Know More About 100GBASE-PSM4 QSFP28 Transceiver

There is an interesting phenomenon that multimode fibers are more expensive than single-mode fibers but the transceivers are the reverse. That is because the multimode core diameter is large and easy to align with VCSEL lasers and detectors while the single mode fiber cable is very hard to build and align transceiver components with and requires very expensive alignment equipment. Therefore, multi-mode transceivers are less expensive than single-mode transceivers. Now the 100G Ethernet network has been widely applied in data centers and there are various types of 100G fiber optic transceivers available on the market. Is there a type of 100G single-mode transceiver which can provide a low-cost solution for long-reach data center optical interconnects? The answer is Yes. The 100GBASE-PSM4 (parallel single-mode 4-lane) QSFP28 transceiver can do that.

Overview of 100GBASE-PSM4 QSFP28 Transceiver

The 100GBASE-PSM4 QSFP28 transceiver supports 100G link over eight single-mode fibers (four fibers for transmit and four fibers for receive) with data transmission distance up to 500 meters. It uses four parallel lanes for each signal direction and each lane carries 25G optical signal. In addition, the 100GBASE-PSM4 QSFP28 transceiver is structured with MTP/MPO interface, so it is usually used with single-mode fiber ribbon cable with MTP/MPO connector.

100GBASE-PSM4 QSFP28 transceiver
Working Principle of 100GBASE-PSM4 QSFP28 Transceiver

The figure below shows the working principle of the 100GBASE-PSM4 QSFP28 transceiver. The transmitter side accepts electrical input signals compatible with common mode logic (CML) levels, wile the receiver side converts parallel optical input signals via a photo detector array into parallel electrical output signals. The receiver module outputs electrical signals are also voltage compatible with CML levels. All data signals are differential and support a data rate up to 25Gbps per channel.

working principle of 100GBASE-PSM4 QSFP28 transceiver
Applications of 100GBASE-PSM4 QSFP28 Transceiver

The 100GBASE-PSM4 QSFP28 transceiver can be used for 100G to 100G connection. As the following figure shows, two 100GBASE-PSM4 QSFP28 transceivers are plugged into Host IC, then these two transceivers are connected by MTP/MPO patch cord and MTP/MPO patch panel.

100G to 100G connection with 100GBASE-PSM4 QSFP28 transceiver

From an optical transceiver module structure viewpoint, PSM uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Therefore, the 100GBASE-PSM4 QSFP28 transceiver can be used for 100G to 4x25G connection. As the following figure shows, the 100GBASE-PSM4 QSFP28 transceiver and four 25G-LR SFP28 transceivers are connected by MTP-LC breakout cable.

100G to 4×25G connection with 100GBASE-PSM4 QSFP28 transceiver
Conclusion

The 100GBASE-PSM4 QSFP28 transceiver meets the requirement for low-cost 100G connections at reaches of 500 meters in applications that fall in between the IEEE multi-wavelength 10 kilometers 100GBASE-LR4 single-mode fiber approach and its multimode-fiber based 100GBASE-SR10 short reach specifications. It can support a link length of 500 meters over single mode fiber cable, which is sufficient for data center interconnect applications.

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Can 40GBASE-LR4 Be Used for 4x10G?

We know that 40GBASE-SR4 QSFP+ transceiver can be used for 4x10G SFP+ connections, because it offers 4 independent transmit and receive channels, each capable of 10G operation for an aggregate data rate of 40G over 100 meters of OM3 MMF or 150 meters of OM4 MMF. However, for 40GBASE-LR4 QSFP+ transceiver, it is commonly utilized over long transmission distance of SMF in 40G network applications. Can 40GBASE-LR4 be used for 4x10G? The answer depends and this article will focus on this question.

40GBASE-LR4 CWDM QSFP+ Transceiver Cannot Be Used for 4x10G

The 40GBASE-LR4 CWDM QSFP+ transceiver, such as QSFP-40GE-LR4, is compliant to 40GBASE-LR4 of the IEEE P802.3ba standard. It contains a duplex LC connector for the optical interface. The maximum transmission distance of the transceiver is 10km over SMF. In the transmit side, the 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 side accepts the 40G CWDM optical signals input, and demultiplexes it into 4 individual 10G channels with different wavelengths. Each wavelength channel is collected by a discrete photo diode and output as electric data after being amplified by a transimpedance amplifier (TIA). Therefore, 40GBASE-LR4 CWDM QSFP+ transceiver cannot be used for 4x10G. It cannot be split into 4x10G, because it uses 4 wavelengths on a pair of single-mode fiber with LC duplex connector, and does not allow itself to split into 4 pairs without substantial complexity to split out the wavelengths.

Working Principle of 40GBASE-LR4 CWDM QSFP+ Transceiver

40GBASE-LR4 PSM QSFP+ Transceiver Can Be Used for 4x10G

The 40GBASE-LR4 PSM QSFP+ transceiver is a parallel single-mode optical transceiver with an MTP/MPO fiber ribbon connector. It also offers 4 independent transmit and receive channels, each capable of 10G operation for an aggregate data rate of 40G on 10km of single-mode fiber. The transmitter side accepts electrical input signals compatible with common mode logic (CML) levels. All input data signals are differential and internally terminated. The receiver side converts parallel optical input signals via a photo detector array into parallel electrical output signals. That’s to say, the parallel optical signals are transmitted parallelly through 8 single mode fibers. As a result, 40GBASE-LR4 PSM QSFP+ transceiver can be used for 4x10G, because it uses parallel (ribbon) fiber with MTP/MPO connector, which allows the creation of 4 fiber pairs.

Working Principle of 40GBASE-LR4 PSM QSFP+ Transceiver

Note: From an optical transceiver module structure viewpoint, PSM uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Therefore, it allows for splitting into 4x10G (single-mode).

Conclusion

In a world, the answer of question “Can 40GBASE-LR4 be used for 4x10G?” depends. The 40GBASE-LR4 CWDM QSFP+ transceiver cannot be split into 4x10G, while for 40GBASE-LR4 PSM QSFP+ transceiver, it cab be used for 4x10G. To put it simply, 40G QSFP+ transceiver which is with MTP/MPO interface can be used for 4x10G connections, otherwise, it can only support 40G link.

Originally published at http://www.china-cable-suppliers.com/can-40gbase-lr4-used-4x10g.html

Focus on MTP-link

Characterized by providing ideal plug-and-play solutions for structure cabling, pre-terminated cabling system has gained great popularity among data center manager in recent years, and it is considered as the norm for data center network deployment. In this cabling system, optical link is accomplished by pre-terminated cabling assemblies, such as MTP/MPO trunk cable, MTP/MPO to LC breakout cable, MTP/MPO cassette and MTP/MPO fiber optic patch panel. It not difficult to find that all these MTP/MPO fiber optic cable assemblies are based on the structure of MTP/MPO connector. And two types of MTP/MPO connectors—12 fiber MTP connector and 24 fiber MTP connector are commonly used for 40G and 100G transmission. This article will focus on MTP-link and share share some opinions about MTP-link performance with you.

12-fiber MTP connector vs. 24-fiber MTP connector

About Space Utilization

High-density cabling makes the available space in data centers always precious. MTP/MPO fiber optic cable assemblies used in MTP-link that contributes to promoting space utilization are reputably appraised by data center managers. With massive cables being adopted in the data centers to carry out data transmission, MTP-link offers cabling solutions with much higher density and flexibility for data center upgrades.

About Insertion Loss

As well know that insertion loss is inevitable during the cabling. Generally, lower overall optical loss allows more margin for the network to operate, or in the case for some users, offers the option of more connections for patching locations. Therefore, components characterized by low insertion loss will be preferred. For both 12-fiber and 24-fiber MTP/MPO connector performance, the industry standard product rating is 0.5 dB maximum. And using low-loss ferrules, both 12 fiber MPO connector and 24 fiber MPO connector can be rated at 0.35 dB maximum. What’s more, there is no need to worry about higher fiber count will lead to higher insertion loss, because when using proper polishing techniques, 24-fiber MPO/MTP terminations can meet the same performance levels as 12-fiber MPO/MTP assemblies.

About Fiber Utilization

Both 12-fiber MPO cable and 24-fiber MPO cable can be used in 100G applications. When used in 4x25G solutions, 4 fibers of 12-fiber MPO cable will remain unused. As for 24-fiber MPO cable, it can be converted into three 8-fiber 100G channels that run over one cable, with all 24 fibers used to support data transmission. Maybe you feel confused about this, let me take an example. If you need to support twelve 100G channels with the 4x25G standard, by using 12-fiber MPO cable, you will need to install 12 connectors, or 144 fibers total, with 33% of the fiber wasted; while by using 24-fiber MPO cable supporting the same 12 channels, only 4 cables would be required, using 96 fibers total, at 100% fiber utilization.

About Network Performance

It is self-evident that MTP-link offers consistent high levels of network performance for improved network integrity, because the assemblies are factory terminated and the transmission testing is performed by the manufacturer before shipment. This will reduce the likelihood of many problems that may occur with field terminations. Also, testing and troubleshooting time can be greatly saved.

Conclusion

By using MTP components, MTP-link can provide fast installation, high density and high performance cabling for data centers. As 40G and 100G Ethernet is now a trend and hotspot for data center cabling system, MTP-link is a great option for data center managers and the network deployment will benefit a lot from this cabling solution. I hope after reading this article, you can have an in-depth understanding of MTP-link.