Optical components

PhoXtal Takes to the ROADM

Swedish startup PhoXtal Communications AB will unveil a nifty add/drop module at the OFC show today. It says it will give carriers a simple way to add reconfigurability to their existing optical networks (see PhoXtal Touts OADM Wavelength Switch).

Founded in January 2002, PhoXtal has has its roots in the Royal Institute of Technology (KTH) in Stockholm. Its founders include Björn Broberg, who previously founded tunable laser startup Altitun, and Fredrik Hånell, former vice president at Dynarc, the metro equipment startup that pioneered a pre-standard version of Resilient Packet Ring Technology technology, before going bust (see Startups Stumble and Succumb).

PhoXtal joins the dozens of startups developing components and subsystems for reconfigurable networks that are taking advantage of what appears to be one of the few bright spots in the components sector right now (see ROADM Vendors Perk Up).

Many optical add/drop multiplexer (OADM) subsystems require carriers to tear out their old networks, and put in new equipment, says Hånell, who is CEO. PhoXtal is taking a different tack, he says, with a device that could be used to upgrade existing gear.

The startup's module -- called an OADM wavelength switch -- is a switched device with an active and a pass-through mode. In active mode, it is designed to add and drop a single, predetermined wavelength from a bunch of Dense Wavelength Division Multiplexing (WDM) channels. In pass-though mode, the module is completely transparent, with a loss of 1 dB maximum.

"It's like a couple of fixed [thin-film] filters, but you also have the option of activating them or not," explains Hånell.

PhoXtal plans to set the initial price of its module as the same as, or only a small premium over, the price of a pair of thin-film filters, he adds. When production quantities increase, that price could come down further.

The loss figure of 1dB is also extremely important, because it's less than a pair of thin-film filters. That means a carrier could replace its existing OADMs with PhoXtal's device, and gain extra functionality with no penalty in terms of price or performance.

PhoXtal's module is also very small, like a thin-film filter. Under the covers, it comprises two switches, two filters, and dispersion compensation, all integrated on a single piece of glass measuring 4cm long by just 1mm wide. Hånell declined to reveal how it works, except to say that many features are covered by patents.

But is it as exciting as it sounds? Joe Davis, CEO of competitor Capella Photonics Inc., says there are good reasons that carriers are looking at more revolutionary designs for OADMs. But, he adds, "Because [PhoXtal's module] only adds or drops a single wavelength, in a real system you would need other components to make it useful."

Services can't be interrupted, so network designers must specify the number of channels to be added or dropped at the outset. A typical number of add/drop channels is eight, although a current request for proposal (RFP) for SBC Communications Inc.'s (NYSE: SBC) metro network, requires all 32 channels to be dropped, according to Davis.

To implement an eight-channel OADM with PhoXtal's module would mean cascading eight of them in a line, or using an eight-way splitter to divide the light between them, and a coupler to combine it again. Even though an individual module has low loss, the total loss would be signficant in an eight-channel system, so it would probably require amplification, Davis contends.

When the cost of the additional components -- splitters, couplers, amplifiers, and gain equalizers -- is taken into account, then a subsystem solution, like the one offered by Capella, will turn out to be less expensive overall, he claims (see Capella Cashes In). In addition, a subsystem solution offers more advanced features such as the ability to drop channels at different ports.

Hånell counters by pointing out that the most favorable solution depends on the channel count. "It's going to be the same economic argument as between AWGs and thin-film filters," he says. "Our solution is comparable to thin-film filters and will be mostly applicable in the metro." Subsystem solutions like Capella's will only make sense for very high channel counts.

PhoXtal has higher channel-count devices on its roadmap, but Hånell figures its too early for them yet. "You need to know which channels you want to add and drop, and the customers themselves don't know yet. Before we design such a chip, we will need a solid relationship with a customer."

PhoXtal is currently shipping prototypes to a single customer, which Hånell declines to name. The startup is also qualifying its manufacturing process with an optical foundry; full production should begin in the fall, if all goes according to plan.

— Pauline Rigby, Senior Editor, Light Reading

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