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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 18 — Sep. 1, 2008
  • pp: 13545–13551
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Design of a trenched bend insensitive single mode optical fiber using spot size definitions

Pramod R. Watekar, Seongmin Ju, Young Sik Yoon, Yeong Seop Lee, and Won-Taek Han  »View Author Affiliations


Optics Express, Vol. 16, Issue 18, pp. 13545-13551 (2008)
http://dx.doi.org/10.1364/OE.16.013545


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Abstract

We have designed a bend insensitive single mode optical fiber with a low-index trench using spot-size definitions and their optimization technique. The bending loss at a 5 mm of bending radius was negligible, while single mode properties were intact.

© 2008 Optical Society of America

1. Introduction

Bend insensitive fibers are exciting engineers and scientists because of possibility of their use in FTTH applications and thereby reducing a huge power penalty caused by sharp bends in optical fibers used in the city network [1

1. P. R. Watekar, S. Ju, and W. -T. Han, “Single-mode optical fiber design with wide-band ultra low bending-loss for FTTH application,” Opt. Express 16, 1180–1185 (2008). [CrossRef] [PubMed]

4

4. Stokeryale bend insensitive fiber (2007), http://www.stockeryale.com/o/fiber/products/bif-1550-l2.htm

]. There are several advantages of using bend insensitive fibers: they allow compact design of the splice-boxes and there is a significant cost saving. Typical parameters of a single mode optical fiber (SMF) which are allowed as per ITU-T recommendations [5

5. ITU-T recommendation G.652.

] are listed in Table 1, which shows a large bending loss at a small bending radius of 5 mm. When the single mode optical fiber is straight, the most power is confined in an optical fiber core. However, when a sharp bending is applied, the power in the optical fiber core is leaked to a cladding region and an outer lossy polymer coating due to a curve induced refractive index change in the cladding, giving rise to a large bending loss in the SMF.

In a current communication, we systematically describe the effect of various parameters of low-index trench on a single mode operation as well as bending loss of the SMF and dig out optimized parameters based on calculated results. To do this, we use a method of spot-size optimization, which was previously used to optimize two-step profile dispersion shifted fibers, where the core index and width were optimized to get dispersion shift [7

7. R. Tewari, B. P. Pal, and U. K. Das, “Dispersion shifted dual-shape core fibers: Optimization based on spot size definitions,” IEEE J. Lightwave Technology 10, 1–5 (1992). [CrossRef]

]. In our case, we have used spot size definitions to optimize cladding parameters (rather than core) as per mode field definitions used in the current communication to minimize the bending loss.

Table 1. Typical optical parameters of the SMF under consideration in the current communication.

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2. Theoretical design

Our aim is to design a bend insensitive single mode optical fiber (BI-SMF) while maintaining key optical properties of the SMF as per ITU-T recommendations. A trenched SMF index profile is shown in Fig. 1. Typical questions that need to be answered for trenched fibers are: (a) How much should be a trench width? If the trench width is too wide, then optical properties of the single mode fiber are significantly altered. (b) How much should be a trench index? This question is important because there are commercial and practical limitations to provide the low index trench inside the cladding region. (c) How far should be the trench placed from the core? If the trench is very near to the core, it can affect SMF properties and if it is too far, it is a very expensive to fabricate the optical fiber. We begin with defining certain parameters. A basic parameter that controls the dispersion is an effective mode field diameter (MFDeff), which is defined as [8

8. A. W. Snyder and J. D. Love, Optical Waveguide Theory, (Chapman and Hall, 1983).

, 9

9. D. Marcuse, “Curvature loss formula for optical fibers,” J. Opt. Soc. Am. 66, 216–220 (1976). [CrossRef]

]

MFDeff=22π(rE2rdr)2(πrE4rdr)
(1)

where E is the mode field, which can be computed from its evolution in the optical fiber using a scalar wave equation [8

8. A. W. Snyder and J. D. Love, Optical Waveguide Theory, (Chapman and Hall, 1983).

, 9

9. D. Marcuse, “Curvature loss formula for optical fibers,” J. Opt. Soc. Am. 66, 216–220 (1976). [CrossRef]

]:

d2Edr2=1rdEdr+(k02n2(r)β2)E+L2r2E
(2)

where E is an electric field along a radius r, k 0 is a propagation constant in the free space, n(r) is a refractive index profile of the optical fiber, L is an azimuthal mode number and β is the propagation constant in the optical fiber.

Fig. 1. Refractive index profile of the trenched SMF.

A Petermann-3 spot size MFD for the SMF is defined as follows [7

7. R. Tewari, B. P. Pal, and U. K. Das, “Dispersion shifted dual-shape core fibers: Optimization based on spot size definitions,” IEEE J. Lightwave Technology 10, 1–5 (1992). [CrossRef]

, 10

10. K. Petermann and R. Kuhne, “Upper and lower limits for the microbending loss in arbitrary single-mode fibers,” J. Lightwave Technology 4, 2–7 (1986). [CrossRef]

]:

MFD=2λπnmaxk0(neffnmin)
(3)

where n max and n min are maximum and minimum values of the refractive index, neff(=β/k 0) is an effective refractive index, λ is a wavelength of operation and k 0=2π/λ. A macrobending loss in units of dB/km can be calculated using a formula [8

8. A. W. Snyder and J. D. Love, Optical Waveguide Theory, (Chapman and Hall, 1983).

, 9

9. D. Marcuse, “Curvature loss formula for optical fibers,” J. Opt. Soc. Am. 66, 216–220 (1976). [CrossRef]

]:

αmacro=10loge10πV816RcRbW3exp(4RbΔW33RcV2)[0(1g)F0rdr]20F02rdr
(4)

where F 0 is a radial field of fundamental mode, Rc denotes the fiber core radius, Rb is a bend radius and other parameters appearing in Eq. (4) are given by:

g=n(r)2nmin2nmax2nmin2;V=k0rcnmax2nmin2;
W=rcβ2(k0nmin)2;Δ=nmax2nmin22nmax2
(5)

Fig. 2. Effect of variations of design parameters of the trenched SMF on bending loss.

To design the BI-SMF, initially we fixed the design criteria so as to follow ITU-T recommendations at 1550 nm: MFDeff>=9.6 µm, dispersion <=18.5 ps/km.nm and dispersion slope <=0.095 ps/km.nm2; additionally, theoretical bending loss <=0.035 dB/cm at 5 mm of bending radius. Considering practical constrains in fabricating the optical fiber, we set maximum limits to various trench parameters: b<=4a, c<=4a and ΔnTrench >=-0.004. The scalar wave equation of the optical fiber was solved at each set of b, c and ΔnTrench to obtain the optimum MFD ratio where bending loss was minimum. Every time it was checked whether the design criteria was followed or not and the values were selected only if the criteria was followed. By repeating this procedure for several times, optimum MFD ratios were obtained and a set of trench parameters associated with an each optimized MFD ratio were selected as optimized trench parameters.

3. Results and discussion

By adopting a procedure for obtaining optimized parameters of the trenched SMF by simulation as explained in section 2, we obtained optimized trench parameters as illustrated in Figs. 3(a) to 3(e). These figures show variations of minimum bending loss with respective MFD ratios and optimized b, c values at particular ΔnTrench values. These are utility curves to design the trenched SMF for minimum bending loss. For example, to design the bend optimized SMF with the bending loss of about 0.02 dB/turn at 1550 nm (for 5 mm of bending radius), one can look at Fig. 3(d), select the MFD ratio of 0.836, which gives b=1.1a, c=4a and ΔnTrench=-0.003 from the figure, where a is the core radius.

Fig. 3. (a). to 3. (e). Optimized design parameters of the BI-SMF. (Wavelength =1550 nm, bending radius =5 mm). ×50 and ×500 in the figures indicate that original bending loss values have been multiplied by 50 and 500 times, respectively.

Calculated optical parameters of typical BI-SMF using optimum profile dimensions as given above, are listed in Table 2 and are shown in Fig. 4, where the bending loss at 1550 nm (for 5 mm of bending radius) is about 474 times smaller than that of the SMF without trench and notably, all other parameters of the BI-SMF are similar to the SMF. This indicates a strong advantage of using the trench in the cladding region; the power loss is almost negligible even for the bending radius of 5 mm, which can be contributed to the reduced effective index of the optical fiber cladding.

Table 2. Optical parameters of the typical BI-SMF.

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Fig. 4. Spectral variations of the dispersion, the MFDeff and the bending loss of the single trenched BI-SMF (b=1.1a, c=4a and ΔnTrench=-0.003). ‘×10’ in the figure indicates that original dispersion slope values have been multiplied by 10 times.
Fig. 5. Spectral variations of the MFDeff, the dispersion and the bending loss of the double trenched BI-SMF (b=1.1a, c=4a and ΔnTrench=-0.003. Additional trench: separation=1.1a, width=4a and refractive index difference=-0.003). ‘×10’ in the figure indicates that original dispersion slope values have been multiplied by 10 times.

Lastly, we analyze the double trenched BI-SMF, where additional trench is introduced with same dimensions as of the single trenched BI-SMF; its profile structure is shown in the inset of Fig. 4(b). The MFD, the dispersion, and the bending loss are almost similar to those of the single trenched BI-SMF as shown in Fig. 4 and Fig. 5. It appears that only one trench in the cladding region is enough to achieve the bend insensitivity in the SMF.

4. Summary

We have designed the trenched SMF having negligible bending loss at 1550 nm upon 5 mm of bending radius using the spot size definitions. Both single and double trenched SMFs showed the same bending insensitivity, while keeping all the other optical properties of SMF intact.

Acknowledgments

This work was supported by the Brain Korea-21 Information Technology Project, Ministry of Education and Human Resources Development, by the National Core Research Center (NCRC) for Hybrid Materials Solution of Pusan National University, by the GIST Top Brand Project (Photonics 2020), Ministry of Science and Technology, and by the Samsung Electronics Hainan Fiberoptics-Korea Co. Ltd., South Korea.

References and links

1.

P. R. Watekar, S. Ju, and W. -T. Han, “Single-mode optical fiber design with wide-band ultra low bending-loss for FTTH application,” Opt. Express 16, 1180–1185 (2008). [CrossRef] [PubMed]

2.

S. Matsuo, M. Ikeda, and K. Himeno, “Bend insensitive and low splice loss optical fiber for indoor wiring in FTTH,” Proceedings of Optical Fiber Communication Conference (OFC), Anaheim, USA, Feb. 23–27, 2004, ThI3 (2004).

3.

M. -J. Li, P. Tandon, D. C. Bookbinder, S. R. Bickham, M. A. McDermott, R. B. Desorcie, D. A. Nolan, J. J. Johnson, K. A. Lewis, and J. J. Englebert, “Ultra-low bending loss single-mode fiber for FTTH,” Proceedings of OFC/NFOEC-2008, San Diego, USA, Feb. 24–28, 2008, PDP10 (2008).

4.

Stokeryale bend insensitive fiber (2007), http://www.stockeryale.com/o/fiber/products/bif-1550-l2.htm

5.

ITU-T recommendation G.652.

6.

J. Van Erps, C. Debaes, T. Nasilowski, J. Watt, J. Wojcik, and H. Thienpont, “Design and tolerance analysis of a low bending loss hole-assisted fiber using statistical design methodology,” Opt. Express 16, 5061–5074 (2008). [CrossRef] [PubMed]

7.

R. Tewari, B. P. Pal, and U. K. Das, “Dispersion shifted dual-shape core fibers: Optimization based on spot size definitions,” IEEE J. Lightwave Technology 10, 1–5 (1992). [CrossRef]

8.

A. W. Snyder and J. D. Love, Optical Waveguide Theory, (Chapman and Hall, 1983).

9.

D. Marcuse, “Curvature loss formula for optical fibers,” J. Opt. Soc. Am. 66, 216–220 (1976). [CrossRef]

10.

K. Petermann and R. Kuhne, “Upper and lower limits for the microbending loss in arbitrary single-mode fibers,” J. Lightwave Technology 4, 2–7 (1986). [CrossRef]

OCIS Codes
(060.2310) Fiber optics and optical communications : Fiber optics
(060.2330) Fiber optics and optical communications : Fiber optics communications

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: June 6, 2008
Revised Manuscript: August 3, 2008
Manuscript Accepted: August 5, 2008
Published: August 19, 2008

Citation
Pramod R. Watekar, Seongmin Ju, Young Sik Yoon, Yeong Seop Lee, and Won-Taek Han, "Design of a trenched bend insensitive single mode optical fiber using spot size definitions," Opt. Express 16, 13545-13551 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-18-13545


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References

  1. P. R. Watekar, S. Ju and W. -T. Han, "Single-mode optical fiber design with wide-band ultra low bending-loss for FTTH application," Opt. Express 16, 1180-1185 (2008). [CrossRef] [PubMed]
  2. S. Matsuo, M. Ikeda and K. Himeno, "Bend insensitive and low splice loss optical fiber for indoor wiring in FTTH," Proceedings of Optical Fiber Communication Conference (OFC), Anaheim, USA, Feb. 23-27, 2004, ThI3 (2004).
  3. M. -J. Li, P. Tandon, D. C. Bookbinder, S. R. Bickham, M. A. McDermott, R. B. Desorcie, D. A. Nolan, J. J. Johnson, K. A. Lewis and J. J. Englebert, "Ultra-low bending loss single-mode fiber for FTTH," Proceedings of OFC/NFOEC-2008, San Diego, USA, Feb. 24-28, 2008, PDP10 (2008).
  4. Stokeryale bend insensitive fiber (2007), http://www.stockeryale.com/o/fiber/products/bif-1550-l2.htm
  5. ITU-T recommendation G.652.
  6. J. Van Erps, C. Debaes, T. Nasilowski, J. Watt, J. Wojcik, and H. Thienpont, "Design and tolerance analysis of a low bending loss hole-assisted fiber using statistical design methodology," Opt. Express 16, 5061-5074 (2008). [CrossRef] [PubMed]
  7. R. Tewari, B. P. Pal and U. K. Das, "Dispersion shifted dual-shape core fibers: Optimization based on spot size definitions," IEEE J. Lightwave Technology 10, 1-5 (1992). [CrossRef]
  8. A. W. Snyder and J. D. Love, Optical Waveguide Theory, (Chapman and Hall, 1983).
  9. D. Marcuse, "Curvature loss formula for optical fibers," J. Opt. Soc. Am. 66, 216-220 (1976). [CrossRef]
  10. K. Petermann and R. Kuhne, "Upper and lower limits for the microbending loss in arbitrary single-mode fibers," J. Lightwave Technology 4, 2-7 (1986). [CrossRef]

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