Factor 1: Wavelength

The wavelength refers to the specific frequency of light that is used to transmit and receive data. It is measured in nanometers (nm). The commonly used wavelengths are 850nm, 1310nm, and 1550nm, as well as CWDM wavelengths of 1270~1610nm and DWDM wavelengths of 1525~1565nm or 1570~1610nm.

In fiber links, data transmits from one end to another. Optical modules at both ends should support the same wavelength to ensure conversion and transmission. A module at a wavelength of 1310nm could not establish communication and interconnection with one at 850nm. Wavelength mismatch could result in data loss during transmission.

How to check and confirm the wavelength of your modules? There are many methods. Take 3C QSFP-DD 400G DR4 module as an example. You can browse the information on 3coptics.com before purchasing, and check the label on the module in use. What's more, if your optical module supports Diagnostics Download Manager (DDM), you can check them directly through commands and Simple Network Management Protocol (SNMP).

Factor 2: Transmission Distance

The transmission distance refers to the maximum distance the module can transmit optic signals without an amplifier or repeater. The short-range optical module is typically designed to transmit data over a distance of up to 300 meters, such as within a data center or local area network (LAN). A long-range module could transmit data over tens of kilometers, such as across a metropolitan area network (MAN) or a wide-area network (WAN). 3C provides multiple choices of high-speed transceiver modules of different transmission distances. You can choose the products corresponding to the transmission distance and application scenarios according to actual needs.

Although it is possible to establish a connection between two modules with different transmission distances, as long as the TX&RX range does not exceed the other end and the wavelength is the same. A 100G DR module and a 400G XDR4 can theoretically establish a connection but are usually not connected in this way since one is a 500m module and the other is a 2km module.

Optical modules with different transmission distances cannot establish a connection directly. Improper use due to inconsistent transmission distances would shorten the service life of the module. In general, the range of output and input optical power increases with the transmission distance. Excessive TX output power can break through the detector of the other module. It might lead to the component’s failure. The light emitted by the long-range module may burn the short-range module, requiring an optical attenuator in the middle. Therefore, the short-range module could be burned when connecting to a long-range module. In this case, you are suggested to adopt an optical attenuator in the middle to prevent such failure.

Factor 3: Modulation

Modulation refers to the process of encoding digital data onto an optical signal that can be transmitted over fiber optic cables using an optical module. At present, there are three forms of modulation, NRZ, PAM4, and QAM.

In the application scenario of 400G to 4x100G breakout, 400G DR4 can establish a breakout connection with 100G DR, 400G XDR4 can establish a breakout connection with 100G FR, and 400G PLR4 can establish a breakout connection with 100G LR. These modules have the same wavelength, transmission distance, and modulation mode. For instance, the 100G DR module's center wavelength is 1310nm. The 400G DR4 module has four sets of waves and each one is 1310nm. DR and DR4 are suitable for 500m scenarios. The transmission distance is the same, so you can establish a 4x100G breakout by MTP to 4xLC fiber patch cable. The optical modules with inconsistent signal modulation modes cannot perform signal conversion transmission.

Factor 4: Form Factor

The form factor of a transceiver is designed to protect electronic components from damage and to provide a standardized form factor that is easily set up and replaced in a wide range of equipment. 3C 100G transceivers are mainly packaged in QSFP28, and 400G transceivers are in QSFP112, OSFP, and QSFP-DD.

Before inserting the optical module into the switch, you need to confirm that the equipment supports the corresponding form factor of the optical module.

Typical Applications

The four-wavelength implementation of Shortwave Wavelength Division Multiplexing (SWDM) is called SWDM4. These four wavelengths are multiplexed/demultiplexed inside the QSFP transceiver into a pair of multimode fibers (one fiber in each direction, i.e., a standard duplex interface). Each of the four wavelengths operates at 25G, enabling the transmission of 100G (4x25G) Ethernet over existing duplex multimode fiber, using standard LC connectors.

3C 100G SWDM4 BiDi module is NRZ modulated. Cisco 100G PAM4 BiDi module is 50G PAM4 modulated. In the figure above, both modules can connect with the respective module. It is worth noting the situation in the 3rd line and you may ask why. As shown in the table below, the wavelengths and the modulation forms are different. That is why the two modules are unable to establish a connection.

Summary

As stated above, high-speed transceiver module connections are generally influenced by four major factors: wavelength, transmission distance, modulation, and form factor. In complex situations, the last two factors may be variable. For example, a built-in gearbox chip (it could convert the QSFP-DD NRZ to PAM4) allows two modules with different modulations to connect. But in most cases, wavelength and transmission distance are decisive.

Through this guidance, you will make informed decisions and choose suitable modules. 3Coptics.com offers comprehensive 100G and 400G data center transceivers at competitive prices. Besides, 3C expert team provides professional technical support and services. Feel free to consult and get a customized solution. Get ready for a successful connection with 3C high-speed transceiver modules like a pro!