  We report on the coupling of a reconfigurable high Q fiber micro-cavity to an
organic color center grafted to a carbon nanotube for telecom wavelength
emission of single photons in the Purcell regime. Using three complementary
approaches we assess various figures of merit of this tunable single photon
source and of the cavity quantum electrodynamical effects : the brightening of
the emitter is obtained by comparison of the count rates of the very same
emitter in free-space and cavity coupled regimes. We demonstrate a fiber
coupled single-photon output rate up to 20 MHz at 1275~nm. Using time-resolved
and saturation measurements, we determine independently the radiative quantum
yield and the Purcell factor of the system with values up to 30 for the
smallest mode volumes. Finally, we take advantage of the tuning capability of
the cavity to measure the spectral profile of the brightness of the source
which gives access to the vacuum Rabi splitting $g$ with values up to $25 \;
\mu$eV.
