The Fabrication And PAM4 Modulation Of High-speed 940nm VCSELs

The full settlement of 5G communication technology has higher requirements for large data centers in terms of transmission capacity,energy consumption and speed.The optical link based on vertical cavity surface emitting laser(VCSEL)seems to be a good choice because of lower energy consumption and cost of the links.For a long time in the past,simply changing the device structure to improve the VCSEL parameters can meet the growth of commercial demand on speed.But now,the situation has changed.In this case,changing the modulation method of the link has become a new important way to improve the links speed.4 Pulse Amplitude Modulation(PAM4)is a new type of modulation method.Compared with the traditional Non-return-to-zero(NRZ)code modulation,the transmission speed can be nearly doubled.Because of that,it has been set as one of the 400 GE link solutions by the IEEE organization.But as the cost of increasing transmission rate,PAM4 modulation will also degrade the signal quality of the links.Therefore,how to balance the relationship between the transmission rate of the links and the signal quality is very important and economical.Based on this background,the purpose of this work is to apply optimized VCSEL and PAM4 modulation techniques to achieve high-speed,high-signal-quality data transmission as much as possible.The main containing of the paper is under the following aspects:Firstly,a brief introduction to the VCSEL device structure and theoretical analysis of its parameters has been displayed.The basic principle and corresponding electronic technology of PAM4 modulation are expounded then.The latest progress of high-speed VCSEL and the ones on PAM4 modulation has been investigated and written as a paper to publish.Next,the micro-nano processing technology of the high-speed vertical cavity surface emitting laser has been systematically described,including: cleaning,lithography,etching,BCB flattening and so on.The precautions in each step are briefly summarized and the specific technological parameters of lithography,etching,BCB flattening were determined during the experiment.Finally,to measure the device.The measurement can be divided into 4 parts: LIV measurement,spectrum measurement,small signal measurement and data transmission measurement.Through the LIV measurement,5?m device's threshold and turnover current is 0.4m A and 3.8m A.The max output power is 2.76 m W and the LI slope efficiency exceeds 1.2W/A.By the spectrum test,it has been proved to be able excite 940 nm light at 3.55 m A,the side mode inhibition ratio is larger than 45 d B which prove it can work in a single mode.The small signal modulation test shows the bandwidth of this device at 3.55 m A is 22 Ghz.During the data transmission experiment,the clear eye under 50 Gbps data transmission was successfully obtained,and high-quality transmission was achieved under the conditions of using pre-emphasis and pulse shaping electronic technology.