Twin-Image-Free Holography: A Compressive Sensing Approach.

Holographic reconstruction is troubled by the phase-conjugate wave front arising from Hermitian symmetry of the complex field. The so-called twin image obfuscates the reconstruction in solving the inverse problem. Here we quantitatively reveal how and how much the twin image affects the reconstruction and propose a compressive sensing (CS) approach to reconstruct a hologram completely free from the twin image. Using the canonical basis, the incoherence condition of CS is naturally satisfied by the Fourier transformation associated with wave propagation. With the propagation kernel function related to the distance, the object wave diffracts into a sharp pattern while the phase-conjugate wave diffracts into a diffuse pattern. An iterative algorithm using a total variation sparsity constraint could filter out the diffuse conjugated signal and overcome the inherent physical symmetry of holographic reconstruction. The feasibility is verified by simulation and experimental results, as well as a comparative study to an existing phase retrieval method.

Analysis of light-emission enhancement of low-efficiency quantum dots by plasmonic nano-particle.

In this paper, a nano-pillar array integrated near quantum dots (QDs), which serves as a Purcell cavity as well as a column antenna, is studied in order to enhance the spontaneous emission (SE) rate of low emission efficiency QDs. A systematic analysis for treating the isolated nano-pillar and loose ordered pillar is demonstrated by solving the electromagnetic field equations. As an illustrative example of potential applications, we proposed a new structure that Germanium (Ge) QDs are located in close proximity to the isolated Indium Tin Oxide (ITO) nano-pillar to raise its efficiency. From the results of numerical calculation, it is predicted that ITO pillars with slim (e.g., the radius is 25 nm and the height is 500 nm) and flat morphology (e.g., the radius is 40 nm and the height is 60 nm) exhibit superior enhancement over 20 folds. Finite difference time domain (FDTD) simulation is utilized for demonstrating the distinctive enhancement when QDs radiate at surface plasmonic resonance frequency of ITO nano-pillar. It can be found that the QDs emission enhancement profile accords with our results obtained from numerical analysis.

Scintillation index and performance analysis of wireless optical links over non-Kolmogorov weak turbulence based on generalized atmospheric spectral model.

Based on the generalized spectral model for non-Kolmogorov atmospheric turbulence, analytic expressions of the scintillation index (SI) are derived for plane, spherical optical waves and a partially coherent Gaussian beam propagating through non-Kolmogorov turbulence horizontally in the weak fluctuation regime. The new expressions relate the SI to the finite turbulence inner and outer scales, spatial coherence of the source and spectral power-law and then used to analyze the effects of atmospheric condition and link length on the performance of wireless optical communication links.

Average capacity of free-space optical systems for a partially coherent beam propagating through non-Kolmogorov turbulence.

The performance of partially coherent free-space optical links is investigated in the moderate to strong fluctuation regime of non-Kolmogorov turbulence. The expressions for large- and small-scale log-irradiance flux variance are obtained in non-Kolmogorov turbulence. By employing the gamma-gamma distribution of irradiance fluctuations, the effects of spatial coherence of the source, index of non-Kolmogorov spectrum, and size of the receiver on channel capacity for horizontal links are discussed. Results show that channel capacity presents fluctuating behaviors with the variation of alpha for longer links and increases for alpha values higher than 11/3.