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40G QSFP+ Optical Module Introduction

January 12,2023

What is QSFP+?

As an upgrade version of the Quad Small Form-factor Pluggable (QSFP), QSFP+ is a compact, hot-pluggable optical module that can transmit data at up to 40Gbps. It conforms to the SFF-8436 protocol and the QSFP Multi-Source Agreement (MSA). QSFP+ has four independent optical signal sending and receiving channels with a rate of 10Gbps and a total bandwidth of 40Gbps. In the application scenarios of data center, high performance computing network, enterprise core layer and distribution layer, 40G QSFP+ optical transceiver module can provide high-density and low-power 40G Ethernet connection transmission applications.



QSFP+ Interface Type

The QSFP+ module can be inserted into all devices with QSFP+ interface (and some devices with QSFP28 interface) to realize 40G network connection. Generally speaking, there are two kinds of interfaces for 40G QSFP+ module: LC duplex interface and MTP/MPO interface (hereafter referred to as MTP), which have obvious differences in transmission distance, cable type and whether 4x10G transmission can be achieved. More information can be found in this article: 40G QSFP+MTP optical module and 40G QSFP+LC optical module comparison.

QSFP+ Optical Module Classification

Nowadays, there are many 40G optical module products on the market. How to distinguish different categories and choose the optical module suitable for your needs is particularly important. The following article will introduce nine common QSFP+ optical modules.

MTP Interface QSFP+ Optical Module

This part will focus on 40GBASE-SR4, 40GBASE-CSR4, 40GBASE-PLRL4, and 40GBASE-PLR4 these four types of optical modules. These four modules are MTP interface modules, and are suitable for access to four 10G Ethernet interfaces.

40GBASE-SR4 Optical Module

40GBASE-SR4 optical module is the most common type of 40G optical module in 40G short-distance transmission. The 40GBASE-SR4 optical module is often used with multi-mode fiber -- with OM3 fiber optical cable, the transmission distance is 100 meters; The transmission distance is 150 meters when paired with OM4 fiber optical cable. There are four independent optical signal transmitting and receiving channels in the module, each channel can support 10Gbps data transmission, and achieve high bandwidth 40G transmission.

40GBASE-CSR4 Optical Module

40GBASE-CSR4 optical module and 40GBASE-SR4 optical module are MTP interface, both have the same working principle. 40GBASE-CSR4 optical module can be combined with 12 core MTP (female) fiber optic cable to achieve 40G optical transmission; Or with 8-core MTP (female) -4*LC duplex branch fiber optic cable, connected with 4 10GBASE-SR optical modules to achieve 4X10G optical transmission. As an upgraded version of SR4, 40GBASE-CSR4 optical module can transmit up to 300 meters (with OM3 fiber optic cable) or 400 meters (with OM4 fiber optic cable).

40GBASE-PLRL4 Optical Module

Generally speaking, there are two basic modes of data transfer - serial and parallel. Parallel transmission refers to the simultaneous transmission of multi-bit data in different channels on the same fiber. The 40GBASE-PLRL4 optical module, SR4 module and CSR4 module all adopt the principle of parallel transmission, usually connected with MTP connector. However, unlike the two optical modules introduced above, the 40GBASE-PLRL4 optical module supports long distance transmission, up to 1 km or 1.4 km on a single mode fiber.

40GBASE-PLR4 Optical Module

The 40GBASE-PLR4 optical module of the MTP interface also uses the parallel transmission principle ""ribed in the above section. Like the 40GBASE-PLRL4 module, it can also use a single-mode branch optic fiber cable to connect the module to four 10GBASE-LR optical interfaces for 4X10G transmission. Like the 40GBASE-PLRL4 optical module, the 40GBASE-PLR4 optical module is also used for long-distance transmission, but its transmission distance is longer, up to 10 km.


Duplex LC Interface QSFP+ Optical Module

This part will focus on the 40GBASE-BiDi, 40GBASE-UNIV, 40GBASE-LR4, 40GBASE-LR4L, and 40GBASE-ER4 these five types of optical modules. All the five modules are LC interface modules, and only one of them, 40GBASE-BiDi, is used for short-distance transmission through multi-mode fiber.

40GBASE-BiDi Optical Module

Unlike other modules, the 40GBASE-BiDi optical module is special in that it has only two independent 20Gbps optical signal transceiver channels. Each transceiver channel can simultaneously transmit and receive optical signals of different wavelengths from a multimode fiber, which is usually used with LC multimode fiber optic cable. It is worth mentioning that the 40GBASE-BiDi optical module can achieve 40G transmission without changing the existing 10G multimode fiber wiring system. The 40GBASE-BiDi optical module can transmit 100 meters through OM3 fiber optic cable r or 150 meters through OM4 fiber optic cable.

40GBASE-UNIV Optical Module

"UNIV" stands for universal. The 40GBASE-UNIV optical module can be used with both single-mode and multi-mode fiber without changing the module configuration or adding other hardware equipment. The time and cost of routing can be reduced to a certain extent by using this module for wiring. 40GBASE-UNIV optical module is equipped with four channels, each channel can transmit or receive 10G signal, through the multiplexer combination of two fiber for 40G transmission. When combined with multi-mode fiber OM3 and OM4, the transmission distance is 150 meters. With single-mode fiber, the transmission range is 500 m to 2 km (depending on different suppliers).

40GBASE-LR4 Optical Module

The 40GBASE-SR4 optical module is widely used for short distance transmission, while the 40GBASE-LR4 optical module is the most commonly used module for long distance transmission. The 40GBASE-LR4 optical module uses a duplex LC interface and can transmit up to 10 km through a single-mode fiber optical cable. This optical module has four independent transmitting and receiving signal channels. The optical signal at the transmitting end is combined and transmitted by a multiplexer, and the transmitted signal is decomposed into four 10Gbps transmission channels at the receiving end by a demultiplexer.

40GBASE-LR4L Optical Module

The 40GBase-LR4L optical module and 40GBase-LR4 optical module work on the same principle, and both achieve 40G long-distance data transmission through a single-mode fiber optic cable. The difference between the two is that the 40GBase-LR4L optical module has a maximum transmission range of only 2 kilometers.

40GBASE-ER4 Optical Module

The last module to be introduced, 40GBASE-ER4, works the same as the previous two modules, LR4 and LR4L, using LC duplex interface with single-mode fiber optic cable. The 40GBASE-ER4 optical module has the longest transmission distance among the nine modules introduced in this article, which can reach 40 km.


The detailed information and comparison of the above nine modules  are shown in the following table: