We demonstrate and characterize a scalable optical subsystem for detecting ion qubit states in a surface electrode ion trap. An array of lithographically fabricated diffractive lenses located below the plane of the trap images ions at multiple locations, relaying the collected light out of the vacuum chamber through multimode fibers. The lenses are designed with solid angle collection efficiencies of 3.58%; with all losses included, a detection efficiency of 0.388% is measured. We measure a minimal effect of the dielectric optical substrate on the temporal variation of stray electric fields and the motional heating rate of the ion.