Electro-Optics - Applied Optics Fundamentals and Device Applications - page 7

with relatively few but very complex processors. Progressing to the right,
the number of processors per system increases, until it reaches a neural net-
work requiring millions of processors, but of much lower complexity than
the Von Neumann case. Looking at Figure 2.2, it becomes apparent that as
the number of processors increases, the number and complexity of intercon-
nects within the system increases dramatically. In fact, on the far right of
the scale, the interconnects become an integral part of the computing archi-
tecture, and the boundary between the processors and the interconnects
becomes blurred.
2.2 OpticalDeviceApplications
The purpose of this section is to examine recent advances in GaAs technol-
ogy with respect to optics applications and fabrication requirements. It will
be seen that, by integrating GaAs devices and fabrication techniques into the
design and development of optical circuits, many of the problems that could
hinder the production of reliable and high-speed optical structures may be
overcome.
Initial circuits designed were for the S to X bands, but the range of MMIC
applications has now been extended as low as 50 MHz and as high as
100 GHz [7]. Frequency ranges through UHF will most likely make more use
of the presently available high-speed integrated circuit silicon-based tech-
nologies than the MMIC technology. MMIC will be used in a wide variety of
electronic warfare applications, such as decoys and jammers, and in phased
array radars. In the commercial markets, there will be uses for MMIC tech-
nology in consumer communications' products and automotive sensors and
global positioning systems. Satellite systems will be redesigned using large-
scale integration and MMIC techniques to improve reliability and increase
functional capacity. One of the applications of optics technology to micro-
wave systems that has received a great deal of attention in the past few years
is the use of fiber-optic modules and feed structures to replace the large and
unwieldy feed structures of past phased array radar systems. The phased
array technology is described in Section 2.2.1.
2.2.1 Phased Array Radar
The key item that distinguishes phased array radar from other radars is the
distributed antenna configuration. The existence of an antenna array does
not necessarily indicate a phased array. As defined by Liao [8], a phased
array is an antenna array whose main beam maximum direction or pattern
shape is controlled primarily by the relative phase of the element excitation
currents. As an example, consider Figure 2.3 depicting a simple linear array