Fiber optic hydrophones for acoustic neutrino detection

The KM3NeT collaboration recently reported the observation of a cosmic neutrino with an estimated energy exceeding 100 PeV -- marking it as the most energetic neutrino event ever detected [1]. It might well be that this event is the first detection of a cosmogenic neutrino, i.e. a neutrino resulting from interaction of an ultra-high-energy cosmic ray particle with the comic microwave background radiation [2]. Cosmogenic neutrinos are of particular interest as they allow to study the cosmic ray spectrum beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off.
The scientific prospects of detecting cosmic neutrinos with an energy close or even higher than the GZK cut-off energy has been discussed extensively in literature. It is clear that due to their expected low flux, the detection of these ultra-high energy neutrinos (Eν > 10^18eV) requires a telescope with an effective detection volume exceeding 100 km^3. Acoustic detection methods [3, 4] offer a promising approach, as the sound waves generated by particle cascades in the deep sea can propagate over long distances with minimal attenuation. This characteristic makes it feasible to construct a large-scale neutrino telescope using acoustic sensors.
To realize such a telescope, it is essential to develop acoustic detection technologies capable of operating with high sensitivity in the deep sea. Significant progress have been made in developing fiber optic hydrophone technology suited for this purpose [5].
In this presentation, I will discuss the recently observed KM3NeT event and our ongoing work toward enabling a future acoustic neutrino telescope.

[1] The KM3NeT Collaboration. Observation of an ultra-high-energy cosmic neutrino with KM3NeT. Nature, 638:376–382, 2025.
[2] The KM3NeT Collaboration. On the potential cosmogenic origin of the ultra-high-energy event km3-230213a. The Astrophysical Journal Letters, 984(2):L41, may 2025.
[3] G. A. Askaryan. Acoustic recording of neutrinos. Zemlia i Vselennaia, 1:13–16, 1979.
[4] J. G. Learned. Acoustic radiation by charged atomic particles in liquids: An analysis. Phys. Rev. D, 19:3293–3307, June 1979.
[5] E.J. Buis, A.M. von Benda-Beckmann, E. Doppenberg, J. Dorant, T.H. Jansen, P. Toet, P. Verhooren, and J. de Vreugd. Characterization of a fiber laser hydrophone for acoustic neutrino detection. Astroparticle Physics, 170:103109, 2025.