A passive double star (PDS) optical subscriber system which employs a newly proposed flexible access and frequency division duplex transmission system has been reported. For the flexible access and efficient channel usage in subscriber PDS system, a modified pipe-line polling with a call-by-call basis channel assignment has been proposed. This access system has a wide covering range which exceeds 10km or more. A newly proposed pulsed PSK transmission and a baseband transmission are used for a single wavelength bi-directional transmission for to and from the central office. A pulsed FM single subcarrier transmission system is also proposed for the analog CATV distribution system, which is overlaid with wavelength division multiplexing on the bi-directional transmission system. The equipments for the pulsed PSK and the pulsed FM transmission can be realized with all digital circuits. Moreover, the pulsed signal's modulation nature has eased the requirement for the laser diode characteristics, such as linearity and RIN. These features are effective for the compact and cost effective transmission systems.

Photonic switching and coherent optical transmission would be key technologies for realizing future all optical broadband wide-area networks. This paper reports results of studies on integrating photonic switching systems and coherent optical transmission technologies. Introducing coherent optical transmission technologies to photonic space-division switching systems will lead to some excellent features, including line handling capacity expansion, transmission span increase and integration capability with coherent WDM/FDM broadcasting systems. Photonic wavelength-division (WD) switching systems with large number of WD channels would also be possible, with coherent optical transmission technologies. Space-division switching experiments in a 100 Mb/s optical FSK transmission system were carried out using LiNbO3 photonic switch matrices. Receiver sensitivity improvement of 7.5 dB was observed in the transmission experiments through a photonic switch matrix and long SMFs (22 km, 100 km). This allows more cascaded connection for photonic switch matrices in a photonic switching system. It was also shown that crosstalk component can be rejected at the receiver by introducing channel separation greater than 3 GHz, even when the crosstalk power is ten times larger than the desired signal. From these experimental results, a photonic SD switching system whose line capacity exceeding 500-lines and whose transmission line length was over 20 km, would be expected.