Coherent effects and aperture averaging in retroreflected light

Mahon, Rita; Rabinovich, William S.; Burris, H. R.; Ferraro, Mike S.; Freeman, Wade T.; Moore, Christopher I.; Murphy, James L.; Suite, Michele R.; Wasiczko, Linda M.

doi:10.1117/12.691317

Cited by 6 publications

(6 citation statements)

References 5 publications

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“…The measured data obtained during this set of experiments correlate well with previously reported experimental work that examines retroreflected light [11,19]. Factors that make this work unique are that this work includes results for retroreflected light at varied levels of optical turbulence as measured by the Rytov variance, to include levels of turbulence that are expected for typical detection scenarios, as well as results for a focused optical system in order to examine applicability to varied optical targets of interest.…”

Section: Discussionmentioning

confidence: 51%

Measured statistics of retroreflected 1064 nm laser light in atmospheric turbulence

Cole

Zacherl

Delong

2010

Journal of Modern Optics

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Detection of optical targets using laser illumination has become an increasingly valuable military tool. In order to better understand typical detection scenarios for a laser illumination system and to improve target detection performance, intensity probability density functions of retroreflected near-infrared laser light were experimentally measured over a near-ground line-of-sight optical path. Returns from a corner cube and a simple lens-mirror system were recorded under a variety of atmospheric conditions, as measured by changes in the refractive-index structure parameter C 2 n . In addition to its applicability to target detection, this work is relevant to atmospheric propagation research and to free-space laser communication studies.

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Section: Discussionmentioning

confidence: 51%

Measured statistics of retroreflected 1064 nm laser light in atmospheric turbulence

Cole

Zacherl

Delong

2010

Journal of Modern Optics

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“…Since atmospheric turbulence in maritime environments is best suited for free space laser communications when wind speeds are low and the difference between air and water temperature is minimal, it is important to note the conditions experienced on both days. [3][4][5] On April 29 th , wind speeds were sustained at 9 m/s with a 4.5ºC difference in air/water temperatures, conditions that produced moderate amounts of turbulence. The plot in Figure 6 shows the pronounced atmospheric effect on each channel of the array during this day of testing.…”

Section: Field Testingmentioning

confidence: 99%

Large area adaptive avalanche photodetector arrays for free-space optical communication

Ferraro

Freeman²,

Mahon

et al. 2008

SPIE Proceedings

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In free space optical communication systems, atmospheric turbulence makes it very difficult to focus transmitted laser power onto small, low capacitance photodetectors. The obvious challenge, therefore, is to take advantage of larger area photodiodes without sacrificing a great deal of bandwidth and sensitivity in the process. In this work, we report on a high sensitivity, high speed adaptive avalanche photodetector array for free-space optical communication. The receiver consists of a 2×2 InGaAs APD array with each 100um element in the array having its own dedicated trans-impedance amplifier and buffering stage. The corresponding voltage outputs for each element are processed through a four channel digital, fast switching and summation circuit. The resulting signal is selectable to be either that of the element in the array with the greatest signal response or the sum of multiple or all channels. Design requirements, laboratory sensitivity measurements, and field testing results are presented.

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“…Physically it means that the spot size at the fiber face should not be much wider or narrower than the fiber width, or equivalently at the entrance plane the projected mode width should be close to the pupil size. Deriving equations (9) we assumed that all quadratic phase terms are compensated by the coupler lens, i.e. coupler focuses the wave at the fiber face.…”

Section: Wave-to-fiber Couplermentioning

confidence: 99%

“…Optimization of the entrance pupil can be extended to the case when turbulence is present. We use equation (13) and Gaussian model (8) and (9) to calculate the coupling efficiency for the quadratic structure function, 2 = γ in equation (21) as follows:…”

Section: Optimizing the Average Coupling Efficiencymentioning

confidence: 99%

“…A number of recent papers [1][2][3][4][5][6][7][8][9][10][11][12][13][14] discussed the issues related to the performance of the Free-Space Optical Communication Systems (FSO) in the turbulent atmosphere. In the literature the emphasis is made on the mitigating the signal fading due to the turbulence-induced fluctuation by the aperture averaging of the scintillations or spatial diversity.…”

Section: Introductionmentioning

confidence: 99%

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Coupling turbulence-distorted wave front to fiber: wave propagation theory perspective

Charnotskii

2010

Free-Space Laser Communications X

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We use the results of the theory of wave propagation in turbulence to analyze the effects of the atmospheric turbulence on the Free-Space Optical Communication systems under weak and strong scintillation conditions. We found that for the traditional fiber coupling arrangement statistics of the Power-in-Fiber (PIF) is sensitive to the phase fluctuation at the collecting aperture, rather than amplitude fluctuation (scintillation). Larger receiving aperture produces stronger PIF fluctuation. Similar to the scintillation of the sharp focused beams second-order scattering dominates PIF fluctuation for the weak and strong scintillation conditions. This should have serious effect on the probability distribution of the PIF.A new coupling arrangement is suggested that alleviates the destructive effect of the phase fluctuation, and allows the use of large receiving apertures. The trade-off is the decreased coupling efficiency. For our new coupling scheme the PIF fluctuation is determined by the power flux fluctuation through the collecting aperture. This allows taking advantage of the scintillation averaging effect to suppress the fading. We review the results of the rigorous Markov-approximationbased theory of the scintillation averaging that is valid both for a weak and strong scintillation conditions. This technique reveals several distinct regimes of the power flux fluctuation including the situation where fluctuation is relatively small, but is not described by the perturbation (Rytov's) theory. We also show how the energy conservation principle inherent to the wave propagation in the clear air turbulence provides an accelerated rate of the scintillation averaging compare to the typical averaging estimates.

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Coherent effects and aperture averaging in retroreflected light

Cited by 6 publications

References 5 publications

Measured statistics of retroreflected 1064 nm laser light in atmospheric turbulence

Measured statistics of retroreflected 1064 nm laser light in atmospheric turbulence

Large area adaptive avalanche photodetector arrays for free-space optical communication

Coupling turbulence-distorted wave front to fiber: wave propagation theory perspective

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