The authors would like to thank Xuan Du for constructing the conceptual diagram of Figure 1. This work was funded by grants from the Natural Science and Engineering Research Council (NSERC) of Canada.

1. Reference Interferometer Construction and FSR Measurement
<ol>
	<li>Construction
	<ol>
		<li>Create an open-top acrylic box. This structure should be large enough to fit snugly into a 16 in x 16 in x 16 in Styrofoam box.</li>
		<li>Fabricate a 3-stage shelving unit to house optical components, which will sit in the open-top acrylic box and will be completely enclosed by the Styrofoam box for thermal isolation. Two elevated holes on the Styrofoam box must be present to allow for fibers to enter and exit the entire en...

<ol>
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Lett. 99 (7), 073701 (2011).</li><li>Swaim, J. D., Knittel, J., Bowen, W. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+limits+in+whispering+gallery+biosensors+with+plasmonic+enhancement.">Detection limits in whispering gallery biosensors with plasmonic enhancement.</a> Appl. Phys. Lett. 99 (24), 243109 (2011).</li><li>Gorodetsky, M. L., Pryamikov, A. D., Ilchenko, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rayleigh+scattering+in+high-Q+microspheres.">Rayleigh scattering in high-Q microspheres.</a> J. Opt. Soc. Am. B. 17 (6), 1051-1057 (2000).</li><li>Lu, T., Su, J., Fraser, S., Vahala, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Split+frequency+sensing+methods+and+systems.">Split frequency sensing methods and systems.</a> Patent granted on. , (2013).</li><li>Zhu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On-chip+single+nanoparticle+detection+and+sizing+by+mode+splitting+in+an+ultrahigh-Q+microresonator.">On-chip single nanoparticle detection and sizing by mode splitting in an ultrahigh-Q microresonator.</a> Nat. Photonics. 4 (1), 46-49 (2010).</li><li>Shopova, S. I., Rajmangal, R., Nishida, Y., Arnold, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasensitive+nanoparticle+using+a+portable+whispering+gallery+mode+biosensor+driven+by+a+periodically+poled+lithium-niobate+frequency+doubled+distributed+feedback+laser.">Ultrasensitive nanoparticle using a portable whispering gallery mode biosensor driven by a periodically poled lithium-niobate frequency doubled distributed feedback laser.</a> Rev. Sci. Instrum. 81 (10), (2010).</li><li>Cai, M., Painter, O., Vahala, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+critical+coupling+in+a+fiber+taper+to+a+silica-microsphere+whispering-gallery+mode+system.">Observation of critical coupling in a fiber taper to a silica-microsphere whispering-gallery mode system.</a> Phys. Rev. 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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+nanoparticles+with+a+frequency+locked+whispering+gallery+mode+microresonator.">Detection of nanoparticles with a frequency locked whispering gallery mode microresonator.</a> Appl. Phys. Lett. 102 (18), (2013).</li><li>Knittel, J., Chow, J. H., Gray, M. B., Taylor, M. A., Bowen, W. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasensitive+real-time+measurement+of+dissipation+and+dispersion+in+a+whispering-gallery+mode+microresonator.">Ultrasensitive real-time measurement of dissipation and dispersion in a whispering-gallery mode microresonator.</a> Opt. Lett. 38 (11), 1915-1917 (2013).</li><li>Shopova, S. 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This current setup is capable of probing a variety of WGM microcavities, such as microdisks, microspheres, and microtoroids, without requiring any feedback control for the probe laser source. A considerable signal-to-noise ratio (SNR) for detection can be obtained due to the step shift enhancements provided by path length and particle-induced backscattering effects. Given the simplicity and low cost of the reference interferometer itself, this method is an efficient technique for studying or exploiting the properties of ...

Research interest has risen significantly on the use of whispering-gallery mode (WGM) microcavities for the purpose of nanodetection and biosensing1-8. This involves ultra-high quality factor (Q) optical cavities that are proficient in identifying miniscule biological particles, down to the single-protein level2. That is, monitoring shifts in resonance and split frequency for transmission with extraordinary sensitivity9-11 can be enabled by the cavity&#8217;s confinement of light energy within a small mode volume. Variations in the optical properties of a resonator are the cause of these shifts, which in turn originate from the binding of discrete molecules or nanoparticles. A less sophisticated example of a three-dimensional WGM structure for such applications is a silica microsphere, which can be fabricated with a near atomically smooth surface by simply ablating a drawn optical fiber using a CO2 laser. As is known, high Q-factors on the order of 109 can be attained1.

The resonant frequency of a microcavity is conventionally monitored by scanning the optical frequency of a tunable laser source while simultaneously photo-detecting the optical transmission that is captured on an oscilloscope. An inherent drawback of this technique is the uncertainty associated with the location of drops in the transmission that arises from fluctuating laser wavelength or laser jitter. To overcome this complication, an interferometer can be used alongside a microcavity to produce a reference signal to cancel the laser jitter and increase the observed sensitivity2. Light input is split into two optical paths: the reference beam that passes through the interferometer (with a free spectral range or FSR large enough to prevent the laser from jittering past one FSR frequency spacing during measurement) and the detection beam that interacts with the WGM microresonator. This feature streamlines experiments in comparison to more advanced configurations, such as that of WGM sensing entailing the combination of a distributed feedback laser (DFB) and periodically poled lithium niobate (PPLN) doubler12. In this publication, an interferometer technique for ultra-high quality factor microcavity based monitoring of nanoscale matter is described3. The setup and data acquisition procedures that are required to accomplish this are outlined, illustrating how cavity quality factor can be determined through reference interferometry.

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implementation of a reference interferometer for nanodetection

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing its free spectral range (FSR), the module is put in parallel with a fiber taper-microcavity system and then calibrated through isolating and eliminating random shifts in the laser frequency (i.e. laser jitter noise). To realize the taper-microcavity junction and to maximize the optical power that is transferred to the resonator, a single-mode optical fiber waveguide is pulled. Solutions containing polystyrene nanobeads are then prepared and flown to the microcavity in order to demonstrate the system&#8217;s ability to sense binding to the surface of the microcavity. Data is post-processed via adaptive curve fitting, which allows for high-resolution measurements of the quality factor as well as the plotting of time-dependent parameters, such as resonant wavelength and split frequency shifts. By carefully inspecting steps in the time-domain response and shifting in the frequency-domain response, this instrument can quantify discrete binding events.

After following the protocol, the traces can be compiled and fitted. Figure 3a shows the typical resonance structure of the microsphere as presented in the video, for which frequency splitting is observed in a DPBS medium. A least-square fit to the double-Lorentzian function indicates that the quality factor of the left and right resonance dips are respectively 2.1 x 108 and 3.8 x 108 in an aqueous environment. The optical frequencies of the FWHM are obtained by comparing the cavity...

Watch this Scientific Journal Video about Implementation of a Reference Interferometer for Nanodetection at JoVE.com

Implementation of a Reference Interferometer for Nanodetection

A reference interferometer technique, which is designed to remove undesirable laser jitter noise for nanodetection, is utilized for probing an ultra-high quality factor microcavity. Instructions for assembly, setup, and data acquisition are provided, alongside the measurement process for specifying the cavity quality factor.

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing ...

implementation-of-a-reference-interferometer-for-nanodetection

Research

JoVE Journal

Engineering

9.2K vues.  University of Victoria.  Une technique de l'interféromètre de référence, qui est conçu pour éliminer le bruit de gigue laser indésirable pour nanodetection, est utilisé pour sonder un facteur microcavité ultra-haute qualité. Instructions pour l'assemblage, l'installation et l'acquisition de données sont fournies, parallèlement au processus de mesure pour spécifier le facteur de qualité de la cavité. 