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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.
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.
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>
Kim, Hyuntai,Lee, Seung-Yeol,Koo, Sukmo,Kim, Jinseob,Park, Kyoungyoon,Lee, Dongyeul,Vazquez-Zuniga, Luis Alonso,Park, Namkyoo,Lee, Byoungho,Jeong, Yoonchan Optical Society of America 2014 Optics express Vol.22 No.22
<P>We propose a novel trench-assisted circular metal nano-slit (CMNS) structure implementable on a fiber platform for the generation of a low-noise cylindrical surface plasmon (CSP) hotspot. We design trench structures based on a multi-pole cancellation method in order that a converging surface plasmon signal is well separated from co-propagating non-confined diffracted light (NCDL) at the hotspot location. In fact, the secondary radiation by the quasi-pole oscillation at the edge of the trench cancels the primary NCDL, thereby enhancing the signal-to-noise ratio (SNR) of the CSP hotspot. In particular, we investigate two types of trench structures: a rectangular-trench (RT) structure and an asymmetric-parabolic-trench (APT) structure, which are considered for the sake of the simplicity of fabrication and of the maximal enhancement of the SNR, respectively. In comparison with a conventional CMNS having no trenches, we highlight that the mean SNR of the CSP hotspot is enhanced by 6.97 and 11.89 dB in case of the optimized RT and APT CMNSs, respectively. The proposed schemes are expected to be useful for increasing the SNR of plasmonic devices that are interfered by NCDL, such as various types of nano-slits for generating high-resolution plasmonic signals, for example.</P>
권영철,박경윤,이동열,장한별,이승종,루이스 알론소 바즈게즈 주니가,이용수,김동환,김현태,정윤찬,Kwon, Youngchul,Park, Kyoungyoon,Lee, Dongyeul,Chang, Hanbyul,Lee, Seungjong,Vazquez-Zuniga, Luis Alonso,Lee, Yong Soo,Kim, Dong Hwan,Kim, Hyun Tae 한국광학회 2016 한국광학회지 Vol.27 No.1
최근 20 여년간의 괄목할만한 발전을 통해 단일 광섬유 레이저의 출력은 이미 kW 수준을 상회하고 있으며, 기존의 벌크 방식 레이저의 대체 기술로서 여전히 학계 및 산업계의 뜨거운 관심을 받고 있다. 본 논문은 이와 같은 광섬유 레이저의 괄목할만한 성장을 가능하게 한, 이터븀(Ytterbium) 혼입 이득 광섬유 사용 방식, 레이저 다이오드 펌프와 이중 클래딩 광섬유 구조를 통한 광학적 펌프 방식, 더 나아가서 양자결함을 최소화 하는 종렬 펌핑 방식 등 그 주요 요소 기술들을 개괄하고, 그 극한적 고출력화에 따른 발진 효율 및 특성 저하, 시스템 열화 및 불안정성 증대 등과 같은 고출력 광섬유 레이저 기술 자체가 직면하고 있는 다양한 기술적 문제점 및 그 완화 방안을 논의한다. 여기에서는 광섬유 레이저의 고출력화와 더불어 야기되는 다양한 형태의 광섬유내 비선형 현상, 광섬유 손상 및 모드 불안정 현상에 대한 논의를 포함한다. 이와 더불어, 전술한 다양한 출력 제한 현상을 극복함과 동시에 광섬유 레이저의 출력을 현격한 수준으로 더욱 증가시키기 위한 대체 방안으로 최근 주목을 많이 받고 있는 다중 빔 결합 기술에 대해 개괄적으로 논의한다. 특히, 분광형 다중 빔 결합 기술의 개념적 시스템 구성 요소 및 각 부문별 요구 기술에 대해 보다 심화된 논점을 둔다. 최종적으로 현 수준을 뛰어 넘는 광섬유 레이저의 출력 증대와 본 기술의 지속적 발전을 위한 앞으로의 발전 방향을 논의한다. Over the past two decades, fiber-based lasers have made remarkable progress, now having reached power levels exceeding kilowatts and drawing a huge amount of attention from academy and industry as a replacement technology for bulk lasers. In this paper we review the significant factors that have led to the progress of fiber lasers, such as gain-fiber regimes based on ytterbium-doped silica, optical pumping schemes through the combination of laser diodes and double-clad fiber geometries, and tandem schemes for minimizing quantum defects. Furthermore, we discuss various power-limitation issues that are expected to incur with respect to the ultimate power scaling of fiber lasers, such as efficiency degradation, thermal hazard, and system-instability growth in fiber lasers, and various relevant methods to alleviate the aforementioned issues. This discussion includes fiber nonlinear effects, fiber damage, and modal-instability issues, which become more significant as the power level is scaled up. In addition, we also review beam-combining techniques, which are currently receiving a lot of attention as an alternative solution to the power-scaling limitation of high-power fiber lasers. In particular, we focus more on the discussion of the schematics of a spectral beam-combining system and their individual requirements. Finally, we discuss prospects for the future development of fiber laser technologies, for them to leap forward from where they are now, and to continue to advance in terms of their power scalability.