KEYWORDS: Signal processing, Signal detection, Photonic devices, Receivers, Free space optics, Data transmission, Phase shift keying, Frequency modulation, Electronic filtering, Signal generators
Working on optical distance measurement a new optical correlator was developed at the Institute for Data Processing of the University of Siegen in the last years. The so called Photonic Mixer Device (PMD), to be meant originally for laser ranging systems, offers a lot of advantages for wireless optical data communication like high speed spatial light demodulation up to the GHz range and inherent backlight suppression. This contribution describes the application of such PMDs in a free space interconnect based on the principle of Multi Dimensional Multiple Access (MDMA) and the advantages of this new approach, starting from the MDMA principle and followed by the fundamental functionality of PMDs. After that an Optical MDMA (O-MDMA) demonstrator and first measurement results will be presented.
A series of micro-robots (MERLIN: Mobile Experimental Robots for Locomotion and Intelligent Navigation) has been designed and implemented for a broad spectrum of indoor and outdoor tasks on basis of standardized functional modules like sensors, actuators, communication by radio link. The sensors onboard on the MERLIN robot can be divided into two categories: internal sensors for low-level control and for measuring the state of the robot and external sensors for obstacle detection, modeling of the environment and position estimation and navigation of the robot in a global co-ordinate system. The special emphasis of this paper is to describe the capabilities of MERLIN for obstacle detection, targets detection and for distance measurement. Besides ultrasonic sensors a new camera based on PMD-technology is used. This Photonic Mixer Device (PMD) represents a new electro-optic device that provides a smart interface between the world of incoherent optical signals and the world of their electronic signal processing. This PMD-technology directly enables 3D-imaging by means of the time-of-flight (TOF) principle. It offers an extremely high potential for new solutions in the robotics application field. The PMD-Technology opens up amazing new perspectives for obstacle detection systems, target acquisition as well as mapping of unknown environments.
In the last years 3D-Vision systems based on the Time-Of-Flight (TOF) principle have gained more importance than Stereo Vision (SV). TOF offers a direct depth-data acquisition, whereas SV involves a great amount of computational power for a comparable 3D data set. Due to the enormous progress in TOF-techniques, nowadays 3D cameras can be manufactured and be used for many practical applications. Hence there is a great demand for new accurate algorithms for 3D object recognition and classification. This paper presents a new strategy and algorithm designed for a fast and solid object classification. A challenging example - accurate classification of a (half-) sphere - demonstrates the performance of the developed algorithm. Finally, the transition from a general model of the system to specific applications such as Intelligent Airbag Control and Robot Assistance in Surgery are introduced. The paper concludes with the current research results in the above mentioned fields.
Many concepts for incoherent optical distance measurement, based on the time-of-flight (TOF) principle, are discussed in the past, but they differ in complexity and accuracy. The used modulation techniques and evaluations methods require different signal sources, which are controllable in frequency or phase delay in high precision. Development effort and outlay of TOF-systems will be reduced with the use of standard logic devices. The restrictions of these devices permit a limited number of phase or frequency steps, but the combination of standard logic devices and the principle of Phase-Shift Interferometry (PSI) offers the possibility to design a plain and precise system, at very low cost. Over the past 20 years many evaluation algorithms for PSI have been presented in different applications. The phase angle of an ideal interferogram is determinable with only three or four sampling values, but the usage of more sampling values will suppress emitter and detector non-linearities, phase shift errors and noise generally. This paper will present the design of the optimal phase-shift algorithm based on Fourier analysis of the complete recorded interferogram.
Optical distance measurement, based on the time-of-flight (TOF) principle, suffer from the unfavorable ratio of desired accuracy and the small received signal power, which is reflected by the target. Many receiver concepts are discussed in the past, but only any concepts are putted into practice. The concept of Photonic Mixer Devices (PMD) offers any interesting features for laser ranging systems, like fast photo-detection with inherent mixing, accumulation of a adequate signal power by a following integration, flicker noise suppression, background illumination, and interference rejection of two-channel designs. The combination of PMD and phase-lock techniques additionally enables a continuous tracking of the object distance, his relative velocity to the measurement system, and the restoration of the received optical signal. Different design concepts of the Photonic Mixer Device (PMD) with their characteristics and advantages as the key component in an Electro-Optical Phase-Locked Loop (OE-PLL) and an Electro-Optical Delay-Locked Loop (OE-DLL) will be discussed.
The PMD-technology opens up a wide area of solutions for all detector problems where a high phase accuracy is required. One important application of the new Photonic Mixer Device is optical distance measurement based on the time-of-flight principle. The high integration of PMD smart-pixels in an array based on CMOS-technology means a breakthrough in optical 3D-imaging. Additionally to the inherent mixing feature, even more functionality could be integrated according to the well-known active pixel sensor concept.
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