With ease of installation, high bandwidth over long distance and better performance, fiber optic patch cable has been a key component in telecommunication infrastructures. Based on different standards, there are a wide range of patch cables available on the market, such as single-mode and multimode patch cables, simplex and duplex patch cables, LC or SC patch cables, etc. Since different types of patch cables can be used in different applications and environments, it is necessary to know their features and distinctions to help choose the best one for your cabling system. In this passage, I will introduce five groups of patch cables one by one, including single-mode vs. multimode patch cables, simplex vs. duplex patch cables, PVC (riser) vs. plenum-rated patch cables, breakout vs. distribution patch cables, tight-buffer vs. loose-tube patch cables.
According to different size of core diameter, patch cables can be divided into single-mode and multimode fiber optic patch cables. Single-mode fiber (SMF) patch cable has a single glass fiber strand with a diameter of 8.3 to 10 microns which features only one transmission mode. It carries higher bandwidth and supports longer link length than multimode patch cable, but requires a light source with a narrow spectral width.
Multimode fiber (MMF) patch cable has a comparatively larger diameter, typically 50 or 62.5 microns, which both features the same glass cladding diameter of 125 microns. The large core makes it possible for multimode patch cable to gather more light and allow more signals to be transmitted. However, transmission of many light modes down a multimode patch cable simultaneously causes signals to weaken over time, so multimode patch cable is more suitable for short distance. The image below shows the different structures of SMF and MMF.
A simplex fiber cable consists of a single strand of fiber, while duplex patch cable has two strands of glass or plastic fiber, typically found in a “zipcord” construction format. Simplex patch cable is mostly used in where only a single transmitting or receiving line is required between devices or when a multiplex data signal is used (bi-directional communication over a single fiber). Unlike simplex, duplex patch cable is often used for duplex communication between devices where separate transmitting and receiving lines are required. More detailed information about structure of simplex and duplex patch cables is shown in the picture below.
PVC cable (also called riser-rated cable even enough not all PVC cable is riser-rated) has an outer polyvinyl chloride jacket giving off toxic fumes when it burns. This type of patch cable is often used for horizontal and vertical runs, but only if the building features a contained ventilation system. A SC patch cable with PVC jacket is shown in the following picture.
Notes: 1. Plenum can replace riser, but riser cannot be used in plenum spaces. 2. “Riser-rated” means that the jacket contains PVC. The cable carries a CMR (communications riser) rating and is not for use in plenum.
Plenum-rated cable has a special insulation that has low smoke and low characteristics. Plenum-rated cable is mandated to be installed in any “ air handling” space. For example, most large office buildings use the ceiling to return air to the AC unit which requires the ceiling to be plenum and all the cables that go through the ceiling must be plenum-rated.
Breakout cable, also known as fan-out style cable, houses several individual fiber lines, which are individually reinforced with aramid yarn, making it easier to terminate the cable. This cable is bigger and more costly than distribution cable, but it offers a strong design that is good for conduit runs and plenum applications.
Distribution cable is a smaller cable that contains many tightly-buffered fibers bundled under the same jacket. Since each individual fiber line inside the cable is not reinforced with the aramid yarn, distribution cable requires a breakout box or patch panel for safe junction and connection of each fiber. This type of patch cable is popular in networking scenarios and is available both for riser and plenum applications. The following picture shows the difference of breakout and distribution cable.
Tight-buffered cable is a type of patch cable with a protective material extruded directly on the acrylate coating of an optical fiber to further allow individual fibers to be handled easily during installation, while protecting them from physical damage. A tight-buffered cable is suitable for indoor applications where the temperature is controlled and the differences in thermal expansion and contraction are not so great between the buffer and fiber as to cause bending.
Loose-tube cable, in contrast, is specially designed in outside plant applications, where extremes of temperature, rough handling and mechanical disturbances make tight-buffered cable unsuitable. It protects the fiber core, cladding, and coating by enclosing everything within fairly rigid protective sleeves or tubes. Many loose tube cables contain a water resistant gel surrounding the fibers, which helps protect the fibers from moisture, making the cable ideal for high humidity conditions. Loose-tube and tight-buffered cable both with 12 fibers are shows in the below picture.
Fiber patch cable is an indispensable part in data centers and it is essential for us to master the features and applications of different types of patch cables. Besides the cables that have been mentioned above, more types of patch cables are available, such as LC to LC, LC to SC, SC to ST fiber optic patch cable.