Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi
Ente Cassa di Risparmio di Firenze (No. 2014.0770A2202.8861)

1. Fabrication of Ultrahigh Factor of Quality Microspheres
<ol>
	<li>Strip about 1-2 cm of a standard single-mode (SMF) silica fiber off its acrylic coating using an optical stripper.</li>
	<li>Clean the stripped part with acetone and cleave it.</li>
	<li>Introduce the cleaved tip in one arm of a fusion splicer and produce a series of electric arc discharges using the splicer controller. Select &#34;manual operation&#34; from the splicer controller menu, set the values for arc power level and arc duration to 60 and 800...

<ol>
	<li>Kozyreff, G., Dominguez-Juarez, J. L., Martorell, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non+linear+optics+in+spheres:+from+second+harmonic+scattering+to+quasi-phase+matched+generation+in+whispering+gallery+modes.">Non linear optics in spheres: from second harmonic scattering to quasi-phase matched generation in whispering gallery modes.</a> Laser Photon. Rev. 5 (6), (2011).</li><li>Farnesi, D., Barucci, A., Righini, G. C., Berneschi, S., Soria, S., Nunzi Conti, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+frequency+generation+in+silica+microspheres.">Optical frequency generation in silica microspheres.</a> Phys. Rev. Lett. 112 (9), 093901 (2014).</li><li>Liang, W., 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=Miniature+multioctave+light+source+based+on+a+monolithic+microcavity.">Miniature multioctave light source based on a monolithic microcavity.</a> Optica. 2 (1), 40-47 (2015).</li><li>Maker, A. J., Armani, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+Silica+Ultra+High+Quality+Factor+Microresonators.">Fabrication of Silica Ultra High Quality Factor Microresonators.</a> J. Vis. Exp. (65), e4164 (2012).</li><li>Coillet, A., Henriet, R., Phan Huy, K., Jacquot, M., Furfaro, L., Balakireva, I., 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=Microwave+Photonics+Systems+Based+on+Whispering-gallery-mode+Resonators.">Microwave Photonics Systems Based on Whispering-gallery-mode Resonators.</a> J. Vis. Exp. (78), e50423 (2013).</li><li>Han, K., Kim, K. H., Kim, J., Lee, W., Liu, J., Fan, X., 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=Fabrication+and+Testing+of+Microfluidic+Optomechanical+Oscillators.">Fabrication and Testing of Microfluidic Optomechanical Oscillators.</a> J. Vis. Exp. (87), e51497 (2014).</li><li>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=Microspheres,+Photonic+Atoms,+and+the+Physics+of+Nothing.">Microspheres, Photonic Atoms, and the Physics of Nothing.</a> American Scientist. 89 (5), 414-421 (2001).</li><li>Chiasera, A., 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=Spherical+whispering+gallery+mode+microresonators.">Spherical whispering gallery mode microresonators.</a> Laser Photon. Rev. 4 (3), 457-482 (2010).</li><li>Helt, L. G., Liscidini, M., Sipe, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+does+it+scale?+Comparing+quantum+and+classical+nonlinear+optical+processes+in+integrated+devices.">How does it scale? Comparing quantum and classical nonlinear optical processes in integrated devices.</a> J. Opt. Soc. Am. B. 29 (8), 2199-2212 (2012).</li><li>Leach, D. H., Chang, R. K., Acker, 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=Stimulated+anti-Stokes+Raman+scattering+in+microdroplets.">Stimulated anti-Stokes Raman scattering in microdroplets.</a> Opt. Lett. 17 (6), 387-389 (1992).</li><li>Farnesi, D., Cosi, F., Trono, C., Righini, G. C., Nunzi Conti, G., Soria, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stimulated+Antistokes+Raman+scattering+resonantly+enhanced+in+silica+microspheres.">Stimulated Antistokes Raman scattering resonantly enhanced in silica microspheres.</a> Opt. Lett. 39 (20), 5993-5996 (2014).</li><li>Qian, S. X., Chang, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiorder+Stokes+emission+from+micrometer+size+droplets.">Multiorder Stokes emission from micrometer size droplets.</a> Phys. Rev. Lett. 56 (9), 926-929 (1986).</li><li>Lin, H. B., Campillo, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CW+nonlinear+optics+in+droplet+microcavities+displaying+enhanced+gain.">CW nonlinear optics in droplet microcavities displaying enhanced gain.</a> Phys. Rev. Lett. 73 (18), 2440-2443 (1994).</li><li>Spillane, S. M., Kippenberg, T. J., 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=Ultralow+threshold+Raman+laser+using+a+spherical+dielectric+microcavity.">Ultralow threshold Raman laser using a spherical dielectric microcavity.</a> Nature. 415 (6872), 621-623 (2002).</li><li>Kippenberg, T. J., Spillane, S. M., 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=Kerr-Nonlinearity+optical+parametrical+oscillation+in+an+ultrahigh+Q+toroid+microcavity.">Kerr-Nonlinearity optical parametrical oscillation in an ultrahigh Q toroid microcavity.</a> Phys. Rev. Lett. 93 (8), 083904 (2004).</li><li>Hill, S. C., Leach, D. H., Chang, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Third+order+sum+frequency+generation+in+droplets:+model+with+numerical+results+for+third-harmonic+generation.">Third order sum frequency generation in droplets: model with numerical results for third-harmonic generation.</a> J. Opt. Soc. Am. B. 10 (1), 16-33 (1993).</li><li>Kozyreff, G., Dominguez Juarez, J. L., Martorell, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whispering+gallery+mode+phase+matching+for+surface+second+order+nonlinear+optical+processes+in+spherical+microresonators.">Whispering gallery mode phase matching for surface second order nonlinear optical processes in spherical microresonators.</a> Phys. Rev. A. 77 (4), 043817 (2008).</li><li>Jouravlev, M. V., Kurizki, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unified+theory+of+Raman+and+parametric+amplification+in+nonlinear+microspheres.">Unified theory of Raman and parametric amplification in nonlinear microspheres.</a> Phys. Rev. A. 70 (5), 053804 (2004).</li><li>Brenci, M., Calzolai, R., Cosi, F., Nunzi Conti, G., Pelli, S., Righini, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microspherical+resonators+for+biophotonic+sensors.">Microspherical resonators for biophotonic sensors.</a> Proc. SPIE. 6158, 61580S (2006).</li><li>Carmon, T., Yang, L., 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=Dynamical+thermal+behavior+and+thermal+self-stability+of+microcavities.">Dynamical thermal behavior and thermal self-stability of microcavities.</a> Opt. Express. 12 (20), 4742-4750 (2004).</li><li>Kippenberg, T. J., Spillane, S. M., Min, B., 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=Theoretical+and+experimental+study+of+stimulated+and+cascaded+Raman+scattering+in+ultrahigh+Q+optical+microcavities.">Theoretical and experimental study of stimulated and cascaded Raman scattering in ultrahigh Q optical microcavities.</a> J. Sel. Quantum Electron. 10 (5), 1219-1228 (2004).</li><li>Bloembergen, N., Shen, Y. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coupling+between+vibrations+and+light+waves+in+Raman+laser+media.">Coupling between vibrations and light waves in Raman laser media.</a> Phys. Rev. Lett. 12 (18), 504-507 (1964).</li><li>Gorodestky, 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>Arnold, S., Ramjit, R., Keng, D., Kolchenko, V., Teraoka, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microparticle+photophysics+illuminates+viral+bio-sensing.">Microparticle photophysics illuminates viral bio-sensing.</a> Faraday Discuss. 137, 65-83 (2008).</li><li>Ozdemir, S. K., 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=Highly+sensitive+detection+of+nanoparticle+with+a+self+referenced+and+self-heterodyned+whispering+gallery+Raman+microlaser.">Highly sensitive detection of nanoparticle with a self referenced and self-heterodyned whispering gallery Raman microlaser.</a> Proc. Natl. Acad. Sci USA. 11 (37), E3836-E3844 (2014).</li></ol>

The authors declare that they have no competing financial interests. D.F. is a PhD student at the University of Parma.

Microspheres are compact and efficient nonlinear oscillators and they are very easy to fabricate and handle. Tapered fibers can be used for coupling and extracting the light in/from the resonator. Resonance contrast up to 95% and Q factors of about 3 x 108 can be obtained.
The main limitation of these fabrication techniques is mass production and integration. Cleanliness of the fibers is critical to both microspheres and tapers, and so is humidity. Both devices must be kept in dry e...

Whispering gallery mode resonators (WGMR) show two unique properties, a long photon lifetime and small mode volume that allow the reduction of the threshold of nonlinear phenomena1-3. Whispering gallery modes are optical modes that are confined at the dielectric air interface by total internal reflection. The small mode volume is due to the high spatial confinement whereas the temporal confinement is related to the quality factor Q of the cavity. WGMR can have different geometries and there are different fabrication techniques suitable for obtaining high Q resonators4-6 Surface tension cavities such as silica microspheres exhibit near atomic scale roughness, which translates in high quality factors. Both types of confinement significantly reduce the threshold for nonlinear effects due to the strong energy buildup inside the WGMR. It also allows continuous wave (CW) nonlinear optics.
WGMR can be described using the quantum numbers n, l, m and their polarization state, in a strong analogy with the hydrogen atom7. The spherical symmetry allows the separation in radial and angular dependencies. The radial solution is given by Bessel functions, the angular ones by the spherical harmonics8.
Silica glass is centrosymmetric and, therefore, second order phenomena related to &#935;(2) interactions are forbidden. At the surface of the microsphere, the inversion of symmetry is broken and &#935;(2) phenomena can be observed1. However, phase matching conditions for second-order frequency generation are more problematic than the equivalent in third order frequency generation, especially because the wavelengths involved are quite different and the role of dispersion can be quite important. The second order interactions are extremely weak. The generated power scales with Q3 whereas for a third order interaction the generated power scales with Q4.9 For that reason, the focus of this work is third order optical non-linear susceptibility &#935;(3) interactions such as Stimulated Raman Scattering (SRS) and Stimulated Antistokes Raman Scattering (SARS), being SARS the less explored interaction10,11. Chang12 and Campillo13 pioneered the studies of nonlinear phenomena using droplets of highly nonlinear materials as WGMR but the pump laser was pulsed instead of CW. Silica microspheres14,10 and microtoroids15 provided more stable and robust platforms compared to the micro-droplets, gaining much of the attention in the last decades. Particularly, silica microspheres are very easy to fabricate and handle.
SRS is a pure gain process that can be easily achieved in silica WGMR14,15, since reaching a threshold is enough. In this case, the high circulating intensity inside the WGMR guarantees Raman lasing, but for parametric oscillations is not sufficient. In these cases, efficient oscillations require phase and mode matching, energy and momentum conservation law and a good spatial overlap of all resonant modes to be fulfilled16-18. This is the case for SARS and FWM in general.

<table border="0" cellpadding="0" cellspacing="0" width="668">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optical Fiber</td>
			<td style="width:93px;">Corning</td>
			<td style="width:119px;">SMF28</td>
			<td style="width:240px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fiber coating stripper</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;">T06S13</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fiber cleaver</td>
			<td style="width:93px;">Fitel</td>
			<td style="width:119px;">S325A</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fusion splicer</td>
			<td style="width:93px;">Furakawa</td>
			<td style="width:119px;">S177A-1R</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Butane and Oxygen Gas</td>
			<td style="width:93px;">n/a</td>
			<td style="width:119px;"></td>
			<td>any vendor</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microscope tube</td>
			<td style="width:93px;">Navitar</td>
			<td style="width:119px;">Zoom 6000</td>
			<td>Modular Kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CCD camera</td>
			<td style="width:93px;">n/a</td>
			<td style="width:119px;">N/A</td>
			<td>any will fit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Monitor</td>
			<td style="width:93px;">n/a</td>
			<td style="width:119px;">N/A</td>
			<td>any monitor is valid</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">3-Axis Stage</td>
			<td style="width:93px;">PI Instruments, Thorlabs, Melles</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Assorted posts and mounts</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;"></td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Polarization control</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;">FPC030</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Attenuator</td>
			<td style="width:93px;">Throlabs</td>
			<td style="width:119px;">VOA50</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Photodiode</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;">PDA400</td>
			<td>discontinued, replaced by PDA10CS-EC</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oscilloscope</td>
			<td style="width:93px;">Tektronix</td>
			<td style="width:119px;">DPO7104</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optical spectrum analyzer</td>
			<td style="width:93px;">Ando</td>
			<td>AQ6317B</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Erbium Doped Fiber Amplifier</td>
			<td style="width:93px;">IPG Photonics</td>
			<td style="width:119px;">EAD-2K-C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tunable Laser</td>
			<td style="width:93px;">Yenista</td>
			<td style="width:119px;">TUNICS</td>
			<td></td>
		</tr>
	</tbody>
</table>

stimulated stokes and antistokes raman scattering in microspherical whispering gallery mode resonators

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres can be thought as a store of energy with a huge variety of applications: compact laser sources, highly sensitive biochemical sensors and nonlinear phenomena. A protocol for the fabrication of both the microspheres and coupling system is given. The couplers described here are tapered fibers. Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS). A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler. In the case of hyperparametric oscillations (four wave mixing and stimulated anti-stokes Raman scattering), the modes must fulfill the energy and momentum conservation and, last but not least, have a good spatial overlap.

The Q factors of the microspheres fabricated following the protocol described above are in excess of 108 (Figure 5) for large diameters (&#62;200 &#956;m) and in excess of 106 for small diameters (&#60; 50 &#956;m). Resonance contrast above 95% (close to critical coupling) can be easily observed. For high circulating intensities, the following nonlinear effects in the infrared region can be observed: stimulated Raman scattering (SRS), cascaded SRS<su...

Watch this Scientific Journal Video about Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators at JoVE.com

Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS).

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres ...

The overall goal of this procedure is to generate new optical frequencies using silica microspherical whispering-gallery-mode resonators for optical and photonics applications ranging from compact laser sources to biochemical sensing. In whispering gallery-mode microresonators light can be guided with a unique combination of strong spatial confinement and long cavity lifetime. Low losses ensure high quality factors.Such resonators are ideally suited for nonlinear optical interactions. In particular, silica microspheres show a great potential as frequency generators for continuous wave compact, narrow-line width and tunable sources. The interest of using fusion techniques for fabrication of the electric microsphere is based on low scattering losses can be achieved and in consequence very high quality factors.We used homemade taper fiber to couple light into the microspheres. The high coupling efficiency and the high cavity buildup factor can trigger nonlinear Kerr effects with low continuous wave pump power. Demonstrating the taper procedure will be Franco Cosi, a technician from our laboratory.To create a microsphere, first get a length of fiber to work with. Gather the equipment needed to create a microsphere using single-mode silica fiber. This includes the fiber, acetone, an optical coating stripper, and a fiber cleaver.In addition, have ready a fusion splicer. Use the stripper to remove about 1-2 centimeters of the acrylic coating from the end of the fiber. Follow this by cleaning the stripped portion with a clean wipe and acetone.Place the end of the fiber into the fiber cleaver and cleave to isolate the stripped portion. Collect the cleaved fiber from the cleaver. Move the fiber tip to the fusion splicer.There, position the fiber and hold it in place according to the manufacturer's guidelines. Close the cover, check that the arc power and the arc duration are correct, then start the arc. Monitor progress on the display.As the arc melts the glass, the fiber shape will begin to form a sphere due to surface tension. When the sphere begins to take shape, stop the arc and open the cover. Access the fiber in the holder, rotate it by 90 degrees to preserve the spherical shape, then secure the fiber in place again.Close the cover and restart the arc. Performing at least three such 90 degree rotations over five to 10 minutes will produce a microsphere of about 160 micrometers. When removing the microsphere and its fiber stem, be prepared to store it or use it within a day.This t-shaped holder is translation stage-mountable for use with light-coupling experiments. It has a channel down its middle for the microsphere's fiber stem. Place the residual stem end of the microsphere in the channel so the microsphere is unobstructed above the holder.Afix the stem with clear tape. Now, begin to create a tapered fiber to couple light into the microsphere. This will require a device that can slowly pull the fiber ends apart.Start with a length of single-mode silica fiber and identify its midpoint. Use the optical coating stripper to remove about 3-4 centimeters of the coating around this point. Once this is done, slip an alumina cylinder over the stripped portion of the fiber to serve as an oven.Next, use a bare fiber terminator to connect one end of the fiber to a laser capable of operating at 635 nanometers. Connect the other end of the fiber to a power meter. Once the fiber is in place, arrange for an oxygen-butane flame to heat the alumina cylinder to a temperature close to the silica melting point of about 2, 100 degrees Celsius.Start the fiber puller so that it slowly moves the two ends away from one another. With the 635 nanometer laser on, monitor the power transmitted through the fiber with the power meter. Changing values reflect the ongoing tapering.At this point, stop pulling the fiber and stop the flame. Occasionally remove the fiber from the power meter input to project the fiber output onto a beam card to check that a homogeneous circular spot is preserved during the tapering process. Work with fiber after it has been freed from all equipment including the cylinder.Position a glass microscope slide cut to form a U'near the fiber's taper. Next, put the fiber on the slide with taper centered on the U'Keep the fiber taut and apply glue where the fiber and slide overlap to hold the fiber in place. At this point, prepare to couple light into the microsphere with the tapered fiber.To do this, use separate translation stages for the microsphere and the tapered fiber. On a stage with piezoelectric actuators, mount the T-shaped holder with the microsphere so that the microsphere points up. On the other translation stage, mount the glass slide with the fiber oriented perpendicular to the microsphere fiber stem.Use a terminated fiber cable to connect one end of the tapered fiber to a tunable diode laser. Connect the other end to an indium-gallium-arsenide photodiode detector. Now, situate both of the translation stages beneath the microscope tube that will be used for observation of the gap between the microsphere and the taper.The two should be placed so the fiber taper and microsphere are within the travel distance of the translation stages. In addition, place a mirror at 45 degrees with respect to the microscope tube to monitor the vertical position of the taper. Position the microsphere using its translation stage and feedback from the microscope tube.The goal is to have the equator of the microsphere in contact with the taper. Once this is done, turn on the continuous wave laser and monitor the transmission spectrum on an oscilloscope. Tune the laser until Lorentzian-shaped dips due to resonances appear in the spectrum.Measure the resonance line widths and calculate the quality factor. Continue the experiment by exploring coupling efficiency as a function of the gap between the taper and the sphere. Fiber coupling is crucial in order to find good resonance to trigger nonlinear effects.A good resonance is narrow, it is high contrast at low power. Prepare the set-up to realize stimulated Raman scattering. Light from a tunable diode laser operating at 15, 015 nanometers enters the tapered fiber.After the laser, there is an erbium doped fiber amplifier to boost the laser power to achieve nonlinear effect. Next, there is an attenuator and then, an inline fiber polarizer. The light then goes through the taper, which is coupled to a microsphere.After passing the microsphere, there is a 3-decibel-milliwatt splitter. One output of the splitter goes to an optical spectrum analyzer. The other goes to a photodetector connected to an oscilloscope.Tune the laser from high to low frequencies to achieve thermal self-locking. On the oscilloscope, observe a resonance with the thermal drift comparable to the wavelength scan speed. The resonance will broaden when thermal self-locking is achieved.Check the output power transmitted into the optical spectrum analyzer. Manipulate the attenuator to increase the power until the Raman laser line appears. The Raman laser line is detuned from the pump wavelength at about 13.5 terahertz.This is a measurement from 50-micrometer diameter microsphere pumped at about 1, 547 nanometers. On either side of the pump wavelength, there are two four-wave mixing lines about 13 nanometers away. Two stimulated Raman scattering lines are at about 1, 610 and 1, 710 nanometers.Measurements of a 98-nanometer sphere produced similar results. In this case, the pump peak is at 1, 551 nanometers. The stimulated Raman scattering line is centered at 1, 646 nanometers.The stimulated antistokes Raman scattering line is centered at about 1, 452 nanometers. The symmetric lines near the stimulated antistokes line are from degenerated four-wave mixing. A Raman cone is centered at 1, 666 nanometers.This spectrum from a microsphere of 40-micrometer diameter provides evidence of stimulated antistokes enhancement when its frequency is resonant with the cavity mode and phased-matched with the pump and stimulated stokes signal. The pump frequency is 1, 540 nanometers, the stokes line is at 1, 630 nanometers, and the antistokes line is at 1, 460 nanometers. This spectrum from a 65-micrometer microsphere has a stimulated antistokes to stimulated stokes scattering ratio close to one.The pump frequency is centered at 1, 572 nanometers, the stokes line at 1, 640 nanometers, the antistokes line at 1, 490 nanometers. After watching this video, you should have a good understanding of how to fabricate high-Q silica microsphere, how to draw a fiber taper, and how to efficiently couple light into microresonator to study fundamental light-matter interactions. The electrical microspheres are photonic platforms that play an extremely important role in modern optics.They can be exploited for CW nonlinear frequency conversion due to their capability to confine light for long time periods in very small volumes. The microresonator technologies that have been demonstrated may also be effectively exploited for biosensing. Our group is achieving excellent results in this area.

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11.1K Görüntüleme.  Enrico Fermi Center. The overall goal of this procedure is to generate new optical frequencies using silica microspherical whispering-gallery-mode resonators for optical and photonics applications ranging from compact laser sources to biochemical sensing. In whispering gallery-mode microresonators light can be guided with a unique combination of strong spatial confinement and long cavity lifetime. Low losses ensure high quality factors.Such resonators are ideally suited for nonlinear optical interactions. ...