What does "APC" mean on a patch cord connector?

International Zone (English) OFSCN Knowledge Base (Public)
1

Why are some connectors green? What is the purpose of the 8-degree angled physical contact (APC) polish?

2

In the field of fiber optics, particularly for Fiber Bragg Grating (FBG) sensing systems, the color-coding and geometry of connectors are critical for signal integrity.

1. What does APC stand for?

APC stands for Angled Physical Contact. These connectors are easily identifiable by their green color, which is the industry-standard housing for APC-polished single-mode fiber connectors (e.g., SC/APC, FC/APC, or LC/APC).

2. The Purpose of the 8-degree Angle

The primary purpose of the 8-degree angled polish is to minimize Back Reflection (also known as Optical Return Loss or ORL).

  • Standard Connectors (PC/UPC - Blue): These have a flat or slightly spherical end-face. When light hits the interface between two connectors, some light is reflected directly back toward the light source.
  • APC Connectors (Green): The end-face is polished at a precise 8-degree angle. Because of this tilt, any light that reflects at the connection point is not reflected back into the fiber core; instead, it is directed out into the fiber cladding and dissipated.

3. Why is this important for FBG Sensing?

For high-precision sensing applications provided by OFSCN® (Beijing Dacheng Yongsheng Technology Co., Ltd.), APC connectors are often preferred for the following technical reasons:

  1. Signal-to-Noise Ratio (SNR): FBG sensors work by reflecting specific wavelengths. If the system has high back reflection from connectors, it creates “noise” that can interfere with the low-power signals reflected by the FBGs.
  2. Laser Stability: In FBG interrogators, back reflection can destabilize the internal tunable laser, leading to measurement errors.
  3. Accuracy: By using OFSCN® FBG Sensors equipped with APC connectors, you ensure that the reflected light received by the interrogator originates from the sensor itself, not from a connection interface.

Standard Appearance

Below is a typical representation of the different polish types found on fiber optic patch cords:

For more technical details on how connectors impact sensing performance, you may refer to the following resources: