Opt. Lett. 43, 4615–4618 (2018)

A compact, highly sensitive all-optical magnetometer has been demonstrated by a United States–Belgium collaboration. The device is based on a magneto-optical material with a large Verdet constant (106) — a polymer film containing dysprosium (Dy3+)-doped magnetite and cobalt ferrite nanoparticles — that is placed in a fibre-optic Sagnac interferometer. The presence of a magnetic field causes a Faraday rotation of the polarization of the 1,310-nm laser beam as it passes through the polymer film and the resulting interference signal is measured by a balanced detector. The team says that the device has a sensitivity of 20 fT Hz–1/2 and is potentially well suited to biomedical applications as it is not only small (around an inch long) and sensitive, but also operates at room temperature, does not require shielding and is highly robust against noise. As a demonstration of its applicability, the team showed that the sensor can detect the magnetic field associated with the beat of the human heart. In principle, it should be able to detect the tiny (50–500 fT) magnetic fields associated with neural activity in the brain.

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