In-band Pumping Research Articles

145 W single-frequency fiber laser at 1607 nm with the seed and MOPA configuration

In this paper, high Er3+ concentration erbium doped fiber (EDF) and erbium-ytterbium co-doped fiber (EYDF) were fabricated for the seed and master oscillator power amplifier (MOPA) system of the single-frequency fiber laser. An in-band pumping source with the wavelength of 1535 nm was proposed to improve the efficiency in the ring-cavity. A slope efficiency of 23.8% with an output power of 49 mW was achieved and the laser linewidth was measured to be 800 Hz. In the MOPA system, a piece of EYDF was used firstly to absorb the backward 1 µm amplified spontaneous emission (ASE) and amplified the signal from the seed. Based on the above methods, an output power of 145 W was achieved at 1607.75 nm. Because of the self-phase modulation, the laser linewidth was expanded to be 10.75 kHz at the output power of 132 W. To the best of our knowledge, this is the highest efficiency and output power of the seed and the highest output power of the 1.6 µm single-frequency fiber laser.

Modeling of multi-kW in-band pumped triple-clad thulium-doped fiber architecture

We present a model and design for a high-power triple-clad thulium doped fiber specifically for in-band or tandem pumping. This fiber is designed to maximize the output signal power while taking into consideration common effects that limit high-power operation. In-band pumping will allow for thulium fiber lasers to reach multi-kW power levels.

In-band pumped, Q-switched thulium-doped fiber laser system delivering 140 W and 7 mJ pulse energy.

We report on a highly efficient, in-band pumped, Q-switched, Tm-doped, rod-type master oscillator power amplifier (MOPA) system delivering up to 140 W average output power and 7 mJ pulse energy with a slope efficiency of 77% at 20 kHz repetition rate. The amplifier is pumped with Raman-shifted fiber lasers centered at 1692 nm. This in-band pump scheme for Tm-doped fiber lasers can significantly mitigate their quantum defect-related heat load limitations. At the same time, this pump wavelength yields a similar amount of storable and extractable energy to the state-of-the-art pumping at 793 nm. This approach has allowed for the development of highly efficient Tm-doped fiber laser systems combining a high average power and a high output pulse energy.

High-temperature-insensitivity high-power Yb-doped fiber laser directly in-band pumping by 1018 nm laser diodes.

In this Letter, we demonstrate a high-power ytterbium-doped fiber laser (YDFL) based on a directly in-band pumping scheme (DIPS) which employs 1018 nm laser diodes (LDs) as pump sources. The wavelength of the LDs is designed theoretically, considering the distribution of Yb3+ absorption cross section (σa) as well as quantum defect (QD). The flat distribution of σa around 1018 nm ensures excellent temperature insensitivity and flexibility for the YDFL. Besides, lower QD and more compact structure promise higher optical-to-optical (O-O) and electrical-to-optical (E-O) efficiencies. Based on the experimental setup, as the cooling temperature of the 1018 nm LDs ranges from 6 to 23°C, an output power of 2 kW level is achieved that varies by only 2.01% without adjusting the operating current of the LDs subjectively. The output power is then scaled up to 5 kW level. Furthermore, there is a great potential to achieve higher output power and E-O efficiency in YDFLs based on the DIPS.

Demonstration of a 0.8 W continuous wave bulk laser around 2 μm in a Tm3+:Ga-rich BGG glass

Efficient lasing of Ga-rich BGG bulk glasses doped with Tm3+ is demonstrated. Two BGG bulk samples with Tm3+ ion concentrations of 1.27×1020 cm−3 and 2.54×1020 cm−3 were tested for their laser performance. In-band pumping was realized using a continuous-wave (CW) homemade Er-doped fiber laser at 1600 nm. A maximum slope efficiency of 27.7% was demonstrated with respect to the absorbed pump power. The emission cross-section was retrieved from the laser efficiency data for three different lasing wavelengths and compared with the theoretical calculations. The power scaling potential of the Tm3+:BGG glass was investigated and a maximum output power of 0.8 W was achieved.

In-band pumped Kerr-lens mode-locked Tm,Ho-codoped calcium aluminate laser

We report on a Kerr-lens mode-locked Tm,Ho-codoped calcium aluminate laser with in-band pumping of the Tm ions by a spatially single-mode 1678 nm Raman fiber laser. The structurally disordered CaGdAlO4 host crystal is also codoped also with the passive Lu ion for additional inhomogeneous line broadening. The Tm,Ho,Lu:CaGdAlO4 laser generates soliton pulses as short as 79 fs at a central wavelength of 2073.6 nm via soft-aperture Kerr-lens mode-locking. The corresponding average output power amounts to 91 mW at a pulse repetition rate of ∼86 MHz. The average output power can be scaled to 842 mW at the expense of slightly longer pulses of 155 fs at 2045.9 nm, which corresponds to a peak power of ∼58 kW. To the best of our knowledge, this represents the first demonstration of an in-band pumped Kerr-lens mode-locked Tm,Ho solid-state laser at ∼2 µm.

A 301 W narrow-linewidth in-band pumped Er:Yb co-doped fiber amplifier at 1585 nm and related modeling for dynamics study and optimization

Abstract To overcome Yb lasing, a kilowatt-level 1535 nm fiber laser is utilized to in-band pump an Er:Yb co-doped fiber (EYDF) amplifier. The output power of a 301 W narrow-linewidth EYDF amplifier operating at 1585 nm, with 3 dB bandwidth of 150 pm and ${M}^2$ < 1.4, is experimentally demonstrated. To the best of our knowledge, it is the highest output power achieved in L-band narrow-linewidth fiber amplifiers with good beam quality. Theoretically, a new ion transition behavior among energy levels for in-band pumping EYDF is uncovered, and a spatial-mode-resolved nonlinearity-assisted theoretical model is developed to understand its internal dynamics. Numerical simulations reveal that the reduction in slope efficiency is significantly related to excited-state absorption (ESA). ESA has a nonlinear hindering effect on power scaling. It can drastically lower the pump absorption and slope efficiency with increasing pump power for in-band pumped EYDF amplifiers. Meanwhile, optimized approaches are proposed to improve its power to the kilowatt level via in-band pumping.

Growth, spectroscopy and laser operation of in-band pumped Ho3+-doped Yttrium Gallium Garnet

We report on the crystal growth of a 2.86 at.% Ho:YGG crystal, its structural and spectroscopic characterization, as well as on its first laser operation near 2.1 µm under in-band pumping by a Tm-fiber laser.

Pedestal-cladding-pumped holmium fiber laser optimization using an analytical model

An analytical model of holmium-doped fiber laser is used to calculate optimal fiber length, pump wavelength and signal wavelength under in-band pumping conditions while considering fiber losses. The calculations show the advantages of a new type of pedestal-cladding-pumped fiber.

Continuous-Wave and Mode-Locked Operation of an In-Band Pumped Tm,Ho,Lu:CaGdAlO4 Laser

We investigate in-band pumping of a Tm,Ho,Lu:CaGdAlO4 laser using a Raman-shifted Er-fiber laser (1678 nm), in the continuous-wave (CW) and mode-locked (ML) regimes. A maximum output power of 524 mW is obtained in the CW regime with a 5% output coupler at an absorbed pump power of 2.04 W, corresponding to a slope efficiency of 27.9%. A maximum CW wavelength tuning range of 160 nm at the zero level, from 1984 to 2144 nm, is obtained with a 0.2% output coupler. In the ML regime, pumping with 5.5 W (unpolarized), the average output power (0.2% output coupler) reaches 148 mW at a repetition rate of ~96 MHz. The output spectrum is centered at 2071.5 nm with a FWHM of 21.5 nm (σ-polarization). The pulse duration amounts to 218 fs (time-bandwidth product equal to 0.327).

Efficient laser emission at 1191 nm based on Ho3+-doped fluoroaluminate glass in a compact fiber configuration

Efficient laser emission at a wavelength of approximately 1.2 μm in Ho3+-doped AlF3-based glass fiber is reported for the first time. Lasing was achieved through in-band pumping at 1150 nm. The laser cavity's front-end feedback was facilitated by a (High reflectivity, HR) HR-FBG written in Corning HI1060 fiber, spliced to one end of the Ho3+-doped AlF3-based fiber. Fresnel's reflection of the gain fiber provided the other end feedback. The laser performance was characterized by different fiber lengths, and a 31 cm-long fiber achieved a maximum slope efficiency of 70.5 % and a maximum output power of 8.3 W. Furthermore, a series of (Low reflectivity, LR) LR-FBGs written in HI1060 fiber with different reflectivity values were used to replace the Fresnel reflection at the emission end of the gain fiber. The maximum slope efficiency was found to be 54.2 % for a LR-FBG with a reflectivity of 10 %. These results confirm that AlF3-based fiber can potentially serve as gain fiber for higher-power fiber lasers.

Monolithic 2-µm single-frequency linearly-polarized gain-switched distributed feedback fiber laser by femtosecond laser direct-writing.

We report a single-frequency, linearly polarized gain-switched, distributed feedback (DFB), 2-µm thulium doped silica fiber laser (TDFL), with an effective cavity length of 2.5 mm. The cavity is based on a heavily thulium doped non-polarization-maintaining silica fiber and composed of a π-phase-shifted fiber Bragg grating (FBG) with a total FBG length of 35 mm. The DFB FBG was written by femtosecond-laser point-by-point (PbP) method. In-band pumping scheme is chosen with a 1550 nm nanosecond pulsed erbium-doped silica fiber laser pump. Single-longitudinal, linearly polarized, gain-switched TDFL at 2002 nm, with a recorded shortest pulse duration of 4.7 ns, a repetition rate of 20 kHz, a maximum peak power of 170 W, and single pulse energy of 0.8 µJ, has been obtained, benefitting from the ultrashort DFB cavity made by the femtosecond laser direct-writing method.

100 W, tunable in-band thulium fiber amplifier pumped by incoherently combined 1.9 µm fiber lasers.

We detail the design and performance of a high efficiency in-band pumped thulium fiber amplifier operating at the 100 W level. Using a novel pumping architecture based on three incoherently combined thulium fiber oscillators at 1904 nm and a seed laser tunable from 1970-1990 nm, efficient amplification is demonstrated in a high dopant concentration 25/65/250µm thulium fiber. Here we use the 65 µm pedestal surrounding the core as a pump cladding to increase the cladding to core overlap and improve the overall pump absorption. Up to 89% slope efficiency is obtained with ∼100 W output power at 1990 nm. These results indicate that in-band pumping is a viable route to circumvent the thermal limitations associated with 793 nm diode pumping and provide a pathway for development of multi-kW laser sources in the 2 µm spectral window.

Kerr-lens mode-locked 49-fs Tm3+:YScO3 single-crystal laser at 2.1 µm.

We report on a continuous wave (CW) and Kerr-lens mode-locked (KLM) Tm3+:YScO3 single-crystal laser centered at 2.1 µm. Efficient CW laser operation with a maximum slope efficiency of 51% was achieved under in-band pumping by an Er:Yb fiber master oscillator power amplifier (MOPA). In KLM operation, pulses as short as 49 fs corresponding to seven optical cycles were achieved at a repetition rate of 96.7 MHz with an average output power of 126 mW. Such short pulse durations are enabled by the inhomogeneously broadened emission spectrum of Tm3+:YScO3 extending to above 2200 nm.

(INVITED)Mid-infrared photoluminescence in Ce3+ doped selenide-chalcogenide glass and fiber

We provide measurements to support our earlier report of continuous wave fiber lasing in a small core Ce3+-doped selenide chalcogenide SIF (step index fiber) of core: Ge-As-Ga-Se chalcogenide glass, doped with 500 ppmw (parts-per-million by weight) of cerium (III). In-band pumping of Ce3+ in fiber, bulk glass and ground glass geometries, at 4.15 μm wavelength, gives MIR (mid-infrared) photoluminescence spanning 3.40–5.80 μm wavelength, corresponding to the 2F5/2 ← 2F7/2 electronic emission transition due to Ce3+. Room temperature emission and MIR absorption spectra together enable interpretation of the manifold energies of the first excited state and there is potential for occupied Stark levels in the ground state at room temperature. Both ‘τrad’ (PL lifetime) and ‘trise’ (rise-time through 10% to 90% of maximum PL intensity) are determined: for ground glass at 4.60 μm wavelength, the best decay fit comprises a primary, and perhaps secondary, lifetime for ground glass of 3.5 ms, and 1.2 ms, and PL rise time of 3.9 ms.

2.1 m, high-energy dissipative soliton resonance from a holmium-doped fiber laser system

Abstract We propose a 2.1 μm high-energy dissipative soliton resonant (DSR) fiber laser system based on a mode-locked seed laser and dual-stage amplifiers. In the seed laser, the nonlinear amplifying loop mirror technique is employed to realize mode-locking. The utilization of an in-band pump scheme and long gain fiber enables effectively exciting 2.1 μm pulses. A section of ultra-high numerical aperture fiber (UHNAF) with normal dispersion and high nonlinearity and an output coupler with a large coupling ratio are used to achieve a high-energy DSR system. By optimizing the UHNAF length to 55 m, a 2103.7 nm, 88.1 nJ DSR laser with a 3-dB spectral bandwidth of 0.48 nm and a pulse width of 17.1 ns is obtained under a proper intracavity polarization state and pump power. The output power and conversion efficiency are 0.233 W and 4.57%, respectively, both an order of magnitude higher than those of previously reported holmium-doped DSR seed lasers. Thanks to the high output power and nanosecond pulse width of the seed laser, the average power of the DSR laser is linearly scaled up to 50.4 W via a dual-stage master oscillator power amplifier system. The 3-dB spectral bandwidth broadens slightly to 0.52 nm, and no distortion occurs in the amplified pulse waveform. The corresponding pulse energy reaches 19.1 μJ, which is the highest pulse energy in a holmium-doped mode-locked fiber laser system to the best of our knowledge. Such a 2.1 μm, high-energy DSR laser with relatively wide pulse width has prospective applications in mid-infrared nonlinear frequency conversion.

Cascaded Mode-Locked Nd:YVO4 Laser Using MgO Doped Periodically-Poled LiNbO3 With Direct In-Band Diode Pumping at 914 nm

We report a cascaded mode-locked Nd:YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> laser at 1064 nm with direct in-band pumping at 914 nm. A 25-mm-long MgO doped periodically-poled LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal was used to produce mode-locked laser pulses. A volume Bragg grating was used to manipulate the output spectrum of the laser. In the positive Kerr-lens scheme, the output power was 3.81 W at 166.8-MHz repetition rate. In the negative Kerr-lens scheme, the output power was 4.81 W at 108.6-MHz repetition rate. Typical pulse duration and the full-width-at-half-maximum spectral width were 35 ps and 0.05 nm, respectively, yielding a time-bandwidth product of 0.5.

High brightness in-band pumped fiber MOPA with output power scaling to >4.6k W.

An in-band pumping technique that employs low numerical aperture (NA) and high brightness fiber lasers emitting at 1018nm enables outstanding power scaling performance by increasing pump power handling capacity of fiber components, reducing thermal load and quantum defect. Here, we present design criteria for an in-band pumped fiber master oscillator power amplifier (MOPA) structure, pumped with 1018nm fiber lasers, as well as mitigation strategies for nonlinear effects for scalable single-mode laser operation at multi-kilowatt power levels. In addition, we report experimental demonstration of an in-band pumped MOPA with an output power scaling up to 4.63kW and a slope efficiency of ∼88%. The MOPA system is pumped by 18×264W high brightness fiber lasers operating at 1017.8±0.3n m with an NA of <0.075. The laser emits at 1080.4nm wavelength with a stimulated Raman scattering suppression of >36.8d B and has a near-diffraction-limited beam quality of M 2∼1.61. To the best of our knowledge, our laser has the highest brightness of 153G W⋅c m -2⋅s r -1 reported at 1080nm in co-pumping configuration.

532 nm pumped visible emission from Ho3+-doped fiber lasers

We report a green fiber laser based on an in-band pumping process for the first time. The impact of the pumping mechanism on output characteristics is addressed, and a new pumping strategy to improve the output performance of visible fiber lasers is presented. We demonstrate the highest power of 0.52 W green fiber laser output using a single-wavelength 532 nm solid-state laser as the pump source, and we also exhibit dual-wavelength excitation with a maximum power output of 0.72 W. Simultaneously, we investigate the reasons of visible dual-wavelength generation and modulation approaches in Ho3+-doped fluoride fibers. This method efficiently tackles the problem of visible light generation in Ho3+-doped fibers being limited, as well as pave the way for more efficient and powerful visible fiber lasers.

Performance Enhancement of Ytterbium-Doped Fiber Amplifier Employing a Dual-Stage In-Band Asymmetrical Pumping

The performance of doped fiber amplifiers can be enhanced significantly with the help of multi-stage pumping technique provided that various critical parameters of pumps including their optical power and wavelength are optimized. We report the performance enhancement of a ytterbium doped fiber amplifier (YDFA) for a 1.02–1.08 m spectral region with an optimized design based on a novel dual-stage in-band asymmetrical pumping scheme. By accurately adjusting the optical power and wavelength of pumps in both the stages, a record peak gain of around 62.5 dB and output power of 4.5 W are achieved for a signal wavelength of 1.0329 m at an optimized length of Ytterbium-doped silica fiber and optimized doping concentration of Yb. Moreover, a minimum noise figure (NF) of 4 dB is observed for a signal wavelength of 1.0329 m at the optimized parameters. Similarly, the effect of using high and low pump powers at the first and the second stage, respectively, on NF of the amplifier is also investigated at different values of signal powers. It is observed that the value of NF increases significantly by using high pump power at the first stage and low pump power at the second stage.