A Miniaturized Sensor Consisting of Concentric Metallic Nanorings on the End Facet of an Optical Fiber
ABSTRACT A polarization-independent optical sensor is created by fabricating a concentric gold ring grating with a period of 900 nm on the end facet of an optical fiber. The sensing function of this miniaturized device is realized by sending white light as a probe to the gold rings and collecting the response signal in the back-reflection through the optical fiber. A pronounced peak due to the Rayleigh anomaly of the gold ring grating is observed in the reflection spectrum, the center wavelength of which is sensitive to the change in the environmental refractive index of the fiber end facet. Theoretical analysis not only shows excellent agreement with the experimental results, but also gives insights into the mechanisms of this kind of sensor. Using the center position of the Rayleigh peak as the response signal, a high sensitivity dλ/dn of 900 nm per unity refractive index is realized for this sensor and a resolution of Δn/n ≈ 1% is demonstrated in preliminary experiments. The sensitivity is solely determined by the period of the grating.
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ABSTRACT: We have recently proposed a valuable fabrication route for the integration and patterning of functional materials at nanoscale onto optical fibers, posing the basis for a new technological vision named “Lab-on-Fiber”. The validation of the proposed process has been carried out through the realization, directly onto the fiber tip, of 2D metallo-dielectric nanocrystals supporting localized surface plasmon resonances. In this work, we demonstrate the effectiveness of the proposed methodology to realize optical nanoprobes for label-free chemical and biological sensing as well as basic components for novel polarization sensitive photonic devices. Specifically, we first demonstrate how it is possible to tailor the field distribution of the plasmonic mode enabling the control on the refractive index sensitivity. With a view toward surface sensitivity, we experimentally observe that the proposed device is able to detect the formation of nanosized overlays over very limited active areas. Moreover, we demonstrate how to control the number and the field distribution of the excited plasmonic resonance posing new basis for the resonance engineering. Finally, we show how to obtain polarization sensitive devices with the same technological platform, by breaking the circular crystal symmetry at both unit cell or entire lattice level.12/2013; 1(1):69–78. DOI:10.1021/ph400075r
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ABSTRACT: The frequency of the Rayleigh anomaly of a metallic grating varies with the refractive index of the surrounding medium. To employ this phenomenon in optical sensors it is essential that the feature, due to the Raleigh anomaly in the sensor's optical response, is very distinct and stable. We study the reflectance of optical structures consisting of a metallic grating with a thin dielectric film on highly reflective silicon substrates in the terahertz (THz) range between 0.6 and 2 THz. A distinct reflectance peak due to the Rayleigh anomaly can only be observed if a dielectric spacer layer is inserted between the metallic grating and silicon substrate. The dielectric layer between the grating and substrate acts as a Fabry–Pérot resonator with a low quality factor. Thus, the corresponding Fabry–Pérot modes only couple weakly to the Rayleigh anomaly. At the frequency of the Rayleigh anomaly, the combined structure exhibits a distinct peak due to the Rayleigh anomaly, no matter whether there is a Fabry–Pérot low or high reflection band at this frequency. In particular, the reflection background in the vicinity of the frequency of the Rayleigh anomaly is suppressed when the Rayleigh anomaly is in resonance with a Fabry–Pérot low reflection band, whilst the Rayleigh reflectance peak itself is retained. The underlying physics is confirmed by a simple analytic model and by numerical calculations. This approach of optimizing the optical response of metallic gratings is important for the design of THz sensing devices based on Rayleigh anomalies.Journal of optics 09/2014; 16(9):094015. DOI:10.1088/2040-8978/16/9/094015 · 2.01 Impact Factor
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ABSTRACT: Metasurfaces are a family of novel wavefront-shaping devices with planar profile and subwavelength thickness. Acoustic metasurfaces with ultralow profile yet extraordinary wave manipulating properties would be highly desirable for improving the performance of many acoustic wave-based applications. However, designing acoustic metasurfaces with similar functionality to their electromagnetic counterparts remains challenging with traditional metamaterial design approaches. Here we present a design and realization of an acoustic metasurface based on tapered labyrinthine metamaterials. The demonstrated metasurface can not only steer an acoustic beam as expected from the generalized Snell's law, but also exhibits various unique properties such as conversion from propagating wave to surface mode, extraordinary beam-steering and apparent negative refraction through higher-order diffraction. Such designer acoustic metasurfaces provide a new design methodology for acoustic signal modulation devices and may be useful for applications such as acoustic imaging, beam steering, ultrasound lens design and acoustic surface wave-based applications.Nature Communications 06/2014; 5:5553. DOI:10.1038/ncomms6553 · 10.74 Impact Factor