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Fiber-optic patch cord
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A fiber-optic patch cord is a fiber-optic cable capped at each end with connectors that allow it to be rapidly and conveniently connected to telecommunication equipment. This is known as interconnect-style cabling.[1]
General characteristics
[edit]Construction
[edit]A fiber-optic patch cord is constructed from a core with a high refractive index, surrounded by a coating with a low refractive index, that is strengthened by aramid yarns and surrounded by a protective jacket. Transparency of the core permits transmission of optic signals with little loss over great distances. The coating's lower refractive index causes light to be reflected back toward the core, minimizing signal loss. The protective aramid yarns and outer jacket minimize physical damage to the core and coating.
Size
[edit]Ordinary fibers measure 125 μm in diameter (a strand of human hair is about 100 μm). The inner diameter measures 9 μm for single-mode cables, and 50 / 62.5 μm for multi-mode cables.
The development of "reduced bend radius" fiber in the mid-2000s, enabled a trend towards smaller cables. Each unit of diameter reduction in a round cable, produces a disproportionate corresponding reduction in the space the cable occupies.[1]
Classification
[edit]
Patch cords are classified by transmission medium, connector construction, and construction of the connector's inserted core cover.
Transmission medium
[edit]Single-mode fiber is generally yellow, with a blue connector, and a longer transmission distance. Multi-mode fiber is generally orange or grey, with a cream or black connector, and a shorter transmission distance.
Connector construction
[edit]Connector design standards include FC, SC, ST, LC, MTRJ, MPO, MU, SMA, FDDI, E2000, DIN4, and D4. Cables are classified by the connectors on either end of the cable; some of the most common cable configurations include FC–FC, FC–SC, FC–LC, FC–ST, SC–SC, and SC–ST.[clarification needed]
Inserted core cover
[edit]The connector's inserted core cover conforms to APC, UPC, or PC configuration. A UPC inserted core cover is flat and is used in SARFT and early CATV. An APC connector's inserted core cover is oblique (about 30°, ±5°). To reduce the back reflection of a connector, UPC polish is used. Industry standard is a maximum of −40 dB for PC back reflection measurement and −50 dB for UPC back reflection measurement. If even less back reflection is required, an APC might be necessary. An APC connector has an 8º angle cut into the ferrule. These connectors are identifiable by their green color. An APC polished connector has a standard reflectivity maximum of −60 dB. APC fiber ends have low back reflection even when disconnected.
Armored fiber patch cord
[edit]Armored fiber-optic patch cord uses a flexible protective tube, usually stainless steel, inside the outer jacket as the armor to protect the fiber glass inside. It will not get damaged even if stepped on, and they are rodent-resistant.
Bend-insensitive fiber-optic patch cord
[edit]Bend-insensitive fiber patch cord is widely used in fiber to the home (FTTH). Single-mode bend-insensitive fibers include G657A1, G657A2, G657B2, and G657B3.
Mode-conditioning patch cord
[edit]A mode-conditioning patch cord is required where Gigabit 1000 Base-LX routers and switches are installed into existing multimode cable plants. The transceiver modules launch only single-mode 1300 nm signals but the existing network is built with multimode cables.
With a single-mode laser aimed into the center of a multimode fiber, the signal arriving at the far end, having followed various paths in the fiber, is spread out in time, making fast transitions between light and dark impossible to discern, and the problem increases with fiber length. This spreading in time is called differential mode delay (DMD) and limits the fiber length for Gigabit Ethernet sigalling. A mode-conditioning patch cord eliminates these multiple signals by aligning the single-mode launch away from the center of a multimode fiber core. This offset launch creates a transmitted signal that is similar to a typical multimode light-emitting diode (LED) launch.
References
[edit]- ^ a b Chappell, Ryan. "The trend toward micro cabling". Lightwave. Retrieved 20 September 2013.
Fiber-optic patch cord
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Overview
Definition and Purpose
A fiber-optic patch cord is a flexible cable assembly containing one or more optical fibers, terminated with connectors on both ends, designed for short-distance interconnections in fiber-optic networks.[2] These patch cords facilitate connections between active equipment such as switches, routers, and optical transceivers, as well as to patch panels, enabling efficient signal routing within data centers, telecommunications rooms, and local area networks.[5] The primary purpose of a fiber-optic patch cord is to provide quick and reliable transmission of light signals between optical devices, minimizing signal loss through precise end-to-end coupling.[2] By serving as a jumper cable in network infrastructures, it supports interconnect and cross-connect applications, allowing for flexible reconfiguration without permanent splicing.[6] Key benefits include high bandwidth capacity for data-intensive applications, low signal attenuation to maintain integrity over distances, immunity to electromagnetic interference due to the non-conductive optical medium, and compatibility with data rates up to 400 Gbps or higher in contemporary systems.[5][7] At its core, the operational principle relies on total internal reflection, where light propagates through the fiber's core by repeatedly reflecting off the boundary with the surrounding cladding, ensuring confined and efficient transmission.[8] The connectors at each end ensure precise alignment of the fiber cores, optimizing light coupling between devices with minimal insertion loss.[2] Patch cords are available in single-mode or multi-mode fiber variants and common connector types such as LC or SC to match specific network requirements.[5]Historical Development
The development of fiber-optic patch cords is rooted in the broader evolution of optical fiber technology, beginning with foundational research in the mid-20th century. In 1966, Charles K. Kao published a seminal paper demonstrating that optical attenuation in glass fibers could theoretically be reduced to below 20 dB/km, enabling long-distance signal transmission via light; this insight earned him the Nobel Prize in Physics in 2009.[9] Building on Kao's work, Corning Glass Works achieved a practical breakthrough in 1970 by producing the first low-loss optical fiber with attenuation under 20 dB/km at 632.8 nm wavelength, paving the way for commercial fiber-optic communications systems.[9] These advancements shifted focus from metallic cables to optical media, but reliable interconnection methods were needed to deploy fibers in networks. Fiber-optic patch cords emerged in the 1980s alongside the expansion of telecommunications infrastructure, where short, flexible cables with connectors became essential for linking equipment in central offices and early data networks. AT&T developed the ST (Straight Tip) connector in 1985, featuring a 2.5 mm ceramic ferrule and bayonet-style coupling for secure, repeatable connections, which was standardized by 1986 and became a de facto industry standard for multimode applications.[10] Concurrently, NTT in Japan introduced the SC (Subscriber Connector) in 1986, incorporating physical contact (PC) technology with a push-pull mechanism and 2.5 mm ferrule optimized for single-mode fibers, enhancing ease of use and low insertion loss in access networks.[10] These early connectors addressed alignment and signal integrity challenges, enabling patch cords to support the first widespread fiber deployments, such as AT&T's transatlantic TAT-8 cable in 1988.[11] The 1990s and 2000s saw innovations driven by demands for higher density and speed in enterprise and data center environments. Lucent Technologies launched the LC (Lucent Connector) in the late 1990s, halving the ferrule size to 1.25 mm for compact duplex designs, which facilitated denser port configurations in Gigabit Ethernet systems.[12] For parallel optics, NTT's MPO (Multi-fiber Push-On) connector, initially developed in 1986, gained traction in the 2000s through enhanced versions like US Conec's MTP (a high-performance MPO variant introduced in the early 1990s), supporting up to 72 fibers for aggregated bandwidth in 10G Ethernet backbones.[10][13] By the 2010s, patch cords adapted to escalating data rates, with LC and MPO/MTP dominating 40G and 100G Ethernet implementations in data centers, where parallel optics enabled scalable, low-latency interconnects.[14] In the 2020s, the focus shifted to pluggable modules like QSFP-DD (Quad Small Form-factor Pluggable Double Density), standardized by the QSFP-DD MSA in 2019, integrating high-fiber-count MPO patch cords for 400G+ speeds and beyond, meeting hyperscale computing needs.[15]Construction and Components
Materials and Fiber Structure
The core of a fiber-optic patch cord, which serves as the primary conduit for light transmission, is typically constructed from ultra-pure silica glass to achieve low signal attenuation over extended distances, though plastic materials are used in some short-range applications.[16] The cladding, surrounding the core, consists of glass or plastic with a lower refractive index than the core, enabling total internal reflection to confine light rays within the core and prevent leakage.[16] Additional coating and buffer layers, often comprising polymers like acrylate, are applied over the cladding to provide mechanical protection against abrasion, bending, and moisture.[16] In multimode fibers commonly found in patch cords, the refractive index profile of the core influences signal propagation: step-index profiles maintain a constant refractive index across the core for simpler manufacturing, while graded-index profiles feature a parabolic decrease in refractive index from the core center outward, mitigating modal dispersion to support higher data rates.[16] The fiber's light acceptance capability is quantified by the numerical aperture (NA), defined as , where is the core's refractive index and is the cladding's; this parameter determines the maximum angle of incident light that can be guided effectively.[17] The protective jacket encasing the fiber assembly enhances overall durability and compliance with safety standards, with polyvinyl chloride (PVC) being a standard material for its flexibility, oxidation resistance, and basic fire retardancy in indoor settings.[18] Low smoke zero halogen (LSZH) jackets, typically made from thermoplastic compounds, are selected for environments demanding reduced smoke emission and absence of toxic halogens during combustion, such as in plenum spaces.[18] Aramid yarn or similar strength members, such as Kevlar, are incorporated between the buffer and jacket to provide tensile support and protect against mechanical stress.[2] Buffer configurations in patch cords are tailored to operational environments: tight-buffered designs apply a direct polymer layer (e.g., 900 μm diameter) around the coated fiber for compact, flexible indoor use and straightforward connectorization.[19]Connector Design and Assembly
Fiber-optic connectors are engineered to provide precise alignment and low-loss mating between fibers, typically comprising a ferrule, body or housing, spring mechanism, and boot for strain relief. The ferrule, often made of zirconia ceramic for durability and precision, holds the fiber end and is available in standard diameters of 2.5 mm (e.g., for SC or ST types) or 1.25 mm (e.g., for LC types) to accommodate different connector sizes while ensuring core alignment.[20] The body or housing, usually constructed from plastic or metal, encases the ferrule and facilitates attachment to the cable jacket and strength members, while the spring applies consistent contact pressure (typically 1-2 N) to maintain physical contact between mated ferrules during connections.[21] The boot, a flexible rubber or plastic component, protects the fiber entry point and provides strain relief to prevent bending-induced damage at the cable-connector interface.[22] Assembly of connectors to fiber-optic patch cords involves several precise steps to achieve reliable terminations, including stripping, cleaving, attachment via epoxy or mechanical methods, and polishing. The process begins with stripping the fiber cable using specialized tools to remove outer jackets, buffers, and coatings (e.g., 900 µm secondary and 250 µm primary buffers) without damaging the glass, followed by thorough cleaning to eliminate contaminants.[23] Next, the fiber is cleaved to create a flat end-face with an angle deviation of less than 0.5° from perpendicular using a precision scribe or laser cleaver, ensuring optimal preparation for attachment to the ferrule.[23] For epoxy-based termination, adhesive is injected into the ferrule bore, the fiber is inserted and cured (e.g., via heat at 100-150°C for 5-10 minutes), and excess fiber is removed before polishing; alternatively, mechanical crimp or fusion splicing methods secure the fiber without epoxy, though fusion is more common for pre-polished pigtails where the connector arrives factory-terminated and field-spliced via fusion to the patch cord.[23] Pre-polished connectors, which use factory-polished ferrules joined by mechanical splice, simplify field assembly but are 5-15 times more expensive than epoxy methods.[23] Polishing refines the ferrule end-face to minimize insertion loss and back reflection, with common types including ultra-physical contact (UPC) and angled physical contact (APC). UPC polishing creates a slightly convex, flat end-face (radius of curvature 10-25 mm) for improved physical contact and return loss of about -50 dB, suitable for most data and telephony applications.[24] APC polishing tilts the end-face at an 8° angle, directing reflections away from the fiber core to achieve return loss exceeding -60 dB, which is essential for analog video, CATV, and high-bitrate systems sensitive to backscatter.[24] The polishing process typically involves multi-stage abrasion with diamond films (e.g., 12 µm coarse, 3 µm medium, and 0.3-1 µm fine grits) on a compliant pad to achieve a smooth, defect-free surface, followed by inspection via microscope for scratches or contaminants.[23] To ensure low optical loss, connector design emphasizes alignment precision, targeting core offset below 0.5 µm through ferrule concentricity tolerances (e.g., ≤0.3 µm for low-loss grades) and active core alignment during manufacturing.[25] This precision minimizes lateral misalignment between mated fibers, achieving typical insertion loss under 0.3 dB per connector pair, with premium grades reaching means of 0.07-0.15 dB as per IEC 61753-1 standards.[25] Such specifications are critical for maintaining signal integrity in high-density networks, where even minor offsets can increase loss beyond acceptable thresholds.[25]Physical Specifications
Dimensions and Lengths
Fiber-optic patch cords are available in standard lengths ranging from 0.5 m to 5 m, which are commonly used for interconnections within patch panels and similar short-distance applications in data centers and telecommunications setups.[26][27] Longer standard options extend up to 10 m, suitable for intra-rack connections where minimal signal degradation is required.[26][28] Custom lengths beyond these standards can be manufactured, often up to 20 m or more, though practical limits are imposed by optical attenuation to maintain signal integrity; for single-mode fibers, attenuation is typically less than 0.4 dB/km at 1310 nm, allowing for extended use in controlled environments without exceeding loss budgets.[29][30][31] The outer diameter of patch cord cables varies by configuration to balance flexibility, durability, and space efficiency. Simplex cords, carrying a single fiber, typically feature a jacket diameter of 2 mm to 3 mm.[26][32] Duplex cords, which pair two fibers in a zipcord design, have an overall diameter of 3 mm to 4 mm, providing compactness for bidirectional applications.[27][33] Within these jackets, the fiber is protected by a 900 μm tight buffer layer, which offers mechanical stability while allowing direct connector termination without additional fanout kits.[34][35] Patch cords are produced in several form factors to accommodate diverse connectivity needs. The simplex form factor supports single-fiber transmission, ideal for unidirectional links.[26] Duplex configurations pair two fibers side-by-side, enabling full-duplex communication in a single cable assembly.[36] Fan-out or breakout designs transition from a multi-fiber connector, such as MPO, to individual simplex or duplex ends, facilitating transitions between high-density backplanes and standard ports.[37] Ribbon configurations, often using MPO connectors, bundle 12 to 72 parallel fibers in a flat array, optimizing for high-throughput applications like 40G/100G Ethernet in data centers.[38][39] To prevent macrobending losses that can degrade signal quality, patch cords must adhere to minimum bend radius specifications, typically 10 to 15 times the cable diameter depending on whether the bend is static (post-installation) or dynamic (during handling).[40][33] For a standard 2 mm diameter simplex cord, this equates to a loaded bend radius of about 20 mm and an unloaded radius of 30 mm, ensuring reliable performance in routed installations.[41][42]Protective Features
Fiber-optic patch cords incorporate various protective features to safeguard the cable against mechanical, environmental, and fire-related hazards, ensuring reliable performance in diverse installation environments. The outer jacket serves as the primary barrier, with materials selected based on fire safety standards. OFNR-rated jackets, typically made from PVC, are designed for vertical riser applications between floors, providing resistance to flame propagation while maintaining flexibility.[18] OFNP-rated jackets, often using fluorinated polymers, offer the highest level of fire resistance and low smoke emission, making them suitable for plenum spaces in air-handling areas to minimize fire spread risks.[43] For multi-fiber configurations, furcation kits provide essential breakout protection by encasing individual fibers in protective tubing, preventing damage during handling and termination. These kits typically include color-coded furcation tubing (e.g., 900 μm or 2 mm diameter) and strength members that secure the breakout section, reducing stress on the fiber subunits and facilitating organized routing in high-density setups.[44] Strain relief mechanisms at the connector ends further enhance durability by mitigating bending and pulling forces. Connector boots, usually made of flexible PVC or silicone, extend over the cable jacket to maintain a minimum bend radius and absorb mechanical stress, preventing kinking that could lead to signal attenuation. Furcation tubing in breakout areas complements this by distributing tension evenly. Many designs are pull-proof, capable of withstanding up to 100 N of tensile force without compromising the fiber integrity, as per industry standards for installation handling.[45][46] Environmental protections address exposure to dust, moisture, and sunlight, particularly in industrial or outdoor deployments. Industrial patch cords often feature IP-rated connectors, such as IP67 or IP68, which seal against dust ingress and withstand temporary immersion in water up to 1.5 meters for 30-60 minutes, ensuring operation in harsh conditions like manufacturing floors or outdoor enclosures. UV-resistant jackets, commonly using polyethylene (PE) materials, protect against degradation from solar exposure, extending cable lifespan in direct sunlight applications.[47][48][49] Internal strength members, such as aramid yarn (commonly Kevlar), reinforce the cable core by providing high tensile strength up to 200 N, absorbing pulling forces to shield the delicate optical fiber from breakage during routing or accidental tugs. This yarn is embedded around the buffered fiber, offering a lightweight yet robust buffer against mechanical abuse without adding significant bulk.[50][51]Classification by Fiber Medium
Single-Mode Fibers
Single-mode fiber patch cords utilize optical fibers with a small core diameter, typically ranging from 8 to 10 μm, surrounded by a standard 125 μm cladding diameter, which confines light propagation to a single mode for high-fidelity signal transmission.[52] These cords are optimized for operation at key wavelengths of 1310 nm and 1550 nm, where the fiber exhibits low attenuation coefficients, generally less than 0.4 dB/km at 1310 nm and 0.3 dB/km at 1550 nm, enabling minimal signal loss over extended distances.[53] The precise core-cladding geometry ensures efficient light guidance while maintaining compatibility with international standards such as ITU-T G.652 for conventional single-mode fibers and G.657 for variants with enhanced bend performance. The fundamental mode structure of single-mode fibers supports only one propagation mode, designated as the LP01 mode, resulting in zero modal dispersion and allowing pulse broadening to be dominated solely by chromatic effects, which are manageable through dispersion-shifted designs.[54] This characteristic makes single-mode patch cords ideal for long-haul applications, supporting transmission distances exceeding 10 km without optical amplification, and up to 100 km in optimized systems, due to their high bandwidth potential and low loss profile.[55] In contrast to multi-mode fibers, single-mode variants prioritize precision over broader light acceptance, necessitating tight connector alignment for optimal coupling efficiency.[52] In telecommunications, single-mode fiber patch cords conforming to OS1 and OS2 standards—where OS1 aligns with ITU-T G.652 for indoor use with maximum attenuation of 1.0 dB/km, and OS2 provides low-water-peak performance per G.652D/G.657 for outdoor and extended-reach scenarios with ≤0.4 dB/km attenuation—are essential for backbone networks and wide-area networks (WANs).[52] These cords facilitate high-speed data routing in carrier-grade infrastructures, supporting protocols from 10 GbE to 100 GbE over vast spans.[56] Their compatibility with wavelength division multiplexing (WDM), particularly dense WDM (DWDM), allows multiplexing of numerous channels on a single fiber pair, achieving aggregate capacities in the terabit-per-second range, as demonstrated in systems with 192 channels at 100 Gbps each yielding 19.2 Tb/s.[57]Multi-Mode Fibers
Multi-mode fibers in fiber-optic patch cords feature a larger core diameter that allows multiple light paths, or modes, to propagate simultaneously, making them suitable for short-distance, high-bandwidth applications such as local area networks (LANs).[58] The core is typically 50 μm or 62.5 μm in diameter, with a standard 125 μm cladding diameter, enabling easier light injection from cost-effective sources like vertical-cavity surface-emitting lasers (VCSELs).[59] These fibers are categorized into grades OM1 through OM5 under the ISO/IEC 11801 standard, each defined by modal bandwidth specifications that determine their support for data rates and distances.[60] OM1, with a 62.5 μm core, offers an overfilled launch (OFL) bandwidth of 200 MHz·km at 850 nm, while OM2 (50 μm core) provides 500 MHz·km at 850 nm.[59] Higher grades like OM3 and OM4, both with 50 μm cores, achieve effective modal bandwidths of 2000 MHz·km and 4700 MHz·km at 850 nm, respectively, optimized for laser sources.[60] OM5 extends this to 4700 MHz·km at 850 nm, specifically supporting short-wavelength division multiplexing (SWDM) for enhanced capacity over multimode infrastructure.[58] The multiple propagation modes in these fibers lead to modal dispersion, where light signals traveling different paths arrive at slightly varying times, which limits transmission distances compared to single-mode fibers.[61] For example, at 10 Gbps using 850 nm VCSEL sources, OM1 supports less than 33 m, OM2 up to 82 m, OM3 up to 300 m, and OM4 up to 550 m, with OM5 offering similar reaches but improved multi-wavelength performance.[59] These limitations arise primarily from differential mode delay, though chromatic dispersion at 1300 nm wavelengths is also a factor in legacy systems.[60]| Fiber Grade | Core Diameter (μm) | OFL Bandwidth (MHz·km) at 850/1300 nm | EMB at 850 nm (MHz·km) | Max Distance at 10 Gbps (m) |
|---|---|---|---|---|
| OM1 | 62.5 | 200 / 500 | N/A | 33 |
| OM2 | 50 | 500 / 500 | N/A | 82 |
| OM3 | 50 | 1500 / 500 | 2000 | 300 |
| OM4 | 50 | 3500 / 500 | 4700 | 550 |
| OM5 | 50 | 3500 / 500 | 4700 (SWDM optimized) | 550 (SWDM) |