Fracture toughness of short carbon fibre reinforced thermoplastic polyimide

The fracture toughness testing of short fibre reinforced thermoplastic materials were performed. Materials tested were the polyimide resin and also that reinforced with 20 wt% or 30 wt% short carbon fibre. For introducing the initial crack, the tapping method, the sliding method and the bridge indentation method were examined. Among them, the sliding method was found to be effective for every case. The fracture tests were conducted by the three-point bending test with several loading rates. Stable crack growth was observed for the neat material while unstable fracture occurred for the reinforced materials. The critical values of the stress intensity factor at crack initiation were greater for the reinforced materials than for the neat resin. The fracture toughness of the 30 wt% reinforced material was independent of loading rate while that of 20 wt% reinforced material increased with loading rate. In order to investigate the fracture mechanisms, fractographic observations were also performed.     

Ultrahigh-Q nanocavities written with a nanoprobe

High-Q nanocavities have been extensively studied recently because they are considered key elements in low-power photonic devices and integrated circuits. Here we demonstrate that ultrahigh-Q (>10(6)) nanocavities can be created by employing scanning probe lithography on a prepatterned line defect in a silicon photonic crystal. This is the first realization of ultrahigh-Q nanocavities by the postprocess modification of photonic crystals. With this method, we can form an ultrahigh-Q nanocavity with controllable cavity parameters at an arbitrary position along a line defect. Furthermore, the fabricated nanocavity achieves ultralow power all-optical bistable operation owing to its large cavity enhancement effect. This demonstration indicates the possibility of realizing photonic integrated circuits on demand, where various circuit patterns are written with a nanoprobe on a universal photonic crystal substrate.     

Singlemode transmission within photonic bandgap of width-variedsingle-line-defect photonic crystal waveguides on SOI substrates

It is demonstrated experimentally that a single missing-hole line defect photonic crystal waveguide fabricated on a silicon-on-insulator substrate can support a single waveguiding mode within the photonic bandgap if the waveguide width is properly tuned     

Hierarchical reachability graph of bounded Petri nets forconcurrent-software analysis

Petri nets have been proposed as a promising tool for modeling and analyzing concurrent-software systems such as Ada programs and communication protocol software. Among analysis techniques available for Petri nets, the most general approach is to generate all possible states (markings) of the system in a form of a so-called reachability graph. However, this conventional reachability graph approach is inefficient or intractable, even for a bounded Petri net, due to state explosion in many practical applications. To cope with this problem, this paper proposes a method for constructing a hierarchically organized state space called the hierarchical reachability graph (HRG). Using the HRG, we obtain necessary and sufficient conditions for reachability and deadlock, as well as algorithms to test whether a given state or marking is reachable from the initial state and whether there is a deadlock state (a state with no successor states)     

Single-mode lightwave transmission in SOI-type photonic-crystalline-defect waveguides with phase-shifted holes

Single-mode lightwave transmission was observed in novel line-defect photonic-crystal (PC) waveguides. The waveguide structure is constructed by adding phase-shifted holes in an ordinary missing-hole line defect. This device permits a fine single-mode lightwave transmission even though the waveguide structure is fabricated on silicon-on-insulator (SOI) substrate, which seriously promotes off-plane leakage of waveguiding modes     

Structural tuning of guiding modes of line-defect waveguides ofsilicon-on-insulator photonic crystal slabs

We experimentally demonstrate the structural tuning of the waveguiding modes of line defects in photonic crystal (PC) slabs. By tuning the defect widths, we realized efficient single-mode waveguides that operate within photonic band gap frequencies in silicon-on-insulator PC slabs. The observed waveguiding characteristics agree very well with three-dimensional finite difference time-domain calculations. We also directly measured the propagation loss of the line defect waveguides and obtained a value of 6 dB/mm     

Carrier Diffusion and Recombination in Photonic Crystal Nanocavity Optical Switches

Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure.     

Broad-band tunable two-section laser diode with external gratingfeedback

A tunable laser light source consisting of a two-section laser diode and an external grating is discussed. A wide tunable range of 154 nm was realized by improving the antireflection (AR) coating and the coupling efficiency. At both edges of the tunable range, however, the tuning characteristics were strongly influenced by the internal mode, in spite of the high-quality AR coating. The effects of the internal mode were avoided by using a phase-control section of the laser. Consequently, single-mode oscillation can be obtained at any desirable wavelength within the above tunable range by controlling the current injected into the phase-control section