Doped Fiber Laser Research Articles

Near-Infrared Soliton Mode-Locked Thulium Doped Fibre Laser Using WS2-ZnO Composite Material as Saturable Absorber

The generation of a highly stable passive mode locking laser is realized in a thulium doped fibre laser using a WS 2 -ZnO composite as a saturable absorber. Soliton mode locking pulses are generated with a central wavelength of 1936 nm and full-width half maximum (FWHM) of 3.06 nm. The first order Kelly's side band is located at around 5.65 nm from the central wavelength which gives the calculated pulse width value of 1.26 ps. This value corresponds well with the measured pulse width of 1.27 ps using the autocorrelator. The output power of the laser is around 0.44 mW with the peak power of 29.7 W and repetition rate of 9.96 MHz. This laser set-up is highly robust and realizes highly stable laser pulses in the mid-IR wavelength range for a multitude of applications.

Investigation of ion-ion interaction effects on Yb3+-doped fiber amplifiers.

Ytterbium (Yb3+)-doped materials have been widely used for high efficiency high energy laser sources at the 1 µm wavelength region because of their very low quantum defect and the unique simple energy level structure of Yb3+, resulting in no excited-state absorption and low occurrence probability of deleterious ion-ion interaction processes. It has been generally recognized that these ion-ion interaction processes have very little influence on the operation of Yb3+-doped fiber lasers at low and moderate power levels. However, our recent study shows that the performance of Yb3+-doped fiber amplifiers operating at low power levels is still influenced by the ion-ion interaction processes due to the large amount of population at the upper laser level 2F5/2. In this paper, experimental evidences of the ion-ion interaction effects in Yb3+-doped fiber amplifiers are presented and a new model including these effects is developed for the numerical simulation. Our experimental and numerical investigations on the 976 nm and 1030 nm Yb3+-doped silica and phosphate fiber amplifiers show that ion-ion interaction has non-negligible impact on the performance of Yb3+-doped fiber amplifiers indeed, and compared to Yb3+-doped silica fibers, Yb3+-doped phosphate fibers suffer much less from the ion-ion interaction effects due to the much less clustered ions.

Q-switched lasing at the 2 µm wavelength induced by Cu18S nanocrystals

In this paper, we first investigated the nonlinear optical properties of Cu1.8S nanocrystals (NCs) by using Z-scan and balanced twin detector measurement technologies, and then demonstrated a passively Q-switched laser at the 2 µm wavelength. The Cu1.8S NCs were synthesized by a solventless thermolysis method and then mixed with sodium carboxymethylcellulose to form the Cu1.8S NCs film. The film exhibited broadband surface plasmon resonance (SPR) absorption from 800 nm to 2000 nm. By incorporating the Cu1.8S NCs film into a thulium doped fiber laser cavity pumped by a 1570 nm fiber laser, stable passive Q-switching at ∼1975.16 nm was obtained for a threshold pump power of ∼931 mW, and ∼3.4 µs pulse duration with a pulse repetition rate of ∼35.14 kHz was also obtained for a pump power of ∼996 mW. Our results showed that Cu1.8S NCs is a promising saturable absorber (SA) for pulse laser generation at the 2 µm wavelength.

Tm/Ho-doped fiber laser systems using coaxial fiber.

Coaxial fiber lasers are studied via numerical simulations as an alternative to conventional cladding-pumped fiber lasers. The coaxial fiber consists of a Ho-doped core surrounded by a Tm-doped ring. When pumped at 805 nm, this fiber type resulted in a 54% power conversion efficiency, defined as the ratio of output signal power to total input pump power. The performance of this laser was numerically compared to conventional Tm/Ho doped fiber lasers under the same pump conditions. Simulations of a Tm:fiber laser pumping a Ho:fiber laser yielded a maximum 43% power conversion efficiency, while simulations of a Tm/Ho co-doped fiber laser yielded a maximum power conversion efficiency of 34%. These results demonstrate that the coaxial fiber laser has the potential for a significant efficiency improvement over conventional methods in addition to being a more compact system.

Crystal-field engineering of ultrabroadband mid-infrared emission in Co2+-doped nano-chalcogenide glass composites

Tunable and ultrabroadband mid-infrared (MIR) emissions in the range of 2.5–4.5 μm are firstly reported from Co2+-doped nano-chalcogenide (ChG) glass composites. The composites embedded with a variety of binary (ZnS, CdS, ZnSe) and ternary (ZnCdS, ZnSSe) ChG nanocrystals (NCs) can be readily obtained by a simple one-step thermal annealing method. They are highly transparent in the near- and mid-infrared wavelength region. Low-cost and commercially available Er3+-doped fiber lasers can be used as the excitation source. By crystal-field engineering of the embedded NCs through cation- or anion-substitution, the emission properties of Co2+ including its emission peak wavelength and bandwidth can be tailored in a broad spectral range. The phenomena can be accounted for by crystal-field theory. Such nano-ChG composites, perfectly filling the 3–4 μm spectral gap between the oscillations of Cr2+ and Fe2+ doped IIVI ChG crystals, may find important MIR photonic applications (e.g., gas sensing), or can be used directly as an efficient pump source for Fe2+: IIVI crystals which are suffering from lack of pump sources.

Investigation of output power in ring CW fiber laser using graphene saturable absorber

This paper reported the effect of different coupling ratio in continuous wave fiber laser in a ring cavity configuration. Different coupling ratios of 10/90 and 50/50 were tested. Where the output power may vary depending on the ratio and it can be applied to specific area that requires either high or low output power. In addition, generation of passive Q-switched erbium doped fiber laser (EDFL) using graphene based saturable absorber in ring cavity using different coupling ratio was experimentally investigated. As a result, wavelength centered at 1566.62nm is obtain from EDFL cavity. Moreover, the cavity using coupler of 50/50 is capable to achieve Q-switched pulses as compared to the cavity using coupler of 10/90. Where the maximum output power recorded is 336mW with pulse repetition rate of 23.74 kHz. In addition, the pulse width is 3.84µs, and pulse energy is 14.15nJ.

High-efficiency, yellow-light Dy3+-doped fiber laser with wavelength tuning from 568.7 to 581.9 nm.

We report, to the best of our knowledge, the first demonstration of a wavelength-tunable and highly efficient Dy3+-doped fiber laser operating in the yellow spectral region. A 2-m-long Dy3+:ZBLAN fiber pumped by a 447-nm GaN laser diode provides a strong down-conversion gain around 575nm. A fiber end-facet mirror and a visible reflective grating in the Littrow configuration construct the resonant cavity and introduce the wavelength tunability. A stable yellow laser with a <0.05-nm narrow linewidth is achieved and continuously tuned from 568.7nm to 581.9nm, covering more than half of the yellow spectral range. The slope efficiency is as high as 34.9%, and the maximum output power is 142mW at 576.44nm, which is 13 times higher than previously reported. It is, to the best of our knowledge, the highest power and conversion efficiency of a yellow-light Dy3+-doped fiber laser with wavelength tunability.

Tungsten disulfide-chitosan film as optical pulse and amplitude modulator in C-band region

A tungsten disulfide (WS2)-Chitosan film based optical modulator for operation in the C-band region is demonstrated. The integration of the WS2-Chitosan film into an erbium doped fiber laser cavity reveals high optical pulse and amplitude modulation efficiency due to the substantial nonlinear absorption properties of the WS2-Chitosan film. The strong thermo-optic effect exhibited by the WS2-Chitosan film enables optical amplitude modulation, with modulation efficiencies of 0.10 dB mW−1 over a pump power ranging from 0.01 mW to 130.10 mW. The proposed WS2-Chitosan based optical modulator has significant potential for integration and application into a multitude of optoelectronic systems.

Emerging transparent conducting oxides material: 2-dimensional plasmonic Zn doped CuGaO2 nanoplates for Q-switched fiber laser.

A passively Q-switched Er3+ doped fiber laser has been realized by using Zn doped hexagonal CuGaO2 (CGZO) nanoplates (NPs) as a saturable absorber (SA) for the first time. The CGZO NPs SA film exhibits strong saturable absorption property, meanwhile with a small nonsaturable loss of 5.179%, and the modulation depth is up to 40.821%. A stable passively Q-switched laser, which was centered at 1559.75 nm, was achieved, and the threshold was as low as 42 mW. With an increase of the pump power from 42mW to 361mW, the pulse duration decreases from 36 μs to 1.71 μs, and the maximum output power of 12.1 mW is achieved. Particularly, the optical-optical conversion efficiency of the Q-Switched laser based on CGZO NPs reached 3.76%. Due to whispering-gallery-mode (WGM) resonance in CGZO NPs, the nonlinear optical response of CGZO NPs has been enhancement. These findings demonstrate that CGZO NPs are promising SA for fabricating high-efficiency and low-threshold pulse lasers.

Radionuclide distribution during ytterbium doped fibre laser cutting for nuclear decommissioning

This article provides data on the radionuclide distribution during ytterbium doped fibre laser cutting of contaminated stainless steel in a simulated nuclear decommissioning scenario. Two stainless steel 25 mm thick plates labelled with Sr-85, Ru-106 and Tc-99, Cs-133 have been laser cut. In all experiments activity is mainly found within dross under the cut test piece and the material deposited within the local filtration system. No active Sr-85, Ru-106 or Tc-99 was analysed to be present on swabs made on the internal walls of the facility or obtained on the samples taken from the ventilation sample on the clean side of the facility HEPA filter during the active cutting trials. Conversely, Cs-133 has been measured in samples and swabs taken from throughout the laser cutting facility at decreasing concentrations correlating with the distance from the cut test piece(s).

Zinc oxide nanoparticles based passive saturable absorber for pulse generation in fiber laser

A stable passive Q-switched pulsed generation in Erbium doped fiber laser by Zinc Oxide nanoparticles embedded in polyvinyl alcohol (ZnONP-PVA)-based saturable absorber is demonstrated in this paper. The surface morphology and thickness profile of the fabricated film were observed using FESEM and 3D measuring laser microscope with the measured thickness of 12 µm. Meanwhile the its optical properties is characterized using Raman spectroscopy. The developed ZnONP-PVA film, has modulation depth of 7.8% and intensity saturation of 88.97 MW/cm2. The threshold input pump power to generate Q-switched pulse is at 45.4 mW and can be tuned until 92.4 mW before the pulse diminished. The operating wavelength of generated pulse is at 1535 nm with 3 dB bandwidth approximately of 2 nm with exclusion of parasitic continuous wave lasing. As the input pump power was tuned from threshold to maximum value, the recorded pulse train of repetition rate is tunable from 73.53 kHz to 103.10 kHz while the pulse width decreases from 6.8 µs to 4.8 µs. The calculated maximum output power and pulse energy at maximum input pump power was 5.14 mW and 49.85 nJ, respectively. The measured signal to noise ratio was 56 dB indicated that the generated pulse by ZnO NP based passive saturable absorber was stable.

Brightness enhancement with Raman fiber lasers and amplifiers using multi-mode or multi-clad fibers

Abstract A large variety of high power, high brightness, rare earth doped fiber lasers have been demonstrated throughout recent years. Several obstacles, such as modal instabilities, heat removal and photo-darkening, have been identified as the limiters and have complicated the further power increase. Raman fiber sources have inherent advantages in regard to these challenges and therefore may offer a high power high brightness alternative. Up to over kW power Raman fiber laser and amplifier sources have recently been demonstrated with multimode graded index fiber (1002 W) as well as with multi-clad clad-pumped fiber (1200 W) in brightness enhancing configurations. In these schemes, the output Stokes-shifted-signal obtained higher brightness than the input pump source, due to the higher Raman gain associated with the lower order modes. A review of the recent results obtained with various configurations is presented, followed by discussion on the challenges and the paths towards further increase in power and brightness towards achieving near diffraction limited multi-kW Raman fiber sources.

Wavelength-tunable thulium-doped fiber laser with sampled fiber Bragg gratings

A continuous wave (CW) wavelength-tunable Tm3+-doped fiber laser with two sampled fiber Bragg gratings (SFBGs) has been proposed and demonstrated. This proposed laser is stable operating with a significant 14.44 nm wavelength range from 1942.09 nm to 1956.53 nm due to the Vernier effect. The laser OSNRs of different wavelengths ranged from 45 dB to 58 dB at a launched pump power of 3.67 W. The wavelength shift and power fluctuation were less than 0.03 nm and 0.46 dB, respectively. An 8.62% slope efficiency was achieved using a grating for laser extracting. To the authors’ knowledge, this is the first time that a wavelength-tunable Tm3+-doped fiber laser with two SFBGs has been demonstrated.

Chaotic regimes and synchronization in Tm3+-doped fiber laser with pump modulation

The dynamical behavior of a thulium-doped fiber laser (Tm-DFL) with pump modulation is investigated numerically. A rate equation model is used. Different routes to chaos are identified via intermittent-like or period-doubling regimes. Pulse width and pulse energy are extracted. In the second part, the dynamics of two parallel cavities with mutual injection-locking is studied. The lag synchronization between mutually coupled Tm-DFLs can be achieved. Under some conditions, the butterfly effect is demonstrated with this system, and the influence of coupling strength on time lag synchronization is detailed.

Improvement of 2-μm Thulium-Doped Fiber Lasers via ASE Suppression Using All-Solid Low-Pass Photonic Bandgap Fibers

All-solid photonic bandgap fibers (PBGFs) were designed and fabricated to work as low-pass filters in 2-μm region. They were used for manipulating thulium doped fiber laser (TDFL) operating in the 2-μm region via amplified spontaneous emission suppression. A sharp lasing peak at 1915 nm was achieved using a single-stage TDFL with full width at half maximum and optical signal-to-noise ratio of 0.3 nm and 39.5 dB, respectively. This lasing is achieved using the fabricated PBGF low-pass filter with cutoff wavelength at 1945 μm and loss of more than 25 dB. In this respect, the resultant TDFL performed better than the one that did not employ the low-pass filter. In this paper, we present a few representative cases involving the all-solid PBGF. We have shown that by increasing the diameter of the fabricated PBGF from 142 to 189 μm, their cutoffs related to their bandgaps shifted from 1727 nm toward longer wavelengths, 2079 nm. As a result, lasers with different wavelengths were generated within 2-μm region.

Passively Q-Switched Yb3+-Doped Fiber Laser With ReS2 Saturable Absorber

Rhenium disulfide (ReS2) is a novel two-dimensional material member in the transition metal dichalcogenides family, which shows unusual saturable absorption properties. A compact and reliable passively Q-switched Yb3+-doped fiber laser at 1047 nm was achieved with ReS2 saturable absorber fabricated by mechanical exfoliation method, which achieved pulse duration decreases from 3.32 to 1.56 μ s and the repetition rate increases from 52 to 134 kHz with the pump power from 56 to 200 mW, corresponding to pulse energy and peak power increases from 6.06 to 13.02 nJ and 1.83 to 8.13 mW, respectively. To the best of our knowledge, this is the first report in the 1 μ m with ReS2 for short-pulsed generation. Our results prove that layered ReS2 is a new saturable absorber for short-pulsed lasers.

High-power all-fiber wavelength-widely-tunable Tm3+-doped fiber laser Q-switched by TI-SA

A wavelength widely tunable all-fiber Tm3+-doped double clad fiber laser by using topological insulator (TI) as saturable absorber (SA), for the generation of large energy passively Q-switched pulse, is demonstrated. This 2 μm fiber laser source can generate an average output power as high as 195 mW, corresponding to a pulse energy of ∼3 μJ, and the laser wavelength can be widely tuned from 1935.42 to 2048.85 nm. This high-performance Q-switched operation is implemented by purpose laser cavity optimization and TI-SA protection. Overall, the above results can provide an easily accessible way to develop large energy wavelength tunable passively Q-switched 2 μm fiber laser sources, which possesses important applications in various fields, including manufacturing, spectroscopy, medicine, and the military.

Study on Energy Level and Spectral Characteristics of High Power Yb Doped Fiber Laser

The energy level structure and spectral characteristics of Yb-doped fiber laser are analyzed,and the absorption and emission cross sections of ytterbium ions in quartz matrix are given. It can beseen that there are two absorption peaks, 915 nm and 975 nm, respectively. The absorption coefficientcorresponding to 915 nm absorption peak is smaller, but the absorption spectrum is wider. Theabsorption coefficient corresponding to the absorption peak at 975 nm is relatively large, but thespectrum width is very narrow. The advantages and disadvantages of Yb3+ doped laser materialscompared with other rare earth ions doped laser materials are analyzed. It is pointed out that Yb3+itself, due to its strong absorption and emission at 980 nm, disperses the pump power in the innercladding of double cladding optical fibers and reduces the pump efficiency.

Experimental observation of a cyclic dynamics of solitons in a fiber laser

We report an experimental observation of a singular soliton dynamics in a mode-locked erbium doped fiber laser. This is the first time, to our knowledge, that output intensity exhibits a cyclic transition from a single-pulse to a multi-pulse regime for a fixed value of both pumping power and polarization controllers orientation. Moreover, the pulse duration of the single- and multi-pulse regimes is the same, in contrast with what is usually observed.

Mode-locked thulium doped fibre laser with copper thin film saturable absorber

ABSTRACTWe demonstrate the generation of mode-locked Thulium-Doped Fibre Laser by employing a newly developed saturable absorber (SA) based on copper (Cu) thin film. The SA was prepared by depositing nano-sized particles of Cu onto the surface of polyvinyl alcohol (PVA) film through the E-Beam evaporation process. A stable mode-locking pulse train operating at 1951 nm was successfully generated by introducing the Cu PVA SA into a laser cavity. The laser generated a pulse train at the fundamental frequency of 8.5 MHz with a calculated minimum pulse width of 14.8 ps. This demonstration proves that the Cu PVA based SA is suitable for generating mode-locked fibre laser at 2 µm region.