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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 12 — Jun. 4, 2012
  • pp: 12893–12898
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Low loss graded index polymer optical fiber with high stability under damp heat conditions

Kenji Makino, Takahiro Kado, Azusa Inoue, and Yasuhiro Koike  »View Author Affiliations


Optics Express, Vol. 20, Issue 12, pp. 12893-12898 (2012)
http://dx.doi.org/10.1364/OE.20.012893


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Abstract

A low loss graded index polymer optical fiber (GI POF) with a wide wavelength range around 650 nm is fabricated using a copolymer of methyl methacrylate and pentafluorophenyl methacrylate as a polymer matrix. Dopant hydrophobicity similar to that of the polymer matrix is an important factor in maintaining the low loss of the GI POF. No loss increment is observed under damp heat conditions of 75°C and 85% relative humidity when using 9-bromo phenanthrene as the high refractive index dopant required to form the GI profile. The copolymer based GI POF can provide an inexpensive premise network with long-term stability.

© 2012 OSA

1. Introduction

We previously proposed and reported a copolymer of MMA and pentafluorophenyl methacrylate (PFPMA) as a polymer matrix for a less expensive and low loss GI POF with a wide wavelength range centered around 650 nm [12

12. K. Koike, T. Kado, Z. Satoh, Y. Okamoto, and Y. Koike, “Optical and thermal properties of methyl methacrylate and pentafluorophenyl methacrylate copolymer: Design of copolymers for low-loss optical fibers for gigabit in-home communications,” Polymer (Guildf.) 51(6), 1377–1385 (2010). [CrossRef]

]. On the other hand, the transmission loss stability is a significant issue for installation of GI POFs in a premise network.

In this paper, we investigate the attenuation stability of the MMA-co-PFPMA based GI POF under damp heat conditions. This paper clarifies that the copolymer based GI POF can maintain low transmission loss at a wide wavelength range around 650 nm even under high-temperature and high-humidity atmospheric conditions, and confirms that the dopant characteristics are important factors in maintaining the low attenuation of the GI POF under damp heat conditions.

2. Fiber fabrication

The GI POF was obtained by heat drawing of a preform with a graded refractive index profile. The GI preform was fabricated by a rod-in-tube method. In the rod-in-tube method, a core rod including a dopant and a cladding tube are prepared separately. The core rod is inserted into the cladding tube, and heated at a temperature of 150°C for 24 h. During the heat treatment, the core rod and cladding tube adhere to each other, and the dopant diffuses into the cladding layer. The dopant has a higher refractive index than the polymer matrix. The distribution of the dopant concentration corresponds to the refractive index profile. Thus, the GI preform was obtained after this diffusion process. The mechanism of forming the GI profile (i.e., heat diffusion of dopant) in the rod-in-tube method is similar to that of a coextrusion method that is adopted in mass production of commercially available GI POFs [13

13. R. Nakao, A. Kondo, and Y. Koike, “Fabrication of high glass transition temperature graded-index plastic optical fiber: Part 2–fiber fabrication and characterizations,” J. Lightwave Technol. 30(7), 969–973 (2012). [CrossRef]

]. Thus, this copolymer based GI POF could be fabricated by the coextrusion method for mass production. The MMA-co-PFPMA (65/35 mol%) composition used here in the feed was experimentally determined to achieve the highest glass transition temperature (Tg) [12

12. K. Koike, T. Kado, Z. Satoh, Y. Okamoto, and Y. Koike, “Optical and thermal properties of methyl methacrylate and pentafluorophenyl methacrylate copolymer: Design of copolymers for low-loss optical fibers for gigabit in-home communications,” Polymer (Guildf.) 51(6), 1377–1385 (2010). [CrossRef]

]. Diphenyl sulfide (DPS) was selected as the high refractive index dopant. The dopant concentration was adjusted to provide a numerical aperture (NA) of 0.20.

3. Results and discussion

Figure 1
Fig. 1 Transmission loss spectra of PMMA and MMA-co-PFPMA based GI POFs.
shows the attenuation spectrum of the fabricated MMA-co-PFPMA based GI POF, compared with that of the PMMA based GI POF. The measured attenuation of the MMA-co-PFPMA based GI POF is approximately 100 dB/km at a wavelength of 650 nm, and the transmission loss is less than 200 dB/km over a wider wavelength range of 630-690 nm. On the other hand, the PMMA based GI POF exhibits a transmission loss of less than 200 dB/km at a narrower wavelength range of 640-660 nm, although the attenuation at 650 nm is below 150 dB/km. This is because polyPFPMA has a smaller number of C-H bonds per unit volume than PMMA, which results in low C-H vibrational absorption, and because PMMA and polyPFPMA have almost the same refractive index, which indicates that the MMA-co-PFPMA induces low excess light scattering, even if the MMA-co-PFPMA includes microphase separation similar to general copolymers. Therefore, the MMA-co-PFPMA based GI POF is expected to be a suitably low loss transmission medium for premise networks, even if the emission wavelength from the light source is shifted by temperature changes.

We performed a cause and correlation analysis of the loss increment under damp heat conditions. Figure 3
Fig. 3 Water absorption of bulk core polymers in water bath at 75°C.
shows the water absorption of the core polymers in a water bath at a temperature of 75°C. The water absorption was determined by the difference between the sample weights before and after the damp heat test. It was experimentally confirmed that the MMA-co-PFPMA absorbed much smaller amounts of water than the PMMA, because PFPMA contains five fluorines, which show high hydrophobicity. The water absorption was reduced by the addition of DPS for both PMMA and MMA-co-PFPMA, which indicates that the DPS is more hydrophobic than both of the polymers. On the other hand, both the PMMA and MMA-co-PFPMA based GI POFs containing DPS exhibited large loss increments, despite the reduction in water absorption. In contrast, almost no loss increment was observed in both the PMMA and MMA-co-PFPMA based SI POFs without DPS doping, despite the greater degree of water absorption. The MMA-co-PFPMA with DPS doping absorbed the smallest amount of water; nonetheless, the MMA-co-PFPMA based GI POF doped with DPS exhibited the greatest loss increment. In contrast, although the PMMA absorbed the largest amount of water, the PMMA based SI POF showed almost no loss increment. These results suggest that the loss increment under the high-temperature and high-humidity conditions is not strongly affected by the absolute amount of water absorbed into the POF, especially at the wavelength of interest.

On the other hand, the PMMA based GI POF showed high attenuation stability under the high-temperature and high-humidity conditions by selection of an appropriate dopant with similar hydrophobicity to PMMA [15

15. T. Ishigure, M. Sato, A. Kondo, Y. Tsukimori, and Y. Koike, “Graded-index polymer optical fiber with high temperature and high humidity stability,” J. Lightwave Technol. 20(10), 1818–1825 (2002). [CrossRef]

]. This is because, in the case of an inappropriate dopant, the absorbed water cannot be homogeneously dispersed in the polymer, and thus aggregates to form large heterogeneous structures, which induce excess light scattering and result in loss increments, even if the amount of water absorption becomes much smaller because of the dopant. We therefore selected 9-bromo phenanthrene (BPT) as the dopant to maintain the low loss of the MMA-co-PFPMA based GI POF under damp heat conditions, because the MMA-co-PFPMA doped with BPT has almost the same water absorption as the MMA-co-PFPMA without the dopant, as shown in Fig. 3, which means that BPT has a hydrophobicity level close to that of MMA-co-PFPMA.

Figure 4
Fig. 4 (a) Refractive index and (b) Tg dependence on dopant concentration of MMA-co-PFPMA.
shows the refractive index and Tg of MMA-co-PFPMA doped with BPT at various concentrations in comparison to those doped with DPS. Figure 4(a) clarifies that the concentration of BPT required to obtain a certain refractive index is lower than that for DPS, because BPT has a higher refractive index than DPS. This reduction in dopant concentration decreases the plasticization effect, and thus increases the Tg in the core region of the GI POF. Figure 4(b) reveals that BPT exhibits lower plasticization efficiency, corresponding to the absolute value of the slope, than DPS. Therefore, MMA-co-PFPMA doped with BPT exhibits a higher Tg value than that doped with DPS, even if the same doping concentration is used. In addition to similar hydrophobicity, BPT offers the valuable advantage of providing a higher Tg to the MMA-co-PFPMA based GI POF because of the two effects described above. The higher Tg would lead to higher thermal stability. Consequently, BPT is expected to be an excellent dopant and will provide the MMA-co-PFPMA based GI POF with high long-term stability.

We fabricated the MMA-co-PFPMA based GI POF doped with BPT, and confirmed that its attenuation is comparable to that of the copolymer based GI POF doped with DPS. Figure 5
Fig. 5 Attenuation stability of MMA-co-PFPMA based GI POF doped with BPT under damp heat conditions (75°C, 85% RH).
shows the attenuation stabilities of the MMA-co-PFPMA based GI POFs doped with DPS and BPT under damp heat conditions. The attenuation stability of the MMA-co-PFPMA based GI POF is dramatically improved by adopting BPT as a dopant, compared to DPS. No loss increment is observed in the MMA-co-PFPMA based GI POF doped with BPT. The GI POF obtained is a promising candidate for inexpensive premise networking. We can also conclude that the loss increment mechanism under damp heat conditions explained in the PMMA based GI POF applies to the MMA-co-PFPMA based GI POF, and that the dopant hydrophobicity, similar to the polymer matrix, plays an important role in maintaining the low loss of the MMA-co-PFPMA based GI POF.

4. Conclusions

We successfully obtained a BPT doped MMA-co-PFPMA based GI POF with low loss at a wide wavelength range around 650 nm, and with high stability under damp heat conditions of 75°C and 85% RH. The dopant selection is a significant issue in maintaining the attenuation under the damp heat conditions, because a change in hydrophobicity induces aggregation of the water absorbed into the GI POF, forming large heterogeneous structures, and leading to a loss increment because of excess light scattering. We demonstrated that the MMA-co-PFPMA based GI POF doped with BPT could be used to provide a premise network with long-term reliability.

Acknowledgments

This research is supported by the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program).”

References and links

1.

P. Polishuk, “Plastic optical fibers branch out,” IEEE Commun. Mag. 44(9), 140–148 (2006). [CrossRef]

2.

Y. Koike, “High-bandwidth graded-index polymer optical fibre,” Polymer (Guildf.) 32(10), 1737–1745 (1991). [CrossRef]

3.

K. Makino, T. Nakamura, T. Ishigure, and Y. Koike, “Analysis of graded-index polymer optical fiber link performance under fiber bending,” J. Lightwave Technol. 23(6), 2062–2072 (2005). [CrossRef]

4.

K. Makino, T. Ishigure, and Y. Koike, “Waveguide parameter design of graded-index plastic optical fibers for bending-loss reduction,” J. Lightwave Technol. 24(5), 2108–2114 (2006). [CrossRef]

5.

P. J. Decker, A. Polley, J. H. Kim, and S. E. Ralph, “Statistical study of graded-index perfluorinated plastic optical fiber,” J. Lightwave Technol. 29(3), 305–315 (2011). [CrossRef]

6.

Y. Koike and K. Koike, “Polymer optical fibers,” in Encyclopedia of Polymer Science and Technology, (John Wiley & Sons, Inc., 2002).

7.

Y. Koike and S. Takahashi, “Plastic optical fibers: Technologies and communication links,” in Optical Fiber Telecommunications V A, I. P. Kaminow, T. Li, and A. E. Willner, eds. (Academic Press, 2008).

8.

R. Gaudino, D. Cardenas, M. Bellec, B. Charbonnier, N. Evanno, P. Guignard, S. Meyer, A. Pizzinat, I. Mollers, and D. Jager, “Perspective in next-generation home networks: Toward optical solutions?” IEEE Commun. Mag. 48(2), 39–47 (2010). [CrossRef]

9.

T. Kibler, S. Poferl, G. Bock, H. P. Huber, and E. Zeeb, “Optical data buses for automotive applications,” J. Lightwave Technol. 22(9), 2184–2199 (2004). [CrossRef]

10.

W. Groh, “Overtone absorption in macromolecules for polymer optical fibers,” Makromol. Chem. 189(12), 2861–2874 (1988). [CrossRef]

11.

J. Zubia and J. Arrue, “Plastic optical fibers: An introduction to their technological processes and applications,” Opt. Fiber Technol. 7(2), 101–140 (2001). [CrossRef]

12.

K. Koike, T. Kado, Z. Satoh, Y. Okamoto, and Y. Koike, “Optical and thermal properties of methyl methacrylate and pentafluorophenyl methacrylate copolymer: Design of copolymers for low-loss optical fibers for gigabit in-home communications,” Polymer (Guildf.) 51(6), 1377–1385 (2010). [CrossRef]

13.

R. Nakao, A. Kondo, and Y. Koike, “Fabrication of high glass transition temperature graded-index plastic optical fiber: Part 2–fiber fabrication and characterizations,” J. Lightwave Technol. 30(7), 969–973 (2012). [CrossRef]

14.

International Electrotechnical Commission, “Optical fibres - part 2-40: Product specifications - sectional specification for category a4 multimode fibres,” in IEC 60793–2-40 Ed. 2.0, (2005).

15.

T. Ishigure, M. Sato, A. Kondo, Y. Tsukimori, and Y. Koike, “Graded-index polymer optical fiber with high temperature and high humidity stability,” J. Lightwave Technol. 20(10), 1818–1825 (2002). [CrossRef]

OCIS Codes
(060.2270) Fiber optics and optical communications : Fiber characterization
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(060.2290) Fiber optics and optical communications : Fiber materials
(060.2330) Fiber optics and optical communications : Fiber optics communications

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: March 26, 2012
Revised Manuscript: May 18, 2012
Manuscript Accepted: May 21, 2012
Published: May 23, 2012

Citation
Kenji Makino, Takahiro Kado, Azusa Inoue, and Yasuhiro Koike, "Low loss graded index polymer optical fiber with high stability under damp heat conditions," Opt. Express 20, 12893-12898 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-12-12893


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References

  1. P. Polishuk, “Plastic optical fibers branch out,” IEEE Commun. Mag.44(9), 140–148 (2006). [CrossRef]
  2. Y. Koike, “High-bandwidth graded-index polymer optical fibre,” Polymer (Guildf.)32(10), 1737–1745 (1991). [CrossRef]
  3. K. Makino, T. Nakamura, T. Ishigure, and Y. Koike, “Analysis of graded-index polymer optical fiber link performance under fiber bending,” J. Lightwave Technol.23(6), 2062–2072 (2005). [CrossRef]
  4. K. Makino, T. Ishigure, and Y. Koike, “Waveguide parameter design of graded-index plastic optical fibers for bending-loss reduction,” J. Lightwave Technol.24(5), 2108–2114 (2006). [CrossRef]
  5. P. J. Decker, A. Polley, J. H. Kim, and S. E. Ralph, “Statistical study of graded-index perfluorinated plastic optical fiber,” J. Lightwave Technol.29(3), 305–315 (2011). [CrossRef]
  6. Y. Koike and K. Koike, “Polymer optical fibers,” in Encyclopedia of Polymer Science and Technology, (John Wiley & Sons, Inc., 2002).
  7. Y. Koike and S. Takahashi, “Plastic optical fibers: Technologies and communication links,” in Optical Fiber Telecommunications V A, I. P. Kaminow, T. Li, and A. E. Willner, eds. (Academic Press, 2008).
  8. R. Gaudino, D. Cardenas, M. Bellec, B. Charbonnier, N. Evanno, P. Guignard, S. Meyer, A. Pizzinat, I. Mollers, and D. Jager, “Perspective in next-generation home networks: Toward optical solutions?” IEEE Commun. Mag.48(2), 39–47 (2010). [CrossRef]
  9. T. Kibler, S. Poferl, G. Bock, H. P. Huber, and E. Zeeb, “Optical data buses for automotive applications,” J. Lightwave Technol.22(9), 2184–2199 (2004). [CrossRef]
  10. W. Groh, “Overtone absorption in macromolecules for polymer optical fibers,” Makromol. Chem.189(12), 2861–2874 (1988). [CrossRef]
  11. J. Zubia and J. Arrue, “Plastic optical fibers: An introduction to their technological processes and applications,” Opt. Fiber Technol.7(2), 101–140 (2001). [CrossRef]
  12. K. Koike, T. Kado, Z. Satoh, Y. Okamoto, and Y. Koike, “Optical and thermal properties of methyl methacrylate and pentafluorophenyl methacrylate copolymer: Design of copolymers for low-loss optical fibers for gigabit in-home communications,” Polymer (Guildf.)51(6), 1377–1385 (2010). [CrossRef]
  13. R. Nakao, A. Kondo, and Y. Koike, “Fabrication of high glass transition temperature graded-index plastic optical fiber: Part 2–fiber fabrication and characterizations,” J. Lightwave Technol.30(7), 969–973 (2012). [CrossRef]
  14. International Electrotechnical Commission, “Optical fibres - part 2-40: Product specifications - sectional specification for category a4 multimode fibres,” in IEC 60793–2-40 Ed. 2.0, (2005).
  15. T. Ishigure, M. Sato, A. Kondo, Y. Tsukimori, and Y. Koike, “Graded-index polymer optical fiber with high temperature and high humidity stability,” J. Lightwave Technol.20(10), 1818–1825 (2002). [CrossRef]

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