Abstract

In this paper, we propose a novel (to our knowledge) broadband and polarization-insensitive dual-core photonic crystal fiber (PCF) coupler through the introduction of an elliptical-shaped central air hole to offset the slight birefringence arising from the dual core. With a full vectorial finite element method and anisotropic perfectly matched layers as the external boundaries, the impact of several fiber parameters on the coupling characteristics of dual-core PCF is investigated in detail. Through optimizing the main fiber parameters, including core diameter, size and ellipticity of the central air hole, and refractive index difference, broadband and polarization-insensitive characteristics are achieved in the wavelength range from 0.8 to 1.7μm. The variation of the coupling ratio is stabilized at 50±1%, and the coupling ratio difference between x polarization and y polarization is less than 2% over the wavelength range. This dual-core PCF makes it easier to develop a 3dB coupler over a wide wavelength for passive optical networks and large optical systems.

© 2011 Optical Society of America

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References

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  1. T. A. Birks, J. C. Knight, and P. St. J. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22, 961–963 (1997).
    [CrossRef] [PubMed]
  2. A. Bajarklev, J. Broeng, and A. S. Bjarklev, Photonic Crystal Fibers (Kluwer Academic, 2003).
    [CrossRef]
  3. N. Florous, K. Saitoh, and M. Koshiba, “A novel approach for designing photonic crystal fiber splitters with polarization-independent propagation characteristics,” Opt. Express 13, 7365–7373 (2005).
    [CrossRef] [PubMed]
  4. J. Lægsgaard, O. Bang, and A. Bjarklev, “Photonic crystal fiber design for broadband directional coupling,” Opt. Lett. 29, 2473–2475 (2004).
    [CrossRef] [PubMed]
  5. S. K. Varshney, N. J. Florous, K. Saitoh, and M. Koshiba, “The impact of elliptical deformations for optimizing the performance of dual-core fluorine-doped photonic crystal fiber couplers,” Opt. Express 14, 1982–1995 (2006).
    [CrossRef] [PubMed]
  6. M. J. Steel, T. P. White, and C. M. de Sterke, “Symmetry and degeneracy in microstructured optical fibers,” Opt. Lett. 26, 488–490 (2001).
    [CrossRef]
  7. G. Ren, Z. Wang, S. Lou, and S. Jian, “Modal interference in dual-core photonic crystal fibers,” Acta Phys. Sin. 53, 2600–2606 (2004) (in Chinese).
  8. G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.
  9. B. J. Mangan, J. C. Knight, and T. A. Birks, “Experimental study of dual-core photonic crystal fiber,” Electron. Lett. 36, 1358–1359 (2000).
    [CrossRef]
  10. B. J. Mangan, J. Aeeiaga, T. A. Birks, and J. C. Knight, “Fundamental-mode cutoff in a photonic crystal fiber with a depressed-index core,” Opt. Lett. 26, 1469–1471(2001).
    [CrossRef]
  11. L. Zhang and C. Yang, “Polarization splitter based on photonic crystal fibers,” Opt. Express 11, 1015–1020 (2003).
    [CrossRef] [PubMed]
  12. L. Zhang and C. Yang, “Polarization-dependent coupling in twin-core photonic crystal fibers,” J. Lightwave Technol. 22, 1367–1372 (2004).
    [CrossRef]
  13. K. Saitoh, Y. Sato, and M. Koshiba, “Coupling characteristics of dual-core photonic crystal fiber couplers,” Opt. Express 11, 3188–3195 (2003).
    [CrossRef] [PubMed]
  14. N. A. Issa, M. A. van Eijkelenborg, and M. Fellew, “Fabrication and study of microstructured optical fibers with elliptical holes,” Opt. Lett. 29, 1336–1338 (2004).
    [CrossRef] [PubMed]
  15. N. Mothe and P. Di Bin, “Numerical analysis of directional coupling in dual-core microstructured optical fibers,” Opt. Express 17, 15778–15789 (2009).
    [CrossRef] [PubMed]

2009 (1)

2006 (1)

2005 (1)

2004 (4)

2003 (2)

2001 (2)

2000 (1)

B. J. Mangan, J. C. Knight, and T. A. Birks, “Experimental study of dual-core photonic crystal fiber,” Electron. Lett. 36, 1358–1359 (2000).
[CrossRef]

1997 (1)

Aeeiaga, J.

Bajarklev, A.

A. Bajarklev, J. Broeng, and A. S. Bjarklev, Photonic Crystal Fibers (Kluwer Academic, 2003).
[CrossRef]

Bang, O.

Birks, T. A.

Bjarklev, A.

Bjarklev, A. S.

A. Bajarklev, J. Broeng, and A. S. Bjarklev, Photonic Crystal Fibers (Kluwer Academic, 2003).
[CrossRef]

Briks, T. A.

G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.

Broeng, J.

A. Bajarklev, J. Broeng, and A. S. Bjarklev, Photonic Crystal Fibers (Kluwer Academic, 2003).
[CrossRef]

de Sterke, C. M.

Di Bin, P.

Fellew, M.

Florous, N.

Florous, N. J.

Issa, N. A.

Jian, S.

G. Ren, Z. Wang, S. Lou, and S. Jian, “Modal interference in dual-core photonic crystal fibers,” Acta Phys. Sin. 53, 2600–2606 (2004) (in Chinese).

Kakarantzas, G.

G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.

Knight, J. C.

B. J. Mangan, J. Aeeiaga, T. A. Birks, and J. C. Knight, “Fundamental-mode cutoff in a photonic crystal fiber with a depressed-index core,” Opt. Lett. 26, 1469–1471(2001).
[CrossRef]

B. J. Mangan, J. C. Knight, and T. A. Birks, “Experimental study of dual-core photonic crystal fiber,” Electron. Lett. 36, 1358–1359 (2000).
[CrossRef]

T. A. Birks, J. C. Knight, and P. St. J. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22, 961–963 (1997).
[CrossRef] [PubMed]

G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.

Koshiba, M.

Lægsgaard, J.

Lou, S.

G. Ren, Z. Wang, S. Lou, and S. Jian, “Modal interference in dual-core photonic crystal fibers,” Acta Phys. Sin. 53, 2600–2606 (2004) (in Chinese).

Mangan, B. J.

B. J. Mangan, J. Aeeiaga, T. A. Birks, and J. C. Knight, “Fundamental-mode cutoff in a photonic crystal fiber with a depressed-index core,” Opt. Lett. 26, 1469–1471(2001).
[CrossRef]

B. J. Mangan, J. C. Knight, and T. A. Birks, “Experimental study of dual-core photonic crystal fiber,” Electron. Lett. 36, 1358–1359 (2000).
[CrossRef]

G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.

Mothe, N.

Ren, G.

G. Ren, Z. Wang, S. Lou, and S. Jian, “Modal interference in dual-core photonic crystal fibers,” Acta Phys. Sin. 53, 2600–2606 (2004) (in Chinese).

Russell, P. St. J.

T. A. Birks, J. C. Knight, and P. St. J. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22, 961–963 (1997).
[CrossRef] [PubMed]

G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.

Saitoh, K.

Sato, Y.

Steel, M. J.

van Eijkelenborg, M. A.

Varshney, S. K.

Wang, Z.

G. Ren, Z. Wang, S. Lou, and S. Jian, “Modal interference in dual-core photonic crystal fibers,” Acta Phys. Sin. 53, 2600–2606 (2004) (in Chinese).

White, T. P.

Yang, C.

Zhang, L.

Acta Phys. Sin. (1)

G. Ren, Z. Wang, S. Lou, and S. Jian, “Modal interference in dual-core photonic crystal fibers,” Acta Phys. Sin. 53, 2600–2606 (2004) (in Chinese).

Electron. Lett. (1)

B. J. Mangan, J. C. Knight, and T. A. Birks, “Experimental study of dual-core photonic crystal fiber,” Electron. Lett. 36, 1358–1359 (2000).
[CrossRef]

J. Lightwave Technol. (1)

Opt. Express (5)

Opt. Lett. (5)

Other (2)

G. Kakarantzas, B. J. Mangan, T. A. Briks, J. C. Knight, and P. St. J. Russell, “Directional coupling in a twin core photonic crystal fiber using heat treatment,” in Conference on Lasers and Electro-Optics, 2001, Tech. Dig. (IEEE, 2001), pp. 599–600.

A. Bajarklev, J. Broeng, and A. S. Bjarklev, Photonic Crystal Fibers (Kluwer Academic, 2003).
[CrossRef]

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Figures (12)

Fig. 1
Fig. 1

Cross section of the proposed dual-core PCF with elliptical central hole. Circular air holes in the cladding are arranged in a hexagonal array with hole diameter d and hole pitch Λ. The elliptical central hole has a major axis r y , a minor axis r x , and ellipticity e = r y / r x . The host material is pure silica. The fluorine-doped dual cores A and B have diameter d c and difference of refractive index Δ.

Fig. 2
Fig. 2

Coupling length of x and y polarization as a function of normalized frequency for different values of d c / Λ . The solid curves correspond to y polarization, and dashed curves correspond to x polarization.

Fig. 3
Fig. 3

Impact of the ellipticity of the central elliptical air hole on coupling length. The two curves on the top correspond to a dual-core PCF with a circular central air hole. The curves corresponding to the ellipticities of 1.26, 1.3, 1.34, and 1.38 are marked with down-pointing triangles, left-pointing triangles, circles, and squares, respectively. Solid curves represent y polarization, and dashed curves represent x polarization.

Fig. 4
Fig. 4

Effect of refractive index difference Δ between the doped-core region and the host material on the coupling length for y polarization (solid curves) and x polarization (dashed curves).

Fig. 5
Fig. 5

(a) Coupling ratio for x polarization (solid curve) and y polarization (dashed curve) and (b) coupling ratio difference between x polarization and y polarization for various wavelengths from 0.8 μm to 1.7 μm .

Fig. 6
Fig. 6

(a) Coupling ratio of x polarization (solid curve) and y polarization (dashed curve), (b) coupling ratio difference between x polarization and y polarization.

Fig. 7
Fig. 7

Optimization of broadband characteristics and polarization insensitivity by changing core diameter. Solid curves represent y polarization, and dashed curves represent x polarization.

Fig. 8
Fig. 8

(a) Optimization of the coupling ratio for x polarization (solid curve) and y polarization (dashed curve), (b) coupling ratio difference between x polarization and y polarization. We confirm that the variation of the coupling ratio can be stabilized at 50 ± 1 % , and the coupling ratio difference between x polarization and y polarization is less than 2% in the wavelength range from 0.8 μm to 1.7 μm for the optimum fiber parameters Λ = 12 μm , d / Λ = 0.45 , d c = 4.7 μm , and Δ = 0.0054 for the proposed dual-core PCF.

Fig. 9
Fig. 9

Tolerance of the dual-core PCF as the ellipticity of the central air hole varies. The curves corresponding to δ e = 2 % , 0, and −2% are plotted with the squares, pluses, and triangles, respectively.

Fig. 10
Fig. 10

Transversal section of the dual-core PCF coupler with three air holes in the central region.

Fig. 11
Fig. 11

(a) Normalized coupling length as a function of normalized frequency, (b) coupling ratios, and (c) coupling ratio difference as a function of the wavelength.

Fig. 12
Fig. 12

Splice loss between the SMF and the proposed dual-core PCF in Fig. 1 with the optimum structure parameters Λ = 12 μm , d / Λ = 0.45 , d c = 4.7 μm , and Δ = 0.0054 .

Equations (4)

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L c x , y ( λ ) = λ 2 ( n even x , y n odd x , y ) ,
C x , y ( λ ) = sin 2 ( π 2 L L c x , y ( λ ) ) ,
C d ( λ ) = C x ( λ ) C y ( λ ) .
L = [ L c x ( 1.3 μm ) / 2 + L c y ( 1.3 μm ) / 2 ] / 2.

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