The paper illustrates both review and original simulation results obtained via the modelling of different set-ups based on optical microresonators for applications in optical sensing, lasing and spectroscopy. Passive microbubbles and microspheres coupled via long period fiber gratings (LPGs) and tapered fibers are designed and/or constructed for sensing of biological fluids in the near infrared (NIR) wavelength range. Rare earth doped chalcogenide glass integrated microdisks are designed for active sensing in the medium infrared (MIR) wavelength range. A home-made numerical code modelling the optical coupling and the active behavior via rate equations of ion population is employed for a realistic design, by taking into account the most important active phenomena in rare earths, such as the absorption rates, the stimulated emission rates, the amplified spontaneous emission, the lifetime and branching ratios, the ion-ion energy transfers and the excited state absorption. Optical coupling is obtained by employing ridge waveguides, for micro-disks, and tapered fibers, for microspheres and microbubbles. Different dopant rare earths as Erbium (Er3+) and Praseodymium (Pr3+) are considered.
The ring-core refractive-index profile in RO-Al2O3-SiO2 glass (R = Ca and Ba) was formed by the manipulation of a platinum (Pt) microsphere via continuous-wave laser irradiation method (the CW-LM3 method). The homogeneously modified area could be obtained in the CAS glass (R = Ca) with a wide velocity of the microsphere, though the BAS glass (R = Ba) showed inhomogeneous modified area with periodic structure. The even-width modified line was fabricated by controlling the velocity of the Pt microsphere, and the ring-core structure with the highest refractive index change was fabricated in the CAS glass with the Pt-microsphere speed of 46 μm/sec.
New spherical resonators with internal defects are introduced to show anomalous whispering gallery modes (WGMs). The defect induces a symmetry breaking spherical cavity and splits the WGMs. A couple of defects, a hollow sphere (bubble), and a hollow ring, have been studied. The hollow sphere was fabricated and the splitting of WGM was observed. In this paper, this "non-degenerated WGMs (non-DWGMs) resonance" in a microsphere with hollow defect structure is reviewed based on our research. The resonance of WGMs in a sphere is identified by three integer parameters: the angular mode number, l, azimuthal mode number m, and radial mode number, n. The placement of the defect such as a hollow ring or single bubble is shown to break symmetry and resolve the degeneracy concerning m. This induces a variety of resonant wavelengths of the spherical cavity. A couple of simulations using the eigenmode and transient analyses propose how the placed defects affect the WGM resonance in the spherical cavity. For the sphere with a single bubble defect, the experimentally observed resonances in Nd-doped tellurite glass microsphere with a single bubble are clarified to be due to the splitting of resonance modes, i.e., the existence of "non-DWGMs" in the sphere. The defect bubble plays a role of opening the optically wide gate to introduce excitation light for Nd3+ pumping using non-DWGMs in the sphere efficiently.
Morphing commonly refers to the smooth transition from a specific shape into another one, in which the initial and final shapes can be significantly different. In this study, we show that the concept of morphing applied to laser micromanufacturing offers an opportunity to change the topology of an initial shape, and to turn it into something more complex, like for instance for creating self-sealed cavities. Such cavities could be filled with various gases, while also achieving an optical surface quality since being shaped by surface tension. Furthermore, we demonstrate that laser morphing can be accurately modelled and predicted. Finally, we illustrate the possible use of ‘laser-morphed’ shape to achieve high-quality resonators that can find applications, for instance, in ultra-small quantities molecules label-free detection through whispering gallery mode resonances.
Terrace-microspheres of high-index multi-component glasses (BaO-SiO2-TiO2, nD=1.93; BaO-ZnO-TiO2, nD=2.2)
containing various Nd3+ contents were used for pumping experiments to investigate the influence of Nd3+ content and
matrix of glasses on the SRS enhancement effect. Pumping the terrace-microspheres containing low content of Nd3+(0.3ppm and 0.9 ppm) at 800-830nm wavelengths, Raman scattering due to glass matrix and Nd3+ fluorescence were
overlapped spectrally in the wavelength region of 860~940nm. Under such conditions, Nd3+ works as a seeding and an
amplifier of SRS, resulting in SRS enhancement at 840~940nm wavelengths. The terrace-microspheres of both highindex
glasses showed SRS gain enhancement of 4 times (Normalized SRS gain = [SRS peak intensities at various
pumping wavelength] / [SRS peak intensity at 790nm pumping wavelength]) and decrease in SRS thresholds from
2.5mW (λpump≈790nm) to 0.3mW (λpump≈810~830nm). On the other hand at high-content Nd3+ (15, 120 and 16000ppm),
Nd3+ fluorescence intensity was far stronger than that of Raman scattering and SRS was not observed clearly. The reason
why SRS decreased in the high-Nd3+-content glass spheres was discussed: Nd3+ absorption in the region of 890~900nm
wavelengths is one of the plausible explanations. Terrace-microsphere of Nd3+ (0.9ppm) BaO-ZnO-TiO2 glass was also
used for pumping experiment, which glass shows 30 times stronger spontaneous Raman scattering than that of silica
glass, and result in strongest SRS emission was performed. The high-index multi-component terrace-microspheres
containing Nd3+ of relatively low content have a potential application to a low-threshold spherical Raman laser for multiwavelength
emission in the near-infrared region (λ=840~940nm).
A super-hemispherical (i.e. a truncated spherical) glass lens with gold (Au) nanoparticles was obtained using a surface
tension mold (StM) technique. Recently, surface plasmon of noble metal nanoparticle has attracted a considerable
amount of interest because it is extremely sensitive to the properties of the materials attached to its surface. On the other
hand, in the field of high-resolution microscopy, solid immersion lenses (SILs) with super-hemispherical shape have
received much attention because it is a convenient and powerful means of improving both the spatial resolution and the
light collection efficiency. A combination of the SIL and the Au nanoparticles could be very suitable for use in surface
plasmon microscopy. In this study, Na2O-CaO-SiO2 glass was heated on Au-coated glassy-carbon substrate up to 800 °C.
The obtained glasses were found to have super-hemispherical shape, and the Au nanoparticles were deposited on its
bottom planar surface. The effects of the deposition condition of Au on the distribution of Au nanoparticles and the
shape of glass were investigated, and the surface plasmon resonance absorption spectra from the obtained samples were
A preparation of microlens array of the super-spherical glasses by a combination of the photolithography and the Surface-tension Mold (StM) techniques is shown. A super-spherical lens has been gathering much attention because of its function as a Solid Immersion Lens (SIL) with the super-resolution, which circumvents the optical diffraction limit. StM technique enables the preparation of a micrometer-sized SIL (μ-SIL) with the desirable shape, and the obtained SILs realize the optical function. In order to develop the optical micro-devices composed of SILs, μ-SIL array module, the micro-fabrication technique of photolithography is combined with StM technique. Na2O-CaO-SiO2 glass film is attached to glassy-carbon, and etched into glass tiles after the formation of masks by the photolithography. They are heated up to 800oC to self-organize into the super-spherical form of the glass droplets. The obtained lens array is found to be composed of the μ-SILs with the uniform radius and thickness.