A continuous stream of manufacturing process improvements and product innovations has given fiber optical system several advantages, like longer distance reach, larger data-carrying capacity, greater bandwidth and lower power consumption. Among these fiber optical product innovations, hot-pluggable transceiver modules should come to the central point with their unique designs. They have been constantly designed, and finally been reinvented as hot-pluggable modules along with the optical technological advances. These small, hot-pluggable serve as the key components in accommodating the demands of higher port density and more networking flexibility.
Transceiver modules come into various types: SFP (small form-factor pluggable), SFP+ (small form-factor pluggable plus), QSFP+ (quad small form-factor pluggable plus), etc. This article mainly introduces SFP transceiver modules which are widely applied in Gigabit Ethernet (GbE) applications, with the focus on several 1000BASE-X interface types, including 1000BASE-SX, 1000BASE-LX, 1000BASE-EX, and 1000BASE-BX10-D/U.
Features and Benefits
1000BASE-X SFP modules provide a wide range of form factor options for enterprise and service provider needs. They are designed with the following features and benefits:
Hot swappable to maximize uptime and simplify serviceability;
Flexibility of media and interface choice on a port-by-port basis, so you can “pay as you populate”;
Sophisticated design for enhanced reliability;
Supports digital optical monitoring (DOM) function;
1000BASE-X SFP Interface Types
1000BASE-SX SFP, compatible with the IEEE 802.3z 1000BASE-SX standard, operates on legacy 50Ľm multi-mode fiber (MMF) links up to 550m and on 62.5Ľm Fiber Distributed Data Interface (FDDI)-grade MMfiber-mart up to 220m. Take DEM-311GT for example, Fiberstore compatible D-Link 1000BASE-SX SFP is able to realize 550m link length through OM2 MMF with duplex LC.
1000BASE-LX SFP, compatible with the IEEE 802.3z 1000BASE-LX standard, is specified to support link length of up to 10km on standard single-mode fiber (SMF), to 550m on MMfiber-mart. When used over legacy MMF, the transmitter should be coupled through a mode conditioning patch cable. The laser is launched at a precise offiber-martet from the center of the fiber which causes it to spread across the diameter of the fiber core, reducing the effect known as differential mode delay which occurs when the laser couples onto only a small number of available modes in MMF.
1000BASE-EX, sometimes referred to as LH, is a non-standard but industry accepted standard which works on standard SMF with fiber link spans up to 40km in length. For back-to-back connectivity, a 5-dB inline optical attenuator should be inserted between the fiber optic cable and the receiving port on the SFP at each end of the link. 1000BASE-EX SFPs (eg. GLC-EX-SMD) run on 1310nm wavelength lasers, and achieves 40km link length.
The 1000BASE-BX-D and 1000BASE-BX-U SFPs, compatible with the IEEE 802.3ah 1000BASE-BX10-D and 1000BASE-BX10-U standards, operate on a single strand of standard SMF (figure shown below). A 1000BASE-BX10-D device is always connected to a 1000BASE-BX10-U device by a single strand of standard SMF with an operating transmission distance up to 10km.
The communication over a single strand of fiber is accomplished by separating the transmission wavelength of the two devices (figure shown above): 1000BASE-BX10-D transmits a 1490nm channel and receives a 1310nm signal, whereas 1000BASE-BX10-U transmits at a 1310-nm wavelength and receives a 1490-nm signal. In this figure, the wavelength-division multiplexing (WDM) splitter is integrated into the SFP to split the 1310nm and 1490nm light paths.