E.A. Ash

Holographic coupler for integrated optics

Coupling optical energy into an integrated optical circuit is essentially a problem of mode conversion from a Gaussian laser beam to the specific mode of waveguide excitation desired. This paper describes preliminary experimental results obtained with couplers in which mode conversion is performed by holographic wave‐shaping techniques.

Microwave Scanning Microscopy for Non-Destructive Testing

A microwave scanning microscope capable of detecting and locating defects in a metal surface is described. Using a technique to obtain super-resolution, previously described, the instrument has proved capable of resolving gratings with periods of ¿/200, and of detecting fatigue cracks less than 2¿ in width.

Analysis of punch-through-injection for a transit-time negative resistance diode†

The non-linearity of the punch-through-injection characteristic is used for the realization of a transit-time microwave oscillator diode. By modulating the height of a potential barrier situated at one end of the drift region of the device, a sharp injection of charge is effected periodically, but without the multiplication noise inherent in the operation of the avalanche transit-time diode. The injected charge, including the effect of mobile space-charge, and the resulting external circuit current, are analysed numerically, using a simplified three-layer silicon PNP structure. It is shown that it is possible to achieve efficiencies of the order of 10%.

Scanning Acoustic Microscopy of Solid Objects Using Aspheric Lenses

Acoustic microscopes are able to image regions within an opaque material. This characteristic is of particular value for a range of NDE problems, including those arising in metal and semiconductor components. Solids have a substantially higher velocity and impedance than water, a fact which implies potentially severe problems in high resolution imaging. The planar interface between the water and the object results in a foreshortening of the focal distance as well as in severe aberrations. Both effects can be seen in the example presented in Figure 1, which shows a ray optics diagram for the case when the velocity ratio, (relative to water) for the lens material is 4.3 and for the object material 3.1. The outer rays from the lens are totally internally reflected; the spherical aberration is severe. Though not apparent from such a ray diagram there is also a considerable amount of apodization arising from the lower efficiency of longitudinal wave transmission for rays with large angles of incidence. It is apparent that this situation implies a substantial degradation of the imaging performance1.

Acoustic and Thermal Wave Microscopy

A decade has elapsed since the emergence of a new form of acoustic microscopy pioneered by Lemons and Quate1 ; in the meantime awareness of the potentiality of this imaging technique has grown rapidly whilst the performance has progressed first to rival the resolution of the optical microscope and then, to exceed it2. There now exists a vast literature to which a number of recent review papers3 provide a helpful guide.

Measurement of Surface Acoustic Wave Slowness Surfaces

In a previous publication(1), we reported a technique whereby the slowness surfaces of acoustic surface waves could be measured over a wide angular range. Although simple theoretical considerations predicted attainable accuracies of a few parts in lO5, the accuracies achieved were rather modest owing to various experimental difficulties. In this communication we present recent results which demonstrate a significant improvement in the accuracy; accuracies of a few parts in lO4 have been achieved using sample lengths of 400 wavelengths.

Applied Acoustic Surface Waves - a Current Assessment

The current status of several classes of acoustic surface wave components are examined with a particular view to assessing their probable impact on microwave systems design.