In this paper, we demonstrate Er3+ doped tellurite multi-mode microlasers in 1.5 μm-1.6 μm wavelength range fabricated via the plasma torch method. It is a simple and cost-effective method to produce microspheres with diameter ranges from 11-88 micrometers. Multimode laser output was observed with 0.98 μm pump laser. In addition, we measured luminescence and decay time of the Er3+ doped (0.5 mol %, 1 mol % and 2 mol %) samples.
Whispering gallery mode microspheres have garnered considerable attention due to their applications in signal processing and telecommunications. Unique properties such as high quality factor and small mode volume of whispering-gallery mode microspheres make them suitable for laser applications with a low pumping power requirement and narrow emission linewidth. Tellurite glass is a promising material for making microlasers because of its high transparency range, high refractive index, and it has been proven as a good host for rare earth ions leading to powerful and broad stimulated emission cross section. We reported lasing in Er3+ doped tellurite glass microspheres fabricated using the plasma torch method. 15Na2O25WO360TeO2 doped with 0.5 mol% Er3+ is used for the fabrication of microspheres. Laser light from the pump is coupled to the microsphere through a half and a full tapered fiber. An optical spectrum analyzer receives the counter propagating light from the microsphere. A pump laser of 980 nm is used to achieve the laser emission at 1570 nm.
To efficiently sense small gas concentrations using a whispering gallery mode resonator a xerogel coating can be applied onto the surface of the resonator. In this way, gas molecules can enter into the xerogel layer where they can interact with the electric filed of the whispering gallery modes. Here we present some results on ammonia gas detection using a silica microsphere coated with a sol-gel porous silica xerogel. The frequency shift of an isolated whispering gallery mode was measured in dependence on the ammonia gas concentration in the testing chamber and efficient gas sensing was observed. We discuss the observed results and elaborate how the proposed systems sensitivity can be tailored in respect to the geometrical parameters of the system including the sphere radius and the coating thickness.
Optical microresonators are a very promising component for use in optoelectronics. They have very high quality factors and low mode volumes which makes them suitable for many applications such as lasing, sensing or non-linear optics. We will present our work on microspheres coated with sol-gel Er3+ activated 70SiO2 - 30HfO2. In particular the lasing properties of such microspheres will be presented. Different coating thicknesses will be employed and the peak lasing power will be discussed in respect to the coating thickness. The lasing peaks will be identified in respect to the radial and azimuthal numbers of the whispering gallery modes and the assignments will be discussed in terms of mode selectivity.
All Er3+ doped dielectric 1-D microcavity are fabricated by RF sputtering technique. The microcavity is composed of half wave Er3+ doped SiO2 active layer inserted, between two Bragg reflectors consisting of seven pairs of SiO2/TiO2 layers also doped with Er3+ ions. The morphology of the structure is inspected with scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1535 nm, respectively. The photoluminescence measurements were obtained by optically exciting at the third order cavity resonance using 514.5 nm Ar+ laser with an excitation angle of 30°. The Full Width at Half Maximum of the emission peak at 1535 nm decrease with the pump power until the spectral resolution of the detection system of 2.3 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 μW.
Surface tension induced whispering gallery mode (WGM) micro-resonators can be made in glass with very high quality factor Q. In fact, low losses amorphous glassy dielectrics can be easily shaped in high-surface-quality spheroids by thermal reflow. Since the pioneering works on fused silica microspheres showing several orders of magnitude higher Qs compared to previous findings, a large number of studies have been performed in the last years on glass based microresonators. Main results include frequency conversion through non-linear effects and micro-lasers, filtering and optical switching, RF photonics and sensing. Besides spheres, alternatives shapes like micro-bottles and micro-bubbles have been implemented to improve the resonator performances depending on the application. Other glasses rather than silica have been considered in order to enhance properties like transparency windows and non-linear effects. This presentation will review the main results we obtained on micro-laser sources in erbium doped microcavities, parametric conversion in silica microspheres, and stimulated Brillouin scattering in silica microbubbles. Potentials of coated silica microspheres implemented to add the functionalities of the coating material will be also presented.
Microresonators are very suitable for sensing application and investigation of nonlinear effects, due to their enormous quality factor and small mode volume. These properties can be extended to the mid-infrared spectral range by creating microresonators from chalcogenide glasses, which are transparent in the mid-infrared and have large third-order optical nonlinearity. We present the analysis of the nonlinear effects observation in chalcogenide microspheres created by inert gas heating.
Structuring surface and bulk of crystalline silicon on different length scales can significantly alter its properties and possibly improve the performance of opto-electronic devices and sensors based on silicon. Different dominant feature scales are responsible for modification of some of electronic and optical properties of silicon. Several easily reproducible chemical methods for facile structuring of silicon on nano and micro-scales, based on both electroless and anodic etching of silicon in hydrofluoric acid based etchants, and chemical anisotropic etching of silicon in basic environments, are presented. We show how successive micro and nano structuring creates hierarchical silicon surfaces, which can be used to simultaneously exploit the advantages of both structuring feature length scales. Finally, we demonstrate a large increase in photocurrent obtained from a hybrid structured silicon/organic near-infrared photodetector. Improved silicon/6,6’-dibromoindigo hybrid photodiodes were prepared by nano- and micro-structuring the silicon part of the heterojunction by wet chemical etching methods. Photocurrent and spectral responsivity were improved in comparison to planar diodes by up to two orders of magnitude by optimization of the silicon structuring process. We show that the improvement in photocurrent is not due to the increase in surface area or light trapping.
Silica microspheres were made by melting the tip of a standard telecom fiber and were coated with a 70SiO2 - 30 HfO2
sol-gel derived glass activated by 0.3 mol % of Er3+ ions. The samples were coated using a dip coating apparatus. The
thickness of the coating was estimated to be around 1 μm. The whispering gallery modes of the coated resonator were
studied using a full taper - microsphere coupling setup. Upon excitation at 1480 nm sharp peaks at wavelengths 1540-
1565 nm were observed. They were attributed to the whispering gallery modes of the microsphere falling in the
wavelength range of the erbium emission.
Coating of spherical microresonators is a very promising technique for optimizing their optical
properties. Optical coatings are constituted by glasses, polymer, and glass ceramics, passive or
activated by luminescent species, Glass ceramic activated by rare earth ions are nanocomposite
systems that exhibit specific morphologic, structural and spectroscopic properties allowing to
develop interesting new physical concepts, for instance the mechanism related to the transparency,
as well as novel photonic devices based on the enhancement of the luminescence. At the state of art
the fabrication techniques based on bottom-up and top-down approaches appear to be viable
although a specific effort is required to achieve the necessary reliability and reproducibility of the
preparation protocols. In particular, the dependence of the final product on the specific parent glass
and on the employed synthesis still remain an important task of the research in material science.
Looking to application, the enhanced spectroscopic properties typical of glass ceramic in respect to
those of the amorphous structures constitute an important point for the development of integrated
optics devices, including coating of spherical microresonators. Here we present a review regarding
spherical microresonators coated by glass and glass-ceramic film activated by Er3+ ions. Er3+ ions
appear to be embedded in a crystalline or amorphous environment and the lifetime dynamic is
influenced by the geometry and by the morphology of the system. Photoluminescence results and
morphologic properties are discussed for both amorphous and glass ceramic films.
D. Ristic, M. Ivanda, M. Marcius, V. Holy, Z. Siketic, I. Bogdanovic-Radovic, O. Gamulin, K. Furic, M. Ristic, S. Music, M. Buljan, M. Ferrari, A. Chiasera, A. Chiappini, G. Righini
Thin silicon rich oxide (SiOx) films were deposited using the LPCVD (Low Pressure Chemical Vapour Deposition)
method. Silane diluted in argon and oxygen were used as the reactant gasses, and the deposition temperature was kept
constant at 570 °C. The films were deposited on silicon (111) and on fused silica substrates. Films with the different
values of the oxygen content were deposited by varying the ratio of the flows of oxygen and silane in the horizontal tube
reactor. The films were characterized in terms on the surface quality (by X-ray specular reflectivity and scanning
electron microscopy) and in terms of the oxygen content x (by time of flight elastic recoil detection analysis). The films
were found to have a very smooth, homogeneous surface and the oxygen content was found to vary from x=0 to x=2 in
dependence on the deposition parameters. The refractive indices of the films were measured both in the visible (405 nm)
and in the infrared (1319 nm and 1542 nm), compared to the values which the Bruggeman's effective medium theory
predicts for such thin films, and were found to be in good agreement. The position of the Si-O stretching peak in the
infrared absorption spectra was used to draw some conclusion about the distribution of the silicon and oxygen atoms
inside the amorphous SiOx matrix. The atoms were found to be inhomogeneously distributed inside the amorphous
matrix, with the average number of oxygen atoms in the vicinity of a given silicon atoms being lower than x.
Low frequency Raman scattering on the acoustic vibrational modes of nanoparticles has been used for determining the size of dielectric, semiconductor and metal nanoparticles embedded in glass. This contribution reports on application of low-frequency Raman scattering on acoustical vibrational modes of nanoparticles. The theoretical background as well as the experimental results of free non-interacting nanoparticles as well as glass containing different nanoparticles for optoelectronics will be presented. The approach is based on a 1/ν dependence of the Raman light of the vibration coupling coefficient and on the fact that each nanocrystallite of diameter D vibrates with its eigenfrequency ν~1/D. The Raman scattering spectra are analyzed using confined acoustical vibrations model. The model-calculation considered homogeneous broadening of the confined acoustical modes due to interaction of the particles with matrix and inhomogeneous broadening due to the contribution of the Raman scattering from the particles of different sizes. The low frequency Raman spectra of different nanoparticles (nc-TiO2, nc-SnO2, nc-CdSxSe1-x, and nc-Si) prepared by Physical Vapour Deposition, thermal quenching and thereafter annealing of glass and sol-gel techniques was used for determination of particles size distribution and results were compared to TEM. The Raman spectroscopy technique has proved to be a simple and fast method that has favorable statistical characteristics due to the macroscopic probe volume and makes in situ measurements possible.
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