Fiber was predicted to be the next big advance within the next five years … for the last 20 years. Now TE’s new Coolbit leads the optical evolution to optimize the performance level only fiber can provide.
The battle between copper and fiber media in I/O and backplane applications has been going on for more than 20 years. Except in long-haul telecommunication applications, copper has been the medium of choice, due to many years of proven experience and manufacturing processes, low cost, and ease of field repair. Fiber was predicted to be the next big advance within the next five years … for the last 20 years.
Limitations of Copper
The advent of multi-gigabit signaling encouraged fiber advocates that the technical limitations of copper would drive the industry to optic alternatives. Remarkable advances in high-speed signaling protocol, together with improved signal conditioning techniques, have enabled copper to continue to dominate the industry even as circuits reach 25Gb/s data rates. At the same time, some of the performance limitations of copper, such as maximum practical length of the channel and power consumption, have begun to impact system design flexibility. Increasing costs associated with required signal conditioning devices and larger-gauge, higher-performance cable are chipping away at the cost advantages of copper channels.
Recognizing that demand for bandwidth will continue to grow, and that the basic laws of physics that apply to electric signal propagation in copper are not likely to change, leading connector manufacturers have continued to explore how optic alternatives could be economically produced. While continuing to develop high-speed copper interfaces to enable next-generation applications, they want to be prepared to support customers who need the performance advantages that only fiber can provide.
New Technologies from Trusted Names
Avago Technologies, a manufacturer of optoelectronic components, and Samtec, a leading miniature connector supplier, have introduced a new class of optical transceivers that are designed to take high-speed signals off the board and convert them to optical signals. These mid-board pluggable devices consume very little footprint space while simplifying the design and manufacturing of the PCB. The Avago parallel optical transceiver can deliver 12 x 10Gb/s, 12 x 12Gb/s, and 12 x 14Gb/s to support applications in Ethernet, Optical Transport Networking, and Infiniband.
The Samtec Firefly Micro FlyOver System enables engineers to design either copper or fiber channels operating at up to 28Gb/s. Equipment applications for this active optical cable assembly in chip-to-chip, board-to board, and rack-to rack can be economically designed with an 11.5 x 18.4mm PCB footprint. This AOC features an integrated heat sink and consumes a maximum of 2.1 watts. The maximum reach of the optical ribbon cable is 10 meters.
Additional suppliers, including US Conec, Finisar, and Reflex Photonics, have introduced on-board optical engines to address this emerging market.
TE Connectivity recently announced a major expansion into the mid-board optical engine arena with the introduction of four products in a new 25Gb/s optical platform. Rather than build an optical engine using off-the-shelf components, TE chose to differentiate its products by focusing the design on the two critical performance requirements of bandwidth density and low power consumption as identified by its customers.
TE designed and tooled a fully integrated fabrication process that has resulted in their new 25Gb active optical platform by utilizing the optical component resources acquired by the purchase of the Zarlink Optical Products Group in 2010.
The heart of the platform is the Coolbit optical engine, which is designed to operate at multiples of 25Gb/s data rates while consuming as little as 380mW per channel. Individual components, including the VCSEL, photodiodes, TIA amplifier, and driver IC, were specifically designed for low power consumption and are mounted on a glass substrate to produce a highly integrated flip-chip package.
The mid-board optical transceiver delivers 12 full duplex channels at 25Gb/s each while consuming less than 4.5 watts. Advanced clock and data recovery (CDR) circuits ensure excellent bit-error rate performance. Each module delivers a total of 300Gb/s per square inch of board space. A digital diagnostic monitoring interface allows user management of key module parameters. The engine is attached to the PCB via a high-speed BGA/LGA socket. Optical connectivity is accomplished via a standard 2 x 12 MT connector to ribbon fiber cable. A secondary heat sink allows tightly packed arrays of transceiver modules.
Coolbit optical engine technology has been integrated into several pluggable front panel I/O interfaces. The QSFP28 active optical cable (AOC) assembly provides four 25Gb/s bi-directional channels with a total power consumption of less than 1.5 watts. These hot-pluggable assemblies feature transmitter input equalization that compensates for loss and are available in a variety of optical lengths.
The QSFP28 4 x 25GB/s transceiver delivers 100Gb/s data rates with the ability to plug an industry standard MPO/MTP connector at the rear of the module for added application flexibility. Total power consumption is 1.5 watts.
The CDFP is an emerging mechanical form factor that is capable of delivering a total of 400Gb/s via sixteen 25Gb/s duplex channels. TE has utilized the Coolbit optical engine to produce an active optical cable assembly that can extend the reach to 100 meters while consuming less than 6 watts per end.
The Industry’s Big Picture
This new optical platform is targeting applications that will require up to 400+Gb/s links in standard equipment faceplates, such as high-speed channels within and between switches, routers, servers in data centers, supercomputers, and eventually optical planar backplanes. Physically smaller connectors that feature greater bandwidth density allow designers to pack more I/O per box, a trend likely to continue well into the future.
The industry seems to be settling on using multiples of 25Gb/s bandwidth as a basic building block to achieve constantly increasing channel data rate targets. Use of optical fiber significantly reduces the bulk and weight of copper cable, which often must be increased in diameter as data rates increase. Optical fiber is very difficult to tap without detection, improving data security. The nearly unlimited bandwidth of optical fiber is very attractive to engineers who are looking for bandwidth headroom to “futureproof” their long-service-life product. Reduced power consumption minimizes thermal management challenges as well as operating costs. Optical transmission of high-speed signals overcomes the length and related signal integrity limitations of copper alternatives, and creates opportunities to change existing system architecture paradigms.
The Coolbit optical engine will not fundamentally change the balance between copper and fiber interfaces as they are used today. Engineers will continue to choose the most cost-effective interconnect solution that satisfies the electrical and mechanical requirements of the product under design. Copper will likely continue to dominate links of less than three meters in most applications, but the development of the Coolbit optical engine does provide a significant step toward offering a cost-competitive alternative to next-generation system designers who require the mechanical and performance advantages it brings.
Robert Hult, Market Director, Bishop & Associates, Inc.