Fiber physical contact (FPC) is proposed and demonstrated as a new method designed to enable fibers to be connected easily with a small structure while maintaining high optical performance. FPC is performed by mating two bare optical fibers in a micro sleeve and fixing them to a holder while they are buckled. Buckling is a phenomenon whereby a long column is bent by compression along its length. PC connection is realized by the buckling force of the fibers themselves and does not require any springs. Optical fiber buckling is studied both theoretically and experimentally. The buckling force, which is determined by an initial span between the optical fiber holding points, remains constant when the span is changed and is useful as the PC force. The buckling amplitude which is determined by the span reduction must be so small that it does not cause excess radiation loss. A suitable span is about 7 mm. This generates a 0.7 N. The allowed span reduction is 0.1 mm. This results in a buckling amplitude of 0.64 mm which prevents radiation losses of above 0.1 dB for 1.31 µm light. Based on a study of fiber buckling, we demonstrate the optical performance for FPC connection with a 0.126 mm diameter micro sleeve in which optical fibers are mated and with polished fiber end faces. The insertion loss is under 0.3 dB and the average return loss is 50 dB for 1.31 µm light. These values are stable in the 20 to 70 temperature range. We confirm that FPC connection realizes high optical performance with a small simple structure.

A novel base station for microwave radio-on-fiber systems is proposed. It consists of an L-band electroabsorption modulator and a uni-traveling-carrier photodiode. We show it is applicable for bias-free operation and full-duplex transmission and demonstrate 100-Mbit/s bidirectional data transmission in the 5-GHz band.

A compact optically-fed radio access point module was developed that consists of a uni-traveling-carrier refracting-facet photodiode, a patch antenna, and an optical input interface. An output power from the photodiode was 1.4 dBm at a frequency of 5.88 GHz without any bias voltage.