Design of 100G SR4 Optical Module


100G SR4 Transmitter Part

A company’s 4-channel VCSEL driver chip is used at the transmitter. The maximum modulation rate of a single channel is 28 Gbps, which can provide 15 mA bias current and 12.8 mA modulation current. In addition, it also has equalization, clock data recovery (CDR), etc. Function. The 4-channel electrical signals are AC-coupled to the VCSEL driver chip. The VCSEL driver chip first performs equalizer (EQ) and clock recovery CDR processing on the input electrical signal to complete the optimal compensation for the high-frequency electrical signal, and then drives the VCSEL array to emit light. . In the process of optical engine design, due to the differences in manufacturer’s design, the high-frequency characteristics of different optical modules will be different. This requires the use of an optical oscilloscope during later debugging, and the parameter configuration in the VCSEL driver chip should be reasonably adjusted according to the shape of the emitted optical eye diagram. Complete the optimization of the emission performance of the 100G optical module.

100G SR4 Receiving Part

A 4-channel transimpedance amplifier chip is used at the receiving end. The chip has pre-emphasis, clock recovery (CDR), and other functions. The 4-channel optical signal converts the optical signal into a weak current signal through the PD array, and the transimpedance amplifier chip converts the current signal into a voltage signal, and then goes through the pre-emphasis and clock recovery (CDR) circuit to compensate and optimize the high-frequency part of the voltage signal and clock it. Signal correction, thereby improving the receiving sensitivity index of the optical module.

100G SR4 Optical Path Part

In the design of the optical path, the active coupling technology of light bending is adopted, in which the light bending is completed by the array lens group, and the array lens is a whole, which contains 8 channels, 4 channels are emission channels; 4 channels for the receive channel.

100G SR4 Performance Analysis

After the optical path coupling is completed, the prototype of the optical module is completed. The next step is to assemble the shell to make it a complete optical module, and test the transmitting and receiving performance of the assembled optical module to verify whether the optical circuit design meets the requirements. During the bonding process, according to the high-frequency signal simulation data in the early stage, the distance between the optical chip and the electrical chip is controlled within 250 μm, and 25 μm gold wire is used for ball bonding process bonding, and the optical chip and the electrical chip are bonded. The length of the inter-gold wires is controlled at about 400 μm.


It can be seen from the test data that the 100G SR4 product has extinction ratio ER: 3.5~4.5 dB, transmit optical power: 0+2 dBm, eye diagram margin > 30%, receiving sensitivity <- 5.2 dBm, fully meeting the requirements of the IEEE 802.3 bm protocol indicator requirements.

In Conclusion

The 100G SR4 parallel optical transceiver module is designed by COB technology, and the optical bending and active coupling process are adopted in the optical path design. Finally, the product transmits and receives under the condition of 0 ℃~70 ℃ through the self-made test system. Performance Testing. From the test data, it can be seen that the product meets the requirements of the index and can meet the requirements of a 100-meter high-speed data communication system. It also verifies the feasibility of the early bonding process and optical coupling process.

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