D. Mergerian

Diamond-Machined Geodesic Lenses In LiNbO3

The application of single point diamond turning to the fabrication of aberration-corrected, aspheric geodesic lenses in LiNb03 for use in integrated optics is reported. F/5 lenses with useful apertures of 4 mm and 5 mm have been produced. Lens profile accuracies ranging between 1.5 and 3 pm total indicator reading and depth accuracies of 0.25 to 2.0 μm have been achieved. The machined surfaces require only light polishing, which produces little effect on the figure accuracy, to remove residual machining marks. Waveguides grown by Ti-indiffusion are found to be characterized by very low scattering losses. Optical image spot sizes of 1.35 to 2.23 times diffraction-limited have been measured for input beam widths of 1.0 to 3.28 mm for a lens in which the edge rounding has not been incorporated into the aspheric correction. The edge rounding has been included in the correction for subsequent lenses.

Geodesic Lens Performance Characteristics

The position of the focal plane, the intensity profile of the first diffraction spot and power losses have been measured for geodesic lenses in Ti-indiffused LiNb03 waveguides. It was intended for the focal plane of a geodesic lens to be situated at a waveguide edge; experimental results have shown that this was achieved to a tolerance of better than 12 im with two of the measured focal planes coinciding with the waveguide edge to within the +2 Inn accuracy of the measurement techniaue. Scans of the intensity profiles of focused diffraction spots have been made for one and two lens systems; the spot sizes in both cases were found to be <1.15 times the diffraction limit at F/12. Throughput losses in geodesic lenses ranged from 2.5 to 17 dB - the larger losses occurring in lenses with small edge rounding and large corrected regions. An analytical program was initiated to determine the various mechanisms responsible for power loss. A simplified model indicates that a significant loss is due to mode mismatch in the vicinity of the edge rounding.

Advanced Integrated Optic Rf Spectrum Analyzer

Efforts to improve upon the reported dynamic range of newly developed integrated optical RF spectrum analyzers center about two separate components. One of these is an efficiently coupled, high power, single mode, narrow-beam-spread GaAlAs laser diode and the other is the photodiode array with its associated read-out circuitry. Recent attempts to realize improvements in both of these components are described, as are the design changes in the spectrum analyzer necessitated by the characteristics of available laser diodes.

Advances In Integrated Optical Spectrum Analyzers

The operating characteristics of a hybrid integrated optical spectrum analyzer and the results of a design analysis performed to permit the development of an improved device are discussed. The existing device incorporates a LiNbO3 substrate, which contains a Ti-indiffused optical waveguide, two near-diffraction-limited geodesic waveguide lenses, and a two-element surface acoustic wave transducer array, and a butt-coupled photodiode array. The optical source is either an end-fire or butt-coupled laser. This unit has been shown to operate over a 400 MHz bandwidth with a resolution which varies from 5.3 MHz for an optical wavelength of 0.6328 μm to 4.0 MHz for 0.83 μm.

Theory Of Geodesic Lenses

The geometrical theory of axially symmetric geodesic lenses is discussed. An algorithm was developed and used to obtain the optimal shape of a lens that is corrected for spherical aberrations. The effects of lens surface distortions on the performance characteristics are determined. For a lens to be near diffraction limited it was found that its ideal shape must be maintained to within 10-4 X lens diameter.

An Integrated Optical Radio Frequency (rf) Spectrum Analyzer

The fabrication and performance of the first operating integrated optical RF spectrum analyzer are described. The device is a three-element hybrid structure consisting of a laser, the I0 substrate, and a photodiode array. It operates over a frequency bandwidth of 400 MHz, centered at 600 MHz, with a complete frame time of 2 psec. Although designed for use with a butt-coupled GaAlAs laser source, it has been tested using an end-fire-coupled HeNe laser. At the Here laser wavelength it divides the 400 MHz frequency band-width among 75 detector elements such that each element represents 5.3 MHz. An RF, input signal dynamic range of at least 18 to 22 dB has been demonstrated, as has the ability to detect two simultaneous pulses of 0.3 µsec duration and 20 MHz frequency separa-tion.

Electron Spin‐Echo Studies of Relaxation Processes in High‐Spin Ferrimyoglobin

The spin‐echo technique is used to study the relaxation processes associated with the trivalent iron ion in horse heart myoglobin at 1.2°K. The destruction of transverse and longitudinal phase memory, as, respectively, measured by the two‐pulse (T2p) and three‐pulse (T3p) echo sequences, is attributed to a spectral diffusion process. Saturation‐recovery data help to affirm this belief. The diffusion process is not dependent upon the concentration of myoglobin in a water solution, which means that it is not dependent upon the Fe3+ concentration (over the range 1017–1019 Fe3+ ions/cc). Moreover, values of T2p and T3p are the same for myoglobin powder as they are for hemoglobin powder. Both of these observations support the conclusion that interactions between the iron spins do not play a major role in the destruction of phase memory; but, rather, that the interaction between the iron magnetic dipoles with the surrounding nuclear moments (particularly the hydrogen nuclei of the water molecule at the sixth li...

Optically implemented residue-number-system processing for large-order systems

Two techniques developed during recent years have significantly enhanced the capabilities of residue-number-system (RNS) based processors to meet the demanding requirements of large- order systems. First, a method of factoring the prime modular subprocessor allows a major reduction in the componentry required to implement a look-up-table (LUT) based processor. Secondly, the use of CORE functions permits a drastic reduction in the number and magnitude of prime moduli required when the processor is applied in the solution of problems with many degrees of freedom. This paper will discuss the use of RNS-based processors in the solution of adaptive antenna problems, the basic drawbacks and the manner in which factored LUTs and CORE functions circumvent these drawbacks.

Optically implemented synthesis of microwave frequencies

An optical approach to the implementation of RF synthesis is described which utilizes the single-sideband feature of acousto-optic modulation to achieve synthesis via the mix-and-divide approach without the use of filters. Alternative approaches to reference signal switching are examined, and their relative advantages evaluated. Preliminary experimental results are presented which demonstrate that the required signal purity and spurious signal suppression can be achieved in the mixing and detection of two AO-modulated beams.

Design and performance of a modulo 61 RNS multiplier/accumulator

The Modulo 61 M/A has been designed using a custom multilayer board, semicustom IC drivers, a light plate, and alignment assembly. A light plate and an accompanying alignment assembly and procedure have been designed to form in excess of 500 optical interconnections at once to interconnect the M/A. A discrete 3 x 3 LUT will perform at 100 MHz; the Modulo 61 M/A will run at between 100 and 200 MHz.