  We show a phase-locked array of three quantum cascade lasers with an
integrated Talbot cavity at one side of the laser array. The coupling scheme is
called diffraction coupling. By controlling the length of Talbot to be a
quarter of Talbot distance (Zt/4), in-phase mode operation can be selected. The
in-phase operation shows great modal stability under different injection
currents, from the threshold current to the full power current. The far-field
radiation pattern of the in-phase operation contains three lobes, one central
maximum lobe and two side lobes. The interval between adjacent lobes is about
10.5{\deg}. The output power is about 1.5 times that of a single-ridge laser.
Further studies should be taken to achieve better beam performance and reduce
optical losses brought by the integrated Talbot cavity.

Optics;Mesoscale and Nanoscale Physics