tia updates standard test conditions

tia updates standard test conditions

by william b. gardner

The Telecommunications Industry Association (tia) recently revised its "umbrella" document eia/tia-455a into tia/eia-455b, "Standard Test Procedure for Fiber Optic Fibers, Cables, Transducers, Sensors, Connecting and Terminating Devices, and Other Fiber Optic Components." The revisions, coordinated by Tom Hanson of Corning Inc. (Corning, NY), used contributions from several working groups in the tia`s Subcommittee FO-6.6 on Optical Fibers and Materials.

This document establishes uniform conditions for conducting measurements of fibers and components in the approximately 150 Fiber Optic Test Procedures (fotps) that have been issued by the tia. The old document never mentioned whether wavelengths, which are almost always measured in air, should be converted to vacuum values. The refractive index of air in a standard atmosphere decreases a measured wavelength in the 1550-nm window by about 0.4 nm. For years, wavelength-division multiplexing consisted of a few wavelengths separated by 100 nm or so. In such an environment, an ambiguity of 0.4 nm in measurement was of little concern.

Now the International Telecommunication Union Recommendations (e.g., G.692) have defined a grid for dense wavelength-division multiplexing in which adjacent wavelengths are separated by only 100 GHz (about 0.8 nm). For such systems, a 0.4-nm ambiguity in the measurement of the characteristic wavelengths of sources and fibers would be unacceptable. The new tia/eia-455b addresses this problem by inserting the following into its Annex A:

Wavelength is the speed of light divided by its optical frequency. For most applications, the speed of light in air is sufficient. For high accuracy applications (less than ۪.4 nm), specify the wavelength in vacuum and make adjustments to compensate for temperature, humidity, and air pressure (see Annex D).

Annex D, created for the revision, contains equations that facilitate wavelength conversions between air and vacuum for a range of temperatures, pressures, and humidities. The magnitude of these corrections can be appreciated from the article "dwdm requires accurate measurements," by Dennis Derickson of Hewlett-Packard Lightwave Div. in the August 1997 Lightwave, page 27. Moving a test set from sea level to Denver (altitude 5280 ft) would increase the measured wavelength about 0.08 nm. Increasing the test set`s temperature by 8C would increase the measured wavelength about 0.01 nm. Increasing the relative humidity from 0% to 100% would increase the measured wavelength about 0.002 nm.

The new tia/eia-455b defines two sets of ambient conditions for nonmilitary applications. Routine measurements could use the "standard ambient" of 23ۯC, relative humidity between 20% and 70%, and whatever atmospheric pressure exists during the measurement. More critical measurements could use the "controlled ambient" conditions of 23۬C, relative humidity between 45% and 55%, and a pressure between 860 and 1060 millibars.

Once the air-vacuum corrections are made, there is the problem of calibrating absolute wavelength to better than 0.01 nm. Derickson points out that the acetylene presently used in absorption cells doesn`t match the 1550-nm window as well as hydrogen cyanide would. The National Institute of Standards and Technology (nist) expects to have hydrogen cyanide cells available this summer under the designation "Standard Reference Material #2519." For information, call nist`s srm Program Office at (301) 975-6776; or e-mail [email protected]. q

William B. Gardner represents Lucent Technologies (Norcross, GA) on sev eral fiber standards committees. He can be contacted at tel: (770) 798-2674; fax: (770) 798-4654; e-mail: [email protected].