In this paper, we present the recent development of a conformal optical system with three adaptive phase-locked fiber elements. The coherent beam combining based on stochastic parallel gradient descent (SPGD) algorithm is investigated. We implement both phase-locking control and wavefront phase tip-tilt control in our conformal optical system. The phase-locking control is performed with fiber-coupled lithium niobate phase shifters which are modulated by an AVR micro-processor based SPGD controller. The perturbation rate of this SPGD controller is ~95,000 iterations per second. Phase-locking compensation bandwidth for phase distortion amplitude of 2π-radian phase shift is >100Hz. The tip-tilt control is realized with piezoelectric fiber positioners which are modulated by a computer-based software SPGD controller. The perturbation rate of the tip-tilt SPGD controller is up to ~950 iterations per second. The tip-tilt compensation bandwidth using fiber positioners is ~10Hz at 60-μrad. jitter swing angle.
A newly developed adaptive optical transceiver telescope is used to investigate the possibility of correcting wavefront
aberrations under strong atmospheric turbulence conditions over a distance of several kilometers. A fiber laser is
connected to a fiber positioner within the telescope, which acts as a transmitter by sending laser light at wavelength 1550
nm through the turbulent air to a retro reflector mounted on the top of a water tower at a distance of 2.33 km. The
reflected laser light is received by the telescope -(acting this time as a receiver) and focused onto the fiber tip. The light
picked up by the fiber is - guided to a photo detector by means of a fiber splitter. The signal from the photo detector is
recorded by a PC and used as feedback signal for the adaptive optics controller, which controls the fiber-tip positioner
as well as an six-channel adaptive mirror using a stochastic parallel gradient descent optimization algorithm.
Experimental results are reported in this paper.
We present the design and evaluation of compact adaptive optical antennas with apertures diameters of 16 mm and
100 mm for 5Gbit/s-class free-space optical communication systems. The antennas provide a bi-directional optically
transparent link between fiber-optical wavelength-division multiplex systems and allow for mitigation of atmospheric-turbulence
induced wavefront phase distortions with adaptive optics components. Beam steering is implemented in the
antennas either with mirrors on novel tip/tilt platforms or a fiber-tip positioning system, both enabling operation
bandwidths of more than 1 kHz. Bimorph piezoelectric actuated deformable mirrors are used for low-order phase-distortion
compensation. An imaging system is integrated in the antennas for coarse pointing and tracking. Beam
steering and wavefront control is based on blind maximization of the received signal level using a stochastic parallel
gradient descent algorithm. The adaptive optics control architecture allowed the use of feedback signals provided locally
within each transceiver system and remotely by the opposite transceiver system via an RF link. First atmospheric
compensation results from communication experiments over a 250 m near-ground propagation path are presented.
Real time wavefront control for adaptive laser communication and imaging system requires fast measurement of image quality.
Statistical analysis of speckle field provides effective image quality criteria for adaptive correction of phase-distorted images. We propose an analog continuous time VLSI (very-large-scale-integration) spectrum analysis chip to provide such a real time image quality measurement. The chip takes the signal sensed by a photo detector which is located in the speckle field as analog input and computes its spectrum distribution continuously. Experiment and analysis on distorted laser beam was conducted with the analog spectrum analysis chip. Target-in-the-loop system is under development to demonstrate the capability of real time adaptive imaging
The propagation of IR radiation through the marine boundary layer is very much dependent on vertical temperature gradients. Due to the Air-Sea Temperature Difference (ASTD) the distance to the visible horizon for an imaging system can be shorter (ASTD < 0) or larger (ASTD > 0) than the distance to the geometric horizon. To analyse these phenomena FGAN-FOM took measurements in the mid and long wave IR. Location of the experiment was the Baltic Sea. A ship, equipped with IR point sources, was tracked while it was sailing in and out up to, and beyond, the horizon. Weather conditions during the measurement period showed interesting variations in ASTD and atmospheric turbulence (see paper 4884-11). Especially strong sub-refractive effects have been observed with ASTDs up to -5.0 °C. This paper deals with the analysis of the detection range of point targets under different meteorological conditions. Experimental results are compared with the propagation model IRBLEM (IR Boundary Layer Effects Model) which was developed by DRDC-RDDC - Valcartier, Canada.