  Optical fibres have transformed the way people interact with the world and
now permeate many areas of science. Optical fibres are traditionally thought of
as insensitive to magnetic fields, however many application areas from mining
to biomedicine would benefit from fibre-based remote magnetometry devices. In
this work, we realise such a device by embedding nanoscale magnetic sensors
into tellurite glass fibres. Remote magnetometry is performed on magnetically
active defect centres in nanodiamonds embedded into the glass matrix. Standard
optical magnetometry techniques are applied to initialize and detect local
magnetic field changes with a measured sensitivity of 26 micron Tesla/square
root(Hz). Our approach utilizes straight-forward optical excitation, simple
focusing elements, and low power components. We demonstrate remote magnetometry
by direct reporting of the magnetic ground states of nitrogen-vacancy defect
centres in the optical fibres. In addition, we present and describe
theoretically an all-optical technique that is ideally suited to remote
fibre-based sensing. The implications of our results broaden the applications
of optical fibres, which now have the potential to underpin a new generation of
medical magneto-endoscopes and remote mining sensors.
