An experimental ray tracer for measuring the optical aberrations of aspherical lenses is presented. Setup is based on the
principle of ray tracing which is used in optical design for virtually tracing rays through an optical system. This method
has the potential to be used in aspherical lens testing because of its flexibility and high dynamic range. Wavefront
aberrations can be calculated from results of experimental ray tracing. Furthermore the method offers the possibility of
retrieval of aspherical surface profiles. Preliminary results with a plano-convex aspherical lens are compared with those
obtained by a commercial surface profiler.
A new approach for quantifying the optical aberrations of aspherical lenses is presented. A measurement setup is
developed which measures the local wavefront slopes using a motorized scanning system. The simulation results of the
setup are presented in order to validate the potential of the measurement principle. Experimental results by the
measurement of a commercial aspherical lens verify the theoretical investigations. Dynamic range of the measurable
Zernike coefficients and Peak to Valley (P-V) wavefronts are quantified. Focal length of the aspheric lens under test is
calculated from the Zernike coefficients which are determined by performing a nonlinear regression analysis for the
measured slopes and the partial derivatives of the wavefront. Furthermore, 3rd order spherical aberration term of the
wavefront is analyzed dependent on different wavelengths.
A novel Fourier spectrometer using thin film technology was developed. The spectrometer based on a semi transparent thin film detector in combination with a tunable micro machined mirror. The semi transparent detector is introduced into a standing wave created in front of the mirror to sample the profile of the standing wave. Varying the position of the mirror results in a shift of the phase of the standing waves and thus in a change of the optical generation profile within the semi transparent detector. The active region of the sensor (thickness-absorption) is thinner than the wavelength of the incoming light, so that the modulation of the intensity results in a modulation of the overall photocurrent. The spectral information of the incoming light can be determined by the Fourier transformation of the sensor signal. Based on the linear arrangement of the sensor and the mirror, the spectrometer facilitates the realization of 1D and 2D arrays of spectrometers combining medium range spectral resolution with medium range spatial resolution. The novel device is filling the gap between solid-state camera technology with only three-color channels (red, green and blue) but high spatial resolution on one hand and precision spectrometers with high spectral resolution but no spatial resolution on the other hand. An analytical optical model of the spectrometer was applied to evaluate different detector concepts. The model was used to study the performance of different device designs regarding the spectral resolution of the spectrometer, the spectral range and the linearity of the response. The calculations will be compared with experimental results of semi transparent amorphous silicon detectors.
The structural and transport properties of pentacene thin film transistors are reported, showing the influence of the deposition temperature, the deposition rate and the substrate on the structural and transport properties of oTFTs. The structure and morphology of pentacene films on thermal oxide and plasma CVD silicon nitride were compared by x-ray diffraction measurements and atomic force microscopy. There is a clear correlation between the morphology and the structural properties of the highly polycrystalline films on the two dielectrics. In the case of silicon nitride the roughness of the film has a distinct influence on the morphology and the structural properties, whereas the films on thermal oxide are in general highly ordered independent of the deposition conditions. The ordered films exhibit a thin film and a crystalline bulk phase, and the crystalline bulk phase fraction increases with the deposition temperature and the film thickness. We find that careful control of the deposition conditions give virtually identical films on the oxide and nitride dielectrics. To study the electronic properties we have realized inverted staggered transistors. The mobility of the TFTs is correlated with the morphology and the structural properties of the films, and increases with the size of the crystals. The TFTs exhibit very similar mobilities of ~0.4 cm2/Vs and on/off ratios >108 on thermal oxide and flat silicon nitride. The impact of the dielectric on the device parameters of mobility, threshold voltage and sub threshold voltage slope are discussed. Bias stress experiments are performed to investigate the stability of the TFTs, and to gain understanding of the transport mechanisms of thermally evaporated pentacene TFTs.
Color images are commonly captured with sensor arrays covered with a mosaic of RGB-filters. In spite of the enormous success of CMOS and CCD color cameras, one-chip color imagers suffer form color aliasing or color moire effects. In order to overcome these limitations we have realized color sensors based on vertical integrated thin film structures. The compete color information of the color aliasing free sensor can be detected at the same position of a sensor array without optical filters. The color separation is realized by the wavelength dependent absorption int eh depth of the material. The thin film systems based on amorphous two terminal deices and stacked diodes are fabricated by a low temperature CVD process. The spectral sensitivity of the sensors can be controlled by the optical and optoelectronic properties of the material son one hand and the design of the devices on the other hand. The working principle of thin film sensors will be presented and the different detection concepts will be compared regarding their application in color recognition and digital imaging.
The purpose of this study was to identify the performance of novel realized color sensors manufactured in thin film technology and to compare the results with simulations. In a previous study, a novel technology of three- and six-channel color sensors was presented. The performance of the sensors was tested in simulations and compared to other sensors for different characterization methods (polynomial regression and smoothing inverse). Now, these method are supplemented by a new linear programming method. Moreover, practical experiments with real color capture have been conducted.
A novel sensor concept for the detection of the fundamental components of visible light has been developed. The multi- channel sensors (3-, 4- and 6-channel detectors) based on three and four stacked amorphous thin film detectors are color moire or color aliasing free due to their vertical integration. The color separation is performed in the depth of the structure without using optical filters. The developed 3- and 4-channel detectors can be read-out with one shot whereas the color information of the 6-channel detector can be read- out with two shots. The sensors are colorimetrically characterized in order to gain further optimization criteria concerning the improvement of the sensor performance. The presented characterization model facilitates the quantification of color errors with regard to the human perception. Furthermore, the color errors of amorphous thin film sensors are compared with a commercial color CCD camera and a BiCMOS color-sensor.
This paper describes a new type of multichannel color sensor with the special property of having all channels per pixel at the same spatial location one on top of the other. This arrangement is accomplished by stacking three amorphous thin film detectors on a glass substrate. It has the advantage that the color noire effect is avoided which produces large color errors when objects of high spatial frequency are captured with a multi-channel sensor array. The new technique enables the design of a three-channel sensor as well as a six-channel sensor. In the latter case, color is captured in two 'shots' by changing the bias voltages. The colorimetric characterization of the sensors is presented, including multiple polynomial regression both for tristimulus and spectral reconstruction, and the smoothing inverse for spectral reconstruction. The result obtained with different types of regression polynomials, different sensors, and different characterization methods are compared. The results show that the three-channel color moire free sensors are able to produce good accuracy, while the six-channels' performance is striking.