For the design of an optical module for deep-sea cubic kilometre sized neutrino telescopes it is important to optimise performance versus cost. In the framework of the KM3NeT design study we have designed an optical module consisting of a single glass pressure vessel and containing up to about 40 small photomultiplier tubes 40 small photomultiplier tubes including their high-voltage supplies and the front-end readout electronics. The advantage is a much larger photocathode area in a single vessel than is possible with large photomultipliers. Significant advantages for triggering are obtained. Tests of a first prototype will be presented.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 5 (HE part 2), pages 1553-1556