What is multimode cable? 

What is multimode cable?

Meet the Cable: Multimode Cable

Multimode cable is a type of fiber optic cable designed to carry multiple light modes or paths simultaneously, enabling high-bandwidth data transmission over relatively short distances, commonly used in data centers and local area networks.

Optical fibers were first developed in the 1950s and 1960s by researchers such as Charles Kao and George Hockham, who demonstrated the potential of using glass fibers for transmitting optical signals. Initially, these fibers were single-mode, meaning they could transmit light along a single path. Multimode fibers were developed next to allow multiple light modes (paths) to propagate through the fiber simultaneously. This development increased the data carrying capacity and transmission speeds of optical fiber networks. In the 1970s, the development of multimode fibers progressed significantly as companies and research institutions like Corning Glass Works and Bell Laboratories played crucial roles in advancing the technology. By optimizing the core diameter and refractive index profile, they improved light transmission characteristics over longer distances.

Types of multimode cable

Multimode fiber cables come in several types, categorized by core diameter and bandwidth capabilities. OM1 has a core diameter of 62.5 microns and supports Ethernet speeds up to 1 Gb/s over short distances. OM2, with a 50-micron core, offers improved bandwidth, suitable for Fast Ethernet and Gigabit Ethernet applications. OM3 and OM4, also 50-micron cores, are designed for higher speeds like 10 Gigabit Ethernet, with OM4 supporting longer distances at these speeds. OM5, a newer addition, supports multiple wavelengths for increased network capacity over extended distances, known as Wideband Multimode Fiber (WBMMF). Each type is chosen based on specific performance needs, such as speed requirements and transmission distances, in optical communication networks.

Design Notes 

Standardization

Multimode cables are subject to SO/IEC Standards covering parameters such as core diameter, numerical aperture, attenuation, and bandwidth; TIA/EIA Standards for network installations; IEEE Standards; and the International Telecommunication Union – Telecommunication Standardization Sector (ITU-T) recommendations related to fiber optic communications.

Material specifications

Multimode fiber cables typically consist of a core made of silica glass with a core diameter of either 50 microns or 62.5 microns, and a cladding layer of 125 microns in diameter. The core’s composition is designed to have a higher refractive index compared to the cladding, creating total internal reflection to guide the light through the fiber. For OM1 and OM2 fibers, the core diameter is 62.5 and 50 microns, respectively, while OM3, OM4, and OM5 fibers have a 50-micron core, optimized for higher bandwidth and performance. The cladding is usually made of pure silica with a lower refractive index, allowing light to stay within the core. The fiber is coated with a protective polymer layer, which provides mechanical strength and environmental protection, essential for maintaining signal integrity and durability in various installation environments. Additionally, fiber connectors and cables are standardized to ensure compatibility and performance across different network systems.

JPC’s 200G QSFP56 is an active optical cable (AOC). Each channel operates with a 26.5625Gbd PAM4 modulation scheme, and the transmission distance through OM3 multimode fiber can reach 100 meters.

Physical properties

Multimode fiber cables are protected by polymer coatings for mechanical resilience and environmental resistance, with outer jackets offering additional safeguarding and flame retardancy, multimode fibers support reliable and high-performance optical communication networks, facilitated by compatible fiber optic connectors like LC, SC, and ST.

Environmental properties

The outer jackets of multimode cables are typically made from materials such as PVC or LSZH (Low Smoke Zero Halogen), which provide protection against moisture, abrasion, and fire hazards while minimizing smoke and toxic emissions in case of combustion. This design not only enhances safety in indoor installations but also meets stringent regulatory requirements for environmental impact mitigation. Moreover, the use of robust polymer coatings on the fibers themselves ensures resistance to environmental factors like humidity and temperature variations, maintaining signal integrity over extended periods. These features collectively contribute to the sustainability and longevity of multimode fiber networks.

Electrical properties

The fiber’s core and cladding materials, typically silica glass, provide excellent insulation and signal transmission characteristics, ensuring that electrical interference and crosstalk are minimized. Additionally, multimode fibers are designed to support various signal frequencies and modulation schemes, making them versatile for applications ranging from local area networks (LANs) and data centers to high-speed telecommunications.

Markets and Applications 

Datacom/Telecom, Military and Aerospace, Industrial, Transportation

Multimode fibers started to be widely used in telecommunications and data networks during the late 1970s and 1980s. They enabled higher bandwidths over shorter distances, making them suitable for applications within buildings and campuses where distances were relatively short compared to long-distance telecommunications.

Over time, advancements in materials, manufacturing techniques, and signal processing technologies have continued to improve multimode fibers’ performance and reliability. Today, multimode fibers are used extensively in local area networks (LANs), data centers, and other high-speed communication applications across markets.

Greene Tweed’s fiber optic assemblies are environmentally sealed to prevent signal degradation and damage from moisture and particulates, ensuring a clear signal throughout a wide range of environments and applications. They are compatible with Greene Tweed FC and ST terminations in both single- and multi-mode, and assemblies have flame-resistant PVC jackets.

Suppliers 

Multimode cable is available in many variations from many suppliers, including AirBorn, Amphenol Aerospace, Amphenol Industrial Operations,  Amphenol LTW, Cinch Connectivity Solutions,  Fischer Connectors, Greene Tweed, HARTING, JPC Connectivity, Phoenix Contact, Rosenberger, Samtec Inc., Smiths Interconnect, TE Connectivity, Teledyne Reynolds Times Microwave Systems, Trexon, Weidmüller.

Related products 

Singlemode optical cable

Fiber optic connectors: LC, SC, and ST.

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