Three-Dimensional Phase Modulator at Telecom Wavelength Acting as a Terahertz Detector with an Electro-Optic Bandwidth of 1.25 Terahertz

We report a thin
film phase modulator employing organic nonlinear
optical molecules, with an electro-optic bandwidth of 1.25 THz. The
device acts as a polarization sensitive broadband Pockels medium for
coherent electric field detection in a dual wavelength terahertz time-domain
spectroscopy setup in the telecom band at 1550 nm. To increase the
sensitivity, we combine a three-dimensional bow-tie antenna structure
with strongly electro-optically active molecules JRD1 in poly­(methyl
methacrylate) supporting polymer. The antenna provides subwavelength
field confinement of the terahertz wave with its waveguide gap with
lateral dimensions of 2.2 μm × 5 μm × 4 μm.
In the gap, the electric field is up to 150× stronger than in
a diffraction limited space-time volume, such that an interaction
length of only 4 μm suffices for the detection of fields below
10 V/m. This device is promising in the growing field of quantum optics
in the terahertz, single photon terahertz detection, nonlinear imaging,
and on-chip telecommunication.