This paper studies complex modulation schemes,
including orthogonal frequency-division multiplexing (OFDM),
received by a single photon avalanche diode (SPAD) array
integrated circuit (IC). A SPAD operates in the Geiger mode,
and is able to detect single photons. This feature enables order
of magnitude receiver sensitivity in intensity modulation (IM)
/ direct detection (DD) Visible Light Communication (VLC)
systems. The tradeoff between received power and bit error ratio
(BER) using both pulse-amplitude modulation (PAM) and OFDM
is shown. A first order model of the noise in a digital SPAD
receiver is derived. The noise in the experimental receiver chip
approaches the predicted noise in our model, and we achieve
receiver sensitivity of −64 dBm with a 100 kbit/s signal at a
BER of 10−5. It is concluded that future improvements in SPAD
VLC receiver architecture will allow sensitivity to approach the
quantum limit.