(2010) Broad spectrum measurement of the birefringence of an isothiocyanate based liquid crystal. Applied Optics, 49 (28). pp. 5212-5216. Permanent WRAP URL:http://wrap.warwick.ac.uk/92169 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:© 2010 Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription.

We propose a fringing-effect model based on the experimentally measured phase response across the phase transition region of a liquid crystal on silicon (LCOS) device. The measured phase profile in the phase transition region is characterized by a scaled error function of the flyback width. The flyback width can be determined by a cubic function of the phase depth between neighboring pixels. This dependence of the flyback width on the phase depth is explained by a linear rotation model of the liquid crystal director. The simulated diffraction efficiency based on the fringing-effect model shows a close agreement with the experimental measurement.

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This paper describes the design, modeling, construction, and testing of a low-cost and compact (80  mm×50  mm) 1×5 wavelength-selective switch. The core beam-deflecting element of the switch is a nematic liquid crystal on silicon spatial light modulator. The switch is designed for coarse wavelength-division multiplexing wavelengths in order to bring the benefit of a low-cost, compact, and robust switching design toward the customer end in the access network. During the system development stage, a single optomechanical assembly was designed and prototyped using the three-dimensional printing technology. The experimental results show an insertion loss of -13.8±1.4  dB and a worst-case scenario crosstalk level of -24.8  dB. Approaches for enhancing the performance of the switch are analyzed and discussed.

Summary Microseismic monitoring is crucial for risk assessment in mining, fracturing, and excavation. In practice, microseismic records are often contaminated by undesired noise, which is an obstacle to high-precision seismic locating and imaging. In this study, we develop a new denoising method to improve the signal-to-noise ratio (SNR) of seismic signals by combining wavelet coefficient thresholding and pixel connectivity thresholding. First, the pure background noise range in the seismic record is estimated using the ratio of variance (ROV) method. Then, the synchrosqueezed continuous wavelet transform (SS-CWT) is employed to project the seismic records onto the time-frequency plane. After that, the wavelet coefficient threshold for each frequency is computed based on the empirical cumulative distribution function (ECDF) of the coefficients of the pure background noise. Next, hard thresholding is conducted to process the wavelet coefficients in the time-frequency domain. Finally, an image processing approach called pixel connectivity thresholding is introduced to further suppress isolated noise on the time-frequency plane. The wavelet coefficient threshold obtained by using pure background noise data is theoretically more accurate than that obtained by using the whole seismic record, because of the discrepancy in the power spectrum between seismic waves and background noise. After hard thresholding, the wavelet coefficients of residual noise exhibit isolated and lower pixel connectivity in the time-frequency plane, compared with those of seismic signals. Thus, pixel connectivity thresholding is utilized to deal with the residual noise and further improve the SNR of seismic records. The proposed new denoising method is tested by synthetic and real seismic data, and the results suggest its effectiveness and robustness when dealing with noisy data from different acquisition environments and sampling rates. The current study provides a useful tool for microseismic data processing.