  Due to the high spontaneous emission coupled into the resonance mode in
metallic nanolasers, there has been a debate concerning the coherence
properties of this family of light sources. The second-order coherence function
can unambiguously determine the nature of a given radiation. In this paper, an
approach to measure the second-order coherence function for broad linewidth
sources in the near-infrared telecommunication band is established based on a
modified Hanbury Brown and Twiss configuration. Using this set-up, it is shown
that metallic coaxial and disk-shaped nanolasers with InGaAsP multiple quantum
well gain systems are indeed capable of generating coherent radiation.
