The transmission distance of an optical module is a core parameter. In view of the market demand and network trend of ultra-long-distance transmission, ultra-long-distance transmission solutions have become the development trend of the future communication industry. In the actual use of ultra-long-distance optical modules, it will be limited by physical obstacles such as dispersion effects and nonlinear effects.
For applications over 10km in 100G networks, there are three main solutions:
100G ER4 (40km), 100G ZR4 (80km) and 100G DCO (2000km).
100G ER4
100G ER4 can achieve a transmission distance of 40km, by using a semiconductor amplifier (SOA) inside the transceiver to increase the power budget. The transmitter can work on four LAN WDM bands of 1295nm, 1300nm, 1305nm and 1310nm. The optical signals in these four bands are multiplexed by a WDM wavelength division multiplexer and then transmitted on a single-mode fiber through a duplex LC connector. At the receiving end, the SOA amplifies the signal before breaking it down into individual channels by a WDM wavelength division multiplexer.
The earliest 100G ER4 optical modules use CFP and CFP2 packages, but due to the large size and power consumption, and the newly launched 100G optical switches are usually equipped with compact QSFP28 ports instead of larger CFP interfaces, they are rarely used in 100G long-distance use them in the application. Therefore, the market is more inclined to use high-density 100G QSFP28 modules to maximize capacity and minimize space, power consumption and maintenance costs.
100G ZR4
The 100G ZR4 can transmit 80km, and the four-channel serial data (NRZ) at the transmitting end is recovered by CDR and passed to four laser drivers, which control four lasers with center wavelengths of 1296nm, 1300nm, 1305nm and 1309nm respectively. Optical signals are multiplexed to single-mode fiber through standard LC connectors.
At the receiving end, the optical signals of the four channels are amplified by the SOA, and then the optical signals are demultiplexed by the integrated optical demultiplexer. Each optical signal is recovered by a PIN detector and then passed through a transimpedance amplifier and CDR to a CAUI-4 compliant output driver. Similarly, the market prefers 100G ZR4 in QSFP28 package.
100G DCO
Transmission applications beyond 80km require the use of coherent modulation techniques. 100G DCO is one of the few options for 100G optical transmission applications over 80km to 2000km. 100G DCOs are available in CFP and CFP2 packages. Among them, CFP2 DCOs offer greater flexibility and support higher panel densities than CFP DCOs.
The CFP2 DCO uses QP-QPSK modulation and, thanks to the built-in DSP, does not require a separate Dispersion Compensation Module (DCM), but automatically has electronic dispersion compensation, enabling it to transmit longer distances between amplification sites. The optical module includes optical multiplexers and Mach-Zehnder modulators, receivers include optical demultiplexers, dual InP 90° optical hybrid mixers, and an integrated balanced PIN photodetector and quad-channel TIA.
The 100G CFP2 DCO is available in three versions, ZR/MR/LH, all in a compact CFP2 package and a mature 16nm DSP. Among them, the transmission distance of ZR mode is 120km, the transmission distance of MR mode is 300km, and the transmission distance of LH mode is 2000km.
The migration of current network infrastructure to 100G systems is inevitable, and more and more enterprises require 100G client interfaces to be extended to longer distances without the use of expensive optical amplifiers, 100G ER4, ZR4 and DCO satisfy these needs.
It is available in 100G QSFP28 ER4, 100G QSFP28 ZR4 and 100G CFP/CFP2 DCO can cover all 100G ultra-long distance optical interconnection applications within 40km to 2000km.
