In fiber optic networks, connectors are essential for linking different sections of optical fibers. The performance of these connectors is greatly influenced by their endface finish, which determines how well the fiber cores align and make contact with each other. Two common types of finishes for fiber optic connector endfaces are Physical Contact (PC) and Angled Physical Contact (APC). Both of these finishes are designed to optimize the connection, but they serve slightly different purposes and offer distinct performance characteristics.
1. Physical Contact (PC) Finish
Physical Contact (PC) finish refers to a connector endface geometry that is polished to ensure that the fiber cores of the two mating connectors come into direct contact with each other. The main goal of the PC finish is to achieve a low insertion loss and minimal back reflection by ensuring good physical contact between the fibers.
Characteristics of PC Finish:
- Flat Endface: The connector endface is polished flat to provide an even, direct contact between the fiber cores.
- No Angle: Unlike APC, the endface of a PC connector is not angled; both fiber cores are aligned directly, which ensures physical contact.
- Connection Type: Typically used in applications where reflection is less critical, such as in short-range, low-speed connections.
Performance Considerations:
- Insertion Loss: The PC finish typically results in low insertion loss, as the fibers are in direct contact with one another.
- Back Reflection: The lack of an angle in the PC finish can lead to higher back reflection, which may be undesirable in high-performance applications where signal integrity is crucial. However, for most applications, the back reflection is within acceptable limits.
- Applications: PC connectors are used in standard networking and telecom applications where moderate performance is acceptable.
2. Angled Physical Contact (APC) Finish
Angled Physical Contact (APC) finish, as the name suggests, is a connector endface that is polished at an angle, typically at 8 degrees. The primary purpose of this angle is to reduce back reflection by ensuring that light reflects at an angle rather than directly back into the fiber core.
Characteristics of APC Finish:
- Angled Endface: The fiber’s endface is polished at an 8-degree angle, which changes the angle at which the light reflects back from the mating connector.
- Reduced Back Reflection: The angled finish significantly reduces the amount of light that is reflected back into the fiber, thus minimizing the possibility of interference or signal degradation.
- Precise Alignment: APC connectors have a more precise alignment mechanism due to the angled endface, requiring that the connectors are mated in a specific orientation.
Performance Considerations:
- Insertion Loss: APC connectors may have slightly higher insertion loss compared to PC connectors due to the angled finish, but this is typically very minimal.
- Back Reflection: APC connectors are specifically designed to reduce back reflection, making them ideal for high-performance, high-speed applications, such as in high-bandwidth telecom systems and data centers.
- Applications: APC connectors are commonly used in long-range communication, particularly where signal integrity is crucial, and in applications such as CATV (cable television) and fiber optic networks that require high signal quality.
Key Differences Between PC and APC Finishes
| Feature | Physical Contact (PC) | Angled Physical Contact (APC) |
|---|---|---|
| Endface Geometry | Flat | Angled (typically 8 degrees) |
| Back Reflection | Higher | Lower (significantly reduced) |
| Insertion Loss | Low but slightly higher than APC | Slightly higher than PC |
| Application | Short-range, low-speed networks | High-speed, high-performance networks |
| Typical Use | Standard fiber optic connections | Long-distance telecom, CATV, high-performance networks |
| Connector Orientation | Does not require specific orientation | Requires precise orientation for correct mating |
Conclusion
Physical Contact (PC) and Angled Physical Contact (APC) finishes are two distinct types of fiber optic connector endface geometries that serve different purposes in optical communications.
- PC finish is primarily used for standard connections where insertion loss is a concern, but back reflection is less critical.
- APC finish, with its angled endface, is designed to reduce back reflection, making it the preferred choice for high-performance, long-range optical communication systems where signal integrity is crucial.
By understanding the differences between these finishes, engineers and technicians can make informed decisions on which type of connector to use, depending on the application’s specific requirements for performance and signal quality.
