Optical amplifier recommendations
LAUREL CLARK
AT&T BELL LABORATORIES
Experts from Working Party 4 of the International Telecommunication Union-T Study Group 15, under the chairmanship of Pietro Di Vita, met in Geneva last February. Participants in Question 26/15, whose charter includes the transmission-related aspects of optical-fiber amplifier devices and subsystems and the transmission characteristics of passive optical components, are preparing two draft recommendations. The scope of these recommendations encompasses long-haul and access systems in single- and multichannel, as well as point-to-point and point-to-multipoint, configurations.
Draft Recommendation G.oa3, "Application-related aspects of optical-fiber
amplifier devices and subsystems," for example, focuses on optical-fiber amplifier devices and subsystems used in digital systems and operating in the 1550-nanometer region. Among the items described in this recommendation are the transmission effects and system impairments that have emerged in optically amplified systems, definitions of common parameter values and value ranges, and the applications for which these parameters must be considered.
Optical-fiber nonlinearities, polarization and dispersion effects, and such optical-fiber amplifier-related properties as noise accumulation and self-filtering effect, are described. In addition, operations, administration and maintenance, environmental, and optical safety aspects of optical-fiber amplifier devices and subsystems are addressed.
A second recommendation, Rec. G.poc, "Transmission characteristics of passive optical components," identifies relevant transmission-related parameters, includes some definitions and references pertinent test methods for passive optical components. This recommendation also includes submarine applications. The types of passive components comprise optical multiplexers/demultiplexers, attenuators, filters, isolators, switches, dispersion compensators, connectors, splices and branching components. In addition to providing transmission-related component and functional parameter definitions, Recommendation G.poc defines common parameter values and value ranges across applications.
In the future, the Q.26/15 participants will work on developing the characteristics of two new optical-fiber amplifier subsystem types--combined optical-amplifier and optical-multiplexing functionality, and combined optical-amplifier and passive dispersion-compensator functionality. For now, the development of component requirements for remotely pumped optical-fiber amplifier devices will remain under the auspices of Q.27/15, "Characteristics of optical-fiber submarine cable systems," because the contemplated application for these devices is underwater systems.
Experts from Question 25/15 also met in Geneva. This question, whose charter covers optical systems for interoffice and long-distance networks, is preparing three draft recommendations covering optical interfaces for synchronous digital hierarchy equipment in systems using optical amplifiers (see Lightwave, Standards Watch, February 1995, page 13).
A 25-gigahert¥frequency grid has been established as a tool to assist in the development of a set of channel frequencies for use in multichannel, optically amplified systems, as described in draft Recommendation G.mcs. During the February meeting, all agreed the frequency grid would be referenced to 193,100 GHz. In the resultant grid, frequencies are evenly separated by 25 GHz, with one frequency defined as the center or reference grid frequency and located at 193,100 GHz. q
Laurel Clark is a member of the technical staff at AT&T Bell Laboratories in Holmdel, NJ. She holds a B.S. in Electrical Engineering from the University of Colorado at Boulder and an M.gifNG from Cornell University, Ithaca, NY.