What is an "end-face inspection scope"?

OFSCN Global Technical Center OFSCN Technical Knowledge Base
1

How can I see on the screen if the fiber optic connector is dirty?

2

To observe in real-time on a screen whether a fiber optic connector end-face is contaminated with micron-level dust, oil, or scratches, engineers typically use a Fiber Optic End-Face Inspection Scope / Microscope.

I. Why Can’t the Naked Eye Observe It?

Standard single-mode optical fibers used for communication and sensing are physically very small:

  • Core Diameter: Approximately 9\ \mu\text{m}
  • Cladding Diameter: Approximately 125\ \mu\text{m}
  • Ferrule Outer Diameter: Typically 2.5\text{mm} (e.g., FC, SC, ST) or 1.25\text{mm} (e.g., LC)

Airborne dust particles just a few micrometers in diameter landing on the core area can cause severe optical loss, worsened back reflection, or even burn the fiber end-face. These are completely imperceptible to the naked eye and require a high-magnification optical imaging system.

II. Working Principle and Usage Procedure of the End-Face Inspection Scope

1. Working Principle

The fiber optic end-face inspection scope consists of an objective lens group, a coaxial illumination system (typically internal diffused LED light), a CMOS/CCD image sensor, and a signal processing and display unit:

  • High Magnification: Generally offers optical and digital magnification of 200\times or 400\times.
  • Coaxial Illumination: Light enters the ferrule end-face parallel to the optical axis and reflects back to the objective lens. This creates high-contrast shadows of subtle pits, scratches, and dust contaminants on the end-face.
  • Video Output: The sensor converts the microscopic optical image and outputs it in real-time to a built-in LCD screen, industrial PC, standard PC, or mobile device.

2. Standard Observation Procedure

  1. Install the Corresponding Adapter Interface: Depending on the connector type to be tested (e.g., FC/PC, FC/APC, LC male connectors) or adapter flange (female connectors), screw on the appropriate metal inspection adapter.
  2. Insert the Connector: Vertically insert the fiber optic connector into the inspection scope interface (if it’s an angled APC connector, align the keyway).
  3. Focus and Align: Fine-tune the focus knob until a clear circular fiber cross-section is displayed in the center of the screen.
  4. Image Interpretation:
    • The brightest spot in the center of the image is usually the Core Area;
    • The uniform concentric ring around the core is the Cladding;
    • The outermost part is the Ferrule Contact Zone.
    • Dust and debris typically appear as irregular dark spots or granular shadows; oil contamination often presents as blurry halo-like dark shadows; scratches appear as thin, elongated bright/dark lines. Engineers usually use the IEC 61300-3-35 standard to make Pass/Fail judgments on the size and quantity of contamination within each zone.

III. Related Notes

General-purpose handheld/desktop fiber end-face microscopes and cleaning tools are common optical communication testing equipment and are not part of Beijing Dacheng Yongsheng Technology Co., Ltd.'s (OFSCN®) core product line. In the assembly and field splicing/testing of Beijing Dacheng Yongsheng Technology Co., Ltd.'s (OFSCN®) Fiber Bragg Grating (FBG) sensors and specialty optical cables, it is recommended to strictly follow the operational procedures of: inspect first, then clean, re-inspect for qualification, and only then proceed with mating.