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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 26 — Dec. 10, 2012
  • pp: B77–B84
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Large-effective-area uncoupled few-mode multi-core fiber

Yusuke Sasaki, Katsuhiro Takenaga, Ning Guan, Shoichiro Matsuo, Kunimasa Saitoh, and Masanori Koshiba  »View Author Affiliations


Optics Express, Vol. 20, Issue 26, pp. B77-B84 (2012)
http://dx.doi.org/10.1364/OE.20.000B77


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Abstract

Characteristics of few-mode multi-core fiber (FM-MCF) were numerically analyzed and experimentally confirmed. The cores of FM-MCF were designed to support transmission of LP01 and LP11 modes from the point of bending loss of LP11 and LP21 modes. Inter-core crosstalk between LP11 mode was calculated to determine core pitch of fibers. It was confirmed that the fabricated fibers was two-mode transmission over C-band and L-band with the effective area of LP01 mode of about 110 μm2 at 1550 nm. The crosstalk of the fibers was estimated to be smaller than −30 dB at 1550 nm after 100-km propagation. The crosstalk dependence on wavelength was also measured and matched well with the simulated results.

© 2012 OSA

1. Introduction

Space division multiplexing (SDM) is expected as a new advanced technology that overcomes the capacity limit of the current optical communication systems [1

1. T. Morioka, “New generation optical infrastructure technologies: “EXAT initiative” towards 2020 and beyond,” in Proceedings of 15th OptoElectronics and Communications Conference (Institute of Electrical and Electronics Engineers, 2009), paper FT4.

]. The SDM is realized by multi-core fiber (MCF) and few-mode fiber (FMF). To improve space multiplicity, 10-core fiber with large effective area (Aeff) [2

2. S. Matsuo, K. Takenaga, Y. Arakawa, Y. Sasaki, S. Taniagwa, K. Saitoh, and M. Koshiba, “Large-effective-area ten-core fiber with cladding diameter of about 200 μm,” Opt. Lett. 36(23), 4626–4628 (2011). [CrossRef] [PubMed]

], 19-core fiber with small Aeff [3

3. J. Sakaguchi, B. J. Puttnam, W. Klaus, Y. Awaji, N. Wada, A. Kanno, T. Kawanishi, K. Imamura, H. Inaba, K. Mukasa, R. Sugizaki, T. Kobayashi, and M. Watanabe, “19-core fiber transmission of 19x100x172-Gb/s SDM-WDM-PDM-QPSK signals at 305Tb/s,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper PDP5C.1.

], and five-mode fiber [4

4. M. Salsi, C. Koebele, G. Charlet, and S. Bigo, “Mode division multiplexed transmission with a weakly coupled few-mode fiber,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper OTu2C.5.

] have been proposed. However, there are limits in improvement of spacial multiplicity only by using those teqnichues each other from the perspective of inter-core crosstalk or inter-mode crosstalk. The combination of MCF and FMF will improve the multiplicity furthermore.

In this paper, we present the characteristics of few-mode multi-core fiber (FM-MCF) that suports LP01 and LP11 modes over C-band and L-band. The fabricated fibers based on simulations realized the Aeff of LP01 mode which is about 110 μm2 at 1550 nm, propagation of both LP01 and LP11 modes over the bands, and 100-km inter-core crosstalk of smaller than −30 dB at 1550 nm. Finally the crosstalk dependence on wavelength was measured and compared with simulated results.

2. FM-MCF design for two-mode transmission

It is effective to enlarge Aeff in order to suppress the non-linearity. Figure 1
Fig. 1 Structural parameter dependence of Aeff of (a) LP01 mode and (b) LP11 mode.
shows the calculated results of Aeff of LP01 and LP11 modes at 1550 nm as functions of relative refractive index difference Δ and core radius a [5

5. K. Takenaga, Y. Sasaki, N. Guan, S. Matsuo, M. Kasahara, K. Saitoh, and M. Koshiba, “A large-effective-area few-mode multi-core fiber,” IEEE Photon. Technol. Lett. 24(21), 1941–1944 (2012). [CrossRef]

]. The full-vector finite-element method was used for the calculation [6

6. K. Saitoh and M. Koshiba, “Full-vectorial imaginary-distance beam propagation method based on a finite element scheme: Application to photonic crystal fibers,” IEEE J. Quantum Electron. 38(7), 927–933 (2002). [CrossRef]

]. The lower side of a black line is where the bending loss of LP21 mode is larger than 1 dB/m at 1530 nm and a bending radius of 140 mm. The upper side of a white line is where the bending loss of LP11 mode is smaller than 0.5 dB/100 turn at 1625 nm and a bending radius of 30 mm. The areas which satisfy both conditions support LP01 and LP11 modes over C-band and L-band and realize the Aeff of both modes which is larger than 100 μm2 at 1550 nm.

3. Fabricated fiber

4. Measurement of inter-core crosstalk

4.1 Measuring higher mode crosstalk

Figure 5
Fig. 5 Measurement system of higher mode crosstalk.
shows a setup for XT11-11 measurement. We reconsidered the measurement system which we use to measure crosstalk in the case of single mode MCF. A single-mode fiber (SMF) connected to light source was offset spliced to a core of a FM-MCF to excite both LP01 mode and LP11 mode. Output power from cores on another end face was measured with a two-mode fiber (TMF) which has almost the same profile as the FM-MCF.

Figure 6
Fig. 6 Measurement procedure of XT11-11.
explains the measurement procedure of XT11-11. At first, we measure Pj which is an output power of an offset excited core (core j) without bend as shown in Fig. 6(a). The Pj is the sum of the power of LP01 and LP11 modes: Pj = Pj-LP01 + Pj-LP11. Then, Pj’ is measured with bends of 20 turns whose diameter was 10 mm to eliminate LP11 mode as shown in Fig. 6(b): Pj’ = Pj-LP01. The difference of the power (PjPj) indicates Pj-LP11. Finally, the output power of core k Pk, which core is not the excited core, is measured without bend condition as shown in Fig. 6(c). The most of Pk is comprised of the power of LP11 mode because the crosstalk between few-mode cores is dominated by LP11-LP11 crosstalk as shown in Fig. 2: Pk = Pk-LP11. Accordingly, we obtain:

XT1111=10log(PkLP11/PjLP11)=10log(Pk/(PjPj')).
(1)

4.2 Results of measured crosstalk and comparison with simulated results

Figure 7
Fig. 7 Results of measured XT11-11 of (a) Fiber A, (b) Fiber B and (c) Fiber C.
shows results of measured XT11-11 of Fiber A, Fiber B and Fiber C, respectively. The lengths of Fiber A, Fiber B and Fiber C were 3709 m, 2730 m and 4403 m, respectively. The fibers were wound on spools with a diameter of 210 mm. The horizontal axis denotes the excited core number and the graph legends denote the measured core number as shown in Fig. 3. The left side is measured crosstalk at 1550 nm and the right side is at 1625 nm. In the case of Fiber A, the crosstalk of the cores that located at the diagonal positions from the excited cores were about −80 dB, which were the lower limit of the measurement setup. On the other hand, in the case of Fiber B and Fiber C, crosstalk was detected even for the diagonal cores. The direct crosstalk between the diagonal cores is estimated to be very small compared to the measured crosstalk because of the large diagonal core pitch of 62 μm. The measured crosstalk of the diagonal cores may originate from the repeat of the crosstalk between adjacent cores.

Figure 8
Fig. 8 The comparison of 100-km crosstalk estimation from measured results and simulation results as a function of core pitch.
shows the 100-km inter-core crosstalk estimated from the measured crosstalk with the coupled-power theory [8

8. K. Takenaga, Y. Arakawa, S. Tanigawa, N. Guan, S. Matsuo, K. Saitoh, and M. Koshiba, “An investigation on crosstalk in multicore fibers by introducing random fluctuation along longitudinal direction,” IEICE Trans. Commun. E94-B(2), 409–416 (2011). [CrossRef]

] and simulated XT11-11 for comparison as a function of core pitch. Lines are simulated results. Deep blue and red lines correspond to Fiber A and Fiber B. The pale blue and red lines correspond to Fiber C. The parameters used in the simulations are also shown. The symbols indicate the averaged crosstalk and the error bars indicate the maximum and the minimum values. The blue ones are at 1550 nm and red ones are at 1625 nm. In the case of Fiber B and Fiber C, estimations match well with simulated results. In the case of Fiber A, there were discrepancies between estimations and simulated results. We think there are two reasons. The first is the simulations were based on the worst case where the overlap of fields of LP11 mode between adjacent cores gets to be maximum. The second is these simulations did not take into account of crosstalk dependence on bending diameter [9

9. T. Hayashi, T. Nagashima, O. Shimakawa, T. Sasaki, and E. Sasaoka, “Crosstalk variation of multi-core fiber due to fiber bend,” in Proceedings of 36th European Conference and Exhibition on Optical Communication (Institute of Electrical and Electronics Engineers, 2010), paper We.8.F.6.

]. Although, the averaged 100-km crosstalk of Fiber A was −42 dB at 1550 nm and −32 dB at 1625 nm, which means Fiber A realized 100-km crosstalk of smaller than −30 dB over C-band and L-band as we had expected.

4.3 Wavelength dependence of crosstalk

5. Conclusion

We have designed and fabricated few-mode multi-core fibers which support both LP01 and LP11 modes over C-band and L-band. The fibers had the Aeff of LP01 mode of about 110 μm2 at 1550 nm. Inter-core crosstalk characteristics of the fibers were numerically analyzed. Large-effective-area uncoupled few-mode multi-core fiber whose inter-core 100-km crosstalk is smaller than −30 dB at 1550 nm was realized.

Acknowledgment

This work was partially supported by National Institute of Information and Communication Technology (NICT), Japan under “Research on Innovative Optical fiber Technology”.

References and links

1.

T. Morioka, “New generation optical infrastructure technologies: “EXAT initiative” towards 2020 and beyond,” in Proceedings of 15th OptoElectronics and Communications Conference (Institute of Electrical and Electronics Engineers, 2009), paper FT4.

2.

S. Matsuo, K. Takenaga, Y. Arakawa, Y. Sasaki, S. Taniagwa, K. Saitoh, and M. Koshiba, “Large-effective-area ten-core fiber with cladding diameter of about 200 μm,” Opt. Lett. 36(23), 4626–4628 (2011). [CrossRef] [PubMed]

3.

J. Sakaguchi, B. J. Puttnam, W. Klaus, Y. Awaji, N. Wada, A. Kanno, T. Kawanishi, K. Imamura, H. Inaba, K. Mukasa, R. Sugizaki, T. Kobayashi, and M. Watanabe, “19-core fiber transmission of 19x100x172-Gb/s SDM-WDM-PDM-QPSK signals at 305Tb/s,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper PDP5C.1.

4.

M. Salsi, C. Koebele, G. Charlet, and S. Bigo, “Mode division multiplexed transmission with a weakly coupled few-mode fiber,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper OTu2C.5.

5.

K. Takenaga, Y. Sasaki, N. Guan, S. Matsuo, M. Kasahara, K. Saitoh, and M. Koshiba, “A large-effective-area few-mode multi-core fiber,” IEEE Photon. Technol. Lett. 24(21), 1941–1944 (2012). [CrossRef]

6.

K. Saitoh and M. Koshiba, “Full-vectorial imaginary-distance beam propagation method based on a finite element scheme: Application to photonic crystal fibers,” IEEE J. Quantum Electron. 38(7), 927–933 (2002). [CrossRef]

7.

R. Maruyama, N. Kuwaki, S. Matsuo, K. Sato, and M. Ohashi, “Mode dispersion compensating optical transmission line composed of two-mode optical fibers,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper JW2A.3.

8.

K. Takenaga, Y. Arakawa, S. Tanigawa, N. Guan, S. Matsuo, K. Saitoh, and M. Koshiba, “An investigation on crosstalk in multicore fibers by introducing random fluctuation along longitudinal direction,” IEICE Trans. Commun. E94-B(2), 409–416 (2011). [CrossRef]

9.

T. Hayashi, T. Nagashima, O. Shimakawa, T. Sasaki, and E. Sasaoka, “Crosstalk variation of multi-core fiber due to fiber bend,” in Proceedings of 36th European Conference and Exhibition on Optical Communication (Institute of Electrical and Electronics Engineers, 2010), paper We.8.F.6.

OCIS Codes
(060.2270) Fiber optics and optical communications : Fiber characterization
(060.2280) Fiber optics and optical communications : Fiber design and fabrication

ToC Category:
Fibers, Fiber Devices, and Amplifiers

History
Original Manuscript: October 1, 2012
Revised Manuscript: November 5, 2012
Manuscript Accepted: November 9, 2012
Published: November 28, 2012

Virtual Issues
European Conference on Optical Communication 2012 (2012) Optics Express

Citation
Yusuke Sasaki, Katsuhiro Takenaga, Ning Guan, Shoichiro Matsuo, Kunimasa Saitoh, and Masanori Koshiba, "Large-effective-area uncoupled few-mode multi-core fiber," Opt. Express 20, B77-B84 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-26-B77


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References

  1. T. Morioka, “New generation optical infrastructure technologies: “EXAT initiative” towards 2020 and beyond,” in Proceedings of 15th OptoElectronics and Communications Conference (Institute of Electrical and Electronics Engineers, 2009), paper FT4.
  2. S. Matsuo, K. Takenaga, Y. Arakawa, Y. Sasaki, S. Taniagwa, K. Saitoh, and M. Koshiba, “Large-effective-area ten-core fiber with cladding diameter of about 200 μm,” Opt. Lett.36(23), 4626–4628 (2011). [CrossRef] [PubMed]
  3. J. Sakaguchi, B. J. Puttnam, W. Klaus, Y. Awaji, N. Wada, A. Kanno, T. Kawanishi, K. Imamura, H. Inaba, K. Mukasa, R. Sugizaki, T. Kobayashi, and M. Watanabe, “19-core fiber transmission of 19x100x172-Gb/s SDM-WDM-PDM-QPSK signals at 305Tb/s,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper PDP5C.1.
  4. M. Salsi, C. Koebele, G. Charlet, and S. Bigo, “Mode division multiplexed transmission with a weakly coupled few-mode fiber,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper OTu2C.5.
  5. K. Takenaga, Y. Sasaki, N. Guan, S. Matsuo, M. Kasahara, K. Saitoh, and M. Koshiba, “A large-effective-area few-mode multi-core fiber,” IEEE Photon. Technol. Lett.24(21), 1941–1944 (2012). [CrossRef]
  6. K. Saitoh and M. Koshiba, “Full-vectorial imaginary-distance beam propagation method based on a finite element scheme: Application to photonic crystal fibers,” IEEE J. Quantum Electron.38(7), 927–933 (2002). [CrossRef]
  7. R. Maruyama, N. Kuwaki, S. Matsuo, K. Sato, and M. Ohashi, “Mode dispersion compensating optical transmission line composed of two-mode optical fibers,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2012), paper JW2A.3.
  8. K. Takenaga, Y. Arakawa, S. Tanigawa, N. Guan, S. Matsuo, K. Saitoh, and M. Koshiba, “An investigation on crosstalk in multicore fibers by introducing random fluctuation along longitudinal direction,” IEICE Trans. Commun.E94-B(2), 409–416 (2011). [CrossRef]
  9. T. Hayashi, T. Nagashima, O. Shimakawa, T. Sasaki, and E. Sasaoka, “Crosstalk variation of multi-core fiber due to fiber bend,” in Proceedings of 36th European Conference and Exhibition on Optical Communication (Institute of Electrical and Electronics Engineers, 2010), paper We.8.F.6.

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