Realization of large energy proportion in the central lobe by coherent beam combination based on conformal projection system

Abstract

In this paper, we experimentally validate a tiled-aperture conformal projection system with the largest array filling factor and element beam truncation factor to the best of our knowledge. The conformal projection system, which is made up of a hexagonal adaptive fiber-optics collimator (AFOC) array with the proximate ideal intensity distributions, is fabricated and the performance of output beam is tested and evaluated properly and carefully. Both of the active phase-locking control and precise tip-tilt control are implemented successfully in the CBC of the hexagonal seven-beam-array. Experimental results show a large energy proportion (47%, which increases by over 10% comparing with the previously demonstrated largest value) in the central lobe is achieved and the residual phase error is lower than λ/27. When the AFOC array performs, the precise tilt control makes the combining beams overlap well and the average normalized metric value is improved from 0.336 without control to 0.947 with both of active piston and tip-tilt phase controls while the fringe contrast increases from 19% to more than 91% correspondingly. This work presents a promising structure for the achievement of large energy proportion in the central lobe in high power fiber laser CBC systems.

Discussion on Piston-Type Phase Ambiguity in a Coherent Beam Combining System

“…(a) (c) (e) On the emissive plane, the sub-apertures are usually arranged in a centrosymmetric shape, which is beneficial to reduce the sidelobe energy and obtain high-quality combined beams [33][34][35][36][37][38]. However, the centrosymmetric arrangement will cause phase ambiguity.…”

Comprehensive investigation on producing high-power orbital angular momentum beams by coherent combining technology

“…The gain fiber of the fiber amplifier is double-clad fiber with a core/inner cladding diameter of 10 µm/125 µm, based on which the power of each channel is amplified to 1 W. Then a mode field adaptor (MFA, the input fiber is double-clad fiber with core/inner cladding diameter of 10 µm/125 µm, and output fiber is double-clad fiber with core/inner cladding diameter of 20 µm/400 µm) is used in each channel to connect the FPM to a fiber end-cap, which is spliced with a 20 µm/400 µm delivery fiber and acts as the output terminal of the fiber laser. Next, the array beams emitted from the end-caps are collimated by an in-housemade collimator array with a focal length of 800 mm and a clear aperture (d) of 58 mm, which generates a collimated Gaussian beam array with a beam waist width ω 0 of 32.5 mm and a beam truncation factor (2ω 0 /d) of 1.12 [45] .…”

Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers

“…In this scheme, amplified laser beams are positioned next to each other, side-by-side in an array, with the largest possible array filling factor (the minimum gap between individual laser beams) [142]. The laser beams are co-aligned and consequently, the beams interfere only in the far-field, indicating that no beam combining element is required in In this scheme, amplified laser beams are positioned next to each other, side-byside in an array, with the largest possible array filling factor (the minimum gap between individual laser beams) [142]. The laser beams are co-aligned and consequently, the beams interfere only in the far-field, indicating that no beam combining element is required in this approach.…”