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Optical components

Lightchip Launches 'AWG Killer'

ANAHEIM, Calif. -- OFC 2002 -- Have Arrayed Waveguide Gratings (AWGs) met their match?

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
http://www.lightreading.com For more information on OFC 2002, please visit: www.nottheofc.com

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dwdm2 12/4/2012 | 10:46:00 PM
re: Lightchip Launches 'AWG Killer' "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."

Boasting about what one's technology can do, and actual deployment of that technology by customers are not the same thing...

I'd like to see some real numbers. Pauline, would be able to get/share some info about realistic (present of future) deployment of their miracle machine?

Regards,
AR
dwdm2 12/4/2012 | 10:45:59 PM
re: Lightchip Launches 'AWG Killer' "AWGs, Katz claims, are highly thermally sensitive -- most require 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.""

Hey, there is some fact twisting here...
AWGs are thermally sensitive BUT they don't need to be cooled!

AWGs need to be heated way above room temperature. And there is no convection current inside the box either.

In fact, no electrical circuit is necessary for the AWG to work. The electronics is only to hold the temperature, and the control circuitry is outside the box.

Katz's emotion is understandable, she is trying to promote her product. But facts are fact...

Regards,
AR
othr132 12/4/2012 | 10:45:58 PM
re: Lightchip Launches 'AWG Killer' Can anyone offer a description of a "bulk diffraction grating" or perhaps point out a reference link. Thanks
sunnyguy 12/4/2012 | 10:45:54 PM
re: Lightchip Launches 'AWG Killer' "In fact, no electrical circuit is necessary for the AWG to work. The electronics is only to hold the temperature, and the control circuitry is outside the box."

So what happens to the performance when the power goes out and there is no temperature control?

dwdm2 12/4/2012 | 10:45:53 PM
re: Lightchip Launches 'AWG Killer' sunnyguy, if there is no power, the whole box shuts down. No matter which gennie is kept in there, it just can't work if there is no power!

An anecdote: The physics professor asked the freshman class, "so what do you think the difference between the light that comes out of a light bulb and the light that we get from the sun?"

The smartest boy in the class answered, "we have to pay electric bill for the bulb-light, but sun-light is free."
endof tunnel 12/4/2012 | 10:45:52 PM
re: Lightchip Launches 'AWG Killer' Bulk grating is what is used in optical spectrometer. It basically contains parallel bars. Light is diffracted and dispersed in the direction vertical to the bar's orientation. Spectrometer can resolve light in single picometer while DWDM wavelength channel separation is typically 400 pm for 50GHz spaced channels. The problems of using conventional bulk grating is that it needs large distance to disperse light and therefore the system length could be long. People can fold length using mirrors. The other problem people having with bulk gratings is that it is a polarization sensitive technology and PDL and PMD could be big. I believe what Lightchip and Bayspec are both doing are either volume hologram which is less sensitive to polarization or planar hologram with double pass compensation schemes.

One very crucial factor which was not mentioned by either camp is the level of chromatic dispersion. AWG can quote +/-15 ps/nm and I don't know what is the bulk grating result. As channel gets denser and higher speed, the Chromatic dispersion is a killer. Thin film and FBG filters have tough time to compete in this aspect due to physics. AWG was said to be better than both. My feeling is that bulk grating could be even better in this aspect. They fundamentally should belong to the non-minimum phase filter category.

endof tunnel 12/4/2012 | 10:45:51 PM
re: Lightchip Launches 'AWG Killer' Both of you are right. AWG does not need electricity to work. It needs it to stablize to a high temperature and lock it there. So, people worry about power shut down and thermal shock. Thermal shock is defined as the certain temperature change and Bellcore qualification calls for 60 C/hour. It is there to prevent a cooling fan failure. AWG needs a temperature sensor to report to its microprocessor the temperature change and uses its feedback loop to adjust the heating to balance the temperature. It works just fine. However, people prefer to use true passive devices which is sourceless. This is the best selling point of thin film filter.

I think AWG also needs to have a long time to start (5 min may be) every time it begins working from 0 power.

The best thing about AWG is its integration platform that allows to build on the same wafer other components, such as VOA's, photodetector, channel tap, etc.
grasslight 12/4/2012 | 10:45:47 PM
re: Lightchip Launches 'AWG Killer' "One very crucial factor which was not mentioned by either camp is the level of chromatic dispersion. AWG can quote +/-15 ps/nm and I don't know what is the bulk grating result. Thin film and FBG filters have tough time to compete in this aspect due to physics. AWG was said to be better than both. My feeling is that bulk grating could be even better in this aspect. They fundamentally should belong to the non-minimum phase filter category."

AWG has fundamental limitation of disperion with flat top profiles. >30 pm/nm I think.
grasslight 12/4/2012 | 10:45:47 PM
re: Lightchip Launches 'AWG Killer' "The problems of using conventional bulk grating is that it needs large distance to disperse light and therefore the system length could be long. People can fold length using mirrors. "

I saw Ligthchip 100 GHz device at OFC today. It is quite small.
BestAWG 12/4/2012 | 10:45:46 PM
re: Lightchip Launches 'AWG Killer' " Scions AWGs are <10ps/nm chromatic dispersion and IL is typically 2.5dB (ie <3dB)...they already offer integrated devices (T-Mux, V-Mux, TV-Mux....) prices are <$100/ch at low channel count for discrete products and integration decreases average price without performance penalty eg 2dB 16ch V-Mux....
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