Fiber Master Oscillator Power Amplifier Research Articles

Very large mode area ytterbium fiber amplifier with aluminum-doped pump cladding made by powder sinter technology

We demonstrate amplification experiments using a very large mode area Yb-doped double-clad fiber with 100 µm aluminum-cer codoped core and 440 µm pump cladding realized by high aluminum codoping. The material for core and pump cladding was fabricated by reactive powder sinter technology. A high numerical aperture (NA) of the pump cladding with NA = 0.21 and a low one of the core with NA = 0.084 could be realized. Using a 0.55 m short fiber sample as the main amplifier in a three-stage ns pulsed fiber master oscillator power amplifier system we achieved 3 ns, 2 mJ output pulses with 360 kW peak power limited by the available pump power. Stimulated Raman scattering effects and amplified spontaneous emission were successfully suppressed.

Fiber-integrated 780 nm source for visible parametric generation.

We report the development of a fully fiber-integrated pulsed master oscillator power fibre amplifier (MOPFA) source at 780 nm, producing 3.5 W of average power with 410 ps pulses at a repetition rate of 50 MHz. The source consists of an intensity modulated 1560 nm laser diode amplified in an erbium fiber amplifier chain, followed by a fiber coupled periodically poled lithium niobate crystal module for frequency doubling. The source is then used for generating visible light through four-wave mixing in a length of highly nonlinear photonic crystal fiber: 105 mW at 668 nm and 95 mW at 662 nm are obtained, with pump to anti-Stokes conversion slope efficiencies exceeding 6% in both cases.

20-W Wavelength-Tunable Picosecond Yb-Doped Fiber MOPA Source Seeded by an NPR Mode-Locked Fiber Laser

We demonstrated a high-power wavelength-tunable picosecond Yb-doped fiber master oscillator power amplifier source without any tunable elements for the first time. This wavelength-tunable output was realized based on the birefringence-induced filter effect of the nonlinear polarization rotation mode-locked fiber laser, which worked as the seed source. Through cascaded single-mode Yb-doped fiber preamplifiers together with two double-cladding Yb-doped fiber amplifiers, the pulses were amplified up to 21.2-W output power in the wavelength range from 1038.4 to 1060 nm with a pulse duration of 9.5 ps, an optical signal-to-noise ratio of 25 dB, and a beam quality M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 1.16 at the repetition rate of 178 MHz.

High power mid-infrared supercontinuum generation in a single-mode ZBLAN fiber with up to 218 W average output power

We report high power mid-infrared (mid-IR) supercontinuum (SC) generation in a single-mode ZBLAN (ZrF₄-BaF₂-LaF₃-AlF₃-NaF) fiber with up to 21.8 W average output power from 1.9 to beyond 3.8 μm pumped by amplified picosecond pulses from a single-mode thulium-doped fiber (TDF) master oscillator power amplifier (MOPA). The optical-optical conversion efficiency from the 793 nm pump laser of the last stage thulium-doped fiber amplifier (TDFA) to mid-IR SC output is 17%. It is, to the best of our knowledge, the highest average power mid-IR SC generation from a ZBLAN fiber to date.

Impact of cavity loss on the performance of a single-mode Yb:silica MOFPA array

In this work, the numerical analysis of an end-pumped continuous-wave (CW) double-clad (DC) master oscillator fiber power amplifier (MOFPA) configuration with linear-cavity has been carried out, based on the set of propagation rate equations. The modified analysis considers the distributed losses of pump coupling, fiber end-face cleaving (air-reflection), splice points, combiners, fiber Bragg gratings (FBGs) as well as scattering losses and parasitic noises due to amplified spontaneous emission (ASE) along the array. Furthermore, a series of experiments have been performed using a home-made oscillator–amplifier configuration. The empirical data taken from the single-mode (SM) ytterbium (Yb)-doped silica fiber laser amplifier were used to verify the numerical simulation accordingly. • The modified simulation for home-made lossy Yb:silica MOFPA array is presented. • Rate equations are developed by considering the loss of each passive component. • Parasitic ASE noise is investigated for fiber amplifier in small-signal regime. • The simulation is validated using data taken by systematic experiments.

Distributed Scheme Versus MOFPA Array on the Power Scaling of a Monolithic Fiber Laser

A couple of amplifying arrays for the power scaling of the fiber lasers under diverse pumping modes are studied. The multifiber series distributed side-pumping arrangement and the cascade amplifier chains in the form of the end-pumped master oscillator fiber power amplifier (MOFPA) scheme are investigated accordingly. Those are numerically modeled based on the propagation rate equations associated with stimulated Brillouin scattering (SBS) as well as the consideration of coupling and splicing losses for large mode area fibers. The continuous wave double-clad Yb:silica fiber laser amplifier is analyzed in various amplifying stages for several cavity lengths at forward pumping regime. Despite the distributed mode exhibits a desirable beam quality, however, it suffers a low SBS threshold. On the other hand, high output power is achieved in the MOFPA configuration far from the onset of SBS.

Kilowatt Ytterbium-Raman fiber laser.

A kilowatt-level Raman fiber laser is demonstrated with an integrated Ytterbium-Raman fiber amplifier architecture. A high power Ytterbium-doped fiber master oscillator power amplifier at 1080 nm is seeded with a 1120 nm fiber laser at the same time. By this way, a kilowatt-level Raman pump laser at 1080 nm and signal laser at 1120 nm is combined in the fiber core. The subsequent power conversion from 1080 nm to 1120 nm is accomplished in a 70 m long passive fiber. A 1.28 kW all-fiber Raman amplifier at 1120 nm with an optical efficiency of 70% is demonstrated, limited only by the available pump power. To the best of our knowledge, this is the first report of Raman fiber laser with over one kilowatt output.

Single polarization picosecond fiber MOPA power scaled to beyond 500 W

We demonstrate a gain-switched diode-seeded, ytterbium-doped fiber based master oscillator power amplifier (MOPA) system, capable of delivering 2.4 μJ, 35 ps pulses at a repetition frequency of 215 MHz in a single-polarization, close to diffraction limited beam. We are aware that the corresponding average power of > 500 W is a record for such a MOPA system. Further pulse energy scaling was limited primarily by the onset of nonlinear effects such as self-phase modulation and stimulated Raman scattering which led to a compromised pulse quality at higher peak powers (> 70 kW).

High-energy diode-seeded nanosecond 2 μm fiber MOPA systems incorporating active pulse shaping

We report on high-energy nanosecond-pulsed fiber master oscillator power amplifier (MOPA) systems seeded by semiconductor laser diodes at 2μm incorporating arbitrary pulse-shaping capabilities. Two MOPA systems, one based on direct diode modulation and the second using additional electro-optic modulator (EOM) based shaping, are investigated, with up to 0.5mJ (25kHz) and 1.0mJ (12.5kHz) pulse energies achieved, respectively, for 100ns pulses with user-defined pulse shapes. Our results indicate that further energy scaling with shaped output pulses is primarily limited by the maximum pulse peak power available from the seed laser diode and the dynamic range offered by the first generation of EOMs at 2μm.

High peak-power mid-infrared ZnGeP_2 optical parametric oscillator pumped by a Tm:fiber master oscillator power amplifier system

We report on the utilization of a novel Tm:fiber laser source for mid-IR ZnGeP2 (ZGP) optical parametric oscillator (OPO) pumping. The pump laser is built in a master oscillator power-amplifier configuration delivering up to 3.36 W of polarized, diffraction limited output power with 7 ns pulse duration and 4 kHz repetition rate. This corresponds to a peak power of ∼121 kW and a pulse energy of ∼0.84 mJ. With this source, we generated 27.9 kW of total mid-IR peak power in a doubly resonant oscillator (DRO) configuration. This is, to the best of our knowledge, the highest ever demonstrated mid-IR peak power from a directly Tm:fiber laser pumped ZGP OPO. Moreover, a DRO output with about 284 μJ of total mid-IR pulse energy was demonstrated using 100 ns pump pulses. The wavelength tuning of the idler was extended to 6 μm with lower output power in another OPO experiment.

High-power supercontinuum generation in a ZBLAN fiber with very efficient power distribution toward the mid-infrared

We report high-power supercontinuum (SC) generation in a step-index fluorozirconate (ZBLAN) fiber with a zero-dispersion wavelength shifted to ~1.9 μm. Pumping the fluoride fiber with 2.75 W of power provided by a thulium-doped fiber amplifier, a continuous spectrum extending from ~0.85 to 4.2 μm with 2.24 W of average output power was achieved. Over 61% (1.37 W) of the total output power corresponds to wavelengths longer than 3 μm, which shows, to the best of our knowledge, the highest power conversion efficiency toward the mid-IR spectral band in relation to the output spectrum width. A linear SC power scalability up to 5.24 W, with a spectral band of ~0.9-4 μm, with repetition rate and pump power provided by a 1.55 μm fiber master-oscillator power amplifier system, is also demonstrated.

High average power supercontinuum generation in a fluoroindate fiber

We report the first demonstration of Watt-level supercontinuum (SC) generation in a step-index fluoroindate (InF3) fiber pumped by a 1.55 μm fiber master-oscillator power amplifier (MOPA) system. The SC is generated in two steps: first ∼1 ns amplified laser diode pulses are broken up into soliton-like sub-pulses leading to initial spectrum extension and then launched into a fluoride fiber to obtain further spectral broadening. The pump MOPA system can operate at a changeable repetition frequency delivering up to 19.2 W of average power at 2 MHz. When the 8-m long InF3 fiber was pumped with 7.54 W at 420 kHz, output average SC power as high as 2.09 W with 27.8% of slope efficiency was recorded. The achieved SC spectrum spread from 1 to 3.05 μm.

Generation of 150 W average and 1 MW peak power picosecond pulses from a rod-type fiber master oscillator power amplifier

We report on the direct amplification of picosecond pulses to megawatt peak power and 150 W average power using a Yb-doped rod-type fiber master oscillator power amplifier. 3 ps pulses at 50 MHz repetition rate are amplified in a 55 cm rod-type fiber amplifier to produce linearly polarized pulses with 3 μJ pulse energy and 1 MW peak power. These results extend megawatt picosecond fiber amplifiers to the 100 W average power regime for the first time. Frequency doubling of the pulses yields 70 W green average power, 1.4 μJ pulse energy, and 500 kW peak power.

Femtosecond-laser pumped CdSiP_2 optical parametric oscillator producing 100 MHz pulses centered at 62 μm

We report the first, to the best of our knowledge, femtosecond-laser-pumped optical parametric oscillator (OPO) based on the newly developed nonlinear crystal, CdSiP₂. The OPO was synchronously pumped by a mode-locked Yb:KYW/Yb:fiber master-oscillator power amplifier, providing 1.053 μm pump pulses with durations of 130 fs at a repetition rate of 100 MHz. The 0.5-mm-thick CdSiP₂ crystal was cut for a type-I noncritical interaction, providing a broad phase-matching bandwidth and ensuring excellent temporal overlap among the pump, signal, and idler pulses. The OPO generated signal pulses with a spectral coverage over 1260-1310 nm and mid-infrared idler pulses with a broad spectral coverage at 5.8-6.6 μm (6.2 THz). With a 2% output coupler (OC), the threshold pump power was 600 mW. At the maximum pump power of 1.6 W, 0.55 W was absorbed due to two-photon absorption and residual linear absorption in the CdSiP₂ crystal, 0.75 W was transmitted, and 53 mW signal power was extracted through the OC. We estimate that the generated idler power was 24 mW.

200 W Diffraction limited, single-polarization, all-fiber picosecond MOPA

A fully fiberized, single-polarization, gain-switched diode-seeded fiber master oscillator power amplifier (MOPA) system is demonstrated delivering 28 ps pulses at variable repetition frequencies ranging from 53 MHz up to 858 MHz. An average signal output power of 200 W was achieved with good OSNR for all operating frequencies. A maximum pulse energy of 3.23 μJ at a repetition frequency of 53 MHz was achieved, corresponding to a pulse peak power of 107 kW. The extraction of higher pulse energy was limited primarily by the onset of nonlinear effects such as SRS which lead to compromised pulse quality at higher peak powers.

High-power all-fiberized thulium-doped fiber MOPA

We demonstrate a high-power all-fiberized thulium-doped fiber laser in a master oscillator power amplifier (MOPA) architecture giving output powers up to 100.4 W. A large-mode-area double-clad active fiber is employed as the gain medium. The laser is pumped by pigtailed laser diodes (LD) with a central wavelength of 792 nm. The slope efficiency of the MOPA system is about 56%. No obvious amplified spontaneous emission (ASE) is observed in the experiment and higher powers can be obtained straightforwardly by scaling the pump power.

Efficient UV generation of a Yb-fiber MOPA producing high peak power for pulse durations of from 100 ps to 2 ns

We demonstrate an average ultraviolet (UV) power generation of 20 W by harmonically converting the output of an all-fiber master oscillator power amplifier (MOPA) system. The third-harmonic generation (THG) UV output provides a conversion efficiency of 40% from the amplified fundamental output. The seed source, which consists of a 1064-nm-wavelength continuous-wave laser diode and two cascaded intensity modulators, produces chirp-free pulses with tunable durations from 100 ps to 2 ns at arbitrary repetition rates and a high dynamic extinction ratio. The fiber MOPA system generates a maximum average power of 50 W and a maximum peak power of 83 kW.

11 mJ all-fiber-based actively Q-switched fiber master oscillator power amplifier

We report a high energy all fiber format nanosecond pulsed laser source at ∼1064 nm in master oscillator power amplifier (MOPA) configuration. The seed source is an acousto-optic Q-switched fiber laser with a varied pulse duration and repetition rate. The output average power of the oscillator is ∼30 mW and two pre-amplifiers were developed to boost the average power to ∼3 W. Pulse energy of >11 mJ for ∼660 ns pulses at 3 kHz was achieved in the final power amplifier using a commercial 50/400 μm (core/cladding diameter) double cladding Yb-doped fiber (DCYF).

230 W average-power all-fiber-based actively Q-switched fiber master oscillator–power amplifier

We report a high-power all-fiber format pulsed laser source at ~1064 nm in a master oscillator-power amplifier configuration. The seed source is an acousto-optic Q-switched fiber laser with a varied pulse duration and repetition rate. The output power of the oscillator is ~1 W, and two double-cladding Yb-doped fiber amplifiers were used to boost the average power of the seed. >230 W average power was achieved for ~1.4 μs pulses at 100 kHz repetition rate. The optical-to-optical efficiency of the main amplifier is 72.81%.

High-power PPMgLN-based optical parametric oscillator pumped by a linearly polarized, semi-fiber-coupled acousto-optic Q-switched fiber master oscillator power amplifier

We have experimentally demonstrated a periodically poled magnesium-oxide-doped lithium niobate (PPMgLN)-based, fiber-laser-pumped optical parametric oscillator (OPO) generating idler wavelength of 3.82 μm. The pump fiber laser was constructed with a linearly polarized, semi-fiber-coupled acousto-optic Q-switched fiber oscillator and a polarization-maintaining fiber amplifier with pulse duration of 190 ns at the highest output power. The OPO was specifically configured in single-pass, singly resonant linear cavity structure to avoid the damage risk of the pump fiber laser, which is always a serious issue in the fiber-laser-pumped, double-pass, singly oscillating structured OPOs. Under the highest pump power of 25 W, an idler average output power of 3.27 W with one-hour peak-to-peak instability of 5.2% was obtained. The measured M2 factors were 1.98 and 1.44 for horizontal and vertical axis, respectively. The high power stability and good beam quality demonstrated the suitability of such technology for practical application.