Coherent Beam Combining of Fiber Amplifiers Using Stochastic Parallel Gradient Descent Algorithm and Its Application

Zhang, Pu; Liu, Zejin; Wang, Xiaolin; Ma, Yanxing; Ma, Haotong; Xu, Xiaojun; Guo, Shan

doi:10.1109/jstqe.2008.2010231

Cited by 206 publications

(93 citation statements)

References 35 publications

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“…PZT phase modulators realize phase modulation by changing the length of the fiber wrapped on PZT based on the inverse piezoelectric effect of PZT. But the resonance phenomenon of PZT phase modulator leads to the linear frequency response range is only several tens kHz [12], which limits the control bandwidth of phase control system, and finally leads to the PZT phase modulator to be rarely used in the CBC system, especially for the system using the dithering technique or SPGD algorithm [2][3][4][5][6][7][8]. It is difficult to design and fabricate one PZT Fig.…”

Section: The Coherent Beam Combination System Based On Double Pzt Phamentioning

confidence: 99%

“…In the CBC system, the phase modulator is a key component for phase modulation and control. At present, LiNbO 3 based phase modulators with high response frequency are widely Y. Ma · P. Zhou · K. Zhang · X. Wang · H. Ma · X. Xu · L. Si · Z. Liu ( ) · Y. Zhao College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073, China e-mail: zejinliu@vip.sina.com used in the CBC system based on multidithering technique or SPGD algorithm [1][2][3][4][5][6][7][8]. However, the insertion loss of available LiNbO 3 phase modulator is higher than 3 dB and the laser-induced damage threshold is lower than 200-mW presently [9,10].…”

Section: Introductionmentioning

confidence: 99%

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A coherent beam combination system based on double PZT phase modulators

Zhang

et al. 2012

Appl. Phys. B

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A novel coherent beam combination system based on double piezoelectric ceramics transducer (PZT) phase modulators is presented and demonstrated for the first time. In this system, two different PZT phase modulators are used for high frequency phase modulation and low frequency phase control, respectively, while in previous demonstrated system, LiNbO 3 phase modulators are often employed. The inherent low insert loss and high laser-induced damage threshold of the PZT phase modulator makes the new proposed system more compact and stable. By the way, the experiment of coherent beam combination of two 5-W fiber laser beams based on double PZT phase modulators is done. In the experiment, the PZT phase modulator with 500-kHz frequency response point made in home is used for high frequency phase modulating and another one with 0∼30-kHz linear frequency response range for phase controlling. When the phase control system is in the closed loop, the fringe contrast of far-field intensity pattern is improved to be more than 90 % from 5 % in open loop.

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Section: The Coherent Beam Combination System Based On Double Pzt Phamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A coherent beam combination system based on double PZT phase modulators

Zhang

et al. 2012

Appl. Phys. B

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“…The combined beam is then propagated many kilometers through a turbulent atmosphere. Recently, much effort has been expended in coherent beam combining [2][3][4][5][6][7]. Coherent beam combining refers to matching the phases of multiple lasers either in the transmitter plane [2,3] or the target plane [4].…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Propagation and Combining of High-Power Lasers

Nelson¹,

Sprangle²,

Davis³

2015

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Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information In this paper we analyze the beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber, and to a lesser extent, slab lasers cause random phase and intensity fluctuations occurring on sub-nanosecond time scales. To coherently combine these high-power lasers would involve instruments capable of precise phase control and operating at rates greater than ~10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase-lock high-power lasers, which is not encountered when phase-locking low-power lasers, for example mW power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers; coherent combining is problematic for DE applications. The dephasing effects of atmospheric turbulence typically encountered in DE applications will degrade the coherent properties of the beam before it reaches the target. Through simulations, we find that coherent beam combining in moderate turbulence and multi-km propagation distances has little advantage over incoherent combining. Additionally, in strong turbulence and multi-km propagation ranges, we find nearly indistinguishable intensity profiles and virtually no difference in the energy on the target between coherently and incoherently combined laser beams. Consequently, we find that coherent beam combining at the transmitter plane is ineffective under typical atmospheric conditions. AbstractIn this paper we analyze the beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber, and to a lesser extent, slab lasers cause random phase and intensity fluctuations occurring on subnanosecond time scales. To coherently combine these high-power lasers would involve instruments capable of precise phase control and operating at rates greater than ~10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase-lock high-power lasers, which is not encountered when phaselocking low-power lasers, for example mW power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers; coherent combining is problematic for DE applications. The dephasing ...

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“…This is achieved by adjusting the fiber collimators mounted on precision translation stages, based on maximizing observed interferences. Optical phases of the input beams are synchronized by monitoring the power of the combined central beam with a sampler and a photodiode, applying a stochastic parallel gradient descent algorithm, which keeps making fast parallel phase dithers and subsequent phase corrections to maximize the sampled signal [14]. Both phase dithers and corrections are applied to the phase modulators in the fiber channels.…”

mentioning

confidence: 99%