Broad-bandwidth and accurate optical vibration sensing by using FDM Φ-OTDR with linear regression analysis of multi-frequency phase responses.

We demonstrate Φ-OTDR distributed acoustic sensing (DAS) that realizes both a broad bandwidth for the vibration frequency and wide dynamic range for the vibration amplitude based on optical frequency-division-multiplexing (FDM). We enhance the sampling rate of DAS by using FDM while suppressing waveform distortion in time domain (spurious components in spectral domain) caused by sensor nonlinearity inherent in Φ-OTDR, thus improving dynamic range, with linear regression analysis of multi-frequency phase responses. The proposed method compares the phase offsets and responses of each frequency to those of a common reference frequency and uses the information to calibrate each of the different responses. We clarify the physical origin of the problem and the validity of the proposed method in both simulations and experiments. Experimental results show an improvement in dynamic range by above 8 dB on average for vibration waveforms with nɛ-order amplitudes and kHz-order frequencies over 10-km single-mode fiber.

Improvement of optical properties of InGaN-based red multiple quantum wells.

The realization of red-emitting InGaN quantum well (QW) is a hot issue in current nitride semiconductor research. It has been shown that using a low-Indium (In)-content pre-well layer is an effective method to improve the crystal quality of red QWs. On the other hand, keeping uniform composition distribution at higher In content in red QWs is an urgent problem to be solved. In this work, the optical properties of blue pre-QW and red QWs with different well width and growth conditions are investigated by photoluminescence (PL). The results prove that the higher-In-content blue pre-QW is beneficial to effectively relieve the residual stress. Meanwhile, higher growth temperature and growth rate can improve the uniformity of In content and the crystal quality of red QWs, enhancing the PL emission intensity. Possible physical process of stress evolution and the model of In fluctuation in the subsequent red QW are discussed. This study provides a useful reference for the development of InGaN-based red emission materials and devices.

Do standardization of the procedure reduce measurement variability of the sonographic anterior drawer test of the ankle?

BACKGROUND: In quantitative ankle stress sonography, different examiners use different techniques, which may cause measurement variability. This study aimed to clarify whether standardizing stress sonography techniques reduces variability in the quantitative measurement of anterior talofibular ligament length change. METHODS: Fourteen examiners with a mean ultrasound experience of 8.7 years participated in this study. Each examiner performed stress ultrasonography of the ankle using their preferred method on one patient with an intact anterior talofibular ligament (Patient 1) and on two patients with chronic ankle instability (Patient 2 and 3). Changes in the ligament length between the resting and stressed positions were determined. A consensus meeting was then conducted to standardize the sonographic technique, which was used by the examiners during a repeat stress sonography on the same patients. The variance and measured values were compared between the preferred and standardized techniques using F-tests and paired t-tests, respectively. RESULTS: At a consensus meeting, a sonographic technique in which the examiner pushed the lower leg posteriorly against the fixed foot was adopted as the standardized technique. In Patient 1, the change in the anterior talofibular ligament length was 0.4 (range, -2.3-1.3) mm and 0.6 (-0.6-1.7) mm using the preferred and standardized techniques, respectively, with no significant difference in the variance (P = 0.51) or the measured value (P = 0.52). The length changes in Patient 2 were 2.0 (0.3-4.4) mm and 1.7 (-0.9-3.8) mm using the preferred and standardized techniques, respectively. In Patient 3, the length changes were 1.4 (-2.7-7.1) mm and 0.7 (-2.0-2.3) mm. There were no significant differences between the techniques in either patient group. CONCLUSION: Variability in the quantitative measurement of ankle stress sonography was not reduced despite the standardization of the technique among examiners. Hence, comparing the measured values between different examiners should be avoided.

Improved performance of InGaN-based red light-emitting diodes by micro-hole arrays.

This study demonstrates the performance improvements of InGaN-based red light-emitting diodes (LEDs) by fabricating micro-holes in the planar mesa. The peak wavelengths of the micro-hole LEDs (MHLEDs) exhibited a blue-shift of around 3 nm compared to the planar LEDs (PLEDs) at the same current density. The lowest full width at half maximum of MHLEDs was 59 nm, which is slightly less than that of the PLEDs. The light output power and external quantum efficiency of the MHLED with a wavelength of 634 nm at 20 mA were 0.6 mW and 1.5%, which are 8.5% higher than those of the PLED.

Photoluminescence of InGaN-based red multiple quantum wells.

Optical properties of InGaN-based red LED structure, with a blue pre-well, are reported. Two emission peaks located at 445.1 nm (PB) and 617.9 nm (PR) are observed in the PL spectrum, which are induced by a low-In-content blue InGaN single quantum well (SQW) and the red InGaN double quantum wells (DQWs), respectively. The peak shift of PB with increase of excitation energy is very small, which reflects the built-in electric field of PB-related InGaN single QW is remarkably decreased, being attributed to the significant reduction of residual stress in the LED structure. On the other hand, the PR peak showed a larger shift with increase of excitation energy, due to both the screening of built-in electric field and the band filling effect. The electric field in the red wells is caused by the large lattice mismatch between high-In-content red-emitting InGaN and surrounding GaN. In addition, the anomalous temperature dependences of the PR peak are well elucidated by assuming that the red emission comes from quasi-QD structures with deep localized states. The deep localization suppresses efficiently the escape of carriers and then enhances the emission in the red, leading to high internal quantum efficiency (IQE) of 24.03%.

Investigation of InGaN-based red/green micro-light-emitting diodes.

We investigated the performance of InGaN-based red/green micro-light-emitting diodes (µLEDs) ranging from 98×98µm2 to 17×17µm2. The average forward voltage at 10A/cm2 was independent of the dimension of µLEDs. Red µLEDs exhibited a larger blueshift of the peak wavelength (∼35nm) and broader full-width at half maximum (≥50nm) at 2-50A/cm2 compared to green µLEDs. We demonstrated that 47×47µm2 red µLEDs had an on-wafer external quantum efficiency of 0.36% at the peak wavelength of 626 nm, close to the red primary color defined in the recommendation 2020 standard.

Ultra-small InGaN green micro-light-emitting diodes fabricated by selective passivation of p-GaN.

Here, we proposed fabricating ultra-small InGaN-based micro-light-emitting diodes (µLEDs). The selective p-GaN areas were intentionally passivated using a H2 plasma treatment and served as the electrical isolation regions to prevent the current from injecting into the InGaN quantum wells below. Three kinds of green µLEDs, two squircle shapes with widths of 5 and 4 µm and one circular shape with a diameter of 2.7 µm, were successfully realized. The current-voltage characteristics indicate that the series resistance and the turn-on voltage increase as the dimension of the µLED decreases. This originates from the diffusion of the hydrogen atoms into the unexpected conductive p-GaN area. The light output power density and the calculated external quantum efficiency of the µLEDs from a 5-µm-squircle to a 2.7-µm-circle were enhanced by 10-20% when compared to 98×98µm2 µLEDs that were fabricated using mesa etching.

Loss measurement of each mode in few-mode fiber links with crosstalk-inducing points based on optical time domain reflectometry.

We propose a novel technique based on optical time domain reflectometry for characterizing the losses of transmission modes along few-mode fiber links. The technique estimates the transfer matrix at a crosstalk-inducing point from the measured backscattered waveforms and then eliminates the crosstalk influence of the point on the waveforms. Waveforms that are free from the crosstalk influence enable us to obtain the true losses independently of the crosstalk-inducing point. A proof-of-concept demonstration is performed on an optical fiber with a crosstalk-inducing splice and a bend, and the results show the usefulness of the proposed technique.

Enhanced performance of N-polar AlGaN-based deep-ultraviolet light-emitting diodes.

We numerically investigated the performance of N-polar AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) with different Al contents in quantum wells (QWs) and barriers. We found that N-polar structures could improve the maximum internal quantum efficiency (IQE) and suppress the efficiency droop, especially for deep-UV LEDs. Compared to metal-polar LEDs, N-polar ones retained higher IQE values even when the acceptor concentrations in the p-layers were one order of magnitude lower. The enhanced performance originated from the higher injection efficiencies of N-polar structures in terms of efficient carrier injection into QWs and suppressed electron overflow at high current densities.

Optimal ITO transparent conductive layers for InGaN-based amber/red light-emitting diodes.

Fabrication of indium tin oxide (ITO) was optimized for InGaN-based amber/red light-emitting diodes (LEDs). A radiofrequency sputtering reduced the sheet resistivity of ITO at low pressures, and a subsequent two-step annealing resulted in a low sheet resistivity (below 2×10-4 Ωcm) and high transmittance (over 98%) in the amber and red regions between 590 nm to 780 nm. Double ITO layers by sputtering could form an excellent ohmic contact with p-GaN. Application of the double ITO layers on amber and red LEDs enhanced light output power by 15.6% and 13.0%, respectively, compared to those using ITO by e-beam evaporation.

Simultaneous mode-by-mode impulse response measurement of multi-mode optical systems based on linear optical sampling.

Linear optical sampling is presented as a useful method to characterize mode-by-mode impulse responses or the spectral transfer matrix of multimode optical systems. In a two non-degenerate linear-polarization (LP) mode transmission line, which actually supported six independent spatial modes, 6 × 6 spectral transfer functions were simultaneously measured using multiplexed mode-by-mode impulse responses in series. According to the singular value analysis of the matrix, the mode-dependent loss spectrum was analyzed over a frequency bandwidth of several hundred GHz, which was determined by the spectra of the probe and reference pulses. The technique would be useful for characterizing various multi-spatial-mode fiber systems that are intensively being developed to overcome the limit in capacity of single-mode optical fibers.

Acutely induced cell mortality in the unicellular green alga Chlamydomonas reinhardtii (Chlorophyceae) following exposure to acrylic resin nanoparticles.

Nanoparticles have unique properties that make them attractive for use in industrial and medical technology industries but can also be harmful to living organisms, making an understanding of their molecular mechanisms of action essential. We examined the effect of three different sized poly(isobutyl-cyanoacrylate) nanoparticles (iBCA-NPs) on the unicellular green alga Chlamydomonas reinhardtii. We found that exposure to iBCA-NPs immediately caused C. reinhardtii to display abnormal swimming behaviors. Furthermore, after one hour, most of the cells had stopped swimming and 10%-30% of cells were stained with trypan blue, suggesting that these cells had severely impaired plasma membranes. Observation of the cyto-ultrastructure showed that the cell walls had been severely damaged and that many iBCA-NPs were located in the space between the cell wall and plasma membrane, as well as inside the cytosol in some cases. A comparison of three strains of C. reinhardtii with different cell wall conditions further showed that the cell mortality ratio increased more rapidly in the absence of a cell wall. Interestingly, cell mortality over time was essentially identical regardless of iBCA-NP size if the total surface area was the same. Furthermore, direct observation of the trails of iBCA-NPs indicated that the first trigger was their contact with the cell wall, which is most likely accompanied by the inactivation or removal of adsorbed proteins from the cell wall surface. Cell mortality was accompanied by the overproduction of reactive oxygen species, which was detected more readily in cells grown under constant light rather than in the dark.

Distributed spatial mode dispersion measurement along strongly coupled multicore fibers based on the correlation analysis of Rayleigh backscattering amplitudes.

We describe a method for measuring spatial mode dispersion (SMD) distribution along a strongly coupled multicore fiber (SC-MCF). The SMD has been defined for characterizing an SC-MCF, and it changes with respect to local fiber bending and twisting. However, conventional measurement methods characterize only the overall SMD, and cannot identify fiber portions where the environmental conditions affect the SMD. This paper demonstrates distributed SMD measurement along an SC-MCF by auto-correlating Rayleigh backscattering amplitudes obtained with coherent optical reflectometry. We confirm our method experimentally, and distinguish the difference between the SMD growth along twisted and non-twisted fiber sections in concatenated SC-MCFs.

Long-range measurement of Rayleigh scatter signature beyond laser coherence length based on coherent optical frequency domain reflectometry.

Long-range C-OFDR measurement of fiber Rayleigh scatter signature is described. The Rayleigh scatter signature, which is an interference pattern of backscatters from the random refractive indices in fibers, is known to be applicable to fiber identification and temperature or strain sensing by measuring its repeatability and its spectral shift. However, these applications have not been realized at ranges beyond the laser coherence length since laser phase noise degrades its repeatability. This paper proposes and demonstrates a method for analyzing the optical power spectrum of local Rayleigh backscatter to overcome the limitation imposed by laser phase noise. The measurable range and spatial performance are also investigated experimentally with respect to the remaining phase noise and noise reduction by signal averaging with the proposed method. The feasibility of Rayleigh scatter signature measurement for long-range applications is confirmed.

Advancing high-performance visible light communication with long-wavelength InGaN-based micro-LEDs.

This study showcases a method for achieving high-performance yellow and red micro-LEDs through precise control of indium content within quantum wells. By employing a hybrid quantum well structure with our six core technologies, we can accomplish outstanding external quantum efficiency (EQE) and robust stripe bandwidth. The resulting 30 µm × 8 micro-LED arrays exhibit maximum EQE values of 11.56% and 5.47% for yellow and red variants, respectively. Notably, the yellow micro-LED arrays achieve data rates exceeding 1 Gbit/s for non-return-to-zero on-off keying (NRZ-OOK) format and 1.5 Gbit/s for orthogonal frequency-division multiplexing (OFDM) format. These findings underscore the significant potential of long-wavelength InGaN-based micro-LEDs, positioning them as highly promising candidates for both full-color microdisplays and visible light communication applications.

Ten-Gram-Scale Total Synthesis of the Anticancer Drug Candidate E7130 to Supply Clinical Trials.

E7130 is a novel drug candidate with an exceedingly complex chemical structure of the halichondrin class, discovered by a total synthesis approach through joint research between the Kishi group at Harvard University and Eisai. Only 18 months after completion of the initial milligram-scale synthesis, ten-gram-scale synthesis of E7130 was achieved, providing the first good manufacturing practice (GMP) batch to supply clinical trials. This paper highlights the challenges in developing ten-gram-scale synthesis from the milligram-scale synthesis.

Dynamic TWDM-PON for mobile radio access networks.

In recent years, the diffusion of mobile terminals has brought about an explosive increase in communication traffic of mobile RANs. The number of radio base stations and optical fiber lines between them is becoming larger. For this reason, we studied effective optical network technologies for mobile RANs and propose the use of TWDM-PON as a means of enabling RANs to be operated flexibly and have wideband communication capability. We confirmed the feasibility of TWDM-PON for this application by numerical simulation. The results show that TWDM-PON can accommodate the bandwidth more than TDM-PON and completely eliminate unused bandwidth in TDM-PON.

Towards the quantification of the chemical mechanism of light-driven water splitting on GaN photoelectrodes.

We present results from a study addressing the unbiased water-splitting process and its side reactions on GaN-based photoelectrodes decorated with NiOx, FeOx, and CoOx nanoparticles. Observations involving physicochemical analyses of liquid and vapour phases after the experiments were performed in 1 M NaOH under ambient conditions. A water-splitting process with GaN-based photoelectrodes results in the generation of hydrogen gas and hydrogen peroxide. Quantification of the water-splitting chemical mechanism gave numerical values indicating an increase in the device performance and restriction of the GaN electrocorrosion with surface modifications of GaN structures. The hydrogen generation efficiencies are ηH2(bare GaN) = 1.23%, ηH2(NiOx/GaN) = 4.31%, ηH2(FeOx/GaN) = 2.69%, and ηH2(CoOx/GaN) = 2.31%. The photoelectrode etching reaction moieties Qetch/Q are 11.5%. 0.21%, 0.26% and 0.20% for bare GaN, NiOx/GaN, FeOx/GaN, and CoOx/GaN, respectively.

The efficacy of right ventricular pacing for symptomatic left mid-ventricular obstruction.

The serial changes in intraventricular pressure gradient in the left ventricle and NYHA functional classification in each case. Both the left intraventricular pressure gradient and symptoms improved after right ventricular pacing. In one case, the left intraventricular pressure gradient disappeared immediately after right ventricular pacing, while in the others it disappeared during the chronic phase, more than a year later.

Investigation of N-polar InGaN growth on misoriented ScAlMgO4 substrates.

We report the growth of N-polar InGaN layers on misoriented ScAlMgO4 (SAM) substrates with offset of 0.3 to 5.8° toward the m-plane. The surface of N-polar InGaN with small-offset substrates exhibited hexagonal hillocks similar to those commonly observed in N-polar GaN layers. Larger misorientation angles resulted in smoother surfaces of the InGaN layers. In contrast, the crystalline quality of InGaN indicated an opposite trend with significantly improved quality observed at smaller misorientation angles. We obtained an unprecedented crystalline quality of N-polar InGaN using SAM substrates with a 0.5° offset, which exhibited a [Formula: see text] X-ray rocking curve full width at half maximum value of 223 arcsec. The crystalline quality and surface morphology of InGaN were significantly influenced by the step surface of substrates according to atomic force microscopy observations.