  Directive optical leaky wave antennas (OLWAs) with tunable radiation pattern
are promising integrated optical modulation and scanning devices. OLWAs
fabricated using CMOS-compatible semiconductor planar waveguide technology have
the potential of providing high directivity with electrical tunability for
modulation and switching capabilities. We experimentally demonstrate directive
radiation from a silicon nitride ($Si_3N_4$) waveguide-based OLWA. The OLWA
design comprises 50 crystalline Si perturbations buried inside the waveguide,
with a period of 1 {\mu}m, each with a length of 260 nm and a height of 150 nm,
leading to a directive radiation pattern at telecom wavelengths. The measured
far-field radiation pattern at the wavelength of 1540 nm is very directive,
with the maximum intensity at the angle of 84.4{\deg} relative to the waveguide
axis and a half-power beam width around 6.2{\deg}, which is consistent with our
theoretical predictions. The use of semiconductor perturbations facilitates
electronic radiation control thanks to the refractive index variation induced
by a carrier density change in the perturbations. To assess the electrical
modulation capability, we study carrier injection and depletion in Si
perturbations, and investigate the Franz-Keldysh effect in germanium as an
alternative way. We theoretically show that the silicon wire modulator has a -3
dB modulation bandwidth of 75 GHz with refractive index change of
$3\times10^{-4}$ in depletion mode, and 350 MHz bandwidth with refractive index
change of $1.5\times10^{-2}$ in injection mode. The Franz-Keldysh effect has
the potential to generate very fast modulation in radiation control at telecom
wavelengths.
