The work for a doctoral thesis is presented in two parts concerning two different projects, connected by the usage of photosensitive devices, in particular, silicon photomultipliers (SiPMs).

The most extensive part of this thesis is dedicated to my work on the application of SiPMs in the future generation of Imagining Atmospheric Cherenkov Telescopes (IACTs). While the remaining part is dedicated to the characterization of scintillating fibers using SIPMs as fiber trackers in the 𝜇3𝑒 experiment.

The work focusing on IACTs is divided into two different projects:

• The design of an innovative Cherenkov telescope camera for the Large-Sized Telescope (LST) as part of the Cherenkov Telescope Array (CTA).

• The characterization of an external light source (LUMP Calibration box) foreseen as a possible tool to help in the calibration of the Single Mirror Small-Sized Telescope (SST-1M), whose camera was built by our group at the University of Geneva.

The remaining part of the thesis belongs to a project in the 𝜇3e experiment whose goal is to search for flavor lepton violation in the Standard Model:

• Characterization of single scintillating fibers for the Scintillating Fiber detector (Sci-Fi).