This research was supported by the Israeli Ministry of Science, Technology &#38; Space; ICore: the Israeli Excellence center &#39;Circle of Light&#39; grant no. 1802/12, and by the Israeli Science Foundation grant no. 2013/15. The authors thank Karen Adie Tankus (KAT) for the helpful editing.

CAUTION: This experiment involves high voltage. It is the reader&#39;s responsibility to verify with the safety authorities that their experiment follows regulations before turning on the high voltage.
NOTE: Any kind of polar liquid can be utilized to produce liquid fibers, such as ethanol, methanol, acetone, or water. The polarity of the liquid dictates the stability and diameter of the created fiber23,24. For best results, use deionized water with 18 M&#8486; resistance. Before choosing optical components, such as optical fibers and light sources, consult the literature to ensure a low absorption in the water/liquid fiber at the desired optical wavelength. The protocol can be paused at any given moment before filling the water reservoir (step 4.5).
1. Preparation of Water Reservoirs and Experimental Station
<ol>
	<li>Manufacture two poly(methyl methacrylate) (PMMA) reservoirs with magnetic connectors for the pipette and the high voltage, according to Figure 1.
	<ol>
		<li>Cut two PMMA plates to 60 x 50 x 10 mm in size, drill cavities of 8 mm in depth and 7 mm in diameter on the backside of the plates. Glue connector magnets inside the cavities.</li>
		<li>For the capillary clamp, cut a stripe of PMMA to 45 x 10 x 2 mm and glue two magnets on the top side of it.</li>
		<li>For the electric connector, wrap magnets in a small piece of metallic foil and connect it electrically with crocodile clamps to the high-voltage (HV) source. The reservoirs hold approximately 100 - 300 &#181;L of water. Place the wrapped magnets in fluidic contact with the water in the reservoir. 
		NOTE: Preferably, use magnetic connectors for clamps and high voltage. If possible, do not to use any kind of glue to attach the clamps or the connectors, as many types of glues dissolve under the influence of high voltage or in the presence of electric arcs and diminish the water fiber stability or optical quality.</li>
	</ol>
	</li>
	<li>Mount one PMMA reservoir on a 5-degree-of-freedom (DOF) micro-positioning stage.</li>
	<li>Thoroughly clean all connectors and areas with isopropanol (spectral grade) followed by deionized water. Blow-dry with nitrogen. Cover the PMMA water reservoir and all clamps with polytetrafluoroethylene (PTFE) tape to avoid any leaking or dripping of water.</li>
	<li>Position the set-up under an optical microscope for imaging. Use far-field objectives (5X, 0.14 NA, and 34 mm WD for long water fibers and 20X, 0.42 NA, and 20 mm WD lens for short water fibers) to avoid unwanted grounding between the HV area of the water fiber and the electrically conductive microscope set-up.</li>
	<li>Set up two optical fiber clamps on linear transitional stages, one behind each water reservoir, according to Figure 1. Each fiber coupler should be able to move back and forward within its micropipette (discussed in the following section).</li>
</ol>
2. Choosing the Micropipettes and Voltage
<ol>
	<li>The inner diameter of the micropipette ensures a maximum radius of the fabricated water fiber. To create a 5-&#181;m radius water fiber, use 150-&#181;m-inner-diameter pipettes, paired with 125-&#181;m-diameter optical fibers. For thicker (20 - 90 &#181;m) and longer (800 - 1,000 &#181;m) water fibers, use micropipettes with an inner diameter of 850 &#181;m. 
	NOTE: As a rule of thumb, the water fiber maximum length is estimated by multiplying the maximal radius by 25. For details, refer to Table 1.
	<ol>
		<li>Break the micropipette by hand over an edge to a length of 3 cm.</li>
	</ol>
	</li>
	<li>To create water fibers with a diameter of up to 110 &#181;m, apply a voltage between the two water reservoirs between 1.5 kV and 3 kV. For water fibers reaching up to a millimeter in length, apply up to 8 kV. Compare with Figure 1 for electrical wiring suggestions.</li>
</ol>
3. Preparation of the Optical Couplers
NOTE: For the best transmission result, use a single-mode tapered fiber to launch laser light into the water fiber and a highly multimode reflowed fiber lens as the output coupler (core &#62; 100 &#181;m). However, for easy operation, use a low multimode fiber as the output coupler (for example, a 1550-nm single-mode fiber for a 780-nm wavelength).
<ol>
	<li>Fabrication of a Tapered Fiber Coupler 
	NOTE: See Figure 2.
	<ol>
		<li>Strip the 780-nm single-mode fiber with a fiber stripper from its plastic cladding to expose an area of 10 - 15 mm of bare fiber. Clean the exposed area with delicate task wipes in combination with acetone. Pass the fiber through the desired micropipette before tapering it. Taper the fiber below the single-mode criteria with a slope smaller than 1/20.</li>
		<li>Use a hydrogen flame for tapering the fiber with a flow rate of 140 mL/min, while simultaneously pulling the taper from both sides at 0.06 mm/s. 
		NOTE: The tapered portion is in total between 6 to 9 mm. If the fiber breaks before reaching the single-mode criteria, adjust the hydrogen flow to higher rates or place the fiber in a hotter area of the torch. If the area is longer, adjust the hydrogen flow to lower rates or place the fiber in a colder area of the torch.</li>
		<li>Turn off the flame and carefully increase the tension in the fiber until it breaks at its thinnest spot. Use this tapered fiber as the input coupler. 
		CAUTION: The tapered fiber is fragile.</li>
	</ol>
	</li>
	<li>Fabrication of a Fiber Lens Coupler
	<ol>
		<li>Strip the 1550-nm single-mode fiber tip with a fiber stripper and clean the exposed area with delicate task wipes in combination with acetone. Choose and prepare a pipette as described above and pass the fiber through it.</li>
		<li>Heat the tip with an electric fusion splicer or CO2 laser at 15-W power, focused through a 200-mm lens, until the glass fiber end becomes liquid and forms a slightly rounded shape, known as a fiber lens.</li>
	</ol>
	</li>
</ol>
4. Assembling
<ol>
	<li>If not done yet, insert the fiber couplers into the desired micropipettes.</li>
	<li>Clamp the micropipette, using the premanufactured, magnetic PMMA clamp, with the fiber couplers onto the PMMA reservoirs. The non-tapered side of the micropipettes should reach into the water reservoir. Clamp each of the fiber couplers on a linear positioning stage.</li>
	<li>Connect the tapered fiber coupler to a 780-nm, continuous wave, fiber-coupled 10-mW laser source and the fiber lens coupler to a power meter. Fill the reservoir with water and ensure that no air bubbles are stuck in the micropipette. If necessary, push or pull them with the optical fiber coupler (from step 3.1 or, accordingly, from step 3.2). 
	NOTE: At this stage, following the optical path, the stations are: the laser light source, the optical fiber, (and this fiber goes through) the fiber clamp on a linear stage, the water in the reservoir with electrical connection, the micropipette filled with water, the optical tapered fiber coupler, free space (later: water fiber), the fiber lens coupler (now the second fiber), the micropipette filled with water, the water reservoir with electric connection, the fiber clamp on a linear stage, and, lastly, the power meter.</li>
	<li>Connect the ends of the mounted micropipettes by adjusting the 5-degre-of-freedom mount of the PMMA water reservoir to establish a fluidic contact between the micropipettes. Turn on the light source and the power meter. Adjust the fiber couplers to have a transmission with the help of the 5-DOF PMMA water reservoir mount. 
	NOTE: Use appropriate laser safety equipment.</li>
	<li>Connect the high voltage electrically with the water reservoir by placing the magnetic connectors wrapped in metallic foil over the magnetic counterparts in the PMMA water reservoir and attaching crocodile clamps to the metallic foil. Connect the crocodile clamps via electrical cables to the HV source (Figure 2a).</li>
</ol>
5. Running the Experiment
<ol>
	<li>Increase the voltage to the desired value. A starting point for a very short and narrow bridge is 1.5 kV. Stable bridges with 100 &#181;m and more in length can be achieved with 2.5 - 3 kV.</li>
	<li>Slowly increase the distance between the micropipettes to the desired length according to the choice of the micropipettes (Figure 2b and 2c). Adjust couplers and pipettes with the 5-DOF stage and the 1-DOF stages to optimize the optical transmission.</li>
	<li>Measure the coupling efficiency by taking a measurement on the power meter and taking the ratio of the coupled-in to the coupled-out laser power.</li>
	<li>Disconnect the power meter and connect a photoreceiver to the output fiber coupler. Connect the photoreceiver to an oscilloscope. Record time trace measurements of the transmitted light, representing the capillary water fiber oscillations.</li>
	<li>Convert the time trace measurements via Fast Fourier Transformation to frequency domain. Take the central frequency over full width at half maximum to receive the capillary quality factor. 
	NOTE: Create a spectrogram to check for frequency jitter.</li>
	<li>Use the top view microscope set-up to characterize the geometrical structure of the water fiber. The fiber radius is obtained at the thinnest portion of the water fiber.</li>
</ol>

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The authors have nothing to disclose.

To conclude, the major advantage and uniqueness of this technique is creating a fiber which hosts three different kinds of waves: capillary, acoustic, and optical. All three waves oscillate in different regimes, opening the possibility for multi-wave detectors. As an example, airborne nanoparticles affect the surface tension of liquids. Already at the current stage, it is possible to monitor changes in the surface tension through variations in the capillary eigenfrequency. Additionally, water-walled devices are a million...

Since the breakthrough of optical fibers in communication, awarded with a Nobel prize in 20091, a series of fiber-based applications grew alongside. Nowadays, fibers are a necessity in laser surgeries2, as well as in coherent X-ray generation3,4, guided-sound5 and supercontinuum6. Naturally, the research on fiber optics expanded from utilizing solids into exploiting liquids for optical wave guiding, where liquid-filled microchannels and laminar flow combine the transportation properties of a liquid with the advantages of optical interrogation7,8,9. However, these devices clamp the liquid between solids and, therefore, forbid it to express its own wave character, known as capillary wave.
Capillary waves, similar to those seen when throwing a stone into a pond, are an important wave in nature. However, due to the obstacles of controlling a liquid without dampening its surface through channels or solids, they are hardly utilized for detection or application. In contrast, the device presented in this protocol has no solid boundaries; it is surrounded by and flows in air, allowing, therefore, capillary waves to develop, propagate, and interact with light.
To fabricate a water fiber, it is necessary to go back to a technique known as the floating water bridge, first reported in 189310, where two beakers filled with distilled water and connected to a high-voltage source will form a fluidic, water thread-like connection between them11. Water bridges can reach up to a length of 3 cm12 or be as thin as 20 nm13. As for the physical origin, it has been shown that surface tensions, as well as dielectric forces, are both responsible for carrying the bridge&#39;s weight14,15,16. To activate the water bridge as a water fiber, we couple light in with an adiabatically tapered silica fiber17,18 and out with a silica fiber lens19. Such a device can host acoustical, capillary, and optical waves, making it advantageous for multi-wave detectors and lab-on-chip20,21,22 applications.

<table><tbody><tr><td>Deioniyzed Water</td><td></td><td></td><td>18MOhm resistance</td></tr><tr><td>Micropipettes, Borosilicate Glass, round, inner diameter 850 micron</td><td>Produstrial.com</td><td>#133260</td><td></td></tr><tr><td>Micropipettes, Borosilicate Glass, round, inner diameter 150 micron</td><td>Produstrial.com</td><td>#133258</td><td></td></tr><tr><td>High voltage, low current source, 3kV with 5 mA.</td><td>Bertan</td><td>Model 215</td><td></td></tr><tr><td>High voltage, low current source, 8 kV with 0.25 mA.</td><td>Home build</td><td></td><td></td></tr><tr><td>Optical fiber</td><td>Corning</td><td>HI 780 C</td><td>5 meter</td></tr><tr><td>Optical fiber</td><td>Thorlabs</td><td>FTO 30</td><td>5 meter</td></tr><tr><td>Optical fiber</td><td>Thorlabs</td><td>FTO 30</td><td>5 meter</td></tr><tr><td>Fiber coupled laser</td><td>FIS</td><td>SMF 28E</td><td></td></tr><tr><td>Photoreceiver</td><td>New Port/ New Focus</td><td>1801-FS</td><td>with fiber connection</td></tr><tr><td>Oscilloscope</td><td>Agilent Technologies</td><td>DSO-X 3034A</td><td></td></tr><tr><td>2 Degree of freedom tilt stagestage</td><td>New Port/ New Focus</td><td>M-562F-TILT</td><td></td></tr><tr><td>3 Degree of freedom linear micro translation stage</td><td>New Port/ New Focus</td><td>M-562F-XYZ</td><td></td></tr><tr><td>A set of magnets</td><td></td><td></td><td></td></tr><tr><td>Objective 5X</td><td>Mitutoyo</td><td>MY5X-802</td><td></td></tr><tr><td>Objective 20 x</td><td>Mitutoyo</td><td>MY20X-804</td><td></td></tr><tr><td>Zoom</td><td>Navitar</td><td>12x Zoom</td><td></td></tr><tr><td>Microscope tube</td><td>Navitar</td><td>1-6015 standard tube</td><td></td></tr><tr><td>Isopropanol</td><td>Sigma Aldrich</td><td>67-63-0</td><td>Spec Grad</td></tr><tr><td>2 x Bare Fiber holder</td><td>Thorlabs</td><td>T711-250</td><td></td></tr><tr><td>2 x Translational Stage</td><td>Thorlabs</td><td>DT12</td><td></td></tr><tr><td>Block of PMMA for fabricating the water reservoir and pipette holder</td><td></td><td></td><td>150 x 60 x 10 mm</td></tr><tr><td>PTFE-Tape</td><td>Gufero</td><td>240453</td><td></td></tr><tr><td>Fiber coupled, cw Laser Light Source</td><td>New Port/ New Focus</td><td>TLB-6712</td><td>765-781 nm</td></tr></tbody></table>

design and fabrication of an optical fiber made of water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

The coupling efficiency from a water fiber to a highly multimode fiber can be as high as 54%25,26. The coupling efficiency to a single-mode fiber is up to 12%25,26. Water fibers can be as thin as 1.6 &#181;m in diameter and can have a length of 46 &#181;m (Figure 3)25,26, or they can b...

Watch this Scientific Journal Video about Design and Fabrication of an Optical Fiber Made of Water at JoVE.com

Design and Fabrication of an Optical Fiber Made of Water

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with ...

design-and-fabrication-of-an-optical-fiber-made-of-water

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8.1K Views.  Technion - Israel Institute of Technology. Deze methode beschrijft de oprichting van een waterbrug en de bediening ervan als een watervezel. De watervezel heeft geen troebel materiaal en zweeft vrij in de lucht. Het belang van de watervezel is dat het co-beperkt capillaire en elektromagnetische golven en opent daarom een nieuwe speeltuin voor onderzoek in de interacties tussen licht en vloeistof put apparaten.Verkrijg twee PMMA-platen om de reservoirs te maken. Snijd elke plaat op dezelfde grootte en boorholtes aan de ene kant ...

Video: Design and Fabrication of an Optical Fiber Made of Water

Fabrication of Silica Ultra High Quality Factor Microresonators

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the quality factor (Q) of the cavity, can be in excess of 500ns for cavities with Q factors above 100 million. As a result of their low material losses, silica microcavities have demonstrated some of the longest photon lifetimes to date1-2. Since a portion of the circulating light extends outside the resonator, these devices can also be used to probe the surroundings. This interaction has enabled numerous experiments in biology, such as single molecule biodetection and antibody-antigen kinetics, as well as discoveries in other fields, such as development of ultra-low-threshold microlasers, characterization of thin films, and cavity quantum electrodynamics studies.3-7
The two primary silica resonant cavity geometries are the microsphere and the microtoroid. Both devices rely on a carbon dioxide laser reflow step to achieve their ultra-high-Q factors (Q&gt;100 million).1-2,8-9 However, there are several notable differences between the two structures. Silica microspheres are free-standing, supported by a single optical fiber, whereas silica microtoroids can be fabricated on a silicon wafer in large arrays using a combination of lithography and etching steps. These differences influence which device is optimal for a given experiment.
Here, we present detailed fabrication protocols for both types of resonant cavities. While the fabrication of microsphere resonant cavities is fairly straightforward, the fabrication of microtoroid resonant cavities requires additional specialized equipment and facilities (cleanroom). Therefore, this additional requirement may also influence which device is selected for a given experiment.
Introduction
An optical resonator efficiently confines light at specific wavelengths, known as the resonant wavelengths of the device. 1-2 The common figure of merit for these optical resonators is the quality factor or Q. This term describes the photon lifetime (&tau;o) within the resonator, which is directly related to the resonator's optical losses. Therefore, an optical resonator with a high Q factor has low optical losses, long photon lifetimes, and very low photon decay rates (1/&tau;o). As a result of the long photon lifetimes, it is possible to build-up extremely large circulating optical field intensities in these devices. This very unique property has allowed these devices to be used as laser sources and integrated biosensors.10
A unique sub-class of resonators is the whispering gallery mode optical microcavity. In these devices, the light is confined in circular orbits at the periphery. Therefore, the field is not completely confined within the device, but evanesces into the environment. Whispering gallery mode optical cavities have demonstrated some of the highest quality factors of any optical resonant cavity to date.9,11 Therefore, these devices are used throughout science and engineering, including in fundamental physics studies and in telecommunications as well as in biodetection experiments. 3-7,12
Optical microcavities can be fabricated from a wide range of materials and in a wide variety of geometries. A few examples include silica and silicon microtoroids, silicon, silicon nitride, and silica microdisks, micropillars, and silica and polymer microrings.13-17 The range in quality factor (Q) varies as dramatically as the geometry. Although both geometry and high Q are important considerations in any field, in many applications, there is far greater leverage in boosting device performance through Q enhancement. Among the numerous options detailed previously, the silica microsphere and the silica microtoroid resonator have achieved some of the highest Q factors to date.1,9 Additionally, as a result of the extremely low optical loss of silica from the visible through the near-IR, both microspheres and microtoroids are able to maintain their Q factors over a wide range of testing wavelengths.18 Finally, because silica is inherently biocompatible, it is routinely used in biodetection experiments.
In addition to high material absorption, there are several other potential loss mechanisms, including surface roughness, radiation loss, and contamination loss.2 Through an optimization of the device size, it is possible to eliminate radiation losses, which arise from poor optical field confinement within the device. Similarly, by storing a device in an appropriately clean environment, contamination of the surface can be minimized. Therefore, in addition to material loss, surface scattering is the primary loss mechanism of concern.2,8
In silica devices, surface scattering is minimized by using a laser reflow technique, which melts the silica through surface tension induced reflow. While spherical optical resonators have been studied for many years, it is only with recent advances in fabrication technologies that researchers been able to fabricate high quality silica optical toroidal microresonators (Q&gt;100 million) on a silicon substrate, thus paving the way for integration with microfluidics.1
The present series of protocols details how to fabricate both silica microsphere and microtoroid resonant cavities. While silica microsphere resonant cavities are well-established, microtoroid resonant cavities were only recently invented.1 As many of the fundamental methods used to fabricate the microsphere are also used in the more complex microtoroid fabrication procedure, by including both in a single protocol it will enable researchers to more easily trouble-shoot their experiments.

We describe the use of a carbon dioxide laser reflow technique to fabricate silica resonant cavities, including free-standing microspheres and on-chip microtoroids. The reflow method removes surface imperfections, allowing long photon lifetimes within both devices. The resulting devices have ultra high quality factors, enabling applications ranging from telecommunications to biodetection.

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the ...

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Development of Whispering Gallery Mode Polymeric Micro-optical Electric Field Sensors

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The optical modes are frequently referred to as "whispering gallery modes" (WGM) or "morphology dependent resonances" (MDR) and exhibit high optical quality factors. Some proposed applications of micro-cavity optical resonators are in spectroscopy1, micro-cavity laser technology2, optical communications3-6 as well as sensor technology. The WGM-based sensor applications include those in biology7, trace gas detection8, and impurity detection in liquids9. Mechanical sensors based on microsphere resonators have also been proposed, including those for force10,11, pressure12, acceleration13 and wall shear stress14. In the present, we demonstrate a WGM-based electric field sensor, which builds on our previous studies15,16. A candidate application of this sensor is in the detection of neuronal action potential.
The electric field sensor is based on polymeric multi-layered dielectric microspheres. The external electric field induces surface and body forces on the spheres (electrostriction effect) leading to elastic deformation. This change in the morphology of the spheres, leads to shifts in the WGM. The electric field-induced WGM shifts are interrogated by exciting the optical modes of the spheres by laser light. Light from a distributed feedback (DFB) laser (nominal wavelength of ~ 1.3 &mu;m) is side-coupled into the microspheres using a tapered section of a single mode optical fiber. The base material of the spheres is polydimethylsiloxane (PDMS). Three microsphere geometries are used: (1) PDMS sphere with a 60:1 volumetric ratio of base-to-curing agent mixture, (2) multi layer sphere with 60:1 PDMS core, in order to increase the dielectric constant of the sphere, a middle layer of 60:1 PDMS that is mixed with varying amounts (2% to 10% by volume) of barium titanate and an outer layer of 60:1 PDMS and (3) solid silica sphere coated with a thin layer of uncured PDMS base. In each type of sensor, laser light from the tapered fiber is coupled into the outermost layer that provides high optical quality factor WGM (Q ~ 106). The microspheres are poled for several hours at electric fields of ~ 1 MV/m to increase their sensitivity to electric field.

A high-sensitivity photonic micro sensor was developed for electric field detection. The sensor exploits the optical modes of a dielectric sphere. Changes in the external electric field perturb the sphere morphology leading to shifts in its optical modes. The electric field strength is measured by monitoring these optical shifts.

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The ...

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 ...

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 ...

Microfluidic Fabrication of Polymeric and Biohybrid Fibers with Predesigned Size and Shape

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and used to dictate the shape as well as the diameter of a core stream.&#160;Grooves in the top and bottom of a microfluidic channel were designed to direct the sheath fluid and shape the core fluid.&#160;By matching the viscosity and hydrophilicity of the sheath and core fluids, the interfacial effects are minimized and complex fluid shapes can be formed.&#160;Controlling the relative flow rates of the sheath and core fluids determines the cross-sectional area of the core fluid.&#160;Fibers have been produced with sizes ranging from 300 nm to ~1 mm, and fiber cross-sections can be round, flat, square, or complex as in the case with double anchor fibers. Polymerization of the core fluid downstream from the shaping region solidifies the fibers.&#160;Photoinitiated click chemistries are well suited for rapid polymerization of the core fluid by irradiation with ultraviolet light.&#160;Fibers with a wide variety of shapes have been produced from a list of polymers including liquid crystals, poly(methylmethacrylate), thiol-ene and thiol-yne resins, polyethylene glycol, and hydrogel derivatives. Minimal shear during the shaping process and mild polymerization conditions also makes the fabrication process well suited for encapsulation of cells and other biological components.

Two adjacent fluids passing through a grooved microfluidic channel can be directed to form a sheath around a prepolymer core; thereby&#160;determining both shape and cross-section. Photoinitiated polymerization, such as thiol click chemistry, is well suited for rapidly solidifying the core fluid into a microfiber with predetermined size and shape.

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and ...

Bioengineering

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using ...

A Silicon-tipped Fiber-optic Sensing Platform with High Resolution and Fast Response

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This FOSP relies on a silicon Fabry-Perot interferometer (FPI) attached to the fiber end, referred to as Si-FOSP in this work. The Si-FOSP generates an interferogram determined by the optical path length (OPL) of the silicon cavity. Measurand alters the OPL and thus shifts the interferogram. Due to the unique optical and thermal properties of the silicon material, this Si-FOSP exhibits an advantageous performance in terms of sensitivity and speed. Furthermore, the mature silicon fabrication industry endows the Si-FOSP with excellent reproducibility and low cost toward practical applications. Depending on the specific applications, either a low-finesse or high-finesse version will be utilized, and two different data demodulation methods will be adopted accordingly. Detailed protocols for fabricating both versions of the Si-FOSP will be provided. Three representative applications and their according results will be shown. The first one is a prototype underwater thermometer for profiling the ocean thermoclines, the second one is a flow meter to measure flow speed in the ocean, and the last one is a bolometer used for monitoring exhaust radiation from magnetically confined high-temperature plasma.

This work reports an innovative silicon-tipped fiber-optic sensing platform (Si-FOSP) for high-resolution and fast-response measurement of a variety of physical parameters, such as temperature, flow, and radiation. Applications of this Si-FOSP span from oceanographic research, mechanical industry, to fusion energy research.

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This ...

Multicolor Fluorescence Detection for Droplet Microfluidics Using Optical Fibers

Fluorescence assays are the most common readouts used in droplet microfluidics due to their bright signals and fast time response. Applications such as multiplex assays, enzyme evolution, and molecular biology enhanced cell sorting require the detection of two or more colors of fluorescence. Standard multicolor detection systems that couple free space lasers to epifluorescence microscopes are bulky, expensive, and difficult to maintain. In this paper, we describe a scheme to perform multicolor detection by exciting discrete regions of a microfluidic channel with lasers coupled to optical fibers. Emitted light is collected by an optical fiber coupled to a single photodetector. Because the excitation occurs at different spatial locations, the identity of emitted light can be encoded as a temporal shift, eliminating the need for more complicated light filtering schemes. The system has been used to detect droplet populations containing four unique combinations of dyes and to detect sub-nanomolar concentrations of fluorescein.

Multicolor fluorescence detection in droplet microfluidics typically involves bulky and complex epifluorescence microscope-based detection systems. Here we describe a compact and modular multicolor detection scheme that utilizes an array of optical fibers to temporally encode multicolor data collected by a single photodetector.

Fluorescence assays are the most common readouts used in droplet microfluidics due to their bright signals and fast time response. Applications such as ...

Design and Fabrication of an Optical Fiber Made of Water

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