Why Do PON Modules Use SC Connectors Instead of LC?

Date 07/01/2025

This article tells you why PON modules widely use SC connectors instead of LC connectors. It analyzes the physical appearance, parameters, and specific applications to help you understand PON modules.

When choosing a PON module, one thing you may notice is that both GPON and EPON modules almost always use SC connector fiber instead of LC connectors for their interfaces. So why do PON modules use SC instead of LC? This article will take you from a number of aspects to understand.

What is the Difference Between SC Connector and LC Connector

SC connector adopts a push-pull structure, which is more convenient for plugging and unplugging, a more stable structure, good mechanical strength, but its size is bigger than that of the LC connector. The LC connector is more compact, which is only half the size of SC fiber optic connector, and adopts the structure of plugging and unplugging structure with a latch, which is more suitable for high-density cabling. The LC connector is more compact, half the size of the SC patch cord, and has a locking structure, making it more suitable for high-density cabling. In the following table, I will compare the specific differences between the two:

Parameter	SC Connector	LC Connector
Interface size	2.5mm	1.25mm
Plug-in structure	Push-pull structure	With a lock plug-in structure
Connection accuracy	Relatively low accuracy	Small ferrule, high connection accuracy
Grinding method	UPC/APC	Usually UPC, but also APC
Return loss	UPC：≥ -50 dB，APC：≥ -60 dB	UPC：≥ -50 dB，APC：≥ -60 dB
Insertion loss	≤ 0.3 dB	≤ 0.25 dB
Port Density	Large size, suitable for low-density deployment	Small size, suitable for high-density deployment
Tensile properties	Strong tensile strength, suitable for complex scenes	Relatively weak tensile strength, suitable for indoor applications
Application scenario	Broadband access network, three-network integration, community FTTH, community cabinet, PON/EPON system	Interconnection between data centers, high-density patch panels, server rooms, and backbone switches

Why PON Module Choose SC Instead of LC

First of all, SC fiber optic connector adopts a push-pull structure, which has stronger stability. In PON network deployment, optical splitter nodes, ODN boxes in the complex environment, the stability of the connector requirements are high, and is connected outdoors, the mechanical strength of the SC connector is also a certain requirement. And it is connected outdoors, there are also certain requirements for mechanical strength.SC connectors are larger, and the plugging surface is flat, so it is easy for maintenance personnel to identify. In contrast, although the LC connector is small in size and supports high-density deployment, its physical structure is not as stable as the SC connector, and its tensile and compression resistance is relatively weak, so in the case of PON modules that need to be deployed in outdoor environments, the SC fiber optic connector is undoubtedly a more suitable choice.

Secondly, SC connectors generally use APC grinding. In the PON system, especially for long-distance transmission and multiple branches, optical signal reflection control is very important. APC, compared to UPC, with lower reflection loss, in the optical power budget constraints, multi-level tapping or OLT under the hanging of more users, appears to be more important.

Third, the use of SC connectors for PON modules is an industry standard, which has been established in the early mass deployment of FTTH, and SC/APC interfaces are used on GPON OLT equipment from most vendors, and the home ONU equipment is also basically SC. This unified standard ensures interoperability and interoperability between equipment from different vendors, and also reduces the cost of coordination between the equipment manufacturers and operators. SC fiber optic connectors are supported by industry standards such as ITU-T G.984 and IEEE 802.3ah.

Finally, bi-directional data transmission is generally used in PON networks, and this transmission method has a large impact on the module interface. It performs BiDi transmission of multiple signals by using different wavelengths in a single fiber. The SC interface has a larger head structure compared to the LC interface, which can accommodate the components required for BiDi transmission, thus improving signal stability and reliability.

Why is the PON Network Use Bidirectional Transmission System?

The reason why PON networks choose to use a BiDi transmission system is because of the ability to transmit both uplink and downlink data in a single fiber, thus saving fiber resources as well as deployment costs. In other words, the main reason for using a single-fiber bi-directional transmission system is its cost advantage.

The core of the PON network is passive splitting, i.e., OLTs to multiple ONUs share the same optical link for one-to-many distribution with the help of passive splitters. The downstream direction adopts the broadcast method, OLT sends signals to all ONUs, and ONUs identify their data. In the uplink direction, TDMA is used, and multiple ONUs send data according to time to avoid signal conflict. The combination of wavelength division multiplexing and time division multiplexing makes bidirectional transmission more efficient.

Dual-fiber bidirectional transmission system requires each PON port to be equipped with two independent fibers, one for uplink and one for downlink transmission. Compared with single-fiber bidirectional, it requires twice the fiber resources, splitters and deployment space, which significantly increases the deployment cost of the optical distribution network, for large-scale PON deployment, such cabling is not cost-effective, and its scalability is also lower.

Another disadvantage of the two-wire bi-directional system is its complex physical connections, its Tx ports and Rx ports must correspond to the strict connection requirements will lead to fiber crossings in the deployment process, increasing the complexity of network deployment, the connection error will lead to communication failures and increased maintenance costs.

Conclusion

In conclusion, SC connectors are widely used in PON modules, not only because they comply with industry standards. Compared with LC connectors, it has stronger stability, better cost-effectiveness and lower loss. And it has stronger reliability in PON module application scenarios, especially outdoor scenarios.