Trends in ROADM Line Card Development

Finisar is not only the leading manufacturer of LCoS-based Wavelength Selective Switches (WSS) but has also been a supplier of ROADM linecards, based on our range of WSS, for over 5 years. During this time, we have established the capability to supply both the components and sub-assemblies comprising line cards (including WSS, Optical Channel Monitors and Optical Amplifiers, both EDFA and Raman) as well as the line cards themselves1.

The evolution of ROADM line cards exemplifies the impact of the network operators’ needs for reductions in both Opex and Capex costs, size and power consumption whilst also providing greater flexibility and capability to support future network architectures.

These requirements are forcing a rethink of how line cards are designed and manufactured. Gone are the days of simply buying a bunch of optical subsystems from different manufacturers and assembling them on a circuit board with some additional control hardware. Instead, many designs require a complex disaggregation of optical modules to allow them to fit in the increasingly constrained space available2. Together with the need to optimize the relative performance of the different subsystems, this is driving changes in the way line cards are designed and manufactured.

To visualize what is happening, consider how an EDFA, which is a key subsystem on most line cards, can be transformed from an integrated module to a distributed system. In the latter, the pumps can be placed in the optimum location for thermal management, the Erbium fiber and fiber components can be arranged to fit around any other optical hardware, whilst the control electronics can be located wherever there’s room on the main line card circuit board.

Building on this idea of a distributed EDFA, the control electronics can also be designed to share common components (e.g. processors) amongst multiple subsystems which saves cost, circuit board real-estate and, critically, power the disaggregation and sharing of components allows the designer to optimize the packing density of optical functionality on the line card but that, in turn raises the problem that higher component density generally leads to greater thermal load (per unit area). Great care must therefore be taken to correctly model the thermal dissipation and ensure (as far as is possible) an effective layout of electronics and optics to optimize the thermal loading across the line card.

In addition to being able to pack more functionality into a given space by disaggregating the components, the fact that Finisar manufactures all the optical subsystems on a line card allows us to optimize the trade-offs between the different optical functions. We can therefore provide not only a smaller, lower power design, but also one that has improved functionality and hence provides more ‘bang for the buck’ for our customers.

To reduce costs, manufacturing practices must also change. For example, the ‘birds-nest’ of individual fibers, spliced together and placed in a fiber organizer is being replaced by ribbonized fibers where ever possible to simplify the assembly process and reduce costs. Ribbonized connectors like MTP assist in the process, as do subsystems such as multi-port Optical Channel Monitors. However, there is still some way to go before all the optical subsystems in a line card can be connected by fiber ribbon assemblies.

Looking ahead, the increased demand for denser packing is driving a requirement for ‘single-slot’ line cards. Whilst these can provide up to 2x the functional density of traditional double-height line cards, they introduce further pressure on component packing density and hence good thermal management engineering becomes even more important. For example, advanced cooling technologies such as heat-pipes3 may be required to prevent localized ‘hot-spots’ exceeding design temperatures.

The author would like to thank Ian Clarke and Ken Falta for useful discussions and inputs to this post.

References
1http://investor.finisar.com/releasedetail.cfm?ReleaseID=707170
2Clarke, I., “Building the next generation of linecards: the pleasure and pain of integration” Asia Communications and Photonics Conference (ACP), Beijing, November 2013
3See e.g. http://www.electronics-cooling.com/1996/09/heat-pipes-for-electronics-cooling-applications/

Finisar Australia Founders Hono(u)red

Finisar Australia’s founders, Dr. Simon Poole and Dr. Steven Frisken, were honored last month as recipients of the prestigious 2013 Australian Academy of Technological Sciences and Engineering Clunies Ross Award for innovation in science and engineering. The citation for the award reads:

“To Dr Simon Poole and Dr Steven Frisken: Australia’s most successful commercialisers of new technologies which have shaped the internet worldwide, some of which are key components of the NBN in Australia. Their products, including undersea communication systems, have been sold to all the major telecommunications equipment manufacturers in Europe, the United States, Japan and China, and have generated exports worth hundreds of millions of dollars for Australia.”

2013 Australian Academy of Technological Sciences and Engineering Clunies Ross  Award

Dr. Poole and Dr. Frisken were presented with certificates and medals by Dr. Megan Clark, CEO of CSIRO Australia.

In accepting the award, Simon Poole and Steve Frisken emphasized that although they were the individuals receiving the award, it was a team effort to build and grow a company and that it was only through the hard work and dedication of everyone involved that technologies could be successfully commercialized.

Congratulations to Simon and Steve!

ECOC 2012 Video: Finisar in the News

New Applications for LCoS Technology Part II

This week’s blog post is provided by featured author, Dr. Simon Poole.

Following on from last months’ blog on alternative uses for LCoS (Liquid Crystal on Silicon) technology, I’d like to return this month to some of the advanced research that’s being done using the LCoS that’s in our WSS and WaveShaper products.

One of the advantages of LCoS over most other approaches to optical switching is the ability to not only switch incoming light between different output ports but also, if properly programmed, to split the incoming light between multiple output ports. We have, for many years, supported a basic power sharing capability(1) in our DWP 100 range of Wavelength Selective Switches, in which optical power can be shared between an express port and an arbitrary drop port for use in drop-and-continue network architectures. This architectural approach can have advantages from both a traffic management perspective and also from an energy-efficiency perspective (2).

The implementation of optical power sharing in a WSS is, by necessity, limited to a very small subset of what is technically possible due to the need for robustness and simplicity of operation. However, this limitation does not apply when considering other potential uses of optical power splitting in R&D applications. Furthermore, it should be possible to implement wavelength-dependent splitting functions while retaining the phase and attenuation control which is present in our WaveShaper range of Programmable Optical Processors. We have therefore been working with the research team at CUDOS, Sydney University to investigate how such functionality might be implemented and some of the potential applications of the technique (3,4).

In general, splitting to different output ports is possible by a generating a superposition of phase patterns on the LCoS. As the splitting can be performed for individual pixel columns of the LCoS-array, it is possible to vary the splitting and phase as a function of wavelength, which enables reconfigurable implementation of complex interferometric structures.

The researchers have demonstrated the capabilities of the technique by creating various complex structures, including a Mach-Zehnder Interferometer (MZI), two interleaved MZIs for the demodulation of differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals, as well as an all-optical implementation of a discrete Fourier Transform (DFT) Filter for demultiplexing optical orthogonal frequency-division multiplexing (OFDM) signals. The results of these are shown in the Figure below.
Finisar Lightspeed LCoSblogpost Fig1 July2012
Figure 1: (a) Insertion loss and phase response of the constructive port of a DPSK Demodulator with an FSR of 43 GHz and an 80 GHz bandwidth; (b) Insertion loss and phase response of the four output ports of a DQPSK demodulator with 40 GHz FSR and 100 GHz bandwidth; (c) Insertion loss and phase response of the three drop ports and one continue port of an all-optical DFT filter with 15GHz channel spacing. In these results, only the phase response of one of the filter channels is shown for clarity.

The results obtained show good agreement with the expected transfer functions of the different devices. In particular, the extinction ratio of the DPSK demodulator is excellent at above 20 dB and the DFT filter shows a sinc response with the maximum in one channel aligning with the nulls of all other channels as expected.

For me, what is particularly exciting about this work is that we have now demonstrated the ability to generate, literally ‘on-the-fly’, multi-port interferometric optical devices with arbitrary transfer functions. This capability should prove a boon to researchers everywhere who need to rapidly prototype demodulators, demultiplexers and other arbitrary interferometric filters.

We will be demonstrating the ability of the WaveShaper to generate these interferometric devices at the ECOC 2012 exhibition in Amsterdam, September 17-19. Feel free to drop by the Finisar booth #500 (you can’t miss it right at the exhibition entrance) any time to see what’s possible!

    REFERENCES

1 “High performance ‘Drop and Continue’ functionality in a Wavelength Selective Switch”, S Frisken et al, Proc OFC 2006, Paper PDP
2 “Energy-efficiency of Drop-and-Continue Traffic Grooming”, F. Farahmand et al , Proc OFC 2011, Paper OTuR6
3 “LCOS-based WaveShaper technology for optical signal processing and performance monitoring”, J Schroeder et al, Proc OECC, July 2012
4 “Multi-output-port spectral pulse-shaping for simulating complex interferometric structures”, J Schroeder et al, Proc CLEO, June 2012

Finisar WSS WHITE PAPER: Balancing Performance, Flexibility, and Scalability in Optical Networks

The availability of Wavelength Selective Switches (WSS) supporting 100 Gb/s and 400 Gb/s data rates enables network operators to significantly increase bandwidth capacity in DWDM optical networks with substantial CAPEX and OPEX savings. Moving to such higher data rates, however, requires a shift from the continuing trend of implementing narrower optical channel spacing given that data rates beyond 100 Gb/s cannot fit within a 50 GHz channel….

Download Finisar’s latest WSS white paper from our website (see blue downloads box): Balancing Performance, Flexibility, and Scalability in Optical Networks