XFP & SFP+ 10GbE Optical Modules Overview

To accommodate an increasing number of bandwidth-hunger applications and traffic types, an ocean of safe-proof network products have been designed and released into market, including optical modules offered to satisfy the changing and fast-growing bandwidth demands in data centers. The optical modules are devices that connect the cabling to the network, providing interface between the equipment and the cabling, sending and receiving data.

There are various transceiver types available to match each Gigabit standard. For Gigabit technology, there are two defined transceiver types: Gigabit Interface Connector (GBIC), and the “mini-GBIC” or Small Form-factor Plable (SFP). For 10 Gigabit Ethernet (GbE) connectivity modules, there are three types: XENPAK (and related X2 and XPAK), XFPSFP+ and SFP+. This text mainly discusses the last two 10GbE optical modules types: XFP and SFP+.

XFP & SFP+ Main Features
Optical modules refer to optical transceivers which consist of a transmitter on one end of a fiber and a receiver on the other end. XFP and SFP+ can be pled into routers, switches, transport gear, or pretty much any network device to transmit and receive signals. They are hot swappable while the device is operating, standardized to be interchangeable among vendors, capable of operating over many different physical medium and at different distances. Being hot-swappable input/output device, XFP and SFP+ have the following main features in common.

Allow flexibility of interface choice;

Support “pay-as-you-populate” model;

Designed with strong digital optical monitoring capability;

Optical interoperability with 10GBASE XENPAK, and 10GBASE X2 on the same link;

XFP Optical Module

Protocol-independent and hot-plable, XFP (10G SFP) is the first small form factor 10GbE optics, typically operating at near-infrared wavelengths of 850nm, 1310nm or 1550nm with LC connector. XFP modules can provide the required optical reach over different fiber optic types (e.g. multi-mode fiber, MMF or single-mode fiber, SMF), commonly available in several categories: SR, LR, ER and ZR.

10GBASE-SR XFP
10GBASE-SR XFP (eg. XFP-10G-MM-SR) is specified to work through MMF using 850nm lasers. This XFP type supports a link length of 26m on standard FDDI-grade MMF. And when using 2000 MHz/km MMF (OM3), 300m link lengths are possible. Fiberstore compatible Cisco XFP-10G-MM-SR is able to realize 300m distance reach over OM3 with the maximum data rate at 10.3125Gbps.

10GBASE-LR XFP
10GBASE-LR XFP is designed to operate via SMF using 1310nm lasers. The maximum link length that XFP 10GBASE-SR port type can support is 10km when it’s used in combination with high-quality optics.

SFP+ Optical Module
As the result of Multi-source Agreements (MSAs) that enable equipment manufacturers to produce 802.3ae-compliant plable transceivers, SFP+ modules use the same physical form factor as a Gigabit SFP. It’s the enhanced version of SFP. Nowadays, SFP+ has become a popular industry format supported by many network component vendors for 10GE systems. Similar to XFP, SFP+ also has different port types, like SR, LX4, LR, and so on.

10GBASE-SR SFP+
10GBase-SR is the original multi-mode optics specification, and is still by far the most commonly used. Since it uses a single, low cost solid state laser assembly, 10GBase-SR is the least expensive of the optical modules available for a 10GbE SFP+ platform. Just like 10GBASE-SR XFP, 10GBase-SR SFP+ is very sensitive to fiber type. When using standard MMF, the possible link length supported by 10GBASE-SR SFP+ is 26m, and when deploying OM3 or 10GbE-optimized fiber, the maximum link length is 300m.

10GBASE-LX4 SFP+
To break through the distance limitations of 10GBASE-SR optics, the 10GBASE-LX4 standard was developed later. LX4 uses 4 lasers, each operating at a different wavelength at a 2.5Gbps data rate, resulting in a range of 240-300m link length which depends on cable grade. However, due to the complex laser assembly, it is not possible to get LX4 optics in SFP+ versions. With the ready availability of OM3 fiber and newer standards that provide long reach over multi-mode with a single laser, LX4 has become obsolete nowadays.

10GBASE-LR SFP+
10GBASE-LR is a port type for SMF, supporting the maximum link length of 10km. During data transmission, a single laser operating at 1310nm is used, which allows LRM optics to be packaged in XFP and SFP+ form factors.