I’m beginning to wonder whether the integrated optical circuit is ever going to happen, and if it does, whether it will matter. Of the many component companies I’ve seen this year that were exciting enough to recommend, none were of the integrated optics variety. Most, however, were pushing what I would call adaptive components, meaning they had as their premise a way to interact in real time within an optical network and perform a critical function – amplification, dispersion mitigation – “intelligently” and dynamically.

A few years ago a number of optical component companies attacked head-on the obvious challenge that optical components have always faced: integration. In electronics, the integrated circuit revolutionized the industry, if not the world, by allowing chip designers to constantly add more functionality and processing power to a silicon chip. The optical component industry, however, could not evolve at the same pace and had long been fighting a battle against itself, that is, against its basic material: glass.

Glass, or silica, is far from silicon. It doesn’t conduct electricity, it doesn’t couple easily to optical fibers or other silica structures, and it does not accommodate miniaturization on the scale of silicon-based ICs. Vendors such as Bookham Technology PLC (Nasdaq: BKHM; London: BHM), Kymata Ltd., and Lightwave Microsystems Corp. have all been working to create the optical IC, but their path to success has been challenged on many fronts. The result is that most of these companies are now selling arrayed waveguide gratings (AWGs) that serve a single function, putting true integration off while they work out the kinks.

David Polifko, formerly of Ciena Corp. (Nasdaq: CIEN) and now Principal at Jafco Ventures, sees it this way: “Integrated optics have failed to deliver, since it is substantially easier to optimize the individual components and then integrate them into a module, subsystem, or system. Most of these optimized components are made from different materials and processes, rendering them unable to be integrated on a single substrate, let alone be spliced or glued together.”

The point here is rather straightforward but important. There simply isn’t a material equivalent to silicon that can be used to create optical circuits. Combinations and hybrids are often proposed, such as silica-on-silicon or polymer-on-silica, but these come with tradeoffs, which typically offset the value of integration. You may get a smaller footprint, but at the cost of higher loss or decreased performance.

“That's what makes the optics industry so interesting,” says Polifko. “It is not just a simple semiconductor process, but in addition you have bulk optics, waveguides, fiber based devices, crystals, etc. – lots of room for innovation and exciting technologies.” As he sees the problem, each of these materials is progressing at a different rate, and what may look one day like the perfect foundation for an optical IC may be inappropriate the next when different functions are required.

Many component vendors claimed they would be able to manufacture optical ICs as easily as semiconductors, yielding huge quantities of optical ICs and driving down costs; but that has also been elusive, though certainly not impossible. Even so, the new components coming out of AWG companies are most often wavelength mux/demux chips, in some cases including integrated variable optical attenuation.

The reality in the optical components market, therefore, is quite different than the one envisioned a few years ago. Instead of the components industry making an evolutionary leap into integrated circuits (often dubbed “planar lightwave circuits”), many companies have instead been focusing on moving up the value chain.

The typical component supplier, such as Corning Inc. (NYSE: GLW) or JDS Uniphase Inc. (Nasdaq: JDSU; Toronto: JDU), has been moving from individual discrete components to modules and subsystems. Optical amps that were once made from scratch are now packaged as a module with an integrated controller and automatic gain function. This has led to cheaper EDFAs (erbium-doped fiber amplifiers), but most of these are simple "set and let be" devices that only respond to command changes or, in some cases, to power-level changes. Optical switching subsystems or wavelength mux/demux subsystems can also be included in this category, though none can be considered particularly "intelligent" or adaptive.

So, just as the optical systems market is moving from static to dynamic, dumb to intelligent, so will the components industry. These are the components to watch and a trend worth following. This column isn’t meant to entirely discount the value of optical ICs, but to point out that these components are in many ways technologies in search of an application, and, as those applications change, particular ICs may find themselves stuck down blind alleys or dead ends. Intelligent or adaptive components, however, address the near-term demand for intelligent subsystems to address amplification, switching, and dispersion compensation, while participating in the transformation of networks by laying the groundwork for a completely adaptive optical network layer.

Until now, such smart subsystems haven't been necessary, since the distances and topologies of optical networks have been fixed, and the signals are 3R'd (reshaped, retimed, retransmitted) at each junction. Only with the addition of optical crossconnect systems and optical add/drop multiplexers (where the total optical channel path length can change if routing paths between two points are changed) does the need to "adapt" arise.

With the higher data rates such as 10- and 40-Gig the signal impairments due to fiber non-linearities and irregularities become even more significant. The mitigation of these impairments is now not only on a per-wavelength basis, it is also required on a real-time basis, as impairments such as PMD (polarization mode dispersion) or insertion loss can change as the fiber heats or is bent slightly.

Already, at least one systems designer, Sycamore Networks Inc. (Nasdaq: SCMR), is building in technology that allows in-field adaptive changes to the environment on a sub-system level, as evidenced by their recent announcement of enhancements to their SN10000 transport product line. Most other systems vendors are following suit, adding tunable components, often as a fundamental part of their system architectures. Atoga Systems, for one, is using tunable lasers not as a simple sparing solution but as a fundamental part of how they allocate bandwidth in metro DWDM-based networks. In a way, Atoga’s solution is based on the concept of “adaptive networking,” in which changing traffic demands or service changes require rapid network reconfiguration at the wavelength layer.

Cinta Corp. also uses tunable lasers as part of an optical transport switching architecture. The tunable laser acts as one dimension of switching, and a low-cost 1xK optical switch provides the second dimension. Other systems vendors, such as Movaz Networks Inc. and Polaris Networks, are leveraging developments in optical layer signaling to make their systems more “adaptive.” Here, an out-of-band optical control plane dynamically controls the interaction between edge gear and a metro core switching system to manage connectivity and bandwidth within a metro.

So down at the component level, which are the companies enabling this transformation? Onetta has introduced the concept of the intelligent optical amplifier; Yafo Networks, the concept of the dynamic PMD mitigation subsystem. Others still in stealth mode are talking about subsystems that provide intelligent dispersion compensation, amplification and gain flattening, optical layer monitoring, protection switching, and optical add/drop multiplexing. There is much more to come, and it appears these are the components systems vendors are clamoring for.

Having adaptive optical subsystems can ensure that as the network path or fiber changes, the transmitters and receivers can adaptively compensate for the distortions incurred. As we evolve slowly but surely to a more dynamic optical layer, the key enablers will be at the component layer. The next wave of optical innovation is happening here. So forget about integrating: Adapt!

— Scott Clavenna, Director of Research, Light Reading
http://www.lightreading.com