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Deep-learning-based phase control method for tiled aperture coherent beam combining systems
摘要： We incorporate deep learning (DL) into tiled aperture coherent beam combining (CBC) systems for the ?rst time, to the best of our knowledge. By using a well-trained convolutional neural network DL model, which has been constructed at a non-focal-plane to avoid the data collision problem, the relative phase of each beamlet could be accurately estimated, and then the phase error in the CBC system could be compensated directly by a servo phase control system. The feasibility and extensibility of the phase control method have been demonstrated by simulating the coherent combining of different hexagonal arrays. This DL-based phase control method offers a new way of eliminating dynamic phase noise in tiled aperture CBC systems, and it could provide a valuable reference on alleviating the long-standing problem that the phase control bandwidth decreases as the number of array elements increases.
关键词： phase control,deep learning,coherent beam combining
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Tolerance Analysis for Piston and Tilt Error in Hexagonal Laser Phased Array
摘要： Coherent Beam Combining is an alternative approach to the construction of high-power lasers, which mitigates the thermo-optic problems occurring in the classic laser construction. However, phased array requires the control of a larger number of parameters, which results in easier beam quality degradation. The most important are phase mismatch (piston error) and tilt error, which cause energy spreading into the side lobes and distortion of the main lobe in far-field intensity pattern. To achieve effective combining, piston and tilt error must be controlled with accuracy to fraction of wavelength. We present numerical model of coherent beam combining of 2D array of laser beams. The analysis of beam combining quality for hexagonal array with seven elements in dependence on Super-Gaussian SGp beam profile for tilt and piston error have been presented. We have taken the tolerance limit as a decrease in Strehl ratio (SR) by 20% for piston and tilt error. Additionally for tilt error as tolerance limit we have taken pointing RMS error equal to diffraction limit 1.5λf/D. Our analysis results in two conclusions. Firstly, the tilt error has higher influence on degradation of beam quality. Secondly, Gaussian beam (p=1) has higher tolerance for both errors than top-hat (p=32).
关键词： tilt error,piston error,hexagonal array,Coherent Beam Combining,Strehl ratio,Super-Gaussian beam profile
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Coherent Beam Combining by Noncollinear Sum-Frequency Generation
摘要： Despite rapid development of fiber laser technologies, highest pulse peak power achievable from fiber lasers eventually approaches limits which are not easy to overcome. Therefore, there is growing interest in methods, which would allow to combine outputs from multiple pulsed fiber lasers into single diffraction-limited beam, and by this enable further scaling. For this reason, numerous coherent and incoherent beam combining methods are being proposed and investigated. Not so well investigated class of beam combining methods is beam combing based on nonlinear interaction. In our earlier work, we have demonstrated beam combining by multiplexing pulses in time, using second-order nonlinear crystal set in noncollinear phase-matching configuration. However, such configuration allows to scale only average power of the beam, leaving pulse energy unchanged (in case of 50 % conversion efficiency). In order to scale pulse energy and peak power, pulses have to be also combined in time, and for this, phase control is needed. Such approach was first proposed by Michailovas et al. and first proof of concept demonstrated by Zhang et al.. However, in previous demonstrations, low-power beams were combined with very low combining efficiency (<0.4 % for 4 beams). Here we apply this method to more realistic scenario and demonstrate combining of pulsed beams from 4 high-power fiber amplifiers with efficiency up to 49 %. Moreover, we demonstrate pulse energy and peak power improvement in the combined beam, exceeding peak-power limitations of single fiber amplifier.
关键词： noncollinear sum-frequency generation,fiber lasers,pulse energy scaling,peak power scaling,coherent beam combining
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Coherent Beam Combining of Fiber Amplifiers Seeded by Commercial Low Cost Diode
摘要： Coherent beam combining (CBC) is one of the methods for power scaling of high power lasers. In the scientific literatures a low power narrow linewidth source is used for CBC, however in this report, a low cost diode laser source (spectral bandwidth <10 MHz) is used to fabricate near diffraction-limited 300 W fiber laser with CBC method. The diode laser is amplified by a preamp fiber amplifier and then divided in to three channels. Each channel is amplified to achieve 120W output with homemade power amplifiers. A 1×3 diffractive optical element is used to combine the output of the amplifiers with ~83% efficiency. Active phase locking is achieved with the stochastic parallel gradient descent (SPGD) method. A major obstacle towards high power narrow-linewidth fiber lasers is stimulated Brillouin scattering (SBS). It has been proven that phase modulation is an effective way to suppress SBS in these kind of lasers. Applying phase modulation to a single frequency laser, splits its spectrum to many spectral lines with the same frequency spacing of the modulation frequency. In this work, we use a sinusoidal signal phase modulation (30 MHz frequency and 10 V amplitude) to suppress SBS effect. The result of this modulation on the spectrum of the laser is illustrated. The maximum achievable output power for each channel without modulation is ~40 W. However, by applying modulation SBS threshold power enhances with a factor of 3. The output power of combined beam versus pump diode current (solid line) is shown. Also the backward output power (dashed line) is illustrated. As it can be seen in the figure the maximum backward power is 110 μW which proves the SBS effect is cancelled.
关键词： stimulated Brillouin scattering,diode laser,phase modulation,Coherent beam combining,fiber amplifiers
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Coherent Beam Combining of 37 Femtosecond Fiber Amplifiers
摘要： For the last few years, coherent beam combining (CBC) has been drastically increasing the performances of ytterbium-doped femtosecond fiber amplifiers, up to more than 10 mJ output energy and to the multi-kilowatt level [1,2]. CBC consists in coherently adding the output beams of several independent amplifiers seeded by a common source. This method involves both an efficient combination process along with a phase detection and control technique applied on all the beams to combine. However, for femtosecond pulses to reach the Joule level and address applications such as particles acceleration, several thousands of fibers need to be combined. Thus, highly scalable CBC architectures along with adapted phase measurements techniques need to be investigated. The XCAN project, a collaboration between Ecole Polytechnique and Thales, aims at demonstrating such a highly scalable CBC system in the femtosecond regime, involving 61 fibers as a target point. It consists in a tiled-aperture configuration where the fibers are stacked in a hexagonal array and collimated by a hexagonal microlens array. Besides, an interferometric phase measurement technique is implemented, which allows to determine the phase shifts of all the beams in one single frame acquired from a fast camera and to correct them with a kHz bandwidth feedback loop. This detection method has been demonstrated to be theoretically scalable up to about 10,000 fibers [3]. First proof of principles of the XCAN project have been published with 19 passive fibers and 7 high power fiber amplifiers [4,5]. In this paper, we report on the CBC of 37 fiber amplifiers in the femtosecond regime in the way towards our goal of 61 channels.
关键词： XCAN project,interferometric phase measurement,femtosecond fiber amplifiers,coherent beam combining
更新于2025-09-11 14:15:04
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Study on the influence of phase noise on coherent beam combined Bessel-Gaussian beam
摘要： Coherent beam combining (CBC) technology is one of the effective methods to obtain the high power laser beam, but the quality of the combined beam is significantly affected by the random phase noise among the sub-beams. In this work, a method for generating a combined Bessel-Gaussian (CBG) beam based on CBC technology is proposed. The correlation coefficient is adopted to evaluate the influence of phase noise on CBG beam including the Gaussian phase noise (GPN) and measured fiber laser phase noise (FLPN). The research results of GPN show that the spiral phase of the n-order CBG beam is unaffected by noise when the amplitude of phase noise is less than λ/5. The phase noise of fiber laser is measured, and its amplitude is around λ/10. Therefore, the spiral phase of the CBG beam is unaffected by the measured FLPN. Moreover, the resisted ability of the CBG beam against phase noise is improved efficiently through increasing the number of sub-beams.
关键词： Phase noise,Vortex beam,Coherent beam combining technology,Correlation coefficient
更新于2025-09-10 09:29:36