External-cavity coherent operation of InGaAsP buried-heterostructure laser array

Coherent operation of a monolithic linear array of InGaAsP buried-heterostructure lasers operating at λ=1.3 μm has been acheived by means of a spatial filter in an external cavity. An array of mass-transported InP microlenses was used to collimate the beams of the individual laser elements and couple the laser array output to the external cavity. The coherent array output exhibited a narrow (3.2 mrad), three-lobe far-field pattern with ∼65% of the energy concentrated in the central peak.