The detection of ultra-high energy cosmic neutrinos, i.e. energies above 10^18 eV, would open a new field of particle astrophysics. These neutrinos would not only provide crucial information on the GZK mechanism, but as the universe is opaque to any other particle with an energy above this energy scale, neutrino are the messengers to detect in search for extreme high energy astrophysical sources. The expected flux of cosmic neutrinos with ultra-high energy is however low, so that large scale neutrino telescopes (> 100 km^3) are needed. A solution is offered by the acoustic detection of neutrinos:
The energy deposition of cosmic ray particle in water generate thermo-acoustic signal, which can travel for many kilometres with only small attenuation in the relevant acoustic frequency range.
Efforts to build a detection system based on piezo-electric hydrophones have already been carried out. An alternative technology is based on optical fibres and that has several advantages over conventional hydrophones: Fibres form a natural way to create a distributed sensing system in which several sensors are attached to a single optical fibre. Fibre optics technology provides a cost-effective and straightforward way to implement a large scale sensor network.
In this talk the fibre optic hydrophone technology will be presented and the results of several measurement campaigns in an anechoic basin that demonstrate the required hydrophone sensitivity will be discussed. Based on these measurements and realistic simulations the feasibility of the application in future large scale cosmic ray experiments will be shown.