Mode Field Modulation and Gain Equalization with Central Depressed Few-Mode Erbium-Doped Fiber

Wenxuan Xu; Li Pei; Jianshuai Wang; Zhiqi Li; Qi Zhao; Jingjing Zheng; Jing Li; Tigang Ning; Li Zhong

doi:10.3788/AOS202242.2106002

Acta Optica Sinica, Volume. 42, Issue 21, 2106002(2022)

Mode Field Modulation and Gain Equalization with Central Depressed Few-Mode Erbium-Doped Fiber

Wenxuan Xu^1,2, Li Pei^1,2、*, Jianshuai Wang^1,2, Zhiqi Li^1,2, Qi Zhao^1,2, Jingjing Zheng^1,2, Jing Li^1,2, Tigang Ning^1,2, and Li Zhong³

Author Affiliations

¹Key Laboratory of All Optical Network and Advanced Telecommunication Network, Ministry of Education, Beijing Jiaotong University, Beijing 100044, China

²Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China

³State Key Laboratory of Optical Fiber and Cable Manufacture Technology, Yangtze Optical Fiber and Cable Joint Stock Limited Company, Wuhan 430073, Hubei , China

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Figures & Tables(13)

$Typical refractive index profiles of fiber in process of central depression. (a) Step-index fiber; (b) central depressed fiber; (c) ring-core fiber$

Fig. 1. Typical refractive index profiles of fiber in process of central depression. (a) Step-index fiber; (b) central depressed fiber; (c) ring-core fiber

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Fig. 2. b-V curve under different liner polarization modes of fiber. (a) Step-index fiber at n_d =0; (b) ring-core fiber at n_d=0.005;(c) ring-core fiber at n_d=0.010; (d) ring-core fiber at n_d=0.015

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$Normalized cutoff frequency variation of LP02 mode and LP31 mode in process of central refractive index depression$

Fig. 3. Normalized cutoff frequency variation of LP₀₂ mode and LP₃₁ mode in process of central refractive index depression

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$Effective refractive index variation in process of central refractive index depression at wavelength of 1550 nm$

Fig. 4. Effective refractive index variation in process of central refractive index depression at wavelength of 1550 nm

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$Mode distribution of supported modes and corresponding effective refractive indexes at neff=n3$

Fig. 5. Mode distribution of supported modes and corresponding effective refractive indexes at n_eff=n₃

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Fig. 6. Schematic diagram of mode field distribution of different fibers. (a) Step-index fiber at n_d=0; (b) central depressed fiber at n_d=9×10^-3; (c) ring-core fiber at n₃=n₁

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Fig. 7. Intensity distribution of different modes. (a) LP₀₁; (b) LP₁₁; (c) LP₂₁; (d) LP₃₁

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$Power confinement factors of modes in central depressed region and high refractive index region at different nd$

Fig. 8. Power confinement factors of modes in central depressed region and high refractive index region at different n_d

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Fig. 9. Gain and DMG varying with fiber length. (a) Step-index fiber with doping area of 0-7.5 μm; (b) step-index fiber with doping area of 4.0-7.5 μm; (c) central depressed fiber with doping area of 0-7.5 μm and n_d=9×10^-3; (d) central depressed fiber with doping area of 4.0-7.5 μm and n_d=9×10^-3; (e) ring-core fiber with doping area of 0-7.5 μm; (f) ring-core fiber with doping area of 4.0-7.5 μm

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Fig. 10. DMGs under different n_d and r_d. (a) Three-dimensional illustration; (b) surface contour lines

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$Refractive index profile of homemade central depressed fiber and schematic diagram of corresponding experimental device. (a) Refractive index profile and scanning electron microscope section of fiber; (b) experimental setup of FM-EDFA based on central depressed fiber$

Fig. 11. Refractive index profile of homemade central depressed fiber and schematic diagram of corresponding experimental device. (a) Refractive index profile and scanning electron microscope section of fiber; (b) experimental setup of FM-EDFA based on central depressed fiber

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Fig. 12. Transmission power of different modes under different pump powers, and modal gain and DMG varying with pump power. (a) Transmission power of LP₀₁ mode under different pump powers; (b) transmission power of LP_11a mode under different pump powers; (c) transmission power of LP_21a mode under different pump powers; (d) modal gain and DMG varying with pump power

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Table 1. Parameters of central depressed fiber for calculating modal gain
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Table 1. Parameters of central depressed fiber for calculating modal gain
Parameter Value Parameter Value
Pump power P_p /W 1 Pump wavelength λ_p /nm 980
Signal input power P_s /mW 0.1 Signal wavelength λ_s /nm 1550
Fiber length L /m 5 Mass fraction of Er³⁺N₀ / $10^{- 6}$ 250

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Wenxuan Xu, Li Pei, Jianshuai Wang, Zhiqi Li, Qi Zhao, Jingjing Zheng, Jing Li, Tigang Ning, Li Zhong. Mode Field Modulation and Gain Equalization with Central Depressed Few-Mode Erbium-Doped Fiber[J]. Acta Optica Sinica, 2022, 42(21): 2106002

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