Whispering Gallery Mode Resonators

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Micro-Ring Resonator Devices Prototyped on Optical Fiber Tapers by Multi-Photon Lithography

Multi-photon lithography -a powerful laser nanoscale additive-manufacturing method- is employed for structuring micro-ring traveling-wave resonators onto micrometric diameter, optical fiber tapers. These weakly guided, micro-ring resonating structures achieve light circulation with Q-factors of the order of ∼2.0e3, for typical diameters of tens of micrometers, in the spectral band of 1550 nm. Moreover, these micro-ring resonators are exemplified into the demonstration of an ethanol vapor sensor, readily achieving detectivities of 0.5 ppm, based on reversible physisorption effects. This demonstration aims at developing a new type of photonic platforms, based on a versatile, laser based prototyping approach onto micrometric size, optical fiber tapers, while exhibiting unique guiding and modal interaction characteristics, for departing the laboratory bench, while being implemented into diverse types of sensing and actuating devices.
(a), (c) & (d) Scanning electron microscope photographs of 20 μm diameter MRRs fabricated using MPL onto OFTs. (b) Optical microscope picture of a 20 μm diameter MRR while being excited using white light.

References

  • Study conducted in collaboration with the groups of Prof M. Kafesaki and Dr Maria Farsari, IESL – FORTH, Greece
  • V. Melissinaki, O. Tsilipakos, M. Kafesaki, M. Farsari and S. Pissadakis, "Micro-Ring Resonator Devices Prototyped on Optical Fiber Tapers by Multi-Photon Lithography," in IEEE Journal of Selected Topics in Quantum Electronics, vol. 27, no. 6, pp. 1-7, Nov.-Dec. 2021, Art no. 5900107, doi: 10.1109/JSTQE.2021.3062716. Link

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Microspherical WGM resonators inside tapered microstructured optical fibers

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 103 and 6.1 x 103, depending on the port and parity excitation.
(a) Scanning electron microscope (SEM) picture of the un-tapered, grapefruit shaped micro-structured optical fiber (MOF) used, with five air capillaries and germanium doped core, (b) SEM image of the attached BaTiO3, microsphere with 25 μm diameter, top fitting in one of the capillaries (diameter: 11.2 μm) of the tapered MOF. (c) optical microscope picture of a side view on the T-shaped light coupling system

References

  • The above work was conducted in collaboration with W. Margulis, RISE, Sweden
  • M.G. Konstantinou, K. Milenko, W. Margulis, S. Pissadakis, Microspherical WGM resonators inside tapered microstructured optical fibers, MDPI Micromachines, 9 (10), 521, 2018, Link

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An “in fiber” Whispering Gallery Mode bi sphere resonator, sensitive to nanometric displacements

A double-cavity, Whispering-Gallery-Mode (WGM) resonator, composed of two polystyrene microspheres, is formed inside the capillary of a microstructured optical fiber. The spectra are compared with the corresponding WGM patterns of the isolated microspheres. We collect scattering spectra from the contact area between the two beads, as the spacing between them is varied, and the evolution of the modes with sphere separation is discussed. Potential applications of the presented optical design are also proposed.
(a) Scanning electron microscopy image of the end face of a suspended-core fiber with one microsphere inside the capillary. (b) Top microscope image of the two microspheres inside the capillary of the collapsed-core fiber and c their optical image after the excitation of Whispering-Gallery Modes. The two microspheres are labeled I, II and CP is their bright contact point. (d, e) The optical excitation–interrogation platform of the WGMs.

References

  • In collaboration with Dr K. Schuster’s group, Leibniz Institute of Photonic Technology, Germany
  • K. Kosma, K. Schuster, J. Kobelke, S. Pissadakis, An “in fiber” Whispering Gallery Mode bi sphere resonator, sensitive to nanometric displacements, Appl. Phys. B 124, pp. 1-8 (2018) Link)

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Probing Stress-Induced Optical Birefringence of Glassy Polymers by Whispering Gallery Modes Light Localization

An optical resonance method for the determination of the strain- and stress-optical coefficients of optically transparent polymers is presented and exemplified for monodisperse and bidisperse molecular weight polystyrene (PS). This method employs whispering gallery modes (WGMs) resonation inside a spheroid polymeric cavity, suspended on an optical fiber taper waist, which, in turn, is used for subjecting the polymeric resonator to controlled strain conditions. The wavelength shifts of equal order transverse electric and transverse magnetic polarization WGMs are measured, as well as their relative birefringence versus applied strain. For monodisperse PS microspheroids (2 and 50 kDa) the stress-optical coefficient is negative, contrary to the results for bulk PS in the glassy state indicating different phenyl group orientation of the PS monomer with respect to the strain direction. In the bidisperse (2 and 50 kDa) spheroid with a symmetric monomer composition, local structural irregularities are probably responsible for the observed coupling between WGMs. The method possesses metrological capabilities for probing the molecular orientation of polymer-based resonators.
Configuration of the polystyrene (PS) resonator and whispering gallery mode (WGM) excitation with TE and TM polarization using a broadband superluminescent laser diode (SLD) and optical spectrum analyzer (OSA) for signal recording. The strain is applied at both fiber taper ends through controllable fiber elongation. TE and TM WGM mode field distributions in the resonator (low inset) and an image of a 30.6 μm diameter PS spheroid, fabricated around the fiber taper (upper inset).

References

  • In collaboration with Prof G. Fytas’ group Department of Materials Science, University of Crete, Greece and Max Planck Institute for Polymer Research, Germany and Dr. G. Gkantzounis, University of Surrey, UK
  • K Milenko, S Pissadakis, G Gkantzounis, A Aluculesei, G Fytas, Probing Stress-Induced Optical Birefringence of Glassy Polymers by Whispering Gallery Modes Light Localization, ACS omega 2 (12), 9127-9135, 2017, Link

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Silver iodide phosphate glass microsphere resonator integrated on an optical fiber taper

A robust and functional whispering gallery mode (WGM) resonating system based on a silver iodide phosphate glass microsphere melted on an optical fiber taper was demonstrated. The temperature response of the resonator was performed, and a linear dependence with temperature was observed. Fiber encapsulation ensures stable and robust operation of the microsphere resonator, without the need for precise 3D positioning system and, thus, opens the prospect for the design and realization of resonator devices with new sensing functionalities and broad applications in harsh environments.

(Left) AFM of a grating inscribed in a 500nm thick Ta2O2 film. Exposure to 2000 pulses of 20mJ/cm2 energy density and development for 135 mins in 1 part KOH/2 parts DI H2O, T=55oC. Grating period: 4142nm. (Right) SEM scan of relief grating in Ta2O2 thin film.

References

  • K. Milenko, I. Konidakis, and S. Pissadakis, Silver iodide phosphate glass microsphere resonator integrated on an optical fiber taper, Optics letters,41(10), 2185-2188, 2016 , Link

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