bluuebunny/crossref_metadata_2025 huggingface dataset:
Breaking the Fabrication Determined Resolution Limit of Photonic Crystal Wavemeter by Machine Learning
Authors: Hofs Jocelyn , Kodama Takumasa , Jin Shengji , Tanabe Takasumi
Published: September 2020

By utilizing random localization patterns as training data for machine learning, we achieved a 0.2-nm wavelength resolution with a fabricated photonic crystal wavemeter, which greatly exceeds the limit imposed by the fabrication.
Optic-Electronic-Optic Interferometer: A First Experimental Demonstration
Authors: Mahmud M. S. , Kemal J. N. , Adib M. , Fullner C. , Schindler A. , Runge P. , Schell M. , Freude W. , Koos C. , Randel S.
Published: September 2020

We demonstrate an interferometer that is opaque in one arm, where the optical signal is coherently detected, processed, and remodulated. In case of constructive interference, stable operation is shown for 5 Gbit/s OOK signaling.
Efficient widely-separated optical parametric oscillation
Authors: Lu Xiyuan , Moille Gregory , Singh Anshuman , Li Qing , Westly Daron , Rao Ashutosh , Yu Su-Peng , Briles Travis C. , Drake Tara , Papp Scott B. , Srinivasan Kartik
Published: September 2020

We demonstrate the first widely-separated optical parametric oscillation in silicon nanophotonics, with milliwatt-level threshold power that is > 50 times smaller than other widely-separated OPOs. This demonstration is promising for on-chip visible light generation.
Pseudo mode-locking
Authors: Ecoto Esmerando , Demircan Ayhan , Babushkin Ihar , Steinmeyer Günter
Published: September 2020

A new mode-locking mechanism is discussed that solely relies on four-wave mixing and does not require a saturable absorber. This mechanism explains a number of previously reported peculiar findings of self-modelocking and comb formation.
Starting Dynamics of a Linear Mamyshev Oscillator
Authors: Chen Yi-Hao , Sidorenko Pavel , Thorne Robert , Wise Frank
Published: September 2020

We investigate the starting dynamics of an environmentally-stable linear Mamyshev oscillator that is started by modulation of the pump power. A moving filter is implemented to generate 21-nJ and 65-fs pulses.
Ultra-Low-Threshold Diode-Pumped Ti:sapphire Laser Modelocked Using Carbon Nanotubes
Authors: Mitchell Toby , Marin Pablo Castro , Sun Jinghua , Reid Derryck T.
Published: September 2020

We demonstrate 55-fs pulses at 802 nm from a directly-diode-pumped Ti:sapphire laser modelocked using single-walled carbon nanotubes spin-coated on a cavity mirror. This low-loss saturable absorber enables modelocking with pump powers as low as 545 mW.
Nanoscale Photodetector Using 7-Atom Wide Armchair-Edge Graphene Nanoribbons
Authors: Alavi Seyed Khalil , Senkovskiy Boris V. , Hertel Dirk , Haberer Danny , Ando Yoichi , Meerholz Klaus , Fischer Felix R. , Griineis Alexander , Lindfors Klas
Published: September 2020

We demonstrate a nanoscale photoconductive photodetector with seven-atom wide armchair-edge graphene nanoribbons as the active material. The detector responsivity is 0.04 mAW-1 with a dark current below 30 pA under a bias voltage of 1.5 V.
On-Chip Monolayer WSe2 Microring Laser Operating At Room Temperature
Authors: Granados-Baez Marissa , Mukherjee Arunabh , Qiu Liangyu , Chakraborty Chitraleema , Vamivakas A. Nick , Cardenas Jaime
Published: September 2020

We demonstrate lasing at room temperature of monolayer WSe2 integrated with a silicon nitride ring resonator. Signatures of lasing are shown by a ‘kink’ in the L-L plot and 30% linewidth narrowing when reaching threshold.
Prediction of Performance Penalty due to Pump-Signal Overlap in Raman-amplified Systems
Authors: Di Rosa Gabriele , Iqbal Md Asif , Richter Andre , Forysiak Wladek
Published: September 2020

We present an efficient numerical model to predict the performance penalty induced by Rayleigh backscattered light arising from counter-propagating pumps in Raman- amplified ultra-wide-band transmission systems. The model is validated through compari-son with experimental findings.
On-chip reconfigurable mode-order converter based on subwavelength symmetric multimode Y-junctions
Authors: Lu Longhui , Liu Deming , Yan Max , Zhang Minming
Published: September 2020

We propose an on-chip reconfigurable mode-order converter based on subwavelength symmetric multimode Y-junctions, assisted by phase shifters. The data information carried among four different mode channels can be arbitrarily converted or remain the same.
Fano Resonant All-dielectric Metasurfaces for Polarization-sensitive Structural Coloration
Authors: Hemmatyar Omid , Lu Zhou , Brown Tyler , Maleki Hossein , Adibi Ali
Published: September 2020

Herein, for the first time to our knowledge, we experimentally demonstrate Fano resonant all-dielectric metasurfaces comprising of high- and median-index nanopillars (HfO2, TiO2 and ZrO2) with zero loss in visible range for polarization-sensitive structural coloration.
Narrow linewidth quantum cascade laser
Authors: Zhao Gang , Bailey D. Michelle , Fleisher Adam J.
Published: September 2020

A narrow linewidth quantum cascade laser was obtained by optical feedback locking to a high finesse linear cavity with locking bandwidth larger than 5 MHz, resulting in an instantaneous linewidth at mHz levels.
Single-Digit Attosecond Carrier-Envelope Phase Stabilization of an Er:Yb:Glass Laser with Feed-Forward Technique
Authors: Lemons Randy , Liu Wei , De Fuentes Irene Fernandez , Droste Stefan , Steinmeyer Gunter , Durfee Charles G. , Carbajo Sergio
Published: September 2020

We present carrier-envelope phase stabilization of an Er:Yb:glass laser at 1.55 pm via the feed-forward method with 2.9 as (1 Hz - 3 MHz) timing jitter and continuous stabilization over 24 hours.
Intra-Oscillator High Harmonic Generation in a -100-fs Kerr-Lens Mode-Locked Thin-Disk Laser
Authors: Fischer Julian , Drs Jakub , Labaye François , Modsching Norbert , Kränke Christian , Wittwer Valentin J. , Südmeyer Thomas
Published: September 2020

We demonstrate HHG with ~1014 W/cm2 peak intensity in argon and '5x103؛ W/cm2 in krypton inside a mode-locked laser oscillator. The system operates with up to 180-W intiacavity average power with 89-fs pulses at 11-2020
Physically unclonable optical functions using native silk
Authors: kim Min Seok , Lee Gil Ju , Choi Seung Ho , Leem Jung Woo , Kim Young L. , Song Young Min
Published: September 2020

Combination of Physically unclonable functions (PUF) and optical materials can potentially enhance hardware and information security. Here, we propose a strong optical PUF device with native silk having inherent disordered structures.
Strong Enhancement of THz Emission in a Metal-Graphene-Silicon Heterostructure
Authors: Zhang Dehui , Xu Zhen , Cheng Gong , Liu Zhe , Gutierrez Audrey Rose , Norris Theodore B , Zhong Zhaohui
Published: September 2020

We report a THz emitter based on a simple metal-graphene-silicon heterostructure, and demonstrate an enhancement of the amplitude by a factor of 80 over its graphene-free counterpart with no tradeoff in bandwidth or SNR. The enhancement is due to an increased carrier collection efficiency by the graphene layer.
A phase-only liquid-crystal based pulse shaper for multi-octave light sources
Authors: Di Pietro Vittorio M. , Bux Simone , Forget Nicolas , Jullien Aurelie
Published: September 2020

Continuous spectral phase shaping is demonstrated over a spectral bandwidth spanning from 540 nm to 2500 nm (450 THz) with a modulation dynamic large enough to shape single-cycle pulses or even transient electric fields in the near infrared.
Coupling of Whispering Gallery Mode with Silicon Photonic Crystal
Authors: Yube Koki , Kumazaki Hajime , Zhuang Yuyang , Fuji Shun , Imamura Riku , Ishida Rammaru , Tanabe Takasumi
Published: September 2020

We demonstrate the coupling of an ultrahigh-Q whispering-gallery mode with silicon photonic crystals. This allows the efficient coupling of a high-Q mode directly with a high-index silicon slab and further advancement of dynamic Q tuning.
LiDAR Beamsteering by Digitally Switched MEMS Gratings on a Silicon Photonics Platform
Authors: Spector S. J. , Cook E. H. , Moebius M. G. , Baruffi F. A. , Bancu M. G. , Benney L. D. , Byrnes S. J. , Chesin J. P. , Geiger S. J. , Goldman D. A. , Hare A. E. , Lane B. F. , Sawyer W. D. , Bessette C. R.
Published: September 2020

A new method for solid-state beamsteering using MEMS grating switches integrated on a Si-PIC has been demonstrated. This method provides fast random access switching, simple digital control, extremely low side-lobes, and is scalable to large arrays, large apertures, and long ranges.
Tapered submicron silicon core fiber for broadband wavelength conversion
Authors: Wu D. , Shen L. , Lacava C. , Petropoulos P. , Hawkins T. , Ballato J. , Gibson U. J. , Peacock A. C.
Published: September 2020

Wavelength conversion of 20 Gb/s quadrature phase shift keying (QPSK) signals is demonstrated in a tapered silicon core fiber extending across the S-, C- and L-bands. The results indicate the platform’s suitability for use in broadband all-optical communication systems.
Enhancement of Optical Valley Coherence in Monolayer WS2 using Strain
Authors: Deshmukh Prathmesh , Chakraborty Biswanath , Khatoniar Mandeep , Menon Vinod
Published: September 2020

We demonstrate significant enhancement (> 40%) in valley coherence of localized excitons in monolayer WS2 via strain engineering. The observed enhancement is attributed to the suppression of inter valley scattering due to strain induced potential.
THz Generation and Spectroscopy with Nonlinear Plasmonic Metasurface Antennas Excited by a Nanojoule Femtosecond Laser
Authors: Tal Mai , Keren-Zur Shay , Ellenbogen Tal
Published: September 2020

We study THz light emitted from nonlinear metasurfaces, excited by low energy femtosecond lasers. Conversion efficiencies comparable to 2500-fold thicker nonlinear crystals allow measurement of a-lactose absorption lines, showing suitability for time domain spectroscopy.
Horizontal-Slot Plasmonic-Organic Hybrid (POH) Modulator
Authors: Ummethala Sandeep , Pammi Venkata Anirudh , Uddin Ahsan H. M. , Hahn Lothar , Freude Wolfgang , Koos Christian
Published: September 2020

We demonstrate horizontal-slot plasmonic-organic hybrid (HS-POH) modulators and show that the n-voltage-loss product aUL is by 25 % better than for conventional vertical-slot devices. The slot is realized by a sacrificial layer, thereby relaxing extreme lithography-resolution requirements.
Solid-state beam scanner based on VCSEL integrated amplifier with scan resolution of over 200
Authors: Hu Shanting , Takanohashi Masashi , Gu Xiaodong , Shimura Keisuke , Koyama Fumio
Published: September 2020

We demonstrate a solid-state beam scanner based on VCSEL-integrated amplifier for 3D sensing. We realized a record beam-steering angle of 16° with 200 resolution points. The integrated chip size is as small as 1 mm.
Compressed Sensing Imaging via Beam Scanning
Authors: Zhang Kangning , Hu Junjie , Yang Weijian
Published: September 2020

We propose a new imaging scheme of compressed sensing by scanning an illumination pattern on the object. Comparing with conventional single-pixel cameras, we expect a >50x increase in imaging speed with similar imaging quality.
Optical Frequency Transfer over Submarine Fibers
Authors: Clivati Cecilia , Marra Giuseppe , Levi Filippo , Mura Alberto , Xuereb André , Calonico Davide
Published: September 2020

We characterized the phase noise and instability of submarine optical fibers and estimate achievable performances of trans-oceanic fiber-based optical frequency transfer, in view of intercontinental atomic clock comparisons. We also show that the low noise of the submarine environment allows exploitation of long-haul telecom fibers as distributed sensors for underwater earthquakes.
A Coherent Optical Fiber Link for Very Long Baseline Interferometry
Authors: Clivati Cecilia , Aiello Roberto , Bianco Giuseppe , Bortolotti Claudio , Di Sarno Valentina , Maddaloni Pasquale , Levi Filippo , Maccaferri Giuseppe , Mura Alberto , Negusini Monia , Perini Federico , Roma Mauro , Ricci Roberto , Amato Luigi Santamaria , De Cumis Mario Siciliani , Stagni Matteo , Calonico Davide
Published: September 2020

We realize a phase-stabilised optical fiber backbone that connects the Italian National Metrology Institute with two radio telescopes over a 600 km baseline. This allows referencing of Very Long Baseline Interferometry (VLBI) facilities with the best atomic frequency standards available today and the implementation of a common-clock architecture, which we are now using to assess VLBI ultimate performances.
Novel Optical Fibers for Silicon Photonic Chip Packaging
Authors: Li Ming-Jun
Published: September 2020

We present new optical fiber designs for silicon photonic chip packing applications, including Titania-clad bend-insensitive fiber for surface coupling, D-shaped fiber for evanescent wave coupling and multicore fiber for edge coupling.
Bridging Between Si and Few-Mode Fiber Higher Order Modes
Authors: Jimenez Gordillo Oscar A. , Dave Utsav D. , Lipson Michal
Published: September 2020

We show a mode converter between silicon and polymer waveguides compatible with few-mode fibers for mode-division multiplexing. We convert 4 TE modes of a silicon waveguide to the TE11, TMii, TE21, TM21 modes of a polymer waveguide.
Six-cycle multi-millijoule 2.5 pm pulses generation by a single-stage Cr2+:ZnSe amplifier
Authors: Wu Yi. , Zhou Fangjie , Larsen Esben W. , Zhuang Fengjiang , Yin Yanchun , Chang Zenghu
Published: September 2020

A single-stage chirped-pulse amplifier centered at 2.5 wm was developed to produce 3.5 mJ, 44 fs pulses at 1 kHz. The 80 GW peak power allows attosecond X-ray pulses generation in the water window.
Ultrafast Laser Inscribed Waveguide Lasers in Tm3+:SrF2
Authors: Llamas Victor , Loiko Pavel , Kifle Esrom , Romero Carolina , Vázquez de Aldana Javier R. , Serres Josep Maria , MauroTonelli  , Damiano Eugenio , Zakharov Viktor , Veniaminov Andrey , Aguiló Magdalena , Díaz Francesc , Chen Weidong , Griebner Uwe , Petrov Valentin , Mateos Xavier
Published: September 2020

Depressed-index low-loss (0.38 dB/cm) buried channel waveguides with a circular cladding are fabricated in bulk Tm3+:SrF2 by ultrafast laser inscription. The waveguide laser generated 148 mW at 1.87 pm with a slope efficiency of 63.9%.
Terahertz quantum plasmonics at nanometer and picometer scales
Authors: Yoon H. S. , Bamadev Das , Park W. K. , Kim Dasom , Rhie J. Y. , Bahk Y. M. , Kim D. S.
Published: September 2020

We bring high aspect ration gaps from nanometer to Angstrom, all the way down to the quantum regime and beyond, achieving multi-functionalities.
Common Pulse Retrieval Algorithm: a Fast and Universal Method to Retrieve Ultrashort Pulses
Authors: Geib Nils C. , Knopf Heiko , Ngo Gia Quyet , Pertsch Thomas , Eilenberger Falk
Published: September 2020

In this work we present a common pulse retrieval algorithm (COPRA) that can be universally applied to many pulse measurement methods and compares favorably in terms of speed and accuracy to existing approaches.
Design of a multi-channel photonic crystal dielectric laser accelerator
Authors: Zhao Zhexin , Black Dylan S. , England R. Joel , Hughes Tyler W. , Miao Yu , Solgaard Olav , Byer Robert L. , Fan Shanhui
Published: September 2020

We propose a photonic crystal architecture for a dielectric laser accelerator that enables simutaneous acceleration of multiple electron beams. To achieve this, the band structure condition is discussed.
Photonic Ising Spin-Glass via Chip-Based Degenerate Kerr Oscillators
Authors: Okawachi Yoshitomo , Yu Mengjie , Jang J. K. , Ji Xingchen , Zhao Yun , Lipson Michal , Gaeta Alexander L.
Published: September 2020

We demonstrate reconfigurable all-optical coupling between two degenerate optical parametric oscillators in silicon-nitride microresonators. We show in-phase and out-of-phase operation which is achieved at a fast regeneration rate of 400 kHz with a large phase tolerance.
Epitaxial GeSn and its integration in MIR Optoelectronics
Authors: Assali Simone , Attiaoui Anis , Atalla Mahmoud R. M. , Dijkstra Alain , Kumar Aashish , Mukherjee Samik , Abdi Salim , Moutanabbir Oussama
Published: September 2020

The effect of strain and composition on the opto-electronic properties of (Si)GeSn semiconductors across the 4-300K temperature range will be discussed to pave the way for future device operation up to 4.5 pm wavelengths.
GaAs epitaxy on (001) Si: below 1×106 cm-2 dislocation density with 2.4 pm buffer thickness
Authors: Shang Chen , Norman Justin , Gossard Arthur C. , Bowers John E.
Published: September 2020

We report a record-low threading dislocation density of 9.3 x105 cm-2 in GaAs thin films directly grown on (001) Si substrates. The total buffer thickness (2.4 pm) is only two thirds of the state-of-art reported value.
Integrated Photon-Pair Generation and ~112 dB Pump Rejection Filters for Silicon Quantum Photonics
Authors: Kumar Rakesh Ranjan , Wu Xinru , Zhang Yaojing , Tsang Hon Ki
Published: September 2020

We demonstrate on-chip quanhrm-correlated photons and rejection of pump photons by ~112 dB using filters on two silicon-on-insulator photonic integrated circuits. The photon pairs had coincidence-to-accidental ratio (CAR) of 155 at 0.2 mW pump power.
Strain-Engineered MoTe2 Photodetector in Silicon Photonics at 1550 nm
Authors: Maiti R. , Patii C. , Xie T. , Azadani J.G. , Amin R. , Miscuglio M. , Van Thourhout D. , Low T. , Bank S. , Sorger V. J.
Published: September 2020

Here we show how strain-engineering (~4% tensile strain) lowers the bandgap (-0.2eV) of MoTe2 nanocrystals heterogeneously integrated around a silicon photonic waveguide, thus enabling photoabsorption at 1550nm, a responsivity of 0.5A/W and NEP of 90pW/Hz^2.
Enhanced Polarization Purity in Twisted-Mode Lasers Using Helically-Structured Mirrors
Authors: Bisson Jean-François , Gallant Gabriel , Bulmer Kristopher , Bader Georges
Published: September 2020

Helically-structured mirrors producing circular Bragg reflection, used as laser mirrors for the twisted-mode operation of compact single frequency microchip lasers, offer better suppression of dual polarization oscillation than linear birefringent nanostruchrred mirrors.
Real-Time Radar for the THz Region
Authors: Amarasinghe Yasith , Mendis Rajind , Mittleman Daniel M.
Published: September 2020

We implement a 2D real-time radar system for the THz region using a leaky parallelplate waveguide. The radar can locate a target within 200ms with an accuracy of 1mm in range and 1.2° in angle. © 2020 The Author(s)
Experimental Demonstration of Broadband Silicon Mode Converter Designed by Wavefront-Matching Method
Authors: Sawada Yusuke , Fujisawa Takeshi , Saitoh Kunimasa
Published: September 2020

A broadband Si-based TE0-TE1 mode converter is successfully designed by a wavefornt-matching method for the first time and experimentally demonstrated. The effect of the broadband design appearing in the optimum waveguide geometry is observed.
Tailoring the phase-matching condition of four-wave mixing via Brillouin scattering in a chalcogenide waveguide
Authors: Zhang Yuanfei , Merklein Moritz , Zhu Zihang , Shu Chester , Vu Khu , Ma Pan , Choi Duk-Yong , Madden Stephen , Eggleton Benjamin J.
Published: September 2020

We controlled the phase matching for four-wave mixing (FWM) in a chalcogenide waveguide by Brillouin-induced phase shift. Over 2n phase shift was realized and a 6-dB improvement in FWM conversion efficiency was obtained.
High-Fidelity Cryogenic Photonic Link for the Readout of Superconducting Qubits
Authors: Quinlan Franklyn , Diddams Scott , Lecocq Florent , Aumentado José , Teufel John
Published: September 2020

We perform readout of a superconducting qubit with microwave pulses delivered via optical fiber and a cryogenic high-speed photodetector. High coherence and readout fidelity are maintained, compatible with the stringent requirements of quantum information systems.
Superconducting nanowire single-photon detector on thin- film lithium niobate photonic waveguide
Authors: Colangelo M. , Desiatov B. , Zhu D. , Holzgrafe J. , Medeiros O. , Loncar M. , Berggren K. K.
Published: September 2020

We integrate niobium nitride superconducting nanowire single-photon detectors (SNSPDs) on thin-film lithium niobate (LN) photonic waveguides. Further development of this technology may push towards more complex circuits and functionalities on this already promising platform.
Characterization of a self-organized deep-ultraviolet micro-light-emitting diode structure for high-speed solar-blind optical wireless communications
Authors: Kojima Kazunobu , Yoshida Yuki , Shiraiwa Masaki , Awaji Yoshinari , Kanno Atsushi , Yamamoto Naokatsu , Hirano Akira , Nagasawa Yosuke , Ippommatsu Masamichi , Chichibu Shigefusa F.
Published: September 2020

Time- and spatio-resolved electroluminescence spectroscopy was performed to characterize a self-organized micro-structure in the AlGaN LEDs, which have realized gigabit- class solar-blind optical wireless communication.
Interband Cascade and Quantum Cascade Ring Lasers
Authors: Knotig Hedwig , Andrews Aaron Maxwell , Hinkov Borislav , Weih Robert , Koeth Johannes , Schwarz Benedikt , Strasser Gottfried
Published: September 2020

Quantum cascade and interband cascade lasers are fabricated into surface and substrate emitting coherent light sources and detectors. We report about latest achievements in terms of power, temperature and dynamic performance of on-chip sensing systems.
Overcoming the Trade-Off Between Loss and Dispersion in Microresonators
Authors: Corato-Zanarella Mateus , Ji Xingchen , Mohanty Aseema , Dave Utsav D. , Gaeta Alexander L. , Lipson Michal
Published: September 2020

We overcome the trade-off between loss and dispersion in high Q microresonators by engineering their cross-section along the length. We show high quality factor of 8.0 million, corresponding to a propagation loss of 4.7 dB/m.
Ultra-Low Loss 698 nm and 450 nm Silicon Nitride Visible Wavelength Waveguides for Strontium Atomic Clock Applications
Authors: Chauhan Nitesh , Wang Jiawei , Bose Debapam , Moreira Renan , Blumenthal Daniel J.
Published: September 2020

We report tightly confining Si3N4 waveguides with record low loss at key strontium clock visible wavelengths, 0.03dB/cm at X=698nm, 0.08dB/cm at 450nm and ring resonators with measured loaded Q of 8.6 million at X=674nm.
Experimental Demonstration of Record 300-km Orbital Angular Momentum (OAM) Mode-Division Multiplexing Transmission Using a Ring-Core Fiber Recirculating Loop
Authors: Wang Hongya , Yang Min , Wang Lulu , Shen Lei , Zhang Lei , Luo Jie , Wang Jian
Published: September 2020

Using two high-order OAM modes each carrying a quadrature phase-shift keying signal, we experimentally demonstrate a record 300-km OAM mode-division multiplexing transmission assisted by a ring-core fiber recirculating loop without multiple-input multiple-output digital signal processing.
Resolution Enhancement in Scanning Electron Microscopy using Deep Learning
Authors: de Haan Kevin , Ballard Zachary S. , Rivenson Yair , Wu Yichen , Ozcan Aydogan
Published: September 2020

We present a deep learning-based framework to perform image super-resolution in scanning electron microscopy. The technique was demonstrated to perform a resolution enhancement using a standard resolution test target and hydrogel samples.
Stabilizing chip-scale combs and infrared sources: a metrological view on the molecular world
Authors: Cappelli Francesco , Consolino Luigi , Simone  , Borri  , Bartalini Saverio , Cancio Pablo , Galli Iacopo , Mazzotti Davide , De Natale Paolo
Published: September 2020

Tight stabilization of infrared sources is proving to be a key technology for opening this broad window to unprecedented measurements in molecular samples in a wide range of thermodynamic conditions. ©2020 The Author(s)
High-Resolution and Gapless Dual Comb Spectroscopy with Current-Tuned Quantum Cascade Lasers
Authors: Gianella Michele , Nataraj Akshay , Tuzson Béla , Faist Jérôme , Emmenegger Lukas
Published: September 2020

We measured gapless, high-resolution absorption spectra spanning 55 cm−1 by simultaneous current-modulation of two quantum cascade laser frequency combs. Detector noise limited spectra were obtained in as little as 10 ms with a resolution of a few MHz.
High-Frequency Photonic Crystal Torsional Optomechanics
Authors: Behera Bishnupada , Kaviani Hamidreza , Hajisalem Ghazal , Luiz Gustavo , Barclay Paul E.
Published: September 2020

An optomechanical system that couples external torque to the harmonic vibrations of a photonic crystal nanobeam is presented. Measurements reveal torque sensitivity Of τ
min
~ 10-22 — 10-19 nh/

Hz

for mechanical frequencies spanning MHz-GHz.
Demystifying semiconductor self-mode-locking without saturable absorber
Authors: Escoto Esmerando , Demircan Ayhan , Babushkin Ihar , Steinmeyer Günter
Published: September 2020

Self-mode-locking of semiconductor lasers has been frequently reported, defying all known solutions of the Haus Master Equation approach. Here we show that four-wave mixing all by itself suffices to mode-lock a laser.
Offset Quantum Dot Mode-Locked Laser Enabled by Passive-Active Integration
Authors: Zhang Zeyu , Norman Justin , Liu Songtao , Malik Aditya , Bowers John E.
Published: September 2020

We report the first demonstration of an offset quantum dot laser platform which enables integration of active gain section with passive waveguide section. Based on this platform, we have designed and fabricated dispersion compensated offset quantum dot mode-locked lasers.
Mid-infrared time-stretch spectroscopy
Authors: Kawai Akira , Dougakiuchi Tatsuo , Badarla Venkata Ramaiah , Hashimoto Kazuki , Imamura Takayuki , Edamura Tadataka , Ideguchi Takuro
Published: September 2020

Speeding up mid-infrared spectroscopy is an essential demand in molecular science. We demonstrate a broadband mid-infrared spectroscopy technique, called time-stretch infrared spectroscopy, spanning over 4.4-4.9 gm at a spectral acquisition rate of 80 MSpectra/s. © 2020 The Author(s)
Sr optical lattice clock assisted by optical frequency combs for contribution to International Atomic Time
Authors: Hisai Yusuke , Akamatsu Daisuke , Kobayashi Takumi , Hosaka Kazumoto , Inaba Hajime , Hong Feng-Lei , Yasuda Masami
Published: September 2020

We evaluate the uncertainty of our Sr optical lattice clock at the 10
-17
level, through robust clock operation with assistance of optical frequency combs. This clock will be operated for contribution to the International Atomic Time.
Two photon-induced chiral structures of azo-polymers
Authors: Shiraishi Ami , Masuda Keigo , Yamane Keisaku , Toyoda Kohei , Miyamoto Katsuhiko , Omatsu Takashige
Published: September 2020

We demonstrate the formation of chiral surface structure of azo-polymers via optical vortex induced two-photon-absorption (TPA). TPA-induced isomerization allows us to create the threedimensional chiral structures with high longitudinal and transverse spatial resolution beyond the diffraction limit.
First Investigation on Double- and Single-sideband Formats in BDFA-enabled O-band Transmission
Authors: Hong Yang , Bottrill Kyle R. H. , Taengnoi Natsupa , Thipparapu Naresh K. , Wang Yu , Sahu Jayanta K. , Richardson David J. , Petropoulos Periklis
Published: September 2020

We experimentally compare 50-Gb/s single- and double-sideband formats in an O-band BDFA-amplified transmission system over different distances. The results show that single-sideband transmission is beneficial for distances beyond ~50km at more dispersive Oband wavelengths. © 2020 The Author(s)
Stable single-longitudinal-mode dual-ring fiber laser with ultra-narrow linewidth
Authors: Wang Zhengkang , Shang Jianming , Mu Kuanlin , Qiao Yaojun , Yu Song
Published: September 2020

A dual-ring-architecture-based single-longitudinal-mode fiber laser with an ultranarrow linewidth of 610 Hz is proposed and experimental demonstrated. We achieved a lasing wavelength stabilization of less than 0.004 nm.
Spatial and dynamical multi-level control over thermal emission
Authors: Xu Ziquan , Li Qiang , Du Kaikai , Long Shiwei , Yang Yang , Cao Xun , Luo Hao , Zhu Huanzheng , Ghosh Pintu , Shen Weidong , Qiu Min
Published: September 2020

We demonstrate a thermal emitter with spatial and dynamic tunability by using phase-transition material vanadium dioxide. Emissivity varies from 0.19 to 0.91 during the insulator-to-metal transition. Multi-level spatial control of thermal emission is also demonstrated.
Tailoring of Effective Refractive Indices: A New Paradigm towards Ultralow Excitation Power of Upconversion Nanoparticles
Authors: Lin Hung-I , Yadav Kanchan , Chang Ting-Jia , Kataria Monika , Shalaginov Mikhail Y. , Shen Kun-Ching , Wang Chun-Che , Chen Yit-Tsong , Chen Yang-Fang
Published: September 2020

The integration of core-multishell nanostructure with upconversion nanoparticles achieve the ultralow pumping power density of 0.7 W cm-2 by continuous-wave infrared laser due to the formation of whispering gallery modes with diverse effective refractive indices.
Highly Efficient Broadband Frequency Entangled Photon Pair Sources for Optical Quantum Applications
Authors: Cao Bo , Hayama Kyohei , Hisamitsu Mamoru , Tokuda Katsuhiko , Kurimura Sunao , Okamoto Ryo , Takeuchi Shigeki
Published: September 2020

We developed highly efficient frequency entangled photon-pair sources using slab type waveguide QPM device for non-collinear emission, as well as ridge type waveguide chirp QPM devices for collinear emission with a 150 THz ultra-broadband.
Towards scalable quantum computing with neutral atoms
Authors: Pritchard J. D.
Published: September 2020

We present progress towards scalable quantum computing with neutral atoms excited to Rydberg states, including recent results of two-qubit gates and design of a hybrid quantum interface between neutral atoms and superconducting circuits.
Space-variant holographic imaging for 3D Rydberg quantum simulators
Authors: Sun Haeun , Song Yunheung , Ahn Jaewook
Published: September 2020

As a scalable and time-efficient means to measure the state of Rydberg-atom quantum simulators, we propose space-variant holographic imaging of three-dimensional single-atom structures. Wave-front shaping in quasi-image planes allows simultaneous and fast quantum-state detections.
Narrow Linewidth Photoluminescence from Top-Down Fabricated 20 nm InGaN/GaN Quantum Dots at Room Temperature
Authors: Melanson Bryan , Starling David , Hartensveld Matt , Howland Gregory , Preble Stefan , Zhang Jing
Published: September 2020

Promising narrow linewidth photoluminescence with a FWHM of 7.1 nm at wavelength 418 nm was achieved at room temperature from InGaN/GaN quantum dots in a 20-nm-diameter top-down fabricated nanowire.
Ordered Configuration of Strained Ge Nanostructures on Si using Mechanical Nano-stamping: Towards Light Sources on Silicon
Authors: Dushaq Ghada , Rasras Mahmoud
Published: September 2020

Highly tensile-strained Ge nanostructures grown on pre-patterned (001) Si substrate is demonstrated. Using depth controlled nanoindentation, 2.7% strain value has been obtained. Results are verified by observing photoluminescence emission properties of the Ge/Si nanostructures.
Unreleased on-chip frequency-shifting optical isolator
Authors: Sohn Donggyu , Kim Soonwook , Bahl Gaurav
Published: September 2020

We demonstrate an unreleased acousto-optic frequency-shifting optical isolator on chip, that exhibits improved mechanical and thermal robustness compared to prior art. The system leverages traveling surface acoustic waves (SAW) to break the symmetry for light propagation via indirect intermodal scattering.
Sub-Parts-Per-Million Level Detection of Ethanol using Mid-Infrared Photonic Crystal Waveguide in Silicon-on-Insulator
Authors: Rostamian Ali , Dalir Hamed , Teimourpour Mohammad H. , Chen Ray T.
Published: September 2020

We experimentally demonstrate an Ethanol sensor based on a slotted photonic crystal waveguide fabricated on a silicon on insulator platform to perform at a center wavelength of 3.4μm. Utilizing a 9mm long PCW, concentrations of down to 500 parts per billion (ppb) of Ethyl alcohol is detected.
A compact and inexpensive coherent Ising machine based on opto-electronic feedback for solving combinatorial optimization problems
Authors: Böhm Fabian , Verschaffelt Guy , Van der Sande Guy
Published: September 2020

We propose and demonstrate a new type of coherent Ising machine based on optoelectronic feedback systems for solving NP-hard optimization problems. The design is significantly cheaper and more compact than current state-of-the-art Ising machines.
Programmable Orbital Angular Momentum beam generated from a 61 channels Coherent Beam Combining femtosecond laser
Authors: Veinhard Matthieu , Bellanger Séverine , Daniault Louis , Fsaifes Ihsan , Chanteloup Jean-Christophe
Published: September 2020

A 61 beamlets Coherent Beam Combination femtosecond laser is used as a programmable phase source to generate high power Orbital Angular Momentum beams and open the path for higher order non-symmetrical user-defined far field distributions.
Eliminating photodarkening effect by H2-loading in high power Yb-doped fiber amplifiers
Authors: Cao Ruiting , Chen Gui , Li Jinyan
Published: September 2020

The radical elimination of photodarkening effect by H2-loading was demonstrated, and the output power was stable during long term operation in high power fiber amplifiers, without mode instability and photodarkening-induced core laser leakage.
Generation of high-field single-cycle terahertz pulses at 100 kHz
Authors: Kramer Patrick L. , Hoffmann Matthias C. , Tavella Franz
Published: September 2020

High-field single-cycle terahertz pulses were generated through optical rectification in LiNbO3 at 100 kHz with 144 mW maximum power using a high energy, spectrally broadened, sub-100 fs Yb:YAG amplifier system for tilted pulse front pumping.
Multi-cycle terahertz generation in a periodically poled Rb:KTP crystal
Authors: Tian Wenlong , Cirmi Giovanni , Canalias Carlota , Zukauskas Andrius , Wang Lu , Olgun Halil T. , Kueny Elias , Calendron Anne-Laure , Reichert Fabian , Hasse Kore , Hua Yi , Schimpf Damian N. , Çankaya Hüseyin , Pergament Mikhail , Hemmer Michael , Matlis Nicholas , Pasiskevicius Valdas , Laurell Fredrik , Kartner Franz X.
Published: September 2020

We investigate multi-cycle 0.5-Terahertz generation in a periodically poled Rb-doped potassium titanyl phosphate (PPKTP) crystal. Up to 0.65-gJ terahertz energy was obtained at 77 K with maximum internal optical-to-terahertz efficiency of 0.09%.
Ultrafast real-time dynamics of frequency microcomb transitions
Authors: Jiang Xinghe , Wang Wenting , Yang Jinghui , Yu Mingbin , Kwong Dim-Lee , Wong Chee Wei
Published: September 2020

We demonstrated a real-time parametric time magnifier (PTM) and recorded the ultrafast transitions between different soliton states in Kerr frequency comb.
Ultra-efficient frequency comb generation in AlGaAs-on-insulator microresonators
Authors: Chang Lin , Xie Weiqiang , Shu Haowen , Yang Qi-Fan , Shen Boqiang , Boes Andreas , Peters Jon D. , Jin Warren , Xiang Chao , Liu Songtao , Moille Gregory , Yu Su-Peng , Wang Xingjun , Srinivasan Kartik , Papp Scott B. , Vahala Kerry , Bowers John E.
Published: September 2020

We demonstrated ultra-efficient frequency comb generation in AlGaAs-on-insulator ring resonators that have a quality factor beyond 1.5*106. The threshold power is as low as 36 pW.
Probing the Limits to Topological Protection in Photonic Crystal Waveguides and Cavities
Authors: Barczyk René , Arora Sonakshi , Bauer Thomas , Parappurath Nikhil , Verhagen Ewold , Kuipers Kobus
Published: September 2020

We employ near- and far-field optical microscopy to characterize the propagation of edge states in topological photonic crystal waveguides and cavities. We test fundamental and practical limits to topological protection, quantifying dispersion, loss, and scattering.
A synthetic Hall effect for photons
Authors: Kim Soonwook , Sohn Donggyu B. , Peterson Christopher W. , Bahl Gaurav
Published: September 2020

We experimentally realize a synthetic Hall effect for light, by producing synthetic electric and magnetic fields in a nanophotonic resonator chain. We show that the effect can be dynamically reconfigured and manifests as non-reciprocal light transmission through the system.
Hybrid external cavity laser with a 160-nm tuning range
Authors: Guo Yuyao , Zhou Linjie , Zhou Gangqiang , Zhao Ruiling , Lu Liangjun , Chen Jianping
Published: September 2020

We present a hybrid laser by using an InP reflective semiconductor optical amplifier chip butt-coupled with a SiN tunable reflector chip. The laser wavelength tuning range is 160 nm and the linewidth is 30 kHz.
Toward Frequency-Selective Surfaces via Doping of Zinc Oxide with a Focused Ion Beam
Authors: Mei Hongyan , Koch Alexander , Salman Jad , Wan Chenghao , Wambold Raymond , Hafermann Martin , Rensberg Jura , Ronning Carsten , Kats Mikhail A.
Published: September 2020

We demonstrate a method to modify the optical properties of zinc oxide by doping with gallium using a focused-ion beam system, which may be a promising way to create ultrathin plasmonic devices.
High-Efficiency Ultraviolet Emission from AlInN/GaN Nanowires Grown by Molecular Beam Epitaxy
Authors: Velpula Ravi Teja , Jain Barsha , Bui Ha Quoc Thang , Nguyen Hieu Pham Trung
Published: September 2020

The epitaxial growth and characterization of AlInN/GaN core-shell nanowire structures with highly stable emission and high internal quantum efficiency of ~52% in the ultraviolet wavelength range are presented.
Integrated ScAlN Photonic Circuits on Silicon Substrate
Authors: Zhu Shiyang , Zhong Qize , Li Nanxi , Hu Ting , Dong Yuan , Xu Zhengji , Zhou Yanyan , Fu Yuan Hsing , Singh Navab
Published: September 2020

ScAlN has been applied in piezoelectric micro-electro-mechanical systems, while application in photonics remains unexplored. Here, ScAlN photonic circuits on silicon are presented, demonstrating waveguide propagation loss of 9±2 dB/cm and microring quality factor of 1.4×104.
Single Photons and Single Spins: NV Centres Encapsulated in Silicon Nitride
Authors: Smith Joe , Ruz Jorge Monroy , Rarity John G. , Balram Krishna C.
Published: September 2020

We demonstrate nitrogen-rich silicon nitride is a viable quantum photonics platform, evidencing both the optical and spin properties of an individual NV centre is preserved after encapsulation, surpassing the single photon and single spin threshold.
Quantum Limits of Optical Beam Deflection Measurements of a Nanomechanical Resonator
Authors: Hao Shan , Singh Robinjeet , Purdy Thomas P.
Published: September 2020

Optical lever detection is a simple and robust method to measure small displacements. We report on our experimental efforts toward reaching and surpassing the quantum backaction limits of this method when probing a high Q nanomechanical resonator.
LiNbO3 Photonic Crystal Optical Modulator
Authors: Li Mingxiao , Ling Jingwei , He Yang , Javid Usman A. , Xue Shixin , Lin Qiang
Published: September 2020

We report LiNbO3 photonic-crystal electro-optic modulators (EOMs) with a modulation efficiency up to 11 pm/V and a bandwidth up to 17.5 GHz, the smallest LiNbO3 EOM ever demonstrated while with the highest modulation efficiency.
Electro-optic frequency shifting using coupled lithium-niobate microring resonators
Authors: Hu Yaowen , Yu Mengjie , Zhu Di , Sinclair Neil , Shams-Ansari Amirhassan , Shao Linbo , Holzgrafe Jeffery , Zhang Mian , Loncar Marko
Published: September 2020

We experimentally investigate electro-optic frequency shifting of continuous wave optical signal using harmonic RF signal. We demonstrate 11GHz shift with 98.2% efficiency and 1.25dB device insertion loss. This was accomplished by unidirectionally controlling the photon flow in frequency domain.
Photonics-to-Free-Space Interface in Lithium Niobate-on-Sapphire
Authors: Rajabzadeh Taha , Sarabalis Christopher J. , Atalar Okan , Safavi-Naeini Amir H.
Published: September 2020

We present a device in thin-film lithium niobate-on-sapphire that scatters light from a ridge waveguide into a 4.5 × 12.6 milliradian beam in free-space that can be steered by tuning the wavelength.
Approaches to Improve Performance of 60 GHz Radio-Over-Fiber Fronthaul Links
Authors: Lim Christina , Tian Yu , Nirmalathas Ampalanavapillai , Lee Ka-Lun
Published: September 2020

In this paper, we review the work we have done to improve the performance of users located at the cell boundary of a 60 GHz radio-over-fibre fronthaul using coordinated-multipoint (CoMP) together with non-orthogonal-multiple-access (NOMA).
5G Service Overlay in WDM Optical Access Network with Colorless Smart Edge Based on SiP MRM
Authors: Guan Xun , Dubé-Demers Raphaël , Shi Wei , Rusch Leslie Ann
Published: September 2020

We propose a low-cost, compact and colorless smart edge using silicon photonic microring modulators to overlay 5G services on wavelength division multiplexing (WDM) optical access networks; experimental results validate the effectiveness of this approach.
Two-dimensional Plasmonic Crystal Surface Emitting Lasers with Gain Medium of InGaAs/GaAs Quantum Wells
Authors: Huang Kuan-Ying , Wu Chu-Chun , Lin Gray , Lin Sheng-Di
Published: September 2020

Room-temperature plasmonic-crystal surface-emitting laser is demonstrated with a square-lattice gold nano-arrays on the surface of InGaAs/GaAs quantum well. The lasing peak determined by lattice constant shows excellent linewidth (<0.5 nm) and thermal stability (~0.083 nm/°C).
Towards a Transferable Standard for Nitrous Oxide Isotopomer Ratio
Authors: Sadiek Ibrahim , Hjältén Adrian , Stuhr Michael , Friedrichs Gernot , Foltynowicz Aleksandra
Published: September 2020

We report a novel approach for identifying the 15N site-preference in N2O from a chemical reaction using continuous wave cavity ringdown spectroscopy and comb-based Fourier transform spectroscopy, with the aim to establish the currently lacking international N2O isotopomer standard.
A Nitride Ring Isolator
Authors: Tian Hao , Liu Junqiu , Skehan Connor , Siddharth Anat , Kippenberg Tobias J. , Bhave Sunil A.
Published: September 2020

A silicon nitride optical ring isolator is realized by spatiotemporal modulation using bulk acoustic wave stress-optical transducers. By driving three actuators with fixed relative phases, over 17 dB isolation is achieved.
Degenerate LP mode asymmetric coupling and OAM mode directional transmission between weakly guiding FMFs
Authors: Fang Liang , Qin Yue , Liang Yize , Cao Han , Zhou Wei , Wang Hongya , Wang Jian
Published: September 2020

We fabricate a directional coupler by side-polishing few-mode fibers (FMFs) to experimentally investigate the higher-order linearly polarized (LP) mode coupling asymmetry, and realize orbital angular momentum (OAM) mode directional transmission by controlling the coupling length.
Beam Shaping with a Multicore Fiber Amplifier
Authors: Lin D. , Carpenter J. , Feng Y. , Jain S. , Jung Y. , Feng Y. , Zervas M. N. , Richardson D. J.
Published: September 2020

We experimentally generate various spatial modes (e.g. optical vector or vortex beams) from a coherently-combined 7-core Er/Yb-doped multicore fiber amplifier through control of the amplitude, phase and polarization state of the individual core beams.
Nonlinear Crystals for Efficient High-Energy Fifth- Harmonic Generation of Near-IR Lasers
Authors: Begishev I. A. , Ivanov V. V. , Patankar S. , Datte P. S. , Yang S. T. , Zuegel J. D. , Bromage J.
Published: September 2020

The fifth harmonic (211 nm) of a pulsed, joule-class Nd:YLF laser has been generated with efficiency up to 30% in BBO, CLBO, and ADP crystals. Nonlinear absorption was demonstrated to be a major limiting factor.
The LCLS-II Photo-Injector Drive Laser System
Authors: Gilevich Sasha , Alverson Shawn , Carbajo Sergio , Droste Stefan , Edstrom Steve , Fry Alan , Greenberg Michael , Lemons Randy , Miahnahri Alan , Polzin Wayne , Vetter Sharon , Zhou Feng
Published: September 2020

We present the new drive laser system for the photo-injector of the LCLS-II XFEL at SLAC, including the first commissioning results and challenges encountered due to high power, high repetition rate ultraviolet laser operation.
What makes the best chip-scale photonic sensor?
Authors: Kita Derek M. , Du Qingyang , Michon Jérôme , Gu Tian , Luo Zhengqian , Johnson Steven G. , Hu Juejun
Published: September 2020

We provide a detailed account regarding the design rationales of different essential components of a photonic chip-based sensing system: the sensing element, the light source, and the light analyzer or spectrometer.
Monitoring and Trimming of Integrated Silicon Photonic Circuits via Laser Irradiation
Authors: Biryukova Vera , Klitis Charalambos , Sorel Marc
Published: September 2020

We demonstrate a laser annealing technique capable of compensating for parameter and fabrication non-uniformity in complex silicon photonic devices. The technique does not compromise device performance and can be used for trimming at wafer level.
Unravelling the role of trap states on carrier dynamics of WS2 quantum dots
Authors: Karmakar Riyanka , Adarsh K.V.
Published: September 2020

Here, we studied the intriguing optical properties of WS2 quantum dots by various time-resolved spectroscopic techniques to get a comprehensive understanding of spectral and dynamical characteristics, specifically, we show long-lived ~ 95 ps trap-state emission.
Fully reconfigurable chip-based Brillouin microwave photonic multi-passband filter with high RF link gain
Authors: Garrett Matthew , Liu Yang , Ma Pan , Choi Duk-Yong , Madden Stephen J. , Eggleton Benjamin J.
Published: September 2020

Using a novel suppressed carrier phase modulation scheme, which increases RF gain for constant on-chip optical power, we demonstrate a microwave photonic filter with three independent passbands, low RF loss (-5dB) and deep out-of-band rejection.
Experimental Characterization of Bismuth-Doped Fibre Amplifier: Electrical NF, PDG, and XGM
Authors: Taengnoi Natsupa , Bottrill Kyle R. H. , Hong Yang , Wang Yu , Thipparapu Naresh K. , Sahu Jayanta K. , Petropoulos Periklis , Richardson David J.
Published: September 2020

We present a detailed characterisation of the emergent bismuth-doped fibre amplifier, characterising performance in terms of electrical noise figure, polarisation dependent gain, and cross gain modulation. The results support its suitability for high capacity links.
Large-area Flat Optics via Immersion Lithography on CMOS Platform for Laser Beam Shaping
Authors: Fu Yuan Hsing , Li Nanxi , Chen Lei , Zhong Qize , Dong Yuan , Li Dongdong , Xu Zhengji , Hu Ting , Zhou Yanyan , Lai Keng Heng , Zhu Min , Zhu Shiyang , Lin Qunying , Huang Shengdi , Singh Navab
Published: September 2020

We report a large-area metasurface beam shaper via 12-inch immersion lithography CMOS platform. A3 × 3 mm2 metasurface beam shaper is designed to transfer a Gaussian intensity distribution to a Top-Hat intensity distribution.
Graphene Assisted Preparation of Large area Ag Nanoparticles with Periodic Arrangement towards Raman Enhancement
Authors: Dong Yibo , Xu Chen , Xie Yiyang , Pan Guanzhong , Wang Qiuhua , Sun Jie
Published: September 2020

A graphene assisted method for preparation of large area Ag NPs with periodic arrangement is introduced in this paper. Graphene is used as a perfect barrier layer to prevent Ag atoms from evaporation.
Z-Scan Measurements of CdSiP2 at OPA Pumping Wavelengths
Authors: Ferdinandus M. R. , Gengler J. J. , Averett K. L. , Zawilski K. T. , Schunemann P. G. , Liebig C. M.
Published: September 2020

We measure the birefringence of nonlinear optical properties of cadmium silicon phosphide via the Z-scan technique at common pumping wavelengths. We discuss the implications of the NLO properties on the parametric conversion efficiency
A Compact MHz-repetition-rate VUV Source: Implementation, Modeling, and Applications
Authors: Hickstein Daniel D. , Couch David E. , Kirchner Matthew S. , Domingue Scott R. , Ramirez Jessica J. , Ellison G. Barney , Labbe Nicole J. , Peterson Brennan , Murnane Margaret M. , Backus Sterling J. , Kapteyn Henry C.
Published: September 2020

Utilizing highly cascaded harmonic generation, we upconvert a MHz fiber laser to the vacuum ultraviolet (up to 18 eV). We apply the source to combustion-chemistry experiments and conduct numerical simulation to understand the nonlinear generation process.