BY JANE E. EHRGOTT
Two major changes made by the International Electrotechnical Commission to the IEC 60825 - Safety of laser products standards have a far-reaching impact on many optical communications systems that use high-power lasers or laser amplifiers.
IEC 60825 Part 1. The first change has to do with the overhaul earlier this year of the classification scheme used for laser safety, which is incorporated in Part 1 of IEC 60825. IEC 60825 Part 1 is the foundation document for laser product safety to which all specific application documents refer. The second amendment to IEC 60825 Part 1 eliminates classes 2A and 3A and replaces them with classes 2M and 1M & 3R, respectively. It also changes some of the measurement criteria associated with the classes. These changes impact optical-component, fiber-optic, and free-space products.
IEC 60825 Part 2. IEC 60825 Part 2 - Laser safety: safety of optical fiber communication systems, is the application document with respect to laser safety of fiber-optic communications systems. In it, there are requirements that must be met by products and systems that emit optical energy into fiber. Because fiber-optic communications systems are enclosed under normal operation, this standard defines acceptable "hazard levels" with respect to the optical radiation that can be accessible in the event of a fiber disconnect or break. These hazard levels are defined in terms of the Accessible Emission Limit (AEL) tables in Part 1 of the standard. (In its current form, Part 2 refers to the older classification scheme of the Part 1 document that has now been modified.)
Following the recent release of Amendment 2 of Part 1 by the IEC last January, guidance was required to address this dilemma of having documents with different AEL schemes. An interpretation sheet has been approved to temporarily bring the Part 2 standard in line with the new Part 1 AEL scheme until the entire Part 2 standard can be rewritten.
In summary, the interpretation sheet modifies hazard levels as appropriate (2 or 2M replaces 2 and 2A, 1M or 3R replaces 3A, and kx3A is deleted) and all informative annexes are temporarily deleted, as many of the calculated power levels in fibers are incorrect under the new Part 1 Amendment 2.
The user must employ appropriate clauses and tables from Part 1 to calculate power levels and assess hazard levels using the new system. For hazard level 1M, at typical far infrared wavelengths used in DWDM or Raman communications technology using standard singlemode fiber, the AEL is relaxed. One consequence is that there is sometimes a relaxation of the limit upon which automatic power reduction systems must be applied. As before, the user must assess hazard level "under reasonably foreseeable fault conditions" as stated in section 4.4.3 of IEC 60825 Part 2.
Jane E. Ehrgott is a consultant in laser safety to the telecommunications industry. She was formerly with Lucent EH&S Bell Laboratories in Murray Hill, NJ, and holds leadership positions in several bodies dealing with laser safety and radiation standards. She can be contacted at [email protected].