How are "end-face scratches" classified?

OFSCN Global Technical Center OFSCN Technical Knowledge Base
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What are zones A, B, and C? Which scratches are most critical?

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In fiber optic communication and optical sensing engineering, the cleanliness and scratches on connector end faces are typically graded and quantitatively inspected according to the International Electrotechnical Commission standard IEC 61300-3-35. To accurately assess end-face damage, the microscopic inspection system divides the end face into several concentric circular regions, using the physical center of the fiber as a benchmark:

I. Definition and Division of Zones A, B, and C

Taking the most common standard single-mode fiber connector (cladding outer diameter 125\ \mu\text{m}) as an example, the end-face regions are defined as follows:

  1. Zone A: Core Zone

    • Range: A central circular area with a diameter of 0 \sim 25\ \mu\text{m}.
    • Physical Significance: This zone covers the optical core of the single-mode fiber (actual guiding core diameter is approximately 9\ \mu\text{m}, mode field diameter is approximately 9.2 \sim 10.4\ \mu\text{m}) and its adjacent electromagnetic field extension area. The absolute majority of optical signal energy is transmitted within this region.

  2. Zone B: Cladding Zone

    • Range: An annular region with a diameter of 25 \sim 115\ \mu\text{m} (or 25 \sim 120\ \mu\text{m} in some standards).
    • Physical Significance: Covers most of the pure silica cladding, primarily responsible for confining light within the core through total internal reflection and providing mechanical support.

  3. Zone C: Adhesive Zone

    • Range: An annular region with a diameter of 115 \sim 135\ \mu\text{m} (or 120 \sim 130\ \mu\text{m}).
    • Physical Significance: The transition gap between the outer wall of the fiber’s quartz glass and the inner bore of the ceramic ferrule, typically filled with cured epoxy resin adhesive, serving to position and secure the bare fiber.

(Note: Outside Zone C, the region with a diameter of 130/135 \sim 250\ \mu\text{m} is Zone D: Contact Zone, representing the physical surface where the two ceramic ferrules make intimate contact during mating.)

II. Where are Scratches Most Critical?

Scratches in Zone A (Core Zone) are the most critical.

According to the IEC 61300-3-35 acceptance criteria, Zone A adheres to the strictest **