We present transmission- and reflection-type measurement methods for the differential mode delay (DMD) of a multimode optical fiber (MMF) optimized for high-speed local area networks (LANs) for the 850-nm band. Compared with a previously reported transmission-type measurement method for the 1550-nm wavelength band, we demonstrate here high-resolution DMD measurement methods for MMFs in the 850-nm band. As the method is based on a Fourier-domain intermodal interference technique, the measurement sensitivity is ∼60-dB, and it requires a fiber only a few meters in length. The shorter wavelength also allows a threefold improvement in the measurement resolution. The reflection-type measurement technique is a more practical than the transmission-type measurement technique for the field testing of short MMFs already installed in networks. We believe that this method will be a practical tool not only for field testing of short-length MMFs already installed in networks but also for the development of new plastic optical fibers (POFs).

Phase performance in a fiber optic temperature sensor using a mode-division multiplex is studied. The phase shift due to the temperature change of a multimode graded-index optical fiber is analyzed. The intensity fluctuation by the interference of two modes is estimated in computer simulation.

In this paper, we propose to use graded-index multimode fibers (GI-MMFs) with Fabry-Perot laser diodes (FP-LDs) for short-span and low-cost feeders. The multimode fiber feeders can be applied to wireless personal communication systems where the required feeder length is within several hundred meters, such as distributed antenna networks for microcellular systems or wireless LANs. The use of multimode fibers makes fiber coupling and connection easier, and has the potential to greatly reduce total system cost. Three types of GI-MMFs are considered as transmission media, (1) silica-based glass optical fiber (GI-GOF),(2) silica-core plastic-clad fiber (GI-PCF), and (3) all-plastic optical fiber (GI-POF). It is shown that GI-GOF and GI-PCF are suitable for use as feeders in the microcells of CDMA cellular and wireless LAN systems within 300m in length. GI-POF is estimated to be suitable for use as feeders in wireless LANs within 100m in length. A multimode fiber feeder with FP-LDs and GI-PCF of 300 m is developed in order to demonstrate its applicability to a wireless LAN system operating in the 2.4 GHz ISM band.

A fiber optic temperature sensor using a conventional graded index multimode optical fiber is proposed. The multimode fiber is excited by two selected modes using a computer-generated holographic filter. A clear periodic signal created by interference between two modes is observed in the experiment.

Mode separation of a multiplex mode in a mode-division multiplexing system is studied. The clear, desired single-mode pattern, which is separated from the multiplex mode by using a holographic filter, is observed in the experiment.