Compact THz time-domain spectroscopy based on pre-chirped pulses from mode-locked Yb-doped fiber laser

Kim, Ji Su,Yang, Hyun Moon,Han, Sang-Pil,Moon, Kiwan,Park, Kyung Hyun,Jeon, Min Yong Elsevier 2018 Optical fiber technology Vol.45 No.-

<P><B>Abstract</B></P> <P>We report on a compact terahertz (THz) time-domain spectroscopy (TDS) system based on fiber-integrated log-spiral low-temperature-grown InGaAs photo-conductive antenna (PCA) modules pumped by pre-chirped pulses from a 1.03-μm mode-locked Yb-doped fiber laser. A mode-locked Yb-doped fiber laser based on a birefringent spectral filter was produced with 240 mW average output power and 2.68-ps pulse duration. The output pulse had high chirp because the mode-locked fiber laser was implemented in the normal dispersion region. Therefore, the 733-fs output pulse was pre-chirped using two parallel diffraction gratings to facilitate its use as an optical pump source with THz radiation. After propagating in the single-mode fiber, the pulse-width of the pre-chirped pulse was compressed to 331 fs and injected into fiber-integrated PCA modules to generate a THz wave. We successfully obtained a THz emission bandwidth of over 2.5 THz for 120 mm in free space using the compact THz measurement setup. THz radiation was achieved by easily aligning two fiber integrated PCA modules. Absorption lines for water vapor were observed at room temperature. We also observed absorption lines from a 30% α-lactose sample. We confirmed that the fiber-integrated PCA modules and mode-locked Yb-doped fiber laser have potential applications in compact and portable THz-TDS systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Compact and movable terahertz (THz) time-domain spectroscopy is demonstrated. </LI> <LI> Pre-chirped pulses from a mode-locked Yb-doped fiber laser has been demonstrated. </LI> <LI> THz emission bandwidth of over 2.5 THz for 120 mm in free space is achieved. </LI> </UL> </P>

Wavelength-stepped, actively mode-locked fiber laser based on wavelength-division-multiplexed optical delay lines

Lee, Eunjoo,Kim, Byoung Yoon Elsevier 2017 OPTICS COMMUNICATIONS - Vol.405 No.-

<P><B>Abstract</B></P> <P>We propose a new scheme for an actively mode-locked wavelength-swept fiber laser that produces a train of discretely wavelength-stepped pulses from a short fiber cavity. Pulses with different wavelengths are split and combined by standard wavelength division multiplexers with fiber delay lines. As a proof of concept, we demonstrate a laser using an erbium doped fiber amplifier and commercially available wavelength-division multiplexers with wavelength spacing of 0.8 nm. The results show simultaneous mode-locking at three different wavelengths. Laser output parameters in time domain, optical and radio frequency spectral domain, and the noise characteristics are presented. Suggestions for the improved design are discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Wavelength stepped mode-locked fiber laser is proposed and demonstrated. </LI> <LI> Standard telecom components are used for the short fiber cavity. </LI> <LI> Gain competition is reduced by temporal–spectral multiplexing. </LI> <LI> Individual control of physical parameters of each pulse is possible. </LI> <LI> Noise characteristics of each wavelength is presented. </LI> </UL> </P>

Linearized Wavelength Interrogation System of Fiber Bragg Grating Strain Sensor Based on Wavelength-Swept Active Mode Locking Fiber Laser

Hwi Don Lee,Gyeong Hun Kim,Tae Joong Eom,Myung Yung Jeong,Chang-Seok Kim IEEE 2015 Journal of Lightwave Technology Vol.33 No.12

<P>We demonstrated a linearized wavelength interrogation system of fiber Bragg grating (FBG) strain sensors, based on a wavelength-swept active mode locking (AML) fiber laser. Since the wavelength sweeping mechanism of the AML fiber laser does not depend on the wavelength selecting filter, we can easily demonstrate the wavelength-linear sweeping by applying a programmable electrical signal to the laser cavity. Both static and dynamic strain measurements of FBG sensors were characterized with high linearity, which has an R-square value of 0.9999 at a sweep rate of 50 kHz.</P>

Wavelength-Tunable, Passively Mode-Locked Erbium-Doped Fiber Master-Oscillator Incorporating a Semiconductor Saturable Absorber Mirror

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.

Mode-Locked All-Fiber Lasers at Both Anomalous and Normal Dispersion Regimes Based on Spin-Coated <named-content content-type='math' xlink:type='simple'> <tex> $\hbox{MoS}_{2}$ </tex></named-content> Nano-Sheets on a Side-Polished Fiber

Khazaeinezhad, Reza,Kassani, Sahar Hosseinzadeh,Hwanseong Jeong,Nazari, Tavakol,Dong-Il Yeom,Kyunghwan Oh IEEE 2015 IEEE photonics journal Vol.7 No.1

<P>We demonstrate an all-fiberized mode-locked laser by employing Molybdenum Disulfide (MoS<SUB>2</SUB>) spin-coated onto a side-polished fiber (SPF) as an in-line saturable absorber. Single crystal MoS<SUB>2</SUB> has been exfoliated via the Li intercalation method and then dispersed with large population of few-layer MoS<SUB>2</SUB> nano-sheets in ethanol. Subsequently, a saturable absorber has been prepared using a relatively simple method: spin-coating the uniform MoS<SUB>2</SUB> solution on the fabricated SPF without using any polymer or toxic procedure. Power-dependent transmission property of the prepared MoS<SUB>2</SUB> nano-sheets on the SPF was experimentally analyzed, providing the feasibility to apply it as an efficient in-line saturable absorption behavior. By deploying the MoS<SUB>2</SUB> SPF into a fiber laser cavity with finely tuned laser pump power and cavity dispersion, mode-locked pulses were obtained at anomalous and normal dispersion of the laser cavity. The self-started soliton pulses at the anomalous dispersion regime were generated with a spectral bandwidth of 9.96 nm at 1584 nm and a pulse duration of 521 fs. Moreover, by managing the dispersion to the normal regime, stable pulses at net-normal intra-cavity dispersion with 11.9 ps pulse duration were obtained with a spectral bandwidth of 18.2 nm at 1570 nm. The results prove the effectiveness of developing MoS<SUB>2</SUB> saturable absorbers and applications for pulsed laser operation.</P>

Power-Scalable, Sub-Nanosecond Mode-Locked Erbium-Doped Fiber Laser Based on a Frequency-Shifted-Feedback Ring Cavity Incorporating a Narrow Bandpass Filter

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.

Ultralow Intensity Noise Pulse Train from an All-fiber Nonlinear Amplifying Loop Mirror-based Femtosecond Laser

권도현,김도현 한국광학회 2023 Current Optics and Photonics Vol.7 No.6

A robust all-fiber nonlinear amplifying loop-mirror-based mode-locked femtosecond laser is demonstrated. Power-dependent nonlinear phase shift in a Sagnac loop enables stable and power-efficient mode-locking working as an artificial saturable absorber. The pump power is adjusted to achieve the lowest intensity noise for stable long-term operation. The minimum pump power for mode-locking is 180 mW, and the optimal pump power is 300 mW. The lowest integrated root-mean-square relative intensity noise of a free-running mode-locked laser is 0.009% [integration bandwidth: 1 Hz–10 MHz]. The long-term repetition-rate instability of a free-running mode-locked laser is 10 −7 over 1,000 s aver-aging time. The repetition-rate phase noise scaled at 10-GHz carrier is −122 dBc/Hz at 10 kHz Fourierfrequency. The demonstrated method can be applied as a seed source in high-precision real-time midinfrared molecular spectroscopy.

분광 영역 모드록킹 레이저를 이용한 공진형 광섬유 격자 센서

최병권,전민용,Choi, Byeong Kwon,Jeon, Min Yong 한국광학회 2012 한국광학회지 Vol.23 No.5

We report a resonance fiber Bragg sensor interrogation based on a Fourier domain mode-locking (FDML) laser. The FDML laser is constructed based on a conventional ring laser cavity configuration with fiber Fabry-Perot tunable filter (FFP-TF). There are two sensor parts which are composed with two FBGs inside the laser cavity. Each sensor part provides a separate laser cavity for the FDML laser. The resonance frequencies of the laser cavities are 46.687 kHz and 44.340 kHz, respectively. We applied a static and a dynamic strain on the FBG sensor system. The slope coefficients of the measured relative wavelength shift and relative time interval from the static strain are found to be $0.61pm/{\mu}{\epsilon}$ and $0.8ns/{\mu}{\epsilon}$, respectively. 본 논문은 분광 영역 모드록킹(Fourier domain mode-locking: FDML) 레이저를 기반으로 공진형 광섬유 격자 센서를 구현한 결과를 보고한다. FDML 레이저는 파브리-페롯 가변 필터를 이용하여 링 형태로 구성하며, 레이저 공진기 안에 광섬유 격자 2개를 한 쌍으로 하여 센서부 2개를 삽입한 구조이다. 광섬유 격자는 반사 거울 역할을 하며, 광섬유 격자의 위치에 따라 독립된 FDML 레이저 공진기를 구성한다. 각각 센서부의 공진 주파수는 46.687 kHz 와 44.340 kHz이다. FBG 센서 시스템에 정적 및 동적 스트레인을 가하였으며, 정적 스트레인에 대해 파장 영역과 시간 영역에서 측정된 스트레인에 대한 변화율은 각각 $0.61pm/{\mu}{\epsilon}$, $0.8ns/{\mu}{\epsilon}$ 이다.

Seed 레이저용 정상분산 영역에서 발진하는 간단한 구조의 이터븀 기반 모드 잠금 광섬유 레이저

김병권(Byeong Kwon Kim),주기남(Ki-Nam Joo) Korean Society for Precision Engineering 2014 한국정밀공학회지 Vol.31 No.9

In this investigation, we constructed and demonstrated a simple Yb-doped fiber laser, of which longitudinal modes are mode-locked without any additional devices to compensate the dispersion caused by optical components. Non-linear polarization rotation (NPR) was adopted for the modelocking mechanism and a polarization controller (PC) was used for a kind of spectral filters to restrict the bandwidth for mode-locking. As the result, the laser was successfully operated as mode-locked with the repetition rate of 42.2 MHz and the spectrum was broadened up to approximately 16 nm at 1033 nm center wavelength when the laser was mode-locked. In this paper, the operation of the developed Yb-doped mode-locked laser is explained with the concept of Lyot filter realized by a PC, which enables mode-locking under normal dispersion. In the industrial applications, this laser can be used as a seed laser of the high power lasers for optical manufacturing.

Ultrafast Pulsed All-Fiber Laser Based on Tapered Fiber Enclosed by Few-Layer WS₂ Nanosheets

Khazaeinezhad, Reza,Kassani, Sahar Hosseinzadeh,Hwanseong Jeong,Kyung Jun Park,Byoung Yoon Kim,Dong-Il Yeom,Kyunghwan Oh IEEE 2015 IEEE photonics technology letters Vol.27 No.15

<P>We demonstrate all-fiber mode-locked laser based on a tapered optical fiber saturable absorber (SA) enclosed in tungsten disulfide (WS<SUB>2</SUB>) nanosheets. Tapered fibers were fabricated using the standard flame brushing method to an interaction length of 3 mm with waist diameters of 10 and 15 μm. WS<SUB>2</SUB> nanosheets were prepared via a liquid phase exfoliation method to form a uniform dispersion. Subsequently, the WS<SUB>2</SUB> nanosheets were optically deposited along the interaction length of the tapered fibers by evanescent field interactions. We built a ring laser including the fabricated mode-lockers. The SA with a 10-μm taper diameter delivers the pulses with a pulse duration of 369 fs and 3-dB spectral bandwidth of 7.5 nm; on the other hand, the output pulses using the mode-locker with 15-μm waist diameter were found to have 563-fs pulse duration and 5.2 nm of 3-dB bandwidth. It is shown that the smaller waist diameter of tapered fiber causes wider spectral bandwidth of the ultrafast pulses and narrower 3-dB bandwidth.</P>