Cisco surprises with silicon photonics move

Karen Liu/Ovum
25 Mar 2013

At OFC/NFOEC 2013, Cisco presented a silicon photonics modulator with integrated driver that competes with potentially both LiNbO and InP modulators for 100G coherent.

The move took many attendees – including me – by surprise. Silicon photonics for client-side 100G has been watched with great attention because there is no satisfactory solution. Coherent line-side, in contrast, has not one but two modulator solutions already. How can a third technology platform wedge its way in, and why?

On the other hand, in retrospect, we should have seen that this application is a great fit for silicon photonics. Low power modulation is what silicon photonics is best at. Since the beginning Lightwire, now part of Cisco, has used the same Mach-Zehnder device structure that line-side is already using. It has always said the driver, already in silicon, could be integrated with the modulator if it made sense.

The next generation of 100G line-side looks to use InP for size reduction into CFP and CFP2 densities. However, many believe the highest-performance versions might have to remain in LiNbO.

If the SiP modulator can deliver the performance, it would avert the issue of having a mix of high density and low density in system offerings. If it can further deliver the price and hybrid integration with the laser, the industry could eventually reconverge on a single external modulation platform.

The device has yet to have commercial-grade packaging and other productization done. But it does show how silicon photonics can compete simply on its true strengths rather than hype about large-scale integration.

Karen Liu is a principal analyst for components at Ovum. For more information, visit

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