Electro-Optics - Applied Optics Fundamentals and Device Applications - page 5

2
Electro-Opt ics
2.1 Introduction
Developing communication, instrumentation, sensors, biomedical, and data
processing systems utilize a diversity of optical technology. Integrated optics
is expected to complement the well-established technologies of microelectron-
ics, optoelectronics, and fiber optics. The requirements for applying integrated
optics technology to telecommunications have been explored extensively and
are well documented [1]. Other applications include sensors for measuring
rotation, electromagnetic fields, temperature, pressure, and many other phe-
nomena. Areas that have received much recent attention include optical tech-
niques for feeding and controlling GaAs monolithic microwave integrated
circuits (MMIC), optical analog and digital computing systems, and optical
interconnects for improving integrated system performance [2].
An example of an MMIC application [3] is a fiber-optic distribution network
interconnecting monolithically integrated optical components with GaAs
MMIC array elements (see Figure 2.1). The particular application described
is for phased array antenna elements operating above 20 GHz. Each module
requires several RF lines, bias lines, and digital lines to provide a combina-
tion of phase and gain control information, presenting an extremely complex
signal distribution problem. Optical techniques transmit both analog and
digital signals as well as provide small size, light weight, mechanical stabil-
ity, decreased complexity (with multiplexing), and large bandwidth.
An identical RF transmission signal must be fed to all modules in parallel.
The optimized system may include an external laser modulator due to limi-
tations of direct current modulation. Much research is needed to develop the
full compatibility of MMIC fabrication processes with optoelectronic compo-
nents. One such device being developed is an MMIC receiver module with
an integrated photodiode [4]. Use of MMIC foundry facilities for fabrication
of these optical structures is discussed in Section 5.11.
Another application area that can significantly benefit from monolithic inte-
gration is optically interconnecting high-speed integrated chips, boards, and
computing systems [5]. There is ongoing demand to increase the through-
put of high-speed processors and computers. To meet this demand, denser
higher speed integrated circuits and new computing architectures are con-
stantly developed. Electrical interconnects and switching are identified as
bottlenecks to the advancement of computer systems. Two trends brought on