ProtoDel Pushes Passives
Commodity components like couplers and filters don't usually make headlines... except when they fail (see JDSU in EDFA Recall).
Let's make an exception for U.K. company ProtoDel International Ltd., which claims it has a superior way of making passive components like couplers. The company will be exhibiting its newest product, an in-line power monitor, at the upcoming Optical Fiber Communication Conference and Exhibit (OFC) (see Protodel to Demo Power Monitor).
While ProtoDel isn't drawing any explicit comparisons with the problems suffered by JDS Uniphase Inc. (Nasdaq: JDSU; Toronto: JDU), it is claiming that its technology leads to higher-performance, higher-reliability components.
The key to it all is that ProtoDel doesn't place anything in the light path, as traditional approaches do. Instead, it gains control of the optical signal through what's called the "evanescent field," which is a tiny fraction of the total optical energy that's carried in the outer cladding of the Optical Fiber, within a few microns of the core. (Laws of physics pertaining to the boundary between core and cladding dictate that some energy is always carried in the cladding.)
"If you don't have to open the core up, it has a significant impact on performance, and it's easier to manufacture, too," says Ian Giles, founder and CEO of ProtoDel.
He adds: "Although there is very little energy in the cladding, by manipulating it we can do anything we want -- modulate, attenuate, you name it. The evanescent field is often called the evanescent tail. We like to say we're using the tail to wag the dog."
ProtoDel's approach isn't entirely unique, but the company seems to be taking the idea further than other vendors, of which there appear to be two -- Molecular OptoElectronics Corp. (MOEC) and Canadian Instrumentation & Research Ltd.
Here's what ProtoDel does. To make components, it polishes away part of the fiber's cladding, creating a D-shaped fiber. Light traveling through such a fiber doesn't really notice the change and continues its journey uninterrupted, resulting in improved performance, such as very low back reflection (-70 dB for the in-line power monitor).
But if a material with a high refractive index is moved close to the core, close enough that it overlaps with the evanescent field, light will leak from the core. The amount of light that leaks out can be controlled very precisely by changing the distance of the high-index material from the core, says Giles. Thus, it's easy to see how this technology can be used to make a variable optical attenuator (VOA) -- ProtoDel's first product, soon to be released in its third generation.
To turn this basic idea into an in-line power monitor, ProtoDel brings a photodiode up close to the fiber and fixes it in place. A small amount of light is tapped off, just enough to allow the photodiode to measure a reasonable dynamic range (-40 dB to +23 dB). It provides an alternative to using a tap-coupler and separate photodiode in a range of applications such as gain modules and protection monitors that prevent sensitive pieces of equipment from optical overload.
To back up its claim of improved performance, ProtoDel reports typical figures such as insertion loss of 0.2 dB, polarization-dependent loss (PDL) of 0.1 dB, and wavelength-dependent loss of less than 0.1 dB. That last figure in particular is worth noting because fused fiber couplers -- one of the main approaches for making tap couplers, used by companies like Gould Fiber Optics and JDSU -- have very strong wavelength dependence.
According to Giles, ProtoDel has spent the last three years or so developing semi-automated manufacturing gear so that it can produce its components cheaply and in quantity. The key part of the process -- removing the cladding -- has been proven to have a yield of 95 percent, he claims. The company has already shipped samples of its in-line power monitor in ones and twos and will be ready for volume production by OFC.
ProtoDel was founded in 1995 to develop fiber optic sensors using its polished fiber approach. It switched attention to telecom in 1998, and in 2000 received an investment from MTI Ventures to help it further its ideas (seeFiber Component Startup to Expand). ProtoDel has plans to integrate different functions in the same piece of fiber. Putting a power monitor immediately next to a VOA, for example, would provide feedback that could be used to control the settings on the VOA.
— Pauline Rigby, Senior Editor, Light Reading