Incremental approach to optoelectronics

July 1, 2003
The merits of optoelectronics — the technology that combines the best features of electronics and photonics — have been relatively obvious since the development of lasers in the 1960s and optical fiber waveguides in the 1970s:
John Rhea
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The merits of optoelectronics — the technology that combines the best features of electronics and photonics — have been relatively obvious since the development of lasers in the 1960s and optical fiber waveguides in the 1970s: orders of magnitude improvements in processing power and bandwidth, immunity to electronic countermeasures, reduced vulnerability due to the elimination of telltale electromagnetic radiation, reduced weight and power, less heat-induced damage to fragile components, and lower costs.

Getting there from here is the tough part, but identifying near-term opportunities and proceeding on a case-by-case basis may ease that task.

That's what the telecommunications industry has been doing with its continuing replacement of copper cables with optical fibers — so vigorous, in fact, that a joke once making the rounds of the industry was that the world's largest copper mine was the Bell system. Telephone companies aren't philanthropic enterprises, so you can bet that the primary consideration is the bottom line.

In this regard, two U.S. military optoelectronics programs of the 1980s may be illustrative.

The Air Force at first took a top-down approach by identifying photonics as the single most important technology in changing the way the service would perform its missions of the 21st century. The Air Force Research Laboratory at Griffiss Air Force Base, in Rome, N.Y., had the responsibility to conduct the initial studies.

The studies covered the entire spectrum of photonics and how this technology could be integrated with advanced electronics, but the immediate benefits were unclear at best and the laboratory's customers among the user commands were reluctant to put their money into further studies until a near-term payoff could be identified.

Based on further in-house studies at Rome, the search for general-purpose optical computing was deferred in favor of more immediate incremental improvements. One of the laboratories at Rome, for example, continues to work on photonic modules for multimode radio frequency (RF) signals and sensors needed for radar, electronic warfare, and communications systems, while another concentrates on interconnects and memories for automatic target recognition and command-and-control functions.

The use of optical switches as the intermediary between the electronic functions that take place within the black boxes and the fiber optic networks that interface with the real world thus becomes the model for further expansion of photonics in both directions: toward the digital world of optical processing and the analog world of sensor functions.

The initial studies by the Air Force and its contractors therefore created a framework for implementation of optoelectronics in systems as permitted by advances in the supporting technologies.

The Marine Corps took a bottom-up approach by using one weapon system as a sort of stalking horse to prove the feasibility of optoelectronics. The system was the AV-8B Advanced Harrier vertical and short takeoff and landing aircraft that McDonnell Douglas in St. Louis (now part of Boeing) was building under an agreement with the British developer.

The proof of concept was a fiber-optic data bus to replace copper cable in non-critical functions on board the aircraft. This exercise gave the airframe manufacturers experience in handling the new technology, and it got the Marine Corps into the optoelectronics business at minimum cost and risk. The participants in the exercise realized that the technology could be more easily used in new systems, but it could also be retrofitted into existing systems.

The lesson of both approaches is that optoelectronics is here to stay, and not just for the military. The same cost-benefit tradeoffs apply to commercial aviation and other non-military applications.

Within the military context, however, it is useful to review the past century of progress in electronics when attempting to get a handle on the potential role of optoelectronics.

What is particularly noteworthy is that military forces throughout this period were able to take advantage of this progress almost by default, in effect capitalizing on the commercial off-the-shelf (COTS) concept long before the term was coined.

The vacuum tube, perfected by Lee De Forest in 1906, made possible the field telephones of World War I and, with further refinements, radar and field telephones in World War II. The transistor, invented in 1947, made the Korean conflict of the 1950s what military analysts have called "the first modern electronic battlefield."

Subsequent progress with integrated circuits laid the foundation for today's era of network-centric warfare, as demonstrated in both the original conflict in Iraq in 1991 and the current operations.

Now, in a world of proliferating weapons of mass destruction, the challenge is to tailor the evolving technology base to the needs of a more mobile and more lethal defensive response.

Here is where advanced technologies based on optoelectronics could change warfare in this century as much as the telegraph changed warfare in the American Civil War. While, from the vantage point of today's computerized world, the telegraph looks like the epitome of low technology, that wasn't the case at the time.

Until the invention of the telegraph, messages were all carried as freight. In fact, the original definition of the word communication meant movement of physical objects.

The telegraph changed all that by introducing the concept of digital signal processing (the Morse code) and increasing the speed of sustained communications from that of a fast horse or sailing ship to nearly light speed, an increase of more than six orders of magnitude.

Even the most sophisticated optoelectronics will be hard-pressed to match that accomplishment.

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