Sunday, 18 April 2021

NTT Technical Review Highlights ITU-T Work on Standards for Higher-Capacity Fiber

International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) Study Group 15 is working on revising standards (Recommendations) for single-mode optical fiber (SMF). There are also discussions toward standardizing space division multiplexing technologies, which are promising for overcoming the capacity limit of SMF. All these are captured in an NTT Technical Review article titled, "Recent Standardization Activities in ITU-T on Single-mode Optical Fiber and Space Division Multiplexing Technologies"

Here is an extract from the article:

The Recommendations shown in red in Table 1 are those being actively discussed. The G.652 fiber is used worldwide and recognized as “standard SMF.” The G.657 fiber has optical characteristics compatible with those of G.652 fiber but has improved bending loss. These two fibers support transmission over the O–L band* (1260–1625 nm) and used for various applications such as access, metro, and core networks. Recommendation G.654 is for a fiber supporting C–L-band* transmission and mainly used for submarine long-haul transmission systems. The revision of these Recommendations are active topics in ITU-T due to the capacity growth in terrestrial and submarine optical fiber networks. In the next section, recent activities for revising these SMF Recommendations are introduced.


Network capacity has been increasing at a rate of a few tens of percent, and the capacity crunch with SMF networks will become a serious issue in the 2020s. To overcome the capacity limit of SMF, fibers for space division multiplexing (SDM) transmission have been intensely investigated. Figure 4(a) shows the conceptual images of SDM fibers. SDM fibers can be basically categorized into two: multi-core fiber or multi-mode fiber. Multi-core fiber has multiple cores within a cladding, and multi-mode fiber has multiple propagation modes within a core. In SDM transmission, multiple signals can be simultaneously transmitted through multiple cores or modes, achieving much higher capacity compared with that in SMF. Before SDM fibers can be used in telecom networks worldwide, it is necessary to establish an SDM fiber Recommendation in the same manner as the SMF Recommendations. 

It was proposed and agreed at ITU-T 2020’s January meeting to start discussion on a new technical report for SDM optical fiber and cable. Although the content of this technical report is under discussion, it was agreed to include the related topics on cable, splice/connectors, and installing technologies. The main discussion pointes are: target application and benefits of SDM technology and categorization of SDM fiber. Regarding the target application for SDM technologies, it is important to compare technologies that use SMF to improve spatial density, such as high-fiber-count cable or reduced coating-diameter fiber technologies, as shown in Fig. 4(b). Although various SDM fibers have been proposed, current multi-core fiber- or few-mode fiber-based SDM fiber is being discussed as a potential candidate of SDM fiber. It is expected that the fiber parameters and test methods for such fibers will be discussed and incorporated into this technical report. The tentative publishing year for this technical report is 2022. The discussion on SDM fiber standardization has been initiated in advance in Japan, and the current technical level or challenges for SDM standardization has/have been summarized as technical report-1077 entitled “Technical Report on Space Division Multiplexing Technologies” (in Japanese) published by the Telecommunication Technology Committee (TTC).

You can read the article here and download the PDF after free registration from here.

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