The authors gratefully acknowledge Dr Matteo Galli, Dr Simone L. Portalupi and Prof. Lucio C. Andreani from the University of Pavia for helpful discussions related to the RS technique and the execution of measurements.

Disclaimer: The following protocol gives a general process flow covering the fabrication and characterization techniques for photonic crystal waveguides and cavities. The process flow is optimized for the specific equipment available in our laboratory, and parameters may differ if other reagents or equipment is used.
1. Sample Preparation
<ol>
	<li>Sample Cleaving - take the silicon-on-insulator (SOI) wafer and use a diamond scribe to scratch a line approximately 1-2 mm long from the edge of the silicon surface, ensuring that the scratch extends over the edge of the wafer. Align the scratch to a straight edge (e.g. that of a microscope slide) and apply even positive pressure to both sides of the scratch: the wafer will cleave along the crystal plane at the scratch location. Repeat this procedure to define the entire chip.</li>
	<li>Sample Cleaning - Place the sample into the CAUTION acetone using tweezers and clean in an ultrasonic bath for 1-2 min. Remove the sample from the acetone; rinse any remaining acetone from the sample using CAUTION isopropanol (30 sec) (both acetone and isopropanol are flammable: use good ventilation and avoid all ignition sources). Dry the sample using a clean dry nitrogen gun.</li>
	<li>Spin resist - place the sample onto the spin-coater. Pipette electron sensitive resist CAUTION ZEP520A (ZEP520A is flammable, harmful by inhalation and contact with skin and eyes should be avoided) onto the sample - use enough resist to completely cover the sample without the resist flowing over the edge. Spin the sample so as to give an approx. 350 nm thick film and bake on a hotplate at 180 &deg;C for 10 min. We found this thickness to be the optimal thickness that balances resolution and etch resistance (see later).</li>
</ol>
2. Pattern Definition
<ol>
	<li>Design - using appropriate software, simulate the required photonic crystal pattern. A number of useful software packages are available, including but not limited to: MIT Photonic Bands (MPB), FullWAVE(RSoft), MIT Electromagnetic Equation Propagation (MEEP).</li>
	<li>Pattern Generation - create the exposure files (gds format in general) and proximity error correct using appropriate software.30</li>
	<li>Pattern Exposure - load the sample into the chamber of the electron beam lithography system (LEO 1530/ Raith Elphy) and pump down. Once vacuum has been achieved, switch on the EHT supply and set to 30 kV. Leave the system in this state for 1 hr to allow the sample, stage and chamber to reach an equilibrium temperature. Set-up the exposure as indicated in the user-manual of your specific electron beam lithography system . Expose the sample using an appropriate basic step size (e.g. 2 nm) (this being the minimum pixel size that the system can expose), a settling time of at least 1 ms (this being the time the system waits between moving the beam and exposing the particular portion of the pattern), and an area dose of 55 &mu;Acm-2.</li>
	<li>Sample Development - using CAUTION Xylene (Xylene is both flammable and highly toxic work in a well-ventilated area away from ignition sources and avoid contact with skin and eyes) at a temperature of 23 &deg;C develop the sample for 45 sec. Rinse in isopropanol.</li>
</ol>
3. Patten Transfer
<ol>
	<li>RIE Chamber Cleaning - Set the flow rates of argon and hydrogen to 200 sccm. Throttle down the pump, via a butterfly valve, to achieve chamber pressure of 1 &times; 10-1 mBar. Set the RF power to 100 W, ignite the plasma and run for at least 10 min - a DC bias of approximately 700 V should be observed. After switching off the Ar/H2 plasma, allow the chamber to pump for approximately 1 min. Set the flow rate of oxygen into the chamber to 200 sccm and again throttle the chamber pressure down to 1 &times; 10-1 mBar. Ignite a second plasma of oxygen with a power of 100 W and run for 5 min. After these procedures, the chamber will be free of contaminants, such as polymer residues, from any previous dry etch. We perform this procedure before every change in etch recipe to ensure maximum repeatability. This procedure is optimised for our system which consists of a parallel-plate, cathode loaded, RIE; with a main chamber 12 inches in diameter by 14 inches in height, including a 12 inch port with both throttling valve and turbo-molecular pump attached.</li>
	<li>Photonic Crystal Etching - load the sample into the RIE main chamber and pump the system down to a background pressure of &lt;3 &times; 10-6 mBar to ensure the chamber is free of water vapour. Begin the etch by pre-conditioning the chamber with the etching gasses (namely CHF3 and SF6): set the flow rate of both gasses to 100 sccm (i.e. set a gas ratio of 1:1) and using the throttle bring the chamber pressure to 5 &times; 10-2 mBar; allow the gasses to flow for at least 10 min. After pre-conditioning, set the RF power to approximately 20 W and ignite a plasma; etch the sample for approximately 2 min (the etch rate of silicon for these etch parameters is approximately 150 nm/min), while ensuring that a chamber pressure of 5 &times; 10-2 mBar is maintained. A DC bias between 200-220 V should be achieved throughout the etching period.</li>
	<li>Sample Cleaning to remove remaining electron sensitive resist - after dry etching, clean the sample by rinsing in CAUTION 1165 Remover (1165 is flammable and can cause irritation to eyes, nose and respiratory tract) with ultrasonic agitation for 1-2 min, followed by acetone and isopropanol as outlined above (step 1.2).</li>
	<li>Membrane Isolation - spin-coat the sample with UV sensitive photo resist CAUTION Microposit S1818 G2 (S1818 G2 is both flammable and causes irritation to eyes, nose and respiratory tract) (see step 1.3). Using an appropriate photomask, define windows within the resist above the photonic crystal patterns using the UV mask aligner. Expose the sample for approximately 30-45 sec. Develop the resist in CAUTION Microposit Developer MF-319 (MF-319 is an alkaline liquid and can cause irritation to eyes, nose and respiratory tract) for 30-45 sec, rinsing afterwards in de-ionised water. Prepare a plastic beaker with a mixture of CAUTION 1:5 Hydrofluoric acid (1.1499 g/ ml 48-51% HF) (HF is extremely corrosive and readily destroys tissue, when handling use full personal protective equipment rated for HF) to de-ionised water. Note that for safety reasons only plastic beakers and tweezers should be used with Hydrofluoric acid. Submerge the sample in the Hydrofluoric acid mixture for 15 min. After etching, rinse the sample thoroughly in de-ionised water. Remove the remaining photo-resist using acetone and isopropanol (see step 1.2) - from this stage and onwards ultrasonic agitation cannot be used. To ensure the sample is as clean as possible, follow the acetone and isopropanol wash with a rinse in CAUTION Piranha solution (Piranha solution is very energetic, potentially explosive and attacks organic materials, when handling use full personal protective equipment) (3:1 CAUTION sulphuric acid (sulphuric acid is corrosive and very toxic, when handling use personal protective equipment and avoid inhalation of vapours or mists) to CAUTION hydrogen peroxide (hydrogen peroxide is very hazardous in case of skin and eye contact, when handling use personal protective equipment)) for 5 min, then rinse the sample in de-ionised water, acetone and isopropanol. Note that for safety reasons only glass beakers and metal tweezers should be used with the Piranha solution. As Piranha solution can explode in contact with acetone or isopropanol, it should be handled away from these reagents.</li>
	<li>Facet Cleaving - if preparing a photonic crystal slow-light waveguide, the sample requires facet cleaving. Cleave the sample by following the same procedure as outlined in step 1.1, except that as small a scratch as possible should be used. An SOI chip with ~700 &mu;m thick substrate can be reliably cleaved down to 4-5 mm long samples.</li>
</ol>
4. Photonic Crystal Slow-light Waveguide Characterization
<ol>
	<li>Preliminary preparation of the setup - connect the output of a CAUTION broadband amplified spontaneous emission (ASE) light source (invisible IR radiation: avoid unnecessary high powers, cover beam path if possible) to a 3 dB fiber splitter and use each of the outputs to couple light into the two arms of a free-space Mach-Zehnder interferometeter (MZI), as shown in Figure 9. Use aspheric lenses to collimate the light output from the fibers. In one of the arms of the interferometer, use two additional aspheric lenses to couple the light beam in and out of the sample chip. Place a polarization beam splitter (PBS) in the sample arm to TE-polarise the light inputting the sample. Use aspheric lenses to couple the collimated output beams from both arms back into a second 3 dB fiber splitter, where they will recombine. Connect one of the outputs to an infrared detector and use the reading of the detector to maximise the light coupling into the sample; connect the other output to an optical spectrum analyzer (OSA). The two arms of the MZI should have approximately the same optical length when in the presence of the sample: make sure that the fibers in the two arms of the MZI have the same nominal length and include a tunable delay stage in the reference arm to allow for fine adjustment of its length. In the sample arm, mount the aspheric lenses onto xyz precision stages to obtain the best coupling into the sample.</li>
	<li>Adjust reference arm length - couple the light beam to a blank (i.e. without photonic crystal) ridge waveguide (of the same type as the access waveguides that feed light inside the photonic crystals) within the same chip in the sample arm. Run a continuous scan on the OSA and observe the measured wavelength spectra. If the two arms of the MZI have approximately the same optical length, the spectra exhibit fringes due to constructive and destructive interference; these fringes will not appear if the arms of the MZI have very different optical lengths (&gt;~cm). The fringe spacing is inversely proportional to the difference in optical path length between the two arms. Move the delay stage to make the reference arm shorter and observe the fringes in the OSA: if they become denser (sparser), the reference arm is shorter (longer) than the sample arm. Set the delay stage to make sure that the reference arm is shorter than the sample arm and results in a fringe spacing of about 5 to 10 fringes in a 10 nm wavelength range (see Figure 10a). Finally, perform this optimization on the device that provides the maximum delay and then keep the delay fixed throughout the measurement of the entire sample.</li>
	<li>Calibration run - while still aligned on the blank waveguide, run three scans on the OSA: one scan for the interference spectrum and one scan for each of the two arms separately (obtained by blocking the other arm). Use a resolution of 0.05-0.1 nm. Record each measured spectrum.</li>
	<li>Slow light data acquisition - run and record three spectra as in step 4.3 for each photonic crystal waveguide on the chip.</li>
	<li>Fourier data analysis - the interference spectrum (interferogram) I(&omega;) is mathematically expressed by: 
 I(&omega;) = S(&omega;) + R(&omega;) + sqrt[S(&omega;)R(&omega;)]{exp[i&Phi;(&omega;) - i&omega;&tau;] + c.c.}, 
 where S(&omega;) and R(&omega;) are the spectral densities measured separately from the sample and reference arms, respectively. The delay &tau; is set by the position of the delay stage in the reference arm. The information on the dispersion of the photonic crystal waveguide is contained in the phase term, which we must extract from the measured data. 
 Subtract the non-interfering background S(&omega;)+R(&omega;) from the interferogram to isolate only the interfering term. Calculate the Fourier transform of the interfering term: the term sqrt(SR)exp[i(&Phi;- &omega;&tau;)] and its complex conjugate correspond to peaks centred at t=&tau; and t=-&tau;, respectively. Filter numerically one of the two terms and transform back to the frequency domain. Differentiate the phase &Phi;(&omega;) - &omega;&tau; of the resulting data with respect to &omega; to obtain &Delta;&tau;g, the difference in group delay between the two arms. The group index ng=c/vg, with vg the group velocity, is given by: 
 ng = (&Delta;&tau;gPhC - &Delta;&tau;gcal)c/L + ncal, 
 where &Delta;&tau;gcal is obtained from the calibration data taken from the blank waveguide, L is the photonic crystal waveguide length and ncal=2.7 is the effective index of the reference ridge waveguide. The contribution to the delay from the various optical elements of the setup is taken into account in the calibration run, and is therefore subtracted in this step.</li>
</ol>
<ol start="6">
	<li>Transmission curve - calculate the transmission curve by normalising the sample spectrum of a photonic crystal waveguide to that of the blank waveguide.</li>
</ol>
5. Photonic Crystal Cavity Characterization
<ol>
	<li>Setup - the preparation of the setup (Figure 14) for RS includes: switching of the exchangeable element to the polarising beam splitter; inserting a polariser in the input arm as well as an analyzer in the output arm; flip a mirror into the probe arm to allow the use of a near-infrared source; allow the illumination of the sample. Mount the sample vertically with a 45&deg; orientation to axis of the polarizer (Figure 18) on a differential driven xyz micro-block and adjust the micro-block so that the sample is in focus and a cavity can be seen with the camera, as in Figure 15 (left). Using an amplified spontaneous emission (ASE) source, align the beam with the centre of the cavity Figure 15 (right). Flip away the illumination mirror and allow the output arm to enter the spectrometer (monochromator with attached array detector). Start a broad scan with a low to moderate resolution in order to identify the cavity peaks. Obtain the coarse wavelength of the resonance in the ASE scan (Figure 16a) with an accuracy of 1 nm. It is also possible to acquire the broad scan with a CAUTION tunable laser source (TLS) (Figure 16b) (invisible IR radiation: avoid unnecessary high powers, cover beam path if possible). One has to be careful that the resolution is set to the highest value in order to sample the line-widths of every peak.</li>
	<li>Perform high-resolution scans on the identified peaks - connect the TLS to the input arm and attenuate the beam to a mW level. Prepare for the high resolution scan by allowing the output arm to be collected by the photodetector and setting up a continuous sweep scan with a resolution of 1 pm for a 2 nm range centred at the previously found resonance wavelength. The importance of this step is to improve the signal-to-noise ratio (SNR) with the aim to obtain a Lorentzian line-shape resonance: change the xyz position of the micro-block and re-run the scan until the SNR is maximised and the line-shape is close to that of a Lorentzian, as shown in the representative result section.</li>
</ol>

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F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light+scattering+and+Fano+resonances+in+high-Q+photonic+crystal+nanocavities.">Light scattering and Fano resonances in high-Q photonic crystal nanocavities.</a> Appl. Phys. Lett. 94 (7), 71101 (2009).</li><li>W&#195;est, R., Strasser, P., Jungo, M., Robin, F., Erni, D., J&#252;ckel, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+efficient+proximity-effect+correction+method+for+electron-beam+patterning+of+photonic-crystal+devices.">An efficient proximity-effect correction method for electron-beam patterning of photonic-crystal devices.</a> Microelectron Eng. 67-68, 182-188 (2003).</li><li>Tanaka, Y., Asano, T., Akahane, Y., Song, B. -. S., Noda, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theoretical+investigation+of+a+two-dimensional+photonic+crystal+slab+with+truncated+cone+air+holes.">Theoretical investigation of a two-dimensional photonic crystal slab with truncated cone air holes.</a> Appl. Phys. Lett. 82 (11), 1661 (2003).</li><li>Asano, T., Song, B. -. S., Noda, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+experimental+Q+factors+(~+1+million)+of+photonic+crystal+nanocavities.">Analysis of the experimental Q factors (~ 1 million) of photonic crystal nanocavities.</a> Opt. Express. 14 (5), 1996-2002 (2006).</li><li>O'Faolain, L., Schulz, S. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Loss+engineered+slow+light+waveguides.">Loss engineered slow light waveguides.</a> Opt. Express. 18 (26), 27627-27638 (2010).</li><li>Joannopoulos, J. D., Johnson, S. G., Winn, J. N., Meade, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Photonic crystals, molding the flow of light. , (2008).</li><li>Li, J., White, T. P., O'Faolain, L., Gomez-Iglesias, A., Krauss, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+design+of+flat+band+slow+light+in+photonic+crystal+waveguides.">Systematic design of flat band slow light in photonic crystal waveguides.</a> Opt. Express. 16 (9), 6227-6232 (2008).</li><li>Takeda, M., Ina, H., Kobayashi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fourier-transform+method+of+fringe-pattern+analysis+for+computer-based+topography+and+interferometry.">Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry.</a> J. Opt. Soc. Am. 72 (1), 156-160 (1982).</li></ol>

No conflicts of interest declared.

Sample fabrication
Our choice of electron-beam resist (i.e. ZEP 520A) is due to its simultaneously high resolution and etch resistance. We believe that ZEP 520A may be affected by the UV light emitted from overhead laboratory lights; as such we recommend placing spin-coated samples in UV opaque containers while moving them from one laboratory to another.
Moving onto defining the photonic crystal pattern, before exposing the sample we have found that allowing t...

<table border="1">
	<tbody>
		<tr>
			<td>Name </td>
			<td>Company </td>
			<td>Catalogue number </td>
			<td>Comments (optional) </td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Fisher Scientific</td>
			<td>A/0520/17</td>
			<td>CAUTION: flammable, use good ventilation and avoid all ignition sources.</td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Fisher Scientific</td>
			<td>P/7500/15</td>
			<td>CAUTION: flammable, use good ventilation and avoid all ignition sources.</td>
		</tr>
		<tr>
			<td>Electron Beam resist</td>
			<td>Marubeni Europe plc.</td>
			<td>ZEP520A</td>
			<td>CAUTION: flammable, harmful by inhalation, avoid contact with skin and eyes.</td>
		</tr>
		<tr>
			<td>Xylene</td>
			<td>Fisher Scientific</td>
			<td>X/0100/17</td>
			<td>CAUTION: flammable and highly toxic, use good ventilation, avoid all ignition sources, avoid contact with skin and eyes.</td>
		</tr>
		<tr>
			<td>Microposit S1818 G2</td>
			<td>Chestech Ltd.</td>
			<td>10277866</td>
			<td>CAUTION: flammable and causes irritation to eyes, nose and respiratory tract.</td>
		</tr>
		<tr>
			<td>Microposit Developer MF-319</td>
			<td>Chestech Ltd.</td>
			<td>10058721</td>
			<td>CAUTION: alkaline liquid and can cause irritation to eyes, nose and respiratory tract.</td>
		</tr>
		<tr>
			<td>Hydrofluoric Acid</td>
			<td>Fisher Scientific</td>
			<td>22333-5000</td>
			<td>CAUTION: extremely corrosive, readily destroys tissue; handle with full personal protective equipment rated for HF.</td>
		</tr>
		<tr>
			<td>Microposit 1165 Remover</td>
			<td>Chestech Ltd.</td>
			<td>10058734</td>
			<td>CAUTION: flammable and causes irritation to eyes, nose and respiratory tract.</td>
		</tr>
		<tr>
			<td>Sulphuric Acid</td>
			<td>Fisher Scientific</td>
			<td>S/9120/PB17</td>
			<td>CAUTION: corrosive and very toxic; handle with personal protective equipment and avoid inhalation of vapours or mists.</td>
		</tr>
		<tr>
			<td>Hydrogen Peroxide</td>
			<td>Fisher Scientific</td>
			<td>BPE2633-500</td>
			<td>CAUTION: very hazardous in case of skin and eye contact; handle with personal protective equipment.</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Silicon-on-Insulator wafer</td>
			<td>Soitec</td>
			<td>G8P-110-01</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Diamond Scribe</td>
			<td>J &amp; M Diamond Tool Inc.</td>
			<td>HS-415</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>Fisher Scientific</td>
			<td>FB58622</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Beakers</td>
			<td>Fisher Scientific</td>
			<td>FB33109</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Tweezers</td>
			<td>SPI Supplies</td>
			<td>PT006-AB</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ultrasonic Bath</td>
			<td>Camlab</td>
			<td>1161436</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Spin-Coater</td>
			<td>Electronic Micro Systems Ltd.</td>
			<td>EMS 4000</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Pipette</td>
			<td>Fisher Scientific</td>
			<td>FB55343</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>E-beam Lithography System</td>
			<td>Raith Gmbh</td>
			<td>Raith 150</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Reactive Ion Etching System</td>
			<td>Proprietary In-house Designed</td>
			<td>--</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>UV Mask Aligner</td>
			<td>Karl Suss</td>
			<td>MJB-3</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>ASE source</td>
			<td>Amonics</td>
			<td>ALS-CL-15-B-FA</td>
			<td>CAUTION: invisible IR radiation.</td>
		</tr>
		<tr>
			<td>Single mode fibers</td>
			<td>Thorlabs</td>
			<td>P1-SMF28E-FC-2</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>3 dB fiber splitters</td>
			<td>Thorlabs</td>
			<td>C-WD-AL-50-H-2210-35-FC/FC</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Aspheric lenses</td>
			<td>New Focus</td>
			<td>5720-C</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>XYZ stages</td>
			<td>Melles Griot</td>
			<td>17AMB003/MD</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Polarizing beamsplitter cube</td>
			<td>Thorlabs</td>
			<td>PBS104</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>IR detector</td>
			<td>New Focus</td>
			<td>2033</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>100&times; Objective</td>
			<td>Nikon</td>
			<td>BD Plan 100x</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Oscilloscope</td>
			<td>Tektronix</td>
			<td>TDS1001B</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Optical Spectrum Analyzer</td>
			<td>Advantest</td>
			<td>Q8384</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>IR sensor card</td>
			<td>Newport</td>
			<td>F-IRC2</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>TLS source</td>
			<td>Agilent</td>
			<td>81940A</td>
			<td>CAUTION: invisible IR radiation.</td>
		</tr>
		<tr>
			<td>IR Camera</td>
			<td>Electrophysics</td>
			<td>7290A</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>IR Detector</td>
			<td>New Focus</td>
			<td>2153</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Digital Multimeter</td>
			<td>Agilent</td>
			<td>34401A</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Illumination</td>
			<td>Stocker Yale</td>
			<td>Lite Mite</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Monochromator</td>
			<td>Spectral Products</td>
			<td>DK480</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Array Detector</td>
			<td>Andor</td>
			<td>DU490A-1.7</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>GIF Fiber</td>
			<td>Thorlabs</td>
			<td>31L02</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

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

Fabricated samples
Figure 1 shows a scanning electron microscope (SEM) image of an exposed and developed pattern in electron beam resist - it is evident from the "clean" edge between the resist and the silicon substrate that complete exposure/development has been accomplished. Exposure of dose test patterns, consisting of simple repeated shapes (in our case 50 &times; 50 &mu;m squares), each with a differing base dose, are used to determine the correct dose factor and developmen...

Watch this Scientific Journal Video about Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities at JoVE.com

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

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 ...

fabrication-characterization-photonic-crystal-slow-light-waveguides

Research

JoVE Journal

Engineering

18.8K Views.  University of St Andrews. 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).

Video: Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ &lambda;/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems.

This protocol outlines the simulation, fabrication and characterization of THz metamaterial absorbers. Such absorbers, when coupled with an appropriate sensor, have applications in THz imaging and spectroscopy.

Metamaterials (MM),  artificial materials engineered to have properties that may not be found in  nature, have been widely explored since the first ...

Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10.

We describe methods for the design, fabrication, and experimental characterization of plasmonic photoconductive emitters, which offer two orders of magnitude higher terahertz power levels compared to conventional photoconductive emitters.

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on ...

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 ...

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned and bonded silicon wafers. Unlike confinements in porous materials often used for these types of experiments3, bonded wafers provide predesigned uniform spaces for confinement. The geometry of each cell is well known, which removes a large source of ambiguity in the interpretation of data.
Exceptionally flat, 5 cm diameter, 375 &#181;m thick Si wafers with about 1 &#181;m variation over the entire wafer can be obtained commercially (from Semiconductor Processing Company, for example). Thermal oxide is grown on the wafers to define the confinement dimension in the z-direction. A pattern is then etched in the oxide using lithographic techniques so as to create a desired enclosure upon bonding. A hole is drilled in one of the wafers (the top) to allow for the introduction of the liquid to be measured. The wafers are cleaned2 in RCA solutions and then put in a microclean chamber where they are rinsed with deionized water4. The wafers are bonded at RT and then annealed at ~1,100 &#176;C. This forms a strong and permanent bond. This process can be used to make uniform enclosures for measuring thermal and hydrodynamic properties of confined liquids from the nanometer to the micrometer scale.

A method for permanently bonding two silicon wafers so as to realize a uniform enclosure is described. This includes wafer preparation, cleaning, RT bonding, and annealing processes. The resulting bonded wafers (cells) have uniformity of enclosure ~1%1,2. The resulting geometry allows for measurements of confined liquids and gasses.

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction.

Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Disordered structures offer new mechanisms for forming photonic bandgaps and unprecedented freedom in functional-defect designs. To circumvent the computational challenges of disordered systems, we construct modular macroscopic samples of the new class of PBG materials and use microwaves to characterize their scale-invariant photonic properties, in an easy and inexpensive manner.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). ...

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 ...

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 ...

Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active layer which consists of blue-fluorescent poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and &#960;-conjugated triphenylamine molecules. This white light emission originates from exciplexes formed between PFD and amines in electronically excited states. A device containing PFD, 4,4&#39;,4&#39;&#39;-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), Poly(ethylene oxide) and K2CF3SO3 showed white light emission with Commission internationale de l&#39;&#233;clairage (CIE) coordinates of (0.33, 0.43) and a Color Rendering Index (CRI) of Ra = 73 at an applied voltage of 3.5 V. Constant voltage measurements showed that the CIE coordinates of (0.27, 0.37), Ra of 67, and the emission color observed immediately after application of a voltage of 5 V were nearly unchanged and stable after 300 sec.

The authors present a method for fabricating stable white-light-emitting electrochemical cells utilizing emission from exciplexes formed between a blue-emitting fluorene polymer and aromatic amines.

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active ...