400G optical modules are expected to be shipped on a large scale in 2020. There are currently two mainstream solutions for 400G optical modules, which are OSFP (25G PAM4*8) and QSFP-DD (50G NRZ*8). Because of its low power consumption and high integration, silicon photonics is expected to significantly reduce costs in the process of large-scale commercial production. Compared with traditional optical devices, silicon optical devices have the following advantages in theory: (1) Low cost: The cost of silicon-based materials is low, and the investment, facilities and processes of CMOS in the field of integrated circuits can be used to greatly improve the manufacturing process level of optical devices. Further cost reduction; (2) Low power consumption: silicon-based materials have low impedance, low device driving voltage, and reduced energy consumption; (3) High integration: silicon-based materials and technologies can provide a unified manufacturing platform for photonics and electronics , providing a way for chip-level optoelectronic integration, further reducing the cost and size of system equipment. In the optical chip industry, due to the different types of functional requirements, the demand for optical chips in the current market is gradually increasing. At present, optical chips mainly include InP series (high-speed direct modulation DFB and EML chips, PIN and APD chips, high-speed modulator chips, multi-channel tunable laser chips), GaAs series (high-speed VCSEL chips, pump laser chips), Si/SiO2 series (PLC, AWG, MEMS chip), SiP series (coherent optical transceiver chips, high-speed modulators, optical switches and other chips; TIA, LDDriver, CDR chips), LiNbO3 series (high-speed modulator chips), etc.

Optical devices can be divided into optical active devices and optical passive devices according to whether they need to be driven by external energy. Optical active devices mainly include lasers (VCSELs, DFB directly modulated lasers, EML externally modulated lasers), optical modulators (PMQ modulators, phase modulators, intensity modulators), photodetectors (PIN, APD), integrated devices (coherent modulators) Optical transceiver devices, array modulators), etc.; optical passive devices include optical isolators, optical splitters, optical switches, optical connectors (MPO connectors), optical backplanes, optical filters (multiplexers/demultiplexers). Next we will introduce the latest 400G module QSFP-DD.

QSFP-DD is the abbreviation of Quad Small Form-factor Pluggable (QSFP) – Double Density (DD), which is a high-speed hot-pluggable form factor defined by the QSFP-DD MSA group. It is the most advanced optical module in the optical communication industry. 400Gbps rate. The best choice for 400G transceiver packages, this QSFP-DD connector enables data centers to efficiently grow and expand transmission efficiency as needed.

QSFP-DD is front and back compatible with QSFP ports, and is also compatible with existing QSFP28 optical module and AOC/DACs. The electrical interface of a QSFP-DD connector consists of 8 electrical channels operating at 25Gb/s NRZ per signal or 50Gb/s PAM4 signal for a total bandwidth of 200Gb/s or 400Gb/s. QSFP-DD can achieve up to 14.4Tb/s aggregate bandwidth when used in 4x25Gbps NRZ mode and up to 28.8Tb/s aggregate bandwidth when used in 4x50Gbps PAM4 mode. This makes QSFP-DD the best choice for 400G module applications.


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