A large effective area multi-core fiber with an optimized cladding thickness

Abstract

Abstract:The cladding thickness of trench-assisted multi-core fibers was theoretically and experimentally investigated in terms of excess losses of outer cores. No significant micro-bending loss increase was observed on multi-core fibers with the cladding thickness of about 30 µm. The tolerance for the micro-bending loss of a multi-core fiber is larger than that of the single core fiber. However, the cladding thickness will be limited by the occurrence of the excess loss on outer cores. The reduction of cladding thickness is probably limited around 40 µm in terms of the excess loss. The multi-core fiber with an effective area of 110 µm 2 at 1.55 µm and 181-µ m cladding diameter was realized without any excess loss.

Multicore fibers for large capacity transmission

“…Coupled MCFs supporting single transverse mode and multi transverse modes have been investigated for high power fiber laser applications [9,10], since they are able to be used as large-mode-area (LMA) fibers, while the coupled MCFs supporting a few supermodes can be used as few-mode fibers (FMFs) for large capacity transmission experiments with mode-division multiplexing (MDM) technique [11][12][13][14]. In terms of core arrangement in uncoupled MCFs, homogeneous MCFs with identical multiple cores [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and heterogeneous MCFs with several kinds of different cores [31][32][33][34][35] have been reported. In addition, each core can be designed to support not only single mode but also few modes and multi modes, and they can be called single-mode MCF (SM-MCF), few-mode MCF (FM-MCF) [36][37][38][39][40][41][42], and multimode MCF (MM-MCF) [43], respectively.…”

“…In addition, each core can be designed to support not only single mode but also few modes and multi modes, and they can be called single-mode MCF (SM-MCF), few-mode MCF (FM-MCF) [36][37][38][39][40][41][42], and multimode MCF (MM-MCF) [43], respectively. Table 1 summarizes the recently fabricated uncoupled SM-MCFs [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. In the uncoupled MCFs, high core density as well as low attenuation and large effective area, A eff , are important characteristics for utilizing MCFs as a transmission fiber to improve optical signal to noise ratio (OSNR) and SDM efficiency.…”

“…In the uncoupled MCFs, high core density as well as low attenuation and large effective area, A eff , are important characteristics for utilizing MCFs as a transmission fiber to improve optical signal to noise ratio (OSNR) and SDM efficiency. In order to compare the core density of MCFs, the spatial efficiency (SE) or the core multiplicity factor (CMF) can be used, which is defined as [44]:…”

“…If we fix the core-to-core distance Λ and the cutoff wavelength λ c of each core, the effective area A eff has to be decreased, to decrease the coupling coefficient between neighboring cores, resulting in an increment of the fiber nonlinearity. In addition, the cladding thickness (CT), which is a distance from a center of outer core to outer cladding edge, should be sufficiently large for reducing micro-/macro-bending losses in outer cores [44]. Therefore, there is a trade-off relationship between inter-core crosstalk, fiber nonlinearity, and core density with keeping single-mode condition.…”

“…Therefore, there is a trade-off relationship between inter-core crosstalk, fiber nonlinearity, and core density with keeping single-mode condition. Figure 3 shows the required core-to-core distance condition in 7-core, 13-core, and 19-core fibers with hexagonally close-pack structure (HCPS), where the maximum cladding diameter is assumed to be 230 μm [24] and the CT is assumed to be 40 μm [44]. We can see that, in 7-core structure, large coreto-core distance is acceptable, while the CMF becomes low.…”