Electric field sensors based on electro-optic photonic crystals – ESENCYAL

The project goal is to develop extremely sensitive electric field (E-field) sensor with flat response in a very large frequency range based on electro-optic photonic crystal devices fabricated on suspended micrometric size membranes of lithium niobate. We aim at nanooptical electric field sensors that will have for 10 dB total optical losses, microV/m sensitivity, ~ 10x10microns2 active area, and large frequency bandwidth [DC, GHz].

The detection will be purely optical which implies the following advantages:
• The sensor provides improved measurement accuracy by reducing susceptibility to electrical noise because the sensor is made of dielectric material.
• The sensor provides a non-perturbative measurement of electric field in comparison to antennas.
• The sensor may be placed in hostile or remote areas because optical fibers are capable of transmitting signals with high fidelity in noisy environments and over long distances.
• The sensor is electrically isolated, thus providing operator instrument safety.
• The sensor is small enough to be used where space is a constraint.
Because the electric field sensor is an all-optical and an all-dielectric device, it offers minimal disturbance to the electric field to be measured and opens the way to near field measurements. It also operates without a battery, so measurements can be conducted over a long period. Its sensing part does not contain any electronic devices or circuits, so it can easily be miniaturized.

The optical device will be a photonic crystal that brings the following advantages with respect to classical electro-optical devices already reported in literature:
- Small size, this is very useful for applications like in f-MRI, EEG or ECG because one can envision hundreds of electrodes (for exemple integrated in a cap for EEG).
- In lithium niobate photonic crystals, electro-optic effect can be enhanced enormously thanks to slow light configurations; Sensitivities of microV/M can be expected which is 1000 times higher than in state of the art electro-optic sensors based in Mach-Zehnder configurations.
The key feature on reaching unprecedented performances on electric field sensitivities never obtained before come from the fact that the optical detector is an active photonic crystal in which light-matter interaction can be enormously enhanced if a suitable dielectric material is chosen. In ESENCYAL, the detector is going to be a photonic crystal fabricated in lithium niobate. This nano-device in lithium niobate will have the unique property of being able to exacerbate the electro-optic effect with respect to bulk devices. Indeed, Photonic crystals (PhCs) are periodic arrangements of dielectric media that exhibit a photonic band structure that is analogous to the electronic band structure in crystalline solids [JJ08]. Because of their potential to offer unprecedented control over the flow of light in extremely small structures, PhCs have been viewed as having some revolutionary impact on photonics as the planar transistor did in electronics. In particular, the possible existence of a photonic band gap -a range of optical wavelengths that cannot propagate through the structure unless line or point defects are incorporated– provides opportunities for device engineering analogous to semiconductors junctions or heterostructures.
The present project falls entirely within the scientific guidelines of the DGA for 2013 and beyond. It fits completely the Nanotechnology axe in applications such as threaten detection, and miniaturized devices to be used in hazardous environments. In addition, our proposal can be used also in applications that are directly related with the axes Waves and Photonics since it could be used in the following cases: Electronic war and electromagnetic aggressions, electromagnetic compatibility and biosignal sensing.