Fiber Optic Connectivity Options for 40G Infrastructure

Dramatic growth in data center throughput has led to the increasing usage and demand for higher speed and more bandwidths. The speed of data center now is increasing to 40 Gbps and eventually to 100 Gbps. Thus, new optical technologies and cabling infrastructure are required. This article will introduce some commonly used fiber optic cabling connectivity options for 40G infrastructure.

Pluggable Optical Modules: 40G QSFP+ Transceivers

As is known to all, fiber optic transceiver is a device that both transmits and receives data. It is the key component in fiber optic transmission. The basic interface of 40G pluggable optical modules are 40GBASE-LR4 and 40GBASE-SR4 in QSFP+ form factor.

40GBASE-LR4 QSFP+: 40GBASE-LR4 transceiver supports with a link length up to 10 kilometers over 1310 nm single mode fiber with LC connector. It is most commonly deployed between data-center or IXP sites with single mode fiber.

40GBASE-SR4 QSFP+: 40GBASE-SR4 transceivers are used in data centers to interconnect two Ethernet switches with 8 fiber parallel multimode fiber OM3/OM4 cables. It can support the transmission distance up to 100 m with OM3 fiber and 150 m with OM4 fiber. The optical interface of 40GBASE-SR4 QSFP+ is MPO/MTP.

Extreme 10319

In addition, for single-mode fiber transmission, there are 40GBASE-LR4 Parallel Single Mode (PSM) transceivers which are used to provide support for up to four 10Gbps Ethernet connections on a QSFP+ port over single mode fiber at distances up to 10 km. For multimode fiber transmission, QSFP+ extended SR4 transceivers are developed which is designed with optimized VCSEL with better performance of RMS spectral width compared with QSFP+ SR4. QSFP+ extended SR4 transceivers can support transmission distance up to 300 m with OM3 fiber and 400 m with OM4.

Passive & Active Direct Attach Copper Cables

The QSFP+ passive or active direct attach copper cables are designed with twinax copper cable and terminated with QSFP+ connectors. The main difference between passive QSFP+ DAC and active QSFP+ DAC is that the passive one is without the active component. They provide short distance (same shelf) inexpensive connectivity at up to 40Gbps rates and operate 4 independent 10G channels using the QSFP connector footprint. Each of the four channels can operate at multi-rate speeds Gigabit to 10Gbps. For example, Juniper QFX-QSFP-DACBO-3M compatible QSFP+ to 4SFP+ copper direct attach cables are suitable for very short distances and offer a very cost-effective way to establish a 40-gigabit link between QSFP port and SFP+ port of Juniper switches within racks and across adjacent racks.

Active Optical Cable (AOC) Assemblies

Active Optical Cable (AOC) is used for short-range multi-lane data communication and interconnect applications. It uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable without sacrificing compatibility with standard electrical interfaces. AOC brings a more flexible cabling than direct attach copper cables with the advantages of lighter weigth, longer transmission distance and higher performance for anti-EMI. Now, 40G AOC assemblies are popular with users.

40G cabling

Fiberstore offers a comprehensive solution for 40G fiber optic cabling connectivity. Apart from the above-mentioned cabling connectivity options, there are also some typical cabling components you will require when building 40G cabling, such as MTP trunk cables, MTP cassettes, LC to MTP jumpers and so on.

What Makes 40G QSFP+ AOC So Popular in Data Center

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. In order to satisfy the demands of higher bandwidth and more applications in a variety of cloud computing environments, active optical cable (AOC) has emerged. This article will introduce a very popular type of AOC —40G QSFP+ AOC in data center 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.


Applications of 40G QSFP+ AOC

Active Optical Cable (AOC) is used for short-range multi-lane data communication and interconnect applications. It uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable without sacrificing compatibility with standard electrical interfaces. The 40G QSFP+ AOC is a high performance, low power consumption integrated cable for short-range multi-lane data communication and interconnect applications, supporting 40G Ethernet, fiber channel and PCIE. It is compliant with the QSFP MSA and IEEE P802.3ba 40GBASE-SR4. It integrates four data lanes in each direction with 40 Gb/s aggregate bandwidth. Each lane is capable of transmitting data at rates up to 10Gb/s with lengths ranging from one to 100 m. With its benefits, 40G QSFP+ AOC is widely used in many fields as well as promoting the traditional data center to step into optical interconnection.

40G QSFP+ AOC vs QSFP+ Optics
  • Cost: 40G AOCs cost lower than SR4 modules and do not need to use with extra fiber patch cables. For instance, HP 720205-B21 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 HP 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.
Fiberstore AOC Solutions

Fiberstore’s AOCs achieve high data rates over long reaches which are the best solutions for high-performance computing and storage applications. We supply AOC products such as 10G SFP+ AOCs, 40G QSFP+ AOCs, QSFP+ to 4 SFP+ AOCs, QSFP+ to 8 x LC AOCs and 120G CXP AOCs etc. In addition, custom cables are also available in various lengths. Recently, Fiberstore has cut the price of its direct attach cable (DAC) products in order to offer a more cost-effective high speed transmission solution for the old and new customers.

Direct Attach Copper Cable VS Active Optical Cable (AOC)

As one kind of optical transceiver assembly, a direct attach cable (DAC) is used to connect one mobility access switch with another when forming a stack, which can be either passive or active. Since the passive DAC cable contains no active components, it provides a direct electrical connection between corresponding cable ends. This process can also be done by an active DAC cable that is considered active because there are optics and/or electronics embedded within the connectors. Active DAC vs. passive DAC: the active one helps to improve signal quality and provides a longer cable distance. The DAC cable is a fixed assembly that is purchased at a given length.

Seen from the material of the cable, DAC cable can be classified into direct attach copper cable and active optical cable (AOC). Direct attach copper cables can either be passive or active, while AOC cables are always active. The following figure shows leading types of passive and active cable for data center:


As two kinds of commonly-used transceiver assemblies, both direct attach copper cable and AOC cable have their advantages and disadvantages.

What Is DAC Cable?

As the development of fiber technology, someone may deem that copper technology is out of fashion. This is not true for direct attach copper cable. In fact, direct attach copper cable still has its advantages in the market.

DAC cable example 10GBASE-CU SFP+ Active Cable

  • Advantages of Direct Attach Copper Cable

Enough data rate for various applications—Today’s direct attach copper cable can support higher data rates than traditional copper interfaces—from 4Gbps to 10Gbps per channel.

Interchangeability—As the development of copper cable technology, direct attach copper cable is interchangeable and hot swappable with fiber optic modules.

Cost effective—Supporting such multiple protocols as Gigabit & 10G Ethernet, 8G FC, FCoE and InfiniBand, direct attach copper cable is a cost effective solution over optical transceivers.

  • Disadvantages of Direct Attach Copper Cable

The defect of direct attach copper cable is that it is heavy and bulky, making it difficult to be managed. Furthermore, due to the nature of electrical signals, direct attach copper cable is vulnerable to the effects of electromagnetic interference (EMI), such as undesirable responses, degradation, or complete system failure.

What Is AOC Cable?

AOC cable is an alternative to optical transceivers, which eliminates the separable interface between transceiver module and optical cable. It offers a number of advantages over direct attach copper cable.

10GBASE SFP+ Active Optical Cable

  • Advantages of AOC

Greater bandwidth—Needing no equipment upgrades, AOC cable has a throughput of up to 40 Gbps with QSFP+.

Lightweight—Due to its material, AOC cable weighs less than a comparable direct attach copper cable.

EMI immunity—Since the optical fiber is a kind of dielectric (not able to conduct electric current), AOC is immune to electromagnetic energy.

  • Disadvantages of AOC

Compared with direct attach copper cable, the drawback of AOC cable is that it may be a little expensive for customers.


DAC cable and AOC cable are widely applied in storage area network, data center, and high-performance computing connectivity, etc. AOC vs. DAC: the correct choice can be made when you are clear about the advantages and disadvantages of each. Fiberstore provides various kinds of high speed interconnect DAC assemblies including 10G SFP+ Cables, 40G QSFP+ Cables, and 120G CXP Cables.

Related Article:
40G QSFP+ Direct Attach Copper Cables
Active Optical Cable (AOC) – Rising Star of Telecommunications & Datacom Transceiver Markets