Differences of QSFP28 PSM4, QSFP28 SR4 and QSFP28 LR4 Optical Transceiver

100G QSFP28 optical transceiver is the rising star in the 100G Ethernet. It is with the same appearance as the 40G QSFP+ transceiver. What is the difference between them is that QSFP28 optical transceiver module is with a 4*25G electrical interface which can transmit optical signals up to 100G. Therefore, the QSFP28 transceiver stands out as the mainstream of 100G optic fiber module and also as the first solution for option to upgrade 100G network. With respect to 100G QSFP28 optical transceiver, there are many series for choice, such as 100G QSFP28 PSM4, 100G QSFP28 SR4 and 100G QSFP28 LR4. Then in this post, there will be an introduction to the difference of QSFP28 PSM4, QSFP28 SR4 and QSFP28 LR4.

The Difference in Definition

The QSFP28 PSM4 optical transceiver is with high-speed, low-power-dissipation product with a hot-pluggable QSFP form factor and built-in digital diagnostics function. Besides, it is with eight optic fibers, each fiber with a data rate of 25Gbps.

The QSFP28 SR4 optical transceiver is a parallel 100G optical transceiver with the advantages such as high port density and low cost. If a optical module for the short-reach transmission is needed to upgrade 100G network, the QSFP28 SR4 optical transceiver can be chosen.

The QSFP28 LR4 optical transceiver is one with transmission distance up to 2km. It provides an ideal solution for the super-large-scale data centers which has ever-increasing requirements for transmission distance. Simultaneously, it will lead the use of single-mode optic fiber in the data center.

The Difference in Transmission Media and Distance

The three modules can support different transmission distances. 100G-SR4 QSFP28 module works over wavelength of 850nm and is used with 12-fiber MTP OM3 or OM4 multimode fiber cables for short transmission distances up to 100m. 100GLR4 QSFP28 module is suggested to be used with single-mode fiber. It works over 1310nm wavelengths and can transmit 100G signals up to 2km. 100G-PSM4 QSFP28 is also used with 12-fiber MTP fiber cables but the fiber type is single-mode and the transmission distance is up to 500m.

The Difference in Transmission Mode

It is known that QSFP28 modules generally use four lanes to transmit 100G with each lane supporting 25G. Thus, the transmission method is just like 40G QSFP+ transceiver. 100G QSFP28 SR4, LR4 and PSM4 all use the 4*25 transmission mode. However, both the QSFP28 SR4 and QSFP28 PSM4 use a 12-fiber MTP interface which achieves dual-way 100G transmission over 8 fibers at the same time. QSFP28 LR4 uses a LC duplex fiber optic interface for 100G transmission on two directions at the same time. QSFP28 LR4 transmit optical signals over four different wavelengths around 1310nm with each wavelength carrying 25G optical signal. The wavelength ranges of the four lanes are as following:

1294.53nm-1296.59nm

1299.02nm-1301.09nm

1303.54nm-1305.63nm

1308.09nm-1310.19nm

The Difference in Cabling Structure

Optical transceiver transmission has playing a very important role in the optical fiber routing. Because the QSFP28 SR4 optical transceiver and the QSFP28 LR4 optical transceiver are used for short-distance transmission and long-distance transmission respectively, their wiring structures are different. The former requires multi-fiber cabling based on a 12-way MMF MTP interface, while the latter requires only a traditional two-fiber SMF cabling. In this case, the conversion between multimode fiber and single-mode fiber is very complicated because they use a completely different wiring structure.

Although the QSFP28 PSM4 optical transceiver operates in single-mode fiber, its wiring structure is the same as that of the QSFP28 SR4 optical transceiver. Using the QSFP28 PSM4 optical transceiver saves conversion costs between multimode and single-mode without changing existing cabling structures.

The Difference in Working Principle

(1) Working Principle of QSFP28 PSM4:

The QSFP28 PSM4 optical transceiver works in much the same way as the QSFP28 SR4 optical transceiver. The difference is that the QSFP28 PSM4 optical transceiver operates on single mode fiber while the QSFP28 SR4 optical transceiver operates on OM4 multimode fiber.

(2) Working Principle of QSFP28 SR4:

QSFP28 SR4 optical transceiver transmits signals at the transmitting end; the electrical signals are converted into optical signals by the laser array and then transmitted in parallel on the ribbon multimode fiber. Upon reaching the receiving termination, the photo detector array converts the parallel optical signals into parallel Electrical signals.

(3) Working Principle of QSFP28 LR4:

QSFP28 LR4 optical transceivers are typically used with LC single-mode fiber optic cables to convert 4 25Gbps electrical signals into 4 LAN WDM optical signals and then multiplexed into a single channel for 100G optical transmission. At the receiving end, the module demultiplexes the 100G optical inputs into 4 LAN WDM optical signals, which are then converted into 4 electrical signal output channels.

Conclusion

Generally speaking, the differences of QSFP28 PSM4, QSFP28 SR4 and QSFP28 LR4 optical transceiver are as above mentioned. If you want to know more other information about them, maybe you can visit Gigalight at gigalight.com.

The Latest QSFP28 Optical Transceivers: QSFP28 4WDM and QSFP28 ER4 Lite

The 100G optical module is with a variety of packaging forms, mainly including the early CFP/CFP2/CFP4 and the new-generation QSFP28. As a hot solution of 100G network, CFP series and QSFP28 optical transceiver have their own advantages. They all play a role in the specific application of 100G network. Currently, it seems that QSFP28 series optical transceiver is in greater favor than CFP series opticcal module transceiver. With respect to QSFP28 series optical module, there are two new types: 100G QSFP28 ER4 Lite optical transceiver module and 100G QSFP28 4WDM optical transceiver module. Then Gigalight will have an introduction to them in this article.

An Introduction to QSFP28 4WDM Optical Transceiver

4WDM(4-Wavelength Wavelength Division Multiplexing) optical module is defined by 4WDM MSA, targeted for longer reaches, lower costs, and lower power consumption, smaller form factor(QSFP28 form factor is usually preferred). 100G QSFP28 4WDM optics have three specifications including 4WDM-10, 4WDM-20, 4WDM-40. 4WDM-10 is one type of 100G (4x25G) optical transceivers for the 10 km based on the CWDM4 wavelength grid; 4WDM-20 and 4WDM-40 are types of 100G (4x25G) optical transceivers respectively for 20kms and 40kms based on the LAN-WDM wavelength grid over duplex single-mode fiber (SMF). With respect to the benefits of 4WDM, its main advantages are lower in cost and power dissipation, and longer in transmission distance.

An Introduction to QSFP28 ER4 Lite Optical Transceiver

IEEE 802.3ba defines that the 100GBASE-LR4 / 100GBASE-ER4 series has a BER requirement of better than 1E-12 w / o FEC for optical modules. Since the receiving sensitivity of 100GBASE-ER4 is not satisfied with the existing APD technology, the SOA size is too large for the QSFP28 series; many optical module companies in the industry defined a non-standard 100GBASE-ER4 Lite with QSFP28 package that the largest transmission distance is up to 30km without FEC.

The receiving sensitivity of 100GBASE-ER4 Lite 30km has no clear definition in IEEE802.3ba. At the current level of 100G APD ROSA, the average of OMA Sensitivity is around -17dbm (BER 1E-12@25.78125Gbps). The description of the100GBASE-ER4 Lite products in the industry is defined as 30km w/o FEC, 40km with FEC.

100G QSFP28 ER4 Lite vs. 100G QSFP28 4WDM: What Are the Difference?

The differences between QSFP28 ER4 Lite and QSFP28 4WDM are shown as the table:

qsfp28 4dwm vs. qsfp28 er4 lite

In addition, in the aspect of application, 100G QSFP28 ER4 Lite is available for both 100GE and OTU4 application, while 100G QSFP28 4WDM 40km is only available for 100GE application.

Summary

The migration of current network infrastructure to 100G systems is inevitable, and a growing number of enterprises require 100G client port to extend up to 40km without the use of expensive optical amplifiers. Thefore, the new ER4 Lite and 4WDM optical transceiver enable cost-effective 100G 40km pluggable solutions in compact QSFP28 transceivers that use Forward Error Correction (FEC) and APD-based receivers. Such evolution is very exciting for not only everyone involved in its development and construction, but also for all those who seek a simple, reliable and cost-effective solution to extend the reach of their networks, without expensive network upgrades. Gigalight, as the design innovator in global optical interconnect field, has pushed out the latest 100G QSFP28 4WDM 40KM optical transceiver and 100G QSFP28 ER4 Lite 40KM optical transceiver. More details are at Gigalight(gigalight.com)

A Brief Introduction to 4WDM Optical Transceiver

In current optical communication market, optical transceiver products are developed in the trend of high data transmission rate, longer reaches, lower power consumption, etc. To keep pace with the trend better, many new optical module products with high transmission rate and longer reaches emerge, such as the latest one, QSFP28 4WDM(4-wavelength Wavelength Division Multiplexing) optical transceiver. In this article, we will mainly talk about it.

What is 4WDM MSA?

The 4WDM MSA is an industry consortium dedicated to defining optical specifications and promoting adoption of interoperable 100G (4x25G) optical transceivers for 10 km based on the CWDM4 wavelength grid, and for 20 km and 40 km based on the LAN-WDM wavelength grid, over duplex single-mode fiber (SMF). These extended reaches are important for modern datacenter interconnects and mobile backhaul applications. The 4WDM MSA participants are responding to previously unmet industry needs for longer reaches, lower costs, and lower power consumption, as compared to previously available standards, in small form factors.

An Introduction to 4WDM Optical Module

4WDM(4-Wavelength Wavelength Division Multiplexing) optical module is defined by 4WDM MSA, targeted for longer reaches, lower costs, and lower power consumption, smaller form factor(QSFP28 form factor is usually preferred). 4WDM optics have three specifications including 4WDM-10, 4WDM-20, 4WDM-40. 4WDM-10 is one type of 100G (4x25G) optical transceivers for the 10 km based on the CWDM4 wavelength grid; 4WDM-20 and 4WDM-40 are types of 100G (4x25G) optical transceivers respectively for 20kms and 40kms based on the LAN-WDM wavelength grid over duplex single-mode fiber (SMF). With respect to the benefits of 4WDM, its main advantages are lower in cost and power dissipation, and longer in transmission distance.

Specifications of 4WDM Optical Module: 4WDM-10, 4WDM-20, 4WDM-40

The 100G-4WDM-10 is based on the CWDM4 wavelength grid. To some degree, the 100G-4WDM-10 technical specification leverages the success of the CWDM4 2 km specification that has found broad acceptance in its target datacenter market. Like CWDM4, the 100G-4WDM-10 specification employs 4 lanes of 25Gb/s using Coarse Wavelength Division Multiplexing (CWDM) technology to transport 100G optical traffic across duplex single mode fiber (SMF). Both specifications take advantage of Forward Error Correction (FEC) on the host port, in accordance with IEEE 802.3bj KR4 RS FEC. One key advantage of CWDM is that the lasers do not need to be cooled or temperature controlled, resulting in lower power consumption and simplicity of manufacturing. 100G 4WDM-10 transceivers share these advantages and furthermore are specified to be fully interoperable with CWDM4 products. The 100G-4WDM-10 specification does not restrict the form-factor although high-density QSFP28 modules are expected to be dominant.

4WDM-20 and 4WDM-40 are added on the basis of the 100G 4WDM-10. They employ LAN-WDM wavelength grid on the basis of IEEE 100GBASE-LR4 and ER4, over duplex single-mode fiber (SMF). Simultaneously, they also utilize the IEEE 802.3 KR4 RS FEC used on the host interface to reduce the cost.

This specification defines 4 x 25Gbps Local Area Network Wavelength Division Multiplex (LANWDM)optical interfaces for 100Gbps optical transceivers for Ethernet applications including 100GbE. Forward Error Correction (FEC) is a link requirement in order to ensure reliable system operation. Two transceivers communicate over single mode fibers (SMF) of length from 2 meters to at least 20 or 40 kilometers. The transceiver electrical interface is not specified by this MSA but can have, for example, four lanes in each direction with a nominal signaling rate of 25.78125Gbps per lane.

In addition, the 4WDM-20 specification, which is an extension of the 100G-4WDM-10 10 km specification, enables customers to increase their reach using the same kind of optical components as 100GBASE-LR4 products. Similarly, the 100G-4WDM-40 enables 40 km reach with lower power consumption and in a smaller form factor than existing 100GBASE-ER4 compliant products that utilize a power-hungry SOA (Semiconductor Optical Amplifier).

Summary

It is commented by related expert that the new 20kms and 40kms specifications are an important milestone to enable this market. Thus, the prospect of 4WDM optical transceivers are worth expecting. For most of optical component suppliers, it means another opportunity. Gigalight, as the design innovator in global optical interconnect field, surely seizes the chance and pushes out one new product: QSFP28 4WDM 40KM. (About this product, you can click it or visit Gigalight website to know more).