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We discuss the previously-reported measurements of a three-beam nulling interferometer without achromatic phase-shifters, using delay lines only. The theoretical rejection ratio of a few thousand has not been achieved experimentally. In order to explain the obtained results, some direct spectral and polarization measurements have been performed. We present here the latest results and discuss some asymmetries in the interference patterns., Optics Research Groep, Applied Sciences

We present a new type of nulling interferometer that makes use of polarization properties to have on-axis destructive interference. The proposed design, which only involves commercial components and no achromatic device, is also suitable for internal modulation. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We implemented that concept on a two-beam white-light interferometer and we present here the first experimental results, Optics Research Groep, Applied Sciences

We present results of experiments obtained using a new nulling technique that enables deep nulling without the use of achromatic phase shifters. The experimental set-up consists of a three-beam interferometer that should provide a nulling depth of several thousands over a wavelength range of 500 to 650 nm. The intended depth of null was not achieved and further experiments on determining the spectrum of each beam revealed why. We describe a method of obtaining accurate beam spectra in a multi-beam interferometer. The insights on the need of spectral shape control were tested with our nulling theory and proved the sensitivity of this nulling approach with respect to spectral mismatches., Imaging Science and Technology, Applied Sciences

An interferometric fiber optic gyroscope employing an integrated, width polished, optic chip containing annealed proton exchange waveguides and a Mach-Zehnder interferometer for sensing a ramp induced signal from loop closing electronics to achieve a highly improved gyroscope scale factor linearity and dynamic range. An edge light emitting diode (ELED) operating at 1.3 micron wavelength is employed as the light source in the gyroscope. A decorrelator optical fiber segment is employed between the light source and the chip, and a Lyot depolarizer optical fiber segment is employed between the chip and one side of the fiber optic coil. Also, an intermediate output of the loop closing electronics is shown to have reduced scale factor sensitivity to light source wavelength change., Supersedes PAT-APPL-534 202-90.

The Phase I in-house effort to develop an optical processor as an electronic counter-counter-measure for radar multipath is discussed. The closed loop system demonstrates the ability to achieve a 15.2+/-2.4 dB adaptive cancellation of a single tone, single delay jamming signal over a 1-5 MHz bandwidth. The open loop optical system proves capable of providing a 30.2+/-3.9 dB cancellation of the same signal when using operator provided information. Key elements of this project include the characterization and selection of a spatial light modulator (SLM) system and the development of a software package which assists the minimization process. This has resulted in the novel use of a two dimensional binary SLM to perform as an enhanced grey scale one dimensional SLM. Additionally, an acousto-optic (AO) deflector has been demonstrated to provide the grey level dynamic range and spatial resolution required by the system. The results of this single channel testbed will be used in the future development of a multichannel optical processor., Prepared in collaboration with COLSA Inc., Huntsville, AL, rept. no. P9-H010.

The radiation pattern of the Completely Overlapped Subarray Antenna can be calculated. Knowledge of the phase and amplitude of the contribution from each element can be used to determine an appropriate weight for each element to achieve a desired pattern. The 16 feed elements on Face B of the antenna allow pattern control at 15 discrete points in the pattern. Success in using this method requires an accurate determination of the individual element contributions. Random phase and amplitude errors cannot be sensed, and, therefore, cannot be compensated for. If the approximate angles of arrival of jamming signals are known, and the number of jammers is smaller than the number of elements in the locating array, a tan loop behind each element can determine the noise covariance matrix. A quiescent noise power level is assumed, and the adjoint of the matrix calculated. When discontinuities occur in the pattern, they indicate the directions of arrival for jamming signals. The pattern of the Overlapped Subarray Antenna may then be changed to place nulls in the directions of the jammers. (Author)

An analysis is performed of nulling in linear array patterns subject to minimization of the weight perturbation. Both combined amplitude and phase perturbation, and phase-only perturbation are treated. The solutions obtained are interpreted in terms of cancellation beams superimposed on the initial pattern. (Author)