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LCoS spatial light modulators as active phase elements of full-field measurement systems and sensors

Kujawinska M., Porras-Aguilar R., Zaperty W.

Metrology and Measurement Systems

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2012

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Vol. 19, nr 3

445-458

EN

Spatial light modulators (SLM) are devices used to modulate amplitude, phase or polarization of a light wave in space and time. Current SLMs are based either on MEMS (micro-electro-mechanical system) or LCD (liquid crystal display) technology. Here we report on the parameters, trends in development and applications of phase SLMs based on liquid crystal on silicon (LCoS) technology. LCoS technology was developed for front and rear projection systems competing with AMLCD (active matrix LCD) and DMD (Digital Mirror Device) SLM. The reflective arrangement due to silicon backplane allows to put a high number of pixels in a small panel, keeping the fill-factor ratio high even for micron-sized pixels. For coherent photonics applications the most important type of LCoS SLM is a phase modulator. In the paper at first we describe the typical parameters of this device and the methods for its calibration. Later we present a review of applications of phase LCoS SLMs in imaging, metrology and beam manipulation, developed by the authors as well as known from the literature. These include active and adaptive interferometers, a smart holographic camera and holographic display, microscopy modified in illuminating and imaging paths and active sensors.

2

On discrete Fourier spectrum of randomly modulated signals

Popiński W.

Artificial Satellites : Journal of Planetary Geodesy

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2010

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Vol. 45, No. 3

143--152

EN

In this work the problem of characterization of Discrete Fourier Transform (DFT) spectrum of an original complex-valued signal modulated by random fluctuations of amplitude and phase is investigated. It is assumed that the amplitude and phase of signal values at discrete time moments of observations are distorted by adding realizations of independent and identically distributed random variables. The obtained results of theoretical analysis of such distorted signal spectra show that only in the case of amplitude modulation the DFT spectrum of the modulated bounded signal can be similar to the original signal spectrum, although there occur random deviations. On the other hand, if phase modulation is present, then the DFT spectrum of the modulated bounded signal not only shows random deviations but also amplitudes of peaks existing in the original spectrum are diminished, and consequently similarity to the original signal spectrum can be significantly blurred.

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Bispectral Analysis in Vibroacoustic Diagnostics of Gears

Radkowski S.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2001

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vol. 49, nr 2

249-265

EN

The work concerns diagnosis of the origins and development of early stages of defects based on information found in the vibroacoustic signal. At the beginning the necessity of selection of diagnostic parameters dependent upon the amount of dissipated energy and related defect development is proven. Assuming that the basic role in transmission of such diagnostic information is played by the phenomena of amplitude and phase modulation of the vibroacoustic signal and non-linear effect of system, it is points to the significance of the signal non-linear components. For that reason in this work a model of signal in the form of a Volterra series is assumed, which enables examination of the influence that disturbances have upon non-linear components. On the basis of exemplary analysis of the contact condition disturbances, the possibility of generation of a bilinear component is presented. What serves this purpose is the model of non-linear and instantaneous contact. Simultaneously problems of selection of signal analysis methods that enable realisation of assumed aims are presented. Emphasising the fact that defect development does not always lead to a significant growth of the vibroacoustic signal power, the author has shown importance of methods of higher-order spectral analysis like, bispectrum and Wigner's distribution.