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Vazquez-Zuniga, Luis Alonso,Jeong, Yoonchan Elsevier 2014 OPTICS COMMUNICATIONS - Vol.322 No.-
We present a comprehensive numerical study on the spectral and temporal behaviors of a mode-locked erbium-doped frequency-shifted-feedback fiber laser as a function of the frequency shift and optical bandwidth of the laser cavity. For this we develop a numerical model which is based on the rate equation and nonlinear Schrodinger equation for the fiber-based active cavity. We numerically verify that if the ratio of the filter bandwidth to the frequency-shift value is higher than 400 times, the spectral broadening of the laser output tends to break up and form a secondary spectral band (SSB) on the wavelength side of the spectrum where the spectral components of the cavity modes are constantly shifted by the intracavity frequency shifter. We also verify that the SSB forms a satellite pulse in the time domain, traveling on either the trailing edge or leading edge of the main pulse, depending on whether the SSB is formed on the shorter or longer wavelength side of the pulse spectrum. We emphasize that these numerical results are also in good agreement with the experimental results discussed in our previous report [251. (c) 2014 Elsevier B.V. All rights reserved.
Vazquez-Zuniga, Luis A.,Jeong, Yoonchan IEEE 2012 IEEE Photonics Technology Letters Vol.24 No.17
<P>We present a compact all-fiberized erbium-doped fiber ring laser, which generates linearly polarized picosecond pulses with a maximum bandwidth of 135 nm and excellent spectral flatness. The pulse energy and width are reconfigurable from 0.7 to 1.1 nJ and from 6.5 to 220 ps, respectively, via controlling the pumping power and/or the cavity finesse. We also analyze the relative intensity noise (RIN) characteristics of the source that results in <TEX>${-}{\rm 97}~{\rm dB}$</TEX> at low frequencies (up to 100 kHz) and <TEX>${-}{\rm 104}~{\rm dB}$</TEX> at high frequencies (up to 5 MHz), respectively. In particular, the high-frequency RIN is attributed to the spontaneous Raman scattering generated in the laser and of a comparable level with that of a commercial supercontinuum source based on a mode-locked fiber laser.</P>
Vazquez-Zuniga, L A,Kim, Hong Sig,Kwon, Youngchul,Jeong, Yoonchan Optical Society of America 2013 Optics express Vol.21 No.6
<P>We experimentally analyze the stimulated Raman scattering characteristics of a high-birefringence fiber (HBF), which presents an extraordinary level of spectral broadening incurred by the strong nonlinear interaction between the pump and Stokes pulses via the polarization-mode dispersion and group-velocity dispersion of the fiber. We also investigate the impact of the inter-pulse time-delay on the additional spectra broadening when dual-wavelength pump pulses are used. Exploiting these unique SRS properties of the HBF, we develop a novel Raman continuum source based on an all-fiber dual-wavelength master-oscillator power amplifier that can generate a dip-free spectrum in the 1200-1400-nm spectral range. We finally obtain a broadband continuum having an average power of ~840 mW and a 3-dB bandwidth of ~240 nm centered at 1200-1400 nm, which also represents a good spectral flatness and conversion efficiency. This type of source is very useful and important for optical coherence tomography applications, for example.</P>
Luis Alonso Vazquez-Zuniga,정윤찬 한국광학회 2013 Current Optics and Photonics Vol.17 No.2
We present an all-fiberized power-scalable, sub-nanosecond mode-locked laser based on a frequencyshifted-feedback ring cavity comprised of an erbium-doped fiber, a downshifting acousto-optic modulator (AOM), and a bandpass filter (BPF). With the aid of the frequency-shifted feedback mechanism provided by the AOM and the narrow filter bandwidth of 0.45 nm, we generate self-starting, mode-locked optical pulses with a spectral bandwidth of ~0.098 nm and a pulsewidth of 432 to 536 ps. In particular, the output power is readily scalable with pump power while keeping the temporal shape and spectral bandwidth. This is obtained via the consolidation of bound pulse modes circulating at the fundamental repetition rate of the cavity. In fact, the consolidated pulses form a single-entity envelope of asymmetric Gaussian shape where no discrete internal pulses are perceived. This result highlights that the inclusion of the narrow BPF into the cavity is crucial to achieving the consolidated pulses.
Luis A. Vazquez-Zuniga,정윤찬 한국광학회 2013 Current Optics and Photonics Vol.17 No.2
We briefly review the recent progress in passively mode-locked fiber lasers (PMLFLs) based on semiconductor saturable absorber mirrors (SESAMs) and discuss the detailed characterization of a SESAM-based, passively mode-locked erbium-doped fiber (EDF) laser operating in the 1.5-μm spectral range for various configurations. A simple and compact design of the laser cavity enables the PMLFL to generate either femtosecond or wavelength-tunable picosecond pulses with high stability as the intra-cavity filtering method is altered. All the cavities investigated in our experiments present self-starting,continuous-wave mode-locking with no Q-switching instabilities. The excellent stability of the source eventually enables the wavelength-tunable PMLFL to be used as a master oscillator for a power-amplifier source based on a large-core EDF, generating picosecond pulses of >10-kW peak power and >100-nJ pulse energy.
Youngchul Kwon,Vazquez-Zuniga, Luis Alonso,Kyoungyoon Park,Seungjong Lee,Hanbyul Chang,Yoonchan Jeong IEEE 2016 IEEE journal of quantum electronics Vol.52 No.6
<P>We numerically study the dynamics of supercontinuum generation (SCG) for a variety of possible combinations of photonic crystal fibers (PCFs) and ultrafast fiber laser pulses that the current technologies offer. Three types of PCFs typically used in SCG and four representative types of ultrafast fiber laser pulses are considered for this combinatorial study. We numerically model and qualitatively discuss the nonlinear evolution of the pulses for their whole 12 combinatorial cases. We also quantitatively analyze their output spectra and organize a performance chart for them in terms of spectral bandwidth, flatness, and degree of spectral coherence. Finally, we suggest the most viable combinations among the given PCFs and ultrafast fiber laser pulses in order for generating a target supercontinuum spectrum for various specific cases.</P>
Rigorous Analysis on Ring-Doped-Core Fibers for Generating Cylindrical Vector Beams
김현태,권영철,Luis Alonso Vazquez-Zuniga,이성종,박원일,함영수,송석영,양종환,정윤찬 한국광학회 2014 Current Optics and Photonics Vol.18 No.6
We propose a novel active fiber design for selectively generating cylindrical vector beams (CVBs) or cylindrical vector modes (CVMs) which can be applied to conventional fiber lasers. A fiber is designed to have a ring-shaped core refractive index profile which can lead to the best overlap between the active dopant distribution profile and the lowest-order CVM (LCVM) field profile. Therefore, the overlap factor (OVF) of the LCVM becomes even higher than that of the fundamental mode. We emphasize that this condition cannot be satisfied by a conventional step-index core fiber (SICF) but by the ring-doped core fiber (RDCF). Because the lasing threshold is inversely proportional to the OVF, the LCVM can predominantly be stimulated even without going through special procedures to impose extra loss mechanisms to the fundamental mode. We numerically verify that the OVF of the LCVM with the doped ions can significantly exceed that of the fundamental mode if the proposed fiber design is applied. In addition, an RDCF of the proposed fiber design can also operate in a regime containing no higher-order modes besides the LCVM, so that it can selectively and efficiently generate the LCVM without being disrupted by the parasitic lasing of the higher-order modes. We highlight that an optimized RDCF can lead to a >30 % higher OVF ratio than a SICF having the same doped area. The proposed model is expected to be useful for enhancing the efficiency of generating CVBs in an all-fiber format.
Kim, Hyuntai,Kim, Jongki,Jung, Yongmin,Vazquez-Zuniga, Luis Alonso,Lee, Seung Jong,Choi, Geunchang,Oh, Kyunghwan,Wang, Pu,Clarkson, W A,Jeong, Yoonchan Optical Society of America 2012 Optics express Vol.20 No.23
<P>We propose a simple and efficient light launch scheme for a helical-core fiber (HCF) by using an adiabatically tapered splice technique, through which we overcome its inherent difficulty with light launch owing to the large lateral offset and angular tilt of its core. We experimentally demonstrate single-mode excitation in the HCF in this configuration, which yields the coupling efficiency of around -5.9 dB (26%) for a ~1.1-μm light input when the splice joint is tapered down to 30 μm in diameter. To our knowledge, this is the first proof-of-principle report on the fusion-splice coupling between an HCF and a conventional single-mode fiber.</P>