Ultrahigh-Q nanocavity with 1D photonic gap.

Recently, various wavelength-sized cavities with theoretical Q values of approximately 10(8) have been reported, however, they all employ 2D or 3D photonic band gaps to realize strong light confinement. Here we numerically demonstrate that ultrahigh-Q (2.0x10(8)) and wavelength-sized (V(eff) approximately 1.4(lambda/n)3) cavities can be achieved by employing only 1D periodicity.

Quality factor control and lasing characteristics of InAs/InGaAs quantum dots embedded in photonic-crystal nanocavities.

We demonstrate lasing action with a high spontaneous emission factor and temperature insensitivity in InAs/InGaAs quantum dots (QD) embedded in photonic crystal nanocavities. A quality factor (Q) of over 10,000 was achieved by suppressing the material absorption by QDs uncoupled to the cavity mode. High Q cavities exhibited ultra low threshold lasing with a spontaneous emission factor of 0.7. Less frequent carrier escape from the QDs, which was primarily favored by high potential barrier energy, enabled low threshold lasing up to 90 K.

Nonlinear and adiabatic control of high-Q photonic crystal nanocavities.

This article overviews our recent studies of ultrahigh-Q and ultrasmall photonic-crystal cavities, and their applications to nonlinear optical processing and novel adiabatic control of light. First, we show our latest achievements of ultrahigh-Q photonic-crystal nanocavities, and present extreme slow-light demonstration. Next, we show all-optical bistable switching and memory operations based on enhanced optical nonlinearity in these nanocavities with extremely low power, and discuss their applicability for realizing chip-scale all-optical logic, such as flip-flop. Finally, we introduce adiabatic tuning of high-Q nanocavities, which leads to novel wavelength conversion and another type of optical memories.

Waveguides, resonators and their coupled elements in photonic crystal slabs.

The design, fabrication, and measurement of photonic-band-gap (PBG) waveguides, resonators and their coupled elements in two-dimensional photonic crystal (PhC) slabs have been investigated. We have studied various loss mechanisms in PBG waveguides and have achieved a very low propagation loss (~1 dB/mm). For these waveguides, we have observed a large group delay (>100 ps) by time-domain measurement. As regards PBG resonators, we realize very high-Q and small volume resonators in PhC slabs by appropriate design. Finally, we demonstrate various forms of coupled elements of waveguides and resonators: 2-port resonant-tunneling transmission devices, 4-port channel-drop devices using the slow light mode, and 3-port channel-drop devices using the resonant-tunneling process.

MR appearance at different ages of osteoporotic compression fractures of the vertebrae.

PURPOSE: To elucidate the MR appearance at different ages of osteoporotic vertebral compression fractures. METHODS: We retrospectively analyzed sequential MR studies of 107 vertebrae in 75 patients with osteoporotic compression fractures. RESULTS: Vertebral deformities comprised 35 anteriorly wedged vertebrae, 65 fish vertebrae, four flat vertebrae, and others. Signal alterations were depicted as geographic areas of low intensity on T1-weighted images (T1-WI) and high intensity on T2*-WI, or linear areas of low intensity on T1-WI and high or low intensity on T2*-WI. In the acute stage, geographic alteration predominated. During a three-month period following the injuries, the extent of the geographic areas increased in 40% of cases on T1-WI. Geographic alteration declined in the chronic stage, whereas the prevalence of linear signals increased. Restoration of fatty marrow was preceded by linear signals without geographic signals on T1-WI (36%). The anteriorly wedged vertebrae collapsed faster than the fish vertebrae. CONCLUSIONS: The acute or subacute stage of compression fractures is characterized by a larger alteration of the geographic signal, whereas the chronic stage was evidenced by a smaller area of alteration of the geographic and linear signals or by restoration of fatty marrow.

Selective lumbosacral radiculography and block.

Selective lumbosacral radiculography and block was performed on 106 patients, using 60% Conray or Dimer-X and 1% lidocaine mixed with corticosteroid. The technique of this method is reported, and the radiculographic findings and diagnostic value of this method are discussed. According to our experience, this method is technically simple and very useful in determining the limit of the lumbosacral nerve root lesion, and occasionally can be used to relieve radicular symptoms. We think it is an especially excellent diagnostic technique for disorders featuring nerve root entrapment in the lateral foraminal recess, in which accurate localization cannot be determined by the other auxiliary diagnostic measures.