backscattering; (300.6340) Spectroscopy, infrared.

Fig. 1

Scheme of the experimental set-up used to measure SiPM after-pulsing, SiPM temperature transients and signal-to-noise ratio. The distance D was about 10 cm for the first two measurements and about 80 cm for the SNR.

Fig. 2

SiPM transient after 529 nm and 735 nm wavelength LED switch-off, averaged on 500 traces, 100 MHz sampling frequency

Fig. 3

SiPM transient after 700 nm (a) and 529 nm (b) LED switch off, averaged on 1000 traces, 5 GHz sampling frequency.

Fig. 4

(a) averaged SiPM response after 700 nm LED switch off (500 traces, 100 MHz sampling rate); (b) averaged SiPM response after 529 nm LED switch off (500 traces, 100 MHz sampling rate); (c) Normalized SiPM switch off transient (after 700 nm LED switch off) at various temperatures. The figure legends indicate the SiPM device temperatures measured in forward bias, see experimental section for further explanation.

Fig. 5

SiPM Dark Current temperature dependence (V bias = 32.5 V).

Fig. 6

(a) SiPM dissipated power as the 700 nm LED is switched on at various levels of LED illumination. When the LED is switched on, the SiPM current and dissipated power rise to a level (L1), and then slowly increase to a steady state L2; (b) reports the temperature rise ΔT as function of steady state SiPM power dissipation (SiPM biased at 30.5 V). ΔT can be estimated from the difference L2-L1, since ΔT is expected to be an increasing function of L2-L1. Figure 6(b) reports the difference L2-L1 as a function of the steady-state dissipated power L2. By considering the temperature dependence of the SiPM dark current reported in Fig. 5, and by assuming the same temperature dependence for the SiPM current under illumination, we can also evaluate the corresponding temperature change in °C, and this is reported on the right axis.

Fig. 7

Signal to Noise Ratio as a function of bias voltages of the SiPM. Photocurrent measured under LED illumination with a square wave of 17 Hz and 50% duty cycle; (a) 700 nm LED; (b) 830 nm LED. (c) SNR at 31.5 V bias voltage measured (dots) and extrapolated (lines, linear fit) as function of the effective sampling frequency.