Autumn 2019 - Optical Connections Magazine



Fibre capacity demand across global networks is driving the need for continued innovation in coherent optical system design. Network requirements are also diverging, creating dierent feature sets for both mechanical form and performance depending on the application. These trends are converging with new wafer scale processing for key foundational technologies that oer benefits of circuit integration, performance and manufacturability. Two technologies underpin the electro-optical transmit and receive chains for today’s coherent systems: indium phosphide (InP) and silicon photonics (SiPhot). Patricia Bower , Senior Manager, Portfolio Marketing at Ciena explains.

F or the last decade, as coherent technology has moved through several generations, a single DSP design, combined with the right photonic components, met the needs of most links requiring capacities of 100Gbps per wavelength. By the second generation there were already designs customised to support dedicated applications. With the emergence of applications needing the benefits of coherent technology in compact, pluggable form factors, a clear delineation between two primary application sets is driving development paths today. These are performance- optimised solutions targeting best system performance enabling maximum optical layer automation; and footprint-optimised solutions targeted to fit into a specific form factor and power envelope. The various network applications driving this dual path include single-span DCI, access, multi-span metro, long-haul and sub-sea. Single-span DCI can be divided into two subsets: 400ZR interoperable plugs deployed in router chassis for IPoDWDM for up to 120km links and high-performance 800G in transport for demarcation between router and transport, providing maximum spectral eciency. In access networks, coherent plugs will replace grey optics, requiring footprint- optimised, pluggable solutions that are hardened for exterior cabinet deployments. In multi-span metro networks, both solution types are applicable, and the

right fit is dependent on the importance of spectral eciency and operational considerations, such as the need to integrate seamlessly with a multi-span photonic layer. Finally, both long-haul and subsea requirements demand solutions that are optimised for highest spectral eciency and performance in order to maximise fibre utilisation. INNOVATION THROUGH SEVERAL COHERENT OPTICAL COMPONENT GENERATIONS Fibre capacity increases over the last decade can be viewed from the perspective of coherent DSP timeline, where each successive generation has doubled the maximum capacity rate on an optical wavelength while also enhancing the capabilities of systems beyond that of a data transport system. Through each successive generation, two key trends have gone hand in hand with innovation in coherent optical system design: the need for more tightly coupled

design and packaging between the electrical and optical components and the need for greater levels of integration in both electrical and photonic circuits. To meet new network requirements, there are challenges for the photonic components that must be met for each type of solution. Parameters like high- bandwidth (>50GHz) and linearity to support high-order modulation formats are required. Low power consumption is required for pluggable coherent solutions. Photonic integration - the implementation of greater levels of functionality in microscale layout and manufacturing - for both InP and SiPhot is enabling support both for high performance and footprint-optimised solutions. Greater levels of functional integration translate to reduced area, such as the ability to combine transmit and receive channels on the same die. It also paves the way for co-packaging of photonic elements in dierent process for higher

Network applications for coherent optical solutions


| ISSUE 18 | Q3 2019

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