The OPERA experiment has succeeded in discovering nu_mu -> nu_tau oscillation appearance in the CNGS (CERN Neutrino to Gran Sasso) neutrino beam.
Its hybrid detector is made of a large set of nuclear emulsion films combined with tracking electronic devices.
Emulsions provide a 3D trajectory reconstruction with an unbeatable intrinsic position resolution of 50 nm.
This detector can effectively couple the function of a target with that of event reconstruction, and it is suitable to construct a powerful tau neutrino detector.
In the OPERA experiment, about 10,000,000 emulsion films are used, forming a sub-micrometric resolution detector with a target mass of about 1,300 tons.
The outstanding features of the experiment are paralleled by the huge advances in the emulsion readout technology that occurred in the last decade.
This made the complex data analysis procedure feasible and successful.
The various aspects of the OPERA detector technology will be presented and critically discussed.
