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Frequencies have been the most accurately measured physical quantity since the second was defined in 1967 based on the microwave atomic transition of a Cs atom. Recently, atomic clocks using optical frequency transitions have shown an order of magnitude better accuracy than microwave clocks. Thanks to their high accuracy and resolution, atomic clocks have become a new tool for investigations involving fundamental science and technology, such as the search for dark matter, gravitational wave detection, the temporal variation of fundamental constants, relativistic geodesy, quantum metrology, and the advanced Global Navigation Satellite System (GNSS). In addition, a redefinition of the second based on the optical frequency is expected. In this paper, we review the principles and applications of optical clocks.

The silicon surface texture significantly affects the current density and efficiency of perovskite/silicon tandem solar cells. However, only a few studies have explored fabricating perovskite on textured silicon and the effect of texture on perovskite films because of the limitations of solution processes. Here we produce conformal perovskite on textured silicon with a dry two-step conversion process that incorporates lead oxide sputtering and direct contact with methyl ammonium iodide. To separately analyze the influence of each texture structure on perovskite films, patterned texture, high-resolution photoluminescence (μ-PL), and light beam-induced current (μ-LBIC), 3D mapping is used. This work elucidates conformal perovskite on textured surfaces and shows the effects of textured silicon on the perovskite layers with high-resolution 3D mapping. This approach can potentially be applied to any type of layer on any type of substrate. The efficiency of perovskite/silicon tandem solar cells is affected by silicon surface texture, however fabrication processes in solution limit surface studies. Here a perovskite layer on textured silicon is formed through a dry two-step conversion process with lead oxide sputtering and direct contact with methyl ammonium iodide.

For the management of rotating machines, machine learning (ML) has been researched with the use of feature parameters that have physical and statistical meanings of vibration signals. Genetic algorithm (GA) and principal component analysis (PCA) are the algorithms used for the selection or extraction process of the features; equipment condition. This study proposes a new method to maximize the advantages of the extraction and selection algorithms, thereby improving the fault classification performance. The proposed method is estimated in a variety of equipment conditions by selecting and extracting the effective features for status classification. To evaluate the performance of the fault classification through feature selection and extraction of the ML, a comparative analysis with the proposed method and the original method is also performed. With Lab-scale gearbox, several types of fault tests are conducted, and seven different fault types of equipment conditions, including the normal status, are simulated. The results of the experiments show that, the performance of classification of GA for feature selection is 85%, while PCA for feature extraction is 53%. The performance result of the proposed method for fault classification is 95%, meaning that the performance of fault diagnosis is more efficient in terms of discriminative learning than the original method. Therefore, the proposed method with feature extraction and selection algorithm can improve the fault classification performance by 10% and more for fault diagnosis through ML.

The angle-variable tunable optical filter was strictly fabricated by two strategies of nanoimprint-coupled metal nanopatterning with improved cost-effectiveness and accessibility. The tunable optical properties and the performances of two strategies were experimentally examined and turned out to be well matched to numerical results. Tunable properties are obtained by three factors: size of fabricated Ag nanodisks, incident illumination angle, and fabrication strategies. The resonant extinction peak shifts were identified to show a large increase along with the increase in fabricated Ag disk size and increase in the incidence angle of illumination. When comparing a fabrication strategy, it was confirmed that the sample fabricated by the strip-off method has better stability on color changes with a consistent dependency on the incident angle. The presented strategies of fabrication are technically viable for obtaining well-defined plasmonic nanostructures so that it has the feasibility to apply for fascinating optical applications including display or tunable optical filters.

Radio frequency (RF) magnetron-sputtered TiO2 (RS-TiO2) is investigated as a hole-blocking layer for perovskite solar cells. RS-TiO2 shows conformal, dense, and efficiently electron transferable pr...

This paper investigates the correlation between the random lasing properties of organic waveguides made by poly-(9-9dioctylfluorene) (PFO) thin films and the morphology of wrinkled corrugated substrates. The capability to individually control the wrinkle wavelength, shape, and height allows us to separately investigate their role on the sample emission properties. We demonstrate that the main parameter determining the presence of coherent random lasing is the substrate roughness and that, contrary to what could be qualitatively expected, as the roughness increases, coherent random lasing is progressively reduced. Coherent random lasing is observed only for a substrate roughness below 33 nm, while higher roughness leads to amplified spontaneous emission (up to 70 nm) or to the absence of light amplification in the film (above 70 nm). We demonstrate that this result is due to a progressive reduction of the light amplification efficiency in the PFO film, evidencing that coherent random lasing can be obtained only with a right interplay between light amplification and scattering. Besides clarifying the basic aspects of random lasing in organic waveguides, our work opens the way to the realization of organic random lasers with predictable emission properties, thanks to the high control level of the scattering properties of the wrinkled corrugated surfaces.

Correction to: Communications Chemistry https://doi.org/10.1038/s42004-020-0283-4, published online 25 March 2020. The original version of this Article incorrectly designated Yoonmook Kang as a corresponding author and listed their e-mail address in error. This has now been corrected in the PDF and HTML versions of the Article.

We demonstrate a fiber delay line-based direct comb-line stabilization with 6X10-15 frequency instability within 1 s. Two combs could be simultaneously stabilized to a single fiber delay-line with ~1-Hz relative linewidth and ~20-Hz absolute linewidth.

Recently, the need for rapid, reliable, and low-cost drug susceptibility testing (DST) methods has increased due to the emergence of multidrug-resistant Mycobacterium tuberculosis. Colorimetric methods of DST provide results more quickly than standard culture methods and are inexpensive than molecular methods. Thus, colorimetric methods, such as the nitrate reductase assay (NRA), are being recommended. We searched Medline PubMed for reports on the NRA for DST of M. tuberculosis written in English and published within the last five years. We selected 20 reports on six major anti-TB drugs and conducted a meta-analysis using Meta-Disc software. The pooled sensitivities for isoniazid, rifampicin, streptomycin, ethambutol, ofloxacin, and kanamycin were 95.4%, 96.4%, 91.5%, 93.1%, 99.3%, and 88.4%, and the pooled specificities were 98.5%, 99.2%, 92.9%, 97.8%, 97.4%, and 99.4%, respectively. The area under the summary receiver operator curve for all drugs was 0.9723-0.9952. The time to results (TTR) for the direct and indirect NRAs was 7-28days and 6-15days, respectively. Quality assessments were conducted using the quality of diagnostic accuracy studies tool (QUADAS-2) items, and most reports showed good performance. However, ethambutol, streptomycin, and kanamycin showed relatively low sensitivity. We performed a quantitative NRA in liquid media at various inoculum concentrations. The TTR at 4.94×106, 1.67×104, and 2.27×102CFU/mL was 4, 14, and 14days, respectively. The minimum absorbance and nitrite concentration for positive samples were 0.8 and 168μM, respectively. We propose a quantitative standard to determine sample positivity to address the problems with the current standard NRA which is much less expensive than the conventional assay conducted on solid medium.

Nanostructured surfaces with quasi-random geometries can manipulate light over broadband wavelengths and wide ranges of angles. Optimization and realization of stochastic patterns have typically relied on serial, direct-write fabrication methods combined with real-space design. However, this approach is not suitable for customizable features or scalable nanomanufacturing. Moreover, trial-and-error processing cannot guarantee fabrication feasibility because processing-structure relations are not included in conventional designs. Here, we report wrinkle lithography integrated with concurrent design to produce quasi-random nanostructures in amorphous silicon at wafer scales that achieved over 160% light absorption enhancement from 800 to 1,200 nm. The quasi-periodicity of patterns, materials filling ratio, and feature depths could be independently controlled. We statistically represented the quasi-random patterns by Fourier spectral density functions (SDFs) that could bridge the processing-structure and structure-performance relations. Iterative search of the optimal structure via the SDF representation enabled concurrent design of nanostructures and processing.

Precise prediction of the antigens that bind to major histocompatibility complex (MHC) molecules is one of the most important steps for many immune response-related studies including identification of neoantigen capable of recognizing cancer cells for the implementation of personalized immunotherapy as well as vaccine/therapeutic protein development. To overcome the limitations of the limited prediction performance of the existing models, we developed a new convolutional neural network (CNN)-based epitope prediction model by incorporating new features including protein sequence vectors (Prot2Vec), chemical and structural characteristics of an epitope and MHC molecule. Our new model is optimized to achieve better prediction performance than the conventional methods when validated with a benchmark dataset from the Immune Epitope Database (IEDB). Along with the new prediction model, we also developed a web-based framework, called Kepre, to provide interfaces to our novel CNN-based epitope prediction functionalities. Kepre provides a user-friendly and automated interface for epitope prediction. Upon the researcher's submission of a sequence of interest, Kepre predicts the binding probability between the sequence and each type of the MHC molecules. Kepre runs the prediction analysis on high-throughput computing infrastructure and provides the prediction results in a user-interactable GUI and also in a pdf formatted report file.

This paper provides a novel best in the domain automatic classifier of sleep stages based on wrist photoplethysmography and 3D-accelerometer data obtained from smartwatches. The sleep is classified into rapid-eye-movement (REM), Light, Deep, or Wake stages. State of the art classifiers based on wearable sensors suffer from motion artifacts and apnea events. Proposed novel techniques of artifacts and apnea events elimination result in the high accuracy of sleep stages classification and robustness to apnea events. The model provides the Cohen's Kappa score of 0.65 and accuracy of 0.80 on 254 night-logs of 173 subjects with a broad distribution of apnea-hypopnea index until 90. The approach is applicable to unobtrusive sleep monitoring by wearables.

This paper proposes a novel automatic classifier of rapid-eye-movement (REM), non-rapid-eye-movement (NREM, combined light and deep sleep stages (SS)), and wake stages based on wrist photoplethysmography and wrist 3-axis accelerometer data. The quality and robustness of the classifier are achieved by a multilevel learning framework, which consists of features extraction, preprocessing, signal treatment, machine learning, and post-processing modules. Subjectspecific Z-score normalization and exponential smoothing are applied to reduce intra-subject and inter-subject variability. The novel features are based on heart rate variability and motion statistics. Leave-one-subject-out cross-validation technique is applied to estimate the quality of the model. Our solution, based on linear discriminant analysis (LDA), shows the Cohen’s Kappa coefficient of 0.58 and accuracy of 77 % for the four class (wake, REM, light, deep) classification problem and Cohen’s Kappa coefficient of 0.67 and accuracy of 85 % for the three class (wake, REM, NREM) classification problem. Comparison of different ML algorithms, like LDA, support vector machines, and random forest is done. The obtained results of sleep stages classification exceed the analogous state of the art solutions.

Fabricating perovskite on textured silicon surface is important for maximizing current density and the power conversion efficiency (PCE) of perovskite/silicon tandem solar cells. However, producing conformal perovskite on textured silicon surface is difficult because most of high efficiency perovskite solar cells have been produced by solution based process. Herein, we investigated possibility of producing perovskite solar cells on textured silicon surface by dry two-step conversion process and analyzing them with periodically patterned texture and photoluminescence mapping. Thickness scale difference between perovskite and silicon substrate have induced focusing problems.

International audience; There is an increasing demand for precise molecular spectroscopy, in particular in the mid-infrared fingerprint window that hosts a considerable number of vibrational signatures, whether it be for modeling our atmosphere, interpreting astrophysical spectra or testing fundamental physics. We present a high-resolution mid-infrared spectrometer traceable to primary frequency standards. It combines a widely tunable ultra-narrow Quantum Cascade Laser (QCL), an optical frequency comb and a compact multipass cell. The QCL frequency is stabilized onto a comb controlled with a remote near-infrared ultra-stable laser, transferred through a fiber link. The resulting QCL frequency stability is below 10-15 from 0.1 to 10s and its frequency uncertainty of 4×10-14 is given by the remote frequency standards. Continuous tuning over ~400 MHz is reported. We use the apparatus to perform saturated absorption spectroscopy of methanol in the low-pressure multipass cell and demonstrate a statistical uncertainty at the kHz level on transition center frequencies, confirming its potential for driving the next generation technology required for precise spectroscopic measurements.

A new clock laser system using an optical cavity with $4.8 \times 10^-17$ thermal noise limit has been developed for rapid evaluation of ytterbium lattice clocks. This was realized by using a 30-cm-long ULE cavity, fused-silica mirror substrates, and crystalline mirror coatings. The frequency stability of the beating signal between the new clock laser and the old clock laser was limited by the latter. The linewidth and the frequency stability of the new clock laser will be measured by comparing the frequency between two similar systems.

A telecommunication optical fiber can stabilize the comb-line frequencies of ultrashort pulse lasers to the quadrillionth level., Frequency-stabilized optical frequency combs have created many high-precision applications. Accurate timing, ultralow phase noise, and narrow linewidth are prerequisites for achieving the ultimate performance of comb-based systems. Ultrastable cavity-based comb-noise stabilization methods have enabled sub–10−15-level frequency instability. However, these methods are complex and alignment sensitive, and their use has been mostly confined to advanced metrology laboratories. Here, we have established a simple, compact, alignment-free, and potentially low-cost all-fiber photonics-based stabilization method for generating multiple ultrastable combs. The achieved performance includes 1-femtosecond timing jitter, few times 10−15-level frequency instability, and

An experimental method is developed for the robust frequency stabilization using a high-finesse cavity when the laser exhibits large intermittent frequency jumps. This is accomplished by applying an additional slow feedback signal from Doppler-free fluorescence spectroscopy in an atomic beam with increased frequency locking range. As a result, a stable and narrow-linewidth 556 nm laser maintains the frequency lock status for more than a week, and contributes to more accurate evaluation of the Yb optical lattice clock. In addition, the reference optical cavity is supported at vibration-insensitive points without any vibration isolation table, making the laser setup more simple and compact., Comment: 7 pages, 6 figures

We are stabilizing the frequency of a mid-infrared quantum cascade lasers (QCLs) to an optical frequency comb itself stabilized to an ultra-stable near-infrared reference signal at $\pmb{1.5\mu} \mathbf{m}$ transferred from SYRTE to LPL using an optical link. The reference stability is copied to the QCL and we benefit from the traceability to the primary standards of SYRTE. The stabilized QCL can be scanned by scanning the near-IR reference with an electro-optic modulator. We use this ultrastable spectrometer to carry out saturated absorption spectroscopy of methanol. A detailed analysis of the frequency measurement uncertainty will be presented.

This paper reports a robust and stretchable nanolaser platform that can preserve its high mode quality by exploiting hybrid quadrupole plasmons as an optical feedback mechanism. Increasing the size of metal nanoparticles in an array can introduce ultrasharp lattice plasmon resonances with out-of-plane charge oscillations that are tolerant to lateral strain. By patterning these nanoparticles onto an elastomeric slab surrounded by liquid gain, we realized reversible, tunable nanolasing with high strain sensitivity and no hysteresis. Our semiquantum modeling demonstrates that lasing build-up occurs at the hybrid quadrupole electromagnetic hot spots, which provides a route toward mechanical modulation of light-matter interactions on the nanoscale.

A high-speed reduction transfer case is usually employed by an excavator, wheel loader, or bulldozer. When powerful torque is required in the case of climbing steep roads or towing heavy equipment, the high-speed reduction mode of the gearbox is used. Generally, a transfer case using a spur gear type with a speed reduction system has a speed reduction ratio of 1 to 1 or 2 to 1. However, the structure of a transfer case achieved at a high speed of 1 to 1 and a low speed of 4.5 or under 5.5 to 1 with the speed reduction by use of a planetary gear type with a speed reduction system was proposed in this study. By employing a planetary gear type with a speed reduction system, the compact structure of the transfer case was achieved, and the impact or the partial defect of gear teeth was eliminated.

In this paper, as a previous step of software development, through an analysis step in the basic design process of the FPSO crane, ERD, which could help develop common understanding between its developer and the user, was introduced. From the flowchart of the design process, the overall work flow in its development was understood. Then, after the design process of the crane was divided into many entities, the attributes of each entity were defined and the relationships between the entities were established, followed by ERD creation through the use of IDEF1X notation. The results of the analysis can be readily understood even by users who lack of software knowledge, and then their change requirements can be immediately reflected in the developed system that requires modification.

We present a hybrid fiber link to realize the local two-way optical frequency comparison with self-synchronization. It enables us to detect round-trip fiber noise and one-way fiber noise, and estimate the residuals. Moreover, we can check, to the best of our knowledge for the first time, the reciprocity of the accumulated noise forth and back over a bi-directional fiber, and also evaluate the noise correlation between two adjacent fibers with the hybrid setup.

We design and develop a new clock laser system for the second Yb optical lattice clock (OLC) at KRISS with the targeted uncertainty of 10−18 level. With a longer ULE cavity, the fused silica substrates, and the crystalline mirror coatings, the overall thermal limit is expected to be 4.3×10−17. The rapid evaluation of the systematic uncertainties of the second OLC will be possible with this new clock laser system.

We present a frequency comb-assisted experimental setup which enables us to both coherently transfer the stability and accuracy of a remote near-infrared (NIR) ultrastable laser to a mid-infrared (MIR) quantum cascade laser (QCL), and widely tune the QCL frequency for spectroscopic applications. The QCL is stabilized at the level of 2×10−15 from 1 to 100 s, with an accuracy of 10−14 after 100 s. The achievable frequency tuning paves the way for high-resolution saturated absorption spectroscopy of molecular transitions, in particular in spectral regions that were previously inaccessible with standard stabilized MIR lasers. Preliminary results show a sensitivity at the kHz level on transition center frequencies.

Recent technological advances have increased interest in personal health monitoring. Electrocardio-gram(ECG) monitoring is a basic healthcare activity and can provide decisive information regarding cardiovascularsystem status. In this study, we developed a capacitive ECG measurement system that can be included within a clothmattress pad. The device permits ECG data to be obtained during sleep by using capacitive electrodes. However,it is difficult to detect R-wave peaks automatically because signals obtained from the system can include a high levelof noise from various sources. Because R-peak detection is important in ECG applications, we developed an algorithmthat can reduce noise and improve detection accuracy under noisy conditions. Algorithm reliability was evaluated bydetermining its sensitivity(Se), positive predictivity(+P), and error rate(Er) by using data from the MIT-BIH Poly-somnographic Database and from our capacitive ECG system. The results showed that Se = 99.75%, +P = 99.77%,and Er = 0.47% for MIT-BIH Polysomnographic Database while Se = 96.47%, +P = 99.32%, and Er = 4.34% forour capacitive ECG system. Based on those results, we conclude that our R-peak detection method is capable of pro-viding useful ECG information, even under noisy signal conditions.Key words: Capacitively Measured ECG, R-peak Detection, Ubiquitous Healthcare, Non-intrusive ECG MonitoringSystem, MIT-BIH Polysomnographic Database

The current status of an Yb optical lattice clock at the Korea Research Institute of Standards and Science (KRISS) is reported. The systematic uncertainty of the Yb clock in the first accuracy evaluation was 1.5 × 10−14 [Park et al., Metrologia 50, 119 (2013)]. The uncertainty was dominated by the large uncertainties in the lattice ac Stark shift and the collisional shift, which were mainly limited by the large linewidth and jitter of the clock laser. Recently, a highly stable clock laser at 578 nm was developed with a short-term linewidth of 3.5 Hz and a frequency jitter of about 25 Hz at 1 s and 10 s measurement times, respectively. The long-term frequency drift showed only a linear dependence on time, confirming that the temperature of the super-cavity was maintained a zero coefficient of thermal expansion. The frequency of the lattice laser at 759 nm was phase locked to the optical frequency comb and could be stabilized at the “absolute” frequency of the “magic wavelength”, to within a 1-MHz uncertainty. This improvement greatly reduced the fractional uncertainty due to the lattice ac Stark shift down to 2 × 10−16. The systematic uncertainty of the clock is currently 5.3 × 10−15 and is dominated by the collisional frequency shift.

Plasmonic nanostructures with enhanced localized optical fields as well as narrow linewidths have driven advances in numerous applications. However, the active engineering of ultranarrow resonances across the visible regime-and within a single system-has not yet been demonstrated. This paper describes how aluminum nanoparticle arrays embedded in an elastomeric slab may exhibit high-quality resonances with linewidths as narrow as 3 nm at wavelengths not accessible by conventional plasmonic materials. We exploited stretching to improve and tune simultaneously the optical response of as-fabricated nanoparticle arrays by shifting the diffraction mode relative to single-particle dipolar or quadrupolar resonances. This dynamic modulation of particle-particle spacing enabled either dipolar or quadrupolar lattice modes to be selectively accessed and individually optimized. Programmable plasmon modes offer a robust way to achieve real-time tunable materials for plasmon-enhanced molecular sensing and plasmonic nanolasers and opens new possibilities for integrating with flexible electronics.

In this paper we report on the implementation and stability analysis of a drift-compensated frequency synthesizer from a cryogenic sapphire oscillator (CSO) designed for a Cs/Rb atomic fountain clock. The synthesizer has two microwave outputs of 7 GHz and 9 GHz for Rb and Cs atom interrogation, respectively. The short-term stability of these microwave signals, measured using an optical frequency comb locked to an ultra-stable laser, is better than $5\times10^{-15}$ at an averaging time of 1 s. We demonstrate that the short-term stability of the synthesizer is lower than the quantum projection noise limit of the Cs fountain clock, KRISS-F1(Cs) by measuring the short-term stability of the fountain with varying trapped atom number. The stability of the fountain at 1-s averaging time reaches $2.5\times10^{-14}$ at the highest atom number in the experiment when the synthesizer is used as an interrogation oscillator of the fountain. In order to compensate the frequency drift of the CSO, the output frequency of a waveform generator in the synthesis chain is ramped linearly. By doing this, the stability of the synthesizer at an average time of one hour reaches a level of $10^{-16}$ which is measured with the fountain clock., 8 pages, 6 figures

This paper introduces an atomic gravimeter under development at KRISS for precise measurement of gravitational acceleration. The gravimeter based on atom interferometer uses two counter-propagating Raman lasers of π/2-π-π/2 pulse sequence and laser cooled 87Rb atoms in free fall. Atomic interference fringes caused by Raman lasers were observed at various time intervals between the three Raman pulses. The frequency sweep rate α which compensates Doppler shift due to gravitational acceleration g was obtained from the interference fringes. In the presentation, the current status and recent results of the KRISS atomic gravimeter will be discussed.

Purpose: Provision of accurate temperature measurement is an essential element to ensure a precise control in greenhouse environment. This study was organized to compare the effects of six solar radiation shields with different shapes for temperature measurement and find the most appropriate shield for greenhouse environment. Methods: A fan-aspirated radiation shield was designed and manufactured. Using the fan-aspirated radiation shield and five other shapes i.e., the cup shape, horizontal pipe, vertical pipe, parallel boards and commercial shields, temperature measurement was conducted over the lawn surface as well as greenhouse indoor environment. The measurement height varied at 0.5, 1.0 and 1.5 m from the floor. Results: The measured temperatures by the fan-aspirated radiation shield were 1.30-1.49℃ lower than the values recorded by other different-shaped shields at 1.5 m of measurement height. As the measurement height decreases, observed differences between measured temperatures of the fan-aspirated radiation shield and other shields demonstrate a declining trend. However, at low measurement heights, the radiation emitted from the bottom surface would be the source of error in temperature measurement. Conclusions: The fan-aspirated radiation shield is a required tool for exact measurement of air temperature in greenhouse temperature control.

Purpose: Utilizing air thermal energy during over-heated time in the greenhouse is a necessary component to save greenhouse heating costs for nighttime. However, there is no practical way to implement the related principles. Methods: In this study, a heating and cooling system which utilizes the surplus air thermal energy in a greenhouse was developed. Available air thermal energy and heating load for this experimental glasshouse were estimated based on temperature conditions of the plant growth and weather data. Results: Estimated values were 400 MJ/day for maximum surplus air thermal energy and 340 MJ/day for maximum heating energy which were target values of the design as well. The system consists of a heat pump, fan-coil units and heat storage tanks which are divided into low and high temperature tanks. Moreover, a new control logic was developed for surplus air thermal energy utilization. Conclusions: This paper explains the details of conceptual design process of the system. Results of test operations showed that the developed system performed the recovery and supply of the thermal energy according to design purposes.

We analyzed frequency-domain characteristics of a femtosecond laser whose carrier-envelope phase (CEP) was stabilized by the direct locking method (DLM). To evaluate the CEP-stabilized laser with zero carrier-envelope-offset frequency (f ceo), as imposed by DLM, a self-referencing f-to-2f interferometer with a shifted frequency comb by an acousto-optic modulator was employed in an out-of-loop. The measurement of the square root of triangle variance confirmed that DLM is a phase-locking method. The tight locking was verified from a narrow bandwidth of f ceo, measured using the out-of-loop interferometer, and from a small frequency jitter measured with a frequency counter referenced to a Rb-clock. The femtosecond laser with CEP stabilized by DLM is, thus, well suited for applications in the frequency domain as well as in the time domain.

This paper presents a novel green laser sequential lateral solidification G-SLS process for AMOLED applications. G-SLS utilizes a high frequency pulsed green laser and 2D mask patterns to manipulate the microstructure of crystallize Si films. Mask patterns have been optimized to obtain uniform microstructure of the crystallized Si films at the overlap region. Thin film transistors based on G-SLS processed Si films have mobility of 150.72 cm2/V-sec and a sub-threshold swing of 0.20V/dec. 14″ qFHD AMOLEDs have been fabricated using the G-SLS process. The advantages and issues of G-SLS technology will be further discussed.

For the first time, photo sensors employing p-type Si and IGZO semiconductor (P-I-OS) have been fabricated with a sensor dimension of W/L = 1600/5. The IGZO layer was deposited using DC sputtering and replaces the conventional n+-doped cathode electrode. The P-I-OS photo sensor is more sensitive to light with shorter wavelengths, and high to low photo-current dynamic range is almost constant from −15V to −2.5V of anode bias. The P-I-OS photo sensor exhibits dynamic range of 53.3 dB under −5V of anode bias and 10,000 lx of illuminated light intensity

A fiber-phase-noise compensating system was constructed for a 1.4 GHz reference frequency transferred through a 13-km-long fiber spool. The transfer instability was dependent on the temperature variation of the compensating system. With the room temperature variation stabilized within 0.3℃, the transfer instability was 4.6×10

Sum frequency generation was utilized to obtain a yellow laser with the wavelength of 578.4 nm for a probe laser of an Yb lattice clock. The output of an Nd:YAG laser with wavelength of 1319 nm and that of an Yb-fiber laser with wavelength of 1030 nm were passed through a waveguided periodically-poled lithium niobate (WG-PPLN) for sum frequency generation. It is required that the probe laser has a linewidth of the order of 1 Hz to fully resolve the Yb lattice clock transition. Thus, the linewidth of the probe laser was reduced by stabilizing the frequency to a super-cavity. This was made of ULE with a low thermal expansion coefficient, and was mounted on an active vibration-isolation table at the optimal point for the reduced sensitivity to vibration. Also, this was installed in a vacuum chamber, and the temperature was stabilized to 1 mK level. This system was installed in an acoustic enclosure to block acoustic noise. The finesse of the super-cavity was measured to be 380 000 from the photon life time of the cavity.

The aligned liquid crystals (LCs) display on SiNx thin films using ion-beam (IB) irradiation was studied with controllability of pretilt angle depending on incident energies of the IB. The LCs alignment property for the SiNx thin films were observed to verify the practical application potential. A good LCs alignment of vertical alignment LCs cells on SiNx thin film surfaces irradiated with incident IB energy of 1800eV was achieved. The atomic force microscopy (AFM) images of LCs on SiNx thin film surfaces irradiated with IB energy was used for the surface analysis.

We studied liquid crystal (LCs) alignment effects on homogeneous polyimide (PI) surfaces induced by polarised UV (PUV) exposure and rubbing in different directions. We found that the LC orientation is not affected by PUV exposure times of less than 90 min after rubbing, and that PUV exposure times over 90 min after rubbing resulted in LC orientations that were more closely aligned with the direction of PUV exposure than the direction of rubbing. Short-term PUV exposure affects the variation of the pretilt angle of the PI and LC. In addition, as PUV exposure time increases, it can convert the LC alignment direction from the rubbing direction to the PUV direction.

We investigated the electrical properties of polycrystalline silicon (poly-Si) thin film transistors (TFTs) employing field-enhanced solid phase crystallization (FESPC). An n+ amorphous silicon (n+ a-Si) layer was deposited to improve the contact resistance between the active Si and source/drain (S/D) metal instead of ion doping. By using C–V measurement method, we could explain the diffused phosphorous ions (P+ ions) on the channel surface caused a negatively shifted threshold voltage (VTH) of −7.81 V at a drain bias of 0.1 V, and stretched out a subthreshold swing (S) of 1.698 V/dec. This process was almost compatible with the widely used hydrogenated amorphous silicon (a-Si:H) TFT fabrication process and also offers a better uniformity when compared to the conventional laser-crystallized poly-Si TFT process because of non-laser crystallization.

A new method for fabricating large-area well-aligned ZnMgO nanowire arrays, using radio frequency (RF) magnetron co-sputtering, is reported. ZnO nanowire arrays, prepared by metal organic chemical vapor deposition (MOCVD), were used as seed layers for ZnMgO nanowires. For the fabrication of ZnMgO nanowires, RF powers and sputtering pressure were varied to control the supersaturation condition and the kinetic energies of the sputtered materials. Vertically aligned ZnMgO nanowires with [0 0 0 1] preferred orientation were obtained at a working pressure of 20 × 10−3 Torr, RF power of 50 W and 15 W for ZnO and Mg targets, respectively. Crystallinity of the nanostructures were improved with rapid thermal annealing (RTA) at 900 °C. Furthermore, the blue shift in the near-band-edge emission of RTA-treated ZnMgO nanowires was observed during photoluminescence study.

We fabricate a low noise erbium-doped fiber ring laser that can be continuously tuned over 102 nm by insertion of the fiber Fabry–Perot tunable filter (FFP-TF) in the ring cavity with a novel cavity structure and the optimal gain medium length. As an application of this fiber ring laser, we performed the absorption spectroscopy of acetylene (13C2H2) and hydrogen cyanide (H13C14N) and measure the absorption spectra of more than 50 transition lines of these gases with an excellent signal to noise ratio (SNR). The pressure broadening coefficients of four acetylene transition lines are obtained using this fiber ring laser and an external cavity laser diode.

A new low power consumption amorphous silicon (a-Si:H) TFT level shifter is designed and verified by SPICE simulation. The a-Si:H TFT level shifter employing cascade inverters successfully shifts low voltage (5 V) to high voltage (23 V) by employing a bootstrapping method. Proposed a-Si:H TFT level shifter has considerably reduced the power consumption by 50% compared with the conventional one (8.03 mW) due to connection of clock pulse on the diode connected node and bootstrapping method. The proposed level shifter may be suitable for mobile display applications.

Highly stable voltage programmed a-Si:H TFT pixel circuit for AMOLED, which employs both Vth-compensation and negative bias annealing, is proposed and fabricated. Experimental results, after 60 hours electrical stress at elevated temperature (60°C) show that the OLED current stability in the proposed pixel is considerably improved compared with a conventional 2-TFT pixel, Vth-compensated pixel, and negative bias annealed pixel, respectively. The proposed pixel can reduce the degradation of a-Si:H TFT by employing negative bias annealing store Vth of a-Si:H TFT so that highly stable and uniform a-Si:H TFT backplane for AMOLED. Our proposed pixel may be suitable for highly stable AMOLED employing the a-Si:H TFT.

In order to establish the national frequency standards for the Korea Research Institute of Standards and Science in the 1.5-mum region, we have developed an acetylene-stabilized laser diode locked to the P(16) transition of 13C2H2. We then measured its absolute frequency using an optical-frequency comb based on a mode-locked Ti:sapphire laser whose repetition frequency and carrier-envelope offset frequency were phase locked to an H-maser. The measured absolute frequency of the laser diode locked to the P(16) transition of 13C2H2 was 194 369 569 386.0 kHz, with an uncertainty of 0.3 kHz, based on the measurements of a single system. Including the contribution of the residual offset, the uncertainty was 1.9 kHz

International audience; We theoretically and experimentally investigate relevant noise processes arising in optical fiber links, which fundamentally limit their relative stability. We derive the unsuppressed delay noise for three configurations of optical links: two-way method, Sagnac interferometry, and actively compensated link, respectively designed for frequency comparison, rotation sensing, and frequency transfer. We also consider an alternative two-way setup allowing real-time frequency comparison and demonstrate its effectiveness on a proof-of-principle experiment with a 25-km fiber spool. For these three configurations, we analyze the noise arising from uncommon fiber paths in the interferometric ensemble and design optimized interferometers. We demonstrate interferometers with very low temperature sensitivity of respectively -2.2, -0.03 and 1 fs/K. We use one of these optimized interferometers on a long haul compensated fiber link of 540 km. We obtain a relative frequency stability of 3x10^-20 after 10,000 s of integration time.

An L-shaped dual-gate device structure, which reduces kink current in polycrystalline silicon thin-film transistors (poly-Si TFTs), has been proposed and fabricated. In the proposed device, the poly-Si TFTs have a lateral grain growth in channels such as TFTs fabricated by sequential lateral solidification (SLS) or CW laser crystallization. The current flow of dual TFTs is strongly affected by grain boundaries showing lateral grain growth. The L-shaped dual gate structure is employed for asymmetry between dual channels. One of the channels is located in a parallel direction of grain growth and the other is located vertically. It is verified by experiment that the proposed L-shaped dual-gate TFT reduced the kink current of poly-Si TFT and showed improved reliability by fixed current flow in the saturation mode.

We have observed the nonlinear magneto-optic effect(NMOE) based on atomic coherence in Rb D-line using the Rb vapor cell containing 50 Torr of Ne. The width of the NMOE signal was measured to be 2464 Hz, when the peak-to-peak B-field variation was 1 mGauss. The result of this work may be applied to a high-sensitivity magnetometer.