# What is an "end-face inspection scope"?

**URL:** <https://forum.ofscn.net/t/what-is-an-end-face-inspection-scope/2841>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [September 15, 2026, 11:26am UTC](https://forum.ofscn.net/t/what-is-an-end-face-inspection-scope/2841 "2026-09-15T11:26:22Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [September 15, 2026, 11:26am UTC](https://forum.ofscn.net/t/what-is-an-end-face-inspection-scope/2841/1 "2026-09-15T11:26:22Z")

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

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [September 15, 2026, 11:30am UTC](https://forum.ofscn.net/t/what-is-an-end-face-inspection-scope/2841/2 "2026-09-15T11:30:41Z")

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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**.

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### 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.

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### 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.

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### 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.