Lightchip Launches 'AWG Killer'
Several signs suggest that an alternative technology -- the bulk diffraction grating -- is muscling in on the niche occupied by the AWG. So far, AWGs have proved to be the most economic wavelength multiplexing solution for high channel-count systems. But several companies say that's about to change.
Lightchip Inc. yesterday launched the fourth generation of its bulk diffraction grating multiplexer, which it claims has better performance than AWGs in every respect (see Lightchip Intros Mux/Demux).
In addition, late last Friday (March 15), Finisar Corp. (Nasdaq: FNSR) announced it's intention to buy BaySpec Inc., which is also developing bulk grating multiplexer technology (see Finisar to Buy BaySpec ).
BaySpec and Lightchip both claim that bulk diffraction gratings offer extremely low insertion loss. Lightchip, which is in volume production of its earlier generation products, is getting "extraordinary performance numbers," says its CEO Isadore Katz.
Katz claims that the devices Lightchip's shipping to customers have insertion loss figures of 4 decibels. Lightchip is also in pilot production of its new product, called G4, which has insertion loss of just 3 dB. What's more, he says these are worst-case figures, including the connectors, and notes that other companies often quote insertion loss figures in different ways -- without the connectors, or typical case rather than worst case -- because it makes the numbers look better.
Katz adds that the best devices available from AWG makers such as Lightwave Microsystems Corp. offer around 5dB insertion loss.
But AWG vendors dispute this. "We have made devices with insertion loss less than 3 dB," claims John Midgley, CEO of Lightwave. Another vendor, Scion Photonics Inc., which made its debut at the Optical Fiber Communication Conference and Exhibit (OFC), also claims its devices have insertion loss of 3 dB or less (see Scion Offers $100/channel AWGs).
Katz, however, contends the AWG vendors are comparing apples and oranges. Lightchip offers a product with a very broad passband, referred to as a "flat-top" response. That means that the incoming wavelength from the system can be slightly detuned from the center wavelength of the multiplexer without the light being significantly attenuated.
Lightwave Microsystems is, in fact, quoting numbers for an AWG with a so-called "Gaussian" response, which isn't so resistant to wavelength detuning. The company also offers flat-top AWGs, but these have an insertion loss of 5 dB.
Therein lies the problem, in Katz's view: AWG performance involves too many tradeoffs. "You hear AWG people say they can give you athermal, low insertion loss, low crosstalk... Then they say 'Which one do you want?' You can't have them all." Bulk diffraction gratings, he claims, are the first product that does it all.
Reliability is another key factor where Lightchip claims to come out on top. "For lots of our telecom customers, the reliability issue is as important as the performance," Katz contends. If a single laser in a system fails, one channel is lost, but if a 40-channel multiplexer fails, all 40 channels are lost simultaneously.
Lightchip promotes its products as highly temperature insensitive, having a wavelength drift with temperature of 0.1 picometers per ° C. AWGs, Katz claims, are highly thermally sensitive -- most require heaters or thermoelectric coolers and control circuitry to stay stable. "When I say they are thermally sensitive, this means somebody touching it, or a convection current inside a box. And it's insidious -- suddenly the receiver at the other end of the line starts reporting errors. It can take days to figure out that it was the mux overheating."
Lightwave's Midgley agrees with the importance of reliability. Both Lightwave Microsystems and Scion Photonics claim their parts were Telcordia Technologies Inc. qualified, which they say is adequate proof that their products are reliable for use in telecom networks (see Lightwave Announces New Products).
It should also be kept in mind that AWGs are a lot more than just another way of splitting and recombining wavelengths. They're a starting point for making a wide range of more integrated optical components such as mux-variable optical attenuators, optical channel monitors, dynamic gain equalizers, and optical add/drop multiplexers (see Photonic Integrated Circuits).
— Pauline Rigby, Senior Editor, Light Reading
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