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    100G QSFP28 light module comparison


    With the development of 100G Ethernet trend, the demand for 100G optical module market is increasing, and now 100G optical module in the network construction costs occupy a large proportion. Of these light modules connected to the 100G link, the 100G QSFP28 is the 100G preferred module for its small size and low power consumption. What are the specific types of 100G QSFP28 modules and what are the differences between them? How do I select these modules? This article will take you closer to 100G QSFP28 to learn about the specific differences and connections between these modules.


    The 100G QSFP28 optical module is suitable for 100G Ethernet, EDR InfiniBand, and 32G Fibre Channel, typically with exactly the same volume and panel density as the 40G QSFP Plus. The 40G QSFP plus features four 10Gbps channels, similar to the 100G QSFP28 module, with four high-speed differential signal channels, data rates of up to 25Gbps and possibly up to 40Gbps. In addition, the QSFP28 has an upgraded electrical interface that supports signals up to 28Gbps. QSFP28 SR4、QSFP28 LR4、QSFP28 PSM4、QSFP28 CWDM4、QSFP28 ER4。 Compared to other package types of 100G optical modules (CFP/CFP2/CFP4), the 100G QSFP28 offers higher density, lower power consumption and significant price advantages.


    Once you understand the basic concepts of 100G QSFP28, this section details the differences in standards, laser types, transmission media, and distance of the 100G QSFP28 module.


    The standard of 100G QSFP28 optical module is mainly defined by IEEE and MSA, of which IEEE defines the standards of QSFP28 SR4, QSFP28 LR4 and QSFP28 ER4. "QSFP" means the package of the optical module; "28" means a maximum transmission rate of 28Gbps per channel, "SR" means a short distance (up to 100m), "LR" means a long distance (up to 10km), "ER" means an extended distance (up to 40km), and '4" means that the module has four channels. For example, the QSFP28 LR4 indicates that the 100G long-range module can transmit 100G signals at four wavelengths, up to a maximum distance of 10km.

    100GBASE-SR4 and 100GBASE-LR4 are the two most common 100G port specifications defined by IEEE, but QSFP28 SR4 has a short transmission distance that does not meet all connectivity requirements, and QSFP28 LR4 is too expensive for large data centers. Fortunately, MSA has brought new solutions to the mid-range transport market: the QSFP28 PSM4 and CWDM4 standards were born. Although the QSFP28 LR4 covers the transmission distance of the QSFP28 CWDM4, the cost of CWDM4 at a distance of 2km is far more affordable and competitive than the LR4.


    Lasers play a huge role in 100G QSFP28 light modules, and there are five common lasers: VCSEL, FP, DFB, DML and EML. These different types of lasers have different operating wavelengths, operating modes, and application environments.

    Laser typeWorking wavelengthWorking modeThe transfer distance
    VCSEL850nmface launchLess than 200m
    FP1310nm/1550nmside launch500m-10km
    DFB1310nm/1550nmside launch40km
    DML1310nm/1550nmDirect modulation500m-10km
    EML1310nm/1550nmElectric absorption modulation40km

    VCSEL lasers are characterized by small size, low power consumption, easy integration, low cost and high coupling efficiency with multimode fibers, and are commonly found in QSFP28 SR4 modules. The QSFP28 LR4 and ER4 modules are used for long-distance transmission (10km or 40km) and require lasers with large eye opening, low dispersion, high extinction ratio and long transmission distance, while EML lasers meet all requirements perfectly. The DML laser can be modulated by modulating the injected current of the laser. Because the size of the injection current changes the refractive index of the active area of the laser, the wavelength drifts to produce dispersion. Therefore, DML is not suitable for long-distance transmission, can not achieve high-speed signal modulation, but is suitable for the transmission distance of 500m or 2km QSFP28 PSM4 and QSFP28 CWDM4 modules.


    The 100G QSFP28 optical module features a duplex LC or MTP/MPO-12 connector with transmission distances ranging from 70m to 40km. The transmission distance of these optical modules determines their application scenarios, and all QSFP28 modules can be used for direct interconnection and interconnection of enterprise networks or data centers. The following table details the differences between them.

    standardIEEE 802.3IEEE 802.3MSAMSAIEEE 802.3
    connectorMTP/MPO-12Duplex LCMTP/MPO-12Duplex LCDuplex LC
    The type of fiberMultimodeSingleSingleSingleSingle
    The transfer distance70/100m10km500m2km40km
    The type of transmitterVCSELEMLDML/FPDMLEML


    After introducing the different kinds of 100G QSFP28 modules, I believe you already have a basic understanding of these modules, let's talk about how to select 100G QSFP28 modules.

    1. When the transmission distance is 5m-100m, it is recommended that you choose the QSFP28 SR4 optical module, which can transmit distance of 70m on OM3 fiber and 100m on OM4 fiber.

    2. When the transmission distance is 100m-2km, you can choose QSFP28 PSM4 or QSFP28 CWDM4 module. CWDM4 unit price is generally higher than PSM4, but CWDM4 in two-way transmission only need 2 single-mode fiber, PSM4 needs 8, so the overall cost of using QSFP28 PSM4 may be more expensive. Therefore, in practical applications, it is necessary to consider the specific transmission distance, and then decide which module is appropriate to choose.

    3. When the transmission distance is 10km-40km, choose QSFP28 LR4 or QSFP28 ER4, the former can transmit up to 10km, the latter can transmit up to 40km.


    Overall, the 100G QSFP28 features high density and low power consumption, meeting current network needs while preparing for future network expansion, making it an ideal optical module solution for large data centers.


    QSFP-100G-CWDM4-S=, 100GBASE CWDM4 QSFP Transceiver, LC, 2km over SMF

    QSFP-100G-DR-S=, 100G QSFP28 Transceiver 100GBASE-DR, 500m SMF, duplex, LC

    QSFP-100G-ER4L-S=, 100GBASE QSFP Transceiver, 40KM reach over SMF, Duplex LC

    QSFP-100G-FR-S=, 100G QSFP28 Transceiver 100G-FR, 2km SMF, duplex, LC

    QSFP-100G-LR4-S=, 100GBASE LR4 QSFP Transceiver, LC, 10km over SMF

    QSFP-100G-LR-S=, 100G QSFP28 100G-LR, 10km SMF, duplex, LC Connector

    QSFP-100G-PSM4-S=, 100GBASE PSM4 QSFP Transceiver, MPO, 500m over SMF

    QSFP-100G-SM-SR=, 100GBASE CWDM4 Lite QSFP Transceiver, 2km over SMF, 10-60C

    QSFP-100G-SR4-S=, 100GBASE SR4 QSFP Transceiver, MPO, 100m over OM4 MMF