We fabricated micro-contact Josephson junctions by self-alignment process, using double-layer-resist electron beam exposure and RIE. We chose Nb as superconductive materials. The junctions show the A.C. Josephson effect under the millimeter wave (70 GHz) radiation less than 100 µW and the 7th Shapiro step.

We successfully fabricated a very narrow gap in niobium film using electron beam lithography and RIE. The width of the gap was about 40 nm. We applied this process to the fabrication of Nb-PbIn-Nb planar Josephson junctions, and one of them showed the Dayem effect.

Experimental results of an N-S junction and analysis of the results using the Arnold theory were reported. Au and Pb were employed as a normal metal and a superconducting material, respectively. The excess current effect due to the Andreev reflection was observed in the current-voltage characteristics of an N-S junction whose normal resistance was 1.603 Ω. The excess current at 4.62 K was about 0.7 mA when the applied voltage was 2 mV. The barrier height and width were estimated to be 1.0169 eV and 0.7 , respectively, by comparing the experimental results and analysis based on the Arnold theory. In the voltage region less than 2 mV, the theory well agreed with the experiment. Moreover, the applied voltage dependence of the supercurrent and quasiparticle current were separately calculated. It was made clear that the supercurrent was larger than the quasiparticle current in the voltage region less than 2Δ/e, where Δ is the superconducting energy gap and e is the absolute value of an electron's charge. The supercurrent began to gradually saturate when the voltage was higher than Δ/e and became constant at the applied voltage greater than 2Δ/e. In our experiment, the excess current larger than expected from the Arnold theory was observed in the voltage region higher than 2Δ/e.

Characteristics of all-hard Nb micro-contact Josephson junctions are investigated under 70 GHz millimeter wave radiation. Typical Ic(T) of the junction is identical with that of an ideal point-contact junction. In the voltage region, higher than the energy gap voltage of Nb, no-heating effect is observed.

The Josephson triode is a superconducting three terminal device and is used as a heterodyne mixer which has the internal frequency-variable local oscillator. We have fabricated the Josephson triode by integrating the planar-type Josephson junctions and investigated their current-voltage characteristics.

We have experimentally observed the dynamics of laser outputs in a microchip laser with frequency-modulated feedback light. We have observed rich dynamics that can be interpreted as three types of dynamics at different frequencies: (1) periodic bursts at twice of the frequency of the modulation of the external mirror, (2) chaotic pulsations at the relaxation oscillation frequency, and (3) clusters at the instantaneous Doppler-shifted frequency. We have confirmed these rich dynamics by using numerical simulations.

We have demonstrated synchronization of chaos in a pair of one-way coupled Colpitts oscillators by both experiment and numerical simulation. We have investigated parameter regions for achieving chaos-synchronization when one of the internal parameters is mismatched between the master and slave oscillators, and clarify the tolerance of parameter regions for synchronization against parameter mismatching.

We have experimentally observed chaotic oscillation of outputs in a diode-pumped Nd:YAG microchip laser array with an external Talbot mirror. The oscillation of chaotic output is observed at frequencies of sub MHz corresponding to the relaxation oscillation frequencies when the Talbot mirror is slightly tilted from the perfect alignment position with the internal cavity. Chaotic intermittent bursts also appear at frequencies of sub kHz due to longitudinal mode hopping. Synchronization of chaos is observed at these two different time scales. The generation of chaotic oscillations at sub MHz is confirmed by using numerical simulations. It is found that synchronized chaotic oscillations can be observed in the vicinity of the boundary of the injection locking range.

We carried out a research for the responses of Pb thin film microbridge Josephson device fabricated by electron lithography under microwave and millimeter wave radiations. The experimental results are reported in this paper.

We have fabricated all-Nb thin film microbridges by nanometer process using new resist developed by us, electron beam lithography (EBL) and reactive ion etching (RIE) using CBrF3 gas. The resistance against CBrF3 plasma of this EB resist is 4-10 times as strong as poly-(methyl methacrylate) PMMA. The merit of RIE using CBrF3 gas is an anisotropic etching and high selectivity about resist and target. Trench of about 20 nm width was fabricated. Using this technique, the bridge with 40 nm length and 50 nm width was fabricated, and the thickness of bridge was 100 nm. The capacitance of the junction was estimated as 0.004 pF. Because of this small capacitance, fabricated samples are suitable for detection of submillimeter wave. The critical current Ic (T) of fabricated samples was proportional to (1T/Tc)3/2 like variable thickness bridge (VTB). Moreover, Shapiro step up to the 11th under the millimeter wave radiation (70 GHz) was observed.

Precise measurements of temperature dependence of the Andreev reflection current for the N–I–S junctions were carried out. Au and Pb were used as N (normal metal) and S (superconducting material), respectively. The experimental results agreed with the analyses based on the Arnold theory.