What is Fiber Optic Cable Adapters

Optical fiber connectors are the most widely used optical passive components in optical fiber communication systems. Most fiber optic connectors are composed of three parts: two fiber optic connectors and a coupler. Two fiber optic connectors are installed into the two fiber tail ends; the coupler acts as an alignment sleeve. In addition, the optical cable couplers are mostly equipped with metal or non-metal flanges to facilitate the installation and fixation of the connectors. Both ends of the fiber optic cable adapter can be inserted into fiber optic connectors of different interface types to realize the conversion between different interfaces such as FC, SC, ST, LC, MTRJ, MPO, E2000. Optical fiber connectors are widely used in optical fiber distribution frames (ODF), optical fiber communication equipment, instruments, etc. due to their superior performance, stability, and reliability.

 

Optical fiber couplers can be divided into two types: fusion taper type and planar waveguide type. The fusion tapered product is formed by fusion splicing two or more optical fibers on the side. The planar waveguide type is a micro-optical element type product. It uses photolithography technology to form an optical waveguide on a medium or semiconductor substrate to realize the branch distribution function. The two types of light splitting principles are similar. They achieve different branch amounts by changing the evanescent field coupling between the fibers (coupling width, coupling length) and changing the fiber radius. Conversely, combining multiple optical signals into one signal is called a synthesizer. Because of its simple manufacturing method, low price, easy connection with external optical fiber, and resistance to mechanical vibration and temperature changes, the fusion taper fiber coupler has become the mainstream manufacturing technology in the market.

 

Coupling principle

The fiber coupler is a device for detaching and connecting an optical fiber and an optical fiber. It precisely connects the two end faces of the optical fiber, so that the light energy output by the transmitting fiber can be coupled to the receiving optical fiber to the maximum extent and intervene in the optical link, thereby minimizing the impact on the system. For the waveguide fiber coupler, it is generally a Y-branched element, and the optical signal input by an optical fiber can be divided into equal parts. The 2 x 2 single-mode fiber coupler can be regarded as two cones formed close to each other, and its basic structure is shown in Figure 1. Its basic idea is: the fields in the two coupled waveguides each maintain the field distribution and transmission coefficient when the waveguide exists independently. The effect of coupling is manifested in the changes along the way of the complex amplitude of the field.

 

 Figure 1

Structure of fiber optic cable adapter

The main purpose of optical fiber connectors is to realize the continuity of optical fibers. The fiber optic connector adapters are now widely used in optical fiber communication systems. There are many types and different structures. But looking closely, the basic structure of various types of optical cable couplers is the same. Most fiber optic cable ends generally use high-precision components (composed of two pins and a coupling tube in three parts) to achieve optical fiber alignment. In this method, the optical fiber is inserted and fixed in the pin, and the surface of the pin is polished to achieve alignment in the coupling tube. The outer components of the pins are made of metal or non-metal materials. The butt end of the pin must be polished, and the other end usually uses a bend limiting member to support the optical fiber or optical fiber cable to relieve stress. Coupling pipes are generally made of two-half synthetic, fastened cylindrical members made of ceramic, bronze, or other materials, and are often equipped with metal or plastic flanges to facilitate the installation and fixation of the fiber optic cable adapter. In order to align the optical fiber as accurately as possible, the processing precision of the pin and coupling tube is very high.

 

Optical fiber connector performance

The performance of optical cable couplers includes optics, interchangeability, repeatability, tensile strength, temperature, and the number of insertions and removals.

 

(1) Optical performance

The requirements for the optical performance of fiber optic connector adapters are mainly the two most basic parameters of insertion loss and return loss. Insertion Loss (Insertion Loss) is the connection loss, which refers to the loss of the effective optical power of the link caused by the introduction of the connector. The smaller the insertion loss, the better. Generally, it should not be greater than 0.5dB. Return Loss (Reflection Loss) refers to the ability of a connector to suppress the reflection of link optical power, and its typical value should not be less than 25dB. In the actual application of the connector, the pin surface has been specially polished, which can make the return loss greater, generally not less than 45dB.

(2) Interchangeability and repeatability

Optical fiber connectors are general passive components. For the same type of optical fiber connectors, they can generally be used in any combination and can be used repeatedly. The additional loss introduced by this is generally within the range of less than 0.2 dB.

(3) Tensile strength

For finished fiber optic connectors, the tensile strength is generally required to be no less than 90N.

(4) Temperature

Generally, the optical fiber connector must be able to be used normally at a temperature of -40℃ ~ +70℃.

(5) Mating times

The optical fiber connectors currently used can generally be plugged and unplugged more than 1,000 times.

 

Fiber optic cable adapter classification

Fiber optic connector adapters can be divided into common silicon-based optical fiber single-mode and multi-mode connectors according to different transmission media, and other optical fiber connectors such as plastics as the transmission media. According to the structure of the connector, it can be divided into FC, SC, ST, LC, D4, DIN, MU, MT, etc. various forms. Among them, ST optical connectors are usually used for wiring equipment, such as optical fiber distribution frames, optical fiber modules, etc. The SC and MT fiber adapters are usually used for network equipment. According to the shape of the fiber end face, there are FC, PC (including SPC or UPC), and APC. According to the number of fiber cores, there are also single-core and multi-core (such as MT-RJ). The fiber optic cable couplers are widely used and have many varieties. In the actual application process, it is generally distinguished according to the structure of the optical fiber connector. The following are some of the more common fiber optic connectors:

 

FC optical connector

The FC fiber optic adapter was first developed by NTT of Japan. FC is the abbreviation of FERRULE CONNECTOR, indicating that the external reinforcement method is a metal sleeve and the fastening method is a turnbuckle. The earliest FC type fiber connector used the butt end of the ceramic pin. This type of connector has a simple structure, convenient operation, and easy manufacture, but the fiber end is more sensitive to fine dust, and it is prone to Fresnel reflection, which makes it difficult to improve the return loss performance. Later, FC optical connector was improved by adopting a spherical contact pin (PC) with the mating end surface, and the external structure was unchanged, which greatly improved the insertion loss and return loss performance.

Characteristics

● The unique design of the integrated internal structure, simpler structure, easier to use, easy to assemble, and improve efficiency

● Good stable performance, small insertion loss in continuous plug test

● Reflection loss＞55dB

● Temperature range -40 ~ +85℃

● Durability 500yclds. Change ≤0.2dB.

Application

● Management room

● Work area

● Equipment room

● Telecommunications, broadcasting, and television

 

LC fiber adapter

The LC fiber connector is researched and developed by the famous BELL Research Institute. It adopts a standardized jack (RJ) door lock structure, easy to plug and unplug, and small in size, which greatly improves the installation density. LC fiber adapters use precision ceramics or copper sleeves to ensure long-term stable mechanical and optical performance. The size of these pins and sleeves is half the size used by ordinary SC, FC, etc., which is 1.25MM, which can increase the density of optical fiber connectors in optical fiber distribution frames. The LC optical connector adopts a 45-type double hook design, which improves the panel density and is easy to install. At present, in single-mode SFF, LC fiber adapters have actually occupied a dominant position, and their applications in multi-mode have also grown rapidly.

Features

● Good compatibility

● Ceramic catheter

● High precision machining size

● High reliability and stability

● Round, square, diamond

● Insert end face PC/UPC/APC

 

Application

● Telecom network, metropolitan area network, access network

● Test Equipment

● Fiber CATV

● FTTH

 

SC coupler

SC fiber adapter is a kind of optical fiber connector developed by Japan NTT company. Its shell is rectangular, and the structural dimensions of the pins and coupling sleeves used are exactly the same as the FC optical connector. Among them, the end face of the pin mostly adopts the PC or APC type grinding method. The fastening method adopts the plug-in bolt type, without rotation, and the plug-in operation is convenient. The SC coupler uses a precision ceramic or copper sleeve to ensure long-term stable mechanical and optical performance. It can be divided into single/double, assembled with metal shrapnel for easy installation. A variety of colors are available, with or without ear structure, saving installation space. SC fiber optic adapters are divided into ear type and no ear type. This type of connector is cheap, easy to plug and unplug, with small fluctuations in insertion loss, high compressive strength, and high installation density.

Structure drawing of SC fiber optic adapter - Simplex (unit: mm)

Structure drawing of SC fiber optic adapter - Duplex (unit: mm)

 

Features

● Low insertion loss.

● Good repeatability

● Good interchangeability

● Easy to install

● Good temperature stability

 

Application 

● Telecommunication system

● Wired TV internet 

● Local area network, optical area network

● Fiber to the home (FTTH)

● Video transmission

● Test instrument

 

ST adapter

The most representative product among ST fiber optic adapters was developed and researched by Bell Labs in the United States. It is composed of two precision-molded cylindrical plugs with frusto-conical ends and a coupling assembly with a double-cone plastic sleeve inside. The ST adapter is installed on the optical fiber distribution frame to connect pigtails and jumpers. Its interface is round, and the exterior is reinforced with a metal sleeve and fastened with a turnbuckle. ST optical fiber adapters are divided into single-mode, multi-mode, and 10G.

 

DIN47256 optical fiber connector

DIN47256 optical connector is a connector developed by Germany. The structural dimensions of the pin and coupling sleeve used in this connector are the same as the FC type. The end face treatment adopts the PC grinding method. Compared with the FC fiber adapter, its structure is more complicated. The internal metal structure has a spring to control the pressure, which can avoid damage to the end face due to excessive insertion pressure. In addition, the mechanical accuracy of this connector is high, so the insertion loss value is small.

 

MT-RJ optical cable coupler

The MT-RJ optical fiber connector started from the MT connector developed by NTT. It has the same latch mechanism as the RJ-45 LAN electrical connector, and the optical fiber is aligned with the guide pins installed on both sides of the small sleeve to facilitate the connection with the optical transceiver. The connector end face optical fiber is a dual-core (0.75mm spacing) arrangement design, which is a next-generation high-density optical fiber connector mainly used for data transmission.

 

MU fiber optic cable ends

MU (MINIATURE UNIT COUPLING) fiber optic cable connector is the world's smallest single-core optical fiber connector developed by NTT based on the most used SC connector. The connector uses a 1.25MM diameter sleeve and self-retaining mechanism, and its advantage is that it can achieve high-density installation. Using MU's L.25MM diameter sleeve, NTT has developed the MU connector series. They have socket type connectors (MU-A series) for optical cable connection; backplane connectors with self-retaining mechanism (MU-B series) and simplified sockets for connecting LD/PD modules and plugs (MU-SR series). With the rapid development of optical fiber networks in the direction of greater bandwidth and greater capacity and the widespread application of DWDM technology, the demand for MU fiber optic cable ends will also grow rapidly.

 

Note:

SC stands for Standard Connector.

ST stands for Straight Tip.

FC stands for Fiber Connector.

The part in front of "/" indicates the applicable fiber connector model.

The "SC" connector is a standard square connector, using engineering plastics, which has the advantages of high-temperature resistance and not easy to oxidize. The optical interface on the transmission equipment side generally uses an SC connector.

The "LC" connector is similar in shape to the SC connector but smaller than the SC connector.

The "FC" connector is a metal connector, which is generally used on the ODF side. The metal connector can be plugged in more times than plastic.

 

Both ends of the fiber optic cable adapter can be inserted into fiber optic connectors of different interface types to realize the conversion between different interfaces such as FC, SC, ST, LC, MTRJ, MPO, E2000, etc. It is widely used in optical fiber distribution frames (ODF), optical fiber communication equipment, Instruments, etc.