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Introduction to 40G QSFP+ LR4, QSFP+ SR4, QSFP+ LR4 PSM

QSFP+ is an evolution of QSFP (quad small form-factor pluggable). QSFP+ can carry 4 channels simultaneously and each channel can handle 10 Gbit/s data rate, aggregated 40 Gbit/s.  40G optical transceiver is very popupar in the market, used in the data center and other high-speed systems. Here we are going to introduce the most popular three types in the market.


40G QSFP LR4 has four channels and speed up to 10Gps each channel, it works with single-mode fiber with LC connector, the transmission distance can reach 10km. It features high density, low cost, high speed, big capacity, low power consumption.

40G QSFP+ LR4 works like this: The four electrical signal comes into the laser driver, then generate four optic signal, and the optical signal passes through the multiplexer and are combined into one signal for transmission on one single-mode fiber. When in receiving mode, one optic signals are decomposed into four channels with a transmission rate of 10Gbps by the demultiplexer, and then the PIN detector or transimpedance amplifier recovers the data stream, and then transmits the electrical signal.


Same as 40G QSFP+ LR4, it has four channels and speed up to 10Gps each channel, it works with multimode fiber with MPO connector, the transmission distance can reach to 100m when working with OM3 fiber, while it reaches 150m working with OM4 fiber.

The working principle of the 40GBASE-SR4 optical module: when in transmitting mode, the four electrical signal is first converted into four optical signals by the laser array, the four optical signals are transmitting on four separate fiber through an MPO/MTP connector;  when in receiving mode, photodetector array converts the parallel optical signals Into parallel electrical signals.


40G LR4 PSM is similar to SR4, it also work with MPO connector, but it uses single-mode fiber to reach far distance. Normally it can reach 10km. Its work principle is the same as SR4.


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