Microscope inspection of connectors and cleaning
This domain covers the first step in every reliable fiber measurement: examining and cleaning connector endfaces. The CFOS/FC candidate is expected to know why contamination causes both insertion loss and reflectance, how to use a microscope or video probe, how the IEC 61300-3-35 endface zones are applied, and when cleaning can rescue a connector versus when a defect is permanent.
Inspection setup
Use a 200×–400× microscope or video inspection probe with the correct adapter tip. Inspect both patch-cord connectors and the bulkhead adapter; a clean jumper mated to a dirty bulkhead is still a dirty connection. Light the endface obliquely so particles and scratches are visible, and never touch an APC endface or use a flat PC adapter on an 8° APC connector.
Zone criteria and cleaning
IEC 61300-3-35 divides the endface into Zone A (core), Zone B (cladding), Zone C (adhesive), and Zone D (contact). For a typical single-mode PC connector, Zone A must have no scratches and no defect at or above 3 µm; Zone B defects at or above 5 µm fail; Zone C and D allow larger features that do not interfere with physical contact. APC connectors use the same idea but add an 8° polish, so contamination that looks minor can create an air gap.
For loose dust, use a dry lint-free wipe or a one-click cleaner. For film or stubborn contamination, use 99% isopropyl alcohol on a lint-free wipe, follow with a dry wipe, and let it dry before mating. Never use canned air; propellant can deposit residue.
Worked example
A single-mode UPC patch cord shows a 2 µm particle near the core edge and a 6 µm pit in Zone B. The particle is removable contamination, but the 6 µm Zone B pit exceeds the 5 µm limit and is permanent. Clean and re-inspect: if the pit remains, reject the cord. If only the 2 µm particle remained, it would not by itself fail Zone A, but the endface must still be free of scratches and contact-damaging features.
Traps
- Inspecting only the patch cord and not the bulkhead, or only one end of a link.
- Calling dirt a pit before cleaning and re-inspecting.
- Using too little magnification or poor lighting and missing a core scratch.
- Using non-99% alcohol or a tissue that sheds lint.
- Assuming a good loss test proves endface quality; a damaged connector can pass loss and still fail reflectance.