Yb-doped Double-clad Fiber Laser Research Articles

THEORETICAL STUDY OF THE THERMAL DISTRIBUTION IN YB-DOPED DOUBLE-CLAD FIBER LASER BY CONSIDERING DIFFERENT HEAT SOURCES

THEORETICAL STUDY OF THE THERMAL DISTRIBUTION IN YB-DOPED DOUBLE-CLAD FIBER LASER BY CONSIDERING DIFFERENT HEAT SOURCES

High Power Switchable Dual-Wavelength Linear Polarized Yb-Dozped Fiber Laser around 1120 nm

A single-and dual-wavelength switchable polarized Yb-doped double-clad fiber laser around 1120 nm based on a pair of fiber Bragg gratings (FBGs) is demonstrated. The polarization-maintaining (PM) linear cavity is composed of a double clad PM Yb-doped fiber (YDF) and a pair of PM FBGs. The laser can operate in stable dual-wavelength or wavelength-switching modes due to the polarization hole burning (PHB) and the spatial hole burning (SHB) enhanced by the PM linear cavity. In dual-wavelength operation, the two orthogonally polarized wavelengths are centered at 1118.912 nm and 1119.152 nm, with an interval of 0.24 nm and a signal to noise ratio (SNR) of 35 dB. The maximum output power is 14.67 W when the launched LD pump is 24 W corresponding to an optical efficiency of 61.1%. The lasing lines switchover may be realized by adjusting the polarization controller (PC) fitted in the cavity. The two single-wavelengths are 1118.912 nm and 1119.152 nm. When the injected LD pump is 24 W, the highest output powers are 7.68 W and 8.64 W corresponding to optical efficiencies of 32% and 36% respectively. The spectral linewidth of the lasing lines are 0.075 nm and 0.07 nm, and the average numerical values of PER aredB and 19.9 dB, respectively.

첨두 출력 1.5 kW급 준연속 이터븀 첨가 광섬유 레이저

본 논문에서는 이터븀(Yb)이 첨가된 이중 클래딩 광섬유를 이용한 고출력 고품질 준연속 레이저 시스템에 대한 연구 개발과 레이저 특성에 대해 보고한다. 이론적 수치 모사를 통해 최적화된 준연속 레이저 발진 조건을 찾았고, 그것을 바탕으로 공진기 구조와 MOPA (Master-Oscillator Power-Amplifier) 구조를 가진 광섬유 레이저 시스템을 각각 구축하였다. 두 레이저 시스템 모두 10 Hz 반복률, 10 ms로 작동시킬 때 최고 평균 출력 >150 W, 첨두 출력 >1.5 kW 이상의 준연속 레이저 빔을 발생시키는데 성공하였고, 레이저 발진 특성 및 빔 특성을 각각 비교하였다. 그리고 향후 더 높은 출력을 얻기 위한 방법과 전망에 대해 논의할 것이다. High-power quasi-continuous-wave (qcw) operation in Yb-doped double-clad fiber lasers with near-diffraction-limited quality of the output beam is reported. Based on numerical simulation, we built a simple, all-fiberized Yb fiber laser, and a fiber-based master-oscillator power amplifier (MOPA). Both laser systems have successfully produced qcw output with average power greater than 150 W at 1080 nm and 10 ms pulse duration at 10 Hz repetition rate, corresponding to a peak power greater than 1.5 kW for 205 W of pump power at 976 nm. Laser performance, including beam quality and slope efficiency, was characterized in both configurations. Prospects for power scaling and applications are discussed.

Fiber fuse behavior in kW-level continuous-wave double-clad field laser**Project supported by the Key Laboratory of Science and Technology on High Energy Laser and China Academy of Engineering Physics (Grant No. 2014HEL02) and the National Natural Science Foundation of China (Grant No. 61307057).

In this study, original experimental data for fiber fuse in kW-level continuous-wave (CW) high power double-clad fiber (DCF) laser are reported. The propagating velocity of the fuse is 9.68 m/s in a 3.1-kW Yb-doped DCF laser. Three other cases in Yb-doped DCF are also observed. We think that the ignition of fiber fuse is caused by thermal mechanism, and the formation of bullet-shaped tracks is attributed to the optical discharge and temperature gradient. The inducements of initial fuse and formation of bullet-shaped voids are analyzed. This investigation of fiber fuse helps better understand the fiber fuse behavior, in order to avoid the catastrophic destruction caused by fiber fuse in high power fiber laser.

Single- and dual-wavelength switchable linear polarized Yb(3+)-doped double-clad fiber laser.

A single- and dual-wavelength switchable linear polarized Yb-doped double-clad fiber laser is proposed, in which the resonance cavity was composed of a fiber Bragg grating fabricated in a polarization-maintaining fiber and a dichromatic mirror with high reflectivity. The polarization hole burning is enhanced through selective polarization feedback by the polarization-maintaining fiber Bragg grating. The switchover of single and dual wavelengths is realized by tuning the rotation angle of a cubic polarization beam splitter that is inserted between the dichromatic mirror and the collimator in the cavity. The laser features wavelengths of 1070.08 and 1070.39 nm, output power of 1.0 W, signal to noise ratio of 45 dB, and slope efficiency of 34%, as well as a very narrow linewidth of 0.022 nm. The polarization characteristics are analyzed by measuring the laser power transmitted through a Glan-Thomson polarizer during rotation.

Mode-locked Er:Yb-doped double-clad fiber laser with 75-nm tuning range.

We demonstrate a widely tunable Er:Yb-doped double-clad multiple-soliton fiber laser based on nonlinear polarization rotation (NPR). Based on both an artificial birefringent filtering effect of the cavity and population inversion related gain variation, the central wavelength can be continuously tuned over 75nm range (1545-1620nm). Wavelength tunability is achieved by controlling both the linear loss of the cavity and the polarization controllers (PCs). This is the widest tunable range yet reported in tunable passively mode-locked erbium-doped fiber lasers.

Direct generation of 2 W average-power and 232 nJ picosecond pulses from an ultra-simple Yb-doped double-clad fiber laser.

We report the generation of 2.06W average-power and 232nJ picosecond mode-locked pulses directly from an ultra-simple Yb-doped fiber laser. A section of Yb-doped double-clad fiber pumped by a 976nm laser diode provides the large gain, and the linear cavity is simply formed by a 1064nm highly reflective fiber Bragg grating and a fiber loop mirror (FLM) using a 5/95 optical coupler. The asymmetric FLM not only acts as the output mirror for providing ∼20% optical feedback, but also equivalently behaves as a nonlinear optical loop mirror (NOLM) to initiate the mode-locking operation in this cavity. Stable mode-locking is therefore achieved over a pump power of 3.76W. The mode-locked pulses show the dissipative soliton resonance (DSR), which has the pulse duration of 695ps to ∼1 ns, and the almost unchanged peak power of ∼200 W as increasing the pump power. In particular, this laser can emit 232nJ high-energy DSR pulses with an average output power of >2 W. This is, to the best of our knowledge, the first demonstration of such an ultra-simple, mode-locked fiber laser that enables watt-level, high energy, picosecond DSR pulses.

An approximate analytical model for temperature and power distribution in high-power Yb-doped double-clad fiber lasers

An analytical power model based on the rate equations of a high-power Yb-doped double-clad fiber laser is presented. Although it considers combiner and splices losses for the first time, the maximum and mean relative errors are less than 2.2% and 3.04% when compared with numerical and experimental results, respectively. Furthermore, an analytical temperature model based on thermal conduction equation has been reported. For the first time, the radial-dependent distribution of the heat density generated inside the fiber core is considered. Radial and longitudinal 3D distributions for temperature are presented. The results show a big difference (can reach 25%) when compared with conventional models, which consider a uniform radial distribution for heat density. In contrast, the mean relative error related to our model is less than 4.7% when compared with experimental results, whereas it reaches 9.3% in the conventional one.

Double-Clad Yb-Doped Fiber Laser and its External Cavity Frequency-Doubling

A master oscillator power amplifier (MOPA) structured double-clad Yb-doped pulse fiber laser was presented, center wavelength of 1064nm, pulse width adjustable between 53ns-147ns, repetition rate adjustable between 50kHz-200kHz. Through external cavity frequency-doubling with a KTP crystal, the green light visibly of 532nm by fundamental beam of 1064nm was obtained. The highest frequency doubling efficiency was 16.2% when repetition rate of 50kHz and pulse width of 53ns. Relation of fundamental input beam and frequency-doubling output beam were studied through change the pulse parameters of fundamental beam and length of KTP crystal, the influences of fiber laser frequency doubling efficiency were analyzed.

Self-pulsing in a large mode area, end-pumped, double-clad ytterbium-doped fiber laser

The characteristics of self-pulsing in a large mode area, end-pumped, double-clad Yb-doped fiber laser are presented. The laser operates in a self-pulsing regime, either by using one or two perpendicularly cleaved ends as the feedback mirrors, while it transforms in a broadband amplified spontaneous emission source when both ends are angle cleaved. In the pulsed regime, up to 2 µs full width at half maximum pulse widths and repetition rates of the order of hundreds of kHz are generated.

Three Multiple-Pulse Operation States of an All-Normal-Dispersion Dissipative Soliton Fiber Laser

Multiple-pulse operation states of an all-normal-dispersion Yb-doped double-clad dissipative soliton fiber laser are investigated in this paper. The proposed laser can deliver harmonic mode-locked pulses, bound states of dissipative solitons, and dual-wavelength dual-pulses. Stable second-harmonic and third-harmonic mode-locked pulse trains are obtained with the output power of 1.39 W and 1.46 W, respectively, and the corresponding single pulse energies are 12.1 nJ and 8.5 nJ. With the adjustment of pump power and the wave plates, the fiber laser generates bound states of two or three dissipative solitons. Moreover, a dual-wavelength dual-pulse state is presented, where the output pulses from the nonlinear polarization rotation rejection port consists of the leading and trailing edges of the pulses circulating in the cavity.

Wavelength tunable passively Q-switched Yb-doped double-clad f iber laser with graphene grown on SiC

A passively Q-switched tunable Yb-doped double-clad fiber laser is demonstrated with graphene epitaxially grown on SiC. The spectral tuning of the Q-switched fiber laser is implemented by rotating a quartz plate filter inside the cavity. The central wavelength of the fiber laser can be continuously tuned from 1038.54 to 1056.22 nm. The maximum pulse energy of 0.65 \mu J is obtained at the pump power of 4.08 W, and the corresponding pulse duration and average output power are 1.60 \mu s and 35 mW, respectively.

Optimization of strongly pumped Yb-doped double-clad fiber lasers using a wide-scope approximate analytical model

Abstract An analytical model based on the rate equations of strongly pumped Yb-doped double-clad fiber laser (DCFLs) is presented. The output power and the distributed laser along the whole fiber have been found. In this paper, most parameters affecting the laser performance have been considered. The influences of scattering losses, pump reflection, output reflectivity, doping concentration and fiber length have been studied. It is shown that for wide ranges of the previous parameters and large variations of the input powers for all types of pumping (forward, backward and two-end), the maximum relative error of the output power would be less than 2.72% when the results are compared with the numerical model. Depending on our analytical model, a simple optimization method has been illustrated for high-power laser oscillators.

Selection of suitable pump diode laser parameters and their effects on efficiency and optimum length of Yb-doped double clad fiber lasers

The effects of diode laser pump parameters on the fiber laser performance are investigated numerically and experimentally. According to our simulation results, the wide spectrum pump diode laser centered at 976 nm wavelength will reduce the fiber laser optical efficiency and increase the optimal fiber length. The effect of pump wavelength on the fiber laser optical efficiency and the output power stability has also been studied. 976 nm pump wavelength is more efficient but the output power at this wavelength is more dependent on the pump wavelength tolerance. The experimental results are in good agreement with the theoretical ones.

Systemic optimization of linear cavity Yb-doped double-clad fiber laser

In order to optimize the double-clad fiber laser system, the laser output power should be as large as possible and the systemic cost should be as cheap as possible under the condition of the optimum fiber length. In this work, the improved approximate analytical solutions of the optimum fiber length and the laser output power are obtained based on the model of linear cavity strongly pumped Yb-doped double-clad fiber laser. And the effects of the laser scattering loss, the pump power, Yb dopant concentration, and the reflection coefficients of the input and output mirrors at laser wavelength on the laser output power and the optimum fiber length are discussed and analyzed in detail. Thereby the optimal laser system can be determined.

Large-Mode-Area Double-Cladding Photonic Crystal Fiber Laser in the Watt Range at 980 nm

We report on a quasi-three-level large-mode-area double-clad Yb-doped fiber laser that adopts a linear cavity consisting of a 0° fiber end and a cavity mirror. Two kinds of Yb-doped photonic crystal fiber (PCF) with different inner-clads (170 μm and 200 μm) and absorption coefficients (4.5 dB/m and 3 dB/m) are used as the gain media. By optimizing the structure and elements of the cavity, maximum output powers of 1.24 W and 1.1 W were yielded with optical conversion efficiencies of 7.8% and 6.8% when the fiber lengths were 25 cm and 40 cm with 170μm and 200μm inner-claddings, respectively.

Development of a Low-Noise Yellow-Green Laser Using a Yb-Doped Double-Clad Fiber Laser and a Periodically Poled LiNbO3 Waveguide Crystal

We have developed a yellow-green laser for fluorescence laser microscopes that is based on micro-optics technology and uses a Yb-doped double-clad fiber laser with an etalon and a periodically poled LiNbO3 waveguide crystal. This laser with an acoustic optical modulator (AOM) for analog modulation has an root-mean-square (RMS) noise of less than 2% in operating power range, a maximum optical power of 30 mW at an output wavelength of 555 nm and an extinction ratio of over 22 dB.

Development of a Low-Noise Yellow-Green Laser Using a Yb-Doped Double-Clad Fiber Laser and a Periodically Poled LiNbO3Waveguide Crystal

Development of a Low-Noise Yellow-Green Laser Using a Yb-Doped Double-Clad Fiber Laser and a Periodically Poled LiNbO₃Waveguide Crystal

Impact of Self-Phase Modulation on Instabilities in Fiber Lasers

Continuously pumped Yb-doped double-clad fiber lasers exhibit two kinds of instabilities, known as self-sustained pulsing and self-mode locking (SML). We study numerically the role of self-phase modulation (SPM) on the onset of these stabilities by using a spatiotemporal model that takes into account fully the length dependence of both the optical gain and spontaneous emission, while also including the nonlinear effects within the fiber. Self-sustained pulsations originate from relaxation oscillations. Although they die out quickly in the absence of SPM, our results show that SPM restores these oscillations when the laser power exceeds a certain value. SML has its origin in the spontaneous-emission noise acting as a seed. The laser cavity amplifies this noise the most at frequencies associated with its longitudinal modes, resulting in periodic power variations with an amplitude <; 1% (without SPM). We find that SPM plays again a critical role and increases their amplitude to above the 10% level. We also show that the SPM-induced instabilities can be suppressed by inserting a passive fiber of suitable length inside the laser cavity, which is in agreement with recent experimental work.

An improved shooting algorithm and its application to high-power fiber lasers

An improved shooting algorithm for high-power fiber laser is proposed based on the relation of the two-end boundary laser powers. By the improved shooting algorithm, the evolutions of the pump and laser powers along the fiber position for Yb-doped and Tm-doped high-power double-clad fiber lasers with the laser scattering loss are analyzed. The results prove that the improved shooting algorithm can be efficient even if the pump power is up to kilowatt level, and the initial value can all be fast convergent as long as the initial guessed laser power is smaller than the truth value. So, this improved shooting algorithm can be used in high-power double-clad fiber lasers efficiently.