What Is Fiber Optic Connector?

Fiber optic connector is a passive device in network communication. The role is to combine the two fiber end face precision, which can achieve the removal and connection of two optical fibers.

Fiber optic connectors are often used with fiber optic adapters. The ferrule of two fiber optic connectors is inserted into two optical fibers, using mechanical and optical structures, through the adapter, the two end faces of the optical fiber are precisely docked together to achieve physical contact between the fiber end faces, in order to maximize the coupling of optical energy from a single fiber transmitted to another fiber.

Types of fiber optic connectors

By different transmission media: single-mode fiber optic connectors and multimode fiber optic connectors.

By different structures: FC, SC, ST, D4, DIN, Biconic, MU, LC, MT and other types.

By connector pin end face: FC, PC (UPC) and APC.

fiber optic connector

Common types of fiber optic connectors on the market

FC Fiber Optic Connector

FC type connector was first developed by NTT Japan, FC is the abbreviation of Ferrule Connector.FC connector is fastened by screw locking, with high tensile strength. FC connector can be used for single-mode fiber or multimode fiber.

Typical Application:
Datacom,telecom,measurement,equipment,single mode lasers

7234007 FC 0.9mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector
7234007 FC 0.9mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector3

SC Fiber Optic Connector

SC fiber optic connector, also called Subscriber Connector/Square Connector/Standard Connector, was developed by NTT Corporation of Japan. The shell is made of molded glass fiber plastic, which is rectangular in shape. SC connectors are tightly fastened by plugging and unplugging pin latch type, without rotation, which is easy to plug and unplug, and the price is low, with small fluctuations in intervention loss and high compressive strength.

Typical Application:
Telecom, GPON, EPON, GBIC

7234004 SC 0.9mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector
7234004 SC 0.9mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector2

LC Connector

LC connector, also known as Lucent Connector/Little Connector/Local Connector, was first developed by the famous Bell Labs, which is made by modular jack (RJ) latching mechanism and is easy to operate. The size of the pins and sleeves used in LC connectors is 1.25mm, which is half the size of ordinary SC, FC, etc.

Typical Application: High density connections, SFP and SFP+ transceivers, XFP transceivers

7234002 LC DX 2.0mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector
7234002 LC DX 2.0mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector2

ST Connector

It was developed by AT&T and became dominant in the 1980s and 1990s for long-wire systems and short-distance applications. The most prominent feature of ST connectors is the straight ferrule, a rigid plastic tube that holds the fiber for proper alignment for interconnection or termination. ST connectors are spring-loaded, which means they are easy to insert and remove. The ST connector setup allows for unidirectional communication, so two ST connectors and two fiber optic cables are used for bi-directional communication.

7234010 ST 2.0-3.0mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector
7234010 ST 2.0-3.0mm Pre-polished Ferrule Field Assembly Fiber Optical patch Connector2

MU Connector

The MU (Miniature Unit Coupling) connector is the world’s smallest single core fiber optic connector developed by NTT based on the most used SC type connector. This connector uses 1.25mm diameter sleeve and self-retaining mechanism, and has the advantage of high-density installation.

MU 0.9mm Series Fiber Optical patch Connector-11

Structure of fiber optic connectors

The basic structure of all types of fiber optic connectors is the same. The majority of fiber optic connectors use highly sophisticated components: fiber ferrule, fiber cable, sub-assembly body, connector housing, and the stress relief boot.

Structure diagram of various types of fiber optic connector components:

LC fibre connector:

LC fibre connector

SC fibre connector:

SC fibre connector

FC fibre connector

FC fibre connector

What are UPC connectors and APC connectors?

UPC, APC, and UPC/APC are often seen in the parameter list of fiber optic connectors, what do they mean?

Before understanding these parameters, you have to know what are ferrule and grinding technology.

The ferrule is the housing for the bare end of the fiber, which holds the fiber in place and helps to align it. The ferrule is available in plastic, ceramic, metal or glass. They are usually cylindrical in shape with a hole in the middle.

ferrule

When a connector is installed on the end face of a fiber, return loss is unavoidable due to reflection from the light source. Severe light loss can damage the laser source and interrupt the transmitted signal. To allow better contact between the end faces of the two fibers, the ferrule end faces of fiber optic patch cords are usually ground into a different structure.

The shape parameters after grinding and polishing of the collar include radius of curvature, vertex offset and core depression, which are also the quality criteria for evaluating fiber optic connectors.

UPC and APC is the grinding method for ferrule

UPC: Ultra Physical Contact

UPC

The end face of the UPC connector shows a slight curvature for more precise docking. UPC is an upgrade from PC (Physical Contact). Usually, PC/UPC connectors are blue in color.

APC: Angled Physical Contact

APC

The fiber end face is usually ground to an 8° bevel. The 8° angled bevel makes the fiber end face tighter and reflects light through its bevel angle to the cladding rather than directly back to the light source, reducing reflections with an industry-standard return loss of -60dB. APC connectors provide better connection performance. Typically, APC connectors are usually green in color.

Application of APC and UPC

When choosing between APC and UPC applications, we have to consider the cost besides the performance.
APC is more suitable for high precision fiber optic signal transmission applications.APC is generally used for optical RF applications in the high wavelength range such as CATV, but also for optical passive applications such as PON network architecture or passive optical LAN.

For applications that are less sensitive to fiber optic signals, UPC fiber optic connectors are available. They are commonly used on Ethernet network equipment (such as ODF fiber optic patch panels, media converters and fiber optic switches), digital, cable TV and telephone systems, etc.

Since the end face of the APC is ground to an 8 degree angle, the APC cannot be connected to the UPC, which would result in degraded connector performance. However, the fiber end faces of both PC and UPC are flat, and the difference is in the quality of the grinding, so the mixed connection of PC and UPC is not enough to form permanent physical damage to the connector.

How To Put Connector On Fiber Optic Cable?

  1. Remove the connector end cover and feed the cable through it;
  2. Peel off the outer skin of the cable with fiber optic strippers to a length of approximately 5cm;
  3. Cut off the exposed coating layer with Miller pliers close to the edge of the clamp to expose the fiber;
  4. Wipe and clean the bare fiber with a dust cloth;
  5. Cut the fiber with the jig;
  6. Align the fiber with the main hole slot and insert it, when the fiber is initially bent, press the crimp cover down;
  7. Screw the end cap on the cable back into the connector body and snap on the shell.

The installation of fiber optic quick connectors is very easy, but it should be noted that fiber optic quick connectors are highly susceptible to contamination and damage thereby causing damage to the performance of the fiber. Keep away from dust and contaminants during installation, and move slowly when inserting.

How To Put Connector On Fiber Optic Cable

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