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首页 > Home > Application Notes > Common fiber optic connectors (ST, SC, LC, FC) and the difference between PC, APC and UPCCommon fiber optic connectors (ST, SC, LC, FC) and the difference between PC, APC and UPC
Time: 2020-03-29
1. Several Common Fiber Optic Connectors (ST, SC, LC, FC)
• FC-type fiber optic connector: It uses a metal sleeve for external reinforcement and adopts a screw-lock fastening method.
• SC-type fiber optic connector: Designed to connect GBIC optical modules or common fiber transceivers, it features a rectangular housing and uses a push-pull latching fastening method without rotation.
• ST-type fiber optic connector: Commonly used in fiber optic distribution frames, it has a round housing and is fastened with a screw lock.
• LC-type fiber optic connector: Specifically designed for SFP modules, it is constructed with an easy-to-operate modular jack (RJ) latching mechanism.
Figure 1: ST, SC, LC, FC Fiber Optic Connectors
2. Fiber Optic Connector End Faces: PC, APC and UPC
In laboratories, the most commonly used fiber optic connectors are mainly FC/PC and FC/APC. Here, FC stands for Ferrule Connector, which uses a steel metal sleeve as the ferrule.
PC refers to Physical Contact, meaning tight physical contact between fiber end faces. Based on different return loss performance, physically contacting connectors are classified into PC, UPC and APC. UPC stands for Ultra Physical Contact. Industry standards specify that the return loss of PC is -35dB, while that of UPC is -50dB. Return loss refers to the proportion of light reflected by the connector end face. Since the return loss value is negative, a larger absolute value (i.e., a more negative number) indicates better performance (less reflection), which can be simply understood as "the larger the value (ignoring the negative sign), the better".
In principle, different types of end faces should not be mixed. However, both PC and UPC end faces are flat, with the only difference lying in grinding quality. Thus, temporary mixing of PC and UPC will not cause permanent physical damage to the connectors, though it may affect return loss performance and is not recommended for long-term use.
APC is completely different from PC and UPC. Its end face is ground to an 8-degree angle relative to the fiber axis, which changes the reflection path of light to minimize back reflection, achieving an industry-standard return loss of -60dB. APC connectors can only be mated with other APC connectors. Due to the structural difference in end faces, mating APC with PC/UPC via an adapter will damage the fiber end faces of the connectors.
Therefore, to avoid confusion in connector use during experiments (and prevent damage to equipment ports such as spectrometers), it is crucial to confirm the interface type before purchasing matching fiber optic patch cords.
Figure 2: PC, APC and UPC End Faces
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