100G QSFP28 Optics Introduction

To meet the growing requirements of collaborative multimedia services and applications, to respond to the fast-changing traffic patterns, and to better accommodate users’ bandwidth demands, 100G connections have been positioned for significant growth in data centers with the introduction of the latest 100G optical modules. The upgrade to 100Gbps is not more than gaining capacity. It’s also about gracefully evolving your network at your own pace to achieve greater efficiency, streamline costs and support new services. Many systems now support four or more 100G ports on each line card, with some systems supporting many hundreds of 100G ports. 100G optical modules, as an integral part of the overall system design, support highly reliable operations, optimized for entire architecture. This article puts its focus on one predominant 100G form factor: QSFP28.

QSFP28 Optics Benefits

100G QSFP28 transceivers are commonly seen in two types: QSFP28 100GBASE-SR4 (QSFP28 SR4) and QSFP28 100GBASE-LR4 (QSFP28 LR4), designed with four 25Gbps lanes for high port-count 100G data center applications, enabling the implementation of various reaches in the QSFP28 MSA form factor in 100G systems. They allow for greater port density, lower power consumption and significantly lower cost of ownership for 100G connectivity. With these optical transceivers, state-of-the-art 100Gbps performance and new levels of infrastructure consolidation have been made possible.

QSFP28 Optics Types

QSFP28 100GBASE-SR4 Overview

The QSFP28 100GBASE-SR4 transceiver is a parallel 100Gbps QSFP28 optical module designed with form factor, optical/electrical connection and digital diagnostic interface according to the QSFP28 Multi-Source Agreement (MSA). It offers 4 independent transmit and receive channels, each capable of 25Gbps operation for an aggregated data rate of 100Gbps for 100 meters on 12-fiber MPO/MTP OM4 multi-mode fiber (MMF). Often, an optical fiber ribbon cable with an MTP/MPO connector can be plugged into the QSFP28 module receptacle for high functionality and feature integration. Proper alignment is ensured by the guide pins inside the receptacle. The cable usually cannot be twisted for proper channel to channel alignment.

The QSFP28 SR4 module is a vertically integrated solution that meets IEEE 802.3 standards and MSA requirements with power dissipation well under 3.5W. It supports both 100GBASE-SR4 as well as 4x25G breakout applications, say 100G QSFP28 to QSFP28 DAC and 100G QSFP28 SR4 to 4x25G SFP28 break-out cables, meeting the harshest external operating conditions including temperature, humidity and EMI interference.

• QSFP28 100GBASE-SR4 Working Principle

QSFP28 SR4 transceiver converts parallel electrical input signals into parallel optical signals, by a driven Vertical Cavity Surface Emitting Laser (VCSEL) array. The transmitter module accepts electrical input signals compatible with Common Mode Logic (CML) levels. All input data signals are differential and internally terminated. The receiver module then 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 Common Mode Logic (CML) levels. All data signals are differential and support a data rates up to 25Gbps per channel. The following figure shows the functional block diagram of this module.

QSFP28 100GBASE-LR4 Overview

The QSFP28 100GBASE-LR4 transceiver is also a 100Gbps transceiver module designed for optical communication applications, compliant to 100GBASE-LR4 of the IEEE P802.3ba standard. This module converts 4 input channels of 25Gbps electrical data to 4 channels of LAN WDM optical signals and then multiplexes them into a single channel for 100Gbps optical transmission. Reversely on the receiver side, the module de-multiplexes a 100Gbps optical input into 4 channels of LAN WDM optical signals and then converts them to 4 output channels of electrical data. The high performance cooled LAN WDM EA-DFB transmitters and high sensitivity PIN receivers provide superior performance for 100GbE applications up to 10km links over single-mode fibers (SMFs) and compliant to optical interface with IEEE802.3ba Clause 88 100GBASE-LR4 requirements.

• QSFP28 100GBASE-LR4 Working Principle

The transceiver module receives 4 channels of 25Gbps electrical data, which are processed by a 4-channel Clock and Data Recovery (CDR) IC that reshapes and reduces the jitter of each electrical signal. Subsequently, each of 4 EML laser driver IC's converts one of the 4 channels of electrical signals to an optical signal that is transmitted from one of the 4 cooled EML lasers which are packaged in the Transmitter Optical Sub-Assembly (TOSA). Each laser launches the optical signal in specific wavelength specified in IEEE802.3ba 100GBASE-LR4 requirements. These 4 lane optical signals will be optically multiplexed into a single fiber by a 4-to-1 optical WDM MUX. The optical output power of each channel is maintained constant by an automatic power control (APC) circuit. The transmitter output can be turned off by TX_DIS hardware signal and/or 2-wire serial interface. Here goes the picture of QSFP28 100GBASE-LR4 module functional block diagram.

Ready for 100G Connections

100G connectivity is now ready for widespread deployment. With so many 100G modules (CFP, CFP2, CFP4 and QSFP28) having been introduced in the market, the number of companies deploying 100GbE networks is sure to see a significant growth. Although the expense of 100G connectivity maybe an issue for some companies, further developments which are under way are expected to reduce the cost.

Conclusion

100G QSFP28 transceivers enable higher speeds, greater scalability, and higher levels of performance and reliability, so as to better meet business demands. To optimize business investment, Fiberstore supplies many 100G QSFP28 modules which experience rigorous qualification and certification testing, sold at affordable prices. Besides QSFP28 transceivers, QSFP28 cable can also be found here. If you want to know more information about QSFP28 optics, you can visit Fiberstore.