Tuning whispering gallery modes using internal aerostatic pressure

Abstract

Aerostatic tuning of whispering gallery modes (WGMs) in a microbubble resonator is demonstrated. The optical modes are redshifted over hundreds of gigahertz (GHz) simply by increasing the air pressure (up to 6 bars) inside the microbubble. A description of the pressure tuning properties of the WGMs in microbubbles is given in terms of the corresponding elasto-optical equations of spherical shells and the results are compared to experimental data. Microbubbles as small as 74 μm are tested and the experimental results show excellent agreement with the theory. An estimation method is developed for calculating the wall thicknesses of the microbubbles from the diameters, which are measured via direct microscopy. A geometrical factor χ is defined and a linear relationship between the shift rate (GHz/bar) of the bubbles modes and χ is observed.

A Packaged Whispering Gallery Mode Strain Sensor Based on a Polymer-Wire Cylindrical Micro Resonator

“…Therefore, in our experiments the strain range is limited so that WGMs shift is less than one FSR corresponding to 0.33% (3250 μɛ) axial elongation of the polymer wire. The spectral shift of the WGM resonant wavelength due to axial strain can be described as a combined effect of changing diameter and the changing refractive index of the resonator [8][9][10][11][12][13][14][15]23]:…”

“…There are many reports concerning WGM strain sensing using spherical [8][9][10][11][12][13][14] as well as bubble [15,16] MRs based on silica and polymer materials. Typically, an evanescent light coupling technique is used to excite the WGMs in such MRs.…”

Dispersion analysis of whispering gallery mode microbubble resonators

“…Microbubble (or microshell) resonators are thin-walled spherical shells that can support whispering gallery modes with evanescent fields inside and outside of the resonator [10]. They typically have wall thicknesses ranging from ~0.4 -8 µm [12,18], and Q-factors up to 10 7 [7,19,20]. When the walls have a thickness of the order of the wavelength of light the evanescent fields can extend far outside the cavity wall resulting in a highly sensitive resonator ideal for various sensing applications [6].…”

“…Some of the applications of microbubble resonators include refractive index sensing [10,14,18,19], optomechanical measurement of mass and acceleration [10], temperature sensing [10,11] and pressure sensing [13,19]. Microbubbles are also of particular interest for biochemical sensing because they allow the samples to be placed inside the resonator, avoiding disturbance of the coupling mechanism with e.g.…”

Strain-induced spectral tuning of the whispering gallery modes in a cylindrical micro-resonator formed by a polymer optical fiber

“…Numerous reports demonstrate the tuning of WGM resonant wavelengths of spherical MRs by changing the surrounding refractive index [15], applying mechanical strain to the resonator [16], changing internal pressure [17], applying external electric field [18], etc. Self-tuning of WGM resonances has been demonstrated for a stand-alone silica microsphere by changing its temperature under the influence of the gas flow surrounding the resonator [19].…”