After years of development, standardized and pluggable optical modules have become the inevitable choice of optical communication line side service transmission. The overall development trend of coherent light modules applied to urban areas and backbone networks is: first, high-speed, from 100G to 400G, and then to 800G; Second, miniaturization, from 100G MSA packaging form to CFP/CFP2 DCO/ACO packaging form, the current industry has proposed 100G/200G/400G OSFP DCO and QSFP-DD DCO packaging standards; Third, low power consumption. Considering the power requirement of the whole system, the power consumption of partially encapsulated coherent optical module products should not be higher than 18W. Fourth is the standardization of interconnection. Traditionally, each equipment manufacturer USES the self-developed special interface board and the private high-order modulation method and FEC algorithm, so the interfaces of different manufacturers cannot be interworking.
With the development of Internet business, the construction of cloud infrastructure and the demand of AI computing, telecom and data center operators have put forward clear requirements for the interoperability of optical modules from different vendors. In terms of FEC standard, although there are different types such as GFEC, SCFEC, RS10, CFEC, OFEC, SDFEC, KR4-FEC and KP4-FEC, corresponding to different rates and standards, the whole system can be divided into three generations. The first generation is block code, with 6dB gain requirement and 6.69% overhead. The second-generation cascade interleave iteration requires 8dB gain and 6.69% overhead. The third generation of soft decision SDFEC, with gain requirement of 11dB and overhead of 15%-20%, adopts Turbo product code (TPC) and low density parity check code (LDPC) algorithm, while the new generation of FEC based on probabilistic integer of constellation has not been released as a standard for the time being. In MIS standards, there are also different types of CFP MIS, C-CMIS and CMIS standards.
Comparative analysis of 400G coherence criteria
The 400G coherent optical module currently has three standards: OIF-400g ZR, OpenRoadm and OpenZR+. Oif-400g ZR target is applied in edge DCI. Only 400GbE rate is defined on the client side, and the transmission distance is 80km. CFEC is adopted for forward error correction. OpenRoadm MSA is mainly aimed at telecom operators' ROADM network applications. It defines 100G, 200G, 400GbE rate &OTN on the customer side, and the transmission distance is 500km. It adopts OFEC forward error correction algorithm. On the other hand, OpenZR+ MSA has a wider application range, facing urban areas, and backbone, DCI and telecom operators. It defines 100G, 200G and 400GbE multi-rate on the customer side to meet the transmission distance of urban areas or long-distance network, and adopts the forward error correction mechanism of OFEC. It can be seen that OpenZR+ is the MSA standard introduced by absorbing the respective advantages of oIF-400G ZR and OpenRoadm standards. The latest version of OpenZR+ was released in September 2020.
Analysis of coherent subsequent evolution over 400G
From the perspective of market trend, in terms of sales volume, the annual growth rate of the global DWDM market will reach 20% from 2020 to 2025 and reach 2.5 billion US dollars by 2025. Sales of 400G and above are expected to reach $150 million in 2020, with an annual growth rate of 19% thereafter, and reach $1.5 billion in 2025, with a compound growth rate of 46%. 400GZR and 400GZR+ are the fastest growing, followed by CFP2 DCO and 100G ZR, which are expected to reach us $6.6, 6.5, 4.2 and 290 million respectively by 2025, with the overall market reaching around US $2.3 billion. In terms of shipments, 400G ZR, 100G ZR, CFP2 DCO, and 400G ZR+ shipments grew fastest, with 400G ZR/ZR+ shipments expected to be 6,000 in 2020 and 550,000 in 2025, while 400/600/800g OnBoard was expected to be 15,000 in 2020 and 40,000 in 2025. In 2025, the number of 400G ZR+, 100G ZR+, 200G ZR+ and 400G ZR+ is expected to reach 330,000, 320,000, 240,000 and 220,000 respectively.
From the perspective of technology trends, the next generation of ultra-400g coherent products will adopt technologies such as single wave 800G, DP-16qAM, 5nm DSP, silicon optical technology and Flip Chip technology. The next generation product electrical interface Baud rate will be up to 4*128GHz, optical component COSA USES DDP -16QAM modulation to achieve 128GHz Baud, TIA/Driver bandwidth will be up to 96GHz. 800G ZR requires about 29dB OSNR, while 800G ZR+ requires about 25dB OSNR.
