Fiber Bragg gratings on the fast track

Southampton Photonics this month announced new developments in fiber Bragg gratings -- devices used to split and recombine light in dense wave division multiplexing systems.

On the face of it, the big news is that Southampton Photonics has shipped the first commercial FBGs with 25-GHz channel separation. This means vendors' DWDM gear will be able to handle 160 wavelengths per channel, which means vendors may be able to honor promises to their customers.

However, the real significance of the announcement might not be in the FBGs themselves but in the way in which they were made. Southampton Photonics has automated the process of setting up the production equipment to make its FBGs to particular customer requirements, shrinking the time required to do this from an average of six to eight weeks to a mere 24 hours.

The company has also automated the manufacturing process, enabling each production line to churn out as many as 5,000 FBGs a month. That’s an average of an FBG every nine minutes, assuming 100% yields -- a figure that’s "impressive," if a little hard to believe, according to Tom Mock, director of product management at Ciena Corp. Ciena makes FBGs for use in its own equipment and has already announced 25-GHz and 12.5-GHz channel spacing.

Automating component manufacturing is good news for end users, since that typically translates into a more reliable and cheaper supply of components. Reducing costs on the component side will likely drive down system costs, which may help reduce end user costs.

Southampton Photonics already has two production lines and plans to build a third one -- facilitating production of 15,000 FBGs a month. This prompts more raised eyebrows. "That’s a very big number," Mock says. Victor Mizrahi, Ciena’s former chief scientist, doubts whether there’s demand for that quantity of FBGs.

Ciena and Southampton Photonics appear to make FBGs in similar ways and reap similar benefits. Both outfits avoid the need to design and make special phase masks for placing over lengths of doped fiber before blasting it with ultraviolet light to create gratings (barcode-like patterns of stripes) -- the way most other vendors make FBGs. Instead, Ciena and Southampton Photonics have developed computer programs that are able to make gratings from a set of standard phase masks.

Eliminating the purpose-designed phase mask avoids lengthy manufacturing delays. It also enables engineers to make longer, more complex gratings that can isolate wavelengths more cleanly than is possible with other processes. This equates to being able to reduce the spacing between wavelengths.

As the fiber can be of any length, Southampton says there’s no real limit to channel spacing. " We can do 12.5 [GHz], we can do six, we can do one, " says David Payne, Southampton Photonics’ chairman and the director of Southampton University’s Optical Research Center. Cramming even more wavelengths into a fiber isn't a technical challenge: "It's a cost equation," he notes.

Being able to create different FBGs by simply tinkering with a computer program also means that Southampton Photonics can shift production from one grating design to another at the drop of a hat. That’s handy, of course, because vendors need a different FBG for each wavelength. In other words, a 160-channel DWDMM system will need 160 different FBGs.

All of this automation leads to lower costs, but Southampton Photonics isn’t keen on talking about how that might effect its prices. A spokesman says that high-performance FBGs like theirs sell for $1,000 apiece. At that rate, the start-up could make a cool $15 million a month from its three production lines, if they worked flat out.

Mizrahi is dubious. "People aren’t willing to pay $1,000 for an FBG," he says. If they would, he’d get into the business of making them himself, he says.

This story, "Fiber Bragg gratings on the fast track " was originally published by Network World.

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