Identifying modes of large whispering-gallery mode resonators from the spectrum and emission pattern
TL;DR: In this paper, a combination of frequency analysis and far-field imaging for high mode numbers of large whispering-gallery mode resonators is proposed to identify the radial mode numbers q and the angular mode numbers p = l-m.
Abstract: Identifying the mode numbers in whispering-gallery mode resonators (WGMRs) is important for tailoring them to experimental needs. Here we report on a novel experimental mode analysis technique based on the combination of frequency analysis and far-field imaging for high mode numbers of large WGMRs. The radial mode numbers q and the angular mode numbers p = l-m are identified and labeled via far-field imaging. The polar mode numbers l are determined unambiguously by fitting the frequency differences between individual whispering gallery modes (WGMs). This allows for the accurate determination of the geometry and the refractive index at different temperatures of the WGMR. For future applications in classical and quantum optics, this mode analysis enables one to control the narrow-band phase-matching conditions in nonlinear processes such as second-harmonic generation or parametric down-conversion.
Citations
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TL;DR: A comprehensive overview of sensor technology exploiting optical whispering gallery mode (WGM) resonances by detailing the fundamental principles and theory of WGMs in optical microcavities and the transduction mechanisms frequently employed for sensing purposes.
Abstract: We present a comprehensive overview of sensor technology exploiting optical whispering gallery mode (WGM) resonances. After a short introduction we begin by detailing the fundamental principles and theory of WGMs in optical microcavities and the transduction mechanisms frequently employed for sensing purposes. Key recent theoretical contributions to the modeling and analysis of WGM systems are highlighted. Subsequently we review the state of the art of WGM sensors by outlining efforts made to date to improve current detection limits. Proposals in this vein are numerous and range, for example, from plasmonic enhancements and active cavities to hybrid optomechanical sensors, which are already working in the shot noise limited regime. In parallel to furthering WGM sensitivity, efforts to improve the time resolution are beginning to emerge. We therefore summarize the techniques being pursued in this vein. Ultimately WGM sensors aim for real-world applications, such as measurements of force and temperature, or alternatively gas and biosensing. Each such application is thus reviewed in turn, and important achievements are discussed. Finally, we adopt a more forward-looking perspective and discuss the outlook of WGM sensors within both a physical and biological context and consider how they may yet push the detection envelope further.
715 citations
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TL;DR: Optical Whispering Gallery Modes (WGMs) derive their name from a famous acoustic phenomenon of guiding a wave by a curved boundary observed nearly a century ago as mentioned in this paper, which enables resonators of unique properties attractive both in science and engineering.
Abstract: Optical Whispering Gallery Modes (WGMs) derive their name from a famous acoustic phenomenon of guiding a wave by a curved boundary observed nearly a century ago. This phenomenon has a rather general nature, equally applicable to sound and all other waves. It enables resonators of unique properties attractive both in science and engineering. Very high quality factors of optical WGM resonators persisting in a wide wavelength range spanning from radio frequencies to ultraviolet light, their small mode volume, and tunable in- and out- coupling make them exceptionally efficient for nonlinear optical applications. Nonlinear optics facilitates interaction of photons with each other and with other physical systems, and is of prime importance in quantum optics. In this paper we review numerous applications of WGM resonators in nonlinear and quantum optics. We outline the current areas of interest, summarize progress, highlight difficulties, and discuss possible future development trends in these areas.
231 citations
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TL;DR: An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point.
Abstract: An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wave vector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.
213 citations
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TL;DR: In this article, the progress in the development of frequency converters based on three-wave mixing in whispering gallery resonators (WGRs) is reviewed, revealing that the phase-matching condition known from conventional devices is replaced by several selection rules and furthermore, the fact that conversion efficiencies of more than 25% can be reached in the overcoupled regime only experimentally.
Abstract: We review the progress in the development of frequency converters based on three-wave mixing in whispering gallery resonators (WGRs) The theoretical description, given in a unified notation for all basic processes, reveals that the phase-matching condition known from conventional devices is replaced by several selection rules and, furthermore, the fact that conversion efficiencies of more than 25% can be reached in the overcoupled regime only Experimentally, the conversion efficiencies exceed 50% already at milliwatt input powers This is achieved, however, so far in bulk resonators only since today the on-chip devices have two orders of magnitude lower quality factors Regarding the stability of the conversion process, one has to consider impurities left from the crystal growth and material specific effects like photoconductivity, photorefractivity, and pyroelectricity The impressive experimental progress paves the way that micrometer-sized frequency converters based on WGRs will find the way out of the lab into real-world applications
134 citations
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TL;DR: Experimental data showing the interferometrically measured evanescent field decay and the sensitivity of mm-sized MgF₂ whispering gallery mode resonators immersed in water show reasonable agreement with the developed theory.
Abstract: We present our experiments on refractometric sensing with ultrahigh-Q, crystalline, birefringent magnesium fluoride (MgF₂) whispering gallery mode resonators. The difference to fused silica which is most commonly used for sensing experiments is the small refractive index of MgF₂ which is very close to that of water. Compared to fused silica this leads to more than 50% longer evanescent fields and a 4.25 times larger sensitivity. Moreover the birefringence amplifies the sensitivity difference between TM and TE type modes which will enhance sensing experiments based on difference frequency measurements. We estimate the performance of our resonators and compare them with fused silica theoretically and present experimental data showing the interferometrically measured evanescent field decay and the sensitivity of mm-sized MgF₂ whispering gallery mode resonators immersed in water. These data show reasonable agreement with the developed theory. Furthermore, we observe stable Q factors in water well above 1 × 10⁸.
85 citations
References
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TL;DR: This work reports a substantially different approach to comb generation, in which equally spaced frequency markers are produced by the interaction between a continuous-wave pump laser of a known frequency with the modes of a monolithic ultra-high-Q microresonator via the Kerr nonlinearity.
Abstract: Optical frequency combs provide equidistant frequency markers in the infrared, visible and ultraviolet, and can be used to link an unknown optical frequency to a radio or microwave frequency reference. Since their inception, frequency combs have triggered substantial advances in optical frequency metrology and precision measurements and in applications such as broadband laser-based gas sensing and molecular fingerprinting. Early work generated frequency combs by intra-cavity phase modulation; subsequently, frequency combs have been generated using the comb-like mode structure of mode-locked lasers, whose repetition rate and carrier envelope phase can be stabilized. Here we report a substantially different approach to comb generation, in which equally spaced frequency markers are produced by the interaction between a continuous-wave pump laser of a known frequency with the modes of a monolithic ultra-high-Q microresonator via the Kerr nonlinearity. The intrinsically broadband nature of parametric gain makes it possible to generate discrete comb modes over a 500-nm-wide span (approximately 70 THz) around 1,550 nm without relying on any external spectral broadening. Optical-heterodyne-based measurements reveal that cascaded parametric interactions give rise to an optical frequency comb, overcoming passive cavity dispersion. The uniformity of the mode spacing has been verified to within a relative experimental precision of 7.3 x 10(-18). In contrast to femtosecond mode-locked lasers, this work represents a step towards a monolithic optical frequency comb generator, allowing considerable reduction in size, complexity and power consumption. Moreover, the approach can operate at previously unattainable repetition rates, exceeding 100 GHz, which are useful in applications where access to individual comb modes is required, such as optical waveform synthesis, high capacity telecommunications or astrophysical spectrometer calibration.
1,950 citations
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TL;DR: The enhancement mechanisms responsible for the extreme sensitivity of the WGM biosensor are described, its current implementations and applications are reviewed, and its future possibilities are discussed.
Abstract: Optical label-free detectors, such as the venerable surface plasmon resonance (SPR) sensor, are generally favored for their ability to obtain quantitative data on intermolecular binding. However, before the recent introduction of resonant microcavities that use whispering gallery mode (WGM) recirculation, sensitivity to single binding events had not materialized. Here we describe the enhancement mechanisms responsible for the extreme sensitivity of the WGM biosensor, review its current implementations and applications, and discuss its future possibilities.
1,621 citations
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TL;DR: In this article, temporal dissipative solitons are observed in a nonlinear, high-finesse, optical microresonator driven by a continuous-wave laser, enabling ultrashort pulses to be generated in spectral regimes lacking broadband laser gain media and saturable absorbers.
Abstract: Temporal dissipative solitons are observed in a nonlinear, high-finesse, optical microresonator driven by a continuous-wave laser. This approach enables ultrashort pulses to be generated in spectral regimes lacking broadband laser gain media and saturable absorbers, making it potentially useful for applications in broadband spectroscopy, telecommunications, astronomy and low-phase-noise microwave generation.
1,602 citations
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TL;DR: Strong coupling is achieved, with the rate of coherent coupling exceeding the dissipative rates of the atom and the cavity, and this work opens the way for investigations of optical processes with single atoms and photons in lithographically fabricated microresonators.
Abstract: Over the past decade, strong interactions of light and matter at the single-photon level have enabled a wide set of scientific advances in quantum optics and quantum information science. This work has been performed principally within the setting of cavity quantum electrodynamics with diverse physical systems, including single atoms in Fabry–Perot resonators, quantum dots coupled to micropillars and photonic bandgap cavities and Cooper pairs interacting with superconducting resonators. Experiments with single, localized atoms have been at the forefront of these advances with the use of optical resonators in high-finesse Fabry–Perot configurations. As a result of the extreme technical challenges involved in further improving the multilayer dielectric mirror coatings of these resonators and in scaling to large numbers of devices, there has been increased interest in the development of alternative microcavity systems. Here we show strong coupling between individual caesium atoms and the fields of a high-quality toroidal microresonator. From observations of transit events for single atoms falling through the resonator's evanescent field, we determine the coherent coupling rate for interactions near the surface of the resonator. We develop a theoretical model to quantify our observations, demonstrating that strong coupling is achieved, with the rate of coherent coupling exceeding the dissipative rates of the atom and the cavity. Our work opens the way for investigations of optical processes with single atoms and photons in lithographically fabricated microresonators. Applications include the implementation of quantum networks, scalable quantum logic with photons, and quantum information processing on atom chips.
857 citations
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TL;DR: In this article, the properties of optical resonators with quality-factor Q⩾108, effective volume of e.m. field localization Veff ≥ 10−9 cm3 and threshold power of optical bistability Wbist≈10−5 W are described.
791 citations