Overview
This article explains classification of fiber patch cords and methods for converting between multimode and singlemode links. Fiber patch cords are fundamental components of optical network cabling and are widely used to build fiber links. Manufacturers offer many types of patch cords to suit different applications, such as MPO, LC, SC, FC, ST, simplex/duplex, and singlemode/multimode. Each type has distinct characteristics and use cases. The following sections describe common patch cord types and conversion methods to aid selection and cabling.
Classification by Connector Type
Based on connector type, patch cords include MPO, MTP, LC, SC, FC, ST, MTRJ, MU, E2000, and DIN. Although these types share similar components (connector and cable) and the same basic function, their characteristics and performance differ, so their application scenarios vary.
LC patch cords
LC patch cords are among the most commonly used in optical networks. They use an LC ferrule with a 1.25 mm diameter, making them compact and well suited for high-density cabling in data centers and server rooms. Variants address specific needs, for example ultra-low insertion loss LC cords and uniboot duplex LC cords.
Ultra-low insertion loss LC: Compared with standard LC cords (typical insertion loss around 0.75 dB), ultra-low insertion loss LC cords use LL technology to reduce insertion loss to as low as 0.12 dB, which is better for long-distance transmission.
Uniboot duplex LC: The uniboot LC uses a specially designed uniboot connector to enable bidirectional signals within a single cable, offering higher density. Compared with standard LC cords, it can increase space utilization and simplify cabling, making it suitable for space-constrained environments.
Short boot LC: To save space, short-boot LC cords use a 12 mm short boot design, shortening connector length by about 30% for more flexible routing. They are suitable for high-density zones such as the main distribution area (MDA) and equipment distribution area (EDA).
SC patch cords
SC patch cords use an SC ferrule with a 2.5 mm diameter. The SC connector is larger than LC and features a push-pull design for easy mating and robust performance, making it common in telecom and data network systems including point-to-point passive optical networks.
MPO/MTP patch cords
MPO/MTP patch cords are commonly used in high-rate data communications such as 40G and 100G direct-connect and interconnects. These multi-fiber connectors can accommodate 6 to 144 fibers and are currently the highest-capacity patch cords. An MPO/MTP assembly includes fibers, jacket, coupling components, metal guide pins, PINs, dust caps, and other parts. MPO/MTP cords are categorized by polarity A/B/C and by male/female pin arrangements, so selection should match the actual link requirements.
FC patch cords
FC patch cords were among the first to use ceramic ferrule connectors. Unlike LC and SC connectors, FC connectors are round, threaded connectors made of nickel-plated brass or stainless steel and require a threaded coupling nut to secure to an adapter. FC cords are still commonly used with optical time-domain reflectometers (OTDRs). Initially used in telecom and data networks, FC has been largely superseded by LC and SC in many applications.
ST patch cords
ST patch cords use a bayonet-style connector with a spring-loaded ceramic ferrule (2.5 mm diameter), developed after FC. Typical insertion loss is about 0.25 dB. ST connectors can be used for both short and long distances, for example in campus and enterprise networks, though their market share has declined in recent years.
Other connector types
MTRJ patch cords: MTRJ connectors are molded precision plastic connectors and are available in male and female versions depending on pin configuration.
MU patch cords: MU connectors are similar to SC but use a 1.25 mm ferrule and self-retaining mechanism, making them compact and suitable for high-density installations and DWDM networks.
DIN patch cords: DIN connectors share the pin and coupling sleeve dimensions with FC but incorporate an internal spring to control pressure, offering higher mechanical precision and lower loss.
E2000 patch cords: E2000 connectors use a push-pull mechanism with an automatic metal shutter and laser protection, enabling rapid one-piece mating for optical terminations.
Classification by Construction
By construction, patch cords are ribbon (tape) or bundle types. Ribbon patch cords use ribbon cable consisting of multiple fibers in a flat layout and allow very high fiber density, saving space and cost. Bundle patch cords use round loose-tube or 0.9 mm buffered fibers and are typically used for indoor structured cabling.
Classification by Application Environment
Patch cords can be standard or ruggedized. Standard patch cords are lightweight and low-cost, suitable for most indoor equipment and high-density data center cabling. Ruggedized patch cords are used in harsh outdoor or exposed environments such as underground ducts and base stations; they typically offer protection against pests, water ingress, and high temperatures. Examples include armored cords, IP67 waterproof cords, and FTTA long-reach cords.
Classification by Jacket Material
PVC and LSZH are common jacket materials. PVC-jacketed cords are flexible and easy to install at normal temperatures and are commonly used for indoor horizontal cabling. LSZH (low-smoke, zero-halogen) jackets contain flame-retardant additives and emit minimal toxic smoke when burned, so they are preferred in public or poorly ventilated spaces such as subways and tunnels.
Classification by Fiber Count
By fiber count, patch cords are simplex (single-fiber) or duplex (two-fiber). A simplex cord contains one fiber and one connector, carrying signal in one direction only. A duplex cord has two fibers and two connectors, allowing bidirectional communication.
Classification by Transmission Mode
Patch cords are singlemode or multimode based on optical transmission mode. Singlemode cords support a single propagation mode with low modal dispersion and are used for long-distance, high-bandwidth applications. Multimode cords support multiple modes, have higher modal dispersion that increases with distance, and are therefore better suited for short-distance links.
Classification by Polish Type
Connector end-face polish types include PC, UPC, and APC. PC uses a slightly spherical polish and is typically black. UPC improves end-face finish and is typically blue. APC uses an 8° angled end-face polish and is typically green. These polish types differ in insertion loss and return loss characteristics, with APC commonly used where low back-reflection is required.
Classification by Termination Method
By manufacturing process, patch cords are field-terminated or factory-terminated. Field-terminated cords require onsite termination steps such as buffer stripping, cleaning, polishing, bonding, and testing, which necessitate termination tools and skilled technicians. Factory-terminated cords are preterminated in the factory; before selecting them, confirm connector types and link length. Factory-terminated cords are plug-and-play and simplify installation.
When Is Multimode-to-Singlemode Conversion Needed?
Before discussing conversion methods, it is important to understand the difference between singlemode and multimode fiber. Because they support different propagation modes, their application scopes differ: singlemode for long-distance, high-bandwidth links, multimode for short-distance links. Networks often include both fiber types, and mode conversion between multimode and singlemode sometimes occurs when system distance or equipment types require it.
When a link distance exceeds the maximum for multimode fiber, conversion between multimode and singlemode may be needed. The need for multimode-to-singlemode conversion depends on deployed equipment and connection types. For example, low-cost legacy devices might have multimode ports that need to connect to singlemode equipment, or building-installed multimode equipment may need to interface with a service provider's singlemode network.
Methods for Multimode-to-Singlemode Conversion
There are three common ways to convert multimode fiber to singlemode fiber.
Fiber transceivers
Fiber transceivers can convert multimode to singlemode, duplex to single-fiber, and change wavelengths. For multimode-to-singlemode conversion, transceivers offer a cost-effective way to extend reach up to tens of kilometers. For example, an SFP gigabit Ethernet transceiver can convert multimode fiber (maximum reach around 550 m) to singlemode fiber for gigabit Ethernet (1000 Mbps) with a reach of up to 20 km. In practice, transceivers can link two Ethernet switches over long distances by converting multimode to singlemode.
WDM transponders
WDM transponders can also convert multimode to singlemode. They are commonly used in WDM systems, particularly DWDM, where multimode-to-singlemode or singlemode-to-multimode conversion may be required for long-distance transmission.
Mode-conditioning patch cords
Mode-conditioning patch cords work differently from the previous two methods. They do not change the fiber type to extend reach; instead, they alter the launch conditions so that singlemode lasers can be launched into multimode fiber with reduced differential mode delay (DMD) effects. A mode-conditioning cord displaces the singlemode launch to the multimode core center so the singlemode laser can propagate within the multimode core diameter, mitigating DMD when multiple modes would otherwise be excited. Mode-conditioning cords are typically used with 1000BASE-LX gigabit Ethernet or certain 10G applications such as 10GBASE-LRM and 10GBASE-LX4.
Summary
In addition to the types described above, mode-conditioning patch cords provide a specific way to connect singlemode and multimode links by changing optical launch mode. As networks evolve toward higher rates, density, and performance, MTP/MPO factory-terminated patch cords are widely used in 40G/100G high-density data centers, while LC patch cords remain common for 1G/10G enterprise and data center cabling. Select patch cords based on actual transmission requirements, application environment, construction, and material. If uncertain, consult a qualified professional to avoid unnecessary issues.
