Why are these threaded, angled-physical-contact (APC) connectors the preferred choice for sensors? In terms of stability, what makes them superior to “push-pull” style SC connectors?
In the field of optical fiber sensing, particularly with Fiber Bragg Grating (FBG) technology, the choice of connector significantly impacts the signal-to-noise ratio and long-term reliability. The preference for FC/APC (Ferrule Connector/Angled Physical Contact) over push-pull styles like SC/UPC is driven by two primary technical factors: Return Loss and Mechanical Stability.
1. Superior Signal Integrity: The 8-Degree Angle
The “APC” designation means the fiber end-face is polished at a precise 8-degree angle.
- Back Reflection: In standard “Physical Contact” (PC or UPC) connectors, reflected light travels directly back toward the source (the FBG interrogator), which can create noise and interference with the sensing signal.
- High Return Loss: With the 8-degree angle of an APC connector, reflected light is coupled into the fiber cladding rather than being sent back down the core. This results in a much higher Return Loss (typically >60 dB compared to 40-50 dB for UPC), which is critical for the high-precision spectral analysis performed by OFSCN® Fiber Bragg Grating Interrogators.
2. Mechanical Stability: The Threaded Locking Mechanism
The “FC” part of the connector refers to the threaded, screw-on coupling mechanism.
- Vibration Resistance: Unlike “push-pull” connectors (like SC or LC) which rely on plastic latches, the FC connector uses a metal screw-down nut. This ensures that the physical contact between the ferrules remains constant even in high-vibration environments common in industrial sensing.
- Repeatability: The threaded connection provides a consistent axial force, minimizing insertion loss variations. This is vital for sensors that must operate reliably over years in the field.
OFSCN® Standard Implementations
At DCYS (OFSCN), we standardize FC/APC connectors for almost all of our sensing products to ensure the highest data accuracy.
For example, our standard patch cords and high-temperature connectors utilize this robust architecture:
Standard FC/APC Visual Reference:
In summary, the FC/APC connector is the “industrial grade” choice. The threads provide the mechanical security needed for harsh environments, while the angled polish provides the optical “darkness” (low back-reflection) required to detect minute shifts in FBG wavelengths.