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The similarities and differences between SFP optical module and SFP+ optical module

Feb. 23, 2021
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As an optical module for photoelectric and electro-optical conversion, it is one of the indispensable components of telecommunication transmission and data communication. For most people, it is not easy to understand the optical module in depth. There are many styles from the packaging method and speed division alone. The common ones are SFP, SFP+, XFP, QSFP+, CFP, GBIC, CXP, X2, Xenpak, CFP2, CFP4, DAC, AOC, etc.

SFP optical modules and SFP+ optical modules look very similar in appearance, and most switches support both SFP modules and SFP+ modules. So are they really the same kind of module? Are there any differences between them? To know the difference between the two, you must first understand the various parameters of the optical module, of which the most important are 3 points (central wavelength, transmission distance , Transmission rate), the main difference between optical modules is also reflected in these points.

Center wavelength

The unit of the center wavelength is nanometer (nm), currently there are three main types:

1) 850nm (MM, multi-mode, low cost but short transmission distance, generally only 500m);

2) 1310nm (SM, single mode, large loss but small dispersion during transmission, generally used for transmission within 40km);

3) 1550nm (SM, single-mode, low loss but large dispersion during transmission, generally used for long-distance transmission above 40km, and can directly transmit 120km without relay at the farthest).

Transmission distance

Transmission distance refers to the distance that optical signals can be directly transmitted without relay amplification. The unit is kilometers (also called kilometers, km). Optical modules generally have the following specifications: multi-mode 550m, single-mode 15km, 40km, 80km, 120km, etc.

Transmission rate

The transmission rate refers to the number of bits (bits) of data transmitted per second, in bps. The transmission rate is as low as 100M, and can be as high as 800Gbps. There are four commonly used rates: 155Mbps, 1.25Gbps, 2.5Gbps and 10Gbps. The transmission rate is generally downward compatible.

Then according to the above introduction to the optical module parameters, let's understand the difference between SFP optical module and SFP+ optical module.

Definition of SFP

SFP (Small form-factor pluggable) means small form-factor pluggable. It is a pluggable module that can support Gigabit Ethernet, SONET, Fibre Channel and other communication standards and plug into the SFP port of the switch. The SFP specification is based on IEEE802.3 and SFF-8472, which can support speeds up to 4.25Gbps. Due to its smaller size, SFP replaces the previously common Gigabit Interface Converter (GBIC)

Definition of SFP+

Because SFP only supports a transmission rate of 4.25Gbps, which cannot meet people's increasing requirements for network speeds, SFP+ was born under this background. The maximum transmission rate of SFP+ can reach 16Gbps. In fact, SFP+ is an enhanced version of SFP. The SFP+ specification is based on SFF-8431. The SFP+ module has replaced the XENPAK and XFP modules that were more commonly used in the early 10 Gigabit Ethernet, and has become the most popular optical module in the 10 Gigabit Ethernet.

After analyzing the above definitions of SFP and SFP+, we can get:

The similarities between SFP and SFP+: the interface definition, shielding cover and other appearance dimensions of the two are the same

The difference between SFP and SFP+: the performance rate is different, the transmission rate that SFP+ can support is much higher than that of SFP, up to 11.1Gbps.

The similarities and differences between SFP optical module and SFP  optical module