Browsing by Author "Hasan, Tawfique"

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  • 152 fs nanotube-mode-locked thulium-doped all-fiber laser
    (2016-07-04) Wang, Jinzhang; Liang, Xiaoyan; Hu, Guohua; Zheng, Zhijian; Lin, Shenghua; Ouyang, Deqin; Wu, Xu; Yan, Peiguang; Ruan, Shuangchen; Sun, Zhipei; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Ultrafast fiber lasers with broad bandwidth and short pulse duration have a variety of applications, such as ultrafast time-resolved spectroscopy and supercontinuum generation. We report a simple and compact all-fiber thulium-doped femtosecond laser mode-locked by carbon nanotubes. The oscillator operates in slightly normal cavity dispersion at 0.055 ps 2, and delivers 152 fs pulses with 52.8 nm bandwidth and 0.19 nJ pulse energy. This is the shortest pulse duration and the widest spectral width demonstrated from Tm-doped all-fiber lasers based on 1 or 2 dimensional nanomaterials, underscoring their growing potential as versatile saturable absorber materials.
  • 172 fs, 24.3 kW peak power pulse generation from a Ho-doped fiber laser system
    (2018-10-01) Wang, Mengmeng; Zhang, Hui; Wei, Rongling; Zhu, Zexiu; Ruan, Shuangchen; Yan, Peiguang; Wang, Jinzhang; Hasan, Tawfique; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We demonstrate a high-peak-power femtosecond fiber laser system based on single-mode holmium (Ho)-doped fibers. 833 fs, 27.7 MHz pulses at 2083.4 nm generated in a passively mode-locked Ho fiber laser are amplified and compressed to near transform-limited 172 fs, 7.2 nJ pulses with 24.3 kW peak power. We achieve this performance level by using the soliton effect and high-order soliton compression. To the best of our knowledge, this is the first demonstration of sub-200 fs pulses, with peak power exceeding 10 kW from a Ho-doped single-mode fiber laser system without using bulk optics compressors.
  • Black phosphorus ink formulation for inkjet printing of optoelectronics and photonics
    (2017-12-01) Hu, Guohua; Albrow-Owen, Tom; Jin, Xinxin; Ali, Ayaz; Hu, Yuwei; Howe, Richard C.T.; Shehzad, Khurram; Yang, Zongyin; Zhu, Xuekun; Woodward, Robert I.; Wu, Tien Chun; Jussila, Henri; Wu, Jiang Bin; Peng, Peng; Tan, Ping Heng; Sun, Zhipei; Kelleher, Edmund J.R.; Zhang, Meng; Xu, Yang; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Black phosphorus is a two-dimensional material of great interest, in part because of its high carrier mobility and thickness dependent direct bandgap. However, its instability under ambient conditions limits material deposition options for device fabrication. Here we show a black phosphorus ink that can be reliably inkjet printed, enabling scalable development of optoelectronic and photonic devices. Our binder-free ink suppresses coffee ring formation through induced recirculating Marangoni flow, and supports excellent consistency (< 2% variation) and spatial uniformity (< 3.4% variation), without substrate pre-treatment. Due to rapid ink drying (< 10 s at < 60 °C), printing causes minimal oxidation. Following encapsulation, the printed black phosphorus is stable against long-term (> 30 days) oxidation. We demonstrate printed black phosphorus as a passive switch for ultrafast lasers, stable against intense irradiation, and as a visible to near-infrared photodetector with high responsivities. Our work highlights the promise of this material as a functional ink platform for printed devices.
  • Broadband miniaturized spectrometers with a van der Waals tunnel diode
    (2024-01-17) Uddin, Md Gius; Das, Susobhan; Shafi, Abde Mayeen; Wang, Lei; Cui, Xiaoqi; Nigmatulin, Fedor; Ahmed, Faisal; Liapis, Andreas C.; Cai, Weiwei; Yang, Zongyin; Lipsanen, Harri; Hasan, Tawfique; Yoon, Hoon Hahn; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Miniaturized spectrometers are of immense interest for various on-chip and implantable photonic and optoelectronic applications. State-of-the-art conventional spectrometer designs rely heavily on bulky dispersive components (such as gratings, photodetector arrays, and interferometric optics) to capture different input spectral components that increase their integration complexity. Here, we report a high-performance broadband spectrometer based on a simple and compact van der Waals heterostructure diode, leveraging a careful selection of active van der Waals materials- molybdenum disulfide and black phosphorus, their electrically tunable photoresponse, and advanced computational algorithms for spectral reconstruction. We achieve remarkably high peak wavelength accuracy of ~2 nanometers, and broad operation bandwidth spanning from ~500 to 1600 nanometers in a device with a ~ 30×20 μm2 footprint. This diode-based spectrometer scheme with broadband operation offers an attractive pathway for various applications, such as sensing, surveillance and spectral imaging.
  • Chirality logic gates
    (2022-12-07) Zhang, Yi; Wang, Yadong; Dai, Yunyun; Bai, Xueyin; Hu, Xuerong; Du, Luojun; Hu, Hai; Yang, Xiaoxia; Li, Diao; Dai, Qing; Hasan, Tawfique; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The ever-growing demand for faster and more efficient data transfer and processing has brought optical computation strategies to the forefront of research in next-generation computing. Here, we report a universal computing approach with the chirality degree of freedom. By exploiting the crystal symmetry–enabled well-known chiral selection rules, we demonstrate the viability of the concept in bulk silica crystals and atomically thin semiconductors and create ultrafast (<100-fs) all-optical chirality logic gates (XNOR, NOR, AND, XOR, OR, and NAND) and a half adder. We also validate the unique advantages of chirality gates by realizing multiple gates with simultaneous operation in a single device and electrical control. Our first demonstrations of logic gates using chiral selection rules suggest that optical chirality could provide a powerful degree of freedom for future optical computing.
  • Engineering symmetry breaking in 2D layered materials
    (2021-03) Du, Luojun; Hasan, Tawfique; Castellanos-Gomez, Andres; Liu, Gui Bin; Yao, Yugui; Lau, Chun Ning; Sun, Zhipei
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    Symmetry breaking in 2D layered materials plays a significant role in their macroscopic electrical, optical, magnetic and topological properties, including, but not limited to, spin-polarization effects, valley-contrasting physics, nonlinear Hall effects, nematic order, ferroelectricity, Bose-Einstein condensation and unconventional superconductivity. Engineering symmetry breaking of 2D layered materials not only offers extraordinary opportunities to tune their physical properties but also provides unprecedented possibilities to introduce completely new physics and technological innovations in electronics, photonics and optoelectronics. Indeed, over the past 15 years, a wide variety of physical, structural and chemical approaches have been developed to engineer the symmetry breaking of 2D layered materials. In this Technical Review, we focus on the recent progress on engineering the breaking of inversion, rotational, time-reversal and gauge symmetries in 2D layered materials, and present our perspectives on how these may lead to new physics and applications.
  • A general ink formulation of 2D crystals for wafer-scale inkjet printing
    (2020-08-01) Hu, Guohua; Yang, Lisong; Yang, Zongyin; Wang, Yubo; Jin, Xinxin; Dai, Jie; Wu, Qing; Liu, Shouhu; Zhu, Xiaoxi; Wang, Xiaoshan; Wu, Tien Chun; Howe, Richard C.T.; Albrow-Owen, Tom; Ng, Leonard W.T.; Yang, Qing; Occhipinti, Luigi G.; Woodward, Robert I.; Kelleher, Edmund J.R.; Sun, Zhipei; Huang, Xiao; Zhang, Meng; Bain, Colin D.; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Recent advances in inkjet printing of two-dimensional (2D) crystals show great promise for next-generation printed electronics development. Printing nonuniformity, however, results in poor reproducibility in device performance and remains a major impediment to their large-scale manufacturing. At the heart of this challenge lies the coffee-ring effect (CRE), ring-shaped nonuniform deposits formed during postdeposition drying. We present an experimental study of the drying mechanism of a binary solvent ink formulation. We show that Marangoni-enhanced spreading in this formulation inhibits contact line pinning and deforms the droplet shape to naturally suppress the capillary flows that give rise to the CRE. This general formulation supports uniform deposition of 2D crystals and their derivatives, enabling scalable and even wafer-scale device fabrication, moving them closer to industrial-level additive manufacturing.
  • Giant All-Optical Modulation of Second-Harmonic Generation Mediated by Dark Excitons
    (2021-08-18) Wang, Yadong; Das, Susobhan; Iyikanat, Fadil; Dai, Yunyun; Li, Shisheng; Guo, Xiangdong; Yang, Xiaoxia; Cheng, Jinluo; Hu, Xuerong; Ghotbi, Masood; Ye, Fangwei; Lipsanen, Harri; Wu, Shiwei; Hasan, Tawfique; Gan, Xuetao; Liu, Kaihui; Sun, Dong; Dai, Qing; García De Abajo, F. Javier; Zhao, Jianlin; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    All-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elusive. Here, we demonstrate giant and broadband all-optical ultrafast modulation of second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides mediated by the modified excitonic oscillation strength produced upon optical pumping. We reveal a dominant role of dark excitons to enhance SHG by up to a factor of ∼386 at room temperature, 2 orders of magnitude larger than the current state-of-the-art all-optical modulation results. The amplitude and sign of the observed SHG modulation can be adjusted over a broad spectral range spanning a few electronvolts with ultrafast response down to the sub-picosecond scale via different carrier dynamics. Our results not only introduce an efficient method to study intriguing exciton dynamics, but also reveal a new mechanism involving dark excitons to regulate all-optical nonlinear photonics.
  • High-Power Femtosecond Pulse Generation from an All-Fiber Er-Doped Chirped Pulse Amplification System
    (2020-04) Wei, Rongling; Wang, Mengmeng; Zhu, Zexiu; Lai, Weiyu; Yan, Peiguang; Ruan, Shuangchen; Wang, Jinzhang; Sun, Zhipei; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We demonstrate a compact all-fiber Er-doped chirped pulse amplification (CPA) system that can produce ∼344 fs pulses with an average power of up to 1.02 W and a repetition rate of 40.6 MHz at 1.56 μm (corresponding to an energy of 25.1 nJ). The pulse compressor in the CPA system is based on a hollow core photonic crystal fiber which is directly butt-coupled to the silica fiber. A mismatched negative third-order dispersion is used to compensate the accumulated nonlinear phase shift in the amplification process for the first time, resulting in the generation of sub-400 fs pulses from an all-fiber Watt-level Er-doped CPA system. Our system architecture offers a possibility for ultrashort pulse generation from all-fiber Er-doped CPA lasers.
  • Inkjet Printed Large-Area Flexible Few-Layer Graphene Thermoelectrics
    (2018-05-30) Juntunen, Taneli; Jussila, Henri; Ruoho, Mikko; Liu, Shouhu; Hu, Guohua; Albrow-Owen, Tom; Ng, Leonard W.T.; Howe, Richard C.T.; Hasan, Tawfique; Sun, Zhipei; Tittonen, Ilkka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Graphene-based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene-based thermoelectric devices, optimization of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet-printed large-area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so-called phonon-glass electron-crystal character (i.e., electrical transport behavior akin to that of few-layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all-graphene films show a room-temperature thermoelectric power factor of 18.7 µW m−1 K−2, representing over a threefold improvement to previous solution-processed all-graphene structures. The demonstration of inkjet-printed thermoelectric devices underscores the potential for future flexible, scalable, and low-cost thermoelectric applications, such as harvesting energy from body heat in wearable applications.
  • Lattice Dynamics, Phonon Chirality, and Spin–Phonon Coupling in 2D Itinerant Ferromagnet Fe3GeTe2
    (2019-11-28) Du, Luojun; Tang, Jian; Zhao, Yanchong; Li, Xiaomei; Yang, Rong; Hu, Xuerong; Bai, Xueyin; Wang, Xiao; Watanabe, Kenji; Taniguchi, Takashi; Shi, Dongxia; Yu, Guoqiang; Bai, Xuedong; Hasan, Tawfique; Zhang, Guangyu; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fe3GeTe2 has emerged as one of the most fascinating van der Waals crystals due to its 2D itinerant ferromagnetism, topological nodal lines, and Kondo lattice behavior. However, lattice dynamics, chirality of phonons, and spin-phonon coupling in this material, which set the foundation for these exotic phenomena, have remained unexplored. Here, the first experimental investigation of the phonons and mutual interactions between spin and lattice degrees of freedom in few-layer Fe3GeTe2 is reported. The results elucidate three prominent Raman modes at room temperature: two A(1g)(Gamma) and one E-2g(Gamma) phonons. The doubly degenerate E-2g(Gamma) mode reverses the helicity of incident photons, indicating the pseudoangular momentum and chirality. Through analysis of temperature-dependent phonon energies and lifetimes, which strongly diverge from the anharmonic model below Curie temperature, the spin-phonon coupling in Fe3GeTe2 is determined. Such interaction between lattice oscillations and spin significantly enhances the Raman susceptibility, allowing to observe two additional Raman modes at the cryogenic temperature range. In addition, laser radiation-induced degradation of Fe3GeTe2 in ambient conditions and the corresponding Raman fingerprint is revealed. The results provide the first experimental analysis of phonons in this novel 2D itinerant ferromagnet and their applicability for further fundamental studies and application development.
  • Metasurface spectrometers beyond resolution-sensitivity constraints
    (2024-12-06) Tang, Feng; Wu, Jingjun; Albrow-Owen, Tom; Cui, Hanxiao; Chen, Fujia; Shi, Yaqi; Zou, Lan; Chen, Jun; Guo, Xuhan; Sun, Yijun; Luo, Jikui; Ju, Bingfeng; Huang, Jing; Liu, Shuangli; Li, Bo; Yang, Liming; Munro, Eric A.; Zheng, Wanguo; Joyce, Hannah J.; Chen, Hongsheng; Che, Lufeng; Dong, Shurong; Sun, Zhipei; Hasan, Tawfique; Ye, Xin; Yang, Yihao; Yang, Zongyin
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Conventional spectrometer designs necessitate a compromise between their resolution and sensitivity, especially as device and detector dimensions are scaled down. Here, we report on a miniaturizable spectrometer platform where light throughput onto the detector is instead enhanced as the resolution is increased. This planar, CMOS-compatible platform is based around metasurface encoders designed to exhibit photonic bound states in the continuum, where operational range can be altered or extended simply through adjusting geometric parameters. This system can enhance photon collection efficiency by up to two orders of magnitude versus conventional designs; we demonstrate this sensitivity advantage through ultralow-intensity fluorescent and astrophotonic spectroscopy. This work represents a step forward for the practical utility of spectrometers, affording a route to integrated, chip-based devices that maintain high resolution and SNR without requiring prohibitively long integration times.
  • Miniaturized spectrometers with a tunable van der Waals junction
    (2022-10-21) Yoon, Hoon Hahn; Fernandez, Henry A.; Nigmatulin, Fedor; Cai, Weiwei; Yang, Zongyin; Cui, Hanxiao; Ahmed, Faisal; Cui, Xiaoqi; Uddin, Md Gius; Minot, Ethan D.; Lipsanen, Harri; Kim, Kwanpyo; Hakonen, Pertti; Hasan, Tawfique; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Miniaturized computational spectrometers, which can obtain incident spectra using a combination of device spectral responses and reconstruction algorithms, are essential for on-chip and implantable applications. Highly sensitive spectral measurement using a single detector allows the footprints of such spectrometers to be scaled down while achieving spectral resolution approaching that of benchtop systems. We report a high-performance computational spectrometer based on a single van der Waals junction with an electrically tunable transport-mediated spectral response. We achieve high peak wavelength accuracy (similar to 0.36 nanometers), high spectral resolution (similar to 3 nanometers), broad operation bandwidth (from similar to 405 to 845 nanometers), and proof-of-concept spectral imaging. Our approach provides a route toward ultraminiaturization and offers unprecedented performance in accuracy, resolution, and operation bandwidth for single-detector computational spectrometers.
  • New Approach for Thickness Determination of Solution-Deposited Graphene Thin Films
    (2017-06-30) Jussila, Henri; Albrow-Owen, Tom; Yang, He; Hu, Guohua; Aksimsek, Sinan; Granqvist, Niko; Lipsanen, Harri; Howe, Richard C.T.; Sun, Zhipei; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Solution processing-based fabrication techniques such as liquid phase exfoliation may enable economically feasible utilization of graphene and related nanomaterials in real-world devices in the near future. However, measurement of the thickness of the thin film structures fabricated by these approaches remains a significant challenge. By using surface plasmon resonance (SPR), a simple, accurate, and quick measurement of the deposited thickness for inkjet-printed graphene thin films is reported here. We show that the SPR technique is convenient and well-suited for the measurement of thin films formulated from nanomaterial inks, even at sub-10 nm thickness. We also demonstrate that the analysis required to obtain results from the SPR measurements is significantly reduced compared to that required for atomic force microscopy (AFM) or stylus profilometer, and much less open to interpretation. The gathered data implies that the film thickness increases linearly with increasing number of printing repetitions. In addition, SPR also reveals the complex refractive index of the printed thin films composed of exfoliated graphene flakes, providing a more rigorous explanation of the optical absorption than that provided by a combination of AFM/profilometer and the extinction coefficient of mechanically exfoliated graphene flakes. Our results suggest that the SPR method may provide a new pathway for the thickness measurement of thin films fabricated from any nanomaterial containing inks.
  • Single-nanowire spectrometers
    (2019-09-06) Yang, Zongyin; Albrow-Owen, Tom; Cui, Hanxiao; Alexander-Webber, Jack; Gu, Fuxing; Wang, Xiaomu; Wu, Tien Chun; Zhuge, Minghua; Williams, Calum; Wang, Pan; Zayats, Anatoly V.; Cai, Weiwei; Dai, Lun; Hofmann, Stephan; Overend, Mauro; Tong, Limin; Yang, Qing; Sun, Zhipei; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Spectrometers with ever-smaller footprints are sought after for a wide range of applications in which minimized size and weight are paramount, including emerging in situ characterization techniques. We report on an ultracompact microspectrometer design based on a single compositionally engineered nanowire. This platform is independent of the complex optical components or cavities that tend to constrain further miniaturization of current systems. We show that incident spectra can be computationally reconstructed from the different spectral response functions and measured photocurrents along the length of the nanowire. Our devices are capable of accurate, visible-range monochromatic and broadband light reconstruction, as well as spectral imaging from centimeter-scale focal planes down to lensless, single-cell-scale in situ mapping.
  • Soliton Mode-Locked Large-Mode-Area Tm-Doped Fiber Oscillator
    (2020-01-15) Zhu, Zexiu; Sun, Zhipei; Zhang, Hui; Wang, Mengmeng; Wei, Rongling; Zheng, Zhijian; Yan, Peiguang; Ruan, Shuangchen; Wang, Jinzhang; Hasan, Tawfique
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report a passively mode-locked fiber oscillator based on thulium-doped large-mode-area (LMA) fiber. Reliably mode-locking soliton operation can be readily achieved after the suppression of the higher-order modes by using mode field adapters in combination with coiling fiber method. The laser delivers 600-fs level pulses at ~\mu \text{m}$ with an average power of up to 243 mW and a repetition rate of 53.7 MHz. The output corresponds to a maximum pulse energy of 4.5 nJ, >5 times larger than that of a similar homemade mode-locked Tm laser with the LMA fibers replaced by single mode fibers, coinciding with theoretical prediction. The successful demonstration of our soliton mode-locked LMA fiber laser at ~\mu \text{m}$ offers another strategy for high performance ultrafast fiber sources at mid-infrared region.
  • Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers
    (2017-12-01) Säynätjoki, Antti; Karvonen, Lasse; Rostami, Habib; Autere, Anton; Mehravar, Soroush; Lombardo, Antonio; Norwood, Robert A.; Hasan, Tawfique; Peyghambarian, Nasser; Lipsanen, Harri; Kieu, Khanh; Ferrari, Andrea C.; Polini, Marco; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large χ (3). We explain this by calculating the nonlinear response functions of 1L-MoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging.
  • Wavelength and pulse duration tunable ultrafast fiber laser mode-locked with carbon nanotubes
    (2018-02-09) Li, Diao; Jussila, Henri; Wang, Yadong; Hu, Guohua; Albrow-Owen, Tom; Howe, Richard C. T.; Ren, Zhaoyu; Bai, Jintao; Hasan, Tawfique; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Ultrafast lasers with tunable parameters in wavelength and time domains are the choice of light source for various applications such as spectroscopy and communication. Here, we report a wavelength and pulse-duration tunable mode-locked Erbium doped fiber laser with single wall carbon nanotube-based saturable absorber. An intra-cavity tunable filter is employed to continuously tune the output wavelength for 34 nm (from 1525 nm to 1559 nm) and pulse duration from 545 fs to 6.1 ps, respectively. Our results provide a novel light source for various applications requiring variable wavelength or pulse duration.