Naoki Ikeda

The effect of higher-order dispersion on slow light propagation in photonic crystal waveguides

We have studied the dispersion of ultrafast pulses in a photonic crystal waveguide as a function of optical frequency, in both experiment and theory. With phase-sensitive and time-resolved near-field microscopy, the light was probed inside the waveguide in a non-invasive manner. The effect of dispersion on the shape of the pulses was determined. As the optical frequency decreased, the group velocity decreased. Simultaneously, the measured pulses were broadened during propagation, due to an increase in group velocity dispersion. On top of that, the pulses exhibited a strong asymmetric distortion as the propagation distance increased. The asymmetry increased as the group velocity decreased. The asymmetry of the pulses is caused by a strong increase of higher-order dispersion. As the group velocity was reduced to 0.116(9)·c, we found group velocity dispersion of -1.1(3)·106 ps2/km and third order dispersion of up to 1.1(4)·105 ps3/km. We have modelled our interferometric measurements and included the full dispersion of the photonic crystal waveguide. Our mathematical model and the experimental findings showed a good correspondence. Our findings show that if the most commonly used slow light regime in photonic crystals is to be exploited, great care has to be taken about higher-order dispersion.

Photonic crystal and quantum dot technologies for all-optical switch and logic device

Nano-photonic technologies of GaAs-based two-dimensional photonic crystal (2DPC) slab waveguides (WGs) and InAs-based quantum dots (QDs) are reviewed for a symmetrical Mach?Zehnder (SMZ) type, ultra-small and ultra-fast all-optical switch (PC-SMZ) and logic device. As the first phase, ultra-fast (~ps) and ultra-low energy (~100?fJ) switching has been demonstrated using a chip 600??m?300??m in size. The second phase is to create a PC-SMZ-based ultra-fast photonic logic switch with a latch function for a future ultra-fast photonic digital processor. One of the priority subjects is to establish a new design method, i.e., topology optimization (TO) method of 2DPC-WGs with wide/flat bandwidth, high transmittance and low reflectivity. Another one is to develop selective-area-grown, high-density and highly uniform InAs QDs with large optical nonlinearity (ONL) by using a metal-mask (MM) molecular beam epitaxy (MBE) growth method. Recent results regarding these two subjects encourage us to reach the final goal.

Epithelial to Mesenchymal Transition Is a Determinant of Sensitivity to Chemoradiotherapy in Non-Small Cell Lung Cancer

BACKGROUND The epithelial to mesenchymal transition (EMT) is a fundamental biological process during which epithelial cells change to a mesenchymal phenotype; it has a profound impact on cancer progression. The purpose of this study was to clarify the role of EMT in the sensitivity of non-small cell lung cancer (NSCLC) to chemoradiotherapy (CRT). METHODS We evaluated the correlation between EMT and sensitivity to chemotherapy or radiotherapy using NSCLC cells induced to undergo EMT with epidermal growth factor or transforming growth factor-β1. Immunohistochemistry was used to examine the expression of EMT markers, E-cadherin, cytokeratin, N-cadherin, and vimentin in 50 tumor specimens obtained from patients with NSCLC both before and after CRT. RESULTS The EMT resulted in increased malignant potential and reduced sensitivity to cisplatin and paclitaxel in NSCLC cells. Furthermore, chronic exposure to cisplatin, paclitaxel, or radiation altered the cells into therapy-resistant sub-lines that showed phenotypic changes such as a spindle-cell shape and increased EMT marker expression. Also, decreased expression of epithelial markers and upregulation of mesenchymal markers were detected in surgically resected specimens after CRT compared with biopsy specimens obtained before treatment. The disease-free survival rate of patients with EMT marker-positive tumors was significantly lower than that of those with EMT marker-negative tumors. CONCLUSIONS The EMT marker expression was detected in NSCLC tumors after CRT, indicating that EMT changes are associated with insensitivity to CRT. New therapeutic combinations using EMT-signaling inhibitors may be needed to circumvent the resistance of some types of cancer to CRT.

Predictive factors for postoperative acute exacerbation of interstitial pneumonia combined with lung cancer

PurposePostoperative acute exacerbation (AE) of usual interstitial pneumonia (UIP) is a serious complication in the surgical treatment for primary lung cancer combined with UIP. The purpose of this study was to determine the predictors of AE of UIP after a major lung resection.MethodsWe retrospectively collected data for 40 patients who had been operated on for lung cancer and were diagnosed as UIP based on postoperative histopathological diagnosis. We then evaluated some predictive factors related to the AE of UIP.ResultsThe incidence of postoperative AE of UIP was 15% (6/40 patients). No correlation between patients who developed AE of UIP and those who did not, in terms of preoperative C-reactive protein, white blood cell count, percentage lymphocytes, forced expiratory volume in 1 s, percentage total lung capacity, percentage diffusing capacity of lung for carbon monoxide, and the alveolar partial pressures of oxygen and carbon dioxide. Preoperative serum lactate dehydrogenase (LDH) and serum KL-6 were significantly higher and the percent vital capacity (%VC) was significantly lower in patients who developed AE of UIP than in those who did not. Furthermore, recursive descent partition analysis revealed that %VC (<80.6%) and LDH (≥241 IU/l) could distinguish patients with AE from those without AE.ConclusionPreoperative %VC plus serum LDH values were considered the predictive factors for AE of UIP after surgery for lung cancer.

Mode identification of high-quality-factor single-defect nanocavities in quantum dot-embedded photonic crystals

We investigate the quality (Q) factor and the mode dispersion of single-defect nanocavities based on a triangular-lattice GaAs photonic-crystal (PC) membrane, which contain InAs quantum dots (QDs) as a broadband emitter. To obtain a high Q factor for the dipole mode, we modulate the radii and positions of the air holes surrounding the nanocavity while keeping sixfold symmetry. A maximum Q of 17 000 is experimentally demonstrated with a mode volume of V=0.39(λ∕n)3. We obtain a Q∕V of 44 000(n∕λ)3, one of the highest values ever reported with QD-embedded PC nanocavities. We also observe ten cavity modes within the first photonic band gap for the modulated structure. Their dispersion and polarization properties agree well with the numerical results.

High transmission recovery of slow light in a photonic crystal waveguide using a hetero groupvelocity waveguide.

High transmission of slow-light in a photonic crystal (PC) waveguide (WG) using a hetero group-velocity (Ht-V(g)) PC-WG was proposed and experimentally investigated. The Ht-V(g) WG, which comprises a low-group-velocity (L-V(g)) PC-WG section between two identical high-group- velocity (H-V(g)) PC-WGs, is designed to decrease the impedance mismatch of the L-V(g) PC-WG. The increase in transmittance of a propagating pulse was confirmed in the Ht-V(g) PC-WG even in the vicinity of the band-gap, whereas the homogeneous PC-WG showed a gradual decrease in transmittance with the pulse wavelength approaching the band-gap. The group index (n(g)) of the L-V(g) region in the Ht-V(g) PC-WG was measured by the cross-correlation method and attained a value above 20. On the other hand, the transmittance of the Ht-V(g) structure recovered approximately 16dB compared to the homogeneous L-V(g) WG having same n(g), 17. This recovery is mainly dominated by the coupling improvement due to the Ht-V(g) structure, around 12dB. These results indicate the effectiveness of the Ht-V(g) structure to use slow light in a PC-WG, which leads to various applications in PC-based optical devices.

Topology optimization of waveguide bends with wide, flat bandwidth in air-bridge-type photonic crystal slabs

We employed the topology optimization (TO) method to improve the transmission bandwidth of waveguide bends in air-bridge-type, two-dimensional photonic crystal slabs. We experimentally confirmed that bend loss at longer wavelengths in the vicinity of the band edge was suppressed by using TO. The optimized bends showed good performance, comparable to that of straight waveguides.

Broadband waveguide intersection with low-crosstalk in two-dimensional photonic crystal circuits by using topology optimization

Topology optimization has been used to design intersections in two-dimensional photonic crystal slab waveguides. We have experimentally confirmed that the optimized intersection displays high-transmittance with low-crosstalk for the straightforward beam-propagation line.

A Remodeling System of the 3-Sulfo-Lewis a and 3-Sulfo-Lewis x Epitopes*

It has been reported that the chemically synthesized 3′-sulfo-Lea and 3′-sulfo-Lex epitopes have a high potential as a ligand for selectins. To elucidate the physiological functions of 3′-sulfated Lewis epitopes, a remodeling system was developed using a combination of a βGal-3-O-sulfotransferase GP3ST, hitherto known α1,3/1,4-fucosyltransferases (FucT-III, IV, V, VI, VII, and IX) and arylsulfatase A. The pyridylaminated (PA) lacto-N-tetraose (Galβ1–3GlcNAcβ1–3Galβ1–4Glc) was first converted to 3′-sulfolacto-N-fucopentaose II (sulfo-3Galβ1–3(Fucα1–4)GlcNAcβ1–3Galβ1–4Glc)-PA by sequential reactions with GP3ST and FucT-III. The 3′-sulfolacto-N-fucopentaose III (sulfo-3Galβ1–4(Fucα1–3)GlcNAcβ1–3Galβ1–4Glc)-PA was then synthesized from lacto-N-neotetraose (Galβ1–4GlcNAcβ1–3Galβ1–4Glc)-PA by GP3ST and FucT-III, -IV, -V, -VI, -VII, or -IX in a similar manner. The substrate specificity for the 3′-sulfated acceptor of the α1,3-fucosyltransferases was considerably different from that for the non-substituted and 3′-sialylated varieties. When the GP3ST gene was introduced into A549 and Chinese hamster ovary cells expressing FucT-III, they began to express 3′-sulfo-Lea and 3′-sulfo-Lex epitopes, respectively, suggesting that GP3ST is responsible for their biosynthesis in vivo. The expression of the 3′-sialyl-Lex epitope on Chinese hamster ovary cells was attenuated by the introduction of GP3STgene, indicating that GP3ST and α2,3-sialyltransferase compete for the common Galβ1–4GlcNAc-R oligosaccharides. Last, arylsulfatase A, which is a lysosomal hydrolase that catalyzes the desulfation of 3-O-sulfogalactosyl residues in glycolipids, was found to hydrolyze the sulfate ester bond on the 3′-sulfo-Lex (type 2 chain) but not that on the 3′-sulfo-Lea (type 1 chain). The present remodeling system might be of potential use as a tool for the study of the physiological roles of 3′-sulfated Lewis epitopes, including interaction with selectins.

Self-phase modulation in photonic-crystal-slab line-defect waveguides

The authors observed self-phase modulation in spectral domain at 1.50μm in AlxGa1−xAs-based photonic-crystal-slab line-defect waveguides. Adopting a sample with x=0.18 has enabled the authors to avoid two-photon absorption, causing undesirable free-carrier-induced refractive-index change. Variation of the observed spectrum with input pulse peak power is well reproduced by theoretical simulation. They find that a 1.6ps light pulse of 2.5pJ suffices for causing a phase shift of π in a 1mm long sample owing to tight light confinement and nonlinear refractive index n2 due to instantaneous optical Kerr effect is (3.8±1.2)×10−13cm2∕W. A possibility of developing ultrafast all-optical switch due to n2 is discussed