For 40GBASE-LR4 QSFP+ Transceiver Link: CWDM or PSM?

Nowadays, the 40 Gigabit Ethernet (GbE) system comes as the popular deployment among some enterprises for their high-performance fiber optic networks. And for 40GbE system, fiber optic transceivers are the indispensable high-capacity modules for multi-lane communications, like 40GBASE-LR4 QSFP+ transceiver. It’s known that 40GBASE-LR4 QSFP+ transceiver has two link options: coarse wavelength division multiplexing (CWDM) and parallel single-mode fiber (PSM). How much do you know about them? Can you figure out the differences between them? Following this article and you will get something.

40GBASE-LR4 CWDM QSFP+ Transceiver Brief

Compliant to 40GBASE-LR4 (eg. QSFP-40G-LR4) of the IEEE P802.3ba standard, this 40GBASE-LR4 CWDM QSFP+ transceiver uses a duplex LC connector as the the optical interface, able to support transmission distance up to 10km over single-mode fiber (SMF) used to minimize the optical dispersion in the long-haul system.

This kind of 40GBASE-LR4 QSFP+ transceiver converts 4 inputs channels of 10G electrical data to 4 CWDM optical signals by a driven 4-wavelength distributed feedback (DFB) laser array, and then multiplexes them into a single channel for 40G optical transmission, propagating out of the transmitter module from the SMF. Reversely, the receiver module accepts the 40G CWDM optical signals input, and demultiplexes it into 4 individual 10G channels with different wavelengths. The central wavelengths of the 4 CWDM channels are 1271, 1291, 1311 and 1331 nm as members of the CWDM wavelength grid defined in ITU-T G694.2. Each wavelength channel is collected by a discrete photo diode and output as electric data after being amplified by a transimpedance amplifier (TIA).

CWDM QSFP+, 2 optical SMFs with a duplex LC connector

40GBASE-LR4 PSM QSFP+ Transceiver Brief

Differently, PSM QSFP+ is a parallel single-mode optical transceiver and uses a MTP/MPO fiber ribbon connector instead of LC. Similarly, PSM QSFP+ also offers 4 independent transmit and receive channels, each capable of 10G operation for an aggregate data rate of 40G with 10km reach over SMF.

In a PSM QSFP+, the transmitter module accepts electrical input signals, while he receiver module converts parallel optical input signals via a photo detector array into parallel electrical output signals. Both the input signals and output signals are compatible with common mode logic (CML) levels.

PSM QSFP+, 8 optical SMFs with a MTP/MPO fiber ribbon connector


Allowing for the transceiver module structure, PSM seems more cost effective, since it uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Additionally, its array-fiber coupling to a MTP connector is relatively simple.

However, when taking the infrastructure into consideration, PSM would be more expensive when the link distance is long, because it uses 8 optical single-mode fibers while CWDM only uses 2 optical single-mode fibers. Besides, in the data center fiber infrastructure, the patch panel has to be changed to accommodate MTP cables, which would cost more than LC connectors and regular SMF cables. Besides, it’s a little difficult to clean MTP connectors. So CWDM is more ideal for 40GBASE-LR4 QSFP+ link.


For 40GBASE-LR4 QSFP+ transceiver link options, both CWDM QSFP+ and PSM QSFP+ support the maximum transmission distance of 10km. The former establishes 40G links over 2 optical SMFs with a duplex LC connector, and the latter achieves 40G links via 8 optical SMFs with a MTP/MPO fiber ribbon connector. Thus no change is required for migration from 10G infrastructure to 40G infrastructure, saving cost when CWDM QSFP+ is chosen. Fiberstore supplies a broad selection of 40GBASE-LR4 QSFP+ transceivers which are fully compatible with major brands, such as Finisar (FTL4C1QE1C). For more information about 40GBASE-LR4 QSFP+ transceivers, please visit Fiberstore.

24-Fiber Trunk Cabling Solution for 40 Gigabit Ethernet

Year by year, the amount of data transmitted at data centers is skyrocketing as networks need to support more devices and advanced applications than ever before. Typical transmission speeds in the data center are also increasing from 10Gbps to 40Gbps, to 100Gbps or beyond, and in 2010, the IEEE ratified the 40 and 100 gigabit Ethernet (GbE) standard.

Data centers, at the heart of tremendous amount of data to be transmitted, need fiber optic links greatly to provide high bandwidth and low latency for data operation. The 24-fiber trunk cables, one type of fiber optic links, are able to deliver higher data transmission speed and bandwidth, better performance and more efficient scalability. 24-fiber trunk cables are considered as the suitable solution for 40GbE transmission. This text mainly introduces one 40GbE cabling solution: 24-fiber trunk cables.

What Does the 40GbE Standard Define?

The efforts aimed to support speeds of 40Gbps led to the ratification of the 802.3ba standard. This standard for 40Gbps uses parallel optics, or multiple lanes of fiber transmitting at the same speed. Most 40GbE infrastructure uses a 12-fiber MPO connector, requiring 8 fibers, with each 4 fibers transmitting at 10Gbps and the other 4 fibers receiving at 10Gbps, while the inner 4 optical fibers are left unused. According to IEEE 802.3ba standard, multi-mode fiber (MMF) supports 40GbE with link lengths up to 100m over OM3 optical fiber and up to 150m over OM4. Single-mode fiber (SMF)supports 40GbE with link lengths up to 40km when applied for longer distance transmission. Besides, copper cable is is also capable of supporting 40GbE when very short distance is required, such as EX-QSFP-40GE-DAC-50CM and QFX-QSFP-DAC-3M. Take QFX-QSFP-DAC-3M for example, Fiberstore compatible Juniper QFX-QSFP-DAC-3M establishes 40GbE with the link lengths of 3m.

QFX-QSFP-DAC-3M establishes 40GbE with the link lengths of 3m

Here introduces a better standards-based 40GbE cabling solution with 24-fiber trunk cables.

The use of 24-fiber trunk cables between switch panels and equipment is a wise solution. In this approach, 24-fiber trunk cables with 24-fiber MPOs on both ends are used to connect from the back of the switch panel to the equipment distribution area. This solution is appropriate for 40GbE owing to its following advantages.

Reduced Cable Congestion

Another advantage of using 24-fiber trunk cables comes to the reduced cable congestion. Data centers’ priority is the space in infrastructure, since congested cables would make cable management more difficult. 24-fiber trunk cables are only appreciably larger than 12-fiber trunk cables at 3.8 mm in diameter, compared to 3 mm. That means the 24-fiber trunk cables provide twice the amount of fiber in less than 21% space. For a 40GbE application, it takes three 12-fiber trunk cables to provide the same number of links as a single 24-fiber trunk cable.

24-fiber trunk  cableS reduce cable congestion

Maximum Fiber Utilization

As mentioned previously, 40GbE uses eight fibers of a 12-fiber MPO connector, the remaining four fibers unused. When using a 12-fiber trunk cable, those same four fibers are also unused. But with the use of 24-fiber trunk cables, all the fibers are actually used. The use of all the 24-fiber trunk cables create three 40GbE links. This recoups 33% of the fibers that would be lost with 12-fiber trunk cables, providing a much better return on investment.


24-fiber trunk cabling solution delivers high bandwidth to data-hungry applications along with low end to end latency, enabling data centers to operate with high performance and efficiency. Fiberstore supplies a large number of 24-fiber trunk cables, and other cables for 40G solution, including EX-QSFP-40GE-DAC-50CM and QFX-QSFP-DAC-3M mentioned above. Besides, Fiberstore also offers other 40G solution products, like 40G QSFP+ transceivers which are fully compatible with major brand, such as Cisco, HP and Dell (eg. Dell QSFP+), You can visit Fiberstore for more information about 40G solution.

MPO/MTP Technology for 40GbE Parallel Optic Solutions

Nowadays, data centers are witnessing a rise in the number of network connections, and it’s necessary for data centers to achieve even higher-density in both ports and cabling to accommodate the bandwidth demands. Parallel optics combining the use of cables and fiber optics serve as the medium to satisfy the growing need for transmission speed and data volume.

Multi-fiber connectors bring together 12 or 24 fibers in a single interface just as compact as a RJ45 connector. The multi-fiber push-on or also multi-path push-on (MPO) technology and especially the MTP connectors from the manufacturer US Conec have proven themselves as a practical solution for high-performance data networks in data centers. This paper mainly introduces MPO/MTP technology, and parallel optics which utilizes this multi-mode connectors in 40 Gigabit Ethernet (GbE) transmission.

Before going into the main body, a table showing the 40GbE standard, cable types and maximum allowable distances is below.

Transmission technology Cable type Signal Rate Maximum distance
40GBASE-KR4 PCB (bus) 4 x 10 Gb/s 1 m
40GBASE-CR4 Copper, Twinax 4 x 10 Gb/s 7 m
40GBASE-SR4 OM3, OM4 4 x 10 Gb/s OM3 100m, OM4 150m
40GBASE-LR4 Single-mode Fiber 4 x 10 Gb/s 10 km
How MPO/MTP Comes out?

As is shown in the table, while establishing 40GbE links, parallel optical channels with multi-mode fiber (MMFs) of the categories OM3 and OM4 are used. The ports have to accommodate four or even ten times the number of connectors. This large number of connectors can no longer be covered with conventional individual connectors, which explain the reason why the 802.3ba standard incorporated the MPO multi-fiber connector for 40GBASE-SR4 and 100GBASE-SR10. It can contact 12 or 24 fibers while saving space.

MPO Connectors Structure

IEC 61754-7 and TIA/EIA 604-5 defined MPO connector that can accommodate up to 72 fibers in the tiniest of spaces, most commonly used for 12 or 24 fibers. This MPO connector is designed for the high-density connection of MMFs, allowing easy connection and disconnection. MPO connector has two alignment pins to align the ferrule, and a clamp spring. When closed, the MT connector is extremely compact and is thus well suited for high-density fiber connection within closures or cabinets. The kind of multi-mode connector combines high-density connection with convenient disconnecting action, ideal in satisfying the need for high-density packaging in equipment. In 40G links, QSFP+ transceivers use MPO connectors as the interface for high performance. Just like, this HP JG709A 40GBASE-CSR4 QSFP+ transceiver listed on Fiberstore achieves 300m link length with MPO connector.


Laser-optimized MMF OM3 and OM4 for 40G Solution

Category OM3 and OM4 MMF are the future-proof cabling choices for 40G links. Lasers are used for OM3 and OM4. These lasers are generally vertical-cavity surface-emitting lasers (VCSELs) which are cheaper than distributed feedback lasers. The VCSELs are able to transmit data at higher rates. According to the table shown above, OM3 has a link length of 100 meters so it supports about 85 percent of all data center channels depending on architecture and size, and OM4 fibers have a link length of 150 meters so they cover nearly 100 percent of the required reach.

Parallel Optical Channels in 40G Links

As noted in the table, the 802.3ba standard defines the parallel operation of four OM3/OM4 fibers for 40GbE in 40GBASE-SR4. Two fibers have to be used per link because this arrangement is full duplex operation, i.e. Simultaneous transmission in both directions. Therefore the number of fibers increases to eight for 40GBASE-SR4. That is four of the twelve fibers remain unused and eight of the twelve fibers are used in each case in connection with 12-fiber and MPO connectors. In the parallel optical link, the signal is split, transmitted over separate fibers and then joined again. That means the individual signals have to arrive at the receiver at the same time.


MPO/MTP technology is performance- and quality-assured as a trend for decision makers in to carefully plan their fiber optics infrastructure for 40GbE transmission. Fiberstore provides not only high-quality MPOMTP connectors, but also MPO-based patch cables (eg. Push-Pull MPO cable). You can visit Fiberstore for more information about MPO connectors and MPO-based cables.

40G Needed for Data Center Networks

Driven by growing bandwidth and network performance demand, data center network infrastructure is witnessing a transformation. As technology evolves, standards are completed to define data rates such as 40 Gigabit Ethernet (GbE) to meet such demands of high networking speed and performance. 40GbE addresses physical layer specifications for communication across backplanes, copper cabling, single-mode fiber(SMF), and multi-mode fiber (MMF).

The Need for Higher Speed – 40G

1G and 10G data rates are not adequate to meet the future needs of high-bandwidth applications. The requirement for higher data rates is being driven by many factors. Switching and routing, virtualization, convergence and high-performance computing environments are examples of where these higher network speeds will be required within the data center environment. Additionally, Internet exchanges and service provider peering points and high-bandwidth applications, such as video-on-demand driving the need for a migration from 10G to 40G interfaces.

40G Physical Layer Alternatives

40GbE standards already exist for SMF, MPO based MMF, as well as copper cables. Listed below are three physical layer solutions for 40GbE.

Single-mode Fiber

Due to its long reach and superior transmission performance, SMF is specified for carrying 40Gbps data up to a distance as long as 10km (40GBASE-LR4). The physical layer electronics and optics consist of four channels, each carrying 10Gbps data with different wavelengths. When there is no need to consider budget or the link distances are long, SMF is the preferred option for 40GbE in data center networks.

Multi-mode Fiber

MMF with parallel optics MPO interface is the most popular medium for 40GbE today (40GBASE-SR4). Take F5-UPG-QSFP+ for example, Fiberstore compatible F5 Networks F5-UPG-QSFP+ (figure shown below) is a 40GBASE-SR4 QSFP+ transceiver with MPO connectors. It supports link lengths of 100m and 150m, respectively, on OM3 and OM4 MMFs at a wavelength of 850nm in a data center network. (OM3 and OM4 fibers were selected as the only MMFs for 40G consideration.)

Copper Twinax

For short reach channels up to a length of 7m, 40GBASE-CR4 standard specifies use of twinax copper cable assembly. One typical application of this kind of copper cable is in 40G QSFP+ direct attach cable (DAC). For instance, Fiberstore compatible Brocade 40G-QSFP-C-0101 is the QSFP+ to QSFP+ passive copper cable assembly for very short distances.

40G Transceivers

40G transceivers were developed along several standard form factors. The C Form-Factor Pluggable (CFP) transceiver features 12 transmit and 12 receive 10-Gbps lanes to support one 100 Gigabit Ethernet port, or up to three 40 Gigabit Ethernet ports. Its larger size is suitable for the needs of single-mode optics and can easily serve multi-mode optics or copper as well. The CXP transceiver form factor also provides 12 lanes in each direction, but is much smaller than the CFP and serves the needs of multi-mode optics and copper. The Quad Small-Form-Factor Pluggable (QSFP) is similar in size to the CXP and provides four transmit and four receive lanes to support 40 Gigabit Ethernet applications
for multi-mode fiber and copper today.


40GbE supports high-speed switching, routing, and application functions in data centers. It provides optimized performance in meeting data center requirements. As a professional fiber optic products supplier and manufacturer, Fiberstore offers various 40GbE products, like 40G transceivers, and 40G cabling available both in fiber and copper. You can visit Fiberstore for more information about 40GbE solutions.