What is fiber optic patch cord?

Fiber optic cables are unfamiliar to many people, and when asked questions such as "What is a fiber optic cable? What are its types and differences? How to choose a fiber optic cable?" they often don't know how to answer. Below, I will comprehensively introduce optical fibers to everyone.

1. What is fiber optic cable?

The fiber optic cable is mainly used as a patch cable from the equipment to the fiber optic cabling system, with a thick protective layer, generally used for the connection between the optical terminal and the terminal box. Fiber patch cords are widely used in fiber optic communication systems, fiber access networks, fiber optic equipment transmission, and local area networks.

With the rapid development of fiber optic communication and the expansion of various equipment needs, more types of fiber patch cords have been developed and used.

2  The classification of the fiber optic cable

2.1 Fiber optic cable classification according to the types of fiber optic connectors, fiber patch cords can be classified as MPO/MTP/LC/SC/FC/ST/MTRJ/MU/E2000/DIN fiber patch cords. Although these different types of fiber patch cords have similar components (consisting of connectors and optical cables) and the same functions, their characteristics and performances differ, resulting in differences in application scenarios.

LC Fiber Patch Cords

LC fiber patch cord is one of the most commonly used fiber patch cords in optical networks. It adopts the LC connector with a ferrule diameter of 1.25mm, which is small in size and very suitable for high-density wiring. Therefore, it is widely used in computer rooms and data centers. According to the different interface modes, it can be divided into LC simplex fiber patch cord and LC duplex fiber patch cord.

SC Fiber Patch Cable

SC fiber patch cable adopts the SC connector with a ferrule diameter of 2.5mm, which is twice the size of the LC connector and is also called a duplex connector (duplex fiber patch cable). This fiber patch cable uses a push-pull structure, which is plug-and-play, and has excellent performance. It is very suitable for telecommunications and data network systems, including point-to-point passive optical networks.

MPO/MTP Fiber Patch Cable

MPO/MTP fiber patch cable is one of the common fiber patch cables in high-speed data communication systems, such as 40G/100G direct connection and interconnection. MPO/MTP fiber patch cable is a type of fiber patch cable that uses multi-core fiber optic connectors and can accommodate 6~144 fibers, which is currently the largest capacity fiber patch cable. MPO/MTP fiber patch cable is composed of fiber optic cables, protective sleeves, coupling components, metal rings, pins, dust caps, etc. Due to the different arrangement positions of fiber cores and pins, it is divided into polarity A/B/C male/female fiber patch cables, and different types are suitable for different applications. Therefore, it is necessary to choose the appropriate MPO/MTP fiber patch cable according to the actual link situation.

FC Optical Fiber

FC optical fiber is the first fiber cable to use a ceramic plug connector. Unlike LC and SC fiber cables, it uses a circular spiral connector made of nickel or stainless steel, which needs to be fixed to the adapter or socket with a threaded clip. Although the installation of an FC fiber cable is more complicated, it is still commonly used for connecting optical time domain reflectometers. Initially, the FC fiber cable was also used in telecommunications and data network systems, but it gradually exited the market with the introduction of LC and SC fiber cables.

ST Fiber Optical Fiber

ST Fiber Optical Fiber is a fiber cable developed and manufactured by AT&T after the FC fiber cable. ST fiber cable uses a bayonet-style connector with a spring-loaded ceramic ferrule (with a diameter of 2.5mm), and the insertion loss is about 0.25 dB. It can be used for long-distance and short-distance applications, such as campus networks, enterprise networks, and military applications. However, in recent years, the market share of ST fiber cables and FC fiber cable is gradually decreasing.

2.2 The above-mentioned fiber optic patch cords are the five most common types of fiber optic patch cords at present, and their connectors and popularity are different. The following will introduce four types of fiber optic patch cords that are less commonly used in today's optical networks.

MTRJ Fiber Optic Patch Cord - The connector of the MTRJ fiber optic patch cord is made of precision plastic and is divided into male and female connectors due to different pins.

MU Fiber Optic Patch Cord - The MU fiber optic patch cord is similar to the SC fiber optic patch cord, using a 1.25mm diameter sleeve and self-retaining mechanism connector. It has a compact structure suitable for high-density installation and can be used in DWDM networks.

DIN Fiber Optic Patch Cord - Although the size of the DIN fiber optic patch cord's plug and coupling sleeve structure is the same as that of the FC fiber optic patch cord, its connector's internal metal structure has a spring with controlled pressure, making it more complex and with higher mechanical accuracy, resulting in smaller losses.

E2000 Fiber Optic Patch Cord - The E2000 fiber optic patch cord uses a push-pull connection mechanism with an automatic metal gate and laser beam protection device on the connector. The one-piece design can quickly achieve terminal connection.

2.3 Classification of fiber optic patch cords according to the working mode of fiber optic connectors

According to the different working modes of fiber optic connectors, fiber optic patch cords can be divided into simplex fiber optic patch cords and duplex fiber optic patch cords. Simplex fiber optic patch cords mean that the signal can only be transmitted in one direction. For example, the signal can be transmitted from A to B through a simplex fiber optic patch cord but cannot be transmitted back from B to A. In contrast, duplex fiber optic patch cords can achieve signal transmission in both directions. Simplex fiber optic patch cords usually consist of one fiber and one connector, while duplex fiber optic patch cords require two fibers and two connectors, as shown in the figure below.

2.4 Classification of fiber optic patch cords according to the polishing type of fiber optic connectors

According to the different polishing types of fiber optic connectors, fiber optic patch cords are divided into three types: PC, UPC, and APC. PC fiber optic patch cords use connectors that are polished with a microspherical surface and are black in color. APC fiber optic patch cords use connectors that are polished with an 8° inclined surface and are green in color. UPC fiber optic patch cords optimize the end-face polishing and surface finish of PC fiber optic patch cords and are blue in color. The three types of polished fiber optic patch cords differ in structure and performance, mainly reflected in insertion loss and return loss. Among them, APC is currently the most popular polishing type.

2.5 Classification of fiber optic patch cords according to the optical transmission mode

According to the different optical transmission modes, fiber optic patch cords are divided into single-mode fiber optic patch cords and multimode fiber optic patch cords. Single-mode fiber optic patch cords can only transmit one mode of light, have small intermodal dispersion, and are suitable for long-distance communication. In contrast, multimode fiber optic patch cords can transmit multiple modes of light at once and have large intermodal dispersion and the intermodal dispersion increases with the transmission distance. Therefore, they are more suitable for short-distance transmission.

2.6 According to the production and processing technology, fiber optic patch cords can be divided into different types. Fiber optic patch cords that are field-terminated with connectors and those that are factory-terminated with connectors. Field-terminated connectors involve stripping the buffer layer, cleaning, polishing, splicing, and testing and require a lot of termination tools and skilled network administrators. Factory-terminated connectors (i.e. pre-terminated fiber optic patch cords) refer to fiber optic connectors and fibers that have already been terminated during production and processing. Before choosing this type of fiber optic patch cord, it is necessary to understand the interface types of the two ends of the equipment and measure the length of the link in advance. Due to their convenient and quick installation (plug and play), and low requirements for users, they are popular among users.

Summary: With the development of networks towards high speed, high density, and high performance, MTP/MPO pre-terminated fiber optic patch cords are popular in 40G/100G high-density data centers, while LC fiber optic patch cords are mainly used in 1G/10G enterprise networks, data center cabling, etc. Fiber optic patch cords with different working modes, transmission modes, and polishing methods, should be selected according to actual transmission conditions.

3. The difference between single-mode and multi-mode optical fibers?

3.1 Appearance: The sheath of a single-mode fiber patch cord is generally yellow, while a multi-mode patch cord is usually orange or a so-called aqua color. The core diameter of a multi-mode patch cord is generally slightly thicker.

3.2 Transmission distance: The transmission distance of single-mode fiber is not less than 5km and is generally used for long-distance communication. The transmission distance of multi-mode fiber can only reach about 2km and is suitable for short-distance communication within buildings or campuses.

3.3 Light source: Because the LED light source is more dispersed and can generate multiple modes of light, it is mostly used for multi-mode fiber; while the laser light source is close to a single mode, it is usually used for single-mode fiber.

3.4 Bandwidth: The bandwidth of single-mode fiber is higher than that of multi-mode fiber.

3.5 Cost: Multi-mode fiber allows for multiple light modes, so it is more expensive than single-mode fiber. However, the solid-state laser diode used as the light source for single-mode fiber is much more expensive than the light source equipment for multi-mode fiber, so the cost of using single-mode fiber is much higher than that of multi-mode fiber.

4. How to choose optical fibers?

4.1 Connector type: If the ports of the two end devices are the same, LC-LC/SC-SC patch cords can be used. If you need to connect devices with different port types, LC-SC/LC-ST/LC-FC patch cords may be suitable.

4.2 Single-mode or multi-mode: Single-mode fiber patch cords use 9/125um fiber, while multi-mode fiber patch cords use 50/125um or 62.5/125um fiber. Single-mode fiber patch cords are mainly used for long-distance data transmission. Multi-mode fiber patch cords are mainly used for short-distance transmission.

4.3 Patch cord length: Choose an appropriate length based on the distance between the devices to be connected.

4.4 Patch cord material: Fiber patch cables can be classified into ordinary, flame-retardant, low-smoke, and low-smoke flame-retardant types based on the outer sheath material. In areas where fire hazards are present or cables and fiber optic cables are installed in building vertical shafts, flame-retardant cables, and fiber optic cables should be used. In large public places, flame-retardant, low-smoke, and low-toxicity cables or fiber optic cables should be used. Flame-retardant wiring equipment should be used in adjacent equipment rooms or junction rooms.

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