OPTICAL NETWORKING TRANSFORMATION - DARYL INNISS
Why photonic integration and silicon photonics is forcing companies to act
The dual benefits of device integration and higher speeds are encouraging network systems providers to add on innovative silicon photonics solution providers – by acquisition or development. It can only be a matter of time before these next-generation developments raise the game in optical networking, writes Daryl Inniss. mode transceivers to connect
For coherent 100 gigabit using polarisation-multiplexed, quadrature phase-shift keying (PM-QPSK) modulation, the transmitter includes polarisation beam splitters, and four modulators to implement PM- QPSK. The receiver includes a 90-degree optical hybrid, the function of which is to mix the received signal with the reference signal to implement coherent detection and photo-detectors to recover the transmission and for monitor purposes. Silicon powers ahead Acacia introduced in 2014 transceiver that is based on monolithic integration of these optical functions in silicon. The laser is the only optical function not integrated. Acacia demonstrates the power of silicon photonics when it introduced its AC-400, a 400-gigabit transceiver a year later. It is the industry’s first dual-carrier transceiver. Its two- wavelength “super-channel” flexible rate design supports 200, 300 and 400 gigabit line rates. The design uses two silicon photonic chips, one per channel, and implements PM-QPSK for 100 gigabit transmission, polarisation multiplexed, 8-quadrature amplitude modulation (PM- 8QAM) for 150 gigabit and PM- 16QAM for 200 gigabit. Each is carried on one of the two carriers to achieve the module’s total rates. Parallelism and integration, areas where silicon design is king, are key to supporting high data rates going forward. In this fast-evolving sector, Ciena is just the latest player to show its hand in a market preparing to use such technology for these applications. But it is not likely to be the last. its impressive AC-100, a 100-gigabit coherent
chip foundries, component and equipment vendors, and end-users. There are start- ups and established players. Furthermore, there are vendors with optical and electrical expertise also participating. Although silicon photonics- based products have yet to deliver significant financial returns, the medium-term outlook is positive for the technology and for the players. Ethernet transitions to 400G Single-mode transceivers supporting 100 gigabit and beyond for data centres have received the most attention, so far. The Web 2.0 players are building mega-data- centres that require tens to hundreds of thousands of single-mode optical connections at 100 gigabit and above. At 100 gigabit, four sets of transmitters, waveguides, photodiodes, and four corresponding receivers are needed. The number of transmitters and receivers doubles at 400 gigabit. Photonic integration is well suited to address this opportunity, and vendors including Luxtera, Skorpios, Aurrion, Kaiam, and Lumentum are all developing solutions. While the high volume make this a good silicon photonics opportunity, greater integration is needed for the coherent metro and long-distance transmission, presenting an even better opportunity for silicon photonics to distinguish itself. Looking at the latest announcement once again, Ciena’s acquisition of TeraXion supports metro and long- distance transmission at 100 and higher gigabit speeds. Photonic integration is an important element at these data rates because multiple optical functions are required.
equipment inside the data center — links that combine four lanes, each supporting 25 gigabits. Although 100 gigabit transceivers have been shipping for five years, the market is transitioning to high-volume. As face-plate space is limited and small size, low power, and low cost are required, many optical devices and functionality such as lasers, receivers and waveguides now must be integrated. Bigger scale – smaller cost Integration of photonic functions in silicon appears to be extremely promising given the large scale and low cost that complementary metal- oxide semiconductor (CMOS) processing has brought to the electronics industry. There have been commercial successes including Mellanox’s variable optical attenuator, Luxtera’s 40 gigabit active optical cable, and Cisco’s 100 gigabit CPAK transceiver. Nonetheless there is significant industry scepticism that silicon photonics will become a mainstream technology because the application of CMOS to photonics has yet to deliver a significant financial or performance return (see the LightCounting article “Is silicon photonics a disruptive technology?” on p22). Transmission at 100 gigabits and beyond presents promising opportunities in numerous areas, fuelling the emergence of a robust silicon photonics ecosystem. gives a snapshot of select vendors currently developing silicon photonics, and it is exciting to see the diversity of the participants. Different levels of the optical communications “food chain” are represented including
C iena announced in January 2015 its plan to acquire the high-speed components assets of Teraxion for $32 million. The move is the latest in a string of transactions where photonic integration and silicon photonics play a central role. The systems vendor is bringing a component supplier in-house to reduce time-to-market, and to tighten the integration of optics with electronics to improve performance and density while reducing cost-per-bit. Photonic integration and silicon photonics acquisitions are a market-wide trend signalling the importance of these technologies for optical links. The market has witnessed a steady stream of silicon photonics transactions over the past five years including Cisco Systems’ acquisition of Lightwire, Mellanox Technologies acquiring Kotura, Huawei acquiring Caliopa, and MACOM Technology Solutions buying Photonic Solutions. In addition, start-ups Aurrion, Skorpios Technology, Kaiam, Acacia Communications, and Sicoya have been funded to develop products using a combination of photonic integration and silicon photonics. DaryL Inniss Director of New Business Development at OFS Photonic integration is a de-facto requirement for 100-gigabit transceivers for transmission distances between hundreds of meters to thousands of kilometers. This is the first time photonic integration is needed for single-
ISSUE 6 | Q1 2016 24
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