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.
A mid-IR amplifier consisting of a tapered chalcogenide fiber coupled to an Er 3+ -doped chalcogenide microsphere has been optimized via a particle swarm optimization (PSO) approach. More precisely, a dedicated three-dimensional numerical model, based on the coupled mode theory and solving the rate equations, has been integrated with the PSO procedure. The rate equations have included the main transitions among the erbium energy levels, the amplified spontaneous emission, and the most important secondary transitions pertaining to the ion-ion interactions. The PSO has allowed the optimal choice of the microsphere and fiber radius, taper angle, and fiber-microsphere gap in order to maximize the amplifier gain. The taper angle and the fiber-microsphere gap have been optimized to efficiently inject into the microsphere both the pump and the signal beams and to improve their spatial overlapping with the rare-earth-doped region. The employment of the PSO approach shows different attractive features, especially when many parameters have to be optimized. The numerical results demonstrate the effectiveness of the proposed approach for the design of amplifying systems. The PSO-based optimization approach has allowed the design of a microsphere-based amplifying system more efficient than a similar device designed by using a deterministic optimization method. In fact, the amplifier designed via the PSO exhibits a simulated gain G=33.7 dB , which is higher than the gain G=6.9 dB of the amplifier designed via the deterministic method.
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).
We have successfully made terrace-microspheres for laser emission: micrometer size spherical cavity laser having terrace
shaped pumping light entrance. "Terrace-microsphere" is a high refractive index glass sphere (nD=1.93) of 30μm in
diameter with terrace portion of organic-inorganic materials. The glass sphere is in BaO-SiO2-TiO2 glass system and
contain a few ppm of Nd3+. Organic-inorganic hybrid materials of refractive index nD=1.45 were prepared by sol-gel
technique using 3-methacryloxypropyltrimethoxysilane and tetramethoxysilane as starting materials. To make terrace
portion, a pico-liter of sol droplet was supplied with a micro-capillary into the boundary between a glass sphere and a
Teflon sheet. The sol-derived part attached to a sphere showed the flat portion like a terrace structure. The
terrace-microspheres were pumped with a tunable CW Ti:sapphire laser (λ=700nm-850nm) for choosing the suitable
pumping wavelengths to WGMs. Pumping the terrace portion at around 800nm wavelength, strong resonances due to
WGMs were demonstrated. The resonances originated from Raman scattering and Nd3+ fluorescence were observed at
840-880nm and 880-940nm wavelength region respectively. Consequently, we can show the potential application for a
multi-wavelength laser (about 100 lines) at the extended wavelength range (840-940nm) in the near-infrared. Stimulated
Raman emission of WGMs was performed with threshold of 4mW.
Buried-type optical waveguide with blanches for the gate of optical signals was fabricated by nano ion-exchange method
using the probe of atomic force microscope (AFM) as an electrode. 2-step procedure of the electric field-assisted Ag/Na-ion
exchange followed by K/Na one was applied to prepare the waveguide structure inside the glass substrate. Pt-coated
AFM probe as a cathode was attached to the glass surface and Ag+ ions in the core underneath the probe were partially
extracted towards the glass surface. The protruding high index regions from the core towards the glass surface were
found to work as the optical gate where the wavelength and intensity of light through the gate was determined by the
condition of nano ion-exchange treatment.
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
measured.
Tellurite glass micro-superspheres (Te-μSSs) were prepared by the surface-tension mold (StM) technique, and their whispering
gallery mode (WGM) resonances have been investigated as the first trial to realize an ultra-broadband Raman
resonator. Micrometer-sized tellurite glass particles were melted on an optical grade glassy-carbon substrate then cooled to
room temperature (StM technique). Resultant Te-μSS possesses a super-spherical shape with high optical transparency. The
size of the partly truncated area, resulting from the contact surface with the substrate, can be controlled by the composition
of the glass and a microsphere with no truncated area was achieved for a glass with 56TeO2-3.5BaO-10.5SrO-8Nb2O5-4WO3-16P2O5 (TBSN-4W-16P) composition. The TBSN-4W-16P μSS was excited at 532 nm, and the WGM resonance
emission attributed to broad Raman scattering of the glass itself was observed. The Q value of the μSS was ≈ 5 × 103.
It was confirmed that the prepared μSSs possess a sufficiently spherical shape and acted as an efficient WGM resonator.
These results predict that the Te-μSS has potential for a novel broadband Raman laser.
A couple of glass plates sandwiching the molten AgNO3-KNO3 mixture at the temperature of 250°C was irradiated by pulsed Nd:YAG laser with a wavelength of 1.06μm. The irradiation induced the color of transparent yellow and orange in the glasses with the irradiation time because of the deposition of silver nanoparticles. In the observations using FE-SEM and AFM, periodically aligned structures, stripes and circles, formed by silver nanoparticles were observed in the irradiated area. The stripes had the interval of 600-700nm, and the circles had the diameters more than 40μm, the latter of which were considered to be due to the Newton's ring interference of laser on bubbles in the molten salt. On the other hand, in the experiment of two-beam irradiation, we obtained strictly aligned stripes pattern with a periodic interval of 2.6μm and a height of 50nm on the glass surface. The observed interval gave a good agreement with the theoretical length that was calculated from the wavelength and the inter-crossing angle of the coherent lasers. Moreover, the stripes pattern showed the Bragg diffraction of visible light from violet to red. From these, it was found that the laser deposition method united with light interference was useful to prepare periodic pattern of nanoparticles on a transparent substrate.
Organic-Inorganic hybrid pillar arrays have been controlled by cohesive force during drying in photolithography.
Two-dimensional periodic pillars with micrometer repetitions were fabricated from an organic-inorganic hybrid
material. The pillars were gathered at the top and gtop-gatheringh pillar patterns were obtained depending on
pillar sizes such as height of the pillars and distance between neighboring pillars and types of rinse liquids. The
top-gathering pillar patterns could be obtained easily in the pillar arrays with same structural parameters using
1-PrOH as a rinse liquid rather than water. From in situ observation of the drying rinse liquids, it was found
that the drying of 1-PrOH differs from that of water in the pillar arrays because of the difference in the contact
angles. Top-gathering pillars were partially introduced in a homogeneous periodic pillar array by the different
pillar formations between two types of rinse liquids.
Multi-beam laser interference (MLI) lithography is known to be one of the fabrication techniques of photonic crystals. In MLI lithography, laser beams are interfered on a scale of the wavelength of light and are irradiated to photosensitive films. We have paid attention to photosensitive TiO2-organic hybrid film, which has high refractive index. TiO2-organic hybrid periodic pillar patterns were fabricated by MLI lithography. The TiO2 hybrid film, which was prepared from Ti-alkoxide and β-diketone by the sol-gel method, was exposed to the interference pattern of femtosecond pulses at 800 nm wavelength. After laser irradiation, the unirradated portion was removed by the development and rinse. Two-dimensional periodic standing alone pillars and 2×2 and 3×3 top-gathering pillars, which were gathered at the top by means of self-organization were formed by changing conditions such as laser irradiation time and film thickness. The pillar patterns depended upon the rinse liquid, the diameter, and the height of pillars. The top-gathering pillars are applicable for diffractive optics.
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.
Capillary Electrophoresis Doping (CED) technique is proposed for the new doping technique of the functional molecules into the hybrid materials. Organic-inorganic hybrid films or waveguides are fabricated on the cathode and the capillary tube bridge is made between the hybrid materials and the anode solution bath. The capillary and the anode bath are filled with the solution of the functional molecules and DC voltage is applied between cathode electrode and the anode one. The functional molecules (ions) move along the electric field, and their doping into the hybrid materials
can be attained by the control of the capillary position and the electric current through the circuit. In this study, siloxane based hybrid films and waveguides are prepared, and the doping of organic laser dyes, Rhodamine6G and Cresyl violet are demonstrated using SiO2 glass capillaries. It is shown that CED technique has a great potential to fabricate the multifunctional optical devices in which various different functional chemicals are contained.
Ion manipulation using micro-probe has been performed to fabricate the nano-scale dots on/or in the glass. Soda-lime-silica glass was subjected to the treatments. Two types of the manipulation treatments were carried out using various probes and electrical conditions. In the Na-extraction treatment, the thick needles and/or STM tips were used as a cathode. At 250°C, Na+ ions were extracted from the inside of the glass towards the cathode tip, and electrochemically reduced to Na-metal. Na-metal are held at the tip/glass interface as liquid state, and grew with the treatment time. After the treatment, they formed the micrometer-size dots of fodium compound on the glass surface, and their size was dependent on the total charge conducting through the tip. In the Ag-migration treatment, Ag-metal probes were prepared and used as an anode at 200°C. Ag atoms on the tip were oxidized to Ag+ ions and migrated into the glass. They could be optically recognized using the luminescence from Ag+ ions under the UV irradiation. a lot of Ag-metal dots with the size 100-300nm were also formed on the glass surface. They are considered to be transferred from the tip of Ag-metal probe onto the glass surface. The size of the Ag+ migrated region was dependent on the total charge of the treatment, and the available small size was found to be defined by the apex of the probe tip. The observed phenomena in these treatments were explained and the possibility of the formation of nano-scale dots on the glass by ion manipulation was discussed.
Micrometer-sized spherical particles containing laser dyes such as Rhodamine 6G, DCM and Pyridine 1 have been fabricated by the vibrating orifice technique for the spherical cavity micro-laser. A cylindrical liquid jet of diluted hybrid raw materials passing through an orifice breaks up into equal-sized droplets by mechanical vibration. Then the solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified into dye-doped hybrid-microspheres in ammonium water trap. The microspheres of different dye contents were pumped by second harmonic pulses of Q-switched Nd: YAG laser (532 nm wavelength, repetition rate is 10 Hz) and their photodegradation of lasing intensities were measured against shot number of pumping pulses. Degree of the degradation strongly depended on the pumping power and the dye content incorporated in the microsphere. Suitable pumping power and dye content gave the best date for the photostability: Laser out-put energy was consumed 50% of the initial value after 100,000 pulses for R6G and Pyridine 1, and 240,000 pulses for DCM.
The effects of heat treatment on the optical quality of organic-norganic hybrid spherical particles were investigated. The spherical particles with a diameter of 6μm were prepared via sol-gel process from phenyl-tetraethyl-silane(PTES) using the vibrating orifice technique, and they showed strong oscillation signals based on the spherical resonance mode with low power threshold of the incident CW-Ar+ laser. Against the heat treatment on the slide glass plate, there were some particles which remained their spherical shape after 400°C heating depending on the condition of sol preparation. The survived particles were also found to have high photo-stability that they were not damaged from the laser irradiation of 514.5nm Ar+ light with a power >120mW/particle, while as-prepared particles were bursted by the irradiation <20mW/particles. From the measurements of micro Raman scattering spectroscopy, optical and secondary electron microscope and thermal analysis, the thermal stability of hybrid materials was considered.
Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for the spherical cavity micro-laser. Using phenyl triethoxy silane (PTES) as a starting material, R6G-doped monodisperse spherical particles were prepared by the vibrating orifice technique. Processing consists of two major processes: (1) Hydrolysis and polymerization of PTES and (2) Droplet formation from PTES oligomers by vibrating orifice technique. A cylindrical liquid jet passing through the orifice of 10 and 20 micrometers in diameter breaks up into equal- sized droplets by mechanical vibration. Alcohol solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified in ammonium water trap. For making smooth surface and god shaped particles, control of molecular weight of PTES oligomer was essential. R6G-doped hybrid spherical particles of 4 to 10 micrometers size of cavity structure were successfully obtained. The spherical particles were pumped by a second harmonic pulse of Q- switched Nd:YAG laser and laser emission peaks were observed at wavelengths which correspond to the resonance modes.
Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for spherical cavity structure. Hydrolysis and polymerization processes of phenyltriethoxysilane (PTES) as a starting material was pursued by observing the change of PTES/R6G in HCl solution with its optical absorption and viscosity. As the polymerization of PTES proceeded, increase of molecular size resulted in change its properties from hydrophilic to hydrophobic, and subsequently the solution separated into two layers of aqueous and organic. Polymerized PTES in the organic layer showed good affinity with incorporated R6G, and high monomer/dimer ratio in particles was achieved. Moreover, using them intermixing of unsuitable particles of submicron size was avoided, because hydrolyzed PTES of small molecular size that is the origin of submicron-sized particles was removed to the aqueous layer. With stirring, titration of diluted droplets containing polymerized PTES was suitable for preparing several micrometer sized particles, and followed by solidification in ammonia water. Degree of the polymerization of PTES and viscosity of liquid droplets were the key factors for determining the properties of R6G-doped spherical particles of optical cavity structure.
The formation of a borosilicate glass film of 10 - 20 micrometers in thickness on a silicon substrate via an interfacial polymerization technique has been studied as the first step for the preparation of a planer waveguide for optical communication. A gel film prepared from the partially hydrolyzed TMOS mixed with boron alkoxides could be densified into a glass film of 16 micrometer in thickness having a smooth surface by the heat treatment up to 1000 degrees Celsius. A good reproducibility in the yield was obtained by completing the hydrolysis and condensation of the whole ingredient in the 5 ml of precursor solution spread over water containing triethylamine as a catalyst within a cylindrical container of about 80 mm inside diameter. The use of saturated aqueous solution of boric acid instead of distilled water was necessary to hinder the re-dissolution of boron from the formed gel film.
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