- Metamaterials with positive (left) and negative (right) refractive index
Optical Sensing is a key technology for a wide spectrum of applications. Robot navigation, visual inspection, and driver assistance systems are only a few examples. Virtually all intelligent beings employ visual perception as their most prominent means to sense, understand and interact with their environment. Encouraged by the fast pace of technical progress in this field, scientists widely expect that the same capability will also allow machines for unprecedented functionalities of interaction with their environment.
A team around C. Stiller (Institute for Measurement & Control Technology) works on mobile machine vision systems. The group has realized an active self-calibrating multi-camera platform for automobile sensing (IEEE IV 2006, in print). Similar to the visual system of vertebrates the platform allows for saccadical vision with a controllable high resolution field of view. Several research partners have successfully adopted the platform.
The research has led to two awards/honors: In a joint team with Ohio State University (Prof. Ozguner), the group has participated in the US DARPA Grand Challenge 2005, an autonomous vehicle race through the Mojave Dessert, Nevada. The vehicle has been equipped with a similar multi-camera platform and robust computer vision techniques that estimate the ground plane position and orientation, obstacles thereon, and a smooth local path. The vehicle successfully reached the final and ranged 10th best among a total of 195 competitors. The research has also led to the Transregional Collaborative Research Center ‘Cognitive Automobiles’ at Karlsruhe Institute of Technology (KIT) and Technische Universität München. C. Stiller acts as the coordinator for this collaborative research effort that has started in 2006.
The second focus of C. Stiller’s group is on automated visual inspection. The group has developed several visual inspection stations that allow the concerted manipulation of the illumination pattern and other optical parameters. Automated acquisition and analysis of image sequences from illumination series with controlled optical parameters provides a highly accurate inspection of technical surfaces. In particular, the group achieved significant advances in deflectometry and is able to perform in-line inspection of surfaces as large as 1 m² with an accuracy of a few microns. These research accomplishments have led to filing of two patents that are meanwhile licensed to an SME. The system is used nationally and internationally for a variety of applications ranging from forensic science (by national and international authorities) to automated car body inspection.
Miniaturization of optical systems not only yields cost reduction but may improve on their performance and functionality. In particular, optical switches and optical sensor systems benefit from the improvement of dynamic behavior and sensitivity. The research group of V. Saile at Forschungszentrum Karlsruhe has developed the LIGA-technique (Lithography, Galvanik und Abformung - Lithography, Galvanic and Impression) that has gained respectable international reputation for the fabrication of micro-systems in polymers and metals. Due to its high precision and smoothness of surfaces, the LIGA-technique offers itself to form precise optical components and accurate optical banks. The group has successfully implemented a micro-spectrograph based on a diffraction grating arranged in a Rowland circle (Microelectronics Journal 35, 131 (2004)). The micro-sensor is meanwhile commercially available from Boehringer microParts for near-infrared medical applications.
As another example, the group of V. Saile has realized a laser microscanner for distance metrology in cooperation with the group of C. Stiller. It uses a ferromagnetic shape memory microactuator, an integrated angle sensor, a pulsed laser diode and a time-of-flight measurement system. The small size and low mass of the microactuator allows the design of compact and robust scanner systems for mobile applications with low sensitivity to vibrations and shock. Robust estimation and tracking techniques based on probabilistic models allow scene interpretation for mobile agents.
Intelligence, miniaturization and cost efficiency are the main driving factors of modern sensor technologies in industrial as well as in many other application areas. The group of K. D. Müller-Glaser and W. Stork has conducted pioneering research in this field with the first miniaturized Laser-Doppler measurement system using low cost laser diodes, diffraction gratings as achromatic beam splitters and an integrated high performance digital signal processing unit (Proc. SPIE 4398, 2001). Classical Laser-Doppler systems used gas lasers with stable radiation frequencies and expensive beam splitting and combining optics. Laser diodes show frequency drifts with temperature and need very good temperature control for precise measurements. A lithographic highly efficient diffraction grating as simple and low-cost beam splitting and combining device shows achromatic behavior and no longer requires a precise and expensive temperature control (Appl. Opt. 36, 4515 (1997)). The embedded DSP performs the signal processing with simple adjustable profiles for different applications. The measurement data are provided with a standard digital interface. The development has led to the foundation of ELOVIS GmbH, a spin-off company founded in 1996 and located in Karlsruhe. The firm has commercialized the system for applications in industrial automation especially for length and speed measurements in paper, textile, cable and foil production.
Optics – due to its unprecedented bandwidth and low loss – is the dominant means for high-speed information transmission. Optical communications nowadays is used for optical interconnects, access networks (fiber-to-the-home), metro networks, the global telecommunications backbone networks and for intersatellite communications.
Each area of application operates at specific wavelengths with its own set of adapted devices and poses its specific challenges. For instance, while challenges in the field of optical interconnects are about offering highly functional and integrated devices with low losses in novel material systems, challenges in the global backbones are about offering highest-speed communications at an optimum spectral efficiency with simultaneous preservation of signal information over thousands of kilometers. The Institute of High-Frequency and Quantum Electronics works in the field of optical communications. It maintains activities and labs for the design, fabrication and system-level testing of the latest high-speed photonic devices and systems. The institute is equipped with latest software for state-of-the-art optical chip and network design, as well as with CAD programs, in-house fabrication, and packaging for optical devices. In addition, measurement setups for telecommunications system level testing up to 160 Gbit/s are available.
J. Leuthold, the head of the Institute of High-Frequency and Quantum Electronics was the first to demonstrate a fully monolithically integrated 100 Gb/s all-optical signal processor (El. Lett. 36, 1129 (2000). He and his team have built optical signal processors that operate at 40 Gb/s with as little as -17 dBm optical signal power. This is more than a decade better than what has been demonstrated by other groups (J. Lightwave Technol. 22, 186 (2004)). He can further claim to be the first to have demonstrated 40 Gb/s data signal transmission over distances of more than a million km (IEEE LEOS Newsletter, Oct. 2002, pp. 15-17 & El. Lett., vol. 38, no. 16, pp. 890-892, Aug. 2002).
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