Chapter 5From a Molecule to an Electro-optic Antenna1
In 1992, Kuwabara et al. [KUW 92] proposed a sensor based on a metal rod dipole antenna and a lithium niobate Mach-Zehnder optical modulator. In this sensor, the ambient electric field produces a voltage in the small gap between the rods where the optical modulator is placed. The latter converts this voltage into an optical signal, then it is measured by a detector, connected by a single mode optical fiber. The authors report detected electric field sensitivity of 79 μV/m. The total device size was 140 mm with the rods, and the maximum frequency was 750 MHz.
In 2004, Gaborit et al. [GAB 04] used an electro-optic crystal (DAST, ZnTE) placed at the end of a polarization maintaining fiber. In this configuration, the probe laser beam is sent through the fiber, travels inside the crystal where polarization is modified according to the ambient electric field, and is then reflected back into the fiber by a dielectric mirror deposited onto the crystal. Measurements show the device can be used in microwave frequencies, up to 20 GHz, without detectable perturbation of the electric field, but it needs a field of many kV/m.
Polymer-based second-order nonlinear optical (NLO) materials have been intensively studied because of their large linear electro-optic coefficients, low dielectric constants and flexibility in processing techniques that are compatible with integrated circuit technology [JEN 05, KAN 07, KIM 07, ...