A High Frequency, Non-intrusive Electro-Optic Field Sensor and its applications

Dong Ho Wu
Naval Research Laboratory

An electro-optic (EO) field sensor, made entirely of dielectric materials with no metallic components, measures an electric field optically and non-intrusively, while negligibly perturbing the field it measures. This is advantageous as it allows for the measurement of the "true" field without altering the existing state. In contrast, conventional field sensors significantly alter the field or existing state when making measurements. This issue is akin to the measurement-disturbance relationship identified by Heisenberg in quantum state measurements. Our experiments have shown a similar problem can arise in classical electromagnetic cases, especially in complex experimental environments. In these environments, the electromagnetic (EM) field pattern and the location of locally concentrated EM fields, also known as "hot spots," change considerably depending on the location of the EM probe and the level of perturbation introduced. To address or mitigate the measurement-disturbance issue, we have developed an EO field probe. The probe exploits the Pockels effect, which causes changes in birefringence of a nonlinear optical material, such as LiNbO3 or KD*P crystals. When the crystal, through which a monochromatic (e.g., laser) probe beam passes, is exposed to an electric field (e.g., RF signal), the crystal's refractive indices are modulated, thereby modulating the polarization of the probe beam. These studies and applications are essential for practical purposes and also intriguing as they provide insights into the nature of quantum interactions, as the high-frequency electromagnetic wave dynamic behavior in macroscale is analogous to quantum interactions.