SFP Transceivers - Multi-mode and Single-mode

SFP transceivers are interface with a motherboard, router, switch or optical media converter. Link connection into a fiber optic/ copper cable. Support SONNET, Fibre Channel, GbE or similar standards. There are both multi-mode and single-mode SFP transceiver types.

Multi-mode SFP (extraction lever)Sx- 850nm~ max of 550m @ 1.25Gbit/s on GbE150m @ 4.25Gbit/s fibre channel

Single-mode SFP(ex lever)LX - 1310 up to 10kmEX- 1310 up to 40kmZX- 1550 up to 80 km using green ex leverEZX- 1550 up to 160 km

In the following, we will discuss the main difference between multi-mode and single-mode SFP transceivers.

1.They are made for different types of optical fibers.Single-mode SFP module will work with single-mode fiber, while multi-mode SFP transceiver will work with multi-mode fiber. Single-mode SFP transceivers are mostly used in long distances(2km or more) transmission environment. Multi-mode is only used for short distances(300m), like in small area or within the building. For example, operating data rate 1.25G single-mode SFP could work at 20km but multi-mode only 550m.*Single-mode SFP 1.55 micron distance >80 KM*Multi-mode SFP 1.22 micron distance 2 km*Multi-mode SFP 0.85 micron distance 500m

2.They using different type of light emitting unit.Single-mode SFP transceivers have fine laser i.e 1310nm or 1550nm. But multi-mode SFP having LED or lower wavelength type light emitting unit.

3.Single mode SFP works in 1310nm and 1550nm windows, whereas multi-mode SFP works in 850nm window.According to IEEE 802.3 standard, interface for 1.25GbE will be as follows,*Multi-mode fiber interface, 820nm-860nm;*Single-mode fiber interface, 1270nm-1355nm;1000Base-ZX - Single-mode fiber interface, 1500nm-1580nm

4.Single-mode SFP transport the optical signal long distance with the wavelength above 1270 as usual, but there is only one signal in the "tunel". Multi-mode SFP with many optical signal in one "tunel", signals may affect each other, and the wave length is about 850nm. It's not able to transport for long distance, but it can transport many kind of optical signals.

5.In SM SFP single pair of fiber required whereas in MM SFP Ribbon fiber is required to connect.

6.Single-mode SFP, uses a single mode (aka one central lambda) in order to perform both transmission and reception of data, using two paired connectors, LC type.Multi-mode SFP, uses two fiber connections as well, but the core fiber is multi-mode type, which has a thicker core, and allows higher speed at shorter distance for the reasons already explained.

7.Another difference is the type of dispersions they deal with. Multi-mode optics are affected by Modal Dispersion, caused because the light rays follow different paths through the fiber and arrive at different times on the other end. This is the main reason the distance on this type of optic is limited.

Whereas single mode optics are affected by wave guide dispersion caused by the light going down the fiber being wider than the core of the fiber. This allows more control of the path of the photons, but is more affected by micro bends, twists, and stress on the fiber.

8.Both are affected by material dispersion, but because single mode optics (especially ITU grid optics) are primarily for long distances they are more affected by other types of dispersion including Polarization Mode Dispersion (PMD) caused by material and waveguide birefringence. And Chromatic dispersion which is caused by the combination of waveguide dispersion and material dispersion, resulting in the different wavelengths arriving at different times.