# Modulation Characteristics of High-Speed Transistor Lasers
## 4 Conclusions  
Owing to the rapid recombination of base region carriers, TL shows enormous potential in the field of optical fiber communication. The design of TL for fast data transfer must consider the parameters of the epitaxial chip. Further, the introduction of the predistortion network and base region signal assist also affect the fast modulation performance of the TL. The modulation bandwidth of TL is enhanced by the fast removal of carriers in the base region, but the output optical power of TL will be reduced for the carrier loss. The output power of the TL is improved with photon-assisted tunneling; thus, TJ-TL is the key step that will allow the practical application of TLs. The results of these studies are shown in Table 1.  
DML also suggests many ways to improve the modulation characteristics, as shown in Table 2. These methods are not only likely to be applicable to TL, but can also possibly be combined with the unique three-electrode structure of TL. Tables 1 and 2 summarize the progress of TL and DML modulation characteristics technology over the past decade, respectively. It can be clearly seen that the modulation characteristic of DML is much better than that of TL. This is because TL was only invented in 2004, and most of the theoretical research on TL still needs to be experimentally confirmed, which also demonstrates the great potential of TL. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Research** & **Optimization** & \multirow{2}{*}{**Performance Improvement**} & **Research Method** & **Reference** \\  & **Institution** & **Method** & & & \\ \hline \multirow{3}{*}{2008} & \multirow{3}{*}{UIUC} & Base Area AC & The modulation bandwidth of & \multirow{3}{*}{Experiments and \multirow{3}{*}{Simulations}} & \multirow{3}{*}{[74]} \\  & & Signal Auxiliary & InGaAs/GaAs-based TL is increased & & \\  & & Modulation & from 10.22 GHz to 22 GHz & & \\ \hline \multirow{3}{*}{2013} & \multirow{3}{*}{UIUC} & Voltage & The first voltage modulation TL, & \multirow{3}{*}{Experimental data} & \multirow{3}{*}{[77]} \\  & & modulation & achieving 20 Gb/s transfer rate at & & \\  & & room temperature & & & \\ \hline \multirow{3}{*}{2013} & Shenzhen & Structural & \multirow{3}{*}{InP-based TL 40 Gb/s transfer rate} & Simulation & \multirow{3}{*}{[28]} \\  & University & optimization & & analysis & \\ \hline \multirow{3}{*}{2014} & University of & \multirow{3}{*}{tunnel injection} & InGaAs/GaAs-based TL bandwidth & Simulation & \multirow{3}{*}{[58]} \\  & Calcutta & & increased to 44.21 GHz & & analysis \\ \hline \multirow{3}{*}{2015} & \multirow{3}{*}{UIUC} & Intracavity Photon & InGaAs/GaAs-based TL achieves & \multirow{3}{*}{Experimental data} & \multirow{3}{*}{[43]} \\  & & Assisted Tunneling & & 10.4 GHz bandwidth and transfer rate & & \\  & & & of 22 Gb/s & & \\ \hline \multirow{3}{*}{2019} & Amirkabir & \multirow{3}{*}{SCH layer} & InGaAs/GaAs-based TL bandwidth & \multirow{3}{*}{Simulation \multirow{3}{*}{[54]}} \\  & University of & & optimization & increased to 26 GHz & analysis \\ \hline \multirow{3}{*}{2020} & National & Voltage & \multirow{3}{*}{0.98 \(\upmu\)M TL transfer rate increased to \multirow{3}{*}{[72]}} & Simulation & \multirow{3}{*}{[72]} \\  & Taiwan & modulation; chirp & & 10 Gb/s & analysis \\ \hline \multirow{3}{*}{2021} & \multirow{3}{*}{Anna & \multirow{3}{*}{
\begin{tabular}{} \end{tabular} } & Adding Schottky & \multirow{3}{*}{1.3 \(\upmu\)M TL bandwidth increased to \multirow{3}{*}{[3.8 GHz]}} & Simulation & \multirow{3}{*}{[76]} \\  & University & & & 13.8 GHz & analysis \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Development of TL modulation characteristics in the past decade. Conceptualization, L.F. and L.Q. ; methodology, Q.C. and Y.L. ; validation, P.J. and Y.C. ; formal analysis, L.F. and P.J. ; investigation, P.J., C.Q. and Y.L. ; resources, L.F., Y.W. and Y.S. ; writing--original draft preparation, L.F.; writing--review and editing, Y.C. ; supervision, Y.C. and L.L. ; project administration, Y.N. ; funding acquisition, L.Q.