A design method is presented for computing the phase functions of an energy efficient system using two holographic elements for converting a Gaussian beam into a uniform beam with rectangular support in the far field of the source. The method is based on a modification of the Gerchberg-Saxton algorithm which includes an x-y separability constraint on the phase of one of the holographic elements. A beamforming system was fabricated using this method, and experimental results were obtained which support the design approach.

No abstract

A new indoor SAL (synthetic aperture LADAR) test range is described that uses a pulsed CO2 TEA laser as the transmitter source.This monostatic range can be used to produce high -resolution 3 -D synthetic aperture (range -Doppler) images of targets. The SAL is a homodyne based receiver system that uses a long path reference signal with a frequency offset generated via an acousto -optic cell. The TEA laser is a multicavity system that is stepped through a series of single frequencies to obtain the ranging information. The transmission frequencies are monitored and controlled by heterodyning part of the transmission signal against a stable low-pressure CW CO2 laser. Azimuth (Doppler) information is generated by stepping through a series of angles on a gimbaled transmit /receive mirror. The target and SAL are mounted on different vibration isolated tables. Motion monitoring interferometers between the tables furnish motion compensation data for the image processing stage while range variations are automatically corrected during data gathering. The TEA laser is run at up to 100 pulses per second.Both the received pulse and the transmitted pulse are recorded by a high speed wavefrom digitizer system. This data, along with motion compensation and reference data, is used to produce imagery via Fourier transform based processing.

Serial transmission of image data through an optical fiber is inefficient in the utilization of the channel capacity of the fiber. Parallel image transmission techniques, on the other hand, generally limit the transmission length to a few meters. A novel approach is introduced with which 2-D image data can be transmitted efficiently at high speed over a single optical fiber using wavelength-time multiplexing. Several system configurations designed for different types of input are presented.

No abstract