Comparative efficiency analysis of fiber-array and conventional beam director systems in volume turbulence.

The performance of two prominent laser beam projection system types is analyzed through wave-optics numerical simulations for various atmospheric turbulence conditions, propagation distances, and adaptive optics (AO) mitigation techniques. Comparisons are made between different configurations of both a conventional beam director (BD) using a monolithic-optics-based Cassegrain telescope and a fiber-array BD that uses an array of densely packed fiber collimators. The BD systems considered have equal input power and aperture diameters.

Target-in-the-loop remote sensing of laser beam and atmospheric turbulence characteristics.

A new target-in-the-loop (TIL) atmospheric sensing concept for in situ remote measurements of major laser beam characteristics and atmospheric turbulence parameters is proposed and analyzed numerically. The technique is based on utilization of an integral relationship between complex amplitudes of the counterpropagating optical waves known as overlapping integral or interference metric, whose value is preserved along the propagation path. It is shown that the interference metric can be directly measured using the proposed TIL sensing system composed of a single-mode fiber-based optical transceiver and a remotely located retro-target.

Speckle-metric-optimization-based adaptive optics for laser beam projection and coherent beam combining.

Maximization of a projected laser beam's power density at a remotely located extended object (speckle target) can be achieved by using an adaptive optics (AO) technique based on sensing and optimization of the target-return speckle field's statistical characteristics, referred to here as speckle metrics (SM). SM AO was demonstrated in a target-in-the-loop coherent beam combining experiment using a bistatic laser beam projection system composed of a coherent fiber-array transmitter and a power-in-the-bucket receiver. SM sensing utilized a 50 MHz rate dithering of the projected beam that provided a stair-mode approximation of the outgoing combined beam's wavefront tip and tilt with subaperture piston phases.

Obscuration-free pupil-plane phase locking of a coherent array of fiber collimators.

Control methods and system architectures that can be used for locking in phase of multiple laser beams that are generated at the transmitter aperture plane of a coherent fiber-collimator array system (pupil-plane phase locking) are considered. In the proposed and analyzed phase-locking techniques, sensing of the piston phase differences is performed using interference of periphery (tail) sections of the laser beams prior to their clipping by the fiber-collimator transmitter apertures. This obscuration-free sensing technique eliminates the need for a beam splitter being directly located inside the optical train of the transmitted beams--one of the major drawbacks of large-aperture and/or high-power fiber-array systems.

Laser beam projection with adaptive array of fiber collimators. II. Analysis of atmospheric compensation efficiency.

We analyze the potential efficiency of laser beam projection onto a remote object in atmosphere with incoherent and coherent phase-locked conformal-beam director systems composed of an adaptive array of fiber collimators. Adaptive optics compensation of turbulence-induced phase aberrations in these systems is performed at each fiber collimator. Our analysis is based on a derived expression for the atmospheric-averaged value of the mean square residual phase error as well as direct numerical simulations.

Laser beam projection with adaptive array of fiber collimators. I. Basic considerations for analysis.

We present a mathematical model and provide an analysis of optical beam director systems composed of adaptive arrays of fiber collimators (subapertures), referred to here as conformal optical systems. Performances of the following two system architectures are compared: A conformal-beam director with mutually incoherent output laser beams transmitted through fiber collimators (beamlets), and a corresponding coherent system whose beamlets can be coherently combined (phase locked) at a remote target plane. The effect of the major characteristics of the conformal systems on the efficiency of laser beam projection is evaluated both analytically and through numerical simulations.

Detection and tracking of small moving objects in image sequences by use of nonlinear spatiotemporal optical systems.

We demonstrate the capability of localized structures of spatiotemporal nonlinear optical systems for detection and tracking of small moving objects. Such nonlinear dynamics based image-processing systems are readily implemented using an existing parallel optoelectronic architecture designed for real-time operation.