Hollow Bottle Research Articles

Asymmetrical Cross-Polarization Coupling in a Whispering-Gallery Microresonator

Cross-polarization coupling between transverse electric (TE) and transverse magnetic (TM) whispering-gallery modes in an optical microresonator produces effects such as coupled-mode induced transparency (CMIT). The detailed analytical theory of this coupling indicates that the TE-to-TM and TM-to-TE couplings may have different strengths. Using an experimental setup centered around a hollow bottle resonator and polarization-sensitive throughput detection, that had been used in previous CMIT experiments, this asymmetry was confirmed and studied. By fitting the throughput spectra of both polarizations to the numerical output of a basic model, the asymmetry parameter defined as the ratio of the coupling amplitudes was determined from the output power in the polarization orthogonal to that of the input. The results of many experiments give a range for this ratio, roughly from 0.2 to 4, that agrees with the range predicted by the detailed theory. An analytical approximation of this ratio shows that the main reason for the asymmetry is a difference in the axial orders of the coupled modes. In some experimental cases, the orthogonal output is not well fitted by the model that assumes a single mode of each polarization, and we demonstrate that this fitting discrepancy can be the result of additional mode interactions.

Confirmation of Dissipative Sensing Enhancement in a Microresonator Using Multimode Input

Optical microresonators have proven to be especially useful for sensing applications. In most cases, the sensing mechanism is dispersive, where the resonance frequency of a mode shifts in response to a change in the ambient index of refraction. It is also possible to conduct dissipative sensing, in which absorption by an analyte causes measurable changes in the mode linewidth and in the throughput dip depth. If the mode is overcoupled, the dip depth response can be more sensitive than the linewidth response, but overcoupling is not always easy to achieve. We have recently shown theoretically that using multimode input to the microresonator can enhance the dip-depth sensitivity by a factor of several thousand relative to that of single-mode input and by a factor of nearly 100 compared to the linewidth sensitivity. Here, we experimentally confirm these enhancements using an absorbing dye dissolved in methanol inside a hollow bottle resonator. We review the theory, describe the setup and procedure, detail the fabrication and characterization of an asymmetrically tapered fiber to produce multimode input, and present sensing enhancement results that agree with all the predictions of the theory.

Propagation dynamics of Janus vortex waves

We study the propagation dynamics of Janus vortex wave under the action of a focusing lens based upon the formula of focused circular vortex Airy beams. Two dark foci would be generated under the action of a lens, and thus a perfect light hollow bottle could be formed. By controlling corresponding parameters, we could control the focal position and the relative intensity between the two focal intensities. The off-axis optical vortex (OV) would rotate rapidly in two focal regions, but keep still in the lens focus region. The angular displacement of OV in each focusing process is nearly π/2. (Note that the angular displacement for an off-axis OV in single focusing process of Gaussian beam is nearly π.) Two same OVs would repel to each other, but two opposite OVs would attract each other and annihilate at first focus plane in Janus vortex waves.

Measurement of hydrostatic pressure using a hollow bottle microresonator

In this paper, we report the experimental results of the design and manufacture of a device in the form of a hollow bottle manufactured from a polymer for the measurement of hydrostatic pressure of microfluids in microcavities. The fabricated device bases its operation on the optical resonances of a capillary optical microresonator that couples the light coming from the evanescent field of an optical fiber taper with a central diameter in the range of 3-5 μm, exciting the resonant optical modes WGMs inside the cavity. The microcavity was manufactured using a heating-pressurization technique by a system built to measure which allowed reaching a minimum wall thickness in the central region of the order of 19.78 μm with a sensitivity of the order of 0.5567 nm/bar.

Optical microresonator in form of hollow bottle for the measurement of hydrostatic pressure: A theoretical study of its sensitivity

In this research, we report the theoretical study of an optical microresonator in form of hollow bottle for the measurement of hydrostatic pressure in microfluidics. The proposed device bases its operating principle on the excitation of the resonant modes WGMs that are confined to the interior of the optical cavity through the evanescent coupling of the light from the outside. The analytical study developed to determine the sensitivity of the device to changes in internal pressure in the hollow micro-bottle, is developed from a layer model with application of boundary conditions in the problem, where it is necessary to consider the excitation of the transverse modes WGMs and the elastic-optical effect produced by the internal pressurization of the resonant cavity. In the investigation we have concluded that the theoretical results present a good approximation with the experimental results using the layer model with which it is possible to optimize the design of this type of devices to improve the sensitivity for the measurement of the hydrostatic pressure in microfluidics.

PH sensing using whispering gallery modes of a silica hollow bottle resonator

The limitations of electrochemical pH sensors have stimulated the development of optical pH sensing methods. In the method reported here, swellable pH-sensitive polymer particles are deposited on the interior surface of a silica hollow bottle resonator. As the pH of the buffer solution in contact with the particles increases, the refractive index of the particles decreases. As a result, whispering gallery modes with internal evanescent components shift in frequency as a function of pH. This shift is monitored by the throughput of tunable diode laser light coupled into the whispering gallery modes using a tapered fiber. Plots of selected mode frequencies vs. pH yielded sigmoid shaped titration curves similar to those obtained using turbidity to monitor refractive index changes of the particles as a function of pH. The response time of 10–15 s and best resolution of 0.06 pH unit represent improvements over previous optical pH sensing methods.

Tunable Fano-Like Lineshape in an Adiabatic Tapered Fiber Coupled to a Hollow Bottle Microresonator

Fano-like resonances and electromagnetic induced transparency (EIT)-like resonances in whispering gallery-mode (WGM) microcavities have important applications in high-sensitivity biosensing, optical switches, and slow light. Hollow microbottle resonators (HMBRs) provide special opportunities for optofluidic devices. Here, we theoretically and experimentally demonstrate a simple system to produce Fano resonance lineshapes in which a HMBR is coupled to the transition region of an adiabatic tapered optical fiber. The Fano resonance results from the interference between the fundamental mode and higher order modes of the taper that are coupled to the WGM of the HMBR. The degree of asymmetry can be tuned by scanning the coupling position along the taper and controlling the input light polarization. It is shown that by tuning polarization, the Fano resonance line converts from a Lorentzian shape to an EIT-like line. This system potentially can be used as an optical filter with the advantage of easy alignment.

Nanoparticle detection by mode splitting in hollow bottle microresonators

Mode splitting (MS) in whispering gallery microresonators provides excellent noise suppression in sensing signal compared to mode shifting. Here, we theoretically studied the ability of hollow bottle microresonators for detection of a single nanoparticle in air and water medium by MS phenomenon. To find out the optimum condition of sensor for nanoparticle (NP) detection, the effects of bottle geometry parameters, mode orders, and mode polarization state was investigated. The first radial transverse electric mode demonstrated the best sensitivity when the resonator radius and wall thickness were 10 and 0.3 μm, respectively. However, transverse magnetic modes manifested slightly better detection limit. In the air core hollow microbottle resonator (HMBR), the best detection limit of 3.1 nm radius for polystyrene NPs was achieved at an optimum condition of 30-μm resonator radius and 0.8-μm wall thickness. While MS could not be resolved in deionized water filled HMBRs for all of the investigated conditions at 1550 nm, changing the wavelength to 780 nm provided a detection limit of 15.1 nm in water. Furthermore, it is found that the sensitivity of HMBR is increased by at least two times in comparison with a microtoroid sensor. HMBRs are optofluidic platforms, so employing them could drastically enhance the applicability of microresonator-based systems for label-free NP detection.

Silica hollow bottle resonators for use as whispering gallery mode based chemical sensors

A simple three-step method for making silica hollow bottle resonators (HBRs) was developed. This procedure is advantageous because it uses commercially available materials, is cost effective, and is easy to implement. Additionally, the use of these HBRs as whispering gallery mode based chemical sensors is demonstrated by preliminary absorption sensing results in the near infrared (1580–1660 nm) using a trace gas (CH4) in air at atmospheric pressure and a dye (SDA2072) in methanol solution.

Hollow-bottle optical microresonators

Selective excitation of whispering-gallery and bottle modes in a robust hollow-bottle optical microresonator, fabricated from a silica microcapillary by a pressure-compensated, "soften-and-compress" method, is demonstrated. Characteristic resonance spectra of bottle modes were obtained by using a tapered fiber coupled at different locations along the hollow bottle. The spectral characteristics (Q-factor, excitation efficiency) are shown to have high tolerance to angular misalignment of the tapered fiber. In addition, introduction of localized losses on the outer surface of the resonator results in selective clean-up of the transmission spectrum and superior performance. A theoretical analysis of modal turning points and associated resonant wavelengths is used to explain the mechanism of mode-suppression and the resultant spectral cleaning.