The SAIL labs are funded through JBH's Australian Laureate Fellowship from the Australian Research Council.
This research was supported by the Australian Research Council Centre of Excellence for Ultrahigh bandwidth Devices for Optical Systems (project number CE110001018).
Experimental work was performed in part at the OptoFab node of the Australian National Fabrication Facility, utilizing NCRIS and NSW state government funding. Fiber hydrogenation services were provided by TE Connectivity in Redfern. SLS would like to acknowledge the Optics and Electronics Laboratory, Fujikura Ltd, Japan for providing the 7-core fiber used in this experiment.

1. Preparation of Polished Capillary Tubes (ANFF OptoFab)
<ol>
	<li>Obtain glass capillary tubes with inner diameter closely matched to fiber diameter. The closer in size, the better the performance, but ensure that a &#177;10 &#181;m variation in capillary size is allowed for. Remove any protective coatings from the capillary tubes. Shave off coatings with a razor blade to remove them without damaging the tubes.</li>
	<li>Taper the capillary tubes to a smaller diameter if required. Use a computer-controlled automatic tapering machine if available.
	<ol>
		<li>Secure a length of tubing with clamps at either end.</li>
		<li>Heat the capillary to melting point evenly around its diameter using a hot filament located between the clamps.</li>
		<li>Draw the capillary through the heating element with a constant tension until the desired length has been tapered to the smaller diameter.</li>
	</ol>
	</li>
	<li>Cut the capillary tube into approximately equal lengths with a glass cutting tool. Ensure that these are at least 2 cm longer than the intended grating length but small enough to fit within the polishing equipment used. Note: For this experiment, a capillary length of 7 cm was used.</li>
	<li>Attach 8-10 of the capillary lengths to a glass puck using UV-curable glue. Install the puck onto a jig compatible with the lapping/polishing machine.</li>
	<li>Use the lapping/polishing machine to grind the exposed walls of the capillary tubes to a flat surface. CAUTION: Do not inhale loose grit. Note: The abrasive element is Al2O3 in a suspension of reverse-osmosis purified water.
	<ol>
		<li>Use 25 &#181;m grit until the remaining thickness of the capillary wall is approximately 70 &#181;m. Use a micrometer to measure the displacement of the jig during grinding and hence the amount that has been removed.</li>
		<li>Switch to 5 &#181;m grit and grind until the remaining thickness of the wall is approximately 50 &#181;m.</li>
	</ol>
	</li>
	<li>Use the lapping/polishing machine to polish the flattened surface for at least 3 hr with high-purity colloidal silica in alkaline dispersion (NaOH). Note: This restores the surface to optical quality. The silica can be prevented from solidifying by adding 1 part 0.004 M NaOH to 3 parts polishing solution.</li>
	<li>Separate the capillary tubes from the holding puck by soaking overnight in acetone.</li>
	<li>Examine the capillary tubes at both ends under a microscope with 10X&#160;magnification to check the wall thickness. Note: A good quality capillary will have a uniform thin (~ 50 &#181;m) wall along its length.</li>
</ol>
2. Creation of Gratings
<ol>
	<li>Hydrogenate the MCF to increase photosensitivity.
	<ol>
		<li>Place the fibers to be hydrogenated into a sealed airtight chamber. CAUTION: Ensure the chamber is securely bolted due to the presence of pressurized gases.</li>
		<li>Pump high purity H2 into the chamber. Use N2 gas as a booster to increase pressure.</li>
		<li>Leave the fibers inside the chamber for an extended period: 2 weeks at 300 bar and room temperature, or 3 days at 380 bar and 80 &#176;C.</li>
		<li>Vent the gases from the chamber and remove the fibers. CAUTION: Ensure the room is well ventilated. Gases may act as asphyxiants, or fire risk in the case of H2.</li>
		<li>Keep the fibers in a freezer with temperature -70 &#176;C or below until they are used. This slows the rate of hydrogen outgassing and preserves the increased photosensitivity.</li>
	</ol>
	</li>
	<li>Strip the protective coating from the MCF. Strip MCFs the same size as SMFs with a standard SMF fiber stripper; otherwise shave off the coating with a razor blade. Remove the coating from the region where the grating is to be written, all the way to the end of the fiber.</li>
	<li>Insert the stripped end of the fiber into the capillary tube, and slide the tube along the fiber so that it covers the region to be inscribed.</li>
	<li>Put on UV-protective eyewear. Mount the fiber on the moving stage which holds the phase mask, with the flat side of the capillary tube angled towards the phase mask. Ensure the fiber is positioned within the interference pattern created by the mask, but not touching the mask itself as this may cause damage.</li>
	<li>Align the 244 nm laser so that the beam is perpendicular to the flat surface of the phase mask. Ensure that the fiber receives at least 90 mW of laser power.</li>
	<li>Expose a 4 cm length of the fiber to the UV interference pattern by moving the fiber and phase mask together with respect to the incoming beam at a rate of 0.25 mm/min.</li>
	<li>Remove the capillary tube from the fiber.</li>
	<li>Anneal the grating at 110 &#176;C for 20 hr to stabilize the wavelength response. Note: This step is optional as the grating will stabilize by itself over the course of approximately three days, but annealing makes the process faster.</li>
</ol>
3. Analysis of Spectra
<ol>
	<li>Cleave both ends of the fiber. Use a fiber cleaver that allows the user to set both fiber diameter and tension to ensure a flat end surface.</li>
	<li>Illuminate one end of the fiber using a tunable laser with a central wavelength approximately matched to the Bragg wavelength.</li>
	<li>Connect a CCD camera to a PC with control software to display and record the fiber output. Image the fiber output with the CCD camera, using a microscope objective lens with 50X magnification in front of the camera to ensure that all cores cover multiple CCD pixels. Note: The following steps 3.4.1 &#8211; 3.5.5 are specific to the custom software used by the authors and represent only one method of capturing spectra.
	<ol>
		<li>Select a circular region of pixels corresponding to each core by clicking on the centers of cores as they appear in the image in the control software. Enter the diameter of the cores in units of pixels in the &#39;Length or Diameter&#39; field.</li>
		<li>Record the pixel values registered by the camera for the selected regions. Sum the values for all pixels covering a given core to quantify the total throughput at that wavelength.</li>
	</ol>
	</li>
	<li>Connect the tunable laser to the control PC so that observations and data collection can be automated.
	<ol>
		<li>Enter a wavelength approximately 5 nm below the Bragg wavelength in the &#39;Start Wavelength&#39; field.</li>
		<li>Set the wavelength increment of the laser to 0.01 nm in the &#39;Scan - Step&#39; field. Note: Set the delay between steps to at least 300 msec so that lasing is stable at each wavelength before measurements are recorded and the next wavelength step occurs.</li>
		<li>Enter a wavelength approximately 5 nm greater than the Bragg wavelength in the &#39;End Wavelength&#39; field.</li>
		<li>Click the &#39;Automatic Scan&#39; button to set the laser to the defined Start Wavelength and increase the wavelength by the chosen increment at regular time intervals.</li>
		<li>Record the intensity transmitted through each core for each wavelength step. Export the calculated values to a text file by enabling the &#39;Text File Save&#39; option.</li>
	</ol>
	</li>
	<li>Repeat the scan at least 3 times and average the data from all runs.</li>
	<li>Plot transmitted power versus wavelength for each core to generate a set of spectra.
	<ol>
		<li>Compare the spectra of all cores to confirm whether they have the same suppression characteristics. Check that the central wavelength, depth and bandwidth of each grating match.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Othonos, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fiber+Bragg+gratings.">Fiber Bragg gratings.</a> Rev. Sci. Instrum. 68 (12), 4309-4341 (1997).</li><li>Bland-Hawthorn, J., Englund, M., Edvell, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+approach+to+atmospheric+OH+suppression+using+an+aperiodic+fiber+Bragg+grating.">New approach to atmospheric OH suppression using an aperiodic fiber Bragg grating.</a> Opt. Express. 12 (24), 5902-5909 (2004).</li><li>Jovanovic, N., Guyon, O., Martinache, F., Schwab, C., Cvetojevic, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+inject+light+efficiently+into+single-mode+fibers.">How to inject light efficiently into single-mode fibers.</a> Proc. SPIE. 9147, 91477P (2014).</li><li>Bland-Hawthorn, 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=A+complex+multi-notch+astronomical+filter+to+suppress+the+bright+infrared+sky.">A complex multi-notch astronomical filter to suppress the bright infrared sky.</a> Nat. Comm. 2, 581 (2011).</li><li>Leon-Saval, S. G., Argyros, A., Bland-Hawthorn, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photonic+lanterns.">Photonic lanterns.</a> Opt. Express. 18 (8), 8430-8439 (2010).</li><li>Trinh, C. Q., 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=GNOSIS:+the+first+instrument+to+use+fiber+Bragg+gratings+for+OH+suppression.">GNOSIS: the first instrument to use fiber Bragg gratings for OH suppression.</a> Astron. J. 145 (2), 51 (2013).</li><li>Content, R., 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=PRAXIS:+low+thermal+emission+high+efficiency+OH+suppressed+fiber+spectrograph.">PRAXIS: low thermal emission high efficiency OH suppressed fiber spectrograph.</a> Proc. SPIE. 9151, 91514W (2014).</li><li>Birks, T. A., Mangan, B. J., D&#236;ez, A., Cruz, J. L., Murphy, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photonic+lantern'+spectral+filters+in+multi-core+fiber.">Photonic lantern' spectral filters in multi-core fiber.</a> Opt. Express. 20 (13), 13996-14008 (2012).</li><li>Askins, C., 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=Inscription+of+fiber+Bragg+gratings+in+multicore+fiber.">Inscription of fiber Bragg gratings in multicore fiber.</a> BGPP. , JWA39 (2007).</li><li>Lindley, E., 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=Core-to-core+uniformity+improvement+in+multicore+fiber+Bragg+gratings.">Core-to-core uniformity improvement in multicore fiber Bragg gratings.</a> Proc. SPIE. 9151, 91515F (2014).</li><li>Lindley, E., 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=Demonstration+of+uniform+multicore+fiber+Bragg+gratings.">Demonstration of uniform multicore fiber Bragg gratings.</a> Opt. Express. 22 (25), 31575-31581 (2014).</li><li>Tomaru, S., Yasu, M., Kawachi, M., Edahiro, T. V. A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=VAD+single-mode+fiber+with+0.2+dB/km+loss.">VAD single-mode fiber with 0.2 dB/km loss.</a> Elec. Lett. 17 (2), 93-93 (1981).</li></ol>

The authors declare that they have no competing financial interests.

Figures 2 and 3 together show that introducing the polished capillary tube (PCT) when writing gratings is sufficient to improve the uniformity of core spectra in the MCFBG. The rest of the inscription process is largely unchanged from established methods for creating SMF gratings and can be used with most existing FBG writing systems. Hence the preparation of PCTs as outlined in section 2 of the protocol is most critical for improving MCFBG uniformity. The best results are achieved with ...

Fiber Bragg gratings (FBGs) are widely used as narrowband filters due to the fact they can be customized for a large number of applications1. They are not limited to suppressing single wavelengths; complex transmission spectra can be created by the use of aperiodic refractive index variations2. One limitation is that FBGs can only be inscribed in single-mode fibers (SMFs), as the wavelength that is suppressed for a given grating period depends on the propagation constant. In a multimode fiber (MMF), where each mode has a different propagation constant, the suppressed wavelength for each mode is different and hence the grating does not give strong suppression at any single wavelength.
The impetus for this experiment comes from astronomy. Under seeing-limited conditions, direct coupling into an SMF is difficult and inefficient; extreme adaptive optics are required to do so3. Because of this, MMFs are typically used when collecting light from the telescope focal plane4. Therefore in order to keep the functionality available only to SMFs, it is necessary to have efficient conversion between SMFs and MMFs. This is made possible with the photonic lantern, a device which consists of a multimode port connected to an array of SMFs via a taper transition5. Photonic lanterns were used in the GNOSIS instrument, in which the SMFs contained FBGs to remove atmospheric emission lines (caused by OH radicals and other molecules) from near-infrared observations6. The drawbacks of using individual, single-core SMFs for this task are that they must be written one by one and spliced individually into the optical train, requiring significant time and manual effort. The technique described in this article attempts to address these shortcomings using a more complex fiber format to provide the single-mode functionality.
The next generation OH suppression instrument PRAXIS7 will make use of multi-core fibers (MCFs). These fibers contain any number of single-moded cores embedded in a single cladding. The advantage of this approach is that the MCF can be tapered into an MMF with the resulting photonic lantern being a compact and robust self-contained unit. In the completed instrument, light from the telescope will be coupled into the MMF port of the lantern; the taper transition will separate this light into the single-mode cores where it will pass through the FBGs. After the wavelength filtering the remaining light is dispersed onto a detector, the spectra collected.
Using MCFs also speeds up the process of writing gratings, as all cores can be inscribed in a single pass. However, the writing process must be modified in order to ensure that all cores have the same reflection characteristics. This is because the curved surface of the cladding acts as a lens during side-writing of the FBGs, resulting in a UV field which varies in power and direction at each core if the standard side-writing method is used. Hence each core will have a different transmission profile, and the fiber will not provide strong suppression at a single wavelength8.
A group at the Naval Research Laboratory experimented with modifying the distribution and photosensitivity of cores to cancel the effects of this variation9. The downside of using such an approach is that the fiber must be redesigned for every combination of cladding size, core size, number of cores and chemical composition. In addition, the lack of axial symmetry in the resulting designs means that the MCF cannot be effectively tapered into an MMF with a circular core. This paper details a different approach to the problem: modifying the field within the fiber by having it pass through a flat surface instead of being directly incident on the curved cladding. Using this approach results in a technique which is transferable to a variety of MCF designs and sizes, particularly the axially symmetric fibers which we wish to incorporate into photonic lanterns.
To create the necessary flat surface, the MCF is placed inside a UV-transparent capillary tube which has been ground and polished on one side to give a flat outer wall. A small gap must be left between the fiber and capillary, since the latter may contain &#177;10 &#181;m variations in diameter. See Figure 1 for a representation. This paper will describe the experimental procedure to write FBGs in this manner and provide examples of the possible improvements. For more information see previously published simulations10 and experimental results11.
<img alt="Figure 1" src="/files/ftp_upload/53326/53326fig1.jpg" /> 
Figure 1.&#160;Diagram of polished capillary tube as used in FBG production. The MCF is placed inside the capillary tube. The gap between the two should be small but allow for small variations in diameter. The UV light which has passed through the phase mask then enters the system through the flat side of the capillary tube. <a href="https://www.jove.com/files/ftp_upload/53326/53326fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="0" cellpadding="0" cellspacing="0" width="1171">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Multicore fiber</td>
			<td style="width:148px;">Fujikura Ltd.</td>
			<td style="width:163px;"></td>
			<td style="width:645px;">7 cores with diameter 5.5 &#181;m, core separation 35 &#181;m, hexagonally arranged within 125 &#181;m cladding, NA = 0.177</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glass tapering machine</td>
			<td style="width:148px;">Vytran</td>
			<td style="width:163px;">GPX-3000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">UV laser</td>
			<td style="width:148px;">Coherent</td>
			<td style="width:163px;">300 FreD Innova</td>
			<td>Frequency doubled 244 nm, at least 150 mW output. CAUTION: eye damage; wear appropriate goggles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Phase mask</td>
			<td style="width:148px;">Lasiris</td>
			<td style="width:163px;">PM-244-1069.50-50.8</td>
			<td>Custom component, 1069.50 nm grating period, 5.08 mm thickness</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Capillary tubes</td>
			<td style="width:148px;">Polymicro</td>
			<td>TSP200794</td>
			<td>Inner diameter 200 &#181;m, outer diameter 794 &#181;m</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Lapping machine</td>
			<td style="width:148px;">Logitech</td>
			<td style="width:163px;">PM5</td>
			<td>Combination grinder/polisher</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">UV-curable glue</td>
			<td style="width:148px;">Norland</td>
			<td style="width:163px;">NOA-61</td>
			<td>Cures rapidly, removable with acetone</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microgrit</td>
			<td style="width:148px;">Eminess</td>
			<td style="width:163px;"></td>
			<td>Al2O3: 25 &#181;m and 5 &#181;m particle size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Polishing fluid</td>
			<td style="width:148px;">Eminess</td>
			<td style="width:163px;">ULTRA-SOL 500S</td>
			<td>SF-500S-5, ULTRA-SOL 500S N/D, 5 GAL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium hydroxide</td>
			<td style="width:148px;"></td>
			<td style="width:163px;"></td>
			<td>0.004M</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fiber cleaver</td>
			<td style="width:148px;">Vytran</td>
			<td style="width:163px;">LDC-400</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tunable laser</td>
			<td style="width:148px;">JDS Uniphase</td>
			<td style="width:163px;">SWS15101</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">IR Camera</td>
			<td style="width:148px;">Xenics</td>
			<td style="width:163px;">XEVA-1429</td>
			<td>320x256 pixel, 16 bit resolution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oven</td>
			<td style="width:148px;">Thermoline Scientific</td>
			<td style="width:163px;">LDO-030N</td>
			<td>For annealing at T=110&#176;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hydrogen gas</td>
			<td style="width:148px;">BOC</td>
			<td style="width:163px;"></td>
			<td>For hydrogenating fiber. CAUTION: flammable, pressurised gas</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nitrogen gas</td>
			<td style="width:148px;">BOC</td>
			<td style="width:163px;"></td>
			<td>Booster for hydrogenation. CAUTION: pressurised gas</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Acetone</td>
			<td style="width:148px;"></td>
			<td style="width:163px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Razor blades</td>
			<td style="width:148px;"></td>
			<td style="width:163px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

writing bragg gratings in multicore fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

The effectiveness of this technique is best demonstrated by comparing the multicore fiber Bragg gratings (MCFBGs) that result from exposure with and without the capillary. Figure 2 shows the transmission characteristics of a 7-core MCF exposed using the standard method for SMFs, with individual core spectra represented by different colors. There is minimal overlap between the suppressed wavelengths, and core #5 has received weaker exposure resulting in a shallower notch. ...

Watch this Scientific Journal Video about Writing Bragg Gratings in Multicore Fibers at JoVE.com

Writing Bragg Gratings in Multicore Fibers

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

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8.1K Views.  University of Sydney. We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Video: Writing Bragg Gratings in Multicore Fibers

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Writing and Low-Temperature Characterization of Oxide Nanostructures

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.

Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions.  Oxide ...

Prescribed 3-D Direct Writing of Suspended Micron/Sub-micron Scale Fiber Structures via a Robotic Dispensing System

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer fiber length and orientation is defined by the spatial positioning of the dispensing system 3-axis stages. The fiber diameter is defined by the prescribed dispense time of the dispensing system valve, the feed rate (the speed at which the stage traverses from an initiating to a terminating position), the gauge diameter of the dispensing tip, the viscosity and surface tension of the polymer solution, and the programmed drawing length. The stage feed rate affects the polymer solution&#8217;s evaporation rate and capillary breakup of the filaments. The dispensing system consists of a pneumatic valve controller, a droplet-dispensing valve and a dispensing tip. Characterization of the direct write process to determine the optimum combination of factors leads to repeatedly acquiring the desired range of fiber diameters. The advantage of this robotic dispensing system is the ease of obtaining a precise range of micron/sub-micron fibers onto a desired, programmed location via automated process control. Here, the discussed self-assembled micron/sub-micron scale 3D structures have been employed to fabricate suspended structures to create micron/sub-micron fluidic devices and bioengineered scaffolds.

Here, we present a protocol to fabricate freely-suspended, micron/sub-micron scale polymer fibers and &#8220;web-like&#8221; structures generated via automated direct writing procedure by means of a 3-axis dispensing system.

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer ...

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

Detection and Recovery of Palladium, Gold and Cobalt Metals from the Urban Mine Using Novel Sensors/Adsorbents Designated with Nanoscale Wagon-wheel-shaped Pores

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in industrialized countries. Here, the development of optical mesosensors/adsorbents (MSAs) for efficient recognition and selective recovery of Pd(II), Au(III), and Co(II) from urban mine was achieved. A simple, general method for preparing MSAs based on using high-order mesoporous monolithic scaffolds was described. Hierarchical cubic Ia3d wagon-wheel-shaped MSAs were fabricated by anchoring chelating agents (colorants) into three-dimensional pores and micrometric particle surfaces of the mesoporous monolithic scaffolds. Findings show, for the first time, evidence of controlled optical recognition of Pd(II), Au(III), and Co(II) ions and a highly selective system for recovery of Pd(II) ions (up to ~95%) in ores and industrial wastes. Furthermore, the controlled assessment processes described herein involve evaluation of intrinsic properties (e.g., visual signal change, long-term stability, adsorption efficiency, extraordinary sensitivity, selectivity, and reusability); thus, expensive, sophisticated instruments are not required. Results show evidence that MSAs will attract worldwide attention as a promising technological means of recovering and recycling palladium, gold and cobalt metals.

Because of the importance and extensive use of palladium, gold and cobalt metals in high-technology equipment, their recovery and recycling constitute an important industrial challenge. The metal recovery system described herein is a simple, low-cost means for the effective detection, removal, and recovery of these metals from the urban mine.

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in ...

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

During embryogenesis, the epicardial contribution to coronary vasculature development has been very well established. Cells derived from the epicardium differentiate into smooth muscle cells, fibroblasts and endothelial cells that contribute to the formation of coronary vessels. Here we have established an in vitro culture method for embryonic epicardial cells. Using genetic labelling, we have demonstrated that the majority of the migrating cells in our explant culture are of epicardial origin. Epicardial explant cells also retain the expression of epicardial markers (Wt1 and Tbx18). Furthermore, we provide evidence that epicardial explant cells undergo epithelial to mesenchymal transition (EMT), migrate and differentiate into smooth muscle cells after Transforming growth factor beta 1 (TGF-&#946;1) treatment in a manner indistinguishable from that of epicardial cells in vivo. In conclusion, we provide a novel method for the culture of embryonic epicardial cells, which will help to explore the role of specific genes in epicardial cell biology.

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

The epicardium is an essential source of multipotent cardiovascular progenitor cells and paracrine factors that are required for cardiovascular development and regeneration. We describe here a method to culture mouse embryonic epicardial cells.

During embryogenesis, the epicardial contribution to coronary vasculature development has been very well established. Cells derived from the epicardium ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...