Reference

Cleaning Connections for Accurate Measurements

Choosing the Right Connector

A critical, but often overlooked, factor in making a good lightwave measurement is the selection and care of the fiber-optic connector. The differences in connector types are mainly in the mechanical assembly that holds the ferrule in position against another identical ferrule. Connectors also vary in the pol- ish, curve, and concentricity of the core within the cladding. Mating one style of cable to another requires an adapter. Hewlett-Packard offers adapters for most instruments to allow testing with many different cables.

The system tolerance for reflection and insertion loss must be known when selecting a connector from the wide variety currently available. Some items to consider when selecting a connector are:

•How much insertion loss can be allowed?

•Will the connector need to make multiple connections? Some connectors are better than others, and some are very poor for making repeated connections.

•What is the reflection tolerance? Can the system take reflection degradation?

•Is an instrument-grade connector with a precision core alignment required?

•Is repeatability tolerance for reflection and loss important? Do your specifica- tions take repeatability uncertainty into account?

•Will a connector degrade the return loss too much, or will a fusion splice be re- quired? For example, many DFB lasers cannot operate with reflections from connectors. Often as much as 90 dB isolation is needed.

Over the last few years the FC/PC style connector has emerged as the most popular connector for fiber-optic applications. While not the highest perform- ing connector, it represents a good compromise between performance, reli- ability, and cost. If properly maintained and cleaned, this connector can withstand many repeated connections.

However, many instrument specifications require tighter tolerances than most connectors, including the FC/PC can deliver. These instruments cannot toler- ate connectors with the large non-concentricities of the fiber common with ceramic style ferrules. When tighter alignment is required, HP instruments typically use a connector such as the Diamond HMS-10, which has concentric tolerances within a few tenths of a micron. HP then uses a special universal adapter which allow other cable types to mate with this precision connector.

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