What is a 400G Optical Transceiver?
What is a 400G Optical Transceiver?
Blog Article
To achieve internal optical network interconnection in data centers, optical transceiver are indispensable. With the increase in the number and density of ports. half of the cost of optical networks in data centers will occupied by optical transceivers. At present, 100G interconnection technology has widely adopted in newly built data centers of major Internet companies. And 400G interconnection technology will commercialized on a large scale in the next 2 to 3 years. Therefore, the implementation technology of 400G optical transceiver has become an important part of the industry’s attention.
According to this progress, hyperscale data centers expected to start deploying 400G Ethernet in 2020. And 400G Ethernet will enter the large-scale deployment stage around 2022.
The development history of optical transceivers
Early 400G optical transceivers were implemented using 16-channel 25Gbps NRZ (such as 400G-SR16) and packaged in CDFP or CFP8. The advantage is that mature 25G NRZ technology can be borrowed on 100G optical transceivers. But the disadvantage is that 16 signals required for parallel transmission. And the power consumption and volume are relatively large. Which is not suitable for data center applications.
In the current 400G optical transceivers, 8 channels of 53Gbps PAM4 (400G-SR8, FR8, LR8) or 4 channels of 106Gbps PAM4 (400G-DR4, FR4, LR4) mainly used to achieve 400G signal transmission on the optical port side. And for 8 channels of 53Gbps PAM4 electrical signals on the electrical port side. Which using OSFP or qsfp-dd packaging. Both OSFP and qsfp-dd packaging can provide 8 electrical signal interfaces. In comparison, the qsfp-dd package size is smaller. Which similar to the QSFP28 package of traditional 100G optical transceivers. Which is more suitable for data center applications. The OSFP package size is slightly larger, because it can provide more power consumption. So it is more suitable for telecommunications applications.
In terms of optical wavelength, 400G optical transceivers can divided into multi-mode (MM) and single-mode (SM). In terms of signal modulation, they divided into NRZ and PAM4 modulation (PAM4 currently the main one). And in terms of transmission distance, 400G optical terminals can divided into SR, DR, FR, and LR. In terms of packaging form, 400G optical transceivers can divided into CDFP, CFP8, OSFP, qsfp-dd, etc.
400G CFP8 optical transceiver
CFP8 is an extension of CFP4, with the number of channels increased to 8 channels. And the size increased accordingly to 40*102*9.5mm^3. The market and application of 400G products quickly completed using 16x25G parallel signals. However, the cost is relatively high. And 16x25G lasers required, or PLC splitters used to reduce the number of lasers. But the loss of the splitter is too high. Which directly leads to the relatively large transmission power of the laser. And the cost will also be high. The power consumption is also high. The panel interface density is too low. And the size is large.
400G OSFP optical transceiver
The full name of OSFP in English is Octal Small Formfactor Pluggable. And Octal refers to 8. Which means that 56g electrical signals used directly. 8*56GbE, but the 56GbE signal formed by 25G DML lasers under PAM4 modulation. This standard is a new interface standard and is incompatible with existing optoelectronic interfaces. OSFP comes with a heat sink. And its size is 100.4*22.58*13mm^3. Which is much smaller than CFP8, and the power consumption is relatively low. The maximum is only 15W, but it is slightly larger than the qsfp-dd that requires a larger area of PCB board.
The Q in Qsfp-dd refers to “Quad”, which means 4 channels, each QSFP56 is 4*56Gbe. Forming a 200G signal; DD refers to “double density”, there are two QSFP56 in parallel. 2*200G generation 400Gbe signal, the full name is Quad small form factor pluggable-double density. This scheme is an extension of QSFP. Which increasing the original 4-channel interface by one row to 8 channels. It is smaller in size than OSFP and is compatible with existing 40GbE QSFP and 100GbE QSFP28 interfaces. The original QSFP28 transceiver can still used. You only need to plug in another transcive to achieve a smooth upgrade. Due to the addition of 4 channels. An additional row of pins added on the upper and lower sides of the electrical interface.
400G COBO optical transceiver
COBO is the abbreviation of “consorTIum for on board opTIcs”. The reflector module placed directly on the PCB board. And no longer limited by the density of the front panel interface. At the same time, the heat dissipation problem can greatly alleviated by reusing the powerful heat sink between the PCB boards. The size of this optical transceiver is very small. Since it is not hot-swappable, once an optical transceiver fails. The entire board business needs to stopped and the board needs to removed. Which is very inconvenient.
400G qsfp-dd optical transceiver
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 the interconnection of optical networks in future data centers. 400G optical transceivers also face challenges in speed, power consumption, volume and cost.
Report this page