Jeffrey M. Raynor

Smart optical and image sensors fabricated with industrial CMOS/CCD semiconductor processes

Photosensitive elements with well-chosen geometry, combined with suitable analog and digital circuitry on the same CMOS/CCD chip, lead to smart image sensors with interesting capabilities and properties. All our smart sensors were fabricated with commercially available multi-process wafer services of CMOS process, one of them with a buried-channel CCD option. Measurement of the optoelectronic properties of standard CMOS/CCD processes (wavelength-dependent quantum efficiency, lateral homogeneity of quantum efficiency/photo- conductivity, CCD charge transport efficiency, etc.) show excellent performance. The smartness that lies in the geometry is illustrated with a single-chip motion detector, a 3-D depth video camera, a single-chip planar distance sensor, and a sine/cosine (Fourier) transform sensor for fast optical phase measurements. The concept of problem-adapted geometry is also shown with a dynamic frame-transfer CCD whose pixel size and shape can be changed electrically in real-time through charge-binning. Based on the wavelength-dependent absorption of silicon, all-solid-state color pixels are demonstrated by properly arranging the available pn-junctions in the third (bulk) dimension. Moderate color measurement performance is achieved using an unmodified CMOS/CCD process, with a CIE general color-rendering index of Ra equals 69.5.

Fabrication of kinoform structures for optical computing

The fabrication of kinoform micro-optical elements for applications in optical computing is described. The elements are recorded as continuous microrelief structures by programmable laser beam writing in photoresist with a computer-controlled precision xy stage and a modulated, focused laser beam. Kinoform structures can be programmed to any desired profile that is required for reproducing complex, optimized structures that are found by computer design techniques.

Fabrication of micro-optical components by laser beam writing in photoresist

A laser beam writing system for the fabrication of micro-optical elements as relief structures in photoresist is described. Using a computer controlled precision xy stage and a modulated, focused laser beam, a wide range of surface relief microstructures has been produced, with typical periods of 10 - 100 micrometers and a maximum relief amplitude of about 5 micrometers . Examples include microlens arrays, kinoforms and other phase structures for applications in optical computing, optical interconnects and micro-optical systems in general.

Active machine vision system for surface quality inspection

The realization of an integrated, flexible, and robust CIM vision system, suitable for performing quality-assurance surface inspections is discussed. The optimized combination of advanced optics, optomechanics, and flexible image sensor realizes a high virtual resolution without penalizing the pixel transfer rate. High computation rates are obtained by complementing the fractal inspection algorithm with a dynamic hologram, a modular data flow processor, and the system computer. The integrated vision system is validated for the surface quality inspection of concrete tiles in an industrial environment. The overall system performance is discussed in detail and the potential of the system for other application fields will be addressed.

Modular image acquisition and measurement system with 12-bit pixel-synchronous sampling

This paper describes the requirements, design, and results of a modular data acquisition system with a resolution of 12 bits at up to 20 MHz sampling frequency. The modularity enables the analog-digital conversion to be separated from the digital processing/storage. This allows the latest, best performing ADC (analog-digital converter) to be easily integrated into the system by a re-design of only the AD board with the rest of the system unchanged. The converter employed operates at frequencies up to 20 MHz. The complete system produces measured quantization noise figures of -75 dB and integral non-linearity of -72 dB. The unit can sample video or non-video waveforms. For video applications, an active clamping system is used to ensure that the black level is accurately maintained. The framestore is connected externally using a high-speed digital data bus. This facilitates the inclusion of real-time digital processing units. The framestore used is doubly buffered to permit simultaneous acquisition and readout. The store is 8 Mbytes to accommodate HDTV images and has an input data rate of 40 Mbytes per second.

Real-time digital color processor for a programmable, high-resolution CCD camera with high colorimetric accuracy

In the course of ESPRIT II project No. 2103 (MASCOT) a high performance color CCD camera was developed. It is based on a 1K X 1K frame-transfer CCD imager whose pixels are covered with an optimized dielectric filter stripe pattern. A microscanning optical unit is employed to displace the image, with a reproducibility of 1/200th of the pixel period, for programmable color image acquisition with a maximum resolution of 3K X 3K color (RGB, XYZ, etc.) pixels. The CCDs output is immediately digitized to 10 bits using an in- house developed ADC subsystem whose performance of 67 dB S/N at 20 MHz is ideal for this application. The data is stored in one of three fast framestores. The raw data is read out simultaneously from these three framestores at a data rate of 30 MBytes per second and processed, fully digitally, in a special color processor. After non-linear transformations to compensate for detector non-linearities, color matrixing is carried out using one set of 16 matrix parameters which have been optimized for different illumination conditions and color temperatures. They also enable the selection of the type of output data to be generated e.g., RGB for specific phosphors, CIE XYZ tristimulus values, etc. After matrixing, a non-linear table-lookup can be used to introduce gamma correction or other calibration functions. The color processor produces 8-bit color pixels at a rate of 20 MBytes per second, writing these data directly into an 8 MBytes commercial framestore plugged into a PC/AT.

Integrated, dynamic machine vision system with virtual high resolution

A novel active vision system for CIM production and inspection applications has been developed in the framework of ESPRIT II project No. 5194 (CIVIS). The system consists of a unique, integrated combination of novel components: camera head, data acquisition electronics, a custom digital image processor, control hardware and a commercial framestore, all under the direction of control and processing software on a PC-486 platform. The camera head incorporates a fast zoom lens in combination with a pan/tilt mirror system, allowing region-of-interest acquisition. The special 256 X 256 MOS image sensor offers programmable resolution and random pixel access. The unique combination of optics, optomechanics and versatile image sensor has a high `virtual resolution, corresponding to more than 1k X 1k pixels but without the overhead of a high pixel transfer rate. The fast computation of the algorithm employed for the fractal inspection of surfaces is realized with an unusual combination of an electrically switchable hologram (for performing all linear operations at the speed of light in the optical domain), a module-based digital processor and the host computer. In this way, active vision for the inspection of concrete tile surfaces has been implemented by acquiring only relevant image data and elegantly processing them in the most appropriate domain.

Universal pixel-synchronous data acquisition system for high-resolution CCD image sensors

The use of CCD sensors in optical metrology requires synchronous sampling of the image with a good signalnoise performance. . A system has been developed to digitize optimally the signals from high-resolution CCD sensors. The data acquisition system is split into two parts -the first is a storage unit for the IBM PC/AT family of computers with a fast, digital, input-output interface, with 8-bit transmission speed DC-4OMHz and 16 bit operation DC-2OMHs. The digitization of the analogue signal is performed on separate units, up to 2m from the computer. Separating the analogue processing from the computer and using a separate power supply not only reduces the electrical noise from the digital electronics to a minimum but also allows greater flexibility in designing custom front ends for a wide range of sensors. The storage card has two 1M byte banks of memory. These are normally used to provide double buffering of 1M pixel images, but can also be used to store 2M byte images without double buffering. Practical experience, using 8 and 10 bit video front ends, indicates that the geometrical resolution possible with modern CCD sensors is approaching 1/100 of the pixel period. The digital signal processing required for this performance does not depend on the CCD cameras PSF and it is insensitive to variations offocus and orientation.

Locometer: on-line inspection of locomotive wheel-to-rail movements using high-precision CCD metrology

A CCD camera based optical metrology system has been developed for the accurate measurement of a railway locomotives wheel movements with respect to the rails. The system is based on the light-sectioning method implemented with four laser diodes projecting light sheets onto the wheel and rail. A high-resolution CCD camera views the four profiles simultaneously using an appropriately folded and combined beam-path. To minimize the effects of ambient light a special narrow-band dielectric filter was designed manufactured and fitted in front of the camera lens. The desired measurement accuracy requires pixel-synchronous acquisition of the CCD video data. This is realized with a custom-built universal CCD data acquistion system with which profile tracking data compression and storage at 12. 5 Hz (half frame-rate) is made possible. A prototype system was built and tested on railway tracks at up to 140 km/h. In laboratory experiments the system surpassed the required measurement accuracies about fivefold attaining an accuracy of 0. 02 mm in relative position and better than 0. 1 mrad in relative angle. 2.