What are the Types of 40G QSFP+ Transceiver?

There are many types of 40G optical module on the market today, such as 40GBASE-SR4/LR4/CR4/CSR4 transceiver in QSFP+ packaging. When choosing, you must have observed that the appearance of these 40G fiber optic transceiver are quite similar, for example, 40GBASE-SR4 and 40GBASE-CSR4, these two kinds of 40G fiber modules and even the color of the pull ring are almost same. So do you really understand these 40G modules? In this article, we will focus on the most common 40G QSFP+ optical transceivers to help you efficiently deploy your network.

40G Transceiver for Short Distance Transmission

Typically, 40G optical transceivers with a wavelength of 850nm are used with multimode fiber patch cords for short distance data transmission. Currently, two common types of short-distance 40G optical modules are 40GBASE-SR4 and 40GBASE-CSR4.

40GBASE-SR4 Optical Module

“SR” means short distance. The 40GBASE-SR4 transceiver module (also known as QSFP-40G-SR4 fiber module) complies with the IEEE 802.3ba 40GBASE-SR4 standard and adopts MPO/MTP interface design. When used with OM3 fiber, the maximum transmission distance can reach 100 meters, and with OM4 fiber, it can go up to 150 meters.

The 40GBASE-SR4 optical transceiver has separate transmit and receive sections inside, each with 4 parallel fibers. When the 40GBASE-SR4 transceiver is used for 40G direct connection, all 8 fibers are to be used for data transmission. At this time, it needs to be connected with MTP/MPO-12 optical fiber jumpers, and 4 fibers in the link are in idle state, as shown in the following figure.

40GBASE-CSR4 Optical Module

40GBASE-CSR4 transceiver module (also known as QSFP-40G-CSR4 fiber module), compliant with IEEE 802.3ba 40GBASE-SR4 standard, is equivalent to an extended version of 40GBASE-SR4 optical module, which works on the same principle. The four channels (10Gbps) of the 40GBASE-CSR4 transceiver all comply with the IEEE 10GBASE-SR specification, with MTP/MPO interface design, the longest distance can be up to 300m with OM3 fiber, and up to 400m with OM4 fiber.

In addition to the two short-distance 40G fiber optic transceivers mentioned above, 40GBASE-SR optical module (i.e. QSFP-BD-40G fiber module) is also suitable for short-distance transmission. Unlike the 40GBASE-SR4 optical module, the 40GBASE-SR optical module uses wavelength division multiplexing technology to couple signals of different wavelengths on one optical fiber for transmission, and needs to be used with LC duplex optical fiber. The 40GBASE-SR transceiver module has a maximum transmission distance of up to 100 meters when used with OM3 fiber optic patch cords, and up to 150 meters when used with OM4.

40G Transceiver for Long Distance Transmission

Typically, 40G optical transceivers with a wavelength of 1310nm are used with single-mode fiber jumpers and are suitable for long-distance data transmission. On the market, the common 40G fiber modules for long distance are 40GBASE-LR4, 40GBASE-PLRL4, 40GBASE-PLR4 and 40GBASE-ER4.

40GBASE-LR4 Optical Module

40GBASE-LR4 transceiver module (also known as QSFP-40G-LR4 fiber module), complies with IEEE 802.3ba 40GBASE-LR4 standard and adopts LC duplex interface design, which can transmit up to 10 kilometers on single-mode fiber optic cable. The 40GBASE-LR4 optical module has the same packaging form as 40GBASE-SR4, providing four independent transceiver channels, and the bandwidth of each channel is 10Gbps.

In order to transmit 4-channel signals on a single-mode fiber, the 40G LR4 transceiver must multiplex or demultiplex the optical signals via the internal MUX/DEMUX. The operating mode of the 40GBASE-LR4 is shown in the following figure:

40GBASE-PLRL4 Optical Module

The 40GBASE-PLRL4 transceiver module (i.e. QSFP-40G-PLRL4) is same as the 40GBASE-SR4 and 40GBASE-CSR4 which were mentioned above, they all adopt the MTP/MPO interface design and the principle of parallel data transmission for communication. However, the difference is that the 40GBASE-PLRL4 optical module supports long-distance transmission, and the maximum transmission distance can reach 1.4 kilometers when used with single-mode fiber.

40GBASE-PLR4 Optical Module

40GBASE-PLR4 transceiver module (i.e. QSFP-40G-PLR4) works same as 40GBASE-PLRL4, when used with MTP/MPO single-mode fiber jumpers, the maximum transmission distance can reach 10 kilometers.

40GBASE-ER4 Optical Module

40GBASE-ER4 transceiver module (i.e. QSFP-40G-ER4) has the same working principle as 40GBASE-LR4, and the maximum transmission distance is up to 40 km when used with LC duplex SM fiber optic patch cords.

How to Choose a 40G transceiver and What Fiber Optic to Connect?

No matter which type of 40G fiber modules you choose, it depends on the actual wiring situation. For example, for short-distance (transmission distance less than 500 meters) application scenarios, 40GBASE-SR4/CSR4 optical modules is more suitable; for long-distance (transmission distance greater than 500 meters) application scenarios, better choose 40GBASE-LR4/PLRL4/PLR4/ER4, etc. Please refer the table below for more details: