ORCID Profile
0000-0002-0735-0447
Current Organisation
Nanyang Technological University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: American Physical Society (APS)
Date: 16-05-2011
Publisher: OSA
Date: 2012
Publisher: Elsevier BV
Date: 02-2007
Publisher: IEE
Date: 2005
DOI: 10.1049/CP:20050707
Publisher: The Optical Society
Date: 13-02-2013
DOI: 10.1364/OE.21.004405
Publisher: American Physical Society (APS)
Date: 18-12-2015
Publisher: OSA
Date: 2012
Publisher: American Physical Society (APS)
Date: 07-11-2011
Publisher: Optica Publishing Group
Date: 19-02-2021
DOI: 10.1364/OE.418217
Abstract: We numerically investigate soliton self-compression in the higher-order modes of a gas-filled capillary with decreasing pressure. We demonstrate four times enhancement in the compression with the decreasing pressure compared to the equivalent constant pressure case in the HE 12 mode, reaching sub-cycle duration of 1.85 fs at its output. Moreover, the negative pressure gradient effectively suppresses the intermodal coupling in the later stage of the compressor, which helps to maintain high output mode purity. These findings are of direct benefit for applications that require ultrashort light pulses in unconventional spatial beam profiles, including in nonlinear frequency conversion, microscopy, micromachining, and particle manipulation.
Publisher: American Physical Society (APS)
Date: 26-08-2015
Publisher: American Physical Society (APS)
Date: 07-11-2011
Publisher: IEEE
Date: 2010
Publisher: American Physical Society (APS)
Date: 13-09-2012
Publisher: OSA
Date: 2012
Publisher: The Optical Society
Date: 16-06-2015
DOI: 10.1364/OL.40.002949
Publisher: OSA
Date: 2012
Publisher: Springer Science and Business Media LLC
Date: 17-12-2019
Publisher: Optica Publishing Group
Date: 30-10-2009
Publisher: Optica Publishing Group
Date: 15-12-2020
DOI: 10.1364/OL.411109
Abstract: We demonstrate frequency down-conversions of femtosecond pulses through dispersive wave generation and degenerate four-wave mixing in a gas-filled anti-resonant hollow-core fiber. These are achieved by exploiting the rapid variation of the dispersion in the fiber’s transmission band edge. In this approach, the wavelength of the down-shifted radiation is governed solely by the thickness of the dielectric wall at the core–cladding interface, while other system parameters are accountable only for inducing sufficient nonlinear phase shifts. With the right choice of cladding wall thickness, the concept can be applied directly for generating high-power mid-infrared femtosecond pulses.
Publisher: American Physical Society (APS)
Date: 26-07-2007
Publisher: The Optical Society
Date: 11-06-2015
Publisher: OSA
Date: 2012
Publisher: MDPI AG
Date: 05-02-2020
DOI: 10.3390/APP10031069
Abstract: This paper presents the fabrication of a fiber Bragg grating (FBG)-based Fabry–Perot (FP) structure (7 mm total length) in an adiabatic fiber taper, investigates its strain and temperature characteristics, and compares the sensing characteristics with a standard polyimide coated FBG sensor. Firstly, a simulation of the said structure is presented, followed by the fabrication of an adiabatic fiber taper having the outer diameter reduced to 70 μ m (core diameter to 4.7 μ m). Next, the sensing structure, composed of two identical uniform FBG spaced apart by a small gap, is directly inscribed point-by-point using infrared femtosecond laser (fs-laser) micromachining. Lastly, the strain and temperature behavior for a range up to 3400 μ ε and 225 ° C, respectively, are investigated for the fabricated sensor and the FBG, and compared. The fabricated sensor attains a higher strain sensitivity (2.32 pm/ μ ε ) than the FBG (0.73 pm/ μ ε ), while both the sensors experience similar sensitivity to temperature (8.85 pm/ ° C). The potential applications of such sensors include continuous health monitoring where precise strain detection is required.
Publisher: OSA
Date: 2012
Publisher: OSA
Date: 2013
Publisher: American Physical Society (APS)
Date: 08-09-2021
Publisher: IOP Publishing
Date: 26-04-2016
Publisher: Optica Publishing Group
Date: 23-11-2021
DOI: 10.1364/OL.447108
Abstract: We present an antiresonant hollow-core fiber-based bandpass optical filter. The device is realized by tapering down a section of tubular hollow-core fiber to a ratio of less than 0.5. Sweeping of the tube wall thickness-induced resonant bands in the down- and up-transition sections of the taper suppresses the blue side of the spectrum, while the red side filtering exploits the increased confinement loss at the taper waist that depends sharply on the wavelength-to-core-diameter ratio. These working principles of the filter make it possible to customize the location and width of the passband by tailoring the fiber design and taper profile. We achieve a 350-nm-wide bandpass filter with the minimum insertion loss of 1.3 dB in the passband and up to 40 dB suppression in the lossbands. We anticipate the filter to become one of the essential components in all-hollow-core fiberized optical systems.
Publisher: American Physical Society (APS)
Date: 17-07-2009
Publisher: IEEE
Date: 05-2013
Publisher: American Association for the Advancement of Science (AAAS)
Date: 15-10-2021
Abstract: Cytotoxic T lymphocytes (CTLs) can terminate both virally infected cells and cancer cells by secreting cytolytic proteins such as perforin and granzyme B. CTLs are particularly effective because they can sequentially kill multiple targets in a process called serial killing. Lisci et al . have identified mitochondria as important regulators of CTL killing. Mice lacking the deubiquitinase USP30 have CTLs acutely depleted of mitochondria, and these cells have reduced killing ability but normal motility, signaling, and secretion. Surprisingly, the mitochondria’s metabolic functions were not required for this process. Rather, mitochondrial translation proved indispensable for CTL cytolytic protein synthesis and sustained CTL killing. —STS
Publisher: The Optical Society
Date: 07-10-2011
DOI: 10.1364/OE.19.021018
Publisher: OSA
Date: 2013
Publisher: The Optical Society
Date: 27-03-2015
Publisher: Office of Scientific and Technical Information (OSTI)
Date: 15-11-2021
DOI: 10.2172/1832347
Publisher: Springer International Publishing
Date: 16-11-2017
Publisher: IOP Publishing
Date: 09-2020
Publisher: The Royal Society
Date: 11-06-2018
Abstract: Prigogine’s ideas of systems far from equilibrium and self-organization (Prigogine & Lefever. 1968 J. Chem. Phys. 48 , 1695–1700 ( doi:10.1063/1.1668896 ) Glansdorff & Prigogine. 1971 Thermodynamic theory of structures, stability and fluctuations . New York, NY/London, UK: Wiley) deeply influenced physics, and soliton science in particular. These ideas allowed the notion of solitons to be extended from purely integrable cases to the concept of dissipative solitons. The latter are qualitatively different from the solitons in integrable and Hamiltonian systems. The variety in their forms is huge. In this paper, one recent ex le is considered—dissipative solitons with extreme spikes (DSESs). It was found that DSESs exist in large regions of the parameter space of the complex cubic–quintic Ginzburg–Landau equation. A continuous variation in any of its parameters results in a rich structure of bifurcations. This article is part of the theme issue ‘Dissipative structures in matter out of equilibrium: from chemistry, photonics and biology (part 1)’.
Publisher: Optica Publishing Group
Date: 23-02-2022
DOI: 10.1364/OE.451033
Abstract: We proposed and demonstrated mode cleaning in a high-power fiber laser by integrating an anti-resonant hollow-core fiber (AR-HCF) into a multimode laser cavity of an ytterbium (Yb)-doped fiber (YDF). An in-house mode-matched AR-HCF was fusion-spliced to a commercial multimode LMA-YDF, ensuring efficient fundamental mode coupling. The AR-HCF inflicts a high propagation loss selectively on higher-order modes, facilitating fundamental mode operation. Thus, the AR-HCF works as an efficient spatial mode filter embedded in the multimode fiber laser cavity and reinforces preferential lification of the fundamental mode. Beam quality factor enhancement was achieved from M 2 = 2.09 to 1.39 at an output power of 57.7 W (pump-power limited). The beam quality can be further improved by refining the AR-HCF fabrication. The proposed technique has a great potential to be exploited in other multimode fiber laser cavities involving erbium- or thulium-doped fibers and obviates the need for complicated specialty active fiber designs. Compared with the commonly used fiber bending technique, our method can achieve an efficient higher-order mode suppression without inducing mode-field deterioration.
Publisher: OSA
Date: 2012
Publisher: IOP Publishing
Date: 16-01-2013
Publisher: IEEE
Date: 06-2017
Publisher: OSA
Date: 2007
Publisher: The Optical Society
Date: 30-11-2011
Publisher: American Physical Society (APS)
Date: 19-08-2008
Publisher: OSA
Date: 2011
Publisher: IEEE
Date: 09-2019
Publisher: OSA
Date: 2014
Publisher: Optica Publishing Group
Date: 07-01-2020
DOI: 10.1364/OE.382516
Abstract: We present a numerical investigation on the effect of introducing the second ring of antiresonant tubes on the guiding properties of the negative-curvature fiber. We determine the range of structural parameters for achieving the optimum light guidance in the double-ring geometry. Our study shows that the double-ring negative-curvature fiber can improve the confinement loss by up to four orders of magnitude with considerably better bending and single-mode performance when compared to its single-ring counterpart.
Publisher: OSA
Date: 2012
Publisher: Springer Science and Business Media LLC
Date: 28-03-2014
Publisher: Optica Publishing Group
Date: 04-10-2023
DOI: 10.1364/OL.501173
Publisher: Optica Publishing Group
Date: 13-11-2008
Publisher: Elsevier BV
Date: 06-2023
Publisher: American Physical Society (APS)
Date: 25-03-2009
Publisher: The Optical Society
Date: 06-02-2017
DOI: 10.1364/OL.42.000703
Publisher: IEEE
Date: 05-2013
Publisher: IEEE
Date: 07-2006
Publisher: Wiley
Date: 22-03-2023
Abstract: A fiber‐based approach that generates mid‐infrared femtosecond pulses in the 3–4 m spectral region with microjoule‐level single pulse energy is demonstrated. This is realized in a piece of gas‐filled antiresonant hollow‐core fiber that is pumped by a two‐micron light source. A rapid variation of the dispersion near a structural resonance of the fiber creates a phase‐matching point in mid‐infrared, which mediates the frequency‐down conversion. Femtosecond pulses centered at 3.16 m wavelength with the pulse energy of more than 1 J are generated, achieving a conversion efficiency as high as 8.2%. The emission wavelength is determined solely by the dielectric wall thickness of cladding elements, while the yield is subject to other experimental parameters. This, combined with high power‐handling capability of hollow‐core fibers, makes it possible to power scale the mid‐infrared output by either increasing the pulse energy or repetition rate of the pump. The technique presents a new pathway to build an all‐fiber‐based mid‐infrared supercontinuum source, which promises to be a powerful new tool for ultrahigh sensitivity molecular spectroscopy.
Publisher: MDPI AG
Date: 14-04-2021
Publisher: American Physical Society (APS)
Date: 26-07-2019
Publisher: American Physical Society (APS)
Date: 23-01-2023
Publisher: OSA
Date: 2012
Publisher: OSA
Date: 2012
Publisher: American Physical Society (APS)
Date: 10-05-2023
Publisher: IOP Publishing
Date: 24-07-2020
Publisher: Optica Publishing Group
Date: 31-03-2021
DOI: 10.1364/PRJ.415778
Abstract: We demonstrate the generation of wavelength-tunable deep-ultraviolet pulses in a small-mode-area hollow-core fiber fabricated by tapering a nodeless tubular-type hollow-core fiber. Down-scaling of the cross-sectional geometry reduces the pump energy requirement for inducing sufficient nonlinear effects, presenting a unique opportunity for staging low-energy-threshold gas-based nonlinear optics. We report the onset of the ultraviolet light with the pump pulse energy as low as 125 nJ. Our numerical analysis shows that the frequency conversion arises due to soliton phase matching, and therefore shot-to-shot coherence of the ultraviolet emission is well-preserved. It offers a promising platform for a compact ultraviolet frequency comb source.
Publisher: The Optical Society
Date: 11-2016
DOI: 10.1364/OL.41.005122
Publisher: OSA
Date: 2012
Publisher: IEEE
Date: 07-2017
Publisher: Wiley
Date: 18-12-2015
Publisher: AIP Publishing
Date: 12-2018
DOI: 10.1063/1.5053941
Abstract: We investigate the dynamics of modulation instability (MI) and the corresponding breather solutions to the extended nonlinear Schrödinger equation that describes the full scale growth-decay cycle of MI. As an ex le, we study modulation instability in connection with the fourth-order equation in detail. The higher-order equations have free parameters that can be used to control the growth-decay cycle of the MI that is, the growth rate curves, the time of evolution, the maximal litude, and the spectral content of the Akhmediev Breather strongly depend on these coefficients.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 15-09-2018
Publisher: Optica Publishing Group
Date: 09-07-2021
DOI: 10.1364/OE.432314
Abstract: We present a numerical analysis on bending-induced loss and bending-enhanced higher-order mode suppression in negative curvature fibers. We provide underlying mechanisms on how geometrical parameters affect the bending properties. We find that fiber parameters influence the bending performance by altering the resonant coupling conditions, as well as light leakage through inter-tube gaps. We identify regions in the parameter space that exhibit excellent bending properties and offer general guidelines for designing negative curvature fibers that are less sensitive to bending. Moreover, we explore the possibility of enhancing higher-order core mode suppression through mechanical bending. We find that up to nine-fold increase in the higher-order mode extinction ratio can be achieved by bending the fiber.
Publisher: The Optical Society
Date: 18-10-2010
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 15-08-2022
Publisher: OSA
Date: 2014
Publisher: IEEE
Date: 06-2019
Publisher: Optica Publishing Group
Date: 09-09-2020
DOI: 10.1364/OE.400267
Abstract: We numerically investigate the role of cladding geometries in two widely used anti-resonant hollow-core fiber designs with negative curvatures, the tubular negative-curvature fiber and ice-cream-cone negative-curvature fiber. The confinement loss governed by the inhibited coupling between the modes in the core and cladding is thoroughly examined systematically against the core-cladding curvature for both types. We show that, in addition to the mode-index mismatch, the mode-field overlap also plays a key role in determining the loss. Simultaneously, we find the ice-cream-cone negative-curvature fiber can exhibit better loss performance than the tubular design within a specific range of the curvature. This enhancement is achieved without sacrificing the transmission bandwidth and is relatively robust against the fabrication error.
Publisher: The Optical Society
Date: 06-08-2013
DOI: 10.1364/OL.38.002984
Publisher: Optica Publishing Group
Date: 30-08-2021
DOI: 10.1364/OL.436054
Abstract: We present the selective excitation of the fundamental mode in an anti-resonant hollow-core fiber (ARHCF) fusion-spliced with a commercial large mode area (LMA) fiber. By designing and fabricating a single-ring ARHCF that is mode-matched to a LMA fiber and by splicing the two using a C O 2 laser-based splicer, we achieve a coupling efficiency of 91.2% into the fundamental mode. We also demonstrate an all-fiber integration of an ARHCF with a commercial ytterbium-doped fiber in a laser cavity for beam delivery application. Coupling of the single-mode laser output beam into the fundamental mode of the ARHCF is demonstrated with 90.4% efficiency ( <!-- 0.45 d B loss) for up to 50 W continuous wave beam in a stable and alignment-free all-fiber laser setup.
Publisher: The Optical Society
Date: 23-08-2012
DOI: 10.1364/OL.37.003576
Publisher: The Australian National University
Date: 2009
Publisher: IEEE
Date: 05-2011
Publisher: Optica Publishing Group
Date: 16-05-2023
DOI: 10.1364/OE.493091
Abstract: We propose an antiresonant hollow-core fiber design that exhibits ultralow loss and exceptional single modedness at 1.55 µm. In this design, the confinement loss of less than 10 −6 dB m −1 can be obtained with excellent bending performance even at a tight bending radius of 3 cm. At the same time, a record-high higher-order mode extinction ratio of 8 × 10 5 can be achieved in the geometry by inducing strong coupling between the higher-order core modes and cladding hole modes. These guiding properties make it an excellent candidate for applications in hollow-core fiber-enabled low-latency telecommunication systems.
Publisher: MDPI AG
Date: 2022
Abstract: We numerically investigate the effect of mode-area dispersion in a tubular-type anti-resonant hollow-core fiber by using a modified generalized nonlinear Schrödinger equation that takes into account the wavelength-dependent mode area in its nonlinear term. The pulse evolution dynamics with and without the effect of mode-area dispersion are compared and analyzed. We show that strong dispersion of the mode area in the proximity of the cladding wall thickness-induced resonances has a significant impact on the soliton pulse propagation, resulting in considerable changes in the conversion efficiencies in nonlinear frequency mixing processes. The differences become more prominent when the pump has higher energy and is nearer to a resonance. Hence, the mode-area dispersion must be accounted for when modeling such a case.
Publisher: IEEE
Date: 09-2013
Publisher: SPIE
Date: 21-12-2007
DOI: 10.1117/12.761199
Publisher: OSA
Date: 2014
Publisher: OSA
Date: 2013
No related grants have been discovered for Wonkeun Chang.