Coherent optical communication, the English full name is called Coherent Optical Communication, is a technology in the field of optical fiber communication. It mainly uses coherent modulation technology at the sending end and heterodyne detection technology at the receiving end for information transmission. During transmission, the wavelength is the same, the vibration direction is the same, and the phase difference is constant.

Compared with traditional incoherent optical communication, coherent optical communication has the technical advantages of longer transmission distance, larger transmission capacity and higher receiving sensitivity, so it has attracted wide attention from all walks of life in the industry.

development path

In the 1980s, countries such as the United Kingdom, the United States, and Japan conducted a lot of research on coherent technology. AT&T and Bell Laboratories conducted 1.3 μm coherent experiments in 1989 and 1990 between two sites 35 kilometers apart in Pennsylvania. And 1.7G signal with 1.55μm wavelength without repeater coherent transmission experiment. In the 1990s, people found that the combination of DWDM+EDFA technology can solve the problem of optical communication expansion and long-distance transmission more simply and effectively, so the development of coherent transmission technology is temporarily sluggish.

Around 2008, with the development of the mobile Internet, the network data traffic increased explosively, and the backbone network (>1000 kilometers) and the metropolitan area network (100-1000 kilometers) faced a sharp increase in the pressure of upgrading and expansion. At this time, DWDM+EDFA technology has already Going to the extreme, the development potential is getting smaller and smaller. On the other hand, with the maturity of DSP and optical device technologies, coherent optical communication based on these technologies is suitable for relaying DWDM+EDFA technology and breaking the technical bottleneck of long-distance and large-bandwidth optical fiber communication. Therefore, coherent optical communication ushers in a second opportunity for development.

The explosion of data traffic has also promoted the large-scale construction of data centers, and then the development of cloud computing has changed the IT infrastructure of data centers, making distributed data centers mainstream. Distributed data centers need to communicate with each other in order to share data, balance loads, provide backup, and expand capacity when needed. Due to its large bandwidth and long-distance optical interconnection requirements (80-120km), distributed data centers urgently need the support of coherent transmission technology.

To sum up, the upgrade and expansion of the backbone network and metropolitan area network, as well as the optical interconnection of the data center, all urgently need the support of coherent optical transmission technology.

Advantages and applications

The main advantages of coherent optical communication include:

1) High sensitivity, long relay distance

2) Good selectivity and large communication capacity

3) With a variety of modulation methods

High-speed coherent optical communication belongs to the world’s leading optical transmission technology, and it is currently only in the hands of a few large enterprises. Foreign companies mainly include II-VI, NeoPhotonics, Ciena and other companies in the United States. my country’s related industries started relatively late, and now an industrial cluster centered on Suzhou, Chengdu, Qingdao, and Wuhan has been formed.

At the same time, in this short two decades, great progress has been made in optical devices, among which the output power, linewidth, stability and noise of lasers, and the bandwidth, power capacity and common-mode rejection of photodetectors The ratio has been greatly improved, and the performance of microwave electronic devices has also been greatly improved. These advances make it possible to commercialize coherent optical communication systems.

[Why develop high-speed coherent optical communication]

With the development of the mobile Internet and the realization of the national strategy of counting from east to west, the demand for optical fiber transceiver modules of cloud operators and telecom operators continues to grow at a high speed, and higher requirements are placed on the transmission bandwidth and distance of optical modules. Traditional optical modules cannot meet the transmission requirements of large bandwidth (over 100G) and long-distance (over 80 kilometers) at the same time, and coherent optical modules just make up for this gap.

Coherent optical transmission technology will greatly change the current network structure and ultra-long-distance transmission capabilities, and greatly reduce the complexity of system equipment. The development of coherent optical transmission products will drive the development of related industries such as integrated optical transmitter ICT, integrated optical receiver ICR, and high-speed flexible PCB boards in the upstream of the industry chain. Local supplier options available.