Taro Shibagaki

Video transmission characteristics in WDM star networks

In local area networks (LANs), it is desirable to transmit not only digital data but also moving video signals. This paper proposes a system employing a wavelength-division multiplexed star network which is satisfactory for the transmission of video signals in addition to digital data, and reports the evaluation results of the video transmission characteristics of the system employing a 32 port-pair star coupler. Video transmission was realized by the pulsed analogue transmission scheme. Pulse frequency modulation (PFM) and pulsed frequency modulation (pulsed-FM) were studied, and it was found that the SNR fluctuation due to modal noise was less by the pulsed-FM than by the PFM. It was also found that the difference in the modal noise was due to the differences in the demodulation characteristics of PFM and pulsed-FM. A 32 port-pair passive star coupler was used and a maximum of a 5-km network was experimented. The results showed that a good video SNR was obtainable in the experimental star network using laser diodes. Thus the feasibility of the broad-band network, employing a multiport-pair passive star coupler by the wavelength division multiplexing scheme, was proven.

Modal noise elimination by monopuise to twin pulse conversion in PFM transmission systems

Modal noise caused by laser coherence is a serious problem, even in a pulse frequency modulation (PFM) transmission system, because transmission information is included in the pulse leading edges in an analog manner.