Electronic Design

Optical Communications Battling Back From Adversity

New players and progressing technologies like SANs and PONs attempt to jumpstart the struggling fiber-optic arena.

The entire market for fiber-optic cable, components, and chips peaked in 2000 and is now trying to correct itself. Over the past three years, the general economic downturn saw the decline of telecommunications carriers, hammering the market for long-haul fiber-optical networks using Sonet/SDH and DWDM transport and switching technologies. Combine the fact that over 50% of the optical marketplace is telecommunications with the lack of any significant new buying, and it's easy to see why many optical companies simply closed shop.

That said, many optical component and semiconductor manufacturers are still cranking out innovative new products for the fiber-optical marketplace. With the market in its "corrective" mode, the survivors are positioning themselves with great new leapfrog products that will bring them a fast return when business comes back.

One fiber-optic market showing promise is metro networks. Sonet/SDH dominates this sector but is being challenged by Ethernet. During the dot-com boom, long-haul and metro networks were overbuilt, and there's still an enormous amount of dark fiber. Some metro networks are being built, although the emphasis is on lower costs and equipment that's easier to provision. Ten Gigabit Ethernet (10GE) just may capture this segment.

Sonet/SDH was originally optimized for voice, although today data is equal to, or even exceeds, voice on some networks. Its fixed time-division multiplexing (TDM) nature makes it inefficient because of the difficulty in scaling and adapting to the nature of bursty data traffic. Considerable effort is under way on a number of fronts to make optical Ethernet a service-bearing technology like Sonet/SDH. Some of the architectural alternatives include Ethernet over Sonet (EoS), Switched Ethernet over Fiber, and Ethernet over WDM (wavelength-division multiplexing). For more information, contact the Metro Ethernet Forum (MEF).

Growth in Ethernet local-area networks (LANs) continues, but with the newer optical versions lagging. Optical options exist in both 1GE and 10GE. The copper CAT5 and CAT6 versions of 1GE have all but won this segment. So why rewire with fiber if plain-old existing unshielded twisted pair works just fine? Most of the newer PCs and laptops have a 10/100/1000-Mbit/s RJ-45 port, and 1GE switches are growing in number in enterprise networks.

More activity is expected in the 10GE optical space as business recovers with investment in 10GE optical LAN backbones. Lots of equipment and components for this market are now available, and competition is heating up. Thus, the outlook looks strong for optical transceiver modules, switches, and routers in this market.

Another sector showing growth right now is storage area networks (SANs). This may be the fastest growing segment for fiber as more companies install Fibre Channel and iSCSI fiber connections to their servers.

For the future, fiber to the home (FTTH) seems to have the most potential. Unless the traditional carriers get off their duffs, the cable companies are going to steal the broadband market from them. While DSL has shown some growth, it's just a stopgap that will ultimately have to yield to fiber. That's because DSL over the plain-old telephone-service local loop can't hack the higher speeds required by movies-on-demand, gaming, and other multimedia services. Some of the smaller independent carriers already install passive optical networks (PONs) in the last mile. However, this enormous segment won't go anywhere until the main carriers decide to do it on their own, or unless they're directly and immediately threatened by the cable companies.

Have we hit the optical nadir? Not yet, according to most market research firms and experts in this field. A leading market research company, iSuppli, projects that a modest turnaround should begin in 2004, with growth continuing through 2007. Sales won't even come close to 2000 levels for many years, but at least the trend shows an upward tick. Chris Emslie of Fibrecore Limited, a maker of specialty fiber in the U.K., indicates that the turnaround may not actually start until 2005. Others predict it could take even longer. Most agree, though, that at this point the only way to go is up.

HOT OPTICAL PRODUCTS
Even with the downtrodden manufacturers hunkering down and enduring the consolidation, they haven't sat still. Existing products have been fine-tuned, and some innovative new products have emerged. This is especially true in the semiconductor sector, where major manufacturers were able to hold on to their optical businesses thanks to larger markets for other component types. Here's a summary of some of the standout new products that are looking for customers.

Maxim Integrated Products' MAX3737 is a multirate laser driver with extinction ratio control for application in Ethernet and Fibre Channel transceiver modules. This device can drive laser diodes at speeds from 155 Mbits/s (OC-3) to 2.7 Gbits/s (OC-48). It may be ac- or dc-coupled to the diode.

The MAX3737 includes automatic power control (APC), extinction ratio control features, and on-chip thermal compensation. It meets all of the SFF-8472 standard timing and diagnostic requirements for SFP modules with digital diagnostics.

Some key specifications include a programmable bias current range from 1 to 100 mA. The modulation current can also be programmed from 5 to 60 mA when dc-coupled and up to 85 mA when ac-coupled. The circuit consumes only 155 mW.

A newer device is the MAX3942 modulator driver. It's designed for Sonet/SDH OC-192 or STM-64 10-Gbit/s systems, as well as 10GE systems for the metro, long-haul, point-to-point, and dense-wavelength-division multiplexing (DWDM) applications. It can drive a Mach-Zehnder modulator or a direct modulated laser. The device operates from a single +5- or −5.2-V supply and consumes only 125 mA. The MAX3942 has an edge speed of 23 ps and a programmable modulation current up to 120 mA.

Recently entering the optical components field is SiGe Semiconductor, which has acquired a portfolio of physical-layer IC licenses from a major telecom company. Its newest products are the LightCharger line of limiting amplifiers and transimpedance amplifiers (TIAs) for use in optical transceiver modules. The highest-performance devices are the SE1250L limiting amplifier and SE1052W TIA for use in the receive path of OC-192/STM-64 Sonet/SDH systems, 10GE, or the forthcoming 10-Gbit/s Fibre Channel transceivers.

The SE1052W TIA has a wide dynamic range of −22 dBm to +1 dBm and 3.7 kΩ of differential transimpedance. It supports a current load of 2.6 mA and can swing up to 300 mV p-p into a 100-Ω load. The device has sufficient output to drive the serializer/deserializer (SERDES) chip directly.

The SE1250L limiting amplifier has 15 GHz of bandwidth and the lowest power consumption of any limiting amplifier. It features a small signal gain of 33 dB differential and a noise figure of less than 12 dB in 10-Gbit/s applications. The power dissipation is only 120 mW. Both the limiting amplifier and TIA operate from 3.3 V.

One of the companies I don't usually think about when looking at the optical field is Intel. Yet, it's a good example of a company with deep pockets as well as diversity that can ride out the hard times. Intel has an extensive and growing line of optical transceiver modules and a wide range of chips that address optical networking. Also, Intel just acquired West Bay Semiconductor, a company that makes Sonet/SDH framer and data-mapper chips and those facilitating Ethernet over Sonet. West Bay's networking architecture savvy plus Intel's 90-nm technology should produce some exciting chips in the future.

But perhaps Intel's best optical achievement was the announcement of its tunable laser modules earlier in the year. No one product makes DWDM more practical than a tunable laser. Instead of buying one laser for each of dozens of different wavelengths, designers can now buy just one tunable laser that can be set to any of the wavelengths in the popular C-band (1550-nm range). Intel's laser module has an output of 20 mW and is voltage tunable over a 50-GHz range. Besides lowering equipment and maintenance costs, it permits new architectures in which data can be switched dynamically on-the-fly from wavelength to wavelength. Intel is a member of the recently formed Tunable Laser Multisource Agreement (MSA) alliance.

Another company with an extensive portfolio of optical transport chips is PMC-Sierra. Typical of its newest products are the PM8377 and PM8369 Fibre Channel (FC) intelligent Port Bypass Controllers. The PM8377 supports four channels, while the PM8369 supports 18 channels. These chips are designed for 4.25-Gbit/s enterprise-class storage arrays and SAN applications. They also support the recent Fibre Channel Industry Association (FCIA) vote to extend 4.25-Gbit/s FC into the SAN fabric.

A companion chip is the PM8358 QuadPHY 10GX, a four-channel, fully redundant 3.2-Gbit/s transceiver offering high-speed serial I/O. This SERDES product supports a broad range of optical-system applications that require multigigabit serial interconnect, including Gigabit Ethernet, Fibre Channel, 10GE, 10-Gbit/s FC, OC-48, OC-192 Sonet/SDH, and InfiniBand interfaces. The chip features bidirectional XGMII-to-XAUI interfaces and includes clock recovery, clock synthesis, byte alignment, trunking, and 8B/10B encode/decode logic.

This year, Scintera Networks' SCN3142 and SCN5028 were two of the top optical-fiber-related chips announced. Scintera Networks is a startup just emerging from stealth mode to announce its Electronic Dispersion Compensation Engines (EDCE). These specialized DSP chips implement filtering and equalization techniques, permitting 10-Gbit/s data to be transmitted over legacy fiber at greater distances. Scintera's Advanced Signal Processing Platform (ASPP) provides automatic and adaptive dispersion compensation that can be incorporated into almost any standard laser transceiver module (Fig. 1).

The SCN3142 device, designed for the enterprise market, can transmit 10-Gbit/s serial data at a range of up to 300 meters in legacy multimode fiber (MMF). This is a far better solution than the four-wavelength, coarse-wavelength-division-multiplexing (CWDM) solution offered by the 802.3ae LX4 standard. The chip is totally adaptive and protocol agnostic, and it requires no training sequence. It syncs and locks in within tens of microseconds. Moreover, it works with Ethernet or Fibre Channel.

The SCN5028 uses the same ASPP techniques but is optimized for the metro optical market. It compensates for nonlinear impairments and dispersion when transmitting data at 10 Gbits/s on metro single-mode fiber (SMF). It can extend the typical 80-km connection to over 140 km. The device compensates for both chromatic and polarization dispersion while using the automatic and adaptive EDCE techniques.

Some examples of all optical components are those from TeraXion and Lightconnect. TeraXion recently announced the availability of its C-band fixed and tunable dispersion compensators. Dispersion, the stretching of a light pulse due to aberrations in the fiber, is a major problem at very high data rates (>10 Gbits/s). Chromatic dispersion seriously limits transmission distances at 10 and 40 Gbits/s with multiple wavelengths unless it can be corrected. The TeraXion dispersion compensators use fiber Bragg gratings to make the correction. A tunable version is available, permitting on-the-fly adjustment of the connection for data-rate changes to 40 Gbits/s or dynamic reconfiguration. The products also come in versions for L-band.

One survivor of the optical shakeout over these past few years is Lightconnect. It has demonstrated that innovation and a clearly superior product will get you through the hard times. The company's newest product is the Fast VOA 5000, the industry's smallest variable optical attenuator (Fig. 2). It uses MEMS (microelectricalmechanical systems) technology with a moving semiconductor structure that modifies the input light to produce an attenuation effect. The attenuation is fully variable from 0.8 to 40 dB with a 0- to 5-V control signal. The device is fast and offers superior attenuation over previous generations of MEMS, liquid crystal, or thermal attenuators. VOAs are used extensively in optical telecom systems to equalize the power levels at different points in the network, as well as correct for differing power levels in multiple-wavelength DWDM systems.

The product can be used for receiver and channel protection, on/off switching, multiplexing, and demultiplexing, as well as in optical add-drop multiplexers (OADMs). Lightconnect also makes dynamic optical equalizers for multiple λ DWDM systems using the same MEMS technology.

One of the fastest growing segments of optical networking involves the aforementioned SANs. They connect servers and other storage devices via a unified network optimized for storage applications, especially database access. The dominant SAN interface to this point has been Fibre Channel (FC). This optical system is complex and expensive with some speed and distance limitations. However, the industry is addressing them. Nevertheless, a competitor has grown quickly and is beginning to cut into FC sales—iSCSI or Internet Small Computer Systems Interface (I-skuzzy). This fast serial version of SCSI uses TCP/IP to transmit storage data over fast optical Ethernet network connections. It's less expensive than FC and has higher speeds that scale better. Needless to say, sizable growth is anticipated in this sector.

One of the companies making iSCSI practical and better than ever is Silverback Systems. Its recently announced iSNAP 2100 is a fast IP storage network access processor (Fig. 3). It is designed for use in servers, iSCSI storage devices, NAS appliances, blade servers, and multiprotocol storage routers. The 2100 accelerates access to IP storage by offloading both networking and upper-layer protocols like iSCSI and RDMA and then mapping them to the iSNAP architecture. What results is superior throughput. Besides the 2100 processor chip, Silverback offers a full line of supporting firmware and software to adapt the product to the specific storage network application.

PON POTENTIAL
Another highly promising area of the fiber-optical business encompasses passive optical networks (PONs). These relatively short-range networks are designed primarily for metro networks and particularly for the FTTH or fiber-to-the-business (FTTB) markets. Their benefit is low cost, because no intermediate active electronic elements are needed between the source and destination. Passive optical splitters/couplers are used to divide a single fiber bandwidth into 16 or 32 channels.

The past few years have seen precious little activity in PONs. But some of the regional Bell operating companies (RBOCs) are beginning to experiment with and invest in PONs, especially for new homes. As the industry works itself out of the usual chicken and egg problem, costs will decrease. No doubt, then, we can look forward to an all-PON telephone system in the distant future that will also provide high-speed Internet access as well as video. Considerable PON activity is taking place in other countries, especially Japan and Korea who are leading the pack, and to a lesser degree in China and Europe.

Multiple types of PONs are being built in the U.S. One of the standards vying for attention is the APON, or PON based upon ATM (asynchronous transfer mode). RBOCs would choose this technology because it fits with their existing ATM switching networks. It can achieve a speed of 155 Mbits/s uplink and 622 Mbits/s downlink using relatively inexpensive components. The standard for APONs is defined by the ITU-T as well as the Full Service Access Network (FSAN) Group, a forum of companies working toward a PON future.

Another emerging standard is the IEEE's Ethernet in the First Mile (EFM) 802.3ah protocol. Known as EPON or Ethernet PON, this standard has been in the works for years but hasn't received final ratification yet. It's close, though. The 802.3ah standard defines both copper and optical Ethernet to the home.

GPONs or Gigabit PONs are PONs that operate at 1 Gbit/s or higher. The FSAN Group has set standards in coordination with the ITU-T for data rates of 1.25 and 2.5 Gbits/s.

One of the companies addressing the PON market is OpticalZonu. It makes a line of optical transceivers for use as central-office optical line terminators (OLTs) and customer premise optical network terminals (ONTs). These are protocol agnostic, so they can be used in APONs and EPONs. Some use a two-wavelength (2λ) full-duplex scheme on 1310 and 1490 nm.

Another company going after the PON market is Alloptic Inc. It has developed a complete line of central-office and customer premise equipment meeting the EPON standards. Alloptic's system brings fiber to the home, business, or multi-unit dwelling. These systems use a symmetrical 1-Gbit/s upstream/downstream format up to a range of about 20 km or more, depending upon the type of fiber used.

Figure 4 shows one of the home units. It has multiple RJ-11 standard phone jacks for regular TDM telephones or the newer forthcoming VoIP phones. Also provided are 10/100-Mbit/s RJ-45 Ethernet jacks for high-speed Internet access. Even a coax cable output is available on some units. It's certainly something we can all look forward to.

Need More Information?
Alloptic Inc.
www.alloptic.com

Ethernet in the First
Mile Alliance

www.efmalliance.com

Fibercore Limited
www.fibercore.com

Full Service Access
Network Group

www.fsan.org

IEEE
www.ieee802/3efm.org

Intel Corp.
www.intel.com

iSuppli Corp.
www.isuppli.com

Lightconnect Inc.
www.lightconnect.com

Maxim Integrated Products
www.maxim-ic.com

Metro Ethernet Forum
www.metroethernetforum.org

OpticalZonu
www.opticalzonu.com

Passive Optical Network Forum
www.ponforum.org

PMC-Sierra
www.pmc-sierra.com

Scintera Networks
www.scinteranetworks.com

SiGe Semiconductor
www.sige.com

Silverback Systems
www.silverbacksystems.com

TeraXion Inc.
www.teraxion.com

Tunable Laser Multisource
Agreement

www.tunablelasermsa.com

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