Comparison of maritime measurements of 2 with NAVSLaM model predictions.

In this paper, a study is made of the refractive index structure parameter 2, as derived from angle-of-arrival (AOA) measurements made on the beam after propagation along a 16 km slant path across the Chesapeake Bay. These measurements are compared with 2 estimates derived from the Navy Atmospheric Vertical Surface Layer Model (NAVSLaM), which are based upon prevailing meteorological conditions. Correlation coefficients for the reported data vary between 0.

Free space quantum key distribution using modulating retro-reflectors.

Quantum key distribution (QKD) can be used to produce a cryptographic key whose security is guaranteed by quantum mechanics. The range of fiber-based QKD links is limited, by loss, to a few hundred kilometers, and cannot be used between mobile platforms. Free space QKD can, in principle, overcome these limitations.

Irradiance correlations in retro-reflected beams.

Communications links that utilize modulating retro-reflectors can make use of turbulence-induced fade information available at the remote data-signal terminal in order to optimize the data transfer rate. Experiments were conducted to measure the irradiance in both the direct and the retro-reflected beams. Both on-axis and off-axis components were recorded in order to further study the enhancement in the scintillation index observed in the retro-reflected beam.

InAlAs/InGaAs avalanche photodiode arrays for free space optical communication.

In free space optical communication, photodetectors serve not only as communications receivers but also as position sensitive detectors (PSDs) for pointing, tracking, and stabilization. Typically, two separate detectors are utilized to perform these tasks, but recent advances in the fabrication and development of large-area, low-noise avalanche photodiode (APD) arrays have enabled these devices to be used both as PSDs and as communications receivers. This combined functionality allows for more flexibility and simplicity in optical system design without sacrificing the sensitivity and bandwidth performance of smaller, single-element data receivers.

Atmospheric turbulence effects measured along horizontal-path optical retro-reflector links.

The scintillation measured over close-to-ground retro-reflector links can be substantially enhanced due to the correlations experienced by both the direct and reflected echo beams. Experiments were carried out at China Lake, California, over a variety of ranges. The emphasis in this paper is on presenting the data from the 1.

Probability density of irradiance fluctuations observed over terrestrial ranges.

The irradiance fluctuations imposed on a laser beam that has propagated over horizontal terrestrial paths in the range of 2 to 24 km are compared to lognormal (LN) and gamma-gamma (GG) distributions. For the direct links reported here the irradiance fluctuations follow a LN distribution except in cases of weak turbulence, characterized by a scintillation index of less than 1 and a Fried parameter larger than the receiver aperture, in which case the GG distribution gives an improved fit. In very weak turbulence the difference between the two distributions is insignificant.

Waveguide micro-opto-electro-mechanical resonant chemical sensors.

We demonstrate a silicon micro-opto-electro-mechanical sensor based on mass-loading of a chemo-selective polymer coated onto a microbridge. The sensor is probed optically using an on-chip waveguide Fabry-Pérot interferometer for high resolution displacement and resonant frequency measurement. The mechanical resonator is designed with paddles to simplify chemo-selective polymer deposition and to minimize any strain effects from the polymer during analyte sorption.