  Recently, experiments showed that the spatial-mode states of entangled
photons are more robust than their polarization-mode states in quantum
communications. Here we construct a complete and deterministic protocol for
analyzing the spatial Bell states using the interaction between a photon and an
electron spin in a charged quantum dot inside a one-side micropillar
microcavity. A quantum nondemolition detector (QND) for checking the parity of
a two-photon system can be constructed with the giant optical Faraday rotation
in this solid state system. With this parity-check QND, we present a complete
and deterministic proposal for the analysis of the four spatial-mode Bell
states. Moreover, we present a robust two-step quantum secure direct
communication protocol based on the spatial-mode Bell states and the photonic
spatial Bell-state analysis. Our analysis shows that our BSA proposal works in
both the strong and the weak coupling regimes if the side leakage and cavity
loss rate is small.
