Nanophotonic Materials and Devices |
| Prof. Hiroaki Misawa | Research Institute for Electronic Science, Hokkaido University | Title and Abstract |
Title： Insight into modal strong coupling and its application to photochemical reactions Abstract： Plasmon-induced hot electron transfer has attracted much attention as a novel strategy for the solar energy conversions. However, the solar energy conversion efficiency is limited by the insufficient absorption on monolayer of metallic nanoparticles. To solve this problem, in the present study, we apply the principle of strong coupling to plasmonic water splitting induced by the plasmon-excited electron transferring into wide-bandgap semiconductor on a Au nanoparticle (Au-NP)/TiO2 thin-film/Au-film (ATA) photoanode. Strong coupling between the Fabry–Pérot nanocavity mode of the TiO2 thin-film/Au-film and the localized surface plasmon mode of the Au-NPs is induced when their resonant frequencies overlap. To increase the coupling strength in this strong coupling regime, a key feature is partially inlaying of Au-NPs into the TiO2 nanocavity by several nanometers. Under a three-electrode system measurement with a saturated calomel electrode (SCE) as a reference electrode, a Pt wire as a counter electrode and an electrolyte of KOH (0.1 mol/dm3), we demonstrated that the action spectrum of incident photon to current conversion efficiency (IPCE) exhibited two bands, which almost corresponds to the absorption spectrum of ATA. The IPCE of ATA is extraordinarily enhanced as compared to that of Au-NPs/TiO2 photoanode. Most importantly, under the strong coupling regime, the internal quantum efficiency (IQE) of the photocurrent generation is also enhanced at the strong coupling wavelengths. The increase in IQE implies the possibility of increasing the generation of hot electrons due to the strong coupling. The plasmon-induced water splitting using a two-electrode system is also discussed. |
Prof. Yuichiro K. Kato | Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics | Title and Abstract |
Title： Single-carbon-nanotube photonics and optoelectronics Abstract： Single-walled carbon nanotubes have unique optical properties as a result of their one-dimensional structure. Reduced screening leads to large exciton binding energies which allow for room-temperature excitonic luminescence, while enhanced interactions give rise to a variety of exciton processes that may be utilized for modulating the emission properties. Furthermore, their luminescence is in the telecom-wavelengths and they can be directly synthesized on silicon substrates, providing new opportunities for nanoscale quantum photonics and optoelectronics.
Here we discuss the use of individual single-walled carbon nanotubes for generation and manipulation of photons on a chip. Strong exciton-exciton annihilation process leads to antibunching at room temperature [1], while specially designed air-mode photonic crystal cavities allow for efficient coupling to nanotube emission [2]. By utilizing dopant states, single photon emission can be enhanced by silicon microcavities [3]. Gate control over carrier density can be used to produce optical pulse trains [4] and to form p-n junctions for electroluminescence [5]. The extreme sensitivity to surface adsorbed molecules gives rise to optical bistability, which can be utilized for all-optical memory operations [6]. Ultimately, these results may be combined to achieve further control over photons at the nanoscale. Work partially supported by JSPS (KAKENHI JP16H05962), MIC (SCOPE 191503001), and MEXT (Nanotechnology Platform). [1] A. Ishii, T. Uda, Y. K. Kato, Phys. Rev. Applied 8, 054039 (2017).
[2] R. Miura, S. Imamura, R. Ohta, A. Ishii, X. Liu, T. Shimada, S. Iwamoto, Y. Arakawa, Y. K. Kato, Nature Commun. 5, 5580 (2014).
[3] A. Ishii, X. He, N. F. Hartmann, H. Machiya, H. Htoon, S. Doorn, Y. K. Kato, Nano Lett. 18, 3873 (2018).
[4] M. Jiang, Y. Kumamoto, A. Ishii, M. Yoshida, T. Shimada, Y. K. Kato, Nature Commun. 6, 6335 (2015).
[5] N. Higashide, M. Yoshida, T. Uda, A. Ishii, Y. K. Kato, Appl. Phys. Lett. 110, 191101 (2017).
[6] T. Uda, A. Ishii, Y. K. Kato, ACS Photonics 5, 559 (2018). |
Prof. Milton Feng | Electrical and Computer Engineering,University of Illinois | Title and Abstract |
Title： Direct Intra-Cavity Tunneling Modulation in Semiconductor Laser for Energy Efficient High-Speed Data Transmission Abstract： Direct current modulated VCSELs for high-speed optical link have been widely deployed in large-scale data centers due to its energy-efficient data transmission. However, the modulation speed is limited by the e-h recombination lifetime (~ 200 ps) and bandwidth (~ 30 GHz) @ room temperature. The transistor laser invented by Feng and Holonyak (2004) overcomes the slow lifetimes of diode lasers by placing the quantum-wells in the highly p-doped base for fast e-h lifetimes toward (~ 10 ps). In addition, the laser cavity can provide intracavity photon-assisted tunneling in the collector junction of transistor which opens the new possibility to directly modulate the laser optical output with voltage bias. The ultrafast tunneling process on the order of femtoseconds (~ 10 fs) makes it possible to significantly improve the laser direct modulation speed (> 100 GHz) beyond the recombination lifetime restriction. |
Optical Waveguides and Communications |
Prof. San-Liang Lee | Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology | Title and Abstract |
Title： Photonic Integrated Circuits for Optical Networking and Sensing Abstract： Photonic integrated circuits (PICs), more specifically PICs on InP and Silicon platforms, are becoming the enabling technologies for many applications because of their ultra-large bandwidth, high metrology resolution, and wavelength-sensitive characteristics for optical/biomedical sensing in addition to their well-known advantages of compactness, low power consumption, and low cost. The applications are wide-spreading to optical interconnect and networking for data centers, next-generation mobile X-hauls, as well as long-distance transmission, and various sensing applications of which the LiDAR and biomedical ones are very promising with large market volumes. In this talk, we will overview some of the key technologies for PICs and describe some results for optical networking and sensing. The PIC devices and circuits that will be addressed include the multi-wavelength/wavelength agile laser sources based on InP or hybrid platforms, the optical spectral processing circuits like optical inter-leavers and wavelength de-multiplexers, and the optical sensing circuits including the design of optical phase arrays for LIDAR applications. |
Prof. Sivasubramanian Arunagiri | Vellore Institute of Technology (VIT) | Title and Abstract |
Title： Modelling and analysis of high-performance silicon PIN phase shifter Abstract： High data rate transmission with low loss is required to meet current network demands. Silicon photonics is capable of meeting the demand with low cost and miniaturized footprint, due to fabrication using advanced Complementary Metal-Oxide-Semiconductor (CMOS) technologies. Significance of phase shifter in silicon photonics is highlighted in Mach-Zehnder or Ring resonator Modulators. Different types of charge carrier movement techniques are being adopted in phase shifters such as carrier injection, depletion, accumulation etc., to produce the modulation of the optical beam.
Carrier depletion type modulators are widely studied because of their high-speed operation and simple fabrication process but are plagued by high insertion loss restricting its commercial applications. Doping concentration and the geometry of the phase shifter determines the performance of the modulator. The modulation efficiency of SiPh modulators is defined by the phase shift (π) at low voltage. This can be achieved by increasing the carrier concentration. With the increase in carrier concentration, the capacitance increases along with the insertion loss. The rise in electron-hole carrier concentration improves the effective index change at the cost of insertion loss. Varying the dopant pattern also improve the capacitance and reduce the Vπ at the cost of insertion loss. Different approaches have been proposed by altering the PN junction geometry such as vertical PN junction, horizontal, lateral, interleaved, etc., and are analyzed in literature with different doping concentrations. The vertical PIN junction with high dopants increased the absorption loss which affects the usage of the phase shifters for high data rate. The optical loss is reduced by reducing the dopant exposure region but at the expense of VπLπ. Interleaved junction increases the capacitance per unit length as the additional PN junctions are formed along the length of the phase shifter. But with the increase in carriers, the absorption loss also increased. The junction area was increased in a vertical PN junction which led to a reduction in VπLπ but as the volume of the carrier concentration increased, the loss is increased with it. A U shaped junction was introduced to make better effective index change at low voltage but due to the large presence of carriers, the loss increased. In order to reduce the loss, LN was used which led to the usage of the phase shifter for a higher bit rate but at the expense of the driving voltage. Modulation efficiency of the phase shifter is based on the overlap between the carrier concentration region and the optical path, whereas the modulation speed is restricted by the amount of charges depleted. An intrinsic layer reduces the carriers in the optical path. Thus intrinsic region in a PIN junction plays a major role in determining the performance of the phase shifter. Phase shifters are being designed to obtain modulation at high speed, low loss, low VπLπ and high ER, to have commercial application. The different designs aim to reduce the loss and to obtain lower VπLπ for higher bit rates with the selection of optimum intrinsic gap. |
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Quantum Electronics and Laser Technology |
Prof. Ole Steuernagel | School of Physics, Astronomy and Mathematics, University of Hertfordshire ,UK | Title and Abstract |
Title： A geometric view of dynamics in quantum phase space Abstract： Classical phase space dynamics is governed by a continuity equation. The same is true for quantum dynamics in phase space: Wigner's quantum phase space current, J, governs the evolution of Wigner's phase space distribution W. Unlike the classical case, W is typically negative in some regions. These negative regions represent quantum coherences. Also, the current's velocity field is ill-defined. It is singular when W = 0.
I show that this implies that there are no trajectories in quantum phase space. With these velocity singularities Liouvillian phase space volumes feature singular changes too. I will show that this is necessary in order for quantum dynamics to create coherences. This is worth knowing particularly for numerical investigations. Stationary points of J are important for both, classical and quantum dynamics, maybe even more so in the quantum case, since the dynamics can move and split or merge these stagnation points. But the existence of stagnation points is constrained by a topological conservation law which quantum mechanics has to obey (see Figure on next page). While velocity fields and trajectories are ill-defined in quantum phase space, I show that the current J is always well behaved. It can be studied, providing new insights, and it can be numerically integrated to study the dynamics. One may wonder how quantum dynamics suppresses the formation of very fine detail in phase space over long evolution times? It turns out that Wigner's current J is 'viscous'. I describe the mechanism that lies behind this observation. This 'viscosity' induces a characteristic polarisation pattern in quantum phase space that quantifies quantum dynamics' detail suppression. Used as a measure, it singles out special states: Wigner current can be used as a sensitive probe. 
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Prof. Dao-Hong Song | School of Physics, Nankai University, Tianjin, China | Title and Abstract |
Title： Dirac-like photonic lattices: from pseudospin to topology Abstract： Photonic lattices have provided a powerful platform to emulate Dirac physics while discovering new phenomena that would otherwise be inaccessible in natural 2D materials. In this talk, I will present some of our recent work based on photonic graphene and Lieb lattices, including pseudospin-mediated vortex generation, valley Bloch oscillations and Landau-Zener tunneling, and unusual flatband states. I will then focus on discussing pseudospin-orbit angular momentum conversion and universal momentum-to-real-space mapping of topological singularities arising from the interplay of pseudospin, orbital angular momentum of light, and the Berry phase. |
Prof. Yuki Inoue | National Central University | Title and Abstract |
Title： Opening of a new era of gravitational wave physics with KAGRA Large-scale Cryogenic interferometer Abstract： The recent observations of gravitational waves by the LIGO and Virgo collaboration have made a impact on physics and astronomy dramatically. A world wide observation with global gravitational wave network will be expected to play a significant role in the unknown of the sources with the follow-up observational telescopes. KAGRA is a new-type Gravitational wave dual-recycling Fabry-Perot interferometer with 3-km baseline arm. To reduce the thermal noise and seismic noise, KAGRA employs the cryogenic and underground technologies. KAGRA will join the worldwide observation 3 to detect the first event in Asia. Taiwan has contributed the development and characterization of KAGRA for the calibration and analytical study. Taiwan is also planning the future upgrade of KAGRA and trying the R&D study of the high power laser and squeezing technology. These technologies will be essential technologies of future KAGRA. In my talk, we would like to explain the currant status of KAGRA and contribution from Taiwan. |
Holography and Information Processing |
Prof. Jun Tanida | Department of Information and Physical Sciences
Graduate School of Information Science and Technology
Osaka University | Title and Abstract |
Title： Machine-learning-based Optical Sensing and Imaging Technology Abstract： Machine learning is a powerful tool to explore relations and knowledge hidden in a bunch of data. Not only object recognition but also more general problems can be achieved by machine learning and deep neural networks. Our group developed effective methods for extending the capabilities of a machine-learning-based framework in optical sensing and imaging through scattering media. Recently, the application targets are enlarged to include other fields of optical technologies. They are super-resolution in diffractive imaging, hologram generation without iterative calculation, and wavefront sensing by a single intensity image. In this presentation, the property and performance of these techniques are presented and the future perspectives will be discussed. |
Prof. Nikolay Petrov | Photonics and Optical Information Technologies, ITMO University | Title and Abstract |
Title： Ultrafast time-resolved digital holography for linear and nonlinear optical processes Abstract： Materials with high optical nonlinear properties are in demand in various appli-cations in optics and photonics. The creation of promising new materials requires new and advanced highly sensitive techniques for measuring nonlinear responses. This talk will address these issues from the perspective of a holographic approach that provides information on the spatial distribution of phase delay. Our recent developments in this eld will be presented, pro- viding the ability to conduct dynamic measurements in a wide temporal range. Prospects for the further development of these techniques regarding the possibilities of measuring local nonlinear responses will be highlighted. |
Prof. Wei-Hung Su | Department of Materials and Optoelectronic Science, National Sun Yat-Sen University | Title and Abstract |
Title： Measurements for Coefficients of Thermal Expansion using Fringe Projection Techniques Abstract： A measurement system embedded into a microscope for coefficients of thermal expansion is presented. Only one-shot measurement is required. The full-field property makes it possible to inspect several objects at the same time. |
Optical Engineering |
| Prof. Pin Han | Graduate Institute of Precision Engineering,National Chung-Hsing University | Title and Abstract |
Title： Spatial-Spectral correspondence relationship and its applications Abstract： The meaning and the importance of the spatial/spectral correspondence relationship for mono/polychromatic light diffraction are introduced first. Then the newest applications of it are presented, including Fresnel Zone Spectra, Talbot Spectra, and more. In the former, it is shown that a Fresnel zone plate can be used as a dynamical filter for polychromatic light; in the later the Talbot spectra are found for a periodic grating in near field, which are the original form of its incident polychromatic spectra, without any influences of the grating diffraction. This is contrasted with the famous Talbot images of monochromatic light case. Some other possibilities are included and discussed. |
Dr. Tatsuro Otaki | Optical Research Laboratory, Research & Development Division, Nikon Corporation | Title and Abstract |
Title： Optical Design and Biomedical Applications of Apodized Phase Contrast Microscopy Abstract： Microscopic observation of unstained living cells is important for biomedical applications. Cells are typically phase objects. Conventional phase-contrast microscopes operate well for observing phase objects, but large phase-object images lose detailed structures because of halo artifacts. Other than for thin specimens, they are often used for finding or checking cultured cells. We developed apodized phase-contrast microscopy to reduce the halos when imaging fine anatomical structures. A relationship exists between the angle of diffraction and phase difference of objects in cells. Apodized phase-contrast microscopy uses an apodized phase plate placed on the Fourier transform plane in the objective lens, which both weakens the diffracted light produced by large objects to lower their relative image contrast and increases the contrast of small objects. The apodized phase plate provides a kind of optical filtering. As a result, one can observe fine structures by apodized phase-contrast microscopy. The optical design and biomedical applications of apodized phase-contrast microscopy will be discussed. |
| Dr. Kenneth Tai | Photonics Industry & Technology Development Association(PIDA) | Title and Abstract |
Title： X on Silicon(CMOS) & Digital Optics Abstract： This presentation provides a comprehensive prospect on the future of photonics industries, with the evolutional perspective of semiconductor industry. In the “Post Moore Law Era”, one of the championed developments is heterogeneous integration, i.e., integrating silicon chips with other materials and devices, including Micro LED, MICRO-OLED, Micro-Mirror, Silicon Photonics, LCoS, ..etc. Heterogeneous integration is also referred as X-on-Silicon (CMOS), using silicon chips as the controlling substrate that is based on the available and affordable semiconductor technologies. Among these developments, LCoS plays a critical role in triggering the coming age of “Digital Optics”. Digital Optics is meant to program the incident light much like digital signal, to easily control and modulate light’s path, amplitude, and phase. A lens can be emulated by a large number of LC pixels, which is scalable and programmable to optimize the effects of diffraction to realize CGH and FFT. Naturally, software and algorithm will play a more important role in digital optics. Digital optics will open a door for various applications, reflecting the note by UNESCO, “Light-based technology is a major economic driver with the potential to revolutionize the 21st century”. |
Biophotonics and Biomedical Imaging |
| Prof. Hideharu Mikami | Department of Chemistry,School of Science, The University of Tokyo | Title and Abstract |
Title： Intelligent image-activated cell sorting Abstract： A fundamental challenge of biology is to understand the large heterogeneity of cells even with identical genomes. The differences in composition, structure, and morphology of cells are strongly linked with their physiological functions such as proliferation, metabolism, secretion, differentiation, and signal transduction and an important aspect of cell identity. To comprehend such cell-to-cell differences, a new technology is needed to rapidly search through and sort out cells with unique chemical and morphological features from large heterogeneous cell populations. To this end, we have developed an intelligent image-activated cell sorter (iIACS) [Nitta et al., Cell 175, 266 (2018)], which integrates a high-speed fluorescence microscope [Mikami et al., Optica 5, 117 (2018)], a real-time image processor including a deep neural network, and a high-throughput cell sorter. The iIACS enables image-based cell sorting at an unprecedentedly high throughput of 100 cells/sec, allowing for exploration of the heterogeneity of cells on a large scale. Here, we present overviews of the iIACS and the high-speed fluorescence microscope as a key component of the iIACS. |
| Prof. Toshiharu Saiki | Department of Electronics and Electrical Engineering, Keio University | Title and Abstract |
Title： Computing and swarm intelligence with light-driven colloidal particles Abstract： We attempt to implement ant pheromone algorithm to find the shortest path between their nest and food using pheromone trails. We used polystyrene beads (PBs) suspended in water as agent ants and employed a phase-change material (PCM) film to mimic the pheromone behavior. The interaction between PBs and the PCM film provides pheromone deposition, enhancement and tracking of pheromone trail, and pheromone evaporation. We also discuss a new approach for physical implementation of spin glass algorithm based on microfluidic interaction of PBs, which are suspended in water and confined between two parallel PCM plates. PBs form a colloidal crystalline structure by applying a lateral fluidic pressure. We observe dynamic behavior of the buckled phase mimicking a frustrated spin system. We can visualize the annealing process to find the global minimum configuration of PBs by gradually changing the lateral pressure. |
| Prof. Jennifer Barton | Biomedical Engineering, The University of Arizona | Title and Abstract |
Title： Multi-Modality Optical Imaging Salpingoscope for Early Cancer Detection Abstract： Advanced optical imaging techniques such as fluorescence imaging (FI), optical coherence tomography (OCT), and multiphoton microscopy (MPM) can be used for early detection of cancer in a miniature endoscopic system. We have developed a tri-modality 3.5 mm diameter endoscope with a single optical channel, plus channels for saline or fluorescent dye introduction, and biopsy forceps. The forward scanning illumination system consists of a quartered piezoelectric tube scanning a dual-clad single mode fiber. The core of the fiber carries visible illumination, OCT, and MPM excitation light. A telescope-like triplet lens and objective contain internal dichroic coatings such that the visible light is relayed to the tissue in a low numerical aperture (NA) broad field of view system, whereas the near-infrared OCT and MPM are relayed as high NA microscopy systems. Remitted light is collected in the fiber core (OCT), inner cladding (MPM), and separate multimode fibers (visible reflectance/FI). Predicted and actual optical performance will be presented. barton@email.arizona.edu |
| Prof. Peter Tze Chin So | Mechanical Engineering and Biological Engineering, Massachusetts Institute of Technology | Title and Abstract |
Title： High Throughput, Wide-Field Multiphoton Microscopy For Deep Structural Imaging of Neuronal Synapse Remodeling Abstract： Neuron structural remodeling is closely related to mammalian memory plasticity. Many pioneering studies in this field were enabled by point scanning multiphoton microscopy. In vivo, high resolution 3D imaging of the whole dendritic tree requires about 30 minutes. Significant remodeling on the synaptic level has been observed within a day but we hypothesize that there are important faster dynamics to be explored. To access events on the time scale of minutes to hours, we are developing high throughput wide-field multiphoton microscopy based on temporal focusing. While this method has been developed for over a decade, it has been limited by having modest penetration in tissues due to scattering of excitation and emission photons. We will explore several approaches to overcome this limitation including three-photon excitation and coupling structured illumination with computation image recovery. |
| Prof. Vincent Daria | Eccles Institute of Neuroscience & Research School of Physics, Australian National University, Australia | Title and Abstract |
Title： Using light to decode the computing power of single cortical neurons Abstract： The challenge to decode the computing power of the brain brings our focus down to single brain cells or neurons. Specifically, we aim to identify the roles of the neuron’s dendrites in the processing of synaptic inputs, which eventually leads the neuron to fire an output. Such processing is key to understanding how different neurons function as fundamental computing components of brain circuits. To achieve this aim, we study single neurons from rat brains using a custom-built two-photon laser microscope that incorporates a holographic projector. Apart from using the microscope to image the neurons and their 3D dendritic morphology, the inclusion of a holographic projector transforms an incident laser into multiple foci, which are spatially distributed in 3D. The hologram is programmable so we can position the different foci anywhere around the neuron. We can use each focus to trigger a synaptic input or as an optical probe to record the activity of the neuron. To artificially trigger synaptic inputs, a focal stimulation represents a synaptic input via two-photon photolysis of caged neurotransmitters. On the other hand, the laser focus can also be used to record neuronal activity by exciting calcium indicators to emit fluorescence. Neuronal activity changes the calcium concentration inside the cell, which in turn changes the emitted fluorescence as a function of time. Using these techniques, we have identified a unique function of a specific set of dendrites that can play a role in the brain’s capacity to learn and memorize. We were able to observe unique properties that allow these dendrites to be more receptive to inputs whenever the neuron fires a series of action potentials. Understanding the functional role different dendrites of a neuron can provide bottom-up approach to decode the computing power of the brain. |
Display Technology |
| Prof. HYUN-SIK KIM | Korea Advanced Institute of Science and Technology (KAIST) | Title and Abstract |
Title： OLED Display Driving Technique with Real-Time Pixel Nonuniformity Compensation Abstract： AMOLED display is currently being a strong candidate for a high-quality mobile and TV markets because of its fast response time, wide viewing angle, and high contrast ratio. However, there are several obstacles that hinder AMOLED displays from penetration into consumer electronic markets. In conventional technologies in AMOLED, it is difficult to obtain a uniform image on an AMOLED display, because the OLED current, to which the amount of light emission in a pixel is proportional, is sensitive to the variation in the current-voltage (I-V) characteristic of a drive thin-film-transistor (TFT). Moreover, an OLED tends to degrade earlier than is appropriate for commercial requirements. The result is so-called image sticking (or burn-in), producing variations in brightness across the image, which reduces the lifetime of a display panel. Thus, there are still many technical challenges in driving OLED displays. In this talk, several approaches to overcome these challenges will be presented. Voltage programming method using VTH-sampling in TFT pixel could compensate for threshold voltage variation of drive TFTs, but lead to an increase of pixel complexity. Current programming method is able to compensate for both threshold and mobility variations of drive TFT, but suffered from long programming time in low gray level. In order to solve problems of conventional schemes, I will also introduce a new voltage-current hybrid display driving technique for real-time compensation of pixels’ non-uniformities. The proposed hybrid AMOLED display driver has advantages of both voltage and current driving methods irrespective of the TFT variations. The hybrid driver can also enable a real-time compensation by driving-while-sensing technique with innovative TFT pixel structure. In virtue of the new hybrid driving method, the users are not required to wait time for sensing electrical characteristics of driving TFTs. Furthermore, fast and cost-efficient sensing operation for compensation of OLED aging will be presented in the hybrid AMOLED driver. To reduce the complexity of the driver IC, the proposed hybrid driver reuses most of the driver circuitry and reconfigures them to be working as OLED sensor and A/D converter; hence, it can keep the AMOLED driver IC compact in spite of adding special functions for image sticking compensation. I will outline some possible research directions for further improving driver circuit for high-quality OLED displays. |
| Prof. Rumiko Yamaguchi | Department of Mathematical Science and Electrical-Electronic-Computer Engineering
Akita University | Title and Abstract |
Title： Thresholdless and Ultra-Low Drive Voltage in Liquid Crystals with Weak Anchoring Boundaries Abstract： Liquid crystal director distributions in hybrid aligned nematic cells with strong and weak polar anchoring boundaries are numerically analyzed. The cell can be changed to homogeneously or homeotropicly orientation by controlling the anchoring, which have no threshold voltage and driving voltage can be reduced less than 0.5 volt. |
| Prof. Chih-Jen Shih | Institute for Chemical and Bioengineering
Swiss Federal Institute of Technology in Zürich (ETH Zürich) | Title and Abstract |
Title： Perovskite Quantum Dot Light-Emitting Technology: Challenges and Opportunities Abstract： Perovskite quantum dots (QDs) are emerging as one of the most promising candidates for the monochromatic light-emitting diodes (LEDs) approaching the Rec. 2020 color gamut due to their extremely narrowband emission. Near-unity photoluminescence and emission directionality in the closed packed films make them promising for light-emitting applications. Considerable research efforts in chemistry, chemical engineering, solid-state physics and material sciences have been made in past years. Here we briefly summarize the opportunities and challenges in both fundamental and technological aspects, based on our recent work in this field. |
| Prof. Tsung-Hsien Lin | National Sun Yat-sen University | Title and Abstract |
Title： Lattice control of 3D Photonic Liquid Crystal Abstract： Blue phase (BP) liquid crystals (LC) are soft 3D photonic crystals with extraordinary tunability, electro-optic properties, as well as optical nonlinearities. While most techniques can only fabricate 3D photonic crystals that work in the infrared–microwave regime, the bandgaps of BPLCs are inherently located in the ultraviolet–visible–near infrared regime. Recently, we have succeeded in developing a gradient temperature scanning technique to grow such 3D photonic crystals into mm2–cm2 in areal size and submillimeter in thickness. These large BP single crystals are however limited to cubic lattice structures, namely body-centered cubic (in BPI) and simple cubic lattices (in BPII). It is known that non-cubic BPs can be induced by stretching a cubic lattice of either BPI or BPII with an electric field but will relax back to the cubic form if removing the applied field. In this research, we propose a method to fabricate non-cubic BPLCs with high stability in this absence of an applied field. The structures are further confirmed by reflective spectroscopy and Kössel diffraction patterns. We also propose a macroscopic model adapted from a soft matter mechanical model to correlate the crystal structure with fabrication parameters. |
Solid State Lighting |
| Prof. Kazuhiro Ohkawa | Department of Electrical Engineering, CEMSE
PI of Energy Conversion Devices and Materials (ECO Devices) Laboratory
King Abdullah University of Science and Technology (KAUST) | Title and Abstract |
Title： Red InGaN-LEDs Grown By Micro-Flow Channel MOVPE Abstract： The development of three primary colors (RGB) InGaN LEDs will be the key technology to realize monolithic full-color lighting and displays in the near future. We have developed micro-flow channel MOVPE that can grow high-In-content InGaN at raised temperatures of 60-100oC compared to conventional MOVPEs. Simulations of the micro-flow channel method show increases in the gas-phase concentrations of decomposed molecules from TMIn and NH3 precursors. Higher concentrations have made it possible to achieve the raised growth temperatures. Alternatively, more In-content InGaN layers were grown at specific temperatures. For example, a typical growth temperature of 600-nm InGaN LED structures is about 710oC, but we have achieved the temperature of 810oC for such InGaN by using the micro-flow channel MOVPE and the strain control. It was confirmed that the quantum efficiency of InGaN QWs by the micro-flow channel method is higher than that of InGaN by the conventional way in the longer wavelength region than green. A bare 620-nm InGaN LED grown by the micro-flow channel MOVPE exhibited 0.23 mW of output and 51 nm FWHM at 20 mA. More technologies will be discussed in the presentation. |
| Prof. Marek Osinski | The University of New Mexico | Title and Abstract |
Title： Cadmium-free high-temperature nanophosphors for solid-state lighting applications Abstract： High-efficiency cadmium-free white LEDs are desirable in solid-state lighting applications for optimal color rendering from the point of view of both human perception and energy efficiency. Our choice of Mn-doped ZnSe quantum dots (QDs) as nanophosphor material is driven by their cadmium-free composition, bright emission well above room temperature, and their peak excitation in the violet blue region. Using colloidal synthesis, ZnSe:Mn/ZnS QDs were synthesized, emitting at the 497 nm peak and the Mn related 587 nm peak. These QDs were shelled with ZnS to provide additional isolation of the ZnSe:Mn cores. We have observed quantum efficiency of Mn-related emission as high as 91%. |
| Prof. Shun-Wei Liu | Department of Electronic Engineering Mingchi University of Technology | Title and Abstract |
Title： Near-infrared organic imaging device with photon-to-photon upconversion efficiency of > 20% Abstract： The organic upconversion device (OUD), which consisted of the near-infrared (NIR) organic photodetector and transparent organic light-emitting device (OLED), has attracted attention for novel electronic imaging applications such as blood vessel mapping and machine vision. In my presentation, I would like to explain a working principle of our proposed OUD that enabled to detect a weak signal or specific object in a dark environment. Besides, such a device with a novel NIR absorption layer demonstrates an efficient upconversion at a forward bias of < 4 V and provides a green emission (515 nm) upon direct illumination (700-1000 nm). As a consequence, the optimal OUD exhibits a current gain as high as 400,000 (defined as the current density underexposed light divided by the dark current density), which is a crucial factor to improve the device’s imaging resolution of > 1000 dpi. However, I believe that further optimization of the NIR absorption layer or OLED could offer better performances over the result presented here and future perspectives will be discussed accordingly. |
| Prof. Ray Hua Horng | Department of Electric Engineering
Distinguished Professor, Institute of Electronics
National Chiao Tung University | Title and Abstract |
Title： Development of microLED light source for wearable physiological information measurement system Abstract： The talk is to introduce the developing self-generating wearable devices for home care, adding innovative features such as physical health, physiological information, and energy planning. First, how to successfully develop a small-size red light and infrared light flip-chip LED, and bonded it to a flexible substrate will be described. After the testing has a good photoelectric properties and light stability. Then, successfully developed a ragged quantum dot light source to enhance the brightness of green light to meet the conditions of an ideal wearable sensing light source, and successfully satisfy the measurement requirement. Third, the flexible solar cell has an output power of 8000 μW/cm2 under the outdoor lighting environment. In addition, the development of UV-enhanced solar batteries, in the LED lighting environment, the output power of 25 μW/cm2. Development of flip chip packaging technology for flexible substrates, integration of thin film solar cells, LEDs and sensors to verify the self-power supply of thin film solar cells to LEDs and sensors: Package area: 1cm X 2cm; Bonding method: Aluminum - Aluminum joints (area 200 μm2). Finally, we use the light source and self-powered system to successfully build and analyze the wearable system's blood oxygen test. The use of this non-invasive system can improve regenerative medicine to measure the blood oxygen in the affected human brain. The use of relevant medical training to match this system has successfully achieved clinically good results. Combined with light source and solar cells, it will be able to monitor and provide real-time information in conjunction with cloud-based technologies for health care related to non-delivery and related industries such as industrial process monitoring and optimization. Integrating the achievements of each sub-project will create a unique domestic self-generating wearable vascular physiological information measurement system for home care. We look forward to making the greatest contribution to the issues of an aging society. |
Photovoltaic Technology |
| Dr. Jay Lin | PV Guider Consultancy | Title and Abstract |
Title： PV Module Failures in the Field and Related Faults in the Factory Abstract： The production process of the PV module is simple but many details need to take care, any minor mistake can result in serious problem after installation. This presentation shows PV module failures in the field, and the related faults in the factory. With the experience, the module manufacturers are able to learn how the failures can be prevented in the production process. It is also helpful for the system owners to determine the root cause of the failures. |
| Prof. Chunlei Yang | Shenzhen Institutes of Advanced Technology, Information photonics and Energy Materials,
Chinese Academy of Sciences | Title and Abstract |
Title： Comparative study of the grain boundaries in CZTS and CIGS photovoltaic thin films using scanning probe microscopy Abstract： The efficiency of CZTS solar cells is still not so high compared with other thin films such as CIGS. The underlying mechanism for the difference is a long-standing question that has remained elusive [1] in spite of tremendous research efforts in the past. For polycrystalline thin film semiconductor, highly populated grain boundaries in the material will certainly have big influences on the photo-generated electron-holes. In this work, a conducting probe atomic force microscopy has been applied to study the electronic structure of CIGS and CZTS thin films with capability of nm-scale resolution. Different electronic structure of the grain-interior (GI) and grain boundary (GB) have been identified in both CIGS and CZTS thin films. We find that the band alignment between GI and GB in CIGS and CZTS is different, which can well explain the different device performance in two type of solar cells. With good Schottky contact between the AFM tip and semiconductor, a local electrical and photovoltaic performance can be measured and the conduction band and valance band offset between GB and neighboring GI can be obtained. In CIGS, we can clearly find that the conduction band bent downward for about 200 meV and the valence band bent downward for about 340 meV at the GB, which makes the GB and GI in CIGS to form a type-II structure [2] that benefits the electron-hole separation to give high photovoltaic performance. For CZTS, it is found that the conduction band bent downward, while the valence band bent upward which is in opposite to the case in CIGS. The GB and GI in CZTS behaves like a type-I hetero-structure that will trap both electron and hole inside the GB to produce strong recombination. Many experiments [3] had demonstrated that air annealing process can improve the CZTS device efficiency with increased open-circuit voltage and fill factor. Our experiments revealed that, after air annealing, the downward bending valence band of GB turned to be upward bending, while the conduction band of GB turned from downward bending to upward bending. This resulted in the formation of electron and hole barrier at GBs which reduced the recombination, which can well explain the increased efficiency. However, the air annealing induced GB states behaved as barriers which can block the transport of electron and holes. Better GB passivation techniques are still in need. |
| Prof. Fang-Chung Chen | Department of Photonics, National Chiao Tung University | Title and Abstract |
Title： Emerging Organic and Perovksite Photovoltaic Devices for Indoor Applications Abstract： Conventional photovoltaic devices, such as crystalline Si cells, exhibit poor efficiency under indoor or low level outdoor lighting. Many applications, however, require efficient, low cost light harvesting ability under dim-light conditions, e.g. wireless sensor nodes in home security and automation etc. Therefore, while Si panels dominate the solar panel market, there remains a need for developing of low-cost photovoltaic technology which can efficiently harvest photon energy under indoor or low-level lighting conditions. In this talk, we will present our recent progress on the development of organic and organic/inorganic hybrid perovskite solar cells especially for indoor applications. In particular, we have found that these photovoltaic devices exhibited extremely high performance under the indoor illumination conditions, thereby making them suitable for low-power indoor applications. Overall, PCE values higher than 20% are achievable under illumination of low-power indoor light sources. Further, assuming the radiative recombination would be the only loss mechanism, we calculated the Shockley–Queisser (SQ) limits using two representative indoor light sources (fluorescent tube and white light-emitting diodes). The details of the SQ limits and device characterization under illumination of indoor light sources will be described. Different methods for further enhancing the device performance, such as introduction of metal nanoparticles for triggering plasmonic effects upon illumination, will be also discussed. |
| Prof. Tzu-Chien Wei | Department of Chemical Engineering, National Tsing Hua University,Taiwan | Title and Abstract |
Title： Toward Clean Production of Plastic Perovskite Solar Cell Using Aqueous Lead Nitrate Precursor Abstract： Lightweight, plastic photovoltaic (PPV) devices are considered attractive renewable energy devices because they can be produced with high-throughput printing processes and they enable the usage of solar power on curved surfaces. Generally, the power conversion efficiency (PCE) of a PPV is lower than that of its rigid counterpart, primarily owing to the limitations of the low thermal budget of plastic substrates. Apart from this problems, its flexibility is, ironically, another reason that causes PCE low due to insufficient light capture from its thin absorbing layer. Perovskite solar cells (PSCs) comprising organometal halide perovskite absorber is considered a favourable candidate for plastic because of its unrivalled extinction coefficient, low exicton binding energy and low formation temperature. However, most published processes to deposit perovskite absorber involves the use of polar organic solvent such as DMF or DMSO, which is toxic and can not be vastly used in production scale. In past few years, we devoted ourselves in developing a low-toxic process to fabricate high PCE PSC using only water as the primary solvent. In this presentation, I would like to share the journey of our efforts in this protocol and our targets in near future. The conversion mechanism, morphology control and device engineering will be highlighted. Currently, we achieved highly efficient (16.5%) plastic PSC using Pb(NO3)2/water as the starting material to prepare organometal halide perovskite layer. |
Thin-Film Technology and Optical Engineering |
| Prof. L. Jay Guo | Department of Electrical Engineeringand Computer Science, University of Michigan, USA | Title and Abstract |
Title： Structural colors and transparent conductors enabled by thin film technology Abstract： Structural colors have shown great promise as an alternative for the existing colorant-based pigments owing to their noticeable advantages, such as high brightness, durability and stability, and environmental safety. They may find potential applications in energy-efficient displays, high-resolution imaging, special effect coatings, and building-integrated photovoltaics. The structural colors can be produced by exploiting optical resonances in various resonators, which can be either 3D, 2D or 1D structures. For such applications, large area patterning is highly desirable, which motivated the development high-throughput roll-to-roll nanoimprint (R2RNIL) technique, as well as other roll-based patterning processes. They can also be designed with layered structures, which can be easily made by additive deposition processes. A new type of flexible transparent conductor based on ultra-thin Ag film, which could find wide range of applications in flexible displays and touch screens, can be made in large area format by industrial roll sputtering processes. |
| Prof. Hsuen-Li Chen | Department of Materials Science and Engineering, National Taiwan University | Title and Abstract |
Title： Techniques of Optical Analysis for Nanomaterials and Structured Optoelectronic Devices Abstract： The optical anisotropy of graphene films could be used as an alternative quality factor for the rapid characterization of large-area graphene films prepared through chemical vapor deposition (CVD). We develop an angle-variable spectroscopic method to rapidly determine the optical anisotropy of graphene films. Unlike approaches using Raman scattering spectroscopy, this optical anisotropy method allows ready characterization of the structural quality of large-area graphene samples without the application of high-intensity laser irradiation or complicated optical setups. Measurements of optical anisotropy also allow us to distinguish graphene samples with different extent of structural imperfections; the results are consistent with those obtained from using Raman scattering spectroscopy. We also developed a reliable method to analyze the interference-enhanced Raman scattering (IERS) effect on graphene by considering the surface electric field (E-field), which can be calculated precisely by measuring the optical admittance of the thin-film assembly. Using this approach, we could enhance both the G and 2D bands of graphene largely, uniformly, and equally. Under certain conditions, the Raman peak of graphene could even be enhanced by over 400 times.We found that the Raman spectra of both SLG and FLG were enhanced without changing the band-to-band ratio or the peak positions of the main Raman bands of graphene. Without inducing any additional signal disturbance, this enhancement technique allowed us to maintain the accurate and precise informational features from the Raman spectra. Thus, by controlling only the surface E-field, the Raman signals of graphene could be enhanced dramatically without any distortion on spectra. We also propose the concept of deep–trench/thin–metal (DTTM) active antenna that take advantage of surface plasmon resonance phenomena, three–dimensional cavity effects, and large–area metal/semiconductor junctions to effectively generate and collect hot electrons arising from plasmon decay and, thereby, increase photocurrent. The DTTM–based devices exhibited superior photoelectron conversion ability and high degrees of detection linearity under infrared light of both low and high intensity. Therefore, these DTTM–based devices have the attractive properties of high responsivity, extremely low power consumption, and polarization–insensitive detection over a broad bandwidth, suggesting great potential for use in photodetection and on–chip Si photonics in many applications of telecommunication fields. |
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