The use of optical fiber connectors is closely related to optical fiber systems under normal circumstances. When connectors are not widely used and are not easy to use, connector manufacturers standardize and simplify connectors to a large extent. In the process of using optical fiber system, it is more convenient for users to use connectors.

—— 1 ——

What is an optical fiber connector?

Optical fiber connector is a movable mechanism between optical fiber and optical fiber connecting device. Its function is to place the optical fiber on two precise platforms, so that the optical output of the optical energy can reach the optical fiber coupler of the receiving optical fiber to the greatest extent, to form an optical link, and to minimize the impact of the system. This is the basic requirement of optical fiber connectors. To a certain extent, optical fiber connectors also have an impact on the reliability of optical fiber transmission and system performance.

—— 2 ——

Key features of optical fiber connectors

The key characteristics of optical fiber connectors include optical properties, interchangeability, reproducibility, tensile strength, temperature, insrtion times, etc.

1. Optical properties: The optical performance requirements of optical fiber connectors are mainly two basic parameters, insrtion loss and return loss. The insrtion loss is the loss of the effective light intensity of the connection, which is due to the insrtion of the connector. The smaller the insrtion loss, the better. Normally, the insrtion loss should not be about 0.5dB. Echo loss (or reflection loss) refers to the suppression of the light intensity of the reflector in the link. Typical values should not be less than 25dB. In the practical application of connectors, the needle surface after special polishing can make the echo loss greater, usually no less than 45dB.

2. Interchangeability and reproducibility: Fiber optic connectors are general passive devices. The same type of fiber optic connectors can be used in any connection and can be used repeatedly. Therefore, in general, the additional entry loss is less than 0.2dB.

3. Tensile strength: For the connected optical fiber connectors, the tensile strength is not less than 90N in general.

4. Temperature: Usually, optical fiber connectors must be used in the temperature range of - 40 C to + 70 C.

5. Plug-in times: Usually, the current optical fiber connector can be plugged in more than 1,000 times.

—— 3 ——

Structure of Optical Fiber Connecto

Connections, permanent connections, or connectors can form optical fiber to optical fiber connections, which are different from plugging in, and can be disconnected and reconnected. With the development of application field, the types of optical fiber connectors are various. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connectors contain four basic components.

   Plug-in pin: The optical fiber is installed in a long thin-walled cylinder, and the pin acts as the alignment mechanism of the optical fiber. The diameter of the pin is slightly larger than that of the optical fiber cladding. The end of the optical fiber is at the end of the pin. Generally, pins are made of metal or pottery, but they may also be plastic.

   Connector body: Also known as connector housing, connector body accommodates pins. Usually the connector body is made of metal or plastic, including one or more assembly parts, which can keep the optical fibers in proper position. Specific details of these connector assemblies vary depending on the type of connector, but welding and/or flanging are usually used to install reinforcement components and cable sheaths on the connector body. The pin extends and passes over the connector body and is clamped in o the bonding device.

   Optical cable: The optical cable is mounted on the connector body. Its function is the input point of optical fiber. In general, a strain relief shield is installed on the joint between the cable and the connector body to provide additional strength for the joint.

   Connector: Most optical fiber connectors do not use the common head-to-head structure used in electronic connections. The structure adopted is a positioning sleeve for pairing connectors. Similar devices can be installed on optical transmitters and receivers, and these devices can be fitted with a connector. These devices are also known as through-type stuffy adapters.

—— 4 ——

Types of Optical Fiber Connectors

According to different classification methods, optical fiber connectors can be divided in o different types. According to different transmission media, optical fiber connectors can be divided in o single-mode and multi-mode optical fiber connectors. According to different structures, optical fiber connectors can be divided in o various types, such as ST, SC, FC, LC, MT-RJ, MPO/MTP, MU, DIN, E2000, SMA, BICONIC, D4, etc. According to the different surface of pin end of connector, it can be divided in o PC, UPC and APC. According to the number of fiber cores, fiber connectors can be divided in o single fiber core and multi-fiber core fiber connectors. Overall, about 100 types of fiber optic connectors have been put on the market, but only a few have a larger share of the market. This is the leading list of connectors in the industry.

ST connectors: ST connectors are about the most popular connectors in multimode networks and are widely used in optical fiber wiring frames (ODFs), such as in most buildings and campuses. In this type of fiber optic connector, there is a clamp mounting base and a long cylindrical 2.5mm ceramic (usually) or polymer pin to accommodate the fiber. Most pins are ceramic, but some models are made of metal or plastic. ST connector with metal shell and nickel plated, can easily and quickly insrt or pull out the optical cable. These connectors have ceramic pins and can perform 500 pairing cycles. In the long run, it is recommended to use a ST connector with a loss margin of 0.5dB or recommended by the vendor.

SC connector: This is an optical fiber connector developed by NTT Company in Japan. SC connector is a kind of plug-in connector with 2.5mm pin. Because of its excellent performance, it is widely used in various fields. The outer shell of the connector is rectangular and adopts a needle-shaped structure and a connecting sleeve. More PC or APC grinding methods are used on the surface of the end of the needle, while the fastening method uses the insrting needle bolt connection method, which does not need to be rotated when insrting. A simple push-pull action can lock the SC connector. Under the positioning of ceramic pins, SC connectors can be positioned accurately. A typical SC connector for matching can achieve 1000 pairing cycles. SC connectors are characterized by low price, low fluctuation loss, high compressive strength and high installation density

FC connector: FC connector was originally developed by NTT in Japan. The pin connector of FC connector is short. The 2.5mm pin is also used on the connector. The surface of the connector is strengthened by metal sleeve and the fastening method is screw joint. FC connector can locate optical fiber cable transmitted by light source transmitter and receiver optical detector very accurately. FC connector features a positioning notch and a threaded socket for positioning. FC connectors are constructed with nickel-plated metal housing. The connector has ceramic pins and can achieve 500 pairing cycles. This type of connector has simple structure and easy operation.

LC connector: LC connector is developed by the famous Bell Research Laboratory. It is easy to use and operates modular jack (RJ) latch mechanism. The size of pin and sleeve is half of that of conventional SC and FC, which is 1.25mm. The connector can improve the density of the optical fiber connector on the optical fiber distribution frame. In addition, standard ceramic pin connectors can be used on the connector, and any adhesive can be used to bond the connector. LC connectors are characterized by excellent performance and are highly suitable for single-mode optical fibers.

MT-RJ connector: MT-RJ connector is a dual connector, using single-mode and multi-mode fiber optic cables. A pin is used as a positioning device in this type of connector, and the model has a male head and a female head. The MT-RJ connector has a plastic shell and uses metal positioning pins and plastic pins to achieve accurate positioning. MT-RJ connector can achieve 1000 pairing cycles. The typical insrtion loss of MT-RJ connectors in matching is 0.25dB for SMF and 0.35dB for MMF.

MPO/MTP Connector: MPO Connector is the acronym of "multi-fiber propulsion". It has push-in insrtion separation mechanism on the connector. It can provide compatible and repeatable connections with 4, 8, 12 or 24 optical fiber models. MTP? It is the trademark of US Conec for MPO connectors. MTP/MPO is a connector specially designed for multi-fiber ribbon cables. The MTP/MPO single-mode connector has an angle pin that allows for a very small back reflection. The pins of multimode connectors are usually flat. The ribbon cable is flat, so it is reasonable to call it flat ribbon structure. In the ribbon cable, the optical fibers are side by side in a sheath.

MU connector: MU connector looks like a miniature SC connector with a 1.25mm pin, simple push-pull design and compact micro structure. This type of connector is used for compact multimode optical connectors and self-retaining mechanisms in backplane applications. The connector has a plastic housing.

DIN Connector: DIN is the abbreviation of Deutsches Institut fur Normung or the German Institute of Standardization, which is the German Manufacturing Standards Agency. The DIN connector includes several types of optical cables, which insrt the plug in o a port connection device. This is a circular structure with pins arranged in a circular pattern. Normally, full-size DIN connectors have three to 14 pins, with a diameter of 13.2 mm. This type of connector is widely used in PC keyboards, MIDI instruments and other special equipment.

E2000 connector: E2000 optical fiber connector is a push-pull connection mechanism with automatic metal gate and laser beam protection device. One-piece design can realize simple and fast terminal connection, which can be used in applications with high security requirements and high power. E2000 connector has single-mode PC, APC and multi-mode PC models. E2000 connector is one of the few optical fiber connectors with compression spring gate, which can protect the pin from dust erosion and abrasion. When the connector is disconnected, the gate automatically closes, which can block the external impurities from entering the socket. These impurities may cause network failure, and the closed gate can block the laser beam which may cause damage.

—— 5 ——

Outdated connectors

SMA Connector: Amphenol developed SMA Connector, also known as SMA Microwave Connector, on the basis of "Miniature A". The 905 has a machined pin with a diameter of 1/8 inch that matches the machined adapter. When the accuracy of the adapter is not enough to match the cable, a pin under the neck matches a Delrin adapter, which can achieve better insrtion loss performance. Machines have been used in military and industrial systems in recent years

BICONIC Connector: This is the BICONIC connector. The yellow appearance indicates that this is the SM version (MMs are usually black). This type of connector was developed by Jack Cook in Bell Laboratory, Murray Hill, NJ. BICONIC is made of glass-filled plastic moulds and is as hard as ceramics. The optical fiber is directly embedded in the insrtion pin in the die. This mode of production persisted until the company was able to insrt 125 micron/5 mil needles in o plastic moulds, at which point it was able to insrt optical fibers in o the needles with epoxy resin. When the block model number first appears, the pin is grounded and the fiber core is positioned at the center of the pin to reduce the loss. Because there is no keyway on the connector, it can rotate on the matching adapter. There is a gap between the pins when matching, so the average loss caused by the reflection of the pins will never be higher than 0.3dB. Usually, the loss of MM Biconics is 0.5-1 dB and SM is 0.7 dB or higher.

D4 connector: D4 connector is about the first connector to use ceramic or ceramic stainless steel pins. The connector has a button and a compressed spring, and the diameter of the pin is 2.0 mm. The D4 connector has a high-performance threaded connection system and a button connector body to achieve reproducibility and mutual matching.

—— 6 ——

色码

n the early days of optical fibers, orange, black or grey were multimode, and yellow was single mode. But after using metal connectors, such as FC and ST, it is very difficult to code with color, so it is normal to use protective shield with color. In TIA 568 color codes for connector bodies and/or shields, beige is multimode fiber, blue is single mode fiber, and green is APC (with angle) connector.