Polymers are often embedded with specific nanofillers such that the functional characteristics and properties of the
resulting polymeric nanocomposite (PNC) are enhanced. The degree to which these enhancements can be achieved
depends not only on the level of particle loading of nanofillers, but most importantly on the resulting dispersion profile
achieved within the matrix. Agglomeration (often referred to as clustering) is a result of the mixing process and very
much depends on the chemistry between the polymer and nanofiller. Depending on the PNC type, different mixing
processes can be applied but the general consensus is that such processes are not repeatable themselves. Not only it is
quite difficult to achieve the desired level of dispersion, but in addition there is a limited number of characterization tools
that can be employed to routinely check the homogeneity achieved within a produced sample. Transmission electron
microscopy (TEM) and X-ray diffraction (XRD) techniques are usually employed, but they are very time consuming,
expensive, require special sample preparation and treatment, often produce results that are difficult to interpret and can
only analyse very small areas of sample. This work reports on the adaptation and development and three optical
techniques that are non-destructive, can accurately characterize the dispersion achieved as a result of the mixing process
and can analyse larger material areas. The techniques reported are based on static and dynamic visible and infra-red light
scattering.
Current methods to characterise specific properties of polymeric nanocomposites (PNCs), such as particle loading and
dispersion profile, rely on a number of techniques that require special sample preparation and treatment, are very
expensive, require long measurement times and quite often produce ambiguous results that are difficult to evaluate and
interpret. In addition, given their complexity, they are not entirely suited for in-situ industrial environments. This paper
presents alternative techniques based on optical diffraction and diffusion mechanisms combined with signal processing
that can successfully discriminate between different particle loadings and levels of dispersion. The techniques discussed
in this paper are Fourier-domain optical coherence tomography in the infra-red, Fraunhofer wavefront correlation in the
visible red and oscillatory photon correlation spectroscopy in the visible green parts of the spectrum. Most importantly,
they are non-invasive, are compact, fast and efficient, can potentially analyse large areas of the material and therefore
suited for a wide variety of research and industrial situations.
De Montfort University, in conjunction with the Heinrich Hertz Institute, is developing a 3D display that is targeted specifically at the television market. It is capable of supplying 3D to several viewers who do not have to wear special glasses, and who are able to move freely over a room-sized area. The display consists of a single liquid crystal display that presents the same stereo pair to every viewer by employing spatial multiplexing. This presents a stereo pair on alternate pixel rows, with the conventional backlight replaced by novel steering optics controlled by the output of a head position tracker. Illumination is achieved using arrays of coaxial optical elements in conjunction with high-density white light emitting diode arrays. The operation of the steering and multiplexing optics in the prototype display are explained. The results obtained from a prototype built under the European Union-funded ATTEST 3D television project are described. The performance of this model was not optimum, but was sufficient to prove that the principle of operation is viable for a 3D television display. A second prototype, incorporating improvements based on experience gained, is currently under construction and this is also described. The prototype is capable of being developed into a display appropriate for a production model that will enable 3D television to come to market within the next ten years. With the current widespread usage of flat panel displays it is likely that customer preference will be for a hang-on-the-wall 3D display, and this challenge will be met by reconfiguring the optics and incorporating novel optical addressing techniques.
A technique for the experimental implementation of fully complex filters with commercially available spatial light modulators (SLMs) is reported. The filters are incorporated into an all-optical correlator and a hybrid digital-optical correlator, the relative merits of each configuration being considered. Various filter functions requiring complex modulation are demonstrated, consideration being given to the degradation of filter performance due to the limited quantization and dynamic range with which they can be implemented using current SLM technology.
A fully complex filter is discussed using a Boulder Nonlinear Systems Smectic A* liquid crystal spatial light modulator. Each pixel is capable of both analogue amplitude modulation and binary phase modulation. Two pixels are used together in a macro pixel giving full complex modulation.
KEYWORDS: Spatial light modulators, Fourier transforms, Digital signal processing, Optical correlators, Lithium, Signal processing, Charge-coupled devices, Field programmable gate arrays, Tolerancing, Digital Light Processing
A consideration of the system advantages of a hybrid digital/optical correlator configuration together with some details of its construction were reported at the OPR X Conference. In this arrangement the input scene is digitally Fourier transformed at video-rate with a digital signal processor, the spectral data mixed with digitally stored templates and the result loaded onto a high frame-rate Spatial Light Modulator (SLM). An optical Fourier transform of this display then implements a correlation between the input scene and the reference template. Since the optical Fourier transform is practically instantaneous and the digital mixing and display on the SLM can accomplished at least two orders of magnitude faster than the digital Fourier transform, many reference templates may be searched during an input frame interval. Thus unconstrained pattern recognition problems may be tackled with this device.
Two-dimensional correlation between a reference template and an input scene is a powerful pattern recognition technique but is demanding of computational power. Coherent optical correlators, exploiting the Fourier transforming properties of a lens and the capability to impart a phase modulation on a wavefront with an appropriate spatial light modulator (SLM), hold the promise of real-time implementation of two- dimensional correlation for realistic pattern recognition problems. However, their practical use has been delayed in many applications by the lack of availability of suitable SLM devices with the required speed and dynamic range, with different needs for input and frequency plane modulators. It is now possible to compute a two-dimensional Fourier transform at video-rates with various digital signal processing chip sets. Thus a hybrid correlator is proposed in which the input scene is digitally Fourier transformed at video-rate, and multiple templates searched during the next video frame interval by optical mixing and Fourier transformation at a speed at least two orders of magnitude faster than possible with digital methods. In this way, the input SLM is avoided and a precise spectrum is available for subsequent digital or optical mixing with the stored templates. The speed advantage over all-digital processing allows unconstrained pattern recognition problems to be tackled that require many template searches to match the input with a reference function. Different hybrid correlator configurations are considered, together with discussion of the various digital chip sets available to perform the video-rate FFT, as well as the SLM devices currently available that are suitable as frequency domain phase modulators.
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