100G 4WDM Optical Module Introduction

Related Protocol of 100G 4WDM Module 

With the development and maturity of related technologies, the design and production of small-sized optical modules with integrated multi-channel signals are gradually feasible. After the development of CFP modules with huge package sizes in the past, small-sized 100G QSFP28 optical modules have become the mainstream of the 100G module market. The 100G QSFP28 optical module has 4 independent transceiver channels, with passive optical paths inside and corresponding optical ports to connect with different optical fiber links. The industry standard organization 4WDM MSA (Four-Wavelength Wavelength Division Multiplexing Multi-Source Agreement) established in 2016 has classified the application scenarios and performance standards of 4WDM optical modules, and formulated standards for the optical regulations of optical modules, as shown in the following table.

Under the definition of 4WDM MSA, the wavelengths of 2km and 10km optical modules adopt CWDM design, and the 20km and 40km optical modules adopt LAN WDM design. Considering that the equipment in the network architecture has the function of FEC (Forward Error Correction, forward error correction), the sensitivity requirement is that the bit error rate is better than 5E-5. The bit error rate requirements of the series are lower, and the bit error rate in IEEE 802.3ba is required to be better than 1E-12. For a more detailed definition of 100GBASE-LR module optical ports in MSA, see the table that the wavelength shift of each independent channel laser should not exceed 6.5nm, the average optical power of a single channel should be between -7 and 2.5dBm, and the extinction ratio should be greater than 3.5dB. The sum of the average optical power of 4 channels shall not be higher than 8.5dBm.

QSFP28-4WDM-LR Module Design Scheme

Referring to the standard protocol above and the existing process level, and combined with the actual application environment, the final single-channel output optical power is set to 0~2dBm level in the actual design. The actual design standard is stricter than the protocol standard. Select the protocol The higher part of the average optical power range in the definition reserves a larger margin for the link loss, which can be better run in the more busy or poor link conditions, and can also be used for actual production. leave a larger tolerance. The actual control optical eye extinction ratio is 5.2dB as the typical value, which is close to the standard of the SFP28 optical module of the access network and can be realized by the DFB laser with high-cost performance and stable performance.

Due to the huge changes in the working environment temperature of the optical module design, the case temperature of the optical module is between -40 and +95 °C. According to the characteristics of the wavelength change of the DFB laser, the wavelength emitted by the DFB laser changes with the temperature change. Due to the individual performance error between the lasers, if there is no temperature control, the wavelength of some lasers will be shifted out of the standard in extreme environmental tests; if a large number of DFB lasers are arranged at high density in a dense space, the heating problem is also very significant, the design should be equipped with TEC (Thermo Electric Cooler, semiconductor Refrigerator) and temperature control circuit.

At the same time, according to practical application requirements, 100G optical modules should also be compatible with other lower-rate signal transmissions such as 40GE rates. The modules of the module are independent of each other, and each channel has different hardware working states when transmitting different signals. When transmitting 25G signals, the transceiver includes CDR (Clock Data Recover, clock data recovery) function, when transmitting 10G signals, this function closure. The optical module can control the working state of the hardware through the register to realize the switching of the operating state of the optical module and includes the DDM (Digital Diagnostics Monitoring, digital diagnostics monitoring) function.