In this article, ETU-LINK will analyze common problems related to 40G QSFP+ optical modules, 40G QSFP+ AOC active optical cables, and 40G QSFP+ DAC high-speed cables.

Q1：Can a 40G optical module be connected with a 10G optical module?

A1: Not all 40G optical modules can be connected to 10G optical modules, only 4*10G parallel transmission optical modules can be connected to 10G optical modules, for example: 40G multi-mode optical modules (QSFP+ SR4) can use MPO-LC Multimode OM3 fiber jumper and 10G multimode optical module (SR) are connected, because they are all multimode optical modules with a wavelength of 850nm, and the 40G SR4 optical module can be backward compatible with IEEE 802.3ae 10GBASE-SR Ethernet Protocol; 40G single-mode optical module (QSFP+ PSM4) can be connected with MPO-LC single-mode OS2 fiber jumper and 10G single-mode optical module (LR), because their wavelength is 1310nm, and the 40G PSM4 optical module is downward Compatible with IEEE 802.3ae 10GBASE-LR Ethernet protocol.

Q2：Where is the 40G DAC cable used?

A2: The 40G DAC cable is mainly used for transmission in the data center cabinet. Because the high-speed cable does not use expensive optical devices and optical fibers as components, the transmission distance is short and the price is low. It is very suitable for the connection of servers and switches inside the cabinet.

Q3：Can 40G ports and 10G ports be connected by cables?

A3: Yes, the 40G AOC/DAC cable has a QSFP+ to 4*SFP+ branch cable, and the 40G port and the 10G port can be interconnected by using this specification of the cable.

Q4：How many kilometers can the 40G optical module transmit?

A4: The single-mode 40G QSFP+ ER4 optical module can transmit up to 40 kilometers.

Q5：Does the 40G optical module support single and multi-mode fiber transmission?

A5: The 40G QSFP+ LX4 optical module supports the use of multi-mode OM3/OM4 optical fiber jumper transmission, up to 150 meters, and also supports single-mode OS2 optical fiber jumper transmission, up to 2 kilometers. Its interface type is dual LC, and the wavelengths are 1271, 1291, 1311, 1331nm. Using LX4 can adapt to more flexible wiring in data centers.

Q6：Are there any more fiber-saving solutions for 40G multimode transmission?

A6: 40G SR4 needs to use at least 8-core multi-mode OM3 optical fiber for transmission, so it increases the cost of optical fiber wiring in the data center. However, 40G multi-mode optical modules are not only SR4, but also multi-mode PAM4 optical modules using PAM4 modulation technology. 40G BiDi optical module, 40G SWDM4 optical module, they are all multi-mode optical modules, the interface type is double LC, only need 2-core multi-mode OM3/OM4 optical fiber to achieve 40G rate transmission.

Q7：What types of 40G single-mode optical modules are there?

A7: There are three common 40G single-mode optical modules: 40G PSM4, 40G LR4, and 40G ER4. Among them, 40G PSM4 can transmit up to 2 kilometers, 40G LR4 can transmit up to 10 kilometers, and 40G ER4 can transmit up to 40 kilometers.

The above are the answers to common questions about 40G optical module AOC/DAC transmission cables of ETU-LINK. If you want to know more, you can refer to previous articles.