  The Schwarzschild-Couder Telescope (SCT) is a proposal for the Medium Size
Telescopes of the Cherenkov Telescope Array. Its concept is based on a
two-mirror optical system designed to improve the telescope field of view and
image resolution with respect to the single mirror Davies-Cotton solution. The
SCT camera is planned to be instrumented with 177 photodetection modules, each
composed of 64 Silicon Photomultiplier (SiPM) pixels. The third generation of
$6 x 6~mm^2$ high density NUV SiPMs (NUV-HD3) produced by Fondazione Bruno
Kessler (FBK) in collaboration with INFN has been used to equip optical units
to be integrated on the upgrade of the camera of the SCT prototype (pSCT). Each
optical unit is composed of an array of 16 NUV-HD3 SiPMs coupled with the
front-end electronics, which is designed for full-waveform nanosecond readout
and digitization using the TARGET-7 ASIC. Several optical units have been
assembled and tested in the laboratories of INFN and have been integrated on
the camera of the pSCT telescope, that is currently operating at the Fred
Lawrence Whipple Observatory. In this contribution we report on the
development, assembly and calibration of the optical units that are currently
taking data on the pSCT camera.
