How Much Do You Know About 40G QSFP+ AOC

40 Gigabit Ethernet era is already upon us and makes a contribution to satisfying the increasing demands of higher throughputs and bandwidth. Existing and emerging network technologies are driving the need for high-density optical connectivity solutions to address the trends to optimized cable management and data center real estate usage. The 40G QSFP+ AOC (active optical cable) has been widely used in data center to achieve 40G interconnection. This article will introduce the 40G QSFP+ AOC in data center applications.

Development of AOC

Primarily, active optical cable (AOC) assemblies were invented to replace copper technology in data centers and high performance computing (HPC) applications. As we know, copper cable is heavy and bulky, making it difficult to physically manage the datacenter. And due to the nature of electrical signals, electromagnetic interference (EMI) limits copper’s performance and reliability. Though there are so many disadvantages of copper cable, at that time, it is the main stream while the idea of AOCs almost seems too good to be true. However, the advantages of AOC make the predecessors look obsolete and unsophisticated, and changes the limitation of copper cable as well as playing an important role in high speed data transmission. Nowadays, a variety of AOCs have been launched in the market, such as 10GbE SFP+ AOCs, 40Gbps QSFP+ AOCs and 120G CXP AOCs, for 10G, 40G and 100G applications.

What Is 40G QSFP+ AOC

40G AOC, is a type of active optical cable for 40GbE applications that is terminated with 40GBASE-QSFP+ on one end, while on the other end, in addition to QSFP+ connector, it can be terminated with SFP+ connector, LC, SC, FC, and ST connector etc. The 40G QSFP+ AOC is a parallel 40Gbps quad small form factor pluggable (QSFP+) active optical cable, which supplies higher port density and total system cost. The QSFP+ optical modules provide four full-duplex independent transmit and receive channels, each are able of 10Gbps operation 40Gbps aggregate bandwidth of at least 100m multimode fiber. Most DAC assemblies have one module on each end of the cable. But there is a special kind of DAC assembly which may have 3 or 4 modules on one end of the cable. For instance, Cisco QSFP-4X10G-AOC5M compatible QSFP+ to 4SFP+ breakout AOC from Fiberstore has a single QSFP+ module rated for 40-Gbps on one end and four SFP+ modules, each rated for 10-Gbps, on the other end.

QSFP-4x10G-AOC5M

40G QSFP+ AOC vs QSFP+ Optics

Cost: 40G AOCs cost lower than SR4 modules and do not need to use together with extra fiber patch cables. For instance, Arista AOC-Q-Q-40G-10M compatible QSFP+ to QSFP+ active optical cables are suitable for very short distances and offer a very cost-effective way to establish a 40-gigabit link between QSFP ports of Arista switches within racks and across adjacent racks. Besides, when using 40G AOC, there are no cleanliness issues in optical connector and there is no need to do termination plug and test when troubleshooting, which can help user save more time and money.
Insertion Loss & Return Loss: Under the same case of transmission distance, the repeatability and interchangeability performances of SR4 module interface are not good as 40G AOC. What’s more, when different fiber optic patch cables plug into the module, it will have the different insertion loss and return loss. Even for the same module, this issue is existed. Of course, the related metrics such as the testing eye pattern will have no significant changes so long as the variation in and conformed to the scope. In contrast, an AOC with good performance is more stable and has better swing performance than SR4 modules in this situation.

All in all, 40G QSFP+ AOC is highly recommended to use in data center interconnection. Apart from the 40G QSFP+ AOC, Fiberstore also supplies 10G SFP+ AOC, QSFP + AOC to 8 x LC and 120G CXP AOC, etc. All of them can meet the ever increasing need to cost-effectively deliver more bandwidth, and can be customized to meet different requirements.