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Silicon Optics Aims to Combine the Best of Both Worlds

Vendors of computer-, networking-, and telecommunications-related equipment have long faced a dilemma. Much of their equipment is based on silicon and copper wiring, which are inexpensive to use but offer limited data rates. Thus, as microprocessor and networking speeds have increased, the speed of communications within chips, between chips or circuit boards, within LANs¹, or even along the “last mile” from ISPs² to customers has not kept pace.

An option is to use optical connections for these communications.

However, optics has been expensive and, therefore, not suitable for any but the largest networking operations with the most traffic and the biggest potential for return on investment. Thus, optics has been used largely in settings such as telecommunications vendors’ backbone networks.

Optical connections have been impractical for communications on or between chips because the shorter distances involved yield fewer bandwidth improvements, which don't justify the expense.

Now, though, vendors are attempting to combine the best of both worlds and offer silicon optics, which uses complementary metal-oxide semiconductor (CMOS³) technology to fabricate optical components on silicon.

This approach would speed up traditionally silicon-based systems. It could also reduce the cost of optical equipment and bring optical systems within reach of more users, including companies and service providers with networking operations smaller than those of large telecommunications providers.

Combining silicon and optics is a complex process. However, some vendors are already selling some less complex silicon-optical components.

Meanwhile, scientists are making progress on more complicated components. For example, Intel and UCLA⁴ researchers have each developed prototype silicon lasers.

Nonetheless, obstacles remain, so while some components are already available, it may be years before silicon optics can be widely and reliably used commercially.

US Air Force researchers pioneered silicon optoelectronics in the mid 1980s for sophisticated communications and signal processing.

Since then, а variety of universities and companies, such as Bookham and Intel, have worked оn silicon optics.

In most current silicon-optical devices, such as waveguides and filters, the silicon is used only as а passive medium through which light can bе transmitted. These devices do not tackle the more fundamental problem of converting signals from optical to electronic and vice versa. This critical capability maximizes the use of optical technology and increases performance.

Many of today’s systems use photodetectors that convert signals only from optical to electronic.

Another key obstacle to achieving true silicon optics has been the lack of а silicon-based laser. Semiconductor physics has limited the ability to build such а laser. The issue is bandgap: the energy difference between а material’s conductive and nonconductive state. Direct bandgap semiconductors such as gallium arsenide and other material used in optics are efficient at emitting light, while indirect bandgap semiconductors such as silicon are not.

Some researchers are looking into techniques such as introducing other materials that will make the silicon transmit light more efficiently or adding dopants that themselves transmit light effectively.

Meanwhile, scientists continue looking for other ways to provide silicon optics.

Notes:

¹LAN – Local Area Network – локальная (вычислительная) сеть, ЛВС;

²ISP – Internet Service Provider – Поставщик Интернет-услуг;

³CMOS – complementary metal-oxide semicondoctor – комплементарная стуктура “метал-оксид-пролупроводник”, дополняющая МОП-структура, КОМП-структура;

⁴UCLA – University of California Los Angeles – Калифорнийский университет /в Лос-Анджелесе/ (США).

VIII. Match the letter of the correct answer to the following questions:

1. What kind of dilemma have vendors of computer -, networking-, and telecommunications-related equipment faced?

a) Silicon and copper wiring are inexpensive to use and offer unlimited data rates.

b)Silicon and copper wiring are inexpensive to use but offer limited data rates.

c) Silicon and copper wiring offer limited data rates but are expensive to use.

2. What are the advantages of silicon optics technology?

a) It would speed up traditionally silicon-based systems and enable to produce different kinds of consumer goods.

b) It would speed up traditionally silicon-based systems and enlarge the cost of optical equipment.

c) It would speed up traditionally silicon-based systems and reduce the cost of optical equipment.

3. Are there obstacles which are necessary to overcome?

a)One of the obstacles is the lack of а silicon-based laser.

b) There is no any obstacle to overcome.

c) One of the main obstacles is to make silicon to transmit light more efficiently.

4. What kind of laser have the scientists developed?

a) They have developed a silicon laser that can be directly driven by an electrical current.

b) They have developed a semiconductor laser.

c) They have developed a prototype silicon laser.

5. How is silicon used in most current silicon-optical devices?

a) It is used to emit a coherent beam of light.

b) It is used as a semiconductor to generate relatively low amounts of heat.

c)It is used as a passive medium through which light can be transmitted.