In this Letter we demonstrate broadband electro-optic modulation with frequencies of up to 40 GHz in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with a nonlinear optical polymer. Two-dimensional photonic crystal waveguides in silicon enable integrated optical devices with an extremely small geometric footprint on the scale of micrometers. The slotted waveguide design optimizes the overlap of the optical and electric fields in the second-order nonlinear optical medium and, hence, the interaction of the optical and electric waves.

Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layernigs of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeßtechnik GmbH, Technische Umversitat Hamburg-Harburg and the Deutsches Zentrum fur Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dormer 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The quality of the recorded data can be monitored on screen and as online analogue plots during the flight.

Since more then 30 years ground-penetrating radar (GPR) has become a useful tool in solving different geophysical tasks in environmental geology, glaciology, archaeology, mineral exploration and for the detection of near-surface objects.The large variety of ground based GPR devices, even for rugged field conditions, is an effective tool for surveying small areas. GPR-equipped fixed-wing aircrafts are used mainly for surveying large areas or inaccessible regions; for example desert areas, permafrost areas or high mountain ranges. A GPR system installed in a helicopter is an effective possibility to survey large areas with high data density. Large areas, even in inaccessible regions, may be surveyed within short time and even under limited logistic demands. The high agility of a helicopter allows to increase the data density in areas of special interest.

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ABSTRACT. We present a newly developed high-resolution frequency-modulated continuous-wave (FM-CW) radar system for sounding the sub-ice topography. The system, working in the frequency range from 200 to 400 MHz, was developed to measure thickness and internal layers in cold ice with a resolution better than 1 m. This system has the potential to measure accumulation rates, an important input for improved knowledge of the mass balance of polar ice sheets. First measurements for the test, calibration and optimization of the new ice sounder were made in December 2005 near the Ellsworth Mountains, specifically in Patriot Hills, West Antarctica, at 80818 0 S, 81822 0 W. The complete radar system was installed on a ski-mounted support frame, and towed by hand across the ice surface. The measurement results show the capability of this system to measure ice thickness up to 1000 m and to define internal layers within the ice body.