Abstract

We demonstrate a new method to tune the resonance of whispering gallery modes in a fused silica optical microsphere resonator by removing atomic layers from the sphere surface with low concentrations of hydrofluoric acid. Our results show that the WGMs can be tuned over 660 pm (430 GHz), more than one free spectral range of the microsphere resonator, with a tuning precision better than 0.2 pm (130 MHz). Both atomic force microscope images and a Q-factor measurement performed in air suggest that no additional degradation in Q-factor due to surface roughness is introduced during this etching process.

© 2005 Optical Society of America

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References

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  1. R. K. Chang and A. J. Campillo, eds., Optical Processes in Microcavities (World Scientific, Singapore, 1996).
    [CrossRef]
  2. K. J. Vahala, "Optical microcavities," Nature 424, 839-846 (2003).
    [CrossRef] [PubMed]
  3. Biophotonics/Optical Interconnects and VLSI Photonics/WBM Microcavities, 2004 Digest of the LEOS Summer Topical Meeting (IEEE, Piscataway, NJ, 2004).
  4. F. Vollmer, D. Braun, and A. Libchaber, "Protein detection by optical shift of a resonant microcavity," Appl. Phys. Lett. 80, 4057-4059 (2002).
    [CrossRef]
  5. F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, "Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities," Biophys. J. 85, 1974-1979 (2003).
    [CrossRef] [PubMed]
  6. J. L. Nadeau, V. S. Ilchenko, D. Kossakovski, G. H. Bearman, L. Maleki, "High-Q whispering-gallery mode sensor in liquids," in Laser Resonators and Beam Control V, A. V. Kudryashov, ed., Proc. SPIE 4629, 172-180 (2002).
    [CrossRef]
  7. I. M. White, N. M. Hanumegowda, and X. Fan, "Sub-femtomole detection of small molecules with microsphere sensors," Opt. Lett. (to be published).
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  8. N. M. Hanumegowda, I. White, and X. Fan, "Aqueous mercuric ion detection with microsphere optical ring resonator sensors," Sens. Actuators, B, (submitted).
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Appl. Phys. Lett. (1)

F. Vollmer, D. Braun, and A. Libchaber, "Protein detection by optical shift of a resonant microcavity," Appl. Phys. Lett. 80, 4057-4059 (2002).
[CrossRef]

Biophys. J. (1)

F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, "Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities," Biophys. J. 85, 1974-1979 (2003).
[CrossRef] [PubMed]

Europhys. Lett. (1)

L. Collot, V. Lefevre-Seguin, M. Brune, J. -M. Raimond, and S. Haroche, "Very high-Q whispering-gallery mode resonances observed on fused silica microspheres," Europhys. Lett. 23, 327-334 (1993).
[CrossRef]

J. Opt. Soc. Am. B (1)

Laser Resonators and Beam Control V (1)

J. L. Nadeau, V. S. Ilchenko, D. Kossakovski, G. H. Bearman, L. Maleki, "High-Q whispering-gallery mode sensor in liquids," in Laser Resonators and Beam Control V, A. V. Kudryashov, ed., Proc. SPIE 4629, 172-180 (2002).
[CrossRef]

Nature (1)

K. J. Vahala, "Optical microcavities," Nature 424, 839-846 (2003).
[CrossRef] [PubMed]

Opt. Commun. (1)

V. S. Ilchenko, P. S. Volikov, V. L. Velichansky, F. Treussart, V. Lefevre-Seguin, J. -M. Raimond, and S. Haroche, "Strain-tunable high-Q optical microsphere resonator," Opt. Commun. 145, 86-90 (1998).
[CrossRef]

Opt. Express (1)

Opt. Lett. (7)

Sens. Actuators, B (1)

N. M. Hanumegowda, I. White, and X. Fan, "Aqueous mercuric ion detection with microsphere optical ring resonator sensors," Sens. Actuators, B, (submitted).

Other (2)

Biophotonics/Optical Interconnects and VLSI Photonics/WBM Microcavities, 2004 Digest of the LEOS Summer Topical Meeting (IEEE, Piscataway, NJ, 2004).

R. K. Chang and A. J. Campillo, eds., Optical Processes in Microcavities (World Scientific, Singapore, 1996).
[CrossRef]

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Figures (6)

Fig. 1.
Fig. 1.

A conceptual illustration of multiplexed detection using optical microspheres

Fig. 2.
Fig. 2.

(a) The resonances of three adjacent azimuthal WGMs shift to lower wavelengths when HF etches spheres of r = 135 μm (solid line) and r = 62.5 μm (dashed line). (b) Size dependent WGM spectral shift rate. HF concentration for both (a) and (b): 0.1% (v/v). Upper inset: Concentration dependent WGM shift rate for an r = 90 μm sphere. Lower inset: the etching process can be promptly changed by diluting HF solution. Arrow indicates when DI water is added to dilute HF.

Fig. 3.
Fig. 3.

WGM initially at position (I) is tuned to a new position (II) to match another WGM whose position (III) is arbitrarily chosen and pre-recorded. Inset (A): WGM tuning is achieved by an initial fast etching followed by multiple dilutions of HF. The etching process is terminated at the final step by rinsing the HF off the fluidic well. Inset (B): The fluctuation in resultant spectral position is less than 0.2 pm.

Fig. 4.
Fig. 4.

WGM can be tuned over one FSR of an r = 100 μm sphere.

Fig. 5.
Fig. 5.

AFM images of the surface of the unetched (A) and etched (B) sphere. Histogram analysis on the right side of the images shows the roughness σ is 0.53 nm and 0.77 nm for (A) and (B), respectively.

Fig. 6.
Fig. 6.

Normalized WGM scattering spectra when the sphere is in air. (a) before etching. Q = 1×107 and 1.5×107 when the sphere is in contact (upper curve) and when the sphere is out of contact with the taper, respectively; (b) after etching. Q = 1×107 and 2.3×107 when the sphere is in contact (upper curve) and when the sphere is out of contact with the taper, respectively.

Equations (2)

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δλ λ = δr r
( Q c γ ) 1 + Q 0 1 = Q 1 ,

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