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.

More on this in a future blog post. Feel free to comment directly on this blog or contact me at simon.poole@finisar.com.