We experimentally demonstrate a nearly wavelength-independent optical reflection from an extremely rough carbon nanotube sample. The sample is made of a vertically aligned nanotube array, is a super dark material, and exhibits a near-perfect blackbody emission at T=450 K-600 K. No other material exhibits such optical properties, i.e., ultralow reflectance accompanied by a lack of wavelength scaling behavior. This observation is a result of the lowest ever measured reflectance (R=0.0003) of the sample over a broad infrared wavelength of 3 μm < λ < 13 μm. This discovery may be attributed to the unique interlocking surface of the nanotube array, consisting of both a global, large scale and a short-range randomness.

In this paper, the channel estimation methods for OFDM systems based on comb-type pilot sub-carrier arrangement are investigated. The channel estimation algorithm based on combtype pilots is divided into pilot signal estimation and channel interpolation. The pilot signal estimation based on LS or MMSE criteria, together with channel interpolation based on piecewise-linear interpolation or piecewise second-order polynomial interpolation is studied. Owing to the MMSE estimate of pilot signals, the inter-carrier interference and additive white Gaussian noise are reduced considerably. The computational complexity of pilot signal estimation based on MMSE criterion can be reduced by using a simplified LMMSE estimator with low-rank approximation using singular value decomposition. Phase compensators before and after interpolation are also presented to combat the phase changes of subchannel symbols arising from the frame synchronization errors. Comparing to the transform-domain processing based channel estimation algorithm, the MMSE estimate of pilot signals together with phase compensated linear interpolation algorithm provides better performance and requires less computations.

Abstract. To achieve the full complex modulated range of the cascaded twisted nematic liquid crystal spatial light modulator ͑TNLC-SLM͒, we propose and demonstrate a novel amplitude compensated technique. Optical reconstructions of complex digital holograms with higher image quality are discussed in both analytical and experimental results.

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