Microwave Photonics Research at KRISS
The Center for Electromagnetic Wave at KRISS (Korea Research Institute of Standards and
Science) has conducted research in microwave photonics for the last eight years. The
capability to measure microwave can be significantly enhanced when it is assisted with
photonic technology. We, KRISS, have employed optical crystals - associated with laser
systems - to overcome several challenges in relation to electromagnetic measurements. The
crystals were utilized to build EO/MO (electrooptic/magnetooptic) probes to measure
challenging electric/magnetic fields. The following topics will be presented:
1. Minimally invasive field probe: The transparent nature of EO/MO probes for both
electromagnetic and optical bands allows the realization of minimally invasive microwave
field measurements. Field distribution images radiated within a wavelength region from
electrical devices are presented.
2. High-intensity field measurements: The all-dielectric embodiment of optical probes
enables us to sense very intense electric fields up to the MV/m scale. Our EO probes show a
dynamic range which exceeds 100 dB with good linearity. The capability of intense field
measurements using a high-power gyrotron, a plasma source, an MRI system, and a 50 kV
AC voltage supply is presented.
3. Millimeter-wave measurements: A photonic-based sensing scheme is also a clear
advantage given that it enhances the sensing bandwidth by extending it to the mm-wave band.
We devised sub-mm scale EO probes for mm-wave sensing to minimize invasiveness. The
stability of the EO probe system was also improved by compensating any system drift with
multiple probes. Stabilized sensing results for various W-band devices are presented.
4. Fast pulse scoping system: Rapid electrical pulses can be measured using an ultrafast laser.
We have built a pump-probe time-domain sensing scheme to sample 100 GHz pulses from a
laser-driven photodiode. The detailed sensing technique is presented and the results are
discussed.
5. Highly sensitive field probes: The sensitivity of the EO probes can be greatly improved
when the electrodes are assisted. We have fabricated a folded Mach-Zehnder type of optical
waveguide on an EO wafer. With free-space electrodes which serve as a dipole antenna along
the waveguide, the EO wafer works as an effective field probe at the bandwidth of the
electrodes. The enhanced performance of such integrated optic probes is presented.