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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 25 — Dec. 6, 2010
  • pp: 25657–25664
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Design of a highly-birefringent microstructured photonic crystal fiber for pressure monitoring

Charles M. Jewart, Sully Mejía Quintero, Arthur M. B. Braga, and Kevin P. Chen  »View Author Affiliations


Optics Express, Vol. 18, Issue 25, pp. 25657-25664 (2010)
http://dx.doi.org/10.1364/OE.18.025657


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Abstract

We present the design of an air hole microstructured photonic crystal fiber for pressure sensing applications. The air-hole photonic crystal lattices were designed to produce a large intrinsic birefringence of 1.16x10-3. The impact of the surrounding air holes for pressure sensing to the propagation mode profiles and indices were studied and improved, which ensures single mode propagation in the fiber core defined by the photonic crystal lattice. An air hole matrix and a practical chemical etching process during the fiber perform preparation stage is proposed to produce an optical fiber with a birefringence-pressure coefficient of 43.89x10-6MPa-1 or a fiber Bragg grating pressure responsivity of 44.15 pm/MPa, which is a 17 times improvement over previous photonic crystal fiber designs.

© 2010 OSA

1. Introduction

Fiber sensors based on air-hole microstructured fibers have received considerable attention recently for their versatility in tuning mechanical, thermal, and optical properties through the design of the fiber. This flexibility has enabled the fabrication of many new and exciting fibers with unique properties that are unattainable in conventional fibers. For example, in many fiber sensing applications, polarization maintaining (PM) fibers are desired because they provide a better signal-to-noise ratio and allow for simplification of the measurements. Using air-hole microstructured designs, PM fibers with birefringences in excess of 1×10-3 [1

1. T. Nasilowski, T. Martynkien, G. Statkiewicz, M. Szpulak, J. Olszewski, G. Golojuch, W. Urbanczyk, J. Wojcik, P. Mergo, M. Makara, F. Berghmans, and H. Thienpont, “Temperature and pressure sensitivities of the highly birefringent photonic crystal fiber with core asymmetry,” Appl. Phys. B 81(2-3), 325–331 (2005). [CrossRef]

5

5. S. Barkou Libori, J. Broeng, E. Knudsen, A. Bjarklev, and H. R. Simonsen, "High-birefringent photonic crystal fiber," OFC2001. Optical Fiber Communication Conference and Exhibit. Technical Digest Postconference Edition. (IEEE, 2001) pp. TuM2-1-3

] can be readily manufactured, which is more than an order of magnitude than that of conventional fibers.

Given the importance of PM fibers, a number of air-hole fiber designs have been proposed and studied. PM fibers derived from Panda fiber with a hexagonal air-hole lattice have become commercially available [6

6. NKT Photonics - Photonic Crystal Fibers, SuperK Continuum Laser, Koheras Fiber Lasers, http://www.blazephotonics.com

]. Fiber sensors based on these types of fibers have been extensively reported.

A review of prior research on photonic crystal fiber (PCF) design and sensor implementation shows that the research focus was placed on the design of an air-hole lattice to achieve a high birefringence. Their suitability for sensing applications was not a priority during the design of the fiber. Due to this reason, fiber sensors using commercially available polarization maintaining photonic crystal fibers (PM-PCF) have lower sensitivities than those using conventional fibers. For example, pressure sensors using PM-PCF [7

7. H. K. Gahir and D. Khanna, “Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm,” Appl. Opt. 46(8), 1184–1189 (2007). [CrossRef] [PubMed]

9

9. F. C. Fávero, S. M. M. Quintero, V. V. Silva, C. Martelli, A. M. B. Braga, I. C. S. Carvalho, and R. W. A. Llerena, “Photonic crystal fiber pressure sensor,” Proc. SPIE 7503, 750364 (2009). [CrossRef]

] have 5.44 times lower birefringence-pressure sensitivities than that of two-hole solid-core optical fibers. Thus, some research efforts were devoted to design PM-PCF with better pressure sensitivity [10

10. M. Szpulak, T. Martynkien, and W. Urbanczyk, “Highly birefringent photonic crystal fibre with enhanced sensitivity to hydrostatic pressure,” 2006 International Conference on Transparent Optical Networks, (ICTON, 2006) pp. 174-177.

,11

11. T. Martynkien, G. Statkiewicz-Barabach, J. Olszewski, J. Wojcik, P. Mergo, T. Geernaert, C. Sonnenfeld, A. Anuszkiewicz, M. K. Szczurowski, K. Tarnowski, M. Makara, K. Skorupski, J. Klimek, K. Poturaj, W. Urbanczyk, T. Nasilowski, F. Berghmans, and H. Thienpont, “Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure,” Opt. Express 18(14), 15113–15121 (2010). [CrossRef] [PubMed]

].

In this paper, we present the design and numerical simulation of a PM-PCF to achieve the best possible pressure sensitivity. Simultaneously, we considered the optical properties of the air-hole PCF matrix to achieve an initial high birefringence and side hole array to maximize the sensor’s sensitivity.

2. PCF fiber design

The fiber was designed to be in single-mode operation at 1550 nm and at the same time to have large intrinsic birefringence. The air-hole matrix design is based on a square lattice, which can be modified to exhibit large birefringence [12

12. S. Kim, C. S. Kee, and C. G. Lee, “Modified rectangular lattice photonic crystal fibers with high birefringence and negative dispersion,” Opt. Express 17(10), 7952–7957 (2009). [CrossRef] [PubMed]

]. The air hole matrix has a 1.34μm pitch (Λ) and 0.66 μm hole diameter (d), respectively based on an existing PCF design [13

13. C. Martelli, J. Canning, N. Groothoff, and K. Lyytikainen, “Strain and temperature characterization of photonic crystal fiber Bragg gratings,” Opt. Lett. 30(14), 1785–1787 (2005). [CrossRef] [PubMed]

]. These values led to an effective cladding index of 1.4 [14

14. R. Ghosh, A. Kumar, J. P. Meunier, and E. Marin, “Modal characteristics of few-mode silica-based photonic crystal fibres,” Opt. Quantum Electron. 32(6/8), 963–970 (2000). [CrossRef]

]. To form a fiber core, a single air hole in the middle row was taken out to create the fiber core. The asymmetry was introduced by displacing the central row of air holes on both sides of the fiber core by 0.46 μm. This displacement value was determined from the V-number calculation [14

14. R. Ghosh, A. Kumar, J. P. Meunier, and E. Marin, “Modal characteristics of few-mode silica-based photonic crystal fibres,” Opt. Quantum Electron. 32(6/8), 963–970 (2000). [CrossRef]

] that a core radius of 1.9 μm was the largest possible size to retain single-mode operation. All dimensions were measured from the center of the fiber core to the center of the adjacent air hole. This resulted in the core having radii of 1.99 μm and 1.34 μm along the x and y axis, respectively. This photonic crystal lattice design ensures single mode operation at 1550 nm with an intrinsic birefringence of 8.04x10-4, this is obtained by the finite element analysis using COMSOL package using 3 rows of air holes above and below the fiber core.

Figure 2
Fig. 2 Electric field distribution of the fundamental mode for x (left) and y (right) polarizations, the black scale bar in the figure indicate 5 μm. The color scale bar indicates relative intensity of guided mode electric fields.
shows the electrical field distribution of the fundamental mode for x and y polarization with the air hole radius of 11.629 μm. The distance between the edges of the large air hole to the center of the upper row of air hole matrix is 0.66 μm. The index of refraction of silica was calculated using the three-term Sellmeier polynomial [18

18. I. H. Malitson, “Interspecimen Comparison of the Refractive Index of Fused Silica,” J. Opt. Soc. Am. 55(10), 1205–1209 (1965). [CrossRef]

] where it was assumed to have a refractive index of n = 1.44504 at 1550 nm, while the air-holes had a refractive index of n = 1. The resulting initial birefringence for the two-hole PCF with the asymmetric core at 1550 nm is 1.16x10-3. The electric field distributions of the fundamental mode for the x (no=1.406739) and y (no=1.405579) polarizations are presented in Fig. 2. The introduction of two air holes actually increases the birefringence to 1.16x10-3, which is 1.44 times larger than the fiber core that used three rows of air holes for the optical confinement.

Numerical simulation also reveals that the air hole lattice cannot support a well confined single mode if only one or two rows of air holes were used above and below the fiber core, due to reduced index contrast between the fiber core and the effective cladding index. This is confirmed in Fig. 3
Fig. 3 Electric field distribution of the fundamental mode for x (left) and y (right) polarizations for single-row PCF matrix in the center region of the fiber, the black scale bar indicates 5 μm. The color scale bar indicates relative intensity of guided mode electric fields.
for the case of one row of air holes.

As the radius of curvature for the air-hole increases the indices of refraction for the two polarization modes decrease exponentially. The fiber remains in single mode operation up to an air-hole radius of 19 μm, at this limit, higher order modes begin to appear. The fiber that possessed the large air-hole with a radius of 11.629 μm possessed effective indices of refraction of 1.406739 and 1.405579 for the two orthogonal polarized modes, respectively, which results in a birefringence of 1.160x10-3. The fiber birefringence changes to1.165x10-3 when the radius of air hole increases to 18 μm.

3. Fiber optimization for hydrostatic pressure sensing

dBdP=BLoadedBunloadedP,
(2)

To increase the sensitivity of the fiber while maintaining single-mode operation for the PCF fiber core, a row of smaller air holes are added to the cladding, which extends from the out-edge of the 30 µm air hole to the edge of the fiber as shown in Fig. 6
Fig. 6 Multi-hole fiber geometry (left), etched fiber geometry (right)
. This row of air holes has diameters of 5.68 μm and 0.5 μm spacing, which is manufacturable in the fiber perform preparation stage. The addition of air holes has no impact on the single-mode operation of the PCF core, while increasing the compressive stress in the x-polarization in the core region. It is also possible to increase the fiber sensitivity by etching away the silica bridge between two adjacent air holes using a buffered oxide etching (BOE) process [15

15. C. Jewart and D. Xu, “J. Canning and K. P. Chen, “Structure optimization of air-hole fibers for high-sensitivity fiber Bragg grating pressure sensors,” Proc. SPIE 7004, 70041Z (2008). [CrossRef]

]. This can be accomplished in the fiber perform before the drawing process, with the core region being able to be sealed from the BOE process. The etching process will remove the silica bridges by etching an amount of the small air holes as shown in Fig. 4b, which improves the pressure transduction into the core region.

Figure. 7
Fig. 7 Stress profile for x-component of stress for the Multi-hole Fiber before (left) and after (right) chemical etching, the color bar has unit of MPa
presents the finite element analysis (FEA) stress analysis of the air-hole fibers before and after etching along x-axis, which is the dominant stress component. The etching process leads to significant increase of compressive stress along x-axis in the core region. The average compressive stress over the entire PCF core region is increased by 2.55 times (from -119.947 to -304.328 at 20 MPa).

4. Summary and conclusion

In this paper, we presented an air hole matrix in the fiber cladding and a practical chemical etching process during the fiber perform preparation stage to produce a highly birefringent photonic crystal fiber with a birefringence-pressure coefficient of 43.89x10-6MPa-1 or a FBG pressure responsivity of 44.15 pm/MPa.

Acknowledgements

This work was supported by a National Science Foundation career program (NSF0644681), C. M. Jewart is supported by a NSF IGERT Program with the Mascaro Center for Sustainable Innovation (NSF0504345). Kevin P. Chen’s e-mail address is pec9@pitt.edu. C. M. Jewart and S. M. Quintero contributed equally to this work.

References and Links

1.

T. Nasilowski, T. Martynkien, G. Statkiewicz, M. Szpulak, J. Olszewski, G. Golojuch, W. Urbanczyk, J. Wojcik, P. Mergo, M. Makara, F. Berghmans, and H. Thienpont, “Temperature and pressure sensitivities of the highly birefringent photonic crystal fiber with core asymmetry,” Appl. Phys. B 81(2-3), 325–331 (2005). [CrossRef]

2.

M. Szpulak, T. Martynkien, and W. Urbanczyk, “Effects of hydrostatic pressure on phase and group modal birefringence in microstructured holey fibers,” Appl. Opt. 43(24), 4739–4744 (2004). [CrossRef] [PubMed]

3.

M. Szpulak, G. Statkiewicz, J. Olszewski, T. Martynkien, W. Urbańczyk, J. Wójcik, M. Makara, J. Klimek, T. Nasilowski, F. Berghmans, and H. Thienpont, “Experimental and theoretical investigations of birefringent holey fibers with a triple defect,” Appl. Opt. 44(13), 2652–2658 (2005). [CrossRef] [PubMed]

4.

M. Antkowiak, R. Kotynski, T. Nasilowski, P. Lesiak, J. Wojcik, W. Urbanczyk, F. Berghmans, and H. Thienpont, “Phase and group modal birefringence of triple-defect photonic crystal fibres,” J. Opt. A, Pure Appl. Opt. 7(12), 763–766 (2005). [CrossRef]

5.

S. Barkou Libori, J. Broeng, E. Knudsen, A. Bjarklev, and H. R. Simonsen, "High-birefringent photonic crystal fiber," OFC2001. Optical Fiber Communication Conference and Exhibit. Technical Digest Postconference Edition. (IEEE, 2001) pp. TuM2-1-3

6.

NKT Photonics - Photonic Crystal Fibers, SuperK Continuum Laser, Koheras Fiber Lasers, http://www.blazephotonics.com

7.

H. K. Gahir and D. Khanna, “Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm,” Appl. Opt. 46(8), 1184–1189 (2007). [CrossRef] [PubMed]

8.

H. Y. Tam, S. K. Khijwania, and X. Y. Dong, "Temperature-Insensitive Pressure Sensor using a Polarization-Maintaining Photonic Crystal Fiber based Sagnac Interferometer," 2007 Asia Optical Fiber Communication and Optoelectronics Conference, (IEEE, 2007) pp. 345-347.

9.

F. C. Fávero, S. M. M. Quintero, V. V. Silva, C. Martelli, A. M. B. Braga, I. C. S. Carvalho, and R. W. A. Llerena, “Photonic crystal fiber pressure sensor,” Proc. SPIE 7503, 750364 (2009). [CrossRef]

10.

M. Szpulak, T. Martynkien, and W. Urbanczyk, “Highly birefringent photonic crystal fibre with enhanced sensitivity to hydrostatic pressure,” 2006 International Conference on Transparent Optical Networks, (ICTON, 2006) pp. 174-177.

11.

T. Martynkien, G. Statkiewicz-Barabach, J. Olszewski, J. Wojcik, P. Mergo, T. Geernaert, C. Sonnenfeld, A. Anuszkiewicz, M. K. Szczurowski, K. Tarnowski, M. Makara, K. Skorupski, J. Klimek, K. Poturaj, W. Urbanczyk, T. Nasilowski, F. Berghmans, and H. Thienpont, “Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure,” Opt. Express 18(14), 15113–15121 (2010). [CrossRef] [PubMed]

12.

S. Kim, C. S. Kee, and C. G. Lee, “Modified rectangular lattice photonic crystal fibers with high birefringence and negative dispersion,” Opt. Express 17(10), 7952–7957 (2009). [CrossRef] [PubMed]

13.

C. Martelli, J. Canning, N. Groothoff, and K. Lyytikainen, “Strain and temperature characterization of photonic crystal fiber Bragg gratings,” Opt. Lett. 30(14), 1785–1787 (2005). [CrossRef] [PubMed]

14.

R. Ghosh, A. Kumar, J. P. Meunier, and E. Marin, “Modal characteristics of few-mode silica-based photonic crystal fibres,” Opt. Quantum Electron. 32(6/8), 963–970 (2000). [CrossRef]

15.

C. Jewart and D. Xu, “J. Canning and K. P. Chen, “Structure optimization of air-hole fibers for high-sensitivity fiber Bragg grating pressure sensors,” Proc. SPIE 7004, 70041Z (2008). [CrossRef]

16.

S. Kreger, S. Calvert, and E. Udd, "High Pressure Sensing Using Fiber Bragg Gratings Written into Birefringent Side Hole Fiber," 2002 15th Optical Fiber Sensors Conference Technical Digest. (IEEE, 2002), pp. 355-358.

17.

J. R. Clowes, S. Syngellakis, and M. N. Zervas, “Pressure Sensitivity of Side-Hole Optical Fibers,” IEEE Photon. Technol. Lett. 10(6), 857–859 (1998). [CrossRef]

18.

I. H. Malitson, “Interspecimen Comparison of the Refractive Index of Fused Silica,” J. Opt. Soc. Am. 55(10), 1205–1209 (1965). [CrossRef]

19.

W. Urbanczyk, T. Martynkien, and W. J. Bock, “Dispersion effects in elliptical-core highly birefringent fibers,” Appl. Opt. 40(12), 1911–1920 (2001). [CrossRef]

20.

J. Noda, K. Okamoto, and Y. Sasaki, “Polarization maintaining fibers and their applications,” J. Lightwave Technol. 4(8), 1071–1089 (1986). [CrossRef]

OCIS Codes
(000.4430) General : Numerical approximation and analysis
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(060.4005) Fiber optics and optical communications : Microstructured fibers
(060.5295) Fiber optics and optical communications : Photonic crystal fibers

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: September 14, 2010
Revised Manuscript: November 4, 2010
Manuscript Accepted: November 5, 2010
Published: November 23, 2010

Citation
Charles M. Jewart, Sully Mejía Quintero, Arthur M. B. Braga, and Kevin P. Chen, "Design of a highly-birefringent microstructured photonic crystal fiber for pressure monitoring," Opt. Express 18, 25657-25664 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-25-25657


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References

  1. T. Nasilowski, T. Martynkien, G. Statkiewicz, M. Szpulak, J. Olszewski, G. Golojuch, W. Urbanczyk, J. Wojcik, P. Mergo, M. Makara, F. Berghmans, and H. Thienpont, “Temperature and pressure sensitivities of the highly birefringent photonic crystal fiber with core asymmetry,” Appl. Phys. B 81(2-3), 325–331 (2005). [CrossRef]
  2. M. Szpulak, T. Martynkien, and W. Urbanczyk, “Effects of hydrostatic pressure on phase and group modal birefringence in microstructured holey fibers,” Appl. Opt. 43(24), 4739–4744 (2004). [CrossRef] [PubMed]
  3. M. Szpulak, G. Statkiewicz, J. Olszewski, T. Martynkien, W. Urbańczyk, J. Wójcik, M. Makara, J. Klimek, T. Nasilowski, F. Berghmans, and H. Thienpont, “Experimental and theoretical investigations of birefringent holey fibers with a triple defect,” Appl. Opt. 44(13), 2652–2658 (2005). [CrossRef] [PubMed]
  4. M. Antkowiak, R. Kotynski, T. Nasilowski, P. Lesiak, J. Wojcik, W. Urbanczyk, F. Berghmans, and H. Thienpont, “Phase and group modal birefringence of triple-defect photonic crystal fibres,” J. Opt. A, Pure Appl. Opt. 7(12), 763–766 (2005). [CrossRef]
  5. S. Barkou Libori, J. Broeng, E. Knudsen, A. Bjarklev, and H. R. Simonsen, "High-birefringent photonic crystal fiber," OFC2001. Optical Fiber Communication Conference and Exhibit. Technical Digest Postconference Edition. (IEEE, 2001) pp. TuM2-1-3
  6. NKT Photonics - Photonic Crystal Fibers, SuperK Continuum Laser, Koheras Fiber Lasers, http://www.blazephotonics.com
  7. H. K. Gahir and D. Khanna, “Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm,” Appl. Opt. 46(8), 1184–1189 (2007). [CrossRef] [PubMed]
  8. H. Y. Tam, S. K. Khijwania, and X. Y. Dong, "Temperature-Insensitive Pressure Sensor using a Polarization-Maintaining Photonic Crystal Fiber based Sagnac Interferometer," 2007 Asia Optical Fiber Communication and Optoelectronics Conference, (IEEE, 2007) pp. 345-347.
  9. F. C. Fávero, S. M. M. Quintero, V. V. Silva, C. Martelli, A. M. B. Braga, I. C. S. Carvalho, and R. W. A. Llerena, “Photonic crystal fiber pressure sensor,” Proc. SPIE 7503, 750364 (2009). [CrossRef]
  10. M. Szpulak, T. Martynkien, and W. Urbanczyk, “Highly birefringent photonic crystal fibre with enhanced sensitivity to hydrostatic pressure,” 2006 International Conference on Transparent Optical Networks, (ICTON, 2006) pp. 174-177.
  11. T. Martynkien, G. Statkiewicz-Barabach, J. Olszewski, J. Wojcik, P. Mergo, T. Geernaert, C. Sonnenfeld, A. Anuszkiewicz, M. K. Szczurowski, K. Tarnowski, M. Makara, K. Skorupski, J. Klimek, K. Poturaj, W. Urbanczyk, T. Nasilowski, F. Berghmans, and H. Thienpont, “Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure,” Opt. Express 18(14), 15113–15121 (2010). [CrossRef] [PubMed]
  12. S. Kim, C. S. Kee, and C. G. Lee, “Modified rectangular lattice photonic crystal fibers with high birefringence and negative dispersion,” Opt. Express 17(10), 7952–7957 (2009). [CrossRef] [PubMed]
  13. C. Martelli, J. Canning, N. Groothoff, and K. Lyytikainen, “Strain and temperature characterization of photonic crystal fiber Bragg gratings,” Opt. Lett. 30(14), 1785–1787 (2005). [CrossRef] [PubMed]
  14. R. Ghosh, A. Kumar, J. P. Meunier, and E. Marin, “Modal characteristics of few-mode silica-based photonic crystal fibres,” Opt. Quantum Electron. 32(6/8), 963–970 (2000). [CrossRef]
  15. C. Jewart and D. Xu, “J. Canning and K. P. Chen, “Structure optimization of air-hole fibers for high-sensitivity fiber Bragg grating pressure sensors,” Proc. SPIE 7004, 70041Z (2008). [CrossRef]
  16. S. Kreger, S. Calvert, and E. Udd, "High Pressure Sensing using Fiber Bragg Gratings Written into Birefringent Side Hole Fiber," 2002 15th Optical Fiber Sensors Conference Technical Digest. (IEEE, 2002), pp. 355-358.
  17. J. R. Clowes, S. Syngellakis, and M. N. Zervas, “Pressure Sensitivity of Side-Hole Optical Fibers,” IEEE Photon. Technol. Lett. 10(6), 857–859 (1998). [CrossRef]
  18. I. H. Malitson, “Interspecimen Comparison of the Refractive Index of Fused Silica,” J. Opt. Soc. Am. 55(10), 1205–1209 (1965). [CrossRef]
  19. W. Urbanczyk, T. Martynkien, and W. J. Bock, “Dispersion effects in elliptical-core highly birefringent fibers,” Appl. Opt. 40(12), 1911–1920 (2001). [CrossRef]
  20. J. Noda, K. Okamoto, and Y. Sasaki, “Polarization maintaining fibers and their applications,” J. Lightwave Technol. 4(8), 1071–1089 (1986). [CrossRef]

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