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Paul T Kidd's Embedded Microprocessors Pages
Article on Optoelectronics
Article on Optoelectronics
Optoelectronics is one of the fundamental enabling technologies driving the development of the Information Society. What is the market potential for optoelectronics? What use does optics have in microelectronic systems. And will it be possible to develop all-optical devices and networks.
Electronics is not the only
science that nature has provided. People experience the world
through many senses, but sight is the most powerful of these.
Optics has been established for hundreds of years and there are
many examples of light being exploited. The power of optics however
increases significantly when it is combined with electronics
- the field today known as optoelectronics. Photons can travel
freely in air and many solids in a way that is impossible for
electrons. Photons can also carry information impressed on them
by electronics. Telecommunications relies heavily on optoelectronics.
Markets and Innovation
Optoelectronics is good business. The market for optoelectronics is growing rapidly especially in the telecommunications sector - 100% growth figures per annum are not unusual. The market for optical components in the telecommunications sector illustrates the growth being experienced. In 1999 this market was worth 6.4 billion dollars. It is projected to grow to 23 billion dollars by the year 2003. European companies are in a very strong position to respond to these market opportunities.
This sort of growth however, poses its own problems, especially for the smaller companies. With orders increasing in the range of 130 to 140 percent per year, the challenge is to grow manufacturing capacity and to learn how to operate larger facilities.
The industry is fast moving and is beginning to mature. The market is very innovative and technology driven. Over the past few years the industry has been subject to restructuring with many players coming together through mergers and acquisitions to form a few large leading companies operating as one stop shops offering complete solutions. But there are also many new start-ups and smaller entrants. These start-ups illustrate that it is still possible for SMEs to operate in this industry. Such companies are active in many areas, including Dense Wavelength Division Multiplexing.
Optics is dominant in long haul transmission. The backbone and the metropolitan areas are also optics based, but optics is also moving into the access area. Fibre to the Curb (FTTC) is the most likely outcome of this. The introduction of Wavelength Division Multiplexing has been responsible for the massive increase in optical transmission capacity seen over the past few years and is driving continuing capacity development. Dense Wavelength Division Multiplexing is the emerging development in this area.
Optical components are also increasing in significance. The trend is to install more and more optical components in the network, although the overall telecommunications system is likely to remain a mixture of both electronics and optics.
In situations where electronic switching and processing needs to be replaced by all optical devices, key technologies will be interferometers with integrated semiconductor optical amplifiers and lasers with dispersive reflectors. The former devices can be used for wavelength conversion and demultiplexing, while the latter devices for decision, clock recovery and signal regeneration.
The main future driver of developments in telecommunications is likely to be next generation Internet, requiring more bandwidth. This means that a higher bit rate is needed. This in turn means that faster components are needed. Also as the speed increases optical fibre impairment management will become important. Although optical fibre is the ideal medium, it has its own limitations, which become important as transmission rates move to 40Gbits/sec and above.
In terms of packaging of optical components the ultimate goal must be to reduce costs and to create multi-function integrated circuits similar to the microelectronic integrated circuit.
One development that might help towards achieving this goal is photonic crystals. Photonic circuits were first conceived in the 1960s. They, like other types of all optical devices, however tend to be large when compared with modern microelectronics. The vision of very high density integrated optical circuits has not yet been achieved. Photonics crystals may provide the answer, possibly providing the means of creating very large scale optical integration. Much fundamental research however needs to be done. The technology is still very much at an early stage of development. The problems to be resolved include how to get light into small circuits, light propagation through the circuits, light dispersion, and undertaking functions like changing wavelengths.
Waveguides are fundamental
components of photonic integrated circuits and this is an area
where much research effort is being expended. Progress has been
made, but problems exist. Bending of light is one of these problem
areas and there has yet be any convincing experimental demonstration
of light bending.
Optics in Microelectronics
The use of optoelectronics is not just limited to devices used in optical networks. Optics also has a role to play as a communications medium within electronic systems and in improving the performance of semiconductor integrated circuits. Over the period 1996-2000, the area of optoelectronic interconnects for integrated circuits was pursued within the MEL-ARIO OPTO initiative. One of the driving forces behind the work was the need to resolve the problems of interference that occur in communications between the different modules within integrated circuits, as well as those communications that take place between integrated circuits. Such problems pose a potential block on the further development of the classical semiconductor technologies used in integrated circuits and microelectronics. In these cases one of the challenges is to integrate optoelectronics and optics in a compact way together with semiconductor technologies such as CMOS. A further challenge is to develop optical pathways, using materials such as Plastic Optical Fibres.
Key technologies for optical interconnections within electronic systems and integrated circuits are two dimensional optoelectronic arrays, optical pathways and hybrid integration with CMOS. In the latter area wafer scale integration still remains something for the future. Progress towards industrial use requires techniques that will lead to evolutionary introduction into electronic systems. The choice of the most appropriate technologies is still an open issue.
Optical Data Storage
Optical techniques are also used in data storage and recording. They form the basis of the CD, with different approaches leading to different media properties (read only, write once, rewritable). The advantages of optical based storage systems are that they are reliable, cheap and they provide a removable storage media. The main applications of this media are archival storage. To remain competitive optical storage needs to remain removable, as most of the cost lies in the reading device not in the disk.
Current capacities stand at about 5Gbytes for a one sided disk. Optical storage capacities still need to be improved. There are two ways to increase the storage capacity. The first is to increase the area density by for example decreasing the laser spot size. The second way is to increase the volume of the disk, for example by using mutli-layered systems.
In the past there has been
competition between magnetic and optical storage media. Hybrid
storage systems are now under development. These use magnetic
means to read (because of better sensitivity) and optical techniques
to write (because of better accuracy). It is expected that this
hybrid approach will lead to improved performance.
Conclusions and Future Directions
In the optics industry there are tremendous opportunities for growth and profitability. However, further technology research is needed. The focus of optics research needs to be on solving problems associated with transmissions at 40Gbits/sec, as well as on developing all optical replacements for electronic circuits. Micro optical integrated circuits also need to be developed and new areas such as photonic crystals need to be further investigated. Research in the area of optoelectronics to improve semiconductor integrated circuits is needed. Innovation is needed terms of packaging and manufacturing.
Research in optical storage technologies is also needed as new technologies provide an opportunity for European firms to enter the market and challenge existing players. There is still room for further development in disk capacity using multi-layered disks and by increasing area density. A significant challenge is too increase the capacity of optical storage media while retaining the existing advantages of low cost and removability.
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