Optical fiber connector Testing

Glass fiber optic connector performance is affected both by the connector and glass. In an otherwise perfect-looking assembled connector, typical adverse factors include: connector (ferrule) concentricity tolerance, fiber diameter tolerance, fiber core concentricity tolerance (within the fiber), core optical parameter tolerance, stress in the polished fiber causing excess return loss, fiber "pistoning" eg lengthwise movement (usually poor glue), incorrect shaping of the connector tip as a result of polishing. It can be readily seen that the connector manufacturer has little control over many of these, so in-service performance may well be below the manufacturer's specification for these reasons.

Testing fiber optic connector assemblies falls into two general categories: factory testing and field testing.

Factory testing is sometimes statistical, eg a process check. For example a profiling system may be used to ensure that the overall polished shape is correct, and a good quality optical microscope to check for blemishes. Optical Loss / Return Loss performance is checked using specific reference conditions, eg against a "reference standard" single mode test lead, or using an "Encircled Flux Compliant" source for multi mode testing. Testing and rejection ("yield") may represent a significant part of the overall manufacturing cost.

Field testing is usually simpler. A special hand-held optical microscope is used to check for dirt or blemishes, and an optical time-domain reflectometer may be used to identify significant point losses or return losses. A power meter and light source or loss test set may also be used to check end-to-end loss.

July 16, 2011

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