The authors acknowledge funding support from the National Aeronautics and Space Administration (NASA)&#39;s ROSES and APRA programs. GC also acknowledges the Universities Space Research Association for administering his appointment at NASA.

1. Microstrip Line Resonator Fabrication14 (Figure&#160;3)
<ol>
	<li>Clean a silicon-on-insulator (SOI) wafer, which has a 0.45-&#181;m-thick silicon device layer, with freshly mixed H2SO4:H2O2 (3:1) for 10 min. Then rinse the wafer in deionized water for 10 min and dry with a nitrogen gun. Immediately prior to subsequently processing, dip the wafer in H2O:HF (10:1) for 10 sec and rinse in deionized water for 5 min.</li>
	<li>Fabricate a lift-off mask, which consists of a germanium (Ge)/positive photoresist such as S-1811.15
	<ol>
		<li>Spin-coat the wafer with thinned positive photoresist bilayer (2 parts thinner-P : 1 part positive photoresist) at 4,000 rpm for 30 sec and then electron-beam deposit Ge.</li>
		<li>Pattern Ge using photo-lithography by first applying hexamethyldisilazane (HMDS) on the wafer for 1 min and then spin off the excess at 3,000 rpm for 30 sec.</li>
		<li>Spin on thinned positive photoresist (2 parts thinner-P : 1 part positive photoresist) at 2,000 rpm for 30 sec and bake it on a hot plate for 1 min at 110 &#176;C. Use a mask aligner to expose photoresist and spray develop resist with a tetramethyl ammonium hydroxide-based solution.</li>
		<li>Reactive-ion etch the Ge with an SF6/O2 plasma at 70 W. Ash underlying photoresist with O2 plasma to achieve undercut of photoresist.</li>
		<li>DC-magnetron sputter-deposit niobium (Nb) ground plane with 3.7 mT of argon (Ar) at 500 W and lift it off by placing the wafer inside an acetone-filled beaker for 4 hr.</li>
	</ol>
	</li>
	<li>Spin-coat bisbenzocyclobutene (BCB) at 4,000 rpm for 30 sec on the Nb-coated surface of the SOI wafer and to one surface of another silicon wafer. Bond the two BCB-coated surfaces together with 3 bar of pressure at 200 &#176;C.</li>
	<li>Manually flip wafer stack upside down to begin processing the backside of the SOI wafer.</li>
	<li>Etch the silicon handle wafer by mechanical lapping using Al2O3 slurry, followed by deep reactive ion etching using the Bosch process.16 Etch the buried SiO2 layer with H2O:HF (10:1) for 20 min.</li>
	<li>Deposit molybdenum nitride (Mo2N) using DC magnetron reactive sputtering at 700 W and 3.3 mT (Ar:N2 partial pressure = 7:1). Pattern resonators by spinning at 2,000 rpm for 30 sec and baking it at 180 &#176;C for 2 min followed by spinning thinned positive photoresist (2 parts thinner-P : 1 part positive photoresist) at 2,000 rpm for 30 sec. Develop photoresist in a tetramethyl ammonium hydroxide-based solution and ash in a reactive ion etcher. Etch Mo2N with a phosphoric acid-based solution.</li>
	<li>Fabricate a lift-off mask consisting of a Ge/PMMA bilayer by spinning on the polymethylmethacrylate (PMMA) at 5,000 rpm for 30 sec and baking it at 180 &#176;C for 2 min followed by electron-beam deposition of Ge. Sputter-deposit Nb transmission lines and lift off in acetone (refer to step 1.2 with the exception that the positive photoresist is substituted with PMMA).</li>
	<li>In some embodiments, radio-frequency (RF) sputter-deposit SiO2, pattern it by spinning with positive photoresist and etch in a hydrofluoric-acid based solution. Then, lift off a sputter-deposited Nb thin film using a germanium/positive photoresist liftoff mask as detailed in step 1.2.</li>
</ol>
2. Procedure for Installation of Microwave Resonator Chip in Test Package
<ol>
	<li>Design and machine a test package consisting of gold (Au)-coated copper cavity (with a base and lid) which matches resonator chip dimensions, feedline input and output locations. NOTE: The cavity size of the housing should be specified to support a single-mode operation with minimal parasitic coupling over the band of interest.</li>
	<li>Design and fabricate a controlled impedance microwave fan-out board17 to route the signals between the chip and Sub-Miniature version A (SMA) connectors.</li>
	<li>Insert the SMA connectors into the input and output of the test package so that the center conductor pin is aligned over the corresponding fan-out board contact pad. Apply a solder mask to protect against shorting, and apply solder in the region of the center conductor pin. Place the package on a hot plate and heat to 200 &#176;C for ~5 min to melt the solder. Let cool and then remove the solder mask.</li>
	<li>Mount the resonator chip into the Au-coated copper package cavity such that the on-chip feedline output and input pads are close and aligned to the corresponding fan-out board coplanar waveguide (CPW) lines. Secure the chip with copper clips which make contact at the edges of the corners of the chip.</li>
	<li>Place superconducting Al wire bonds between the fan-out board and on-chip contact pads. Place a maximum number (~4 in the case presented here &#8212; see Figure&#160;4) of ~500-600-&#956;m-long, ~250-&#181;m-in-height wire bonds, to provide impedance match between the SMA connector input and outputs and the on-chip CPW feedline.</li>
	<li>After wire-bonding, with a multimeter check the DC resistance between the center pins of the input and output connectors, and between a center pin and ground, to confirm there is an electrical connection across the two center pins and an open connection between the center line and ground.</li>
</ol>
3. Procedure for Installation of Microwave Resonator in a Cryogenic Helium-3 Microwave Testbed
<ol>
	<li>Assemble the testbed as in the configuration shown in Figure 2, in which a series of SMA cables are routed from RT to the 0.3-K cold stage where the device will be mounted.</li>
	<li>Install copper (Cu) and superconducting niobium-titanium (NbTi) cables as shown in Figure 2 to provide low microwave loss and, in the case of the NbTi cables, a low thermal conductance. Use the NbTi cables as a thermal break between the 2-K and 0.3-K stages.</li>
	<li>Mount a cryogenic high electron mobility transistor (HEMT) amplifier at the 2-K stage on the output line for low-noise amplification in the band of the resonator device and install a circulator.</li>
	<li>Insert a cryogenic circulator on the output line at the input to this amplifier.</li>
	<li>Mount the packaged resonator devices onto a bracket bolted to the 0.3-K cold stage.</li>
	<li>Connect a microwave attenuator on the input side of the package to provide for matched termination and connect the appropriate SMA cables to this attenuator input and package output. Ensure that these controlled impedance terminations are well matched and are as close to the device under test as possible &#8212; they define the &#34;device calibration plane&#34; (see Figure 2).</li>
	<li>Close up the cryostat. Follow standard procedure to cool the devices to 0.3 K.</li>
</ol>
4. Procedure for Microwave Resonator Measurements
<ol>
	<li>Set the VNA to scan over a wide frequency band (10 MHz - 8 GHz, for the device considered here) at the device-under-test design frequencies. Adjust the power levels on the VNA to suitable levels for the device under test (~-30 dBm, for the device considered here). &#160; 
	NOTE: Ensure that the input RF power level is low enough so as not to exceed the critical current of the superconducting microwave resonator and superconducting feedline. Ensure that the power level is high enough to provide an adequate signal-to-noise ratio.</li>
	<li>Calibrate the flexible RF cables following standard Short-Open-Load-Thru (SOLT) procedure, following VNA software directions found in the VNA manual. Insert in shorted, open, terminated and thru standards at the output of each of the flexible cables, which route from the vector network analyzer and which will later be connected to the input of the cryostat for measurements. This calibration defines the &#34;instrument reference plane&#34; (e.g., see Figure 2).</li>
	<li>Following this SOLT calibration, verify the fidelity of the calibration by confirming that the transmission, S21, with the thru line connected measured with the VNA, has low residual errors (i.e., the response is at ~0 dB level and S11 and S22 are low, e.g., &#8804; -50 dB).</li>
	<li>Connect the flexible cables to the input and output lines of the cryostat.</li>
	<li>Turn on the cryogenic microwave amplifier by applying the required DC bias voltage as specified in the company-provided documentation for the microwave amplifier.</li>
	<li>First, complete a wideband scan of VNA (10 MHz - 8 GHz, for the device considered here) to observe the S21 baseline structure and to look for any sharp high-Q structures indicative of microwave resonators.</li>
	<li>Then, narrow the frequency range (to ~2 - 4 GHz, for the device considered here) and adjust the number of data points (~30,000 for the device considered here) of the VNA to scan over the resonator band. Use a frequency band wide enough to provide an adequate baseline span for later fits to this baseline to carry out an in-situ calibration (see discussion in Introduction). 
	NOTE: Depending on the noise level, increase the number of averages, or reduce the IF bandwidth to improve signal-to-noise.</li>
	<li>Save these VNA data scans of the complex transmission data to file for post-measurement in-situ calibration, and analysis and extraction of quality factors and resonance frequencies.11</li>
</ol>

<ol>
	<li>Monfardini, 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=The+N&#233;el+IRAM+KID+Arrays+(NIKA).">The N&#233;el IRAM KID Arrays (NIKA).</a> J. Low Temp. Phys. 167 (5-6), 834-839 (2012).</li><li>Schlaerth, 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=The+Status+of+Music:+A+Multicolor+Sub/millimeter+MKID+Instrument.">The Status of Music: A Multicolor Sub/millimeter MKID Instrument.</a> J. Low Temp. Phys. 167 (3-4), 347-353 (2012).</li><li>Swenson, L. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MAKO:+a+pathfinder+instrument+for+on-sky+demonstration+of+low-cost+350+micron+imaging+arrays.">MAKO: a pathfinder instrument for on-sky demonstration of low-cost 350 micron imaging arrays.</a> Proc. SPIE. 8452, 84520P (2012).</li><li>Mazin, B. A., Bumble, B., Meeker, S. R., O'Brien, K., McHugh, S., Langman, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+superconducting+focal+plane+array+for+ultraviolet,+optical,+and+near-infrared+astrophysics.">A superconducting focal plane array for ultraviolet, optical, and near-infrared astrophysics.</a> Opt. Express. 20 (2), 1503-1511 (2012).</li><li>Mazin, B. 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The authors declare that they have no competing financial interests.

The single-flip fabrication process provides a means for realizing superconducting resonators on both sides of a thin 0.45-&#181;m single-crystal Si substrate. One may be motivated to use a single-crystal Si dielectric because it has more than an order of magnitude lower loss than deposited dielectrics (such as Si3N4) with loss tangents in the 4.0-6.5-GHz range &#60; 1 x 10-5. 23-24 The ability to pattern features on both sides of this substrate allows one to employ a microstri...

Advances in astrophysical instrumentation have recently introduced superconducting microwave resonators for the detection of infrared light.1-4 A superconducting resonator will respond to infrared radiation of energy E = hv &#62; 2&#916; (where h is Planck&#39;s constant, v is the radiation frequency and &#916; is the superconducting gap energy). When the resonator is cooled to a temperature well below the superconductor critical temperature, this incident radiation breaks Cooper pairs in the resonator volume and generates quasiparticle excitations. The increase in the density of quasiparticle excitations changes the kinetic inductance, and thus the complex surface impedance of the superconductor. This optical response is observed as a shift in the resonance frequency to lower frequency and a reduction in the quality factor of the resonator. In the canonical read-out scheme for a microwave kinetic inductance detector (MKID), the resonator is coupled to a microwave feedline and one monitors the complex transmission through this feedline at a single microwave frequency tone on resonance. Here, the optical response is observed as a change in both the amplitude and phase of transmission5 (Figure 1). Frequency-domain multiplexing schemes are capable of reading out arrays of thousands of resonators.6-7
To successfully design and implement superconducting-resonator-based instrumentation, the properties of these resonant structures need to be characterized accurately and efficiently. For example, precision measurements of the noise properties, quality factors Q, resonance frequencies (including their temperature dependence) and optical response properties of superconducting resonators are desired in the context of MKID device physics,8 quantum computing,9 and the determination of low-temperature materials properties.10
In all of these cases, the measurement of the circuit&#39;s complex transmission scattering parameters is desired. This work concentrates on the determination of the resonator&#39;s complex transmission coefficient, S21, whose amplitude and phase can be measured with a vector network analyzer (VNA). Ideally, the VNA reference plane (or test port) would be directly connected to the device under test (DUT), but a cryogenic setting normally requires the use of additional transmission line structures to realize a thermal break between RT (~300 K) and the cold stage (~0.3 K in this work; see Figure 2). Additional microwave components such as directional couplers, circulators, isolators, amplifiers, attenuators, and associated interconnecting cables may be needed to appropriately prepare, excite, read out and bias the device of interest. The phase velocities and dimensions of these components vary when cooling from room to cryogenic temperatures, and therefore they affect the observed response at the device calibration plane. These intervening components between the instrument and the device calibration plane influence the complex gain and need to be appropriately accounted for in the interpretation of the measured response.11
In theory, a scheme is needed that sets the measurement reference plane, identical to the one employed during calibration, at the DUT. To reach this target, one could measure the calibration standards over multiple cool-downs; however, this poses constraints on the stability of the VNA and the repeatability of the cryogenic instrument, which are difficult to attain. To mitigate these concerns, one could place the necessary standards in the cooled test environment and switch between them. This is, for example, similar to what is found in microwave probe stations, where the sample and calibration standards are cooled to 4 K by a continuous liquid helium flow or a closed-cycle refrigeration system.12 This method was demonstrated at sub-kelvin temperatures but requires a low-power, high-performance microwave switch in the test band of interest.13
An in-situ calibration procedure is therefore desired which accounts for the instrumental transmission response between the VNA reference plane and the device calibration plane (Figure 2) and which overcomes the limitations of the methods described above. This cryogenic calibration method, presented and discussed in detail in Cataldo et al.11, allows one to characterize multiple resonators over a frequency range wide compared to the resonator line width and inter-resonator spacing with an accuracy of ~1%. This paper will focus on the details of the sample fabrication and preparation processes, experimental test set-up and measurement procedures used to characterize superconducting microwave resonators with planar line geometries.11

<table border="0" cellpadding="0" cellspacing="0" width="715">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microposit S-1811 Photoresist</td>
			<td style="width:111px;">Shipley</td>
			<td style="width:187px;"></td>
			<td style="width:201px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">BCB</td>
			<td style="width:111px;">Dow</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">3022-35</td>
		</tr>
		<tr height="45">
			<td height="45" style="height:45px;width:216px;">SOI wafers</td>
			<td style="width:111px;">SOITec</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">Fabricated with SmartCutTM process</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Mo</td>
			<td style="width:111px;">Kamis</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">99.99%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nb</td>
			<td style="width:111px;">Kamis</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">99.95% (excludes Ta)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">E-6 metal etch w/AES</td>
			<td style="width:111px;">Fujifilm</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">CPG Grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Acetone</td>
			<td style="width:111px;">JT Baker</td>
			<td style="width:187px;">9005-05</td>
			<td style="width:201px;">CMOS Grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HF dip (1:10)</td>
			<td style="width:111px;">JT Baker</td>
			<td style="width:187px;">5397-03</td>
			<td style="width:201px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PMMA</td>
			<td style="width:111px;">Microchem</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">950 PMMA A2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">GE 7031</td>
			<td style="width:111px;">General Electric</td>
			<td style="width:187px;"></td>
			<td style="width:201px;">Low-temperature adhesive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cryogenic Microwave Amplifier</td>
			<td style="width:111px;">MITEQ</td>
			<td>AF S3-02000400-08-CR-4</td>
			<td style="width:201px;">2-4 GHz, gain ~30dB</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NbTi Semi-rigid SMA cables</td>
			<td style="width:111px;">Coax. Co.</td>
			<td style="width:187px;">SC-086/50-NbTi-NbTi</td>
			<td style="width:201px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Circulator</td>
			<td>PamTech</td>
			<td>CTD1229K</td>
			<td style="width:201px;">return loss &#62; -20 dB from 2-4 GHz</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">RF attenuator</td>
			<td>Weinschel</td>
			<td>Model-4M</td>
			<td style="width:201px;">7 dB attenuation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Flexible SMA cables</td>
			<td style="width:111px;">Teledyne-Storm</td>
			<td>R94-240</td>
			<td style="width:201px;">ACCU-TEST</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Vector Network Analyzer</td>
			<td style="width:111px;">Agilent</td>
			<td>N5242A PNA-X</td>
			<td style="width:201px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Liquid He-4 cryogen</td>
			<td>Praxair&#160;</td>
			<td style="width:187px;"></td>
			<td style="width:201px;"></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:216px;">Liquid N2 cryogen</td>
			<td style="width:111px;">Praxair&#160;</td>
			<td style="width:187px;"></td>
			<td style="width:201px;"></td>
		</tr>
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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.

The response of a half-wave Mo2N resonator (Figure 5) fabricated on a 0.45-&#181;m single-crystal silicon dielectric was validated with this methodology. In this instance, coupling to a Nb coplanar waveguide (CPW) feedline for read-out is achieved via capacitive coupling through a sputter-deposited SiO2 dielectric, in the &#34;H&#34; shaped region at one of the open ends of the resonator (see Protocol section 1.6). In other instances, capacitive coup...

Watch this Scientific Journal Video about Fabrication and Characterization of Superconducting Resonators at JoVE.com

Fabrication and Characterization of Superconducting Resonators

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 ...

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10.3K Views.  NASA Goddard Space Flight Center. 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.

Video: Fabrication and Characterization of Superconducting Resonators

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 ...

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

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

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

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

Microwave Photonics Systems Based on Whispering-gallery-mode Resonators

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various areas of technology and applied science, such as aerospace and communication engineering, sensing, metrology, nonlinear photonics, and quantum optics. In this article, we present the principal techniques used in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators. First detailed in this article is the protocol for resonator polishing, which is based on a grind-and-polish technique close to the ones used to polish optical components such as lenses or telescope mirrors. Then, a white light interferometric profilometer measures surface roughness, which is a key parameter to characterize the quality of the polishing. In order to launch light in the resonator, a tapered silica fiber with diameter in the micrometer range is used. To reach such small diameters, we adopt the "flame-brushing" technique, using simultaneously computer-controlled motors to pull the fiber apart, and a blowtorch to heat the fiber area to be tapered. The resonator and the tapered fiber are later approached to one another to visualize the resonance signal of the whispering gallery modes using a wavelength-scanning laser. By increasing the optical power in the resonator, nonlinear phenomena are triggered until the formation of a Kerr optical frequency comb is observed with a spectrum made of equidistant spectral lines. These Kerr comb spectra have exceptional characteristics that are suitable for several applications in science and technology. We consider the application related to ultra-stable microwave frequency synthesis and demonstrate the generation of a Kerr comb with GHz intermodal frequency.

The customized techniques developed in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators are presented. The protocols to obtain and characterize these resonators are detailed, and an explanation of some of their applications in microwave photonics is given.

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various ...

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 and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

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 ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

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 ...

Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres can be thought as a store of energy with a huge variety of applications: compact laser sources, highly sensitive biochemical sensors and nonlinear phenomena. A protocol for the fabrication of both the microspheres and coupling system is given. The couplers described here are tapered fibers. Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS). A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler. In the case of hyperparametric oscillations (four wave mixing and stimulated anti-stokes Raman scattering), the modes must fulfill the energy and momentum conservation and, last but not least, have a good spatial overlap.

Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS).

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres ...