Seikoh-Giken, with NPL, has developed a range of electro-optic field sensors and antenna links. The sensors are based on LiNO3 electro-optic crystals onto which a pair of optical waveguides form a Michelson Interferometer. Small antenna elements apply an RF voltage across one arm of the interferometer when the sensor is placed in a field, resulting in amplitude modulation of the laser light, and this is demodulated at the receiver to give the RF signal.

The system provides full time-domain measurement (i.e. both the amplitude and phase of the field is measured). The sensor head contains three orthogonal sensors, so that the three E-field components can be measured. Limited use of metal means the sensors are minimally perturbing to the measured fields, and the sensor head requires no power supply or batteries, making it ideal for remote monitoring applications.

Also an RF-to-optical transducer has been developed whose main advantage is its small size. Instead of a dipole antenna, a SMA connector is connected across one arm of interferometer. This can be connected to any antenna, as shown in the photograph. This miniature transducer enables small antennas to be measured without connecting them to a coaxial cable that can severely distort the performance of the antenna.

OEFS-system- Left to right: Controller unit containing laser source and photo-detector, Sensor head type OEFS-NS (3-axis E-field), and sensor head type OEFS-1B (miniature 3 axis E-field).

Examples of application of these sensors are:

Specifications of OEFS sensors