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.

A new kind of optical modulator, utilizing a laser diode optical amplifier, which can solve the insertion loss problem for optical modulators, is proposed and demonstrated. Fabricated devices have shown 10 dB fiber to fiber optical gain and 600 MHz modulation bandwidth at 1.55µm wavelength.

With the foreseen growth of communication capacity, further capacity and flexibility enhancements are required for future transport networks. Photonic switching is expected to be a key technology to solve the potential bottleneck, which could be found in transport network nodes. This paper first explains the "Optical Fiber Freeway" concept, as an example of future transport networks. Following this, the possible optical transport network structure using photonic switching technologies, for realizing the Optical Fiber Freeway concept, is explained. An Optical CrossConnect (OXC) and optical Add/Drop Multiplexer (ADM) are key components. Examples of recent development of photonic switching systems toward these targets are also reviewed. An OXC using photonic Space-Division (SD) switching technology has been proposed and demonstrated. This type of OXC will realize flexible reconfiguration and optical hitless switching, and it can meet the introduction of Wavelength Division Multiplexing (WDM) technique. Line failure restoration operation at 2.4Gb/s has been successfully demonstrated. An optical packet network with a slotted ring/bus structure using a wavelength address technique has been proposed as a packet/cell based optical ADM. The experimental system employs a practical media access control system as well as a fast-wavelength switched transmitter suppressing thermally induced wavelength drift. Cell communication at 622Mb/s has been demonstrated with the experimental system. These results show that hardware technologies have been developed steadily. With a future study on an all optical network management scheme, a high capacity and flexible optical network would be realized.

The photonic Space-Division (SD) switching network is attractive for constructing flexible broadband networks. This paper first describes possible applications of the network. A broadband STM switching system, Digital Cross-connect System (DCS) and Video signal distribution switch, especially for HDTV signals, are attractive near term applications. Recent activities on photonic SD switching network developments aiming at these application are also reviewed. A 128 line prototype switching system has been developed. This system utilizes LiNbO3 photonic switch matrices, semiconductor traveling wave amplifiers (TWAs) and three dimensional optical interconnections for multi stage switching networks. It is confirmed that the system has been operating in providing 150Mb/s TV phone services and 600Mb/s HDTV distribution services with high stability. An experimental optical Digital Crossconnect System (optical DCS) has also been demonstrated. Line failure restoration operation at 2.4Gb/s has been successfully demonstrated. These experimental demonstrations prove that practical photonic switching systems are feasible with current technologies.

A photonic switching system is expected to have advantages over a conventional electronic switching system in exchanging broadband signals. Extensive studies have recently done on various photonic switching systems. State-of-art technology in photonic switching systems is surveyed in this paper. Small-capacity space-division switching systems using waveguide optical matrix switches are most practical and expected to be introduced to broadband local-area network in the near future. Wavelength division switching technology is important in extending switching capacity to large value. Application of photonic switching technology for ATM switching systems is also recently extensively studied to achieve switching throughput larger than that of electronic ATM switches.

A new kind of optical local area network (LAN), using a demand assign wavelength division multiple access (DA-WDMA) scheme, has been proposed. The proposed LAN consists of two parts; an ordinary standardized LAN and an overlaid network using wavelength division (WD) channels. The proposed network can provide bit-rate independent communication channels on the ordinary LAN without limiting the capacities for the other channels. It also exhibits upgrade possibilities from present standardized networks. An access controller, which consists of software in addition to the ordinary LAN controller, a digital signal processor (DSP) etc., was developed for DA-WDMA control. The network node operation has been demonstrated using guided-wave acousto-optic (AO) mode converters as a tunable wavelength add-drop multiplexer (ADM).