There's an insatiable demand for more telecommunications bandwidth, and MEMS is viewed as the key technology—the only technology according to many telecommunications experts—that will satisfy this demand. The trend is accelerating toward an all-optical network for moderate- and long-haul telecommunications networks, and eventually to local-access networks, using a variety of optical switching techniques including micromachined mirror arrays.
Much of today's telecommunication is performed in an optical-electronic-optical (O-E-O) fashion. Transmitted optical signals are converted to electronic form for processing and converted back to optical form at the receiver.
Taking an all-optical (O-O) approach can minimize, if not entirely eliminate, speed, bandwidth, and cost bottlenecks imposed by electronic circuits. Also, switching and routing costs can be reduced through integration. As one expert put it, "Our telecommunications networks are advancing at such a rapid pace that they're outstripping the ability of the electronic circuits to process the data that the networks are handling, and an all-optical network is the only foreseeable solution."
"Optical MEMS is one of the fastest-growing applications in MEMS, along with biomedical, chemical, and RF applications," says Roger Grace, president of Roger Grace Associates, a strategic marketing firm specializing in MEMS. Grace estimates the compound annual growth rate for MEMS in these areas as 20.1%, going from $14.1 billion this year to $36.2 billion in 2005.
One of the biggest advantages of an O-O network is that it doesn't depend on the signal format or protocol as an O-E-O network does. This makes it transparent to the signal format and protocol, as well as more reliable. Plus, it provides greater end-to-end scalability and flexibility.
Because the demand for greater bandwidth is mounting, customers may not be able to wait for the all-optical approach to mature. Nitish Mandal, manager of strategic markets for Tellium Inc., discussed this in a recent executive briefing on photonics sponsored by Information Gatekeepers. Mandal said that optical switches are great for transferring high-speed data, but not for processing that data. On the other hand, electronics are great for information processing, but limited on high-speed switching. Having a high-speed optical fabric on the inside of a network and smart optoelectronic interfaces on the outside might be better options.
Last year, Tellium announced its Aurora Full-Spectrum system, which combines all-optical cross-connect switches with electronic control and processing circuitry. An agreement signed this year between the company and Analog Devices allows the latter to manufacture a series of advanced MEMS chips for Tellium's Aurora line.
A Field Of Many
Dozens of startup companies have sprung up in the last couple of years, offering what each perceives as the right switching and routing solution to wideband communications. These companies were formed while mindful that larger enterprises like Nortel, Corning, JDS Uniphase, Cisco, Lucent, and Sycamore have purchased some of the smaller startups and companies specializing in optical MEMS. The startups also are ready to do battle in an increasingly crowded optical-switching marketplace. Even a company like Goodrich (formerly BF Goodrich), which has always been better known for making tires, has gotten into the act. It has aligned itself with Movaz Networks, a producer of optical transport systems, to make next-generation MEMS optical switches. Much of this interest began over the last several years when Lucent Technologies introduced its LambdaRouter, a 3D MEMS switch mirror array.
This interest in the industry is illustrated in studies revealing that about 50% of all data traffic today goes over distances of more than 300 km, distances that can greatly benefit from O-O networks. Today's networks have hundreds of wavelengths, with each wavelength operating at tens of gigabits/s. Switching and routing that many signals via an O-E-O approach is very difficult because several fiber pairs terminate into a telephone company's central office. Switching and routing such signals requires a large array of all-optical switches with thousands of ports. The rush to solve the bandwidth bottleneck has given rise to new terms of terabits and petabits. A terabit is a trillion bits (1012), and a petabit is a quadrillion bits (1015).
Presently, the big market is the long-haul backbones where the idea is to "set the standards in this market, and then cash in on the peripheral markets like metropolitan-area networks (MANs), which can eventually be a much bigger market," says Bob Solouf, director of business development for Analog Devices. Right now, the MAN market is still small.
The lure of an all-optical network for long-haul telecommunications using MEMS technology is seen in the adaptability advantage that such a network offers (Fig. 1). MEMS devices such as switches and tunable lasers will offer programmable cross-connects and add/drop multiplexers, things not available with present fixed-value components. This will catapult the development of dense wavelength-division multiplexing (DWDM) to the next level. DWDM is driving the demand for greater bandwidth.
One of the costliest components of current DWDM systems is the trans-ponder, which can be replaced by a MEMS tunable laser. Such a laser may be cheaper than the transponder because it can be mass produced using standard IC processing. Yet, producing it in smaller quantities might raise costs. Passive thin-film and arrayed waveguide gratings (AWGs) are presently used in DWDM systems. These are fixed elements that offer no flexibility. MEMS optical devices will change all of this with the ability to program them to adapt to different add/drop and network architecture needs.
Many see the tunable laser as the next hot optical MEMS device after switches. Tunable lasers are now becoming available, although they're rather costly. Given their use in large enough volumes, however, they can be produced less expensively. They would also cost much less than the transponders that they can replace, which have inhibited the growth of DWDM systems.
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