Committees address dwdm laser safety

By JANE EHRGOTT

Along with the ability of dense wavelength-division multiplexing (dwdm) systems to carry high-powered, optically amplified signals come safety considerations related to their deployment. The International Electro-technical Commission (iec) TC76 WG5 has developed Part 2 of iec 60825: "Safety of laser products," which addresses the safety concerns of optical fiber communications systems (ofcss).

In an effort to increase manufacturers` awareness of laser safety issues associated with the emerging dwdm technology, a joint meeting was held last February in Geneva between TC76 WG5 and itu SG15 WP4/15, the committee of the International Telecommunications Union (itu) that addresses characteristics of optical systems for interoffice and long-distance networks.

Serving as convenor of iec TC76 WG5, Bryan Tozer of the United Kingdom gave a brief review of iec 60825 Part 2. He stressed that most issues concerning current technology can be addressed within the existing standard. The Hazard Level terminology, he said, should be used in the context of the products addressed by itu SG15 WP4/15. If automatic power reduction is used to control emission, the Hazard Level would be determined based on the emissions after the automatic power reduction, provided certain conditions are met.

He described a new amendment to iec 60825 Part 2 now under consideration that introduces 1- and 3-sec automatic power-reduction intervals. This evaluation is based on the maximum power carried by the system, with maximum power levels during the shutdown not exceeding the maximum permissible exposure limits as defined in iec 60825 Part 1 in any 100-sec time period. The introduction of these changes would give the manufacturers of optical terminal equipment considerable flexibility in their optical power budgets.

Here is a brief summary of key questions asked by the itu committee and addressed by Tozer.

Is terminal equipment to be classified as Class 1 (safe under reasonably foreseeable conditions of operation) regardless of internal optical power levels? Based on iec 60825 Part 2, it is arguable that the piece of terminal equipment or comparable subassembly is a component of a larger end-to-end system, the ofcs. The ofcs is Class 1 because the emissions are enclosed in the optical fiber during operation. The manufacturer of the subassembly need not classify its equipment, which is a component of the ofcs. However, the manufacturer must label optical apertures and connectors as to the appropriate Hazard Level and provide the service provider and installer with information as required in the standard.

Is manual restart permissible if it disables the automatic shutdown mechanism? If these situations are infrequent and occur under controlled conditions, it is recommended that the automatic shutdown mechanism be disabled for only the minimum time required. Then, the automatic shutdown mechanism must immediately and automatically reset. It is the subassembly manufacturer`s responsibility to give full details of these conditions, as well as the automatic reset, and inform the operator/installer of safe work practices and administrative controls.

When asked about liaison activity with the itu committee, Tozer invited committee members to join TC76 WG5 through their national committee representative. q