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Li Feng, Geng Chao, Huang Guan, et al. Wavefront sensing based on fiber coupling of the fiber laser array[J]. Opto-Electronic Engineering, 2018, 45(4): 170691. doi: 10.12086/oee.2018.170691
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Wavefront sensing based on fiber coupling of the fiber laser array
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Abstract
A new method of wavefront sensing based on fiber coupling in the fiber laser array has been proposed. The scheme and the recovery process of this sensor are introduced. Numerical simulations of detecting the turbulence-induced aberrations utilizing such method and experiments of recovering static aberrations with 7-element adaptive fiber optics collimator (AFOC) array are presented. Numerical results show that such sensor could effectively recover the wavefront with turbulence-induced aberrations. For hexagonal array with different units, the optimum reconstructed Zernike mode is also different. Smaller array filled factor leads to larger recovery residual error. Compared with array filled factor of 1.0, value of 0.8 is easy to obtain and brings in recovery residual error increment less than 10%. Experimental results reveal that RMS less than 0.075 μm of the recovery residual error is obtained when detecting the static aberration with 7-element AFOC array with filled factor of 0.875. The aberration is with RMS of 0.433 μm and mainly includes Zernike modes of low orders like defocus. Results here validate the effectiveness of the wavefront sensing method proposed here. Such method would get further application in systems like laser array propagating and turbulence aberrations correcting.-
Keywords:
- wavefront sensing /
- adaptive optics /
- fiber laser array /
- fiber coupler
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References
[1] Goodno G D, Mcnaught S J, Rothenberg J E, et al. Active phase and polarization locking of a 1.4 kW fiber amplifier[J]. Optics Letters, 2010, 35(10): 1542-1544. doi: 10.1364/OL.35.001542 [2] Yu C X, Augst S J, Redmond S M, et al. Coherent combining of a 4 kW, eight-element fiber amplifier array[J]. Optics Letters, 2011, 36(14): 2686-2688. doi: 10.1364/OL.36.002686 [3] Wang X L, Zhou P, Ma Y X, et al. Active phasing a nine-element 1.14 kW all-fiber two-tone MOPA array using SPGD algorithm[J]. Optics Letters, 2011, 36(16): 3121-3123. doi: 10.1364/OL.36.003121 [4] Vorontsov M, Filimonov G, Ovchinnikov V, et al. Comparative efficiency analysis of fiber-array and conventional beam director systems in volume turbulence[J]. Applied Optics, 2016, 55(15): 4170-4185. doi: 10.1364/AO.55.004170 [5] Geng C, Luo W, Tan Y, et al. Experimental demonstration of using divergence cost-function in SPGD algorithm for coherent beam combining with tip/tilt control[J]. Optics Express, 2013, 21(21): 25045-25055. doi: 10.1364/OE.21.025045 [6] Vorontsov M A, Weyrauch T, Beresnev L A, et al. Adaptive array of phase-locked fiber collimators: analysis and experimental demonstration[J]. IEEE Journal of Selected Topics in Quantum Electronics, 2009, 15(2): 269-280. doi: 10.1109/JSTQE.2008.2010875 [7] Weyrauch T, Vorontsov M A, Carhart G W, et al. Experimental demonstration of coherent beam combining over a 7 km propagation path[J]. Optics Letters, 2011, 36(22): 4455-4457. doi: 10.1364/OL.36.004455 [8] Weyrauch T, Vorontsov M, Mangano J, et al. Deep turbulence effects mitigation with coherent combining of 21 laser beams over 7 km[J]. Optics Letters, 2016, 41(4): 840-843. doi: 10.1364/OL.41.000840 [9] Li F, Geng C, Li X Y, et al. Co-aperture transceiving of two combined beams based on adaptive fiber coupling control[J]. IEEE Photonics Technology Letters, 2015, 27(17): 1787-1790. doi: 10.1109/LPT.2015.2438172 [10] Li F, Geng C, Huang G, et al. Experimental demonstration of coherent combining with tip/tilt control based on adaptive space-to-fiber laser beam coupling[J]. IEEE Photonics Journal, 2017, 9(2): 7102812. [11] 李枫, 耿超, 李新阳, 等.基于光纤耦合器的全光纤链路锁相控制[J].光电工程, 2017, 44(6): 602-609. Li F, Geng C, Li X Y, et al. Phase-locking control in all fiber link based on fiber coupler[J]. Opto-Electronic Engineering, 2017, 44(6): 602-609. [12] Luo W, Geng C, Wu Y Y, et al. Experimental demonstration of single-mode fiber coupling using adaptive fiber coupler[J]. Chinese Physics B, 2014, 23(1): 014207. doi: 10.1088/1674-1056/23/1/014207 -
Overview
Overview: Coherent beam combining (CBC) of fiber amplifiers with a master-oscillator-power amplifier (MOPA) architecture is a promising way for brightness scaling with excellent beam quality. Fiber laser array, as a typical CBC architecture, has been widely applied in laboratory experiments. Further application aims at eliminating the turbulence-induced dynamic aberrations. The correctable aberrations of the fiber laser array are tip/tilts and pistons distribute on the sub-aperture. Target-in-the-loop (TIL) technique cooperating with optimal method is the only way reported to achieve CBC in atmosphere. Such method suffers from low bandwidth due to large array scale and long air path. Active detecting the atmospheric aberrations becomes necessary. Conventional wavefront sensor, like Hartmann-Shack, needs beam zooming and splitting in the back end of the telescope. Direct spatial beam zooming and splitting in the back end of fiber laser array system is impossible because the system is discrete in space. Meanwhile, setting a splitter large enough to cover the whole array aperture is inconceivable and breaks the compact and flexible character of the fiber laser array architecture. A new method of wavefront sensing based on fiber coupling in the fiber laser array has been proposed. The scheme and the recovery process of this sensor are introduced. Numerical simulations of detecting the turbulence-induced aberrations utilizing such method and experiments of recovering static aberrations with 7-element AFOC array are presented. Numerical results show that such sensor could effectively recover the wavefront with turbulence-induced aberrations. For hexagonal array with different units, the optimum reconstructed Zernike mode is also different. Smaller array filled factor leads to larger recovery residual error. Compared with array filled factor of 1.0, value of 0.8 is easy to obtain and brings in recovery residual error increment less than 10%. Experimental results reveal that RMS less than 0.075 μm of the recovery residual error is obtained when detecting the static aberration with 7-element AFOC array with filled factor of 0.875. The aberration is with RMS of 0.433 μm and mainly includes Zernike modes of low orders like defocus. Results here validate the effectiveness of the wavefront sensing method proposed. Such method would get further application in systems like laser array propagating and turbulence aberrations correcting.
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Li Feng, Geng Chao, Huang Guan, et al. Wavefront sensing based on fiber coupling of the fiber laser array[J]. Opto-Electronic Engineering, 2018, 45(4): 170691. doi: 10.12086/oee.2018.170691
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Figure 1.
Scheme of the wavefront sensor based on adaptive fiber optics collimator array
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Figure 2.
Structure of the adaptive fiber optics collimator
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Figure 3.
Hexagonal AFOC array with different element number. (a) 7-element; (b) 19-element; (c) 37-element
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Figure 4.
Phase screen and its focal spot array focused by the AFOC array. (a) Simulated turbulence phase screen with D/r0=10; (b) Spot array focused by the lens in the AFOC array
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Figure 5.
Results of sub-aperture wavefront slope detected. (a) X-direction; (b) Y-direction
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Figure 6.
Normalized RMS curve of the recovery residual error as a function of array element number and reconstructed Zernike mode
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Figure 7.
Reconstructed wavefront with AFOC array of different element number. (a) Sample phase screen; (b) 7-element; (c) 19-element; (d) 37-element
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Figure 8.
Normalized RMS curve of the recovery residual error as a function of array element number and filled factor. (a) 7-element; (b) 19-element; (c) 37-element
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Figure 9.
Experimental setup of the wavefront sensing based on AFOC array
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Figure 10.
Sub-aperture slope detected through the voltages. (a) X-direction; (b) Y-direction
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Figure 11.
Zernike coefficients detected through the voltages
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Figure 12.
Wavefront recovery results. (a) Actual aberrations; (b) Reconstructed wavefront; (c) Recovery residual error
