Controlled Excitation of Supermodes in a Multicore Fiber with a 5 × 5 Square Array of Strongly Coupled Cores

Abstract

Coherent propagation of supermodes in a multicore fiber is promising for power scaling of fiber laser systems, eliminating the need for the active feedback system to maintain the phases between the channels. We studied the propagation of broadband pulsed radiation at a central wavelength of 1030 nm in a multicore fiber with coupled cores arranged in a square array. We designed and fabricated a silica multicore fiber with a 5 × 5 array of cores. For controllable excitation of a desired supermode, we developed a beam-forming system based on a spatial light modulator. We experimentally measured intensity and phase distributions of the supermodes, in particular, the in-phase and out-of-phase supermodes, which matched well the numerically calculated profiles. We obtained selective excitation and coherent propagation of broadband radiation with the content of the out-of-phase supermode of up to 90% maintained without active feedback. Using three-dimensional numerical modeling with allowance for a refractive index profile similar to those of the developed fiber, we demonstrated stable propagation of the out-of-phase supermode and collapse of the in-phase supermode at a high signal power.

Theoretical investigations of weakly- and strongly-coupled multi-core fibers for the applications of optical submarine communications under power and fiber count limits

“…This assumption is accurate when the step size of SSF is smaller than or equal to the coupling length 𝐿 𝑐 . In this paper, we utilize the coupling length 𝐿 𝑐 = 1/𝐾 𝑎𝑏 as a parameter to investigate IC-XT influence to submarine cables [16]. Here, we typically investigate the 4-core SC-MCF [13] to compare the 4-core WC-MCF for the trans-Atlantic and Pacific cables.…”

Group velocity dispersion of a multicore fibre with 5 × 5 coupled cores for in-phase and out-of-phase supermodes

“…We studied a silica-based MCF consisting of a square array of 5 × 5 cores with diameters of about 6 µm, numerical aperture (NA) = 0.12, and the distance between the nearest cores of 8.5 µm (figures 1(b) and (c)). Details of the fibre design and manufacturing technology are presented in [12]. To measure the dispersion for the fundamental and highest supermodes, we used an interferometric scheme based on a Mach-Zehnder interferometer with a 67 cm MCF located in the 1st arm and a free-space motorized delay line located in the 2nd arm for the compensation of a group delay.…”

“…In our experiment >90% of the pulse power was contained in the respective supermode. The experimental details can be found in [12]. The spatial phase distributions of selectively excited in-phase and out-of-phase supermodes are presented in figures 2 (a) and (b), respectively.…”

“…paid to studies of the fundamental in-phase supermode with the same spatial phases in all cores [9]. At the same time, the recent works demonstrated that the highest out-of-phase supermode (with the spatial phase difference of π in the nearest cores) is also of great importance due to its stability in nonlinear regimes [10][11][12]. Group velocity dispersion (GVD) impacts significantly on the nonlinear dynamics of ultrashort optical pulses with high peak powers, so its analysis is highly important for MCFs.…”

Nonlinear pulse dynamic in a weak coupled normal dispersion multicore fiber

“…In recent years, the propagation of laser radiation in multicore fibers (MCF) with weak coupling between the cores has attracted much attention. [1][2][3][4][5][6] Thanks to the use of such fibers, it becomes possible to amplify coherently high-power laser pulses with the maintaining of radiation characteristics, 7,8 and it also becomes possible to combine radiation from different laser sources into one beam with minimal power loss. 9 Powerful ultrashort laser pulses can further be used for material processing, medicine, spectroscopy, etc.…”