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Optics Express

Optics Express

  • Editor: C. Martijin de Sterke
  • Vol. 19, Iss. 7 — Mar. 28, 2011
  • pp: 5753–5759
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Packaged silica microsphere-taper coupling system for robust thermal sensing application

Ying-Zhan Yan, Chang-Ling Zou, Shu-Bin Yan, Fang-Wen Sun, Zhe Ji, Jun Liu, Yu-Guang Zhang, Li Wang, Chen-Yang Xue, Wen-Dong Zhang, Zheng-Fu Han, and Ji-Jun Xiong  »View Author Affiliations


Optics Express, Vol. 19, Issue 7, pp. 5753-5759 (2011)
http://dx.doi.org/10.1364/OE.19.005753


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Abstract

We propose and realize a novel packaged microsphere-taper coupling structure (PMTCS) with a high quality factor (Q) up to 5 × 106 by using the low refractive index (RI) ultraviolet (UV) glue as the coating material. The optical loss of the PMTCS is analyzed experimentally and theoretically, which indicate that the Q is limited by the glue absorption and the radiation loss. Moreover, to verify the practicability of the PMTCS, thermal sensing experiments are carried out, showing the excellent convenience and anti-jamming ability of the PMTCS with a high temperature resolution of 1.1 × 10−3°C. The experiments also demonstrate that the PMTCS holds predominant advantages, such as the robustness, mobility, isolation, and the PMTCS can maintain the high Q for a long time. The above advantages make the PMTCS strikingly attractive and potential in the fiber-integrated sensors and laser.

© 2011 Optical Society of America

1. Introduction

In this paper, for the first time, we propose and realize a novel packaged microsphere-taper coupling structure (PMTCS) experimentally. We demonstrate that the PMTCS can avoid the problems addressed above. The PMTCS is stable without 3D translation stages, robust against the vibration and free to move. Moreover, as a protective layer, the package body isolates the microsphere-taper from the surroundings, and maintains the Q above 106 for a long time. In addition, by using the PMTCS, we realize a high sensitive and robust fiber-integrated thermal sensor which is potential for the distributed sensor network.

2. Fabrication

In experiments, individual microspheres are fabricated with the diameter (D) ranging from 180μm to 650μm by melting the end of the optical fiber. WGMs are excited by a tunable laser (1550nm wavelength band, linewidth < 300kHz) through a fiber taper. And the gap between microsphere and taper is controlled by electromechanical 3D X-Y-Z stages with 20nm resolution, as shown in Fig. 1(a).

Fig. 1 (a)–(d) Illustration of the packaging process. (e) A micrograph of a typical PMTCS structure.

Fig. 2 (a) and (b) are contrast resonant spectra for a microsphere (D = 421μm) before and after the packaging, respectively. (c) Tested and fitted Q versus microsphere D.

Figure 1(e) shows a typical micrograph (side view) of a PMTCS (D = 340μm), in which the package body is asymmetric due to the gravity. As the backbone, the tapered fiber traverses across the package body to hold the PMTCS. At the package boundary (marked with blue triangles), there are two contact points which cause extra scattering loss (less than 20%). In the package experiments, the scattering loss can be reduced through using a shorter taper and encapsulating it completely. This is also an effective way to improve the robustness which is determined by the un-stretched single-model fiber after packaging while depending on the fragile taper for an unpackaged system. In addition, the evanescent decay length (d) of WGMs ( d=λ/(2πns2n2)1001[3], ns and n are the RI of the microsphere and the surroundings, respectively.) increases from 0.1516λ to 0.3008λ, which causes a larger field overlap between WGMs and the taper. This makes the critical coupling easier to fulfill for a thicker taper. Besides, the coating layer with the minimum thickness about 30μm (≫ d) ensures the complete isolation of WGMs from the outside, as shown in Fig. 1(e).

3. Test results and analysis

By comparing the spectra before and after the packaging, a red shift to the longer wavelength (S) has been observed, which can be estimated through S=λ2πD(1ns2ng21ns2nair2) [3

3. A. B. Matsko and V. S. Ilchenko, “Optical Resonators With Whispering-Gallery Modes-Part I: Basics,” IEEE J. Quantum Electron. 12, 3–14 (2006). [CrossRef]

], where nair is the air RI. For a microsphere with D ≈ 421μm, the S we observed is 2.35nm, which agrees well with theoretical prediction of 2.3nm, as shown in Fig. 2(a) and Fig. 2(b). The package can also eliminate high radial order WGMs and offer much more regular spectra. Because after the package, the relative RI (ns/n) decreases from 1.44 to 1.07, corresponding to an increase of the total reflection critical angle from 43.62 to 70.92 degree, which results in much larger leakage for high radial order WGMs [2

2. A. Chiasera, Y. Dumeige, P. Fron, M. Ferrari, Y. Jestin, G. Nunzi Conti, S. Pelli, S. Soria, and G. C. Righini, “Spherical whispering-gallery-mode microresonators,” Laser Photon. Rev. 4, 457–482 (2010). [CrossRef]

].

It is obvious that the package body isolates the whole coupling system from the surroundings, excluding Q spoiling factors from the dust and water in the air. As shown in Fig. 3(a), when exposing a microsphere in the air, the Q shows a quick decay due to the water absorption in a few minutes after its fabrication [13

13. M. L. Gorodetsky, A. A. Savchenkov, and V. S. Ilchenko, “Ultimate Q of optical microsphere resonators,” Opt. Lett. 21, 453–455 (1996). [CrossRef] [PubMed]

]. When putting it in the smoke, the Q has another remarkable decrease due to the scattering by the dust adhering to the surface. By contrast, the Q of PMTCS is much more stable and independent of the surrounding influences. In fact, we have maintained the Q above 106 for a few months. Thus, the package provides a feasible way to maintain the Q, paving the way for devices research in practical application.

Fig. 3 (a) Tested Q versus elapsed time of a microsphere coupling system in the air and in the smoke, for un-packaged (in black) and packaged (in red) samples, respectively. (b) WGM wavelength shifts as a function of the surrounding temperature, in NaCl resolution and in pure water, respectively.

4. Thermal sensing experiments

To verify the practicability of the PTMCS, thermal sensing experiments are carried out in complex dynamic water environment. A beaker containing 600ml water with a stirrer in it is adopted as the testing environment. The stirrer, not only helps to equalize the temperature, but also simulates a flowing water environment. A thermocouple and a heater are placed in the vicinity of the PMTCS, to measure and change the temperature, respectively.

The robustness is confirmed by the undisturbed spectra in the water flow. Furthermore, the completeness of the encapsulation is verified through the unshifted spectra when adding Sodium Chloride (NaCl) in the water gradually (keep the same temperature) to change the water RI about 2 × 10−3, which could cause a WGM wavelength shift about 20pm for an unpackaged silica microsphere [20

20. N. M. Hanumegowda, C. J. Stica, B. C. Patel, I. White, and X. Fan, “Refractometric sensors based on microsphere resonators,” Appl. Phys. Lett. 87, 201107 (2005). [CrossRef]

]. Wavelength shifts against the temperature are recorded, in saturated NaCl solution and in pure water, respectively. As shown in Fig. 3(b), wavelength shifts are not affected by RI changes of the water. The temperature variation leads to changes both in the size and the RI of the silica microsphere, which subsequently causes resonance wavelength shifts [21

21. B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96, 251109 (2010). [CrossRef]

24

24. Y. Wu, Y.-J. Rao, Y.-H. Chen, and Y. Gong, “Miniature fiber-optic temperature sensors based on silica/polymer microfiber knot resonators,” Opt. Express 17, 18142–18147 (2009). [CrossRef] [PubMed]

]. The resonant wavelength shows a red shift about 160.39 pm when the temperature increases from 14°C to 26°C, which indicates a sensitivity of 13.37pmC with a relevant coefficient in linear fitting about 0.998. Taking into account the spectral resolution (Δλmin) of our system, which is 0.015 pm, we estimate the resolution (ΔTmin = Δλmin/(/dT)) of the PMTCS microsphere temperature sensor as 1.1 × 10−3°C.

This resolution is in the same order of magnitude with the traditional silica microcavity thermal sensor [23

23. Q. Ma, T. Rossmann, and Z. Guo, “Temperature sensitivity of silica micro-resonators,” J. Phys. D: Appl. Phys. 41, 245111 (2008). [CrossRef]

]. What’s more, the practicability is greatly enhanced in the PMTCS, in which only the temperature change causes the WGM shift, while the change of external RI fails to cause the shift. Besides, the PMTCS thermal sensor shows an excellent anti-jamming ability, and can be used in harsh environments. Furthermore, the PMTCS can provide much more stable performance (for instance, the resolution) due to its superior Q maintenance ability. Additionally, the bulky translation stages are no longer unnecessary in the PMTCS. The portable structure makes these sensors easy to move and miniature, which is important in practical applications, especially in microsystem technology research.

Further efforts will be focused on exploring new package materials and improving the package technology to enhance the packaged Qtot. The PMTCS could be extended to multi-packaged microsphere-taper system on one fiber to monitor the real-time temperature at different locations, or package multi-microspheres in a certain point to study the classical analog to electromagnetic induced transparency (EIT), even its application on gyroscopic [25

25. Y.-F. Xiao, X.-B. Zou, W. Jiang, Y.-L. Chen, and G.-C. Guo, “Analog to multiple electromagnetically induced transparency in all-optical drop-filter systems,” Phys. Rev. A 75, 063833 (2007). [CrossRef]

, 26

26. J. Scheuer and A. Yariv, “Sagnac Effect in Coupled-Resonator Slow-Light Waveguide Structures,” Phys. Rev. Lett. 96, 053901 (2006). [CrossRef] [PubMed]

].

5. Conclusion

In summary, we have packaged silica microsphere-taper coupling systems by using the low RI UV glue. In our experiments, the (Q) of the packaged structure reaches 5 × 106 which is limited by the radiation loss and the glue absorption. The anti-jamming ability and the isolation performance in PMTCS are verified experimentally. Temperature sensing experiments are also carried out. The results show that the PMTCS possesses a high resolution of 1.1 × 10−3°C with the remarkable practicability, robustness and convenience. Not only the PMTCS can be applied to microcavity thermal sensors, but promote the developments of other microcavity-based devices, such as the low threshold laser.

Acknowledgments

Y. Z. Yan and C. L. Zou contributed equally to this work. The work was supported by the National Basic Research Program of China under Grant No. 2009CB326206, National Science Foundation of China under Grant Nos. 60707014, 60778029 and 50975266, and the Innovation Project under Grant Nos. 7130907, 9140C1204040909 and 9140C1204040706. Y. Z. Yan was also supported by Innovation Project (Grant Nos. 20093076 and 100115122).

References and links

1.

K. J. Vahala, “Optical microcavities,” Nature (London) 424, 839–846 (2003). [CrossRef]

2.

A. Chiasera, Y. Dumeige, P. Fron, M. Ferrari, Y. Jestin, G. Nunzi Conti, S. Pelli, S. Soria, and G. C. Righini, “Spherical whispering-gallery-mode microresonators,” Laser Photon. Rev. 4, 457–482 (2010). [CrossRef]

3.

A. B. Matsko and V. S. Ilchenko, “Optical Resonators With Whispering-Gallery Modes-Part I: Basics,” IEEE J. Quantum Electron. 12, 3–14 (2006). [CrossRef]

4.

F. Vollmer and S. Arnold, “Whispering-gallery-mode biosensing: label-free detection down to single molecules,” Nat. Methods 5, 591–596 (2008). [CrossRef] [PubMed]

5.

Y. Sun and X. Fan, “Analysis of ring resonators for chemical vapor sensor development,” Opt. Express 16, 10254–10268 (2008). [CrossRef] [PubMed]

6.

M. Sumetsky, R. S. Windeler, Y. Dulashko, and X. Fan, “Optical liquid ring resonator sensor,” Opt. Express 15, 14376–14381 (2007). [CrossRef] [PubMed]

7.

F. Xu, V. Pruneri, V. Finazzi, and G. Brambilla, “An embedded optical nanowire loop resonator refractometric sensor,” Opt. Express 16, 1062–1067 (2008). [CrossRef] [PubMed]

8.

F. Xu and G. Brambilla, “Demonstration of a refractometric sensor based on optical microfiber coil resonator,” Appl. Phys. Lett. 92, 101126 (2008). [CrossRef]

9.

I. M. White and X. Fan, “On the performance quantification of resonant refractive index sensors,” Opt. Express 16, 1020–1028 (2008). [CrossRef] [PubMed]

10.

M. Cai, O. Painter, and K. J. Vahala, “Observation of Critical Coupling in a Fiber Taper to a Silica-Microsphere Whispering-Gallery Mode System,” Phys. Rev. Lett. 85, 74–77 (2000). [CrossRef] [PubMed]

11.

J. C. Knight, G. Cheung, F. Jacques, and T. A. Birks, “Phase-matched excitation of whispering-gallery-mode resonances by a fiber taper,” Opt. Lett. 22, 1129–1131 (1997). [CrossRef] [PubMed]

12.

M. Hossein-Zadeh and K. J. Vahala, “Fiber-taper coupling to Whispering-Gallery modes of fluidic resonators embedded in a liquid medium,” Opt. Express 14, 10800–10810 (2006). [CrossRef] [PubMed]

13.

M. L. Gorodetsky, A. A. Savchenkov, and V. S. Ilchenko, “Ultimate Q of optical microsphere resonators,” Opt. Lett. 21, 453–455 (1996). [CrossRef] [PubMed]

14.

D. W. Vernooy, V. S. Ilchenko, H. Mabuchi, E. W. Streed, and H. J. Kimble, “High-Q measurements of fused-silica microspheres in the near infrared,” Opt. Lett. 23, 247–249 (1998). [CrossRef]

15.

A. M. Armani, D. K. Armani, B. Min, K. J. Vahala, and S. M. Spillane, “Ultra-high-Q microcavity operation in H2O and D2O,” Appl. Phys. Lett. 87, 151118 (2005). [CrossRef]

16.

C.-H. Dong, F.-W. Sun, C.-L. Zou, X.-F. Ren, G.-C. Guo, and Z.-F. Han, “High-Q silica microsphere by poly(ethyl methacrylate) coating and modifying,” Appl. Phys. Lett. 96, 061106 (2010). [CrossRef]

17.

M. L. Gorodetsky, A. D. Pryamikov, and V. S. Ilchenko, “Rayleigh scattering in high- Q microspheres,” J. Opt. Soc. Am. B 17, 1051–1057 (2000). [CrossRef]

18.

X.-W. Wu, C.-L. Zou, J. M. Cui, Y. Yang, Z.-F. Han, and G. C. Guo, “Modal coupling strength in a fibre taper coupled silica microsphere,” J. Phys. B: At. Mol. Opt. Phys. 42, 085401 (2009). [CrossRef]

19.

Y. Jung, G. S. Murugan, G. Brambilla, and D. J. Richardson, “Embedded optical microfiber coil resonator with enhanced high-Q,” IEEE Photon. Technol. Lett. 22, 1638–1640 (2010).

20.

N. M. Hanumegowda, C. J. Stica, B. C. Patel, I. White, and X. Fan, “Refractometric sensors based on microsphere resonators,” Appl. Phys. Lett. 87, 201107 (2005). [CrossRef]

21.

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96, 251109 (2010). [CrossRef]

22.

C.-H. Dong, L. He, Y.-F. Xiao, V. R. Gaddam, S. K. Ozdemir, Z.-F. Han, G.-C. Guo, and L. Yang, “Fabrication of high-Q polydimethylsiloxane optical microspheres for thermal sensing,” Appl. Phys. Lett. 94, 231119 (2009). [CrossRef]

23.

Q. Ma, T. Rossmann, and Z. Guo, “Temperature sensitivity of silica micro-resonators,” J. Phys. D: Appl. Phys. 41, 245111 (2008). [CrossRef]

24.

Y. Wu, Y.-J. Rao, Y.-H. Chen, and Y. Gong, “Miniature fiber-optic temperature sensors based on silica/polymer microfiber knot resonators,” Opt. Express 17, 18142–18147 (2009). [CrossRef] [PubMed]

25.

Y.-F. Xiao, X.-B. Zou, W. Jiang, Y.-L. Chen, and G.-C. Guo, “Analog to multiple electromagnetically induced transparency in all-optical drop-filter systems,” Phys. Rev. A 75, 063833 (2007). [CrossRef]

26.

J. Scheuer and A. Yariv, “Sagnac Effect in Coupled-Resonator Slow-Light Waveguide Structures,” Phys. Rev. Lett. 96, 053901 (2006). [CrossRef] [PubMed]

OCIS Codes
(230.3990) Optical devices : Micro-optical devices
(230.5750) Optical devices : Resonators
(280.4788) Remote sensing and sensors : Optical sensing and sensors

ToC Category:
Sensors

History
Original Manuscript: December 20, 2010
Revised Manuscript: February 24, 2011
Manuscript Accepted: February 24, 2011
Published: March 14, 2011

Citation
Ying-Zhan Yan, Chang-Ling Zou, Shu-Bin Yan, Fang-Wen Sun, Zhe Ji, Jun Liu, Yu-Guang Zhang, Li Wang, Chen-Yang Xue, Wen-Dong Zhang, Zheng-Fu Han, and Ji-Jun Xiong, "Packaged silica microsphere-taper coupling system for robust thermal sensing application," Opt. Express 19, 5753-5759 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-7-5753


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References

  1. K. J. Vahala, “Optical microcavities,” Nature 424, 839–846 (2003). [CrossRef]
  2. A. Chiasera, Y. Dumeige, P. Fron, M. Ferrari, Y. Jestin, G. Nunzi Conti, S. Pelli, S. Soria, and G. C. Righini, “Spherical whispering-gallery-mode microresonators,” Laser Photonics Rev. 4, 457–482 (2010). [CrossRef]
  3. A. B. Matsko and V. S. Ilchenko, “Optical Resonators With Whispering-Gallery Modes-Part I: Basics,” IEEE J. Quantum Electron. 12, 3–14 (2006). [CrossRef]
  4. F. Vollmer and S. Arnold, “Whispering-gallery-mode biosensing: label-free detection down to single molecules,” Nat. Methods 5, 591–596 (2008). [CrossRef] [PubMed]
  5. Y. Sun and X. Fan, “Analysis of ring resonators for chemical vapor sensor development,” Opt. Express 16, 10254–10268 (2008). [CrossRef] [PubMed]
  6. M. Sumetsky, R. S. Windeler, Y. Dulashko, and X. Fan, “Optical liquid ring resonator sensor,” Opt. Express 15, 14376–14381 (2007). [CrossRef] [PubMed]
  7. F. Xu, V. Pruneri, V. Finazzi, and G. Brambilla, “An embedded optical nanowire loop resonator refractometric sensor,” Opt. Express 16, 1062–1067 (2008). [CrossRef] [PubMed]
  8. F. Xu and G. Brambilla, “Demonstration of a refractometric sensor based on optical microfiber coil resonator,” Appl. Phys. Lett. 92, 101126 (2008). [CrossRef]
  9. I. M. White and X. Fan, “On the performance quantification of resonant refractive index sensors,” Opt. Express 16, 1020–1028 (2008). [CrossRef] [PubMed]
  10. M. Cai, O. Painter, and K. J. Vahala, “Observation of Critical Coupling in a Fiber Taper to a Silica-Microsphere Whispering-Gallery Mode System,” Phys. Rev. Lett. 85, 74–77 (2000). [CrossRef] [PubMed]
  11. J. C. Knight, G. Cheung, F. Jacques, and T. A. Birks, “Phase-matched excitation of whispering-gallery-mode resonances by a fiber taper,” Opt. Lett. 22, 1129–1131 (1997). [CrossRef] [PubMed]
  12. M. Hossein-Zadeh and K. J. Vahala, “Fiber-taper coupling to Whispering-Gallery modes of fluidic resonators embedded in a liquid medium,” Opt. Express 14, 10800–10810 (2006). [CrossRef] [PubMed]
  13. M. L. Gorodetsky, A. A. Savchenkov, and V. S. Ilchenko, “Ultimate Q of optical microsphere resonators,” Opt. Lett. 21, 453–455 (1996). [CrossRef] [PubMed]
  14. D. W. Vernooy, V. S. Ilchenko, H. Mabuchi, E. W. Streed, and H. J. Kimble, “High-Q measurements of fused-silica microspheres in the near infrared,” Opt. Lett. 23, 247–249 (1998). [CrossRef]
  15. A. M. Armani, D. K. Armani, B. Min, K. J. Vahala, and S. M. Spillane, “Ultra-high-Q microcavity operation in H2O and D2O,” Appl. Phys. Lett. 87, 151118 (2005). [CrossRef]
  16. C.-H. Dong, F.-W. Sun, C.-L. Zou, X.-F. Ren, G.-C. Guo, and Z.-F. Han, “High-Q silica microsphere by poly(ethyl methacrylate) coating and modifying,” Appl. Phys. Lett. 96, 061106 (2010). [CrossRef]
  17. M. L. Gorodetsky, A. D. Pryamikov, and V. S. Ilchenko, “Rayleigh scattering in high- Q microspheres,” J. Opt. Soc. Am. B 17, 1051–1057 (2000). [CrossRef]
  18. X.-W. Wu, C.-L. Zou, J. M. Cui, Y. Yang, Z.-F. Han, and G. C. Guo, “Modal coupling strength in a fibre taper coupled silica microsphere,” J. Phys. B: At. Mol. Opt. Phys. 42, 085401 (2009). [CrossRef]
  19. Y. Jung, G. S. Murugan, G. Brambilla, and D. J. Richardson, “Embedded optical microfiber coil resonator with enhanced high-Q,” IEEE Photon. Technol. Lett. 22, 1638–1640 (2010).
  20. N. M. Hanumegowda, C. J. Stica, B. C. Patel, I. White, and X. Fan, “Refractometric sensors based on microsphere resonators,” Appl. Phys. Lett. 87, 201107 (2005). [CrossRef]
  21. B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96, 251109 (2010). [CrossRef]
  22. C.-H. Dong, L. He, Y.-F. Xiao, V. R. Gaddam, S. K. Ozdemir, Z.-F. Han, G.-C. Guo, and L. Yang, “Fabrication of high-Q polydimethylsiloxane optical microspheres for thermal sensing,” Appl. Phys. Lett. 94, 231119 (2009). [CrossRef]
  23. Q. Ma, T. Rossmann, and Z. Guo, “Temperature sensitivity of silica micro-resonators,” J. Phys. D: Appl. Phys. 41, 245111 (2008). [CrossRef]
  24. Y. Wu, Y.-J. Rao, Y.-H. Chen, and Y. Gong, “Miniature fiber-optic temperature sensors based on silica/polymer microfiber knot resonators,” Opt. Express 17, 18142–18147 (2009). [CrossRef] [PubMed]
  25. Y.-F. Xiao, X.-B. Zou, W. Jiang, Y.-L. Chen, and G.-C. Guo, “Analog to multiple electromagnetically induced transparency in all-optical drop-filter systems,” Phys. Rev. A 75, 063833 (2007). [CrossRef]
  26. J. Scheuer and A. Yariv, “Sagnac Effect in Coupled-Resonator Slow-Light Waveguide Structures,” Phys. Rev. Lett. 96, 053901 (2006). [CrossRef] [PubMed]

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