An immersion cooling method of cooling ICT equipment directly in a liquid has succeeded in optical transmission between servers.
～Energy-saving data centers for the realization of a decarbonized society～.
AIO Core Co., Ltd. (hereinafter referred to as "AIO Core "), in collaboration with NTT DATA and NTT Communications Corporation (hereinafter referred to as "NTT Com"). has succeeded in achieving stable optical transmission in a data center cooling system that uses an immersion cooling method (hereinafter referred to as "immersion cooling system"). The immersion cooling method is a method of directly cooling ICT equipment such as servers in a special liquid, which is more energy-efficient than conventional air cooling and is attracting attention as a next-generation method for the realization of a decarbonized society.
Optical transmission is used for high-speed transmission of data between ICT equipment, but there is a problem that common optical transceivers cannot be used in immersion cooling systems due to air gaps. AIO Core has developed IOCore®, the world's only optical transceiver that can be used for immersion cooling due to no air gap.
From April ~ August 2023, we conducted an actual verification of optical transmission between ICT equipment in two types of immersion cooling systems in order to confirm efficiency and operational performance and identify issues for commercialization. As a result, optical transmission between ICT equipment has been successfully achieved in both the "twophase type" (a method that utilizes the heat of vaporization caused by boiling liquid) owned by NTT DATA and the "one-phase type" (a method of cooling by circulation of liquid) owned by NTT Com. We have identified practical issues related to equipment operation, including maintenance related to optical transmission.
AIO Core will continue to work on the implementation and provision of IOCore®, which realizes optical transmission in various harsh environments, such as high temperatures, vibrations, and electromagnetic noise, including the immersion cooling system that was tested this time.
About this verification
Due to the dramatic increase in the amount of information brought about by the digitalization of society as a whole, the power consumption of data centers is steadily increasing. While "decarbonization" is regarded as an important management issue, reducing power consumption has become one of the challenges for data centers. Improving the cooling efficiency of ICT equipment is effective in saving energy in data centers, and the immersion cooling method is attracting attention.
Optical transmission is used for high-speed transmission of data between ICT equipment, but there is a problem that common optical transceivers cannot be used in immersion cooling systems due to air gaps. AIO Core has developed IOCore® (Fig. 1), the world's smallest 5x5mm optical transceiver at low cost with no air gap, using silicon photonics technology. and has succeeded in optical transmission between ICT equipment in the immersion cooling system, which is attracting attention as a next-generation cooling method.
2. Verification Overview
Immersion cooling is a cooling method in which ICT equipment is immersed in an insulating liquid (such as an inert liquid or silicon oil) to achieve efficient cooling. It is said that the failure rate is reduced because high-heat generation servers can be operated in a closed environment at a constant temperature, and can be densely arranged, which makes it possible to save space compared to conventional methods that use air. In this verification, we conducted optical transmission tests using two types of cooling methods: a one-phase cooling system (NTT Com owns equipment, Fig. 2) that cools the liquid by circulating it, and a twophase cooling system that uses the heat of vaporization from the boiling of the liquid for cooling (NTT DATA owns equipment, Fig. 3).
Fig. 2 Single-phase immersion cooling system owned by NTT Com Optical Transmission Experiment of Immersed Server
Fig. 3 Two-phase immersion cooling system owned by NTT DATA Optical Transmission Experiment of Immersed Servers
Optical transmission is used for high-speed transmission of data between ICT equipment in data centers, but common optical transceivers have air gaps, so when the optical path is filled with liquid, the optical properties deteriorate, and they cannot be used in immersion cooling systems. Optical transceivers with enhanced airtightness specifically for immersion cooling have problems such as high costs and reliability issues. AIO Core has solved this problem by developing IOCore®, the world's only optical transceiver that can be used for immersion cooling with no air gap and equipped with a reliable quantum dot laser.
・In accordance with the QSFP28 electrical interface, which is a common module standard between ICT equipment in data centers, we tested the optical connection of a server and a switch immersed in refrigerant in two types of immersion cooling system, one phase and one two-phase, using an optical module equipped with IOCore®. We have succeeded in achieving an error-free optical transmission with a transmission rate of 25 Gbps per channel, 100 Gbps per transceiver (4 channels), and a distance of 30 m for two types of immersion cooling system.
・In contrast to optical fiber cables, which are capable of high-speed data transmission over long distances, conventional copper cables are limited to a few meters in length for high-speed data transmission, making it difficult to configure flexible systems between servers, switches, and storage for immersion cooling. Conventional optical transceivers cannot be used for immersion cooling, but in this verification, it was confirmed that optical fiber cables can be used for immersion cooling by applying a module equipped with an optical transceiver IOCore® that can be used for immersion cooling, and it is possible to flexibly arrange connections between ICT equipment in the same way as in a normal data center.
・Once the ICT equipment is immersed in the refrigerant in the immersion cooling system, the equipment is immersed in silicon oil, etc., so it is not easy to replace the equipment and perform maintenance. For this reason, optical transceivers must be highly reliable. It has been confirmed that the transmission characteristics of IOCore® do not change even after immersion for one year, and in the future, we will conduct further reliability evaluations to show that IOCore® has high reliability.
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