Generation of vectorial vortex beams by a coherently combined laser array.

With the superpositions of spin and orbital angular momentum, vectorial vortex beams (VVBs) have attracted great attention in recent years. Many approaches have been developed to generate such beams, but high-power output is not supported. Here, we report the coherent beam combining (CBC) for generating VVBs that are compatible with high-power fiber amplifiers.

Target-in-the-loop coherent beam combining based on an all-fiber structure.

Coherent beam combining (CBC) is a promising technique to realize high-brightness laser output. As a key point to implement CBC, an appropriate phase control feedback structure should be established. With the advantages of a compact structure and no requirement for mirrors to sample, the all-fiber phase control feedback structure has been widely studied.

Coherent beam combining of two all-PM thulium-doped fiber chirped pulse amplifiers.

In this paper, we report a coherent beam combining (CBC) system that involves two thulium-doped all-polarization maintaining (PM) fiber chirped pulse amplifiers. Through phase-locking the two channels via a fiber stretcher by using the stochastic parallel gradient descent (SPGD) algorithm, a maximum average power of 265 W is obtained, with a CBC efficiency of 81% and a residual phase error of λ/17. After de-chirping by a pair of diffraction gratings, the duration of the combined laser pulse is compressed to 690 fs.

Single-frequency pulsed fiber laser based on an electro-optic modulator with injection seeding technique.

A single-frequency linearly polarization pulsed fiber laser based on an electro-optic modulator with injection seeding technique is demonstrated. The single-frequency performance of the fiber ring-cavity laser is guaranteed by the seed source, which is a distributed-feedback fiber laser based on the -phase-shifted fiber Bragg grating. The electro-optic modulator triggers active -switching of the laser for pulse generation.

Generating the 1.5 kW mode-tunable fractional vortex beam by a coherent beam combining system.

As an essential component of the vortex beam, the fractional vortex beam has significantly advanced various applications, such as optical imaging, optical communication, and particle manipulation. However, practical applications face a significant challenge as generating high average power fractional vortex beams remains difficult. Here, we proposed and experimentally demonstrated a high average power mode-tunable fractional vortex beam generator based on an internally sensed coherent beam combining (CBC) system.

Numerical simulation of the internal active phase-locking coherent beam combining system.

As a promising way to realize high output power while maintaining high beam quality, coherent beam combining (CBC) of fiber lasers has drawn much interest. Phase control is one of the main technologies to fulfill CBC, which is employed to keep the phases of different fiber lasers consistent. Traditional phase control techniques employ beam splitters after the emitting array to obtain phase mismatch information.

System design for coherent combined massive fiber laser array based on cascaded internal phase control.

Coherent beam combining (CBC) of a fiber laser can scale the output power while maintaining high beam quality. However, phase detection and control remain a challenge for a high-power CBC system with a massive laser array. This paper provides a novel, to the best of our knowledge, cascaded phase-control technique based on internal phase detection and control, called the cascaded internal phase-control technique.

M factor estimation in few-mode fibers based on a shallow neural network.

A high-accuracy, high-speed, and low-cost M factor estimation method for few-mode fibers based on a shallow neural network is presented in this work. Benefiting from the dimensionality reduction technique, which transforms the two-dimension near-field image into a one-dimension vector, a neural network with only two hidden layers can estimate the M factor directly. In the simulation, the mean estimation error is smaller than 3% even when the mode number increases to 10.

Internal phase control of coherent fiber laser array without ambiguous phase based on double wavelength detection.

High-power fiber lasers have been widely utilized in manufacturing, medical care, and many other fields. Due to mode instability, nonlinear effects, and so on, the output power of a monolithic fiber laser is limited. Coherent beam combining (CBC) of fiber lasers is a promising way to obtain higher output power.

Cantilevered adaptive fiber-optics collimator based on piezoelectric bimorph actuators.

A novel, to the best of our knowledge, cantilever construction design of an adaptive fiber-optics collimator (AFOC) based on piezoelectric bimorph actuators for tip/tilt control is introduced. With this new cantilever structure, an AFOC with a diameter of only 6 mm was developed, and the output laser beam deviation angle and resonance frequency of the device were measured. The experimental results show that this new AFOC can provide more than 1 mrad deflection angle at a 20 V driving voltage, and the first resonance frequency is about 500 Hz.

Distributed active phase-locking of an all-fiber structured laser array by a stochastic parallel gradient descent (SPGD) algorithm.

Coherent beam combining (CBC) of fiber laser array is a promising way to achieve high output power. Phase control is one key point to implement CBC. Appropriate feedback structures should be established to achieve phase control.

Iteration-free, simultaneous correction of piston and tilt distortions in large-scale coherent beam combination systems.

Coherent beam combination (CBC) holds promise for scaling the output power of the laser system while maintaining good beam quality. Owing to the thermal effect and mechanics instability, piston and tilt distortions always exist and affect the performance of the combined beam. To ensure the constructive interference in the far-field, dynamic correction of the distortions is highly required.

Generation of optical vortex lattices by a coherent beam combining system.

Owing to the unique features in intensity and phase structures, optical vortex lattices (OVLs) have attracted intensive attention and promoted various applications. However, the power scaling of OVLs always presents a critical challenge. Here we take advantage of the brightness enhancement of coherent beam combining (CBC) technology and propose an architecture for creating OVLs based on the CBC system.

Suppressing stimulated Raman scattering by adopting a composite cavity in a narrow linewidth fiber oscillator.

The master oscillator power amplifier structure has been widely employed to realize high-power and narrow-linewidth output in fiber lasers. However, the stimulated Raman scattering (SRS) effect would appear in high-power operation and even become an important limitation on further power scaling, especially when the seed lasers are based on a fiber Bragg grating (FBG) pair. In order to improve SRS suppressing ability, a composite cavity structure was demonstrated by employing an additional wide-bandwidth low-reflectivity FBG outside the conventional oscillator.

Switching the orbital angular momentum state of light with mode sorting assisted coherent laser array system.

Light beams carrying orbital angular momentum (OAM) have important implications for future classical and quantum systems. In many applications, controlled switching of the OAM state at high speed is crucial, while accelerating the switching rate presents a long-standing challenge. Here we present a method for flexibly switching the OAM state of light based on a coherent laser array system.

Comprehensive investigation on the power scaling of a tapered Yb-doped fiber-based monolithic linearly polarized high-peak-power near-transform-limited nanosecond fiber laser.

An all-fiberized linearly polarized nanosecond master oscillator power amplifier based on polarization-maintaining large-mode-area Yb-doped tapered double cladding fiber (T-DCF) is comprehensively investigated. Firstly, excellent performance of the Yb-doped T-DCF for suppressing nonlinear effects, including stimulated Brillouin scattering (SBS) effect and spectral broadening effects, is experimentally demonstrated and qualitatively analyzed. An SBS-free average output power of 8.

Tight focusing properties and focal field tailoring of cylindrical vector beams generated from a linearly polarized coherent beam array.

We investigate the focusing properties of cylindrical vector beams (CVBs) generated from the combination of an array of beams, each with sub-apertures and controllable polarization. The analytical expression of the tight focusing field of the combined CVBs has been derived based on the Richard-Wolf vector diffraction integral. To obtain a desired focal spot size which includes efficient sidelobe suppression, the required parameters, such as the exit sub-aperture, numerical aperture and truncation parameter, have been studied in detail.

Tapered Yb-doped fiber enabled monolithic high-power linearly polarized single-frequency laser.

The all-fiber high-power linearly polarized single-frequency fiber laser based on the polarization-maintaining tapered Yb-doped fiber (T-YDF) is systematically studied. As a result, a 300 W-level stable output with linear polarization and nearly diffraction-limited beam quality is demonstrated. In particular, the overall properties of the transverse mode instability (MI) effect in such a single-frequency laser system are discussed in detail for the first time, to the best of our knowledge, including temporal, frequency, polarization, and spatial domains.

Near-Infrared Optical Modulation for Ultrashort Pulse Generation Employing Indium Monosulfide (InS) Two-Dimensional Semiconductor Nanocrystals.

In recent years, metal chalcogenide nanomaterials have received much attention in the field of ultrafast lasers due to their unique band-gap characteristic and excellent optical properties. In this work, two-dimensional (2D) indium monosulfide (InS) nanosheets were synthesized through a modified liquid-phase exfoliation method. In addition, a film-type InS-polyvinyl alcohol (PVA) saturable absorber (SA) was prepared as an optical modulator to generate ultrashort pulses.

High-power vortex beam generation enabled by a phased beam array fed at the nonfocal-plane.

High-power vortex beams have extensive applications in optical communication, nonlinear frequency conversion, and laser processing. To overcome a single beam's power limitation, generating vortex beams, based on a phased beam array, is an intuitive idea that requires locking each beamlet's phase to a specific different value. Conventionally, the intensity profiles of the focal plane (far field) are used for extracting the cost functions in active phase control systems.

Coherent fiber-optics-array collimator based on a single unitary collimating lens: proposal design and experimental verification.

In this paper, we propose a design of coherent fiber-optics-array collimator (CFAC) that is mainly composed of a single unitary collimating lens and a prism. The CFAC system is presented conceptually, and corresponding parameters are theoretically analyzed using a geometrical optics method. Then, we set up a proof-of-concept experiment to verify the validity of the CFAC system with three coherent fiber lasers distributed along the symmetry axis through the center of the single unitary lens.

Ultra-stable pulse generation in ytterbium-doped fiber laser based on black phosphorus.

We demonstrated a high-quality black phosphorus (BP) crystal fabricated a modified electrochemical delamination exfoliation process. Employing the nonlinear transmittance method and Z-scan technique, the nonlinear optical properties of BP were characterized. Based on the saturable absorber (SA) of BP, we designed a passively Q-switched ytterbium (Yb)-doped fiber laser operating at 1.

Coherent beam combining of fiber lasers using a CDMA-based single-frequency dithering technique.

Coherent beam combination (CBC) is a promising method to obtain high-power and high-brightness laser output. In this paper, we present a novel single-frequency dithering technique based on code division multiple access (CDMA). By using orthogonal phase control signals, the number of channels can be increased and the phase control speed in the coherent beam combination system can be boosted.

>1 kW all-fiberized narrow-linewidth polarization-maintained fiber amplifiers with wavelength spanning from 1065 to 1090 nm.

We demonstrate all-fiberized, kilowatt-level, narrow-linewidth, Yb-doped and polarization-maintained (PM) amplifiers with a central wavelength spanning from 1065 to 1090 nm. The laser system consists of a tunable single-frequency laser seed and multistage PM fiber amplifiers in the master oscillator power amplifier configuration. The stimulated Brillouin scattering effect is suppressed by phase modulation based on a white noise source.

500 W level MOPA laser with switchable output modes based on active control.

We report a high power transverse-mode-switchable fiber laser in a master oscillator power amplifier (MOPA) configuration. The output modes of a few-mode fiber amplifier can be actively controlled by the input polarization state of the fundamental mode seed laser using SPGD algorithm. A fast, stable and safety mode switching between LP01 and LP11 modes is achieved in the amplifier at output power of 500 W level.