Whispering-gallery wave

Résumé

Whispering-gallery waves, or whispering-gallery modes, are a type of wave that can travel around a concave surface. Originally discovered for sound waves in the whispering gallery of St Paul's Cathedral, they can exist for light and for other waves, with important applications in nondestructive testing, lasing, cooling and sensing, as well as in astronomy. Introduction Whispering-gallery waves were first explained for the case of St Paul's Cathedral circa 1878 by Lord Rayleigh, who revised a previous misconception that whispers could be heard across the dome but not at any intermediate position. He explained the phenomenon of travelling whispers with a series of specularly reflected sound rays making up chords of the circular gallery. Clinging to the walls the sound should decay in intensity only as the inverse of the distance — rather than the inverse square as in the case of a point source of sound radiating in all directions. This accounts for the whispers being audi

Source officielle

https://en.wikipedia.org/wiki/Whispering-gallery_wave

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Morphing commonly refers to the smooth transition from a specific shape into another one, in which the initial and final shapes can be significantly different. In this study, we show that the concept of morphing applied to laser micro-manufacturing offers an opportunity to change the topology of an initial shape, and to turn it into something more complex, like for instance for creating self-sealed cavities. Such cavities could be filled with various gases, while also achieving an optical surface quality since being shaped by surface tension. Furthermore, we demonstrate that laser morphing can be accurately modelled and predicted. Finally, we illustrate the possible use of 'laser-morphed' shape to achieve high-quality resonators that can find applications, for instance, in ultra-small quantities molecules label-free detection through whispering gallery mode resonances.

Spie-Int Soc Optical Engineering2016

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Mid-infrared ultra-high-Q resonators based on fluoride crystalline materials

Clément Christian Javerzac-Galy, Tobias Kippenberg, Caroline Marie Anne Lecaplain

The unavailability of highly transparent materials in the mid-infrared has been the main limitation in the development of ultra-sensitive molecular sensors or cavity-based spectroscopy applications. Whispering gallery mode microresonators have attained ultra-high-quality (Q) factor resonances in the near-infrared and visible. Here we report ultra-high Q factors in the mid-infrared using polished alkaline earth metal fluoride crystals. Using an uncoated chalcogenide tapered fibre as a high-ideality coupler in the mid-infrared, we study via cavity ringdown technique the losses of BaF2, CaF2, MgF2 and SrF2 microresonators. We show that MgF2 is limited by multiphonon absorption by studying the temperature dependence of the Q factor. In contrast, in SrF2 and BaF2 the lower multiphonon absorption leads to ultra-high Q factors at 4.5 mu m. These values correspond to an optical finesse of F > 1 x 10(5), the highest value achieved for any type of mid-infrared resonator to date.

Nature Publishing Group2016

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Multiple Light Coupling and Routing via a Microspherical Resonator Integrated in a T-Shaped Optical Fiber Configuration System

Georgia Konstantinou

We demonstrate a three-port, light guiding and routing T-shaped configuration based on the combination of whispering gallery modes (WGMs) and micro-structured optical fibers (MOFs). This system includes a single mode optical fiber taper (SOFT), a slightly tapered MOF and a BaTiO3 microsphere for efficient light coupling and routing between these two optical fibers. The BaTiO3 glass microsphere is semi-immersed into one of the hollow capillaries of the MOF taper, while the single mode optical fiber taper is placed perpendicularly to the latter and in contact with the equatorial region of the microsphere. Experimental results are presented for different excitation and reading conditions through the WGM microspherical resonator, namely, through single mode optical fiber taper or the MOF. The experimental results indicate that light coupling between the MOF and the single mode optical fiber taper is facilitated at specific wavelengths, supported by the light localization characteristics of the BaTiO3 glass microsphere, with spectral Q-factors varying between 4.5 x 10(3) and 6.1 x 10(3), depending on the port and parity excitation.

MDPI2018

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