Agilent Technologies Agilent 86120C manual Measuring insertion loss and return loss

Making Measurements

Cleaning Connections for Accurate Measurements

tor pressure. Also, if a piece of grit does happen to get by the cleaning procedure, the tighter connection is more likely to damage the glass. Tighten the connectors just until the two fibers touch.

•Keep connectors covered when not in use.

•Use fusion splices on the more permanent critical nodes. Choose the best connector possible. Replace connecting cables regularly. Frequently measure the return loss of the connector to check for degradation, and clean every connector, every time.

All connectors should be treated like the high- quality lens of a good camera. The weak link in instrument and system reliability is often the inappropriate use and care of the connector. Because current connec- tors are so easy to use, there tends to be reduced vigilance in connec- tor care and cleaning. It takes only one missed cleaning for a piece of grit to permanently damage the glass and ruin the connector.

Measuring insertion loss and return loss

Consistent measurements with your lightwave equipment are a good indication that you have good connections. Since return loss and inser- tion loss are key factors in determining optical connector performance they can be used to determine connector degradation. A smooth, pol- ished fiber end should produce a good return- loss measurement. The quality of the polish establishes the difference between the “PC” (phys- ical contact) and the “Super PC” connectors. Most connectors today are physical contact which make glass- to- glass connections, therefore it is critical that the area around the glass core be clean and free of scratches. Although the major area of a connector, excluding the glass, may show scratches and wear, if the glass has maintained its polished smoothness, the connector can still provide a good low level return loss connection.

If you test your cables and accessories for insertion loss and return loss upon receipt, and retain the measured data for comparison, you will be able to tell in the future if any degradation has occurred. Typ- ical values are less than 0.5 dB of loss, and sometimes as little as 0.1 dB of loss with high performance connectors. Return loss is a measure of reflection: the less reflection the better (the larger the return loss, the smaller the reflection). The best physically contacting connectors have return losses better than 50 dB, although 30 to 40 dB is more common.

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