Computational ghost imaging is a structured-illumination active imager coupled with a single-pixel detector that has potential applications in remote sensing. Here we report on an architecture that acquires the two-dimensional spatial Fourier transform of the target object (which can be inverted to obtain a conventional image). We determine its image signature, resolution, and signal-to-noise ratio in the presence of practical constraints such as atmospheric turbulence, background radiation, and photodetector noise. We consider a bistatic imaging geometry and quantify the resolution impact of nonuniform Kolmogorov-spectrum turbulence along the propagation paths. We show that, in some cases, short-exposure intensity averaging can mitigate atmospheric-turbulence-induced resolution loss. Our analysis reveals some key performance differences between computational ghost imaging and conventional active imaging, and identifies scenarios in which theory predicts that the former will perform better than the latter.

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Computational Ghost Imaging for Remote Sensing

Optical wireless communication (OWC) is gaining acceptance in an increasing number of sectors of science and industry, owing to its unique combination of features: extremely high bandwidth, rapid deployment time, license- and tariff-free bandwidth allocation, and low power consumption, weight, and size. However, the major drawback of OWC in terrestrial applications is the threat of downtime caused by adverse weather conditions, such as fog and haze. Several researchers have proposed and developed communication systems that use far-IR radiation to mitigate weather effects. In this study we analyze the performance of a short-distance terrestrial OWC system as a function of wavelength. A mathematical model for OWC link performance is derived. Using this model, we perform a simulation of our system under different weather conditions. From the results of our calculations, the improvement of link availability for 10 µm compared with 0.785–1.55 µm for a distance of 1-km propagation is 0.2% (99.6–99.8%). This modest improvement should be considered relative to the complexity and cost of quantum cascade laser transmitters and far-IR receivers.

Performance of an optical wireless communication system as a function of wavelength.

Communication theory applied to lightwave channels is ordinarily carried out using the semiclassical theory of photodetection. Recent development of nonclassical light sources-whose photodetection statistics require the use of quantum theory-plus increasing interest in optics-based approaches to quantum information processing necessitates a thorough understanding of the similarities and distinctions between the semiclassical and quantum theories of optical communications. This paper is addressed to that need, focusing, for convenience, on the free-space communication channel using Gaussian states of light. The quantum version of the Huygens-Fresnel diffraction integral is reviewed, along with the semiclassical and quantum theories of direct, homodyne, and heterodyne detection. Maximally entangled Gaussian state light is used, in conjunction with quantum photodetection theory, to explain the nonclassical effects seen in Hong-Ou-Mandel interferometry and violation of the Clauser-Horne-Shimony-Holt form of Bell's inequality. The classical information capacities of several bosonic channels are reviewed, and shown to exceed what can be achieved using conventional optical receivers.

The Quantum Theory of Optical Communications

This paper is concerned with the mitigation of simple contrast loss due to added lightness in an image. This added lightness has been referred to as "airlight" in the literature since it is often caused by optical scattering due to fog or mist. A statistical model for scene content is formulated that gives a way of detecting the presence of airlight in an arbitrary image. An algorithm is described for estimating the level of this airlight given the assumption that it is constant throughout the image. This algorithm is based on finding the minimum of a global cost function and is applicable to both monochrome and color images. The method is robust and insensitive to scaling. Once an estimate of airlight is achieved, then image correction is straightforward. The performance of the algorithm is explored using the Monte Carlo simulation with synthetic images under different statistical assumptions. Several examples of before and after color images are given. Results with real video data obtained in poor visibility conditions indicate frame-to-frame consistency of better than 1% of maximum level

Correction of Simple Contrast Loss in Color Images

P-i-N (PIN) diodes and avalanche photo-diodes (APD) are the most commonly used photo-detectors in terrestrial FSO systems. In this paper, we review the photo-detection process for the cases of PIN- and APD-based receivers and provide a comprehensive study of different noise sources that affect signal detection in an FSO system. We present a complete and precise model for the receiver noise by taking different receiver parts into account. In particular, we study the impact of thermal, shot, background, and transmitter noises on the receiver performance by considering practical and realistic case studies. We bring clearance on the impact of the interaction of signal and background noise due to non-linear characteristic of the photo-detector, and on the role of the trans-impedance load resistance. We discuss the dominant noise components for the cases of using a PIN or an APD, and compare their performances at the presence or not of background radiations.

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Impact of different noise sources on the performance of PIN- and APD-based FSO receivers

The origin and magnitude of the several kinds of background noise that perturb optical communication receivers are discussed, including background radiation sources viewed directly, radiation reflected from background objects, and radiation scattered by the atmosphere into the receiver field of view. An extensive bibliography on this topic is presented.

J. Bordogna

Papers

Background noise in optical communication systems