A dual-wavelength spread spectrum-based spectroscopic system For time-domain near-infrared diffuse optical imaging

Abstract

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Dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses

“…The FWHM has been computed for each wavelength and it has been found to be 660 ps and 630 ps for the 680 nm and 850 nm source, respectively. The presented IRFs indicate that the performance of the custom-made optical transceivers is comparable to the performance of commercially available optical transceivers, with respect to speed and noise properties [ 14 , 15 ]. The log-scale representation of both IRFs, shown in Fig.…”

“…A low-power integrated limiting amplifier and VCSEL driver integrated circuit (IC)(MAX3798, Maxim) has been used to drive both VCSELs at 10 Gb/s by providing appropriate modulation and bias currents, both fully controllable via a 3-wire digital interface. The VCSEL driver IC can provide modulation current up to 12 mA and bias current up to 15 mA, with deterministic jitter <6 ps and rise and fall times at the transmitter output down to 26 ps [ 15 ]. A summary of the properties of the VCSEL sources of the instrument can be found in Table 1 .…”

“…Because the SPC-130 is a single channel TCSPC card, an 8-channel router (HRT-81, Becker & Hickl) is used to multiplex to both high-speed EVENT signals [ 14 ]. Finally, the collected raw TCSPC data are post-processed according to our previous work [ 14 , 15 ].…”

“…In our previous research, we have demonstrated the potential of an alternative technique for TD measurements, relying upon the spread spectrum paradigm for ToF-resolved measurements [ 14 , 15 ]. The spread spectrum approach to (f)NIRS operates by the same principle as has been employed in telecommunications and radar over the past 50 years [ 16 ].…”

“…This sequence is transmitted optically to the subjects under test, and the diffused light is collected based on standard time correlated single photon counting (TCSPC)-based detection techniques. Following cross-correlation of the detected signal with the transmitted input sequence, the system’s impulse response function (IRF) or temporal point spread function (TPSF) [ 14 , 15 ] are recovered. A related approach has also been taken by other groups [ 17 , 18 ] where the demodulation at a particular point in time, or in the domain of the Laplace transform, is performed in the analogue electronics prior to sampling; this has the advantage of reducing the requirements for data acquisition and processing.…”