Design and Fabrication of a Non-zero Dispersion Shifted Fiber with Low Dispersion Slope in S+C+L Band and Large Effective Area Based on Outside Vapor Deposition
Existing optical fibers struggle to support broadband dense wavelength division multiplexing and coarse wavelength division multiplexing transmissions,necessitating the development of optimized fibers with moderate dispersion,low dispersion slope,enlarged effective area,and low attenuation.Currently,None Zero Dispersion Shifted Fiber(NZDSF)fibers have a small effective area incompatible with conventional fibers,emphasizing the need for precise design control of the refractive index profile.Therefore,creating a S+C+L band NZDSF with a large effective area and low slope is crucial for meeting the escalating demand for bulk data transmission.The dispersion slope,a crucial parameter in optics,is determined by the interplay between waveguide and material properties.The effective area,a metric that signifies the fiber's optical performance,relies heavily on the refractive index profile and the chosen input wavelength.In order to find the appropriate dispersion slope and effective area,we need to find a suitable refractive index profile.In our research,we have employed a refined profile structure modal,featuring a triangular+ring core configuration embellished by a central depression and fabricated by a two-step process to prepare the core and cladding by using the Outside Vapor Deposition(OVD).Through experiments,adjustments were made to the doping levels in the core,thereby modifying the relative refractive index Δn1 and radius R1 of the first core layer.This enabled the formation of a triangular cross-sectional structure.Simultaneously,the relative refractive index Δn3 and thickness R3-R2 of the third core layer were also adjusted,resulting in distinct refractive index waveguide configurations.This approach strucks a balance between achieving low attenuation,a large effective area,a reduced dispersion slope,and an appropriate zero dispersion wavelength.After optimizing the preform preparation and drawing process,the optical fiber cross-section obtained has a high matching with the designed cross-section.The triangular structure of the first core layer has a relatively straight slope,and Δn1 is between 0.52%and 0.57%.In the third core layer,a slightly curved convex structure is formed due to the diffusion of GeO2,and Δn3 is between 0.13%and 0.17%.In line with the experimental findings,it has been observed that when the first core layer radius R1,the third core layer R3,and the second core layer's relative refractive index Δn2 remain relatively constant,an increase in Δn1 and a subsequent decrease in R2/R1 lead to a gradual reduction in the zero dispersion wavelength λ0 and a corresponding decline in the effective area Aeff.Our experimental target is to achieve a zero dispersion wavelength λ0 below 1460 nm,even approximating 1420 nm,while maintaining a significant effective area Aeff.To balance these parameters,it is necessary to slightly reduce Δn1 to the range of 0.52%to 0.53%and adjust R2/R1 to approximately 2.6 to 2.7.By these adjustments,we can achieve a suitable equilibrium between the effective area Aeff and the zero dispersion wavelength λ0.The experimental fiber design achieved a mode field diameter of 9.35 μm and an effective area Aeff of 68 μm².Additionally,the zero dispersion coefficient exceeding 1.5 ps·nm-1·km-1 at 1460 nm,well-suited for S-band wavelength division multiplexing applications while effectively suppressing four-wave mixing in the S-band.Furthermore,the fiber exhibited a low dispersion slope of only 0.059 ps·nm-2·km-1,providing relatively suitable dispersion characteristics in the C and L bands.The fiber also exhibited superior attenuation coefficients of 0.276 dB·km-1 at 1383 nm,effectively mitigating the impact of water absorption peaks.The attenuation coefficients at 1550 nm and 1625 nm were 0.195 dB·km-1 and 0.205 dB·km-1,respectively,facilitating extended transmission distances.Through comparison,it was confirmed that this S+C+L band NZDSF with low dispersion slope and large effective area is well-suited for high-speed,high-capacity,and long-distance optical communication systems.
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