Microsphere Resonator Research Articles

Dielectric microsphere sizing using fluorescence microscopy of whispering gallery mode resonances from adsorbed dyes

Whispering gallery mode (WGM) resonances in dielectric microspheres are very sensitive to their size and environment, which can be used for sensing but also as an indirect proxy to determine their size. By coating them with suitable fluorescent dyes and using fluorescence microscopy, we show that the WGM resonances of individual microspheres in solution can be easily studied with a high throughput. Brownian motion ensures that a representative sample is probed over time in the scattering volume. To analyze these WGM-imprinted fluorescent spectra, we propose a simple algorithm based on monitoring the spacing between resonances and comparing it to Mie theory predictions to infer their size. This allows us to measure the size distribution of typical polystyrene microsphere solutions. We also discuss the potential effects of dye concentration and choice of particle refractive index on the analysis. This method can be used, for example, for quality-testing microsphere solutions.

A Spectral Cleaning Method of Whispering Gallery Modes Resonance in the Microsphere Resonator

A Spectral Cleaning Method of Whispering Gallery Modes Resonance in the Microsphere Resonator

Role of the inverse Čerenkov effect in the formation of ultrashort Raman solitons in silica microspheres.

We theoretically demonstrate a new regime, to the best of our knowledge, of the formation of ultrashort optical solitons in spherical silica microresonators with whispering gallery modes. The solitons are driven by a coherent CW pump at the frequency in the range of normal dispersion, and the energy is transferred from this pump to the solitons via two channels: the Raman amplification and inverse Čerenkov effect. We discuss three different regimes of soliton propagation and we also show that these Raman solitons can be controlled by weak coherent CW signals.

All-optically controlled mode-coupling induced transparency with tunable efficiency in a microsphere resonator.

The optical analogs of electromagnetically induced transparency (EIT) have attracted vast attention recently. The generation and manipulation of EIT in microcavities have sparked research in both fundamental physics and photonic applications, including light storage, slow light propagation, and optical communication. In this Letter, the generation and tuning of an all-optically controlled mode-coupling induced transparency (MCIT) are proposed, experimentally demonstrated, and theoretically analyzed. The MCIT effect originated from the intermodal coupling between the plethora of modes generated in our fabricated optical microcavity, and the tuning of the transparency mode utilized the cavity's thermal bistability nature. Furthermore, based on our method, a novel, to the best of our knowledge, controlling of the mode shifting efficiency is also achieved with an increase up to two times and more. The proposed scheme paves a unique, simple, and efficient way to manipulate the induced transparency mode, which can be useful for applications like cavity lasing and thermal sensing.

Tuning Multipolar Mie Scattering of Particles on a Dielectric-Covered Mirror.

Optically resonant particles are key building blocks of many nanophotonic devices such as optical antennas and metasurfaces. Because the functionalities of such devices are largely determined by the optical properties of individual resonators, extending the attainable responses from a given particle is highly desirable. Practically, this is usually achieved by introducing an asymmetric dielectric environment. However, commonly used simple substrates have limited influences on the optical properties of the particles atop. Here, we show that the multipolar scattering of silicon microspheres can be effectively modified by placing the particles on a dielectric-covered mirror, which tunes the coupling between the Mie resonances of microspheres and the standing waves and waveguide modes in the dielectric spacer. This tunability allows selective excitation, enhancement, suppression, and even elimination of the multipolar resonances and enables scattering at extended wavelengths, providing transformative opportunities in controlling light-matter interactions for various applications. We further demonstrate with experiments the detection of molecular fingerprints by single-particle mid-infrared spectroscopy and with simulations strong optical repulsive forces that could elevate the particles from a substrate.

Bidirectional Raman soliton-like combs with unidirectional pump in a spherical microresonator.

We experimentally demonstrate bidirectional Raman soliton-like combs in a whispering gallery mode microresonator with a unidirectional pump for the first time, to the best of our knowledge. We develop a relatively simple theoretical model and find an analytical solution for forward- and backward-propagating Raman sech2-shaped solitons in an anomalous dispersion region under unidirectional pumping in a normal dispersion region. Raman solitons exist, thanks to the balance between losses and Raman gain from a CW wave (which is equal in both directions) as well as between dispersion and Kerr nonlinearity.

A Reflective Whispering Gallery Mode Microsphere Resonator Integrated With a Thick-Wall Capillary Tube

A Reflective Whispering Gallery Mode Microsphere Resonator Integrated With a Thick-Wall Capillary Tube

Microsphere-Enabled Micropillar Array for Whispering Gallery Mode Virus Detection.

Rapid detection of pathogens and analytes at the point of care offers an opportunity for prompt patient management and public health control. This paper reports an open microfluidic platform coupled with active whispering gallery mode (WGM) microsphere resonators for the rapid detection of influenza viruses. The WGM microsphere resonators, precoated with influenza A polyclonal antibodies, are mechanically trapped in the open micropillar array, where the evaporation-driven flow continuously transports a small volume (∼μL) of sample to the resonators without auxiliaries. Selective chemical modification of the pillar array changes surface wettability and flow pattern, which enhances the detection sensitivity of the WGM resonator-based virus sensor. The optofluidic sensing platform is able to specifically detect influenza A viruses within 15 min using a few microliters of sample and displays a linear response to different virus concentrations.

Multi-format all-optical modulating of microsphere resonator operating in O-band

We propose and demonstrate an all-optical tunable silica microsphere resonator based on a dual-laser pumping scheme. The resonance tunable microsphere resonator can act as a modulator and operates in the O-band. We discussed the relationship between the extinction ratio and pump power in different coupling state, and realized an extinction ratio over 15 dB. Also, we measured the rise and fall time of the modulated signal, which is below 1 μs, and discussed its relationship with the modulation frequency. In addition, based on this scheme, a multi-format modulation is realized for the first time with signals shaping in triangular, sinusoidal and square wave under different duty cycles. Our work reveals the detail of all-optical tunning of the resonance of the silica microresonator and opens up possible applications in optical communication, microwave photonics and quantum photonics.

Optical properties and behavior of whispering gallery mode resonators in complex microsphere configurations: Insights for sensing and information processing applications

AbstractThis paper delves into the intricate world of whispering gallery mode (WGM) resonators within complex microsphere configurations, exploring their optical properties and behavior. Integrated with optical sensing and processing technology, WGM resonators offer compact size, high sensitivity, rapid response, and tunability. The study investigates the impact of configuration, size, excitation, polarization, and coupling effects on WGM properties. Notable findings include enhanced sensitivity in single microsphere resonators, influence of unequal sphere sizes and excitation locations on WGM modes, and higher quality factors (Q‐factors) in triangular three‐microsphere resonator configurations. Circular polarization was found to elevate Q‐factors, while the nine‐microsphere resonator configuration exhibited increased intensity of dominant WGM peaks with higher laser power, suppressing other peaks. These insights guide the design and optimization of microsphere resonator systems, positioning them for applications in sensing and optical information processing.

Comparison of Resonance Modes in Two-Dimensional and Three-Dimensional Microsphere Structures

In this article, we have investigated the performance of a resonator in 2D, in an asymmetric form using the physical method and using the Matlab software, we have analyzed it in 3D. According to the simulation results, in asymmetric 2D and 3D structures, whispering gallery modes, or resonances appeared at similar wavelengths for the same radial and polar mode number. Also, the results obtained from the simulations indicated that the resonances of the asymmetric 2D structure would occur at wavelengths close to the wavelengths of 3D structure and the resonance wavelengths for transverse electric (TE) and while transverse magnetic (TM) modes would not change by altering the lateral mode number. Accordingly, 2D structures can be used to obtain resonance wavelengths in microsphere resonators. Achieving results with high accuracy, as well as faster speed offered by smaller meshing volume is one of the advantages of 2D structures in the physical method.

Fano-like line shape and its tuning effect in a double-handle whispering gallery mode microsphere resonator

Fano-like line shape and its tuning effect in a double-handle whispering gallery mode microsphere resonator

Second-order coherence across the Brillouin lasing threshold

Brillouin–Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave-mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a “flickering” in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the “flickering,” are a result of the full nonlinear three-wave-mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.

Single and dual optical microsphere resonator as Humidity Sensor

This study explores into the influence of whispering gallery mode (WGMs) on single and dual microsphere resonator (MSR) as a humidity sensor which can confine light by continuous internal reflection. The construction of the device is simple, and it has a low cost as MSR is made of silica material with a high refractive index. MSR coupling tapered optical fibers with size 5µm to the surfaces of single and two microspheres is demonstrated as a relative humidity (RH) sensor. The Q-factor was measured 7.754 × 105 dBm for single MSR while for dual MSR, Q-factor is 7.765 × 105 dBm. When sensitivity, linearity, and repeatability were analyzed based on transmitted power, the results were conclusively excellent for the performance of the double MSR.

A cascaded dual-wavelength laser based on an Er3+-doped fluorozirconate glass microsphere resonator

Cascaded dual-wavelength lasing at 0.85 μm and 1.55 μm from an Er3+-doped ZBYA fluorozirconate glass microsphere is demonstrated for the first time. Two wavelengths corresponding to the transitions of Er3+: 4S3/2 → 4I13/2 and 4I13/2 → 4I15/2 are generated due to up-conversion and down-conversion processes respectively. Cascade lasing from ZBYA microsphere resonators with various Er3+ doping concentrations and diameters are experimentally studied by utilizing a 980 nm laser diode as the pump source. The influence of concentration and diameter on up-conversion and down-conversion lasers are investigated. The results indicate that Er3+-doped ZBYA fluorozirconate glass microspheres are promising candidates for practical applications requiring multi-wavelength micro-lasers and in optical communications.

Mode Selection Method in Spherical Optical Cavities with Thin Metal Film

A new method for the selection of the radial modes of a spherical microresonator by the quality factor, based on the effect of absorption in a thin metal film deposited on a sphere together with a dielectric layer, is proposed. The method was proved by numerical simulation on the example of the second and third radial modes TEl,l,q, l = 455, q = 2, 3 selection in 80 μm radius quartz microsphere with 5 nm thick nickel film. The structure of the metal-dielectric coating was determined using analytical formulas in such a way that the metal film was placed at the node of the selected mode E-field distribution. The finite element method was used to refine the calculation, optimizing the position of the film in terms of obtaining the maximum quality factor. As a result, it was shown that the selected mode could have a relatively high quality factor (Q~107), while the other radial modes are significantly suppressed (Q~103). In addition, it is shown that selection is carried out by the mode index number (l) simultaneously with selection by the radial index.

High-Q lasing in Nd3+-doped phosphate glass microsphere resonators.

Nd3+-doped glasses are the most widely used laser gain media. However, Nd3+-doped non-silica microsphere lasers generally have lower quality (Q) factors due to the presence of non-radiative energy-loss impurities in traditional glass systems. In this work, we report the first, to the best of our knowledge, Nd3+-doped phosphate glass microsphere laser with the highest Q-factor of 1.54 × 106 among all Nd3+-doped non-silica glass microsphere lasers. Whispering gallery modes in the 1020-1120-nm band can be obtained for a typical microsphere with a diameter of 82.57 µm. When the pump power exceeds the threshold of 0.17 mW, single- and multi-mode microsphere lasing can be generated under 808-nm laser diode (LD) pumping. Typical Q-factors of the phosphate glass microspheres can reach 106, which is at least an order of magnitude higher than those of other Nd3+-doped non-silica glass microsphere lasers. The Nd3+-doped phosphate glass microsphere laser reported in this work can be considered as an active optical/photonic device with low pump thresholds.

Whispering gallery mode microsphere resonator based on cylindrical air cavity coupling.

In this Letter, an optical fiber whispering gallery mode microsphere resonator based on cylindrical air cavity coupling is proposed and demonstrated. The cylindrical air cavity is vertical to the axis of a single-mode fiber and in touch with the fiber core, fabricated by using femtosecond laser micromachining together with hydrofluoric acid etching. A microsphere is inserted into the cylindrical air cavity and in tangential contact with the inner cavity wall, which is in touch with or inside the fiber core. The light traveling in the fiber core is coupled into the microsphere via an evanescent wave when the light path is tangential to the contacting point of the microsphere and the inner cavity wall, resulting in whispering gallery mode resonance when the phase-matching condition is satisfied. Such a device is highly integrated, robust in structure, low in cost, stable in operation, and has a good quality factor (Q) of 1.44 × 104.

Multi-wavelength passively Q-switched laser with Co2+:ZnSe thin film coated microsphere

We experimentally demonstrate an all-fiber passively Q-switched erbium-doped laser based on a microsphere resonator coated with Co2+:ZnSe film, which can achieve multi-wavelength pulse laser. With electron beam evaporation technology, the saturable absorber (SA) with a modulation depth of 55% was prepared by depositing Co2+:ZnSe film on the microsphere for the loss modulation of the laser cavity. The passively Q-switched output pulses were obtained by inserting the SA into the laser cavity and the narrowest pulse width of ∼3 μs was obtained. The fiber laser can stably output quintuple-wavelength laser pulses with a 3 dB bandwidth of ∼0.1 nm. The wavelength interval of multi-wavelengths was stably maintained at ∼1 nm and the smallest optical signal-to-noise ratio of ∼10 dB at the pump power of 400 mW was measured. The signal-to-noise ratio was ∼58 dB, which confirms excellent output stability. The results prove that it is a promising SA device to achieve passively Q-switched multi-wavelength pulse fiber lasers.

Modeling of Luminescence Spectra in Spherical Microresonators with an Emitting Shell

Modeling of Luminescence Spectra in Spherical Microresonators with an Emitting Shell