This research is supported by grant number 1029547 from the National Science Foundation. The authors would like to acknowledge D.J. Welker from Paradigm Optics Inc. for providing the initial fiber segments and the redrawing of the final optical fiber. Authors also acknowledge Steven Hardcastle and Heather A. Owen for SEM imaging.

1. Fabricating a Disordered Polymer Optical Fiber
<ol>
	<li>Spread about 200 of the PMMA strands on a table and spread the same number of PS strands on top of the PMMA. Mix and repack the strands. Repeat this procedure until 40,000 strands of PMMA are randomly mixed with 40,000 strands of PS.</li>
	<li>Assemble the randomly mixed strands into a square preform with a side width of about 2.5 inches.</li>
	<li>Draw the preform into an optical fiber with a diameter of 250 &mu;m . The preform is drawn at Paradigm Optics Incorporated using their standard procedure 16.</li>
</ol>
2. Imaging the Refractive Index Profile of the Disordered Fiber
<ol>
	<li>Use an SEM such as Topcon ABT to image the refractive index profile of the resulting optical fiber.</li>
	<li>Submerge the polymer optical fiber samples in liquid nitrogen for about 10 min and then break in half.</li>
	<li>Submerge the broken tips of the samples in ethyl alcohol. Keep the temperature of the solution at about 65 &deg;C. Leave the samples in the solution for about 3 min, until the ethyl alcohol dissolves the PMMA sites in the fiber.</li>
	<li>Coat each sample with a 10-nm-thick layer of Au/Pd and place the sample in the chamber of the SEM.</li>
</ol>
3. Preparing the Fiber Samples for Optical Characterization
<ol>
	<li>Prepare 5 cm long fiber samples.</li>
	<li>Heat a curved blade to 65 &deg;C , and the fiber to 37 &deg;C . Using the right temperatures prevents the deformation of the fiber tip that can occur in the cleaving process.</li>
	<li>Align the tip of the fiber on a cutting surface, so that a clean, perpendicular cut can be made. Place the blade on the side of the fiber, and then quickly roll across.</li>
	<li>Inspect the fiber tip using an optical microscope to make sure the fiber tip is cleaved perpendicular to the fiber sides. Keep the razor blade at a right angle in the cleaving process to prevent tilting of the tip.</li>
	<li>Use a polishing paper such as Thorlabs LFG03P Aluminum Oxide Polishing Paper (0.3 &mu;m) to polish the fiber samples. To polish the fiber end, hold it in a pair of tweezers, with the tweezers gripping the fiber approximately 1.5 mm away from the face being polished. Draw the fiber over the paper in one-inch long figure-8-shaped paths, approximately eight times. Figure-8-shaped paths ensure that the whole tip is polished.</li>
</ol>
4. Measuring the Beam Profile of the Propagated Beam in the Fiber Samples
<ol>
	<li>Couple the He-Ne laser into a SMF630hp fiber using a 20X objective and two flat mirrors. Place the flat mirrors on stages with two degrees of freedom. Place the objective on a stage with three degrees of freedom. Initially keep the SMF fiber a distance of 8 mm away from the objective tip. Using the knobs on the mirror holders and the objective holder, illuminate the laser light to the tip of the fiber. Connect the other side of the SMF to a power meter. Couple power into the SMF using the knobs on the mirror holders as well as the transversal knobs on the objective holder. The efficiency of coupling can be significantly increased by using the longitudinal positioning knob on the objective holder. A coupled power of 1 mW is enough for the measurements.</li>
	<li>Couple the SMF630hp fiber to the polymer optical fiber using Thorlabs MAX343 motorized stage. The motorized stage can be moved in the three Cartesian directions. Using the transversal degrees of freedoms, couple the SMF fiber to the center of the polymer fiber tip. Using the longitudinal displacement of the stage, place the SMF fiber as closely as possible to the polymer fiber. A smaller air-gap between the SMF and polymer fiber reduces the expansion of the beam. Place the entire setup on a second motorized stage that moves in the longitudinal direction. The second motorized stage is used for imaging as will be described in 4.4.</li>
	<li>Using an optical microscope and a right-angled mirror, monitor the position of the SMF and polymer fiber to make sure that the SMF is coupled in the center of the polymer fiber, and that the air-gap between the two fibers is as small as possible. A small tilt in the polymer fiber tip or deformations in the polymer fiber tip because of cleaving or polishing processes can limit the minimum air-gap between SMF and polymer fiber. A small gap between the fibers is required because the SMF fiber should be able to move around at the tip of the polymer fiber. Place the SMF at the center of the polymer fiber solely to make the coupling process easier. During the experiment, transversely sweep the incident beam that comes out of the SMF across the tip of the polymer fiber to observe localization in different regions of the polymer fiber.</li>
	<li>Use a CCD camera beam profiler to measure the output of the fiber using a 40X objective. First, saturate the CCD camera to monitor the boundaries of the polymer fiber. Using the knobs on the objective holder, make sure that the polymer fiber boundaries can be observed on the CCD.</li>
	<li>Use a motorized stage that moves the whole setup (described in 4.2) longitudinally, make sure the image on the CCD is focused by moving the setup away or towards the 40X objective while the CCD and objective are fixed. As a metric for focusing, an imaged profile on the CCD should have the minimum size at the focus. A focused image of the beam should not be visually winding.</li>
	<li>Move the incident beam at the input tip and measure the output beam intensity for different incident beam positions. Collect data for 5 different positions of the incident beam. Carry out the measurements for 20 fiber samples and collect a total of 100 different measurements.</li>
</ol>

<ol>
	<li>Anderson, P. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Absence+of+diffusion+in+certain+random+lattices.">Absence of diffusion in certain random lattices.</a> Phys. Rev. 109, 1492-1505 (1958).</li><li>John, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strong+localization+of+photons+in+certain+disordered+dielectric+super+lattices.">Strong localization of photons in certain disordered dielectric super lattices.</a> Phys. Rev. Lett. 58, 2486-2489 (1987).</li><li>Anderson, P. 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+question+of+classical+localization:+a+theory+of+white+paint?.">The question of classical localization: a theory of white paint?.</a> Phil. Mag. B. 52, 505-509 (1985).</li><li>Wiersma, D. S., Bartolini, P., Lagendijk, A., Righini, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+light+in+a+disordered+medium.">Localization of light in a disordered medium.</a> Nature. 390, 671-673 (1997).</li><li>Dalichaouch, R., Armstrong, J. P., Schultz, S., Platzman, P. M., McCall, 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=Microwave+localization+by+two-dimensional+random+scattering.">Microwave localization by two-dimensional random scattering.</a> Nature. 354, 53-55 (1991).</li><li>Lagendijk, A. D., de Vries, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transverse+localization+of+light.">Transverse localization of light.</a> Phys. Rev. Lett. 62, 47 (1989).</li><li>Schwartz, T., Bartal, G., Fishman, S., Segev, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transport+and+Anderson+localization+in+disordered+two+dimensional+photonic+lattices.">Transport and Anderson localization in disordered two dimensional photonic lattices.</a> Nature. 446, 52-55 (2007).</li><li>Szameit, A., Kartashov, Y. V., Zeil, P., Dreisow, F., Heinrich, M., Keil, R., Nolte, S., Tunnermann, A., Vysloukh, V. A., Torner, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wave+localization+at+the+boundary+of+disordered+photonic+lattices.">Wave localization at the boundary of disordered photonic lattices.</a> Opt. Lett. 35, 1172-1174 (2010).</li><li>Martin, L., Giuseppe, G. D., Perez-Leij, A. a., Keil, R., Dreisow, F., Heinrich, M., Nolte, S., Szameit, A., Abouraddy, A. F., Christodoulides, D. N., Saleh, B. E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anderson+localization+in+optical+waveguide+arrays+with+off-diagonal+coupling+disorder.">Anderson localization in optical waveguide arrays with off-diagonal coupling disorder.</a> Opt. Express. 19, 13636-13646 (2011).</li><li>Lahini, Y., Avidan, A., Pozzi, F., Sorel, M., Morandotti, R., Christodoulides, D. N., Silberberg, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anderson+localization+and+nonlinearity+in+one-dimensional+disordered+photonic+lattices.">Anderson localization and nonlinearity in one-dimensional disordered photonic lattices.</a> Phys. Rev. Lett. 100, 013906 (2008).</li><li>Karbasi, S., Mirr, C. R., Yarandi, P. G., Frazier, R. J., Koch, K. W., Mafi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+transverse+Anderson+localization+in+an+optical+fiber.">Observation of transverse Anderson localization in an optical fiber.</a> Opt. Lett. 37, 2304-2306 (2012).</li><li>Karbasi, S., Mirr, C. R., Frazier, R. J., Yarandi, P. G., Koch, K. W., Mafi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detailed+investigation+of+the+impact+of+the+fiber+design+parameters+on+the+transverse+Anderson+localization+of+light+in+disordered+optical+fibers.">Detailed investigation of the impact of the fiber design parameters on the transverse Anderson localization of light in disordered optical fibers.</a> Opt. Express. 20, 18692-18706 (2012).</li><li>Karbasi, S., Koch, K. W., Mafi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple-beam+propagation+in+an+Anderson+localized+optical+fiber.">Multiple-beam propagation in an Anderson localized optical fiber.</a> Opt. Express. 21, (2013).</li><li>Abdi, O., Wong, K. C., Hassan, T., Peters, K. J., Kowalsky, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cleaving+of+solid+single+mode+polymer+optical+fiber+for+strain+sensor+applications.">Cleaving of solid single mode polymer optical fiber for strain sensor applications.</a> Opt. Commun. 282, 856-861 (2009).</li><li>Karbasi, S., Koch, K. W., Mafi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modal+perspective+on+the+transverse+Anderson+localization+of+light+in+disordered+optical+lattices.">A modal perspective on the transverse Anderson localization of light in disordered optical lattices.</a> arXiv. 1301.2385v1, (2013).</li><li>Karbasi, S., Hawkins, T., Ballato, J., Koch, K. W., Mafi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transverse+Anderson+localization+in+a+disordered+glass+optical+fiber.">Transverse Anderson localization in a disordered glass optical fiber.</a> Opt. Mater. Express. 2, 1496-1503 (2012).</li></ol>

The authors declare that they have no competing financial interests.

In the fiber draw process, the refractive index profile does not remain constant for more than a meter, both because of the cross-overs of the original fiber strands and also because of the variations of the fiber diameter in the draw process. We expect that a more stable draw process will help to fabricate an optical fiber that is invariant over longer fiber lengths compared with that reported here.
In preparing a sample for the SEM imaging of the fiber tip, we need to ensure that the sample ...

In a theoretical work by P.W. Anderson 1, it was shown that in the presence of disorder in a quantum electronic system, the diffusion process stops and localized electronic states develop. Anderson localization is a wave phenomenon that can also occur for classical waves such as light. Since the theoretical prediction of Anderson localization in optics 2,3, there have been many efforts to realize this phenomenon experimentally with electromagnetic waves 4,5. However, it has been very difficult to achieve strong localization because the optical scattering cross sections are often too small due to the low refractive index contrast of most optical materials. In 1989, De Raedt et al. 6 showed that it is possible to observe the Anderson localization in a quasi-two-dimensional disordered optical system with low refractive index contrasts. They showed that if the disorder is confined to the transverse plane of a propagating wave in a longitudinally invariant medium, the beam can remain confined to a small region in the transverse direction due to strong transverse scattering. Transverse Anderson localization was first observed in two-dimensional waveguides that were created by using interference patterns in a photo-refractive crystal 7. Fused silica is the other medium that has been used for the observation of transverse Anderson localization 8,9, where disordered waveguides are written using femtosecond pulses along the sample. The refractive index difference of disordered sites in the above mentioned systems are on the order of 10-4 , so the localization radius is quite large. Additionally, the typical waveguides are usually not longer than several centimeters; therefore, they may not be practical for guided-wave applications. We point out that the observation of transverse Anderson localization in a one-dimensional disordered waveguide was reported earlier in Ref 10.
The optical fiber developed here has several advantages over the previous realizations of transverse Anderson localization for guided-wave applications 11,12. First, the large refractive difference of 0.1 between the disorder sites of the fiber results in a small localized beam comparable to the beam radius of regular optical fibers. Second, the polymer disordered optical fiber can be made much longer than the disordered waveguides written externally into photorefractive crystals or fused silica. We were able to observe transverse Anderson localization in a 60-cm-long fiber 11. Third, the polymer disordered optical fiber is flexible, making it practical for real world device-level applications that rely on the transport of light waves in fibers 13.
In order to fabricate the disordered optical fiber, 40,000 strands of PMMA and 40,000 strands of PS were randomly mixed, where each strand was 8 inches long and 250 &mu;m in diameter. The randomly mixed strands were assembled into a square cross-section preform with a side-width of about 2.5 inches. The preform was then drawn to a square optical fiber with a side width of about 250 &mu;m (Figure 1). In order to randomly mix the original fiber strands, we spread a layer of PMMA fiber strands on a large table, added a layer of PS fiber strands, and then randomly mixed them together. The procedure was repeated many times until a good random mixture was obtained.
We used a scanning electron microscope (SEM) to image the refractive index profile of the disordered polymer optical fiber. Regular cleaving techniques such as using a sharp heated blade cannot be used to prepare the fiber samples for the SEM imaging of the fiber end to map its refractive index profile, because the blade damages the morphology of the fiber end. Polishing the fiber has a similar detrimental impact on the quality of the fiber end. In order to prepare high-quality samples for the SEM imaging, we submerged each fiber in liquid nitrogen for several minutes and then broke the fiber; if done on enough fiber samples, this method results in a few good fiber pieces (around 15% success rate) with very high-quality and smooth end surfaces for the SEM imaging. We then used a 70% ethyl alcohol solution at 60 &deg;C for about 3 min to dissolve the PMMA sites on the fiber end; longer exposure can disintegrate the entire fiber end. We then coated the samples with Au/Pd and placed them in the SEM chamber. The zoomed-in SEM image of the disordered polymer optical fiber is shown in Figure 2. The light gray sites are PS and the dark sites are PMMA. The total width of the image is 24 &mu;m where the smallest features sizes in this image are ~0.9 &mu;m, corresponding to the individual site sizes of the fiber strands, after the draw process.
In order to characterize the waveguide properties of the disordered optical fiber, we used a He-Ne laser at 633 nm wavelength. The He-Ne laser is coupled to a single mode SMF630hp optical fiber with a mode field diameter of about 4 &mu;m, which is then butt-coupled to the disordered polymer optical fiber using a high-precision motorized stage. The output is then imaged on a CCD camera beam profiler using a 40X objective.
In the first set of experiments, we chose 20 different disordered fiber samples, each 5-cm long; the 5-cm length was chosen to match the propagation length in our numerical simulations. The numerical simulations of the disordered fiber are generally very time consuming, even on a high performance computing cluster with 1,100 elements. The full transverse Anderson localization for the wavelength of 633 nm happens only after about 2.5 cm of propagation 11,12; therefore, we decided that the 5-cm length is sufficient for our purposes. Because of the stochastic nature of the Anderson localization, we needed to repeat both the experiments and the simulations for 100 realizations, in order to collect sufficient statistics to compare the experimental and numerical values of the average beam diameter. In practice, 100 different measurements are obtained by taking five spatially separated measurements on each of the 20 different disordered fiber samples.
It is fairly hard to prepare the disordered polymer optical fibers for measurements, compared with glass optical fibers. For example, one cannot use the advanced cleaving and polishing tools and techniques that are well-developed for standard silica-based fiber. A refined procedure for cleaving and polishing polymer optical fibers has been reported by Abdi et al. 14; we used their methods with some minor modifications to prepare our fiber samples. In order to cleave a polymer disordered optical fiber, a curved X-Acto blade is heated to 65 &deg;C , and the fiber to 37 &deg;C . The tip of the fiber is aligned on a cutting surface so that a clean, perpendicular cut can be made. The blade is placed on the side of the fiber, and quickly rolled across. The entire cleaving process should be done as fast as possible to ensure that the temperatures of the blade and fiber do not change considerably. After cleaving the fiber and inspecting it under an optical microscope, the fiber end is polished using standard fiber lapping sheets (0.3 &mu;m Thorlabs LFG03P Aluminum Oxide Polishing Paper) to ensure that any minor imperfections are removed. To polish the fiber end, it is held in a pair of tweezers with the tweezers holding the fiber approximately 1.5 mm away from the end face being polished. The fiber is drawn over the paper in one-inch long figure-8-shaped paths, approximately eight times. Polishing the fiber results in smoother edges as inspected under the optical microscope. Moreover, polishing facilitates proper coupling to a localized spot in the fiber, which in turn reduces the attenuation both in the coupling and also in the initial propagation distance before the localized spot is formed.
We used a CCD camera beam profiler to image the output beam intensity. The near-field intensity profile was captured using a 40X objective. In order to find the boundaries of the fiber, we saturated the CCD by increasing the power of the incoming light from the SMF630hp fiber. After detecting the intensity profile of the localized beam with respect to the boundaries, we set the CCD beam profiler to the auto-exposure option. We used the image of the intensity profile in order to calculate the effective beam radius. In order to remove the effect of the ambient noise, we calibrated our image processing procedure to ensure that we obtain the expected beam diameter of the SMF630hp fiber. The average measured value of the beam radius and its variations around the average value agree well with the numerical simulations, as shown in Ref. 11. The output beam profile in the polymer fiber clearly follows a change in the position of the incident beam as shown in Refs. 11,12,13.
A comprehensive study of the impact of the design parameters such as the disorder site sizes and the incident wavelength on the beam radius of the localized beam was presented in Refs.12,15.

<table border="1">
	<tbody>
		<tr>
			<td>poly (methyl methacrylate) (PMMA)</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>polystyrene (PS)</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>70% ethyl alcohol solution at 65 &deg;C</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

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.

The SEM image of the polished fiber is shown in Figure 1. The SEM image in Figure 1 shows that, for most regions of the fiber tip, the polish quality is good. The SEM image of the fiber samples with their ends dissolved in ethyl alcohol solution, Figure 2, shows the PMMA sites in dark and PS sites in gray colors. The SEM image in Figure 2 is zoomed in on a 24 &mu;m width of the fiber. For SEM imaging, the fiber samples are coated with a 10-nm thick layer...

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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. 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 ...

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11.3K Views.  University of Wisconsin-Milwaukee. 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.

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

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Quasi-light Storage for Optical Data Packets

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

The article describes a procedure to store optical data packets with an arbitrary modulation, wavelength, and data rate. These packets are the basis of modern telecommunications.

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing ...

Patterning via Optical Saturable Transitions - Fabrication and Characterization

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.

We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

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.

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 ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Free-form Light Actuators &amp;#8212; Fabrication and Control of Actuation in Microscopic Scale

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

Methods Article

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