The end-to-end round trip time (RTT) is one of the most important communication characteristics for Internet applications. From the viewpoint of network operators, RTT may also become one of the important metrics to understand the network conditions. Given this background, we should know how a factor such as a network incident influences RTTs. It is obvious that two or more factors may interfere in the observed delay characteristics, because packet transmission delays in the Internet are strongly dependent on the time-variant condition of the network. In this paper, we propose a modeling method by using mixed distribution which enables us to express delay characteristic more accurately where two or more factors exist together. And, we also propose an inferring method of network behavior by decomposition of the mixed distribution based on modeling results. Furthermore, in experiments we investigate the influence caused by each network impact factor independently. Our proposed method can presume the events that occur in a network from the measurements of RTTs by using the decomposition of the mixed distribution.

We fabricated ultrafast nonlinear optical films of squarylium J-aggregates and studied their properties including the absorption spectrum, the refractive index, the third-order nonlinear optical coefficients, the extent of absorption saturation, and the recovery of absorption saturation. The transmittance of the film was increased by 30% due to absorption saturation at a pump energy of several hundreds fJ/µm2/pulse. The half decay time constant of absorption saturation was found to be approximately 100 fs for off-resonant excitation. Two-dimensional demultiplexing was demonstrated using the squarylium film as a switching material. From a train of 8 optical pulses with 100 fs duration and 1 ps interval corresponding to a bit rate of 1 Tbps, 24 spatially resolved spots were obained.

The switch LSI described here takes advantage of the special characteristics of fully-depleted CMOS/SIMOX devicesthat is, source/drain capacitances and threshold voltages that are lower than those of conventional bulk CMOS devicesto boost the I/O bit rate. The double-edge triggered MUX/DEMUX which uses a frame synchronization logic, and the active-pull-up I/O provide a 144-pin, 2. 5-Gbps/pin interface on the chip. The 220-kgate rerouting banyan switching network with 110-kbit RAM operates at an internal clock frequency of 312 MHz. The CMOS/SIMOX LSI consumes 8. 4 W when operating with a 2-V power supply, and has four times the throughput of conventional one-chip ATM switch LSIs.

We analyze subjective assessments by comparative evaluations of bulk data transmission by using two psychological methods (the method of successive categories and the constant method). From the results of the first experiment, the thresholds at which participants downloading a data file began to feel dissatisfaction with service degradation are 15.7 Mbps and 11.6 Mbps obtained by the two different methods when the throughput without the service degradation is approximately 22 Mbps. In the second experiment, we investigate the threshold of user satisfaction for various network environments. The threshold is 63% of the throughput of the user's usual network environment. Moreover, from the viewpoint of download time, users feel dissatisfaction with the quality when download time becomes 1.5 times longer. These values can be used to more effectively allocate network resources and thereby achieve higher service quality.

A demonstration of power enhancement by nonlinear oscillation in a millimeter-sized electrostatic vibrational energy harvester for the future Internet of Things is presented. To enable nonlinearity in microelectromechanical system (MEMS) devices, we selected a gold spring as a component of the MEMS structure for its lower Young's modulus than conventional materials, a ductile characteristic, and an electrical conductivity. The mechanical characteristics of the fabricated MEMS device related to the nonlinear phenomenon were examined. The charging characteristics of an ethylene tetrafluoroethylene copolymer (ETFE) electret film for electrostatic induction were also evaluated. Nonlinear oscillation for the millimeter-sized energy harvester with the ETFE electret was confirmed experimentally by applying external vibration. The oscillation resulted in a bandwidth two times broader than that by linear oscillation. The normalized harvester effectiveness of the nonlinear oscillation was 5.1 times higher than that of the linear one.

Using ultrafast nonlinear-optical response of organic dye films, a train of picosecond optical pulses can be converted into a space pattern of a mm scale. As applications of this technique we demonstrate a single-shot multichannel optical switching for 1 Tbit/s pulse trains, and a timing jitter suppression of pulse trains using a control system with femtoseconds time resolution.

Principle of a single shot demultiplextion by means of time-to-space conversion was investigated using femtosecond nonlinear optical response of absorption bleaching of squarylium dye (SQ) J-aggregates. Spincoated films of squarylium dye J-aggregates on glass substrates exhibit efficient and ultrafast transmittance change, which recovers 73% of its initial level (0 fs) within 1 ps. A simple method for time-to-space conversion was applied for this film. We took our attention to one of the characteristics of femtosecond pulse, which is the spatial thinness in its propagation direction. Femtosecond pulses of a single pump pulse and train of four probe pulses were illuminated to the same area (diameter of 10 mm) of the surface of the SQ J-aggregates film. Direction of the probe beam was normal to the surface of the film and that of the pump beam was oblique angle in horizontal plane. Caused by spatial delay of a pump pulse due to the illumination in oblique angle to the film, four probe pulses with interval time of 1 ps (1 THz) meet separate places on the film. Because of the fast response of the SQ J-aggregates, the film picked out part of each probe pulse, which has narrower shapes in horizontal direction compared to the initial circular one by transmittance change of the film. The spatially separated four lines were observed by a CCD camera for an image of the transmitted probe pulse train. These results suggest that the response time of SQ J-aggregate film, which determines the horizontal width of each line, to be enough for demultiplexing of 1 THz optical signals.