Imaging Hidden Objects with Spatial Speckle Intensity Correlations over Object Position.

We present a coherent optical method for wavelength-resolution imaging of moving objects hidden within thick randomly scattering media. Spatial speckle intensity correlations as a function of object position are shown to provide access to the spatially dependent dielectric constant of the moving object. This speckle correlation imaging method yields field-based information previously inaccessible in heavily scattering environments. Proof of concept experimental results show excellent agreement with the theory. This new imaging approach will be valuable in high resolution imaging in tissue and other scattering environments where natural motion occurs or the object position can be controlled.

Zero-mean circular Bessel statistics and Anderson localization.

We demonstrate that a circular Bessel density function describes the electromagnetic field statistics in the Anderson localization regime using example numerical terahertz field data in strongly scattering media. This density function for localized fields provides a measure that allows identification and description in a manner akin to the Gaussian density function for weakly interacting scatterers, the mathematical framework to date for statistical optics. Our theory provides a framework for improved understanding of wave propagation in random media, random scattering media characterization, and imaging in and through randomly scattering media.

Imaging optical fields through heavily scattering media.

Coherent imaging and communication through or within heavily scattering random media has been considered impossible due to the randomization of the information contained in the scattered electromagnetic field. We report a remarkable result based on speckle correlations over incident field position that demonstrates that the field incident on a heavily scattering random medium can be obtained using a method that is not restricted to weak scatter and is, in principle, independent of the thickness of the scattering medium. Natural motion can be exploited, and the approach can be extended to other geometries. The near-infrared optical results presented indicate that the approach is applicable to other frequency regimes, as well as other wave types. This work presents opportunities to enhance communication channel capacity in the large source and detector number regime, for a new method to view binary stars from Earth, and in biomedical applications.

Circular Bessel statistics: derivation and application to wave propagation in random media.

We present a family of circular Bessel probability density functions that are capable of describing the intensity, amplitude, and field statistics of waves in any random medium, with only the assumption of circularity. The well-known zero-mean circular Gaussian statistics break down in the Anderson localization and the weakly scattering regimes, where the field can no longer be regarded as the sum of a multitude of independent random phasors. We find that in such scenarios circular Bessel statistics apply because the field can be modeled as a random phasor sum with a random number of contributing phasors. The validity of our density functions is verified through numerical simulations of electromagnetic waves propagating in 2D random media. Having a set of density functions that work in all scattering regimes provides a framework for modeling wave propagation in random media, facilitating random media characterization, imaging in and through scatter, and random laser design.

Temporal response of surface-relief fiber Bragg gratings to high temperature CO2 laser heating.

The authors use a fiber sensor integrated monitor (FSIM) as a fully functioning system to characterize the temporal response of a surface-relief fiber Bragg grating (SR-FBG) to temperature heating above 1000 degrees C. The SR-FBG is shown to have a rise time of about 77 ms for heating and a fall time of about 143 ms for cooling. The FSIM also provides full spectral scans at high speed that can be used to gain further insights into the temperature dynamics of a given system.

Compact optical fiber sensor smart node.

We present a new optical fiber sensor interrogator specifically designed for an embedded instrumentation system. The proposed system consists of a super luminescent diode as a broadband source, a high speed tunable micro-electro-mechanical system (MEMS) filter, photodetector, and an integrated microprocessor for data aggregation, processing, and communication. The entire system is integrated together in a compact package to create a fiber "smart" sensor. The system is capable of interrogating a variety of multiplexed fiber sensors, processing the data, and communicating the results digitally. As an example, the system has been calibrated with an array of fiber Bragg grating sensors.