What is a Fiber Optic Connector?

Catalog

Ⅰ Introduction

A fiber optic connector is a detachable (movable) device between optical fibers. It precisely connects the two end faces of the optical fiber so that the optical energy output by the transmitting fiber can be coupled to the receiving fiber to the maximum extent. And it minimizes the impact on the system due to its involvement in the optical link. This is the basic requirement of fiber optic connectors. To a certain extent, fiber optic connectors affect the reliability and performance of optical transmission systems.

Ⅱ Key features of fiber optic connectors

The performance of the fiber optic connector is first of all the optical performance. Also, the interchangeability, repeatability, tensile strength, temperature, and the number of insertions and removals of the fiber optic connector must be considered.

fiber optic connector

1 Optical performance

The requirements for the optical performance of fiber optic connectors are mainly the two most basic parameters: insertion loss and return 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. The general requirement should be no more than 0.5dB. Return loss refers to the connector's ability to suppress link optical power reflection, and its typical value should not be less than 25dB. In actual connectors, the pin surface has been specially polished to make the return loss larger, generally not less than 45dB.

2 Interchangeability and repeatability

Fiber optic connectors are universal passive devices. For the same type of fiber optic connectors, they can generally be used in any combination and can be used repeatedly many times. The additional losses introduced are generally within the range of less than 0.2dB.

3 Tensile strength

For a good fiber optic connector, it is generally required that its tensile strength should not be less than 90N.

4 Temperature

As a general requirement, fiber optic connectors must be able to be used normally at temperatures from -40oC to +70oC.

5 Number of plugging and unplugging

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

Ⅲ Structure of fiber optic connectors

The main purpose of fiber optic connectors is to realize the splicing of optical fiber. Fiber optic connectors that have been widely used in fiber optic communication systems have many types and different structures. However, in detail, the basic structure of various types of fiber optic connectors is the same, that is, most fiber optic connectors generally use high-precision components (composed of two pins and a coupling tube for a total of three parts) to realize optical fiber alignment connection.

Fiber optic connector docking principle

In this method, the optical fiber is penetrated 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 pin are made of metal or non-metal materials. The butt end of the pin must be ground, and the other end usually uses a bending restricting member to support the optical fiber to release the stress. The coupling tube is generally made of two semi-synthetic, fastened cylindrical members made of ceramic, bronze or other materials, and is usually equipped with metal or plastic flanges to facilitate the installation and fixation of the connector. To align the optical fiber as accurately as possible, the processing accuracy of the pin and the coupling tube is very high.

With the development of application fields, the types of fiber optic connectors are diverse. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connectors contain four basic components.

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

Connector body: Also known as the connector housing, the connector body accommodates the pins. Normally the connector body is made of metal or plastic, including one or more assembly parts, which can hold the fiber in place. The specific details of these connector body assemblies vary depending on the type of connector, but welding and/or flanging are usually used to install the reinforcing member and the cable sheath on the connector body. The pin extends over the connector body and snaps into the coupling device.

Optical cable: The optical cable is installed on the connector body which is the input point of the fiber. In general, a strain relief protective cover is installed on the joint between the optical cable and the connector body to provide additional strength to the joint.

Connection device: Most fiber optic connectors do not use the male-female structure commonly used in electronic connections. The structure used is a positioning sleeve for mating connectors. Similar devices can be installed on fiber optic transmitters and receivers, and these devices can be paired using a connector. These devices are also known as pass-through bulkhead adapters.

Ⅳ Types of fiber optic connectors

Fiber optic connectors can be divided into common single-mode and multimode connectors of silicon-based fiber optics according to different transmission media, as well as other fiber optic connectors that use plastic as a transmission medium. According to the structure of the connector, they can be divided into FC, SC, ST, LC, D4, DIN, MU, MT, and other forms. Among them, ST connectors are usually used for wiring equipment ends, such as fiber optic distribution frames, fiber optic modules, etc.; and SC and MT connectors are usually used for network equipment ends. 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 single-core and multi-core (such as MT-RJ). Fiber optic connectors are widely used and have a wide variety. In the actual application process, we generally distinguish according to the structure of the fiber optic connector. The following are some common fiber optic connectors:

1 FC connector

The FC fiber optic connector was first developed by Japan NTT. FC is the abbreviation of Ferrule Connector, which indicates that the external reinforcement method is to use a metal sleeve, and the fastening method is a screw buckle. The mating end face of the ceramic pin of the earliest FC connector is a flat contact (FC). This type of connector is simple in structure, easy to operate, and easy to manufacture, but the fiber end is more sensitive to dust, and Fresnel reflection is easy to produce, and it is more difficult to improve return loss performance. Later, this type of connector was improved, using a spherical pin (PC) with a mating end face, and the external structure was not changed, which made the insertion loss and return loss performance greatly improved.

FC fiber optic connector

2 SC connector

This is a fiber optic connector developed by Japan NTT. The outer shell is rectangular, and the structural dimensions of the used pin and coupling sleeve are exactly the same as the FC type. Among them, the end face of the pin is mostly PC or APC type grinding method; the fastening method is the plug pin type, without rotating. This type of connector is inexpensive, easy to plug, and unplug. It has small fluctuations in insertion loss, has high compressive strength, and has a high installation density.

SC fiber optic connector

ST and SC interfaces are two types of fiber optic connectors. For 10Base-F connections, the connectors are usually ST type, and for 100Base-FX, the connectors are mostly SC type. The core of the ST connector is exposed, and the core of the SC connector is inside the connector.

3 Biconic Connector

The most representative product of this type of fiber optic connector is developed by Bell Laboratories of the United States. It is composed of a precision-molded cylindrical plug and a coupling assembly. The end of the cylindrical plug is frusto-conical and the coupling assembly is equipped with a double tapered plastic sleeve. DIN47256 fiber optic connector is a connector developed by Germany. The structure size of the pin and coupling sleeve used in this connector is the same as the FC type, and the PC surface grinding method is used for the end surface treatment. Compared with FC connectors, the structure is more complicated. There is a pressure control spring in the internal metal structure, which can avoid damage to the end face due to excessive insertion pressure. Also, the mechanical accuracy of this connector is high, so the insertion loss value is small.

4 MT-RJ connector

MT-RJ started with the MT connector developed by NTT. It has the same latch mechanism as the RJ-45 type LAN electrical connector. It is aligned with the fiber optic through the guide pins installed on both sides of the small sleeve. For an easy connection with an optical transceiver, the fiber at the end of the connector is arranged in a double-core (interval 0.75mm) arrangement. It is the next-generation high-density fiber connector mainly used for data transmission.

5 LC connector

The LC-type connector was developed by the famous Bell Research Institute and is made of a modular jack (RJ) latch mechanism that is easy to operate. The size of the pins and sleeves used is half that of ordinary SC, FC, etc., which is 1.25mm. This can increase the density of fiber connectors in the fiber distribution frame. At present, in the single-mode SFF, the LC-type connector has occupied a dominant position, and the application in multi-mode is also growing rapidly.

LC connector

6 MU connector

MU (Miniature unit Coupling) connector is the smallest single-core fiber optic connector developed by NTT based on the most used SC connector. The connector uses a 1.25mm diameter sleeve and a self-retaining mechanism, which has the advantage of enabling high-density installation. Using MU's 1.25mm diameter sleeve, NTT has developed a series of MU connectors. They have socket-type connectors (MU-A series) for optical cable connection; backplane connectors with self-retaining mechanism (MU-B series) and simplified sockets (MU-SR series) for connecting LD/PD modules and plugs. With the rapid development of fiber optic networks towards larger bandwidths and larger capacities and the widespread application of DWDM technology, the demand for MU-type connectors will also grow rapidly.

7 MC connector

In 2012, a communication company independently developed an MC connector that is smaller and denser than LC connectors. Rihai MC fiber optic connector is a high-density single-core fiber optic connector, which is suitable for various high-density occasions, such as large-capacity central computer room and high-density data center. The density of MC fiber optic connectors is high, which can be up to twice that of LC connectors in the same space. It is the smallest and highest density connector in the world.

8 Others

Fiber optic connector can also refer to FICON, the IBM mainframe channel launched by FIber Connector and G5 server in 1998. Based on the Fibre Channel standard, it increases ESCON's half-duplex 17MB/s transmission rate to full-duplex 100MB/s. Each FICON channel can support up to 4000 I/O operations per second, which is equivalent to 8 ESCON channels.