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What are the 400G Optical Modules?——400G optical module introduction

Date: 2020-06-10 10:11 From: C-light Onclick:
To realize the interconnection of optical networks within a data center, optical modules are indispensable. With the increase in the number and density of ports, half of the cost of optical networks in data centers will be occupied by optical modules. At present, 100G interconnection technology has been widely adopted in data centers newly built by major Internet companies, and 400G interconnection technology will be commercially used in large scale in the next 2 to 3 years . Therefore, the implementation technology of 400G optical modules has become the focus of the industry.
The demand for network bandwidth of hyperscale data centers has almost doubled from one and a half years to two years. 2014 began to deploy 40G Ethernet , 2017 began to deploy 100G Ethernet, according to this schedule, the country's ultra-large-scale data center is expected in 2020 it began to deploy 400G Ethernet, about in 2022 400G Ethernet will enter the large-scale deployment phase.
The early 400G optical modules used 16-channel 25G bps NRZ implementation (such as 400G-SR16), and were packaged in CDFP or CFP8 . The advantage is that it can borrow the mature 25G NRZ technology on the 100G optical module , but the disadvantage is that it requires 16 signals for parallel transmission, the power consumption and volume are relatively large, and it is not suitable for data center applications.
The current 400G optical module, the optical port side primarily to use 8 way 53Gbps PAM4 (400G-SR8 , FR8 , LR8) or 4 -way 106Gbps PAM4 (400G-of DR4 , FR4 , LR4) to achieve 400G signal transmission, in the electrical port side 8- channel 53Gbps PAM4 electrical signal, using OSFP or QSFP-DD package. Both OSFP and QSFP-DD packages can provide 8 electrical signal interfaces . In comparison, the package size of QSFP-DD is smaller (similar to the QSFP28 package of traditional 100G optical modules), which is more suitable for data center applications; OSFP package size is slightly larger, because it can provide more power consumption, so it is more suitable for telecommunications applications.
Distinguish from the optical wavelength, the 400G optical module can be divided into multi-mode (MM) and single-mode (SM); from the signal modulation method, it is divided into NRZ and PAM4 modulation (currently mainly PAM4); distinguish from the transmission distance, 400G optical modules can be divided into SR , DR , FR , LR ; from the form of packaging, 400G optical modules can be divided into CDFP , CFP8 , OSFP , QSFP-DD, etc.
400G optical module products:
  1  CFP8 optical module
        CFP8 is an extension of CFP4 . The number of channels is increased to 8 channels, and the size is also increased accordingly, which is 40*102*9.5 mm^3 . With 16 Ge 25G parallel signal to be done quickly to 400G to market products and applications work. However, high cost, need to use the 16 th 25G of the laser device, or using PLC splitter to reduce the number of lasers, the splitter LOSS too high, resulting in a direct transmit power of the laser is relatively large, so the cost will be high. The power consumption is also high, the panel interface density is too low, and the size is large.
      2  OSFP optical module
  OSFP English name is Octal Small Formfactor Pluggable , Octal referring 8 , octal meaning, which means directly with 56G electrical signals, 8 * 56GbE , but 56GbE signals from 25G of DML laser PAM4 forming a lower modulation . This standard is a new interface standard and is not compatible with existing photoelectric interfaces. OSFP comes with a heat sink, its size is 100.4*22.58*13 mm^3 , much smaller than CFP8 , and the power consumption is relatively low, the maximum is only 15W , but it is slightly larger than QSFP-DD , so it needs a larger area PCB, the mechanical structure of the PCB and HosTIng cage and 1RU front panel need to be rebuilt. The pins of its electrical interface are different from QSFP-DD, with a row above and below.
  3  the QSFP DD- optical module
       Q in QSFP-DD refers to the "Quad". 4 -way means, each QSFP56 is 4 * 56Gbe , formed 200G signal; DD refers to a "Double Density" , there are two QSFP56 parallel, 2 * 200G produced The 400Gbe signal, the full name is Quad Small Form Factor Pluggable-Double Density , this solution is an expansion of QSFP , adding a line to the original 4- channel interface to 8 channels. The size is smaller than OSFP , and it is compatible with the existing 40GbE QSFP and 100GbE QSFP28 interfaces. The original QSFP28 module can still be used. Just insert another module to achieve a smooth upgrade. Due to the addition of 4 channels, the pins of the electrical interfaces on the upper and lower sides have been added in a row.
        4  COBO optical module
  COBO is the abbreviation of "consorTIum for on board opTIcs" . The reflective module is directly placed on the PCB board, which is no longer limited by the density of the front panel interface. At the same time, the heat dissipation problem can reuse the powerful heat dissipation between the PCB boards. The device can be greatly eased. The size of this module is small, and the size is not suitable for further reduction of space. However, because it is not hot-swappable, once a module fails, it is necessary to stop the whole board business and take it out after removing the board, which is very inconvenient.
  From the perspective of size, power consumption and cost, the application of QSFP-DD and COBO in the future data center 400G is more promising.
The optical interconnection network of the data center is facing a transition from 100G to 400G , and technologies for different application scenarios are also competing with each other. As a key hardware device for interconnection of internal optical networks in future data centers, 400G optical modules also face challenges in terms of speed, power consumption, volume, and cost.
At the same time, the widespread adoption of PAM4 and FEC technologies also makes the testing and evaluation methods of 400G optical modules quite different from traditional 100G optical modules. In order to ensure its performance under limited cost and power consumption, it is necessary to conduct detailed tests on the output quality, reception tolerance, and bit error rate of real optical data for the optical and electrical ports to ensure the equipment Good interconnection and reliable data transmission.
C-light provides a wide range of supported optical transceivers including 400G modules. Each one of them has been tested with assured 100% compatibility to them.
C-light 400G/200G product list 
Model Specification
400G  QSFPDD 400G 850nm 
QSFPDD 400G 1310nm 
200G  QSFPDD 200G 850nm 
QSFPDD 200G 1310nm 2km
QSFPDD 200G 1310nm 10km
QSFPDD 200G 1310nm 40km

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Links: IEEE | ECOC