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Optics Express

Optics Express

  • Editor: J. H. Eberly
  • Vol. 9, Iss. 13 — Dec. 17, 2001
  • pp: 676–680
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Optical properties of a low-loss polarization-maintaining photonic crystal fiber

Kazunori Suzuki, Hirokazu Kubota, Satoki Kawanishi, Masatoshi Tanaka, and Moriyuki Fujita  »View Author Affiliations


Optics Express, Vol. 9, Issue 13, pp. 676-680 (2001)
http://dx.doi.org/10.1364/OE.9.000676


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Abstract

A low-loss and highly birefringent polarization maintaining photonic crystal fiber has been fabricated. The fiber loss and modal birefringence at 1550 nm were 1.3 dB/km and 1.4×10-3, respectively.

© Optical Society of America

1. Introduction

Photonic crystal fibers (PCFs) are of great interest for optical communication in new wavelength regions and for new optical functional devices [3

3. J. C. Knight, T. A. Birks, P. St. Russel, and D. M. Atkin, “All-silica single-mode optical fiber with photonic crystal cladding,” Opt. Lett. , 21, 1547–1549 (1996). [CrossRef] [PubMed]

5

5. H. Kubota, K. Suzuki, S. Kawanishi, M. Nakazawa, M. Tanaka, and M. Fujita, “Low-loss, 2 km-long photonic crystal fiber with zero GVD in the near IR suitable for picosecond pulse propagation at the 800 nm band,” in Proc. Conference on Lasers and Electro-Optics (CLEO), Vol. 56 of OSA Proceedings Series (Optical Society of America, Washington, D.C., 2001) CPD3.

]. It is also possible to realize highly birefringent fiber with a photonic crystal structure [6

6. A. Ortigosa-Blanch, J. C. Knight, W. J. Wadsworth, J. Arriaga, B. J. Mangan, T. A Birks, and P. St. J. Russell, “Highly birefringent photonic crystal fibers,” Opt. Lett. 25, 1325–1327 (2000). [CrossRef]

9

9. T. P. Hansen, J. Broeng, E. B. Libori, E. Knudsen, A. Bjarklev, J. R. Jensen, and H. Simonsen, “Highly birefringent index-guiding photonic crystal fibers,” IEEE Photon. Tech. Lett. , 13, 588–590 (2001). [CrossRef]

]. Polarization maintaining (PM) PCFs have different air-hole diameters along two orthogonal axes near the core region [6

6. A. Ortigosa-Blanch, J. C. Knight, W. J. Wadsworth, J. Arriaga, B. J. Mangan, T. A Birks, and P. St. J. Russell, “Highly birefringent photonic crystal fibers,” Opt. Lett. 25, 1325–1327 (2000). [CrossRef]

8

8. S. B. Libori, J. Broeng, E. Knudsen, A. Bjarklev, and H. R. Simomsen, “High-birefringent photonic crystal fiber,” in Proc. Optical Fiber Conference (OFC), Vol. 54 of OSA Proceedings Series (Optical Society of America, Washington, D.C., 2001), TuM2.

], which provide an effective index difference between the two orthogonal polarization modes. It has been shown that their birefringence is of the order of 10-3, which is one order of magnitude larger than that of conventional PMFs, and better PM characteristics are expected. However, neither low loss PM-PCF with a length of ~km nor high-speed transmission experiments have been reported.

In this paper, we report for the first time a 1.5 km-long ultra low-loss PM-PCF whose transmission loss and crosstalk at 1550 nm were 1.3 dB/km and less than -22 dB, respectively. The polarization properties, such as birefringence, PMD, and group velocity dispersion (GVD) were measured and analyzed using a numerical simulation.

2. Design of PM-PCF

Figure 1 shows the schematic design and a scanning electron microscope (SEM) photograph of a PM-PCF. To introduce large birefringence into the PCF, we enlarged two of the central air holes. The birefringence arises from the effective refractive index difference between the x and y polarization modes. The diameters of the small and large air holes, (d1) and (d2), respectively, and the air hole pitch (Λ) gives the characteristics of PM-PCF. This is a variation of the structure described in Ref. 7. This fiber was designed to have high birefringence and low loss with a simple structure. The structure in Ref. 8 appears similar to ours, however it is difficult to use that structure to fabricate fiber with high dimensional precision because the large air holes shift towards the core. By contrast, our fiber has a constant Λ, making it easier to fabricate with a conventional multiple-capillary drawing method.

Fig. 1. Schematic view (a) and SEM photograph (b) of a polarization maintaining photonic crystal fiber.

The wavelength dependence of the fiber loss is shown in Fig. 2(a). The fiber losses at 1550, 1300, and 850 nm were 1.3, 2.0, and 4.2 dB/km, respectively. The Rayleigh scattering coefficient of the PCF and the structural imperfection loss were 1.9 dB/km/(µm)4 and 1.0 dB/km, respectively. If we can reduce the structural imperfection loss, the fiber loss will be reduced to less than 0.5 dB/km, which is of the same order as that of conventional polarization maintaining fiber. We measured the fiber loss along the fiber length using an optical time domain reflectometer (OTDR) at 1.55 µm as shown in Fig. 2(b). It is clear from the figure that the slope is constant and there is no discontinuity caused by structural imperfections.

The maximum loss difference of the two orthogonal polarization modes (PDL) in the 1.5 µm band, measured using polarization analyzer, was 0.27 dB/km. This shows that the large air holes have little influence on PDL.

Fig. 2. (a) Loss spectrum and (b) OTDR waveform of a PM-PCF

3. Polarization characteristics of PM-PCF

LB=2πβxβy=λnxny=λB,
(1)

Fig.3. Wavelength dependence of PM-PCF birefringence. The solid curve shows the calculated results.

The PMD at 1550 nm was 4.7 ps/m, which we measured from the pulse separation due to PMD by using a subpicosecond optical pulse from an optical parametric oscillator operating in the 1.5 µm band. The PMD wavelength dependence is shown in Fig. 4. The PMD decreases monotonously as the wavelength decreases, which is similar to the birefringence. Calculated results are also shown in Fig. 4.

Fig. 4. Wavelength dependence of PM-PCF polarization mode dispersion.

The crosstalk between the polarization modes for 100 m and 1.5 km-long fibers were -35 and -22 dB, respectively. These values are better than that of conventional PANDA fiber. By optimizing the fiber parameters, we can realize higher birefringence and lower crosstalk, which means that we can use this PM-PCF as a polarization maintaining optical transmission line.

Figure 5 shows the GVD wavelength dependence for each (fast and slow) polarization mode. Measurements were performed by launching a linearly polarized signal along the one of the polarization axes of the fiber. The black and blue circles show the measured results for the fast and slow polarization modes, respectively. The GVDs for the two polarization modes at 1550 nm were 59.5 and 66.8 ps/km/nm, and the difference was as much as 7.3 ps/m/nm. The dispersion slopes for each polarization mode were 0.070 and 0.071, respectively. This can be explained as follows. The GVD is given by

σ=1c1λkd2βdk2,
(2)

where c is the light velocity in a vacuum, and k=2π/λ. GVD is mainly comprised by waveguide dispersion and the material dispersion. As mentioned above, the frequency dependence of the propagation constant β is calculated by using the geometrical parameters of the fiber. And, the material dispersion is given by Sellmeier’s formula. The difference between the GVD values of the two orthogonal polarization modes, which is the same as the difference in waveguide dispersion, is given as

δσ=σxσy=1c1λ(kd2βxdk2kd2βydk2).
(3)

The experimental and calculated values of δσ at 1550 nm were 7.3 and 9.5 ps/km/nm, respectively. The calculated dispersion slopes for both modes were 0.047 and 0.052. These show that there is good agreement between the calculated and experimental results.

Fig. 5. GVD characteristics for both polarization modes. Measured and calculated results are shown.

4. Conclusion

A low-loss (1.3 dB/km) and high extinction ratio polarization-maintaining photonic crystal fiber was successfully fabricated. Its birefringence of 1.4×10-3 was higher than that of conventional stress-induced PM fibers. The polarization properties (birefringence, PMD, GVD) were well explained by using a numerical simulation.

Acknowledgements

The authors thank Dr. M. Kawachi, Dr. K. Sato, and H. Tanaka for their encouragement.

References and Links

1.

T. Hosaka, K. Okamoto, T. Miya, Y. Sasaki, and T. Edahiro, “Low-loss single polarisation fibres with asymmetrical strain birefringence,” Electron. Lett. , 17, 530–531 (1981). [CrossRef]

2.

R. D. Birch, D. N. Payne, and M. P. Varnham, “Fabrication of polarisation-maintaining fibres using gas-phase etching,” Electron. Lett. , 18, 1036–1038 (1982). [CrossRef]

3.

J. C. Knight, T. A. Birks, P. St. Russel, and D. M. Atkin, “All-silica single-mode optical fiber with photonic crystal cladding,” Opt. Lett. , 21, 1547–1549 (1996). [CrossRef] [PubMed]

4.

J. K. Ranka, R. S. Windeler, and A. J. Stentz “Optical properties of high-delta air-silica microstructure optical fibers,” Opt. Lett. , 25, 796–798 (2000). [CrossRef]

5.

H. Kubota, K. Suzuki, S. Kawanishi, M. Nakazawa, M. Tanaka, and M. Fujita, “Low-loss, 2 km-long photonic crystal fiber with zero GVD in the near IR suitable for picosecond pulse propagation at the 800 nm band,” in Proc. Conference on Lasers and Electro-Optics (CLEO), Vol. 56 of OSA Proceedings Series (Optical Society of America, Washington, D.C., 2001) CPD3.

6.

A. Ortigosa-Blanch, J. C. Knight, W. J. Wadsworth, J. Arriaga, B. J. Mangan, T. A Birks, and P. St. J. Russell, “Highly birefringent photonic crystal fibers,” Opt. Lett. 25, 1325–1327 (2000). [CrossRef]

7.

S. Kawanishi and K. Okamoto, “Polarization maintaining holey optical fiber,” IEICE Soc. Conf. 2000, 2000, B-10-153 (in Japanese).

8.

S. B. Libori, J. Broeng, E. Knudsen, A. Bjarklev, and H. R. Simomsen, “High-birefringent photonic crystal fiber,” in Proc. Optical Fiber Conference (OFC), Vol. 54 of OSA Proceedings Series (Optical Society of America, Washington, D.C., 2001), TuM2.

9.

T. P. Hansen, J. Broeng, E. B. Libori, E. Knudsen, A. Bjarklev, J. R. Jensen, and H. Simonsen, “Highly birefringent index-guiding photonic crystal fibers,” IEEE Photon. Tech. Lett. , 13, 588–590 (2001). [CrossRef]

10.

M. J. Steel, T. P. White, C. Martijn de Sterke, R. C. McPhedran, and L. C. Botten, “Symmetry and degeneracy in microstructured optical fibers,” Opt. Lett. , 26, 488–490 (2001). [CrossRef]

11.

D. N. Payne, A. J. Barlow, and J. J. R. Hansen, “Development of low- and high-birefringence optical fibers,” IEEE J. Quantum Electron. , QE-18, 477–488 (1982). [CrossRef]

12.

S. G. Johnson and J. D. Joannopoulos, “The MIT Photonic-Bands Package,” http://ab-initio.mit.edu/mpb/

OCIS Codes
(060.2400) Fiber optics and optical communications : Fiber properties
(060.2420) Fiber optics and optical communications : Fibers, polarization-maintaining

ToC Category:
Focus Issue: Photonic crystal fiber

History
Original Manuscript: November 26, 2001
Published: December 17, 2001

Citation
Kazunori Suzuki, Hirokazu Kubota, Satoki Kawanishi, Masatoshi Tanaka, and Moriyuki Fujita, "Optical properties of a low-loss polarization-maintaining photonic crystal fiber," Opt. Express 9, 676-680 (2001)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-9-13-676


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References

  1. T. Hosaka, K. Okamoto, T. Miya, Y. Sasaki, and T. Edahiro, "Low-loss single polarisation fibres with asymmetrical strain birefringence," Electron. Lett. 17, 530-531 (1981). [CrossRef]
  2. R. D. Birch, D. N. Payne, and M. P. Varnham, "Fabrication of polarisation-maintaining fibres using gas-phase etching," Electron. Lett. 18, 1036-1038 (1982). [CrossRef]
  3. J. C. Knight, T. A. Birks, P. St. Russel, and D. M. Atkin, "All-silica single-mode optical fiber with photonic crystal cladding," Opt. Lett. 21, 1547-1549 (1996). [CrossRef] [PubMed]
  4. J. K. Ranka, R. S. Windeler, and A. J. Stentz "Optical properties of high-delta air-silica microstructure optical fibers," Opt. Lett. 25, 796-798 (2000). [CrossRef]
  5. H. Kubota, K. Suzuki, S. Kawanishi, M. Nakazawa, M. Tanaka, and M. Fujita, "Low-loss, 2 km-long photonic crystal fiber with zero GVD in the near IR suitable for picosecond pulse propagation at the 800 nm band," in Proc. Conference on Lasers and Electro-Optics (CLEO), Vol. 56 of OSA Proceedings Series (Optical Society of America, Washington, D.C., 2001) CPD3.
  6. A. Ortigosa-Blanch, J. C. Knight, W. J. Wadsworth, J. Arriaga, B. J. Mangan, T. A Birks, and P. St. J. Russell, "Highly birefringent photonic crystal fibers," Opt. Lett. 25, 1325-1327 (2000). [CrossRef]
  7. S. Kawanishi and K. Okamoto, "Polarization maintaining holey optical fiber," IEICE Soc. Conf. 2000, 2000, B-10-153 (in Japanese).
  8. S. B. Libori, J. Broeng, E. Knudsen, A. Bjarklev, and H. R. Simomsen, "High-birefringent photonic crystal fiber," in Proc. Optical Fiber Conference (OFC), Vol. 54 of OSA Proceedings Series (Optical Society of America, Washington, D.C., 2001), TuM2.
  9. T. P. Hansen, J. Broeng, E. B. Libori, E. Knudsen, A. Bjarklev, J. R. Jensen, and H. Simonsen, "Highly birefringent index-guiding photonic crystal fibers," IEEE Photon. Tech. Lett. 13, 588-590 (2001). [CrossRef]
  10. M. J. Steel, T. P. White, C. Martijn de Sterke, R. C. McPhedran, and L. C. Botten, "Symmetry and degeneracy in microstructured optical fibers," Opt. Lett. 26, 488-490 (2001). [CrossRef]
  11. D. N. Payne, A. J. Barlow, and J. J. R. Hansen, "Development of low- and high-birefringence optical fibers," IEEE J. Quantum Electron. QE-18, 477-488 (1982). [CrossRef]
  12. S. G. Johnson and J. D. Joannopoulos, "The MIT Photonic-Bands Package," http://ab-initio.mit.edu/mpb/

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