Name: in-situ tapering of chalcogenide fiber for mid-infrared supercontinuum generation
Uploaded: 2013-05-27T13:00:00
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The authors would like to thank G. Shambat, C. Phillips, K. Aghaei for invaluable discussions, F. Afshinmanesh for SEM images, T. Marvdashti for experimental support, and M.F. Churbanov and G.E. Snopatin from the Institute of Chemistry of High-Purity Substances and V.G. Plotnichenko and E.M. Dianov from the Fiber Optics Research Center of the Russian Academy of Sciences for providing the As2S3 fiber. We also are grateful for support from the Office of Naval Research, NASA, the Air Force Office of Scientific Research, Agilent, and the Joint Technologies Office.

1. Tapering Setup Fabrication (See Assembled Setup in Figure 1)
<ol>
	<li>Secure the motorized linear stages on the breadboard (roughly centered) so that the stages are in contact and will translate towards and away from one another</li>
	<li>Prepare and place the fiber mounts
	<ol>
		<li>Attach two optical posts to the motorized linear stage plates (one each) using the holes closest to each other.</li>
		<li>Attach the bare optical fiber mounts to the tops of the posts. Make sure that the v-grooves for the fiber are a...

<ol>
	<li>Marandi, A., Rudy, C. W., Plotnichenko, V. G., Dianov, E. M., Vodopyanov, K. L., Byer, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mid-infrared+supercontinuum+generation+in+tapered+chalcogenide+fiber+for+producing+octave-spanning+frequency+comb+around+3+&#956;m.">Mid-infrared supercontinuum generation in tapered chalcogenide fiber for producing octave-spanning frequency comb around 3 &#956;m.</a> Optics Express. 20, 24218-24225 (2012).</li><li>Schliesser, A., Picque, N., Hansch, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mid-infrared+frequency+combs.">Mid-infrared frequency combs.</a> Nature Photonics. 6, 440-449 (2012).</li><li>Diddams, S. A., Hollberg, L., Mbele, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+fingerprinting+with+the+resolved+modes+of+a+femtosecond+laser+frequency+comb.">Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb.</a> Nature. 445, 627-630 (2007).</li><li>Thorpe, M. J., Balslev-Clausen, D., Kirchner, M. S., Ye, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cavity-enhanced+optical+frequency+comb+spectroscopy:+application+to+human+breath+analysis.">Cavity-enhanced optical frequency comb spectroscopy: application to human breath analysis.</a> Optics Express. 16, 2387-2397 (2008).</li><li>Sears, C. M. S., Colby, E., England, R. J., Ischebeck, R., McGuinness, C., Nelson, J., Noble, R., Siemann, R. H., Spencer, J., Walz, D., Plettner, T., Byer, R. 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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Supercontinuum generation in optical fibers. , (2010).</li><li>Birks, T. A., Wadsworth, W. J., Russell, P. S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Supercontinuum+generation+in+tapered+fibers.">Supercontinuum generation in tapered fibers.</a> Optics Letters. 25, 1415-1417 (2000).</li><li>Leindecker, N., Marandi, A., Byer, R. L., Vodopyanov, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Broadband+degenerate+OPO+for+mid-infrared+frequency+comb+generation.">Broadband degenerate OPO for mid-infrared frequency comb generation.</a> Optics Express. 19, 6296-6302 (2011).</li><li>Liao, M., Yan, X., Gao, W., Duan, Z., Qin, G., Suzuki, T., Ohishi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Five-order+SRSs+and+supercontinuum+generation+from+a+tapered+tellurite+microstructured+fiber+with+longitudinally+varying+dispersion.">Five-order SRSs and supercontinuum generation from a tapered tellurite microstructured fiber with longitudinally varying dispersion.</a> Optics Express. 19, 15389-15396 (2011).</li><li>M&#228;gi, E. C., Steinvurzel, P., Eggleton, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tapered+photonic+crystal+fibers.">Tapered photonic crystal fibers.</a> Optics Express. 12, 776-784 (2004).</li><li>Ozeki, T., Kawasaki, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+directional+coupler+using+tapered+sections+in+multimode+fibers.">Optical directional coupler using tapered sections in multimode fibers.</a> Applied Physics Letters. 28, 528-529 (1976).</li><li>Yataki, M. S., Payne, D. N., Varnahm, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-fibre+wavelength+filters+using+concatenated+fused-taper+couplers.">All-fibre wavelength filters using concatenated fused-taper couplers.</a> Electronic Letters. 21, 248-249 (1985).</li><li>Chandalia, J. K., Eggleton, B. J., Windeler, R. S., Kosinski, S. G., Liu, X., Xu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adiabatic+coupling+in+tapered+air-silica+microstructured+optical+fiber.">Adiabatic coupling in tapered air-silica microstructured optical fiber.</a> IEEE Photonics Technology Letters. 13, 52-54 (2001).</li><li>Mora, J., D&#237;ez, A., Fonjallaz Andr&#233;z, P. Y., Popov, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tunable+dispersion+compensator+based+on+a+fiber+Bragg+grating+written+in+a+tapered+fiber.">Tunable dispersion compensator based on a fiber Bragg grating written in a tapered fiber.</a> IEEE Photonics Technology Letters. 16, 2631-2633 (2004).</li><li>Rusu, M., Herda, R., Kivist&#246;, S., Okhotnikov, O. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fiber+taper+for+dispersion+management+in+a+mode-locked+ytterbium+fiber+laser.">Fiber taper for dispersion management in a mode-locked ytterbium fiber laser.</a> Optics Letters. 31, 2257-2259 (2006).</li><li>Alfanao, R. R., Shapiro, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emission+in+the+region+4000+to+7000+A+via+four-photon+coupling+in+glass.">Emission in the region 4000 to 7000 A via four-photon coupling in glass.</a> Physical Review Letters. 24, 584-587 (1970).</li><li>Eggleton, B. J., Luther-Davies, B., Richardson, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chalcogenide+photonics.">Chalcogenide photonics.</a> Nature Photonics. 5, 141148 (2011).</li><li>Snopatin, G. E., Shiryaev, V. S., Plotnichenko, V. G., Dianov, E. M., Churbanov, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-purity+chalcogenide+glasses+for+fiber+optics.">High-purity chalcogenide glasses for fiber optics.</a> Inorganic Materials. 45, 1439-1460 (2009).</li><li>Harbold, J. M., Ilday, F. O., Wise, F. W., Sanghera, J. S., Nguyen, V. Q., Shaw, L. B., Aggarwal, I. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+nonlinear+As-S-Se+glasses+for+all-optical+switching.">Highly nonlinear As-S-Se glasses for all-optical switching.</a> Optics Letters. 27, 119-121 (2002).</li><li>Hudson, D. D., Dekker, S. A., Magi, E. C., Judge, A. C., Jackson, S. D., Li, E., Sanghera, J. S., Shaw, L. B., Aggarwal, I. D., Eggleton, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Octave+spanning+supercontinuum+in+an+As2S3+taper+using+ultralow+pump+pulse+energy.">Octave spanning supercontinuum in an As2S3 taper using ultralow pump pulse energy.</a> Optics Letters. 36, 1122-1124 (2011).</li><li>Domachuk, P., Wolchover, N. A., Cronin-Golomb, M., Wang, A., George, A. K., Cordeiro, C. M. B., Knight, J. C., Omenetto, F. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Over+4000+nm+bandwidth+of+mid-IR+supercontinuum+generation+in+sub-centimeter+segments+ofhighly+nonlinear+tellurite+PCFs.">Over 4000 nm bandwidth of mid-IR supercontinuum generation in sub-centimeter segments ofhighly nonlinear tellurite PCFs.</a> Optics Express. 6, 7161-7168 (2008).</li><li>Hu, J., Menyuk, C. R., Shaw, L. B., Sanghera, J. S., Aggarwal, I. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maximizing+the+bandwidth+of+supercontinuum+generation+in+As2Se3+chalcogenide+fibers.">Maximizing the bandwidth of supercontinuum generation in As2Se3 chalcogenide fibers.</a> Optics Express. 18, 6722-6739 (2010).</li><li>El-Amraoui, M., Fatome, J., Jules, J. C., Kibler, B., Gadret, G., Fortier, C., Smektala, F., Skripatchev, I., Polacchini, C. F., Messaddeq, Y., Troles, J., Brilland, L., Szpulak, M., Renversez, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strong+infrared+spectral+broadening+inlow-loss+As-S+chalcogenide+suspended+core+microstructured+optical+fibers.">Strong infrared spectral broadening inlow-loss As-S chalcogenide suspended core microstructured optical fibers.</a> Optics Express. 18, 4547-4556 (2010).</li><li>Marandi, A., Leindecker, N., Byer, R. L., Vodopyanov, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coherence+properties+of+a+broadband+femtosecond+mid-IR+optical+parametric+oscillator+operating+at+degeneracy.">Coherence properties of a broadband femtosecond mid-IR optical parametric oscillator operating at degeneracy.</a> Optics Express. 20, 7255-7262 (2012).</li><li>Dudley, J. M., Coen, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coherence+properties+of+supercontinuum+spectra+generated+in+photonic+crystal+and+tapered+optical+fibers.">Coherence properties of supercontinuum spectra generated in photonic crystal and tapered optical fibers.</a> Optics Letters. 27, 1180-1182 (2002).</li><li>Corwin, K. L., Newbury, N. R., Dudley, J. M., Coen, S., Diddams, S. A., Weber, K., Windeler, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamental+noise+limitations+to+supercontinuum+generation+in+microstructure+fiber.">Fundamental noise limitations to supercontinuum generation in microstructure fiber.</a> Physical Review Letters. 90, 113904 (2003).</li><li>Birks, T. A., Li, Y. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+shape+of+fiber+tapers.">The shape of fiber tapers.</a> Journal of Lightwave Technology. 10, 432-438 (1992).</li><li>Churbanov, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-purity+chalcogenide+glasses+as+materials+for+fiber+optics.">High-purity chalcogenide glasses as materials for fiber optics.</a> Journal of Non-Crystalline Solids. 184, 25-29 (1995).</li></ol>

We have demonstrated a novel fiber tapering procedure and verified its validity by performing SCG in the mid-IR. To the best of our knowledge, the alternative method for this application is based on determining the fiber pulling length required to create a tapered fiber diameter that adds enough waveguide dispersion to optimize SCG in the fiber taper through calculation; however, since the pulling length needed to maximize the spectral broadening for a specific length of fiber varies for each experiment, this calc...

After being first produced in the visible wavelength range1,7 SCG sources have shifted towards the mid-IR, largely driven by applications in spectroscopy.3, 4 Chalcogenide fibers, which include sulfides, selenides, and tellurides, have been a popular material for the mid-IR due to their low propagation loss and high nonlinearity,18 less than 100 dB/km19 and ~200 times that of silica for As2S3,20 respectively. However, the zero GVD wavelength of most chalcogenides is located in the mid-IR, beyond the center wavelength of the majority of available ultrafast pump sources, making SCG challenging in a bulk material or a standard single mode chalcogenide fiber. Waveguide dispersion can be used to modify the zero GVD point for SCG.7 Methods for introducing strong waveguide dispersion include fiber tapering,8, 21 using microstructured fibers,22-24 or even a combination of the two.10 By shifting the zero GVD wavelength below the pump wavelength, the pump will experience anomalous dispersion in the fiber. In the anomalous dispersion regime, soliton formation occurs through balancing the nonlinear chirp caused by self phase modulation and the linear chirp caused by GVD. For a femtosecond pump source, spectral broadening is usually dominated by soliton fission or pulse breaking, which occurs after an initial temporal compression as the pulse propagates along the fiber.7 In the case of fiber tapering, calculating the total GVD-including both material and waveguide dispersion-can provide an approximation of the final taper diameter needed to produce a significantly broadened spectrum. Due to SCG's strong dependence on GVD and fluctuations between experimental trials, including changes to the fiber length before the tapered region and coupling of the pump to the fiber, the calculated approximation is not sufficient for achieving an optimized taper in a single trial. Spectral monitoring allows for these variations in experimental setup to be observed and accounted for in in-situ tapering.
Moreover, generating an efficient supercontinuum (SC) in a short tapered fiber reduces the amount of nonlinear noise amplification preserving the coherence of the SCG and the frequency comb properties of the pump source.25-27 Proper dispersion management, and therefore the necessity of in-situ tapering, becomes even more critical when the fiber length is short, as the SCG tolerance scales with length.
The in-situ tapering setup begins with the pump source, which is the subharmonic of a mode-locked Er-doped fiber laser,9 coupled into the core of the As2S3 fiber that will be tapered. The output of the fiber is then coupled to a device that characterizes the spectral profile. In the experiment, a InSb detector after a monochromator with ~20 nm of resolution is used to monitor a portion of the output spectrum where there is initially a very low signal from the pump source (at ~3.9 &mu;m) so that the fiber may be monitored while tapering. When the fiber is tapered and the spectrum broadens, the spectral measurement signal increases as the dispersion is optimized for the individual experiment. By monitoring the spectrum during the tapering procedure, tapering can be stopped at the moment when the spectral broadening has been maximized. In-situ tapering allows for optimized dispersion management for efficient SCG in a single fiber taper. Tapering with a static, narrow heat zone produces a short fiber taper waist,28 which allows for low-noise SCG. Together, in-situ static tapering can enable coherent, low-noise, octave-spanning SCG in the mid-IR.

<table border="1">
		<tbody>
		 <tr>
			<td>Name of Equipment</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		 </tr>
		 <tr>
			<td>Motorized Linear Stages</td>
			<td>Newport</td>
			<td>MFA-PPD</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Motorized Stage Controller</td>
			<td>Newport</td>
			<td>ESP301</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Aluminum Block</td>
			<td>Any vendor.</td>
			<td></td>
			<td>Dimensions will vary depending on desired taper length.</td>
		 </tr>
		 <tr>
			<td>RTD Sensor</td>
			<td>Omega</td>
			<td>1PT100GX1510</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Cartridge Heaters</td>
			<td>Omega</td>
			<td>CSS-01115/120V</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Temperature Controller</td>
			<td>Omega</td>
			<td>CSC32</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Input Coupling Linear Translation Stage</td>
			<td>CVI</td>
			<td>07TXS224</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Output Coupling Linear Translation Stage</td>
			<td>Newport</td>
			<td>422-1S</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>XYZ Linear Translation Stage</td>
			<td>Newport</td>
			<td>461</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Assorted posts, optics mounts, bases, and forks</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Optical Breadboard</td>
			<td>Thorlabs</td>
			<td>MB12</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Input Coupling ZnSe Lens</td>
			<td>Thorlabs</td>
			<td>AL72512-E</td>
			<td>Available from other vendors. Input coupling focal length depends on pump source and fiber mode field diameter.</td>
		 </tr>
		 <tr>
			<td>Output Coupling ZnSe Lens</td>
			<td>Edmund Optics</td>
			<td>NT62-961</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Box</td>
			<td>Any type will do.</td>
			<td></td>
			<td>Must be large enough to allow stage movement. Needs apertures for input and output coupling of light.</td>
		 </tr>
		 <tr>
			<td>Ceramic Optical Post</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Digital Microscope</td>
			<td>Any vendor.</td>
			<td></td>
			<td>Optional.</td>
		 </tr>
		 <tr>
			<td>Table Clamps</td>
			<td>Thorlabs</td>
			<td>CL5</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Bare Fiber clamps</td>
			<td>Thorlabs</td>
			<td>HFF003</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
		 <td></td>
		 <td></td>
		 <td></td>
		 <td>Table 1. Tapering Setup Materials.</td>
	 </tr>
		 <tr>
			<td>As2S3 Optical Fiber</td>
			<td>Fiber Optics Research Center of the Russian Academy of Sciences</td>
			<td></td>
			<td>Available from other vendors, such as CorActive. </td>
		 </tr>
		 <tr>
			<td>Beavertail Cleaver</td>
			<td>Fiber Network Tools</td>
			<td>S-315</td>
			<td>Available from other vendors. Hand cleaving or polishing fiber tips can also produce high quality fiber tips.</td>
		 </tr>
		 <tr>
			<td>KimWipes</td>
			<td>Kimberly-Clark Professional</td>
			<td>34120</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Acetone, Isopropanol</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
		 <td></td>
		 <td></td>
		 <td></td>
		 <td>Table 2. Materials for Chalcogenide Fiber Preparation.</td>
	 </tr>
		 <tr>
			<td>Pyrocam</td>
			<td>Ophir Photonics</td>
			<td>Pyrocam III Series</td>
			<td>Any camera with sensitivity at pump wavelength will work.</td>
		 </tr>
		 <tr>
			<td>Monochromator</td>
			<td>Photon Technology International</td>
			<td></td>
			<td>A 100 line/mm grating was used. Any spectral measurement device will work (e.g. longpass filter). </td>
		 </tr>
		 <tr>
			<td>CaF2 Lenses</td>
			<td>Thorlabs</td>
			<td>LB5922</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>InAs Filter</td>
			<td>Any vendor.</td>
			<td></td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Amplified InSb Detector</td>
			<td>Hamamatsu</td>
			<td>P4631-03</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Computer</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>DAQ</td>
			<td>National Instruments</td>
			<td>USB X Series</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Labview software for motorized stages</td>
			<td>National Instruments</td>
			<td></td>
			<td>Optional. Custom program.</td>
		 </tr>
		 <tr>
			<td>Labview software for collecting detector data</td>
			<td>National Instruments</td>
			<td></td>
			<td>Optional. Custom program.</td>
		 </tr>
		 <tr>
			<td>Assorted posts, optics mounts, bases, and forks</td>
			<td></td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>1" Gold mirrors</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Chopper and controller</td>
			<td>Any vendor.</td>
			<td>SRS Model SR540</td>
			<td>Optional. Depends on detector being used.</td>
		 </tr>
		 <tr>
		 <td></td>
		 <td></td>
		 <td></td>
		 <td>Table 3. Materials for In-situ Tapering Procedure.</td>
	 </tr>
		</tbody>
 </table>

in-situ tapering of chalcogenide fiber for mid-infrared supercontinuum generation

Supercontinuum generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared (or mid-IR, roughly the 2-20 &mu;m wavelength range) frequency combs1, 2 for applications such as molecular fingerprinting, 3 trace gas detection, 4 laser-driven particle acceleration, 5 and x-ray production via high harmonic generation. 6 Achieving efficient SCG in a tapered optical fiber requires precise control of the group velocity dispersion (GVD) and the temporal properties of the optical pulses at the beginning of the fiber, 7 which depend strongly on the geometry of the taper. 8 Due to variations in the tapering setup and procedure for successive SCG experiments-such as fiber length, tapering environment temperature, or power coupled into the fiber, in-situ spectral monitoring of the SCG is necessary to optimize the output spectrum for a single experiment.
	In-situ fiber tapering for SCG consists of coupling the pump source through the fiber to be tapered to a spectral measurement device. The fiber is then tapered while the spectral measurement signal is observed in real-time. When the signal reaches its peak, the tapering is stopped. The in-situ tapering procedure allows for generation of a stable, octave-spanning, mid-IR frequency comb from the sub harmonic of a commercially available near-IR frequency comb. 9 This method lowers cost due to the reduction in time and materials required to fabricate an optimal taper with a waist length of only 2 mm.
	The in-situ tapering technique can be extended to optimizing microstructured optical fiber (MOF) for SCG10 or tuning of the passband of MOFs, 11 optimizing tapered fiber pairs for fused fiber couplers12 and wavelength division multiplexers (WDMs), 13 or modifying dispersion compensation for compression or stretching of optical pulses.14-16

After successful completion of the in-situ tapering procedure, the pump spectrum broadened to cover from 2.2 to 5 &mu;m (at ~40 dB below the peak), as seen in Figure 3. The pump pulse energy in the As2S3 fiber was ~250 pJ with an initial pulse length under 100 fsec. The short length of the tapered waist, ~2.1 mm, allows for generation of a broadband, coherent SC. This preserves the frequency comb properties of the pump source. More information about the frequency comb and o...

Watch this Scientific Journal Video about In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation at JoVE.com

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

We describe a method for in-situ tapering of As2S3 fibers to achieve efficient mid-infrared supercontinuum generation. By tapering while monitoring the supercontinuum&#x2019;s spectrum, the spectral width can be maximized for a fiber taper. In-situ fiber tapering can be applied to optimize the performance of other fiber-based devices.

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

Supercontinuum  generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared  (or mid-IR, roughly the 2-20 &mu;m wavelength ...

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