  We experimentally demonstrate an integrated semiconductor ridge microcavity
source of counterpropagating twin photons at room temperature in the telecom
range. Based on parametric down conversion with a counterpropagating
phase-matching, pump photons generate photon pairs with an efficiency of about
10^(-11) and a spectral linewidth of 0.3 nm for a 1mm long sample. The
indistiguishability of the photons of the pair are measured via a two-photon
interference experiment showing a visibility of 85%. This work opens a route
towards new guided-wave semiconductor quantum devices.
