This work was performed in part at the Cornell University NanoScale Science and Technology Facility, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (Grant ECCS-1542081). We acknowledge support for this work from the Air Force Research Lab (AFRL). This material is based upon work partially supported by the National Science Foundation under Award No. ECCS14052481.

NOTE: This protocol assumes that the photonic chip has already been fabricated. The chip described here (shown in Figure 1A) was fabricated at the Cornell University NanoScale Science &#38; Technology Facility using standard processing techniques for silicon photonic devices11. These include the use of silicon-on-insulator wafers (composed of a 220 nm-thick silicon layer, a 3-&#181;m layer of silicon dioxide, and a 525 &#181;m-thick silicon substrate), electron-beam lithography to define the strip waveguides (500 nm-wide), and the plasma-enhanced chemical vapor deposition of the silicon dioxide cladding (~3 &#181;m-thick). The micro-ring resonators were designed with an inner radius of 18.5 &#181;m and a waveguide-to-ring gap of 150 nm. Figures of merit for this device include loss, quality factor, free spectral range, and dispersion.
1. Photonic Chip Preparation
<ol>
	<li>Place a small amount of wax on a cross-sectioning polishing mount and heat it to ~130 &#176;C. 
	NOTE: The amount of wax to be used depends upon the size of the sample being mounted. There must be enough wax to keep the chip immobile, while too much will result in wax on the chip facets.</li>
	<li>Place the photonic chip on the portion of the polishing mount with the wax. Ensure that the wax is melted completely so that the chip is flat against the mount. Use plastic tweezers when handling the chip to avoid damaging the facets.</li>
	<li>Allow the mount to cool in ambient air so that the wax solidifies. Cooling faster than this may result in damage to the chip.</li>
	<li>Polishing the chip facets. 
	NOTE: It is important to choose the correct lapping pad as starting with a pad that is too aggressive can result in polishing away more of the chip than desired.
	<ol>
		<li>Attach the polishing mount to the polisher and polish for only a few seconds. A pad with a 3-&#181;m roughness has shown to be a good starting point for silicon chips with facet lengths of ~1 cm.</li>
		<li>Remove the polishing mount and inspect the chip facet to determine how level the chip is mounted. 
		NOTE: A microscope is useful for measuring the distance between the ends of the waveguides and the facet of the chip. These measurements allow for the angle between the facet and the waveguide to be determined.</li>
		<li>Make the necessary adjustments to the micrometers on the polisher in order to improve the leveling of the chip.</li>
		<li>Repeat steps 1.4.1-1.4.3 until the facet of the chip and the waveguides are within 0.15&#176; of being orthogonal to each other.</li>
		<li>Polish the chip in steps of ~50 &#181;m, inspecting the chip between each step to monitor the distance remaining, until there is ~100 &#181;m left to polish. If at any point the cladding appears to be delaminating from the surface, ensure that the pad is rotating so as to polish from the top of the chip to the bottom. 
		NOTE: It may also help to use a polishing lubricant instead of water. This delamination is a result of stress in the cladding and is an indication that the fabrication process needs to be optimized.</li>
		<li>Change to a 1-&#181;m lapping pad and polish until there is ~20 &#181;m remaining.</li>
		<li>Change to a 0.5-&#181;m pad and continue polishing for another 15 &#181;m.</li>
		<li>Use a 0.1-&#181;m pad for the final 5 &#181;m to ensure a smooth facet. Microscope images of the facet of a silicon photonic chip before and after polishing are shown in Figure 2.</li>
	</ol>
	</li>
	<li>Heat the mount with the attached chip to ~130 &#176;C to allow the wax to melt.</li>
	<li>Once the wax is completely melted, remove the chip from the mount and allow it to cool slowly.</li>
	<li>Clean any of the remaining wax from the chip using acetone, isopropanol, and water.</li>
</ol>
2. Preparation of Fiber Pigtails
<ol>
	<li>Strip any buffer or coating from the end of a single mode fiber (SMF) pigtail and from one end of an ultra-high numerical aperture (UHNA) fiber.</li>
	<li>Clean the bare ends of the fibers with a mixture of acetone and methanol.</li>
	<li>Cleave the bare ends of both fibers with a commercial fiber cleaver.</li>
	<li>Fusion splice the cleaved end of the fibers. A recipe for splicing SMF to UHNA fiber is shown in Table 1.</li>
	<li>Slide a protective sleeve over the splice and place it in the sleeve oven to permanently attach it to the fiber.</li>
	<li>Repeat steps 2.1-2.5 to prepare a total of three fibers.</li>
</ol>
3. Configuration of the Testing Setup
NOTE: A diagram of the testing setup is shown in Figure 1B. The mount for the chip is a copper pedestal that is in contact with a thermo-electric cooler (TEC). There is a microscope fitted with both visible and infrared (IR) cameras for viewing the photonic chip.
<ol>
	<li>Place a small amount of wax on the chip mount and apply voltage to the TEC to melt the wax.</li>
	<li>Place the chip on the melted wax, ensuring that it is sitting flat on the mount.</li>
	<li>Remove the voltage from the TEC and allow the mount and chip to cool slowly.</li>
	<li>Attach each of the spliced fibers to a fiber v-groove with polyimide tape and mount a single v-groove to each of the 3-axis stages using the manufacturer-supplied mounting hardware.</li>
	<li>Fiber edge coupling.
	<ol>
		<li>Connect the three fibers to their respective components: one to the optical output of the laser and the other two to optical power meters.</li>
		<li>Adjust the microscope so that it is focused on the chip where the waveguides reach the edge.</li>
		<li>Position the fibers close to the chip edge so that they are in the view of the visible camera and adjust their heights so that the core of each fiber is in focus.</li>
		<li>Adjust the horizontal positioning of the fibers with the stage micrometers so that they are lined up with the waveguides.</li>
		<li>Turn on the optical output of the laser and tune the horizontal and vertical micrometer positions of the input fiber until the light is coupling into the waveguide. This will show up on the IR camera as scattering along the input waveguide.</li>
		<li>Tune the wavelength of the laser to a point where the micro-ring resonator is lit up on the camera. This indicates that the resonance condition is being satisfied and that the light is reaching the output waveguides.</li>
		<li>Adjust the horizontal and vertical micrometer positions of the output fibers until there is a measurable amount of light extending from the waveguides to the power meters.</li>
		<li>Maximize the power to both detectors by manipulating the horizontal and vertical micrometer positions of the three fibers.</li>
		<li>Further maximize the power to the detectors by making fine adjustments to the horizontal and vertical fiber positions using the piezo controllers.</li>
		<li>Use the piezo controllers to move the fibers slightly closer to the chip. Make sure not to use the micrometers to push the fibers onto the chip, as doing so will likely damage the cleaved ends of the fibers.</li>
		<li>Repeat steps 3.5.9 and 3.5.10 until the fibers are firmly pressed against the sides of the chip. 
		NOTE: Excessive scattered light from the waveguides, coupled with poor waveguide transmission, can be an indication of waveguide defects. These can include, but are not limited to, material defect sites, stitching boundaries, and excessive waveguide roughness.</li>
	</ol>
	</li>
	<li>Place a fiber-based polarization controller between the laser and the chip. This allows for control of the polarization state that makes it to the chip. The waveguides, being wider than they are tall, aid in minimizing any on-chip polarization rotation.</li>
	<li>Dispersion characterization.
	<ol>
		<li>Tune the polarization of the laser output to maximize the coupling to the chip. This device was designed for transverse-electric (TE) polarization and, as such, the transverse-magnetic (TM) polarization has a much higher loss.</li>
		<li>Scan a tunable laser over the wavelength range of interest (1,510 nm to 1,600 nm in this case) and monitor the power meters. Any artifacts in the transmission spectra are likely due to a combination of the TM component of the polarization and etalon effects from the fiber-chip interface.</li>
		<li>Locate the resonant wavelengths in the spectrum and also extract the bandwidth of each resonance. This particular chip had bandwidths as small as 65 pm, which translates to quality factors (Q) of up to 23,000.</li>
		<li>Determine the free spectral range (FSR), the separation between resonances, for each adjacent pair of resonances. This particular device had an FSR of ~5 nm.</li>
		<li>Calculate the group index (ng) of the guided mode for each value of the FSR using the following equation: 
		<img alt="Equation 5" src="/files/ftp_upload/55257/55257eq5.jpg" /> 
		where &#955; is the wavelength and r is the radius of the micro-ring resonator. The above equation is a first-order approximation of the group index.</li>
		<li>Use the bandwidth of each resonance to determine a width (&#916;ng) associated with each value of the group index.</li>
		<li>Choose the wavelengths for the two pump lasers such that they coincide with resonances in the spectrum and have an odd number of resonances between them (Figure 1C).</li>
		<li>Determine the wavelength of the degenerate bi-photons using the following equation: 
		<img alt="Equation 6" src="/files/ftp_upload/55257/55257eq6.jpg" /> 
		where &#955;Pump 1 and &#955;Pump 2 are the wavelengths of the pump photons.</li>
		<li>Add a horizontal line on the plot of group index versus wavelength that extends between the two pump wavelengths (Figure 3). If it is possible for the line to sit within ng &#177; &#916;ng at all three wavelengths of interest simultaneously, the phase-matching condition is satisfied and photons can be generated via SFWM. If it is not possible, try choosing pump wavelengths that are closer together and check again.</li>
	</ol>
	</li>
	<li>Add a second tunable laser source and polarization controller to the setup and combine the optical outputs from both lasers with a 1 x 2 fiber combiner.</li>
	<li>Add a series of fiber-based notch filters (enough of them achieve ~120 dB of attenuation) immediately before the chip. 
	NOTE: The filters allow both pump wavelengths to pass but reject the bi-photon wavelength. They help to remove excess noise (i.e., broadband Raman scattering in the optical fiber) before coupling to the chip. The filter spectrum is shown in Figure 1B.</li>
	<li>Add a series of fiber-based bandpass filters (enough of them to achieve ~150 dB of attenuation) immediately after the chip. 
	NOTE: The filters should be wide enough to allow the bi-photons to pass but narrow enough to reject the pump photons. Two sets of these are needed, one set for each output. The filter spectrum is shown in Figure 1B.</li>
	<li>Send the rejected photons from each set of filters to separate power meters. 
	NOTE: These power meters are used to monitor the optical coupling to the chip and can also be used to determine if the pump lasers are remaining on-resonance.</li>
	<li>Connect the individual optical output from each set of fiber-based filters to a single photon detector (SPD) and connect both electrical signal outputs from the SPDs to a coincidence correlator.</li>
	<li>Cross a pair of tungsten probes and set the tips down on one of the spiral legs (~1 mm in length) of the MZI.</li>
	<li>Connect a power supply to the two crossed probes such that they generate heat when voltage is applied. This will act as the phase-shifter for the MZI. 
	NOTE: See the discussion for a description of the more standardized method for the thermal tuning of photonic devices.</li>
</ol>
4. Measuring Two-photon Interference
<ol>
	<li>Tune both of the pump lasers to the chosen wavelengths. Use the power meters that are monitoring the rejected pump photons to ensure that both lasers are tuned to the resonances. When the lasers are properly tuned to the desired resonances, the rejected signal from the filters will be maximized.</li>
	<li>Set the optical power output from each laser to -3 dBm. 
	NOTE: This will result in &#60;100 &#181;W at the chip. It is important to keep the pump power this low in order to minimize loss (from multi-photon absorption and free-carrier absorption) and maintain stability (by minimizing light-induced thermal shifts). PN junctions can be used to remove carriers from the waveguide to better accommodate higher pump powers.</li>
	<li>Monitor the coincidence counts (synchronous singles across two ports) by integrating over ~220 ps about the peak of the data. A sufficient integration time has passed when a minimum of 100 coincidence counts have been collected. 
	Note: The integration window should be wide enough to account for the timing jitter of the SPDs.</li>
	<li>Set the power supply for the phase-shifter to the initial voltage (e.g., 0 V).</li>
	<li>Scan one of the tunable lasers over the entire wavelength range and use the power meters that are collecting the rejected pump photons to confirm the location of the resonances of interest. Set the pump lasers to the wavelengths corresponding to the desired resonances. 
	Note: It is important to complete this step every time the phase shifter voltage is changed as the thermal tuning can result in small shifts in the resonant wavelengths.</li>
	<li>Collect the resulting data (single-photon counts as well as the coincidence counts) from the coincidence correlator for the previously chosen integration time. Here, an integration time of 90 s was chosen with a timing resolution of 32 ps.</li>
	<li>Increase the voltage applied to the phase-shifter by 5 mV.</li>
	<li>Repeat steps 4.4-4.6 until data has been collected for the desired range of voltages. 
	NOTE: The maximum voltage was limited to 2.4 V due to rapid degradation of the probes above this voltage.</li>
	<li>Integrate the coincidence peaks for each power-supply voltage over ~220 ps to determine the total number of coincidences (Figure 4).</li>
	<li>Integrate over 320 ns away from the coincidence peak to obtain the accidental coincidences. Use this result to calculate the number of accidentals in the coincidence peak.</li>
	<li>Fit the singles counts from each detector with the following modified sine function: 
	<img alt="Equation 7" src="/files/ftp_upload/55257/55257eq7.jpg" /> 
	where A, B, C, D, E, and F are the fit parameters. This fit is necessary due to the nonlinear relationship between the voltage and the induced thermal shift (relative phase).</li>
	<li>Convert the independent variable to relative phase for all three sets of data (the singles counts from each detector and the coincidence counts) with the following equation: 
	<img alt="Equation 8" src="/files/ftp_upload/55257/55257eq8.jpg" /> 
	where B, C, D, and E are the fit parameters from step 4.11. This conversion is possible due to the well-known sinusoidal transfer function of an MZI12.</li>
	<li>Fit the coincidence data (with the relative phase as the independent variable) with the following sine function: 
	<img alt="Equation 9" src="/files/ftp_upload/55257/55257eq9.jpg" /> 
	where A and B are the fit parameters.</li>
	<li>Calculate the visibility of each interference pattern with the following equation: 
	<img alt="Equation 10" src="/files/ftp_upload/55257/55257eq10.jpg" /> 
	where &#402;(&#952;)max and &#402;(&#952;)min are the maximum and minimum values of &#402;(&#952;), respectively. A visibility of 1 corresponds to a perfect interference pattern.</li>
</ol>

<ol>
	<li>Silverstone, J. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On-chip+quantum+interference+between+silicon+photon-pair+sources.">On-chip quantum interference between silicon photon-pair sources.</a> Nat. Photon. 8 (2), 104-108 (2014).</li><li>Harris, N. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrated+Source+of+Spectrally+Filtered+Correlated+Photons+for+Large-Scale+Quantum+Photonic+Systems.">Integrated Source of Spectrally Filtered Correlated Photons for Large-Scale Quantum Photonic Systems.</a> Phys. Rev. X. 041047, 1-10 (2014).</li><li>Grassani, D., 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=Micrometer-scale+integrated+silicon+source+of+time-energy+entangled+photons.">Micrometer-scale integrated silicon source of time-energy entangled photons.</a> Optica. 2 (2), 88 (2015).</li><li>Najafi, F., 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=Scalable+Integration+of+Single-Photon+Detectors.">Scalable Integration of Single-Photon Detectors.</a> Nat. Commun. 6, 1-8 (2015).</li><li>Dutt, 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=On-Chip+Optical+Squeezing.">On-Chip Optical Squeezing.</a> Phys. Rev. Appl. 3 (4), 1-7 (2015).</li><li>Azzini, S., 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=Ultra-low+power+generation+of+twin+photons+in+a+compact+silicon+ring+resonator.">Ultra-low power generation of twin photons in a compact silicon ring resonator.</a> Opt. Express. 20 (21), 23100-23107 (2012).</li><li>Clemmen, S., 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=Continuous+wave+photon+pair+generation+in+silicon-on-insulator+waveguides+and+ring+resonators+erratum.">Continuous wave photon pair generation in silicon-on-insulator waveguides and ring resonators erratum.</a> Opt. Express. 17 (19), 16558 (2009).</li><li>Engin, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photon+pair+generation+in+a+silicon+micro-ring+resonator+with+reverse+bias+enhancement.">Photon pair generation in a silicon micro-ring resonator with reverse bias enhancement.</a> Opt. Express. 21 (23), 27826-27834 (2013).</li><li>Steidle, J. 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=High+spectral+purity+silicon+ring+resonator+photon-pair+source.">High spectral purity silicon ring resonator photon-pair source.</a> Proc. of SPIE. 9500, 950015 (2015).</li><li>Preble, S. F., 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=On-Chip+Quantum+Interference+from+a+Single+Silicon+Ring-Resonator+Source.">On-Chip Quantum Interference from a Single Silicon Ring-Resonator Source.</a> Phys. Rev. Appl. 4, 021001 (2015).</li><li>Cao, L., Aboketaf, A. A., Preble, S. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CMOS+compatible+micro-oven+heater+for+efficient+thermal+control+of+silicon+photonic+devices.">CMOS compatible micro-oven heater for efficient thermal control of silicon photonic devices.</a> Opt. Commun. 305, 66-70 (2013).</li><li>Chrostowski, L., Hochberg, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Silicon Photonics Design. , (2013).</li></ol>

We have nothing to disclose.

There are multiple challenges for the field of integrated photonics to overcome in order for complex and scalable systems of photonic devices to be feasible. These include, but are not limited to: tight fabrication tolerances, isolation from environmental instabilities, and minimization of all forms of loss. There are critical steps in the above protocol that help to minimize the loss of photonic devices.
One of the most crucial requirements in minimizing loss is closely matching the optical modes of the fibers and the waveguides. Part of the difficulty stems from the large mode field diameter (MFD) of SMF (~10 &#181;m). On the integrated device side, there is a 500 nm-wide silicon waveguide with a much smaller MFD (&#60;1 &#181;m). This mode transition between the fiber and the waveguide can be improved in two ways: the SMF to a length of UHNA fiber or placing an inverse taper to the edge of the photonic chip. The spliced region between the SMF and UHNA fiber acts as a mode converter, reducing the size of the mode to ~3 &#181;m. The inverse taper is used to expand the mode on the chip by reducing the width of the waveguide as it approaches the facet. This chip uses a linear taper from the 500 nm waveguides to the 150 nm tips (at the chip facets), with a transition length of 300 &#181;m. The tapering of the waveguide width to the edge of the chip results in a decrease in the effective index of the optical mode and, in turn, the mode expands.
The polishing of the chip facet is also very important in mitigating optical loss. Two concerns while polishing are stopping at the desired surface and delaminating the upper cladding material. Ideally, the final position of the facet would be precisely at the end of the taper. However, this is quite difficult to achieve, and for that reason, the tip of the taper is extended by 100 &#181;m so that the polishing can be stopped a few microns before the taper starts. If too little material is removed, the mode will not be captured as efficiently by the taper. If too much material is removed, there will be a larger mode mismatch at the fiber/chip interface, and more of the light will be lost. The other main concern is the delamination of the upper cladding. If there are problems with fabrication (cleanliness or excessive stress in the cladding), the cladding may not adhere to the substrate at the edge of the chip. When delamination happens to occur at one of the waveguides, it will result in very poor coupling efficiencies. If it is noticed during polishing, a polishing lubricant other than water can often improve results.
There is room for improvement in the above protocol. The largest improvement would come from using a more standard method for thermally tuning the device. The method used here was a result of a simplified fabrication process that did not include any metal layers. Typically, a resistive metal layer is used for heater elements, and a highly-conductive metal layer is used for contact pads and wires from the pads to the heater elements. A stage can then be used to set down probes onto the pads, allowing a voltage to be applied to the heaters. This enables a greater level of control and stability. A silicon photonic chip similar to what was tested here but with metal heaters is shown in the accompanying video.
There are other methods of coupling light to the photonic chip. For this work, edge coupling was used. Other common methods include free space coupling and grating coupling. Free space coupling relies upon bulk optical elements to align and focus the beam into the waveguide at the edge of the chip. The drawback with coupling in this manner is that it can be very difficult to optimize the alignment of the beam, and there will always be a reflection at the interface due to the index difference. Grating couplers scatter the light from the waveguide vertically, so that the end of a fiber can be placed at the surface of the cladding to couple to the device. These also have some issues, including difficult alignment (the fiber is often in the line of sight of the microscope) and higher losses. Fiber edge coupling is not perfect either. Pressing the fibers against the chip can damage the ends of the fibers, and both the fibers and the chip edge need to be cleaned frequently. The benefit of fiber edge coupling is that the alignment is far easier than the other two methods and is capable of achieving lower losses.
As the complexity of optical systems increases, the only feasible way for them to scale into a stable platform is in an integrated system, much like the path of electronic technology. The challenge is merging the integrated photonics platform with the bulk and fiber-based optical systems that are already deployed. With the utilization of photon-based quantum information systems, where the information space scales exponentially (compared to the linear scaling of classical systems), phase stability and low-loss integrated photonic technologies are paramount for success. The protocol we have described serves as an initial path forward for advancing this emerging technology.

Silicon is showing great promise as a photonics platform for quantum information processing1,2,3,4,5. One of the vital components of quantum photonic circuits is the photon source. Photon-pair sources have been developed from silicon in the form of micro-ring resonators made via a third-order nonlinear process, spontaneous four-wave mixing (SFWM)6,7,8. These sources are capable of producing pairs of indistinguishable photons, which are ideal for experiments involving photon entanglement9.
It is important to note that ring resonator sources can operate with both clockwise and counter-clockwise propagation, and the two different propagation directions are generally independent from one another. This allows a single ring to function as two sources. When optically pumped from both directions, these sources generate the following entangled state:
<img alt="Equation 1" src="/files/ftp_upload/55257/55257eq1.jpg" />
where <img alt="Equation 2" src="/files/ftp_upload/55257/55257eq2.jpg" /> and <img alt="Equation 3" src="/files/ftp_upload/55257/55257eq3.jpg" /> are the independent creation operators for clockwise- and counterclockwise-propagating bi-photons, respectively. This is a very desirable form of entangled state known as a N00N state (N=2)10.
Passing this state through an on-chip Mach-Zehnder interferometer (MZI) results in the state:
<img alt="Equation 4" src="/files/ftp_upload/55257/55257eq4.jpg" />
This state oscillates between maximum coincidence and zero coincidence at twice the frequency of classical interference in an MZI, effectively doubling the sensitivity of the interferometer10. Here, we present the procedure used to test such an integrated photon source and MZI device.

<table border="0" cellpadding="0" cellspacing="0" width="781">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">3-Axis NanoMax Flexure Stage</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">MAX312D</td>
			<td style="width:167px;">Precision 3-axis stages</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Three Channel Piezo Controller</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">MDT693B</td>
			<td>Piezo controllers for NanoMax stages</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fiber Polarization Controller</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">FPC562</td>
			<td>3-Paddle fiber-based polarization controller</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fiber Cleaver</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">XL411</td>
			<td>Fiber cleaver</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Standard V-Groove Fiber Holder</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">HFV001</td>
			<td>standard v-groove mount</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tapered V-Groove Fiber Holder</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">HFV002</td>
			<td>tapered v-groove mount</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Right-Angle Top Plate for NanoMax Stage</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">AMA011</td>
			<td>right-angle bracket</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">50:50 Fiber Optic Coupler</td>
			<td style="width:149px;">Thorlabs</td>
			<td style="width:127px;">TW1550R5F1</td>
			<td>50/50 combiner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Optical Fiber Fusion Splicer</td>
			<td style="width:149px;">Fujikura</td>
			<td style="width:127px;">FSM-40S</td>
			<td>Fusion splicer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">MultiPrep Polishing System - 8&#34;</td>
			<td style="width:149px;">Allied High Tech</td>
			<td style="width:127px;">15-2100</td>
			<td>Chip polisher</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Cross-Sectioning Paddle with Reference Edge</td>
			<td style="width:149px;">Allied High Tech</td>
			<td style="width:127px;">15-1010-RE</td>
			<td>Polishing mount</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Lightwave Measurement System</td>
			<td style="width:149px;">Keysight</td>
			<td style="width:127px;">8164B</td>
			<td>Mainframe for tunable laser</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Tunable Laser Source</td>
			<td style="width:149px;">Keysight</td>
			<td style="width:127px;">81606A</td>
			<td>Tunable laser</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Optical Power Sensor</td>
			<td style="width:149px;">Keysight</td>
			<td style="width:127px;">81634B</td>
			<td>Power meter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">NIR Single Photon Detector</td>
			<td style="width:149px;">ID Quantique</td>
			<td style="width:127px;">ID210</td>
			<td>Single photon detectors</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">NIR Single Photon Detector</td>
			<td style="width:149px;">ID Quantique</td>
			<td style="width:127px;">ID230</td>
			<td>Low noise, free-running single photon detectors</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">PicoHarp</td>
			<td style="width:149px;">PicoQuant</td>
			<td style="width:127px;">PicoHarp 300</td>
			<td>Time-correlated single photon counting</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">WiDy SWIR InGaAs Camera</td>
			<td style="width:149px;">NIT</td>
			<td style="width:127px;">640U-S</td>
			<td>IR Camera</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">WDM Bandpass Filter</td>
			<td style="width:149px;">JDS Uniphase</td>
			<td style="width:127px;">30055053-368-2.2</td>
			<td>pump cleanup filters</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">WDM Bandpass Filter</td>
			<td style="width:149px;">JDS Uniphase</td>
			<td style="width:127px;">1011787-012</td>
			<td>pump rejection filters</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Ultra-High Numerical Aperture Fiber</td>
			<td style="width:149px;">Nufern</td>
			<td style="width:127px;">UHNA-7</td>
			<td>high index fiber</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:339px;">Ultra Optical Single Mode Fiber</td>
			<td style="width:149px;">Corning</td>
			<td style="width:127px;">SMF-28</td>
			<td>standard single mode fiber</td>
		</tr>
	</tbody>
</table>

measurement of quantum interference in a silicon ring resonator photon source

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit manipulation, and integrated single-photon detectors. Here, we present the key aspects of preparing and testing a silicon photonic quantum chip with an integrated photon source and two-photon interferometer. The most important aspect of an integrated quantum circuit is minimizing loss so that all of the generated photons are detected with the highest possible fidelity. Here, we describe how to perform low-loss edge coupling by using an ultra-high numerical aperture fiber to closely match the mode of the silicon waveguides. By using an optimized fusion splicing recipe, the UHNA fiber is seamlessly interfaced with a standard single-mode fiber. This low-loss coupling allows the measurement of high-fidelity photon production in an integrated silicon ring resonator and the subsequent two-photon interference of the produced photons in a closely integrated Mach-Zehnder interferometer. This paper describes the essential procedures for the preparation and characterization of high-performance and scalable silicon quantum photonic circuits.

Individual photon counts from each detector, as well as the coincidence counts, were collected as the relative phase between the two paths was tuned. The individual counts (Figure 5A) show the classical interference pattern from an MZI with visibilities of 94.5 &#177; 1.6% and 94.9 &#177; 0.9%. The coincidence measurements (Figure 5B) show the quantum interference of the entangled state, as is evident by the oscillation at twice the frequency of the classical interference pattern, with a visibility of 93.3 &#177; 2.0% (96.0 &#177; 2.1% with the accidentals subtracted). To confirm that the photons are primarily being generated in the ring, the pumps were configured into two resonances that would require the bi-photons to be generated at a wavelength not supported by the ring. The orange line in Figure 5B confirms that, with such a configuration, there are no significant coincidences. Figure 6 shows the coincidence counts for the available resonance pairs that are symmetric in frequency about the resonance corresponding to the desired bi-photons. In all cases, the 2&#952; dependence of the relative phase is evident.
<img alt="Figure 1" src="/files/ftp_upload/55257/55257fig1.jpg" /> 
Figure 1: Experimental Testbed for the Silicon Waveguide Circuit. (a) Image of the silicon photonic quantum chip indicating the propagation direction of the photons. The inset is an energy conservation diagram for the four-wave mixing process that occurs within the ring. (b) Experimental setup used to test the silicon photonic circuit. (c) Transmission spectrum of the micro-ring cavity, with arrows indicating the pumping configuration as well as the wavelength of the generated bi-photons. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55257/55257fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55257/55257fig2.jpg" /> 
Figure 2: Facet Improvement from Polishing. Images of the facet of a silicon photonic chip (a) after fabrication but before polishing and (b) after polishing. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55257/55257fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55257/55257fig3.jpg" /> 
Figure 3: Characterization of Waveguide Dispersion. Plot of the wavelength dependence of the group index. The red-shaded region is representative of the bandwidth of the resonances and allows for the easy evaluation of the phase-matching condition. The green dashed line is horizontal and lies completely within the shaded region, demonstrating that the phase-matching condition is satisfied. The fact that the data is flat across the entire range is confirmation of zero dispersion. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55257/55257fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55257/55257fig4.jpg" /> 
Figure 4: Measurement of Coincident Photons. Plot of the coincidence peak measured with the time-correlator with an integration time of 90 s and a timing resolution of 32 ps. The red dashed lines indicate the edges of the coincidence window, in which there are a total of 459 coincidences. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55257/55257fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55257/55257fig5.jpg" /> 
Figure 5: Classical and Quantum Interference Measurements. (a) Classical light demonstrating the typical interference pattern from an MZI as the relative phase between the two paths is varied. (b) Coincidence correlation measurements showing the&#160;2&#952; dependence of the relative phase. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55257/55257fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/55257/55257fig6.jpg" /> 
Figure 6: Bi-Photon Visibility for Various Pump Wavelength Configurations. Plots of the coincidences correlation measurements and calculated visibilities for the pumping wavelengths of (a) 1,513.5 nm and 1,592.0 nm, (b) 1,518.2 nm and 1,586.9 nm, (c) 1,522.9 nm and 1,581.8 nm, (d) 1,527.7 nm and 1,576.7 nm, (e) 1,532.4 nm and 1,571.6 nm, and (f) 1,537.2 nm and 1,566.6 nm. In all cases, the 2&#952; dependence of the relative phase is evident. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55257/55257fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td colspan="2">SMF to UHNA Fiber Splicing Parameters</td>
		</tr>
		<tr>
			<td>Align: Core</td>
			<td>Focus: Auto</td>
		</tr>
		<tr>
			<td>ECF: Off</td>
			<td>Auto Power: Off</td>
		</tr>
		<tr>
			<td>Cleave Limit: 1&#176;</td>
			<td>Core Angle Limit: 1&#176;</td>
		</tr>
		<tr>
			<td>Cleaning Arc: 150 ms</td>
			<td>Gap: 15 &#181;m</td>
		</tr>
		<tr>
			<td>Gapset Position: Center</td>
			<td>Prefuse Power: 20 bit</td>
		</tr>
		<tr>
			<td>Prefuse Time: 180 ms</td>
			<td>Overlap: 10 &#181;m</td>
		</tr>
		<tr>
			<td>Arc1 Power: 20 bit</td>
			<td>Arc1 Time: 18,000 ms</td>
		</tr>
		<tr>
			<td>Arc2: Off</td>
			<td>Rearc Time: 800 ms</td>
		</tr>
		<tr>
			<td>Taper Splice: Off</td>
			<td></td>
		</tr>
	</tbody>
</table>
Table 1: Settings for Fusion Splicing SMF to UHNA Fiber.

Watch this Scientific Journal Video about Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source at JoVE.com

Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

Silicon photonic chips have the potential to realize complex integrated quantum systems. Presented here is a method for preparing and testing a silicon photonic chip for quantum measurements.

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit ...

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Nanyang Technological University

Research

JoVE Journal

Engineering

8.3K Views.  Rochester Institute of Technology. Silicon photonic chips have the potential to realize complex integrated quantum systems. Presented here is a method for preparing and testing a silicon photonic chip for quantum measurements.

Video: Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

Gradient Echo Quantum Memory in Warm Atomic Vapor

Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.

The gradient echo memory is a protocol for storing optical quantum states of light in atomic ensembles. Quantum memory is a key element of a quantum repeater, which can extend the range of quantum key distribution. We outline the operation of the scheme when implemented in a 3-level atomic ensemble.

Gradient  echo memory (GEM) is a protocol for storing optical quantum states of light in  atomic ensembles. The primary motivation for such a technology ...

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

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 ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard &#960;/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45&#176; and 135&#176; directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.

The measurement protocol and data analysis procedure are given for obtaining transverse coherence of a synchrotron radiation X-ray source along four directions simultaneously using a single 2-D checkerboard phase grating. This simple technique can be applied for complete transverse coherence characterization of X-ray sources and X-ray optics.

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is ...

Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Optimized sampling protocols and the development of new wipe materials can be facilitated by standardized measurements of collection efficiency from wipe-sampling. Our approach for sampling trace explosives uses an automated device to control speed, force, and distance during wipe-sampling followed by extraction of collected explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Synchrotron X-ray Microdiffraction and Fluorescence Imaging of Mineral and Rock Samples

In this report, we describe a detailed procedure for acquiring and processing&#160;x-ray microfluorescence (&#956;XRF), and Laue and powder microdiffraction two-dimensional (2D) maps at beamline 12.3.2 of the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. Measurements can be performed on any sample that is less than 10 cm x 10 cm x 5 cm, with a flat exposed surface. The experimental geometry is calibrated using standard materials (elemental standards for XRF, and crystalline samples such as Si, quartz, or Al2O3 for diffraction). Samples are aligned to the focal point of the x-ray microbeam, and raster scans are performed, where each pixel of a map corresponds to one measurement, e.g., one XRF spectrum or one diffraction pattern. The data are then processed using the in-house developed software XMAS, which outputs text files, where each row corresponds to a pixel position. Representative data from moissanite and an olive snail shell are presented to demonstrate data quality, collection, and analysis strategies.

We describe a beamline setup meant to carry out rapid two-dimensional x-ray fluorescence and x-ray microdiffraction mapping of single crystal or powder samples using either Laue (polychromatic radiation) or powder (monochromatic radiation) diffraction. The resulting maps give information about strain, orientation, phase distribution, and plastic deformation.