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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 1 — Jan. 14, 2013
  • pp: 122–128
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Unique characteristics of a selective-filling photonic crystal fiber Sagnac interferometer and its application as high sensitivity sensor

Tingting Han, Yan-ge Liu, Zhi Wang, Junqi Guo, Zhifang Wu, Shuanxia Wang, Zhili Li, and Wenyuan Zhou  »View Author Affiliations


Optics Express, Vol. 21, Issue 1, pp. 122-128 (2013)
http://dx.doi.org/10.1364/OE.21.000122


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Abstract

We demonstrate a Sagnac interferometer (SI) based on a selective-filling photonic crystal fiber (SF-PCF), which is achieved by infiltrating a liquid with higher refractive index than background silica into two adjacent air holes of the innermost layer. The SF-PCF guides light by both index-guiding and bandgap-guiding. The modal birefringence of the SF-PCF is decidedly dependent on wavelength, and the modal group birefringence has zero value at a certain wavelength. We also theoretically and experimentally investigate in detail the transmission and temperature characteristics of the SI. Results reveal that the temperature sensitivity of the interference spectrum is also acutely dependent on wavelength and temperature, and an ultrahigh even theoretically infinite sensitivity can be achieved at a certain temperature by choosing proper fiber length. An ultrahigh sensitivity with −26.0 nm/°C (63,882 nm/RIU) at 50.0 °C is experimentally achieved.

© 2013 OSA

1. Introduction

2. Theoretical analysis

Figure 1(a)
Fig. 1 (a) Schematic diagram of the proposed SF-PCF based SI. The inset is the cross-section of the PCF used in this paper (top inset) and theory model for simulation (bottom inset), where, the white circles are air holes and the red circles are high index inclusions. (b) Calculated phase birefringence B and group birefringence Bg dependence on wavelength under different temperatures.
illustrates the schematic diagram of the proposed SF-PCF based SI, which consists of a 3 dB optical coupler (OC) with a splitting ratio of ~50:50 at a wavelength range from 1300.0 nm to 1600.0 nm and a section of SF-PCF. The light from a supercontinuum source (SCS) (600.0 nm-1700.0 nm) propagates around the fiber loop, and the transmission interference spectrum is measured by an optical spectral analyzer (OSA) with the highest resolution of 0.02 nm. The top inset of Fig. 1 shows the microscopic image of the transverse cross-section of the original PCF used in this paper, which is fabricated by Yangtze Optical Fiber and Cable Corporation Ltd. of China. The pure silica fiber includes five rings of air holes arranged in a regular hexagonal pattern. The holes diameter and adjacent holes distance are ~3.6 μm and ~5.9 μm, respectively. The refractive index of the background silica is 1.444 at 1550 nm wavelength. The bottom inset shows the theoretical simulation model, where the white circles are air holes, and the red circles are the high index inclusions. The SF-PCF is realized by selectively infiltrating two adjacent air holes of the innermost layer of the PCF with liquid, which is produced by Cargille Laboratories Inc and possesses a refractive index of 1.52 at 589.3 nm for 25°C and a thermal-optic coefficient of −0.000407/°C. The coupling between the two high index rods produce guided modes therein at certain frequencies. And, meanwhile, the bandgaps-like core transmission spectra are formed. Hence, in this direction, light is guided in the core by bandgap-guiding. While in the other directions, light is guided in the core by index-guiding. And light is guided at solid core only when the guiding conditions of both index-guiding and bandgap-guiding are satisfied.

λ(T)=1m[(LL1)B(λ,T0)+L1B(λ,T)].
(2)

According to Eq. (3), we calculate the temperature sensitivity S versus wavelength for different heated length ratio (γ) at 50.0 °C, as shown in Fig. 2
Fig. 2 Calculated temperature sensitivity S(T) versus wavelength for different heated length ratio γ at 50.0 °C.
. The vertical lines stand for the zero denominators of Eq. (3), which results in theoretically infinite temperature sensitivity at this temperature. In addition, the temperature sensitivities increase with the decreasing distance between the resonant interference dip and the vertical lines. According to the phase-matching condition defined by Eq. (2), the total length L and heated length L1 of the SF-PCF determine where the interference dips locate. Therefore, by choosing proper L and L1, higher sensitivity at this temperature can be achieved, for example, a sensitivity of −98.3 nm/°C at wavelength of 1516.0 nm is achieved when choosing L = L1 = 17.5 cm and −74.0 nm/°C at wavelength of 1610.0 nm is achieved when L = 25.0cm and L1 = 12.0cm.

Then, we fix the filling length at 25.0 cm and change the heated length ratio γ at 0.48 (L1 = 12.0 cm), the wavelength variation of dips A and B with temperature is also shown in Fig. 3(b) (red curves). We can see that the shift velocities of the two dips at the smaller ratio γ is slower than those at the lager ratio γ. Furthermore, the temperatures at which the sensitivities reach the highest value are different for different γ. The γ (or the length of the heated fiber L1) can be controlled by regulating the relative location of the temperature chamber to the SF-PCF. Thus, the highest sensitivity can be achieved at different temperatures only by changing the heated fiber length (or the location of the temperature chamber) without changing the total filling length. It makes the practical application more convenient.

3. Experimental results

In the experiment, the two adjacent air holes located at the innermost layer of the PCF are selectively infiltrated with the high index liquid by the direct manual gluing method described in detail in [18

18. B. T. Kuhlmey, B. J. Eggleton, and D. K. C. Wu, “Fluid-filled solid-core photonic bandgap fibers,” J. Lightwave Technol. 27(11), 1617–1630 (2009). [CrossRef]

]. The filling length L is ~25.0 cm. Two ends of the SF-PCF are infiltrated into a bit of air to avoid high loss when fusion splicing with infiltrated fluid. Then SF-PCF is splicing fusion to SMFs and put into the SI as shown in Fig. 1(a) and 12.0 cm length of the SF-PCF is located inside the temperature chamber with temperature stability of ± 0.1°C. Figure 4(a)
Fig. 4 (a) The experimental transmission spectra of the SI from 46.4°C to 71.3°C when L = 25 cm and L1 = 12 cm. (b) (top) The experimental wavelength variation (the circles) AEX-DEX and theoretical wavelength variation (the solid curves) ATHE-DTHE of dips A, B, C and D dependence on temperature. The blue solid curves are the nonlinear fitting curves of the experimental results. (bottom) The temperature sensitivity of dips A, B, C and D dependence on temperature.
shows the transmission spectra of the SI from 46.4°C to 71.3°C. Interference dips A and B shift to the opposite direction with temperature increasing, and the wavelength space between the two dips decreases gradually, accompanying the interference contrast reducing. Until 50.5°C, the two dips disappear, and a wide loss dip appears. With temperature increasing, the dip becomes shallower, and finally disappears at 58.3°C. Interference dips C and D have the similar change tendency as dips A and B.

Then the specific temperature sensitivities of interference dips A, B, C and D are further discussed. Figure 4(b) (top) shows the wavelength variation of dips A, B, C and D (AEX-DEX) dependence on temperature (the circles). And the theoretical results are shown with the solid curves (ATHE-DTHE), which have different wavelength scales compared to experimental results. This is because, in PBGFs, the diameter and index of high index rods greatly affect the bandgap wavelengths based on the ARROW theory [18

18. B. T. Kuhlmey, B. J. Eggleton, and D. K. C. Wu, “Fluid-filled solid-core photonic bandgap fibers,” J. Lightwave Technol. 27(11), 1617–1630 (2009). [CrossRef]

]. Hence, small derivation in the diameter and index of high index rods between theoretical model and actual experimental measurement can lead to mismatched wavelength scales. But, the total discussed wavelength ranges in theory and experiment are both 500nm, from 1430nm to 1930nm and from 1350nm to 1850nm, respectively. Furthermore, the variation tendencies of experimental results basically match with that of theoretical results. Then, the experimental results are analyzed and fitted with 6-order polynomial, as shown with the blue solid curves. We use the first-order derivative of the fitting curves, and get the temperature sensitivity, as shown in Fig. 4(b) (bottom). It is clearly seen that the sensitivities change nonlinearly with temperature, and increase with temperature increasing. Dips B and D have sensitivities higher than −10.0 nm/°C from 44°C to 50°C and from 56.7°C to 66.5°C, and the sensitivities reaches up to −26.0 nm/°C at 50.0 °C and −23.0 nm/°C at 66.5°C, respectively. This can be adopted for sensitively detecting tiny temperature variation at a certain temperature. In practice, this valid sensing temperature ranges can be changed and even wider by choosing proper fiber length.

In addition, the change in temperature essentially brings about the variation in the refractive index of the filled liquid analyte, so this device also can be used for optical detection of small change in refractive index within liquid analyte. The refractive index sensitivity corresponding to −26nm/°C is 63882.1 nm/RIU.

4. Conclusion

In conclusion, the characteristics and temperature response of a SI based on a HiBi SF-PCF are theoretically and experimentally investigated. The selective filling pattern affects the guiding mechanism of the SF-PCF which guides light by a combination of both index-guiding and bandgap-guiding. The birefringence characteristics are different from the traditional index guiding HiBi PCF [5

5. C. Kerbage and B. J. Eggleton, “Numerical analysis and experimental design of tunable birefringence in microstructured optical fiber,” Opt. Express 10(5), 246–255 (2002). [CrossRef] [PubMed]

] and HiBi PBGFs [7

7. K. Saitoh and M. Koshiba, “Photonic bandgap fibers with high birefringence,” IEEE Photon. Technol. Lett. 14(9), 1291–1293 (2002). [CrossRef]

9

9. X. Yu, M. Yan, L. W. Luo, and P. Shum, “Theoretical investigation of highly birefringent all-solid photonic bandgap fiber with elliptical cladding rods,” IEEE Photon. Technol. Lett. 18(11), 1243–1245 (2006). [CrossRef]

]. Based on the unique birefringence features, the temperature response of the SI based on the SF-PCF presents a temperature sensitivity of higher than ~-10.0 nm/°C, and the highest sensitivity of ~-26.0 nm/°C at 50.0 °C is experimentally achieved. Furthermore, the highest sensitivity can be achieved at different temperatures only by changing the heated fiber length (or the location of the temperature chamber) without changing the total filling length. This device can be adopted for sensitively detecting tiny variations of temperature and refractive index of filled liquid analyte.

In addition to the flexible selective filling pattern, the anti-crossing points in the bandgap [10

10. P. J. Roberts, D. P. Williams, H. Sabert, B. J. Mangan, D. M. Bird, T. A. Birks, J. C. Knight, and P. St. J. Russell, “Design of low-loss and highly birefringent hollow-core photonic crystal fiber,” Opt. Express 14(16), 7329–7341 (2006). [CrossRef] [PubMed]

] also affect the birefringence features. By combing the selective filling pattern and different bandgaps, we predict diverse selective-filled HiBi PCFs with unique characteristics would have very large capacity for multi-parameter sensing and tunable optical devices.

Acknowledgment

This work was supported by the National Key Basic Research and Development Program of China under Grant 2010CB327605, the National Natural Science Foundation of China under grant Nos. 11174154 and 11174155, the Tianjin Natural Science Foundation under grant No. 12JCZDJC20600 and by the Program for New Century Excellent Talents in University (NCET-09-0483). The authors thank Yangtze Optical Fiber and Cable Co. Ltd. (Wuhan, China) for providing the PCF.

References and links

1.

V. Vali and R. W. Shorthill, “Fiber ring interferometer,” Appl. Opt. 15(5), 1099–1100 (1976). [CrossRef] [PubMed]

2.

Y. G. Liu, B. Liu, X. H. Feng, W. Zhang, G. Zhou, S. Z. Yuan, G. Y. Kai, and X. Y. Dong, “High-birefringence fiber loop mirrors and their applications as sensors,” Appl. Opt. 44(12), 2382–2390 (2005). [CrossRef] [PubMed]

3.

C. L. Zhao, X. F. Yang, C. E. Lu, W. Jin, and M. S. Demokan, “Temperature-insensitive interferometer using a highly birefringent photonic crystal fiber loop mirror,” IEEE Photon. Technol. Lett. 16(11), 2535–2537 (2004). [CrossRef]

4.

H. Y. Fu, H. Y. Tam, L. Y. Shao, X. Y. Dong, P. K. A. Wai, C. Lu, and S. K. Khijwania, “Pressure sensor realized with polarization-maintaining photonic crystal fiber-based Sagnac interferometer,” Appl. Opt. 47(15), 2835–2839 (2008). [CrossRef] [PubMed]

5.

C. Kerbage and B. J. Eggleton, “Numerical analysis and experimental design of tunable birefringence in microstructured optical fiber,” Opt. Express 10(5), 246–255 (2002). [CrossRef] [PubMed]

6.

W. W. Qian, C. L. Zhao, S. L. He, X. Y. Dong, S. Q. Zhang, Z. X. Zhang, S. Z. Jin, J. T. Guo, and H. F. Wei, “High-sensitivity temperature sensor based on an alcohol-filled photonic crystal fiber loop mirror,” Opt. Lett. 36(9), 1548–1550 (2011). [CrossRef] [PubMed]

7.

K. Saitoh and M. Koshiba, “Photonic bandgap fibers with high birefringence,” IEEE Photon. Technol. Lett. 14(9), 1291–1293 (2002). [CrossRef]

8.

M. S. Alam, K. Saitoh, and M. Koshiba, “High group birefringence in air-core photonic bandgap fibers,” Opt. Lett. 30(8), 824–826 (2005). [CrossRef] [PubMed]

9.

X. Yu, M. Yan, L. W. Luo, and P. Shum, “Theoretical investigation of highly birefringent all-solid photonic bandgap fiber with elliptical cladding rods,” IEEE Photon. Technol. Lett. 18(11), 1243–1245 (2006). [CrossRef]

10.

P. J. Roberts, D. P. Williams, H. Sabert, B. J. Mangan, D. M. Bird, T. A. Birks, J. C. Knight, and P. St. J. Russell, “Design of low-loss and highly birefringent hollow-core photonic crystal fiber,” Opt. Express 14(16), 7329–7341 (2006). [CrossRef] [PubMed]

11.

V. Pureur, G. Bouwmans, K. Delplace, Y. Quiquempois, and M. Douay, “Birefringent solid-core photonic bandgap fibers assisted by interstitial air holes,” Appl. Phys. Lett. 94(13), 131102 (2009). [CrossRef]

12.

T. R. Wolinski, A. Czapla, S. Ertman, M. Tefelska, A. Domanski, E. Nowinowski-Kruszelnicki, and R. Dabrowski, “Tunable highly birefringent solid-core photonic liquid crystal fibers,” Opt. Quantum Electron. 39(12-13), 1021–1032 (2007). [CrossRef]

13.

X. B. Zheng, Y. G. Liu, Z. Wang, T. T. Han, C. L. Wei, and J. J. Chen, “Transmission and temperature sensing characteristics of a selectively liquid-filled photonic-bandgap-fiber-based Sagnac interferometer,” Appl. Phys. Lett. 100(14), 141104 (2012). [CrossRef]

14.

G. Kim, T. Y. Cho, K. Hwang, K. Lee, K. S. Lee, Y. G. Han, and S. B. Lee, “Strain and temperature sensitivities of an elliptical hollow-core photonic bandgap fiber based on Sagnac interferometer,” Opt. Express 17(4), 2481–2486 (2009). [CrossRef] [PubMed]

15.

L. M. Xiao, W. Jin, and M. S. Demokan, “Photonic crystal fibers confining light by both index-guiding and bandgap-guiding: hybrid PCFs,” Opt. Express 15(24), 15637–15647 (2007). [CrossRef] [PubMed]

16.

R. Goto, S. D. Jackson, and K. Takenaga, “Single-polarization operation in birefringent all-solid hybrid microstructured fiber with additional stress applying parts,” Opt. Lett. 34(20), 3119–3121 (2009). [CrossRef] [PubMed]

17.

A. Cucinotta, S. Selleri, L. Vincetti, and M. Zoboli, “Holey fiber analysis through the finite-element method,” IEEE Photon. Technol. Lett. 14(11), 1530–1532 (2002). [CrossRef]

18.

B. T. Kuhlmey, B. J. Eggleton, and D. K. C. Wu, “Fluid-filled solid-core photonic bandgap fibers,” J. Lightwave Technol. 27(11), 1617–1630 (2009). [CrossRef]

OCIS Codes
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(060.2420) Fiber optics and optical communications : Fibers, polarization-maintaining
(060.5295) Fiber optics and optical communications : Photonic crystal fibers

ToC Category:
Sensors

History
Original Manuscript: October 22, 2012
Revised Manuscript: December 7, 2012
Manuscript Accepted: December 8, 2012
Published: January 2, 2013

Citation
Tingting Han, Yan-ge Liu, Zhi Wang, Junqi Guo, Zhifang Wu, Shuanxia Wang, Zhili Li, and Wenyuan Zhou, "Unique characteristics of a selective-filling photonic crystal fiber Sagnac interferometer and its application as high sensitivity sensor," Opt. Express 21, 122-128 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-1-122


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References

  1. V. Vali and R. W. Shorthill, “Fiber ring interferometer,” Appl. Opt.15(5), 1099–1100 (1976). [CrossRef] [PubMed]
  2. Y. G. Liu, B. Liu, X. H. Feng, W. Zhang, G. Zhou, S. Z. Yuan, G. Y. Kai, and X. Y. Dong, “High-birefringence fiber loop mirrors and their applications as sensors,” Appl. Opt.44(12), 2382–2390 (2005). [CrossRef] [PubMed]
  3. C. L. Zhao, X. F. Yang, C. E. Lu, W. Jin, and M. S. Demokan, “Temperature-insensitive interferometer using a highly birefringent photonic crystal fiber loop mirror,” IEEE Photon. Technol. Lett.16(11), 2535–2537 (2004). [CrossRef]
  4. H. Y. Fu, H. Y. Tam, L. Y. Shao, X. Y. Dong, P. K. A. Wai, C. Lu, and S. K. Khijwania, “Pressure sensor realized with polarization-maintaining photonic crystal fiber-based Sagnac interferometer,” Appl. Opt.47(15), 2835–2839 (2008). [CrossRef] [PubMed]
  5. C. Kerbage and B. J. Eggleton, “Numerical analysis and experimental design of tunable birefringence in microstructured optical fiber,” Opt. Express10(5), 246–255 (2002). [CrossRef] [PubMed]
  6. W. W. Qian, C. L. Zhao, S. L. He, X. Y. Dong, S. Q. Zhang, Z. X. Zhang, S. Z. Jin, J. T. Guo, and H. F. Wei, “High-sensitivity temperature sensor based on an alcohol-filled photonic crystal fiber loop mirror,” Opt. Lett.36(9), 1548–1550 (2011). [CrossRef] [PubMed]
  7. K. Saitoh and M. Koshiba, “Photonic bandgap fibers with high birefringence,” IEEE Photon. Technol. Lett.14(9), 1291–1293 (2002). [CrossRef]
  8. M. S. Alam, K. Saitoh, and M. Koshiba, “High group birefringence in air-core photonic bandgap fibers,” Opt. Lett.30(8), 824–826 (2005). [CrossRef] [PubMed]
  9. X. Yu, M. Yan, L. W. Luo, and P. Shum, “Theoretical investigation of highly birefringent all-solid photonic bandgap fiber with elliptical cladding rods,” IEEE Photon. Technol. Lett.18(11), 1243–1245 (2006). [CrossRef]
  10. P. J. Roberts, D. P. Williams, H. Sabert, B. J. Mangan, D. M. Bird, T. A. Birks, J. C. Knight, and P. St. J. Russell, “Design of low-loss and highly birefringent hollow-core photonic crystal fiber,” Opt. Express14(16), 7329–7341 (2006). [CrossRef] [PubMed]
  11. V. Pureur, G. Bouwmans, K. Delplace, Y. Quiquempois, and M. Douay, “Birefringent solid-core photonic bandgap fibers assisted by interstitial air holes,” Appl. Phys. Lett.94(13), 131102 (2009). [CrossRef]
  12. T. R. Wolinski, A. Czapla, S. Ertman, M. Tefelska, A. Domanski, E. Nowinowski-Kruszelnicki, and R. Dabrowski, “Tunable highly birefringent solid-core photonic liquid crystal fibers,” Opt. Quantum Electron.39(12-13), 1021–1032 (2007). [CrossRef]
  13. X. B. Zheng, Y. G. Liu, Z. Wang, T. T. Han, C. L. Wei, and J. J. Chen, “Transmission and temperature sensing characteristics of a selectively liquid-filled photonic-bandgap-fiber-based Sagnac interferometer,” Appl. Phys. Lett.100(14), 141104 (2012). [CrossRef]
  14. G. Kim, T. Y. Cho, K. Hwang, K. Lee, K. S. Lee, Y. G. Han, and S. B. Lee, “Strain and temperature sensitivities of an elliptical hollow-core photonic bandgap fiber based on Sagnac interferometer,” Opt. Express17(4), 2481–2486 (2009). [CrossRef] [PubMed]
  15. L. M. Xiao, W. Jin, and M. S. Demokan, “Photonic crystal fibers confining light by both index-guiding and bandgap-guiding: hybrid PCFs,” Opt. Express15(24), 15637–15647 (2007). [CrossRef] [PubMed]
  16. R. Goto, S. D. Jackson, and K. Takenaga, “Single-polarization operation in birefringent all-solid hybrid microstructured fiber with additional stress applying parts,” Opt. Lett.34(20), 3119–3121 (2009). [CrossRef] [PubMed]
  17. A. Cucinotta, S. Selleri, L. Vincetti, and M. Zoboli, “Holey fiber analysis through the finite-element method,” IEEE Photon. Technol. Lett.14(11), 1530–1532 (2002). [CrossRef]
  18. B. T. Kuhlmey, B. J. Eggleton, and D. K. C. Wu, “Fluid-filled solid-core photonic bandgap fibers,” J. Lightwave Technol.27(11), 1617–1630 (2009). [CrossRef]

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