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40G QSFP+ Optical Module Interfaces
Knowledge Base + 2024.02.01

To meet the demand for higher-density high-speed pluggable solutions, the 40G QSFP+ optical module has emerged. What are the interfaces of the 40G QSFP+ optical module? And where are they used?

I. Interfaces of 40G QSFP+ Optical Modules

LC Interface

The LC interface connects with LC fiber connectors. LC fiber connectors feature a convenient modular plug (RJ) latch mechanism, resulting in a smaller form factor. The dimensions of the pins and sleeves used in LC interfaces are half the size of those used in typical SC or FC connectors, measuring 1.25mm. Consequently, this interface enhances the density of fiber connectors in systems.

MPO/MTP Interface

The MPO/MTP interface connects with MPO/MTP fiber connectors. MPO (Multi-fiber Pull Off) fiber connectors engage mechanically, while MTP fiber connectors boast improved optical and mechanical performance compared to MPO connectors. Therefore, MPO/MTP interfaces offer better transmission performance, lower losses, and higher tolerances.

II. Specifications of 40G QSFP+ Optical Module Interfaces


The 40G LR4 QSFP+ optical module complies with the 802.3ba (40GBASE-LR4) standard. It connects with LC fiber connectors for use with single-mode fiber, achieving a maximum transmission distance of 10km.


The 40G SR4 QSFP+ optical module complies with the D3.2 (40GBASE-SR4) standard. It connects with MPO/MTP fiber connectors for 40G transmission applications. When used with multimode OM3 fiber patch cords, the transmission distance is 100m, while with OM4 fiber patch cords, it can reach up to 150m.

III. Types of 40G QSFP+ Optical Modules

40G SR4 QSFP+ Optical Module

The interface of the 40G SR4 QSFP+ optical module is MPO/MTP. Its operation involves converting electrical signals to optical signals at the transmitting end using a laser array. At the receiving end, an array of photodetectors converts parallel optical signals back into parallel electrical signals.

40G LR4 QSFP+ Optical Module

The interface of the 40G LR4 QSFP+ optical module is LC duplex. It boasts advantages such as high density, high speed, large capacity, low cost, and low power consumption. Its operation involves modulating the wavelength of serial data using laser drivers. A multiplexer combines the modulated optical signals for transmission. Upon reaching the receiving end, these signals are demultiplexed into four 10Gbps channels. PIN detectors or transimpedance amplifiers recover the data stream, and the optical signals are then transmitted.

40G LR4 PSM Optical Module

The interface of the 40G LR4 PSM optical module is MPO/MTP. It utilizes Parallel Single Mode (PSM) technology. Its operation is similar to the 40G SR4 QSFP+ optical module, with the difference being that the 40G LR4 PSM optical module transmits parallel optical signals through 8 single-mode fibers in parallel.

IV. Different Applications of 40G QSFP+ Optical Modules

The 40G SR4 QSFP+ optical module is primarily used for connecting network equipment within data centers, suitable for short-distance transmission. It is commonly used with OM3/OM4 ribbon fiber cables to connect Ethernet switches in data centers. The 40G LR4 QSFP+ optical module and 40G LR4 PSM optical module are suitable for long-distance transmission. The former only requires two single-mode fibers, offering a higher cost-effectiveness, while the latter requires eight single-mode fibers, providing higher port density and significant cost savings.


In data center, high-performance computing networks, and enterprise core and distribution layer applications, 40G QSFP+ optical modules provide high-density and low-power 40G Ethernet connection transmission applications. Understanding the interfaces, types, and applications of 40G QSFP+ optical modules is crucial when selecting them.

Additional Learning Hub Resources

40G QSFP+ AOC Active Optical Cable Overview 

What is the difference between 40G QSFP+ singlemode and QSFP+ multimode?