In this report we demonstrate the characteristics of the opt-electrical transducer that is newly designed for a fiber-optic wireless access system. This transducer consists of a monolithic microwave integrated circuit (MMIC) oscillator whose oscillation frequency is over 30 GHz. The active element of the oscillator is an InAlAs/InGaAs high electron mobility transistor (HEMT). The shift of frequency is observed when we illuminate 1.55 µm wavelength light onto the HEMT area. The size of the frequency shift is -150 MHz/mW, and it does not change as a function of gate bias conditions. We also confirm that the oscillator is able to respond with an optical signal of 500 MHz, which is sufficiently fast to achieve 156 Mbit/s communication. If this transducer is introduced into the base station (BS) of a fiber-optic wireless access system, a high-speed optical modulator no longer has to be incorporated into the control station. As a result, the configuration of the system becomes simpler than that of Radio on Fiber. We constructed a system that adopts the frequency shift keying technique with application of the transducer into the BS and then performed a transmission experiment at 5 Mbit/s. The demodulated data is sufficiently clear to distinguish high from low. Therefore, we can put forth that the fabricated transducer is a promising candidate as a device for the BS of a fiber-optic millimeter-wave wireless access system.

A normal-distribution-function-shaped superconducting tunnel junction (NDF-STJ) which consists of Nb/Al-AlOx/Al/Nb has been fabricated as an X-ray detector. Current - voltage characteristics were measured at 0.4 K using three kinds of STJs, which have the dispersion parameters σ of 0.25, 0.45 and 0.75. These STJs showed very low subgap leakage current of about 5 nA. By irradiating with 5.9 keV X-rays, we obtained the spectrum of these NDF-STJs. They showed good energy resolution with small magnetic fields of below 3 mT, which is about one-tenth of those for conventional-shaped STJs.