This paper reports the influence of optical reflection induced noise and distortion for optical fiber feeder systems for microcellular mobile communication systems. Since the optical feeder requires very wide dynamic range, noise and distortion must be suppressed to an extremely low level. From optical transmission experiments and theoretical analysis, the basic characteristics of the reflection induced noise and distortion were investigated. By using these results, it was estimated that, for currently used analog mobile telephone systems, the number of connectors with 35 dB reflectance must be limited to less than 17, in order to suppress the noise caused by the connector reflections. Moreover, it was confirmed that the reflection induced distortion drastically decreases according to the increase of the length between reflectors. Therefore, the distortion can be suppressed by expanding the connector spacing to more than 7 meters.

This paper reports performance improvement in an optical fiber feeder for microcellular mobile radio systems. A low noise optical receiver using a transformer resonant circuit is described. With this receiver, CNR degradation due to receiver noise is suppressed to less than 0.9dB. Furthermore, two novel techniques, the use of a multiple-LD transmitter and automatic LD input level control, are proposed. The multiple-LD transmitter increases transmitter output power and reduces the transmitter noise. With a dual-LD transmitter, it is possible to increase the optical loss margin by 3.1dB, which corresponds to transmission length expansion of 6.2km, or to improve the received CNR by 2.8dB, which enables communication range expansion. Automatic LD input level control, which optimizes LD input level according to the received radio power, can expand the actual dynamic range of the up link.

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.

Receiver sensitivity improvements as much as 16.4 dB and 4.1 dB over direct detection and ASK heterodyne detection, respectively, have been realized in 32 Mb/s PSK heterodyne detection simulation experiments using a 1.3µm wavelength laser diode.

This paper summarizes basic system design for an optical fiber feeder for microcellular mobile communication systems. The optical feeder enables compact and low cost base stations, easy radio channel control and flexible mobile communication systems. Basic transmission characteristics are investigated through optical transmission experiments. By using these results, feeder performance is estimated and optimal system parameters are designed.