An initial trial of the optical fiber transmission system in NTT is reported in this paper. In NTT's transmission networks, the shorthaul application appears attractive in the near future. The laboratory test is primarily targeted to 32 Mb/s bit rate and 8 km long repeater spacing. We report here the design philosophy of step-index multimode fibers and repeaters for this trial. Through the design and manufacturing of fibers, the fundamental and common characteristics of fibers are clarified. Stable, compact and low power consuming optical repeaters are realized. Trere is no trouble of optical repeatered line and all repeaters in the line are operating with sufficient optical power margin. Multi-repeatered test has confirmed that experimental results are in good agreement with the design values.

This letter presents the measuring method for obtaining the baseband swept-frequency response of multimode optical fibers. With the description of the measuring system, examples of fiber characteristics are given. The SNR and frequency resolution of the method are briefly discussed in comparison with the pulse broadning methods.