Day 1 :
University of Wisconsin-Madison, USA
Keynote: High-internal-efficiency quantum cascade lasers: the road to mid-infrared lasers of 40% CW wall-plug efficiency
Time : 09:30-10:00
Dan Botez is Philip Dunham Reed Professor in the Department of Electrical and Computer Engineering at University of Wisconsin (UW) - Madison. In 1976, he obtained a PhD degree in Electrical Engineering from University of California, Berkeley. He has carried out and led research in semiconductor lasers at RCA Labs, Princeton, NJ and TRW Research Center, Redondo Beach, CA before joining, in 1993, the faculty at UW-Madison. His research interests lie in three areas of semiconductor-laser physics: high-power, coherent edge-emitting lasers; high-power, coherent grating-coupled surface-emitting lasers; and quantum cascade lasers. The first two are based on one- and two-dimensional, high-index-contrast, photonic-crystal structures, respectively, for insuring both long-range spatial coherence and stable operation under continuous-wave (CW) driving conditions. The third involves electron transitions between the sub-bands of multi-quantum-well structures and is focused on achieving high-efficiency CW operation in the mid-infrared wavelength range: 3-10 microns, via multi-dimensional conduction-band engineering
The internal efficiency hi of quantum cascade lasers (QCLs) is the factor in the expression for the external differential efficiency that encompasses all differential carrier-usage (i.e., the injection efficiency) and lasing-photon-transition efficiencies. For conventional QCLs the hI values have been found to be rather low: 50-60% in the 4.5-6.0 μm wavelength range and 57-67% in the 7-11 μm wavelength range; with, until recently, no clear explanation why that was the case. With the advent of combining carrier-leakage suppression with fast, efficient carrier extraction out of the active regions of QCLs, the hi values have steadily increased and are approaching their fundamental upper limit of ~ 90% for mid-infrared (IR)-emitting devices. We will review the developments that led to high hi values throughout the mid-IR wavelength range. Conduction-band engineering has led to the so-called step-taper active-region (STA) QCLs which have provided hi values 30-50% higher than in conventional QCLs over both the 4.5-6.0 μm and 7-11 μm wavelength ranges. A record-high, single-facet, continuous-wave (CW) power, for 8.0 μm-emitting QCLs, of 1.0 Watt has been achieved from STA-type QCLs. Furthermore, the recognition that the fundamental limit for hi (i.e., 90%) is 34% higher than the hi value employed a decade ago when determining the fundamental limit for the wall-plug efficiency of mid-IR QCLs, has led to the realization that wall-plug efficiencies ≥ 40% can be achieved for 4.5-5.0 μm-emitting QCLs. The practical benefits of achieving such high performance from mid-IR emitting semiconductor lasers will be discussed as well.
Wall-plug-efficiency fundamental limits for mid-infrared-emitting QCLs
- Kirch J et al (2016) 86% internal differential efficiency from 8-9 µm-emitting, step-taper active-region quantum cascade lasers. Optics Express 24: 24483-24494.
- Botez D, Chang C-C, Mawst L J (2016) Temperature sensitivity of the electro-optical characteristics for mid-infrared-emitting quantum cascade lasers. J. Phys. D: Applied Physics 49: 043001.
- Botez D et al. (2013) Multidimensional conduction-band engineering for maximizing the continuous-wave (cw) wallplug efficiencies of mid-infrared quantum cascade lasers. IEEE Journal Selected Topics in Quantum Electronics 19 (4): 1200312.
- Kirch J et al. (2012) Tapered active-region quantum cascade lasers for suppression of carrier-leakage currents. Electron Lett. 48: 234.
5. Botez D et al. (2010) Temperature dependence of the key electro-optical characteristics for mid-infra-red emitting quantum cascade lasers. Applied Physics Letters 97: 071101.
Lawrence Livermore National Laboratory, USA
Keynote: Understanding laser materials processing: the dichotomy between laser damage and laser machining
Time : 10:00-10:30
Manyalibo J Matthews currently serves as Deputy Group Leader in the Optical Materials and Target Science group in MSD. He holds a PhD in Physics from MIT and a BS in Applied Physics from UC Davis. His research interests at LLNL include novel applications in laser-assisted material processing (e.g. metal additive manufacturing, laser-based CVD, nano-coarsening of metal films, non-contact laser polishing of glass), optical damage science, vibrational spectroscopy and in-situ optical characterization of transient processes. Prior to LLNL, he was a Member of Technical Staff at Bell Labs and worked on materials characterization of optical devices using novel spectroscopic techniques, stress-induced birefringence management in planar optical devices and research in advanced broadband access networks. He is a Fellow of the Optical Society of America.
In the decades since the invention of the laser, new applications and discoveries in materials science have continued year after year as laser sources evolve and more areas of research exploit them. The transformation of materials using focused, high irradiance laser beams fundamentally involves multiple physical phenomena such as optical absorption, heat transport, structural mechanics and material phase transitions. For example, nonlinear absorption of nanosecond pulsed laser light can lead to a nano-scale thermal runaway effects and subsequent damage, which can be detrimental in the operation of high power laser systems. On the other hand, laser processing of materials often involves ablative removal of material or transformations which rely on efficient coupling of laser energy into a work piece. In both cases, understanding laser-material interactions is essential for the optimization of the high power optical system design. In this talk, we will present a few examples of high photon flux laser material processing, using both experiment and finite element modeling to understand energy deposition, heat transport and material transformation. Specifically, we will explore the conditions which bring about optical damage in ultraviolet Q-switched laser optics and compare these conditions to those used in typical microscale laser materials processing technologies. Among the laser processing techniques discussed, we will focus on microsecond-pulsed, resonant IR laser heating for laser micro-machining and metal powder bed additive manufacturing (3D printing). We will discuss how our results can be used to elucidate material behavior, optimize processing and develop new technologies based on laser modified materials.
- C A R Chapman, L Wang, J Biener, E Seker, M M Biener, and M J Matthews (2016) Engineering on-chip nanoporous gold material libraries via precision photothermal treatment. Nanoscale. 8:785-795.
- M J Matthews, G Guss, S A Khairallah, A M Rubenchik, P J Depond and W E King (2016) Denudation of metal powder layers in laser powder bed fusion processes. Acta Materialia. 114:33-42.
- M J Matthews, S T Yang, N Shen, S Elhadj, R N Raman, G Guss, I L Bass, M C Nostrand and P J Wegner (2015) Micro-shaping, polishing, and damage repair of fused silica surfaces using focused infrared laser beams. Advanced Engineering Materials. 17:247-254.
- J H Yoo, J B In, I Sakellari, R N Raman, M J Matthews, S Elhadj, C Zheng and C Grigoropoulos (2015) Directed dewetting of amorphous silicon film by a donut-shaped laser pulse. Nanotechnology 26: 165303.
- M J Matthews (2015) Simulating laser-material interactions, Laser Focus World 51: 33-38.
National Taiwan University of Science and Technology, Taiwan
Time : 10:50-11:20
Shien-Kuei Liaw received Double Doctorate from National Chiao-Tung University in Photonics Engineering and from National Taiwan University in Mechanical Engineering, respectively. He joined the Chunghua Telecommunication, Taiwan, in 1993. Since then, he has been working on Optical Communication and Fiber Based Technologies. He joined the Department of Electronic Engineering, National Taiwan University of Science and Technology (NTUST) in 2000. He has ever been Director of the Optoelectronics Research Center and the Technology Transfer Center, NTUST. He was a Visiting Researcher at Bellcore (now Telcordia), USA for six months in 1996 and a visiting Professor at University of Oxford, UK for three months in 2011. He owned six US patents, and authored or coauthored for 250 journal articles and international conference presentations. He earned many domestic honors and international honors. He has been actively contributing for numerous conferences as a conference chair, technical program chair, organizing committee chair, steering committee and/or keynote speaker. He serves as an Associate Editor for Fiber and Integrated Optics. Currently, he is a Distinguished Professor of National Taiwan University of Science and Technology (NTUST), Vice President of the Optical Society (OSA) Taiwan Chapter and Secretary-General of Taiwan Photonic Society. His research interests are in Optical Sensing, Optical Communication and Reliability Testing.
In this talk, high-speed free space optics communication (FSO) technologies will be reviewed and introduced. Then we will design and demonstrate two proposed FSO schemes. The first scheme is bi-directional short-range free-space optical (FSO) communication with 2x4x10 Gb/s capacity in wavelength division multiplexing (WDM) channels short transmission distance. The single-mode-fiber components are used in the optical terminals for both optical transmitting and receiving functions. The measured power penalties for bi-directional, four-channel WDM FSO communication are less than 0.8 dB and 0.2 dB, compared with the back-to-back link and uni-directional transmission system, respectively. The second scheme is hybrid optical fiber and FSO link in outdoor environments such as cross bridge or inter-building system. A sensor head is used for monitoring the condition of bridge, and in the case of the bridge being damaged the transmission path could be changed from fiber link to FSO link to ensure data link connectivity. In both cases, the single-mode-fiber (SMF) components are used in the optical terminals for both optical transmitting and receiving functions. The influences of environmental factor including window glasses, air turbulence and rainfall will also be addressed. The colorless and colored window glasses introduce losses under various incident angles, but did not induce substantial power penalties. The air turbulence induces extra transmission loss and instability in the received power. Raindrops are the most influential environmental factor. The bit error rate (BER) test shows that raindrops result in a seriously impaired BER to interrupt the transmission instantaneously. After appropriate performance improvement, these proposed transmission structures show potential applications for outdoor transmission under various natural weather conditions.
CCJ Software, Germany
Time : 11:20-11:50
Carl C Jung has his expertise in finding mathematical models for engineering, physical and physical chemistry questions and implementing them in evaluation and simulation software. His way led from amperometric biosensors (Cambridge University, UK), via biophysics employing florescence (Max Planck Institute, Frankfurt a M) to display technology and ellipsometry (IDM, Berlin and Potsdam). Here the presented topic was generated. Thereafter he returned to biophysics and fluorescence (Bayreuth University), and after one year in research management (Fraunhofer, Munich) he finally performed theoretical and experimental studies on the heating of bond wires used in integrated circuits by electronic engineers (Robert Bosch Center for Power Electronics, Reutlingen).
If looking at optically thin layers or thin films with an anisotropic structure, the main applications of such films are in display technology. There are different ways, such layers can be used: as polarisers, if absorbing, as retarders, if transparent, as photo-alignment films, if very thin and with a specific surface, that can be used to align other attaching films during an annealing step in fabrication. Of course, the optical properties of the resulting display depend on the quality of the layers used to produce it. Therefore, we developed a new method, which can very accurately determine the three-dimensional refractive index and its orientation in a thin layer. Even films, whose properties vary in the direction perpendicular to the film plane, can be studied with success. We employed a combination of transmission in two different media - immersion transmission ellipsometry and reflection ellipsometry at one single wavelength. Ellipsometry is the measurement of the alteration of the polarization state of light transmitted or reflected by the layer or film studied. The accuracy of the method was very high compared to conventional reflection ellipsometry in only one medium. If compared to combined transmission and reflection measurements in air, we also reached a drastic improvement. The method of immersion transmission ellipsometry is a significant step forward in the development of non-destructive optical characterization methods for thin films with complex anisotropic structure.
Figure 1: Three normally indistinguishable sets of data can be expanded by immersion transmission ellipsometry. Depicted is the ellipsometric parameter Δ measured in transmission under immersion. The first 3 figures are the refractive indices of the film. Then wavelength in µm, and immersion and substrate index follow.
- Jung C, Stumpe J (2015) Immersion transmission ellipsometry (ITE) for the determination of orientation gradients in photoalignment layers. Appl. Phys. B DOI 10.1007/s00340-013-5729-2.
- Jung C, Stumpe J (2005) Immersion transmission ellipsometry (ITE) – a new method for the precise determination of the 3D indicatrix of thin films. Appl. Phys. B 80:231-238.
- Jung C, Stumpe J, Peeters E, van der Zande B (2005) A novel way for the full characterisation of splayed retarders using the Wentzel-Kramers-Brillouin (WKB) method. Jpn. J. Appl. Phys. 44: 4000-4005.
Aix Marseille University, France
Keynote: Energy transfer dynamics in molecular junctions under ultra-short excitation pulses from non-equilibrium Green’s function formalism
Time : 11:50-12:20
Fabienne Michelini has worked on the theoretical/numerical building of empirical models within the k·p method to understand the electronic properties of realistic condensed-matter systems. In parallel, she has gained a great expertise in high performance computing for large-scale numerical problems. For the last years, she has investigated the transport properties of opened quantum structures for novel nanodevices using effective methods within the Green function formalism. She is now focusing on time-dependent and non-linear regimes of nanosystems interacting with light for optoelectronic and thermoelectric applications at the nanoscale.
The problem of energy transfer is emerging as one of the most crucial issues of our occidental societies. At a fundamental level, how energy flows at the nanometre scale is gaining specific interests due to its implications in both alternative energy production and basics of quantum thermodynamics. The nature of our work is hence two-fold. In the first part, we provide a definition of energy current operator in the Heisenberg representation, while discussing certain conditions which an operator shall fulfill. The obtained expression is applicable to non-stationary as steady-state situations. We implement this definition to derive time-dependent energy current using non-equilibrium Green’s function formalism, which represents a suitable approach for calculating measurable quantities in opened nanosystems. The second part applies these developments to molecular junctions sandwiched in between two thermal reservoirs. Molecular electronic devices are indeed a promising alternative to standard electronic switches due to their fast response on the picosecond time scale. Here, the approach is used for the study of molecular junctions subjected to ultra-short excitation pulses. We thus analyze the electronic energy fluxes across the molecular junction engendered by femtosecond laser pulses. Our numerical implementation enables us to correlate the time-dependent energy current to the underlying intra-molecular dynamics, with special attention paid to the impacts of intra-molecular coupling and incoherence on the energy transfer time-resolved measurables.
Figure 1: We consider a junction made of two donors (D) that interact with light and an acceptor (A), the whole is in contact with tow thermal reservoirs. Effects of the intra-molecular D-D coupling on the time-resolved energy current flowing from D to A during a 30 fs laser pulse
Michelini F, Crépieux A, Beltako K (2017) Entropy production in photovoltaic-thermoelectric nanodevices from the non- equilibrium Green’s function formalism, J. Phys.: Condens. Matter 29: 175301.
- Beltako K, Cavassilas N, Michelini F (2016) State hybridization shapes the photocurrent in triple quantum dot nanojunctions, Appl. Phys. Lett. 109: 073501.
- Crépieux A, Michelini F (2015) Mixed, charge and heat noises in thermoelectric nanosystems, J. Phys.: Condens. Matter 27: 015302.
- Berbezier A, Autran JL, Michelini F (2013) Photovoltaic response in a resonant tunneling wire-dot-wire junction, Appl. Phys. Lett. 103: 041113.
- Crépieux A, Simkovic F, Cambon B, Michelini F (2011), Enhanced thermopower under a time-dependent gate voltage, Phys. Rev. B 83: 153417.
Chinese Academy of Sciences, China
Time : 00
Shao-Wei Wang received his Ph.D. (2003) degree in microelectronics and solid state electronics from Shanghai Institute of Technical Physics, Chinese Academy of Sciences, China. He is a professor of the institute and works at National Laboratory for Infrared Physics from 2010. His research interests include artificial photonic structure and devices, such as interaction between high-Q optical cavity and low-dimensional materials, integrated-cavities for miniature spectrometers, solar selective absorbers, metamaterial polarizers, and optical thin films. He has published more than 50 research papers and authorized one US patent. He got LU JIAXI Young talent award (2009), RAO YUTAI basic optical award (2007) , National Natural science award (2014, 4th principal achiever), National Technological Invention Award (2011, 5th principal achiever), Shanghai Technological Invention Award (2010, 7th principal achiever), Shanghai Natural science award (2007, 5th principal achiever), etc.
Compact, lightweight, and rigid miniature spectrometers without moving parts are needed for a wide variety of applications, including space applications, where every inch of payload counts. Miniaturization increases the portability and paves the way for making in situ spectral measurements for daily life of Food-safety and health etc. It also eases the integration of microspectrometers and miniature spectrometers into other technologies, such as microelectronics, and helps to realize lab-on-a-chip devices.
It attracts many research interests in recent years. There are many novel wavelength devision approaches have been proposed for miniature spectrometers, such as colloidal quantum dot spectrometer and disordered photonic chip. The optical filter array is one of the most important components in wavelength-division multiplexing, multispectral devices, and parallel array optics, which are widely used in communication and electrooptical systems.
We proposed and realized the concept of integrated narrow bandpass filter array from 2004, which can totally match with detectors array with very high spectral resolution and high structure & spectrum flexibility, and resulting in simple structure and small volume with high reliability. We developed the combinatorial etching technique and combinatorial deposition technique for fabrication of such devices. We also demonstrated a concept of a high-resolution miniature spectrometer using an integrated filter array. Such a device has already been succefully used in a multi-spectral luminescence imaging for plant growth research setup of Shijian ten satellite launched in 2016.
- Xingxing Liu, Shao-Wei Wang, Hui Xia, Xutao Zhang, Ruonan Ji, Tianxin Li, Wei Lu (2016) Interference-aided spectrum fitting method for accurately film thickness determination. Chinese Optics Letters. 14(8):081203.
- Shao-Wei Wang, et al. (2007) Concept of a high-resolution miniature spectrometer using an integrated filter array. Optics Letters 32(6) 632-634.
- Shao-Wei Wang, et al. (2007) 128 Channels of integrated filter array rapidly fabricated by using the combinatorial deposition technique. Appl. Phys. B 88(2):281-284.
- Shao-Wei Wang, et al. (2006) 16 x 1 integrated filter array in the MIR region prepared by using a combinatorial etching technique. Appl. Phys. B 82(4):637-641.
- Shao-Wei Wang, et al. (2006) Integrated optical filter arrays fabricated by using the combinatorial etching technique. Optics Letters 31(3):332-334.