# Integrated Components and Solutions for High-Speed Short-Reach Data Transmission
## 5 Discussion
As depicted in Tables 3 and 4, the common bandwidths of MZM and EML are beyond 30-GHz in beyond 100-Gbit/s per lane transmission systems, although the state-of-art bandwidth 100-GHz of EML had been reported [13]. In general, for hundreds of meters of high-speed intra-data center optical interconnects, VCSEL with low-cost and small footprint size is commonly considered as the best candidate transmitter. For a few and tens of kilometers high-speed optical interconnects, the best choice becomes unobvious between DML and EML. Of course, in terms of cost, a few kilometers high-speed optical interconnects prefer to use DML. In here, for the cost-sensitive short-reach transmission systems, LiNbO\({}_{3}\)-based MZM and IQ modulator with large footprint size and high-cost may not be the best transmitter option. Currently, with the help of monolithic integration technology, the MZM and IQ modulator-based monolithic integrated transmitters based on InP-based monolithic integration or SiP have shown irreplaceable advantages in cost, package, bandwidth, and transmission distance compared with other transmitters. Therefore, we believe that the monolithic integrated transmitters have the potential to gradually replace other transmitters in high-speed short-reach transmission systems in the future, especially in tens of kilometers of high-speed optical interconnects. Figure 16: The technological and component options for high-speed short-reach transmission systems. In recent years, various receivers such as single-end PD, Kramers-Kronig receiver, Stokes vector receiver, coherent receiver, and monolithic integrated receiver have been widely reported in beyond 100-Gbit/s short-reach transmission systems. Here, as depicted in Table 7, we compare the supported transmission distance, detection sensitivity, footprint, and cost of different receiver components in beyond 100-Gbit/s per lane transmission system. For the IM/DD transmission system, beyond 100-Gbit/s researches mainly use the single-end PD with low-cost to detect the transmission signals. The single-end PD can only detect intensity information, and its applications are often limited to less than tens of kilometers of transmission distance because CD effect would lead to serious inter-symbol interference. While, this phenomenon may be even worse for high-speed transmission links as these links can be more sensitive to signal impairments. Many advanced direct detection technologies such as Kramers-Kronig receiver and Stokes vector receiver have been proposed and studied extensively, and the gap between conventional direct detection and advanced coherent detection is getting closer. Since these techniques can reconstruct the complex domain of the modulation signal, the CD effect can be compensated in the DSP module of receiver side. Meanwhile, to combine complex vector modulation with polarization division multiplexing, the rate-distance product can be further improved. Despite these advanced direct detection technologies having large footprint size and moderate cost compared to a single-end PD, they still show the potential in certain application scenarios. Coherent receiver with high detection sensitivity has the ability to achieve high rate-distance product, but its cost is too high to use directly in cost-sensitive short-reach transmission systems. In recent years, InP/SiP-based monolithic integrated receivers incorporating various schemes, such as single-end PD, Kramers-Kronig receiver, Stokes vector receiver, and coherent receiver have been widely reported and have the advantages of low-cost and small footprint size. Furthermore, some effective solutions combining simplified direct scheme and transceiver integration scheme have also been reported in short-reach transmission systems for the purpose of cost and energy effectiveness.