Posts tagged: WSS

Finisar Demonstrates 40G CFP Optical Transceiver at ECOC in Vienna

In Vienna this week? Then come and see us at this year’s ECOC exhibition and conference. We’ll be showcasing our latest technologies – including our 40G LR4 CFP module new EWP 1×2 WSS module for edge applications, and the advanced WaveShaper S-Series, a reduced form factor version of the existing WaveShaper product to afford more space within test systems. If you’d like to hear more about this and our other product lines, or chat about what’s next for the optical communications industry, stop by and visit the Finisar team at booth #640. You can also follow us on twitter for live updates at the #ECOC event this week.

ECOC 2009 ends September 23; don’t miss your chance to catch us while we’re in town. And if you have some time on Sunday, it’s worth a visit to hear what Finisar’s Engineering Director, Chris Cole has to say about 100G client interface applications. For more details on his panel session, visit:

Hope to see you there!

Wavelength Selective Switches and Mixed Channel Spacing

In my last posting about Liquid Crystal on Silicon (LCoS) technology I mentioned that one of the technical differentiators of the LCoS technology was the ability of a single WSS to support both 50- and 100-GHz channel spacing at the same time.

The flexibility of Finisar’s core LCoS technology means that all Finisar WSSes have the ability to carry a mixture of optical channels with arbitrary bandwidths. Unlike other standard MEMs or Liquid Crystal switches the LCoS switching element contains, literally, millions of individual switching elements in a continuous grid which are linked together (under software control) to form the required channels for switching and attenuation.

For example, our high-resolution DWP50 platform uses around 6,000 pixels to switch each 50GHz channel, providing extremely granular control of the channel properties. To switch a 100 GHz channel, all we need to do is to group together two adjacent sets of 6,000 pixels and control them as a single entity, which is very simple to do. This ‘channel bonding’ capability can be achieved ‘on the fly’ and so provides operators with the advantage that they do not have to pre-define channel bandwidth allocations but can vary them as required by the data rate and modulation format that each individual channel is carrying.

Since the software defines where a channel starts and finishes, there is no reason that the frequency widths of channels shouldn’t vary arbitrarily across the C-band. In practice, anything but a simple grid can become quite confusing and difficult to manage from a network operating system perspective and so a mix of 50- and 100-GHz channels is all that is currently required.

However, as the demand for increased capacity on any given fiber continues unabated, it is possible to envisage a future network in which the combination of a completely flexible WSS (such as Finisar’s DWP range) together with arbitrarily tunable lasers, means that channels of arbitrary bandwidth and centre frequency can be placed anywhere within the C- (or L-) band to optimize the data-carrying capacity of the fibre. Indeed, it is already possible to start investigating how such a network might operate by using our WaveShaper 4000E Programmable Optical Processor to create a WSS with arbitrary channel centre frequencies and bandwidth, as shown in the image below.

Mixed Channel_Finisar Illustration_2009

More on this in a future blog post. Feel free to comment directly on this blog or contact me at

OFC ‘09, ROADM technology and the future network

This week’s entry comes from Ian Clarke. Ian is one of our key technical guys in our Sydney facility, where Finisar develops and manufactures our WSS (Wavelength Selective Switch) modules.


OFC 2009 felt like a giant planning meeting for 100 Gb/s systems. Everywhere could be heard debate and proposals for components, protocols and modulation methods. The most difficult component is clearly the transponder. In particular, the ASICs for the receivers look very challenging to build. How do you build an analog–to-digital converter that runs at 60+ Gb/s; and when you do, how do you process the data fast enough?

However, my real interest was the requirements for wavelength selective switches (WSS), which also received plenty of attention. The most interesting requirement for an engineering manager like me is to know when we need to deliver these parts.

On Sunday, Glenn Wellbrock from Verizon described a series of trials of 100 Gb/s Ethernet signals. On Monday Jim King from AT&T described their initial build out of their 40 Gb/s system between “NFL cities” (the 25 biggest cities in the US). He stated that he could use 100 Gb/s channels now if he could get them, but in reality he didn’t think he would be deploying them seriously until 2011. Similarly, a Nokia–Siemens paper suggested that 2012 would be the critical year for 100 Gb/s systems. However, Glen Wellbrock’s message was that they wanted to be building 100 Gb/s ready systems that ran 40 Gb/s until the transponders were ready. This suggests that we are likely to see requirements for ROADMs, amplifiers and other components to be “100 Gb/s ready” quite soon.

This raises the question: what sort of WSS should we be building for 100 Gb/s systems? The required bandwidth depends on the modulation format that finally dominates. Last year, Chandresekhar’s paper from ALU Bell Labs used PM-RZ DQPSK (polarization multiplexed return-to-zero differential quadrature phase shift keying) needing a huge 44.5 GHz bandwidth (try to fit that in a 50 GHz window!). Renaudier’s paper (also from ALU, this time from France and also published last year, but mentioned in this year’s workshop) needed only 35 GHz to achieve zero penalty on a PM-RZ-QPSK with coherent detection. 16-QAM (quadrature-amplitude modulation) systems are more efficient, but are so complex to build that I feel would be unlikely to be the first system used. Other contenders are 8-PSK (phase shift keyed) and OFDM (orthogonal frequency division multiplexing), but these have their own issues. Coherent detection systems have advantages in CD chromatic dispersion) and PMD (polarization mode dispersion) tolerance. If we assume that the initial 100 Gb/s systems will use a coherent PM-RZ-QPSK modulation format, which is a reasonable guess at the moment, then targeting a ±17.5 GHz real, concatenated bandwidth for 2010 would be reasonable.

Ian Clarke is an Engineering Manager for Finisar Australia (

Ian Clark works at Finisar Corporation.