SFP

SFP transceivers are expected to perform at data speeds of up to five gigabits per second (5 Gbps), and possibly higher. Because SFP modules can be easily interchanged, electro-optical or fiber optic networks can be upgraded and maintained more conveniently than has been the case with traditional soldered-in modules. Rather than replacing an entire circuit board containing several soldered-in modules, a single module can be removed and replaced for repair or upgrading. This can result in a substantial cost savings, both in maintenance and in upgrading efforts.

The SFP is a popular industry standard format supported by many vendors including Cisco, HP, 3Com, SFPlus, Alcatel-Lucent, D-Link, Force10, Extreme, Nortel and so on.  The vendors have formed a consortium supporting the use of SFP transceivers to meet their common objectives of broad bandwidth, small physical size and mass, and ease of removal and replacement.

SFP Types

SFP transceivers are available with a variety of different transmitter and receiver types, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type (e.g. multi-mode fiber or single-mode fiber). Optical SFP modules are commonly available in several different categories:

    850 nm 550m MMF (SX)
    1310 nm 10 km SMF (LX)
    1550 nm [40 km (XD), 80 km (ZX), 120 km (EX or EZX)]
    DWDM

SFP transceivers are also available with a copper cable interface, allowing a host device designed primarily for optical fiber communications to also communicate over unshielded twisted pair networking cable. There are also CWDM and single-fiber "bi-directional" (1310/1490 nm Upstream/Downstream) SFPs.

SFP transceivers are commercially available with capability for data rates up to 4.25 Gbit/s. The standard is expanding to SFP+ which will be able to support data rates up to 10.0 Gbit/s (that will include the data rates for 8 gigabit Fibre Channel, 10GbE, and OTU2). SFP+ module versions for optics as well as copper are being introduced. In comparison to Xenpak, X2 or XFP type of modules, SFP+ modules leave some of the circuitry to be implemented on the host board instead of inside the module.

SFP Standardization

The SFP transceiver is specified by a multi-source agreement (MSA) between competing manufacturers. The SFP was designed after the GBIC interface, and allows greater port density (number of transceivers per inch along the edge of a mother board) than the GBIC, which is why SFP is also known as mini-GBIC. The related Small Form Factor transceiver is similar in size to the SFP, but is soldered to the host board as a pin through-hole device, rather than plugged into an edge-card socket.

SFP Dimensions

• Height: 0.33 inches (8.5 mm)
• Width: 0.53 inches (13.4 mm)
• Depth: 2.22 inches (56.5 mm)

Digital Diagnostics Monitoring

Modern optical SFP transceivers support digital diagnostics monitoring (DDM) functions according to the industry-standard SFF-8472. This feature is also known as digital optical monitoring (DOM). This feature gives the end user the ability to monitor real-time parameters of the SFP, such as optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage.

The diagnostic monitoring controller is available as I²C device at address 1010001X (A2h).

Mating of SFP Transceiver PCB to SFP Electrical Connector

The SFP transceiver contains a printed circuit board that mates with the SFP electrical
connector. The pads are designed for a sequenced mating:

• First mate – ground contacts
• Second mate – power contacts
• Third mate – signal contacts

Labeling of SFP Transceivers

Each SFP transceiver should be clearly labeled. The complete labeling need not be visible when the SFP transceiver is installed. Labeling should include appropriate manufacturing and part number identification, appropriate regulatory compliance labeling, and a clear specification of the external port characteristics. The external port characteristic label may include such information as optical wavelength, required fiber characteristics, operating data rate, interface standards supported, and link length supported.

Bezel Design for Systems Using SFP Transceivers

Host enclosures that use SFP devices should provide appropriate clearances between the SFP transceivers to allow insertion and extraction without the use of special tools and a bezel enclosure with sufficient mechanical strength. For most systems a nominal centerline to centerline spacing of 16.25mm (0.640”) is sufficient.

The SFP transceiver insertion slot should be clear of nearby moldings and covers that might block convenient access to the latching mechanisms, the SFP transceiver, or the cables connected to the SFP transceiver.