Polarization-maintaining Fiber Amplifier Research Articles

Coherent polarization beam combining of four fiber amplifiers in 100 ns pulsed-regime

We demonstrate the coherent polarization beam combining (CPBC) of four polarization-maintained fiber amplifiers in 100ns-pulse regime using single frequency dithering technique for the first time. Experimental results reveal that phase noise of each amplifier chain can be effectively suppressed. The combining efficiency of the CPBC system is 92% and the residual phase error is less than λ/20. The intensity profile of the coherently polarization combined beam is steady for long time observation without degradation of the beam quality.

High-power multichannel PPMgLN-based optical parametric oscillator pumped by a master oscillation power amplification-structured Q-switched fiber laser

We experimentally demonstrated a compact fiber laser-pumped multichannel PPMgLN-based optical parametric oscillator (OPO) generating total OPO output power of 15.8, 15.2, 14.2, 12.9, and 8.8 W with idler output power of 4.7, 4.3, 4.1, 3.3, and 2.1 W at the wavelength of 3.43, 3.63, 3.72, 3.83, and 3.99 μm, respectively. The OPO was pumped by a fully fiberized polarization maintaining (PM) ytterbium-doped pulsed fiber master oscillation power amplifier (MOPA) operating at 1064 nm at a repetition rate of 65 kHz with effective pump power of 28.7 W. The MOPA system was constructed with an acousto-optic Q-switched fiber laser seed and only one stage PM fiber amplifier without any free space components, which makes the pump system compact and stable in the long-term. Comparisons on efficiencies and signal wavelength shifts between different channels showed that the idler absorption was the main factor preventing high average-power OPO operation with long idler wavelength.

Coherent beam combining of fiber amplifier based on adaptive polarization and active phase control

Coherent beam combining (CBC) of a polarization-maintaining fiber amplifier and a non-polarization-maintaining fiber amplifier is presented. The experiment is based on adaptive polarization control and active phase control. The stochastic parallel gradient decent (SPGD) algorithm is used for the adaptive polarization control in the non-polarization-maintaining fiber amplifier and the active phase control is realized by single frequency dithering (SFD) algorithm. When the adaptive polarization control system and the phase control system go into closed loop, the fringe contrast of far-field intensity pattern is improved to more than 87.7%. A scalable architecture for CBC of two styles fiber amplifiers is also proposed.

1 mJ pulse bursts from a Yb-doped fiber amplifier

We demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier capable of generating 60 μJ pulses within bursts of 11 pulses with extremely uniform energy distribution facilitated by a novel feedback mechanism shaping the seed of the burst-mode amplifier. The burst energy can be scaled up to 1 mJ, comprising 25 pulses with 40 μJ average individual energy. The amplifier is synchronously pulse pumped to minimize amplified spontaneous emission between the bursts. Pulse propagation is entirely in fiber and fiber-integrated components until the grating compressor, which allows for highly robust operation. The burst repetition rate is set to 1 kHz and spacing between individual pulses is 10 ns. The 40 μJ pulses are externally compressible to a full width at half-maximum of 600 fs. However, due to the substantial pedestal of the compressed pulses, the effective pulse duration is longer, estimated to be 1.2 ps.

Coherent Polarization Beam Combining of Four High-Power Fiber Amplifiers Using Single-Frequency Dithering Technique

We demonstrate a coherent polarization beam combining (CPBC) of four all polarization-maintained high-power fiber amplifiers with a total output power of 60 W, using the single-frequency dithering technique. When the control system is in the closed loop, the intensity profile is steady and the phase noise can be suppressed effectively. The experimental results show that the combining efficiency of the whole system is as high as 90% in the circumstance of imbalance power ratios of the four beams. The technique used in this letter can be straightforwardly scaled to CPBC of a large array of high-power fiber amplifiers.

Coherent polarization beam combining of four polarization-maintained f iber amplif iers using single-frequency dithering technique

In this manuscript, coherent polarization beam combining of four polarization-maintained fiber amplifiers is demonstrated. In each fiber amplifier, two cascaded fiber amplification stages are used to boost the output power to watt level. The compact and robust single-frequency dithering technique is employed in the active phase-locking of the four laser beams. When the system is in the closed loop, the phase noise can be suppressed effectively for long-time observation. The experimental results show that the combining efficiency of the whole system is as high as 95%.

Polarization-maintaining amplification of phase modulated pulse employing ytterbium-doped single-mode fiber amplifier

Polarization-maintaining fiber amplifier using ytterbium-doped single-mode fiber (SMF) is proposed. A 45° Faraday rotator mirror (FRM) and a polarization independent fiber loop circulator (FLC) with polarization-maintaining fiber (PMF) pigtails are used to realize double-pass amplification and birefringence self-compensation. Arbitrary state of polarization (SOP) such as the linear polarization and elliptical polarization can be maintained. Polarization-maintaining amplification of phase modulated pulse with this amplifier is experimentally demonstrated while introducing little intensity modulation itself.

Fiber amplification of pulse bursts up to 20 μJpulse energy at 1 kHz repetition rate

We demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier. Groups of pulses with a temporal spacing of 10 ns and 1 kHz overall repetition rate are amplified to an average pulse energy of ∼20 μJ and total burst energy of 0.25 mJ. The pulses are externally compressed to ∼400 fs. The amplifier is synchronously pulsed-pumped to minimize amplified spontaneous emission between the bursts. We characterize the influence of pump pulse duration, pump-to-signal delay, and signal burst length.

Coherent beam combination of 137W fiber amplifier array using single frequency dithering technique

Abstract We demonstrate coherent beam combination of 137 W fiber amplifier array using single frequency dithering technique. Four polarization-maintained fiber amplifiers are tiled into 2×2 array and the output power of each amplifier is about 35 W. Single frequency dithering algorithm is run on a signal processor based on field programmable gate array (FPGA) for phase control on the fiber amplifiers. When the phase control system goes into closed-loop, the fringe contrast of far-field intensity pattern is improved by more than 87% from 0 in open-loop, and the residual phase error is less than λ/20.

Coherent Beam Combination of Eight Watt-Level Polarization-Maintained Fiber Amplifiers

We demonstrate the coherent beam combination of eight Watt-level polarization-maintained fiber amplifiers. The phase control signal of each amplifier is generated by running a stochastic parallel gradient descent algorithm on a digital signal processor (DSP). The experimental result shows that the whole system in close-loop performs well for long-time observation. Energy encircled in the target pinhole is 6.68 times more than that in open-loop. The combination efficiency is as high as 84.5%.

Experimental investigation of a seven-element hexagonal fiber coherent array

The phase noises of a 10-m polarization-maintaining (PM) fiber and a 10-W PM fiber amplifier are experimentally measured. The results indicate that the 10-m PM fiber with similar phase noise could be used to investigate the architecture of master oscillator power amplifier coherent combination. A seven-element hexagonal fiber coherent array is developed to investigate the far-field distribution and phase controlling technique of a coherently combining fiber laser array. A hexagonal prism is designed as the combining and splitting component to achieve a fill factor of 0.66. The hill climbing method is employed to detect and lock the element phase.

高功率单频保偏光纤放大器输出特性研究

高功率单频保偏光纤放大器输出特性研究

Experimental and theoretical investigations of photonic crystal fiber amplifier with 260 W output

We report on a polarization-maintaining narrow-linewidth high power ytterbium-doped photonic crystal fiber amplifier with an output as high as 260 W and a slope efficiency of approximately 74%. Measurements of the beam quality yielded M2 values in the range of 1.2-1.3. The linewidth was determined at two different powers using an optical heterodyne detection technique and yielded values that were less than 10 KHz. Our maximum output power was pump limited and measurements of the reflected light indicated that we operated below the stimulated Brillouin scattering (SBS) threshold. Using a pump-probe technique, we estimated the Brillouin gain bandwidth to be approximately 68 MHz. In addition, the Brillouin gain spectrum revealed secondary peaks lying at the high-frequency side. In order to study the power limitations of our amplifier, we developed a detailed model that included a distributed noise source for the SBS process and a temperature gradient obtained via quantum defect heating. Our simulations indicated that for this particular fiber amplifier configuration an output power approaching 1 KW can be achieved. We also found that for forced air cooling the SBS threshold saturates regardless of the operating temperature of the polymer coating. Finally, we show that relatively small enhancement is obtained if a continuous transverse acoustic velocity gradient was implemented in conjunction with the thermal gradient. The latter conclusions drawn from our simulations also hold true for conventional fibers.

Coherent beam combination of a hexagonal distributed high power fiber amplifier array

We demonstrate the coherent beam combination of a hexagonal distributed high power fiber amplifier array. Six polarization-maintained fiber amplifiers are tiled into a hexagonal array by use of a novel beam combiner. The phase control signal for fiber amplifiers is generated by running a stochastic parallel gradient descent algorithm on a digital signal processor. The coherent beam combination with a total output power of 73.5 W is demonstrated. The contrast of the coherent combined beam profile is as high as 81% when the system is closed-loop controlled.

Coherent beam combination of two-dimensional high power fiber amplifier array using stochastic parallel gradient descent algorithm

We demonstrate coherent beam combination of two-dimensional high power fiber amplifier array using stochastic parallel gradient descent (SPGD) algorithm. Four polarization-maintained fiber amplifiers are tiled side by side into a 2×2 laser array with a fill factor of 54% in the near-field. Phase control on the fiber amplifiers are performed by running SPGD algorithm on a digital dignal processor with updating rate of 50 000 Hz/channel. Coherent beam combination of the four fiber amplifiers with a total output power of 60.1 W using SPGD algorithm is demonstrated. Beam quality of the combined beam is computed to be BQ<1.4.

Study of Nd3+-doped polarization maintaining fiber amplifier

The distribution of pump light and signal light power of Nd3+-doped fiber amplifier along the fiber is numerically simulated. The Nd3 +-doped polarization-maintaining fiber amplifier is experimentally studied, which is pumped by 808nm semiconductor laser. The enlargement factor of small-signal is 300（the gain is 25dB）, and the steady 5W amplificatory pulse is obtained by using the self-made Nd:YAG passive mode-locking laser as seed source. The 86142B-type spectrograph and TDS5104 oscillograph are employed to detect the output laser, and the output power is measured by power meter.

High-peak-power femtosecond pulse compression with polarization-maintaining ytterbium-doped fiber amplification

We report the generation of 140 fs pulses with a peak power of up to 270 kW using a fiber pulse source based on a polarization-maintaining ytterbium-doped fiber amplifier and a semiconductor saturable absorber mirror mode-locked fiber laser seed. The seed laser pulses were amplified and chirped in the fiber amplifier and subsequently compressed in an external transmission grating pair. The use of a polarization-maintaining amplifier addresses nonlinear polarization-induced limitations to the obtainable compressed pulse duration and quality that can arise if isotropic fiber amplification is used. Numerical simulations of the system support the experimental measurements and also confirm the role of fiber dispersion in obtaining high-quality compressed pulses.

Linearly-polarized single-transverse-mode high-energy multi-ten nanosecond fiber amplifier with 50W average power

A linearly polarized single-transverse-mode Yb-doped double clad polarization-maintaining fiber amplifier at 1064nm is reported, which delivers 53.1W average power at 40kHz repetition rate, with pulse energy >1mJ, duration 30ns, polarization extinction ratio 13dB, and M(2)1.2. Stimulated Brillouin scattering (SBS) phenomenon during amplification is discussed, and a new SBS suppression approach using linewidth broadening induced by self-phase modulation (SPM) is demonstrated.

Polarization-maintaining hybrid erbium-Brillouin amplifier for high-power low-noise sources

A low-noise high-power source incorporating a polarization-maintaining erbium-Brillouin fiber amplifier is presented. The output noise power is analyzed and a theoretical noise spectral density is determined. Shot-noise-limited performance is predicted and experimentally achieved within the 1-8-GHz-offset frequency range. The polarization extinction ratio was measured as 25 dB.