  In the present work, the effect of resonant pumping schemes in improving the
photon coherence is investigated on InAs/InGaAs/GaAs quantum dots emitting in
the telecom C-band. The linewidths of transitions of multiple exemplary quantum
dots are determined under above-band pumping and resonance fluorescence via
Fourier-transform spectroscopy and resonance scans, respectively. The average
linewidth is reduced from $9.74\,\mathrm{GHz}$ in above-band excitation to
$3.50\,\mathrm{GHz}$ in resonance fluorescence underlining its superior
coherence properties. Furthermore, the feasibility of coherent state
preparation with a fidelity of $49.2\,\%$ is demonstrated, constituting a step
towards on-demand generation of coherent, single C-band photons from quantum
dots. Finally, two-photon excitation of the biexciton is investigated as a
resonant pumping scheme. A deconvoluted single-photon purity value of
$g^{(2)}_{\mathrm{HBT}}(0)=0.072\pm 0.104$ and a degree of indistinguishability
of $V_{\mathrm{HOM}}=0.894\pm0.109$ are determined for the biexciton
transition. This represents an important step towards fulfilling the
prerequisites for quantum communication applications like quantum repeater
schemes at telecom wavelength.
