40G active optical cable (AOC) is a cabling technology used for deploying 40G Ethernet network, which uses electrical-to-optical conversion on the cable ends, accepting the same electrical signals as a 40G direct attach cable (DAC). It is terminated with a 40G QSFP+ module on one end, while a 40G QSFP+ module, four 10G SFP+ modules or four duplex LC connectors on the opposite end, as shown in the following figure. To satisfy the increasing needs of higher bandwidth and transmission speed, it was designed for 40G short distance transmission and came into market with a broad prospect under the rapidly developing optical networks.
It is well know that both 40G DAC and 40G QSFP+ module can be also used to achieve 40G short distance interconnection in data center, but 40G AOC seems more widely applied with the same function. Why? In this paper, it will analyze the advantages and disadvantages of 40G AOC in details, giving the answer.
In contrast to 40G DAC solution, 40G AOC solution has a higher performance in the deployment of 40G Ethernet network, especially when the transmission distance of the network is longer than 7 meters. Except the advantage of longer transmission distance, 40G AOC is much thinner, lighter and has a tighter bend radius, all of which make the 40G cabling easier and airflow system more efficient. Undoubtedly, 40G AOC solution is a better choice than 40G DAC solution to deploy 40G Ethernet network.
40G QSFP+ module solution for short distance transmission has all the advantages of 40G DAC solution mentioned above to achieve 40G connection in data center. However, 40G DAC is still a better solution that should be highly recommended. Why? The following will analysis the differences between the two solutions, seeking the reason why 40G DAC is more popularly used than 40G QSFP+ module for short distance transmission.
Cost Difference
There is no doubt that 40G AOC has a much lower cost than 40G QSFP+ module because of the following reasons. Firstly, 40G AOC can be directly connected to the system, while 40G QSFP+ module should be connected with extra fiber patch cables. For this reason, 40G AOC, like QSFP to SFP+ breakout cable, is a more cost-effective solution than 40G QSFP+ module. Secondly, there is always the cleanliness issue in the optical connector when 40G QSFP+ module is selected, but 40G AOC can be used without the worry. Thirdly, when troubleshooting the system deployed by 40G AOC, the termination plug don’t need to test, too. All these advantages of 40G AOC allow the 40 migration to be done with less time and money.
Insertion & Return Loss Difference
As we know, when the modules are connected by fiber optic patch cables, it will cause an insertion loss and return loss. However, the issue can be ignored if 40G AOC is selected, because AOC don’t need to connect fiber optic patch cable. Meanwhile, the repeatability and interchangeability of 40G AOC perform better than that of module. As a result, the insertion loss and return loss caused by 40G AOC will be less when the 40 signals is transmitted in the network. Hence, 40G AOC has a higher performance than 40G QSFP+ module for short distance transmission in this aspect.
Transmission Distance Difference
Both QSFP+ module and AOC can support 40G Ethernet network for short distance transmission through OM3 fiber without apparent difference, but the QSFP+ module can control the performance better than AOCs. Hence, it the transmission distance is longer than 300 meters, the QSFP+ module for 40G short transmission distance will be more suitable in order to ensure a good performance.
It can be concluded that AOC is able to support 40G network with longer transmission distance, make the network cabling easier and has a more efficient airflow system than 40G DAC. It can also be found that AOC takes less money and time to make the 40G migration with less insertion loss and return loss than QSFP+ module for short distance transmission. What should be paid attention to is that QSFP+ module will be a better solution when the transmission distance is longer than 300 meters.
Fiber Optic Communication 