1,721,726 research outputs found
Nanostructured optical fibre tapers and related applications
No full textIn the last decade, optical fibre tapers have attracted considerable interest because they offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These distinctive features have been exploited in a wealth of applications ranging from telecommunication devices to sensors, from optical manipulation to high-Q resonators. Nanostructures on the optical fibre tapers are very promising since the size of the device can be extremely small. With the development of nanostructuring methods, sub-wavelength feature sizes have been achieved. In this thesis, nanostructured optical fibre tapers and some related applications are discussed.Light confinement is limited by diffraction and the minimum spot size is related to the light wavelength. In this thesis, light confinement in two and three dimensions is proposed and achieved with two typologies of nanostructured optical fibre tapers. The first group of devices exploits plasmons excited at the optical fibre tips to obtain high transmissivity, and confine light to a sub-wavelength dimension. Optical fibre tips were designed according to numerical simulations and coated by a layer of gold; an extremely small aperture was then opened at the tip apex. The experimental characterization and simulation results showed their improved transmission efficiency (higher than 10-2) and thermal expansion measurements showed no shape changes could be detected within the accuracy of the system (~2 nm) for 9 mW injected powers. Effective confinements to 10 nm or smaller can be envisaged by decreasing the aperture size and slope angle. Application of this small spot size source can include scanning near-field optical microscope, optical recording, photolithography and bio-sensing.The second group achieves three dimensional light confinement exploiting a Fabry-Perot microcavity formed by a microfibre grating similar to those used in distributed feedback lasers. Microfibres were patterned using a Focused Ion Beam (FIB) system. In this structure, the microcavity provides longitudinal light confinement, whereas air dielectric guiding by the microfibre provides diffraction limited confinement in the other two dimensions. Due to the high refractive index contrast between silica and air, strong reflection can be obtained by only dozens of notches. This device can be used for a wide range of applications, e.g. sensing and triggered single-photon sources.Light confinement in nanostructured optical fibre tapers was exploited in a micrometric thermometer. A compact thermometer based on a broadband microfibre coupler tip showed a dynamic range spanning from room temperature to 1511ºC with a response time of tens of microseconds. This is the highest temperature measured with a silica optical fibre device. An average sensitivity of 11.96 pm/ºC was achieved for a coupler tip with ~2.5 µm diameter. A resolution of 0.66ºC was achieved for a coupler tip diameter of ~12.6 µm. Better resolution can be achieved with smaller size microfibre coupler tips.Optical fibre tapers are commonly used to couple light to selected resonator modes. Here FIB was used to inscribe microgrooves on optical Bottleneck Microresonator (BMR) surfaces to excite selected whispering gallery modes. By monitoring the transmission spectrum of the optical fibre taper, substantial spectral clean-up was obtained in appropriately scarred BMRs. Single high-Q mode operation can be achieved by either using two asymmetrical perpendicular scars or placing the grooves closer to the BMR centre, providing the potential for high performance sensors and other optical devices.Finally, strong three dimensional localization has been achieved in Plasmonic Slot Nano-Resonators (PSNRs) embedded in a gold-coated optical fibre tapers. Different shapes PSNRs, embedded in thin gold metal film coated plasmonic microfibre, were numerically investigated. The intensity enhancement (in excess of 106) and the resonance wavelength depend on both the PSNR and microfibre dimensions. Theoretically and experimentally, the transversal excitation of a rectangular PSNR embedded in a thin gold film coated plasmonic fibre tip was discussed for the first time, and showed high localization and strong enhancement (7.24×103). This device can find a wide range of applications such as surface-enhanced Raman scattering, optical filtering, spectroscopy and bio-sensing
Optical fibre nanowire sensors and applications
No full textOptical fibre nanowires (OFN) have recently attracted increased attention because of their numerous applications in sensing and particle manipulation [1] and their extraordinary optical and mechanical properties, which include, amongst others:biocompatibility: OFNs show good compatibility with cells/ biological matter as they are made from silica.configurability/flexibility: OFN are manufactured stretching optical fibres, thus they maintain their original size at the extremities (fig. 1), allowing for prompt connection to any fiberised source/detector. robustness: OFNs are extremely strong and have a conventional fibre pigtail at their extremity, thus can be handled with tools typical of the macroscopic world.large evanescent fields: a considerable fraction of the transmitted power can propagate outside the OFN physical boundary when the OFN size is small, allowing for enhanced sensing and optical manipulation. strong confinement: when OFNs are nanostructured and metal coated, light can be confined to 50-100 nm spot sizes, allowing for nanosensing and single nanoparticle trapping/manipulation
A compact temperature sensor based on micrometric optical fiber coupler tip
No full textA compact temperature sensor based on a coupler tip with micrometric size is demonstrated. This sensor can measure a temperatures as high as 1283 °C with an average sensitivity of ~12 pm/°C
Fast-response high-temperature microfiber coupler tip thermometer
Full text linkA compact temperature sensor based on a broadband microfiber coupler tip is demonstrated. The thermometer dynamic range spans from room temperature to 1511°C with a response time of tens of ms. This is the highest temperature measured with a silica optical fiber device. A resolution of 0.66°C was achieved for a coupler tip diameter of ~12.56 µm. Better resolution can be achieved with smaller size microfiber coupler tips
Transverse excitation of plasmonic slot nano-resonators embedded in gold-coated microfiber tips
No full textNanoscale aperture in thin noble-metal films, with dimensions comparable to the light wavelength, can form plasmonic nano-resonators (PNRs) and show astonishing optical properties leading to enhanced and selective light transmission and confinement. In contrast to conventional optical systems using lenses and mirrors, PNRs can provide hot spots in the near field with dimensions determined mainly by the structure size rather than by the diffraction limit. A number of different nano-structures have been considered and studied in detail for their ability to concentrate light [1]. In this paper, for the first time we study both theoretically and experimentally the transverse excitation of a strongly-coupled 3D plasmonic slot nano-resonator (PSNR) by embedding a rectangular slot nano-cavity in a plasmonic structure formed by a thin-metal-film coated microfiber tip: a schematic of the structure is shown in the inset of Fig. 1(a). Light is launched from the untapered side of the fiber and coupled to the nano-cavity. The various resonances can be identified simply monitoring the reflected light. In the experiment, a PSNR with 400 nm length, 200 nm width and 30 nm depth was inscribed on a 30 nm goldcoated microfiber tip by focused ion beam (FIB). Light with the polarization state which is perpendicular to the PSNR was launched into the tip and reflection spectra were recorded
Plasmonic slot nano-resonators in gold-coated microfibers
No full textIn recent years, research in plasmonics and related devices has attracted considerable interest. Nanoscale apertures in thin noble-metal films, with dimensions comparable to the light wavelength, can form plasmonic nano-resonators (PNRs) and such structures can concentrate an incident light field into a small volume which overcomes the diffraction limit with orders-of-magnitude intensity enhancement. So far, the transmission properties of plasmonic slot nano-resonators (PSNRs) have been studied under plane-wave excitation directed perpendicularly to the plane of the resonator [1,2]
A fast-response microfiber coupler tip high temperature sensor
No full textA compact fast temperature sensor based on a broadband microfiber coupler tip is demonstrated. The thermometer dynamic range spans from room temperature to 1511 °C with a response time of tens of ms. This is the highest temperature measured with an optical fiber device. The resolution of 0.66 °C was achieved for a coupler tip diameter of ~12.56 µm
Curvature sensor based on resonance mode splitting of multimode interference combined with a long-period grating
No full textOptical microfiber/nanowire-based photonic devices have been widely used in a range of sensing applications, including refractive index, stain, humidity, chemical gas and temperature. Optical fiber based refractive index (RI) sensors have attracted extensive attention due to their unique advantages such as immunity to electromagnetic interference, small size, high sensitivity, etc. The techniques used to implement fiber based RI sensing include a fiber Bragg grating (FBG), long period fiber grating (LPFG), surface plasmon resonance, tapered fiber and a singlemode– multimode–singlemode (SMS) fiber structure. Among these techniques, an SMS fiber structure has the advantages of simplicity and ease of fabrication and previous investigations have shown that an SMS fiber structure can excite and couple multiple modes to an SMF. For Bragg-grating-based sensors, which suffer from limited temperature- and strain-induced spectral displacements, is often required that one use complex interferometric techniques to detect these shifts. On the other hand, the LPFG is a promising technique for optical sensing and may exhibit wavelength blue-shift as the RI increases. If the two types of sensors are combined with each other, the sensitivity will be improved by monitoring the separation wavelength shifts between the resonant wavelengths of the LPFG and SMS fiber structures. Our proposed technique has advantages of simple configuration, easy fabrication, and simultaneously measurement of both RI and temperature
Efficient light confinement in optical fibre tapers using plasmonics
No full textLight confinement is limited by diffraction and the ultimate spot size is related to the light wavelength, lambda, and to the refractive index n of the medium where light is being focused. Because of its evanescent wave nature, plasmonics gain a fundamental role in sub-wavelength confinement. In fact plasmons are relatively unaffected by diffraction, can propagate for moderately long distances and can be confined well below the so-called "diffraction limit"
Plasmonic slot nanoresonators embedded in metal-coated plasmonic microfibers
No full textWe have studied plasmonic slot nanoresonators (PSNRs) embedded in a gold-coated microfiber. Light is coupled from the plasmonic waveguide into the PSNR, showing strong localization in three dimensions. Single bow-tie and rectangular PSNRs, as well as, cascades of multiple bow-tie PSNRs have been considered. The intensity enhancement and the resonance wavelength depend on both the PSNR and microfiber dimensions. The PSNRs embedded in plasmonics microfibers could find wide range of applications, such as surface enhanced Raman scattering, optical filtering, bio-sensing and spectroscopy.<br/
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