Migration path leads to SFP+

Interface chip vendors in growing numbers are tailoring chips to support the migration of datacom and telecom routers and switches to SFP+, the latest pluggable optical module form factor for use in 10-Gbit/second Ethernet and 8.5-Gbit/s Fibre Channel systems.

SFP+ offers a more compact form factor than X2 and XFP packages and runs on less than 1 watt. In addition, it offers higher mounting densities than current 10-Gbit/s devices. A more streamlined design has made SFP+ the same size as the SFP (small-form-factor pluggable) industry standard, used for data rates up to 4 Gbits/s.

The newer standard reduces cost by removing everything except the optics from the modules. Signal-conditioning functions are moved from the module to the host card, as are the serializer/deserializer (serdes), media access controller (MAC), clock and data recovery (CDR) and electronic dispersion compensation (EDC) functions. The result is a simplified transceiver module with electrical-to-optical and optical-to-electrical polarization-mode dispersion (PMD) functions.

Three SFP+ ranges have been standardized for 10-Gbit/s nets: 10GBase-SR (30 to 300 meters with OM3-grade multimode fiber), 10GBase-LR (10 km across single-mode fiber) and 10GBase-LRM (220 meters with FDDI-grade multimode fiber).

Last month, Avago Technologies (San Jose, Calif.) began offering production quantities of a 10-Gbit/s Ethernet SFP+ short-reach optical transceiver. At the core of the AFBR-700SDZ are Avago's own 850-nanometer vertical-cavity surface-emitting lasers (VCSELs), which leverage technology from its 4G VCSEL design. According to the company, that earlier design has undergone more than 2 billion device-hours of testing without failure. The AFBR-700SDZ uses multimode fiber (MMF) and extends coverage to 300 meters.

The transceiver supports the SFF-8431 specification for enhanced 10-Gbit/s SFP+, as well as SFF-8472 for the digital monitoring interface (DMI) in optical transceivers. The RoHS 6-compliant, Pb-free device delivers real-time temperature, supply voltage, laser bias current and laser average output power, and it receives input power information through a two-wire interface. The digital diagnostic interface allows disabling of the transmitter to check for faults, as well as for the monitoring of potential loss of signal in the receiver.

Last year, Applied Micro Circuits Corp. (Sunnyvale, Calif.) claimed to be the first vendor to ship a fully integrated dual-port SFP+ transceiver. The QT1215 is a 9.95- to 10.6-Gbit/s CDR circuit with fully adaptive EDC capability. It not only provides an interface between a 10-Gbit/s serdes and an SFP+ optical module but also converts a single differential input XFI data stream into a serial 9.95- to 10.5-Gbit/s output data stream, in compliance with the SFP+ standard.

In the SFP+ side receive direction, the QT1215 contains a sophisticated EDC engine that complies with both the SFP+ and LRM standards. The EDC permits the recovery of signals degraded by differential mode delay (DMD), chromatic dispersion (CD) and PMD. Using internal algorithms, the chip continuously adapts to channel characteristics.

The EDC engine in the QT1215 uses a low-power mixed-signal architecture that instantly adapts to fiber impulse response changes. The transceiver was designed to exceed the performance specified in 10GBase-LRM, thereby providing a robust product for MMF applications, according to the company.

The QT1215 includes a standard two-wire interface for communicating with external E²PROM for the embedded microprocessor. A separate two-wire interface provides control and status capability for the IC. The integrated high-performance embedded controller provides EDC adaptation control and can be programmed for various value-added capabilities.

At the core of Avago's 10-Gbit/s SFP+ transceiver are its own 850-nm VCSELs.

Sumitomo Electric Industries Ltd. (Osaka, Japan) recently launched a line of SFP+ transceivers for 10-Gbit/s applications that is available in production quantities. The SPP series is designed to meet IEEE 802.3ae and 802.3aq specifications for 10G Ethernet.

Sumitomo released three transceivers in the SPP5000 series. SPP5101SR, for 10GBase-SR, uses an 850-nm VCSEL for operation over MMF at distances up to 300 meters. SPP5101LM is for 10GBase-LRM, using a 1,310-nm Fabry-Perot laser for operation over MMF at up to 220 meters. SPP5101LR is for 10GBase-LR and uses a 1,310-nm DFB laser for operation over single-mode fiber (SMF) at up to 10 km.

In December, Vitesse (Camarillo, Calif.) released the VSC8242, a CDR chip with EDC. Although the device is initially aimed at X2, the dominant optical module for 10-Gbit Ethernet shipments today, its lead application is enabling the migration of datacom and telecom routers and switches to the SFP+ optical module form factor. The VSC8242 supports all three SFP+ range applications and complies with 802.3aq, 802.3ae and SFF-8431 electrical specifications. That functionality allows existing module designs to move quickly and cost-effectively to the SFP+ form factor.

The VSC8242 incorporates two bidirectional 10-Gbit/s paths to support the increased port densities. Additional features include various lookbacks, a complete set of programmable Rx and Tx path functionality (such as output preemphasis) and full Gigabit Ethernet data rate support. Packaged as a 12 x 12-mm flip-chip CSP, the VSC8242 has an integrated microcontroller that automatically adapts to dispersed optical signals. Typical power dissipation is 750 mW for each bidirectional channel.

Finisar (Sunnyvale, Calif.) recently introduced 8-Gbit/s long-wavelength SFP+ transceivers for advanced storage networking applications. The 1,310-nm transceivers support 1.4-km and 10-km transmission over SMF and are well-suited for FICON and disaster-recovery storage applications. Based on edge-emitting laser technology, the devices include Finisar's digital diagnostics technology and dissipate less than 1 W. Finisar's SFP+ family now includes short- and long-wave transceivers at both 8 Gbits/s and 10 Gbits/s.