  Quantum networks have the potential to transform secure communication via
quantum key distribution and enable novel concepts in distributed quantum
computing and sensing. Coherent quantum light generation at telecom wavelengths
is fundamental for fibre-based network implementations, but Fourier-limited
emission and subnatural linewidth photons have so far only been reported from
systems operating in the visible to near-infrared wavelength range. Here, we
use InAs/InP quantum dots to demonstrate photons with coherence times much
longer than the Fourier limit at telecom wavelength. Evidence of the
responsible elastic laser scattering mechanism is observed in a distinct
signature in two-photon interference measurements, and is confirmed using a
direct measurement of the emission coherence. Further, we show that even the
inelastically scattered photons have coherence times within the error bars of
the Fourier limit. Finally, we make direct use of the minimal attenuation in
fibre for these photons by measuring two-photon interference after 25 km of
fibre, thereby demonstrating indistinguishability of photons emitted about 100
000 excitation cycles apart.
