Package
The package form is the most important feature of the optical module. The earliest package form was 1*9, and then GBIC, SFF, SFP, Xenpak, X2, XFP, etc. came one after another. Due to the limitations of the era, the 10G optical modules in the early 2000s were made extremely cumbersome, such as Xenpak and X2, which have now been eliminated and replaced by compact SFP+.
After more than 20 years development, the SFP (small pluggable) package has been shining brilliantly and won the favor of the market. 10G mainstream packaging is SFP+, the evolution of SFP, XFP only accounts for a small share. There is only QSFP+ packaging in the 40G market, and no other choice. In the 100G market, everyone originally thought that CFP series packaging could be the same as QSFP28, but it's just a flash in the pan. The CFP series now has to be reduced to a corner of the long-distance trunk system. The subsequent 50G, 200G, and 400G series packages are also the world of SFP descendants: QSFP28, QSFP56, QSFP-DD, OSFP. The SFP family has a glorious moment.
Rate
The early optical modules started at 155Mb/s (about 155 million bits transmitted in one second), and then gradually climbed: 622Mb/s, 1.25 Gb/s, 2.5Gb/s, 10Gb/s, and now the mass-produced single channel laser optical module SFP28 has reached 25G/s, and QSFP28, the optical module of the commercial optical module with 4 channels lasers has reached 100G/s. If the optical module wants to achieve a higher speed, there are only three solutions: increasing the optical source baud rate, the number of channels and high-order modulation. Increasing the baud rate of the optical source faces the performance bottleneck of III-V semiconductor lasers. At present, the 50G optical source solutions launched by equipment vendors are all externally modulated EML. Increasing the number of parallel channels will face design and packaging difficulties such as volume, power consumption, and heat dissipation, and increase the cost of optical fiber resources for customers. There are two main types of high-level modulation: PAM4 or coherent modulation. PAM4 is currently the most commonly used method to increase the single-channel rate of 400G optical modules under the traditional scheme, which is twice higher than the NRZ modulation rate, but the cost of DSP and CDR chips is increased accordingly. At present, various device giants are seizing the market of 400G QSFP-DD modules in the high-end field, and the establishment of the QSFP-DD800MSA working group also officially announced that the battle in the field of 800G high-speed optical modules is brewing. It is believed that in the future there will be a speed race for optical modules.
In the field of optical communication, faster and farther has always been the unremitting pursuit of communication area. The 1.25G SFP optical module can transmit 160 kilometers, the 10G SFP+ optical module can transmit up to 100 kilometers, and the 25G SFP28 module can transmit 40 kilometers. The higher the rate, the shorter the transmission distance. If the distance exceeds the above limit, we can use erbium-doped fiber amplifier (EDFA) to amplify the weak optical signal to make it transmit farther; or use coherent optical module to transmit. Of course, both are not cheap and require additional costs.
With the advent of the 5G era, the information generated by the popularization of the Internet has exploded, and higher transmission performance requirements have been put forward on the basic physical layer of the entire communication system. As an important part, it will make due contributions to the development of communications.
