The need for speed has driven high-density OM3/OM4 optical connections in data centers

From the popularization of mobile Internet for all to the large-scale implementation of large model AI computing power clusters, the all-round layout of edge cloud computing, 4K/8K real-time live streaming, and the explosive growth of cross-border e-commerce millisecond-level interaction services, global data traffic has entered an exponential growth cycle. Speed has become the first core demand for data center construction.

According to the authoritative global cloud infrastructure research report in 2026, the bandwidth demand for a single cabinet in large and medium-sized cloud data centers has increased by as much as six times in the past five years. The traditional gigabit and 10-gigabit copper cable access architecture has been completely phased out. 40G/100G has become the standard configuration for the backbone networking of data centers, and 400G optical ports have been continuously extended to the cabinet access layer. The transmission of computing power has entered the era of high-speed parallel.

This top-down wave of speed-up across the entire domain has completely broken through the physical transmission limits of traditional copper cables and outdated OM1/OM2 multimode optical fibers, compelling the iterative innovation of the structured cabling system in data centers. Among them, OM3 and OM4 multimode fibers, which have four major advantages including high bandwidth, low insertion loss, compatibility with MPO modular integration, and compatibility with high-density cabinet networking, have become the mainstream optical connection solutions for newly-built and expanded high-density IDC data centers at present, laying a solid foundation for the underlying transmission of interconnection and interoperability of computing power clusters.

I. Business acceleration forces infrastructure upgrading: Traditional cabling architectures have comprehensively hit a bottleneck

Looking at the development history of data center cabling, the iterative logic of link connection has always been consistent: the demand for business speed forces the upgrade of hardware infrastructure. In the early years, domestic small and medium-sized enterprises' data centers and IDC hosting services were relatively limited, mainly focusing on static website hosting, offline file storage, and internal network office transmission. They had a high tolerance for business latency and small concurrent server traffic. They were equipped with Category 6 and super Category 6 copper cables and old multimode optical fibers with orange outer sheath, such as OM1 (62.5/125μm) and OM2 (50/125μm). It can stably support 1G/10G low-speed networking. In addition, the copper cable installation is simple and the optical fiber procurement cost is low. This combined solution has firmly occupied the mainstream market of computer room cabling for more than ten years and is suitable for the early low-speed and low-density computer room construction standards.

However, at present, the business logic of computing power has been completely restructured, and high speed, low latency, and high density have become hard and fast standards The AI large model training cluster requires millisecond-level parameter synchronization among thousands of server nodes, the core data centers of securities and banks demand microsecond-level packet lossless transmission of transaction data, the dual-active data centers of government and enterprises in the same city need batch virtual machines for real-time migration around the clock, and the short video live streaming data centers need multiple high-definition code streams for concurrent forwarding. After high-speed services are combined with the high-density deployment requirements of cabinets, the three fatal shortcomings of the traditional copper cable + outdated multimode optical fiber cabling system have been completely exposed, and it is completely unable to adapt to the new generation of data center networking standards.

First, the physical bottleneck of copper cable transmission cannot be broken through.

 Due to the three physical characteristics of high-frequency transmission skin effect, strong electromagnetic interference in the machine room, and cable crosstalk, the maximum bandwidth of super Category 6 shielded copper cables only supports 10Gbps transmission, and the compliant transmission distance is strictly limited to within 100 meters. The network cables in high-density cabinets are stacked in a disorderly manner, and the electromagnetic interference between the cables can easily cause packet loss and delay fluctuations in the network. At the same time, a large number of network cables block the air ducts of the cabinets, hindering the circulation of cold and hot air ducts, directly increasing the energy consumption of air conditioning for cooling in the computer room and the long-term operation and maintenance electricity cost of the computer room, which does not meet the current requirements for green and low-carbon computer room construction.

Second, the bandwidth margin of the old OM1/OM2 optical fibers is insufficient.

 The two first-generation multimode optical fibers with a mainstream working window of 850nm have effective bandwidths of only 500MHz·km and 1000MHz·km respectively. They were originally designed to be suitable only for single-channel low-speed transmission of 10G or less. When adapting to the 40G parallel optical module networking, the effective and compliant transmission distance is less than 30 meters. Even the basic wiring distance from the computer room cabinet to the floor distribution frame cannot meet the standard. To speed up the existing computer room, the only option is to replace all the optical cables and distribution modules. The overall renovation period is long, the renovation cost is extremely high, and the cost performance is very low.

Thirdly, the connection density of the SC split-type connector is too low, resulting in low operation and maintenance efficiency.

Traditional single-core optical fiber patch cords and SC duplex independent connectors occupy an extremely large port space on the patch panel. A standard 42U server cabinet can only stably deploy over a hundred optical connections. Nowadays, AI computing power cabinets and high-performance computing cabinets are standard-equipped with 48-port and 96-port high-speed network cards. Split connectors will directly lead to insufficient wiring ports and chaotic wiring. At the same time, manual core fusion splicing and termination construction are inefficient, which cannot adapt to the rapid online and expansion business rhythm of ultra-large-scale data centers.

The new generation of multimode optical fiber, which directly addresses the three major pain points of speed increase, capacity expansion and cost reduction in computer rooms, and takes into account the four major advantages of short-distance high speed, low-cost networking, modular integration and high-density cabinets, has become the best solution. Among them, OM3 and OM4 are both optimized 50/125μm gradient refractive index multimode fibers, which are perfectly compatible with the mainstream VCSEL vertical cavity surface emitting lasers in the computer room. They have extremely low mode dispersion values, stronger signal transmission integrity, and are downward compatible with the old OM1/OM2 links. There is no need to modify the computer room bridge frame, pipeline infrastructure, etc. Seamless adaptation to the one-stop deployment of new data centers and low-cost upgrades of existing data centers have become the core options for high-density optical connections at present.

Ii. Core Performance Breakdown: OM3 and OM4 are differentiated for data center speed-up scenarios

OM3 and OM4 are upgraded multimode optical fibers with the same source. Their core diameters are uniformly set at the industry standard of 50/125μm and are fully backward compatible with the old OM1/OM2 links. They can be seamlessly mixed with new and old cabling in the computer room without the need to modify the pipeline or cabinet structure. They are suitable for the renovation of existing computer rooms. The core differences between the two lie in bandwidth, transmission distance, and link loss. Precisely match the networking requirements of high-density data centers of different levels. The following is a comparison of the core parameters measured in accordance with the 2026 industry standard:

From the perspective of transmission logic, the current mainstream in data centers adopts an 850nm short-wave parallel transmission solution, combined with low-cost multi-mode VCSEL optical modules. Compared with single-mode 1310nm long-distance transmission modules, the procurement cost is reduced by more than 60%, and the cost-performance advantage of networking is prominent. OM3 optical fiber focuses on cost-performance expansion, meeting the requirements of 40G/100G backbone networking for small and medium-sized computer rooms, and is compatible with floor wiring and horizontal interconnection of cabinets. OM4 optimizes the refractive index structure, significantly reducing mode dispersion and upgrading the anti-macro bending loss performance. After 100 turns of bending with a 30mm bending radius, the 850nm loss is ≤0.5dB. It is suitable for bending wiring in the corner of the computer room bridge frame and the narrow space of the cabinet. At the same time, it supports 400G short-distance parallel transmission and reserves bandwidth margin for the expansion of computing power in the next 3-5 years.

Compared with single-mode optical fibers, the OM3/OM4 complete optical connection system has an irreplaceable advantage of high density: When paired with MPO multi-core integrated connectors, it can achieve 12-core, 24-core, and 48-core integrated termination. A single MPO port can replace more than ten sets of SC independent connectors, significantly reducing the space occupied by the patch panel and realizing the ultimate high-density wiring in the cabinet and patch room, perfectly meeting the modern data center construction standards of "high-density cabinets, space-intensive, and lightweight operation and maintenance".

Iii. Core of High-density Networking: OM3/OM4+MPO integrated connection Reconfigens the wiring logic of the computer room

When the industry mentions OM3/OM4 optical connection, it does not merely refer to the optical fiber cables themselves, but rather a set of integrated high-density optical link systems, including four major components: optical fiber cables, MPO connectors, high-density patch cords, and low-loss patch cords. It is also the mainstream pre-termination cabling solution for large data centers at present, completely rewriting the inefficient mode of traditional on-site splicing.

First, the port density is doubled to save the infrastructure space of the computer room.

Traditional SC duplex cabling, a 1U patch panel can accommodate up to 48 ports at most. It adopts OM3/OM4 with 24-core MPO high-density distribution modules. In 1U space, it can achieve 96-core optical path connection. Under the same cabinet space, the optical path carrying capacity is increased by 2 times. There is no need to add new cabinets or cable trays. It is suitable for the expansion of limited space in existing computer rooms and reduces the cost of computer room civil construction and cooling support. For AI computing power cluster data centers, the number of servers in a single cabinet is dense and the number of uplink and downlink optical paths is huge. MPO pre-ends OM4 links, which can directly achieve one-click cluster cabling on the top of the cabinet, significantly improving the cabling neatness.

Second, low-loss adaptation for multi-level networking ensures the stability of high-speed links.

 High-speed parallel optical networks rely on extremely low link losses. The superposition of multi-core docking losses will directly lead to 40G/100G link bit error and disconnection. The industry-standardized OM3/OM4 pre-termination component optimizes the end face grinding process. The total loss of the OM4 complete set of channel connectors is controlled within 1.0dB. It supports three-level networking of switches - patch panels - servers and multi-level connection. Even after multi-level transfer, it still meets the high-speed transmission threshold and is compatible with the leaf-spine architecture and the Spine-Leaf new-generation data center network architecture.

Third, modular rapid deployment shortens the time for the data center to go online.

In traditional single-core optical fiber on-site splicing, a single technician can only complete the termination of 80 cores in a day. Human errors can easily lead to end face contamination and excessive loss. Factory-prefabricated OM3/OM4-MPO wiring harnesses are plug-and-play upon entry. They can complete the deployment of over 500 optical paths in a single day, reducing the construction period by 70%. Meanwhile, standardized end faces avoid defects in manual construction, lowering the link failure rate by 90%. They are suitable for the rapid production needs of government and enterprise, cloud service providers.

Fourth, it is compatible with hierarchical speed-up and smooth iteration without the need to change lines.

The OM3/OM4 cabling links support graded bandwidth upgrades. At present, 100G services are deployed in the data center. Later, the speed can be directly increased by replacing the 400G parallel optical modules without removing the original optical cables and distribution modules. Compared with the mode of completely removing and replacing copper cables, the long-term operation and maintenance expansion cost is reduced by 45%, which is in line with the cost reduction construction concept throughout the data center's life cycle.

Iv. Industry Application Selection: The Logic of choosing between OM3 and OM4 in Different Scenarios

Based on the domestic IDC construction norms of 2026 and the IEEE Ethernet standards, taking into account speed requirements, cabling distances, and budget costs, the industry has formed standardized selection criteria to precisely match the speed demands of different business data centers

1. Edge data centers, secondary data centers in parks, and self-built data centers of enterprises: For business peaks within 100G and cabinet interconnection distances within 80 meters, OM3 high-density optical connections are preferred. It meets the needs of office cloud, edge storage, and security data forwarding services, with sufficient bandwidth and lower wiring costs. The existing OM2 links can be mixed and matched for use, making it suitable for low-cost speed-up and transformation.

2. Large-scale cloud data centers, computing power hub computer rooms, and financial dual-active computer rooms within the same city: 100G is used for regular business operation, 400G ports are frequently scheduled, and the interconnection distance between cabinets is 100-150 meters. OM4 high-density MPO optical links must be deployed throughout the entire area. Relying on higher bandwidth margin and lower bending loss, it can deal with sudden AI computing power traffic and millisecond-level financial transaction transmission, avoid the problem of packet loss due to high-speed transmission dispersion, and at the same time reserve the capacity for the next-generation 800G short-range networking expansion.

3. Special high-density sealed cabinets: Micro-module integrated computer rooms, water-cooled high-density cabinets, with many internal wiring corners and limited wiring space, uniformly select the upgraded version of OM4 optical fiber with bending resistance, and pair it with compact 12-core MPO connectors to avoid link speed reduction caused by bending loss and ensure long-term stable optical transmission in a sealed high-temperature environment.

V. Industry Misconceptions and Future Evolution: Understanding the Long-Term Value of OM3/OM4

At present, there are two major cognitive misunderstandings in the cabling of computer rooms: First, it is believed that single-mode optical fibers can fully cover high-speed services, and there is no need to lay out multi-mode OM3/OM4. Secondly, skip OM4 directly and deploy OM5 broadband multimode fiber in one step. In terms of implementation cost, the price of shortwave OM3/OM4 optical modules is only one-third of that of single-mode long-range modules. The interconnection distance of 95% of the cabinets in data centers is within 150 meters. Multi-mode is more than sufficient. Blindly deploying single-mode will significantly increase the procurement cost for networking. The OM5 focuses on dual-band transmission at 850/950nm. At present, its adaptability to 400G scenarios is limited, the supporting module industry chain is not mature, and its cost is much higher than that of the OM4. In the short term, it does not have the conditions for large-scale popularization.

Looking ahead to the next 2 to 4 years, the trend of high density, low latency and intensification in data centers will not reverse. The deployment of 100G and the popularization of 400G will become the industry standard. OM3 will continue to undertake the task of affordable expansion of existing data centers. OM4, with its balanced advantages in bandwidth, distance, cost and density, will become the standard optical configuration for new computing power data centers. Essentially, it is not fiber optic technology that drives industry upgrades, but rather the endless demands for data transmission speed and concurrent computing power across the entire network, which have driven high-density, low-loss, and easy-to-integrate OM3/OM4 optical connections to become an irreplaceable underlying carrier for data center infrastructure.

Conclusion

In the digital age, speed is the competitiveness of computing power, and high-quality optical connectivity is the core lifeblood of computing power flow in data centers.

From low-speed copper cables to high-speed optical fibers, from scattered SC cabling to integrated MPO high-density networking, the popularization of OM3 and OM4 multimode optical fibers is never an accidental result of material iteration, but an inevitable choice for business acceleration and the centralized construction of computer rooms. In the current era when 400G large-scale commercial use and high-density micro-module data centers have become the mainstream of construction, OM3 is suitable for low-cost upgrades of existing data centers, while OM4 is capable of long-term expansion of newly built computing power data centers. The two complement each other to meet the cabling requirements of all scenarios of IDC, taking into account transmission performance, deployment efficiency, and full-cycle operation and maintenance costs. In the future, as computing power and traffic continue to soar, high-density, low-latency, and modular optical connections will remain the core direction of data center cabling. OM3/OM4 will also firmly hold the mainstream position in medium and short-distance high-speed networking for a long time, building a stable, efficient, and intensive optical transmission foundation for AI cloud computing, financial transactions, and government and enterprise computing power hubs, and empowering the efficient operation of digital services across the entire domain.